1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
34 @set DATE December 2001
36 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
54 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``Free Software'' and ``Free Software Needs
60 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
61 and with the Back-Cover Texts as in (a) below.
63 (a) The Free Software Foundation's Back-Cover Text is: ``You have
64 freedom to copy and modify this GNU Manual, like GNU software. Copies
65 published by the Free Software Foundation raise funds for GNU
70 @title Debugging with @value{GDBN}
71 @subtitle The @sc{gnu} Source-Level Debugger
73 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
74 @subtitle @value{DATE}
75 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
79 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
80 \hfill {\it Debugging with @value{GDBN}}\par
81 \hfill \TeX{}info \texinfoversion\par
85 @vskip 0pt plus 1filll
86 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
87 1996, 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
89 Published by the Free Software Foundation @*
90 59 Temple Place - Suite 330, @*
91 Boston, MA 02111-1307 USA @*
94 Permission is granted to copy, distribute and/or modify this document
95 under the terms of the GNU Free Documentation License, Version 1.1 or
96 any later version published by the Free Software Foundation; with the
97 Invariant Sections being ``Free Software'' and ``Free Software Needs
98 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
99 and with the Back-Cover Texts as in (a) below.
101 (a) The Free Software Foundation's Back-Cover Text is: ``You have
102 freedom to copy and modify this GNU Manual, like GNU software. Copies
103 published by the Free Software Foundation raise funds for GNU
109 @node Top, Summary, (dir), (dir)
111 @top Debugging with @value{GDBN}
113 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
115 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
118 Copyright (C) 1988-2002 Free Software Foundation, Inc.
121 * Summary:: Summary of @value{GDBN}
122 * Sample Session:: A sample @value{GDBN} session
124 * Invocation:: Getting in and out of @value{GDBN}
125 * Commands:: @value{GDBN} commands
126 * Running:: Running programs under @value{GDBN}
127 * Stopping:: Stopping and continuing
128 * Stack:: Examining the stack
129 * Source:: Examining source files
130 * Data:: Examining data
131 * Macros:: Preprocessor Macros
132 * Tracepoints:: Debugging remote targets non-intrusively
133 * Overlays:: Debugging programs that use overlays
135 * Languages:: Using @value{GDBN} with different languages
137 * Symbols:: Examining the symbol table
138 * Altering:: Altering execution
139 * GDB Files:: @value{GDBN} files
140 * Targets:: Specifying a debugging target
141 * Remote Debugging:: Debugging remote programs
142 * Configurations:: Configuration-specific information
143 * Controlling GDB:: Controlling @value{GDBN}
144 * Sequences:: Canned sequences of commands
145 * TUI:: @value{GDBN} Text User Interface
146 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
147 * Annotations:: @value{GDBN}'s annotation interface.
148 * GDB/MI:: @value{GDBN}'s Machine Interface.
150 * GDB Bugs:: Reporting bugs in @value{GDBN}
151 * Formatting Documentation:: How to format and print @value{GDBN} documentation
153 * Command Line Editing:: Command Line Editing
154 * Using History Interactively:: Using History Interactively
155 * Installing GDB:: Installing GDB
156 * Maintenance Commands:: Maintenance Commands
157 * Remote Protocol:: GDB Remote Serial Protocol
158 * Copying:: GNU General Public License says
159 how you can copy and share GDB
160 * GNU Free Documentation License:: The license for this documentation
169 @unnumbered Summary of @value{GDBN}
171 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
172 going on ``inside'' another program while it executes---or what another
173 program was doing at the moment it crashed.
175 @value{GDBN} can do four main kinds of things (plus other things in support of
176 these) to help you catch bugs in the act:
180 Start your program, specifying anything that might affect its behavior.
183 Make your program stop on specified conditions.
186 Examine what has happened, when your program has stopped.
189 Change things in your program, so you can experiment with correcting the
190 effects of one bug and go on to learn about another.
193 You can use @value{GDBN} to debug programs written in C and C++.
194 For more information, see @ref{Support,,Supported languages}.
195 For more information, see @ref{C,,C and C++}.
197 @c OBSOLETE @cindex Chill
200 @c OBSOLETE and Chill
201 is partial. For information on Modula-2, see @ref{Modula-2,,Modula-2}.
202 @c OBSOLETE For information on Chill, see @ref{Chill}.
205 Debugging Pascal programs which use sets, subranges, file variables, or
206 nested functions does not currently work. @value{GDBN} does not support
207 entering expressions, printing values, or similar features using Pascal
211 @value{GDBN} can be used to debug programs written in Fortran, although
212 it may be necessary to refer to some variables with a trailing
216 * Free Software:: Freely redistributable software
217 * Contributors:: Contributors to GDB
221 @unnumberedsec Free software
223 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
224 General Public License
225 (GPL). The GPL gives you the freedom to copy or adapt a licensed
226 program---but every person getting a copy also gets with it the
227 freedom to modify that copy (which means that they must get access to
228 the source code), and the freedom to distribute further copies.
229 Typical software companies use copyrights to limit your freedoms; the
230 Free Software Foundation uses the GPL to preserve these freedoms.
232 Fundamentally, the General Public License is a license which says that
233 you have these freedoms and that you cannot take these freedoms away
236 @unnumberedsec Free Software Needs Free Documentation
238 The biggest deficiency in the free software community today is not in
239 the software---it is the lack of good free documentation that we can
240 include with the free software. Many of our most important
241 programs do not come with free reference manuals and free introductory
242 texts. Documentation is an essential part of any software package;
243 when an important free software package does not come with a free
244 manual and a free tutorial, that is a major gap. We have many such
247 Consider Perl, for instance. The tutorial manuals that people
248 normally use are non-free. How did this come about? Because the
249 authors of those manuals published them with restrictive terms---no
250 copying, no modification, source files not available---which exclude
251 them from the free software world.
253 That wasn't the first time this sort of thing happened, and it was far
254 from the last. Many times we have heard a GNU user eagerly describe a
255 manual that he is writing, his intended contribution to the community,
256 only to learn that he had ruined everything by signing a publication
257 contract to make it non-free.
259 Free documentation, like free software, is a matter of freedom, not
260 price. The problem with the non-free manual is not that publishers
261 charge a price for printed copies---that in itself is fine. (The Free
262 Software Foundation sells printed copies of manuals, too.) The
263 problem is the restrictions on the use of the manual. Free manuals
264 are available in source code form, and give you permission to copy and
265 modify. Non-free manuals do not allow this.
267 The criteria of freedom for a free manual are roughly the same as for
268 free software. Redistribution (including the normal kinds of
269 commercial redistribution) must be permitted, so that the manual can
270 accompany every copy of the program, both on-line and on paper.
272 Permission for modification of the technical content is crucial too.
273 When people modify the software, adding or changing features, if they
274 are conscientious they will change the manual too---so they can
275 provide accurate and clear documentation for the modified program. A
276 manual that leaves you no choice but to write a new manual to document
277 a changed version of the program is not really available to our
280 Some kinds of limits on the way modification is handled are
281 acceptable. For example, requirements to preserve the original
282 author's copyright notice, the distribution terms, or the list of
283 authors, are ok. It is also no problem to require modified versions
284 to include notice that they were modified. Even entire sections that
285 may not be deleted or changed are acceptable, as long as they deal
286 with nontechnical topics (like this one). These kinds of restrictions
287 are acceptable because they don't obstruct the community's normal use
290 However, it must be possible to modify all the @emph{technical}
291 content of the manual, and then distribute the result in all the usual
292 media, through all the usual channels. Otherwise, the restrictions
293 obstruct the use of the manual, it is not free, and we need another
294 manual to replace it.
296 Please spread the word about this issue. Our community continues to
297 lose manuals to proprietary publishing. If we spread the word that
298 free software needs free reference manuals and free tutorials, perhaps
299 the next person who wants to contribute by writing documentation will
300 realize, before it is too late, that only free manuals contribute to
301 the free software community.
303 If you are writing documentation, please insist on publishing it under
304 the GNU Free Documentation License or another free documentation
305 license. Remember that this decision requires your approval---you
306 don't have to let the publisher decide. Some commercial publishers
307 will use a free license if you insist, but they will not propose the
308 option; it is up to you to raise the issue and say firmly that this is
309 what you want. If the publisher you are dealing with refuses, please
310 try other publishers. If you're not sure whether a proposed license
311 is free, write to @email{licensing@@gnu.org}.
313 You can encourage commercial publishers to sell more free, copylefted
314 manuals and tutorials by buying them, and particularly by buying
315 copies from the publishers that paid for their writing or for major
316 improvements. Meanwhile, try to avoid buying non-free documentation
317 at all. Check the distribution terms of a manual before you buy it,
318 and insist that whoever seeks your business must respect your freedom.
319 Check the history of the book, and try to reward the publishers that
320 have paid or pay the authors to work on it.
322 The Free Software Foundation maintains a list of free documentation
323 published by other publishers, at
324 @url{http://www.fsf.org/doc/other-free-books.html}.
327 @unnumberedsec Contributors to @value{GDBN}
329 Richard Stallman was the original author of @value{GDBN}, and of many
330 other @sc{gnu} programs. Many others have contributed to its
331 development. This section attempts to credit major contributors. One
332 of the virtues of free software is that everyone is free to contribute
333 to it; with regret, we cannot actually acknowledge everyone here. The
334 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
335 blow-by-blow account.
337 Changes much prior to version 2.0 are lost in the mists of time.
340 @emph{Plea:} Additions to this section are particularly welcome. If you
341 or your friends (or enemies, to be evenhanded) have been unfairly
342 omitted from this list, we would like to add your names!
345 So that they may not regard their many labors as thankless, we
346 particularly thank those who shepherded @value{GDBN} through major
348 Andrew Cagney (releases 5.0 and 5.1);
349 Jim Blandy (release 4.18);
350 Jason Molenda (release 4.17);
351 Stan Shebs (release 4.14);
352 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
353 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
354 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
355 Jim Kingdon (releases 3.5, 3.4, and 3.3);
356 and Randy Smith (releases 3.2, 3.1, and 3.0).
358 Richard Stallman, assisted at various times by Peter TerMaat, Chris
359 Hanson, and Richard Mlynarik, handled releases through 2.8.
361 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
362 in @value{GDBN}, with significant additional contributions from Per
363 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
364 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
365 much general update work leading to release 3.0).
367 @value{GDBN} uses the BFD subroutine library to examine multiple
368 object-file formats; BFD was a joint project of David V.
369 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
371 David Johnson wrote the original COFF support; Pace Willison did
372 the original support for encapsulated COFF.
374 Brent Benson of Harris Computer Systems contributed DWARF2 support.
376 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
377 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
379 Jean-Daniel Fekete contributed Sun 386i support.
380 Chris Hanson improved the HP9000 support.
381 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
382 David Johnson contributed Encore Umax support.
383 Jyrki Kuoppala contributed Altos 3068 support.
384 Jeff Law contributed HP PA and SOM support.
385 Keith Packard contributed NS32K support.
386 Doug Rabson contributed Acorn Risc Machine support.
387 Bob Rusk contributed Harris Nighthawk CX-UX support.
388 Chris Smith contributed Convex support (and Fortran debugging).
389 Jonathan Stone contributed Pyramid support.
390 Michael Tiemann contributed SPARC support.
391 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
392 Pace Willison contributed Intel 386 support.
393 Jay Vosburgh contributed Symmetry support.
395 Andreas Schwab contributed M68K Linux support.
397 Rich Schaefer and Peter Schauer helped with support of SunOS shared
400 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
401 about several machine instruction sets.
403 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
404 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
405 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
406 and RDI targets, respectively.
408 Brian Fox is the author of the readline libraries providing
409 command-line editing and command history.
411 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
412 Modula-2 support, and contributed the Languages chapter of this manual.
414 Fred Fish wrote most of the support for Unix System Vr4.
415 He also enhanced the command-completion support to cover C@t{++} overloaded
418 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
421 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
423 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
425 Toshiba sponsored the support for the TX39 Mips processor.
427 Matsushita sponsored the support for the MN10200 and MN10300 processors.
429 Fujitsu sponsored the support for SPARClite and FR30 processors.
431 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
434 Michael Snyder added support for tracepoints.
436 Stu Grossman wrote gdbserver.
438 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
439 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
441 The following people at the Hewlett-Packard Company contributed
442 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
443 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
444 compiler, and the terminal user interface: Ben Krepp, Richard Title,
445 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
446 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
447 information in this manual.
449 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
450 Robert Hoehne made significant contributions to the DJGPP port.
452 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
453 development since 1991. Cygnus engineers who have worked on @value{GDBN}
454 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
455 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
456 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
457 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
458 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
459 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
460 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
461 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
462 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
463 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
464 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
465 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
466 Zuhn have made contributions both large and small.
468 Jim Blandy added support for preprocessor macros, while working for Red
472 @chapter A Sample @value{GDBN} Session
474 You can use this manual at your leisure to read all about @value{GDBN}.
475 However, a handful of commands are enough to get started using the
476 debugger. This chapter illustrates those commands.
479 In this sample session, we emphasize user input like this: @b{input},
480 to make it easier to pick out from the surrounding output.
483 @c FIXME: this example may not be appropriate for some configs, where
484 @c FIXME...primary interest is in remote use.
486 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
487 processor) exhibits the following bug: sometimes, when we change its
488 quote strings from the default, the commands used to capture one macro
489 definition within another stop working. In the following short @code{m4}
490 session, we define a macro @code{foo} which expands to @code{0000}; we
491 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
492 same thing. However, when we change the open quote string to
493 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
494 procedure fails to define a new synonym @code{baz}:
503 @b{define(bar,defn(`foo'))}
507 @b{changequote(<QUOTE>,<UNQUOTE>)}
509 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
512 m4: End of input: 0: fatal error: EOF in string
516 Let us use @value{GDBN} to try to see what is going on.
519 $ @b{@value{GDBP} m4}
520 @c FIXME: this falsifies the exact text played out, to permit smallbook
521 @c FIXME... format to come out better.
522 @value{GDBN} is free software and you are welcome to distribute copies
523 of it under certain conditions; type "show copying" to see
525 There is absolutely no warranty for @value{GDBN}; type "show warranty"
528 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
533 @value{GDBN} reads only enough symbol data to know where to find the
534 rest when needed; as a result, the first prompt comes up very quickly.
535 We now tell @value{GDBN} to use a narrower display width than usual, so
536 that examples fit in this manual.
539 (@value{GDBP}) @b{set width 70}
543 We need to see how the @code{m4} built-in @code{changequote} works.
544 Having looked at the source, we know the relevant subroutine is
545 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
546 @code{break} command.
549 (@value{GDBP}) @b{break m4_changequote}
550 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
554 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
555 control; as long as control does not reach the @code{m4_changequote}
556 subroutine, the program runs as usual:
559 (@value{GDBP}) @b{run}
560 Starting program: /work/Editorial/gdb/gnu/m4/m4
568 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
569 suspends execution of @code{m4}, displaying information about the
570 context where it stops.
573 @b{changequote(<QUOTE>,<UNQUOTE>)}
575 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
577 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
581 Now we use the command @code{n} (@code{next}) to advance execution to
582 the next line of the current function.
586 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
591 @code{set_quotes} looks like a promising subroutine. We can go into it
592 by using the command @code{s} (@code{step}) instead of @code{next}.
593 @code{step} goes to the next line to be executed in @emph{any}
594 subroutine, so it steps into @code{set_quotes}.
598 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
600 530 if (lquote != def_lquote)
604 The display that shows the subroutine where @code{m4} is now
605 suspended (and its arguments) is called a stack frame display. It
606 shows a summary of the stack. We can use the @code{backtrace}
607 command (which can also be spelled @code{bt}), to see where we are
608 in the stack as a whole: the @code{backtrace} command displays a
609 stack frame for each active subroutine.
612 (@value{GDBP}) @b{bt}
613 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
615 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
617 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
618 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
620 #4 0x79dc in expand_input () at macro.c:40
621 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
625 We step through a few more lines to see what happens. The first two
626 times, we can use @samp{s}; the next two times we use @code{n} to avoid
627 falling into the @code{xstrdup} subroutine.
631 0x3b5c 532 if (rquote != def_rquote)
633 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
634 def_lquote : xstrdup(lq);
636 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
639 538 len_lquote = strlen(rquote);
643 The last line displayed looks a little odd; we can examine the variables
644 @code{lquote} and @code{rquote} to see if they are in fact the new left
645 and right quotes we specified. We use the command @code{p}
646 (@code{print}) to see their values.
649 (@value{GDBP}) @b{p lquote}
650 $1 = 0x35d40 "<QUOTE>"
651 (@value{GDBP}) @b{p rquote}
652 $2 = 0x35d50 "<UNQUOTE>"
656 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
657 To look at some context, we can display ten lines of source
658 surrounding the current line with the @code{l} (@code{list}) command.
664 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
666 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
669 538 len_lquote = strlen(rquote);
670 539 len_rquote = strlen(lquote);
677 Let us step past the two lines that set @code{len_lquote} and
678 @code{len_rquote}, and then examine the values of those variables.
682 539 len_rquote = strlen(lquote);
685 (@value{GDBP}) @b{p len_lquote}
687 (@value{GDBP}) @b{p len_rquote}
692 That certainly looks wrong, assuming @code{len_lquote} and
693 @code{len_rquote} are meant to be the lengths of @code{lquote} and
694 @code{rquote} respectively. We can set them to better values using
695 the @code{p} command, since it can print the value of
696 any expression---and that expression can include subroutine calls and
700 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
702 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
707 Is that enough to fix the problem of using the new quotes with the
708 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
709 executing with the @code{c} (@code{continue}) command, and then try the
710 example that caused trouble initially:
716 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
723 Success! The new quotes now work just as well as the default ones. The
724 problem seems to have been just the two typos defining the wrong
725 lengths. We allow @code{m4} exit by giving it an EOF as input:
729 Program exited normally.
733 The message @samp{Program exited normally.} is from @value{GDBN}; it
734 indicates @code{m4} has finished executing. We can end our @value{GDBN}
735 session with the @value{GDBN} @code{quit} command.
738 (@value{GDBP}) @b{quit}
742 @chapter Getting In and Out of @value{GDBN}
744 This chapter discusses how to start @value{GDBN}, and how to get out of it.
748 type @samp{@value{GDBP}} to start @value{GDBN}.
750 type @kbd{quit} or @kbd{C-d} to exit.
754 * Invoking GDB:: How to start @value{GDBN}
755 * Quitting GDB:: How to quit @value{GDBN}
756 * Shell Commands:: How to use shell commands inside @value{GDBN}
760 @section Invoking @value{GDBN}
762 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
763 @value{GDBN} reads commands from the terminal until you tell it to exit.
765 You can also run @code{@value{GDBP}} with a variety of arguments and options,
766 to specify more of your debugging environment at the outset.
768 The command-line options described here are designed
769 to cover a variety of situations; in some environments, some of these
770 options may effectively be unavailable.
772 The most usual way to start @value{GDBN} is with one argument,
773 specifying an executable program:
776 @value{GDBP} @var{program}
780 You can also start with both an executable program and a core file
784 @value{GDBP} @var{program} @var{core}
787 You can, instead, specify a process ID as a second argument, if you want
788 to debug a running process:
791 @value{GDBP} @var{program} 1234
795 would attach @value{GDBN} to process @code{1234} (unless you also have a file
796 named @file{1234}; @value{GDBN} does check for a core file first).
798 Taking advantage of the second command-line argument requires a fairly
799 complete operating system; when you use @value{GDBN} as a remote
800 debugger attached to a bare board, there may not be any notion of
801 ``process'', and there is often no way to get a core dump. @value{GDBN}
802 will warn you if it is unable to attach or to read core dumps.
804 You can optionally have @code{@value{GDBP}} pass any arguments after the
805 executable file to the inferior using @code{--args}. This option stops
808 gdb --args gcc -O2 -c foo.c
810 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
811 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
813 You can run @code{@value{GDBP}} without printing the front material, which describes
814 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
821 You can further control how @value{GDBN} starts up by using command-line
822 options. @value{GDBN} itself can remind you of the options available.
832 to display all available options and briefly describe their use
833 (@samp{@value{GDBP} -h} is a shorter equivalent).
835 All options and command line arguments you give are processed
836 in sequential order. The order makes a difference when the
837 @samp{-x} option is used.
841 * File Options:: Choosing files
842 * Mode Options:: Choosing modes
846 @subsection Choosing files
848 When @value{GDBN} starts, it reads any arguments other than options as
849 specifying an executable file and core file (or process ID). This is
850 the same as if the arguments were specified by the @samp{-se} and
851 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
852 first argument that does not have an associated option flag as
853 equivalent to the @samp{-se} option followed by that argument; and the
854 second argument that does not have an associated option flag, if any, as
855 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
856 If the second argument begins with a decimal digit, @value{GDBN} will
857 first attempt to attach to it as a process, and if that fails, attempt
858 to open it as a corefile. If you have a corefile whose name begins with
859 a digit, you can prevent @value{GDBN} from treating it as a pid by
860 prefixing it with @file{./}, eg. @file{./12345}.
862 If @value{GDBN} has not been configured to included core file support,
863 such as for most embedded targets, then it will complain about a second
864 argument and ignore it.
866 Many options have both long and short forms; both are shown in the
867 following list. @value{GDBN} also recognizes the long forms if you truncate
868 them, so long as enough of the option is present to be unambiguous.
869 (If you prefer, you can flag option arguments with @samp{--} rather
870 than @samp{-}, though we illustrate the more usual convention.)
872 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
873 @c way, both those who look for -foo and --foo in the index, will find
877 @item -symbols @var{file}
879 @cindex @code{--symbols}
881 Read symbol table from file @var{file}.
883 @item -exec @var{file}
885 @cindex @code{--exec}
887 Use file @var{file} as the executable file to execute when appropriate,
888 and for examining pure data in conjunction with a core dump.
892 Read symbol table from file @var{file} and use it as the executable
895 @item -core @var{file}
897 @cindex @code{--core}
899 Use file @var{file} as a core dump to examine.
901 @item -c @var{number}
902 @item -pid @var{number}
903 @itemx -p @var{number}
906 Connect to process ID @var{number}, as with the @code{attach} command.
907 If there is no such process, @value{GDBN} will attempt to open a core
908 file named @var{number}.
910 @item -command @var{file}
912 @cindex @code{--command}
914 Execute @value{GDBN} commands from file @var{file}. @xref{Command
915 Files,, Command files}.
917 @item -directory @var{directory}
918 @itemx -d @var{directory}
919 @cindex @code{--directory}
921 Add @var{directory} to the path to search for source files.
925 @cindex @code{--mapped}
927 @emph{Warning: this option depends on operating system facilities that are not
928 supported on all systems.}@*
929 If memory-mapped files are available on your system through the @code{mmap}
930 system call, you can use this option
931 to have @value{GDBN} write the symbols from your
932 program into a reusable file in the current directory. If the program you are debugging is
933 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
934 Future @value{GDBN} debugging sessions notice the presence of this file,
935 and can quickly map in symbol information from it, rather than reading
936 the symbol table from the executable program.
938 The @file{.syms} file is specific to the host machine where @value{GDBN}
939 is run. It holds an exact image of the internal @value{GDBN} symbol
940 table. It cannot be shared across multiple host platforms.
944 @cindex @code{--readnow}
946 Read each symbol file's entire symbol table immediately, rather than
947 the default, which is to read it incrementally as it is needed.
948 This makes startup slower, but makes future operations faster.
952 You typically combine the @code{-mapped} and @code{-readnow} options in
953 order to build a @file{.syms} file that contains complete symbol
954 information. (@xref{Files,,Commands to specify files}, for information
955 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
956 but build a @file{.syms} file for future use is:
959 gdb -batch -nx -mapped -readnow programname
963 @subsection Choosing modes
965 You can run @value{GDBN} in various alternative modes---for example, in
966 batch mode or quiet mode.
973 Do not execute commands found in any initialization files. Normally,
974 @value{GDBN} executes the commands in these files after all the command
975 options and arguments have been processed. @xref{Command Files,,Command
981 @cindex @code{--quiet}
982 @cindex @code{--silent}
984 ``Quiet''. Do not print the introductory and copyright messages. These
985 messages are also suppressed in batch mode.
988 @cindex @code{--batch}
989 Run in batch mode. Exit with status @code{0} after processing all the
990 command files specified with @samp{-x} (and all commands from
991 initialization files, if not inhibited with @samp{-n}). Exit with
992 nonzero status if an error occurs in executing the @value{GDBN} commands
993 in the command files.
995 Batch mode may be useful for running @value{GDBN} as a filter, for
996 example to download and run a program on another computer; in order to
997 make this more useful, the message
1000 Program exited normally.
1004 (which is ordinarily issued whenever a program running under
1005 @value{GDBN} control terminates) is not issued when running in batch
1010 @cindex @code{--nowindows}
1012 ``No windows''. If @value{GDBN} comes with a graphical user interface
1013 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1014 interface. If no GUI is available, this option has no effect.
1018 @cindex @code{--windows}
1020 If @value{GDBN} includes a GUI, then this option requires it to be
1023 @item -cd @var{directory}
1025 Run @value{GDBN} using @var{directory} as its working directory,
1026 instead of the current directory.
1030 @cindex @code{--fullname}
1032 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1033 subprocess. It tells @value{GDBN} to output the full file name and line
1034 number in a standard, recognizable fashion each time a stack frame is
1035 displayed (which includes each time your program stops). This
1036 recognizable format looks like two @samp{\032} characters, followed by
1037 the file name, line number and character position separated by colons,
1038 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1039 @samp{\032} characters as a signal to display the source code for the
1043 @cindex @code{--epoch}
1044 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1045 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1046 routines so as to allow Epoch to display values of expressions in a
1049 @item -annotate @var{level}
1050 @cindex @code{--annotate}
1051 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1052 effect is identical to using @samp{set annotate @var{level}}
1053 (@pxref{Annotations}).
1054 Annotation level controls how much information does @value{GDBN} print
1055 together with its prompt, values of expressions, source lines, and other
1056 types of output. Level 0 is the normal, level 1 is for use when
1057 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1058 maximum annotation suitable for programs that control @value{GDBN}.
1061 @cindex @code{--async}
1062 Use the asynchronous event loop for the command-line interface.
1063 @value{GDBN} processes all events, such as user keyboard input, via a
1064 special event loop. This allows @value{GDBN} to accept and process user
1065 commands in parallel with the debugged process being
1066 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1067 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1068 suspended when the debuggee runs.}, so you don't need to wait for
1069 control to return to @value{GDBN} before you type the next command.
1070 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1071 operation is not yet in place, so @samp{-async} does not work fully
1073 @c FIXME: when the target side of the event loop is done, the above NOTE
1074 @c should be removed.
1076 When the standard input is connected to a terminal device, @value{GDBN}
1077 uses the asynchronous event loop by default, unless disabled by the
1078 @samp{-noasync} option.
1081 @cindex @code{--noasync}
1082 Disable the asynchronous event loop for the command-line interface.
1085 @cindex @code{--args}
1086 Change interpretation of command line so that arguments following the
1087 executable file are passed as command line arguments to the inferior.
1088 This option stops option processing.
1090 @item -baud @var{bps}
1092 @cindex @code{--baud}
1094 Set the line speed (baud rate or bits per second) of any serial
1095 interface used by @value{GDBN} for remote debugging.
1097 @item -tty @var{device}
1098 @itemx -t @var{device}
1099 @cindex @code{--tty}
1101 Run using @var{device} for your program's standard input and output.
1102 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1104 @c resolve the situation of these eventually
1106 @cindex @code{--tui}
1107 Activate the Terminal User Interface when starting.
1108 The Terminal User Interface manages several text windows on the terminal,
1109 showing source, assembly, registers and @value{GDBN} command outputs
1110 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1111 Do not use this option if you run @value{GDBN} from Emacs
1112 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1115 @c @cindex @code{--xdb}
1116 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1117 @c For information, see the file @file{xdb_trans.html}, which is usually
1118 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1121 @item -interpreter @var{interp}
1122 @cindex @code{--interpreter}
1123 Use the interpreter @var{interp} for interface with the controlling
1124 program or device. This option is meant to be set by programs which
1125 communicate with @value{GDBN} using it as a back end.
1127 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1128 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1129 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1130 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1133 @cindex @code{--write}
1134 Open the executable and core files for both reading and writing. This
1135 is equivalent to the @samp{set write on} command inside @value{GDBN}
1139 @cindex @code{--statistics}
1140 This option causes @value{GDBN} to print statistics about time and
1141 memory usage after it completes each command and returns to the prompt.
1144 @cindex @code{--version}
1145 This option causes @value{GDBN} to print its version number and
1146 no-warranty blurb, and exit.
1151 @section Quitting @value{GDBN}
1152 @cindex exiting @value{GDBN}
1153 @cindex leaving @value{GDBN}
1156 @kindex quit @r{[}@var{expression}@r{]}
1157 @kindex q @r{(@code{quit})}
1158 @item quit @r{[}@var{expression}@r{]}
1160 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1161 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1162 do not supply @var{expression}, @value{GDBN} will terminate normally;
1163 otherwise it will terminate using the result of @var{expression} as the
1168 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1169 terminates the action of any @value{GDBN} command that is in progress and
1170 returns to @value{GDBN} command level. It is safe to type the interrupt
1171 character at any time because @value{GDBN} does not allow it to take effect
1172 until a time when it is safe.
1174 If you have been using @value{GDBN} to control an attached process or
1175 device, you can release it with the @code{detach} command
1176 (@pxref{Attach, ,Debugging an already-running process}).
1178 @node Shell Commands
1179 @section Shell commands
1181 If you need to execute occasional shell commands during your
1182 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1183 just use the @code{shell} command.
1187 @cindex shell escape
1188 @item shell @var{command string}
1189 Invoke a standard shell to execute @var{command string}.
1190 If it exists, the environment variable @code{SHELL} determines which
1191 shell to run. Otherwise @value{GDBN} uses the default shell
1192 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1195 The utility @code{make} is often needed in development environments.
1196 You do not have to use the @code{shell} command for this purpose in
1201 @cindex calling make
1202 @item make @var{make-args}
1203 Execute the @code{make} program with the specified
1204 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1208 @chapter @value{GDBN} Commands
1210 You can abbreviate a @value{GDBN} command to the first few letters of the command
1211 name, if that abbreviation is unambiguous; and you can repeat certain
1212 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1213 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1214 show you the alternatives available, if there is more than one possibility).
1217 * Command Syntax:: How to give commands to @value{GDBN}
1218 * Completion:: Command completion
1219 * Help:: How to ask @value{GDBN} for help
1222 @node Command Syntax
1223 @section Command syntax
1225 A @value{GDBN} command is a single line of input. There is no limit on
1226 how long it can be. It starts with a command name, which is followed by
1227 arguments whose meaning depends on the command name. For example, the
1228 command @code{step} accepts an argument which is the number of times to
1229 step, as in @samp{step 5}. You can also use the @code{step} command
1230 with no arguments. Some commands do not allow any arguments.
1232 @cindex abbreviation
1233 @value{GDBN} command names may always be truncated if that abbreviation is
1234 unambiguous. Other possible command abbreviations are listed in the
1235 documentation for individual commands. In some cases, even ambiguous
1236 abbreviations are allowed; for example, @code{s} is specially defined as
1237 equivalent to @code{step} even though there are other commands whose
1238 names start with @code{s}. You can test abbreviations by using them as
1239 arguments to the @code{help} command.
1241 @cindex repeating commands
1242 @kindex RET @r{(repeat last command)}
1243 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1244 repeat the previous command. Certain commands (for example, @code{run})
1245 will not repeat this way; these are commands whose unintentional
1246 repetition might cause trouble and which you are unlikely to want to
1249 The @code{list} and @code{x} commands, when you repeat them with
1250 @key{RET}, construct new arguments rather than repeating
1251 exactly as typed. This permits easy scanning of source or memory.
1253 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1254 output, in a way similar to the common utility @code{more}
1255 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1256 @key{RET} too many in this situation, @value{GDBN} disables command
1257 repetition after any command that generates this sort of display.
1259 @kindex # @r{(a comment)}
1261 Any text from a @kbd{#} to the end of the line is a comment; it does
1262 nothing. This is useful mainly in command files (@pxref{Command
1263 Files,,Command files}).
1265 @cindex repeating command sequences
1266 @kindex C-o @r{(operate-and-get-next)}
1267 The @kbd{C-o} binding is useful for repeating a complex sequence of
1268 commands. This command accepts the current line, like @kbd{RET}, and
1269 then fetches the next line relative to the current line from the history
1273 @section Command completion
1276 @cindex word completion
1277 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1278 only one possibility; it can also show you what the valid possibilities
1279 are for the next word in a command, at any time. This works for @value{GDBN}
1280 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1282 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1283 of a word. If there is only one possibility, @value{GDBN} fills in the
1284 word, and waits for you to finish the command (or press @key{RET} to
1285 enter it). For example, if you type
1287 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1288 @c complete accuracy in these examples; space introduced for clarity.
1289 @c If texinfo enhancements make it unnecessary, it would be nice to
1290 @c replace " @key" by "@key" in the following...
1292 (@value{GDBP}) info bre @key{TAB}
1296 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1297 the only @code{info} subcommand beginning with @samp{bre}:
1300 (@value{GDBP}) info breakpoints
1304 You can either press @key{RET} at this point, to run the @code{info
1305 breakpoints} command, or backspace and enter something else, if
1306 @samp{breakpoints} does not look like the command you expected. (If you
1307 were sure you wanted @code{info breakpoints} in the first place, you
1308 might as well just type @key{RET} immediately after @samp{info bre},
1309 to exploit command abbreviations rather than command completion).
1311 If there is more than one possibility for the next word when you press
1312 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1313 characters and try again, or just press @key{TAB} a second time;
1314 @value{GDBN} displays all the possible completions for that word. For
1315 example, you might want to set a breakpoint on a subroutine whose name
1316 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1317 just sounds the bell. Typing @key{TAB} again displays all the
1318 function names in your program that begin with those characters, for
1322 (@value{GDBP}) b make_ @key{TAB}
1323 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1324 make_a_section_from_file make_environ
1325 make_abs_section make_function_type
1326 make_blockvector make_pointer_type
1327 make_cleanup make_reference_type
1328 make_command make_symbol_completion_list
1329 (@value{GDBP}) b make_
1333 After displaying the available possibilities, @value{GDBN} copies your
1334 partial input (@samp{b make_} in the example) so you can finish the
1337 If you just want to see the list of alternatives in the first place, you
1338 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1339 means @kbd{@key{META} ?}. You can type this either by holding down a
1340 key designated as the @key{META} shift on your keyboard (if there is
1341 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1343 @cindex quotes in commands
1344 @cindex completion of quoted strings
1345 Sometimes the string you need, while logically a ``word'', may contain
1346 parentheses or other characters that @value{GDBN} normally excludes from
1347 its notion of a word. To permit word completion to work in this
1348 situation, you may enclose words in @code{'} (single quote marks) in
1349 @value{GDBN} commands.
1351 The most likely situation where you might need this is in typing the
1352 name of a C@t{++} function. This is because C@t{++} allows function
1353 overloading (multiple definitions of the same function, distinguished
1354 by argument type). For example, when you want to set a breakpoint you
1355 may need to distinguish whether you mean the version of @code{name}
1356 that takes an @code{int} parameter, @code{name(int)}, or the version
1357 that takes a @code{float} parameter, @code{name(float)}. To use the
1358 word-completion facilities in this situation, type a single quote
1359 @code{'} at the beginning of the function name. This alerts
1360 @value{GDBN} that it may need to consider more information than usual
1361 when you press @key{TAB} or @kbd{M-?} to request word completion:
1364 (@value{GDBP}) b 'bubble( @kbd{M-?}
1365 bubble(double,double) bubble(int,int)
1366 (@value{GDBP}) b 'bubble(
1369 In some cases, @value{GDBN} can tell that completing a name requires using
1370 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1371 completing as much as it can) if you do not type the quote in the first
1375 (@value{GDBP}) b bub @key{TAB}
1376 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1377 (@value{GDBP}) b 'bubble(
1381 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1382 you have not yet started typing the argument list when you ask for
1383 completion on an overloaded symbol.
1385 For more information about overloaded functions, see @ref{C plus plus
1386 expressions, ,C@t{++} expressions}. You can use the command @code{set
1387 overload-resolution off} to disable overload resolution;
1388 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1392 @section Getting help
1393 @cindex online documentation
1396 You can always ask @value{GDBN} itself for information on its commands,
1397 using the command @code{help}.
1400 @kindex h @r{(@code{help})}
1403 You can use @code{help} (abbreviated @code{h}) with no arguments to
1404 display a short list of named classes of commands:
1408 List of classes of commands:
1410 aliases -- Aliases of other commands
1411 breakpoints -- Making program stop at certain points
1412 data -- Examining data
1413 files -- Specifying and examining files
1414 internals -- Maintenance commands
1415 obscure -- Obscure features
1416 running -- Running the program
1417 stack -- Examining the stack
1418 status -- Status inquiries
1419 support -- Support facilities
1420 tracepoints -- Tracing of program execution without@*
1421 stopping the program
1422 user-defined -- User-defined commands
1424 Type "help" followed by a class name for a list of
1425 commands in that class.
1426 Type "help" followed by command name for full
1428 Command name abbreviations are allowed if unambiguous.
1431 @c the above line break eliminates huge line overfull...
1433 @item help @var{class}
1434 Using one of the general help classes as an argument, you can get a
1435 list of the individual commands in that class. For example, here is the
1436 help display for the class @code{status}:
1439 (@value{GDBP}) help status
1444 @c Line break in "show" line falsifies real output, but needed
1445 @c to fit in smallbook page size.
1446 info -- Generic command for showing things
1447 about the program being debugged
1448 show -- Generic command for showing things
1451 Type "help" followed by command name for full
1453 Command name abbreviations are allowed if unambiguous.
1457 @item help @var{command}
1458 With a command name as @code{help} argument, @value{GDBN} displays a
1459 short paragraph on how to use that command.
1462 @item apropos @var{args}
1463 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1464 commands, and their documentation, for the regular expression specified in
1465 @var{args}. It prints out all matches found. For example:
1476 set symbol-reloading -- Set dynamic symbol table reloading
1477 multiple times in one run
1478 show symbol-reloading -- Show dynamic symbol table reloading
1479 multiple times in one run
1484 @item complete @var{args}
1485 The @code{complete @var{args}} command lists all the possible completions
1486 for the beginning of a command. Use @var{args} to specify the beginning of the
1487 command you want completed. For example:
1493 @noindent results in:
1504 @noindent This is intended for use by @sc{gnu} Emacs.
1507 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1508 and @code{show} to inquire about the state of your program, or the state
1509 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1510 manual introduces each of them in the appropriate context. The listings
1511 under @code{info} and under @code{show} in the Index point to
1512 all the sub-commands. @xref{Index}.
1517 @kindex i @r{(@code{info})}
1519 This command (abbreviated @code{i}) is for describing the state of your
1520 program. For example, you can list the arguments given to your program
1521 with @code{info args}, list the registers currently in use with @code{info
1522 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1523 You can get a complete list of the @code{info} sub-commands with
1524 @w{@code{help info}}.
1528 You can assign the result of an expression to an environment variable with
1529 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1530 @code{set prompt $}.
1534 In contrast to @code{info}, @code{show} is for describing the state of
1535 @value{GDBN} itself.
1536 You can change most of the things you can @code{show}, by using the
1537 related command @code{set}; for example, you can control what number
1538 system is used for displays with @code{set radix}, or simply inquire
1539 which is currently in use with @code{show radix}.
1542 To display all the settable parameters and their current
1543 values, you can use @code{show} with no arguments; you may also use
1544 @code{info set}. Both commands produce the same display.
1545 @c FIXME: "info set" violates the rule that "info" is for state of
1546 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1547 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1551 Here are three miscellaneous @code{show} subcommands, all of which are
1552 exceptional in lacking corresponding @code{set} commands:
1555 @kindex show version
1556 @cindex version number
1558 Show what version of @value{GDBN} is running. You should include this
1559 information in @value{GDBN} bug-reports. If multiple versions of
1560 @value{GDBN} are in use at your site, you may need to determine which
1561 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1562 commands are introduced, and old ones may wither away. Also, many
1563 system vendors ship variant versions of @value{GDBN}, and there are
1564 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1565 The version number is the same as the one announced when you start
1568 @kindex show copying
1570 Display information about permission for copying @value{GDBN}.
1572 @kindex show warranty
1574 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1575 if your version of @value{GDBN} comes with one.
1580 @chapter Running Programs Under @value{GDBN}
1582 When you run a program under @value{GDBN}, you must first generate
1583 debugging information when you compile it.
1585 You may start @value{GDBN} with its arguments, if any, in an environment
1586 of your choice. If you are doing native debugging, you may redirect
1587 your program's input and output, debug an already running process, or
1588 kill a child process.
1591 * Compilation:: Compiling for debugging
1592 * Starting:: Starting your program
1593 * Arguments:: Your program's arguments
1594 * Environment:: Your program's environment
1596 * Working Directory:: Your program's working directory
1597 * Input/Output:: Your program's input and output
1598 * Attach:: Debugging an already-running process
1599 * Kill Process:: Killing the child process
1601 * Threads:: Debugging programs with multiple threads
1602 * Processes:: Debugging programs with multiple processes
1606 @section Compiling for debugging
1608 In order to debug a program effectively, you need to generate
1609 debugging information when you compile it. This debugging information
1610 is stored in the object file; it describes the data type of each
1611 variable or function and the correspondence between source line numbers
1612 and addresses in the executable code.
1614 To request debugging information, specify the @samp{-g} option when you run
1617 Most compilers do not include information about preprocessor macros in
1618 the debugging information if you specify the @option{-g} flag alone,
1619 because this information is rather large. Version 3.1 of @value{NGCC},
1620 the @sc{gnu} C compiler, provides macro information if you specify the
1621 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1622 debugging information in the Dwarf 2 format, and the latter requests
1623 ``extra information''. In the future, we hope to find more compact ways
1624 to represent macro information, so that it can be included with
1627 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1628 options together. Using those compilers, you cannot generate optimized
1629 executables containing debugging information.
1631 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1632 without @samp{-O}, making it possible to debug optimized code. We
1633 recommend that you @emph{always} use @samp{-g} whenever you compile a
1634 program. You may think your program is correct, but there is no sense
1635 in pushing your luck.
1637 @cindex optimized code, debugging
1638 @cindex debugging optimized code
1639 When you debug a program compiled with @samp{-g -O}, remember that the
1640 optimizer is rearranging your code; the debugger shows you what is
1641 really there. Do not be too surprised when the execution path does not
1642 exactly match your source file! An extreme example: if you define a
1643 variable, but never use it, @value{GDBN} never sees that
1644 variable---because the compiler optimizes it out of existence.
1646 Some things do not work as well with @samp{-g -O} as with just
1647 @samp{-g}, particularly on machines with instruction scheduling. If in
1648 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1649 please report it to us as a bug (including a test case!).
1651 Older versions of the @sc{gnu} C compiler permitted a variant option
1652 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1653 format; if your @sc{gnu} C compiler has this option, do not use it.
1657 @section Starting your program
1663 @kindex r @r{(@code{run})}
1666 Use the @code{run} command to start your program under @value{GDBN}.
1667 You must first specify the program name (except on VxWorks) with an
1668 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1669 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1670 (@pxref{Files, ,Commands to specify files}).
1674 If you are running your program in an execution environment that
1675 supports processes, @code{run} creates an inferior process and makes
1676 that process run your program. (In environments without processes,
1677 @code{run} jumps to the start of your program.)
1679 The execution of a program is affected by certain information it
1680 receives from its superior. @value{GDBN} provides ways to specify this
1681 information, which you must do @emph{before} starting your program. (You
1682 can change it after starting your program, but such changes only affect
1683 your program the next time you start it.) This information may be
1684 divided into four categories:
1687 @item The @emph{arguments.}
1688 Specify the arguments to give your program as the arguments of the
1689 @code{run} command. If a shell is available on your target, the shell
1690 is used to pass the arguments, so that you may use normal conventions
1691 (such as wildcard expansion or variable substitution) in describing
1693 In Unix systems, you can control which shell is used with the
1694 @code{SHELL} environment variable.
1695 @xref{Arguments, ,Your program's arguments}.
1697 @item The @emph{environment.}
1698 Your program normally inherits its environment from @value{GDBN}, but you can
1699 use the @value{GDBN} commands @code{set environment} and @code{unset
1700 environment} to change parts of the environment that affect
1701 your program. @xref{Environment, ,Your program's environment}.
1703 @item The @emph{working directory.}
1704 Your program inherits its working directory from @value{GDBN}. You can set
1705 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1706 @xref{Working Directory, ,Your program's working directory}.
1708 @item The @emph{standard input and output.}
1709 Your program normally uses the same device for standard input and
1710 standard output as @value{GDBN} is using. You can redirect input and output
1711 in the @code{run} command line, or you can use the @code{tty} command to
1712 set a different device for your program.
1713 @xref{Input/Output, ,Your program's input and output}.
1716 @emph{Warning:} While input and output redirection work, you cannot use
1717 pipes to pass the output of the program you are debugging to another
1718 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1722 When you issue the @code{run} command, your program begins to execute
1723 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1724 of how to arrange for your program to stop. Once your program has
1725 stopped, you may call functions in your program, using the @code{print}
1726 or @code{call} commands. @xref{Data, ,Examining Data}.
1728 If the modification time of your symbol file has changed since the last
1729 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1730 table, and reads it again. When it does this, @value{GDBN} tries to retain
1731 your current breakpoints.
1734 @section Your program's arguments
1736 @cindex arguments (to your program)
1737 The arguments to your program can be specified by the arguments of the
1739 They are passed to a shell, which expands wildcard characters and
1740 performs redirection of I/O, and thence to your program. Your
1741 @code{SHELL} environment variable (if it exists) specifies what shell
1742 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1743 the default shell (@file{/bin/sh} on Unix).
1745 On non-Unix systems, the program is usually invoked directly by
1746 @value{GDBN}, which emulates I/O redirection via the appropriate system
1747 calls, and the wildcard characters are expanded by the startup code of
1748 the program, not by the shell.
1750 @code{run} with no arguments uses the same arguments used by the previous
1751 @code{run}, or those set by the @code{set args} command.
1756 Specify the arguments to be used the next time your program is run. If
1757 @code{set args} has no arguments, @code{run} executes your program
1758 with no arguments. Once you have run your program with arguments,
1759 using @code{set args} before the next @code{run} is the only way to run
1760 it again without arguments.
1764 Show the arguments to give your program when it is started.
1768 @section Your program's environment
1770 @cindex environment (of your program)
1771 The @dfn{environment} consists of a set of environment variables and
1772 their values. Environment variables conventionally record such things as
1773 your user name, your home directory, your terminal type, and your search
1774 path for programs to run. Usually you set up environment variables with
1775 the shell and they are inherited by all the other programs you run. When
1776 debugging, it can be useful to try running your program with a modified
1777 environment without having to start @value{GDBN} over again.
1781 @item path @var{directory}
1782 Add @var{directory} to the front of the @code{PATH} environment variable
1783 (the search path for executables) that will be passed to your program.
1784 The value of @code{PATH} used by @value{GDBN} does not change.
1785 You may specify several directory names, separated by whitespace or by a
1786 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1787 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1788 is moved to the front, so it is searched sooner.
1790 You can use the string @samp{$cwd} to refer to whatever is the current
1791 working directory at the time @value{GDBN} searches the path. If you
1792 use @samp{.} instead, it refers to the directory where you executed the
1793 @code{path} command. @value{GDBN} replaces @samp{.} in the
1794 @var{directory} argument (with the current path) before adding
1795 @var{directory} to the search path.
1796 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1797 @c document that, since repeating it would be a no-op.
1801 Display the list of search paths for executables (the @code{PATH}
1802 environment variable).
1804 @kindex show environment
1805 @item show environment @r{[}@var{varname}@r{]}
1806 Print the value of environment variable @var{varname} to be given to
1807 your program when it starts. If you do not supply @var{varname},
1808 print the names and values of all environment variables to be given to
1809 your program. You can abbreviate @code{environment} as @code{env}.
1811 @kindex set environment
1812 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1813 Set environment variable @var{varname} to @var{value}. The value
1814 changes for your program only, not for @value{GDBN} itself. @var{value} may
1815 be any string; the values of environment variables are just strings, and
1816 any interpretation is supplied by your program itself. The @var{value}
1817 parameter is optional; if it is eliminated, the variable is set to a
1819 @c "any string" here does not include leading, trailing
1820 @c blanks. Gnu asks: does anyone care?
1822 For example, this command:
1829 tells the debugged program, when subsequently run, that its user is named
1830 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1831 are not actually required.)
1833 @kindex unset environment
1834 @item unset environment @var{varname}
1835 Remove variable @var{varname} from the environment to be passed to your
1836 program. This is different from @samp{set env @var{varname} =};
1837 @code{unset environment} removes the variable from the environment,
1838 rather than assigning it an empty value.
1841 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1843 by your @code{SHELL} environment variable if it exists (or
1844 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1845 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1846 @file{.bashrc} for BASH---any variables you set in that file affect
1847 your program. You may wish to move setting of environment variables to
1848 files that are only run when you sign on, such as @file{.login} or
1851 @node Working Directory
1852 @section Your program's working directory
1854 @cindex working directory (of your program)
1855 Each time you start your program with @code{run}, it inherits its
1856 working directory from the current working directory of @value{GDBN}.
1857 The @value{GDBN} working directory is initially whatever it inherited
1858 from its parent process (typically the shell), but you can specify a new
1859 working directory in @value{GDBN} with the @code{cd} command.
1861 The @value{GDBN} working directory also serves as a default for the commands
1862 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1867 @item cd @var{directory}
1868 Set the @value{GDBN} working directory to @var{directory}.
1872 Print the @value{GDBN} working directory.
1876 @section Your program's input and output
1881 By default, the program you run under @value{GDBN} does input and output to
1882 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1883 to its own terminal modes to interact with you, but it records the terminal
1884 modes your program was using and switches back to them when you continue
1885 running your program.
1888 @kindex info terminal
1890 Displays information recorded by @value{GDBN} about the terminal modes your
1894 You can redirect your program's input and/or output using shell
1895 redirection with the @code{run} command. For example,
1902 starts your program, diverting its output to the file @file{outfile}.
1905 @cindex controlling terminal
1906 Another way to specify where your program should do input and output is
1907 with the @code{tty} command. This command accepts a file name as
1908 argument, and causes this file to be the default for future @code{run}
1909 commands. It also resets the controlling terminal for the child
1910 process, for future @code{run} commands. For example,
1917 directs that processes started with subsequent @code{run} commands
1918 default to do input and output on the terminal @file{/dev/ttyb} and have
1919 that as their controlling terminal.
1921 An explicit redirection in @code{run} overrides the @code{tty} command's
1922 effect on the input/output device, but not its effect on the controlling
1925 When you use the @code{tty} command or redirect input in the @code{run}
1926 command, only the input @emph{for your program} is affected. The input
1927 for @value{GDBN} still comes from your terminal.
1930 @section Debugging an already-running process
1935 @item attach @var{process-id}
1936 This command attaches to a running process---one that was started
1937 outside @value{GDBN}. (@code{info files} shows your active
1938 targets.) The command takes as argument a process ID. The usual way to
1939 find out the process-id of a Unix process is with the @code{ps} utility,
1940 or with the @samp{jobs -l} shell command.
1942 @code{attach} does not repeat if you press @key{RET} a second time after
1943 executing the command.
1946 To use @code{attach}, your program must be running in an environment
1947 which supports processes; for example, @code{attach} does not work for
1948 programs on bare-board targets that lack an operating system. You must
1949 also have permission to send the process a signal.
1951 When you use @code{attach}, the debugger finds the program running in
1952 the process first by looking in the current working directory, then (if
1953 the program is not found) by using the source file search path
1954 (@pxref{Source Path, ,Specifying source directories}). You can also use
1955 the @code{file} command to load the program. @xref{Files, ,Commands to
1958 The first thing @value{GDBN} does after arranging to debug the specified
1959 process is to stop it. You can examine and modify an attached process
1960 with all the @value{GDBN} commands that are ordinarily available when
1961 you start processes with @code{run}. You can insert breakpoints; you
1962 can step and continue; you can modify storage. If you would rather the
1963 process continue running, you may use the @code{continue} command after
1964 attaching @value{GDBN} to the process.
1969 When you have finished debugging the attached process, you can use the
1970 @code{detach} command to release it from @value{GDBN} control. Detaching
1971 the process continues its execution. After the @code{detach} command,
1972 that process and @value{GDBN} become completely independent once more, and you
1973 are ready to @code{attach} another process or start one with @code{run}.
1974 @code{detach} does not repeat if you press @key{RET} again after
1975 executing the command.
1978 If you exit @value{GDBN} or use the @code{run} command while you have an
1979 attached process, you kill that process. By default, @value{GDBN} asks
1980 for confirmation if you try to do either of these things; you can
1981 control whether or not you need to confirm by using the @code{set
1982 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1986 @section Killing the child process
1991 Kill the child process in which your program is running under @value{GDBN}.
1994 This command is useful if you wish to debug a core dump instead of a
1995 running process. @value{GDBN} ignores any core dump file while your program
1998 On some operating systems, a program cannot be executed outside @value{GDBN}
1999 while you have breakpoints set on it inside @value{GDBN}. You can use the
2000 @code{kill} command in this situation to permit running your program
2001 outside the debugger.
2003 The @code{kill} command is also useful if you wish to recompile and
2004 relink your program, since on many systems it is impossible to modify an
2005 executable file while it is running in a process. In this case, when you
2006 next type @code{run}, @value{GDBN} notices that the file has changed, and
2007 reads the symbol table again (while trying to preserve your current
2008 breakpoint settings).
2011 @section Debugging programs with multiple threads
2013 @cindex threads of execution
2014 @cindex multiple threads
2015 @cindex switching threads
2016 In some operating systems, such as HP-UX and Solaris, a single program
2017 may have more than one @dfn{thread} of execution. The precise semantics
2018 of threads differ from one operating system to another, but in general
2019 the threads of a single program are akin to multiple processes---except
2020 that they share one address space (that is, they can all examine and
2021 modify the same variables). On the other hand, each thread has its own
2022 registers and execution stack, and perhaps private memory.
2024 @value{GDBN} provides these facilities for debugging multi-thread
2028 @item automatic notification of new threads
2029 @item @samp{thread @var{threadno}}, a command to switch among threads
2030 @item @samp{info threads}, a command to inquire about existing threads
2031 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2032 a command to apply a command to a list of threads
2033 @item thread-specific breakpoints
2037 @emph{Warning:} These facilities are not yet available on every
2038 @value{GDBN} configuration where the operating system supports threads.
2039 If your @value{GDBN} does not support threads, these commands have no
2040 effect. For example, a system without thread support shows no output
2041 from @samp{info threads}, and always rejects the @code{thread} command,
2045 (@value{GDBP}) info threads
2046 (@value{GDBP}) thread 1
2047 Thread ID 1 not known. Use the "info threads" command to
2048 see the IDs of currently known threads.
2050 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2051 @c doesn't support threads"?
2054 @cindex focus of debugging
2055 @cindex current thread
2056 The @value{GDBN} thread debugging facility allows you to observe all
2057 threads while your program runs---but whenever @value{GDBN} takes
2058 control, one thread in particular is always the focus of debugging.
2059 This thread is called the @dfn{current thread}. Debugging commands show
2060 program information from the perspective of the current thread.
2062 @cindex @code{New} @var{systag} message
2063 @cindex thread identifier (system)
2064 @c FIXME-implementors!! It would be more helpful if the [New...] message
2065 @c included GDB's numeric thread handle, so you could just go to that
2066 @c thread without first checking `info threads'.
2067 Whenever @value{GDBN} detects a new thread in your program, it displays
2068 the target system's identification for the thread with a message in the
2069 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2070 whose form varies depending on the particular system. For example, on
2071 LynxOS, you might see
2074 [New process 35 thread 27]
2078 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2079 the @var{systag} is simply something like @samp{process 368}, with no
2082 @c FIXME!! (1) Does the [New...] message appear even for the very first
2083 @c thread of a program, or does it only appear for the
2084 @c second---i.e.@: when it becomes obvious we have a multithread
2086 @c (2) *Is* there necessarily a first thread always? Or do some
2087 @c multithread systems permit starting a program with multiple
2088 @c threads ab initio?
2090 @cindex thread number
2091 @cindex thread identifier (GDB)
2092 For debugging purposes, @value{GDBN} associates its own thread
2093 number---always a single integer---with each thread in your program.
2096 @kindex info threads
2098 Display a summary of all threads currently in your
2099 program. @value{GDBN} displays for each thread (in this order):
2102 @item the thread number assigned by @value{GDBN}
2104 @item the target system's thread identifier (@var{systag})
2106 @item the current stack frame summary for that thread
2110 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2111 indicates the current thread.
2115 @c end table here to get a little more width for example
2118 (@value{GDBP}) info threads
2119 3 process 35 thread 27 0x34e5 in sigpause ()
2120 2 process 35 thread 23 0x34e5 in sigpause ()
2121 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2127 @cindex thread number
2128 @cindex thread identifier (GDB)
2129 For debugging purposes, @value{GDBN} associates its own thread
2130 number---a small integer assigned in thread-creation order---with each
2131 thread in your program.
2133 @cindex @code{New} @var{systag} message, on HP-UX
2134 @cindex thread identifier (system), on HP-UX
2135 @c FIXME-implementors!! It would be more helpful if the [New...] message
2136 @c included GDB's numeric thread handle, so you could just go to that
2137 @c thread without first checking `info threads'.
2138 Whenever @value{GDBN} detects a new thread in your program, it displays
2139 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2140 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2141 whose form varies depending on the particular system. For example, on
2145 [New thread 2 (system thread 26594)]
2149 when @value{GDBN} notices a new thread.
2152 @kindex info threads
2154 Display a summary of all threads currently in your
2155 program. @value{GDBN} displays for each thread (in this order):
2158 @item the thread number assigned by @value{GDBN}
2160 @item the target system's thread identifier (@var{systag})
2162 @item the current stack frame summary for that thread
2166 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2167 indicates the current thread.
2171 @c end table here to get a little more width for example
2174 (@value{GDBP}) info threads
2175 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2177 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2178 from /usr/lib/libc.2
2179 1 system thread 27905 0x7b003498 in _brk () \@*
2180 from /usr/lib/libc.2
2184 @kindex thread @var{threadno}
2185 @item thread @var{threadno}
2186 Make thread number @var{threadno} the current thread. The command
2187 argument @var{threadno} is the internal @value{GDBN} thread number, as
2188 shown in the first field of the @samp{info threads} display.
2189 @value{GDBN} responds by displaying the system identifier of the thread
2190 you selected, and its current stack frame summary:
2193 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2194 (@value{GDBP}) thread 2
2195 [Switching to process 35 thread 23]
2196 0x34e5 in sigpause ()
2200 As with the @samp{[New @dots{}]} message, the form of the text after
2201 @samp{Switching to} depends on your system's conventions for identifying
2204 @kindex thread apply
2205 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2206 The @code{thread apply} command allows you to apply a command to one or
2207 more threads. Specify the numbers of the threads that you want affected
2208 with the command argument @var{threadno}. @var{threadno} is the internal
2209 @value{GDBN} thread number, as shown in the first field of the @samp{info
2210 threads} display. To apply a command to all threads, use
2211 @code{thread apply all} @var{args}.
2214 @cindex automatic thread selection
2215 @cindex switching threads automatically
2216 @cindex threads, automatic switching
2217 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2218 signal, it automatically selects the thread where that breakpoint or
2219 signal happened. @value{GDBN} alerts you to the context switch with a
2220 message of the form @samp{[Switching to @var{systag}]} to identify the
2223 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2224 more information about how @value{GDBN} behaves when you stop and start
2225 programs with multiple threads.
2227 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2228 watchpoints in programs with multiple threads.
2231 @section Debugging programs with multiple processes
2233 @cindex fork, debugging programs which call
2234 @cindex multiple processes
2235 @cindex processes, multiple
2236 On most systems, @value{GDBN} has no special support for debugging
2237 programs which create additional processes using the @code{fork}
2238 function. When a program forks, @value{GDBN} will continue to debug the
2239 parent process and the child process will run unimpeded. If you have
2240 set a breakpoint in any code which the child then executes, the child
2241 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2242 will cause it to terminate.
2244 However, if you want to debug the child process there is a workaround
2245 which isn't too painful. Put a call to @code{sleep} in the code which
2246 the child process executes after the fork. It may be useful to sleep
2247 only if a certain environment variable is set, or a certain file exists,
2248 so that the delay need not occur when you don't want to run @value{GDBN}
2249 on the child. While the child is sleeping, use the @code{ps} program to
2250 get its process ID. Then tell @value{GDBN} (a new invocation of
2251 @value{GDBN} if you are also debugging the parent process) to attach to
2252 the child process (@pxref{Attach}). From that point on you can debug
2253 the child process just like any other process which you attached to.
2255 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2256 debugging programs that create additional processes using the
2257 @code{fork} or @code{vfork} function.
2259 By default, when a program forks, @value{GDBN} will continue to debug
2260 the parent process and the child process will run unimpeded.
2262 If you want to follow the child process instead of the parent process,
2263 use the command @w{@code{set follow-fork-mode}}.
2266 @kindex set follow-fork-mode
2267 @item set follow-fork-mode @var{mode}
2268 Set the debugger response to a program call of @code{fork} or
2269 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2270 process. The @var{mode} can be:
2274 The original process is debugged after a fork. The child process runs
2275 unimpeded. This is the default.
2278 The new process is debugged after a fork. The parent process runs
2282 The debugger will ask for one of the above choices.
2285 @item show follow-fork-mode
2286 Display the current debugger response to a @code{fork} or @code{vfork} call.
2289 If you ask to debug a child process and a @code{vfork} is followed by an
2290 @code{exec}, @value{GDBN} executes the new target up to the first
2291 breakpoint in the new target. If you have a breakpoint set on
2292 @code{main} in your original program, the breakpoint will also be set on
2293 the child process's @code{main}.
2295 When a child process is spawned by @code{vfork}, you cannot debug the
2296 child or parent until an @code{exec} call completes.
2298 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2299 call executes, the new target restarts. To restart the parent process,
2300 use the @code{file} command with the parent executable name as its
2303 You can use the @code{catch} command to make @value{GDBN} stop whenever
2304 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2305 Catchpoints, ,Setting catchpoints}.
2308 @chapter Stopping and Continuing
2310 The principal purposes of using a debugger are so that you can stop your
2311 program before it terminates; or so that, if your program runs into
2312 trouble, you can investigate and find out why.
2314 Inside @value{GDBN}, your program may stop for any of several reasons,
2315 such as a signal, a breakpoint, or reaching a new line after a
2316 @value{GDBN} command such as @code{step}. You may then examine and
2317 change variables, set new breakpoints or remove old ones, and then
2318 continue execution. Usually, the messages shown by @value{GDBN} provide
2319 ample explanation of the status of your program---but you can also
2320 explicitly request this information at any time.
2323 @kindex info program
2325 Display information about the status of your program: whether it is
2326 running or not, what process it is, and why it stopped.
2330 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2331 * Continuing and Stepping:: Resuming execution
2333 * Thread Stops:: Stopping and starting multi-thread programs
2337 @section Breakpoints, watchpoints, and catchpoints
2340 A @dfn{breakpoint} makes your program stop whenever a certain point in
2341 the program is reached. For each breakpoint, you can add conditions to
2342 control in finer detail whether your program stops. You can set
2343 breakpoints with the @code{break} command and its variants (@pxref{Set
2344 Breaks, ,Setting breakpoints}), to specify the place where your program
2345 should stop by line number, function name or exact address in the
2348 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2349 breakpoints in shared libraries before the executable is run. There is
2350 a minor limitation on HP-UX systems: you must wait until the executable
2351 is run in order to set breakpoints in shared library routines that are
2352 not called directly by the program (for example, routines that are
2353 arguments in a @code{pthread_create} call).
2356 @cindex memory tracing
2357 @cindex breakpoint on memory address
2358 @cindex breakpoint on variable modification
2359 A @dfn{watchpoint} is a special breakpoint that stops your program
2360 when the value of an expression changes. You must use a different
2361 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2362 watchpoints}), but aside from that, you can manage a watchpoint like
2363 any other breakpoint: you enable, disable, and delete both breakpoints
2364 and watchpoints using the same commands.
2366 You can arrange to have values from your program displayed automatically
2367 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2371 @cindex breakpoint on events
2372 A @dfn{catchpoint} is another special breakpoint that stops your program
2373 when a certain kind of event occurs, such as the throwing of a C@t{++}
2374 exception or the loading of a library. As with watchpoints, you use a
2375 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2376 catchpoints}), but aside from that, you can manage a catchpoint like any
2377 other breakpoint. (To stop when your program receives a signal, use the
2378 @code{handle} command; see @ref{Signals, ,Signals}.)
2380 @cindex breakpoint numbers
2381 @cindex numbers for breakpoints
2382 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2383 catchpoint when you create it; these numbers are successive integers
2384 starting with one. In many of the commands for controlling various
2385 features of breakpoints you use the breakpoint number to say which
2386 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2387 @dfn{disabled}; if disabled, it has no effect on your program until you
2390 @cindex breakpoint ranges
2391 @cindex ranges of breakpoints
2392 Some @value{GDBN} commands accept a range of breakpoints on which to
2393 operate. A breakpoint range is either a single breakpoint number, like
2394 @samp{5}, or two such numbers, in increasing order, separated by a
2395 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2396 all breakpoint in that range are operated on.
2399 * Set Breaks:: Setting breakpoints
2400 * Set Watchpoints:: Setting watchpoints
2401 * Set Catchpoints:: Setting catchpoints
2402 * Delete Breaks:: Deleting breakpoints
2403 * Disabling:: Disabling breakpoints
2404 * Conditions:: Break conditions
2405 * Break Commands:: Breakpoint command lists
2406 * Breakpoint Menus:: Breakpoint menus
2407 * Error in Breakpoints:: ``Cannot insert breakpoints''
2411 @subsection Setting breakpoints
2413 @c FIXME LMB what does GDB do if no code on line of breakpt?
2414 @c consider in particular declaration with/without initialization.
2416 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2419 @kindex b @r{(@code{break})}
2420 @vindex $bpnum@r{, convenience variable}
2421 @cindex latest breakpoint
2422 Breakpoints are set with the @code{break} command (abbreviated
2423 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2424 number of the breakpoint you've set most recently; see @ref{Convenience
2425 Vars,, Convenience variables}, for a discussion of what you can do with
2426 convenience variables.
2428 You have several ways to say where the breakpoint should go.
2431 @item break @var{function}
2432 Set a breakpoint at entry to function @var{function}.
2433 When using source languages that permit overloading of symbols, such as
2434 C@t{++}, @var{function} may refer to more than one possible place to break.
2435 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2437 @item break +@var{offset}
2438 @itemx break -@var{offset}
2439 Set a breakpoint some number of lines forward or back from the position
2440 at which execution stopped in the currently selected @dfn{stack frame}.
2441 (@xref{Frames, ,Frames}, for a description of stack frames.)
2443 @item break @var{linenum}
2444 Set a breakpoint at line @var{linenum} in the current source file.
2445 The current source file is the last file whose source text was printed.
2446 The breakpoint will stop your program just before it executes any of the
2449 @item break @var{filename}:@var{linenum}
2450 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2452 @item break @var{filename}:@var{function}
2453 Set a breakpoint at entry to function @var{function} found in file
2454 @var{filename}. Specifying a file name as well as a function name is
2455 superfluous except when multiple files contain similarly named
2458 @item break *@var{address}
2459 Set a breakpoint at address @var{address}. You can use this to set
2460 breakpoints in parts of your program which do not have debugging
2461 information or source files.
2464 When called without any arguments, @code{break} sets a breakpoint at
2465 the next instruction to be executed in the selected stack frame
2466 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2467 innermost, this makes your program stop as soon as control
2468 returns to that frame. This is similar to the effect of a
2469 @code{finish} command in the frame inside the selected frame---except
2470 that @code{finish} does not leave an active breakpoint. If you use
2471 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2472 the next time it reaches the current location; this may be useful
2475 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2476 least one instruction has been executed. If it did not do this, you
2477 would be unable to proceed past a breakpoint without first disabling the
2478 breakpoint. This rule applies whether or not the breakpoint already
2479 existed when your program stopped.
2481 @item break @dots{} if @var{cond}
2482 Set a breakpoint with condition @var{cond}; evaluate the expression
2483 @var{cond} each time the breakpoint is reached, and stop only if the
2484 value is nonzero---that is, if @var{cond} evaluates as true.
2485 @samp{@dots{}} stands for one of the possible arguments described
2486 above (or no argument) specifying where to break. @xref{Conditions,
2487 ,Break conditions}, for more information on breakpoint conditions.
2490 @item tbreak @var{args}
2491 Set a breakpoint enabled only for one stop. @var{args} are the
2492 same as for the @code{break} command, and the breakpoint is set in the same
2493 way, but the breakpoint is automatically deleted after the first time your
2494 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2497 @item hbreak @var{args}
2498 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2499 @code{break} command and the breakpoint is set in the same way, but the
2500 breakpoint requires hardware support and some target hardware may not
2501 have this support. The main purpose of this is EPROM/ROM code
2502 debugging, so you can set a breakpoint at an instruction without
2503 changing the instruction. This can be used with the new trap-generation
2504 provided by SPARClite DSU and some x86-based targets. These targets
2505 will generate traps when a program accesses some data or instruction
2506 address that is assigned to the debug registers. However the hardware
2507 breakpoint registers can take a limited number of breakpoints. For
2508 example, on the DSU, only two data breakpoints can be set at a time, and
2509 @value{GDBN} will reject this command if more than two are used. Delete
2510 or disable unused hardware breakpoints before setting new ones
2511 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2514 @item thbreak @var{args}
2515 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2516 are the same as for the @code{hbreak} command and the breakpoint is set in
2517 the same way. However, like the @code{tbreak} command,
2518 the breakpoint is automatically deleted after the
2519 first time your program stops there. Also, like the @code{hbreak}
2520 command, the breakpoint requires hardware support and some target hardware
2521 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2522 See also @ref{Conditions, ,Break conditions}.
2525 @cindex regular expression
2526 @item rbreak @var{regex}
2527 Set breakpoints on all functions matching the regular expression
2528 @var{regex}. This command sets an unconditional breakpoint on all
2529 matches, printing a list of all breakpoints it set. Once these
2530 breakpoints are set, they are treated just like the breakpoints set with
2531 the @code{break} command. You can delete them, disable them, or make
2532 them conditional the same way as any other breakpoint.
2534 The syntax of the regular expression is the standard one used with tools
2535 like @file{grep}. Note that this is different from the syntax used by
2536 shells, so for instance @code{foo*} matches all functions that include
2537 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2538 @code{.*} leading and trailing the regular expression you supply, so to
2539 match only functions that begin with @code{foo}, use @code{^foo}.
2541 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2542 breakpoints on overloaded functions that are not members of any special
2545 @kindex info breakpoints
2546 @cindex @code{$_} and @code{info breakpoints}
2547 @item info breakpoints @r{[}@var{n}@r{]}
2548 @itemx info break @r{[}@var{n}@r{]}
2549 @itemx info watchpoints @r{[}@var{n}@r{]}
2550 Print a table of all breakpoints, watchpoints, and catchpoints set and
2551 not deleted, with the following columns for each breakpoint:
2554 @item Breakpoint Numbers
2556 Breakpoint, watchpoint, or catchpoint.
2558 Whether the breakpoint is marked to be disabled or deleted when hit.
2559 @item Enabled or Disabled
2560 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2561 that are not enabled.
2563 Where the breakpoint is in your program, as a memory address.
2565 Where the breakpoint is in the source for your program, as a file and
2570 If a breakpoint is conditional, @code{info break} shows the condition on
2571 the line following the affected breakpoint; breakpoint commands, if any,
2572 are listed after that.
2575 @code{info break} with a breakpoint
2576 number @var{n} as argument lists only that breakpoint. The
2577 convenience variable @code{$_} and the default examining-address for
2578 the @code{x} command are set to the address of the last breakpoint
2579 listed (@pxref{Memory, ,Examining memory}).
2582 @code{info break} displays a count of the number of times the breakpoint
2583 has been hit. This is especially useful in conjunction with the
2584 @code{ignore} command. You can ignore a large number of breakpoint
2585 hits, look at the breakpoint info to see how many times the breakpoint
2586 was hit, and then run again, ignoring one less than that number. This
2587 will get you quickly to the last hit of that breakpoint.
2590 @value{GDBN} allows you to set any number of breakpoints at the same place in
2591 your program. There is nothing silly or meaningless about this. When
2592 the breakpoints are conditional, this is even useful
2593 (@pxref{Conditions, ,Break conditions}).
2595 @cindex negative breakpoint numbers
2596 @cindex internal @value{GDBN} breakpoints
2597 @value{GDBN} itself sometimes sets breakpoints in your program for
2598 special purposes, such as proper handling of @code{longjmp} (in C
2599 programs). These internal breakpoints are assigned negative numbers,
2600 starting with @code{-1}; @samp{info breakpoints} does not display them.
2601 You can see these breakpoints with the @value{GDBN} maintenance command
2602 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2605 @node Set Watchpoints
2606 @subsection Setting watchpoints
2608 @cindex setting watchpoints
2609 @cindex software watchpoints
2610 @cindex hardware watchpoints
2611 You can use a watchpoint to stop execution whenever the value of an
2612 expression changes, without having to predict a particular place where
2615 Depending on your system, watchpoints may be implemented in software or
2616 hardware. @value{GDBN} does software watchpointing by single-stepping your
2617 program and testing the variable's value each time, which is hundreds of
2618 times slower than normal execution. (But this may still be worth it, to
2619 catch errors where you have no clue what part of your program is the
2622 On some systems, such as HP-UX, Linux and some other x86-based targets,
2623 @value{GDBN} includes support for
2624 hardware watchpoints, which do not slow down the running of your
2629 @item watch @var{expr}
2630 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2631 is written into by the program and its value changes.
2634 @item rwatch @var{expr}
2635 Set a watchpoint that will break when watch @var{expr} is read by the program.
2638 @item awatch @var{expr}
2639 Set a watchpoint that will break when @var{expr} is either read or written into
2642 @kindex info watchpoints
2643 @item info watchpoints
2644 This command prints a list of watchpoints, breakpoints, and catchpoints;
2645 it is the same as @code{info break}.
2648 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2649 watchpoints execute very quickly, and the debugger reports a change in
2650 value at the exact instruction where the change occurs. If @value{GDBN}
2651 cannot set a hardware watchpoint, it sets a software watchpoint, which
2652 executes more slowly and reports the change in value at the next
2653 statement, not the instruction, after the change occurs.
2655 When you issue the @code{watch} command, @value{GDBN} reports
2658 Hardware watchpoint @var{num}: @var{expr}
2662 if it was able to set a hardware watchpoint.
2664 Currently, the @code{awatch} and @code{rwatch} commands can only set
2665 hardware watchpoints, because accesses to data that don't change the
2666 value of the watched expression cannot be detected without examining
2667 every instruction as it is being executed, and @value{GDBN} does not do
2668 that currently. If @value{GDBN} finds that it is unable to set a
2669 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2670 will print a message like this:
2673 Expression cannot be implemented with read/access watchpoint.
2676 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2677 data type of the watched expression is wider than what a hardware
2678 watchpoint on the target machine can handle. For example, some systems
2679 can only watch regions that are up to 4 bytes wide; on such systems you
2680 cannot set hardware watchpoints for an expression that yields a
2681 double-precision floating-point number (which is typically 8 bytes
2682 wide). As a work-around, it might be possible to break the large region
2683 into a series of smaller ones and watch them with separate watchpoints.
2685 If you set too many hardware watchpoints, @value{GDBN} might be unable
2686 to insert all of them when you resume the execution of your program.
2687 Since the precise number of active watchpoints is unknown until such
2688 time as the program is about to be resumed, @value{GDBN} might not be
2689 able to warn you about this when you set the watchpoints, and the
2690 warning will be printed only when the program is resumed:
2693 Hardware watchpoint @var{num}: Could not insert watchpoint
2697 If this happens, delete or disable some of the watchpoints.
2699 The SPARClite DSU will generate traps when a program accesses some data
2700 or instruction address that is assigned to the debug registers. For the
2701 data addresses, DSU facilitates the @code{watch} command. However the
2702 hardware breakpoint registers can only take two data watchpoints, and
2703 both watchpoints must be the same kind. For example, you can set two
2704 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2705 @strong{or} two with @code{awatch} commands, but you cannot set one
2706 watchpoint with one command and the other with a different command.
2707 @value{GDBN} will reject the command if you try to mix watchpoints.
2708 Delete or disable unused watchpoint commands before setting new ones.
2710 If you call a function interactively using @code{print} or @code{call},
2711 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2712 kind of breakpoint or the call completes.
2714 @value{GDBN} automatically deletes watchpoints that watch local
2715 (automatic) variables, or expressions that involve such variables, when
2716 they go out of scope, that is, when the execution leaves the block in
2717 which these variables were defined. In particular, when the program
2718 being debugged terminates, @emph{all} local variables go out of scope,
2719 and so only watchpoints that watch global variables remain set. If you
2720 rerun the program, you will need to set all such watchpoints again. One
2721 way of doing that would be to set a code breakpoint at the entry to the
2722 @code{main} function and when it breaks, set all the watchpoints.
2725 @cindex watchpoints and threads
2726 @cindex threads and watchpoints
2727 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2728 usefulness. With the current watchpoint implementation, @value{GDBN}
2729 can only watch the value of an expression @emph{in a single thread}. If
2730 you are confident that the expression can only change due to the current
2731 thread's activity (and if you are also confident that no other thread
2732 can become current), then you can use watchpoints as usual. However,
2733 @value{GDBN} may not notice when a non-current thread's activity changes
2736 @c FIXME: this is almost identical to the previous paragraph.
2737 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2738 have only limited usefulness. If @value{GDBN} creates a software
2739 watchpoint, it can only watch the value of an expression @emph{in a
2740 single thread}. If you are confident that the expression can only
2741 change due to the current thread's activity (and if you are also
2742 confident that no other thread can become current), then you can use
2743 software watchpoints as usual. However, @value{GDBN} may not notice
2744 when a non-current thread's activity changes the expression. (Hardware
2745 watchpoints, in contrast, watch an expression in all threads.)
2748 @node Set Catchpoints
2749 @subsection Setting catchpoints
2750 @cindex catchpoints, setting
2751 @cindex exception handlers
2752 @cindex event handling
2754 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2755 kinds of program events, such as C@t{++} exceptions or the loading of a
2756 shared library. Use the @code{catch} command to set a catchpoint.
2760 @item catch @var{event}
2761 Stop when @var{event} occurs. @var{event} can be any of the following:
2765 The throwing of a C@t{++} exception.
2769 The catching of a C@t{++} exception.
2773 A call to @code{exec}. This is currently only available for HP-UX.
2777 A call to @code{fork}. This is currently only available for HP-UX.
2781 A call to @code{vfork}. This is currently only available for HP-UX.
2784 @itemx load @var{libname}
2786 The dynamic loading of any shared library, or the loading of the library
2787 @var{libname}. This is currently only available for HP-UX.
2790 @itemx unload @var{libname}
2791 @kindex catch unload
2792 The unloading of any dynamically loaded shared library, or the unloading
2793 of the library @var{libname}. This is currently only available for HP-UX.
2796 @item tcatch @var{event}
2797 Set a catchpoint that is enabled only for one stop. The catchpoint is
2798 automatically deleted after the first time the event is caught.
2802 Use the @code{info break} command to list the current catchpoints.
2804 There are currently some limitations to C@t{++} exception handling
2805 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2809 If you call a function interactively, @value{GDBN} normally returns
2810 control to you when the function has finished executing. If the call
2811 raises an exception, however, the call may bypass the mechanism that
2812 returns control to you and cause your program either to abort or to
2813 simply continue running until it hits a breakpoint, catches a signal
2814 that @value{GDBN} is listening for, or exits. This is the case even if
2815 you set a catchpoint for the exception; catchpoints on exceptions are
2816 disabled within interactive calls.
2819 You cannot raise an exception interactively.
2822 You cannot install an exception handler interactively.
2825 @cindex raise exceptions
2826 Sometimes @code{catch} is not the best way to debug exception handling:
2827 if you need to know exactly where an exception is raised, it is better to
2828 stop @emph{before} the exception handler is called, since that way you
2829 can see the stack before any unwinding takes place. If you set a
2830 breakpoint in an exception handler instead, it may not be easy to find
2831 out where the exception was raised.
2833 To stop just before an exception handler is called, you need some
2834 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2835 raised by calling a library function named @code{__raise_exception}
2836 which has the following ANSI C interface:
2839 /* @var{addr} is where the exception identifier is stored.
2840 @var{id} is the exception identifier. */
2841 void __raise_exception (void **addr, void *id);
2845 To make the debugger catch all exceptions before any stack
2846 unwinding takes place, set a breakpoint on @code{__raise_exception}
2847 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2849 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2850 that depends on the value of @var{id}, you can stop your program when
2851 a specific exception is raised. You can use multiple conditional
2852 breakpoints to stop your program when any of a number of exceptions are
2857 @subsection Deleting breakpoints
2859 @cindex clearing breakpoints, watchpoints, catchpoints
2860 @cindex deleting breakpoints, watchpoints, catchpoints
2861 It is often necessary to eliminate a breakpoint, watchpoint, or
2862 catchpoint once it has done its job and you no longer want your program
2863 to stop there. This is called @dfn{deleting} the breakpoint. A
2864 breakpoint that has been deleted no longer exists; it is forgotten.
2866 With the @code{clear} command you can delete breakpoints according to
2867 where they are in your program. With the @code{delete} command you can
2868 delete individual breakpoints, watchpoints, or catchpoints by specifying
2869 their breakpoint numbers.
2871 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2872 automatically ignores breakpoints on the first instruction to be executed
2873 when you continue execution without changing the execution address.
2878 Delete any breakpoints at the next instruction to be executed in the
2879 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2880 the innermost frame is selected, this is a good way to delete a
2881 breakpoint where your program just stopped.
2883 @item clear @var{function}
2884 @itemx clear @var{filename}:@var{function}
2885 Delete any breakpoints set at entry to the function @var{function}.
2887 @item clear @var{linenum}
2888 @itemx clear @var{filename}:@var{linenum}
2889 Delete any breakpoints set at or within the code of the specified line.
2891 @cindex delete breakpoints
2893 @kindex d @r{(@code{delete})}
2894 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2895 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2896 ranges specified as arguments. If no argument is specified, delete all
2897 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2898 confirm off}). You can abbreviate this command as @code{d}.
2902 @subsection Disabling breakpoints
2904 @kindex disable breakpoints
2905 @kindex enable breakpoints
2906 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2907 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2908 it had been deleted, but remembers the information on the breakpoint so
2909 that you can @dfn{enable} it again later.
2911 You disable and enable breakpoints, watchpoints, and catchpoints with
2912 the @code{enable} and @code{disable} commands, optionally specifying one
2913 or more breakpoint numbers as arguments. Use @code{info break} or
2914 @code{info watch} to print a list of breakpoints, watchpoints, and
2915 catchpoints if you do not know which numbers to use.
2917 A breakpoint, watchpoint, or catchpoint can have any of four different
2918 states of enablement:
2922 Enabled. The breakpoint stops your program. A breakpoint set
2923 with the @code{break} command starts out in this state.
2925 Disabled. The breakpoint has no effect on your program.
2927 Enabled once. The breakpoint stops your program, but then becomes
2930 Enabled for deletion. The breakpoint stops your program, but
2931 immediately after it does so it is deleted permanently. A breakpoint
2932 set with the @code{tbreak} command starts out in this state.
2935 You can use the following commands to enable or disable breakpoints,
2936 watchpoints, and catchpoints:
2939 @kindex disable breakpoints
2941 @kindex dis @r{(@code{disable})}
2942 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2943 Disable the specified breakpoints---or all breakpoints, if none are
2944 listed. A disabled breakpoint has no effect but is not forgotten. All
2945 options such as ignore-counts, conditions and commands are remembered in
2946 case the breakpoint is enabled again later. You may abbreviate
2947 @code{disable} as @code{dis}.
2949 @kindex enable breakpoints
2951 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2952 Enable the specified breakpoints (or all defined breakpoints). They
2953 become effective once again in stopping your program.
2955 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2956 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2957 of these breakpoints immediately after stopping your program.
2959 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2960 Enable the specified breakpoints to work once, then die. @value{GDBN}
2961 deletes any of these breakpoints as soon as your program stops there.
2964 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2965 @c confusing: tbreak is also initially enabled.
2966 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2967 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2968 subsequently, they become disabled or enabled only when you use one of
2969 the commands above. (The command @code{until} can set and delete a
2970 breakpoint of its own, but it does not change the state of your other
2971 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2975 @subsection Break conditions
2976 @cindex conditional breakpoints
2977 @cindex breakpoint conditions
2979 @c FIXME what is scope of break condition expr? Context where wanted?
2980 @c in particular for a watchpoint?
2981 The simplest sort of breakpoint breaks every time your program reaches a
2982 specified place. You can also specify a @dfn{condition} for a
2983 breakpoint. A condition is just a Boolean expression in your
2984 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2985 a condition evaluates the expression each time your program reaches it,
2986 and your program stops only if the condition is @emph{true}.
2988 This is the converse of using assertions for program validation; in that
2989 situation, you want to stop when the assertion is violated---that is,
2990 when the condition is false. In C, if you want to test an assertion expressed
2991 by the condition @var{assert}, you should set the condition
2992 @samp{! @var{assert}} on the appropriate breakpoint.
2994 Conditions are also accepted for watchpoints; you may not need them,
2995 since a watchpoint is inspecting the value of an expression anyhow---but
2996 it might be simpler, say, to just set a watchpoint on a variable name,
2997 and specify a condition that tests whether the new value is an interesting
3000 Break conditions can have side effects, and may even call functions in
3001 your program. This can be useful, for example, to activate functions
3002 that log program progress, or to use your own print functions to
3003 format special data structures. The effects are completely predictable
3004 unless there is another enabled breakpoint at the same address. (In
3005 that case, @value{GDBN} might see the other breakpoint first and stop your
3006 program without checking the condition of this one.) Note that
3007 breakpoint commands are usually more convenient and flexible than break
3009 purpose of performing side effects when a breakpoint is reached
3010 (@pxref{Break Commands, ,Breakpoint command lists}).
3012 Break conditions can be specified when a breakpoint is set, by using
3013 @samp{if} in the arguments to the @code{break} command. @xref{Set
3014 Breaks, ,Setting breakpoints}. They can also be changed at any time
3015 with the @code{condition} command.
3017 You can also use the @code{if} keyword with the @code{watch} command.
3018 The @code{catch} command does not recognize the @code{if} keyword;
3019 @code{condition} is the only way to impose a further condition on a
3024 @item condition @var{bnum} @var{expression}
3025 Specify @var{expression} as the break condition for breakpoint,
3026 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3027 breakpoint @var{bnum} stops your program only if the value of
3028 @var{expression} is true (nonzero, in C). When you use
3029 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3030 syntactic correctness, and to determine whether symbols in it have
3031 referents in the context of your breakpoint. If @var{expression} uses
3032 symbols not referenced in the context of the breakpoint, @value{GDBN}
3033 prints an error message:
3036 No symbol "foo" in current context.
3041 not actually evaluate @var{expression} at the time the @code{condition}
3042 command (or a command that sets a breakpoint with a condition, like
3043 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3045 @item condition @var{bnum}
3046 Remove the condition from breakpoint number @var{bnum}. It becomes
3047 an ordinary unconditional breakpoint.
3050 @cindex ignore count (of breakpoint)
3051 A special case of a breakpoint condition is to stop only when the
3052 breakpoint has been reached a certain number of times. This is so
3053 useful that there is a special way to do it, using the @dfn{ignore
3054 count} of the breakpoint. Every breakpoint has an ignore count, which
3055 is an integer. Most of the time, the ignore count is zero, and
3056 therefore has no effect. But if your program reaches a breakpoint whose
3057 ignore count is positive, then instead of stopping, it just decrements
3058 the ignore count by one and continues. As a result, if the ignore count
3059 value is @var{n}, the breakpoint does not stop the next @var{n} times
3060 your program reaches it.
3064 @item ignore @var{bnum} @var{count}
3065 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3066 The next @var{count} times the breakpoint is reached, your program's
3067 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3070 To make the breakpoint stop the next time it is reached, specify
3073 When you use @code{continue} to resume execution of your program from a
3074 breakpoint, you can specify an ignore count directly as an argument to
3075 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3076 Stepping,,Continuing and stepping}.
3078 If a breakpoint has a positive ignore count and a condition, the
3079 condition is not checked. Once the ignore count reaches zero,
3080 @value{GDBN} resumes checking the condition.
3082 You could achieve the effect of the ignore count with a condition such
3083 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3084 is decremented each time. @xref{Convenience Vars, ,Convenience
3088 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3091 @node Break Commands
3092 @subsection Breakpoint command lists
3094 @cindex breakpoint commands
3095 You can give any breakpoint (or watchpoint or catchpoint) a series of
3096 commands to execute when your program stops due to that breakpoint. For
3097 example, you might want to print the values of certain expressions, or
3098 enable other breakpoints.
3103 @item commands @r{[}@var{bnum}@r{]}
3104 @itemx @dots{} @var{command-list} @dots{}
3106 Specify a list of commands for breakpoint number @var{bnum}. The commands
3107 themselves appear on the following lines. Type a line containing just
3108 @code{end} to terminate the commands.
3110 To remove all commands from a breakpoint, type @code{commands} and
3111 follow it immediately with @code{end}; that is, give no commands.
3113 With no @var{bnum} argument, @code{commands} refers to the last
3114 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3115 recently encountered).
3118 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3119 disabled within a @var{command-list}.
3121 You can use breakpoint commands to start your program up again. Simply
3122 use the @code{continue} command, or @code{step}, or any other command
3123 that resumes execution.
3125 Any other commands in the command list, after a command that resumes
3126 execution, are ignored. This is because any time you resume execution
3127 (even with a simple @code{next} or @code{step}), you may encounter
3128 another breakpoint---which could have its own command list, leading to
3129 ambiguities about which list to execute.
3132 If the first command you specify in a command list is @code{silent}, the
3133 usual message about stopping at a breakpoint is not printed. This may
3134 be desirable for breakpoints that are to print a specific message and
3135 then continue. If none of the remaining commands print anything, you
3136 see no sign that the breakpoint was reached. @code{silent} is
3137 meaningful only at the beginning of a breakpoint command list.
3139 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3140 print precisely controlled output, and are often useful in silent
3141 breakpoints. @xref{Output, ,Commands for controlled output}.
3143 For example, here is how you could use breakpoint commands to print the
3144 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3150 printf "x is %d\n",x
3155 One application for breakpoint commands is to compensate for one bug so
3156 you can test for another. Put a breakpoint just after the erroneous line
3157 of code, give it a condition to detect the case in which something
3158 erroneous has been done, and give it commands to assign correct values
3159 to any variables that need them. End with the @code{continue} command
3160 so that your program does not stop, and start with the @code{silent}
3161 command so that no output is produced. Here is an example:
3172 @node Breakpoint Menus
3173 @subsection Breakpoint menus
3175 @cindex symbol overloading
3177 Some programming languages (notably C@t{++}) permit a single function name
3178 to be defined several times, for application in different contexts.
3179 This is called @dfn{overloading}. When a function name is overloaded,
3180 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3181 a breakpoint. If you realize this is a problem, you can use
3182 something like @samp{break @var{function}(@var{types})} to specify which
3183 particular version of the function you want. Otherwise, @value{GDBN} offers
3184 you a menu of numbered choices for different possible breakpoints, and
3185 waits for your selection with the prompt @samp{>}. The first two
3186 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3187 sets a breakpoint at each definition of @var{function}, and typing
3188 @kbd{0} aborts the @code{break} command without setting any new
3191 For example, the following session excerpt shows an attempt to set a
3192 breakpoint at the overloaded symbol @code{String::after}.
3193 We choose three particular definitions of that function name:
3195 @c FIXME! This is likely to change to show arg type lists, at least
3198 (@value{GDBP}) b String::after
3201 [2] file:String.cc; line number:867
3202 [3] file:String.cc; line number:860
3203 [4] file:String.cc; line number:875
3204 [5] file:String.cc; line number:853
3205 [6] file:String.cc; line number:846
3206 [7] file:String.cc; line number:735
3208 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3209 Breakpoint 2 at 0xb344: file String.cc, line 875.
3210 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3211 Multiple breakpoints were set.
3212 Use the "delete" command to delete unwanted
3218 @c @ifclear BARETARGET
3219 @node Error in Breakpoints
3220 @subsection ``Cannot insert breakpoints''
3222 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3224 Under some operating systems, breakpoints cannot be used in a program if
3225 any other process is running that program. In this situation,
3226 attempting to run or continue a program with a breakpoint causes
3227 @value{GDBN} to print an error message:
3230 Cannot insert breakpoints.
3231 The same program may be running in another process.
3234 When this happens, you have three ways to proceed:
3238 Remove or disable the breakpoints, then continue.
3241 Suspend @value{GDBN}, and copy the file containing your program to a new
3242 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3243 that @value{GDBN} should run your program under that name.
3244 Then start your program again.
3247 Relink your program so that the text segment is nonsharable, using the
3248 linker option @samp{-N}. The operating system limitation may not apply
3249 to nonsharable executables.
3253 A similar message can be printed if you request too many active
3254 hardware-assisted breakpoints and watchpoints:
3256 @c FIXME: the precise wording of this message may change; the relevant
3257 @c source change is not committed yet (Sep 3, 1999).
3259 Stopped; cannot insert breakpoints.
3260 You may have requested too many hardware breakpoints and watchpoints.
3264 This message is printed when you attempt to resume the program, since
3265 only then @value{GDBN} knows exactly how many hardware breakpoints and
3266 watchpoints it needs to insert.
3268 When this message is printed, you need to disable or remove some of the
3269 hardware-assisted breakpoints and watchpoints, and then continue.
3272 @node Continuing and Stepping
3273 @section Continuing and stepping
3277 @cindex resuming execution
3278 @dfn{Continuing} means resuming program execution until your program
3279 completes normally. In contrast, @dfn{stepping} means executing just
3280 one more ``step'' of your program, where ``step'' may mean either one
3281 line of source code, or one machine instruction (depending on what
3282 particular command you use). Either when continuing or when stepping,
3283 your program may stop even sooner, due to a breakpoint or a signal. (If
3284 it stops due to a signal, you may want to use @code{handle}, or use
3285 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3289 @kindex c @r{(@code{continue})}
3290 @kindex fg @r{(resume foreground execution)}
3291 @item continue @r{[}@var{ignore-count}@r{]}
3292 @itemx c @r{[}@var{ignore-count}@r{]}
3293 @itemx fg @r{[}@var{ignore-count}@r{]}
3294 Resume program execution, at the address where your program last stopped;
3295 any breakpoints set at that address are bypassed. The optional argument
3296 @var{ignore-count} allows you to specify a further number of times to
3297 ignore a breakpoint at this location; its effect is like that of
3298 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3300 The argument @var{ignore-count} is meaningful only when your program
3301 stopped due to a breakpoint. At other times, the argument to
3302 @code{continue} is ignored.
3304 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3305 debugged program is deemed to be the foreground program) are provided
3306 purely for convenience, and have exactly the same behavior as
3310 To resume execution at a different place, you can use @code{return}
3311 (@pxref{Returning, ,Returning from a function}) to go back to the
3312 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3313 different address}) to go to an arbitrary location in your program.
3315 A typical technique for using stepping is to set a breakpoint
3316 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3317 beginning of the function or the section of your program where a problem
3318 is believed to lie, run your program until it stops at that breakpoint,
3319 and then step through the suspect area, examining the variables that are
3320 interesting, until you see the problem happen.
3324 @kindex s @r{(@code{step})}
3326 Continue running your program until control reaches a different source
3327 line, then stop it and return control to @value{GDBN}. This command is
3328 abbreviated @code{s}.
3331 @c "without debugging information" is imprecise; actually "without line
3332 @c numbers in the debugging information". (gcc -g1 has debugging info but
3333 @c not line numbers). But it seems complex to try to make that
3334 @c distinction here.
3335 @emph{Warning:} If you use the @code{step} command while control is
3336 within a function that was compiled without debugging information,
3337 execution proceeds until control reaches a function that does have
3338 debugging information. Likewise, it will not step into a function which
3339 is compiled without debugging information. To step through functions
3340 without debugging information, use the @code{stepi} command, described
3344 The @code{step} command only stops at the first instruction of a source
3345 line. This prevents the multiple stops that could otherwise occur in
3346 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3347 to stop if a function that has debugging information is called within
3348 the line. In other words, @code{step} @emph{steps inside} any functions
3349 called within the line.
3351 Also, the @code{step} command only enters a function if there is line
3352 number information for the function. Otherwise it acts like the
3353 @code{next} command. This avoids problems when using @code{cc -gl}
3354 on MIPS machines. Previously, @code{step} entered subroutines if there
3355 was any debugging information about the routine.
3357 @item step @var{count}
3358 Continue running as in @code{step}, but do so @var{count} times. If a
3359 breakpoint is reached, or a signal not related to stepping occurs before
3360 @var{count} steps, stepping stops right away.
3363 @kindex n @r{(@code{next})}
3364 @item next @r{[}@var{count}@r{]}
3365 Continue to the next source line in the current (innermost) stack frame.
3366 This is similar to @code{step}, but function calls that appear within
3367 the line of code are executed without stopping. Execution stops when
3368 control reaches a different line of code at the original stack level
3369 that was executing when you gave the @code{next} command. This command
3370 is abbreviated @code{n}.
3372 An argument @var{count} is a repeat count, as for @code{step}.
3375 @c FIX ME!! Do we delete this, or is there a way it fits in with
3376 @c the following paragraph? --- Vctoria
3378 @c @code{next} within a function that lacks debugging information acts like
3379 @c @code{step}, but any function calls appearing within the code of the
3380 @c function are executed without stopping.
3382 The @code{next} command only stops at the first instruction of a
3383 source line. This prevents multiple stops that could otherwise occur in
3384 @code{switch} statements, @code{for} loops, etc.
3386 @kindex set step-mode
3388 @cindex functions without line info, and stepping
3389 @cindex stepping into functions with no line info
3390 @itemx set step-mode on
3391 The @code{set step-mode on} command causes the @code{step} command to
3392 stop at the first instruction of a function which contains no debug line
3393 information rather than stepping over it.
3395 This is useful in cases where you may be interested in inspecting the
3396 machine instructions of a function which has no symbolic info and do not
3397 want @value{GDBN} to automatically skip over this function.
3399 @item set step-mode off
3400 Causes the @code{step} command to step over any functions which contains no
3401 debug information. This is the default.
3405 Continue running until just after function in the selected stack frame
3406 returns. Print the returned value (if any).
3408 Contrast this with the @code{return} command (@pxref{Returning,
3409 ,Returning from a function}).
3412 @kindex u @r{(@code{until})}
3415 Continue running until a source line past the current line, in the
3416 current stack frame, is reached. This command is used to avoid single
3417 stepping through a loop more than once. It is like the @code{next}
3418 command, except that when @code{until} encounters a jump, it
3419 automatically continues execution until the program counter is greater
3420 than the address of the jump.
3422 This means that when you reach the end of a loop after single stepping
3423 though it, @code{until} makes your program continue execution until it
3424 exits the loop. In contrast, a @code{next} command at the end of a loop
3425 simply steps back to the beginning of the loop, which forces you to step
3426 through the next iteration.
3428 @code{until} always stops your program if it attempts to exit the current
3431 @code{until} may produce somewhat counterintuitive results if the order
3432 of machine code does not match the order of the source lines. For
3433 example, in the following excerpt from a debugging session, the @code{f}
3434 (@code{frame}) command shows that execution is stopped at line
3435 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3439 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3441 (@value{GDBP}) until
3442 195 for ( ; argc > 0; NEXTARG) @{
3445 This happened because, for execution efficiency, the compiler had
3446 generated code for the loop closure test at the end, rather than the
3447 start, of the loop---even though the test in a C @code{for}-loop is
3448 written before the body of the loop. The @code{until} command appeared
3449 to step back to the beginning of the loop when it advanced to this
3450 expression; however, it has not really gone to an earlier
3451 statement---not in terms of the actual machine code.
3453 @code{until} with no argument works by means of single
3454 instruction stepping, and hence is slower than @code{until} with an
3457 @item until @var{location}
3458 @itemx u @var{location}
3459 Continue running your program until either the specified location is
3460 reached, or the current stack frame returns. @var{location} is any of
3461 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3462 ,Setting breakpoints}). This form of the command uses breakpoints,
3463 and hence is quicker than @code{until} without an argument.
3466 @kindex si @r{(@code{stepi})}
3468 @itemx stepi @var{arg}
3470 Execute one machine instruction, then stop and return to the debugger.
3472 It is often useful to do @samp{display/i $pc} when stepping by machine
3473 instructions. This makes @value{GDBN} automatically display the next
3474 instruction to be executed, each time your program stops. @xref{Auto
3475 Display,, Automatic display}.
3477 An argument is a repeat count, as in @code{step}.
3481 @kindex ni @r{(@code{nexti})}
3483 @itemx nexti @var{arg}
3485 Execute one machine instruction, but if it is a function call,
3486 proceed until the function returns.
3488 An argument is a repeat count, as in @code{next}.
3495 A signal is an asynchronous event that can happen in a program. The
3496 operating system defines the possible kinds of signals, and gives each
3497 kind a name and a number. For example, in Unix @code{SIGINT} is the
3498 signal a program gets when you type an interrupt character (often @kbd{C-c});
3499 @code{SIGSEGV} is the signal a program gets from referencing a place in
3500 memory far away from all the areas in use; @code{SIGALRM} occurs when
3501 the alarm clock timer goes off (which happens only if your program has
3502 requested an alarm).
3504 @cindex fatal signals
3505 Some signals, including @code{SIGALRM}, are a normal part of the
3506 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3507 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3508 program has not specified in advance some other way to handle the signal.
3509 @code{SIGINT} does not indicate an error in your program, but it is normally
3510 fatal so it can carry out the purpose of the interrupt: to kill the program.
3512 @value{GDBN} has the ability to detect any occurrence of a signal in your
3513 program. You can tell @value{GDBN} in advance what to do for each kind of
3516 @cindex handling signals
3517 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3518 @code{SIGALRM} be silently passed to your program
3519 (so as not to interfere with their role in the program's functioning)
3520 but to stop your program immediately whenever an error signal happens.
3521 You can change these settings with the @code{handle} command.
3524 @kindex info signals
3527 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3528 handle each one. You can use this to see the signal numbers of all
3529 the defined types of signals.
3531 @code{info handle} is an alias for @code{info signals}.
3534 @item handle @var{signal} @var{keywords}@dots{}
3535 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3536 can be the number of a signal or its name (with or without the
3537 @samp{SIG} at the beginning); a list of signal numbers of the form
3538 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3539 known signals. The @var{keywords} say what change to make.
3543 The keywords allowed by the @code{handle} command can be abbreviated.
3544 Their full names are:
3548 @value{GDBN} should not stop your program when this signal happens. It may
3549 still print a message telling you that the signal has come in.
3552 @value{GDBN} should stop your program when this signal happens. This implies
3553 the @code{print} keyword as well.
3556 @value{GDBN} should print a message when this signal happens.
3559 @value{GDBN} should not mention the occurrence of the signal at all. This
3560 implies the @code{nostop} keyword as well.
3564 @value{GDBN} should allow your program to see this signal; your program
3565 can handle the signal, or else it may terminate if the signal is fatal
3566 and not handled. @code{pass} and @code{noignore} are synonyms.
3570 @value{GDBN} should not allow your program to see this signal.
3571 @code{nopass} and @code{ignore} are synonyms.
3575 When a signal stops your program, the signal is not visible to the
3577 continue. Your program sees the signal then, if @code{pass} is in
3578 effect for the signal in question @emph{at that time}. In other words,
3579 after @value{GDBN} reports a signal, you can use the @code{handle}
3580 command with @code{pass} or @code{nopass} to control whether your
3581 program sees that signal when you continue.
3583 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3584 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3585 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3588 You can also use the @code{signal} command to prevent your program from
3589 seeing a signal, or cause it to see a signal it normally would not see,
3590 or to give it any signal at any time. For example, if your program stopped
3591 due to some sort of memory reference error, you might store correct
3592 values into the erroneous variables and continue, hoping to see more
3593 execution; but your program would probably terminate immediately as
3594 a result of the fatal signal once it saw the signal. To prevent this,
3595 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3599 @section Stopping and starting multi-thread programs
3601 When your program has multiple threads (@pxref{Threads,, Debugging
3602 programs with multiple threads}), you can choose whether to set
3603 breakpoints on all threads, or on a particular thread.
3606 @cindex breakpoints and threads
3607 @cindex thread breakpoints
3608 @kindex break @dots{} thread @var{threadno}
3609 @item break @var{linespec} thread @var{threadno}
3610 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3611 @var{linespec} specifies source lines; there are several ways of
3612 writing them, but the effect is always to specify some source line.
3614 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3615 to specify that you only want @value{GDBN} to stop the program when a
3616 particular thread reaches this breakpoint. @var{threadno} is one of the
3617 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3618 column of the @samp{info threads} display.
3620 If you do not specify @samp{thread @var{threadno}} when you set a
3621 breakpoint, the breakpoint applies to @emph{all} threads of your
3624 You can use the @code{thread} qualifier on conditional breakpoints as
3625 well; in this case, place @samp{thread @var{threadno}} before the
3626 breakpoint condition, like this:
3629 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3634 @cindex stopped threads
3635 @cindex threads, stopped
3636 Whenever your program stops under @value{GDBN} for any reason,
3637 @emph{all} threads of execution stop, not just the current thread. This
3638 allows you to examine the overall state of the program, including
3639 switching between threads, without worrying that things may change
3642 @cindex continuing threads
3643 @cindex threads, continuing
3644 Conversely, whenever you restart the program, @emph{all} threads start
3645 executing. @emph{This is true even when single-stepping} with commands
3646 like @code{step} or @code{next}.
3648 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3649 Since thread scheduling is up to your debugging target's operating
3650 system (not controlled by @value{GDBN}), other threads may
3651 execute more than one statement while the current thread completes a
3652 single step. Moreover, in general other threads stop in the middle of a
3653 statement, rather than at a clean statement boundary, when the program
3656 You might even find your program stopped in another thread after
3657 continuing or even single-stepping. This happens whenever some other
3658 thread runs into a breakpoint, a signal, or an exception before the
3659 first thread completes whatever you requested.
3661 On some OSes, you can lock the OS scheduler and thus allow only a single
3665 @item set scheduler-locking @var{mode}
3666 Set the scheduler locking mode. If it is @code{off}, then there is no
3667 locking and any thread may run at any time. If @code{on}, then only the
3668 current thread may run when the inferior is resumed. The @code{step}
3669 mode optimizes for single-stepping. It stops other threads from
3670 ``seizing the prompt'' by preempting the current thread while you are
3671 stepping. Other threads will only rarely (or never) get a chance to run
3672 when you step. They are more likely to run when you @samp{next} over a
3673 function call, and they are completely free to run when you use commands
3674 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3675 thread hits a breakpoint during its timeslice, they will never steal the
3676 @value{GDBN} prompt away from the thread that you are debugging.
3678 @item show scheduler-locking
3679 Display the current scheduler locking mode.
3684 @chapter Examining the Stack
3686 When your program has stopped, the first thing you need to know is where it
3687 stopped and how it got there.
3690 Each time your program performs a function call, information about the call
3692 That information includes the location of the call in your program,
3693 the arguments of the call,
3694 and the local variables of the function being called.
3695 The information is saved in a block of data called a @dfn{stack frame}.
3696 The stack frames are allocated in a region of memory called the @dfn{call
3699 When your program stops, the @value{GDBN} commands for examining the
3700 stack allow you to see all of this information.
3702 @cindex selected frame
3703 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3704 @value{GDBN} commands refer implicitly to the selected frame. In
3705 particular, whenever you ask @value{GDBN} for the value of a variable in
3706 your program, the value is found in the selected frame. There are
3707 special @value{GDBN} commands to select whichever frame you are
3708 interested in. @xref{Selection, ,Selecting a frame}.
3710 When your program stops, @value{GDBN} automatically selects the
3711 currently executing frame and describes it briefly, similar to the
3712 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3715 * Frames:: Stack frames
3716 * Backtrace:: Backtraces
3717 * Selection:: Selecting a frame
3718 * Frame Info:: Information on a frame
3723 @section Stack frames
3725 @cindex frame, definition
3727 The call stack is divided up into contiguous pieces called @dfn{stack
3728 frames}, or @dfn{frames} for short; each frame is the data associated
3729 with one call to one function. The frame contains the arguments given
3730 to the function, the function's local variables, and the address at
3731 which the function is executing.
3733 @cindex initial frame
3734 @cindex outermost frame
3735 @cindex innermost frame
3736 When your program is started, the stack has only one frame, that of the
3737 function @code{main}. This is called the @dfn{initial} frame or the
3738 @dfn{outermost} frame. Each time a function is called, a new frame is
3739 made. Each time a function returns, the frame for that function invocation
3740 is eliminated. If a function is recursive, there can be many frames for
3741 the same function. The frame for the function in which execution is
3742 actually occurring is called the @dfn{innermost} frame. This is the most
3743 recently created of all the stack frames that still exist.
3745 @cindex frame pointer
3746 Inside your program, stack frames are identified by their addresses. A
3747 stack frame consists of many bytes, each of which has its own address; each
3748 kind of computer has a convention for choosing one byte whose
3749 address serves as the address of the frame. Usually this address is kept
3750 in a register called the @dfn{frame pointer register} while execution is
3751 going on in that frame.
3753 @cindex frame number
3754 @value{GDBN} assigns numbers to all existing stack frames, starting with
3755 zero for the innermost frame, one for the frame that called it,
3756 and so on upward. These numbers do not really exist in your program;
3757 they are assigned by @value{GDBN} to give you a way of designating stack
3758 frames in @value{GDBN} commands.
3760 @c The -fomit-frame-pointer below perennially causes hbox overflow
3761 @c underflow problems.
3762 @cindex frameless execution
3763 Some compilers provide a way to compile functions so that they operate
3764 without stack frames. (For example, the @value{GCC} option
3766 @samp{-fomit-frame-pointer}
3768 generates functions without a frame.)
3769 This is occasionally done with heavily used library functions to save
3770 the frame setup time. @value{GDBN} has limited facilities for dealing
3771 with these function invocations. If the innermost function invocation
3772 has no stack frame, @value{GDBN} nevertheless regards it as though
3773 it had a separate frame, which is numbered zero as usual, allowing
3774 correct tracing of the function call chain. However, @value{GDBN} has
3775 no provision for frameless functions elsewhere in the stack.
3778 @kindex frame@r{, command}
3779 @cindex current stack frame
3780 @item frame @var{args}
3781 The @code{frame} command allows you to move from one stack frame to another,
3782 and to print the stack frame you select. @var{args} may be either the
3783 address of the frame or the stack frame number. Without an argument,
3784 @code{frame} prints the current stack frame.
3786 @kindex select-frame
3787 @cindex selecting frame silently
3789 The @code{select-frame} command allows you to move from one stack frame
3790 to another without printing the frame. This is the silent version of
3799 @cindex stack traces
3800 A backtrace is a summary of how your program got where it is. It shows one
3801 line per frame, for many frames, starting with the currently executing
3802 frame (frame zero), followed by its caller (frame one), and on up the
3807 @kindex bt @r{(@code{backtrace})}
3810 Print a backtrace of the entire stack: one line per frame for all
3811 frames in the stack.
3813 You can stop the backtrace at any time by typing the system interrupt
3814 character, normally @kbd{C-c}.
3816 @item backtrace @var{n}
3818 Similar, but print only the innermost @var{n} frames.
3820 @item backtrace -@var{n}
3822 Similar, but print only the outermost @var{n} frames.
3827 @kindex info s @r{(@code{info stack})}
3828 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3829 are additional aliases for @code{backtrace}.
3831 Each line in the backtrace shows the frame number and the function name.
3832 The program counter value is also shown---unless you use @code{set
3833 print address off}. The backtrace also shows the source file name and
3834 line number, as well as the arguments to the function. The program
3835 counter value is omitted if it is at the beginning of the code for that
3838 Here is an example of a backtrace. It was made with the command
3839 @samp{bt 3}, so it shows the innermost three frames.
3843 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3845 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3846 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3848 (More stack frames follow...)
3853 The display for frame zero does not begin with a program counter
3854 value, indicating that your program has stopped at the beginning of the
3855 code for line @code{993} of @code{builtin.c}.
3858 @section Selecting a frame
3860 Most commands for examining the stack and other data in your program work on
3861 whichever stack frame is selected at the moment. Here are the commands for
3862 selecting a stack frame; all of them finish by printing a brief description
3863 of the stack frame just selected.
3866 @kindex frame@r{, selecting}
3867 @kindex f @r{(@code{frame})}
3870 Select frame number @var{n}. Recall that frame zero is the innermost
3871 (currently executing) frame, frame one is the frame that called the
3872 innermost one, and so on. The highest-numbered frame is the one for
3875 @item frame @var{addr}
3877 Select the frame at address @var{addr}. This is useful mainly if the
3878 chaining of stack frames has been damaged by a bug, making it
3879 impossible for @value{GDBN} to assign numbers properly to all frames. In
3880 addition, this can be useful when your program has multiple stacks and
3881 switches between them.
3883 On the SPARC architecture, @code{frame} needs two addresses to
3884 select an arbitrary frame: a frame pointer and a stack pointer.
3886 On the MIPS and Alpha architecture, it needs two addresses: a stack
3887 pointer and a program counter.
3889 On the 29k architecture, it needs three addresses: a register stack
3890 pointer, a program counter, and a memory stack pointer.
3891 @c note to future updaters: this is conditioned on a flag
3892 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3893 @c as of 27 Jan 1994.
3897 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3898 advances toward the outermost frame, to higher frame numbers, to frames
3899 that have existed longer. @var{n} defaults to one.
3902 @kindex do @r{(@code{down})}
3904 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3905 advances toward the innermost frame, to lower frame numbers, to frames
3906 that were created more recently. @var{n} defaults to one. You may
3907 abbreviate @code{down} as @code{do}.
3910 All of these commands end by printing two lines of output describing the
3911 frame. The first line shows the frame number, the function name, the
3912 arguments, and the source file and line number of execution in that
3913 frame. The second line shows the text of that source line.
3921 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3923 10 read_input_file (argv[i]);
3927 After such a printout, the @code{list} command with no arguments
3928 prints ten lines centered on the point of execution in the frame.
3929 @xref{List, ,Printing source lines}.
3932 @kindex down-silently
3934 @item up-silently @var{n}
3935 @itemx down-silently @var{n}
3936 These two commands are variants of @code{up} and @code{down},
3937 respectively; they differ in that they do their work silently, without
3938 causing display of the new frame. They are intended primarily for use
3939 in @value{GDBN} command scripts, where the output might be unnecessary and
3944 @section Information about a frame
3946 There are several other commands to print information about the selected
3952 When used without any argument, this command does not change which
3953 frame is selected, but prints a brief description of the currently
3954 selected stack frame. It can be abbreviated @code{f}. With an
3955 argument, this command is used to select a stack frame.
3956 @xref{Selection, ,Selecting a frame}.
3959 @kindex info f @r{(@code{info frame})}
3962 This command prints a verbose description of the selected stack frame,
3967 the address of the frame
3969 the address of the next frame down (called by this frame)
3971 the address of the next frame up (caller of this frame)
3973 the language in which the source code corresponding to this frame is written
3975 the address of the frame's arguments
3977 the address of the frame's local variables
3979 the program counter saved in it (the address of execution in the caller frame)
3981 which registers were saved in the frame
3984 @noindent The verbose description is useful when
3985 something has gone wrong that has made the stack format fail to fit
3986 the usual conventions.
3988 @item info frame @var{addr}
3989 @itemx info f @var{addr}
3990 Print a verbose description of the frame at address @var{addr}, without
3991 selecting that frame. The selected frame remains unchanged by this
3992 command. This requires the same kind of address (more than one for some
3993 architectures) that you specify in the @code{frame} command.
3994 @xref{Selection, ,Selecting a frame}.
3998 Print the arguments of the selected frame, each on a separate line.
4002 Print the local variables of the selected frame, each on a separate
4003 line. These are all variables (declared either static or automatic)
4004 accessible at the point of execution of the selected frame.
4007 @cindex catch exceptions, list active handlers
4008 @cindex exception handlers, how to list
4010 Print a list of all the exception handlers that are active in the
4011 current stack frame at the current point of execution. To see other
4012 exception handlers, visit the associated frame (using the @code{up},
4013 @code{down}, or @code{frame} commands); then type @code{info catch}.
4014 @xref{Set Catchpoints, , Setting catchpoints}.
4020 @chapter Examining Source Files
4022 @value{GDBN} can print parts of your program's source, since the debugging
4023 information recorded in the program tells @value{GDBN} what source files were
4024 used to build it. When your program stops, @value{GDBN} spontaneously prints
4025 the line where it stopped. Likewise, when you select a stack frame
4026 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4027 execution in that frame has stopped. You can print other portions of
4028 source files by explicit command.
4030 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4031 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4032 @value{GDBN} under @sc{gnu} Emacs}.
4035 * List:: Printing source lines
4036 * Search:: Searching source files
4037 * Source Path:: Specifying source directories
4038 * Machine Code:: Source and machine code
4042 @section Printing source lines
4045 @kindex l @r{(@code{list})}
4046 To print lines from a source file, use the @code{list} command
4047 (abbreviated @code{l}). By default, ten lines are printed.
4048 There are several ways to specify what part of the file you want to print.
4050 Here are the forms of the @code{list} command most commonly used:
4053 @item list @var{linenum}
4054 Print lines centered around line number @var{linenum} in the
4055 current source file.
4057 @item list @var{function}
4058 Print lines centered around the beginning of function
4062 Print more lines. If the last lines printed were printed with a
4063 @code{list} command, this prints lines following the last lines
4064 printed; however, if the last line printed was a solitary line printed
4065 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4066 Stack}), this prints lines centered around that line.
4069 Print lines just before the lines last printed.
4072 By default, @value{GDBN} prints ten source lines with any of these forms of
4073 the @code{list} command. You can change this using @code{set listsize}:
4076 @kindex set listsize
4077 @item set listsize @var{count}
4078 Make the @code{list} command display @var{count} source lines (unless
4079 the @code{list} argument explicitly specifies some other number).
4081 @kindex show listsize
4083 Display the number of lines that @code{list} prints.
4086 Repeating a @code{list} command with @key{RET} discards the argument,
4087 so it is equivalent to typing just @code{list}. This is more useful
4088 than listing the same lines again. An exception is made for an
4089 argument of @samp{-}; that argument is preserved in repetition so that
4090 each repetition moves up in the source file.
4093 In general, the @code{list} command expects you to supply zero, one or two
4094 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4095 of writing them, but the effect is always to specify some source line.
4096 Here is a complete description of the possible arguments for @code{list}:
4099 @item list @var{linespec}
4100 Print lines centered around the line specified by @var{linespec}.
4102 @item list @var{first},@var{last}
4103 Print lines from @var{first} to @var{last}. Both arguments are
4106 @item list ,@var{last}
4107 Print lines ending with @var{last}.
4109 @item list @var{first},
4110 Print lines starting with @var{first}.
4113 Print lines just after the lines last printed.
4116 Print lines just before the lines last printed.
4119 As described in the preceding table.
4122 Here are the ways of specifying a single source line---all the
4127 Specifies line @var{number} of the current source file.
4128 When a @code{list} command has two linespecs, this refers to
4129 the same source file as the first linespec.
4132 Specifies the line @var{offset} lines after the last line printed.
4133 When used as the second linespec in a @code{list} command that has
4134 two, this specifies the line @var{offset} lines down from the
4138 Specifies the line @var{offset} lines before the last line printed.
4140 @item @var{filename}:@var{number}
4141 Specifies line @var{number} in the source file @var{filename}.
4143 @item @var{function}
4144 Specifies the line that begins the body of the function @var{function}.
4145 For example: in C, this is the line with the open brace.
4147 @item @var{filename}:@var{function}
4148 Specifies the line of the open-brace that begins the body of the
4149 function @var{function} in the file @var{filename}. You only need the
4150 file name with a function name to avoid ambiguity when there are
4151 identically named functions in different source files.
4153 @item *@var{address}
4154 Specifies the line containing the program address @var{address}.
4155 @var{address} may be any expression.
4159 @section Searching source files
4161 @kindex reverse-search
4163 There are two commands for searching through the current source file for a
4168 @kindex forward-search
4169 @item forward-search @var{regexp}
4170 @itemx search @var{regexp}
4171 The command @samp{forward-search @var{regexp}} checks each line,
4172 starting with the one following the last line listed, for a match for
4173 @var{regexp}. It lists the line that is found. You can use the
4174 synonym @samp{search @var{regexp}} or abbreviate the command name as
4177 @item reverse-search @var{regexp}
4178 The command @samp{reverse-search @var{regexp}} checks each line, starting
4179 with the one before the last line listed and going backward, for a match
4180 for @var{regexp}. It lists the line that is found. You can abbreviate
4181 this command as @code{rev}.
4185 @section Specifying source directories
4188 @cindex directories for source files
4189 Executable programs sometimes do not record the directories of the source
4190 files from which they were compiled, just the names. Even when they do,
4191 the directories could be moved between the compilation and your debugging
4192 session. @value{GDBN} has a list of directories to search for source files;
4193 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4194 it tries all the directories in the list, in the order they are present
4195 in the list, until it finds a file with the desired name. Note that
4196 the executable search path is @emph{not} used for this purpose. Neither is
4197 the current working directory, unless it happens to be in the source
4200 If @value{GDBN} cannot find a source file in the source path, and the
4201 object program records a directory, @value{GDBN} tries that directory
4202 too. If the source path is empty, and there is no record of the
4203 compilation directory, @value{GDBN} looks in the current directory as a
4206 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4207 any information it has cached about where source files are found and where
4208 each line is in the file.
4212 When you start @value{GDBN}, its source path includes only @samp{cdir}
4213 and @samp{cwd}, in that order.
4214 To add other directories, use the @code{directory} command.
4217 @item directory @var{dirname} @dots{}
4218 @item dir @var{dirname} @dots{}
4219 Add directory @var{dirname} to the front of the source path. Several
4220 directory names may be given to this command, separated by @samp{:}
4221 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4222 part of absolute file names) or
4223 whitespace. You may specify a directory that is already in the source
4224 path; this moves it forward, so @value{GDBN} searches it sooner.
4228 @vindex $cdir@r{, convenience variable}
4229 @vindex $cwdr@r{, convenience variable}
4230 @cindex compilation directory
4231 @cindex current directory
4232 @cindex working directory
4233 @cindex directory, current
4234 @cindex directory, compilation
4235 You can use the string @samp{$cdir} to refer to the compilation
4236 directory (if one is recorded), and @samp{$cwd} to refer to the current
4237 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4238 tracks the current working directory as it changes during your @value{GDBN}
4239 session, while the latter is immediately expanded to the current
4240 directory at the time you add an entry to the source path.
4243 Reset the source path to empty again. This requires confirmation.
4245 @c RET-repeat for @code{directory} is explicitly disabled, but since
4246 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4248 @item show directories
4249 @kindex show directories
4250 Print the source path: show which directories it contains.
4253 If your source path is cluttered with directories that are no longer of
4254 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4255 versions of source. You can correct the situation as follows:
4259 Use @code{directory} with no argument to reset the source path to empty.
4262 Use @code{directory} with suitable arguments to reinstall the
4263 directories you want in the source path. You can add all the
4264 directories in one command.
4268 @section Source and machine code
4270 You can use the command @code{info line} to map source lines to program
4271 addresses (and vice versa), and the command @code{disassemble} to display
4272 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4273 mode, the @code{info line} command causes the arrow to point to the
4274 line specified. Also, @code{info line} prints addresses in symbolic form as
4279 @item info line @var{linespec}
4280 Print the starting and ending addresses of the compiled code for
4281 source line @var{linespec}. You can specify source lines in any of
4282 the ways understood by the @code{list} command (@pxref{List, ,Printing
4286 For example, we can use @code{info line} to discover the location of
4287 the object code for the first line of function
4288 @code{m4_changequote}:
4290 @c FIXME: I think this example should also show the addresses in
4291 @c symbolic form, as they usually would be displayed.
4293 (@value{GDBP}) info line m4_changequote
4294 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4298 We can also inquire (using @code{*@var{addr}} as the form for
4299 @var{linespec}) what source line covers a particular address:
4301 (@value{GDBP}) info line *0x63ff
4302 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4305 @cindex @code{$_} and @code{info line}
4306 @kindex x@r{(examine), and} info line
4307 After @code{info line}, the default address for the @code{x} command
4308 is changed to the starting address of the line, so that @samp{x/i} is
4309 sufficient to begin examining the machine code (@pxref{Memory,
4310 ,Examining memory}). Also, this address is saved as the value of the
4311 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4316 @cindex assembly instructions
4317 @cindex instructions, assembly
4318 @cindex machine instructions
4319 @cindex listing machine instructions
4321 This specialized command dumps a range of memory as machine
4322 instructions. The default memory range is the function surrounding the
4323 program counter of the selected frame. A single argument to this
4324 command is a program counter value; @value{GDBN} dumps the function
4325 surrounding this value. Two arguments specify a range of addresses
4326 (first inclusive, second exclusive) to dump.
4329 The following example shows the disassembly of a range of addresses of
4330 HP PA-RISC 2.0 code:
4333 (@value{GDBP}) disas 0x32c4 0x32e4
4334 Dump of assembler code from 0x32c4 to 0x32e4:
4335 0x32c4 <main+204>: addil 0,dp
4336 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4337 0x32cc <main+212>: ldil 0x3000,r31
4338 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4339 0x32d4 <main+220>: ldo 0(r31),rp
4340 0x32d8 <main+224>: addil -0x800,dp
4341 0x32dc <main+228>: ldo 0x588(r1),r26
4342 0x32e0 <main+232>: ldil 0x3000,r31
4343 End of assembler dump.
4346 Some architectures have more than one commonly-used set of instruction
4347 mnemonics or other syntax.
4350 @kindex set disassembly-flavor
4351 @cindex assembly instructions
4352 @cindex instructions, assembly
4353 @cindex machine instructions
4354 @cindex listing machine instructions
4355 @cindex Intel disassembly flavor
4356 @cindex AT&T disassembly flavor
4357 @item set disassembly-flavor @var{instruction-set}
4358 Select the instruction set to use when disassembling the
4359 program via the @code{disassemble} or @code{x/i} commands.
4361 Currently this command is only defined for the Intel x86 family. You
4362 can set @var{instruction-set} to either @code{intel} or @code{att}.
4363 The default is @code{att}, the AT&T flavor used by default by Unix
4364 assemblers for x86-based targets.
4369 @chapter Examining Data
4371 @cindex printing data
4372 @cindex examining data
4375 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4376 @c document because it is nonstandard... Under Epoch it displays in a
4377 @c different window or something like that.
4378 The usual way to examine data in your program is with the @code{print}
4379 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4380 evaluates and prints the value of an expression of the language your
4381 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4382 Different Languages}).
4385 @item print @var{expr}
4386 @itemx print /@var{f} @var{expr}
4387 @var{expr} is an expression (in the source language). By default the
4388 value of @var{expr} is printed in a format appropriate to its data type;
4389 you can choose a different format by specifying @samp{/@var{f}}, where
4390 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4394 @itemx print /@var{f}
4395 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4396 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4397 conveniently inspect the same value in an alternative format.
4400 A more low-level way of examining data is with the @code{x} command.
4401 It examines data in memory at a specified address and prints it in a
4402 specified format. @xref{Memory, ,Examining memory}.
4404 If you are interested in information about types, or about how the
4405 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4406 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4410 * Expressions:: Expressions
4411 * Variables:: Program variables
4412 * Arrays:: Artificial arrays
4413 * Output Formats:: Output formats
4414 * Memory:: Examining memory
4415 * Auto Display:: Automatic display
4416 * Print Settings:: Print settings
4417 * Value History:: Value history
4418 * Convenience Vars:: Convenience variables
4419 * Registers:: Registers
4420 * Floating Point Hardware:: Floating point hardware
4421 * Memory Region Attributes:: Memory region attributes
4422 * Dump/Restore Files:: Copy between memory and a file
4426 @section Expressions
4429 @code{print} and many other @value{GDBN} commands accept an expression and
4430 compute its value. Any kind of constant, variable or operator defined
4431 by the programming language you are using is valid in an expression in
4432 @value{GDBN}. This includes conditional expressions, function calls,
4433 casts, and string constants. It also includes preprocessor macros, if
4434 you compiled your program to include this information; see
4437 @value{GDBN} supports array constants in expressions input by
4438 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4439 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4440 memory that is @code{malloc}ed in the target program.
4442 Because C is so widespread, most of the expressions shown in examples in
4443 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4444 Languages}, for information on how to use expressions in other
4447 In this section, we discuss operators that you can use in @value{GDBN}
4448 expressions regardless of your programming language.
4450 Casts are supported in all languages, not just in C, because it is so
4451 useful to cast a number into a pointer in order to examine a structure
4452 at that address in memory.
4453 @c FIXME: casts supported---Mod2 true?
4455 @value{GDBN} supports these operators, in addition to those common
4456 to programming languages:
4460 @samp{@@} is a binary operator for treating parts of memory as arrays.
4461 @xref{Arrays, ,Artificial arrays}, for more information.
4464 @samp{::} allows you to specify a variable in terms of the file or
4465 function where it is defined. @xref{Variables, ,Program variables}.
4467 @cindex @{@var{type}@}
4468 @cindex type casting memory
4469 @cindex memory, viewing as typed object
4470 @cindex casts, to view memory
4471 @item @{@var{type}@} @var{addr}
4472 Refers to an object of type @var{type} stored at address @var{addr} in
4473 memory. @var{addr} may be any expression whose value is an integer or
4474 pointer (but parentheses are required around binary operators, just as in
4475 a cast). This construct is allowed regardless of what kind of data is
4476 normally supposed to reside at @var{addr}.
4480 @section Program variables
4482 The most common kind of expression to use is the name of a variable
4485 Variables in expressions are understood in the selected stack frame
4486 (@pxref{Selection, ,Selecting a frame}); they must be either:
4490 global (or file-static)
4497 visible according to the scope rules of the
4498 programming language from the point of execution in that frame
4501 @noindent This means that in the function
4516 you can examine and use the variable @code{a} whenever your program is
4517 executing within the function @code{foo}, but you can only use or
4518 examine the variable @code{b} while your program is executing inside
4519 the block where @code{b} is declared.
4521 @cindex variable name conflict
4522 There is an exception: you can refer to a variable or function whose
4523 scope is a single source file even if the current execution point is not
4524 in this file. But it is possible to have more than one such variable or
4525 function with the same name (in different source files). If that
4526 happens, referring to that name has unpredictable effects. If you wish,
4527 you can specify a static variable in a particular function or file,
4528 using the colon-colon notation:
4530 @cindex colon-colon, context for variables/functions
4532 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4533 @cindex @code{::}, context for variables/functions
4536 @var{file}::@var{variable}
4537 @var{function}::@var{variable}
4541 Here @var{file} or @var{function} is the name of the context for the
4542 static @var{variable}. In the case of file names, you can use quotes to
4543 make sure @value{GDBN} parses the file name as a single word---for example,
4544 to print a global value of @code{x} defined in @file{f2.c}:
4547 (@value{GDBP}) p 'f2.c'::x
4550 @cindex C@t{++} scope resolution
4551 This use of @samp{::} is very rarely in conflict with the very similar
4552 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4553 scope resolution operator in @value{GDBN} expressions.
4554 @c FIXME: Um, so what happens in one of those rare cases where it's in
4557 @cindex wrong values
4558 @cindex variable values, wrong
4560 @emph{Warning:} Occasionally, a local variable may appear to have the
4561 wrong value at certain points in a function---just after entry to a new
4562 scope, and just before exit.
4564 You may see this problem when you are stepping by machine instructions.
4565 This is because, on most machines, it takes more than one instruction to
4566 set up a stack frame (including local variable definitions); if you are
4567 stepping by machine instructions, variables may appear to have the wrong
4568 values until the stack frame is completely built. On exit, it usually
4569 also takes more than one machine instruction to destroy a stack frame;
4570 after you begin stepping through that group of instructions, local
4571 variable definitions may be gone.
4573 This may also happen when the compiler does significant optimizations.
4574 To be sure of always seeing accurate values, turn off all optimization
4577 @cindex ``No symbol "foo" in current context''
4578 Another possible effect of compiler optimizations is to optimize
4579 unused variables out of existence, or assign variables to registers (as
4580 opposed to memory addresses). Depending on the support for such cases
4581 offered by the debug info format used by the compiler, @value{GDBN}
4582 might not be able to display values for such local variables. If that
4583 happens, @value{GDBN} will print a message like this:
4586 No symbol "foo" in current context.
4589 To solve such problems, either recompile without optimizations, or use a
4590 different debug info format, if the compiler supports several such
4591 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4592 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4593 in a format that is superior to formats such as COFF. You may be able
4594 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4595 debug info. See @ref{Debugging Options,,Options for Debugging Your
4596 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4601 @section Artificial arrays
4603 @cindex artificial array
4604 @kindex @@@r{, referencing memory as an array}
4605 It is often useful to print out several successive objects of the
4606 same type in memory; a section of an array, or an array of
4607 dynamically determined size for which only a pointer exists in the
4610 You can do this by referring to a contiguous span of memory as an
4611 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4612 operand of @samp{@@} should be the first element of the desired array
4613 and be an individual object. The right operand should be the desired length
4614 of the array. The result is an array value whose elements are all of
4615 the type of the left argument. The first element is actually the left
4616 argument; the second element comes from bytes of memory immediately
4617 following those that hold the first element, and so on. Here is an
4618 example. If a program says
4621 int *array = (int *) malloc (len * sizeof (int));
4625 you can print the contents of @code{array} with
4631 The left operand of @samp{@@} must reside in memory. Array values made
4632 with @samp{@@} in this way behave just like other arrays in terms of
4633 subscripting, and are coerced to pointers when used in expressions.
4634 Artificial arrays most often appear in expressions via the value history
4635 (@pxref{Value History, ,Value history}), after printing one out.
4637 Another way to create an artificial array is to use a cast.
4638 This re-interprets a value as if it were an array.
4639 The value need not be in memory:
4641 (@value{GDBP}) p/x (short[2])0x12345678
4642 $1 = @{0x1234, 0x5678@}
4645 As a convenience, if you leave the array length out (as in
4646 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4647 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4649 (@value{GDBP}) p/x (short[])0x12345678
4650 $2 = @{0x1234, 0x5678@}
4653 Sometimes the artificial array mechanism is not quite enough; in
4654 moderately complex data structures, the elements of interest may not
4655 actually be adjacent---for example, if you are interested in the values
4656 of pointers in an array. One useful work-around in this situation is
4657 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4658 variables}) as a counter in an expression that prints the first
4659 interesting value, and then repeat that expression via @key{RET}. For
4660 instance, suppose you have an array @code{dtab} of pointers to
4661 structures, and you are interested in the values of a field @code{fv}
4662 in each structure. Here is an example of what you might type:
4672 @node Output Formats
4673 @section Output formats
4675 @cindex formatted output
4676 @cindex output formats
4677 By default, @value{GDBN} prints a value according to its data type. Sometimes
4678 this is not what you want. For example, you might want to print a number
4679 in hex, or a pointer in decimal. Or you might want to view data in memory
4680 at a certain address as a character string or as an instruction. To do
4681 these things, specify an @dfn{output format} when you print a value.
4683 The simplest use of output formats is to say how to print a value
4684 already computed. This is done by starting the arguments of the
4685 @code{print} command with a slash and a format letter. The format
4686 letters supported are:
4690 Regard the bits of the value as an integer, and print the integer in
4694 Print as integer in signed decimal.
4697 Print as integer in unsigned decimal.
4700 Print as integer in octal.
4703 Print as integer in binary. The letter @samp{t} stands for ``two''.
4704 @footnote{@samp{b} cannot be used because these format letters are also
4705 used with the @code{x} command, where @samp{b} stands for ``byte'';
4706 see @ref{Memory,,Examining memory}.}
4709 @cindex unknown address, locating
4710 @cindex locate address
4711 Print as an address, both absolute in hexadecimal and as an offset from
4712 the nearest preceding symbol. You can use this format used to discover
4713 where (in what function) an unknown address is located:
4716 (@value{GDBP}) p/a 0x54320
4717 $3 = 0x54320 <_initialize_vx+396>
4721 The command @code{info symbol 0x54320} yields similar results.
4722 @xref{Symbols, info symbol}.
4725 Regard as an integer and print it as a character constant.
4728 Regard the bits of the value as a floating point number and print
4729 using typical floating point syntax.
4732 For example, to print the program counter in hex (@pxref{Registers}), type
4739 Note that no space is required before the slash; this is because command
4740 names in @value{GDBN} cannot contain a slash.
4742 To reprint the last value in the value history with a different format,
4743 you can use the @code{print} command with just a format and no
4744 expression. For example, @samp{p/x} reprints the last value in hex.
4747 @section Examining memory
4749 You can use the command @code{x} (for ``examine'') to examine memory in
4750 any of several formats, independently of your program's data types.
4752 @cindex examining memory
4754 @kindex x @r{(examine memory)}
4755 @item x/@var{nfu} @var{addr}
4758 Use the @code{x} command to examine memory.
4761 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4762 much memory to display and how to format it; @var{addr} is an
4763 expression giving the address where you want to start displaying memory.
4764 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4765 Several commands set convenient defaults for @var{addr}.
4768 @item @var{n}, the repeat count
4769 The repeat count is a decimal integer; the default is 1. It specifies
4770 how much memory (counting by units @var{u}) to display.
4771 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4774 @item @var{f}, the display format
4775 The display format is one of the formats used by @code{print},
4776 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4777 The default is @samp{x} (hexadecimal) initially.
4778 The default changes each time you use either @code{x} or @code{print}.
4780 @item @var{u}, the unit size
4781 The unit size is any of
4787 Halfwords (two bytes).
4789 Words (four bytes). This is the initial default.
4791 Giant words (eight bytes).
4794 Each time you specify a unit size with @code{x}, that size becomes the
4795 default unit the next time you use @code{x}. (For the @samp{s} and
4796 @samp{i} formats, the unit size is ignored and is normally not written.)
4798 @item @var{addr}, starting display address
4799 @var{addr} is the address where you want @value{GDBN} to begin displaying
4800 memory. The expression need not have a pointer value (though it may);
4801 it is always interpreted as an integer address of a byte of memory.
4802 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4803 @var{addr} is usually just after the last address examined---but several
4804 other commands also set the default address: @code{info breakpoints} (to
4805 the address of the last breakpoint listed), @code{info line} (to the
4806 starting address of a line), and @code{print} (if you use it to display
4807 a value from memory).
4810 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4811 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4812 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4813 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4814 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4816 Since the letters indicating unit sizes are all distinct from the
4817 letters specifying output formats, you do not have to remember whether
4818 unit size or format comes first; either order works. The output
4819 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4820 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4822 Even though the unit size @var{u} is ignored for the formats @samp{s}
4823 and @samp{i}, you might still want to use a count @var{n}; for example,
4824 @samp{3i} specifies that you want to see three machine instructions,
4825 including any operands. The command @code{disassemble} gives an
4826 alternative way of inspecting machine instructions; see @ref{Machine
4827 Code,,Source and machine code}.
4829 All the defaults for the arguments to @code{x} are designed to make it
4830 easy to continue scanning memory with minimal specifications each time
4831 you use @code{x}. For example, after you have inspected three machine
4832 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4833 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4834 the repeat count @var{n} is used again; the other arguments default as
4835 for successive uses of @code{x}.
4837 @cindex @code{$_}, @code{$__}, and value history
4838 The addresses and contents printed by the @code{x} command are not saved
4839 in the value history because there is often too much of them and they
4840 would get in the way. Instead, @value{GDBN} makes these values available for
4841 subsequent use in expressions as values of the convenience variables
4842 @code{$_} and @code{$__}. After an @code{x} command, the last address
4843 examined is available for use in expressions in the convenience variable
4844 @code{$_}. The contents of that address, as examined, are available in
4845 the convenience variable @code{$__}.
4847 If the @code{x} command has a repeat count, the address and contents saved
4848 are from the last memory unit printed; this is not the same as the last
4849 address printed if several units were printed on the last line of output.
4852 @section Automatic display
4853 @cindex automatic display
4854 @cindex display of expressions
4856 If you find that you want to print the value of an expression frequently
4857 (to see how it changes), you might want to add it to the @dfn{automatic
4858 display list} so that @value{GDBN} prints its value each time your program stops.
4859 Each expression added to the list is given a number to identify it;
4860 to remove an expression from the list, you specify that number.
4861 The automatic display looks like this:
4865 3: bar[5] = (struct hack *) 0x3804
4869 This display shows item numbers, expressions and their current values. As with
4870 displays you request manually using @code{x} or @code{print}, you can
4871 specify the output format you prefer; in fact, @code{display} decides
4872 whether to use @code{print} or @code{x} depending on how elaborate your
4873 format specification is---it uses @code{x} if you specify a unit size,
4874 or one of the two formats (@samp{i} and @samp{s}) that are only
4875 supported by @code{x}; otherwise it uses @code{print}.
4879 @item display @var{expr}
4880 Add the expression @var{expr} to the list of expressions to display
4881 each time your program stops. @xref{Expressions, ,Expressions}.
4883 @code{display} does not repeat if you press @key{RET} again after using it.
4885 @item display/@var{fmt} @var{expr}
4886 For @var{fmt} specifying only a display format and not a size or
4887 count, add the expression @var{expr} to the auto-display list but
4888 arrange to display it each time in the specified format @var{fmt}.
4889 @xref{Output Formats,,Output formats}.
4891 @item display/@var{fmt} @var{addr}
4892 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4893 number of units, add the expression @var{addr} as a memory address to
4894 be examined each time your program stops. Examining means in effect
4895 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4898 For example, @samp{display/i $pc} can be helpful, to see the machine
4899 instruction about to be executed each time execution stops (@samp{$pc}
4900 is a common name for the program counter; @pxref{Registers, ,Registers}).
4903 @kindex delete display
4905 @item undisplay @var{dnums}@dots{}
4906 @itemx delete display @var{dnums}@dots{}
4907 Remove item numbers @var{dnums} from the list of expressions to display.
4909 @code{undisplay} does not repeat if you press @key{RET} after using it.
4910 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4912 @kindex disable display
4913 @item disable display @var{dnums}@dots{}
4914 Disable the display of item numbers @var{dnums}. A disabled display
4915 item is not printed automatically, but is not forgotten. It may be
4916 enabled again later.
4918 @kindex enable display
4919 @item enable display @var{dnums}@dots{}
4920 Enable display of item numbers @var{dnums}. It becomes effective once
4921 again in auto display of its expression, until you specify otherwise.
4924 Display the current values of the expressions on the list, just as is
4925 done when your program stops.
4927 @kindex info display
4929 Print the list of expressions previously set up to display
4930 automatically, each one with its item number, but without showing the
4931 values. This includes disabled expressions, which are marked as such.
4932 It also includes expressions which would not be displayed right now
4933 because they refer to automatic variables not currently available.
4936 If a display expression refers to local variables, then it does not make
4937 sense outside the lexical context for which it was set up. Such an
4938 expression is disabled when execution enters a context where one of its
4939 variables is not defined. For example, if you give the command
4940 @code{display last_char} while inside a function with an argument
4941 @code{last_char}, @value{GDBN} displays this argument while your program
4942 continues to stop inside that function. When it stops elsewhere---where
4943 there is no variable @code{last_char}---the display is disabled
4944 automatically. The next time your program stops where @code{last_char}
4945 is meaningful, you can enable the display expression once again.
4947 @node Print Settings
4948 @section Print settings
4950 @cindex format options
4951 @cindex print settings
4952 @value{GDBN} provides the following ways to control how arrays, structures,
4953 and symbols are printed.
4956 These settings are useful for debugging programs in any language:
4959 @kindex set print address
4960 @item set print address
4961 @itemx set print address on
4962 @value{GDBN} prints memory addresses showing the location of stack
4963 traces, structure values, pointer values, breakpoints, and so forth,
4964 even when it also displays the contents of those addresses. The default
4965 is @code{on}. For example, this is what a stack frame display looks like with
4966 @code{set print address on}:
4971 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4973 530 if (lquote != def_lquote)
4977 @item set print address off
4978 Do not print addresses when displaying their contents. For example,
4979 this is the same stack frame displayed with @code{set print address off}:
4983 (@value{GDBP}) set print addr off
4985 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4986 530 if (lquote != def_lquote)
4990 You can use @samp{set print address off} to eliminate all machine
4991 dependent displays from the @value{GDBN} interface. For example, with
4992 @code{print address off}, you should get the same text for backtraces on
4993 all machines---whether or not they involve pointer arguments.
4995 @kindex show print address
4996 @item show print address
4997 Show whether or not addresses are to be printed.
5000 When @value{GDBN} prints a symbolic address, it normally prints the
5001 closest earlier symbol plus an offset. If that symbol does not uniquely
5002 identify the address (for example, it is a name whose scope is a single
5003 source file), you may need to clarify. One way to do this is with
5004 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5005 you can set @value{GDBN} to print the source file and line number when
5006 it prints a symbolic address:
5009 @kindex set print symbol-filename
5010 @item set print symbol-filename on
5011 Tell @value{GDBN} to print the source file name and line number of a
5012 symbol in the symbolic form of an address.
5014 @item set print symbol-filename off
5015 Do not print source file name and line number of a symbol. This is the
5018 @kindex show print symbol-filename
5019 @item show print symbol-filename
5020 Show whether or not @value{GDBN} will print the source file name and
5021 line number of a symbol in the symbolic form of an address.
5024 Another situation where it is helpful to show symbol filenames and line
5025 numbers is when disassembling code; @value{GDBN} shows you the line
5026 number and source file that corresponds to each instruction.
5028 Also, you may wish to see the symbolic form only if the address being
5029 printed is reasonably close to the closest earlier symbol:
5032 @kindex set print max-symbolic-offset
5033 @item set print max-symbolic-offset @var{max-offset}
5034 Tell @value{GDBN} to only display the symbolic form of an address if the
5035 offset between the closest earlier symbol and the address is less than
5036 @var{max-offset}. The default is 0, which tells @value{GDBN}
5037 to always print the symbolic form of an address if any symbol precedes it.
5039 @kindex show print max-symbolic-offset
5040 @item show print max-symbolic-offset
5041 Ask how large the maximum offset is that @value{GDBN} prints in a
5045 @cindex wild pointer, interpreting
5046 @cindex pointer, finding referent
5047 If you have a pointer and you are not sure where it points, try
5048 @samp{set print symbol-filename on}. Then you can determine the name
5049 and source file location of the variable where it points, using
5050 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5051 For example, here @value{GDBN} shows that a variable @code{ptt} points
5052 at another variable @code{t}, defined in @file{hi2.c}:
5055 (@value{GDBP}) set print symbol-filename on
5056 (@value{GDBP}) p/a ptt
5057 $4 = 0xe008 <t in hi2.c>
5061 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5062 does not show the symbol name and filename of the referent, even with
5063 the appropriate @code{set print} options turned on.
5066 Other settings control how different kinds of objects are printed:
5069 @kindex set print array
5070 @item set print array
5071 @itemx set print array on
5072 Pretty print arrays. This format is more convenient to read,
5073 but uses more space. The default is off.
5075 @item set print array off
5076 Return to compressed format for arrays.
5078 @kindex show print array
5079 @item show print array
5080 Show whether compressed or pretty format is selected for displaying
5083 @kindex set print elements
5084 @item set print elements @var{number-of-elements}
5085 Set a limit on how many elements of an array @value{GDBN} will print.
5086 If @value{GDBN} is printing a large array, it stops printing after it has
5087 printed the number of elements set by the @code{set print elements} command.
5088 This limit also applies to the display of strings.
5089 When @value{GDBN} starts, this limit is set to 200.
5090 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5092 @kindex show print elements
5093 @item show print elements
5094 Display the number of elements of a large array that @value{GDBN} will print.
5095 If the number is 0, then the printing is unlimited.
5097 @kindex set print null-stop
5098 @item set print null-stop
5099 Cause @value{GDBN} to stop printing the characters of an array when the first
5100 @sc{null} is encountered. This is useful when large arrays actually
5101 contain only short strings.
5104 @kindex set print pretty
5105 @item set print pretty on
5106 Cause @value{GDBN} to print structures in an indented format with one member
5107 per line, like this:
5122 @item set print pretty off
5123 Cause @value{GDBN} to print structures in a compact format, like this:
5127 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5128 meat = 0x54 "Pork"@}
5133 This is the default format.
5135 @kindex show print pretty
5136 @item show print pretty
5137 Show which format @value{GDBN} is using to print structures.
5139 @kindex set print sevenbit-strings
5140 @item set print sevenbit-strings on
5141 Print using only seven-bit characters; if this option is set,
5142 @value{GDBN} displays any eight-bit characters (in strings or
5143 character values) using the notation @code{\}@var{nnn}. This setting is
5144 best if you are working in English (@sc{ascii}) and you use the
5145 high-order bit of characters as a marker or ``meta'' bit.
5147 @item set print sevenbit-strings off
5148 Print full eight-bit characters. This allows the use of more
5149 international character sets, and is the default.
5151 @kindex show print sevenbit-strings
5152 @item show print sevenbit-strings
5153 Show whether or not @value{GDBN} is printing only seven-bit characters.
5155 @kindex set print union
5156 @item set print union on
5157 Tell @value{GDBN} to print unions which are contained in structures. This
5158 is the default setting.
5160 @item set print union off
5161 Tell @value{GDBN} not to print unions which are contained in structures.
5163 @kindex show print union
5164 @item show print union
5165 Ask @value{GDBN} whether or not it will print unions which are contained in
5168 For example, given the declarations
5171 typedef enum @{Tree, Bug@} Species;
5172 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5173 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5184 struct thing foo = @{Tree, @{Acorn@}@};
5188 with @code{set print union on} in effect @samp{p foo} would print
5191 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5195 and with @code{set print union off} in effect it would print
5198 $1 = @{it = Tree, form = @{...@}@}
5204 These settings are of interest when debugging C@t{++} programs:
5208 @kindex set print demangle
5209 @item set print demangle
5210 @itemx set print demangle on
5211 Print C@t{++} names in their source form rather than in the encoded
5212 (``mangled'') form passed to the assembler and linker for type-safe
5213 linkage. The default is on.
5215 @kindex show print demangle
5216 @item show print demangle
5217 Show whether C@t{++} names are printed in mangled or demangled form.
5219 @kindex set print asm-demangle
5220 @item set print asm-demangle
5221 @itemx set print asm-demangle on
5222 Print C@t{++} names in their source form rather than their mangled form, even
5223 in assembler code printouts such as instruction disassemblies.
5226 @kindex show print asm-demangle
5227 @item show print asm-demangle
5228 Show whether C@t{++} names in assembly listings are printed in mangled
5231 @kindex set demangle-style
5232 @cindex C@t{++} symbol decoding style
5233 @cindex symbol decoding style, C@t{++}
5234 @item set demangle-style @var{style}
5235 Choose among several encoding schemes used by different compilers to
5236 represent C@t{++} names. The choices for @var{style} are currently:
5240 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5243 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5244 This is the default.
5247 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5250 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5253 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5254 @strong{Warning:} this setting alone is not sufficient to allow
5255 debugging @code{cfront}-generated executables. @value{GDBN} would
5256 require further enhancement to permit that.
5259 If you omit @var{style}, you will see a list of possible formats.
5261 @kindex show demangle-style
5262 @item show demangle-style
5263 Display the encoding style currently in use for decoding C@t{++} symbols.
5265 @kindex set print object
5266 @item set print object
5267 @itemx set print object on
5268 When displaying a pointer to an object, identify the @emph{actual}
5269 (derived) type of the object rather than the @emph{declared} type, using
5270 the virtual function table.
5272 @item set print object off
5273 Display only the declared type of objects, without reference to the
5274 virtual function table. This is the default setting.
5276 @kindex show print object
5277 @item show print object
5278 Show whether actual, or declared, object types are displayed.
5280 @kindex set print static-members
5281 @item set print static-members
5282 @itemx set print static-members on
5283 Print static members when displaying a C@t{++} object. The default is on.
5285 @item set print static-members off
5286 Do not print static members when displaying a C@t{++} object.
5288 @kindex show print static-members
5289 @item show print static-members
5290 Show whether C@t{++} static members are printed, or not.
5292 @c These don't work with HP ANSI C++ yet.
5293 @kindex set print vtbl
5294 @item set print vtbl
5295 @itemx set print vtbl on
5296 Pretty print C@t{++} virtual function tables. The default is off.
5297 (The @code{vtbl} commands do not work on programs compiled with the HP
5298 ANSI C@t{++} compiler (@code{aCC}).)
5300 @item set print vtbl off
5301 Do not pretty print C@t{++} virtual function tables.
5303 @kindex show print vtbl
5304 @item show print vtbl
5305 Show whether C@t{++} virtual function tables are pretty printed, or not.
5309 @section Value history
5311 @cindex value history
5312 Values printed by the @code{print} command are saved in the @value{GDBN}
5313 @dfn{value history}. This allows you to refer to them in other expressions.
5314 Values are kept until the symbol table is re-read or discarded
5315 (for example with the @code{file} or @code{symbol-file} commands).
5316 When the symbol table changes, the value history is discarded,
5317 since the values may contain pointers back to the types defined in the
5322 @cindex history number
5323 The values printed are given @dfn{history numbers} by which you can
5324 refer to them. These are successive integers starting with one.
5325 @code{print} shows you the history number assigned to a value by
5326 printing @samp{$@var{num} = } before the value; here @var{num} is the
5329 To refer to any previous value, use @samp{$} followed by the value's
5330 history number. The way @code{print} labels its output is designed to
5331 remind you of this. Just @code{$} refers to the most recent value in
5332 the history, and @code{$$} refers to the value before that.
5333 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5334 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5335 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5337 For example, suppose you have just printed a pointer to a structure and
5338 want to see the contents of the structure. It suffices to type
5344 If you have a chain of structures where the component @code{next} points
5345 to the next one, you can print the contents of the next one with this:
5352 You can print successive links in the chain by repeating this
5353 command---which you can do by just typing @key{RET}.
5355 Note that the history records values, not expressions. If the value of
5356 @code{x} is 4 and you type these commands:
5364 then the value recorded in the value history by the @code{print} command
5365 remains 4 even though the value of @code{x} has changed.
5370 Print the last ten values in the value history, with their item numbers.
5371 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5372 values} does not change the history.
5374 @item show values @var{n}
5375 Print ten history values centered on history item number @var{n}.
5378 Print ten history values just after the values last printed. If no more
5379 values are available, @code{show values +} produces no display.
5382 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5383 same effect as @samp{show values +}.
5385 @node Convenience Vars
5386 @section Convenience variables
5388 @cindex convenience variables
5389 @value{GDBN} provides @dfn{convenience variables} that you can use within
5390 @value{GDBN} to hold on to a value and refer to it later. These variables
5391 exist entirely within @value{GDBN}; they are not part of your program, and
5392 setting a convenience variable has no direct effect on further execution
5393 of your program. That is why you can use them freely.
5395 Convenience variables are prefixed with @samp{$}. Any name preceded by
5396 @samp{$} can be used for a convenience variable, unless it is one of
5397 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5398 (Value history references, in contrast, are @emph{numbers} preceded
5399 by @samp{$}. @xref{Value History, ,Value history}.)
5401 You can save a value in a convenience variable with an assignment
5402 expression, just as you would set a variable in your program.
5406 set $foo = *object_ptr
5410 would save in @code{$foo} the value contained in the object pointed to by
5413 Using a convenience variable for the first time creates it, but its
5414 value is @code{void} until you assign a new value. You can alter the
5415 value with another assignment at any time.
5417 Convenience variables have no fixed types. You can assign a convenience
5418 variable any type of value, including structures and arrays, even if
5419 that variable already has a value of a different type. The convenience
5420 variable, when used as an expression, has the type of its current value.
5423 @kindex show convenience
5424 @item show convenience
5425 Print a list of convenience variables used so far, and their values.
5426 Abbreviated @code{show conv}.
5429 One of the ways to use a convenience variable is as a counter to be
5430 incremented or a pointer to be advanced. For example, to print
5431 a field from successive elements of an array of structures:
5435 print bar[$i++]->contents
5439 Repeat that command by typing @key{RET}.
5441 Some convenience variables are created automatically by @value{GDBN} and given
5442 values likely to be useful.
5445 @vindex $_@r{, convenience variable}
5447 The variable @code{$_} is automatically set by the @code{x} command to
5448 the last address examined (@pxref{Memory, ,Examining memory}). Other
5449 commands which provide a default address for @code{x} to examine also
5450 set @code{$_} to that address; these commands include @code{info line}
5451 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5452 except when set by the @code{x} command, in which case it is a pointer
5453 to the type of @code{$__}.
5455 @vindex $__@r{, convenience variable}
5457 The variable @code{$__} is automatically set by the @code{x} command
5458 to the value found in the last address examined. Its type is chosen
5459 to match the format in which the data was printed.
5462 @vindex $_exitcode@r{, convenience variable}
5463 The variable @code{$_exitcode} is automatically set to the exit code when
5464 the program being debugged terminates.
5467 On HP-UX systems, if you refer to a function or variable name that
5468 begins with a dollar sign, @value{GDBN} searches for a user or system
5469 name first, before it searches for a convenience variable.
5475 You can refer to machine register contents, in expressions, as variables
5476 with names starting with @samp{$}. The names of registers are different
5477 for each machine; use @code{info registers} to see the names used on
5481 @kindex info registers
5482 @item info registers
5483 Print the names and values of all registers except floating-point
5484 registers (in the selected stack frame).
5486 @kindex info all-registers
5487 @cindex floating point registers
5488 @item info all-registers
5489 Print the names and values of all registers, including floating-point
5492 @item info registers @var{regname} @dots{}
5493 Print the @dfn{relativized} value of each specified register @var{regname}.
5494 As discussed in detail below, register values are normally relative to
5495 the selected stack frame. @var{regname} may be any register name valid on
5496 the machine you are using, with or without the initial @samp{$}.
5499 @value{GDBN} has four ``standard'' register names that are available (in
5500 expressions) on most machines---whenever they do not conflict with an
5501 architecture's canonical mnemonics for registers. The register names
5502 @code{$pc} and @code{$sp} are used for the program counter register and
5503 the stack pointer. @code{$fp} is used for a register that contains a
5504 pointer to the current stack frame, and @code{$ps} is used for a
5505 register that contains the processor status. For example,
5506 you could print the program counter in hex with
5513 or print the instruction to be executed next with
5520 or add four to the stack pointer@footnote{This is a way of removing
5521 one word from the stack, on machines where stacks grow downward in
5522 memory (most machines, nowadays). This assumes that the innermost
5523 stack frame is selected; setting @code{$sp} is not allowed when other
5524 stack frames are selected. To pop entire frames off the stack,
5525 regardless of machine architecture, use @code{return};
5526 see @ref{Returning, ,Returning from a function}.} with
5532 Whenever possible, these four standard register names are available on
5533 your machine even though the machine has different canonical mnemonics,
5534 so long as there is no conflict. The @code{info registers} command
5535 shows the canonical names. For example, on the SPARC, @code{info
5536 registers} displays the processor status register as @code{$psr} but you
5537 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5538 is an alias for the @sc{eflags} register.
5540 @value{GDBN} always considers the contents of an ordinary register as an
5541 integer when the register is examined in this way. Some machines have
5542 special registers which can hold nothing but floating point; these
5543 registers are considered to have floating point values. There is no way
5544 to refer to the contents of an ordinary register as floating point value
5545 (although you can @emph{print} it as a floating point value with
5546 @samp{print/f $@var{regname}}).
5548 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5549 means that the data format in which the register contents are saved by
5550 the operating system is not the same one that your program normally
5551 sees. For example, the registers of the 68881 floating point
5552 coprocessor are always saved in ``extended'' (raw) format, but all C
5553 programs expect to work with ``double'' (virtual) format. In such
5554 cases, @value{GDBN} normally works with the virtual format only (the format
5555 that makes sense for your program), but the @code{info registers} command
5556 prints the data in both formats.
5558 Normally, register values are relative to the selected stack frame
5559 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5560 value that the register would contain if all stack frames farther in
5561 were exited and their saved registers restored. In order to see the
5562 true contents of hardware registers, you must select the innermost
5563 frame (with @samp{frame 0}).
5565 However, @value{GDBN} must deduce where registers are saved, from the machine
5566 code generated by your compiler. If some registers are not saved, or if
5567 @value{GDBN} is unable to locate the saved registers, the selected stack
5568 frame makes no difference.
5570 @node Floating Point Hardware
5571 @section Floating point hardware
5572 @cindex floating point
5574 Depending on the configuration, @value{GDBN} may be able to give
5575 you more information about the status of the floating point hardware.
5580 Display hardware-dependent information about the floating
5581 point unit. The exact contents and layout vary depending on the
5582 floating point chip. Currently, @samp{info float} is supported on
5583 the ARM and x86 machines.
5586 @node Memory Region Attributes
5587 @section Memory region attributes
5588 @cindex memory region attributes
5590 @dfn{Memory region attributes} allow you to describe special handling
5591 required by regions of your target's memory. @value{GDBN} uses attributes
5592 to determine whether to allow certain types of memory accesses; whether to
5593 use specific width accesses; and whether to cache target memory.
5595 Defined memory regions can be individually enabled and disabled. When a
5596 memory region is disabled, @value{GDBN} uses the default attributes when
5597 accessing memory in that region. Similarly, if no memory regions have
5598 been defined, @value{GDBN} uses the default attributes when accessing
5601 When a memory region is defined, it is given a number to identify it;
5602 to enable, disable, or remove a memory region, you specify that number.
5606 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
5607 Define memory region bounded by @var{lower} and @var{upper} with
5608 attributes @var{attributes}@dots{}. Note that @var{upper} == 0 is a
5609 special case: it is treated as the the target's maximum memory address.
5610 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
5613 @item delete mem @var{nums}@dots{}
5614 Remove memory regions @var{nums}@dots{}.
5617 @item disable mem @var{nums}@dots{}
5618 Disable memory regions @var{nums}@dots{}.
5619 A disabled memory region is not forgotten.
5620 It may be enabled again later.
5623 @item enable mem @var{nums}@dots{}
5624 Enable memory regions @var{nums}@dots{}.
5628 Print a table of all defined memory regions, with the following columns
5632 @item Memory Region Number
5633 @item Enabled or Disabled.
5634 Enabled memory regions are marked with @samp{y}.
5635 Disabled memory regions are marked with @samp{n}.
5638 The address defining the inclusive lower bound of the memory region.
5641 The address defining the exclusive upper bound of the memory region.
5644 The list of attributes set for this memory region.
5649 @subsection Attributes
5651 @subsubsection Memory Access Mode
5652 The access mode attributes set whether @value{GDBN} may make read or
5653 write accesses to a memory region.
5655 While these attributes prevent @value{GDBN} from performing invalid
5656 memory accesses, they do nothing to prevent the target system, I/O DMA,
5657 etc. from accessing memory.
5661 Memory is read only.
5663 Memory is write only.
5665 Memory is read/write. This is the default.
5668 @subsubsection Memory Access Size
5669 The acccess size attributes tells @value{GDBN} to use specific sized
5670 accesses in the memory region. Often memory mapped device registers
5671 require specific sized accesses. If no access size attribute is
5672 specified, @value{GDBN} may use accesses of any size.
5676 Use 8 bit memory accesses.
5678 Use 16 bit memory accesses.
5680 Use 32 bit memory accesses.
5682 Use 64 bit memory accesses.
5685 @c @subsubsection Hardware/Software Breakpoints
5686 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5687 @c will use hardware or software breakpoints for the internal breakpoints
5688 @c used by the step, next, finish, until, etc. commands.
5692 @c Always use hardware breakpoints
5693 @c @item swbreak (default)
5696 @subsubsection Data Cache
5697 The data cache attributes set whether @value{GDBN} will cache target
5698 memory. While this generally improves performance by reducing debug
5699 protocol overhead, it can lead to incorrect results because @value{GDBN}
5700 does not know about volatile variables or memory mapped device
5705 Enable @value{GDBN} to cache target memory.
5707 Disable @value{GDBN} from caching target memory. This is the default.
5710 @c @subsubsection Memory Write Verification
5711 @c The memory write verification attributes set whether @value{GDBN}
5712 @c will re-reads data after each write to verify the write was successful.
5716 @c @item noverify (default)
5719 @node Dump/Restore Files
5720 @section Copy between memory and a file
5721 @cindex dump/restore files
5722 @cindex append data to a file
5723 @cindex dump data to a file
5724 @cindex restore data from a file
5729 The commands @code{dump}, @code{append}, and @code{restore} are used
5730 for copying data between target memory and a file. Data is written
5731 into a file using @code{dump} or @code{append}, and restored from a
5732 file into memory by using @code{restore}. Files may be binary, srec,
5733 intel hex, or tekhex (but only binary files can be appended).
5737 @kindex append binary
5738 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5739 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5740 raw binary format file @var{filename}.
5742 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5743 Append contents of memory from @var{start_addr} to @var{end_addr} to
5744 raw binary format file @var{filename}.
5746 @item dump binary value @var{filename} @var{expression}
5747 Dump value of @var{expression} into raw binary format file @var{filename}.
5749 @item append binary memory @var{filename} @var{expression}
5750 Append value of @var{expression} to raw binary format file @var{filename}.
5753 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5754 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5755 intel hex format file @var{filename}.
5757 @item dump ihex value @var{filename} @var{expression}
5758 Dump value of @var{expression} into intel hex format file @var{filename}.
5761 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5762 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5763 srec format file @var{filename}.
5765 @item dump srec value @var{filename} @var{expression}
5766 Dump value of @var{expression} into srec format file @var{filename}.
5769 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5770 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5771 tekhex format file @var{filename}.
5773 @item dump tekhex value @var{filename} @var{expression}
5774 Dump value of @var{expression} into tekhex format file @var{filename}.
5776 @item restore @var{filename} [@var{binary}] @var{bias} @var{start} @var{end}
5777 Restore the contents of file @var{filename} into memory. The @code{restore}
5778 command can automatically recognize any known bfd file format, except for
5779 raw binary. To restore a raw binary file you must use the optional argument
5780 @var{binary} after the filename.
5782 If @var{bias} is non-zero, its value will be added to the addresses
5783 contained in the file. Binary files always start at address zero, so
5784 they will be restored at address @var{bias}. Other bfd files have
5785 a built-in location; they will be restored at offset @var{bias}
5788 If @var{start} and/or @var{end} are non-zero, then only data between
5789 file offset @var{start} and file offset @var{end} will be restored.
5790 These offsets are relative to the addresses in the file, before
5791 the @var{bias} argument is applied.
5796 @chapter C Preprocessor Macros
5798 Some languages, such as C and C++, provide a way to define and invoke
5799 ``preprocessor macros'' which expand into strings of tokens.
5800 @value{GDBN} can evaluate expressions containing macro invocations, show
5801 the result of macro expansion, and show a macro's definition, including
5802 where it was defined.
5804 You may need to compile your program specially to provide @value{GDBN}
5805 with information about preprocessor macros. Most compilers do not
5806 include macros in their debugging information, even when you compile
5807 with the @option{-g} flag. @xref{Compilation}.
5809 A program may define a macro at one point, remove that definition later,
5810 and then provide a different definition after that. Thus, at different
5811 points in the program, a macro may have different definitions, or have
5812 no definition at all. If there is a current stack frame, @value{GDBN}
5813 uses the macros in scope at that frame's source code line. Otherwise,
5814 @value{GDBN} uses the macros in scope at the current listing location;
5817 At the moment, @value{GDBN} does not support the @code{##}
5818 token-splicing operator, the @code{#} stringification operator, or
5819 variable-arity macros.
5821 Whenever @value{GDBN} evaluates an expression, it always expands any
5822 macro invocations present in the expression. @value{GDBN} also provides
5823 the following commands for working with macros explicitly.
5827 @kindex macro expand
5828 @cindex macro expansion, showing the results of preprocessor
5829 @cindex preprocessor macro expansion, showing the results of
5830 @cindex expanding preprocessor macros
5831 @item macro expand @var{expression}
5832 @itemx macro exp @var{expression}
5833 Show the results of expanding all preprocessor macro invocations in
5834 @var{expression}. Since @value{GDBN} simply expands macros, but does
5835 not parse the result, @var{expression} need not be a valid expression;
5836 it can be any string of tokens.
5838 @kindex macro expand-once
5839 @item macro expand-once @var{expression}
5840 @itemx macro exp1 @var{expression}
5841 @i{(This command is not yet implemented.)} Show the results of
5842 expanding those preprocessor macro invocations that appear explicitly in
5843 @var{expression}. Macro invocations appearing in that expansion are
5844 left unchanged. This command allows you to see the effect of a
5845 particular macro more clearly, without being confused by further
5846 expansions. Since @value{GDBN} simply expands macros, but does not
5847 parse the result, @var{expression} need not be a valid expression; it
5848 can be any string of tokens.
5851 @cindex macro definition, showing
5852 @cindex definition, showing a macro's
5853 @item info macro @var{macro}
5854 Show the definition of the macro named @var{macro}, and describe the
5855 source location where that definition was established.
5857 @kindex macro define
5858 @cindex user-defined macros
5859 @cindex defining macros interactively
5860 @cindex macros, user-defined
5861 @item macro define @var{macro} @var{replacement-list}
5862 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
5863 @i{(This command is not yet implemented.)} Introduce a definition for a
5864 preprocessor macro named @var{macro}, invocations of which are replaced
5865 by the tokens given in @var{replacement-list}. The first form of this
5866 command defines an ``object-like'' macro, which takes no arguments; the
5867 second form defines a ``function-like'' macro, which takes the arguments
5868 given in @var{arglist}.
5870 A definition introduced by this command is in scope in every expression
5871 evaluated in @value{GDBN}, until it is removed with the @command{macro
5872 undef} command, described below. The definition overrides all
5873 definitions for @var{macro} present in the program being debugged, as
5874 well as any previous user-supplied definition.
5877 @item macro undef @var{macro}
5878 @i{(This command is not yet implemented.)} Remove any user-supplied
5879 definition for the macro named @var{macro}. This command only affects
5880 definitions provided with the @command{macro define} command, described
5881 above; it cannot remove definitions present in the program being
5886 @cindex macros, example of debugging with
5887 Here is a transcript showing the above commands in action. First, we
5888 show our source files:
5896 #define ADD(x) (M + x)
5901 printf ("Hello, world!\n");
5903 printf ("We're so creative.\n");
5905 printf ("Goodbye, world!\n");
5912 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
5913 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
5914 compiler includes information about preprocessor macros in the debugging
5918 $ gcc -gdwarf-2 -g3 sample.c -o sample
5922 Now, we start @value{GDBN} on our sample program:
5926 GNU gdb 2002-05-06-cvs
5927 Copyright 2002 Free Software Foundation, Inc.
5928 GDB is free software, @dots{}
5932 We can expand macros and examine their definitions, even when the
5933 program is not running. @value{GDBN} uses the current listing position
5934 to decide which macro definitions are in scope:
5940 5 #define ADD(x) (M + x)
5945 10 printf ("Hello, world!\n");
5947 12 printf ("We're so creative.\n");
5948 (gdb) info macro ADD
5949 Defined at /home/jimb/gdb/macros/play/sample.c:5
5950 #define ADD(x) (M + x)
5952 Defined at /home/jimb/gdb/macros/play/sample.h:1
5953 included at /home/jimb/gdb/macros/play/sample.c:2
5955 (gdb) macro expand ADD(1)
5956 expands to: (42 + 1)
5957 (gdb) macro expand-once ADD(1)
5958 expands to: once (M + 1)
5962 In the example above, note that @command{macro expand-once} expands only
5963 the macro invocation explicit in the original text --- the invocation of
5964 @code{ADD} --- but does not expand the invocation of the macro @code{M},
5965 which was introduced by @code{ADD}.
5967 Once the program is running, GDB uses the macro definitions in force at
5968 the source line of the current stack frame:
5972 Breakpoint 1 at 0x8048370: file sample.c, line 10.
5974 Starting program: /home/jimb/gdb/macros/play/sample
5976 Breakpoint 1, main () at sample.c:10
5977 10 printf ("Hello, world!\n");
5981 At line 10, the definition of the macro @code{N} at line 9 is in force:
5985 Defined at /home/jimb/gdb/macros/play/sample.c:9
5987 (gdb) macro expand N Q M
5994 As we step over directives that remove @code{N}'s definition, and then
5995 give it a new definition, @value{GDBN} finds the definition (or lack
5996 thereof) in force at each point:
6001 12 printf ("We're so creative.\n");
6003 The symbol `N' has no definition as a C/C++ preprocessor macro
6004 at /home/jimb/gdb/macros/play/sample.c:12
6007 14 printf ("Goodbye, world!\n");
6009 Defined at /home/jimb/gdb/macros/play/sample.c:13
6011 (gdb) macro expand N Q M
6012 expands to: 1729 < 42
6020 @chapter Tracepoints
6021 @c This chapter is based on the documentation written by Michael
6022 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6025 In some applications, it is not feasible for the debugger to interrupt
6026 the program's execution long enough for the developer to learn
6027 anything helpful about its behavior. If the program's correctness
6028 depends on its real-time behavior, delays introduced by a debugger
6029 might cause the program to change its behavior drastically, or perhaps
6030 fail, even when the code itself is correct. It is useful to be able
6031 to observe the program's behavior without interrupting it.
6033 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6034 specify locations in the program, called @dfn{tracepoints}, and
6035 arbitrary expressions to evaluate when those tracepoints are reached.
6036 Later, using the @code{tfind} command, you can examine the values
6037 those expressions had when the program hit the tracepoints. The
6038 expressions may also denote objects in memory---structures or arrays,
6039 for example---whose values @value{GDBN} should record; while visiting
6040 a particular tracepoint, you may inspect those objects as if they were
6041 in memory at that moment. However, because @value{GDBN} records these
6042 values without interacting with you, it can do so quickly and
6043 unobtrusively, hopefully not disturbing the program's behavior.
6045 The tracepoint facility is currently available only for remote
6046 targets. @xref{Targets}. In addition, your remote target must know how
6047 to collect trace data. This functionality is implemented in the remote
6048 stub; however, none of the stubs distributed with @value{GDBN} support
6049 tracepoints as of this writing.
6051 This chapter describes the tracepoint commands and features.
6055 * Analyze Collected Data::
6056 * Tracepoint Variables::
6059 @node Set Tracepoints
6060 @section Commands to Set Tracepoints
6062 Before running such a @dfn{trace experiment}, an arbitrary number of
6063 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6064 tracepoint has a number assigned to it by @value{GDBN}. Like with
6065 breakpoints, tracepoint numbers are successive integers starting from
6066 one. Many of the commands associated with tracepoints take the
6067 tracepoint number as their argument, to identify which tracepoint to
6070 For each tracepoint, you can specify, in advance, some arbitrary set
6071 of data that you want the target to collect in the trace buffer when
6072 it hits that tracepoint. The collected data can include registers,
6073 local variables, or global data. Later, you can use @value{GDBN}
6074 commands to examine the values these data had at the time the
6077 This section describes commands to set tracepoints and associated
6078 conditions and actions.
6081 * Create and Delete Tracepoints::
6082 * Enable and Disable Tracepoints::
6083 * Tracepoint Passcounts::
6084 * Tracepoint Actions::
6085 * Listing Tracepoints::
6086 * Starting and Stopping Trace Experiment::
6089 @node Create and Delete Tracepoints
6090 @subsection Create and Delete Tracepoints
6093 @cindex set tracepoint
6096 The @code{trace} command is very similar to the @code{break} command.
6097 Its argument can be a source line, a function name, or an address in
6098 the target program. @xref{Set Breaks}. The @code{trace} command
6099 defines a tracepoint, which is a point in the target program where the
6100 debugger will briefly stop, collect some data, and then allow the
6101 program to continue. Setting a tracepoint or changing its commands
6102 doesn't take effect until the next @code{tstart} command; thus, you
6103 cannot change the tracepoint attributes once a trace experiment is
6106 Here are some examples of using the @code{trace} command:
6109 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6111 (@value{GDBP}) @b{trace +2} // 2 lines forward
6113 (@value{GDBP}) @b{trace my_function} // first source line of function
6115 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6117 (@value{GDBP}) @b{trace *0x2117c4} // an address
6121 You can abbreviate @code{trace} as @code{tr}.
6124 @cindex last tracepoint number
6125 @cindex recent tracepoint number
6126 @cindex tracepoint number
6127 The convenience variable @code{$tpnum} records the tracepoint number
6128 of the most recently set tracepoint.
6130 @kindex delete tracepoint
6131 @cindex tracepoint deletion
6132 @item delete tracepoint @r{[}@var{num}@r{]}
6133 Permanently delete one or more tracepoints. With no argument, the
6134 default is to delete all tracepoints.
6139 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6141 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6145 You can abbreviate this command as @code{del tr}.
6148 @node Enable and Disable Tracepoints
6149 @subsection Enable and Disable Tracepoints
6152 @kindex disable tracepoint
6153 @item disable tracepoint @r{[}@var{num}@r{]}
6154 Disable tracepoint @var{num}, or all tracepoints if no argument
6155 @var{num} is given. A disabled tracepoint will have no effect during
6156 the next trace experiment, but it is not forgotten. You can re-enable
6157 a disabled tracepoint using the @code{enable tracepoint} command.
6159 @kindex enable tracepoint
6160 @item enable tracepoint @r{[}@var{num}@r{]}
6161 Enable tracepoint @var{num}, or all tracepoints. The enabled
6162 tracepoints will become effective the next time a trace experiment is
6166 @node Tracepoint Passcounts
6167 @subsection Tracepoint Passcounts
6171 @cindex tracepoint pass count
6172 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6173 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6174 automatically stop a trace experiment. If a tracepoint's passcount is
6175 @var{n}, then the trace experiment will be automatically stopped on
6176 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6177 @var{num} is not specified, the @code{passcount} command sets the
6178 passcount of the most recently defined tracepoint. If no passcount is
6179 given, the trace experiment will run until stopped explicitly by the
6185 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6186 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6188 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6189 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6190 (@value{GDBP}) @b{trace foo}
6191 (@value{GDBP}) @b{pass 3}
6192 (@value{GDBP}) @b{trace bar}
6193 (@value{GDBP}) @b{pass 2}
6194 (@value{GDBP}) @b{trace baz}
6195 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6196 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6197 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6198 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6202 @node Tracepoint Actions
6203 @subsection Tracepoint Action Lists
6207 @cindex tracepoint actions
6208 @item actions @r{[}@var{num}@r{]}
6209 This command will prompt for a list of actions to be taken when the
6210 tracepoint is hit. If the tracepoint number @var{num} is not
6211 specified, this command sets the actions for the one that was most
6212 recently defined (so that you can define a tracepoint and then say
6213 @code{actions} without bothering about its number). You specify the
6214 actions themselves on the following lines, one action at a time, and
6215 terminate the actions list with a line containing just @code{end}. So
6216 far, the only defined actions are @code{collect} and
6217 @code{while-stepping}.
6219 @cindex remove actions from a tracepoint
6220 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6221 and follow it immediately with @samp{end}.
6224 (@value{GDBP}) @b{collect @var{data}} // collect some data
6226 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6228 (@value{GDBP}) @b{end} // signals the end of actions.
6231 In the following example, the action list begins with @code{collect}
6232 commands indicating the things to be collected when the tracepoint is
6233 hit. Then, in order to single-step and collect additional data
6234 following the tracepoint, a @code{while-stepping} command is used,
6235 followed by the list of things to be collected while stepping. The
6236 @code{while-stepping} command is terminated by its own separate
6237 @code{end} command. Lastly, the action list is terminated by an
6241 (@value{GDBP}) @b{trace foo}
6242 (@value{GDBP}) @b{actions}
6243 Enter actions for tracepoint 1, one per line:
6252 @kindex collect @r{(tracepoints)}
6253 @item collect @var{expr1}, @var{expr2}, @dots{}
6254 Collect values of the given expressions when the tracepoint is hit.
6255 This command accepts a comma-separated list of any valid expressions.
6256 In addition to global, static, or local variables, the following
6257 special arguments are supported:
6261 collect all registers
6264 collect all function arguments
6267 collect all local variables.
6270 You can give several consecutive @code{collect} commands, each one
6271 with a single argument, or one @code{collect} command with several
6272 arguments separated by commas: the effect is the same.
6274 The command @code{info scope} (@pxref{Symbols, info scope}) is
6275 particularly useful for figuring out what data to collect.
6277 @kindex while-stepping @r{(tracepoints)}
6278 @item while-stepping @var{n}
6279 Perform @var{n} single-step traces after the tracepoint, collecting
6280 new data at each step. The @code{while-stepping} command is
6281 followed by the list of what to collect while stepping (followed by
6282 its own @code{end} command):
6286 > collect $regs, myglobal
6292 You may abbreviate @code{while-stepping} as @code{ws} or
6296 @node Listing Tracepoints
6297 @subsection Listing Tracepoints
6300 @kindex info tracepoints
6301 @cindex information about tracepoints
6302 @item info tracepoints @r{[}@var{num}@r{]}
6303 Display information about the tracepoint @var{num}. If you don't specify
6304 a tracepoint number, displays information about all the tracepoints
6305 defined so far. For each tracepoint, the following information is
6312 whether it is enabled or disabled
6316 its passcount as given by the @code{passcount @var{n}} command
6318 its step count as given by the @code{while-stepping @var{n}} command
6320 where in the source files is the tracepoint set
6322 its action list as given by the @code{actions} command
6326 (@value{GDBP}) @b{info trace}
6327 Num Enb Address PassC StepC What
6328 1 y 0x002117c4 0 0 <gdb_asm>
6329 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6330 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6335 This command can be abbreviated @code{info tp}.
6338 @node Starting and Stopping Trace Experiment
6339 @subsection Starting and Stopping Trace Experiment
6343 @cindex start a new trace experiment
6344 @cindex collected data discarded
6346 This command takes no arguments. It starts the trace experiment, and
6347 begins collecting data. This has the side effect of discarding all
6348 the data collected in the trace buffer during the previous trace
6352 @cindex stop a running trace experiment
6354 This command takes no arguments. It ends the trace experiment, and
6355 stops collecting data.
6357 @strong{Note:} a trace experiment and data collection may stop
6358 automatically if any tracepoint's passcount is reached
6359 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6362 @cindex status of trace data collection
6363 @cindex trace experiment, status of
6365 This command displays the status of the current trace data
6369 Here is an example of the commands we described so far:
6372 (@value{GDBP}) @b{trace gdb_c_test}
6373 (@value{GDBP}) @b{actions}
6374 Enter actions for tracepoint #1, one per line.
6375 > collect $regs,$locals,$args
6380 (@value{GDBP}) @b{tstart}
6381 [time passes @dots{}]
6382 (@value{GDBP}) @b{tstop}
6386 @node Analyze Collected Data
6387 @section Using the collected data
6389 After the tracepoint experiment ends, you use @value{GDBN} commands
6390 for examining the trace data. The basic idea is that each tracepoint
6391 collects a trace @dfn{snapshot} every time it is hit and another
6392 snapshot every time it single-steps. All these snapshots are
6393 consecutively numbered from zero and go into a buffer, and you can
6394 examine them later. The way you examine them is to @dfn{focus} on a
6395 specific trace snapshot. When the remote stub is focused on a trace
6396 snapshot, it will respond to all @value{GDBN} requests for memory and
6397 registers by reading from the buffer which belongs to that snapshot,
6398 rather than from @emph{real} memory or registers of the program being
6399 debugged. This means that @strong{all} @value{GDBN} commands
6400 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6401 behave as if we were currently debugging the program state as it was
6402 when the tracepoint occurred. Any requests for data that are not in
6403 the buffer will fail.
6406 * tfind:: How to select a trace snapshot
6407 * tdump:: How to display all data for a snapshot
6408 * save-tracepoints:: How to save tracepoints for a future run
6412 @subsection @code{tfind @var{n}}
6415 @cindex select trace snapshot
6416 @cindex find trace snapshot
6417 The basic command for selecting a trace snapshot from the buffer is
6418 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6419 counting from zero. If no argument @var{n} is given, the next
6420 snapshot is selected.
6422 Here are the various forms of using the @code{tfind} command.
6426 Find the first snapshot in the buffer. This is a synonym for
6427 @code{tfind 0} (since 0 is the number of the first snapshot).
6430 Stop debugging trace snapshots, resume @emph{live} debugging.
6433 Same as @samp{tfind none}.
6436 No argument means find the next trace snapshot.
6439 Find the previous trace snapshot before the current one. This permits
6440 retracing earlier steps.
6442 @item tfind tracepoint @var{num}
6443 Find the next snapshot associated with tracepoint @var{num}. Search
6444 proceeds forward from the last examined trace snapshot. If no
6445 argument @var{num} is given, it means find the next snapshot collected
6446 for the same tracepoint as the current snapshot.
6448 @item tfind pc @var{addr}
6449 Find the next snapshot associated with the value @var{addr} of the
6450 program counter. Search proceeds forward from the last examined trace
6451 snapshot. If no argument @var{addr} is given, it means find the next
6452 snapshot with the same value of PC as the current snapshot.
6454 @item tfind outside @var{addr1}, @var{addr2}
6455 Find the next snapshot whose PC is outside the given range of
6458 @item tfind range @var{addr1}, @var{addr2}
6459 Find the next snapshot whose PC is between @var{addr1} and
6460 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6462 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6463 Find the next snapshot associated with the source line @var{n}. If
6464 the optional argument @var{file} is given, refer to line @var{n} in
6465 that source file. Search proceeds forward from the last examined
6466 trace snapshot. If no argument @var{n} is given, it means find the
6467 next line other than the one currently being examined; thus saying
6468 @code{tfind line} repeatedly can appear to have the same effect as
6469 stepping from line to line in a @emph{live} debugging session.
6472 The default arguments for the @code{tfind} commands are specifically
6473 designed to make it easy to scan through the trace buffer. For
6474 instance, @code{tfind} with no argument selects the next trace
6475 snapshot, and @code{tfind -} with no argument selects the previous
6476 trace snapshot. So, by giving one @code{tfind} command, and then
6477 simply hitting @key{RET} repeatedly you can examine all the trace
6478 snapshots in order. Or, by saying @code{tfind -} and then hitting
6479 @key{RET} repeatedly you can examine the snapshots in reverse order.
6480 The @code{tfind line} command with no argument selects the snapshot
6481 for the next source line executed. The @code{tfind pc} command with
6482 no argument selects the next snapshot with the same program counter
6483 (PC) as the current frame. The @code{tfind tracepoint} command with
6484 no argument selects the next trace snapshot collected by the same
6485 tracepoint as the current one.
6487 In addition to letting you scan through the trace buffer manually,
6488 these commands make it easy to construct @value{GDBN} scripts that
6489 scan through the trace buffer and print out whatever collected data
6490 you are interested in. Thus, if we want to examine the PC, FP, and SP
6491 registers from each trace frame in the buffer, we can say this:
6494 (@value{GDBP}) @b{tfind start}
6495 (@value{GDBP}) @b{while ($trace_frame != -1)}
6496 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6497 $trace_frame, $pc, $sp, $fp
6501 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6502 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6503 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6504 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6505 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6506 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6507 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6508 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6509 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6510 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6511 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6514 Or, if we want to examine the variable @code{X} at each source line in
6518 (@value{GDBP}) @b{tfind start}
6519 (@value{GDBP}) @b{while ($trace_frame != -1)}
6520 > printf "Frame %d, X == %d\n", $trace_frame, X
6530 @subsection @code{tdump}
6532 @cindex dump all data collected at tracepoint
6533 @cindex tracepoint data, display
6535 This command takes no arguments. It prints all the data collected at
6536 the current trace snapshot.
6539 (@value{GDBP}) @b{trace 444}
6540 (@value{GDBP}) @b{actions}
6541 Enter actions for tracepoint #2, one per line:
6542 > collect $regs, $locals, $args, gdb_long_test
6545 (@value{GDBP}) @b{tstart}
6547 (@value{GDBP}) @b{tfind line 444}
6548 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6550 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6552 (@value{GDBP}) @b{tdump}
6553 Data collected at tracepoint 2, trace frame 1:
6554 d0 0xc4aa0085 -995491707
6558 d4 0x71aea3d 119204413
6563 a1 0x3000668 50333288
6566 a4 0x3000698 50333336
6568 fp 0x30bf3c 0x30bf3c
6569 sp 0x30bf34 0x30bf34
6571 pc 0x20b2c8 0x20b2c8
6575 p = 0x20e5b4 "gdb-test"
6582 gdb_long_test = 17 '\021'
6587 @node save-tracepoints
6588 @subsection @code{save-tracepoints @var{filename}}
6589 @kindex save-tracepoints
6590 @cindex save tracepoints for future sessions
6592 This command saves all current tracepoint definitions together with
6593 their actions and passcounts, into a file @file{@var{filename}}
6594 suitable for use in a later debugging session. To read the saved
6595 tracepoint definitions, use the @code{source} command (@pxref{Command
6598 @node Tracepoint Variables
6599 @section Convenience Variables for Tracepoints
6600 @cindex tracepoint variables
6601 @cindex convenience variables for tracepoints
6604 @vindex $trace_frame
6605 @item (int) $trace_frame
6606 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6607 snapshot is selected.
6610 @item (int) $tracepoint
6611 The tracepoint for the current trace snapshot.
6614 @item (int) $trace_line
6615 The line number for the current trace snapshot.
6618 @item (char []) $trace_file
6619 The source file for the current trace snapshot.
6622 @item (char []) $trace_func
6623 The name of the function containing @code{$tracepoint}.
6626 Note: @code{$trace_file} is not suitable for use in @code{printf},
6627 use @code{output} instead.
6629 Here's a simple example of using these convenience variables for
6630 stepping through all the trace snapshots and printing some of their
6634 (@value{GDBP}) @b{tfind start}
6636 (@value{GDBP}) @b{while $trace_frame != -1}
6637 > output $trace_file
6638 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6644 @chapter Debugging Programs That Use Overlays
6647 If your program is too large to fit completely in your target system's
6648 memory, you can sometimes use @dfn{overlays} to work around this
6649 problem. @value{GDBN} provides some support for debugging programs that
6653 * How Overlays Work:: A general explanation of overlays.
6654 * Overlay Commands:: Managing overlays in @value{GDBN}.
6655 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6656 mapped by asking the inferior.
6657 * Overlay Sample Program:: A sample program using overlays.
6660 @node How Overlays Work
6661 @section How Overlays Work
6662 @cindex mapped overlays
6663 @cindex unmapped overlays
6664 @cindex load address, overlay's
6665 @cindex mapped address
6666 @cindex overlay area
6668 Suppose you have a computer whose instruction address space is only 64
6669 kilobytes long, but which has much more memory which can be accessed by
6670 other means: special instructions, segment registers, or memory
6671 management hardware, for example. Suppose further that you want to
6672 adapt a program which is larger than 64 kilobytes to run on this system.
6674 One solution is to identify modules of your program which are relatively
6675 independent, and need not call each other directly; call these modules
6676 @dfn{overlays}. Separate the overlays from the main program, and place
6677 their machine code in the larger memory. Place your main program in
6678 instruction memory, but leave at least enough space there to hold the
6679 largest overlay as well.
6681 Now, to call a function located in an overlay, you must first copy that
6682 overlay's machine code from the large memory into the space set aside
6683 for it in the instruction memory, and then jump to its entry point
6686 @c NB: In the below the mapped area's size is greater or equal to the
6687 @c size of all overlays. This is intentional to remind the developer
6688 @c that overlays don't necessarily need to be the same size.
6692 Data Instruction Larger
6693 Address Space Address Space Address Space
6694 +-----------+ +-----------+ +-----------+
6696 +-----------+ +-----------+ +-----------+<-- overlay 1
6697 | program | | main | .----| overlay 1 | load address
6698 | variables | | program | | +-----------+
6699 | and heap | | | | | |
6700 +-----------+ | | | +-----------+<-- overlay 2
6701 | | +-----------+ | | | load address
6702 +-----------+ | | | .-| overlay 2 |
6704 mapped --->+-----------+ | | +-----------+
6706 | overlay | <-' | | |
6707 | area | <---' +-----------+<-- overlay 3
6708 | | <---. | | load address
6709 +-----------+ `--| overlay 3 |
6716 @anchor{A code overlay}A code overlay
6720 The diagram (@pxref{A code overlay}) shows a system with separate data
6721 and instruction address spaces. To map an overlay, the program copies
6722 its code from the larger address space to the instruction address space.
6723 Since the overlays shown here all use the same mapped address, only one
6724 may be mapped at a time. For a system with a single address space for
6725 data and instructions, the diagram would be similar, except that the
6726 program variables and heap would share an address space with the main
6727 program and the overlay area.
6729 An overlay loaded into instruction memory and ready for use is called a
6730 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6731 instruction memory. An overlay not present (or only partially present)
6732 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6733 is its address in the larger memory. The mapped address is also called
6734 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6735 called the @dfn{load memory address}, or @dfn{LMA}.
6737 Unfortunately, overlays are not a completely transparent way to adapt a
6738 program to limited instruction memory. They introduce a new set of
6739 global constraints you must keep in mind as you design your program:
6744 Before calling or returning to a function in an overlay, your program
6745 must make sure that overlay is actually mapped. Otherwise, the call or
6746 return will transfer control to the right address, but in the wrong
6747 overlay, and your program will probably crash.
6750 If the process of mapping an overlay is expensive on your system, you
6751 will need to choose your overlays carefully to minimize their effect on
6752 your program's performance.
6755 The executable file you load onto your system must contain each
6756 overlay's instructions, appearing at the overlay's load address, not its
6757 mapped address. However, each overlay's instructions must be relocated
6758 and its symbols defined as if the overlay were at its mapped address.
6759 You can use GNU linker scripts to specify different load and relocation
6760 addresses for pieces of your program; see @ref{Overlay Description,,,
6761 ld.info, Using ld: the GNU linker}.
6764 The procedure for loading executable files onto your system must be able
6765 to load their contents into the larger address space as well as the
6766 instruction and data spaces.
6770 The overlay system described above is rather simple, and could be
6771 improved in many ways:
6776 If your system has suitable bank switch registers or memory management
6777 hardware, you could use those facilities to make an overlay's load area
6778 contents simply appear at their mapped address in instruction space.
6779 This would probably be faster than copying the overlay to its mapped
6780 area in the usual way.
6783 If your overlays are small enough, you could set aside more than one
6784 overlay area, and have more than one overlay mapped at a time.
6787 You can use overlays to manage data, as well as instructions. In
6788 general, data overlays are even less transparent to your design than
6789 code overlays: whereas code overlays only require care when you call or
6790 return to functions, data overlays require care every time you access
6791 the data. Also, if you change the contents of a data overlay, you
6792 must copy its contents back out to its load address before you can copy a
6793 different data overlay into the same mapped area.
6798 @node Overlay Commands
6799 @section Overlay Commands
6801 To use @value{GDBN}'s overlay support, each overlay in your program must
6802 correspond to a separate section of the executable file. The section's
6803 virtual memory address and load memory address must be the overlay's
6804 mapped and load addresses. Identifying overlays with sections allows
6805 @value{GDBN} to determine the appropriate address of a function or
6806 variable, depending on whether the overlay is mapped or not.
6808 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6809 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6814 Disable @value{GDBN}'s overlay support. When overlay support is
6815 disabled, @value{GDBN} assumes that all functions and variables are
6816 always present at their mapped addresses. By default, @value{GDBN}'s
6817 overlay support is disabled.
6819 @item overlay manual
6820 @kindex overlay manual
6821 @cindex manual overlay debugging
6822 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6823 relies on you to tell it which overlays are mapped, and which are not,
6824 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6825 commands described below.
6827 @item overlay map-overlay @var{overlay}
6828 @itemx overlay map @var{overlay}
6829 @kindex overlay map-overlay
6830 @cindex map an overlay
6831 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6832 be the name of the object file section containing the overlay. When an
6833 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6834 functions and variables at their mapped addresses. @value{GDBN} assumes
6835 that any other overlays whose mapped ranges overlap that of
6836 @var{overlay} are now unmapped.
6838 @item overlay unmap-overlay @var{overlay}
6839 @itemx overlay unmap @var{overlay}
6840 @kindex overlay unmap-overlay
6841 @cindex unmap an overlay
6842 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6843 must be the name of the object file section containing the overlay.
6844 When an overlay is unmapped, @value{GDBN} assumes it can find the
6845 overlay's functions and variables at their load addresses.
6848 @kindex overlay auto
6849 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6850 consults a data structure the overlay manager maintains in the inferior
6851 to see which overlays are mapped. For details, see @ref{Automatic
6854 @item overlay load-target
6856 @kindex overlay load-target
6857 @cindex reloading the overlay table
6858 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6859 re-reads the table @value{GDBN} automatically each time the inferior
6860 stops, so this command should only be necessary if you have changed the
6861 overlay mapping yourself using @value{GDBN}. This command is only
6862 useful when using automatic overlay debugging.
6864 @item overlay list-overlays
6866 @cindex listing mapped overlays
6867 Display a list of the overlays currently mapped, along with their mapped
6868 addresses, load addresses, and sizes.
6872 Normally, when @value{GDBN} prints a code address, it includes the name
6873 of the function the address falls in:
6877 $3 = @{int ()@} 0x11a0 <main>
6880 When overlay debugging is enabled, @value{GDBN} recognizes code in
6881 unmapped overlays, and prints the names of unmapped functions with
6882 asterisks around them. For example, if @code{foo} is a function in an
6883 unmapped overlay, @value{GDBN} prints it this way:
6887 No sections are mapped.
6889 $5 = @{int (int)@} 0x100000 <*foo*>
6892 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6897 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6898 mapped at 0x1016 - 0x104a
6900 $6 = @{int (int)@} 0x1016 <foo>
6903 When overlay debugging is enabled, @value{GDBN} can find the correct
6904 address for functions and variables in an overlay, whether or not the
6905 overlay is mapped. This allows most @value{GDBN} commands, like
6906 @code{break} and @code{disassemble}, to work normally, even on unmapped
6907 code. However, @value{GDBN}'s breakpoint support has some limitations:
6911 @cindex breakpoints in overlays
6912 @cindex overlays, setting breakpoints in
6913 You can set breakpoints in functions in unmapped overlays, as long as
6914 @value{GDBN} can write to the overlay at its load address.
6916 @value{GDBN} can not set hardware or simulator-based breakpoints in
6917 unmapped overlays. However, if you set a breakpoint at the end of your
6918 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6919 you are using manual overlay management), @value{GDBN} will re-set its
6920 breakpoints properly.
6924 @node Automatic Overlay Debugging
6925 @section Automatic Overlay Debugging
6926 @cindex automatic overlay debugging
6928 @value{GDBN} can automatically track which overlays are mapped and which
6929 are not, given some simple co-operation from the overlay manager in the
6930 inferior. If you enable automatic overlay debugging with the
6931 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6932 looks in the inferior's memory for certain variables describing the
6933 current state of the overlays.
6935 Here are the variables your overlay manager must define to support
6936 @value{GDBN}'s automatic overlay debugging:
6940 @item @code{_ovly_table}:
6941 This variable must be an array of the following structures:
6946 /* The overlay's mapped address. */
6949 /* The size of the overlay, in bytes. */
6952 /* The overlay's load address. */
6955 /* Non-zero if the overlay is currently mapped;
6957 unsigned long mapped;
6961 @item @code{_novlys}:
6962 This variable must be a four-byte signed integer, holding the total
6963 number of elements in @code{_ovly_table}.
6967 To decide whether a particular overlay is mapped or not, @value{GDBN}
6968 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6969 @code{lma} members equal the VMA and LMA of the overlay's section in the
6970 executable file. When @value{GDBN} finds a matching entry, it consults
6971 the entry's @code{mapped} member to determine whether the overlay is
6974 In addition, your overlay manager may define a function called
6975 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
6976 will silently set a breakpoint there. If the overlay manager then
6977 calls this function whenever it has changed the overlay table, this
6978 will enable @value{GDBN} to accurately keep track of which overlays
6979 are in program memory, and update any breakpoints that may be set
6980 in overlays. This will allow breakpoints to work even if the
6981 overlays are kept in ROM or other non-writable memory while they
6982 are not being executed.
6984 @node Overlay Sample Program
6985 @section Overlay Sample Program
6986 @cindex overlay example program
6988 When linking a program which uses overlays, you must place the overlays
6989 at their load addresses, while relocating them to run at their mapped
6990 addresses. To do this, you must write a linker script (@pxref{Overlay
6991 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
6992 since linker scripts are specific to a particular host system, target
6993 architecture, and target memory layout, this manual cannot provide
6994 portable sample code demonstrating @value{GDBN}'s overlay support.
6996 However, the @value{GDBN} source distribution does contain an overlaid
6997 program, with linker scripts for a few systems, as part of its test
6998 suite. The program consists of the following files from
6999 @file{gdb/testsuite/gdb.base}:
7003 The main program file.
7005 A simple overlay manager, used by @file{overlays.c}.
7010 Overlay modules, loaded and used by @file{overlays.c}.
7013 Linker scripts for linking the test program on the @code{d10v-elf}
7014 and @code{m32r-elf} targets.
7017 You can build the test program using the @code{d10v-elf} GCC
7018 cross-compiler like this:
7021 $ d10v-elf-gcc -g -c overlays.c
7022 $ d10v-elf-gcc -g -c ovlymgr.c
7023 $ d10v-elf-gcc -g -c foo.c
7024 $ d10v-elf-gcc -g -c bar.c
7025 $ d10v-elf-gcc -g -c baz.c
7026 $ d10v-elf-gcc -g -c grbx.c
7027 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7028 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7031 The build process is identical for any other architecture, except that
7032 you must substitute the appropriate compiler and linker script for the
7033 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7037 @chapter Using @value{GDBN} with Different Languages
7040 Although programming languages generally have common aspects, they are
7041 rarely expressed in the same manner. For instance, in ANSI C,
7042 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7043 Modula-2, it is accomplished by @code{p^}. Values can also be
7044 represented (and displayed) differently. Hex numbers in C appear as
7045 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7047 @cindex working language
7048 Language-specific information is built into @value{GDBN} for some languages,
7049 allowing you to express operations like the above in your program's
7050 native language, and allowing @value{GDBN} to output values in a manner
7051 consistent with the syntax of your program's native language. The
7052 language you use to build expressions is called the @dfn{working
7056 * Setting:: Switching between source languages
7057 * Show:: Displaying the language
7058 * Checks:: Type and range checks
7059 * Support:: Supported languages
7063 @section Switching between source languages
7065 There are two ways to control the working language---either have @value{GDBN}
7066 set it automatically, or select it manually yourself. You can use the
7067 @code{set language} command for either purpose. On startup, @value{GDBN}
7068 defaults to setting the language automatically. The working language is
7069 used to determine how expressions you type are interpreted, how values
7072 In addition to the working language, every source file that
7073 @value{GDBN} knows about has its own working language. For some object
7074 file formats, the compiler might indicate which language a particular
7075 source file is in. However, most of the time @value{GDBN} infers the
7076 language from the name of the file. The language of a source file
7077 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7078 show each frame appropriately for its own language. There is no way to
7079 set the language of a source file from within @value{GDBN}, but you can
7080 set the language associated with a filename extension. @xref{Show, ,
7081 Displaying the language}.
7083 This is most commonly a problem when you use a program, such
7084 as @code{cfront} or @code{f2c}, that generates C but is written in
7085 another language. In that case, make the
7086 program use @code{#line} directives in its C output; that way
7087 @value{GDBN} will know the correct language of the source code of the original
7088 program, and will display that source code, not the generated C code.
7091 * Filenames:: Filename extensions and languages.
7092 * Manually:: Setting the working language manually
7093 * Automatically:: Having @value{GDBN} infer the source language
7097 @subsection List of filename extensions and languages
7099 If a source file name ends in one of the following extensions, then
7100 @value{GDBN} infers that its language is the one indicated.
7119 @c OBSOLETE @item .ch
7120 @c OBSOLETE @itemx .c186
7121 @c OBSOLETE @itemx .c286
7122 @c OBSOLETE CHILL source file
7125 Modula-2 source file
7129 Assembler source file. This actually behaves almost like C, but
7130 @value{GDBN} does not skip over function prologues when stepping.
7133 In addition, you may set the language associated with a filename
7134 extension. @xref{Show, , Displaying the language}.
7137 @subsection Setting the working language
7139 If you allow @value{GDBN} to set the language automatically,
7140 expressions are interpreted the same way in your debugging session and
7143 @kindex set language
7144 If you wish, you may set the language manually. To do this, issue the
7145 command @samp{set language @var{lang}}, where @var{lang} is the name of
7147 @code{c} or @code{modula-2}.
7148 For a list of the supported languages, type @samp{set language}.
7150 Setting the language manually prevents @value{GDBN} from updating the working
7151 language automatically. This can lead to confusion if you try
7152 to debug a program when the working language is not the same as the
7153 source language, when an expression is acceptable to both
7154 languages---but means different things. For instance, if the current
7155 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7163 might not have the effect you intended. In C, this means to add
7164 @code{b} and @code{c} and place the result in @code{a}. The result
7165 printed would be the value of @code{a}. In Modula-2, this means to compare
7166 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7169 @subsection Having @value{GDBN} infer the source language
7171 To have @value{GDBN} set the working language automatically, use
7172 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7173 then infers the working language. That is, when your program stops in a
7174 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7175 working language to the language recorded for the function in that
7176 frame. If the language for a frame is unknown (that is, if the function
7177 or block corresponding to the frame was defined in a source file that
7178 does not have a recognized extension), the current working language is
7179 not changed, and @value{GDBN} issues a warning.
7181 This may not seem necessary for most programs, which are written
7182 entirely in one source language. However, program modules and libraries
7183 written in one source language can be used by a main program written in
7184 a different source language. Using @samp{set language auto} in this
7185 case frees you from having to set the working language manually.
7188 @section Displaying the language
7190 The following commands help you find out which language is the
7191 working language, and also what language source files were written in.
7193 @kindex show language
7194 @kindex info frame@r{, show the source language}
7195 @kindex info source@r{, show the source language}
7198 Display the current working language. This is the
7199 language you can use with commands such as @code{print} to
7200 build and compute expressions that may involve variables in your program.
7203 Display the source language for this frame. This language becomes the
7204 working language if you use an identifier from this frame.
7205 @xref{Frame Info, ,Information about a frame}, to identify the other
7206 information listed here.
7209 Display the source language of this source file.
7210 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7211 information listed here.
7214 In unusual circumstances, you may have source files with extensions
7215 not in the standard list. You can then set the extension associated
7216 with a language explicitly:
7218 @kindex set extension-language
7219 @kindex info extensions
7221 @item set extension-language @var{.ext} @var{language}
7222 Set source files with extension @var{.ext} to be assumed to be in
7223 the source language @var{language}.
7225 @item info extensions
7226 List all the filename extensions and the associated languages.
7230 @section Type and range checking
7233 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7234 checking are included, but they do not yet have any effect. This
7235 section documents the intended facilities.
7237 @c FIXME remove warning when type/range code added
7239 Some languages are designed to guard you against making seemingly common
7240 errors through a series of compile- and run-time checks. These include
7241 checking the type of arguments to functions and operators, and making
7242 sure mathematical overflows are caught at run time. Checks such as
7243 these help to ensure a program's correctness once it has been compiled
7244 by eliminating type mismatches, and providing active checks for range
7245 errors when your program is running.
7247 @value{GDBN} can check for conditions like the above if you wish.
7248 Although @value{GDBN} does not check the statements in your program, it
7249 can check expressions entered directly into @value{GDBN} for evaluation via
7250 the @code{print} command, for example. As with the working language,
7251 @value{GDBN} can also decide whether or not to check automatically based on
7252 your program's source language. @xref{Support, ,Supported languages},
7253 for the default settings of supported languages.
7256 * Type Checking:: An overview of type checking
7257 * Range Checking:: An overview of range checking
7260 @cindex type checking
7261 @cindex checks, type
7263 @subsection An overview of type checking
7265 Some languages, such as Modula-2, are strongly typed, meaning that the
7266 arguments to operators and functions have to be of the correct type,
7267 otherwise an error occurs. These checks prevent type mismatch
7268 errors from ever causing any run-time problems. For example,
7276 The second example fails because the @code{CARDINAL} 1 is not
7277 type-compatible with the @code{REAL} 2.3.
7279 For the expressions you use in @value{GDBN} commands, you can tell the
7280 @value{GDBN} type checker to skip checking;
7281 to treat any mismatches as errors and abandon the expression;
7282 or to only issue warnings when type mismatches occur,
7283 but evaluate the expression anyway. When you choose the last of
7284 these, @value{GDBN} evaluates expressions like the second example above, but
7285 also issues a warning.
7287 Even if you turn type checking off, there may be other reasons
7288 related to type that prevent @value{GDBN} from evaluating an expression.
7289 For instance, @value{GDBN} does not know how to add an @code{int} and
7290 a @code{struct foo}. These particular type errors have nothing to do
7291 with the language in use, and usually arise from expressions, such as
7292 the one described above, which make little sense to evaluate anyway.
7294 Each language defines to what degree it is strict about type. For
7295 instance, both Modula-2 and C require the arguments to arithmetical
7296 operators to be numbers. In C, enumerated types and pointers can be
7297 represented as numbers, so that they are valid arguments to mathematical
7298 operators. @xref{Support, ,Supported languages}, for further
7299 details on specific languages.
7301 @value{GDBN} provides some additional commands for controlling the type checker:
7303 @kindex set check@r{, type}
7304 @kindex set check type
7305 @kindex show check type
7307 @item set check type auto
7308 Set type checking on or off based on the current working language.
7309 @xref{Support, ,Supported languages}, for the default settings for
7312 @item set check type on
7313 @itemx set check type off
7314 Set type checking on or off, overriding the default setting for the
7315 current working language. Issue a warning if the setting does not
7316 match the language default. If any type mismatches occur in
7317 evaluating an expression while type checking is on, @value{GDBN} prints a
7318 message and aborts evaluation of the expression.
7320 @item set check type warn
7321 Cause the type checker to issue warnings, but to always attempt to
7322 evaluate the expression. Evaluating the expression may still
7323 be impossible for other reasons. For example, @value{GDBN} cannot add
7324 numbers and structures.
7327 Show the current setting of the type checker, and whether or not @value{GDBN}
7328 is setting it automatically.
7331 @cindex range checking
7332 @cindex checks, range
7333 @node Range Checking
7334 @subsection An overview of range checking
7336 In some languages (such as Modula-2), it is an error to exceed the
7337 bounds of a type; this is enforced with run-time checks. Such range
7338 checking is meant to ensure program correctness by making sure
7339 computations do not overflow, or indices on an array element access do
7340 not exceed the bounds of the array.
7342 For expressions you use in @value{GDBN} commands, you can tell
7343 @value{GDBN} to treat range errors in one of three ways: ignore them,
7344 always treat them as errors and abandon the expression, or issue
7345 warnings but evaluate the expression anyway.
7347 A range error can result from numerical overflow, from exceeding an
7348 array index bound, or when you type a constant that is not a member
7349 of any type. Some languages, however, do not treat overflows as an
7350 error. In many implementations of C, mathematical overflow causes the
7351 result to ``wrap around'' to lower values---for example, if @var{m} is
7352 the largest integer value, and @var{s} is the smallest, then
7355 @var{m} + 1 @result{} @var{s}
7358 This, too, is specific to individual languages, and in some cases
7359 specific to individual compilers or machines. @xref{Support, ,
7360 Supported languages}, for further details on specific languages.
7362 @value{GDBN} provides some additional commands for controlling the range checker:
7364 @kindex set check@r{, range}
7365 @kindex set check range
7366 @kindex show check range
7368 @item set check range auto
7369 Set range checking on or off based on the current working language.
7370 @xref{Support, ,Supported languages}, for the default settings for
7373 @item set check range on
7374 @itemx set check range off
7375 Set range checking on or off, overriding the default setting for the
7376 current working language. A warning is issued if the setting does not
7377 match the language default. If a range error occurs and range checking is on,
7378 then a message is printed and evaluation of the expression is aborted.
7380 @item set check range warn
7381 Output messages when the @value{GDBN} range checker detects a range error,
7382 but attempt to evaluate the expression anyway. Evaluating the
7383 expression may still be impossible for other reasons, such as accessing
7384 memory that the process does not own (a typical example from many Unix
7388 Show the current setting of the range checker, and whether or not it is
7389 being set automatically by @value{GDBN}.
7393 @section Supported languages
7395 @value{GDBN} supports C, C@t{++}, Fortran, Java,
7397 assembly, and Modula-2.
7398 @c This is false ...
7399 Some @value{GDBN} features may be used in expressions regardless of the
7400 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7401 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7402 ,Expressions}) can be used with the constructs of any supported
7405 The following sections detail to what degree each source language is
7406 supported by @value{GDBN}. These sections are not meant to be language
7407 tutorials or references, but serve only as a reference guide to what the
7408 @value{GDBN} expression parser accepts, and what input and output
7409 formats should look like for different languages. There are many good
7410 books written on each of these languages; please look to these for a
7411 language reference or tutorial.
7415 * Modula-2:: Modula-2
7416 @c OBSOLETE * Chill:: Chill
7420 @subsection C and C@t{++}
7422 @cindex C and C@t{++}
7423 @cindex expressions in C or C@t{++}
7425 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7426 to both languages. Whenever this is the case, we discuss those languages
7430 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7431 @cindex @sc{gnu} C@t{++}
7432 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7433 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7434 effectively, you must compile your C@t{++} programs with a supported
7435 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7436 compiler (@code{aCC}).
7438 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7439 format. You can select that format explicitly with the @code{g++}
7440 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7441 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7442 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7445 * C Operators:: C and C@t{++} operators
7446 * C Constants:: C and C@t{++} constants
7447 * C plus plus expressions:: C@t{++} expressions
7448 * C Defaults:: Default settings for C and C@t{++}
7449 * C Checks:: C and C@t{++} type and range checks
7450 * Debugging C:: @value{GDBN} and C
7451 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7455 @subsubsection C and C@t{++} operators
7457 @cindex C and C@t{++} operators
7459 Operators must be defined on values of specific types. For instance,
7460 @code{+} is defined on numbers, but not on structures. Operators are
7461 often defined on groups of types.
7463 For the purposes of C and C@t{++}, the following definitions hold:
7468 @emph{Integral types} include @code{int} with any of its storage-class
7469 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7472 @emph{Floating-point types} include @code{float}, @code{double}, and
7473 @code{long double} (if supported by the target platform).
7476 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7479 @emph{Scalar types} include all of the above.
7484 The following operators are supported. They are listed here
7485 in order of increasing precedence:
7489 The comma or sequencing operator. Expressions in a comma-separated list
7490 are evaluated from left to right, with the result of the entire
7491 expression being the last expression evaluated.
7494 Assignment. The value of an assignment expression is the value
7495 assigned. Defined on scalar types.
7498 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7499 and translated to @w{@code{@var{a} = @var{a op b}}}.
7500 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7501 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7502 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7505 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7506 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7510 Logical @sc{or}. Defined on integral types.
7513 Logical @sc{and}. Defined on integral types.
7516 Bitwise @sc{or}. Defined on integral types.
7519 Bitwise exclusive-@sc{or}. Defined on integral types.
7522 Bitwise @sc{and}. Defined on integral types.
7525 Equality and inequality. Defined on scalar types. The value of these
7526 expressions is 0 for false and non-zero for true.
7528 @item <@r{, }>@r{, }<=@r{, }>=
7529 Less than, greater than, less than or equal, greater than or equal.
7530 Defined on scalar types. The value of these expressions is 0 for false
7531 and non-zero for true.
7534 left shift, and right shift. Defined on integral types.
7537 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7540 Addition and subtraction. Defined on integral types, floating-point types and
7543 @item *@r{, }/@r{, }%
7544 Multiplication, division, and modulus. Multiplication and division are
7545 defined on integral and floating-point types. Modulus is defined on
7549 Increment and decrement. When appearing before a variable, the
7550 operation is performed before the variable is used in an expression;
7551 when appearing after it, the variable's value is used before the
7552 operation takes place.
7555 Pointer dereferencing. Defined on pointer types. Same precedence as
7559 Address operator. Defined on variables. Same precedence as @code{++}.
7561 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7562 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7563 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7564 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7568 Negative. Defined on integral and floating-point types. Same
7569 precedence as @code{++}.
7572 Logical negation. Defined on integral types. Same precedence as
7576 Bitwise complement operator. Defined on integral types. Same precedence as
7581 Structure member, and pointer-to-structure member. For convenience,
7582 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7583 pointer based on the stored type information.
7584 Defined on @code{struct} and @code{union} data.
7587 Dereferences of pointers to members.
7590 Array indexing. @code{@var{a}[@var{i}]} is defined as
7591 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7594 Function parameter list. Same precedence as @code{->}.
7597 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7598 and @code{class} types.
7601 Doubled colons also represent the @value{GDBN} scope operator
7602 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7606 If an operator is redefined in the user code, @value{GDBN} usually
7607 attempts to invoke the redefined version instead of using the operator's
7615 @subsubsection C and C@t{++} constants
7617 @cindex C and C@t{++} constants
7619 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7624 Integer constants are a sequence of digits. Octal constants are
7625 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7626 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7627 @samp{l}, specifying that the constant should be treated as a
7631 Floating point constants are a sequence of digits, followed by a decimal
7632 point, followed by a sequence of digits, and optionally followed by an
7633 exponent. An exponent is of the form:
7634 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7635 sequence of digits. The @samp{+} is optional for positive exponents.
7636 A floating-point constant may also end with a letter @samp{f} or
7637 @samp{F}, specifying that the constant should be treated as being of
7638 the @code{float} (as opposed to the default @code{double}) type; or with
7639 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7643 Enumerated constants consist of enumerated identifiers, or their
7644 integral equivalents.
7647 Character constants are a single character surrounded by single quotes
7648 (@code{'}), or a number---the ordinal value of the corresponding character
7649 (usually its @sc{ascii} value). Within quotes, the single character may
7650 be represented by a letter or by @dfn{escape sequences}, which are of
7651 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7652 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7653 @samp{@var{x}} is a predefined special character---for example,
7654 @samp{\n} for newline.
7657 String constants are a sequence of character constants surrounded by
7658 double quotes (@code{"}). Any valid character constant (as described
7659 above) may appear. Double quotes within the string must be preceded by
7660 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7664 Pointer constants are an integral value. You can also write pointers
7665 to constants using the C operator @samp{&}.
7668 Array constants are comma-separated lists surrounded by braces @samp{@{}
7669 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7670 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7671 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7675 * C plus plus expressions::
7682 @node C plus plus expressions
7683 @subsubsection C@t{++} expressions
7685 @cindex expressions in C@t{++}
7686 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7688 @cindex C@t{++} support, not in @sc{coff}
7689 @cindex @sc{coff} versus C@t{++}
7690 @cindex C@t{++} and object formats
7691 @cindex object formats and C@t{++}
7692 @cindex a.out and C@t{++}
7693 @cindex @sc{ecoff} and C@t{++}
7694 @cindex @sc{xcoff} and C@t{++}
7695 @cindex @sc{elf}/stabs and C@t{++}
7696 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7697 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7698 @c periodically whether this has happened...
7700 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7701 proper compiler. Typically, C@t{++} debugging depends on the use of
7702 additional debugging information in the symbol table, and thus requires
7703 special support. In particular, if your compiler generates a.out, MIPS
7704 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7705 symbol table, these facilities are all available. (With @sc{gnu} CC,
7706 you can use the @samp{-gstabs} option to request stabs debugging
7707 extensions explicitly.) Where the object code format is standard
7708 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7709 support in @value{GDBN} does @emph{not} work.
7714 @cindex member functions
7716 Member function calls are allowed; you can use expressions like
7719 count = aml->GetOriginal(x, y)
7722 @vindex this@r{, inside C@t{++} member functions}
7723 @cindex namespace in C@t{++}
7725 While a member function is active (in the selected stack frame), your
7726 expressions have the same namespace available as the member function;
7727 that is, @value{GDBN} allows implicit references to the class instance
7728 pointer @code{this} following the same rules as C@t{++}.
7730 @cindex call overloaded functions
7731 @cindex overloaded functions, calling
7732 @cindex type conversions in C@t{++}
7734 You can call overloaded functions; @value{GDBN} resolves the function
7735 call to the right definition, with some restrictions. @value{GDBN} does not
7736 perform overload resolution involving user-defined type conversions,
7737 calls to constructors, or instantiations of templates that do not exist
7738 in the program. It also cannot handle ellipsis argument lists or
7741 It does perform integral conversions and promotions, floating-point
7742 promotions, arithmetic conversions, pointer conversions, conversions of
7743 class objects to base classes, and standard conversions such as those of
7744 functions or arrays to pointers; it requires an exact match on the
7745 number of function arguments.
7747 Overload resolution is always performed, unless you have specified
7748 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7749 ,@value{GDBN} features for C@t{++}}.
7751 You must specify @code{set overload-resolution off} in order to use an
7752 explicit function signature to call an overloaded function, as in
7754 p 'foo(char,int)'('x', 13)
7757 The @value{GDBN} command-completion facility can simplify this;
7758 see @ref{Completion, ,Command completion}.
7760 @cindex reference declarations
7762 @value{GDBN} understands variables declared as C@t{++} references; you can use
7763 them in expressions just as you do in C@t{++} source---they are automatically
7766 In the parameter list shown when @value{GDBN} displays a frame, the values of
7767 reference variables are not displayed (unlike other variables); this
7768 avoids clutter, since references are often used for large structures.
7769 The @emph{address} of a reference variable is always shown, unless
7770 you have specified @samp{set print address off}.
7773 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7774 expressions can use it just as expressions in your program do. Since
7775 one scope may be defined in another, you can use @code{::} repeatedly if
7776 necessary, for example in an expression like
7777 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7778 resolving name scope by reference to source files, in both C and C@t{++}
7779 debugging (@pxref{Variables, ,Program variables}).
7782 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7783 calling virtual functions correctly, printing out virtual bases of
7784 objects, calling functions in a base subobject, casting objects, and
7785 invoking user-defined operators.
7788 @subsubsection C and C@t{++} defaults
7790 @cindex C and C@t{++} defaults
7792 If you allow @value{GDBN} to set type and range checking automatically, they
7793 both default to @code{off} whenever the working language changes to
7794 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7795 selects the working language.
7797 If you allow @value{GDBN} to set the language automatically, it
7798 recognizes source files whose names end with @file{.c}, @file{.C}, or
7799 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7800 these files, it sets the working language to C or C@t{++}.
7801 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7802 for further details.
7804 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7805 @c unimplemented. If (b) changes, it might make sense to let this node
7806 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7809 @subsubsection C and C@t{++} type and range checks
7811 @cindex C and C@t{++} checks
7813 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7814 is not used. However, if you turn type checking on, @value{GDBN}
7815 considers two variables type equivalent if:
7819 The two variables are structured and have the same structure, union, or
7823 The two variables have the same type name, or types that have been
7824 declared equivalent through @code{typedef}.
7827 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7830 The two @code{struct}, @code{union}, or @code{enum} variables are
7831 declared in the same declaration. (Note: this may not be true for all C
7836 Range checking, if turned on, is done on mathematical operations. Array
7837 indices are not checked, since they are often used to index a pointer
7838 that is not itself an array.
7841 @subsubsection @value{GDBN} and C
7843 The @code{set print union} and @code{show print union} commands apply to
7844 the @code{union} type. When set to @samp{on}, any @code{union} that is
7845 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7846 appears as @samp{@{...@}}.
7848 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7849 with pointers and a memory allocation function. @xref{Expressions,
7853 * Debugging C plus plus::
7856 @node Debugging C plus plus
7857 @subsubsection @value{GDBN} features for C@t{++}
7859 @cindex commands for C@t{++}
7861 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7862 designed specifically for use with C@t{++}. Here is a summary:
7865 @cindex break in overloaded functions
7866 @item @r{breakpoint menus}
7867 When you want a breakpoint in a function whose name is overloaded,
7868 @value{GDBN} breakpoint menus help you specify which function definition
7869 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7871 @cindex overloading in C@t{++}
7872 @item rbreak @var{regex}
7873 Setting breakpoints using regular expressions is helpful for setting
7874 breakpoints on overloaded functions that are not members of any special
7876 @xref{Set Breaks, ,Setting breakpoints}.
7878 @cindex C@t{++} exception handling
7881 Debug C@t{++} exception handling using these commands. @xref{Set
7882 Catchpoints, , Setting catchpoints}.
7885 @item ptype @var{typename}
7886 Print inheritance relationships as well as other information for type
7888 @xref{Symbols, ,Examining the Symbol Table}.
7890 @cindex C@t{++} symbol display
7891 @item set print demangle
7892 @itemx show print demangle
7893 @itemx set print asm-demangle
7894 @itemx show print asm-demangle
7895 Control whether C@t{++} symbols display in their source form, both when
7896 displaying code as C@t{++} source and when displaying disassemblies.
7897 @xref{Print Settings, ,Print settings}.
7899 @item set print object
7900 @itemx show print object
7901 Choose whether to print derived (actual) or declared types of objects.
7902 @xref{Print Settings, ,Print settings}.
7904 @item set print vtbl
7905 @itemx show print vtbl
7906 Control the format for printing virtual function tables.
7907 @xref{Print Settings, ,Print settings}.
7908 (The @code{vtbl} commands do not work on programs compiled with the HP
7909 ANSI C@t{++} compiler (@code{aCC}).)
7911 @kindex set overload-resolution
7912 @cindex overloaded functions, overload resolution
7913 @item set overload-resolution on
7914 Enable overload resolution for C@t{++} expression evaluation. The default
7915 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7916 and searches for a function whose signature matches the argument types,
7917 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7918 expressions}, for details). If it cannot find a match, it emits a
7921 @item set overload-resolution off
7922 Disable overload resolution for C@t{++} expression evaluation. For
7923 overloaded functions that are not class member functions, @value{GDBN}
7924 chooses the first function of the specified name that it finds in the
7925 symbol table, whether or not its arguments are of the correct type. For
7926 overloaded functions that are class member functions, @value{GDBN}
7927 searches for a function whose signature @emph{exactly} matches the
7930 @item @r{Overloaded symbol names}
7931 You can specify a particular definition of an overloaded symbol, using
7932 the same notation that is used to declare such symbols in C@t{++}: type
7933 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7934 also use the @value{GDBN} command-line word completion facilities to list the
7935 available choices, or to finish the type list for you.
7936 @xref{Completion,, Command completion}, for details on how to do this.
7940 @subsection Modula-2
7942 @cindex Modula-2, @value{GDBN} support
7944 The extensions made to @value{GDBN} to support Modula-2 only support
7945 output from the @sc{gnu} Modula-2 compiler (which is currently being
7946 developed). Other Modula-2 compilers are not currently supported, and
7947 attempting to debug executables produced by them is most likely
7948 to give an error as @value{GDBN} reads in the executable's symbol
7951 @cindex expressions in Modula-2
7953 * M2 Operators:: Built-in operators
7954 * Built-In Func/Proc:: Built-in functions and procedures
7955 * M2 Constants:: Modula-2 constants
7956 * M2 Defaults:: Default settings for Modula-2
7957 * Deviations:: Deviations from standard Modula-2
7958 * M2 Checks:: Modula-2 type and range checks
7959 * M2 Scope:: The scope operators @code{::} and @code{.}
7960 * GDB/M2:: @value{GDBN} and Modula-2
7964 @subsubsection Operators
7965 @cindex Modula-2 operators
7967 Operators must be defined on values of specific types. For instance,
7968 @code{+} is defined on numbers, but not on structures. Operators are
7969 often defined on groups of types. For the purposes of Modula-2, the
7970 following definitions hold:
7975 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7979 @emph{Character types} consist of @code{CHAR} and its subranges.
7982 @emph{Floating-point types} consist of @code{REAL}.
7985 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7989 @emph{Scalar types} consist of all of the above.
7992 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7995 @emph{Boolean types} consist of @code{BOOLEAN}.
7999 The following operators are supported, and appear in order of
8000 increasing precedence:
8004 Function argument or array index separator.
8007 Assignment. The value of @var{var} @code{:=} @var{value} is
8011 Less than, greater than on integral, floating-point, or enumerated
8015 Less than or equal to, greater than or equal to
8016 on integral, floating-point and enumerated types, or set inclusion on
8017 set types. Same precedence as @code{<}.
8019 @item =@r{, }<>@r{, }#
8020 Equality and two ways of expressing inequality, valid on scalar types.
8021 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8022 available for inequality, since @code{#} conflicts with the script
8026 Set membership. Defined on set types and the types of their members.
8027 Same precedence as @code{<}.
8030 Boolean disjunction. Defined on boolean types.
8033 Boolean conjunction. Defined on boolean types.
8036 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8039 Addition and subtraction on integral and floating-point types, or union
8040 and difference on set types.
8043 Multiplication on integral and floating-point types, or set intersection
8047 Division on floating-point types, or symmetric set difference on set
8048 types. Same precedence as @code{*}.
8051 Integer division and remainder. Defined on integral types. Same
8052 precedence as @code{*}.
8055 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8058 Pointer dereferencing. Defined on pointer types.
8061 Boolean negation. Defined on boolean types. Same precedence as
8065 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8066 precedence as @code{^}.
8069 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8072 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8076 @value{GDBN} and Modula-2 scope operators.
8080 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8081 treats the use of the operator @code{IN}, or the use of operators
8082 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8083 @code{<=}, and @code{>=} on sets as an error.
8087 @node Built-In Func/Proc
8088 @subsubsection Built-in functions and procedures
8089 @cindex Modula-2 built-ins
8091 Modula-2 also makes available several built-in procedures and functions.
8092 In describing these, the following metavariables are used:
8097 represents an @code{ARRAY} variable.
8100 represents a @code{CHAR} constant or variable.
8103 represents a variable or constant of integral type.
8106 represents an identifier that belongs to a set. Generally used in the
8107 same function with the metavariable @var{s}. The type of @var{s} should
8108 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8111 represents a variable or constant of integral or floating-point type.
8114 represents a variable or constant of floating-point type.
8120 represents a variable.
8123 represents a variable or constant of one of many types. See the
8124 explanation of the function for details.
8127 All Modula-2 built-in procedures also return a result, described below.
8131 Returns the absolute value of @var{n}.
8134 If @var{c} is a lower case letter, it returns its upper case
8135 equivalent, otherwise it returns its argument.
8138 Returns the character whose ordinal value is @var{i}.
8141 Decrements the value in the variable @var{v} by one. Returns the new value.
8143 @item DEC(@var{v},@var{i})
8144 Decrements the value in the variable @var{v} by @var{i}. Returns the
8147 @item EXCL(@var{m},@var{s})
8148 Removes the element @var{m} from the set @var{s}. Returns the new
8151 @item FLOAT(@var{i})
8152 Returns the floating point equivalent of the integer @var{i}.
8155 Returns the index of the last member of @var{a}.
8158 Increments the value in the variable @var{v} by one. Returns the new value.
8160 @item INC(@var{v},@var{i})
8161 Increments the value in the variable @var{v} by @var{i}. Returns the
8164 @item INCL(@var{m},@var{s})
8165 Adds the element @var{m} to the set @var{s} if it is not already
8166 there. Returns the new set.
8169 Returns the maximum value of the type @var{t}.
8172 Returns the minimum value of the type @var{t}.
8175 Returns boolean TRUE if @var{i} is an odd number.
8178 Returns the ordinal value of its argument. For example, the ordinal
8179 value of a character is its @sc{ascii} value (on machines supporting the
8180 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8181 integral, character and enumerated types.
8184 Returns the size of its argument. @var{x} can be a variable or a type.
8186 @item TRUNC(@var{r})
8187 Returns the integral part of @var{r}.
8189 @item VAL(@var{t},@var{i})
8190 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8194 @emph{Warning:} Sets and their operations are not yet supported, so
8195 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8199 @cindex Modula-2 constants
8201 @subsubsection Constants
8203 @value{GDBN} allows you to express the constants of Modula-2 in the following
8209 Integer constants are simply a sequence of digits. When used in an
8210 expression, a constant is interpreted to be type-compatible with the
8211 rest of the expression. Hexadecimal integers are specified by a
8212 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8215 Floating point constants appear as a sequence of digits, followed by a
8216 decimal point and another sequence of digits. An optional exponent can
8217 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8218 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8219 digits of the floating point constant must be valid decimal (base 10)
8223 Character constants consist of a single character enclosed by a pair of
8224 like quotes, either single (@code{'}) or double (@code{"}). They may
8225 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8226 followed by a @samp{C}.
8229 String constants consist of a sequence of characters enclosed by a
8230 pair of like quotes, either single (@code{'}) or double (@code{"}).
8231 Escape sequences in the style of C are also allowed. @xref{C
8232 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8236 Enumerated constants consist of an enumerated identifier.
8239 Boolean constants consist of the identifiers @code{TRUE} and
8243 Pointer constants consist of integral values only.
8246 Set constants are not yet supported.
8250 @subsubsection Modula-2 defaults
8251 @cindex Modula-2 defaults
8253 If type and range checking are set automatically by @value{GDBN}, they
8254 both default to @code{on} whenever the working language changes to
8255 Modula-2. This happens regardless of whether you or @value{GDBN}
8256 selected the working language.
8258 If you allow @value{GDBN} to set the language automatically, then entering
8259 code compiled from a file whose name ends with @file{.mod} sets the
8260 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8261 the language automatically}, for further details.
8264 @subsubsection Deviations from standard Modula-2
8265 @cindex Modula-2, deviations from
8267 A few changes have been made to make Modula-2 programs easier to debug.
8268 This is done primarily via loosening its type strictness:
8272 Unlike in standard Modula-2, pointer constants can be formed by
8273 integers. This allows you to modify pointer variables during
8274 debugging. (In standard Modula-2, the actual address contained in a
8275 pointer variable is hidden from you; it can only be modified
8276 through direct assignment to another pointer variable or expression that
8277 returned a pointer.)
8280 C escape sequences can be used in strings and characters to represent
8281 non-printable characters. @value{GDBN} prints out strings with these
8282 escape sequences embedded. Single non-printable characters are
8283 printed using the @samp{CHR(@var{nnn})} format.
8286 The assignment operator (@code{:=}) returns the value of its right-hand
8290 All built-in procedures both modify @emph{and} return their argument.
8294 @subsubsection Modula-2 type and range checks
8295 @cindex Modula-2 checks
8298 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8301 @c FIXME remove warning when type/range checks added
8303 @value{GDBN} considers two Modula-2 variables type equivalent if:
8307 They are of types that have been declared equivalent via a @code{TYPE
8308 @var{t1} = @var{t2}} statement
8311 They have been declared on the same line. (Note: This is true of the
8312 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8315 As long as type checking is enabled, any attempt to combine variables
8316 whose types are not equivalent is an error.
8318 Range checking is done on all mathematical operations, assignment, array
8319 index bounds, and all built-in functions and procedures.
8322 @subsubsection The scope operators @code{::} and @code{.}
8324 @cindex @code{.}, Modula-2 scope operator
8325 @cindex colon, doubled as scope operator
8327 @vindex colon-colon@r{, in Modula-2}
8328 @c Info cannot handle :: but TeX can.
8331 @vindex ::@r{, in Modula-2}
8334 There are a few subtle differences between the Modula-2 scope operator
8335 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8340 @var{module} . @var{id}
8341 @var{scope} :: @var{id}
8345 where @var{scope} is the name of a module or a procedure,
8346 @var{module} the name of a module, and @var{id} is any declared
8347 identifier within your program, except another module.
8349 Using the @code{::} operator makes @value{GDBN} search the scope
8350 specified by @var{scope} for the identifier @var{id}. If it is not
8351 found in the specified scope, then @value{GDBN} searches all scopes
8352 enclosing the one specified by @var{scope}.
8354 Using the @code{.} operator makes @value{GDBN} search the current scope for
8355 the identifier specified by @var{id} that was imported from the
8356 definition module specified by @var{module}. With this operator, it is
8357 an error if the identifier @var{id} was not imported from definition
8358 module @var{module}, or if @var{id} is not an identifier in
8362 @subsubsection @value{GDBN} and Modula-2
8364 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8365 Five subcommands of @code{set print} and @code{show print} apply
8366 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8367 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8368 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8369 analogue in Modula-2.
8371 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8372 with any language, is not useful with Modula-2. Its
8373 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8374 created in Modula-2 as they can in C or C@t{++}. However, because an
8375 address can be specified by an integral constant, the construct
8376 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8378 @cindex @code{#} in Modula-2
8379 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8380 interpreted as the beginning of a comment. Use @code{<>} instead.
8382 @c OBSOLETE @node Chill
8383 @c OBSOLETE @subsection Chill
8385 @c OBSOLETE The extensions made to @value{GDBN} to support Chill only support output
8386 @c OBSOLETE from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8387 @c OBSOLETE supported, and attempting to debug executables produced by them is most
8388 @c OBSOLETE likely to give an error as @value{GDBN} reads in the executable's symbol
8391 @c OBSOLETE @c This used to say "... following Chill related topics ...", but since
8392 @c OBSOLETE @c menus are not shown in the printed manual, it would look awkward.
8393 @c OBSOLETE This section covers the Chill related topics and the features
8394 @c OBSOLETE of @value{GDBN} which support these topics.
8397 @c OBSOLETE * How modes are displayed:: How modes are displayed
8398 @c OBSOLETE * Locations:: Locations and their accesses
8399 @c OBSOLETE * Values and their Operations:: Values and their Operations
8400 @c OBSOLETE * Chill type and range checks::
8401 @c OBSOLETE * Chill defaults::
8402 @c OBSOLETE @end menu
8404 @c OBSOLETE @node How modes are displayed
8405 @c OBSOLETE @subsubsection How modes are displayed
8407 @c OBSOLETE The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8408 @c OBSOLETE with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8409 @c OBSOLETE slightly from the standard specification of the Chill language. The
8410 @c OBSOLETE provided modes are:
8412 @c OBSOLETE @c FIXME: this @table's contents effectively disable @code by using @r
8413 @c OBSOLETE @c on every @item. So why does it need @code?
8414 @c OBSOLETE @table @code
8415 @c OBSOLETE @item @r{@emph{Discrete modes:}}
8416 @c OBSOLETE @itemize @bullet
8418 @c OBSOLETE @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8419 @c OBSOLETE UINT, LONG, ULONG},
8421 @c OBSOLETE @emph{Boolean Mode} which is predefined by @code{BOOL},
8423 @c OBSOLETE @emph{Character Mode} which is predefined by @code{CHAR},
8425 @c OBSOLETE @emph{Set Mode} which is displayed by the keyword @code{SET}.
8426 @c OBSOLETE @smallexample
8427 @c OBSOLETE (@value{GDBP}) ptype x
8428 @c OBSOLETE type = SET (karli = 10, susi = 20, fritzi = 100)
8429 @c OBSOLETE @end smallexample
8430 @c OBSOLETE If the type is an unnumbered set the set element values are omitted.
8432 @c OBSOLETE @emph{Range Mode} which is displayed by
8433 @c OBSOLETE @smallexample
8434 @c OBSOLETE @code{type = <basemode>(<lower bound> : <upper bound>)}
8435 @c OBSOLETE @end smallexample
8436 @c OBSOLETE where @code{<lower bound>, <upper bound>} can be of any discrete literal
8437 @c OBSOLETE expression (e.g. set element names).
8438 @c OBSOLETE @end itemize
8440 @c OBSOLETE @item @r{@emph{Powerset Mode:}}
8441 @c OBSOLETE A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8442 @c OBSOLETE the member mode of the powerset. The member mode can be any discrete mode.
8443 @c OBSOLETE @smallexample
8444 @c OBSOLETE (@value{GDBP}) ptype x
8445 @c OBSOLETE type = POWERSET SET (egon, hugo, otto)
8446 @c OBSOLETE @end smallexample
8448 @c OBSOLETE @item @r{@emph{Reference Modes:}}
8449 @c OBSOLETE @itemize @bullet
8451 @c OBSOLETE @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8452 @c OBSOLETE followed by the mode name to which the reference is bound.
8454 @c OBSOLETE @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8455 @c OBSOLETE @end itemize
8457 @c OBSOLETE @item @r{@emph{Procedure mode}}
8458 @c OBSOLETE The procedure mode is displayed by @code{type = PROC(<parameter list>)
8459 @c OBSOLETE <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8460 @c OBSOLETE list>} is a list of the parameter modes. @code{<return mode>} indicates
8461 @c OBSOLETE the mode of the result of the procedure if any. The exceptionlist lists
8462 @c OBSOLETE all possible exceptions which can be raised by the procedure.
8465 @c OBSOLETE @item @r{@emph{Instance mode}}
8466 @c OBSOLETE The instance mode is represented by a structure, which has a static
8467 @c OBSOLETE type, and is therefore not really of interest.
8468 @c OBSOLETE @end ignore
8470 @c OBSOLETE @item @r{@emph{Synchronization Modes:}}
8471 @c OBSOLETE @itemize @bullet
8473 @c OBSOLETE @emph{Event Mode} which is displayed by
8474 @c OBSOLETE @smallexample
8475 @c OBSOLETE @code{EVENT (<event length>)}
8476 @c OBSOLETE @end smallexample
8477 @c OBSOLETE where @code{(<event length>)} is optional.
8479 @c OBSOLETE @emph{Buffer Mode} which is displayed by
8480 @c OBSOLETE @smallexample
8481 @c OBSOLETE @code{BUFFER (<buffer length>)<buffer element mode>}
8482 @c OBSOLETE @end smallexample
8483 @c OBSOLETE where @code{(<buffer length>)} is optional.
8484 @c OBSOLETE @end itemize
8486 @c OBSOLETE @item @r{@emph{Timing Modes:}}
8487 @c OBSOLETE @itemize @bullet
8489 @c OBSOLETE @emph{Duration Mode} which is predefined by @code{DURATION}
8491 @c OBSOLETE @emph{Absolute Time Mode} which is predefined by @code{TIME}
8492 @c OBSOLETE @end itemize
8494 @c OBSOLETE @item @r{@emph{Real Modes:}}
8495 @c OBSOLETE Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8497 @c OBSOLETE @item @r{@emph{String Modes:}}
8498 @c OBSOLETE @itemize @bullet
8500 @c OBSOLETE @emph{Character String Mode} which is displayed by
8501 @c OBSOLETE @smallexample
8502 @c OBSOLETE @code{CHARS(<string length>)}
8503 @c OBSOLETE @end smallexample
8504 @c OBSOLETE followed by the keyword @code{VARYING} if the String Mode is a varying
8507 @c OBSOLETE @emph{Bit String Mode} which is displayed by
8508 @c OBSOLETE @smallexample
8509 @c OBSOLETE @code{BOOLS(<string
8510 @c OBSOLETE length>)}
8511 @c OBSOLETE @end smallexample
8512 @c OBSOLETE @end itemize
8514 @c OBSOLETE @item @r{@emph{Array Mode:}}
8515 @c OBSOLETE The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8516 @c OBSOLETE followed by the element mode (which may in turn be an array mode).
8517 @c OBSOLETE @smallexample
8518 @c OBSOLETE (@value{GDBP}) ptype x
8519 @c OBSOLETE type = ARRAY (1:42)
8520 @c OBSOLETE ARRAY (1:20)
8521 @c OBSOLETE SET (karli = 10, susi = 20, fritzi = 100)
8522 @c OBSOLETE @end smallexample
8524 @c OBSOLETE @item @r{@emph{Structure Mode}}
8525 @c OBSOLETE The Structure mode is displayed by the keyword @code{STRUCT(<field
8526 @c OBSOLETE list>)}. The @code{<field list>} consists of names and modes of fields
8527 @c OBSOLETE of the structure. Variant structures have the keyword @code{CASE <field>
8528 @c OBSOLETE OF <variant fields> ESAC} in their field list. Since the current version
8529 @c OBSOLETE of the GNU Chill compiler doesn't implement tag processing (no runtime
8530 @c OBSOLETE checks of variant fields, and therefore no debugging info), the output
8531 @c OBSOLETE always displays all variant fields.
8532 @c OBSOLETE @smallexample
8533 @c OBSOLETE (@value{GDBP}) ptype str
8534 @c OBSOLETE type = STRUCT (
8537 @c OBSOLETE CASE bs OF
8538 @c OBSOLETE (karli):
8544 @c OBSOLETE @end smallexample
8545 @c OBSOLETE @end table
8547 @c OBSOLETE @node Locations
8548 @c OBSOLETE @subsubsection Locations and their accesses
8550 @c OBSOLETE A location in Chill is an object which can contain values.
8552 @c OBSOLETE A value of a location is generally accessed by the (declared) name of
8553 @c OBSOLETE the location. The output conforms to the specification of values in
8554 @c OBSOLETE Chill programs. How values are specified
8555 @c OBSOLETE is the topic of the next section, @ref{Values and their Operations}.
8557 @c OBSOLETE The pseudo-location @code{RESULT} (or @code{result}) can be used to
8558 @c OBSOLETE display or change the result of a currently-active procedure:
8560 @c OBSOLETE @smallexample
8561 @c OBSOLETE set result := EXPR
8562 @c OBSOLETE @end smallexample
8564 @c OBSOLETE @noindent
8565 @c OBSOLETE This does the same as the Chill action @code{RESULT EXPR} (which
8566 @c OBSOLETE is not available in @value{GDBN}).
8568 @c OBSOLETE Values of reference mode locations are printed by @code{PTR(<hex
8569 @c OBSOLETE value>)} in case of a free reference mode, and by @code{(REF <reference
8570 @c OBSOLETE mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8571 @c OBSOLETE represents the address where the reference points to. To access the
8572 @c OBSOLETE value of the location referenced by the pointer, use the dereference
8573 @c OBSOLETE operator @samp{->}.
8575 @c OBSOLETE Values of procedure mode locations are displayed by
8576 @c OBSOLETE @smallexample
8577 @c OBSOLETE @code{@{ PROC
8578 @c OBSOLETE (<argument modes> ) <return mode> @} <address> <name of procedure
8579 @c OBSOLETE location>}
8580 @c OBSOLETE @end smallexample
8581 @c OBSOLETE @code{<argument modes>} is a list of modes according to the parameter
8582 @c OBSOLETE specification of the procedure and @code{<address>} shows the address of
8583 @c OBSOLETE the entry point.
8586 @c OBSOLETE Locations of instance modes are displayed just like a structure with two
8587 @c OBSOLETE fields specifying the @emph{process type} and the @emph{copy number} of
8588 @c OBSOLETE the investigated instance location@footnote{This comes from the current
8589 @c OBSOLETE implementation of instances. They are implemented as a structure (no
8590 @c OBSOLETE na). The output should be something like @code{[<name of the process>;
8591 @c OBSOLETE <instance number>]}.}. The field names are @code{__proc_type} and
8592 @c OBSOLETE @code{__proc_copy}.
8594 @c OBSOLETE Locations of synchronization modes are displayed like a structure with
8595 @c OBSOLETE the field name @code{__event_data} in case of a event mode location, and
8596 @c OBSOLETE like a structure with the field @code{__buffer_data} in case of a buffer
8597 @c OBSOLETE mode location (refer to previous paragraph).
8599 @c OBSOLETE Structure Mode locations are printed by @code{[.<field name>: <value>,
8600 @c OBSOLETE ...]}. The @code{<field name>} corresponds to the structure mode
8601 @c OBSOLETE definition and the layout of @code{<value>} varies depending of the mode
8602 @c OBSOLETE of the field. If the investigated structure mode location is of variant
8603 @c OBSOLETE structure mode, the variant parts of the structure are enclosed in curled
8604 @c OBSOLETE braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8605 @c OBSOLETE on the same memory location and represent the current values of the
8606 @c OBSOLETE memory location in their specific modes. Since no tag processing is done
8607 @c OBSOLETE all variants are displayed. A variant field is printed by
8608 @c OBSOLETE @code{(<variant name>) = .<field name>: <value>}. (who implements the
8609 @c OBSOLETE stuff ???)
8610 @c OBSOLETE @smallexample
8611 @c OBSOLETE (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8612 @c OBSOLETE [.cs: []], (susi) = [.ds: susi]}]
8613 @c OBSOLETE @end smallexample
8614 @c OBSOLETE @end ignore
8616 @c OBSOLETE Substructures of string mode-, array mode- or structure mode-values
8617 @c OBSOLETE (e.g. array slices, fields of structure locations) are accessed using
8618 @c OBSOLETE certain operations which are described in the next section, @ref{Values
8619 @c OBSOLETE and their Operations}.
8621 @c OBSOLETE A location value may be interpreted as having a different mode using the
8622 @c OBSOLETE location conversion. This mode conversion is written as @code{<mode
8623 @c OBSOLETE name>(<location>)}. The user has to consider that the sizes of the modes
8624 @c OBSOLETE have to be equal otherwise an error occurs. Furthermore, no range
8625 @c OBSOLETE checking of the location against the destination mode is performed, and
8626 @c OBSOLETE therefore the result can be quite confusing.
8628 @c OBSOLETE @smallexample
8629 @c OBSOLETE (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8630 @c OBSOLETE @end smallexample
8632 @c OBSOLETE @node Values and their Operations
8633 @c OBSOLETE @subsubsection Values and their Operations
8635 @c OBSOLETE Values are used to alter locations, to investigate complex structures in
8636 @c OBSOLETE more detail or to filter relevant information out of a large amount of
8637 @c OBSOLETE data. There are several (mode dependent) operations defined which enable
8638 @c OBSOLETE such investigations. These operations are not only applicable to
8639 @c OBSOLETE constant values but also to locations, which can become quite useful
8640 @c OBSOLETE when debugging complex structures. During parsing the command line
8641 @c OBSOLETE (e.g. evaluating an expression) @value{GDBN} treats location names as
8642 @c OBSOLETE the values behind these locations.
8644 @c OBSOLETE This section describes how values have to be specified and which
8645 @c OBSOLETE operations are legal to be used with such values.
8647 @c OBSOLETE @table @code
8648 @c OBSOLETE @item Literal Values
8649 @c OBSOLETE Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8650 @c OBSOLETE For detailed specification refer to the @sc{gnu} Chill implementation Manual
8651 @c OBSOLETE chapter 1.5.
8652 @c OBSOLETE @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8653 @c OBSOLETE @c be converted to a @ref.
8656 @c OBSOLETE @itemize @bullet
8658 @c OBSOLETE @emph{Integer Literals} are specified in the same manner as in Chill
8659 @c OBSOLETE programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8661 @c OBSOLETE @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8663 @c OBSOLETE @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8664 @c OBSOLETE @code{'M'})
8666 @c OBSOLETE @emph{Set Literals} are defined by a name which was specified in a set
8667 @c OBSOLETE mode. The value delivered by a Set Literal is the set value. This is
8668 @c OBSOLETE comparable to an enumeration in C/C@t{++} language.
8670 @c OBSOLETE @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8671 @c OBSOLETE emptiness literal delivers either the empty reference value, the empty
8672 @c OBSOLETE procedure value or the empty instance value.
8675 @c OBSOLETE @emph{Character String Literals} are defined by a sequence of characters
8676 @c OBSOLETE enclosed in single- or double quotes. If a single- or double quote has
8677 @c OBSOLETE to be part of the string literal it has to be stuffed (specified twice).
8679 @c OBSOLETE @emph{Bitstring Literals} are specified in the same manner as in Chill
8680 @c OBSOLETE programs (refer z200/88 chpt 5.2.4.8).
8682 @c OBSOLETE @emph{Floating point literals} are specified in the same manner as in
8683 @c OBSOLETE (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8684 @c OBSOLETE @end itemize
8685 @c OBSOLETE @end ignore
8687 @c OBSOLETE @item Tuple Values
8688 @c OBSOLETE A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8689 @c OBSOLETE name>} can be omitted if the mode of the tuple is unambiguous. This
8690 @c OBSOLETE unambiguity is derived from the context of a evaluated expression.
8691 @c OBSOLETE @code{<tuple>} can be one of the following:
8693 @c OBSOLETE @itemize @bullet
8694 @c OBSOLETE @item @emph{Powerset Tuple}
8695 @c OBSOLETE @item @emph{Array Tuple}
8696 @c OBSOLETE @item @emph{Structure Tuple}
8697 @c OBSOLETE Powerset tuples, array tuples and structure tuples are specified in the
8698 @c OBSOLETE same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8699 @c OBSOLETE @end itemize
8701 @c OBSOLETE @item String Element Value
8702 @c OBSOLETE A string element value is specified by
8703 @c OBSOLETE @smallexample
8704 @c OBSOLETE @code{<string value>(<index>)}
8705 @c OBSOLETE @end smallexample
8706 @c OBSOLETE where @code{<index>} is a integer expression. It delivers a character
8707 @c OBSOLETE value which is equivalent to the character indexed by @code{<index>} in
8708 @c OBSOLETE the string.
8710 @c OBSOLETE @item String Slice Value
8711 @c OBSOLETE A string slice value is specified by @code{<string value>(<slice
8712 @c OBSOLETE spec>)}, where @code{<slice spec>} can be either a range of integer
8713 @c OBSOLETE expressions or specified by @code{<start expr> up <size>}.
8714 @c OBSOLETE @code{<size>} denotes the number of elements which the slice contains.
8715 @c OBSOLETE The delivered value is a string value, which is part of the specified
8718 @c OBSOLETE @item Array Element Values
8719 @c OBSOLETE An array element value is specified by @code{<array value>(<expr>)} and
8720 @c OBSOLETE delivers a array element value of the mode of the specified array.
8722 @c OBSOLETE @item Array Slice Values
8723 @c OBSOLETE An array slice is specified by @code{<array value>(<slice spec>)}, where
8724 @c OBSOLETE @code{<slice spec>} can be either a range specified by expressions or by
8725 @c OBSOLETE @code{<start expr> up <size>}. @code{<size>} denotes the number of
8726 @c OBSOLETE arrayelements the slice contains. The delivered value is an array value
8727 @c OBSOLETE which is part of the specified array.
8729 @c OBSOLETE @item Structure Field Values
8730 @c OBSOLETE A structure field value is derived by @code{<structure value>.<field
8731 @c OBSOLETE name>}, where @code{<field name>} indicates the name of a field specified
8732 @c OBSOLETE in the mode definition of the structure. The mode of the delivered value
8733 @c OBSOLETE corresponds to this mode definition in the structure definition.
8735 @c OBSOLETE @item Procedure Call Value
8736 @c OBSOLETE The procedure call value is derived from the return value of the
8737 @c OBSOLETE procedure@footnote{If a procedure call is used for instance in an
8738 @c OBSOLETE expression, then this procedure is called with all its side
8739 @c OBSOLETE effects. This can lead to confusing results if used carelessly.}.
8741 @c OBSOLETE Values of duration mode locations are represented by @code{ULONG} literals.
8743 @c OBSOLETE Values of time mode locations appear as
8744 @c OBSOLETE @smallexample
8745 @c OBSOLETE @code{TIME(<secs>:<nsecs>)}
8746 @c OBSOLETE @end smallexample
8750 @c OBSOLETE This is not implemented yet:
8751 @c OBSOLETE @item Built-in Value
8752 @c OBSOLETE @noindent
8753 @c OBSOLETE The following built in functions are provided:
8755 @c OBSOLETE @table @code
8756 @c OBSOLETE @item @code{ADDR()}
8757 @c OBSOLETE @item @code{NUM()}
8758 @c OBSOLETE @item @code{PRED()}
8759 @c OBSOLETE @item @code{SUCC()}
8760 @c OBSOLETE @item @code{ABS()}
8761 @c OBSOLETE @item @code{CARD()}
8762 @c OBSOLETE @item @code{MAX()}
8763 @c OBSOLETE @item @code{MIN()}
8764 @c OBSOLETE @item @code{SIZE()}
8765 @c OBSOLETE @item @code{UPPER()}
8766 @c OBSOLETE @item @code{LOWER()}
8767 @c OBSOLETE @item @code{LENGTH()}
8768 @c OBSOLETE @item @code{SIN()}
8769 @c OBSOLETE @item @code{COS()}
8770 @c OBSOLETE @item @code{TAN()}
8771 @c OBSOLETE @item @code{ARCSIN()}
8772 @c OBSOLETE @item @code{ARCCOS()}
8773 @c OBSOLETE @item @code{ARCTAN()}
8774 @c OBSOLETE @item @code{EXP()}
8775 @c OBSOLETE @item @code{LN()}
8776 @c OBSOLETE @item @code{LOG()}
8777 @c OBSOLETE @item @code{SQRT()}
8778 @c OBSOLETE @end table
8780 @c OBSOLETE For a detailed description refer to the GNU Chill implementation manual
8781 @c OBSOLETE chapter 1.6.
8782 @c OBSOLETE @end ignore
8784 @c OBSOLETE @item Zero-adic Operator Value
8785 @c OBSOLETE The zero-adic operator value is derived from the instance value for the
8786 @c OBSOLETE current active process.
8788 @c OBSOLETE @item Expression Values
8789 @c OBSOLETE The value delivered by an expression is the result of the evaluation of
8790 @c OBSOLETE the specified expression. If there are error conditions (mode
8791 @c OBSOLETE incompatibility, etc.) the evaluation of expressions is aborted with a
8792 @c OBSOLETE corresponding error message. Expressions may be parenthesised which
8793 @c OBSOLETE causes the evaluation of this expression before any other expression
8794 @c OBSOLETE which uses the result of the parenthesised expression. The following
8795 @c OBSOLETE operators are supported by @value{GDBN}:
8797 @c OBSOLETE @table @code
8798 @c OBSOLETE @item @code{OR, ORIF, XOR}
8799 @c OBSOLETE @itemx @code{AND, ANDIF}
8800 @c OBSOLETE @itemx @code{NOT}
8801 @c OBSOLETE Logical operators defined over operands of boolean mode.
8803 @c OBSOLETE @item @code{=, /=}
8804 @c OBSOLETE Equality and inequality operators defined over all modes.
8806 @c OBSOLETE @item @code{>, >=}
8807 @c OBSOLETE @itemx @code{<, <=}
8808 @c OBSOLETE Relational operators defined over predefined modes.
8810 @c OBSOLETE @item @code{+, -}
8811 @c OBSOLETE @itemx @code{*, /, MOD, REM}
8812 @c OBSOLETE Arithmetic operators defined over predefined modes.
8814 @c OBSOLETE @item @code{-}
8815 @c OBSOLETE Change sign operator.
8817 @c OBSOLETE @item @code{//}
8818 @c OBSOLETE String concatenation operator.
8820 @c OBSOLETE @item @code{()}
8821 @c OBSOLETE String repetition operator.
8823 @c OBSOLETE @item @code{->}
8824 @c OBSOLETE Referenced location operator which can be used either to take the
8825 @c OBSOLETE address of a location (@code{->loc}), or to dereference a reference
8826 @c OBSOLETE location (@code{loc->}).
8828 @c OBSOLETE @item @code{OR, XOR}
8829 @c OBSOLETE @itemx @code{AND}
8830 @c OBSOLETE @itemx @code{NOT}
8831 @c OBSOLETE Powerset and bitstring operators.
8833 @c OBSOLETE @item @code{>, >=}
8834 @c OBSOLETE @itemx @code{<, <=}
8835 @c OBSOLETE Powerset inclusion operators.
8837 @c OBSOLETE @item @code{IN}
8838 @c OBSOLETE Membership operator.
8839 @c OBSOLETE @end table
8840 @c OBSOLETE @end table
8842 @c OBSOLETE @node Chill type and range checks
8843 @c OBSOLETE @subsubsection Chill type and range checks
8845 @c OBSOLETE @value{GDBN} considers two Chill variables mode equivalent if the sizes
8846 @c OBSOLETE of the two modes are equal. This rule applies recursively to more
8847 @c OBSOLETE complex datatypes which means that complex modes are treated
8848 @c OBSOLETE equivalent if all element modes (which also can be complex modes like
8849 @c OBSOLETE structures, arrays, etc.) have the same size.
8851 @c OBSOLETE Range checking is done on all mathematical operations, assignment, array
8852 @c OBSOLETE index bounds and all built in procedures.
8854 @c OBSOLETE Strong type checks are forced using the @value{GDBN} command @code{set
8855 @c OBSOLETE check strong}. This enforces strong type and range checks on all
8856 @c OBSOLETE operations where Chill constructs are used (expressions, built in
8857 @c OBSOLETE functions, etc.) in respect to the semantics as defined in the z.200
8858 @c OBSOLETE language specification.
8860 @c OBSOLETE All checks can be disabled by the @value{GDBN} command @code{set check
8864 @c OBSOLETE @c Deviations from the Chill Standard Z200/88
8865 @c OBSOLETE see last paragraph ?
8866 @c OBSOLETE @end ignore
8868 @c OBSOLETE @node Chill defaults
8869 @c OBSOLETE @subsubsection Chill defaults
8871 @c OBSOLETE If type and range checking are set automatically by @value{GDBN}, they
8872 @c OBSOLETE both default to @code{on} whenever the working language changes to
8873 @c OBSOLETE Chill. This happens regardless of whether you or @value{GDBN}
8874 @c OBSOLETE selected the working language.
8876 @c OBSOLETE If you allow @value{GDBN} to set the language automatically, then entering
8877 @c OBSOLETE code compiled from a file whose name ends with @file{.ch} sets the
8878 @c OBSOLETE working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8879 @c OBSOLETE the language automatically}, for further details.
8882 @chapter Examining the Symbol Table
8884 The commands described in this chapter allow you to inquire about the
8885 symbols (names of variables, functions and types) defined in your
8886 program. This information is inherent in the text of your program and
8887 does not change as your program executes. @value{GDBN} finds it in your
8888 program's symbol table, in the file indicated when you started @value{GDBN}
8889 (@pxref{File Options, ,Choosing files}), or by one of the
8890 file-management commands (@pxref{Files, ,Commands to specify files}).
8892 @cindex symbol names
8893 @cindex names of symbols
8894 @cindex quoting names
8895 Occasionally, you may need to refer to symbols that contain unusual
8896 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8897 most frequent case is in referring to static variables in other
8898 source files (@pxref{Variables,,Program variables}). File names
8899 are recorded in object files as debugging symbols, but @value{GDBN} would
8900 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8901 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8902 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8909 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8912 @kindex info address
8913 @cindex address of a symbol
8914 @item info address @var{symbol}
8915 Describe where the data for @var{symbol} is stored. For a register
8916 variable, this says which register it is kept in. For a non-register
8917 local variable, this prints the stack-frame offset at which the variable
8920 Note the contrast with @samp{print &@var{symbol}}, which does not work
8921 at all for a register variable, and for a stack local variable prints
8922 the exact address of the current instantiation of the variable.
8925 @cindex symbol from address
8926 @item info symbol @var{addr}
8927 Print the name of a symbol which is stored at the address @var{addr}.
8928 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8929 nearest symbol and an offset from it:
8932 (@value{GDBP}) info symbol 0x54320
8933 _initialize_vx + 396 in section .text
8937 This is the opposite of the @code{info address} command. You can use
8938 it to find out the name of a variable or a function given its address.
8941 @item whatis @var{expr}
8942 Print the data type of expression @var{expr}. @var{expr} is not
8943 actually evaluated, and any side-effecting operations (such as
8944 assignments or function calls) inside it do not take place.
8945 @xref{Expressions, ,Expressions}.
8948 Print the data type of @code{$}, the last value in the value history.
8951 @item ptype @var{typename}
8952 Print a description of data type @var{typename}. @var{typename} may be
8953 the name of a type, or for C code it may have the form @samp{class
8954 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8955 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8957 @item ptype @var{expr}
8959 Print a description of the type of expression @var{expr}. @code{ptype}
8960 differs from @code{whatis} by printing a detailed description, instead
8961 of just the name of the type.
8963 For example, for this variable declaration:
8966 struct complex @{double real; double imag;@} v;
8970 the two commands give this output:
8974 (@value{GDBP}) whatis v
8975 type = struct complex
8976 (@value{GDBP}) ptype v
8977 type = struct complex @{
8985 As with @code{whatis}, using @code{ptype} without an argument refers to
8986 the type of @code{$}, the last value in the value history.
8989 @item info types @var{regexp}
8991 Print a brief description of all types whose names match @var{regexp}
8992 (or all types in your program, if you supply no argument). Each
8993 complete typename is matched as though it were a complete line; thus,
8994 @samp{i type value} gives information on all types in your program whose
8995 names include the string @code{value}, but @samp{i type ^value$} gives
8996 information only on types whose complete name is @code{value}.
8998 This command differs from @code{ptype} in two ways: first, like
8999 @code{whatis}, it does not print a detailed description; second, it
9000 lists all source files where a type is defined.
9003 @cindex local variables
9004 @item info scope @var{addr}
9005 List all the variables local to a particular scope. This command
9006 accepts a location---a function name, a source line, or an address
9007 preceded by a @samp{*}, and prints all the variables local to the
9008 scope defined by that location. For example:
9011 (@value{GDBP}) @b{info scope command_line_handler}
9012 Scope for command_line_handler:
9013 Symbol rl is an argument at stack/frame offset 8, length 4.
9014 Symbol linebuffer is in static storage at address 0x150a18, length 4.
9015 Symbol linelength is in static storage at address 0x150a1c, length 4.
9016 Symbol p is a local variable in register $esi, length 4.
9017 Symbol p1 is a local variable in register $ebx, length 4.
9018 Symbol nline is a local variable in register $edx, length 4.
9019 Symbol repeat is a local variable at frame offset -8, length 4.
9023 This command is especially useful for determining what data to collect
9024 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
9029 Show information about the current source file---that is, the source file for
9030 the function containing the current point of execution:
9033 the name of the source file, and the directory containing it,
9035 the directory it was compiled in,
9037 its length, in lines,
9039 which programming language it is written in,
9041 whether the executable includes debugging information for that file, and
9042 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
9044 whether the debugging information includes information about
9045 preprocessor macros.
9049 @kindex info sources
9051 Print the names of all source files in your program for which there is
9052 debugging information, organized into two lists: files whose symbols
9053 have already been read, and files whose symbols will be read when needed.
9055 @kindex info functions
9056 @item info functions
9057 Print the names and data types of all defined functions.
9059 @item info functions @var{regexp}
9060 Print the names and data types of all defined functions
9061 whose names contain a match for regular expression @var{regexp}.
9062 Thus, @samp{info fun step} finds all functions whose names
9063 include @code{step}; @samp{info fun ^step} finds those whose names
9064 start with @code{step}. If a function name contains characters
9065 that conflict with the regular expression language (eg.
9066 @samp{operator*()}), they may be quoted with a backslash.
9068 @kindex info variables
9069 @item info variables
9070 Print the names and data types of all variables that are declared
9071 outside of functions (i.e.@: excluding local variables).
9073 @item info variables @var{regexp}
9074 Print the names and data types of all variables (except for local
9075 variables) whose names contain a match for regular expression
9079 This was never implemented.
9080 @kindex info methods
9082 @itemx info methods @var{regexp}
9083 The @code{info methods} command permits the user to examine all defined
9084 methods within C@t{++} program, or (with the @var{regexp} argument) a
9085 specific set of methods found in the various C@t{++} classes. Many
9086 C@t{++} classes provide a large number of methods. Thus, the output
9087 from the @code{ptype} command can be overwhelming and hard to use. The
9088 @code{info-methods} command filters the methods, printing only those
9089 which match the regular-expression @var{regexp}.
9092 @cindex reloading symbols
9093 Some systems allow individual object files that make up your program to
9094 be replaced without stopping and restarting your program. For example,
9095 in VxWorks you can simply recompile a defective object file and keep on
9096 running. If you are running on one of these systems, you can allow
9097 @value{GDBN} to reload the symbols for automatically relinked modules:
9100 @kindex set symbol-reloading
9101 @item set symbol-reloading on
9102 Replace symbol definitions for the corresponding source file when an
9103 object file with a particular name is seen again.
9105 @item set symbol-reloading off
9106 Do not replace symbol definitions when encountering object files of the
9107 same name more than once. This is the default state; if you are not
9108 running on a system that permits automatic relinking of modules, you
9109 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
9110 may discard symbols when linking large programs, that may contain
9111 several modules (from different directories or libraries) with the same
9114 @kindex show symbol-reloading
9115 @item show symbol-reloading
9116 Show the current @code{on} or @code{off} setting.
9119 @kindex set opaque-type-resolution
9120 @item set opaque-type-resolution on
9121 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
9122 declared as a pointer to a @code{struct}, @code{class}, or
9123 @code{union}---for example, @code{struct MyType *}---that is used in one
9124 source file although the full declaration of @code{struct MyType} is in
9125 another source file. The default is on.
9127 A change in the setting of this subcommand will not take effect until
9128 the next time symbols for a file are loaded.
9130 @item set opaque-type-resolution off
9131 Tell @value{GDBN} not to resolve opaque types. In this case, the type
9132 is printed as follows:
9134 @{<no data fields>@}
9137 @kindex show opaque-type-resolution
9138 @item show opaque-type-resolution
9139 Show whether opaque types are resolved or not.
9141 @kindex maint print symbols
9143 @kindex maint print psymbols
9144 @cindex partial symbol dump
9145 @item maint print symbols @var{filename}
9146 @itemx maint print psymbols @var{filename}
9147 @itemx maint print msymbols @var{filename}
9148 Write a dump of debugging symbol data into the file @var{filename}.
9149 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9150 symbols with debugging data are included. If you use @samp{maint print
9151 symbols}, @value{GDBN} includes all the symbols for which it has already
9152 collected full details: that is, @var{filename} reflects symbols for
9153 only those files whose symbols @value{GDBN} has read. You can use the
9154 command @code{info sources} to find out which files these are. If you
9155 use @samp{maint print psymbols} instead, the dump shows information about
9156 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9157 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9158 @samp{maint print msymbols} dumps just the minimal symbol information
9159 required for each object file from which @value{GDBN} has read some symbols.
9160 @xref{Files, ,Commands to specify files}, for a discussion of how
9161 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9165 @chapter Altering Execution
9167 Once you think you have found an error in your program, you might want to
9168 find out for certain whether correcting the apparent error would lead to
9169 correct results in the rest of the run. You can find the answer by
9170 experiment, using the @value{GDBN} features for altering execution of the
9173 For example, you can store new values into variables or memory
9174 locations, give your program a signal, restart it at a different
9175 address, or even return prematurely from a function.
9178 * Assignment:: Assignment to variables
9179 * Jumping:: Continuing at a different address
9180 * Signaling:: Giving your program a signal
9181 * Returning:: Returning from a function
9182 * Calling:: Calling your program's functions
9183 * Patching:: Patching your program
9187 @section Assignment to variables
9190 @cindex setting variables
9191 To alter the value of a variable, evaluate an assignment expression.
9192 @xref{Expressions, ,Expressions}. For example,
9199 stores the value 4 into the variable @code{x}, and then prints the
9200 value of the assignment expression (which is 4).
9201 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9202 information on operators in supported languages.
9204 @kindex set variable
9205 @cindex variables, setting
9206 If you are not interested in seeing the value of the assignment, use the
9207 @code{set} command instead of the @code{print} command. @code{set} is
9208 really the same as @code{print} except that the expression's value is
9209 not printed and is not put in the value history (@pxref{Value History,
9210 ,Value history}). The expression is evaluated only for its effects.
9212 If the beginning of the argument string of the @code{set} command
9213 appears identical to a @code{set} subcommand, use the @code{set
9214 variable} command instead of just @code{set}. This command is identical
9215 to @code{set} except for its lack of subcommands. For example, if your
9216 program has a variable @code{width}, you get an error if you try to set
9217 a new value with just @samp{set width=13}, because @value{GDBN} has the
9218 command @code{set width}:
9221 (@value{GDBP}) whatis width
9223 (@value{GDBP}) p width
9225 (@value{GDBP}) set width=47
9226 Invalid syntax in expression.
9230 The invalid expression, of course, is @samp{=47}. In
9231 order to actually set the program's variable @code{width}, use
9234 (@value{GDBP}) set var width=47
9237 Because the @code{set} command has many subcommands that can conflict
9238 with the names of program variables, it is a good idea to use the
9239 @code{set variable} command instead of just @code{set}. For example, if
9240 your program has a variable @code{g}, you run into problems if you try
9241 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9242 the command @code{set gnutarget}, abbreviated @code{set g}:
9246 (@value{GDBP}) whatis g
9250 (@value{GDBP}) set g=4
9254 The program being debugged has been started already.
9255 Start it from the beginning? (y or n) y
9256 Starting program: /home/smith/cc_progs/a.out
9257 "/home/smith/cc_progs/a.out": can't open to read symbols:
9259 (@value{GDBP}) show g
9260 The current BFD target is "=4".
9265 The program variable @code{g} did not change, and you silently set the
9266 @code{gnutarget} to an invalid value. In order to set the variable
9270 (@value{GDBP}) set var g=4
9273 @value{GDBN} allows more implicit conversions in assignments than C; you can
9274 freely store an integer value into a pointer variable or vice versa,
9275 and you can convert any structure to any other structure that is the
9276 same length or shorter.
9277 @comment FIXME: how do structs align/pad in these conversions?
9278 @comment /doc@cygnus.com 18dec1990
9280 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9281 construct to generate a value of specified type at a specified address
9282 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9283 to memory location @code{0x83040} as an integer (which implies a certain size
9284 and representation in memory), and
9287 set @{int@}0x83040 = 4
9291 stores the value 4 into that memory location.
9294 @section Continuing at a different address
9296 Ordinarily, when you continue your program, you do so at the place where
9297 it stopped, with the @code{continue} command. You can instead continue at
9298 an address of your own choosing, with the following commands:
9302 @item jump @var{linespec}
9303 Resume execution at line @var{linespec}. Execution stops again
9304 immediately if there is a breakpoint there. @xref{List, ,Printing
9305 source lines}, for a description of the different forms of
9306 @var{linespec}. It is common practice to use the @code{tbreak} command
9307 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9310 The @code{jump} command does not change the current stack frame, or
9311 the stack pointer, or the contents of any memory location or any
9312 register other than the program counter. If line @var{linespec} is in
9313 a different function from the one currently executing, the results may
9314 be bizarre if the two functions expect different patterns of arguments or
9315 of local variables. For this reason, the @code{jump} command requests
9316 confirmation if the specified line is not in the function currently
9317 executing. However, even bizarre results are predictable if you are
9318 well acquainted with the machine-language code of your program.
9320 @item jump *@var{address}
9321 Resume execution at the instruction at address @var{address}.
9324 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9325 On many systems, you can get much the same effect as the @code{jump}
9326 command by storing a new value into the register @code{$pc}. The
9327 difference is that this does not start your program running; it only
9328 changes the address of where it @emph{will} run when you continue. For
9336 makes the next @code{continue} command or stepping command execute at
9337 address @code{0x485}, rather than at the address where your program stopped.
9338 @xref{Continuing and Stepping, ,Continuing and stepping}.
9340 The most common occasion to use the @code{jump} command is to back
9341 up---perhaps with more breakpoints set---over a portion of a program
9342 that has already executed, in order to examine its execution in more
9347 @section Giving your program a signal
9351 @item signal @var{signal}
9352 Resume execution where your program stopped, but immediately give it the
9353 signal @var{signal}. @var{signal} can be the name or the number of a
9354 signal. For example, on many systems @code{signal 2} and @code{signal
9355 SIGINT} are both ways of sending an interrupt signal.
9357 Alternatively, if @var{signal} is zero, continue execution without
9358 giving a signal. This is useful when your program stopped on account of
9359 a signal and would ordinary see the signal when resumed with the
9360 @code{continue} command; @samp{signal 0} causes it to resume without a
9363 @code{signal} does not repeat when you press @key{RET} a second time
9364 after executing the command.
9368 Invoking the @code{signal} command is not the same as invoking the
9369 @code{kill} utility from the shell. Sending a signal with @code{kill}
9370 causes @value{GDBN} to decide what to do with the signal depending on
9371 the signal handling tables (@pxref{Signals}). The @code{signal} command
9372 passes the signal directly to your program.
9376 @section Returning from a function
9379 @cindex returning from a function
9382 @itemx return @var{expression}
9383 You can cancel execution of a function call with the @code{return}
9384 command. If you give an
9385 @var{expression} argument, its value is used as the function's return
9389 When you use @code{return}, @value{GDBN} discards the selected stack frame
9390 (and all frames within it). You can think of this as making the
9391 discarded frame return prematurely. If you wish to specify a value to
9392 be returned, give that value as the argument to @code{return}.
9394 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9395 frame}), and any other frames inside of it, leaving its caller as the
9396 innermost remaining frame. That frame becomes selected. The
9397 specified value is stored in the registers used for returning values
9400 The @code{return} command does not resume execution; it leaves the
9401 program stopped in the state that would exist if the function had just
9402 returned. In contrast, the @code{finish} command (@pxref{Continuing
9403 and Stepping, ,Continuing and stepping}) resumes execution until the
9404 selected stack frame returns naturally.
9407 @section Calling program functions
9409 @cindex calling functions
9412 @item call @var{expr}
9413 Evaluate the expression @var{expr} without displaying @code{void}
9417 You can use this variant of the @code{print} command if you want to
9418 execute a function from your program, but without cluttering the output
9419 with @code{void} returned values. If the result is not void, it
9420 is printed and saved in the value history.
9423 @section Patching programs
9425 @cindex patching binaries
9426 @cindex writing into executables
9427 @cindex writing into corefiles
9429 By default, @value{GDBN} opens the file containing your program's
9430 executable code (or the corefile) read-only. This prevents accidental
9431 alterations to machine code; but it also prevents you from intentionally
9432 patching your program's binary.
9434 If you'd like to be able to patch the binary, you can specify that
9435 explicitly with the @code{set write} command. For example, you might
9436 want to turn on internal debugging flags, or even to make emergency
9442 @itemx set write off
9443 If you specify @samp{set write on}, @value{GDBN} opens executable and
9444 core files for both reading and writing; if you specify @samp{set write
9445 off} (the default), @value{GDBN} opens them read-only.
9447 If you have already loaded a file, you must load it again (using the
9448 @code{exec-file} or @code{core-file} command) after changing @code{set
9449 write}, for your new setting to take effect.
9453 Display whether executable files and core files are opened for writing
9458 @chapter @value{GDBN} Files
9460 @value{GDBN} needs to know the file name of the program to be debugged,
9461 both in order to read its symbol table and in order to start your
9462 program. To debug a core dump of a previous run, you must also tell
9463 @value{GDBN} the name of the core dump file.
9466 * Files:: Commands to specify files
9467 * Symbol Errors:: Errors reading symbol files
9471 @section Commands to specify files
9473 @cindex symbol table
9474 @cindex core dump file
9476 You may want to specify executable and core dump file names. The usual
9477 way to do this is at start-up time, using the arguments to
9478 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9479 Out of @value{GDBN}}).
9481 Occasionally it is necessary to change to a different file during a
9482 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9483 a file you want to use. In these situations the @value{GDBN} commands
9484 to specify new files are useful.
9487 @cindex executable file
9489 @item file @var{filename}
9490 Use @var{filename} as the program to be debugged. It is read for its
9491 symbols and for the contents of pure memory. It is also the program
9492 executed when you use the @code{run} command. If you do not specify a
9493 directory and the file is not found in the @value{GDBN} working directory,
9494 @value{GDBN} uses the environment variable @code{PATH} as a list of
9495 directories to search, just as the shell does when looking for a program
9496 to run. You can change the value of this variable, for both @value{GDBN}
9497 and your program, using the @code{path} command.
9499 On systems with memory-mapped files, an auxiliary file named
9500 @file{@var{filename}.syms} may hold symbol table information for
9501 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9502 @file{@var{filename}.syms}, starting up more quickly. See the
9503 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9504 (available on the command line, and with the commands @code{file},
9505 @code{symbol-file}, or @code{add-symbol-file}, described below),
9506 for more information.
9509 @code{file} with no argument makes @value{GDBN} discard any information it
9510 has on both executable file and the symbol table.
9513 @item exec-file @r{[} @var{filename} @r{]}
9514 Specify that the program to be run (but not the symbol table) is found
9515 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9516 if necessary to locate your program. Omitting @var{filename} means to
9517 discard information on the executable file.
9520 @item symbol-file @r{[} @var{filename} @r{]}
9521 Read symbol table information from file @var{filename}. @code{PATH} is
9522 searched when necessary. Use the @code{file} command to get both symbol
9523 table and program to run from the same file.
9525 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9526 program's symbol table.
9528 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9529 of its convenience variables, the value history, and all breakpoints and
9530 auto-display expressions. This is because they may contain pointers to
9531 the internal data recording symbols and data types, which are part of
9532 the old symbol table data being discarded inside @value{GDBN}.
9534 @code{symbol-file} does not repeat if you press @key{RET} again after
9537 When @value{GDBN} is configured for a particular environment, it
9538 understands debugging information in whatever format is the standard
9539 generated for that environment; you may use either a @sc{gnu} compiler, or
9540 other compilers that adhere to the local conventions.
9541 Best results are usually obtained from @sc{gnu} compilers; for example,
9542 using @code{@value{GCC}} you can generate debugging information for
9545 For most kinds of object files, with the exception of old SVR3 systems
9546 using COFF, the @code{symbol-file} command does not normally read the
9547 symbol table in full right away. Instead, it scans the symbol table
9548 quickly to find which source files and which symbols are present. The
9549 details are read later, one source file at a time, as they are needed.
9551 The purpose of this two-stage reading strategy is to make @value{GDBN}
9552 start up faster. For the most part, it is invisible except for
9553 occasional pauses while the symbol table details for a particular source
9554 file are being read. (The @code{set verbose} command can turn these
9555 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9556 warnings and messages}.)
9558 We have not implemented the two-stage strategy for COFF yet. When the
9559 symbol table is stored in COFF format, @code{symbol-file} reads the
9560 symbol table data in full right away. Note that ``stabs-in-COFF''
9561 still does the two-stage strategy, since the debug info is actually
9565 @cindex reading symbols immediately
9566 @cindex symbols, reading immediately
9568 @cindex memory-mapped symbol file
9569 @cindex saving symbol table
9570 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9571 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9572 You can override the @value{GDBN} two-stage strategy for reading symbol
9573 tables by using the @samp{-readnow} option with any of the commands that
9574 load symbol table information, if you want to be sure @value{GDBN} has the
9575 entire symbol table available.
9577 If memory-mapped files are available on your system through the
9578 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9579 cause @value{GDBN} to write the symbols for your program into a reusable
9580 file. Future @value{GDBN} debugging sessions map in symbol information
9581 from this auxiliary symbol file (if the program has not changed), rather
9582 than spending time reading the symbol table from the executable
9583 program. Using the @samp{-mapped} option has the same effect as
9584 starting @value{GDBN} with the @samp{-mapped} command-line option.
9586 You can use both options together, to make sure the auxiliary symbol
9587 file has all the symbol information for your program.
9589 The auxiliary symbol file for a program called @var{myprog} is called
9590 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9591 than the corresponding executable), @value{GDBN} always attempts to use
9592 it when you debug @var{myprog}; no special options or commands are
9595 The @file{.syms} file is specific to the host machine where you run
9596 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9597 symbol table. It cannot be shared across multiple host platforms.
9599 @c FIXME: for now no mention of directories, since this seems to be in
9600 @c flux. 13mar1992 status is that in theory GDB would look either in
9601 @c current dir or in same dir as myprog; but issues like competing
9602 @c GDB's, or clutter in system dirs, mean that in practice right now
9603 @c only current dir is used. FFish says maybe a special GDB hierarchy
9604 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9609 @item core-file @r{[} @var{filename} @r{]}
9610 Specify the whereabouts of a core dump file to be used as the ``contents
9611 of memory''. Traditionally, core files contain only some parts of the
9612 address space of the process that generated them; @value{GDBN} can access the
9613 executable file itself for other parts.
9615 @code{core-file} with no argument specifies that no core file is
9618 Note that the core file is ignored when your program is actually running
9619 under @value{GDBN}. So, if you have been running your program and you
9620 wish to debug a core file instead, you must kill the subprocess in which
9621 the program is running. To do this, use the @code{kill} command
9622 (@pxref{Kill Process, ,Killing the child process}).
9624 @kindex add-symbol-file
9625 @cindex dynamic linking
9626 @item add-symbol-file @var{filename} @var{address}
9627 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9628 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9629 The @code{add-symbol-file} command reads additional symbol table
9630 information from the file @var{filename}. You would use this command
9631 when @var{filename} has been dynamically loaded (by some other means)
9632 into the program that is running. @var{address} should be the memory
9633 address at which the file has been loaded; @value{GDBN} cannot figure
9634 this out for itself. You can additionally specify an arbitrary number
9635 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9636 section name and base address for that section. You can specify any
9637 @var{address} as an expression.
9639 The symbol table of the file @var{filename} is added to the symbol table
9640 originally read with the @code{symbol-file} command. You can use the
9641 @code{add-symbol-file} command any number of times; the new symbol data
9642 thus read keeps adding to the old. To discard all old symbol data
9643 instead, use the @code{symbol-file} command without any arguments.
9645 @cindex relocatable object files, reading symbols from
9646 @cindex object files, relocatable, reading symbols from
9647 @cindex reading symbols from relocatable object files
9648 @cindex symbols, reading from relocatable object files
9649 @cindex @file{.o} files, reading symbols from
9650 Although @var{filename} is typically a shared library file, an
9651 executable file, or some other object file which has been fully
9652 relocated for loading into a process, you can also load symbolic
9653 information from relocatable @file{.o} files, as long as:
9657 the file's symbolic information refers only to linker symbols defined in
9658 that file, not to symbols defined by other object files,
9660 every section the file's symbolic information refers to has actually
9661 been loaded into the inferior, as it appears in the file, and
9663 you can determine the address at which every section was loaded, and
9664 provide these to the @code{add-symbol-file} command.
9668 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9669 relocatable files into an already running program; such systems
9670 typically make the requirements above easy to meet. However, it's
9671 important to recognize that many native systems use complex link
9672 procedures (@code{.linkonce} section factoring and C++ constructor table
9673 assembly, for example) that make the requirements difficult to meet. In
9674 general, one cannot assume that using @code{add-symbol-file} to read a
9675 relocatable object file's symbolic information will have the same effect
9676 as linking the relocatable object file into the program in the normal
9679 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9681 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9682 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9683 table information for @var{filename}.
9685 @kindex add-shared-symbol-file
9686 @item add-shared-symbol-file
9687 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9688 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9689 shared libraries, however if @value{GDBN} does not find yours, you can run
9690 @code{add-shared-symbol-file}. It takes no arguments.
9694 The @code{section} command changes the base address of section SECTION of
9695 the exec file to ADDR. This can be used if the exec file does not contain
9696 section addresses, (such as in the a.out format), or when the addresses
9697 specified in the file itself are wrong. Each section must be changed
9698 separately. The @code{info files} command, described below, lists all
9699 the sections and their addresses.
9705 @code{info files} and @code{info target} are synonymous; both print the
9706 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9707 including the names of the executable and core dump files currently in
9708 use by @value{GDBN}, and the files from which symbols were loaded. The
9709 command @code{help target} lists all possible targets rather than
9712 @kindex maint info sections
9713 @item maint info sections
9714 Another command that can give you extra information about program sections
9715 is @code{maint info sections}. In addition to the section information
9716 displayed by @code{info files}, this command displays the flags and file
9717 offset of each section in the executable and core dump files. In addition,
9718 @code{maint info sections} provides the following command options (which
9719 may be arbitrarily combined):
9723 Display sections for all loaded object files, including shared libraries.
9724 @item @var{sections}
9725 Display info only for named @var{sections}.
9726 @item @var{section-flags}
9727 Display info only for sections for which @var{section-flags} are true.
9728 The section flags that @value{GDBN} currently knows about are:
9731 Section will have space allocated in the process when loaded.
9732 Set for all sections except those containing debug information.
9734 Section will be loaded from the file into the child process memory.
9735 Set for pre-initialized code and data, clear for @code{.bss} sections.
9737 Section needs to be relocated before loading.
9739 Section cannot be modified by the child process.
9741 Section contains executable code only.
9743 Section contains data only (no executable code).
9745 Section will reside in ROM.
9747 Section contains data for constructor/destructor lists.
9749 Section is not empty.
9751 An instruction to the linker to not output the section.
9752 @item COFF_SHARED_LIBRARY
9753 A notification to the linker that the section contains
9754 COFF shared library information.
9756 Section contains common symbols.
9759 @kindex set trust-readonly-sections
9760 @item set trust-readonly-sections on
9761 Tell @value{GDBN} that readonly sections in your object file
9762 really are read-only (i.e.@: that their contents will not change).
9763 In that case, @value{GDBN} can fetch values from these sections
9764 out of the object file, rather than from the target program.
9765 For some targets (notably embedded ones), this can be a significant
9766 enhancement to debugging performance.
9770 @item set trust-readonly-sections off
9771 Tell @value{GDBN} not to trust readonly sections. This means that
9772 the contents of the section might change while the program is running,
9773 and must therefore be fetched from the target when needed.
9776 All file-specifying commands allow both absolute and relative file names
9777 as arguments. @value{GDBN} always converts the file name to an absolute file
9778 name and remembers it that way.
9780 @cindex shared libraries
9781 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9784 @value{GDBN} automatically loads symbol definitions from shared libraries
9785 when you use the @code{run} command, or when you examine a core file.
9786 (Before you issue the @code{run} command, @value{GDBN} does not understand
9787 references to a function in a shared library, however---unless you are
9788 debugging a core file).
9790 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9791 automatically loads the symbols at the time of the @code{shl_load} call.
9793 @c FIXME: some @value{GDBN} release may permit some refs to undef
9794 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9795 @c FIXME...lib; check this from time to time when updating manual
9797 There are times, however, when you may wish to not automatically load
9798 symbol definitions from shared libraries, such as when they are
9799 particularly large or there are many of them.
9801 To control the automatic loading of shared library symbols, use the
9805 @kindex set auto-solib-add
9806 @item set auto-solib-add @var{mode}
9807 If @var{mode} is @code{on}, symbols from all shared object libraries
9808 will be loaded automatically when the inferior begins execution, you
9809 attach to an independently started inferior, or when the dynamic linker
9810 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9811 is @code{off}, symbols must be loaded manually, using the
9812 @code{sharedlibrary} command. The default value is @code{on}.
9814 @kindex show auto-solib-add
9815 @item show auto-solib-add
9816 Display the current autoloading mode.
9819 To explicitly load shared library symbols, use the @code{sharedlibrary}
9823 @kindex info sharedlibrary
9826 @itemx info sharedlibrary
9827 Print the names of the shared libraries which are currently loaded.
9829 @kindex sharedlibrary
9831 @item sharedlibrary @var{regex}
9832 @itemx share @var{regex}
9833 Load shared object library symbols for files matching a
9834 Unix regular expression.
9835 As with files loaded automatically, it only loads shared libraries
9836 required by your program for a core file or after typing @code{run}. If
9837 @var{regex} is omitted all shared libraries required by your program are
9841 On some systems, such as HP-UX systems, @value{GDBN} supports
9842 autoloading shared library symbols until a limiting threshold size is
9843 reached. This provides the benefit of allowing autoloading to remain on
9844 by default, but avoids autoloading excessively large shared libraries,
9845 up to a threshold that is initially set, but which you can modify if you
9848 Beyond that threshold, symbols from shared libraries must be explicitly
9849 loaded. To load these symbols, use the command @code{sharedlibrary
9850 @var{filename}}. The base address of the shared library is determined
9851 automatically by @value{GDBN} and need not be specified.
9853 To display or set the threshold, use the commands:
9856 @kindex set auto-solib-limit
9857 @item set auto-solib-limit @var{threshold}
9858 Set the autoloading size threshold, in an integral number of megabytes.
9859 If @var{threshold} is nonzero and shared library autoloading is enabled,
9860 symbols from all shared object libraries will be loaded until the total
9861 size of the loaded shared library symbols exceeds this threshold.
9862 Otherwise, symbols must be loaded manually, using the
9863 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9866 @kindex show auto-solib-limit
9867 @item show auto-solib-limit
9868 Display the current autoloading size threshold, in megabytes.
9872 @section Errors reading symbol files
9874 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9875 such as symbol types it does not recognize, or known bugs in compiler
9876 output. By default, @value{GDBN} does not notify you of such problems, since
9877 they are relatively common and primarily of interest to people
9878 debugging compilers. If you are interested in seeing information
9879 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9880 only one message about each such type of problem, no matter how many
9881 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9882 to see how many times the problems occur, with the @code{set
9883 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9886 The messages currently printed, and their meanings, include:
9889 @item inner block not inside outer block in @var{symbol}
9891 The symbol information shows where symbol scopes begin and end
9892 (such as at the start of a function or a block of statements). This
9893 error indicates that an inner scope block is not fully contained
9894 in its outer scope blocks.
9896 @value{GDBN} circumvents the problem by treating the inner block as if it had
9897 the same scope as the outer block. In the error message, @var{symbol}
9898 may be shown as ``@code{(don't know)}'' if the outer block is not a
9901 @item block at @var{address} out of order
9903 The symbol information for symbol scope blocks should occur in
9904 order of increasing addresses. This error indicates that it does not
9907 @value{GDBN} does not circumvent this problem, and has trouble
9908 locating symbols in the source file whose symbols it is reading. (You
9909 can often determine what source file is affected by specifying
9910 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9913 @item bad block start address patched
9915 The symbol information for a symbol scope block has a start address
9916 smaller than the address of the preceding source line. This is known
9917 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9919 @value{GDBN} circumvents the problem by treating the symbol scope block as
9920 starting on the previous source line.
9922 @item bad string table offset in symbol @var{n}
9925 Symbol number @var{n} contains a pointer into the string table which is
9926 larger than the size of the string table.
9928 @value{GDBN} circumvents the problem by considering the symbol to have the
9929 name @code{foo}, which may cause other problems if many symbols end up
9932 @item unknown symbol type @code{0x@var{nn}}
9934 The symbol information contains new data types that @value{GDBN} does
9935 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9936 uncomprehended information, in hexadecimal.
9938 @value{GDBN} circumvents the error by ignoring this symbol information.
9939 This usually allows you to debug your program, though certain symbols
9940 are not accessible. If you encounter such a problem and feel like
9941 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9942 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9943 and examine @code{*bufp} to see the symbol.
9945 @item stub type has NULL name
9947 @value{GDBN} could not find the full definition for a struct or class.
9949 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9950 The symbol information for a C@t{++} member function is missing some
9951 information that recent versions of the compiler should have output for
9954 @item info mismatch between compiler and debugger
9956 @value{GDBN} could not parse a type specification output by the compiler.
9961 @chapter Specifying a Debugging Target
9963 @cindex debugging target
9966 A @dfn{target} is the execution environment occupied by your program.
9968 Often, @value{GDBN} runs in the same host environment as your program;
9969 in that case, the debugging target is specified as a side effect when
9970 you use the @code{file} or @code{core} commands. When you need more
9971 flexibility---for example, running @value{GDBN} on a physically separate
9972 host, or controlling a standalone system over a serial port or a
9973 realtime system over a TCP/IP connection---you can use the @code{target}
9974 command to specify one of the target types configured for @value{GDBN}
9975 (@pxref{Target Commands, ,Commands for managing targets}).
9978 * Active Targets:: Active targets
9979 * Target Commands:: Commands for managing targets
9980 * Byte Order:: Choosing target byte order
9981 * Remote:: Remote debugging
9982 * KOD:: Kernel Object Display
9986 @node Active Targets
9987 @section Active targets
9989 @cindex stacking targets
9990 @cindex active targets
9991 @cindex multiple targets
9993 There are three classes of targets: processes, core files, and
9994 executable files. @value{GDBN} can work concurrently on up to three
9995 active targets, one in each class. This allows you to (for example)
9996 start a process and inspect its activity without abandoning your work on
9999 For example, if you execute @samp{gdb a.out}, then the executable file
10000 @code{a.out} is the only active target. If you designate a core file as
10001 well---presumably from a prior run that crashed and coredumped---then
10002 @value{GDBN} has two active targets and uses them in tandem, looking
10003 first in the corefile target, then in the executable file, to satisfy
10004 requests for memory addresses. (Typically, these two classes of target
10005 are complementary, since core files contain only a program's
10006 read-write memory---variables and so on---plus machine status, while
10007 executable files contain only the program text and initialized data.)
10009 When you type @code{run}, your executable file becomes an active process
10010 target as well. When a process target is active, all @value{GDBN}
10011 commands requesting memory addresses refer to that target; addresses in
10012 an active core file or executable file target are obscured while the
10013 process target is active.
10015 Use the @code{core-file} and @code{exec-file} commands to select a new
10016 core file or executable target (@pxref{Files, ,Commands to specify
10017 files}). To specify as a target a process that is already running, use
10018 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
10021 @node Target Commands
10022 @section Commands for managing targets
10025 @item target @var{type} @var{parameters}
10026 Connects the @value{GDBN} host environment to a target machine or
10027 process. A target is typically a protocol for talking to debugging
10028 facilities. You use the argument @var{type} to specify the type or
10029 protocol of the target machine.
10031 Further @var{parameters} are interpreted by the target protocol, but
10032 typically include things like device names or host names to connect
10033 with, process numbers, and baud rates.
10035 The @code{target} command does not repeat if you press @key{RET} again
10036 after executing the command.
10038 @kindex help target
10040 Displays the names of all targets available. To display targets
10041 currently selected, use either @code{info target} or @code{info files}
10042 (@pxref{Files, ,Commands to specify files}).
10044 @item help target @var{name}
10045 Describe a particular target, including any parameters necessary to
10048 @kindex set gnutarget
10049 @item set gnutarget @var{args}
10050 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
10051 knows whether it is reading an @dfn{executable},
10052 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
10053 with the @code{set gnutarget} command. Unlike most @code{target} commands,
10054 with @code{gnutarget} the @code{target} refers to a program, not a machine.
10057 @emph{Warning:} To specify a file format with @code{set gnutarget},
10058 you must know the actual BFD name.
10062 @xref{Files, , Commands to specify files}.
10064 @kindex show gnutarget
10065 @item show gnutarget
10066 Use the @code{show gnutarget} command to display what file format
10067 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
10068 @value{GDBN} will determine the file format for each file automatically,
10069 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
10072 Here are some common targets (available, or not, depending on the GDB
10076 @kindex target exec
10077 @item target exec @var{program}
10078 An executable file. @samp{target exec @var{program}} is the same as
10079 @samp{exec-file @var{program}}.
10081 @kindex target core
10082 @item target core @var{filename}
10083 A core dump file. @samp{target core @var{filename}} is the same as
10084 @samp{core-file @var{filename}}.
10086 @kindex target remote
10087 @item target remote @var{dev}
10088 Remote serial target in GDB-specific protocol. The argument @var{dev}
10089 specifies what serial device to use for the connection (e.g.
10090 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
10091 supports the @code{load} command. This is only useful if you have
10092 some other way of getting the stub to the target system, and you can put
10093 it somewhere in memory where it won't get clobbered by the download.
10097 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
10105 works; however, you cannot assume that a specific memory map, device
10106 drivers, or even basic I/O is available, although some simulators do
10107 provide these. For info about any processor-specific simulator details,
10108 see the appropriate section in @ref{Embedded Processors, ,Embedded
10113 Some configurations may include these targets as well:
10117 @kindex target nrom
10118 @item target nrom @var{dev}
10119 NetROM ROM emulator. This target only supports downloading.
10123 Different targets are available on different configurations of @value{GDBN};
10124 your configuration may have more or fewer targets.
10126 Many remote targets require you to download the executable's code
10127 once you've successfully established a connection.
10131 @kindex load @var{filename}
10132 @item load @var{filename}
10133 Depending on what remote debugging facilities are configured into
10134 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10135 is meant to make @var{filename} (an executable) available for debugging
10136 on the remote system---by downloading, or dynamic linking, for example.
10137 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10138 the @code{add-symbol-file} command.
10140 If your @value{GDBN} does not have a @code{load} command, attempting to
10141 execute it gets the error message ``@code{You can't do that when your
10142 target is @dots{}}''
10144 The file is loaded at whatever address is specified in the executable.
10145 For some object file formats, you can specify the load address when you
10146 link the program; for other formats, like a.out, the object file format
10147 specifies a fixed address.
10148 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10150 @code{load} does not repeat if you press @key{RET} again after using it.
10154 @section Choosing target byte order
10156 @cindex choosing target byte order
10157 @cindex target byte order
10159 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10160 offer the ability to run either big-endian or little-endian byte
10161 orders. Usually the executable or symbol will include a bit to
10162 designate the endian-ness, and you will not need to worry about
10163 which to use. However, you may still find it useful to adjust
10164 @value{GDBN}'s idea of processor endian-ness manually.
10167 @kindex set endian big
10168 @item set endian big
10169 Instruct @value{GDBN} to assume the target is big-endian.
10171 @kindex set endian little
10172 @item set endian little
10173 Instruct @value{GDBN} to assume the target is little-endian.
10175 @kindex set endian auto
10176 @item set endian auto
10177 Instruct @value{GDBN} to use the byte order associated with the
10181 Display @value{GDBN}'s current idea of the target byte order.
10185 Note that these commands merely adjust interpretation of symbolic
10186 data on the host, and that they have absolutely no effect on the
10190 @section Remote debugging
10191 @cindex remote debugging
10193 If you are trying to debug a program running on a machine that cannot run
10194 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10195 For example, you might use remote debugging on an operating system kernel,
10196 or on a small system which does not have a general purpose operating system
10197 powerful enough to run a full-featured debugger.
10199 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10200 to make this work with particular debugging targets. In addition,
10201 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10202 but not specific to any particular target system) which you can use if you
10203 write the remote stubs---the code that runs on the remote system to
10204 communicate with @value{GDBN}.
10206 Other remote targets may be available in your
10207 configuration of @value{GDBN}; use @code{help target} to list them.
10210 @section Kernel Object Display
10212 @cindex kernel object display
10213 @cindex kernel object
10216 Some targets support kernel object display. Using this facility,
10217 @value{GDBN} communicates specially with the underlying operating system
10218 and can display information about operating system-level objects such as
10219 mutexes and other synchronization objects. Exactly which objects can be
10220 displayed is determined on a per-OS basis.
10222 Use the @code{set os} command to set the operating system. This tells
10223 @value{GDBN} which kernel object display module to initialize:
10226 (@value{GDBP}) set os cisco
10229 If @code{set os} succeeds, @value{GDBN} will display some information
10230 about the operating system, and will create a new @code{info} command
10231 which can be used to query the target. The @code{info} command is named
10232 after the operating system:
10235 (@value{GDBP}) info cisco
10236 List of Cisco Kernel Objects
10238 any Any and all objects
10241 Further subcommands can be used to query about particular objects known
10244 There is currently no way to determine whether a given operating system
10245 is supported other than to try it.
10248 @node Remote Debugging
10249 @chapter Debugging remote programs
10252 * Server:: Using the gdbserver program
10253 * NetWare:: Using the gdbserve.nlm program
10254 * remote stub:: Implementing a remote stub
10258 @section Using the @code{gdbserver} program
10261 @cindex remote connection without stubs
10262 @code{gdbserver} is a control program for Unix-like systems, which
10263 allows you to connect your program with a remote @value{GDBN} via
10264 @code{target remote}---but without linking in the usual debugging stub.
10266 @code{gdbserver} is not a complete replacement for the debugging stubs,
10267 because it requires essentially the same operating-system facilities
10268 that @value{GDBN} itself does. In fact, a system that can run
10269 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10270 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10271 because it is a much smaller program than @value{GDBN} itself. It is
10272 also easier to port than all of @value{GDBN}, so you may be able to get
10273 started more quickly on a new system by using @code{gdbserver}.
10274 Finally, if you develop code for real-time systems, you may find that
10275 the tradeoffs involved in real-time operation make it more convenient to
10276 do as much development work as possible on another system, for example
10277 by cross-compiling. You can use @code{gdbserver} to make a similar
10278 choice for debugging.
10280 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10281 or a TCP connection, using the standard @value{GDBN} remote serial
10285 @item On the target machine,
10286 you need to have a copy of the program you want to debug.
10287 @code{gdbserver} does not need your program's symbol table, so you can
10288 strip the program if necessary to save space. @value{GDBN} on the host
10289 system does all the symbol handling.
10291 To use the server, you must tell it how to communicate with @value{GDBN};
10292 the name of your program; and the arguments for your program. The usual
10296 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10299 @var{comm} is either a device name (to use a serial line) or a TCP
10300 hostname and portnumber. For example, to debug Emacs with the argument
10301 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10305 target> gdbserver /dev/com1 emacs foo.txt
10308 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10311 To use a TCP connection instead of a serial line:
10314 target> gdbserver host:2345 emacs foo.txt
10317 The only difference from the previous example is the first argument,
10318 specifying that you are communicating with the host @value{GDBN} via
10319 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10320 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10321 (Currently, the @samp{host} part is ignored.) You can choose any number
10322 you want for the port number as long as it does not conflict with any
10323 TCP ports already in use on the target system (for example, @code{23} is
10324 reserved for @code{telnet}).@footnote{If you choose a port number that
10325 conflicts with another service, @code{gdbserver} prints an error message
10326 and exits.} You must use the same port number with the host @value{GDBN}
10327 @code{target remote} command.
10329 On some targets, @code{gdbserver} can also attach to running programs.
10330 This is accomplished via the @code{--attach} argument. The syntax is:
10333 target> gdbserver @var{comm} --attach @var{pid}
10336 @var{pid} is the process ID of a currently running process. It isn't necessary
10337 to point @code{gdbserver} at a binary for the running process.
10339 @item On the @value{GDBN} host machine,
10340 you need an unstripped copy of your program, since @value{GDBN} needs
10341 symbols and debugging information. Start up @value{GDBN} as usual,
10342 using the name of the local copy of your program as the first argument.
10343 (You may also need the @w{@samp{--baud}} option if the serial line is
10344 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10345 remote} to establish communications with @code{gdbserver}. Its argument
10346 is either a device name (usually a serial device, like
10347 @file{/dev/ttyb}), or a TCP port descriptor in the form
10348 @code{@var{host}:@var{PORT}}. For example:
10351 (@value{GDBP}) target remote /dev/ttyb
10355 communicates with the server via serial line @file{/dev/ttyb}, and
10358 (@value{GDBP}) target remote the-target:2345
10362 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10363 For TCP connections, you must start up @code{gdbserver} prior to using
10364 the @code{target remote} command. Otherwise you may get an error whose
10365 text depends on the host system, but which usually looks something like
10366 @samp{Connection refused}.
10370 @section Using the @code{gdbserve.nlm} program
10372 @kindex gdbserve.nlm
10373 @code{gdbserve.nlm} is a control program for NetWare systems, which
10374 allows you to connect your program with a remote @value{GDBN} via
10375 @code{target remote}.
10377 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10378 using the standard @value{GDBN} remote serial protocol.
10381 @item On the target machine,
10382 you need to have a copy of the program you want to debug.
10383 @code{gdbserve.nlm} does not need your program's symbol table, so you
10384 can strip the program if necessary to save space. @value{GDBN} on the
10385 host system does all the symbol handling.
10387 To use the server, you must tell it how to communicate with
10388 @value{GDBN}; the name of your program; and the arguments for your
10389 program. The syntax is:
10392 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10393 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10396 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10397 the baud rate used by the connection. @var{port} and @var{node} default
10398 to 0, @var{baud} defaults to 9600@dmn{bps}.
10400 For example, to debug Emacs with the argument @samp{foo.txt}and
10401 communicate with @value{GDBN} over serial port number 2 or board 1
10402 using a 19200@dmn{bps} connection:
10405 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10408 @item On the @value{GDBN} host machine,
10409 you need an unstripped copy of your program, since @value{GDBN} needs
10410 symbols and debugging information. Start up @value{GDBN} as usual,
10411 using the name of the local copy of your program as the first argument.
10412 (You may also need the @w{@samp{--baud}} option if the serial line is
10413 running at anything other than 9600@dmn{bps}. After that, use @code{target
10414 remote} to establish communications with @code{gdbserve.nlm}. Its
10415 argument is a device name (usually a serial device, like
10416 @file{/dev/ttyb}). For example:
10419 (@value{GDBP}) target remote /dev/ttyb
10423 communications with the server via serial line @file{/dev/ttyb}.
10427 @section Implementing a remote stub
10429 @cindex debugging stub, example
10430 @cindex remote stub, example
10431 @cindex stub example, remote debugging
10432 The stub files provided with @value{GDBN} implement the target side of the
10433 communication protocol, and the @value{GDBN} side is implemented in the
10434 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10435 these subroutines to communicate, and ignore the details. (If you're
10436 implementing your own stub file, you can still ignore the details: start
10437 with one of the existing stub files. @file{sparc-stub.c} is the best
10438 organized, and therefore the easiest to read.)
10440 @cindex remote serial debugging, overview
10441 To debug a program running on another machine (the debugging
10442 @dfn{target} machine), you must first arrange for all the usual
10443 prerequisites for the program to run by itself. For example, for a C
10448 A startup routine to set up the C runtime environment; these usually
10449 have a name like @file{crt0}. The startup routine may be supplied by
10450 your hardware supplier, or you may have to write your own.
10453 A C subroutine library to support your program's
10454 subroutine calls, notably managing input and output.
10457 A way of getting your program to the other machine---for example, a
10458 download program. These are often supplied by the hardware
10459 manufacturer, but you may have to write your own from hardware
10463 The next step is to arrange for your program to use a serial port to
10464 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10465 machine). In general terms, the scheme looks like this:
10469 @value{GDBN} already understands how to use this protocol; when everything
10470 else is set up, you can simply use the @samp{target remote} command
10471 (@pxref{Targets,,Specifying a Debugging Target}).
10473 @item On the target,
10474 you must link with your program a few special-purpose subroutines that
10475 implement the @value{GDBN} remote serial protocol. The file containing these
10476 subroutines is called a @dfn{debugging stub}.
10478 On certain remote targets, you can use an auxiliary program
10479 @code{gdbserver} instead of linking a stub into your program.
10480 @xref{Server,,Using the @code{gdbserver} program}, for details.
10483 The debugging stub is specific to the architecture of the remote
10484 machine; for example, use @file{sparc-stub.c} to debug programs on
10487 @cindex remote serial stub list
10488 These working remote stubs are distributed with @value{GDBN}:
10493 @cindex @file{i386-stub.c}
10496 For Intel 386 and compatible architectures.
10499 @cindex @file{m68k-stub.c}
10500 @cindex Motorola 680x0
10502 For Motorola 680x0 architectures.
10505 @cindex @file{sh-stub.c}
10508 For Hitachi SH architectures.
10511 @cindex @file{sparc-stub.c}
10513 For @sc{sparc} architectures.
10515 @item sparcl-stub.c
10516 @cindex @file{sparcl-stub.c}
10519 For Fujitsu @sc{sparclite} architectures.
10523 The @file{README} file in the @value{GDBN} distribution may list other
10524 recently added stubs.
10527 * Stub Contents:: What the stub can do for you
10528 * Bootstrapping:: What you must do for the stub
10529 * Debug Session:: Putting it all together
10532 @node Stub Contents
10533 @subsection What the stub can do for you
10535 @cindex remote serial stub
10536 The debugging stub for your architecture supplies these three
10540 @item set_debug_traps
10541 @kindex set_debug_traps
10542 @cindex remote serial stub, initialization
10543 This routine arranges for @code{handle_exception} to run when your
10544 program stops. You must call this subroutine explicitly near the
10545 beginning of your program.
10547 @item handle_exception
10548 @kindex handle_exception
10549 @cindex remote serial stub, main routine
10550 This is the central workhorse, but your program never calls it
10551 explicitly---the setup code arranges for @code{handle_exception} to
10552 run when a trap is triggered.
10554 @code{handle_exception} takes control when your program stops during
10555 execution (for example, on a breakpoint), and mediates communications
10556 with @value{GDBN} on the host machine. This is where the communications
10557 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10558 representative on the target machine. It begins by sending summary
10559 information on the state of your program, then continues to execute,
10560 retrieving and transmitting any information @value{GDBN} needs, until you
10561 execute a @value{GDBN} command that makes your program resume; at that point,
10562 @code{handle_exception} returns control to your own code on the target
10566 @cindex @code{breakpoint} subroutine, remote
10567 Use this auxiliary subroutine to make your program contain a
10568 breakpoint. Depending on the particular situation, this may be the only
10569 way for @value{GDBN} to get control. For instance, if your target
10570 machine has some sort of interrupt button, you won't need to call this;
10571 pressing the interrupt button transfers control to
10572 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10573 simply receiving characters on the serial port may also trigger a trap;
10574 again, in that situation, you don't need to call @code{breakpoint} from
10575 your own program---simply running @samp{target remote} from the host
10576 @value{GDBN} session gets control.
10578 Call @code{breakpoint} if none of these is true, or if you simply want
10579 to make certain your program stops at a predetermined point for the
10580 start of your debugging session.
10583 @node Bootstrapping
10584 @subsection What you must do for the stub
10586 @cindex remote stub, support routines
10587 The debugging stubs that come with @value{GDBN} are set up for a particular
10588 chip architecture, but they have no information about the rest of your
10589 debugging target machine.
10591 First of all you need to tell the stub how to communicate with the
10595 @item int getDebugChar()
10596 @kindex getDebugChar
10597 Write this subroutine to read a single character from the serial port.
10598 It may be identical to @code{getchar} for your target system; a
10599 different name is used to allow you to distinguish the two if you wish.
10601 @item void putDebugChar(int)
10602 @kindex putDebugChar
10603 Write this subroutine to write a single character to the serial port.
10604 It may be identical to @code{putchar} for your target system; a
10605 different name is used to allow you to distinguish the two if you wish.
10608 @cindex control C, and remote debugging
10609 @cindex interrupting remote targets
10610 If you want @value{GDBN} to be able to stop your program while it is
10611 running, you need to use an interrupt-driven serial driver, and arrange
10612 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10613 character). That is the character which @value{GDBN} uses to tell the
10614 remote system to stop.
10616 Getting the debugging target to return the proper status to @value{GDBN}
10617 probably requires changes to the standard stub; one quick and dirty way
10618 is to just execute a breakpoint instruction (the ``dirty'' part is that
10619 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10621 Other routines you need to supply are:
10624 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10625 @kindex exceptionHandler
10626 Write this function to install @var{exception_address} in the exception
10627 handling tables. You need to do this because the stub does not have any
10628 way of knowing what the exception handling tables on your target system
10629 are like (for example, the processor's table might be in @sc{rom},
10630 containing entries which point to a table in @sc{ram}).
10631 @var{exception_number} is the exception number which should be changed;
10632 its meaning is architecture-dependent (for example, different numbers
10633 might represent divide by zero, misaligned access, etc). When this
10634 exception occurs, control should be transferred directly to
10635 @var{exception_address}, and the processor state (stack, registers,
10636 and so on) should be just as it is when a processor exception occurs. So if
10637 you want to use a jump instruction to reach @var{exception_address}, it
10638 should be a simple jump, not a jump to subroutine.
10640 For the 386, @var{exception_address} should be installed as an interrupt
10641 gate so that interrupts are masked while the handler runs. The gate
10642 should be at privilege level 0 (the most privileged level). The
10643 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10644 help from @code{exceptionHandler}.
10646 @item void flush_i_cache()
10647 @kindex flush_i_cache
10648 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10649 instruction cache, if any, on your target machine. If there is no
10650 instruction cache, this subroutine may be a no-op.
10652 On target machines that have instruction caches, @value{GDBN} requires this
10653 function to make certain that the state of your program is stable.
10657 You must also make sure this library routine is available:
10660 @item void *memset(void *, int, int)
10662 This is the standard library function @code{memset} that sets an area of
10663 memory to a known value. If you have one of the free versions of
10664 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10665 either obtain it from your hardware manufacturer, or write your own.
10668 If you do not use the GNU C compiler, you may need other standard
10669 library subroutines as well; this varies from one stub to another,
10670 but in general the stubs are likely to use any of the common library
10671 subroutines which @code{@value{GCC}} generates as inline code.
10674 @node Debug Session
10675 @subsection Putting it all together
10677 @cindex remote serial debugging summary
10678 In summary, when your program is ready to debug, you must follow these
10683 Make sure you have defined the supporting low-level routines
10684 (@pxref{Bootstrapping,,What you must do for the stub}):
10686 @code{getDebugChar}, @code{putDebugChar},
10687 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10691 Insert these lines near the top of your program:
10699 For the 680x0 stub only, you need to provide a variable called
10700 @code{exceptionHook}. Normally you just use:
10703 void (*exceptionHook)() = 0;
10707 but if before calling @code{set_debug_traps}, you set it to point to a
10708 function in your program, that function is called when
10709 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10710 error). The function indicated by @code{exceptionHook} is called with
10711 one parameter: an @code{int} which is the exception number.
10714 Compile and link together: your program, the @value{GDBN} debugging stub for
10715 your target architecture, and the supporting subroutines.
10718 Make sure you have a serial connection between your target machine and
10719 the @value{GDBN} host, and identify the serial port on the host.
10722 @c The "remote" target now provides a `load' command, so we should
10723 @c document that. FIXME.
10724 Download your program to your target machine (or get it there by
10725 whatever means the manufacturer provides), and start it.
10728 To start remote debugging, run @value{GDBN} on the host machine, and specify
10729 as an executable file the program that is running in the remote machine.
10730 This tells @value{GDBN} how to find your program's symbols and the contents
10734 @cindex serial line, @code{target remote}
10735 Establish communication using the @code{target remote} command.
10736 Its argument specifies how to communicate with the target
10737 machine---either via a devicename attached to a direct serial line, or a
10738 TCP or UDP port (usually to a terminal server which in turn has a serial line
10739 to the target). For example, to use a serial line connected to the
10740 device named @file{/dev/ttyb}:
10743 target remote /dev/ttyb
10746 @cindex TCP port, @code{target remote}
10747 To use a TCP connection, use an argument of the form
10748 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10749 For example, to connect to port 2828 on a
10750 terminal server named @code{manyfarms}:
10753 target remote manyfarms:2828
10756 If your remote target is actually running on the same machine as
10757 your debugger session (e.g.@: a simulator of your target running on
10758 the same host), you can omit the hostname. For example, to connect
10759 to port 1234 on your local machine:
10762 target remote :1234
10766 Note that the colon is still required here.
10768 @cindex UDP port, @code{target remote}
10769 To use a UDP connection, use an argument of the form
10770 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10771 on a terminal server named @code{manyfarms}:
10774 target remote udp:manyfarms:2828
10777 When using a UDP connection for remote debugging, you should keep in mind
10778 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10779 busy or unreliable networks, which will cause havoc with your debugging
10784 Now you can use all the usual commands to examine and change data and to
10785 step and continue the remote program.
10787 To resume the remote program and stop debugging it, use the @code{detach}
10790 @cindex interrupting remote programs
10791 @cindex remote programs, interrupting
10792 Whenever @value{GDBN} is waiting for the remote program, if you type the
10793 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10794 program. This may or may not succeed, depending in part on the hardware
10795 and the serial drivers the remote system uses. If you type the
10796 interrupt character once again, @value{GDBN} displays this prompt:
10799 Interrupted while waiting for the program.
10800 Give up (and stop debugging it)? (y or n)
10803 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10804 (If you decide you want to try again later, you can use @samp{target
10805 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10806 goes back to waiting.
10809 @node Configurations
10810 @chapter Configuration-Specific Information
10812 While nearly all @value{GDBN} commands are available for all native and
10813 cross versions of the debugger, there are some exceptions. This chapter
10814 describes things that are only available in certain configurations.
10816 There are three major categories of configurations: native
10817 configurations, where the host and target are the same, embedded
10818 operating system configurations, which are usually the same for several
10819 different processor architectures, and bare embedded processors, which
10820 are quite different from each other.
10825 * Embedded Processors::
10832 This section describes details specific to particular native
10837 * SVR4 Process Information:: SVR4 process information
10838 * DJGPP Native:: Features specific to the DJGPP port
10839 * Cygwin Native:: Features specific to the Cygwin port
10845 On HP-UX systems, if you refer to a function or variable name that
10846 begins with a dollar sign, @value{GDBN} searches for a user or system
10847 name first, before it searches for a convenience variable.
10849 @node SVR4 Process Information
10850 @subsection SVR4 process information
10853 @cindex process image
10855 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10856 used to examine the image of a running process using file-system
10857 subroutines. If @value{GDBN} is configured for an operating system with
10858 this facility, the command @code{info proc} is available to report on
10859 several kinds of information about the process running your program.
10860 @code{info proc} works only on SVR4 systems that include the
10861 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10862 and Unixware, but not HP-UX or Linux, for example.
10867 Summarize available information about the process.
10869 @kindex info proc mappings
10870 @item info proc mappings
10871 Report on the address ranges accessible in the program, with information
10872 on whether your program may read, write, or execute each range.
10874 @comment These sub-options of 'info proc' were not included when
10875 @comment procfs.c was re-written. Keep their descriptions around
10876 @comment against the day when someone finds the time to put them back in.
10877 @kindex info proc times
10878 @item info proc times
10879 Starting time, user CPU time, and system CPU time for your program and
10882 @kindex info proc id
10884 Report on the process IDs related to your program: its own process ID,
10885 the ID of its parent, the process group ID, and the session ID.
10887 @kindex info proc status
10888 @item info proc status
10889 General information on the state of the process. If the process is
10890 stopped, this report includes the reason for stopping, and any signal
10893 @item info proc all
10894 Show all the above information about the process.
10899 @subsection Features for Debugging @sc{djgpp} Programs
10900 @cindex @sc{djgpp} debugging
10901 @cindex native @sc{djgpp} debugging
10902 @cindex MS-DOS-specific commands
10904 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10905 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10906 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10907 top of real-mode DOS systems and their emulations.
10909 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10910 defines a few commands specific to the @sc{djgpp} port. This
10911 subsection describes those commands.
10916 This is a prefix of @sc{djgpp}-specific commands which print
10917 information about the target system and important OS structures.
10920 @cindex MS-DOS system info
10921 @cindex free memory information (MS-DOS)
10922 @item info dos sysinfo
10923 This command displays assorted information about the underlying
10924 platform: the CPU type and features, the OS version and flavor, the
10925 DPMI version, and the available conventional and DPMI memory.
10930 @cindex segment descriptor tables
10931 @cindex descriptor tables display
10933 @itemx info dos ldt
10934 @itemx info dos idt
10935 These 3 commands display entries from, respectively, Global, Local,
10936 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10937 tables are data structures which store a descriptor for each segment
10938 that is currently in use. The segment's selector is an index into a
10939 descriptor table; the table entry for that index holds the
10940 descriptor's base address and limit, and its attributes and access
10943 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10944 segment (used for both data and the stack), and a DOS segment (which
10945 allows access to DOS/BIOS data structures and absolute addresses in
10946 conventional memory). However, the DPMI host will usually define
10947 additional segments in order to support the DPMI environment.
10949 @cindex garbled pointers
10950 These commands allow to display entries from the descriptor tables.
10951 Without an argument, all entries from the specified table are
10952 displayed. An argument, which should be an integer expression, means
10953 display a single entry whose index is given by the argument. For
10954 example, here's a convenient way to display information about the
10955 debugged program's data segment:
10958 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10959 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10963 This comes in handy when you want to see whether a pointer is outside
10964 the data segment's limit (i.e.@: @dfn{garbled}).
10966 @cindex page tables display (MS-DOS)
10968 @itemx info dos pte
10969 These two commands display entries from, respectively, the Page
10970 Directory and the Page Tables. Page Directories and Page Tables are
10971 data structures which control how virtual memory addresses are mapped
10972 into physical addresses. A Page Table includes an entry for every
10973 page of memory that is mapped into the program's address space; there
10974 may be several Page Tables, each one holding up to 4096 entries. A
10975 Page Directory has up to 4096 entries, one each for every Page Table
10976 that is currently in use.
10978 Without an argument, @kbd{info dos pde} displays the entire Page
10979 Directory, and @kbd{info dos pte} displays all the entries in all of
10980 the Page Tables. An argument, an integer expression, given to the
10981 @kbd{info dos pde} command means display only that entry from the Page
10982 Directory table. An argument given to the @kbd{info dos pte} command
10983 means display entries from a single Page Table, the one pointed to by
10984 the specified entry in the Page Directory.
10986 @cindex direct memory access (DMA) on MS-DOS
10987 These commands are useful when your program uses @dfn{DMA} (Direct
10988 Memory Access), which needs physical addresses to program the DMA
10991 These commands are supported only with some DPMI servers.
10993 @cindex physical address from linear address
10994 @item info dos address-pte @var{addr}
10995 This command displays the Page Table entry for a specified linear
10996 address. The argument linear address @var{addr} should already have the
10997 appropriate segment's base address added to it, because this command
10998 accepts addresses which may belong to @emph{any} segment. For
10999 example, here's how to display the Page Table entry for the page where
11000 the variable @code{i} is stored:
11003 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
11004 @exdent @code{Page Table entry for address 0x11a00d30:}
11005 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
11009 This says that @code{i} is stored at offset @code{0xd30} from the page
11010 whose physical base address is @code{0x02698000}, and prints all the
11011 attributes of that page.
11013 Note that you must cast the addresses of variables to a @code{char *},
11014 since otherwise the value of @code{__djgpp_base_address}, the base
11015 address of all variables and functions in a @sc{djgpp} program, will
11016 be added using the rules of C pointer arithmetics: if @code{i} is
11017 declared an @code{int}, @value{GDBN} will add 4 times the value of
11018 @code{__djgpp_base_address} to the address of @code{i}.
11020 Here's another example, it displays the Page Table entry for the
11024 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
11025 @exdent @code{Page Table entry for address 0x29110:}
11026 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
11030 (The @code{+ 3} offset is because the transfer buffer's address is the
11031 3rd member of the @code{_go32_info_block} structure.) The output of
11032 this command clearly shows that addresses in conventional memory are
11033 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11035 This command is supported only with some DPMI servers.
11038 @node Cygwin Native
11039 @subsection Features for Debugging MS Windows PE executables
11040 @cindex MS Windows debugging
11041 @cindex native Cygwin debugging
11042 @cindex Cygwin-specific commands
11044 @value{GDBN} supports native debugging of MS Windows programs, and
11045 defines a few commands specific to the Cygwin port. This
11046 subsection describes those commands.
11051 This is a prefix of MS Windows specific commands which print
11052 information about the target system and important OS structures.
11054 @item info w32 selector
11055 This command displays information returned by
11056 the Win32 API @code{GetThreadSelectorEntry} function.
11057 It takes an optional argument that is evaluated to
11058 a long value to give the information about this given selector.
11059 Without argument, this command displays information
11060 about the the six segment registers.
11064 This is a Cygwin specific alias of info shared.
11066 @kindex dll-symbols
11068 This command loads symbols from a dll similarly to
11069 add-sym command but without the need to specify a base address.
11071 @kindex set new-console
11072 @item set new-console @var{mode}
11073 If @var{mode} is @code{on} the debuggee will
11074 be started in a new console on next start.
11075 If @var{mode} is @code{off}i, the debuggee will
11076 be started in the same console as the debugger.
11078 @kindex show new-console
11079 @item show new-console
11080 Displays whether a new console is used
11081 when the debuggee is started.
11083 @kindex set new-group
11084 @item set new-group @var{mode}
11085 This boolean value controls whether the debuggee should
11086 start a new group or stay in the same group as the debugger.
11087 This affects the way the Windows OS handles
11090 @kindex show new-group
11091 @item show new-group
11092 Displays current value of new-group boolean.
11094 @kindex set debugevents
11095 @item set debugevents
11096 This boolean value adds debug output concerning events seen by the debugger.
11098 @kindex set debugexec
11099 @item set debugexec
11100 This boolean value adds debug output concerning execute events
11101 seen by the debugger.
11103 @kindex set debugexceptions
11104 @item set debugexceptions
11105 This boolean value adds debug ouptut concerning exception events
11106 seen by the debugger.
11108 @kindex set debugmemory
11109 @item set debugmemory
11110 This boolean value adds debug ouptut concerning memory events
11111 seen by the debugger.
11115 This boolean values specifies whether the debuggee is called
11116 via a shell or directly (default value is on).
11120 Displays if the debuggee will be started with a shell.
11125 @section Embedded Operating Systems
11127 This section describes configurations involving the debugging of
11128 embedded operating systems that are available for several different
11132 * VxWorks:: Using @value{GDBN} with VxWorks
11135 @value{GDBN} includes the ability to debug programs running on
11136 various real-time operating systems.
11139 @subsection Using @value{GDBN} with VxWorks
11145 @kindex target vxworks
11146 @item target vxworks @var{machinename}
11147 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11148 is the target system's machine name or IP address.
11152 On VxWorks, @code{load} links @var{filename} dynamically on the
11153 current target system as well as adding its symbols in @value{GDBN}.
11155 @value{GDBN} enables developers to spawn and debug tasks running on networked
11156 VxWorks targets from a Unix host. Already-running tasks spawned from
11157 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11158 both the Unix host and on the VxWorks target. The program
11159 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11160 installed with the name @code{vxgdb}, to distinguish it from a
11161 @value{GDBN} for debugging programs on the host itself.)
11164 @item VxWorks-timeout @var{args}
11165 @kindex vxworks-timeout
11166 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11167 This option is set by the user, and @var{args} represents the number of
11168 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11169 your VxWorks target is a slow software simulator or is on the far side
11170 of a thin network line.
11173 The following information on connecting to VxWorks was current when
11174 this manual was produced; newer releases of VxWorks may use revised
11177 @kindex INCLUDE_RDB
11178 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11179 to include the remote debugging interface routines in the VxWorks
11180 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11181 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11182 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11183 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11184 information on configuring and remaking VxWorks, see the manufacturer's
11186 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11188 Once you have included @file{rdb.a} in your VxWorks system image and set
11189 your Unix execution search path to find @value{GDBN}, you are ready to
11190 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11191 @code{vxgdb}, depending on your installation).
11193 @value{GDBN} comes up showing the prompt:
11200 * VxWorks Connection:: Connecting to VxWorks
11201 * VxWorks Download:: VxWorks download
11202 * VxWorks Attach:: Running tasks
11205 @node VxWorks Connection
11206 @subsubsection Connecting to VxWorks
11208 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11209 network. To connect to a target whose host name is ``@code{tt}'', type:
11212 (vxgdb) target vxworks tt
11216 @value{GDBN} displays messages like these:
11219 Attaching remote machine across net...
11224 @value{GDBN} then attempts to read the symbol tables of any object modules
11225 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11226 these files by searching the directories listed in the command search
11227 path (@pxref{Environment, ,Your program's environment}); if it fails
11228 to find an object file, it displays a message such as:
11231 prog.o: No such file or directory.
11234 When this happens, add the appropriate directory to the search path with
11235 the @value{GDBN} command @code{path}, and execute the @code{target}
11238 @node VxWorks Download
11239 @subsubsection VxWorks download
11241 @cindex download to VxWorks
11242 If you have connected to the VxWorks target and you want to debug an
11243 object that has not yet been loaded, you can use the @value{GDBN}
11244 @code{load} command to download a file from Unix to VxWorks
11245 incrementally. The object file given as an argument to the @code{load}
11246 command is actually opened twice: first by the VxWorks target in order
11247 to download the code, then by @value{GDBN} in order to read the symbol
11248 table. This can lead to problems if the current working directories on
11249 the two systems differ. If both systems have NFS mounted the same
11250 filesystems, you can avoid these problems by using absolute paths.
11251 Otherwise, it is simplest to set the working directory on both systems
11252 to the directory in which the object file resides, and then to reference
11253 the file by its name, without any path. For instance, a program
11254 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11255 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11256 program, type this on VxWorks:
11259 -> cd "@var{vxpath}/vw/demo/rdb"
11263 Then, in @value{GDBN}, type:
11266 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11267 (vxgdb) load prog.o
11270 @value{GDBN} displays a response similar to this:
11273 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11276 You can also use the @code{load} command to reload an object module
11277 after editing and recompiling the corresponding source file. Note that
11278 this makes @value{GDBN} delete all currently-defined breakpoints,
11279 auto-displays, and convenience variables, and to clear the value
11280 history. (This is necessary in order to preserve the integrity of
11281 debugger's data structures that reference the target system's symbol
11284 @node VxWorks Attach
11285 @subsubsection Running tasks
11287 @cindex running VxWorks tasks
11288 You can also attach to an existing task using the @code{attach} command as
11292 (vxgdb) attach @var{task}
11296 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11297 or suspended when you attach to it. Running tasks are suspended at
11298 the time of attachment.
11300 @node Embedded Processors
11301 @section Embedded Processors
11303 This section goes into details specific to particular embedded
11309 * H8/300:: Hitachi H8/300
11310 * H8/500:: Hitachi H8/500
11311 * i960:: Intel i960
11312 * M32R/D:: Mitsubishi M32R/D
11313 * M68K:: Motorola M68K
11314 @c OBSOLETE * M88K:: Motorola M88K
11315 * MIPS Embedded:: MIPS Embedded
11316 * PA:: HP PA Embedded
11319 * Sparclet:: Tsqware Sparclet
11320 * Sparclite:: Fujitsu Sparclite
11321 * ST2000:: Tandem ST2000
11322 * Z8000:: Zilog Z8000
11331 @item target rdi @var{dev}
11332 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11333 use this target to communicate with both boards running the Angel
11334 monitor, or with the EmbeddedICE JTAG debug device.
11337 @item target rdp @var{dev}
11343 @subsection Hitachi H8/300
11347 @kindex target hms@r{, with H8/300}
11348 @item target hms @var{dev}
11349 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11350 Use special commands @code{device} and @code{speed} to control the serial
11351 line and the communications speed used.
11353 @kindex target e7000@r{, with H8/300}
11354 @item target e7000 @var{dev}
11355 E7000 emulator for Hitachi H8 and SH.
11357 @kindex target sh3@r{, with H8/300}
11358 @kindex target sh3e@r{, with H8/300}
11359 @item target sh3 @var{dev}
11360 @itemx target sh3e @var{dev}
11361 Hitachi SH-3 and SH-3E target systems.
11365 @cindex download to H8/300 or H8/500
11366 @cindex H8/300 or H8/500 download
11367 @cindex download to Hitachi SH
11368 @cindex Hitachi SH download
11369 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11370 board, the @code{load} command downloads your program to the Hitachi
11371 board and also opens it as the current executable target for
11372 @value{GDBN} on your host (like the @code{file} command).
11374 @value{GDBN} needs to know these things to talk to your
11375 Hitachi SH, H8/300, or H8/500:
11379 that you want to use @samp{target hms}, the remote debugging interface
11380 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11381 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11382 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11383 H8/300, or H8/500.)
11386 what serial device connects your host to your Hitachi board (the first
11387 serial device available on your host is the default).
11390 what speed to use over the serial device.
11394 * Hitachi Boards:: Connecting to Hitachi boards.
11395 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11396 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11399 @node Hitachi Boards
11400 @subsubsection Connecting to Hitachi boards
11402 @c only for Unix hosts
11404 @cindex serial device, Hitachi micros
11405 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11406 need to explicitly set the serial device. The default @var{port} is the
11407 first available port on your host. This is only necessary on Unix
11408 hosts, where it is typically something like @file{/dev/ttya}.
11411 @cindex serial line speed, Hitachi micros
11412 @code{@value{GDBN}} has another special command to set the communications
11413 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11414 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11415 the DOS @code{mode} command (for instance,
11416 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11418 The @samp{device} and @samp{speed} commands are available only when you
11419 use a Unix host to debug your Hitachi microprocessor programs. If you
11421 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11422 called @code{asynctsr} to communicate with the development board
11423 through a PC serial port. You must also use the DOS @code{mode} command
11424 to set up the serial port on the DOS side.
11426 The following sample session illustrates the steps needed to start a
11427 program under @value{GDBN} control on an H8/300. The example uses a
11428 sample H8/300 program called @file{t.x}. The procedure is the same for
11429 the Hitachi SH and the H8/500.
11431 First hook up your development board. In this example, we use a
11432 board attached to serial port @code{COM2}; if you use a different serial
11433 port, substitute its name in the argument of the @code{mode} command.
11434 When you call @code{asynctsr}, the auxiliary comms program used by the
11435 debugger, you give it just the numeric part of the serial port's name;
11436 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11440 C:\H8300\TEST> asynctsr 2
11441 C:\H8300\TEST> mode com2:9600,n,8,1,p
11443 Resident portion of MODE loaded
11445 COM2: 9600, n, 8, 1, p
11450 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11451 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11452 disable it, or even boot without it, to use @code{asynctsr} to control
11453 your development board.
11456 @kindex target hms@r{, and serial protocol}
11457 Now that serial communications are set up, and the development board is
11458 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11459 the name of your program as the argument. @code{@value{GDBN}} prompts
11460 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11461 commands to begin your debugging session: @samp{target hms} to specify
11462 cross-debugging to the Hitachi board, and the @code{load} command to
11463 download your program to the board. @code{load} displays the names of
11464 the program's sections, and a @samp{*} for each 2K of data downloaded.
11465 (If you want to refresh @value{GDBN} data on symbols or on the
11466 executable file without downloading, use the @value{GDBN} commands
11467 @code{file} or @code{symbol-file}. These commands, and @code{load}
11468 itself, are described in @ref{Files,,Commands to specify files}.)
11471 (eg-C:\H8300\TEST) @value{GDBP} t.x
11472 @value{GDBN} is free software and you are welcome to distribute copies
11473 of it under certain conditions; type "show copying" to see
11475 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11477 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11478 (@value{GDBP}) target hms
11479 Connected to remote H8/300 HMS system.
11480 (@value{GDBP}) load t.x
11481 .text : 0x8000 .. 0xabde ***********
11482 .data : 0xabde .. 0xad30 *
11483 .stack : 0xf000 .. 0xf014 *
11486 At this point, you're ready to run or debug your program. From here on,
11487 you can use all the usual @value{GDBN} commands. The @code{break} command
11488 sets breakpoints; the @code{run} command starts your program;
11489 @code{print} or @code{x} display data; the @code{continue} command
11490 resumes execution after stopping at a breakpoint. You can use the
11491 @code{help} command at any time to find out more about @value{GDBN} commands.
11493 Remember, however, that @emph{operating system} facilities aren't
11494 available on your development board; for example, if your program hangs,
11495 you can't send an interrupt---but you can press the @sc{reset} switch!
11497 Use the @sc{reset} button on the development board
11500 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11501 no way to pass an interrupt signal to the development board); and
11504 to return to the @value{GDBN} command prompt after your program finishes
11505 normally. The communications protocol provides no other way for @value{GDBN}
11506 to detect program completion.
11509 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11510 development board as a ``normal exit'' of your program.
11513 @subsubsection Using the E7000 in-circuit emulator
11515 @kindex target e7000@r{, with Hitachi ICE}
11516 You can use the E7000 in-circuit emulator to develop code for either the
11517 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11518 e7000} command to connect @value{GDBN} to your E7000:
11521 @item target e7000 @var{port} @var{speed}
11522 Use this form if your E7000 is connected to a serial port. The
11523 @var{port} argument identifies what serial port to use (for example,
11524 @samp{com2}). The third argument is the line speed in bits per second
11525 (for example, @samp{9600}).
11527 @item target e7000 @var{hostname}
11528 If your E7000 is installed as a host on a TCP/IP network, you can just
11529 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11532 @node Hitachi Special
11533 @subsubsection Special @value{GDBN} commands for Hitachi micros
11535 Some @value{GDBN} commands are available only for the H8/300:
11539 @kindex set machine
11540 @kindex show machine
11541 @item set machine h8300
11542 @itemx set machine h8300h
11543 Condition @value{GDBN} for one of the two variants of the H8/300
11544 architecture with @samp{set machine}. You can use @samp{show machine}
11545 to check which variant is currently in effect.
11554 @kindex set memory @var{mod}
11555 @cindex memory models, H8/500
11556 @item set memory @var{mod}
11558 Specify which H8/500 memory model (@var{mod}) you are using with
11559 @samp{set memory}; check which memory model is in effect with @samp{show
11560 memory}. The accepted values for @var{mod} are @code{small},
11561 @code{big}, @code{medium}, and @code{compact}.
11566 @subsection Intel i960
11570 @kindex target mon960
11571 @item target mon960 @var{dev}
11572 MON960 monitor for Intel i960.
11574 @kindex target nindy
11575 @item target nindy @var{devicename}
11576 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11577 the name of the serial device to use for the connection, e.g.
11584 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11585 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11586 tell @value{GDBN} how to connect to the 960 in several ways:
11590 Through command line options specifying serial port, version of the
11591 Nindy protocol, and communications speed;
11594 By responding to a prompt on startup;
11597 By using the @code{target} command at any point during your @value{GDBN}
11598 session. @xref{Target Commands, ,Commands for managing targets}.
11602 @cindex download to Nindy-960
11603 With the Nindy interface to an Intel 960 board, @code{load}
11604 downloads @var{filename} to the 960 as well as adding its symbols in
11608 * Nindy Startup:: Startup with Nindy
11609 * Nindy Options:: Options for Nindy
11610 * Nindy Reset:: Nindy reset command
11613 @node Nindy Startup
11614 @subsubsection Startup with Nindy
11616 If you simply start @code{@value{GDBP}} without using any command-line
11617 options, you are prompted for what serial port to use, @emph{before} you
11618 reach the ordinary @value{GDBN} prompt:
11621 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11625 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11626 identifies the serial port you want to use. You can, if you choose,
11627 simply start up with no Nindy connection by responding to the prompt
11628 with an empty line. If you do this and later wish to attach to Nindy,
11629 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11631 @node Nindy Options
11632 @subsubsection Options for Nindy
11634 These are the startup options for beginning your @value{GDBN} session with a
11635 Nindy-960 board attached:
11638 @item -r @var{port}
11639 Specify the serial port name of a serial interface to be used to connect
11640 to the target system. This option is only available when @value{GDBN} is
11641 configured for the Intel 960 target architecture. You may specify
11642 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11643 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11644 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11647 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11648 the ``old'' Nindy monitor protocol to connect to the target system.
11649 This option is only available when @value{GDBN} is configured for the Intel 960
11650 target architecture.
11653 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11654 connect to a target system that expects the newer protocol, the connection
11655 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11656 attempts to reconnect at several different line speeds. You can abort
11657 this process with an interrupt.
11661 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11662 system, in an attempt to reset it, before connecting to a Nindy target.
11665 @emph{Warning:} Many target systems do not have the hardware that this
11666 requires; it only works with a few boards.
11670 The standard @samp{-b} option controls the line speed used on the serial
11675 @subsubsection Nindy reset command
11680 For a Nindy target, this command sends a ``break'' to the remote target
11681 system; this is only useful if the target has been equipped with a
11682 circuit to perform a hard reset (or some other interesting action) when
11683 a break is detected.
11688 @subsection Mitsubishi M32R/D
11692 @kindex target m32r
11693 @item target m32r @var{dev}
11694 Mitsubishi M32R/D ROM monitor.
11701 The Motorola m68k configuration includes ColdFire support, and
11702 target command for the following ROM monitors.
11706 @kindex target abug
11707 @item target abug @var{dev}
11708 ABug ROM monitor for M68K.
11710 @kindex target cpu32bug
11711 @item target cpu32bug @var{dev}
11712 CPU32BUG monitor, running on a CPU32 (M68K) board.
11714 @kindex target dbug
11715 @item target dbug @var{dev}
11716 dBUG ROM monitor for Motorola ColdFire.
11719 @item target est @var{dev}
11720 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11722 @kindex target rom68k
11723 @item target rom68k @var{dev}
11724 ROM 68K monitor, running on an M68K IDP board.
11728 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11729 instead have only a single special target command:
11733 @kindex target es1800
11734 @item target es1800 @var{dev}
11735 ES-1800 emulator for M68K.
11743 @kindex target rombug
11744 @item target rombug @var{dev}
11745 ROMBUG ROM monitor for OS/9000.
11749 @c OBSOLETE @node M88K
11750 @c OBSOLETE @subsection M88K
11752 @c OBSOLETE @table @code
11754 @c OBSOLETE @kindex target bug
11755 @c OBSOLETE @item target bug @var{dev}
11756 @c OBSOLETE BUG monitor, running on a MVME187 (m88k) board.
11758 @c OBSOLETE @end table
11760 @node MIPS Embedded
11761 @subsection MIPS Embedded
11763 @cindex MIPS boards
11764 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11765 MIPS board attached to a serial line. This is available when
11766 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11769 Use these @value{GDBN} commands to specify the connection to your target board:
11772 @item target mips @var{port}
11773 @kindex target mips @var{port}
11774 To run a program on the board, start up @code{@value{GDBP}} with the
11775 name of your program as the argument. To connect to the board, use the
11776 command @samp{target mips @var{port}}, where @var{port} is the name of
11777 the serial port connected to the board. If the program has not already
11778 been downloaded to the board, you may use the @code{load} command to
11779 download it. You can then use all the usual @value{GDBN} commands.
11781 For example, this sequence connects to the target board through a serial
11782 port, and loads and runs a program called @var{prog} through the
11786 host$ @value{GDBP} @var{prog}
11787 @value{GDBN} is free software and @dots{}
11788 (@value{GDBP}) target mips /dev/ttyb
11789 (@value{GDBP}) load @var{prog}
11793 @item target mips @var{hostname}:@var{portnumber}
11794 On some @value{GDBN} host configurations, you can specify a TCP
11795 connection (for instance, to a serial line managed by a terminal
11796 concentrator) instead of a serial port, using the syntax
11797 @samp{@var{hostname}:@var{portnumber}}.
11799 @item target pmon @var{port}
11800 @kindex target pmon @var{port}
11803 @item target ddb @var{port}
11804 @kindex target ddb @var{port}
11805 NEC's DDB variant of PMON for Vr4300.
11807 @item target lsi @var{port}
11808 @kindex target lsi @var{port}
11809 LSI variant of PMON.
11811 @kindex target r3900
11812 @item target r3900 @var{dev}
11813 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11815 @kindex target array
11816 @item target array @var{dev}
11817 Array Tech LSI33K RAID controller board.
11823 @value{GDBN} also supports these special commands for MIPS targets:
11826 @item set processor @var{args}
11827 @itemx show processor
11828 @kindex set processor @var{args}
11829 @kindex show processor
11830 Use the @code{set processor} command to set the type of MIPS
11831 processor when you want to access processor-type-specific registers.
11832 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11833 to use the CPU registers appropriate for the 3041 chip.
11834 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11835 is using. Use the @code{info reg} command to see what registers
11836 @value{GDBN} is using.
11838 @item set mipsfpu double
11839 @itemx set mipsfpu single
11840 @itemx set mipsfpu none
11841 @itemx show mipsfpu
11842 @kindex set mipsfpu
11843 @kindex show mipsfpu
11844 @cindex MIPS remote floating point
11845 @cindex floating point, MIPS remote
11846 If your target board does not support the MIPS floating point
11847 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11848 need this, you may wish to put the command in your @value{GDBN} init
11849 file). This tells @value{GDBN} how to find the return value of
11850 functions which return floating point values. It also allows
11851 @value{GDBN} to avoid saving the floating point registers when calling
11852 functions on the board. If you are using a floating point coprocessor
11853 with only single precision floating point support, as on the @sc{r4650}
11854 processor, use the command @samp{set mipsfpu single}. The default
11855 double precision floating point coprocessor may be selected using
11856 @samp{set mipsfpu double}.
11858 In previous versions the only choices were double precision or no
11859 floating point, so @samp{set mipsfpu on} will select double precision
11860 and @samp{set mipsfpu off} will select no floating point.
11862 As usual, you can inquire about the @code{mipsfpu} variable with
11863 @samp{show mipsfpu}.
11865 @item set remotedebug @var{n}
11866 @itemx show remotedebug
11867 @kindex set remotedebug@r{, MIPS protocol}
11868 @kindex show remotedebug@r{, MIPS protocol}
11869 @cindex @code{remotedebug}, MIPS protocol
11870 @cindex MIPS @code{remotedebug} protocol
11871 @c FIXME! For this to be useful, you must know something about the MIPS
11872 @c FIXME...protocol. Where is it described?
11873 You can see some debugging information about communications with the board
11874 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11875 @samp{set remotedebug 1}, every packet is displayed. If you set it
11876 to @code{2}, every character is displayed. You can check the current value
11877 at any time with the command @samp{show remotedebug}.
11879 @item set timeout @var{seconds}
11880 @itemx set retransmit-timeout @var{seconds}
11881 @itemx show timeout
11882 @itemx show retransmit-timeout
11883 @cindex @code{timeout}, MIPS protocol
11884 @cindex @code{retransmit-timeout}, MIPS protocol
11885 @kindex set timeout
11886 @kindex show timeout
11887 @kindex set retransmit-timeout
11888 @kindex show retransmit-timeout
11889 You can control the timeout used while waiting for a packet, in the MIPS
11890 remote protocol, with the @code{set timeout @var{seconds}} command. The
11891 default is 5 seconds. Similarly, you can control the timeout used while
11892 waiting for an acknowledgement of a packet with the @code{set
11893 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11894 You can inspect both values with @code{show timeout} and @code{show
11895 retransmit-timeout}. (These commands are @emph{only} available when
11896 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11898 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11899 is waiting for your program to stop. In that case, @value{GDBN} waits
11900 forever because it has no way of knowing how long the program is going
11901 to run before stopping.
11905 @subsection PowerPC
11909 @kindex target dink32
11910 @item target dink32 @var{dev}
11911 DINK32 ROM monitor.
11913 @kindex target ppcbug
11914 @item target ppcbug @var{dev}
11915 @kindex target ppcbug1
11916 @item target ppcbug1 @var{dev}
11917 PPCBUG ROM monitor for PowerPC.
11920 @item target sds @var{dev}
11921 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11926 @subsection HP PA Embedded
11930 @kindex target op50n
11931 @item target op50n @var{dev}
11932 OP50N monitor, running on an OKI HPPA board.
11934 @kindex target w89k
11935 @item target w89k @var{dev}
11936 W89K monitor, running on a Winbond HPPA board.
11941 @subsection Hitachi SH
11945 @kindex target hms@r{, with Hitachi SH}
11946 @item target hms @var{dev}
11947 A Hitachi SH board attached via serial line to your host. Use special
11948 commands @code{device} and @code{speed} to control the serial line and
11949 the communications speed used.
11951 @kindex target e7000@r{, with Hitachi SH}
11952 @item target e7000 @var{dev}
11953 E7000 emulator for Hitachi SH.
11955 @kindex target sh3@r{, with SH}
11956 @kindex target sh3e@r{, with SH}
11957 @item target sh3 @var{dev}
11958 @item target sh3e @var{dev}
11959 Hitachi SH-3 and SH-3E target systems.
11964 @subsection Tsqware Sparclet
11968 @value{GDBN} enables developers to debug tasks running on
11969 Sparclet targets from a Unix host.
11970 @value{GDBN} uses code that runs on
11971 both the Unix host and on the Sparclet target. The program
11972 @code{@value{GDBP}} is installed and executed on the Unix host.
11975 @item remotetimeout @var{args}
11976 @kindex remotetimeout
11977 @value{GDBN} supports the option @code{remotetimeout}.
11978 This option is set by the user, and @var{args} represents the number of
11979 seconds @value{GDBN} waits for responses.
11982 @cindex compiling, on Sparclet
11983 When compiling for debugging, include the options @samp{-g} to get debug
11984 information and @samp{-Ttext} to relocate the program to where you wish to
11985 load it on the target. You may also want to add the options @samp{-n} or
11986 @samp{-N} in order to reduce the size of the sections. Example:
11989 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11992 You can use @code{objdump} to verify that the addresses are what you intended:
11995 sparclet-aout-objdump --headers --syms prog
11998 @cindex running, on Sparclet
12000 your Unix execution search path to find @value{GDBN}, you are ready to
12001 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12002 (or @code{sparclet-aout-gdb}, depending on your installation).
12004 @value{GDBN} comes up showing the prompt:
12011 * Sparclet File:: Setting the file to debug
12012 * Sparclet Connection:: Connecting to Sparclet
12013 * Sparclet Download:: Sparclet download
12014 * Sparclet Execution:: Running and debugging
12017 @node Sparclet File
12018 @subsubsection Setting file to debug
12020 The @value{GDBN} command @code{file} lets you choose with program to debug.
12023 (gdbslet) file prog
12027 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12028 @value{GDBN} locates
12029 the file by searching the directories listed in the command search
12031 If the file was compiled with debug information (option "-g"), source
12032 files will be searched as well.
12033 @value{GDBN} locates
12034 the source files by searching the directories listed in the directory search
12035 path (@pxref{Environment, ,Your program's environment}).
12037 to find a file, it displays a message such as:
12040 prog: No such file or directory.
12043 When this happens, add the appropriate directories to the search paths with
12044 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12045 @code{target} command again.
12047 @node Sparclet Connection
12048 @subsubsection Connecting to Sparclet
12050 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12051 To connect to a target on serial port ``@code{ttya}'', type:
12054 (gdbslet) target sparclet /dev/ttya
12055 Remote target sparclet connected to /dev/ttya
12056 main () at ../prog.c:3
12060 @value{GDBN} displays messages like these:
12066 @node Sparclet Download
12067 @subsubsection Sparclet download
12069 @cindex download to Sparclet
12070 Once connected to the Sparclet target,
12071 you can use the @value{GDBN}
12072 @code{load} command to download the file from the host to the target.
12073 The file name and load offset should be given as arguments to the @code{load}
12075 Since the file format is aout, the program must be loaded to the starting
12076 address. You can use @code{objdump} to find out what this value is. The load
12077 offset is an offset which is added to the VMA (virtual memory address)
12078 of each of the file's sections.
12079 For instance, if the program
12080 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12081 and bss at 0x12010170, in @value{GDBN}, type:
12084 (gdbslet) load prog 0x12010000
12085 Loading section .text, size 0xdb0 vma 0x12010000
12088 If the code is loaded at a different address then what the program was linked
12089 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12090 to tell @value{GDBN} where to map the symbol table.
12092 @node Sparclet Execution
12093 @subsubsection Running and debugging
12095 @cindex running and debugging Sparclet programs
12096 You can now begin debugging the task using @value{GDBN}'s execution control
12097 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12098 manual for the list of commands.
12102 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12104 Starting program: prog
12105 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12106 3 char *symarg = 0;
12108 4 char *execarg = "hello!";
12113 @subsection Fujitsu Sparclite
12117 @kindex target sparclite
12118 @item target sparclite @var{dev}
12119 Fujitsu sparclite boards, used only for the purpose of loading.
12120 You must use an additional command to debug the program.
12121 For example: target remote @var{dev} using @value{GDBN} standard
12127 @subsection Tandem ST2000
12129 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12132 To connect your ST2000 to the host system, see the manufacturer's
12133 manual. Once the ST2000 is physically attached, you can run:
12136 target st2000 @var{dev} @var{speed}
12140 to establish it as your debugging environment. @var{dev} is normally
12141 the name of a serial device, such as @file{/dev/ttya}, connected to the
12142 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12143 connection (for example, to a serial line attached via a terminal
12144 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12146 The @code{load} and @code{attach} commands are @emph{not} defined for
12147 this target; you must load your program into the ST2000 as you normally
12148 would for standalone operation. @value{GDBN} reads debugging information
12149 (such as symbols) from a separate, debugging version of the program
12150 available on your host computer.
12151 @c FIXME!! This is terribly vague; what little content is here is
12152 @c basically hearsay.
12154 @cindex ST2000 auxiliary commands
12155 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12159 @item st2000 @var{command}
12160 @kindex st2000 @var{cmd}
12161 @cindex STDBUG commands (ST2000)
12162 @cindex commands to STDBUG (ST2000)
12163 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12164 manual for available commands.
12167 @cindex connect (to STDBUG)
12168 Connect the controlling terminal to the STDBUG command monitor. When
12169 you are done interacting with STDBUG, typing either of two character
12170 sequences gets you back to the @value{GDBN} command prompt:
12171 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12172 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12176 @subsection Zilog Z8000
12179 @cindex simulator, Z8000
12180 @cindex Zilog Z8000 simulator
12182 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12185 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12186 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12187 segmented variant). The simulator recognizes which architecture is
12188 appropriate by inspecting the object code.
12191 @item target sim @var{args}
12193 @kindex target sim@r{, with Z8000}
12194 Debug programs on a simulated CPU. If the simulator supports setup
12195 options, specify them via @var{args}.
12199 After specifying this target, you can debug programs for the simulated
12200 CPU in the same style as programs for your host computer; use the
12201 @code{file} command to load a new program image, the @code{run} command
12202 to run your program, and so on.
12204 As well as making available all the usual machine registers
12205 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12206 additional items of information as specially named registers:
12211 Counts clock-ticks in the simulator.
12214 Counts instructions run in the simulator.
12217 Execution time in 60ths of a second.
12221 You can refer to these values in @value{GDBN} expressions with the usual
12222 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12223 conditional breakpoint that suspends only after at least 5000
12224 simulated clock ticks.
12226 @node Architectures
12227 @section Architectures
12229 This section describes characteristics of architectures that affect
12230 all uses of @value{GDBN} with the architecture, both native and cross.
12243 @kindex set rstack_high_address
12244 @cindex AMD 29K register stack
12245 @cindex register stack, AMD29K
12246 @item set rstack_high_address @var{address}
12247 On AMD 29000 family processors, registers are saved in a separate
12248 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12249 extent of this stack. Normally, @value{GDBN} just assumes that the
12250 stack is ``large enough''. This may result in @value{GDBN} referencing
12251 memory locations that do not exist. If necessary, you can get around
12252 this problem by specifying the ending address of the register stack with
12253 the @code{set rstack_high_address} command. The argument should be an
12254 address, which you probably want to precede with @samp{0x} to specify in
12257 @kindex show rstack_high_address
12258 @item show rstack_high_address
12259 Display the current limit of the register stack, on AMD 29000 family
12267 See the following section.
12272 @cindex stack on Alpha
12273 @cindex stack on MIPS
12274 @cindex Alpha stack
12276 Alpha- and MIPS-based computers use an unusual stack frame, which
12277 sometimes requires @value{GDBN} to search backward in the object code to
12278 find the beginning of a function.
12280 @cindex response time, MIPS debugging
12281 To improve response time (especially for embedded applications, where
12282 @value{GDBN} may be restricted to a slow serial line for this search)
12283 you may want to limit the size of this search, using one of these
12287 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12288 @item set heuristic-fence-post @var{limit}
12289 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12290 search for the beginning of a function. A value of @var{0} (the
12291 default) means there is no limit. However, except for @var{0}, the
12292 larger the limit the more bytes @code{heuristic-fence-post} must search
12293 and therefore the longer it takes to run.
12295 @item show heuristic-fence-post
12296 Display the current limit.
12300 These commands are available @emph{only} when @value{GDBN} is configured
12301 for debugging programs on Alpha or MIPS processors.
12304 @node Controlling GDB
12305 @chapter Controlling @value{GDBN}
12307 You can alter the way @value{GDBN} interacts with you by using the
12308 @code{set} command. For commands controlling how @value{GDBN} displays
12309 data, see @ref{Print Settings, ,Print settings}. Other settings are
12314 * Editing:: Command editing
12315 * History:: Command history
12316 * Screen Size:: Screen size
12317 * Numbers:: Numbers
12318 * Messages/Warnings:: Optional warnings and messages
12319 * Debugging Output:: Optional messages about internal happenings
12327 @value{GDBN} indicates its readiness to read a command by printing a string
12328 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12329 can change the prompt string with the @code{set prompt} command. For
12330 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12331 the prompt in one of the @value{GDBN} sessions so that you can always tell
12332 which one you are talking to.
12334 @emph{Note:} @code{set prompt} does not add a space for you after the
12335 prompt you set. This allows you to set a prompt which ends in a space
12336 or a prompt that does not.
12340 @item set prompt @var{newprompt}
12341 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12343 @kindex show prompt
12345 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12349 @section Command editing
12351 @cindex command line editing
12353 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12354 @sc{gnu} library provides consistent behavior for programs which provide a
12355 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12356 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12357 substitution, and a storage and recall of command history across
12358 debugging sessions.
12360 You may control the behavior of command line editing in @value{GDBN} with the
12361 command @code{set}.
12364 @kindex set editing
12367 @itemx set editing on
12368 Enable command line editing (enabled by default).
12370 @item set editing off
12371 Disable command line editing.
12373 @kindex show editing
12375 Show whether command line editing is enabled.
12379 @section Command history
12381 @value{GDBN} can keep track of the commands you type during your
12382 debugging sessions, so that you can be certain of precisely what
12383 happened. Use these commands to manage the @value{GDBN} command
12387 @cindex history substitution
12388 @cindex history file
12389 @kindex set history filename
12390 @kindex GDBHISTFILE
12391 @item set history filename @var{fname}
12392 Set the name of the @value{GDBN} command history file to @var{fname}.
12393 This is the file where @value{GDBN} reads an initial command history
12394 list, and where it writes the command history from this session when it
12395 exits. You can access this list through history expansion or through
12396 the history command editing characters listed below. This file defaults
12397 to the value of the environment variable @code{GDBHISTFILE}, or to
12398 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12401 @cindex history save
12402 @kindex set history save
12403 @item set history save
12404 @itemx set history save on
12405 Record command history in a file, whose name may be specified with the
12406 @code{set history filename} command. By default, this option is disabled.
12408 @item set history save off
12409 Stop recording command history in a file.
12411 @cindex history size
12412 @kindex set history size
12413 @item set history size @var{size}
12414 Set the number of commands which @value{GDBN} keeps in its history list.
12415 This defaults to the value of the environment variable
12416 @code{HISTSIZE}, or to 256 if this variable is not set.
12419 @cindex history expansion
12420 History expansion assigns special meaning to the character @kbd{!}.
12421 @ifset have-readline-appendices
12422 @xref{Event Designators}.
12425 Since @kbd{!} is also the logical not operator in C, history expansion
12426 is off by default. If you decide to enable history expansion with the
12427 @code{set history expansion on} command, you may sometimes need to
12428 follow @kbd{!} (when it is used as logical not, in an expression) with
12429 a space or a tab to prevent it from being expanded. The readline
12430 history facilities do not attempt substitution on the strings
12431 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12433 The commands to control history expansion are:
12436 @kindex set history expansion
12437 @item set history expansion on
12438 @itemx set history expansion
12439 Enable history expansion. History expansion is off by default.
12441 @item set history expansion off
12442 Disable history expansion.
12444 The readline code comes with more complete documentation of
12445 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12446 or @code{vi} may wish to read it.
12447 @ifset have-readline-appendices
12448 @xref{Command Line Editing}.
12452 @kindex show history
12454 @itemx show history filename
12455 @itemx show history save
12456 @itemx show history size
12457 @itemx show history expansion
12458 These commands display the state of the @value{GDBN} history parameters.
12459 @code{show history} by itself displays all four states.
12465 @item show commands
12466 Display the last ten commands in the command history.
12468 @item show commands @var{n}
12469 Print ten commands centered on command number @var{n}.
12471 @item show commands +
12472 Print ten commands just after the commands last printed.
12476 @section Screen size
12477 @cindex size of screen
12478 @cindex pauses in output
12480 Certain commands to @value{GDBN} may produce large amounts of
12481 information output to the screen. To help you read all of it,
12482 @value{GDBN} pauses and asks you for input at the end of each page of
12483 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12484 to discard the remaining output. Also, the screen width setting
12485 determines when to wrap lines of output. Depending on what is being
12486 printed, @value{GDBN} tries to break the line at a readable place,
12487 rather than simply letting it overflow onto the following line.
12489 Normally @value{GDBN} knows the size of the screen from the terminal
12490 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12491 together with the value of the @code{TERM} environment variable and the
12492 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12493 you can override it with the @code{set height} and @code{set
12500 @kindex show height
12501 @item set height @var{lpp}
12503 @itemx set width @var{cpl}
12505 These @code{set} commands specify a screen height of @var{lpp} lines and
12506 a screen width of @var{cpl} characters. The associated @code{show}
12507 commands display the current settings.
12509 If you specify a height of zero lines, @value{GDBN} does not pause during
12510 output no matter how long the output is. This is useful if output is to a
12511 file or to an editor buffer.
12513 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12514 from wrapping its output.
12519 @cindex number representation
12520 @cindex entering numbers
12522 You can always enter numbers in octal, decimal, or hexadecimal in
12523 @value{GDBN} by the usual conventions: octal numbers begin with
12524 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12525 begin with @samp{0x}. Numbers that begin with none of these are, by
12526 default, entered in base 10; likewise, the default display for
12527 numbers---when no particular format is specified---is base 10. You can
12528 change the default base for both input and output with the @code{set
12532 @kindex set input-radix
12533 @item set input-radix @var{base}
12534 Set the default base for numeric input. Supported choices
12535 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12536 specified either unambiguously or using the current default radix; for
12546 sets the base to decimal. On the other hand, @samp{set radix 10}
12547 leaves the radix unchanged no matter what it was.
12549 @kindex set output-radix
12550 @item set output-radix @var{base}
12551 Set the default base for numeric display. Supported choices
12552 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12553 specified either unambiguously or using the current default radix.
12555 @kindex show input-radix
12556 @item show input-radix
12557 Display the current default base for numeric input.
12559 @kindex show output-radix
12560 @item show output-radix
12561 Display the current default base for numeric display.
12564 @node Messages/Warnings
12565 @section Optional warnings and messages
12567 By default, @value{GDBN} is silent about its inner workings. If you are
12568 running on a slow machine, you may want to use the @code{set verbose}
12569 command. This makes @value{GDBN} tell you when it does a lengthy
12570 internal operation, so you will not think it has crashed.
12572 Currently, the messages controlled by @code{set verbose} are those
12573 which announce that the symbol table for a source file is being read;
12574 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12577 @kindex set verbose
12578 @item set verbose on
12579 Enables @value{GDBN} output of certain informational messages.
12581 @item set verbose off
12582 Disables @value{GDBN} output of certain informational messages.
12584 @kindex show verbose
12586 Displays whether @code{set verbose} is on or off.
12589 By default, if @value{GDBN} encounters bugs in the symbol table of an
12590 object file, it is silent; but if you are debugging a compiler, you may
12591 find this information useful (@pxref{Symbol Errors, ,Errors reading
12596 @kindex set complaints
12597 @item set complaints @var{limit}
12598 Permits @value{GDBN} to output @var{limit} complaints about each type of
12599 unusual symbols before becoming silent about the problem. Set
12600 @var{limit} to zero to suppress all complaints; set it to a large number
12601 to prevent complaints from being suppressed.
12603 @kindex show complaints
12604 @item show complaints
12605 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12609 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12610 lot of stupid questions to confirm certain commands. For example, if
12611 you try to run a program which is already running:
12615 The program being debugged has been started already.
12616 Start it from the beginning? (y or n)
12619 If you are willing to unflinchingly face the consequences of your own
12620 commands, you can disable this ``feature'':
12624 @kindex set confirm
12626 @cindex confirmation
12627 @cindex stupid questions
12628 @item set confirm off
12629 Disables confirmation requests.
12631 @item set confirm on
12632 Enables confirmation requests (the default).
12634 @kindex show confirm
12636 Displays state of confirmation requests.
12640 @node Debugging Output
12641 @section Optional messages about internal happenings
12643 @kindex set debug arch
12644 @item set debug arch
12645 Turns on or off display of gdbarch debugging info. The default is off
12646 @kindex show debug arch
12647 @item show debug arch
12648 Displays the current state of displaying gdbarch debugging info.
12649 @kindex set debug event
12650 @item set debug event
12651 Turns on or off display of @value{GDBN} event debugging info. The
12653 @kindex show debug event
12654 @item show debug event
12655 Displays the current state of displaying @value{GDBN} event debugging
12657 @kindex set debug expression
12658 @item set debug expression
12659 Turns on or off display of @value{GDBN} expression debugging info. The
12661 @kindex show debug expression
12662 @item show debug expression
12663 Displays the current state of displaying @value{GDBN} expression
12665 @kindex set debug overload
12666 @item set debug overload
12667 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12668 info. This includes info such as ranking of functions, etc. The default
12670 @kindex show debug overload
12671 @item show debug overload
12672 Displays the current state of displaying @value{GDBN} C@t{++} overload
12674 @kindex set debug remote
12675 @cindex packets, reporting on stdout
12676 @cindex serial connections, debugging
12677 @item set debug remote
12678 Turns on or off display of reports on all packets sent back and forth across
12679 the serial line to the remote machine. The info is printed on the
12680 @value{GDBN} standard output stream. The default is off.
12681 @kindex show debug remote
12682 @item show debug remote
12683 Displays the state of display of remote packets.
12684 @kindex set debug serial
12685 @item set debug serial
12686 Turns on or off display of @value{GDBN} serial debugging info. The
12688 @kindex show debug serial
12689 @item show debug serial
12690 Displays the current state of displaying @value{GDBN} serial debugging
12692 @kindex set debug target
12693 @item set debug target
12694 Turns on or off display of @value{GDBN} target debugging info. This info
12695 includes what is going on at the target level of GDB, as it happens. The
12697 @kindex show debug target
12698 @item show debug target
12699 Displays the current state of displaying @value{GDBN} target debugging
12701 @kindex set debug varobj
12702 @item set debug varobj
12703 Turns on or off display of @value{GDBN} variable object debugging
12704 info. The default is off.
12705 @kindex show debug varobj
12706 @item show debug varobj
12707 Displays the current state of displaying @value{GDBN} variable object
12712 @chapter Canned Sequences of Commands
12714 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12715 command lists}), @value{GDBN} provides two ways to store sequences of
12716 commands for execution as a unit: user-defined commands and command
12720 * Define:: User-defined commands
12721 * Hooks:: User-defined command hooks
12722 * Command Files:: Command files
12723 * Output:: Commands for controlled output
12727 @section User-defined commands
12729 @cindex user-defined command
12730 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12731 which you assign a new name as a command. This is done with the
12732 @code{define} command. User commands may accept up to 10 arguments
12733 separated by whitespace. Arguments are accessed within the user command
12734 via @var{$arg0@dots{}$arg9}. A trivial example:
12738 print $arg0 + $arg1 + $arg2
12742 To execute the command use:
12749 This defines the command @code{adder}, which prints the sum of
12750 its three arguments. Note the arguments are text substitutions, so they may
12751 reference variables, use complex expressions, or even perform inferior
12757 @item define @var{commandname}
12758 Define a command named @var{commandname}. If there is already a command
12759 by that name, you are asked to confirm that you want to redefine it.
12761 The definition of the command is made up of other @value{GDBN} command lines,
12762 which are given following the @code{define} command. The end of these
12763 commands is marked by a line containing @code{end}.
12768 Takes a single argument, which is an expression to evaluate.
12769 It is followed by a series of commands that are executed
12770 only if the expression is true (nonzero).
12771 There can then optionally be a line @code{else}, followed
12772 by a series of commands that are only executed if the expression
12773 was false. The end of the list is marked by a line containing @code{end}.
12777 The syntax is similar to @code{if}: the command takes a single argument,
12778 which is an expression to evaluate, and must be followed by the commands to
12779 execute, one per line, terminated by an @code{end}.
12780 The commands are executed repeatedly as long as the expression
12784 @item document @var{commandname}
12785 Document the user-defined command @var{commandname}, so that it can be
12786 accessed by @code{help}. The command @var{commandname} must already be
12787 defined. This command reads lines of documentation just as @code{define}
12788 reads the lines of the command definition, ending with @code{end}.
12789 After the @code{document} command is finished, @code{help} on command
12790 @var{commandname} displays the documentation you have written.
12792 You may use the @code{document} command again to change the
12793 documentation of a command. Redefining the command with @code{define}
12794 does not change the documentation.
12796 @kindex help user-defined
12797 @item help user-defined
12798 List all user-defined commands, with the first line of the documentation
12803 @itemx show user @var{commandname}
12804 Display the @value{GDBN} commands used to define @var{commandname} (but
12805 not its documentation). If no @var{commandname} is given, display the
12806 definitions for all user-defined commands.
12808 @kindex show max-user-call-depth
12809 @kindex set max-user-call-depth
12810 @item show max-user-call-depth
12811 @itemx set max-user-call-depth
12812 The value of @code{max-user-call-depth} controls how many recursion
12813 levels are allowed in user-defined commands before GDB suspects an
12814 infinite recursion and aborts the command.
12818 When user-defined commands are executed, the
12819 commands of the definition are not printed. An error in any command
12820 stops execution of the user-defined command.
12822 If used interactively, commands that would ask for confirmation proceed
12823 without asking when used inside a user-defined command. Many @value{GDBN}
12824 commands that normally print messages to say what they are doing omit the
12825 messages when used in a user-defined command.
12828 @section User-defined command hooks
12829 @cindex command hooks
12830 @cindex hooks, for commands
12831 @cindex hooks, pre-command
12835 You may define @dfn{hooks}, which are a special kind of user-defined
12836 command. Whenever you run the command @samp{foo}, if the user-defined
12837 command @samp{hook-foo} exists, it is executed (with no arguments)
12838 before that command.
12840 @cindex hooks, post-command
12843 A hook may also be defined which is run after the command you executed.
12844 Whenever you run the command @samp{foo}, if the user-defined command
12845 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12846 that command. Post-execution hooks may exist simultaneously with
12847 pre-execution hooks, for the same command.
12849 It is valid for a hook to call the command which it hooks. If this
12850 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12852 @c It would be nice if hookpost could be passed a parameter indicating
12853 @c if the command it hooks executed properly or not. FIXME!
12855 @kindex stop@r{, a pseudo-command}
12856 In addition, a pseudo-command, @samp{stop} exists. Defining
12857 (@samp{hook-stop}) makes the associated commands execute every time
12858 execution stops in your program: before breakpoint commands are run,
12859 displays are printed, or the stack frame is printed.
12861 For example, to ignore @code{SIGALRM} signals while
12862 single-stepping, but treat them normally during normal execution,
12867 handle SIGALRM nopass
12871 handle SIGALRM pass
12874 define hook-continue
12875 handle SIGLARM pass
12879 As a further example, to hook at the begining and end of the @code{echo}
12880 command, and to add extra text to the beginning and end of the message,
12888 define hookpost-echo
12892 (@value{GDBP}) echo Hello World
12893 <<<---Hello World--->>>
12898 You can define a hook for any single-word command in @value{GDBN}, but
12899 not for command aliases; you should define a hook for the basic command
12900 name, e.g. @code{backtrace} rather than @code{bt}.
12901 @c FIXME! So how does Joe User discover whether a command is an alias
12903 If an error occurs during the execution of your hook, execution of
12904 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12905 (before the command that you actually typed had a chance to run).
12907 If you try to define a hook which does not match any known command, you
12908 get a warning from the @code{define} command.
12910 @node Command Files
12911 @section Command files
12913 @cindex command files
12914 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12915 commands. Comments (lines starting with @kbd{#}) may also be included.
12916 An empty line in a command file does nothing; it does not mean to repeat
12917 the last command, as it would from the terminal.
12920 @cindex @file{.gdbinit}
12921 @cindex @file{gdb.ini}
12922 When you start @value{GDBN}, it automatically executes commands from its
12923 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
12924 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
12925 limitations of file names imposed by DOS filesystems.}.
12926 During startup, @value{GDBN} does the following:
12930 Reads the init file (if any) in your home directory@footnote{On
12931 DOS/Windows systems, the home directory is the one pointed to by the
12932 @code{HOME} environment variable.}.
12935 Processes command line options and operands.
12938 Reads the init file (if any) in the current working directory.
12941 Reads command files specified by the @samp{-x} option.
12944 The init file in your home directory can set options (such as @samp{set
12945 complaints}) that affect subsequent processing of command line options
12946 and operands. Init files are not executed if you use the @samp{-nx}
12947 option (@pxref{Mode Options, ,Choosing modes}).
12949 @cindex init file name
12950 On some configurations of @value{GDBN}, the init file is known by a
12951 different name (these are typically environments where a specialized
12952 form of @value{GDBN} may need to coexist with other forms, hence a
12953 different name for the specialized version's init file). These are the
12954 environments with special init file names:
12956 @cindex @file{.vxgdbinit}
12959 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12961 @cindex @file{.os68gdbinit}
12963 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12965 @cindex @file{.esgdbinit}
12967 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12970 You can also request the execution of a command file with the
12971 @code{source} command:
12975 @item source @var{filename}
12976 Execute the command file @var{filename}.
12979 The lines in a command file are executed sequentially. They are not
12980 printed as they are executed. An error in any command terminates
12981 execution of the command file and control is returned to the console.
12983 Commands that would ask for confirmation if used interactively proceed
12984 without asking when used in a command file. Many @value{GDBN} commands that
12985 normally print messages to say what they are doing omit the messages
12986 when called from command files.
12988 @value{GDBN} also accepts command input from standard input. In this
12989 mode, normal output goes to standard output and error output goes to
12990 standard error. Errors in a command file supplied on standard input do
12991 not terminate execution of the command file --- execution continues with
12995 gdb < cmds > log 2>&1
12998 (The syntax above will vary depending on the shell used.) This example
12999 will execute commands from the file @file{cmds}. All output and errors
13000 would be directed to @file{log}.
13003 @section Commands for controlled output
13005 During the execution of a command file or a user-defined command, normal
13006 @value{GDBN} output is suppressed; the only output that appears is what is
13007 explicitly printed by the commands in the definition. This section
13008 describes three commands useful for generating exactly the output you
13013 @item echo @var{text}
13014 @c I do not consider backslash-space a standard C escape sequence
13015 @c because it is not in ANSI.
13016 Print @var{text}. Nonprinting characters can be included in
13017 @var{text} using C escape sequences, such as @samp{\n} to print a
13018 newline. @strong{No newline is printed unless you specify one.}
13019 In addition to the standard C escape sequences, a backslash followed
13020 by a space stands for a space. This is useful for displaying a
13021 string with spaces at the beginning or the end, since leading and
13022 trailing spaces are otherwise trimmed from all arguments.
13023 To print @samp{@w{ }and foo =@w{ }}, use the command
13024 @samp{echo \@w{ }and foo = \@w{ }}.
13026 A backslash at the end of @var{text} can be used, as in C, to continue
13027 the command onto subsequent lines. For example,
13030 echo This is some text\n\
13031 which is continued\n\
13032 onto several lines.\n
13035 produces the same output as
13038 echo This is some text\n
13039 echo which is continued\n
13040 echo onto several lines.\n
13044 @item output @var{expression}
13045 Print the value of @var{expression} and nothing but that value: no
13046 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13047 value history either. @xref{Expressions, ,Expressions}, for more information
13050 @item output/@var{fmt} @var{expression}
13051 Print the value of @var{expression} in format @var{fmt}. You can use
13052 the same formats as for @code{print}. @xref{Output Formats,,Output
13053 formats}, for more information.
13056 @item printf @var{string}, @var{expressions}@dots{}
13057 Print the values of the @var{expressions} under the control of
13058 @var{string}. The @var{expressions} are separated by commas and may be
13059 either numbers or pointers. Their values are printed as specified by
13060 @var{string}, exactly as if your program were to execute the C
13062 @c FIXME: the above implies that at least all ANSI C formats are
13063 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13064 @c Either this is a bug, or the manual should document what formats are
13068 printf (@var{string}, @var{expressions}@dots{});
13071 For example, you can print two values in hex like this:
13074 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13077 The only backslash-escape sequences that you can use in the format
13078 string are the simple ones that consist of backslash followed by a
13083 @chapter @value{GDBN} Text User Interface
13087 * TUI Overview:: TUI overview
13088 * TUI Keys:: TUI key bindings
13089 * TUI Commands:: TUI specific commands
13090 * TUI Configuration:: TUI configuration variables
13093 The @value{GDBN} Text User Interface, TUI in short,
13094 is a terminal interface which uses the @code{curses} library
13095 to show the source file, the assembly output, the program registers
13096 and @value{GDBN} commands in separate text windows.
13097 The TUI is available only when @value{GDBN} is configured
13098 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13101 @section TUI overview
13103 The TUI has two display modes that can be switched while
13108 A curses (or TUI) mode in which it displays several text
13109 windows on the terminal.
13112 A standard mode which corresponds to the @value{GDBN} configured without
13116 In the TUI mode, @value{GDBN} can display several text window
13121 This window is the @value{GDBN} command window with the @value{GDBN}
13122 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13123 managed using readline but through the TUI. The @emph{command}
13124 window is always visible.
13127 The source window shows the source file of the program. The current
13128 line as well as active breakpoints are displayed in this window.
13129 The current program position is shown with the @samp{>} marker and
13130 active breakpoints are shown with @samp{*} markers.
13133 The assembly window shows the disassembly output of the program.
13136 This window shows the processor registers. It detects when
13137 a register is changed and when this is the case, registers that have
13138 changed are highlighted.
13142 The source, assembly and register windows are attached to the thread
13143 and the frame position. They are updated when the current thread
13144 changes, when the frame changes or when the program counter changes.
13145 These three windows are arranged by the TUI according to several
13146 layouts. The layout defines which of these three windows are visible.
13147 The following layouts are available:
13157 source and assembly
13160 source and registers
13163 assembly and registers
13168 @section TUI Key Bindings
13169 @cindex TUI key bindings
13171 The TUI installs several key bindings in the readline keymaps
13172 (@pxref{Command Line Editing}).
13173 They allow to leave or enter in the TUI mode or they operate
13174 directly on the TUI layout and windows. The following key bindings
13175 are installed for both TUI mode and the @value{GDBN} standard mode.
13184 Enter or leave the TUI mode. When the TUI mode is left,
13185 the curses window management is left and @value{GDBN} operates using
13186 its standard mode writing on the terminal directly. When the TUI
13187 mode is entered, the control is given back to the curses windows.
13188 The screen is then refreshed.
13192 Use a TUI layout with only one window. The layout will
13193 either be @samp{source} or @samp{assembly}. When the TUI mode
13194 is not active, it will switch to the TUI mode.
13196 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13200 Use a TUI layout with at least two windows. When the current
13201 layout shows already two windows, a next layout with two windows is used.
13202 When a new layout is chosen, one window will always be common to the
13203 previous layout and the new one.
13205 Think of it as the Emacs @kbd{C-x 2} binding.
13209 The following key bindings are handled only by the TUI mode:
13214 Scroll the active window one page up.
13218 Scroll the active window one page down.
13222 Scroll the active window one line up.
13226 Scroll the active window one line down.
13230 Scroll the active window one column left.
13234 Scroll the active window one column right.
13238 Refresh the screen.
13242 In the TUI mode, the arrow keys are used by the active window
13243 for scrolling. This means they are not available for readline. It is
13244 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13245 @key{C-b} and @key{C-f}.
13248 @section TUI specific commands
13249 @cindex TUI commands
13251 The TUI has specific commands to control the text windows.
13252 These commands are always available, that is they do not depend on
13253 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13254 is in the standard mode, using these commands will automatically switch
13259 @kindex layout next
13260 Display the next layout.
13263 @kindex layout prev
13264 Display the previous layout.
13268 Display the source window only.
13272 Display the assembly window only.
13275 @kindex layout split
13276 Display the source and assembly window.
13279 @kindex layout regs
13280 Display the register window together with the source or assembly window.
13282 @item focus next | prev | src | asm | regs | split
13284 Set the focus to the named window.
13285 This command allows to change the active window so that scrolling keys
13286 can be affected to another window.
13290 Refresh the screen. This is similar to using @key{C-L} key.
13294 Update the source window and the current execution point.
13296 @item winheight @var{name} +@var{count}
13297 @itemx winheight @var{name} -@var{count}
13299 Change the height of the window @var{name} by @var{count}
13300 lines. Positive counts increase the height, while negative counts
13305 @node TUI Configuration
13306 @section TUI configuration variables
13307 @cindex TUI configuration variables
13309 The TUI has several configuration variables that control the
13310 appearance of windows on the terminal.
13313 @item set tui border-kind @var{kind}
13314 @kindex set tui border-kind
13315 Select the border appearance for the source, assembly and register windows.
13316 The possible values are the following:
13319 Use a space character to draw the border.
13322 Use ascii characters + - and | to draw the border.
13325 Use the Alternate Character Set to draw the border. The border is
13326 drawn using character line graphics if the terminal supports them.
13330 @item set tui active-border-mode @var{mode}
13331 @kindex set tui active-border-mode
13332 Select the attributes to display the border of the active window.
13333 The possible values are @code{normal}, @code{standout}, @code{reverse},
13334 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13336 @item set tui border-mode @var{mode}
13337 @kindex set tui border-mode
13338 Select the attributes to display the border of other windows.
13339 The @var{mode} can be one of the following:
13342 Use normal attributes to display the border.
13348 Use reverse video mode.
13351 Use half bright mode.
13353 @item half-standout
13354 Use half bright and standout mode.
13357 Use extra bright or bold mode.
13359 @item bold-standout
13360 Use extra bright or bold and standout mode.
13367 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13370 @cindex @sc{gnu} Emacs
13371 A special interface allows you to use @sc{gnu} Emacs to view (and
13372 edit) the source files for the program you are debugging with
13375 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13376 executable file you want to debug as an argument. This command starts
13377 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13378 created Emacs buffer.
13379 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13381 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13386 All ``terminal'' input and output goes through the Emacs buffer.
13389 This applies both to @value{GDBN} commands and their output, and to the input
13390 and output done by the program you are debugging.
13392 This is useful because it means that you can copy the text of previous
13393 commands and input them again; you can even use parts of the output
13396 All the facilities of Emacs' Shell mode are available for interacting
13397 with your program. In particular, you can send signals the usual
13398 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13403 @value{GDBN} displays source code through Emacs.
13406 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13407 source file for that frame and puts an arrow (@samp{=>}) at the
13408 left margin of the current line. Emacs uses a separate buffer for
13409 source display, and splits the screen to show both your @value{GDBN} session
13412 Explicit @value{GDBN} @code{list} or search commands still produce output as
13413 usual, but you probably have no reason to use them from Emacs.
13416 @emph{Warning:} If the directory where your program resides is not your
13417 current directory, it can be easy to confuse Emacs about the location of
13418 the source files, in which case the auxiliary display buffer does not
13419 appear to show your source. @value{GDBN} can find programs by searching your
13420 environment's @code{PATH} variable, so the @value{GDBN} input and output
13421 session proceeds normally; but Emacs does not get enough information
13422 back from @value{GDBN} to locate the source files in this situation. To
13423 avoid this problem, either start @value{GDBN} mode from the directory where
13424 your program resides, or specify an absolute file name when prompted for the
13425 @kbd{M-x gdb} argument.
13427 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13428 switch to debugging a program in some other location, from an existing
13429 @value{GDBN} buffer in Emacs.
13432 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13433 you need to call @value{GDBN} by a different name (for example, if you keep
13434 several configurations around, with different names) you can set the
13435 Emacs variable @code{gdb-command-name}; for example,
13438 (setq gdb-command-name "mygdb")
13442 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13443 in your @file{.emacs} file) makes Emacs call the program named
13444 ``@code{mygdb}'' instead.
13446 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13447 addition to the standard Shell mode commands:
13451 Describe the features of Emacs' @value{GDBN} Mode.
13454 Execute to another source line, like the @value{GDBN} @code{step} command; also
13455 update the display window to show the current file and location.
13458 Execute to next source line in this function, skipping all function
13459 calls, like the @value{GDBN} @code{next} command. Then update the display window
13460 to show the current file and location.
13463 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13464 display window accordingly.
13466 @item M-x gdb-nexti
13467 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13468 display window accordingly.
13471 Execute until exit from the selected stack frame, like the @value{GDBN}
13472 @code{finish} command.
13475 Continue execution of your program, like the @value{GDBN} @code{continue}
13478 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13481 Go up the number of frames indicated by the numeric argument
13482 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13483 like the @value{GDBN} @code{up} command.
13485 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13488 Go down the number of frames indicated by the numeric argument, like the
13489 @value{GDBN} @code{down} command.
13491 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13494 Read the number where the cursor is positioned, and insert it at the end
13495 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13496 around an address that was displayed earlier, type @kbd{disassemble};
13497 then move the cursor to the address display, and pick up the
13498 argument for @code{disassemble} by typing @kbd{C-x &}.
13500 You can customize this further by defining elements of the list
13501 @code{gdb-print-command}; once it is defined, you can format or
13502 otherwise process numbers picked up by @kbd{C-x &} before they are
13503 inserted. A numeric argument to @kbd{C-x &} indicates that you
13504 wish special formatting, and also acts as an index to pick an element of the
13505 list. If the list element is a string, the number to be inserted is
13506 formatted using the Emacs function @code{format}; otherwise the number
13507 is passed as an argument to the corresponding list element.
13510 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13511 tells @value{GDBN} to set a breakpoint on the source line point is on.
13513 If you accidentally delete the source-display buffer, an easy way to get
13514 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13515 request a frame display; when you run under Emacs, this recreates
13516 the source buffer if necessary to show you the context of the current
13519 The source files displayed in Emacs are in ordinary Emacs buffers
13520 which are visiting the source files in the usual way. You can edit
13521 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13522 communicates with Emacs in terms of line numbers. If you add or
13523 delete lines from the text, the line numbers that @value{GDBN} knows cease
13524 to correspond properly with the code.
13526 @c The following dropped because Epoch is nonstandard. Reactivate
13527 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13529 @kindex Emacs Epoch environment
13533 Version 18 of @sc{gnu} Emacs has a built-in window system
13534 called the @code{epoch}
13535 environment. Users of this environment can use a new command,
13536 @code{inspect} which performs identically to @code{print} except that
13537 each value is printed in its own window.
13540 @include annotate.texi
13541 @include gdbmi.texinfo
13544 @chapter Reporting Bugs in @value{GDBN}
13545 @cindex bugs in @value{GDBN}
13546 @cindex reporting bugs in @value{GDBN}
13548 Your bug reports play an essential role in making @value{GDBN} reliable.
13550 Reporting a bug may help you by bringing a solution to your problem, or it
13551 may not. But in any case the principal function of a bug report is to help
13552 the entire community by making the next version of @value{GDBN} work better. Bug
13553 reports are your contribution to the maintenance of @value{GDBN}.
13555 In order for a bug report to serve its purpose, you must include the
13556 information that enables us to fix the bug.
13559 * Bug Criteria:: Have you found a bug?
13560 * Bug Reporting:: How to report bugs
13564 @section Have you found a bug?
13565 @cindex bug criteria
13567 If you are not sure whether you have found a bug, here are some guidelines:
13570 @cindex fatal signal
13571 @cindex debugger crash
13572 @cindex crash of debugger
13574 If the debugger gets a fatal signal, for any input whatever, that is a
13575 @value{GDBN} bug. Reliable debuggers never crash.
13577 @cindex error on valid input
13579 If @value{GDBN} produces an error message for valid input, that is a
13580 bug. (Note that if you're cross debugging, the problem may also be
13581 somewhere in the connection to the target.)
13583 @cindex invalid input
13585 If @value{GDBN} does not produce an error message for invalid input,
13586 that is a bug. However, you should note that your idea of
13587 ``invalid input'' might be our idea of ``an extension'' or ``support
13588 for traditional practice''.
13591 If you are an experienced user of debugging tools, your suggestions
13592 for improvement of @value{GDBN} are welcome in any case.
13595 @node Bug Reporting
13596 @section How to report bugs
13597 @cindex bug reports
13598 @cindex @value{GDBN} bugs, reporting
13600 A number of companies and individuals offer support for @sc{gnu} products.
13601 If you obtained @value{GDBN} from a support organization, we recommend you
13602 contact that organization first.
13604 You can find contact information for many support companies and
13605 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13607 @c should add a web page ref...
13609 In any event, we also recommend that you submit bug reports for
13610 @value{GDBN}. The prefered method is to submit them directly using
13611 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13612 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13615 @strong{Do not send bug reports to @samp{info-gdb}, or to
13616 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13617 not want to receive bug reports. Those that do have arranged to receive
13620 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13621 serves as a repeater. The mailing list and the newsgroup carry exactly
13622 the same messages. Often people think of posting bug reports to the
13623 newsgroup instead of mailing them. This appears to work, but it has one
13624 problem which can be crucial: a newsgroup posting often lacks a mail
13625 path back to the sender. Thus, if we need to ask for more information,
13626 we may be unable to reach you. For this reason, it is better to send
13627 bug reports to the mailing list.
13629 The fundamental principle of reporting bugs usefully is this:
13630 @strong{report all the facts}. If you are not sure whether to state a
13631 fact or leave it out, state it!
13633 Often people omit facts because they think they know what causes the
13634 problem and assume that some details do not matter. Thus, you might
13635 assume that the name of the variable you use in an example does not matter.
13636 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13637 stray memory reference which happens to fetch from the location where that
13638 name is stored in memory; perhaps, if the name were different, the contents
13639 of that location would fool the debugger into doing the right thing despite
13640 the bug. Play it safe and give a specific, complete example. That is the
13641 easiest thing for you to do, and the most helpful.
13643 Keep in mind that the purpose of a bug report is to enable us to fix the
13644 bug. It may be that the bug has been reported previously, but neither
13645 you nor we can know that unless your bug report is complete and
13648 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13649 bell?'' Those bug reports are useless, and we urge everyone to
13650 @emph{refuse to respond to them} except to chide the sender to report
13653 To enable us to fix the bug, you should include all these things:
13657 The version of @value{GDBN}. @value{GDBN} announces it if you start
13658 with no arguments; you can also print it at any time using @code{show
13661 Without this, we will not know whether there is any point in looking for
13662 the bug in the current version of @value{GDBN}.
13665 The type of machine you are using, and the operating system name and
13669 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13670 ``@value{GCC}--2.8.1''.
13673 What compiler (and its version) was used to compile the program you are
13674 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13675 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13676 information; for other compilers, see the documentation for those
13680 The command arguments you gave the compiler to compile your example and
13681 observe the bug. For example, did you use @samp{-O}? To guarantee
13682 you will not omit something important, list them all. A copy of the
13683 Makefile (or the output from make) is sufficient.
13685 If we were to try to guess the arguments, we would probably guess wrong
13686 and then we might not encounter the bug.
13689 A complete input script, and all necessary source files, that will
13693 A description of what behavior you observe that you believe is
13694 incorrect. For example, ``It gets a fatal signal.''
13696 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13697 will certainly notice it. But if the bug is incorrect output, we might
13698 not notice unless it is glaringly wrong. You might as well not give us
13699 a chance to make a mistake.
13701 Even if the problem you experience is a fatal signal, you should still
13702 say so explicitly. Suppose something strange is going on, such as, your
13703 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13704 the C library on your system. (This has happened!) Your copy might
13705 crash and ours would not. If you told us to expect a crash, then when
13706 ours fails to crash, we would know that the bug was not happening for
13707 us. If you had not told us to expect a crash, then we would not be able
13708 to draw any conclusion from our observations.
13711 If you wish to suggest changes to the @value{GDBN} source, send us context
13712 diffs. If you even discuss something in the @value{GDBN} source, refer to
13713 it by context, not by line number.
13715 The line numbers in our development sources will not match those in your
13716 sources. Your line numbers would convey no useful information to us.
13720 Here are some things that are not necessary:
13724 A description of the envelope of the bug.
13726 Often people who encounter a bug spend a lot of time investigating
13727 which changes to the input file will make the bug go away and which
13728 changes will not affect it.
13730 This is often time consuming and not very useful, because the way we
13731 will find the bug is by running a single example under the debugger
13732 with breakpoints, not by pure deduction from a series of examples.
13733 We recommend that you save your time for something else.
13735 Of course, if you can find a simpler example to report @emph{instead}
13736 of the original one, that is a convenience for us. Errors in the
13737 output will be easier to spot, running under the debugger will take
13738 less time, and so on.
13740 However, simplification is not vital; if you do not want to do this,
13741 report the bug anyway and send us the entire test case you used.
13744 A patch for the bug.
13746 A patch for the bug does help us if it is a good one. But do not omit
13747 the necessary information, such as the test case, on the assumption that
13748 a patch is all we need. We might see problems with your patch and decide
13749 to fix the problem another way, or we might not understand it at all.
13751 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13752 construct an example that will make the program follow a certain path
13753 through the code. If you do not send us the example, we will not be able
13754 to construct one, so we will not be able to verify that the bug is fixed.
13756 And if we cannot understand what bug you are trying to fix, or why your
13757 patch should be an improvement, we will not install it. A test case will
13758 help us to understand.
13761 A guess about what the bug is or what it depends on.
13763 Such guesses are usually wrong. Even we cannot guess right about such
13764 things without first using the debugger to find the facts.
13767 @c The readline documentation is distributed with the readline code
13768 @c and consists of the two following files:
13770 @c inc-hist.texinfo
13771 @c Use -I with makeinfo to point to the appropriate directory,
13772 @c environment var TEXINPUTS with TeX.
13773 @include rluser.texinfo
13774 @include inc-hist.texinfo
13777 @node Formatting Documentation
13778 @appendix Formatting Documentation
13780 @cindex @value{GDBN} reference card
13781 @cindex reference card
13782 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13783 for printing with PostScript or Ghostscript, in the @file{gdb}
13784 subdirectory of the main source directory@footnote{In
13785 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13786 release.}. If you can use PostScript or Ghostscript with your printer,
13787 you can print the reference card immediately with @file{refcard.ps}.
13789 The release also includes the source for the reference card. You
13790 can format it, using @TeX{}, by typing:
13796 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13797 mode on US ``letter'' size paper;
13798 that is, on a sheet 11 inches wide by 8.5 inches
13799 high. You will need to specify this form of printing as an option to
13800 your @sc{dvi} output program.
13802 @cindex documentation
13804 All the documentation for @value{GDBN} comes as part of the machine-readable
13805 distribution. The documentation is written in Texinfo format, which is
13806 a documentation system that uses a single source file to produce both
13807 on-line information and a printed manual. You can use one of the Info
13808 formatting commands to create the on-line version of the documentation
13809 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13811 @value{GDBN} includes an already formatted copy of the on-line Info
13812 version of this manual in the @file{gdb} subdirectory. The main Info
13813 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13814 subordinate files matching @samp{gdb.info*} in the same directory. If
13815 necessary, you can print out these files, or read them with any editor;
13816 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13817 Emacs or the standalone @code{info} program, available as part of the
13818 @sc{gnu} Texinfo distribution.
13820 If you want to format these Info files yourself, you need one of the
13821 Info formatting programs, such as @code{texinfo-format-buffer} or
13824 If you have @code{makeinfo} installed, and are in the top level
13825 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13826 version @value{GDBVN}), you can make the Info file by typing:
13833 If you want to typeset and print copies of this manual, you need @TeX{},
13834 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13835 Texinfo definitions file.
13837 @TeX{} is a typesetting program; it does not print files directly, but
13838 produces output files called @sc{dvi} files. To print a typeset
13839 document, you need a program to print @sc{dvi} files. If your system
13840 has @TeX{} installed, chances are it has such a program. The precise
13841 command to use depends on your system; @kbd{lpr -d} is common; another
13842 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13843 require a file name without any extension or a @samp{.dvi} extension.
13845 @TeX{} also requires a macro definitions file called
13846 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13847 written in Texinfo format. On its own, @TeX{} cannot either read or
13848 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13849 and is located in the @file{gdb-@var{version-number}/texinfo}
13852 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13853 typeset and print this manual. First switch to the the @file{gdb}
13854 subdirectory of the main source directory (for example, to
13855 @file{gdb-@value{GDBVN}/gdb}) and type:
13861 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
13863 @node Installing GDB
13864 @appendix Installing @value{GDBN}
13865 @cindex configuring @value{GDBN}
13866 @cindex installation
13868 @value{GDBN} comes with a @code{configure} script that automates the process
13869 of preparing @value{GDBN} for installation; you can then use @code{make} to
13870 build the @code{gdb} program.
13872 @c irrelevant in info file; it's as current as the code it lives with.
13873 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
13874 look at the @file{README} file in the sources; we may have improved the
13875 installation procedures since publishing this manual.}
13878 The @value{GDBN} distribution includes all the source code you need for
13879 @value{GDBN} in a single directory, whose name is usually composed by
13880 appending the version number to @samp{gdb}.
13882 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
13883 @file{gdb-@value{GDBVN}} directory. That directory contains:
13886 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
13887 script for configuring @value{GDBN} and all its supporting libraries
13889 @item gdb-@value{GDBVN}/gdb
13890 the source specific to @value{GDBN} itself
13892 @item gdb-@value{GDBVN}/bfd
13893 source for the Binary File Descriptor library
13895 @item gdb-@value{GDBVN}/include
13896 @sc{gnu} include files
13898 @item gdb-@value{GDBVN}/libiberty
13899 source for the @samp{-liberty} free software library
13901 @item gdb-@value{GDBVN}/opcodes
13902 source for the library of opcode tables and disassemblers
13904 @item gdb-@value{GDBVN}/readline
13905 source for the @sc{gnu} command-line interface
13907 @item gdb-@value{GDBVN}/glob
13908 source for the @sc{gnu} filename pattern-matching subroutine
13910 @item gdb-@value{GDBVN}/mmalloc
13911 source for the @sc{gnu} memory-mapped malloc package
13914 The simplest way to configure and build @value{GDBN} is to run @code{configure}
13915 from the @file{gdb-@var{version-number}} source directory, which in
13916 this example is the @file{gdb-@value{GDBVN}} directory.
13918 First switch to the @file{gdb-@var{version-number}} source directory
13919 if you are not already in it; then run @code{configure}. Pass the
13920 identifier for the platform on which @value{GDBN} will run as an
13926 cd gdb-@value{GDBVN}
13927 ./configure @var{host}
13932 where @var{host} is an identifier such as @samp{sun4} or
13933 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
13934 (You can often leave off @var{host}; @code{configure} tries to guess the
13935 correct value by examining your system.)
13937 Running @samp{configure @var{host}} and then running @code{make} builds the
13938 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
13939 libraries, then @code{gdb} itself. The configured source files, and the
13940 binaries, are left in the corresponding source directories.
13943 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
13944 system does not recognize this automatically when you run a different
13945 shell, you may need to run @code{sh} on it explicitly:
13948 sh configure @var{host}
13951 If you run @code{configure} from a directory that contains source
13952 directories for multiple libraries or programs, such as the
13953 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
13954 creates configuration files for every directory level underneath (unless
13955 you tell it not to, with the @samp{--norecursion} option).
13957 You can run the @code{configure} script from any of the
13958 subordinate directories in the @value{GDBN} distribution if you only want to
13959 configure that subdirectory, but be sure to specify a path to it.
13961 For example, with version @value{GDBVN}, type the following to configure only
13962 the @code{bfd} subdirectory:
13966 cd gdb-@value{GDBVN}/bfd
13967 ../configure @var{host}
13971 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
13972 However, you should make sure that the shell on your path (named by
13973 the @samp{SHELL} environment variable) is publicly readable. Remember
13974 that @value{GDBN} uses the shell to start your program---some systems refuse to
13975 let @value{GDBN} debug child processes whose programs are not readable.
13978 * Separate Objdir:: Compiling @value{GDBN} in another directory
13979 * Config Names:: Specifying names for hosts and targets
13980 * Configure Options:: Summary of options for configure
13983 @node Separate Objdir
13984 @section Compiling @value{GDBN} in another directory
13986 If you want to run @value{GDBN} versions for several host or target machines,
13987 you need a different @code{gdb} compiled for each combination of
13988 host and target. @code{configure} is designed to make this easy by
13989 allowing you to generate each configuration in a separate subdirectory,
13990 rather than in the source directory. If your @code{make} program
13991 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
13992 @code{make} in each of these directories builds the @code{gdb}
13993 program specified there.
13995 To build @code{gdb} in a separate directory, run @code{configure}
13996 with the @samp{--srcdir} option to specify where to find the source.
13997 (You also need to specify a path to find @code{configure}
13998 itself from your working directory. If the path to @code{configure}
13999 would be the same as the argument to @samp{--srcdir}, you can leave out
14000 the @samp{--srcdir} option; it is assumed.)
14002 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14003 separate directory for a Sun 4 like this:
14007 cd gdb-@value{GDBVN}
14010 ../gdb-@value{GDBVN}/configure sun4
14015 When @code{configure} builds a configuration using a remote source
14016 directory, it creates a tree for the binaries with the same structure
14017 (and using the same names) as the tree under the source directory. In
14018 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14019 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14020 @file{gdb-sun4/gdb}.
14022 One popular reason to build several @value{GDBN} configurations in separate
14023 directories is to configure @value{GDBN} for cross-compiling (where
14024 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14025 programs that run on another machine---the @dfn{target}).
14026 You specify a cross-debugging target by
14027 giving the @samp{--target=@var{target}} option to @code{configure}.
14029 When you run @code{make} to build a program or library, you must run
14030 it in a configured directory---whatever directory you were in when you
14031 called @code{configure} (or one of its subdirectories).
14033 The @code{Makefile} that @code{configure} generates in each source
14034 directory also runs recursively. If you type @code{make} in a source
14035 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14036 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14037 will build all the required libraries, and then build GDB.
14039 When you have multiple hosts or targets configured in separate
14040 directories, you can run @code{make} on them in parallel (for example,
14041 if they are NFS-mounted on each of the hosts); they will not interfere
14045 @section Specifying names for hosts and targets
14047 The specifications used for hosts and targets in the @code{configure}
14048 script are based on a three-part naming scheme, but some short predefined
14049 aliases are also supported. The full naming scheme encodes three pieces
14050 of information in the following pattern:
14053 @var{architecture}-@var{vendor}-@var{os}
14056 For example, you can use the alias @code{sun4} as a @var{host} argument,
14057 or as the value for @var{target} in a @code{--target=@var{target}}
14058 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14060 The @code{configure} script accompanying @value{GDBN} does not provide
14061 any query facility to list all supported host and target names or
14062 aliases. @code{configure} calls the Bourne shell script
14063 @code{config.sub} to map abbreviations to full names; you can read the
14064 script, if you wish, or you can use it to test your guesses on
14065 abbreviations---for example:
14068 % sh config.sub i386-linux
14070 % sh config.sub alpha-linux
14071 alpha-unknown-linux-gnu
14072 % sh config.sub hp9k700
14074 % sh config.sub sun4
14075 sparc-sun-sunos4.1.1
14076 % sh config.sub sun3
14077 m68k-sun-sunos4.1.1
14078 % sh config.sub i986v
14079 Invalid configuration `i986v': machine `i986v' not recognized
14083 @code{config.sub} is also distributed in the @value{GDBN} source
14084 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14086 @node Configure Options
14087 @section @code{configure} options
14089 Here is a summary of the @code{configure} options and arguments that
14090 are most often useful for building @value{GDBN}. @code{configure} also has
14091 several other options not listed here. @inforef{What Configure
14092 Does,,configure.info}, for a full explanation of @code{configure}.
14095 configure @r{[}--help@r{]}
14096 @r{[}--prefix=@var{dir}@r{]}
14097 @r{[}--exec-prefix=@var{dir}@r{]}
14098 @r{[}--srcdir=@var{dirname}@r{]}
14099 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14100 @r{[}--target=@var{target}@r{]}
14105 You may introduce options with a single @samp{-} rather than
14106 @samp{--} if you prefer; but you may abbreviate option names if you use
14111 Display a quick summary of how to invoke @code{configure}.
14113 @item --prefix=@var{dir}
14114 Configure the source to install programs and files under directory
14117 @item --exec-prefix=@var{dir}
14118 Configure the source to install programs under directory
14121 @c avoid splitting the warning from the explanation:
14123 @item --srcdir=@var{dirname}
14124 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14125 @code{make} that implements the @code{VPATH} feature.}@*
14126 Use this option to make configurations in directories separate from the
14127 @value{GDBN} source directories. Among other things, you can use this to
14128 build (or maintain) several configurations simultaneously, in separate
14129 directories. @code{configure} writes configuration specific files in
14130 the current directory, but arranges for them to use the source in the
14131 directory @var{dirname}. @code{configure} creates directories under
14132 the working directory in parallel to the source directories below
14135 @item --norecursion
14136 Configure only the directory level where @code{configure} is executed; do not
14137 propagate configuration to subdirectories.
14139 @item --target=@var{target}
14140 Configure @value{GDBN} for cross-debugging programs running on the specified
14141 @var{target}. Without this option, @value{GDBN} is configured to debug
14142 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14144 There is no convenient way to generate a list of all available targets.
14146 @item @var{host} @dots{}
14147 Configure @value{GDBN} to run on the specified @var{host}.
14149 There is no convenient way to generate a list of all available hosts.
14152 There are many other options available as well, but they are generally
14153 needed for special purposes only.
14155 @node Maintenance Commands
14156 @appendix Maintenance Commands
14157 @cindex maintenance commands
14158 @cindex internal commands
14160 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14161 includes a number of commands intended for @value{GDBN} developers.
14162 These commands are provided here for reference.
14165 @kindex maint info breakpoints
14166 @item @anchor{maint info breakpoints}maint info breakpoints
14167 Using the same format as @samp{info breakpoints}, display both the
14168 breakpoints you've set explicitly, and those @value{GDBN} is using for
14169 internal purposes. Internal breakpoints are shown with negative
14170 breakpoint numbers. The type column identifies what kind of breakpoint
14175 Normal, explicitly set breakpoint.
14178 Normal, explicitly set watchpoint.
14181 Internal breakpoint, used to handle correctly stepping through
14182 @code{longjmp} calls.
14184 @item longjmp resume
14185 Internal breakpoint at the target of a @code{longjmp}.
14188 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14191 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14194 Shared library events.
14198 @kindex maint print registers
14199 @kindex maint print raw-registers
14200 @kindex maint print cooked-registers
14201 @item @anchor{maint print registers}maint print registers
14202 @itemx @anchor{maint print raw-registers}maint print raw-registers
14203 @itemx @anchor{maint print cooked-registers}maint print cooked-registers
14204 Print @value{GDBN}'s internal register structure. @samp{maint print
14205 raw-registers} includes the raw register cache value while @samp{maint
14206 print cooked-registers} includes the cooked register value.
14208 Takes an optional file parameter.
14213 @node Remote Protocol
14214 @appendix @value{GDBN} Remote Serial Protocol
14216 There may be occasions when you need to know something about the
14217 protocol---for example, if there is only one serial port to your target
14218 machine, you might want your program to do something special if it
14219 recognizes a packet meant for @value{GDBN}.
14221 In the examples below, @samp{<-} and @samp{->} are used to indicate
14222 transmitted and received data respectfully.
14224 @cindex protocol, @value{GDBN} remote serial
14225 @cindex serial protocol, @value{GDBN} remote
14226 @cindex remote serial protocol
14227 All @value{GDBN} commands and responses (other than acknowledgments) are
14228 sent as a @var{packet}. A @var{packet} is introduced with the character
14229 @samp{$}, the actual @var{packet-data}, and the terminating character
14230 @samp{#} followed by a two-digit @var{checksum}:
14233 @code{$}@var{packet-data}@code{#}@var{checksum}
14237 @cindex checksum, for @value{GDBN} remote
14239 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14240 characters between the leading @samp{$} and the trailing @samp{#} (an
14241 eight bit unsigned checksum).
14243 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14244 specification also included an optional two-digit @var{sequence-id}:
14247 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14250 @cindex sequence-id, for @value{GDBN} remote
14252 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14253 has never output @var{sequence-id}s. Stubs that handle packets added
14254 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14256 @cindex acknowledgment, for @value{GDBN} remote
14257 When either the host or the target machine receives a packet, the first
14258 response expected is an acknowledgment: either @samp{+} (to indicate
14259 the package was received correctly) or @samp{-} (to request
14263 <- @code{$}@var{packet-data}@code{#}@var{checksum}
14268 The host (@value{GDBN}) sends @var{command}s, and the target (the
14269 debugging stub incorporated in your program) sends a @var{response}. In
14270 the case of step and continue @var{command}s, the response is only sent
14271 when the operation has completed (the target has again stopped).
14273 @var{packet-data} consists of a sequence of characters with the
14274 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14277 Fields within the packet should be separated using @samp{,} @samp{;} or
14278 @samp{:}. Except where otherwise noted all numbers are represented in
14279 HEX with leading zeros suppressed.
14281 Implementors should note that prior to @value{GDBN} 5.0, the character
14282 @samp{:} could not appear as the third character in a packet (as it
14283 would potentially conflict with the @var{sequence-id}).
14285 Response @var{data} can be run-length encoded to save space. A @samp{*}
14286 means that the next character is an @sc{ascii} encoding giving a repeat count
14287 which stands for that many repetitions of the character preceding the
14288 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14289 where @code{n >=3} (which is where rle starts to win). The printable
14290 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14291 value greater than 126 should not be used.
14293 Some remote systems have used a different run-length encoding mechanism
14294 loosely refered to as the cisco encoding. Following the @samp{*}
14295 character are two hex digits that indicate the size of the packet.
14302 means the same as "0000".
14304 The error response returned for some packets includes a two character
14305 error number. That number is not well defined.
14307 For any @var{command} not supported by the stub, an empty response
14308 (@samp{$#00}) should be returned. That way it is possible to extend the
14309 protocol. A newer @value{GDBN} can tell if a packet is supported based
14312 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14313 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14316 Below is a complete list of all currently defined @var{command}s and
14317 their corresponding response @var{data}:
14319 @multitable @columnfractions .30 .30 .40
14324 @item extended mode
14327 Enable extended mode. In extended mode, the remote server is made
14328 persistent. The @samp{R} packet is used to restart the program being
14331 @tab reply @samp{OK}
14333 The remote target both supports and has enabled extended mode.
14338 Indicate the reason the target halted. The reply is the same as for step
14347 @tab Reserved for future use
14349 @item set program arguments @strong{(reserved)}
14350 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
14355 Initialized @samp{argv[]} array passed into program. @var{arglen}
14356 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14357 See @file{gdbserver} for more details.
14359 @tab reply @code{OK}
14361 @tab reply @code{E}@var{NN}
14363 @item set baud @strong{(deprecated)}
14364 @tab @code{b}@var{baud}
14366 Change the serial line speed to @var{baud}. JTC: @emph{When does the
14367 transport layer state change? When it's received, or after the ACK is
14368 transmitted. In either case, there are problems if the command or the
14369 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
14370 to add something like this, and get it working for the first time, they
14371 ought to modify ser-unix.c to send some kind of out-of-band message to a
14372 specially-setup stub and have the switch happen "in between" packets, so
14373 that from remote protocol's point of view, nothing actually
14376 @item set breakpoint @strong{(deprecated)}
14377 @tab @code{B}@var{addr},@var{mode}
14379 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14380 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
14384 @tab @code{c}@var{addr}
14386 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14392 @item continue with signal
14393 @tab @code{C}@var{sig}@code{;}@var{addr}
14395 Continue with signal @var{sig} (hex signal number). If
14396 @code{;}@var{addr} is omitted, resume at same address.
14401 @item toggle debug @strong{(deprecated)}
14409 Detach @value{GDBN} from the remote system. Sent to the remote target before
14410 @value{GDBN} disconnects.
14412 @tab reply @emph{no response}
14414 @value{GDBN} does not check for any response after sending this packet.
14418 @tab Reserved for future use
14422 @tab Reserved for future use
14426 @tab Reserved for future use
14430 @tab Reserved for future use
14432 @item read registers
14434 @tab Read general registers.
14436 @tab reply @var{XX...}
14438 Each byte of register data is described by two hex digits. The bytes
14439 with the register are transmitted in target byte order. The size of
14440 each register and their position within the @samp{g} @var{packet} are
14441 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
14442 @var{REGISTER_NAME} macros. The specification of several standard
14443 @code{g} packets is specified below.
14445 @tab @code{E}@var{NN}
14449 @tab @code{G}@var{XX...}
14451 See @samp{g} for a description of the @var{XX...} data.
14453 @tab reply @code{OK}
14456 @tab reply @code{E}@var{NN}
14461 @tab Reserved for future use
14464 @tab @code{H}@var{c}@var{t...}
14466 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14467 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
14468 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
14469 thread used in other operations. If zero, pick a thread, any thread.
14471 @tab reply @code{OK}
14474 @tab reply @code{E}@var{NN}
14478 @c 'H': How restrictive (or permissive) is the thread model. If a
14479 @c thread is selected and stopped, are other threads allowed
14480 @c to continue to execute? As I mentioned above, I think the
14481 @c semantics of each command when a thread is selected must be
14482 @c described. For example:
14484 @c 'g': If the stub supports threads and a specific thread is
14485 @c selected, returns the register block from that thread;
14486 @c otherwise returns current registers.
14488 @c 'G' If the stub supports threads and a specific thread is
14489 @c selected, sets the registers of the register block of
14490 @c that thread; otherwise sets current registers.
14492 @item cycle step @strong{(draft)}
14493 @tab @code{i}@var{addr}@code{,}@var{nnn}
14495 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14496 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14497 step starting at that address.
14499 @item signal then cycle step @strong{(reserved)}
14502 See @samp{i} and @samp{S} for likely syntax and semantics.
14506 @tab Reserved for future use
14510 @tab Reserved for future use
14515 FIXME: @emph{There is no description of how to operate when a specific
14516 thread context has been selected (i.e.@: does 'k' kill only that thread?)}.
14520 @tab Reserved for future use
14524 @tab Reserved for future use
14527 @tab @code{m}@var{addr}@code{,}@var{length}
14529 Read @var{length} bytes of memory starting at address @var{addr}.
14530 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
14531 using word alligned accesses. FIXME: @emph{A word aligned memory
14532 transfer mechanism is needed.}
14534 @tab reply @var{XX...}
14536 @var{XX...} is mem contents. Can be fewer bytes than requested if able
14537 to read only part of the data. Neither @value{GDBN} nor the stub assume that
14538 sized memory transfers are assumed using word alligned accesses. FIXME:
14539 @emph{A word aligned memory transfer mechanism is needed.}
14541 @tab reply @code{E}@var{NN}
14542 @tab @var{NN} is errno
14545 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
14547 Write @var{length} bytes of memory starting at address @var{addr}.
14548 @var{XX...} is the data.
14550 @tab reply @code{OK}
14553 @tab reply @code{E}@var{NN}
14555 for an error (this includes the case where only part of the data was
14560 @tab Reserved for future use
14564 @tab Reserved for future use
14568 @tab Reserved for future use
14572 @tab Reserved for future use
14574 @item read reg @strong{(reserved)}
14575 @tab @code{p}@var{n...}
14577 See write register.
14579 @tab return @var{r....}
14580 @tab The hex encoded value of the register in target byte order.
14583 @tab @code{P}@var{n...}@code{=}@var{r...}
14585 Write register @var{n...} with value @var{r...}, which contains two hex
14586 digits for each byte in the register (target byte order).
14588 @tab reply @code{OK}
14591 @tab reply @code{E}@var{NN}
14594 @item general query
14595 @tab @code{q}@var{query}
14597 Request info about @var{query}. In general @value{GDBN} queries
14598 have a leading upper case letter. Custom vendor queries should use a
14599 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
14600 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
14601 must ensure that they match the full @var{query} name.
14603 @tab reply @code{XX...}
14604 @tab Hex encoded data from query. The reply can not be empty.
14606 @tab reply @code{E}@var{NN}
14610 @tab Indicating an unrecognized @var{query}.
14613 @tab @code{Q}@var{var}@code{=}@var{val}
14615 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
14616 naming conventions.
14618 @item reset @strong{(deprecated)}
14621 Reset the entire system.
14623 @item remote restart
14624 @tab @code{R}@var{XX}
14626 Restart the program being debugged. @var{XX}, while needed, is ignored.
14627 This packet is only available in extended mode.
14632 The @samp{R} packet has no reply.
14635 @tab @code{s}@var{addr}
14637 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14643 @item step with signal
14644 @tab @code{S}@var{sig}@code{;}@var{addr}
14646 Like @samp{C} but step not continue.
14652 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
14654 Search backwards starting at address @var{addr} for a match with pattern
14655 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
14656 bytes. @var{addr} must be at least 3 digits.
14659 @tab @code{T}@var{XX}
14660 @tab Find out if the thread XX is alive.
14662 @tab reply @code{OK}
14663 @tab thread is still alive
14665 @tab reply @code{E}@var{NN}
14666 @tab thread is dead
14670 @tab Reserved for future use
14674 @tab Reserved for future use
14678 @tab Reserved for future use
14682 @tab Reserved for future use
14686 @tab Reserved for future use
14690 @tab Reserved for future use
14694 @tab Reserved for future use
14696 @item write mem (binary)
14697 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
14699 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
14700 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14701 escaped using @code{0x7d}.
14703 @tab reply @code{OK}
14706 @tab reply @code{E}@var{NN}
14711 @tab Reserved for future use
14715 @tab Reserved for future use
14717 @item remove break or watchpoint @strong{(draft)}
14718 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14722 @item insert break or watchpoint @strong{(draft)}
14723 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
14725 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
14726 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
14727 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
14728 bytes. For a software breakpoint, @var{length} specifies the size of
14729 the instruction to be patched. For hardware breakpoints and watchpoints
14730 @var{length} specifies the memory region to be monitored. To avoid
14731 potential problems with duplicate packets, the operations should be
14732 implemented in an idempotent way.
14734 @tab reply @code{E}@var{NN}
14737 @tab reply @code{OK}
14741 @tab If not supported.
14745 @tab Reserved for future use
14749 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
14750 receive any of the below as a reply. In the case of the @samp{C},
14751 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
14752 when the target halts. In the below the exact meaning of @samp{signal
14753 number} is poorly defined. In general one of the UNIX signal numbering
14754 conventions is used.
14756 @multitable @columnfractions .4 .6
14758 @item @code{S}@var{AA}
14759 @tab @var{AA} is the signal number
14761 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
14763 @var{AA} = two hex digit signal number; @var{n...} = register number
14764 (hex), @var{r...} = target byte ordered register contents, size defined
14765 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
14766 thread process ID, this is a hex integer; @var{n...} = (@samp{watch} |
14767 @samp{rwatch} | @samp{awatch}, @var{r...} = data address, this is a hex
14768 integer; @var{n...} = other string not starting with valid hex digit.
14769 @value{GDBN} should ignore this @var{n...}, @var{r...} pair and go on
14770 to the next. This way we can extend the protocol.
14772 @item @code{W}@var{AA}
14774 The process exited, and @var{AA} is the exit status. This is only
14775 applicable for certains sorts of targets.
14777 @item @code{X}@var{AA}
14779 The process terminated with signal @var{AA}.
14781 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
14783 @var{AA} = signal number; @var{t...} = address of symbol "_start";
14784 @var{d...} = base of data section; @var{b...} = base of bss section.
14785 @emph{Note: only used by Cisco Systems targets. The difference between
14786 this reply and the "qOffsets" query is that the 'N' packet may arrive
14787 spontaneously whereas the 'qOffsets' is a query initiated by the host
14790 @item @code{O}@var{XX...}
14792 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
14793 while the program is running and the debugger should continue to wait
14798 The following set and query packets have already been defined.
14800 @multitable @columnfractions .2 .2 .6
14802 @item current thread
14803 @tab @code{q}@code{C}
14804 @tab Return the current thread id.
14806 @tab reply @code{QC}@var{pid}
14808 Where @var{pid} is a HEX encoded 16 bit process id.
14811 @tab Any other reply implies the old pid.
14813 @item all thread ids
14814 @tab @code{q}@code{fThreadInfo}
14816 @tab @code{q}@code{sThreadInfo}
14818 Obtain a list of active thread ids from the target (OS). Since there
14819 may be too many active threads to fit into one reply packet, this query
14820 works iteratively: it may require more than one query/reply sequence to
14821 obtain the entire list of threads. The first query of the sequence will
14822 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
14823 sequence will be the @code{qs}@code{ThreadInfo} query.
14826 @tab NOTE: replaces the @code{qL} query (see below).
14828 @tab reply @code{m}@var{<id>}
14829 @tab A single thread id
14831 @tab reply @code{m}@var{<id>},@var{<id>...}
14832 @tab a comma-separated list of thread ids
14834 @tab reply @code{l}
14835 @tab (lower case 'el') denotes end of list.
14839 In response to each query, the target will reply with a list of one
14840 or more thread ids, in big-endian hex, separated by commas. GDB will
14841 respond to each reply with a request for more thread ids (using the
14842 @code{qs} form of the query), until the target responds with @code{l}
14843 (lower-case el, for @code{'last'}).
14845 @item extra thread info
14846 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
14851 Where @var{<id>} is a thread-id in big-endian hex.
14852 Obtain a printable string description of a thread's attributes from
14853 the target OS. This string may contain anything that the target OS
14854 thinks is interesting for @value{GDBN} to tell the user about the thread.
14855 The string is displayed in @value{GDBN}'s @samp{info threads} display.
14856 Some examples of possible thread extra info strings are "Runnable", or
14857 "Blocked on Mutex".
14859 @tab reply @var{XX...}
14861 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
14862 printable string containing the extra information about the thread's
14865 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
14866 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
14871 Obtain thread information from RTOS. Where: @var{startflag} (one hex
14872 digit) is one to indicate the first query and zero to indicate a
14873 subsequent query; @var{threadcount} (two hex digits) is the maximum
14874 number of threads the response packet can contain; and @var{nextthread}
14875 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
14876 returned in the response as @var{argthread}.
14879 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
14882 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
14887 Where: @var{count} (two hex digits) is the number of threads being
14888 returned; @var{done} (one hex digit) is zero to indicate more threads
14889 and one indicates no further threads; @var{argthreadid} (eight hex
14890 digits) is @var{nextthread} from the request packet; @var{thread...} is
14891 a sequence of thread IDs from the target. @var{threadid} (eight hex
14892 digits). See @code{remote.c:parse_threadlist_response()}.
14894 @item compute CRC of memory block
14895 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
14898 @tab reply @code{E}@var{NN}
14899 @tab An error (such as memory fault)
14901 @tab reply @code{C}@var{CRC32}
14902 @tab A 32 bit cyclic redundancy check of the specified memory region.
14904 @item query sect offs
14905 @tab @code{q}@code{Offsets}
14907 Get section offsets that the target used when re-locating the downloaded
14908 image. @emph{Note: while a @code{Bss} offset is included in the
14909 response, @value{GDBN} ignores this and instead applies the @code{Data}
14910 offset to the @code{Bss} section.}
14912 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
14914 @item thread info request
14915 @tab @code{q}@code{P}@var{mode}@var{threadid}
14920 Returns information on @var{threadid}. Where: @var{mode} is a hex
14921 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
14925 See @code{remote.c:remote_unpack_thread_info_response()}.
14927 @item remote command
14928 @tab @code{q}@code{Rcmd,}@var{COMMAND}
14933 @var{COMMAND} (hex encoded) is passed to the local interpreter for
14934 execution. Invalid commands should be reported using the output string.
14935 Before the final result packet, the target may also respond with a
14936 number of intermediate @code{O}@var{OUTPUT} console output
14937 packets. @emph{Implementors should note that providing access to a
14938 stubs's interpreter may have security implications}.
14940 @tab reply @code{OK}
14942 A command response with no output.
14944 @tab reply @var{OUTPUT}
14946 A command response with the hex encoded output string @var{OUTPUT}.
14948 @tab reply @code{E}@var{NN}
14950 Indicate a badly formed request.
14955 When @samp{q}@samp{Rcmd} is not recognized.
14957 @item symbol lookup
14958 @tab @code{qSymbol::}
14960 Notify the target that @value{GDBN} is prepared to serve symbol lookup
14961 requests. Accept requests from the target for the values of symbols.
14966 @tab reply @code{OK}
14968 The target does not need to look up any (more) symbols.
14970 @tab reply @code{qSymbol:}@var{sym_name}
14974 The target requests the value of symbol @var{sym_name} (hex encoded).
14975 @value{GDBN} may provide the value by using the
14976 @code{qSymbol:}@var{sym_value}:@var{sym_name}
14977 message, described below.
14980 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
14984 Set the value of SYM_NAME to SYM_VALUE.
14988 @var{sym_name} (hex encoded) is the name of a symbol whose value
14989 the target has previously requested.
14993 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
14994 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
14995 field will be empty.
14997 @tab reply @code{OK}
14999 The target does not need to look up any (more) symbols.
15001 @tab reply @code{qSymbol:}@var{sym_name}
15005 The target requests the value of a new symbol @var{sym_name} (hex encoded).
15006 @value{GDBN} will continue to supply the values of symbols (if available),
15007 until the target ceases to request them.
15011 The following @samp{g}/@samp{G} packets have previously been defined.
15012 In the below, some thirty-two bit registers are transferred as sixty-four
15013 bits. Those registers should be zero/sign extended (which?) to fill the
15014 space allocated. Register bytes are transfered in target byte order.
15015 The two nibbles within a register byte are transfered most-significant -
15018 @multitable @columnfractions .5 .5
15022 All registers are transfered as thirty-two bit quantities in the order:
15023 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15024 registers; fsr; fir; fp.
15028 All registers are transfered as sixty-four bit quantities (including
15029 thirty-two bit registers such as @code{sr}). The ordering is the same
15034 Example sequence of a target being re-started. Notice how the restart
15035 does not get any direct output:
15040 @emph{target restarts}
15043 -> @code{T001:1234123412341234}
15047 Example sequence of a target being stepped by a single instruction:
15055 -> @code{T001:1234123412341234}
15073 % I think something like @colophon should be in texinfo. In the
15075 \long\def\colophon{\hbox to0pt{}\vfill
15076 \centerline{The body of this manual is set in}
15077 \centerline{\fontname\tenrm,}
15078 \centerline{with headings in {\bf\fontname\tenbf}}
15079 \centerline{and examples in {\tt\fontname\tentt}.}
15080 \centerline{{\it\fontname\tenit\/},}
15081 \centerline{{\bf\fontname\tenbf}, and}
15082 \centerline{{\sl\fontname\tensl\/}}
15083 \centerline{are used for emphasis.}\vfill}
15085 % Blame: doc@cygnus.com, 1991.