1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
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 3.12 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) 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
54 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 FSF's Back-Cover Text is: ``You have freedom to copy and modify
64 this GNU Manual, like GNU software. Copies published by the Free
65 Software Foundation raise funds for GNU development.''
69 @title Debugging with @value{GDBN}
70 @subtitle The @sc{gnu} Source-Level Debugger
72 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
73 @subtitle @value{DATE}
74 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
78 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
79 \hfill {\it Debugging with @value{GDBN}}\par
80 \hfill \TeX{}info \texinfoversion\par
84 @vskip 0pt plus 1filll
85 Copyright @copyright{} 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
86 Free Software Foundation, Inc.
88 Published by the Free Software Foundation @*
89 59 Temple Place - Suite 330, @*
90 Boston, MA 02111-1307 USA @*
93 Permission is granted to copy, distribute and/or modify this document
94 under the terms of the GNU Free Documentation License, Version 1.1 or
95 any later version published by the Free Software Foundation; with the
96 Invariant Sections being ``Free Software'' and ``Free Software Needs
97 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
98 and with the Back-Cover Texts as in (a) below.
100 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
101 this GNU Manual, like GNU software. Copies published by the Free
102 Software Foundation raise funds for GNU development.''
107 @node Top, Summary, (dir), (dir)
109 @top Debugging with @value{GDBN}
111 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
113 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
116 Copyright (C) 1988-2001 Free Software Foundation, Inc.
119 * Summary:: Summary of @value{GDBN}
120 * Sample Session:: A sample @value{GDBN} session
122 * Invocation:: Getting in and out of @value{GDBN}
123 * Commands:: @value{GDBN} commands
124 * Running:: Running programs under @value{GDBN}
125 * Stopping:: Stopping and continuing
126 * Stack:: Examining the stack
127 * Source:: Examining source files
128 * Data:: Examining data
129 * Tracepoints:: Debugging remote targets non-intrusively
130 * Overlays:: Debugging programs that use overlays
132 * Languages:: Using @value{GDBN} with different languages
134 * Symbols:: Examining the symbol table
135 * Altering:: Altering execution
136 * GDB Files:: @value{GDBN} files
137 * Targets:: Specifying a debugging target
138 * Configurations:: Configuration-specific information
139 * Controlling GDB:: Controlling @value{GDBN}
140 * Sequences:: Canned sequences of commands
141 * TUI:: @value{GDBN} Text User Interface
142 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
143 * Annotations:: @value{GDBN}'s annotation interface.
144 * GDB/MI:: @value{GDBN}'s Machine Interface.
146 * GDB Bugs:: Reporting bugs in @value{GDBN}
147 * Formatting Documentation:: How to format and print @value{GDBN} documentation
149 * Command Line Editing:: Command Line Editing
150 * Using History Interactively:: Using History Interactively
151 * Installing GDB:: Installing GDB
157 @c the replication sucks, but this avoids a texinfo 3.12 lameness
162 @top Debugging with @value{GDBN}
164 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
166 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
169 Copyright (C) 1988-2000 Free Software Foundation, Inc.
172 * Summary:: Summary of @value{GDBN}
173 * Sample Session:: A sample @value{GDBN} session
175 * Invocation:: Getting in and out of @value{GDBN}
176 * Commands:: @value{GDBN} commands
177 * Running:: Running programs under @value{GDBN}
178 * Stopping:: Stopping and continuing
179 * Stack:: Examining the stack
180 * Source:: Examining source files
181 * Data:: Examining data
182 * Tracepoints:: Debugging remote targets non-intrusively
183 * Overlays:: Debugging programs that use overlays
185 * Languages:: Using @value{GDBN} with different languages
187 * Symbols:: Examining the symbol table
188 * Altering:: Altering execution
189 * GDB Files:: @value{GDBN} files
190 * Targets:: Specifying a debugging target
191 * Configurations:: Configuration-specific information
192 * Controlling GDB:: Controlling @value{GDBN}
193 * Sequences:: Canned sequences of commands
194 * TUI:: @value{GDBN} Text User Interface
195 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
196 * Annotations:: @value{GDBN}'s annotation interface.
197 * GDB/MI:: @value{GDBN}'s Machine Interface.
199 * GDB Bugs:: Reporting bugs in @value{GDBN}
200 * Formatting Documentation:: How to format and print @value{GDBN} documentation
202 * Command Line Editing:: Command Line Editing
203 * Using History Interactively:: Using History Interactively
204 * Installing GDB:: Installing GDB
210 @c TeX can handle the contents at the start but makeinfo 3.12 can not
216 @unnumbered Summary of @value{GDBN}
218 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
219 going on ``inside'' another program while it executes---or what another
220 program was doing at the moment it crashed.
222 @value{GDBN} can do four main kinds of things (plus other things in support of
223 these) to help you catch bugs in the act:
227 Start your program, specifying anything that might affect its behavior.
230 Make your program stop on specified conditions.
233 Examine what has happened, when your program has stopped.
236 Change things in your program, so you can experiment with correcting the
237 effects of one bug and go on to learn about another.
240 You can use @value{GDBN} to debug programs written in C and C++.
241 For more information, see @ref{Support,,Supported languages}.
242 For more information, see @ref{C,,C and C++}.
246 Support for Modula-2 and Chill is partial. For information on Modula-2,
247 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
250 Debugging Pascal programs which use sets, subranges, file variables, or
251 nested functions does not currently work. @value{GDBN} does not support
252 entering expressions, printing values, or similar features using Pascal
256 @value{GDBN} can be used to debug programs written in Fortran, although
257 it may be necessary to refer to some variables with a trailing
261 * Free Software:: Freely redistributable software
262 * Contributors:: Contributors to GDB
266 @unnumberedsec Free software
268 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
269 General Public License
270 (GPL). The GPL gives you the freedom to copy or adapt a licensed
271 program---but every person getting a copy also gets with it the
272 freedom to modify that copy (which means that they must get access to
273 the source code), and the freedom to distribute further copies.
274 Typical software companies use copyrights to limit your freedoms; the
275 Free Software Foundation uses the GPL to preserve these freedoms.
277 Fundamentally, the General Public License is a license which says that
278 you have these freedoms and that you cannot take these freedoms away
281 @unnumberedsec Free Software Needs Free Documentation
283 The biggest deficiency in the free software community today is not in
284 the software---it is the lack of good free documentation that we can
285 include with the free software. Many of our most important
286 programs do not come with free reference manuals and free introductory
287 texts. Documentation is an essential part of any software package;
288 when an important free software package does not come with a free
289 manual and a free tutorial, that is a major gap. We have many such
292 Consider Perl, for instance. The tutorial manuals that people
293 normally use are non-free. How did this come about? Because the
294 authors of those manuals published them with restrictive terms---no
295 copying, no modification, source files not available---which exclude
296 them from the free software world.
298 That wasn't the first time this sort of thing happened, and it was far
299 from the last. Many times we have heard a GNU user eagerly describe a
300 manual that he is writing, his intended contribution to the community,
301 only to learn that he had ruined everything by signing a publication
302 contract to make it non-free.
304 Free documentation, like free software, is a matter of freedom, not
305 price. The problem with the non-free manual is not that publishers
306 charge a price for printed copies---that in itself is fine. (The Free
307 Software Foundation sells printed copies of manuals, too.) The
308 problem is the restrictions on the use of the manual. Free manuals
309 are available in source code form, and give you permission to copy and
310 modify. Non-free manuals do not allow this.
312 The criteria of freedom for a free manual are roughly the same as for
313 free software. Redistribution (including the normal kinds of
314 commercial redistribution) must be permitted, so that the manual can
315 accompany every copy of the program, both on-line and on paper.
317 Permission for modification of the technical content is crucial too.
318 When people modify the software, adding or changing features, if they
319 are conscientious they will change the manual too---so they can
320 provide accurate and clear documentation for the modified program. A
321 manual that leaves you no choice but to write a new manual to document
322 a changed version of the program is not really available to our
325 Some kinds of limits on the way modification is handled are
326 acceptable. For example, requirements to preserve the original
327 author's copyright notice, the distribution terms, or the list of
328 authors, are ok. It is also no problem to require modified versions
329 to include notice that they were modified. Even entire sections that
330 may not be deleted or changed are acceptable, as long as they deal
331 with nontechnical topics (like this one). These kinds of restrictions
332 are acceptable because they don't obstruct the community's normal use
335 However, it must be possible to modify all the @emph{technical}
336 content of the manual, and then distribute the result in all the usual
337 media, through all the usual channels. Otherwise, the restrictions
338 obstruct the use of the manual, it is not free, and we need another
339 manual to replace it.
341 Please spread the word about this issue. Our community continues to
342 lose manuals to proprietary publishing. If we spread the word that
343 free software needs free reference manuals and free tutorials, perhaps
344 the next person who wants to contribute by writing documentation will
345 realize, before it is too late, that only free manuals contribute to
346 the free software community.
348 If you are writing documentation, please insist on publishing it under
349 the GNU Free Documentation License or another free documentation
350 license. Remember that this decision requires your approval---you
351 don't have to let the publisher decide. Some commercial publishers
352 will use a free license if you insist, but they will not propose the
353 option; it is up to you to raise the issue and say firmly that this is
354 what you want. If the publisher you are dealing with refuses, please
355 try other publishers. If you're not sure whether a proposed license
356 is free, write to @email{licensing@@gnu.org}.
358 You can encourage commercial publishers to sell more free, copylefted
359 manuals and tutorials by buying them, and particularly by buying
360 copies from the publishers that paid for their writing or for major
361 improvements. Meanwhile, try to avoid buying non-free documentation
362 at all. Check the distribution terms of a manual before you buy it,
363 and insist that whoever seeks your business must respect your freedom.
364 Check the history of the book, and try to reward the publishers that
365 have paid or pay the authors to work on it.
367 The Free Software Foundation maintains a list of free documentation
368 published by other publishers, at
369 @url{http://www.fsf.org/doc/other-free-books.html}.
372 @unnumberedsec Contributors to @value{GDBN}
374 Richard Stallman was the original author of @value{GDBN}, and of many
375 other @sc{gnu} programs. Many others have contributed to its
376 development. This section attempts to credit major contributors. One
377 of the virtues of free software is that everyone is free to contribute
378 to it; with regret, we cannot actually acknowledge everyone here. The
379 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
380 blow-by-blow account.
382 Changes much prior to version 2.0 are lost in the mists of time.
385 @emph{Plea:} Additions to this section are particularly welcome. If you
386 or your friends (or enemies, to be evenhanded) have been unfairly
387 omitted from this list, we would like to add your names!
390 So that they may not regard their many labors as thankless, we
391 particularly thank those who shepherded @value{GDBN} through major
393 Andrew Cagney (releases 5.0 and 5.1);
394 Jim Blandy (release 4.18);
395 Jason Molenda (release 4.17);
396 Stan Shebs (release 4.14);
397 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
398 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
399 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
400 Jim Kingdon (releases 3.5, 3.4, and 3.3);
401 and Randy Smith (releases 3.2, 3.1, and 3.0).
403 Richard Stallman, assisted at various times by Peter TerMaat, Chris
404 Hanson, and Richard Mlynarik, handled releases through 2.8.
406 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
407 in @value{GDBN}, with significant additional contributions from Per
408 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
409 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
410 much general update work leading to release 3.0).
412 @value{GDBN} uses the BFD subroutine library to examine multiple
413 object-file formats; BFD was a joint project of David V.
414 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
416 David Johnson wrote the original COFF support; Pace Willison did
417 the original support for encapsulated COFF.
419 Brent Benson of Harris Computer Systems contributed DWARF2 support.
421 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
422 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
424 Jean-Daniel Fekete contributed Sun 386i support.
425 Chris Hanson improved the HP9000 support.
426 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
427 David Johnson contributed Encore Umax support.
428 Jyrki Kuoppala contributed Altos 3068 support.
429 Jeff Law contributed HP PA and SOM support.
430 Keith Packard contributed NS32K support.
431 Doug Rabson contributed Acorn Risc Machine support.
432 Bob Rusk contributed Harris Nighthawk CX-UX support.
433 Chris Smith contributed Convex support (and Fortran debugging).
434 Jonathan Stone contributed Pyramid support.
435 Michael Tiemann contributed SPARC support.
436 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
437 Pace Willison contributed Intel 386 support.
438 Jay Vosburgh contributed Symmetry support.
440 Andreas Schwab contributed M68K Linux support.
442 Rich Schaefer and Peter Schauer helped with support of SunOS shared
445 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
446 about several machine instruction sets.
448 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
449 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
450 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
451 and RDI targets, respectively.
453 Brian Fox is the author of the readline libraries providing
454 command-line editing and command history.
456 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
457 Modula-2 support, and contributed the Languages chapter of this manual.
459 Fred Fish wrote most of the support for Unix System Vr4.
460 He also enhanced the command-completion support to cover C@t{++} overloaded
463 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
466 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
468 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
470 Toshiba sponsored the support for the TX39 Mips processor.
472 Matsushita sponsored the support for the MN10200 and MN10300 processors.
474 Fujitsu sponsored the support for SPARClite and FR30 processors.
476 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
479 Michael Snyder added support for tracepoints.
481 Stu Grossman wrote gdbserver.
483 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
484 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
486 The following people at the Hewlett-Packard Company contributed
487 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
488 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
489 compiler, and the terminal user interface: Ben Krepp, Richard Title,
490 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
491 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
492 information in this manual.
494 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
495 Robert Hoehne made significant contributions to the DJGPP port.
497 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
498 development since 1991. Cygnus engineers who have worked on @value{GDBN}
499 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
500 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
501 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
502 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
503 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
504 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
505 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
506 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
507 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
508 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
509 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
510 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
511 Zuhn have made contributions both large and small.
515 @chapter A Sample @value{GDBN} Session
517 You can use this manual at your leisure to read all about @value{GDBN}.
518 However, a handful of commands are enough to get started using the
519 debugger. This chapter illustrates those commands.
522 In this sample session, we emphasize user input like this: @b{input},
523 to make it easier to pick out from the surrounding output.
526 @c FIXME: this example may not be appropriate for some configs, where
527 @c FIXME...primary interest is in remote use.
529 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
530 processor) exhibits the following bug: sometimes, when we change its
531 quote strings from the default, the commands used to capture one macro
532 definition within another stop working. In the following short @code{m4}
533 session, we define a macro @code{foo} which expands to @code{0000}; we
534 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
535 same thing. However, when we change the open quote string to
536 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
537 procedure fails to define a new synonym @code{baz}:
546 @b{define(bar,defn(`foo'))}
550 @b{changequote(<QUOTE>,<UNQUOTE>)}
552 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
555 m4: End of input: 0: fatal error: EOF in string
559 Let us use @value{GDBN} to try to see what is going on.
562 $ @b{@value{GDBP} m4}
563 @c FIXME: this falsifies the exact text played out, to permit smallbook
564 @c FIXME... format to come out better.
565 @value{GDBN} is free software and you are welcome to distribute copies
566 of it under certain conditions; type "show copying" to see
568 There is absolutely no warranty for @value{GDBN}; type "show warranty"
571 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
576 @value{GDBN} reads only enough symbol data to know where to find the
577 rest when needed; as a result, the first prompt comes up very quickly.
578 We now tell @value{GDBN} to use a narrower display width than usual, so
579 that examples fit in this manual.
582 (@value{GDBP}) @b{set width 70}
586 We need to see how the @code{m4} built-in @code{changequote} works.
587 Having looked at the source, we know the relevant subroutine is
588 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
589 @code{break} command.
592 (@value{GDBP}) @b{break m4_changequote}
593 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
597 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
598 control; as long as control does not reach the @code{m4_changequote}
599 subroutine, the program runs as usual:
602 (@value{GDBP}) @b{run}
603 Starting program: /work/Editorial/gdb/gnu/m4/m4
611 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
612 suspends execution of @code{m4}, displaying information about the
613 context where it stops.
616 @b{changequote(<QUOTE>,<UNQUOTE>)}
618 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
620 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
624 Now we use the command @code{n} (@code{next}) to advance execution to
625 the next line of the current function.
629 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
634 @code{set_quotes} looks like a promising subroutine. We can go into it
635 by using the command @code{s} (@code{step}) instead of @code{next}.
636 @code{step} goes to the next line to be executed in @emph{any}
637 subroutine, so it steps into @code{set_quotes}.
641 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
643 530 if (lquote != def_lquote)
647 The display that shows the subroutine where @code{m4} is now
648 suspended (and its arguments) is called a stack frame display. It
649 shows a summary of the stack. We can use the @code{backtrace}
650 command (which can also be spelled @code{bt}), to see where we are
651 in the stack as a whole: the @code{backtrace} command displays a
652 stack frame for each active subroutine.
655 (@value{GDBP}) @b{bt}
656 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
658 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
660 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
661 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
663 #4 0x79dc in expand_input () at macro.c:40
664 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
668 We step through a few more lines to see what happens. The first two
669 times, we can use @samp{s}; the next two times we use @code{n} to avoid
670 falling into the @code{xstrdup} subroutine.
674 0x3b5c 532 if (rquote != def_rquote)
676 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
677 def_lquote : xstrdup(lq);
679 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
682 538 len_lquote = strlen(rquote);
686 The last line displayed looks a little odd; we can examine the variables
687 @code{lquote} and @code{rquote} to see if they are in fact the new left
688 and right quotes we specified. We use the command @code{p}
689 (@code{print}) to see their values.
692 (@value{GDBP}) @b{p lquote}
693 $1 = 0x35d40 "<QUOTE>"
694 (@value{GDBP}) @b{p rquote}
695 $2 = 0x35d50 "<UNQUOTE>"
699 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
700 To look at some context, we can display ten lines of source
701 surrounding the current line with the @code{l} (@code{list}) command.
707 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
709 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
712 538 len_lquote = strlen(rquote);
713 539 len_rquote = strlen(lquote);
720 Let us step past the two lines that set @code{len_lquote} and
721 @code{len_rquote}, and then examine the values of those variables.
725 539 len_rquote = strlen(lquote);
728 (@value{GDBP}) @b{p len_lquote}
730 (@value{GDBP}) @b{p len_rquote}
735 That certainly looks wrong, assuming @code{len_lquote} and
736 @code{len_rquote} are meant to be the lengths of @code{lquote} and
737 @code{rquote} respectively. We can set them to better values using
738 the @code{p} command, since it can print the value of
739 any expression---and that expression can include subroutine calls and
743 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
745 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
750 Is that enough to fix the problem of using the new quotes with the
751 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
752 executing with the @code{c} (@code{continue}) command, and then try the
753 example that caused trouble initially:
759 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
766 Success! The new quotes now work just as well as the default ones. The
767 problem seems to have been just the two typos defining the wrong
768 lengths. We allow @code{m4} exit by giving it an EOF as input:
772 Program exited normally.
776 The message @samp{Program exited normally.} is from @value{GDBN}; it
777 indicates @code{m4} has finished executing. We can end our @value{GDBN}
778 session with the @value{GDBN} @code{quit} command.
781 (@value{GDBP}) @b{quit}
785 @chapter Getting In and Out of @value{GDBN}
787 This chapter discusses how to start @value{GDBN}, and how to get out of it.
791 type @samp{@value{GDBP}} to start @value{GDBN}.
793 type @kbd{quit} or @kbd{C-d} to exit.
797 * Invoking GDB:: How to start @value{GDBN}
798 * Quitting GDB:: How to quit @value{GDBN}
799 * Shell Commands:: How to use shell commands inside @value{GDBN}
803 @section Invoking @value{GDBN}
805 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
806 @value{GDBN} reads commands from the terminal until you tell it to exit.
808 You can also run @code{@value{GDBP}} with a variety of arguments and options,
809 to specify more of your debugging environment at the outset.
811 The command-line options described here are designed
812 to cover a variety of situations; in some environments, some of these
813 options may effectively be unavailable.
815 The most usual way to start @value{GDBN} is with one argument,
816 specifying an executable program:
819 @value{GDBP} @var{program}
823 You can also start with both an executable program and a core file
827 @value{GDBP} @var{program} @var{core}
830 You can, instead, specify a process ID as a second argument, if you want
831 to debug a running process:
834 @value{GDBP} @var{program} 1234
838 would attach @value{GDBN} to process @code{1234} (unless you also have a file
839 named @file{1234}; @value{GDBN} does check for a core file first).
841 Taking advantage of the second command-line argument requires a fairly
842 complete operating system; when you use @value{GDBN} as a remote
843 debugger attached to a bare board, there may not be any notion of
844 ``process'', and there is often no way to get a core dump. @value{GDBN}
845 will warn you if it is unable to attach or to read core dumps.
847 You can optionally have @code{@value{GDBP}} pass any arguments after the
848 executable file to the inferior using @code{--args}. This option stops
851 gdb --args gcc -O2 -c foo.c
853 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
854 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
856 You can run @code{@value{GDBP}} without printing the front material, which describes
857 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
864 You can further control how @value{GDBN} starts up by using command-line
865 options. @value{GDBN} itself can remind you of the options available.
875 to display all available options and briefly describe their use
876 (@samp{@value{GDBP} -h} is a shorter equivalent).
878 All options and command line arguments you give are processed
879 in sequential order. The order makes a difference when the
880 @samp{-x} option is used.
884 * File Options:: Choosing files
885 * Mode Options:: Choosing modes
889 @subsection Choosing files
891 When @value{GDBN} starts, it reads any arguments other than options as
892 specifying an executable file and core file (or process ID). This is
893 the same as if the arguments were specified by the @samp{-se} and
894 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
895 first argument that does not have an associated option flag as
896 equivalent to the @samp{-se} option followed by that argument; and the
897 second argument that does not have an associated option flag, if any, as
898 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
899 If the second argument begins with a decimal digit, @value{GDBN} will
900 first attempt to attach to it as a process, and if that fails, attempt
901 to open it as a corefile. If you have a corefile whose name begins with
902 a digit, you can prevent @value{GDBN} from treating it as a pid by
903 prefixing it with @file{./}, eg. @file{./12345}.
905 If @value{GDBN} has not been configured to included core file support,
906 such as for most embedded targets, then it will complain about a second
907 argument and ignore it.
909 Many options have both long and short forms; both are shown in the
910 following list. @value{GDBN} also recognizes the long forms if you truncate
911 them, so long as enough of the option is present to be unambiguous.
912 (If you prefer, you can flag option arguments with @samp{--} rather
913 than @samp{-}, though we illustrate the more usual convention.)
915 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
916 @c way, both those who look for -foo and --foo in the index, will find
920 @item -symbols @var{file}
922 @cindex @code{--symbols}
924 Read symbol table from file @var{file}.
926 @item -exec @var{file}
928 @cindex @code{--exec}
930 Use file @var{file} as the executable file to execute when appropriate,
931 and for examining pure data in conjunction with a core dump.
935 Read symbol table from file @var{file} and use it as the executable
938 @item -core @var{file}
940 @cindex @code{--core}
942 Use file @var{file} as a core dump to examine.
944 @item -c @var{number}
945 @item -pid @var{number}
946 @itemx -p @var{number}
949 Connect to process ID @var{number}, as with the @code{attach} command.
950 If there is no such process, @value{GDBN} will attempt to open a core
951 file named @var{number}.
953 @item -command @var{file}
955 @cindex @code{--command}
957 Execute @value{GDBN} commands from file @var{file}. @xref{Command
958 Files,, Command files}.
960 @item -directory @var{directory}
961 @itemx -d @var{directory}
962 @cindex @code{--directory}
964 Add @var{directory} to the path to search for source files.
968 @cindex @code{--mapped}
970 @emph{Warning: this option depends on operating system facilities that are not
971 supported on all systems.}@*
972 If memory-mapped files are available on your system through the @code{mmap}
973 system call, you can use this option
974 to have @value{GDBN} write the symbols from your
975 program into a reusable file in the current directory. If the program you are debugging is
976 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
977 Future @value{GDBN} debugging sessions notice the presence of this file,
978 and can quickly map in symbol information from it, rather than reading
979 the symbol table from the executable program.
981 The @file{.syms} file is specific to the host machine where @value{GDBN}
982 is run. It holds an exact image of the internal @value{GDBN} symbol
983 table. It cannot be shared across multiple host platforms.
987 @cindex @code{--readnow}
989 Read each symbol file's entire symbol table immediately, rather than
990 the default, which is to read it incrementally as it is needed.
991 This makes startup slower, but makes future operations faster.
995 You typically combine the @code{-mapped} and @code{-readnow} options in
996 order to build a @file{.syms} file that contains complete symbol
997 information. (@xref{Files,,Commands to specify files}, for information
998 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
999 but build a @file{.syms} file for future use is:
1002 gdb -batch -nx -mapped -readnow programname
1006 @subsection Choosing modes
1008 You can run @value{GDBN} in various alternative modes---for example, in
1009 batch mode or quiet mode.
1016 Do not execute commands found in any initialization files. Normally,
1017 @value{GDBN} executes the commands in these files after all the command
1018 options and arguments have been processed. @xref{Command Files,,Command
1024 @cindex @code{--quiet}
1025 @cindex @code{--silent}
1027 ``Quiet''. Do not print the introductory and copyright messages. These
1028 messages are also suppressed in batch mode.
1031 @cindex @code{--batch}
1032 Run in batch mode. Exit with status @code{0} after processing all the
1033 command files specified with @samp{-x} (and all commands from
1034 initialization files, if not inhibited with @samp{-n}). Exit with
1035 nonzero status if an error occurs in executing the @value{GDBN} commands
1036 in the command files.
1038 Batch mode may be useful for running @value{GDBN} as a filter, for
1039 example to download and run a program on another computer; in order to
1040 make this more useful, the message
1043 Program exited normally.
1047 (which is ordinarily issued whenever a program running under
1048 @value{GDBN} control terminates) is not issued when running in batch
1053 @cindex @code{--nowindows}
1055 ``No windows''. If @value{GDBN} comes with a graphical user interface
1056 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1057 interface. If no GUI is available, this option has no effect.
1061 @cindex @code{--windows}
1063 If @value{GDBN} includes a GUI, then this option requires it to be
1066 @item -cd @var{directory}
1068 Run @value{GDBN} using @var{directory} as its working directory,
1069 instead of the current directory.
1073 @cindex @code{--fullname}
1075 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1076 subprocess. It tells @value{GDBN} to output the full file name and line
1077 number in a standard, recognizable fashion each time a stack frame is
1078 displayed (which includes each time your program stops). This
1079 recognizable format looks like two @samp{\032} characters, followed by
1080 the file name, line number and character position separated by colons,
1081 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1082 @samp{\032} characters as a signal to display the source code for the
1086 @cindex @code{--epoch}
1087 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1088 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1089 routines so as to allow Epoch to display values of expressions in a
1092 @item -annotate @var{level}
1093 @cindex @code{--annotate}
1094 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1095 effect is identical to using @samp{set annotate @var{level}}
1096 (@pxref{Annotations}).
1097 Annotation level controls how much information does @value{GDBN} print
1098 together with its prompt, values of expressions, source lines, and other
1099 types of output. Level 0 is the normal, level 1 is for use when
1100 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1101 maximum annotation suitable for programs that control @value{GDBN}.
1104 @cindex @code{--async}
1105 Use the asynchronous event loop for the command-line interface.
1106 @value{GDBN} processes all events, such as user keyboard input, via a
1107 special event loop. This allows @value{GDBN} to accept and process user
1108 commands in parallel with the debugged process being
1109 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1110 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1111 suspended when the debuggee runs.}, so you don't need to wait for
1112 control to return to @value{GDBN} before you type the next command.
1113 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1114 operation is not yet in place, so @samp{-async} does not work fully
1116 @c FIXME: when the target side of the event loop is done, the above NOTE
1117 @c should be removed.
1119 When the standard input is connected to a terminal device, @value{GDBN}
1120 uses the asynchronous event loop by default, unless disabled by the
1121 @samp{-noasync} option.
1124 @cindex @code{--noasync}
1125 Disable the asynchronous event loop for the command-line interface.
1128 @cindex @code{--args}
1129 Change interpretation of command line so that arguments following the
1130 executable file are passed as command line arguments to the inferior.
1131 This option stops option processing.
1133 @item -baud @var{bps}
1135 @cindex @code{--baud}
1137 Set the line speed (baud rate or bits per second) of any serial
1138 interface used by @value{GDBN} for remote debugging.
1140 @item -tty @var{device}
1141 @itemx -t @var{device}
1142 @cindex @code{--tty}
1144 Run using @var{device} for your program's standard input and output.
1145 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1147 @c resolve the situation of these eventually
1149 @cindex @code{--tui}
1150 Activate the Terminal User Interface when starting.
1151 The Terminal User Interface manages several text windows on the terminal,
1152 showing source, assembly, registers and @value{GDBN} command outputs
1153 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1154 Do not use this option if you run @value{GDBN} from Emacs
1155 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1158 @c @cindex @code{--xdb}
1159 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1160 @c For information, see the file @file{xdb_trans.html}, which is usually
1161 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1164 @item -interpreter @var{interp}
1165 @cindex @code{--interpreter}
1166 Use the interpreter @var{interp} for interface with the controlling
1167 program or device. This option is meant to be set by programs which
1168 communicate with @value{GDBN} using it as a back end.
1170 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1171 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1172 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1173 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1176 @cindex @code{--write}
1177 Open the executable and core files for both reading and writing. This
1178 is equivalent to the @samp{set write on} command inside @value{GDBN}
1182 @cindex @code{--statistics}
1183 This option causes @value{GDBN} to print statistics about time and
1184 memory usage after it completes each command and returns to the prompt.
1187 @cindex @code{--version}
1188 This option causes @value{GDBN} to print its version number and
1189 no-warranty blurb, and exit.
1194 @section Quitting @value{GDBN}
1195 @cindex exiting @value{GDBN}
1196 @cindex leaving @value{GDBN}
1199 @kindex quit @r{[}@var{expression}@r{]}
1200 @kindex q @r{(@code{quit})}
1201 @item quit @r{[}@var{expression}@r{]}
1203 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1204 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1205 do not supply @var{expression}, @value{GDBN} will terminate normally;
1206 otherwise it will terminate using the result of @var{expression} as the
1211 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1212 terminates the action of any @value{GDBN} command that is in progress and
1213 returns to @value{GDBN} command level. It is safe to type the interrupt
1214 character at any time because @value{GDBN} does not allow it to take effect
1215 until a time when it is safe.
1217 If you have been using @value{GDBN} to control an attached process or
1218 device, you can release it with the @code{detach} command
1219 (@pxref{Attach, ,Debugging an already-running process}).
1221 @node Shell Commands
1222 @section Shell commands
1224 If you need to execute occasional shell commands during your
1225 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1226 just use the @code{shell} command.
1230 @cindex shell escape
1231 @item shell @var{command string}
1232 Invoke a standard shell to execute @var{command string}.
1233 If it exists, the environment variable @code{SHELL} determines which
1234 shell to run. Otherwise @value{GDBN} uses the default shell
1235 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1238 The utility @code{make} is often needed in development environments.
1239 You do not have to use the @code{shell} command for this purpose in
1244 @cindex calling make
1245 @item make @var{make-args}
1246 Execute the @code{make} program with the specified
1247 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1251 @chapter @value{GDBN} Commands
1253 You can abbreviate a @value{GDBN} command to the first few letters of the command
1254 name, if that abbreviation is unambiguous; and you can repeat certain
1255 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1256 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1257 show you the alternatives available, if there is more than one possibility).
1260 * Command Syntax:: How to give commands to @value{GDBN}
1261 * Completion:: Command completion
1262 * Help:: How to ask @value{GDBN} for help
1265 @node Command Syntax
1266 @section Command syntax
1268 A @value{GDBN} command is a single line of input. There is no limit on
1269 how long it can be. It starts with a command name, which is followed by
1270 arguments whose meaning depends on the command name. For example, the
1271 command @code{step} accepts an argument which is the number of times to
1272 step, as in @samp{step 5}. You can also use the @code{step} command
1273 with no arguments. Some commands do not allow any arguments.
1275 @cindex abbreviation
1276 @value{GDBN} command names may always be truncated if that abbreviation is
1277 unambiguous. Other possible command abbreviations are listed in the
1278 documentation for individual commands. In some cases, even ambiguous
1279 abbreviations are allowed; for example, @code{s} is specially defined as
1280 equivalent to @code{step} even though there are other commands whose
1281 names start with @code{s}. You can test abbreviations by using them as
1282 arguments to the @code{help} command.
1284 @cindex repeating commands
1285 @kindex RET @r{(repeat last command)}
1286 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1287 repeat the previous command. Certain commands (for example, @code{run})
1288 will not repeat this way; these are commands whose unintentional
1289 repetition might cause trouble and which you are unlikely to want to
1292 The @code{list} and @code{x} commands, when you repeat them with
1293 @key{RET}, construct new arguments rather than repeating
1294 exactly as typed. This permits easy scanning of source or memory.
1296 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1297 output, in a way similar to the common utility @code{more}
1298 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1299 @key{RET} too many in this situation, @value{GDBN} disables command
1300 repetition after any command that generates this sort of display.
1302 @kindex # @r{(a comment)}
1304 Any text from a @kbd{#} to the end of the line is a comment; it does
1305 nothing. This is useful mainly in command files (@pxref{Command
1306 Files,,Command files}).
1308 @cindex repeating command sequences
1309 @kindex C-o @r{(operate-and-get-next)}
1310 The @kbd{C-o} binding is useful for repeating a complex sequence of
1311 commands. This command accepts the current line, like @kbd{RET}, and
1312 then fetches the next line relative to the current line from the history
1316 @section Command completion
1319 @cindex word completion
1320 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1321 only one possibility; it can also show you what the valid possibilities
1322 are for the next word in a command, at any time. This works for @value{GDBN}
1323 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1325 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1326 of a word. If there is only one possibility, @value{GDBN} fills in the
1327 word, and waits for you to finish the command (or press @key{RET} to
1328 enter it). For example, if you type
1330 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1331 @c complete accuracy in these examples; space introduced for clarity.
1332 @c If texinfo enhancements make it unnecessary, it would be nice to
1333 @c replace " @key" by "@key" in the following...
1335 (@value{GDBP}) info bre @key{TAB}
1339 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1340 the only @code{info} subcommand beginning with @samp{bre}:
1343 (@value{GDBP}) info breakpoints
1347 You can either press @key{RET} at this point, to run the @code{info
1348 breakpoints} command, or backspace and enter something else, if
1349 @samp{breakpoints} does not look like the command you expected. (If you
1350 were sure you wanted @code{info breakpoints} in the first place, you
1351 might as well just type @key{RET} immediately after @samp{info bre},
1352 to exploit command abbreviations rather than command completion).
1354 If there is more than one possibility for the next word when you press
1355 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1356 characters and try again, or just press @key{TAB} a second time;
1357 @value{GDBN} displays all the possible completions for that word. For
1358 example, you might want to set a breakpoint on a subroutine whose name
1359 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1360 just sounds the bell. Typing @key{TAB} again displays all the
1361 function names in your program that begin with those characters, for
1365 (@value{GDBP}) b make_ @key{TAB}
1366 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1367 make_a_section_from_file make_environ
1368 make_abs_section make_function_type
1369 make_blockvector make_pointer_type
1370 make_cleanup make_reference_type
1371 make_command make_symbol_completion_list
1372 (@value{GDBP}) b make_
1376 After displaying the available possibilities, @value{GDBN} copies your
1377 partial input (@samp{b make_} in the example) so you can finish the
1380 If you just want to see the list of alternatives in the first place, you
1381 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1382 means @kbd{@key{META} ?}. You can type this either by holding down a
1383 key designated as the @key{META} shift on your keyboard (if there is
1384 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1386 @cindex quotes in commands
1387 @cindex completion of quoted strings
1388 Sometimes the string you need, while logically a ``word'', may contain
1389 parentheses or other characters that @value{GDBN} normally excludes from
1390 its notion of a word. To permit word completion to work in this
1391 situation, you may enclose words in @code{'} (single quote marks) in
1392 @value{GDBN} commands.
1394 The most likely situation where you might need this is in typing the
1395 name of a C@t{++} function. This is because C@t{++} allows function
1396 overloading (multiple definitions of the same function, distinguished
1397 by argument type). For example, when you want to set a breakpoint you
1398 may need to distinguish whether you mean the version of @code{name}
1399 that takes an @code{int} parameter, @code{name(int)}, or the version
1400 that takes a @code{float} parameter, @code{name(float)}. To use the
1401 word-completion facilities in this situation, type a single quote
1402 @code{'} at the beginning of the function name. This alerts
1403 @value{GDBN} that it may need to consider more information than usual
1404 when you press @key{TAB} or @kbd{M-?} to request word completion:
1407 (@value{GDBP}) b 'bubble( @kbd{M-?}
1408 bubble(double,double) bubble(int,int)
1409 (@value{GDBP}) b 'bubble(
1412 In some cases, @value{GDBN} can tell that completing a name requires using
1413 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1414 completing as much as it can) if you do not type the quote in the first
1418 (@value{GDBP}) b bub @key{TAB}
1419 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1420 (@value{GDBP}) b 'bubble(
1424 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1425 you have not yet started typing the argument list when you ask for
1426 completion on an overloaded symbol.
1428 For more information about overloaded functions, see @ref{C plus plus
1429 expressions, ,C@t{++} expressions}. You can use the command @code{set
1430 overload-resolution off} to disable overload resolution;
1431 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1435 @section Getting help
1436 @cindex online documentation
1439 You can always ask @value{GDBN} itself for information on its commands,
1440 using the command @code{help}.
1443 @kindex h @r{(@code{help})}
1446 You can use @code{help} (abbreviated @code{h}) with no arguments to
1447 display a short list of named classes of commands:
1451 List of classes of commands:
1453 aliases -- Aliases of other commands
1454 breakpoints -- Making program stop at certain points
1455 data -- Examining data
1456 files -- Specifying and examining files
1457 internals -- Maintenance commands
1458 obscure -- Obscure features
1459 running -- Running the program
1460 stack -- Examining the stack
1461 status -- Status inquiries
1462 support -- Support facilities
1463 tracepoints -- Tracing of program execution without@*
1464 stopping the program
1465 user-defined -- User-defined commands
1467 Type "help" followed by a class name for a list of
1468 commands in that class.
1469 Type "help" followed by command name for full
1471 Command name abbreviations are allowed if unambiguous.
1474 @c the above line break eliminates huge line overfull...
1476 @item help @var{class}
1477 Using one of the general help classes as an argument, you can get a
1478 list of the individual commands in that class. For example, here is the
1479 help display for the class @code{status}:
1482 (@value{GDBP}) help status
1487 @c Line break in "show" line falsifies real output, but needed
1488 @c to fit in smallbook page size.
1489 info -- Generic command for showing things
1490 about the program being debugged
1491 show -- Generic command for showing things
1494 Type "help" followed by command name for full
1496 Command name abbreviations are allowed if unambiguous.
1500 @item help @var{command}
1501 With a command name as @code{help} argument, @value{GDBN} displays a
1502 short paragraph on how to use that command.
1505 @item apropos @var{args}
1506 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1507 commands, and their documentation, for the regular expression specified in
1508 @var{args}. It prints out all matches found. For example:
1519 set symbol-reloading -- Set dynamic symbol table reloading
1520 multiple times in one run
1521 show symbol-reloading -- Show dynamic symbol table reloading
1522 multiple times in one run
1527 @item complete @var{args}
1528 The @code{complete @var{args}} command lists all the possible completions
1529 for the beginning of a command. Use @var{args} to specify the beginning of the
1530 command you want completed. For example:
1536 @noindent results in:
1547 @noindent This is intended for use by @sc{gnu} Emacs.
1550 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1551 and @code{show} to inquire about the state of your program, or the state
1552 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1553 manual introduces each of them in the appropriate context. The listings
1554 under @code{info} and under @code{show} in the Index point to
1555 all the sub-commands. @xref{Index}.
1560 @kindex i @r{(@code{info})}
1562 This command (abbreviated @code{i}) is for describing the state of your
1563 program. For example, you can list the arguments given to your program
1564 with @code{info args}, list the registers currently in use with @code{info
1565 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1566 You can get a complete list of the @code{info} sub-commands with
1567 @w{@code{help info}}.
1571 You can assign the result of an expression to an environment variable with
1572 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1573 @code{set prompt $}.
1577 In contrast to @code{info}, @code{show} is for describing the state of
1578 @value{GDBN} itself.
1579 You can change most of the things you can @code{show}, by using the
1580 related command @code{set}; for example, you can control what number
1581 system is used for displays with @code{set radix}, or simply inquire
1582 which is currently in use with @code{show radix}.
1585 To display all the settable parameters and their current
1586 values, you can use @code{show} with no arguments; you may also use
1587 @code{info set}. Both commands produce the same display.
1588 @c FIXME: "info set" violates the rule that "info" is for state of
1589 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1590 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1594 Here are three miscellaneous @code{show} subcommands, all of which are
1595 exceptional in lacking corresponding @code{set} commands:
1598 @kindex show version
1599 @cindex version number
1601 Show what version of @value{GDBN} is running. You should include this
1602 information in @value{GDBN} bug-reports. If multiple versions of
1603 @value{GDBN} are in use at your site, you may need to determine which
1604 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1605 commands are introduced, and old ones may wither away. Also, many
1606 system vendors ship variant versions of @value{GDBN}, and there are
1607 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1608 The version number is the same as the one announced when you start
1611 @kindex show copying
1613 Display information about permission for copying @value{GDBN}.
1615 @kindex show warranty
1617 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1618 if your version of @value{GDBN} comes with one.
1623 @chapter Running Programs Under @value{GDBN}
1625 When you run a program under @value{GDBN}, you must first generate
1626 debugging information when you compile it.
1628 You may start @value{GDBN} with its arguments, if any, in an environment
1629 of your choice. If you are doing native debugging, you may redirect
1630 your program's input and output, debug an already running process, or
1631 kill a child process.
1634 * Compilation:: Compiling for debugging
1635 * Starting:: Starting your program
1636 * Arguments:: Your program's arguments
1637 * Environment:: Your program's environment
1639 * Working Directory:: Your program's working directory
1640 * Input/Output:: Your program's input and output
1641 * Attach:: Debugging an already-running process
1642 * Kill Process:: Killing the child process
1644 * Threads:: Debugging programs with multiple threads
1645 * Processes:: Debugging programs with multiple processes
1649 @section Compiling for debugging
1651 In order to debug a program effectively, you need to generate
1652 debugging information when you compile it. This debugging information
1653 is stored in the object file; it describes the data type of each
1654 variable or function and the correspondence between source line numbers
1655 and addresses in the executable code.
1657 To request debugging information, specify the @samp{-g} option when you run
1660 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1661 options together. Using those compilers, you cannot generate optimized
1662 executables containing debugging information.
1664 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1665 without @samp{-O}, making it possible to debug optimized code. We
1666 recommend that you @emph{always} use @samp{-g} whenever you compile a
1667 program. You may think your program is correct, but there is no sense
1668 in pushing your luck.
1670 @cindex optimized code, debugging
1671 @cindex debugging optimized code
1672 When you debug a program compiled with @samp{-g -O}, remember that the
1673 optimizer is rearranging your code; the debugger shows you what is
1674 really there. Do not be too surprised when the execution path does not
1675 exactly match your source file! An extreme example: if you define a
1676 variable, but never use it, @value{GDBN} never sees that
1677 variable---because the compiler optimizes it out of existence.
1679 Some things do not work as well with @samp{-g -O} as with just
1680 @samp{-g}, particularly on machines with instruction scheduling. If in
1681 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1682 please report it to us as a bug (including a test case!).
1684 Older versions of the @sc{gnu} C compiler permitted a variant option
1685 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1686 format; if your @sc{gnu} C compiler has this option, do not use it.
1690 @section Starting your program
1696 @kindex r @r{(@code{run})}
1699 Use the @code{run} command to start your program under @value{GDBN}.
1700 You must first specify the program name (except on VxWorks) with an
1701 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1702 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1703 (@pxref{Files, ,Commands to specify files}).
1707 If you are running your program in an execution environment that
1708 supports processes, @code{run} creates an inferior process and makes
1709 that process run your program. (In environments without processes,
1710 @code{run} jumps to the start of your program.)
1712 The execution of a program is affected by certain information it
1713 receives from its superior. @value{GDBN} provides ways to specify this
1714 information, which you must do @emph{before} starting your program. (You
1715 can change it after starting your program, but such changes only affect
1716 your program the next time you start it.) This information may be
1717 divided into four categories:
1720 @item The @emph{arguments.}
1721 Specify the arguments to give your program as the arguments of the
1722 @code{run} command. If a shell is available on your target, the shell
1723 is used to pass the arguments, so that you may use normal conventions
1724 (such as wildcard expansion or variable substitution) in describing
1726 In Unix systems, you can control which shell is used with the
1727 @code{SHELL} environment variable.
1728 @xref{Arguments, ,Your program's arguments}.
1730 @item The @emph{environment.}
1731 Your program normally inherits its environment from @value{GDBN}, but you can
1732 use the @value{GDBN} commands @code{set environment} and @code{unset
1733 environment} to change parts of the environment that affect
1734 your program. @xref{Environment, ,Your program's environment}.
1736 @item The @emph{working directory.}
1737 Your program inherits its working directory from @value{GDBN}. You can set
1738 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1739 @xref{Working Directory, ,Your program's working directory}.
1741 @item The @emph{standard input and output.}
1742 Your program normally uses the same device for standard input and
1743 standard output as @value{GDBN} is using. You can redirect input and output
1744 in the @code{run} command line, or you can use the @code{tty} command to
1745 set a different device for your program.
1746 @xref{Input/Output, ,Your program's input and output}.
1749 @emph{Warning:} While input and output redirection work, you cannot use
1750 pipes to pass the output of the program you are debugging to another
1751 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1755 When you issue the @code{run} command, your program begins to execute
1756 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1757 of how to arrange for your program to stop. Once your program has
1758 stopped, you may call functions in your program, using the @code{print}
1759 or @code{call} commands. @xref{Data, ,Examining Data}.
1761 If the modification time of your symbol file has changed since the last
1762 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1763 table, and reads it again. When it does this, @value{GDBN} tries to retain
1764 your current breakpoints.
1767 @section Your program's arguments
1769 @cindex arguments (to your program)
1770 The arguments to your program can be specified by the arguments of the
1772 They are passed to a shell, which expands wildcard characters and
1773 performs redirection of I/O, and thence to your program. Your
1774 @code{SHELL} environment variable (if it exists) specifies what shell
1775 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1776 the default shell (@file{/bin/sh} on Unix).
1778 On non-Unix systems, the program is usually invoked directly by
1779 @value{GDBN}, which emulates I/O redirection via the appropriate system
1780 calls, and the wildcard characters are expanded by the startup code of
1781 the program, not by the shell.
1783 @code{run} with no arguments uses the same arguments used by the previous
1784 @code{run}, or those set by the @code{set args} command.
1789 Specify the arguments to be used the next time your program is run. If
1790 @code{set args} has no arguments, @code{run} executes your program
1791 with no arguments. Once you have run your program with arguments,
1792 using @code{set args} before the next @code{run} is the only way to run
1793 it again without arguments.
1797 Show the arguments to give your program when it is started.
1801 @section Your program's environment
1803 @cindex environment (of your program)
1804 The @dfn{environment} consists of a set of environment variables and
1805 their values. Environment variables conventionally record such things as
1806 your user name, your home directory, your terminal type, and your search
1807 path for programs to run. Usually you set up environment variables with
1808 the shell and they are inherited by all the other programs you run. When
1809 debugging, it can be useful to try running your program with a modified
1810 environment without having to start @value{GDBN} over again.
1814 @item path @var{directory}
1815 Add @var{directory} to the front of the @code{PATH} environment variable
1816 (the search path for executables) that will be passed to your program.
1817 The value of @code{PATH} used by @value{GDBN} does not change.
1818 You may specify several directory names, separated by whitespace or by a
1819 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1820 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1821 is moved to the front, so it is searched sooner.
1823 You can use the string @samp{$cwd} to refer to whatever is the current
1824 working directory at the time @value{GDBN} searches the path. If you
1825 use @samp{.} instead, it refers to the directory where you executed the
1826 @code{path} command. @value{GDBN} replaces @samp{.} in the
1827 @var{directory} argument (with the current path) before adding
1828 @var{directory} to the search path.
1829 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1830 @c document that, since repeating it would be a no-op.
1834 Display the list of search paths for executables (the @code{PATH}
1835 environment variable).
1837 @kindex show environment
1838 @item show environment @r{[}@var{varname}@r{]}
1839 Print the value of environment variable @var{varname} to be given to
1840 your program when it starts. If you do not supply @var{varname},
1841 print the names and values of all environment variables to be given to
1842 your program. You can abbreviate @code{environment} as @code{env}.
1844 @kindex set environment
1845 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1846 Set environment variable @var{varname} to @var{value}. The value
1847 changes for your program only, not for @value{GDBN} itself. @var{value} may
1848 be any string; the values of environment variables are just strings, and
1849 any interpretation is supplied by your program itself. The @var{value}
1850 parameter is optional; if it is eliminated, the variable is set to a
1852 @c "any string" here does not include leading, trailing
1853 @c blanks. Gnu asks: does anyone care?
1855 For example, this command:
1862 tells the debugged program, when subsequently run, that its user is named
1863 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1864 are not actually required.)
1866 @kindex unset environment
1867 @item unset environment @var{varname}
1868 Remove variable @var{varname} from the environment to be passed to your
1869 program. This is different from @samp{set env @var{varname} =};
1870 @code{unset environment} removes the variable from the environment,
1871 rather than assigning it an empty value.
1874 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1876 by your @code{SHELL} environment variable if it exists (or
1877 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1878 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1879 @file{.bashrc} for BASH---any variables you set in that file affect
1880 your program. You may wish to move setting of environment variables to
1881 files that are only run when you sign on, such as @file{.login} or
1884 @node Working Directory
1885 @section Your program's working directory
1887 @cindex working directory (of your program)
1888 Each time you start your program with @code{run}, it inherits its
1889 working directory from the current working directory of @value{GDBN}.
1890 The @value{GDBN} working directory is initially whatever it inherited
1891 from its parent process (typically the shell), but you can specify a new
1892 working directory in @value{GDBN} with the @code{cd} command.
1894 The @value{GDBN} working directory also serves as a default for the commands
1895 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1900 @item cd @var{directory}
1901 Set the @value{GDBN} working directory to @var{directory}.
1905 Print the @value{GDBN} working directory.
1909 @section Your program's input and output
1914 By default, the program you run under @value{GDBN} does input and output to
1915 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1916 to its own terminal modes to interact with you, but it records the terminal
1917 modes your program was using and switches back to them when you continue
1918 running your program.
1921 @kindex info terminal
1923 Displays information recorded by @value{GDBN} about the terminal modes your
1927 You can redirect your program's input and/or output using shell
1928 redirection with the @code{run} command. For example,
1935 starts your program, diverting its output to the file @file{outfile}.
1938 @cindex controlling terminal
1939 Another way to specify where your program should do input and output is
1940 with the @code{tty} command. This command accepts a file name as
1941 argument, and causes this file to be the default for future @code{run}
1942 commands. It also resets the controlling terminal for the child
1943 process, for future @code{run} commands. For example,
1950 directs that processes started with subsequent @code{run} commands
1951 default to do input and output on the terminal @file{/dev/ttyb} and have
1952 that as their controlling terminal.
1954 An explicit redirection in @code{run} overrides the @code{tty} command's
1955 effect on the input/output device, but not its effect on the controlling
1958 When you use the @code{tty} command or redirect input in the @code{run}
1959 command, only the input @emph{for your program} is affected. The input
1960 for @value{GDBN} still comes from your terminal.
1963 @section Debugging an already-running process
1968 @item attach @var{process-id}
1969 This command attaches to a running process---one that was started
1970 outside @value{GDBN}. (@code{info files} shows your active
1971 targets.) The command takes as argument a process ID. The usual way to
1972 find out the process-id of a Unix process is with the @code{ps} utility,
1973 or with the @samp{jobs -l} shell command.
1975 @code{attach} does not repeat if you press @key{RET} a second time after
1976 executing the command.
1979 To use @code{attach}, your program must be running in an environment
1980 which supports processes; for example, @code{attach} does not work for
1981 programs on bare-board targets that lack an operating system. You must
1982 also have permission to send the process a signal.
1984 When you use @code{attach}, the debugger finds the program running in
1985 the process first by looking in the current working directory, then (if
1986 the program is not found) by using the source file search path
1987 (@pxref{Source Path, ,Specifying source directories}). You can also use
1988 the @code{file} command to load the program. @xref{Files, ,Commands to
1991 The first thing @value{GDBN} does after arranging to debug the specified
1992 process is to stop it. You can examine and modify an attached process
1993 with all the @value{GDBN} commands that are ordinarily available when
1994 you start processes with @code{run}. You can insert breakpoints; you
1995 can step and continue; you can modify storage. If you would rather the
1996 process continue running, you may use the @code{continue} command after
1997 attaching @value{GDBN} to the process.
2002 When you have finished debugging the attached process, you can use the
2003 @code{detach} command to release it from @value{GDBN} control. Detaching
2004 the process continues its execution. After the @code{detach} command,
2005 that process and @value{GDBN} become completely independent once more, and you
2006 are ready to @code{attach} another process or start one with @code{run}.
2007 @code{detach} does not repeat if you press @key{RET} again after
2008 executing the command.
2011 If you exit @value{GDBN} or use the @code{run} command while you have an
2012 attached process, you kill that process. By default, @value{GDBN} asks
2013 for confirmation if you try to do either of these things; you can
2014 control whether or not you need to confirm by using the @code{set
2015 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
2019 @section Killing the child process
2024 Kill the child process in which your program is running under @value{GDBN}.
2027 This command is useful if you wish to debug a core dump instead of a
2028 running process. @value{GDBN} ignores any core dump file while your program
2031 On some operating systems, a program cannot be executed outside @value{GDBN}
2032 while you have breakpoints set on it inside @value{GDBN}. You can use the
2033 @code{kill} command in this situation to permit running your program
2034 outside the debugger.
2036 The @code{kill} command is also useful if you wish to recompile and
2037 relink your program, since on many systems it is impossible to modify an
2038 executable file while it is running in a process. In this case, when you
2039 next type @code{run}, @value{GDBN} notices that the file has changed, and
2040 reads the symbol table again (while trying to preserve your current
2041 breakpoint settings).
2044 @section Debugging programs with multiple threads
2046 @cindex threads of execution
2047 @cindex multiple threads
2048 @cindex switching threads
2049 In some operating systems, such as HP-UX and Solaris, a single program
2050 may have more than one @dfn{thread} of execution. The precise semantics
2051 of threads differ from one operating system to another, but in general
2052 the threads of a single program are akin to multiple processes---except
2053 that they share one address space (that is, they can all examine and
2054 modify the same variables). On the other hand, each thread has its own
2055 registers and execution stack, and perhaps private memory.
2057 @value{GDBN} provides these facilities for debugging multi-thread
2061 @item automatic notification of new threads
2062 @item @samp{thread @var{threadno}}, a command to switch among threads
2063 @item @samp{info threads}, a command to inquire about existing threads
2064 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2065 a command to apply a command to a list of threads
2066 @item thread-specific breakpoints
2070 @emph{Warning:} These facilities are not yet available on every
2071 @value{GDBN} configuration where the operating system supports threads.
2072 If your @value{GDBN} does not support threads, these commands have no
2073 effect. For example, a system without thread support shows no output
2074 from @samp{info threads}, and always rejects the @code{thread} command,
2078 (@value{GDBP}) info threads
2079 (@value{GDBP}) thread 1
2080 Thread ID 1 not known. Use the "info threads" command to
2081 see the IDs of currently known threads.
2083 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2084 @c doesn't support threads"?
2087 @cindex focus of debugging
2088 @cindex current thread
2089 The @value{GDBN} thread debugging facility allows you to observe all
2090 threads while your program runs---but whenever @value{GDBN} takes
2091 control, one thread in particular is always the focus of debugging.
2092 This thread is called the @dfn{current thread}. Debugging commands show
2093 program information from the perspective of the current thread.
2095 @cindex @code{New} @var{systag} message
2096 @cindex thread identifier (system)
2097 @c FIXME-implementors!! It would be more helpful if the [New...] message
2098 @c included GDB's numeric thread handle, so you could just go to that
2099 @c thread without first checking `info threads'.
2100 Whenever @value{GDBN} detects a new thread in your program, it displays
2101 the target system's identification for the thread with a message in the
2102 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2103 whose form varies depending on the particular system. For example, on
2104 LynxOS, you might see
2107 [New process 35 thread 27]
2111 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2112 the @var{systag} is simply something like @samp{process 368}, with no
2115 @c FIXME!! (1) Does the [New...] message appear even for the very first
2116 @c thread of a program, or does it only appear for the
2117 @c second---i.e., when it becomes obvious we have a multithread
2119 @c (2) *Is* there necessarily a first thread always? Or do some
2120 @c multithread systems permit starting a program with multiple
2121 @c threads ab initio?
2123 @cindex thread number
2124 @cindex thread identifier (GDB)
2125 For debugging purposes, @value{GDBN} associates its own thread
2126 number---always a single integer---with each thread in your program.
2129 @kindex info threads
2131 Display a summary of all threads currently in your
2132 program. @value{GDBN} displays for each thread (in this order):
2135 @item the thread number assigned by @value{GDBN}
2137 @item the target system's thread identifier (@var{systag})
2139 @item the current stack frame summary for that thread
2143 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2144 indicates the current thread.
2148 @c end table here to get a little more width for example
2151 (@value{GDBP}) info threads
2152 3 process 35 thread 27 0x34e5 in sigpause ()
2153 2 process 35 thread 23 0x34e5 in sigpause ()
2154 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2160 @cindex thread number
2161 @cindex thread identifier (GDB)
2162 For debugging purposes, @value{GDBN} associates its own thread
2163 number---a small integer assigned in thread-creation order---with each
2164 thread in your program.
2166 @cindex @code{New} @var{systag} message, on HP-UX
2167 @cindex thread identifier (system), on HP-UX
2168 @c FIXME-implementors!! It would be more helpful if the [New...] message
2169 @c included GDB's numeric thread handle, so you could just go to that
2170 @c thread without first checking `info threads'.
2171 Whenever @value{GDBN} detects a new thread in your program, it displays
2172 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2173 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2174 whose form varies depending on the particular system. For example, on
2178 [New thread 2 (system thread 26594)]
2182 when @value{GDBN} notices a new thread.
2185 @kindex info threads
2187 Display a summary of all threads currently in your
2188 program. @value{GDBN} displays for each thread (in this order):
2191 @item the thread number assigned by @value{GDBN}
2193 @item the target system's thread identifier (@var{systag})
2195 @item the current stack frame summary for that thread
2199 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2200 indicates the current thread.
2204 @c end table here to get a little more width for example
2207 (@value{GDBP}) info threads
2208 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2210 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2211 from /usr/lib/libc.2
2212 1 system thread 27905 0x7b003498 in _brk () \@*
2213 from /usr/lib/libc.2
2217 @kindex thread @var{threadno}
2218 @item thread @var{threadno}
2219 Make thread number @var{threadno} the current thread. The command
2220 argument @var{threadno} is the internal @value{GDBN} thread number, as
2221 shown in the first field of the @samp{info threads} display.
2222 @value{GDBN} responds by displaying the system identifier of the thread
2223 you selected, and its current stack frame summary:
2226 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2227 (@value{GDBP}) thread 2
2228 [Switching to process 35 thread 23]
2229 0x34e5 in sigpause ()
2233 As with the @samp{[New @dots{}]} message, the form of the text after
2234 @samp{Switching to} depends on your system's conventions for identifying
2237 @kindex thread apply
2238 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2239 The @code{thread apply} command allows you to apply a command to one or
2240 more threads. Specify the numbers of the threads that you want affected
2241 with the command argument @var{threadno}. @var{threadno} is the internal
2242 @value{GDBN} thread number, as shown in the first field of the @samp{info
2243 threads} display. To apply a command to all threads, use
2244 @code{thread apply all} @var{args}.
2247 @cindex automatic thread selection
2248 @cindex switching threads automatically
2249 @cindex threads, automatic switching
2250 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2251 signal, it automatically selects the thread where that breakpoint or
2252 signal happened. @value{GDBN} alerts you to the context switch with a
2253 message of the form @samp{[Switching to @var{systag}]} to identify the
2256 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2257 more information about how @value{GDBN} behaves when you stop and start
2258 programs with multiple threads.
2260 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2261 watchpoints in programs with multiple threads.
2264 @section Debugging programs with multiple processes
2266 @cindex fork, debugging programs which call
2267 @cindex multiple processes
2268 @cindex processes, multiple
2269 On most systems, @value{GDBN} has no special support for debugging
2270 programs which create additional processes using the @code{fork}
2271 function. When a program forks, @value{GDBN} will continue to debug the
2272 parent process and the child process will run unimpeded. If you have
2273 set a breakpoint in any code which the child then executes, the child
2274 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2275 will cause it to terminate.
2277 However, if you want to debug the child process there is a workaround
2278 which isn't too painful. Put a call to @code{sleep} in the code which
2279 the child process executes after the fork. It may be useful to sleep
2280 only if a certain environment variable is set, or a certain file exists,
2281 so that the delay need not occur when you don't want to run @value{GDBN}
2282 on the child. While the child is sleeping, use the @code{ps} program to
2283 get its process ID. Then tell @value{GDBN} (a new invocation of
2284 @value{GDBN} if you are also debugging the parent process) to attach to
2285 the child process (@pxref{Attach}). From that point on you can debug
2286 the child process just like any other process which you attached to.
2288 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2289 debugging programs that create additional processes using the
2290 @code{fork} or @code{vfork} function.
2292 By default, when a program forks, @value{GDBN} will continue to debug
2293 the parent process and the child process will run unimpeded.
2295 If you want to follow the child process instead of the parent process,
2296 use the command @w{@code{set follow-fork-mode}}.
2299 @kindex set follow-fork-mode
2300 @item set follow-fork-mode @var{mode}
2301 Set the debugger response to a program call of @code{fork} or
2302 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2303 process. The @var{mode} can be:
2307 The original process is debugged after a fork. The child process runs
2308 unimpeded. This is the default.
2311 The new process is debugged after a fork. The parent process runs
2315 The debugger will ask for one of the above choices.
2318 @item show follow-fork-mode
2319 Display the current debugger response to a @code{fork} or @code{vfork} call.
2322 If you ask to debug a child process and a @code{vfork} is followed by an
2323 @code{exec}, @value{GDBN} executes the new target up to the first
2324 breakpoint in the new target. If you have a breakpoint set on
2325 @code{main} in your original program, the breakpoint will also be set on
2326 the child process's @code{main}.
2328 When a child process is spawned by @code{vfork}, you cannot debug the
2329 child or parent until an @code{exec} call completes.
2331 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2332 call executes, the new target restarts. To restart the parent process,
2333 use the @code{file} command with the parent executable name as its
2336 You can use the @code{catch} command to make @value{GDBN} stop whenever
2337 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2338 Catchpoints, ,Setting catchpoints}.
2341 @chapter Stopping and Continuing
2343 The principal purposes of using a debugger are so that you can stop your
2344 program before it terminates; or so that, if your program runs into
2345 trouble, you can investigate and find out why.
2347 Inside @value{GDBN}, your program may stop for any of several reasons,
2348 such as a signal, a breakpoint, or reaching a new line after a
2349 @value{GDBN} command such as @code{step}. You may then examine and
2350 change variables, set new breakpoints or remove old ones, and then
2351 continue execution. Usually, the messages shown by @value{GDBN} provide
2352 ample explanation of the status of your program---but you can also
2353 explicitly request this information at any time.
2356 @kindex info program
2358 Display information about the status of your program: whether it is
2359 running or not, what process it is, and why it stopped.
2363 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2364 * Continuing and Stepping:: Resuming execution
2366 * Thread Stops:: Stopping and starting multi-thread programs
2370 @section Breakpoints, watchpoints, and catchpoints
2373 A @dfn{breakpoint} makes your program stop whenever a certain point in
2374 the program is reached. For each breakpoint, you can add conditions to
2375 control in finer detail whether your program stops. You can set
2376 breakpoints with the @code{break} command and its variants (@pxref{Set
2377 Breaks, ,Setting breakpoints}), to specify the place where your program
2378 should stop by line number, function name or exact address in the
2381 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2382 breakpoints in shared libraries before the executable is run. There is
2383 a minor limitation on HP-UX systems: you must wait until the executable
2384 is run in order to set breakpoints in shared library routines that are
2385 not called directly by the program (for example, routines that are
2386 arguments in a @code{pthread_create} call).
2389 @cindex memory tracing
2390 @cindex breakpoint on memory address
2391 @cindex breakpoint on variable modification
2392 A @dfn{watchpoint} is a special breakpoint that stops your program
2393 when the value of an expression changes. You must use a different
2394 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2395 watchpoints}), but aside from that, you can manage a watchpoint like
2396 any other breakpoint: you enable, disable, and delete both breakpoints
2397 and watchpoints using the same commands.
2399 You can arrange to have values from your program displayed automatically
2400 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2404 @cindex breakpoint on events
2405 A @dfn{catchpoint} is another special breakpoint that stops your program
2406 when a certain kind of event occurs, such as the throwing of a C@t{++}
2407 exception or the loading of a library. As with watchpoints, you use a
2408 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2409 catchpoints}), but aside from that, you can manage a catchpoint like any
2410 other breakpoint. (To stop when your program receives a signal, use the
2411 @code{handle} command; see @ref{Signals, ,Signals}.)
2413 @cindex breakpoint numbers
2414 @cindex numbers for breakpoints
2415 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2416 catchpoint when you create it; these numbers are successive integers
2417 starting with one. In many of the commands for controlling various
2418 features of breakpoints you use the breakpoint number to say which
2419 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2420 @dfn{disabled}; if disabled, it has no effect on your program until you
2423 @cindex breakpoint ranges
2424 @cindex ranges of breakpoints
2425 Some @value{GDBN} commands accept a range of breakpoints on which to
2426 operate. A breakpoint range is either a single breakpoint number, like
2427 @samp{5}, or two such numbers, in increasing order, separated by a
2428 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2429 all breakpoint in that range are operated on.
2432 * Set Breaks:: Setting breakpoints
2433 * Set Watchpoints:: Setting watchpoints
2434 * Set Catchpoints:: Setting catchpoints
2435 * Delete Breaks:: Deleting breakpoints
2436 * Disabling:: Disabling breakpoints
2437 * Conditions:: Break conditions
2438 * Break Commands:: Breakpoint command lists
2439 * Breakpoint Menus:: Breakpoint menus
2440 * Error in Breakpoints:: ``Cannot insert breakpoints''
2444 @subsection Setting breakpoints
2446 @c FIXME LMB what does GDB do if no code on line of breakpt?
2447 @c consider in particular declaration with/without initialization.
2449 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2452 @kindex b @r{(@code{break})}
2453 @vindex $bpnum@r{, convenience variable}
2454 @cindex latest breakpoint
2455 Breakpoints are set with the @code{break} command (abbreviated
2456 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2457 number of the breakpoint you've set most recently; see @ref{Convenience
2458 Vars,, Convenience variables}, for a discussion of what you can do with
2459 convenience variables.
2461 You have several ways to say where the breakpoint should go.
2464 @item break @var{function}
2465 Set a breakpoint at entry to function @var{function}.
2466 When using source languages that permit overloading of symbols, such as
2467 C@t{++}, @var{function} may refer to more than one possible place to break.
2468 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2470 @item break +@var{offset}
2471 @itemx break -@var{offset}
2472 Set a breakpoint some number of lines forward or back from the position
2473 at which execution stopped in the currently selected @dfn{stack frame}.
2474 (@xref{Frames, ,Frames}, for a description of stack frames.)
2476 @item break @var{linenum}
2477 Set a breakpoint at line @var{linenum} in the current source file.
2478 The current source file is the last file whose source text was printed.
2479 The breakpoint will stop your program just before it executes any of the
2482 @item break @var{filename}:@var{linenum}
2483 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2485 @item break @var{filename}:@var{function}
2486 Set a breakpoint at entry to function @var{function} found in file
2487 @var{filename}. Specifying a file name as well as a function name is
2488 superfluous except when multiple files contain similarly named
2491 @item break *@var{address}
2492 Set a breakpoint at address @var{address}. You can use this to set
2493 breakpoints in parts of your program which do not have debugging
2494 information or source files.
2497 When called without any arguments, @code{break} sets a breakpoint at
2498 the next instruction to be executed in the selected stack frame
2499 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2500 innermost, this makes your program stop as soon as control
2501 returns to that frame. This is similar to the effect of a
2502 @code{finish} command in the frame inside the selected frame---except
2503 that @code{finish} does not leave an active breakpoint. If you use
2504 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2505 the next time it reaches the current location; this may be useful
2508 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2509 least one instruction has been executed. If it did not do this, you
2510 would be unable to proceed past a breakpoint without first disabling the
2511 breakpoint. This rule applies whether or not the breakpoint already
2512 existed when your program stopped.
2514 @item break @dots{} if @var{cond}
2515 Set a breakpoint with condition @var{cond}; evaluate the expression
2516 @var{cond} each time the breakpoint is reached, and stop only if the
2517 value is nonzero---that is, if @var{cond} evaluates as true.
2518 @samp{@dots{}} stands for one of the possible arguments described
2519 above (or no argument) specifying where to break. @xref{Conditions,
2520 ,Break conditions}, for more information on breakpoint conditions.
2523 @item tbreak @var{args}
2524 Set a breakpoint enabled only for one stop. @var{args} are the
2525 same as for the @code{break} command, and the breakpoint is set in the same
2526 way, but the breakpoint is automatically deleted after the first time your
2527 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2530 @item hbreak @var{args}
2531 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2532 @code{break} command and the breakpoint is set in the same way, but the
2533 breakpoint requires hardware support and some target hardware may not
2534 have this support. The main purpose of this is EPROM/ROM code
2535 debugging, so you can set a breakpoint at an instruction without
2536 changing the instruction. This can be used with the new trap-generation
2537 provided by SPARClite DSU and some x86-based targets. These targets
2538 will generate traps when a program accesses some data or instruction
2539 address that is assigned to the debug registers. However the hardware
2540 breakpoint registers can take a limited number of breakpoints. For
2541 example, on the DSU, only two data breakpoints can be set at a time, and
2542 @value{GDBN} will reject this command if more than two are used. Delete
2543 or disable unused hardware breakpoints before setting new ones
2544 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2547 @item thbreak @var{args}
2548 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2549 are the same as for the @code{hbreak} command and the breakpoint is set in
2550 the same way. However, like the @code{tbreak} command,
2551 the breakpoint is automatically deleted after the
2552 first time your program stops there. Also, like the @code{hbreak}
2553 command, the breakpoint requires hardware support and some target hardware
2554 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2555 See also @ref{Conditions, ,Break conditions}.
2558 @cindex regular expression
2559 @item rbreak @var{regex}
2560 Set breakpoints on all functions matching the regular expression
2561 @var{regex}. This command sets an unconditional breakpoint on all
2562 matches, printing a list of all breakpoints it set. Once these
2563 breakpoints are set, they are treated just like the breakpoints set with
2564 the @code{break} command. You can delete them, disable them, or make
2565 them conditional the same way as any other breakpoint.
2567 The syntax of the regular expression is the standard one used with tools
2568 like @file{grep}. Note that this is different from the syntax used by
2569 shells, so for instance @code{foo*} matches all functions that include
2570 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2571 @code{.*} leading and trailing the regular expression you supply, so to
2572 match only functions that begin with @code{foo}, use @code{^foo}.
2574 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2575 breakpoints on overloaded functions that are not members of any special
2578 @kindex info breakpoints
2579 @cindex @code{$_} and @code{info breakpoints}
2580 @item info breakpoints @r{[}@var{n}@r{]}
2581 @itemx info break @r{[}@var{n}@r{]}
2582 @itemx info watchpoints @r{[}@var{n}@r{]}
2583 Print a table of all breakpoints, watchpoints, and catchpoints set and
2584 not deleted, with the following columns for each breakpoint:
2587 @item Breakpoint Numbers
2589 Breakpoint, watchpoint, or catchpoint.
2591 Whether the breakpoint is marked to be disabled or deleted when hit.
2592 @item Enabled or Disabled
2593 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2594 that are not enabled.
2596 Where the breakpoint is in your program, as a memory address.
2598 Where the breakpoint is in the source for your program, as a file and
2603 If a breakpoint is conditional, @code{info break} shows the condition on
2604 the line following the affected breakpoint; breakpoint commands, if any,
2605 are listed after that.
2608 @code{info break} with a breakpoint
2609 number @var{n} as argument lists only that breakpoint. The
2610 convenience variable @code{$_} and the default examining-address for
2611 the @code{x} command are set to the address of the last breakpoint
2612 listed (@pxref{Memory, ,Examining memory}).
2615 @code{info break} displays a count of the number of times the breakpoint
2616 has been hit. This is especially useful in conjunction with the
2617 @code{ignore} command. You can ignore a large number of breakpoint
2618 hits, look at the breakpoint info to see how many times the breakpoint
2619 was hit, and then run again, ignoring one less than that number. This
2620 will get you quickly to the last hit of that breakpoint.
2623 @value{GDBN} allows you to set any number of breakpoints at the same place in
2624 your program. There is nothing silly or meaningless about this. When
2625 the breakpoints are conditional, this is even useful
2626 (@pxref{Conditions, ,Break conditions}).
2628 @cindex negative breakpoint numbers
2629 @cindex internal @value{GDBN} breakpoints
2630 @value{GDBN} itself sometimes sets breakpoints in your program for special
2631 purposes, such as proper handling of @code{longjmp} (in C programs).
2632 These internal breakpoints are assigned negative numbers, starting with
2633 @code{-1}; @samp{info breakpoints} does not display them.
2635 You can see these breakpoints with the @value{GDBN} maintenance command
2636 @samp{maint info breakpoints}.
2639 @kindex maint info breakpoints
2640 @item maint info breakpoints
2641 Using the same format as @samp{info breakpoints}, display both the
2642 breakpoints you've set explicitly, and those @value{GDBN} is using for
2643 internal purposes. Internal breakpoints are shown with negative
2644 breakpoint numbers. The type column identifies what kind of breakpoint
2649 Normal, explicitly set breakpoint.
2652 Normal, explicitly set watchpoint.
2655 Internal breakpoint, used to handle correctly stepping through
2656 @code{longjmp} calls.
2658 @item longjmp resume
2659 Internal breakpoint at the target of a @code{longjmp}.
2662 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2665 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2668 Shared library events.
2675 @node Set Watchpoints
2676 @subsection Setting watchpoints
2678 @cindex setting watchpoints
2679 @cindex software watchpoints
2680 @cindex hardware watchpoints
2681 You can use a watchpoint to stop execution whenever the value of an
2682 expression changes, without having to predict a particular place where
2685 Depending on your system, watchpoints may be implemented in software or
2686 hardware. @value{GDBN} does software watchpointing by single-stepping your
2687 program and testing the variable's value each time, which is hundreds of
2688 times slower than normal execution. (But this may still be worth it, to
2689 catch errors where you have no clue what part of your program is the
2692 On some systems, such as HP-UX, Linux and some other x86-based targets,
2693 @value{GDBN} includes support for
2694 hardware watchpoints, which do not slow down the running of your
2699 @item watch @var{expr}
2700 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2701 is written into by the program and its value changes.
2704 @item rwatch @var{expr}
2705 Set a watchpoint that will break when watch @var{expr} is read by the program.
2708 @item awatch @var{expr}
2709 Set a watchpoint that will break when @var{expr} is either read or written into
2712 @kindex info watchpoints
2713 @item info watchpoints
2714 This command prints a list of watchpoints, breakpoints, and catchpoints;
2715 it is the same as @code{info break}.
2718 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2719 watchpoints execute very quickly, and the debugger reports a change in
2720 value at the exact instruction where the change occurs. If @value{GDBN}
2721 cannot set a hardware watchpoint, it sets a software watchpoint, which
2722 executes more slowly and reports the change in value at the next
2723 statement, not the instruction, after the change occurs.
2725 When you issue the @code{watch} command, @value{GDBN} reports
2728 Hardware watchpoint @var{num}: @var{expr}
2732 if it was able to set a hardware watchpoint.
2734 Currently, the @code{awatch} and @code{rwatch} commands can only set
2735 hardware watchpoints, because accesses to data that don't change the
2736 value of the watched expression cannot be detected without examining
2737 every instruction as it is being executed, and @value{GDBN} does not do
2738 that currently. If @value{GDBN} finds that it is unable to set a
2739 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2740 will print a message like this:
2743 Expression cannot be implemented with read/access watchpoint.
2746 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2747 data type of the watched expression is wider than what a hardware
2748 watchpoint on the target machine can handle. For example, some systems
2749 can only watch regions that are up to 4 bytes wide; on such systems you
2750 cannot set hardware watchpoints for an expression that yields a
2751 double-precision floating-point number (which is typically 8 bytes
2752 wide). As a work-around, it might be possible to break the large region
2753 into a series of smaller ones and watch them with separate watchpoints.
2755 If you set too many hardware watchpoints, @value{GDBN} might be unable
2756 to insert all of them when you resume the execution of your program.
2757 Since the precise number of active watchpoints is unknown until such
2758 time as the program is about to be resumed, @value{GDBN} might not be
2759 able to warn you about this when you set the watchpoints, and the
2760 warning will be printed only when the program is resumed:
2763 Hardware watchpoint @var{num}: Could not insert watchpoint
2767 If this happens, delete or disable some of the watchpoints.
2769 The SPARClite DSU will generate traps when a program accesses some data
2770 or instruction address that is assigned to the debug registers. For the
2771 data addresses, DSU facilitates the @code{watch} command. However the
2772 hardware breakpoint registers can only take two data watchpoints, and
2773 both watchpoints must be the same kind. For example, you can set two
2774 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2775 @strong{or} two with @code{awatch} commands, but you cannot set one
2776 watchpoint with one command and the other with a different command.
2777 @value{GDBN} will reject the command if you try to mix watchpoints.
2778 Delete or disable unused watchpoint commands before setting new ones.
2780 If you call a function interactively using @code{print} or @code{call},
2781 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2782 kind of breakpoint or the call completes.
2784 @value{GDBN} automatically deletes watchpoints that watch local
2785 (automatic) variables, or expressions that involve such variables, when
2786 they go out of scope, that is, when the execution leaves the block in
2787 which these variables were defined. In particular, when the program
2788 being debugged terminates, @emph{all} local variables go out of scope,
2789 and so only watchpoints that watch global variables remain set. If you
2790 rerun the program, you will need to set all such watchpoints again. One
2791 way of doing that would be to set a code breakpoint at the entry to the
2792 @code{main} function and when it breaks, set all the watchpoints.
2795 @cindex watchpoints and threads
2796 @cindex threads and watchpoints
2797 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2798 usefulness. With the current watchpoint implementation, @value{GDBN}
2799 can only watch the value of an expression @emph{in a single thread}. If
2800 you are confident that the expression can only change due to the current
2801 thread's activity (and if you are also confident that no other thread
2802 can become current), then you can use watchpoints as usual. However,
2803 @value{GDBN} may not notice when a non-current thread's activity changes
2806 @c FIXME: this is almost identical to the previous paragraph.
2807 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2808 have only limited usefulness. If @value{GDBN} creates a software
2809 watchpoint, it can only watch the value of an expression @emph{in a
2810 single thread}. If you are confident that the expression can only
2811 change due to the current thread's activity (and if you are also
2812 confident that no other thread can become current), then you can use
2813 software watchpoints as usual. However, @value{GDBN} may not notice
2814 when a non-current thread's activity changes the expression. (Hardware
2815 watchpoints, in contrast, watch an expression in all threads.)
2818 @node Set Catchpoints
2819 @subsection Setting catchpoints
2820 @cindex catchpoints, setting
2821 @cindex exception handlers
2822 @cindex event handling
2824 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2825 kinds of program events, such as C@t{++} exceptions or the loading of a
2826 shared library. Use the @code{catch} command to set a catchpoint.
2830 @item catch @var{event}
2831 Stop when @var{event} occurs. @var{event} can be any of the following:
2835 The throwing of a C@t{++} exception.
2839 The catching of a C@t{++} exception.
2843 A call to @code{exec}. This is currently only available for HP-UX.
2847 A call to @code{fork}. This is currently only available for HP-UX.
2851 A call to @code{vfork}. This is currently only available for HP-UX.
2854 @itemx load @var{libname}
2856 The dynamic loading of any shared library, or the loading of the library
2857 @var{libname}. This is currently only available for HP-UX.
2860 @itemx unload @var{libname}
2861 @kindex catch unload
2862 The unloading of any dynamically loaded shared library, or the unloading
2863 of the library @var{libname}. This is currently only available for HP-UX.
2866 @item tcatch @var{event}
2867 Set a catchpoint that is enabled only for one stop. The catchpoint is
2868 automatically deleted after the first time the event is caught.
2872 Use the @code{info break} command to list the current catchpoints.
2874 There are currently some limitations to C@t{++} exception handling
2875 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2879 If you call a function interactively, @value{GDBN} normally returns
2880 control to you when the function has finished executing. If the call
2881 raises an exception, however, the call may bypass the mechanism that
2882 returns control to you and cause your program either to abort or to
2883 simply continue running until it hits a breakpoint, catches a signal
2884 that @value{GDBN} is listening for, or exits. This is the case even if
2885 you set a catchpoint for the exception; catchpoints on exceptions are
2886 disabled within interactive calls.
2889 You cannot raise an exception interactively.
2892 You cannot install an exception handler interactively.
2895 @cindex raise exceptions
2896 Sometimes @code{catch} is not the best way to debug exception handling:
2897 if you need to know exactly where an exception is raised, it is better to
2898 stop @emph{before} the exception handler is called, since that way you
2899 can see the stack before any unwinding takes place. If you set a
2900 breakpoint in an exception handler instead, it may not be easy to find
2901 out where the exception was raised.
2903 To stop just before an exception handler is called, you need some
2904 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2905 raised by calling a library function named @code{__raise_exception}
2906 which has the following ANSI C interface:
2909 /* @var{addr} is where the exception identifier is stored.
2910 @var{id} is the exception identifier. */
2911 void __raise_exception (void **addr, void *id);
2915 To make the debugger catch all exceptions before any stack
2916 unwinding takes place, set a breakpoint on @code{__raise_exception}
2917 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2919 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2920 that depends on the value of @var{id}, you can stop your program when
2921 a specific exception is raised. You can use multiple conditional
2922 breakpoints to stop your program when any of a number of exceptions are
2927 @subsection Deleting breakpoints
2929 @cindex clearing breakpoints, watchpoints, catchpoints
2930 @cindex deleting breakpoints, watchpoints, catchpoints
2931 It is often necessary to eliminate a breakpoint, watchpoint, or
2932 catchpoint once it has done its job and you no longer want your program
2933 to stop there. This is called @dfn{deleting} the breakpoint. A
2934 breakpoint that has been deleted no longer exists; it is forgotten.
2936 With the @code{clear} command you can delete breakpoints according to
2937 where they are in your program. With the @code{delete} command you can
2938 delete individual breakpoints, watchpoints, or catchpoints by specifying
2939 their breakpoint numbers.
2941 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2942 automatically ignores breakpoints on the first instruction to be executed
2943 when you continue execution without changing the execution address.
2948 Delete any breakpoints at the next instruction to be executed in the
2949 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2950 the innermost frame is selected, this is a good way to delete a
2951 breakpoint where your program just stopped.
2953 @item clear @var{function}
2954 @itemx clear @var{filename}:@var{function}
2955 Delete any breakpoints set at entry to the function @var{function}.
2957 @item clear @var{linenum}
2958 @itemx clear @var{filename}:@var{linenum}
2959 Delete any breakpoints set at or within the code of the specified line.
2961 @cindex delete breakpoints
2963 @kindex d @r{(@code{delete})}
2964 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2965 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2966 ranges specified as arguments. If no argument is specified, delete all
2967 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2968 confirm off}). You can abbreviate this command as @code{d}.
2972 @subsection Disabling breakpoints
2974 @kindex disable breakpoints
2975 @kindex enable breakpoints
2976 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2977 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2978 it had been deleted, but remembers the information on the breakpoint so
2979 that you can @dfn{enable} it again later.
2981 You disable and enable breakpoints, watchpoints, and catchpoints with
2982 the @code{enable} and @code{disable} commands, optionally specifying one
2983 or more breakpoint numbers as arguments. Use @code{info break} or
2984 @code{info watch} to print a list of breakpoints, watchpoints, and
2985 catchpoints if you do not know which numbers to use.
2987 A breakpoint, watchpoint, or catchpoint can have any of four different
2988 states of enablement:
2992 Enabled. The breakpoint stops your program. A breakpoint set
2993 with the @code{break} command starts out in this state.
2995 Disabled. The breakpoint has no effect on your program.
2997 Enabled once. The breakpoint stops your program, but then becomes
3000 Enabled for deletion. The breakpoint stops your program, but
3001 immediately after it does so it is deleted permanently. A breakpoint
3002 set with the @code{tbreak} command starts out in this state.
3005 You can use the following commands to enable or disable breakpoints,
3006 watchpoints, and catchpoints:
3009 @kindex disable breakpoints
3011 @kindex dis @r{(@code{disable})}
3012 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3013 Disable the specified breakpoints---or all breakpoints, if none are
3014 listed. A disabled breakpoint has no effect but is not forgotten. All
3015 options such as ignore-counts, conditions and commands are remembered in
3016 case the breakpoint is enabled again later. You may abbreviate
3017 @code{disable} as @code{dis}.
3019 @kindex enable breakpoints
3021 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3022 Enable the specified breakpoints (or all defined breakpoints). They
3023 become effective once again in stopping your program.
3025 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
3026 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3027 of these breakpoints immediately after stopping your program.
3029 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
3030 Enable the specified breakpoints to work once, then die. @value{GDBN}
3031 deletes any of these breakpoints as soon as your program stops there.
3034 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
3035 @c confusing: tbreak is also initially enabled.
3036 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3037 ,Setting breakpoints}), breakpoints that you set are initially enabled;
3038 subsequently, they become disabled or enabled only when you use one of
3039 the commands above. (The command @code{until} can set and delete a
3040 breakpoint of its own, but it does not change the state of your other
3041 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3045 @subsection Break conditions
3046 @cindex conditional breakpoints
3047 @cindex breakpoint conditions
3049 @c FIXME what is scope of break condition expr? Context where wanted?
3050 @c in particular for a watchpoint?
3051 The simplest sort of breakpoint breaks every time your program reaches a
3052 specified place. You can also specify a @dfn{condition} for a
3053 breakpoint. A condition is just a Boolean expression in your
3054 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3055 a condition evaluates the expression each time your program reaches it,
3056 and your program stops only if the condition is @emph{true}.
3058 This is the converse of using assertions for program validation; in that
3059 situation, you want to stop when the assertion is violated---that is,
3060 when the condition is false. In C, if you want to test an assertion expressed
3061 by the condition @var{assert}, you should set the condition
3062 @samp{! @var{assert}} on the appropriate breakpoint.
3064 Conditions are also accepted for watchpoints; you may not need them,
3065 since a watchpoint is inspecting the value of an expression anyhow---but
3066 it might be simpler, say, to just set a watchpoint on a variable name,
3067 and specify a condition that tests whether the new value is an interesting
3070 Break conditions can have side effects, and may even call functions in
3071 your program. This can be useful, for example, to activate functions
3072 that log program progress, or to use your own print functions to
3073 format special data structures. The effects are completely predictable
3074 unless there is another enabled breakpoint at the same address. (In
3075 that case, @value{GDBN} might see the other breakpoint first and stop your
3076 program without checking the condition of this one.) Note that
3077 breakpoint commands are usually more convenient and flexible than break
3079 purpose of performing side effects when a breakpoint is reached
3080 (@pxref{Break Commands, ,Breakpoint command lists}).
3082 Break conditions can be specified when a breakpoint is set, by using
3083 @samp{if} in the arguments to the @code{break} command. @xref{Set
3084 Breaks, ,Setting breakpoints}. They can also be changed at any time
3085 with the @code{condition} command.
3087 You can also use the @code{if} keyword with the @code{watch} command.
3088 The @code{catch} command does not recognize the @code{if} keyword;
3089 @code{condition} is the only way to impose a further condition on a
3094 @item condition @var{bnum} @var{expression}
3095 Specify @var{expression} as the break condition for breakpoint,
3096 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3097 breakpoint @var{bnum} stops your program only if the value of
3098 @var{expression} is true (nonzero, in C). When you use
3099 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3100 syntactic correctness, and to determine whether symbols in it have
3101 referents in the context of your breakpoint. If @var{expression} uses
3102 symbols not referenced in the context of the breakpoint, @value{GDBN}
3103 prints an error message:
3106 No symbol "foo" in current context.
3111 not actually evaluate @var{expression} at the time the @code{condition}
3112 command (or a command that sets a breakpoint with a condition, like
3113 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3115 @item condition @var{bnum}
3116 Remove the condition from breakpoint number @var{bnum}. It becomes
3117 an ordinary unconditional breakpoint.
3120 @cindex ignore count (of breakpoint)
3121 A special case of a breakpoint condition is to stop only when the
3122 breakpoint has been reached a certain number of times. This is so
3123 useful that there is a special way to do it, using the @dfn{ignore
3124 count} of the breakpoint. Every breakpoint has an ignore count, which
3125 is an integer. Most of the time, the ignore count is zero, and
3126 therefore has no effect. But if your program reaches a breakpoint whose
3127 ignore count is positive, then instead of stopping, it just decrements
3128 the ignore count by one and continues. As a result, if the ignore count
3129 value is @var{n}, the breakpoint does not stop the next @var{n} times
3130 your program reaches it.
3134 @item ignore @var{bnum} @var{count}
3135 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3136 The next @var{count} times the breakpoint is reached, your program's
3137 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3140 To make the breakpoint stop the next time it is reached, specify
3143 When you use @code{continue} to resume execution of your program from a
3144 breakpoint, you can specify an ignore count directly as an argument to
3145 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3146 Stepping,,Continuing and stepping}.
3148 If a breakpoint has a positive ignore count and a condition, the
3149 condition is not checked. Once the ignore count reaches zero,
3150 @value{GDBN} resumes checking the condition.
3152 You could achieve the effect of the ignore count with a condition such
3153 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3154 is decremented each time. @xref{Convenience Vars, ,Convenience
3158 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3161 @node Break Commands
3162 @subsection Breakpoint command lists
3164 @cindex breakpoint commands
3165 You can give any breakpoint (or watchpoint or catchpoint) a series of
3166 commands to execute when your program stops due to that breakpoint. For
3167 example, you might want to print the values of certain expressions, or
3168 enable other breakpoints.
3173 @item commands @r{[}@var{bnum}@r{]}
3174 @itemx @dots{} @var{command-list} @dots{}
3176 Specify a list of commands for breakpoint number @var{bnum}. The commands
3177 themselves appear on the following lines. Type a line containing just
3178 @code{end} to terminate the commands.
3180 To remove all commands from a breakpoint, type @code{commands} and
3181 follow it immediately with @code{end}; that is, give no commands.
3183 With no @var{bnum} argument, @code{commands} refers to the last
3184 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3185 recently encountered).
3188 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3189 disabled within a @var{command-list}.
3191 You can use breakpoint commands to start your program up again. Simply
3192 use the @code{continue} command, or @code{step}, or any other command
3193 that resumes execution.
3195 Any other commands in the command list, after a command that resumes
3196 execution, are ignored. This is because any time you resume execution
3197 (even with a simple @code{next} or @code{step}), you may encounter
3198 another breakpoint---which could have its own command list, leading to
3199 ambiguities about which list to execute.
3202 If the first command you specify in a command list is @code{silent}, the
3203 usual message about stopping at a breakpoint is not printed. This may
3204 be desirable for breakpoints that are to print a specific message and
3205 then continue. If none of the remaining commands print anything, you
3206 see no sign that the breakpoint was reached. @code{silent} is
3207 meaningful only at the beginning of a breakpoint command list.
3209 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3210 print precisely controlled output, and are often useful in silent
3211 breakpoints. @xref{Output, ,Commands for controlled output}.
3213 For example, here is how you could use breakpoint commands to print the
3214 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3220 printf "x is %d\n",x
3225 One application for breakpoint commands is to compensate for one bug so
3226 you can test for another. Put a breakpoint just after the erroneous line
3227 of code, give it a condition to detect the case in which something
3228 erroneous has been done, and give it commands to assign correct values
3229 to any variables that need them. End with the @code{continue} command
3230 so that your program does not stop, and start with the @code{silent}
3231 command so that no output is produced. Here is an example:
3242 @node Breakpoint Menus
3243 @subsection Breakpoint menus
3245 @cindex symbol overloading
3247 Some programming languages (notably C@t{++}) permit a single function name
3248 to be defined several times, for application in different contexts.
3249 This is called @dfn{overloading}. When a function name is overloaded,
3250 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3251 a breakpoint. If you realize this is a problem, you can use
3252 something like @samp{break @var{function}(@var{types})} to specify which
3253 particular version of the function you want. Otherwise, @value{GDBN} offers
3254 you a menu of numbered choices for different possible breakpoints, and
3255 waits for your selection with the prompt @samp{>}. The first two
3256 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3257 sets a breakpoint at each definition of @var{function}, and typing
3258 @kbd{0} aborts the @code{break} command without setting any new
3261 For example, the following session excerpt shows an attempt to set a
3262 breakpoint at the overloaded symbol @code{String::after}.
3263 We choose three particular definitions of that function name:
3265 @c FIXME! This is likely to change to show arg type lists, at least
3268 (@value{GDBP}) b String::after
3271 [2] file:String.cc; line number:867
3272 [3] file:String.cc; line number:860
3273 [4] file:String.cc; line number:875
3274 [5] file:String.cc; line number:853
3275 [6] file:String.cc; line number:846
3276 [7] file:String.cc; line number:735
3278 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3279 Breakpoint 2 at 0xb344: file String.cc, line 875.
3280 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3281 Multiple breakpoints were set.
3282 Use the "delete" command to delete unwanted
3288 @c @ifclear BARETARGET
3289 @node Error in Breakpoints
3290 @subsection ``Cannot insert breakpoints''
3292 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3294 Under some operating systems, breakpoints cannot be used in a program if
3295 any other process is running that program. In this situation,
3296 attempting to run or continue a program with a breakpoint causes
3297 @value{GDBN} to print an error message:
3300 Cannot insert breakpoints.
3301 The same program may be running in another process.
3304 When this happens, you have three ways to proceed:
3308 Remove or disable the breakpoints, then continue.
3311 Suspend @value{GDBN}, and copy the file containing your program to a new
3312 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3313 that @value{GDBN} should run your program under that name.
3314 Then start your program again.
3317 Relink your program so that the text segment is nonsharable, using the
3318 linker option @samp{-N}. The operating system limitation may not apply
3319 to nonsharable executables.
3323 A similar message can be printed if you request too many active
3324 hardware-assisted breakpoints and watchpoints:
3326 @c FIXME: the precise wording of this message may change; the relevant
3327 @c source change is not committed yet (Sep 3, 1999).
3329 Stopped; cannot insert breakpoints.
3330 You may have requested too many hardware breakpoints and watchpoints.
3334 This message is printed when you attempt to resume the program, since
3335 only then @value{GDBN} knows exactly how many hardware breakpoints and
3336 watchpoints it needs to insert.
3338 When this message is printed, you need to disable or remove some of the
3339 hardware-assisted breakpoints and watchpoints, and then continue.
3342 @node Continuing and Stepping
3343 @section Continuing and stepping
3347 @cindex resuming execution
3348 @dfn{Continuing} means resuming program execution until your program
3349 completes normally. In contrast, @dfn{stepping} means executing just
3350 one more ``step'' of your program, where ``step'' may mean either one
3351 line of source code, or one machine instruction (depending on what
3352 particular command you use). Either when continuing or when stepping,
3353 your program may stop even sooner, due to a breakpoint or a signal. (If
3354 it stops due to a signal, you may want to use @code{handle}, or use
3355 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3359 @kindex c @r{(@code{continue})}
3360 @kindex fg @r{(resume foreground execution)}
3361 @item continue @r{[}@var{ignore-count}@r{]}
3362 @itemx c @r{[}@var{ignore-count}@r{]}
3363 @itemx fg @r{[}@var{ignore-count}@r{]}
3364 Resume program execution, at the address where your program last stopped;
3365 any breakpoints set at that address are bypassed. The optional argument
3366 @var{ignore-count} allows you to specify a further number of times to
3367 ignore a breakpoint at this location; its effect is like that of
3368 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3370 The argument @var{ignore-count} is meaningful only when your program
3371 stopped due to a breakpoint. At other times, the argument to
3372 @code{continue} is ignored.
3374 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3375 debugged program is deemed to be the foreground program) are provided
3376 purely for convenience, and have exactly the same behavior as
3380 To resume execution at a different place, you can use @code{return}
3381 (@pxref{Returning, ,Returning from a function}) to go back to the
3382 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3383 different address}) to go to an arbitrary location in your program.
3385 A typical technique for using stepping is to set a breakpoint
3386 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3387 beginning of the function or the section of your program where a problem
3388 is believed to lie, run your program until it stops at that breakpoint,
3389 and then step through the suspect area, examining the variables that are
3390 interesting, until you see the problem happen.
3394 @kindex s @r{(@code{step})}
3396 Continue running your program until control reaches a different source
3397 line, then stop it and return control to @value{GDBN}. This command is
3398 abbreviated @code{s}.
3401 @c "without debugging information" is imprecise; actually "without line
3402 @c numbers in the debugging information". (gcc -g1 has debugging info but
3403 @c not line numbers). But it seems complex to try to make that
3404 @c distinction here.
3405 @emph{Warning:} If you use the @code{step} command while control is
3406 within a function that was compiled without debugging information,
3407 execution proceeds until control reaches a function that does have
3408 debugging information. Likewise, it will not step into a function which
3409 is compiled without debugging information. To step through functions
3410 without debugging information, use the @code{stepi} command, described
3414 The @code{step} command only stops at the first instruction of a source
3415 line. This prevents the multiple stops that could otherwise occur in
3416 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3417 to stop if a function that has debugging information is called within
3418 the line. In other words, @code{step} @emph{steps inside} any functions
3419 called within the line.
3421 Also, the @code{step} command only enters a function if there is line
3422 number information for the function. Otherwise it acts like the
3423 @code{next} command. This avoids problems when using @code{cc -gl}
3424 on MIPS machines. Previously, @code{step} entered subroutines if there
3425 was any debugging information about the routine.
3427 @item step @var{count}
3428 Continue running as in @code{step}, but do so @var{count} times. If a
3429 breakpoint is reached, or a signal not related to stepping occurs before
3430 @var{count} steps, stepping stops right away.
3433 @kindex n @r{(@code{next})}
3434 @item next @r{[}@var{count}@r{]}
3435 Continue to the next source line in the current (innermost) stack frame.
3436 This is similar to @code{step}, but function calls that appear within
3437 the line of code are executed without stopping. Execution stops when
3438 control reaches a different line of code at the original stack level
3439 that was executing when you gave the @code{next} command. This command
3440 is abbreviated @code{n}.
3442 An argument @var{count} is a repeat count, as for @code{step}.
3445 @c FIX ME!! Do we delete this, or is there a way it fits in with
3446 @c the following paragraph? --- Vctoria
3448 @c @code{next} within a function that lacks debugging information acts like
3449 @c @code{step}, but any function calls appearing within the code of the
3450 @c function are executed without stopping.
3452 The @code{next} command only stops at the first instruction of a
3453 source line. This prevents multiple stops that could otherwise occur in
3454 @code{switch} statements, @code{for} loops, etc.
3456 @kindex set step-mode
3458 @cindex functions without line info, and stepping
3459 @cindex stepping into functions with no line info
3460 @itemx set step-mode on
3461 The @code{set step-mode on} command causes the @code{step} command to
3462 stop at the first instruction of a function which contains no debug line
3463 information rather than stepping over it.
3465 This is useful in cases where you may be interested in inspecting the
3466 machine instructions of a function which has no symbolic info and do not
3467 want @value{GDBN} to automatically skip over this function.
3469 @item set step-mode off
3470 Causes the @code{step} command to step over any functions which contains no
3471 debug information. This is the default.
3475 Continue running until just after function in the selected stack frame
3476 returns. Print the returned value (if any).
3478 Contrast this with the @code{return} command (@pxref{Returning,
3479 ,Returning from a function}).
3482 @kindex u @r{(@code{until})}
3485 Continue running until a source line past the current line, in the
3486 current stack frame, is reached. This command is used to avoid single
3487 stepping through a loop more than once. It is like the @code{next}
3488 command, except that when @code{until} encounters a jump, it
3489 automatically continues execution until the program counter is greater
3490 than the address of the jump.
3492 This means that when you reach the end of a loop after single stepping
3493 though it, @code{until} makes your program continue execution until it
3494 exits the loop. In contrast, a @code{next} command at the end of a loop
3495 simply steps back to the beginning of the loop, which forces you to step
3496 through the next iteration.
3498 @code{until} always stops your program if it attempts to exit the current
3501 @code{until} may produce somewhat counterintuitive results if the order
3502 of machine code does not match the order of the source lines. For
3503 example, in the following excerpt from a debugging session, the @code{f}
3504 (@code{frame}) command shows that execution is stopped at line
3505 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3509 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3511 (@value{GDBP}) until
3512 195 for ( ; argc > 0; NEXTARG) @{
3515 This happened because, for execution efficiency, the compiler had
3516 generated code for the loop closure test at the end, rather than the
3517 start, of the loop---even though the test in a C @code{for}-loop is
3518 written before the body of the loop. The @code{until} command appeared
3519 to step back to the beginning of the loop when it advanced to this
3520 expression; however, it has not really gone to an earlier
3521 statement---not in terms of the actual machine code.
3523 @code{until} with no argument works by means of single
3524 instruction stepping, and hence is slower than @code{until} with an
3527 @item until @var{location}
3528 @itemx u @var{location}
3529 Continue running your program until either the specified location is
3530 reached, or the current stack frame returns. @var{location} is any of
3531 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3532 ,Setting breakpoints}). This form of the command uses breakpoints,
3533 and hence is quicker than @code{until} without an argument.
3536 @kindex si @r{(@code{stepi})}
3538 @itemx stepi @var{arg}
3540 Execute one machine instruction, then stop and return to the debugger.
3542 It is often useful to do @samp{display/i $pc} when stepping by machine
3543 instructions. This makes @value{GDBN} automatically display the next
3544 instruction to be executed, each time your program stops. @xref{Auto
3545 Display,, Automatic display}.
3547 An argument is a repeat count, as in @code{step}.
3551 @kindex ni @r{(@code{nexti})}
3553 @itemx nexti @var{arg}
3555 Execute one machine instruction, but if it is a function call,
3556 proceed until the function returns.
3558 An argument is a repeat count, as in @code{next}.
3565 A signal is an asynchronous event that can happen in a program. The
3566 operating system defines the possible kinds of signals, and gives each
3567 kind a name and a number. For example, in Unix @code{SIGINT} is the
3568 signal a program gets when you type an interrupt character (often @kbd{C-c});
3569 @code{SIGSEGV} is the signal a program gets from referencing a place in
3570 memory far away from all the areas in use; @code{SIGALRM} occurs when
3571 the alarm clock timer goes off (which happens only if your program has
3572 requested an alarm).
3574 @cindex fatal signals
3575 Some signals, including @code{SIGALRM}, are a normal part of the
3576 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3577 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3578 program has not specified in advance some other way to handle the signal.
3579 @code{SIGINT} does not indicate an error in your program, but it is normally
3580 fatal so it can carry out the purpose of the interrupt: to kill the program.
3582 @value{GDBN} has the ability to detect any occurrence of a signal in your
3583 program. You can tell @value{GDBN} in advance what to do for each kind of
3586 @cindex handling signals
3587 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3588 @code{SIGALRM} be silently passed to your program
3589 (so as not to interfere with their role in the program's functioning)
3590 but to stop your program immediately whenever an error signal happens.
3591 You can change these settings with the @code{handle} command.
3594 @kindex info signals
3597 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3598 handle each one. You can use this to see the signal numbers of all
3599 the defined types of signals.
3601 @code{info handle} is an alias for @code{info signals}.
3604 @item handle @var{signal} @var{keywords}@dots{}
3605 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3606 can be the number of a signal or its name (with or without the
3607 @samp{SIG} at the beginning); a list of signal numbers of the form
3608 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3609 known signals. The @var{keywords} say what change to make.
3613 The keywords allowed by the @code{handle} command can be abbreviated.
3614 Their full names are:
3618 @value{GDBN} should not stop your program when this signal happens. It may
3619 still print a message telling you that the signal has come in.
3622 @value{GDBN} should stop your program when this signal happens. This implies
3623 the @code{print} keyword as well.
3626 @value{GDBN} should print a message when this signal happens.
3629 @value{GDBN} should not mention the occurrence of the signal at all. This
3630 implies the @code{nostop} keyword as well.
3634 @value{GDBN} should allow your program to see this signal; your program
3635 can handle the signal, or else it may terminate if the signal is fatal
3636 and not handled. @code{pass} and @code{noignore} are synonyms.
3640 @value{GDBN} should not allow your program to see this signal.
3641 @code{nopass} and @code{ignore} are synonyms.
3645 When a signal stops your program, the signal is not visible to the
3647 continue. Your program sees the signal then, if @code{pass} is in
3648 effect for the signal in question @emph{at that time}. In other words,
3649 after @value{GDBN} reports a signal, you can use the @code{handle}
3650 command with @code{pass} or @code{nopass} to control whether your
3651 program sees that signal when you continue.
3653 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3654 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3655 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3658 You can also use the @code{signal} command to prevent your program from
3659 seeing a signal, or cause it to see a signal it normally would not see,
3660 or to give it any signal at any time. For example, if your program stopped
3661 due to some sort of memory reference error, you might store correct
3662 values into the erroneous variables and continue, hoping to see more
3663 execution; but your program would probably terminate immediately as
3664 a result of the fatal signal once it saw the signal. To prevent this,
3665 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3669 @section Stopping and starting multi-thread programs
3671 When your program has multiple threads (@pxref{Threads,, Debugging
3672 programs with multiple threads}), you can choose whether to set
3673 breakpoints on all threads, or on a particular thread.
3676 @cindex breakpoints and threads
3677 @cindex thread breakpoints
3678 @kindex break @dots{} thread @var{threadno}
3679 @item break @var{linespec} thread @var{threadno}
3680 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3681 @var{linespec} specifies source lines; there are several ways of
3682 writing them, but the effect is always to specify some source line.
3684 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3685 to specify that you only want @value{GDBN} to stop the program when a
3686 particular thread reaches this breakpoint. @var{threadno} is one of the
3687 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3688 column of the @samp{info threads} display.
3690 If you do not specify @samp{thread @var{threadno}} when you set a
3691 breakpoint, the breakpoint applies to @emph{all} threads of your
3694 You can use the @code{thread} qualifier on conditional breakpoints as
3695 well; in this case, place @samp{thread @var{threadno}} before the
3696 breakpoint condition, like this:
3699 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3704 @cindex stopped threads
3705 @cindex threads, stopped
3706 Whenever your program stops under @value{GDBN} for any reason,
3707 @emph{all} threads of execution stop, not just the current thread. This
3708 allows you to examine the overall state of the program, including
3709 switching between threads, without worrying that things may change
3712 @cindex continuing threads
3713 @cindex threads, continuing
3714 Conversely, whenever you restart the program, @emph{all} threads start
3715 executing. @emph{This is true even when single-stepping} with commands
3716 like @code{step} or @code{next}.
3718 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3719 Since thread scheduling is up to your debugging target's operating
3720 system (not controlled by @value{GDBN}), other threads may
3721 execute more than one statement while the current thread completes a
3722 single step. Moreover, in general other threads stop in the middle of a
3723 statement, rather than at a clean statement boundary, when the program
3726 You might even find your program stopped in another thread after
3727 continuing or even single-stepping. This happens whenever some other
3728 thread runs into a breakpoint, a signal, or an exception before the
3729 first thread completes whatever you requested.
3731 On some OSes, you can lock the OS scheduler and thus allow only a single
3735 @item set scheduler-locking @var{mode}
3736 Set the scheduler locking mode. If it is @code{off}, then there is no
3737 locking and any thread may run at any time. If @code{on}, then only the
3738 current thread may run when the inferior is resumed. The @code{step}
3739 mode optimizes for single-stepping. It stops other threads from
3740 ``seizing the prompt'' by preempting the current thread while you are
3741 stepping. Other threads will only rarely (or never) get a chance to run
3742 when you step. They are more likely to run when you @samp{next} over a
3743 function call, and they are completely free to run when you use commands
3744 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3745 thread hits a breakpoint during its timeslice, they will never steal the
3746 @value{GDBN} prompt away from the thread that you are debugging.
3748 @item show scheduler-locking
3749 Display the current scheduler locking mode.
3754 @chapter Examining the Stack
3756 When your program has stopped, the first thing you need to know is where it
3757 stopped and how it got there.
3760 Each time your program performs a function call, information about the call
3762 That information includes the location of the call in your program,
3763 the arguments of the call,
3764 and the local variables of the function being called.
3765 The information is saved in a block of data called a @dfn{stack frame}.
3766 The stack frames are allocated in a region of memory called the @dfn{call
3769 When your program stops, the @value{GDBN} commands for examining the
3770 stack allow you to see all of this information.
3772 @cindex selected frame
3773 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3774 @value{GDBN} commands refer implicitly to the selected frame. In
3775 particular, whenever you ask @value{GDBN} for the value of a variable in
3776 your program, the value is found in the selected frame. There are
3777 special @value{GDBN} commands to select whichever frame you are
3778 interested in. @xref{Selection, ,Selecting a frame}.
3780 When your program stops, @value{GDBN} automatically selects the
3781 currently executing frame and describes it briefly, similar to the
3782 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3785 * Frames:: Stack frames
3786 * Backtrace:: Backtraces
3787 * Selection:: Selecting a frame
3788 * Frame Info:: Information on a frame
3793 @section Stack frames
3795 @cindex frame, definition
3797 The call stack is divided up into contiguous pieces called @dfn{stack
3798 frames}, or @dfn{frames} for short; each frame is the data associated
3799 with one call to one function. The frame contains the arguments given
3800 to the function, the function's local variables, and the address at
3801 which the function is executing.
3803 @cindex initial frame
3804 @cindex outermost frame
3805 @cindex innermost frame
3806 When your program is started, the stack has only one frame, that of the
3807 function @code{main}. This is called the @dfn{initial} frame or the
3808 @dfn{outermost} frame. Each time a function is called, a new frame is
3809 made. Each time a function returns, the frame for that function invocation
3810 is eliminated. If a function is recursive, there can be many frames for
3811 the same function. The frame for the function in which execution is
3812 actually occurring is called the @dfn{innermost} frame. This is the most
3813 recently created of all the stack frames that still exist.
3815 @cindex frame pointer
3816 Inside your program, stack frames are identified by their addresses. A
3817 stack frame consists of many bytes, each of which has its own address; each
3818 kind of computer has a convention for choosing one byte whose
3819 address serves as the address of the frame. Usually this address is kept
3820 in a register called the @dfn{frame pointer register} while execution is
3821 going on in that frame.
3823 @cindex frame number
3824 @value{GDBN} assigns numbers to all existing stack frames, starting with
3825 zero for the innermost frame, one for the frame that called it,
3826 and so on upward. These numbers do not really exist in your program;
3827 they are assigned by @value{GDBN} to give you a way of designating stack
3828 frames in @value{GDBN} commands.
3830 @c The -fomit-frame-pointer below perennially causes hbox overflow
3831 @c underflow problems.
3832 @cindex frameless execution
3833 Some compilers provide a way to compile functions so that they operate
3834 without stack frames. (For example, the @value{GCC} option
3836 @samp{-fomit-frame-pointer}
3838 generates functions without a frame.)
3839 This is occasionally done with heavily used library functions to save
3840 the frame setup time. @value{GDBN} has limited facilities for dealing
3841 with these function invocations. If the innermost function invocation
3842 has no stack frame, @value{GDBN} nevertheless regards it as though
3843 it had a separate frame, which is numbered zero as usual, allowing
3844 correct tracing of the function call chain. However, @value{GDBN} has
3845 no provision for frameless functions elsewhere in the stack.
3848 @kindex frame@r{, command}
3849 @cindex current stack frame
3850 @item frame @var{args}
3851 The @code{frame} command allows you to move from one stack frame to another,
3852 and to print the stack frame you select. @var{args} may be either the
3853 address of the frame or the stack frame number. Without an argument,
3854 @code{frame} prints the current stack frame.
3856 @kindex select-frame
3857 @cindex selecting frame silently
3859 The @code{select-frame} command allows you to move from one stack frame
3860 to another without printing the frame. This is the silent version of
3869 @cindex stack traces
3870 A backtrace is a summary of how your program got where it is. It shows one
3871 line per frame, for many frames, starting with the currently executing
3872 frame (frame zero), followed by its caller (frame one), and on up the
3877 @kindex bt @r{(@code{backtrace})}
3880 Print a backtrace of the entire stack: one line per frame for all
3881 frames in the stack.
3883 You can stop the backtrace at any time by typing the system interrupt
3884 character, normally @kbd{C-c}.
3886 @item backtrace @var{n}
3888 Similar, but print only the innermost @var{n} frames.
3890 @item backtrace -@var{n}
3892 Similar, but print only the outermost @var{n} frames.
3897 @kindex info s @r{(@code{info stack})}
3898 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3899 are additional aliases for @code{backtrace}.
3901 Each line in the backtrace shows the frame number and the function name.
3902 The program counter value is also shown---unless you use @code{set
3903 print address off}. The backtrace also shows the source file name and
3904 line number, as well as the arguments to the function. The program
3905 counter value is omitted if it is at the beginning of the code for that
3908 Here is an example of a backtrace. It was made with the command
3909 @samp{bt 3}, so it shows the innermost three frames.
3913 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3915 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3916 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3918 (More stack frames follow...)
3923 The display for frame zero does not begin with a program counter
3924 value, indicating that your program has stopped at the beginning of the
3925 code for line @code{993} of @code{builtin.c}.
3928 @section Selecting a frame
3930 Most commands for examining the stack and other data in your program work on
3931 whichever stack frame is selected at the moment. Here are the commands for
3932 selecting a stack frame; all of them finish by printing a brief description
3933 of the stack frame just selected.
3936 @kindex frame@r{, selecting}
3937 @kindex f @r{(@code{frame})}
3940 Select frame number @var{n}. Recall that frame zero is the innermost
3941 (currently executing) frame, frame one is the frame that called the
3942 innermost one, and so on. The highest-numbered frame is the one for
3945 @item frame @var{addr}
3947 Select the frame at address @var{addr}. This is useful mainly if the
3948 chaining of stack frames has been damaged by a bug, making it
3949 impossible for @value{GDBN} to assign numbers properly to all frames. In
3950 addition, this can be useful when your program has multiple stacks and
3951 switches between them.
3953 On the SPARC architecture, @code{frame} needs two addresses to
3954 select an arbitrary frame: a frame pointer and a stack pointer.
3956 On the MIPS and Alpha architecture, it needs two addresses: a stack
3957 pointer and a program counter.
3959 On the 29k architecture, it needs three addresses: a register stack
3960 pointer, a program counter, and a memory stack pointer.
3961 @c note to future updaters: this is conditioned on a flag
3962 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3963 @c as of 27 Jan 1994.
3967 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3968 advances toward the outermost frame, to higher frame numbers, to frames
3969 that have existed longer. @var{n} defaults to one.
3972 @kindex do @r{(@code{down})}
3974 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3975 advances toward the innermost frame, to lower frame numbers, to frames
3976 that were created more recently. @var{n} defaults to one. You may
3977 abbreviate @code{down} as @code{do}.
3980 All of these commands end by printing two lines of output describing the
3981 frame. The first line shows the frame number, the function name, the
3982 arguments, and the source file and line number of execution in that
3983 frame. The second line shows the text of that source line.
3991 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3993 10 read_input_file (argv[i]);
3997 After such a printout, the @code{list} command with no arguments
3998 prints ten lines centered on the point of execution in the frame.
3999 @xref{List, ,Printing source lines}.
4002 @kindex down-silently
4004 @item up-silently @var{n}
4005 @itemx down-silently @var{n}
4006 These two commands are variants of @code{up} and @code{down},
4007 respectively; they differ in that they do their work silently, without
4008 causing display of the new frame. They are intended primarily for use
4009 in @value{GDBN} command scripts, where the output might be unnecessary and
4014 @section Information about a frame
4016 There are several other commands to print information about the selected
4022 When used without any argument, this command does not change which
4023 frame is selected, but prints a brief description of the currently
4024 selected stack frame. It can be abbreviated @code{f}. With an
4025 argument, this command is used to select a stack frame.
4026 @xref{Selection, ,Selecting a frame}.
4029 @kindex info f @r{(@code{info frame})}
4032 This command prints a verbose description of the selected stack frame,
4037 the address of the frame
4039 the address of the next frame down (called by this frame)
4041 the address of the next frame up (caller of this frame)
4043 the language in which the source code corresponding to this frame is written
4045 the address of the frame's arguments
4047 the address of the frame's local variables
4049 the program counter saved in it (the address of execution in the caller frame)
4051 which registers were saved in the frame
4054 @noindent The verbose description is useful when
4055 something has gone wrong that has made the stack format fail to fit
4056 the usual conventions.
4058 @item info frame @var{addr}
4059 @itemx info f @var{addr}
4060 Print a verbose description of the frame at address @var{addr}, without
4061 selecting that frame. The selected frame remains unchanged by this
4062 command. This requires the same kind of address (more than one for some
4063 architectures) that you specify in the @code{frame} command.
4064 @xref{Selection, ,Selecting a frame}.
4068 Print the arguments of the selected frame, each on a separate line.
4072 Print the local variables of the selected frame, each on a separate
4073 line. These are all variables (declared either static or automatic)
4074 accessible at the point of execution of the selected frame.
4077 @cindex catch exceptions, list active handlers
4078 @cindex exception handlers, how to list
4080 Print a list of all the exception handlers that are active in the
4081 current stack frame at the current point of execution. To see other
4082 exception handlers, visit the associated frame (using the @code{up},
4083 @code{down}, or @code{frame} commands); then type @code{info catch}.
4084 @xref{Set Catchpoints, , Setting catchpoints}.
4090 @chapter Examining Source Files
4092 @value{GDBN} can print parts of your program's source, since the debugging
4093 information recorded in the program tells @value{GDBN} what source files were
4094 used to build it. When your program stops, @value{GDBN} spontaneously prints
4095 the line where it stopped. Likewise, when you select a stack frame
4096 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4097 execution in that frame has stopped. You can print other portions of
4098 source files by explicit command.
4100 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4101 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4102 @value{GDBN} under @sc{gnu} Emacs}.
4105 * List:: Printing source lines
4106 * Search:: Searching source files
4107 * Source Path:: Specifying source directories
4108 * Machine Code:: Source and machine code
4112 @section Printing source lines
4115 @kindex l @r{(@code{list})}
4116 To print lines from a source file, use the @code{list} command
4117 (abbreviated @code{l}). By default, ten lines are printed.
4118 There are several ways to specify what part of the file you want to print.
4120 Here are the forms of the @code{list} command most commonly used:
4123 @item list @var{linenum}
4124 Print lines centered around line number @var{linenum} in the
4125 current source file.
4127 @item list @var{function}
4128 Print lines centered around the beginning of function
4132 Print more lines. If the last lines printed were printed with a
4133 @code{list} command, this prints lines following the last lines
4134 printed; however, if the last line printed was a solitary line printed
4135 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4136 Stack}), this prints lines centered around that line.
4139 Print lines just before the lines last printed.
4142 By default, @value{GDBN} prints ten source lines with any of these forms of
4143 the @code{list} command. You can change this using @code{set listsize}:
4146 @kindex set listsize
4147 @item set listsize @var{count}
4148 Make the @code{list} command display @var{count} source lines (unless
4149 the @code{list} argument explicitly specifies some other number).
4151 @kindex show listsize
4153 Display the number of lines that @code{list} prints.
4156 Repeating a @code{list} command with @key{RET} discards the argument,
4157 so it is equivalent to typing just @code{list}. This is more useful
4158 than listing the same lines again. An exception is made for an
4159 argument of @samp{-}; that argument is preserved in repetition so that
4160 each repetition moves up in the source file.
4163 In general, the @code{list} command expects you to supply zero, one or two
4164 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4165 of writing them, but the effect is always to specify some source line.
4166 Here is a complete description of the possible arguments for @code{list}:
4169 @item list @var{linespec}
4170 Print lines centered around the line specified by @var{linespec}.
4172 @item list @var{first},@var{last}
4173 Print lines from @var{first} to @var{last}. Both arguments are
4176 @item list ,@var{last}
4177 Print lines ending with @var{last}.
4179 @item list @var{first},
4180 Print lines starting with @var{first}.
4183 Print lines just after the lines last printed.
4186 Print lines just before the lines last printed.
4189 As described in the preceding table.
4192 Here are the ways of specifying a single source line---all the
4197 Specifies line @var{number} of the current source file.
4198 When a @code{list} command has two linespecs, this refers to
4199 the same source file as the first linespec.
4202 Specifies the line @var{offset} lines after the last line printed.
4203 When used as the second linespec in a @code{list} command that has
4204 two, this specifies the line @var{offset} lines down from the
4208 Specifies the line @var{offset} lines before the last line printed.
4210 @item @var{filename}:@var{number}
4211 Specifies line @var{number} in the source file @var{filename}.
4213 @item @var{function}
4214 Specifies the line that begins the body of the function @var{function}.
4215 For example: in C, this is the line with the open brace.
4217 @item @var{filename}:@var{function}
4218 Specifies the line of the open-brace that begins the body of the
4219 function @var{function} in the file @var{filename}. You only need the
4220 file name with a function name to avoid ambiguity when there are
4221 identically named functions in different source files.
4223 @item *@var{address}
4224 Specifies the line containing the program address @var{address}.
4225 @var{address} may be any expression.
4229 @section Searching source files
4231 @kindex reverse-search
4233 There are two commands for searching through the current source file for a
4238 @kindex forward-search
4239 @item forward-search @var{regexp}
4240 @itemx search @var{regexp}
4241 The command @samp{forward-search @var{regexp}} checks each line,
4242 starting with the one following the last line listed, for a match for
4243 @var{regexp}. It lists the line that is found. You can use the
4244 synonym @samp{search @var{regexp}} or abbreviate the command name as
4247 @item reverse-search @var{regexp}
4248 The command @samp{reverse-search @var{regexp}} checks each line, starting
4249 with the one before the last line listed and going backward, for a match
4250 for @var{regexp}. It lists the line that is found. You can abbreviate
4251 this command as @code{rev}.
4255 @section Specifying source directories
4258 @cindex directories for source files
4259 Executable programs sometimes do not record the directories of the source
4260 files from which they were compiled, just the names. Even when they do,
4261 the directories could be moved between the compilation and your debugging
4262 session. @value{GDBN} has a list of directories to search for source files;
4263 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4264 it tries all the directories in the list, in the order they are present
4265 in the list, until it finds a file with the desired name. Note that
4266 the executable search path is @emph{not} used for this purpose. Neither is
4267 the current working directory, unless it happens to be in the source
4270 If @value{GDBN} cannot find a source file in the source path, and the
4271 object program records a directory, @value{GDBN} tries that directory
4272 too. If the source path is empty, and there is no record of the
4273 compilation directory, @value{GDBN} looks in the current directory as a
4276 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4277 any information it has cached about where source files are found and where
4278 each line is in the file.
4282 When you start @value{GDBN}, its source path includes only @samp{cdir}
4283 and @samp{cwd}, in that order.
4284 To add other directories, use the @code{directory} command.
4287 @item directory @var{dirname} @dots{}
4288 @item dir @var{dirname} @dots{}
4289 Add directory @var{dirname} to the front of the source path. Several
4290 directory names may be given to this command, separated by @samp{:}
4291 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4292 part of absolute file names) or
4293 whitespace. You may specify a directory that is already in the source
4294 path; this moves it forward, so @value{GDBN} searches it sooner.
4298 @vindex $cdir@r{, convenience variable}
4299 @vindex $cwdr@r{, convenience variable}
4300 @cindex compilation directory
4301 @cindex current directory
4302 @cindex working directory
4303 @cindex directory, current
4304 @cindex directory, compilation
4305 You can use the string @samp{$cdir} to refer to the compilation
4306 directory (if one is recorded), and @samp{$cwd} to refer to the current
4307 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4308 tracks the current working directory as it changes during your @value{GDBN}
4309 session, while the latter is immediately expanded to the current
4310 directory at the time you add an entry to the source path.
4313 Reset the source path to empty again. This requires confirmation.
4315 @c RET-repeat for @code{directory} is explicitly disabled, but since
4316 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4318 @item show directories
4319 @kindex show directories
4320 Print the source path: show which directories it contains.
4323 If your source path is cluttered with directories that are no longer of
4324 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4325 versions of source. You can correct the situation as follows:
4329 Use @code{directory} with no argument to reset the source path to empty.
4332 Use @code{directory} with suitable arguments to reinstall the
4333 directories you want in the source path. You can add all the
4334 directories in one command.
4338 @section Source and machine code
4340 You can use the command @code{info line} to map source lines to program
4341 addresses (and vice versa), and the command @code{disassemble} to display
4342 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4343 mode, the @code{info line} command causes the arrow to point to the
4344 line specified. Also, @code{info line} prints addresses in symbolic form as
4349 @item info line @var{linespec}
4350 Print the starting and ending addresses of the compiled code for
4351 source line @var{linespec}. You can specify source lines in any of
4352 the ways understood by the @code{list} command (@pxref{List, ,Printing
4356 For example, we can use @code{info line} to discover the location of
4357 the object code for the first line of function
4358 @code{m4_changequote}:
4360 @c FIXME: I think this example should also show the addresses in
4361 @c symbolic form, as they usually would be displayed.
4363 (@value{GDBP}) info line m4_changequote
4364 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4368 We can also inquire (using @code{*@var{addr}} as the form for
4369 @var{linespec}) what source line covers a particular address:
4371 (@value{GDBP}) info line *0x63ff
4372 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4375 @cindex @code{$_} and @code{info line}
4376 @kindex x@r{(examine), and} info line
4377 After @code{info line}, the default address for the @code{x} command
4378 is changed to the starting address of the line, so that @samp{x/i} is
4379 sufficient to begin examining the machine code (@pxref{Memory,
4380 ,Examining memory}). Also, this address is saved as the value of the
4381 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4386 @cindex assembly instructions
4387 @cindex instructions, assembly
4388 @cindex machine instructions
4389 @cindex listing machine instructions
4391 This specialized command dumps a range of memory as machine
4392 instructions. The default memory range is the function surrounding the
4393 program counter of the selected frame. A single argument to this
4394 command is a program counter value; @value{GDBN} dumps the function
4395 surrounding this value. Two arguments specify a range of addresses
4396 (first inclusive, second exclusive) to dump.
4399 The following example shows the disassembly of a range of addresses of
4400 HP PA-RISC 2.0 code:
4403 (@value{GDBP}) disas 0x32c4 0x32e4
4404 Dump of assembler code from 0x32c4 to 0x32e4:
4405 0x32c4 <main+204>: addil 0,dp
4406 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4407 0x32cc <main+212>: ldil 0x3000,r31
4408 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4409 0x32d4 <main+220>: ldo 0(r31),rp
4410 0x32d8 <main+224>: addil -0x800,dp
4411 0x32dc <main+228>: ldo 0x588(r1),r26
4412 0x32e0 <main+232>: ldil 0x3000,r31
4413 End of assembler dump.
4416 Some architectures have more than one commonly-used set of instruction
4417 mnemonics or other syntax.
4420 @kindex set disassembly-flavor
4421 @cindex assembly instructions
4422 @cindex instructions, assembly
4423 @cindex machine instructions
4424 @cindex listing machine instructions
4425 @cindex Intel disassembly flavor
4426 @cindex AT&T disassembly flavor
4427 @item set disassembly-flavor @var{instruction-set}
4428 Select the instruction set to use when disassembling the
4429 program via the @code{disassemble} or @code{x/i} commands.
4431 Currently this command is only defined for the Intel x86 family. You
4432 can set @var{instruction-set} to either @code{intel} or @code{att}.
4433 The default is @code{att}, the AT&T flavor used by default by Unix
4434 assemblers for x86-based targets.
4439 @chapter Examining Data
4441 @cindex printing data
4442 @cindex examining data
4445 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4446 @c document because it is nonstandard... Under Epoch it displays in a
4447 @c different window or something like that.
4448 The usual way to examine data in your program is with the @code{print}
4449 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4450 evaluates and prints the value of an expression of the language your
4451 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4452 Different Languages}).
4455 @item print @var{expr}
4456 @itemx print /@var{f} @var{expr}
4457 @var{expr} is an expression (in the source language). By default the
4458 value of @var{expr} is printed in a format appropriate to its data type;
4459 you can choose a different format by specifying @samp{/@var{f}}, where
4460 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4464 @itemx print /@var{f}
4465 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4466 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4467 conveniently inspect the same value in an alternative format.
4470 A more low-level way of examining data is with the @code{x} command.
4471 It examines data in memory at a specified address and prints it in a
4472 specified format. @xref{Memory, ,Examining memory}.
4474 If you are interested in information about types, or about how the
4475 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4476 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4480 * Expressions:: Expressions
4481 * Variables:: Program variables
4482 * Arrays:: Artificial arrays
4483 * Output Formats:: Output formats
4484 * Memory:: Examining memory
4485 * Auto Display:: Automatic display
4486 * Print Settings:: Print settings
4487 * Value History:: Value history
4488 * Convenience Vars:: Convenience variables
4489 * Registers:: Registers
4490 * Floating Point Hardware:: Floating point hardware
4491 * Memory Region Attributes:: Memory region attributes
4495 @section Expressions
4498 @code{print} and many other @value{GDBN} commands accept an expression and
4499 compute its value. Any kind of constant, variable or operator defined
4500 by the programming language you are using is valid in an expression in
4501 @value{GDBN}. This includes conditional expressions, function calls, casts
4502 and string constants. It unfortunately does not include symbols defined
4503 by preprocessor @code{#define} commands.
4505 @value{GDBN} supports array constants in expressions input by
4506 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4507 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4508 memory that is @code{malloc}ed in the target program.
4510 Because C is so widespread, most of the expressions shown in examples in
4511 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4512 Languages}, for information on how to use expressions in other
4515 In this section, we discuss operators that you can use in @value{GDBN}
4516 expressions regardless of your programming language.
4518 Casts are supported in all languages, not just in C, because it is so
4519 useful to cast a number into a pointer in order to examine a structure
4520 at that address in memory.
4521 @c FIXME: casts supported---Mod2 true?
4523 @value{GDBN} supports these operators, in addition to those common
4524 to programming languages:
4528 @samp{@@} is a binary operator for treating parts of memory as arrays.
4529 @xref{Arrays, ,Artificial arrays}, for more information.
4532 @samp{::} allows you to specify a variable in terms of the file or
4533 function where it is defined. @xref{Variables, ,Program variables}.
4535 @cindex @{@var{type}@}
4536 @cindex type casting memory
4537 @cindex memory, viewing as typed object
4538 @cindex casts, to view memory
4539 @item @{@var{type}@} @var{addr}
4540 Refers to an object of type @var{type} stored at address @var{addr} in
4541 memory. @var{addr} may be any expression whose value is an integer or
4542 pointer (but parentheses are required around binary operators, just as in
4543 a cast). This construct is allowed regardless of what kind of data is
4544 normally supposed to reside at @var{addr}.
4548 @section Program variables
4550 The most common kind of expression to use is the name of a variable
4553 Variables in expressions are understood in the selected stack frame
4554 (@pxref{Selection, ,Selecting a frame}); they must be either:
4558 global (or file-static)
4565 visible according to the scope rules of the
4566 programming language from the point of execution in that frame
4569 @noindent This means that in the function
4584 you can examine and use the variable @code{a} whenever your program is
4585 executing within the function @code{foo}, but you can only use or
4586 examine the variable @code{b} while your program is executing inside
4587 the block where @code{b} is declared.
4589 @cindex variable name conflict
4590 There is an exception: you can refer to a variable or function whose
4591 scope is a single source file even if the current execution point is not
4592 in this file. But it is possible to have more than one such variable or
4593 function with the same name (in different source files). If that
4594 happens, referring to that name has unpredictable effects. If you wish,
4595 you can specify a static variable in a particular function or file,
4596 using the colon-colon notation:
4598 @cindex colon-colon, context for variables/functions
4600 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4601 @cindex @code{::}, context for variables/functions
4604 @var{file}::@var{variable}
4605 @var{function}::@var{variable}
4609 Here @var{file} or @var{function} is the name of the context for the
4610 static @var{variable}. In the case of file names, you can use quotes to
4611 make sure @value{GDBN} parses the file name as a single word---for example,
4612 to print a global value of @code{x} defined in @file{f2.c}:
4615 (@value{GDBP}) p 'f2.c'::x
4618 @cindex C@t{++} scope resolution
4619 This use of @samp{::} is very rarely in conflict with the very similar
4620 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4621 scope resolution operator in @value{GDBN} expressions.
4622 @c FIXME: Um, so what happens in one of those rare cases where it's in
4625 @cindex wrong values
4626 @cindex variable values, wrong
4628 @emph{Warning:} Occasionally, a local variable may appear to have the
4629 wrong value at certain points in a function---just after entry to a new
4630 scope, and just before exit.
4632 You may see this problem when you are stepping by machine instructions.
4633 This is because, on most machines, it takes more than one instruction to
4634 set up a stack frame (including local variable definitions); if you are
4635 stepping by machine instructions, variables may appear to have the wrong
4636 values until the stack frame is completely built. On exit, it usually
4637 also takes more than one machine instruction to destroy a stack frame;
4638 after you begin stepping through that group of instructions, local
4639 variable definitions may be gone.
4641 This may also happen when the compiler does significant optimizations.
4642 To be sure of always seeing accurate values, turn off all optimization
4645 @cindex ``No symbol "foo" in current context''
4646 Another possible effect of compiler optimizations is to optimize
4647 unused variables out of existence, or assign variables to registers (as
4648 opposed to memory addresses). Depending on the support for such cases
4649 offered by the debug info format used by the compiler, @value{GDBN}
4650 might not be able to display values for such local variables. If that
4651 happens, @value{GDBN} will print a message like this:
4654 No symbol "foo" in current context.
4657 To solve such problems, either recompile without optimizations, or use a
4658 different debug info format, if the compiler supports several such
4659 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4660 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4661 in a format that is superior to formats such as COFF. You may be able
4662 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4663 debug info. See @ref{Debugging Options,,Options for Debugging Your
4664 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4669 @section Artificial arrays
4671 @cindex artificial array
4672 @kindex @@@r{, referencing memory as an array}
4673 It is often useful to print out several successive objects of the
4674 same type in memory; a section of an array, or an array of
4675 dynamically determined size for which only a pointer exists in the
4678 You can do this by referring to a contiguous span of memory as an
4679 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4680 operand of @samp{@@} should be the first element of the desired array
4681 and be an individual object. The right operand should be the desired length
4682 of the array. The result is an array value whose elements are all of
4683 the type of the left argument. The first element is actually the left
4684 argument; the second element comes from bytes of memory immediately
4685 following those that hold the first element, and so on. Here is an
4686 example. If a program says
4689 int *array = (int *) malloc (len * sizeof (int));
4693 you can print the contents of @code{array} with
4699 The left operand of @samp{@@} must reside in memory. Array values made
4700 with @samp{@@} in this way behave just like other arrays in terms of
4701 subscripting, and are coerced to pointers when used in expressions.
4702 Artificial arrays most often appear in expressions via the value history
4703 (@pxref{Value History, ,Value history}), after printing one out.
4705 Another way to create an artificial array is to use a cast.
4706 This re-interprets a value as if it were an array.
4707 The value need not be in memory:
4709 (@value{GDBP}) p/x (short[2])0x12345678
4710 $1 = @{0x1234, 0x5678@}
4713 As a convenience, if you leave the array length out (as in
4714 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4715 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4717 (@value{GDBP}) p/x (short[])0x12345678
4718 $2 = @{0x1234, 0x5678@}
4721 Sometimes the artificial array mechanism is not quite enough; in
4722 moderately complex data structures, the elements of interest may not
4723 actually be adjacent---for example, if you are interested in the values
4724 of pointers in an array. One useful work-around in this situation is
4725 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4726 variables}) as a counter in an expression that prints the first
4727 interesting value, and then repeat that expression via @key{RET}. For
4728 instance, suppose you have an array @code{dtab} of pointers to
4729 structures, and you are interested in the values of a field @code{fv}
4730 in each structure. Here is an example of what you might type:
4740 @node Output Formats
4741 @section Output formats
4743 @cindex formatted output
4744 @cindex output formats
4745 By default, @value{GDBN} prints a value according to its data type. Sometimes
4746 this is not what you want. For example, you might want to print a number
4747 in hex, or a pointer in decimal. Or you might want to view data in memory
4748 at a certain address as a character string or as an instruction. To do
4749 these things, specify an @dfn{output format} when you print a value.
4751 The simplest use of output formats is to say how to print a value
4752 already computed. This is done by starting the arguments of the
4753 @code{print} command with a slash and a format letter. The format
4754 letters supported are:
4758 Regard the bits of the value as an integer, and print the integer in
4762 Print as integer in signed decimal.
4765 Print as integer in unsigned decimal.
4768 Print as integer in octal.
4771 Print as integer in binary. The letter @samp{t} stands for ``two''.
4772 @footnote{@samp{b} cannot be used because these format letters are also
4773 used with the @code{x} command, where @samp{b} stands for ``byte'';
4774 see @ref{Memory,,Examining memory}.}
4777 @cindex unknown address, locating
4778 @cindex locate address
4779 Print as an address, both absolute in hexadecimal and as an offset from
4780 the nearest preceding symbol. You can use this format used to discover
4781 where (in what function) an unknown address is located:
4784 (@value{GDBP}) p/a 0x54320
4785 $3 = 0x54320 <_initialize_vx+396>
4789 The command @code{info symbol 0x54320} yields similar results.
4790 @xref{Symbols, info symbol}.
4793 Regard as an integer and print it as a character constant.
4796 Regard the bits of the value as a floating point number and print
4797 using typical floating point syntax.
4800 For example, to print the program counter in hex (@pxref{Registers}), type
4807 Note that no space is required before the slash; this is because command
4808 names in @value{GDBN} cannot contain a slash.
4810 To reprint the last value in the value history with a different format,
4811 you can use the @code{print} command with just a format and no
4812 expression. For example, @samp{p/x} reprints the last value in hex.
4815 @section Examining memory
4817 You can use the command @code{x} (for ``examine'') to examine memory in
4818 any of several formats, independently of your program's data types.
4820 @cindex examining memory
4822 @kindex x @r{(examine memory)}
4823 @item x/@var{nfu} @var{addr}
4826 Use the @code{x} command to examine memory.
4829 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4830 much memory to display and how to format it; @var{addr} is an
4831 expression giving the address where you want to start displaying memory.
4832 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4833 Several commands set convenient defaults for @var{addr}.
4836 @item @var{n}, the repeat count
4837 The repeat count is a decimal integer; the default is 1. It specifies
4838 how much memory (counting by units @var{u}) to display.
4839 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4842 @item @var{f}, the display format
4843 The display format is one of the formats used by @code{print},
4844 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4845 The default is @samp{x} (hexadecimal) initially.
4846 The default changes each time you use either @code{x} or @code{print}.
4848 @item @var{u}, the unit size
4849 The unit size is any of
4855 Halfwords (two bytes).
4857 Words (four bytes). This is the initial default.
4859 Giant words (eight bytes).
4862 Each time you specify a unit size with @code{x}, that size becomes the
4863 default unit the next time you use @code{x}. (For the @samp{s} and
4864 @samp{i} formats, the unit size is ignored and is normally not written.)
4866 @item @var{addr}, starting display address
4867 @var{addr} is the address where you want @value{GDBN} to begin displaying
4868 memory. The expression need not have a pointer value (though it may);
4869 it is always interpreted as an integer address of a byte of memory.
4870 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4871 @var{addr} is usually just after the last address examined---but several
4872 other commands also set the default address: @code{info breakpoints} (to
4873 the address of the last breakpoint listed), @code{info line} (to the
4874 starting address of a line), and @code{print} (if you use it to display
4875 a value from memory).
4878 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4879 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4880 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4881 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4882 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4884 Since the letters indicating unit sizes are all distinct from the
4885 letters specifying output formats, you do not have to remember whether
4886 unit size or format comes first; either order works. The output
4887 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4888 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4890 Even though the unit size @var{u} is ignored for the formats @samp{s}
4891 and @samp{i}, you might still want to use a count @var{n}; for example,
4892 @samp{3i} specifies that you want to see three machine instructions,
4893 including any operands. The command @code{disassemble} gives an
4894 alternative way of inspecting machine instructions; see @ref{Machine
4895 Code,,Source and machine code}.
4897 All the defaults for the arguments to @code{x} are designed to make it
4898 easy to continue scanning memory with minimal specifications each time
4899 you use @code{x}. For example, after you have inspected three machine
4900 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4901 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4902 the repeat count @var{n} is used again; the other arguments default as
4903 for successive uses of @code{x}.
4905 @cindex @code{$_}, @code{$__}, and value history
4906 The addresses and contents printed by the @code{x} command are not saved
4907 in the value history because there is often too much of them and they
4908 would get in the way. Instead, @value{GDBN} makes these values available for
4909 subsequent use in expressions as values of the convenience variables
4910 @code{$_} and @code{$__}. After an @code{x} command, the last address
4911 examined is available for use in expressions in the convenience variable
4912 @code{$_}. The contents of that address, as examined, are available in
4913 the convenience variable @code{$__}.
4915 If the @code{x} command has a repeat count, the address and contents saved
4916 are from the last memory unit printed; this is not the same as the last
4917 address printed if several units were printed on the last line of output.
4920 @section Automatic display
4921 @cindex automatic display
4922 @cindex display of expressions
4924 If you find that you want to print the value of an expression frequently
4925 (to see how it changes), you might want to add it to the @dfn{automatic
4926 display list} so that @value{GDBN} prints its value each time your program stops.
4927 Each expression added to the list is given a number to identify it;
4928 to remove an expression from the list, you specify that number.
4929 The automatic display looks like this:
4933 3: bar[5] = (struct hack *) 0x3804
4937 This display shows item numbers, expressions and their current values. As with
4938 displays you request manually using @code{x} or @code{print}, you can
4939 specify the output format you prefer; in fact, @code{display} decides
4940 whether to use @code{print} or @code{x} depending on how elaborate your
4941 format specification is---it uses @code{x} if you specify a unit size,
4942 or one of the two formats (@samp{i} and @samp{s}) that are only
4943 supported by @code{x}; otherwise it uses @code{print}.
4947 @item display @var{expr}
4948 Add the expression @var{expr} to the list of expressions to display
4949 each time your program stops. @xref{Expressions, ,Expressions}.
4951 @code{display} does not repeat if you press @key{RET} again after using it.
4953 @item display/@var{fmt} @var{expr}
4954 For @var{fmt} specifying only a display format and not a size or
4955 count, add the expression @var{expr} to the auto-display list but
4956 arrange to display it each time in the specified format @var{fmt}.
4957 @xref{Output Formats,,Output formats}.
4959 @item display/@var{fmt} @var{addr}
4960 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4961 number of units, add the expression @var{addr} as a memory address to
4962 be examined each time your program stops. Examining means in effect
4963 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4966 For example, @samp{display/i $pc} can be helpful, to see the machine
4967 instruction about to be executed each time execution stops (@samp{$pc}
4968 is a common name for the program counter; @pxref{Registers, ,Registers}).
4971 @kindex delete display
4973 @item undisplay @var{dnums}@dots{}
4974 @itemx delete display @var{dnums}@dots{}
4975 Remove item numbers @var{dnums} from the list of expressions to display.
4977 @code{undisplay} does not repeat if you press @key{RET} after using it.
4978 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4980 @kindex disable display
4981 @item disable display @var{dnums}@dots{}
4982 Disable the display of item numbers @var{dnums}. A disabled display
4983 item is not printed automatically, but is not forgotten. It may be
4984 enabled again later.
4986 @kindex enable display
4987 @item enable display @var{dnums}@dots{}
4988 Enable display of item numbers @var{dnums}. It becomes effective once
4989 again in auto display of its expression, until you specify otherwise.
4992 Display the current values of the expressions on the list, just as is
4993 done when your program stops.
4995 @kindex info display
4997 Print the list of expressions previously set up to display
4998 automatically, each one with its item number, but without showing the
4999 values. This includes disabled expressions, which are marked as such.
5000 It also includes expressions which would not be displayed right now
5001 because they refer to automatic variables not currently available.
5004 If a display expression refers to local variables, then it does not make
5005 sense outside the lexical context for which it was set up. Such an
5006 expression is disabled when execution enters a context where one of its
5007 variables is not defined. For example, if you give the command
5008 @code{display last_char} while inside a function with an argument
5009 @code{last_char}, @value{GDBN} displays this argument while your program
5010 continues to stop inside that function. When it stops elsewhere---where
5011 there is no variable @code{last_char}---the display is disabled
5012 automatically. The next time your program stops where @code{last_char}
5013 is meaningful, you can enable the display expression once again.
5015 @node Print Settings
5016 @section Print settings
5018 @cindex format options
5019 @cindex print settings
5020 @value{GDBN} provides the following ways to control how arrays, structures,
5021 and symbols are printed.
5024 These settings are useful for debugging programs in any language:
5027 @kindex set print address
5028 @item set print address
5029 @itemx set print address on
5030 @value{GDBN} prints memory addresses showing the location of stack
5031 traces, structure values, pointer values, breakpoints, and so forth,
5032 even when it also displays the contents of those addresses. The default
5033 is @code{on}. For example, this is what a stack frame display looks like with
5034 @code{set print address on}:
5039 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5041 530 if (lquote != def_lquote)
5045 @item set print address off
5046 Do not print addresses when displaying their contents. For example,
5047 this is the same stack frame displayed with @code{set print address off}:
5051 (@value{GDBP}) set print addr off
5053 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5054 530 if (lquote != def_lquote)
5058 You can use @samp{set print address off} to eliminate all machine
5059 dependent displays from the @value{GDBN} interface. For example, with
5060 @code{print address off}, you should get the same text for backtraces on
5061 all machines---whether or not they involve pointer arguments.
5063 @kindex show print address
5064 @item show print address
5065 Show whether or not addresses are to be printed.
5068 When @value{GDBN} prints a symbolic address, it normally prints the
5069 closest earlier symbol plus an offset. If that symbol does not uniquely
5070 identify the address (for example, it is a name whose scope is a single
5071 source file), you may need to clarify. One way to do this is with
5072 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5073 you can set @value{GDBN} to print the source file and line number when
5074 it prints a symbolic address:
5077 @kindex set print symbol-filename
5078 @item set print symbol-filename on
5079 Tell @value{GDBN} to print the source file name and line number of a
5080 symbol in the symbolic form of an address.
5082 @item set print symbol-filename off
5083 Do not print source file name and line number of a symbol. This is the
5086 @kindex show print symbol-filename
5087 @item show print symbol-filename
5088 Show whether or not @value{GDBN} will print the source file name and
5089 line number of a symbol in the symbolic form of an address.
5092 Another situation where it is helpful to show symbol filenames and line
5093 numbers is when disassembling code; @value{GDBN} shows you the line
5094 number and source file that corresponds to each instruction.
5096 Also, you may wish to see the symbolic form only if the address being
5097 printed is reasonably close to the closest earlier symbol:
5100 @kindex set print max-symbolic-offset
5101 @item set print max-symbolic-offset @var{max-offset}
5102 Tell @value{GDBN} to only display the symbolic form of an address if the
5103 offset between the closest earlier symbol and the address is less than
5104 @var{max-offset}. The default is 0, which tells @value{GDBN}
5105 to always print the symbolic form of an address if any symbol precedes it.
5107 @kindex show print max-symbolic-offset
5108 @item show print max-symbolic-offset
5109 Ask how large the maximum offset is that @value{GDBN} prints in a
5113 @cindex wild pointer, interpreting
5114 @cindex pointer, finding referent
5115 If you have a pointer and you are not sure where it points, try
5116 @samp{set print symbol-filename on}. Then you can determine the name
5117 and source file location of the variable where it points, using
5118 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5119 For example, here @value{GDBN} shows that a variable @code{ptt} points
5120 at another variable @code{t}, defined in @file{hi2.c}:
5123 (@value{GDBP}) set print symbol-filename on
5124 (@value{GDBP}) p/a ptt
5125 $4 = 0xe008 <t in hi2.c>
5129 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5130 does not show the symbol name and filename of the referent, even with
5131 the appropriate @code{set print} options turned on.
5134 Other settings control how different kinds of objects are printed:
5137 @kindex set print array
5138 @item set print array
5139 @itemx set print array on
5140 Pretty print arrays. This format is more convenient to read,
5141 but uses more space. The default is off.
5143 @item set print array off
5144 Return to compressed format for arrays.
5146 @kindex show print array
5147 @item show print array
5148 Show whether compressed or pretty format is selected for displaying
5151 @kindex set print elements
5152 @item set print elements @var{number-of-elements}
5153 Set a limit on how many elements of an array @value{GDBN} will print.
5154 If @value{GDBN} is printing a large array, it stops printing after it has
5155 printed the number of elements set by the @code{set print elements} command.
5156 This limit also applies to the display of strings.
5157 When @value{GDBN} starts, this limit is set to 200.
5158 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5160 @kindex show print elements
5161 @item show print elements
5162 Display the number of elements of a large array that @value{GDBN} will print.
5163 If the number is 0, then the printing is unlimited.
5165 @kindex set print null-stop
5166 @item set print null-stop
5167 Cause @value{GDBN} to stop printing the characters of an array when the first
5168 @sc{null} is encountered. This is useful when large arrays actually
5169 contain only short strings.
5172 @kindex set print pretty
5173 @item set print pretty on
5174 Cause @value{GDBN} to print structures in an indented format with one member
5175 per line, like this:
5190 @item set print pretty off
5191 Cause @value{GDBN} to print structures in a compact format, like this:
5195 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5196 meat = 0x54 "Pork"@}
5201 This is the default format.
5203 @kindex show print pretty
5204 @item show print pretty
5205 Show which format @value{GDBN} is using to print structures.
5207 @kindex set print sevenbit-strings
5208 @item set print sevenbit-strings on
5209 Print using only seven-bit characters; if this option is set,
5210 @value{GDBN} displays any eight-bit characters (in strings or
5211 character values) using the notation @code{\}@var{nnn}. This setting is
5212 best if you are working in English (@sc{ascii}) and you use the
5213 high-order bit of characters as a marker or ``meta'' bit.
5215 @item set print sevenbit-strings off
5216 Print full eight-bit characters. This allows the use of more
5217 international character sets, and is the default.
5219 @kindex show print sevenbit-strings
5220 @item show print sevenbit-strings
5221 Show whether or not @value{GDBN} is printing only seven-bit characters.
5223 @kindex set print union
5224 @item set print union on
5225 Tell @value{GDBN} to print unions which are contained in structures. This
5226 is the default setting.
5228 @item set print union off
5229 Tell @value{GDBN} not to print unions which are contained in structures.
5231 @kindex show print union
5232 @item show print union
5233 Ask @value{GDBN} whether or not it will print unions which are contained in
5236 For example, given the declarations
5239 typedef enum @{Tree, Bug@} Species;
5240 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5241 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5252 struct thing foo = @{Tree, @{Acorn@}@};
5256 with @code{set print union on} in effect @samp{p foo} would print
5259 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5263 and with @code{set print union off} in effect it would print
5266 $1 = @{it = Tree, form = @{...@}@}
5272 These settings are of interest when debugging C@t{++} programs:
5276 @kindex set print demangle
5277 @item set print demangle
5278 @itemx set print demangle on
5279 Print C@t{++} names in their source form rather than in the encoded
5280 (``mangled'') form passed to the assembler and linker for type-safe
5281 linkage. The default is on.
5283 @kindex show print demangle
5284 @item show print demangle
5285 Show whether C@t{++} names are printed in mangled or demangled form.
5287 @kindex set print asm-demangle
5288 @item set print asm-demangle
5289 @itemx set print asm-demangle on
5290 Print C@t{++} names in their source form rather than their mangled form, even
5291 in assembler code printouts such as instruction disassemblies.
5294 @kindex show print asm-demangle
5295 @item show print asm-demangle
5296 Show whether C@t{++} names in assembly listings are printed in mangled
5299 @kindex set demangle-style
5300 @cindex C@t{++} symbol decoding style
5301 @cindex symbol decoding style, C@t{++}
5302 @item set demangle-style @var{style}
5303 Choose among several encoding schemes used by different compilers to
5304 represent C@t{++} names. The choices for @var{style} are currently:
5308 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5311 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5312 This is the default.
5315 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5318 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5321 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5322 @strong{Warning:} this setting alone is not sufficient to allow
5323 debugging @code{cfront}-generated executables. @value{GDBN} would
5324 require further enhancement to permit that.
5327 If you omit @var{style}, you will see a list of possible formats.
5329 @kindex show demangle-style
5330 @item show demangle-style
5331 Display the encoding style currently in use for decoding C@t{++} symbols.
5333 @kindex set print object
5334 @item set print object
5335 @itemx set print object on
5336 When displaying a pointer to an object, identify the @emph{actual}
5337 (derived) type of the object rather than the @emph{declared} type, using
5338 the virtual function table.
5340 @item set print object off
5341 Display only the declared type of objects, without reference to the
5342 virtual function table. This is the default setting.
5344 @kindex show print object
5345 @item show print object
5346 Show whether actual, or declared, object types are displayed.
5348 @kindex set print static-members
5349 @item set print static-members
5350 @itemx set print static-members on
5351 Print static members when displaying a C@t{++} object. The default is on.
5353 @item set print static-members off
5354 Do not print static members when displaying a C@t{++} object.
5356 @kindex show print static-members
5357 @item show print static-members
5358 Show whether C@t{++} static members are printed, or not.
5360 @c These don't work with HP ANSI C++ yet.
5361 @kindex set print vtbl
5362 @item set print vtbl
5363 @itemx set print vtbl on
5364 Pretty print C@t{++} virtual function tables. The default is off.
5365 (The @code{vtbl} commands do not work on programs compiled with the HP
5366 ANSI C@t{++} compiler (@code{aCC}).)
5368 @item set print vtbl off
5369 Do not pretty print C@t{++} virtual function tables.
5371 @kindex show print vtbl
5372 @item show print vtbl
5373 Show whether C@t{++} virtual function tables are pretty printed, or not.
5377 @section Value history
5379 @cindex value history
5380 Values printed by the @code{print} command are saved in the @value{GDBN}
5381 @dfn{value history}. This allows you to refer to them in other expressions.
5382 Values are kept until the symbol table is re-read or discarded
5383 (for example with the @code{file} or @code{symbol-file} commands).
5384 When the symbol table changes, the value history is discarded,
5385 since the values may contain pointers back to the types defined in the
5390 @cindex history number
5391 The values printed are given @dfn{history numbers} by which you can
5392 refer to them. These are successive integers starting with one.
5393 @code{print} shows you the history number assigned to a value by
5394 printing @samp{$@var{num} = } before the value; here @var{num} is the
5397 To refer to any previous value, use @samp{$} followed by the value's
5398 history number. The way @code{print} labels its output is designed to
5399 remind you of this. Just @code{$} refers to the most recent value in
5400 the history, and @code{$$} refers to the value before that.
5401 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5402 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5403 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5405 For example, suppose you have just printed a pointer to a structure and
5406 want to see the contents of the structure. It suffices to type
5412 If you have a chain of structures where the component @code{next} points
5413 to the next one, you can print the contents of the next one with this:
5420 You can print successive links in the chain by repeating this
5421 command---which you can do by just typing @key{RET}.
5423 Note that the history records values, not expressions. If the value of
5424 @code{x} is 4 and you type these commands:
5432 then the value recorded in the value history by the @code{print} command
5433 remains 4 even though the value of @code{x} has changed.
5438 Print the last ten values in the value history, with their item numbers.
5439 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5440 values} does not change the history.
5442 @item show values @var{n}
5443 Print ten history values centered on history item number @var{n}.
5446 Print ten history values just after the values last printed. If no more
5447 values are available, @code{show values +} produces no display.
5450 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5451 same effect as @samp{show values +}.
5453 @node Convenience Vars
5454 @section Convenience variables
5456 @cindex convenience variables
5457 @value{GDBN} provides @dfn{convenience variables} that you can use within
5458 @value{GDBN} to hold on to a value and refer to it later. These variables
5459 exist entirely within @value{GDBN}; they are not part of your program, and
5460 setting a convenience variable has no direct effect on further execution
5461 of your program. That is why you can use them freely.
5463 Convenience variables are prefixed with @samp{$}. Any name preceded by
5464 @samp{$} can be used for a convenience variable, unless it is one of
5465 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5466 (Value history references, in contrast, are @emph{numbers} preceded
5467 by @samp{$}. @xref{Value History, ,Value history}.)
5469 You can save a value in a convenience variable with an assignment
5470 expression, just as you would set a variable in your program.
5474 set $foo = *object_ptr
5478 would save in @code{$foo} the value contained in the object pointed to by
5481 Using a convenience variable for the first time creates it, but its
5482 value is @code{void} until you assign a new value. You can alter the
5483 value with another assignment at any time.
5485 Convenience variables have no fixed types. You can assign a convenience
5486 variable any type of value, including structures and arrays, even if
5487 that variable already has a value of a different type. The convenience
5488 variable, when used as an expression, has the type of its current value.
5491 @kindex show convenience
5492 @item show convenience
5493 Print a list of convenience variables used so far, and their values.
5494 Abbreviated @code{show conv}.
5497 One of the ways to use a convenience variable is as a counter to be
5498 incremented or a pointer to be advanced. For example, to print
5499 a field from successive elements of an array of structures:
5503 print bar[$i++]->contents
5507 Repeat that command by typing @key{RET}.
5509 Some convenience variables are created automatically by @value{GDBN} and given
5510 values likely to be useful.
5513 @vindex $_@r{, convenience variable}
5515 The variable @code{$_} is automatically set by the @code{x} command to
5516 the last address examined (@pxref{Memory, ,Examining memory}). Other
5517 commands which provide a default address for @code{x} to examine also
5518 set @code{$_} to that address; these commands include @code{info line}
5519 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5520 except when set by the @code{x} command, in which case it is a pointer
5521 to the type of @code{$__}.
5523 @vindex $__@r{, convenience variable}
5525 The variable @code{$__} is automatically set by the @code{x} command
5526 to the value found in the last address examined. Its type is chosen
5527 to match the format in which the data was printed.
5530 @vindex $_exitcode@r{, convenience variable}
5531 The variable @code{$_exitcode} is automatically set to the exit code when
5532 the program being debugged terminates.
5535 On HP-UX systems, if you refer to a function or variable name that
5536 begins with a dollar sign, @value{GDBN} searches for a user or system
5537 name first, before it searches for a convenience variable.
5543 You can refer to machine register contents, in expressions, as variables
5544 with names starting with @samp{$}. The names of registers are different
5545 for each machine; use @code{info registers} to see the names used on
5549 @kindex info registers
5550 @item info registers
5551 Print the names and values of all registers except floating-point
5552 registers (in the selected stack frame).
5554 @kindex info all-registers
5555 @cindex floating point registers
5556 @item info all-registers
5557 Print the names and values of all registers, including floating-point
5560 @item info registers @var{regname} @dots{}
5561 Print the @dfn{relativized} value of each specified register @var{regname}.
5562 As discussed in detail below, register values are normally relative to
5563 the selected stack frame. @var{regname} may be any register name valid on
5564 the machine you are using, with or without the initial @samp{$}.
5567 @value{GDBN} has four ``standard'' register names that are available (in
5568 expressions) on most machines---whenever they do not conflict with an
5569 architecture's canonical mnemonics for registers. The register names
5570 @code{$pc} and @code{$sp} are used for the program counter register and
5571 the stack pointer. @code{$fp} is used for a register that contains a
5572 pointer to the current stack frame, and @code{$ps} is used for a
5573 register that contains the processor status. For example,
5574 you could print the program counter in hex with
5581 or print the instruction to be executed next with
5588 or add four to the stack pointer@footnote{This is a way of removing
5589 one word from the stack, on machines where stacks grow downward in
5590 memory (most machines, nowadays). This assumes that the innermost
5591 stack frame is selected; setting @code{$sp} is not allowed when other
5592 stack frames are selected. To pop entire frames off the stack,
5593 regardless of machine architecture, use @code{return};
5594 see @ref{Returning, ,Returning from a function}.} with
5600 Whenever possible, these four standard register names are available on
5601 your machine even though the machine has different canonical mnemonics,
5602 so long as there is no conflict. The @code{info registers} command
5603 shows the canonical names. For example, on the SPARC, @code{info
5604 registers} displays the processor status register as @code{$psr} but you
5605 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5606 is an alias for the @sc{eflags} register.
5608 @value{GDBN} always considers the contents of an ordinary register as an
5609 integer when the register is examined in this way. Some machines have
5610 special registers which can hold nothing but floating point; these
5611 registers are considered to have floating point values. There is no way
5612 to refer to the contents of an ordinary register as floating point value
5613 (although you can @emph{print} it as a floating point value with
5614 @samp{print/f $@var{regname}}).
5616 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5617 means that the data format in which the register contents are saved by
5618 the operating system is not the same one that your program normally
5619 sees. For example, the registers of the 68881 floating point
5620 coprocessor are always saved in ``extended'' (raw) format, but all C
5621 programs expect to work with ``double'' (virtual) format. In such
5622 cases, @value{GDBN} normally works with the virtual format only (the format
5623 that makes sense for your program), but the @code{info registers} command
5624 prints the data in both formats.
5626 Normally, register values are relative to the selected stack frame
5627 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5628 value that the register would contain if all stack frames farther in
5629 were exited and their saved registers restored. In order to see the
5630 true contents of hardware registers, you must select the innermost
5631 frame (with @samp{frame 0}).
5633 However, @value{GDBN} must deduce where registers are saved, from the machine
5634 code generated by your compiler. If some registers are not saved, or if
5635 @value{GDBN} is unable to locate the saved registers, the selected stack
5636 frame makes no difference.
5638 @node Floating Point Hardware
5639 @section Floating point hardware
5640 @cindex floating point
5642 Depending on the configuration, @value{GDBN} may be able to give
5643 you more information about the status of the floating point hardware.
5648 Display hardware-dependent information about the floating
5649 point unit. The exact contents and layout vary depending on the
5650 floating point chip. Currently, @samp{info float} is supported on
5651 the ARM and x86 machines.
5654 @node Memory Region Attributes
5655 @section Memory Region Attributes
5656 @cindex memory region attributes
5658 @dfn{Memory region attributes} allow you to describe special handling
5659 required by regions of your target's memory. @value{GDBN} uses attributes
5660 to determine whether to allow certain types of memory accesses; whether to
5661 use specific width accesses; and whether to cache target memory.
5663 Defined memory regions can be individually enabled and disabled. When a
5664 memory region is disabled, @value{GDBN} uses the default attributes when
5665 accessing memory in that region. Similarly, if no memory regions have
5666 been defined, @value{GDBN} uses the default attributes when accessing
5669 When a memory region is defined, it is given a number to identify it;
5670 to enable, disable, or remove a memory region, you specify that number.
5674 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5675 Define memory region bounded by @var{address1} and @var{address2}
5676 with attributes @var{attributes}@dots{}.
5679 @item delete mem @var{nums}@dots{}
5680 Remove memory region numbers @var{nums}.
5683 @item disable mem @var{nums}@dots{}
5684 Disable memory region numbers @var{nums}.
5685 A disabled memory region is not forgotten.
5686 It may be enabled again later.
5689 @item enable mem @var{nums}@dots{}
5690 Enable memory region numbers @var{nums}.
5694 Print a table of all defined memory regions, with the following columns
5698 @item Memory Region Number
5699 @item Enabled or Disabled.
5700 Enabled memory regions are marked with @samp{y}.
5701 Disabled memory regions are marked with @samp{n}.
5704 The address defining the inclusive lower bound of the memory region.
5707 The address defining the exclusive upper bound of the memory region.
5710 The list of attributes set for this memory region.
5715 @subsection Attributes
5717 @subsubsection Memory Access Mode
5718 The access mode attributes set whether @value{GDBN} may make read or
5719 write accesses to a memory region.
5721 While these attributes prevent @value{GDBN} from performing invalid
5722 memory accesses, they do nothing to prevent the target system, I/O DMA,
5723 etc. from accessing memory.
5727 Memory is read only.
5729 Memory is write only.
5731 Memory is read/write (default).
5734 @subsubsection Memory Access Size
5735 The acccess size attributes tells @value{GDBN} to use specific sized
5736 accesses in the memory region. Often memory mapped device registers
5737 require specific sized accesses. If no access size attribute is
5738 specified, @value{GDBN} may use accesses of any size.
5742 Use 8 bit memory accesses.
5744 Use 16 bit memory accesses.
5746 Use 32 bit memory accesses.
5748 Use 64 bit memory accesses.
5751 @c @subsubsection Hardware/Software Breakpoints
5752 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5753 @c will use hardware or software breakpoints for the internal breakpoints
5754 @c used by the step, next, finish, until, etc. commands.
5758 @c Always use hardware breakpoints
5759 @c @item swbreak (default)
5762 @subsubsection Data Cache
5763 The data cache attributes set whether @value{GDBN} will cache target
5764 memory. While this generally improves performance by reducing debug
5765 protocol overhead, it can lead to incorrect results because @value{GDBN}
5766 does not know about volatile variables or memory mapped device
5771 Enable @value{GDBN} to cache target memory.
5772 @item nocache (default)
5773 Disable @value{GDBN} from caching target memory.
5776 @c @subsubsection Memory Write Verification
5777 @c The memory write verification attributes set whether @value{GDBN}
5778 @c will re-reads data after each write to verify the write was successful.
5782 @c @item noverify (default)
5786 @chapter Tracepoints
5787 @c This chapter is based on the documentation written by Michael
5788 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5791 In some applications, it is not feasible for the debugger to interrupt
5792 the program's execution long enough for the developer to learn
5793 anything helpful about its behavior. If the program's correctness
5794 depends on its real-time behavior, delays introduced by a debugger
5795 might cause the program to change its behavior drastically, or perhaps
5796 fail, even when the code itself is correct. It is useful to be able
5797 to observe the program's behavior without interrupting it.
5799 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5800 specify locations in the program, called @dfn{tracepoints}, and
5801 arbitrary expressions to evaluate when those tracepoints are reached.
5802 Later, using the @code{tfind} command, you can examine the values
5803 those expressions had when the program hit the tracepoints. The
5804 expressions may also denote objects in memory---structures or arrays,
5805 for example---whose values @value{GDBN} should record; while visiting
5806 a particular tracepoint, you may inspect those objects as if they were
5807 in memory at that moment. However, because @value{GDBN} records these
5808 values without interacting with you, it can do so quickly and
5809 unobtrusively, hopefully not disturbing the program's behavior.
5811 The tracepoint facility is currently available only for remote
5812 targets. @xref{Targets}. In addition, your remote target must know how
5813 to collect trace data. This functionality is implemented in the remote
5814 stub; however, none of the stubs distributed with @value{GDBN} support
5815 tracepoints as of this writing.
5817 This chapter describes the tracepoint commands and features.
5821 * Analyze Collected Data::
5822 * Tracepoint Variables::
5825 @node Set Tracepoints
5826 @section Commands to Set Tracepoints
5828 Before running such a @dfn{trace experiment}, an arbitrary number of
5829 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5830 tracepoint has a number assigned to it by @value{GDBN}. Like with
5831 breakpoints, tracepoint numbers are successive integers starting from
5832 one. Many of the commands associated with tracepoints take the
5833 tracepoint number as their argument, to identify which tracepoint to
5836 For each tracepoint, you can specify, in advance, some arbitrary set
5837 of data that you want the target to collect in the trace buffer when
5838 it hits that tracepoint. The collected data can include registers,
5839 local variables, or global data. Later, you can use @value{GDBN}
5840 commands to examine the values these data had at the time the
5843 This section describes commands to set tracepoints and associated
5844 conditions and actions.
5847 * Create and Delete Tracepoints::
5848 * Enable and Disable Tracepoints::
5849 * Tracepoint Passcounts::
5850 * Tracepoint Actions::
5851 * Listing Tracepoints::
5852 * Starting and Stopping Trace Experiment::
5855 @node Create and Delete Tracepoints
5856 @subsection Create and Delete Tracepoints
5859 @cindex set tracepoint
5862 The @code{trace} command is very similar to the @code{break} command.
5863 Its argument can be a source line, a function name, or an address in
5864 the target program. @xref{Set Breaks}. The @code{trace} command
5865 defines a tracepoint, which is a point in the target program where the
5866 debugger will briefly stop, collect some data, and then allow the
5867 program to continue. Setting a tracepoint or changing its commands
5868 doesn't take effect until the next @code{tstart} command; thus, you
5869 cannot change the tracepoint attributes once a trace experiment is
5872 Here are some examples of using the @code{trace} command:
5875 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5877 (@value{GDBP}) @b{trace +2} // 2 lines forward
5879 (@value{GDBP}) @b{trace my_function} // first source line of function
5881 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5883 (@value{GDBP}) @b{trace *0x2117c4} // an address
5887 You can abbreviate @code{trace} as @code{tr}.
5890 @cindex last tracepoint number
5891 @cindex recent tracepoint number
5892 @cindex tracepoint number
5893 The convenience variable @code{$tpnum} records the tracepoint number
5894 of the most recently set tracepoint.
5896 @kindex delete tracepoint
5897 @cindex tracepoint deletion
5898 @item delete tracepoint @r{[}@var{num}@r{]}
5899 Permanently delete one or more tracepoints. With no argument, the
5900 default is to delete all tracepoints.
5905 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5907 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5911 You can abbreviate this command as @code{del tr}.
5914 @node Enable and Disable Tracepoints
5915 @subsection Enable and Disable Tracepoints
5918 @kindex disable tracepoint
5919 @item disable tracepoint @r{[}@var{num}@r{]}
5920 Disable tracepoint @var{num}, or all tracepoints if no argument
5921 @var{num} is given. A disabled tracepoint will have no effect during
5922 the next trace experiment, but it is not forgotten. You can re-enable
5923 a disabled tracepoint using the @code{enable tracepoint} command.
5925 @kindex enable tracepoint
5926 @item enable tracepoint @r{[}@var{num}@r{]}
5927 Enable tracepoint @var{num}, or all tracepoints. The enabled
5928 tracepoints will become effective the next time a trace experiment is
5932 @node Tracepoint Passcounts
5933 @subsection Tracepoint Passcounts
5937 @cindex tracepoint pass count
5938 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5939 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5940 automatically stop a trace experiment. If a tracepoint's passcount is
5941 @var{n}, then the trace experiment will be automatically stopped on
5942 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5943 @var{num} is not specified, the @code{passcount} command sets the
5944 passcount of the most recently defined tracepoint. If no passcount is
5945 given, the trace experiment will run until stopped explicitly by the
5951 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5953 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5954 // most recently defined tracepoint.
5955 (@value{GDBP}) @b{trace foo}
5956 (@value{GDBP}) @b{pass 3}
5957 (@value{GDBP}) @b{trace bar}
5958 (@value{GDBP}) @b{pass 2}
5959 (@value{GDBP}) @b{trace baz}
5960 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5961 // executed 3 times OR when bar has
5962 // been executed 2 times
5963 // OR when baz has been executed 1 time.
5967 @node Tracepoint Actions
5968 @subsection Tracepoint Action Lists
5972 @cindex tracepoint actions
5973 @item actions @r{[}@var{num}@r{]}
5974 This command will prompt for a list of actions to be taken when the
5975 tracepoint is hit. If the tracepoint number @var{num} is not
5976 specified, this command sets the actions for the one that was most
5977 recently defined (so that you can define a tracepoint and then say
5978 @code{actions} without bothering about its number). You specify the
5979 actions themselves on the following lines, one action at a time, and
5980 terminate the actions list with a line containing just @code{end}. So
5981 far, the only defined actions are @code{collect} and
5982 @code{while-stepping}.
5984 @cindex remove actions from a tracepoint
5985 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5986 and follow it immediately with @samp{end}.
5989 (@value{GDBP}) @b{collect @var{data}} // collect some data
5991 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5993 (@value{GDBP}) @b{end} // signals the end of actions.
5996 In the following example, the action list begins with @code{collect}
5997 commands indicating the things to be collected when the tracepoint is
5998 hit. Then, in order to single-step and collect additional data
5999 following the tracepoint, a @code{while-stepping} command is used,
6000 followed by the list of things to be collected while stepping. The
6001 @code{while-stepping} command is terminated by its own separate
6002 @code{end} command. Lastly, the action list is terminated by an
6006 (@value{GDBP}) @b{trace foo}
6007 (@value{GDBP}) @b{actions}
6008 Enter actions for tracepoint 1, one per line:
6017 @kindex collect @r{(tracepoints)}
6018 @item collect @var{expr1}, @var{expr2}, @dots{}
6019 Collect values of the given expressions when the tracepoint is hit.
6020 This command accepts a comma-separated list of any valid expressions.
6021 In addition to global, static, or local variables, the following
6022 special arguments are supported:
6026 collect all registers
6029 collect all function arguments
6032 collect all local variables.
6035 You can give several consecutive @code{collect} commands, each one
6036 with a single argument, or one @code{collect} command with several
6037 arguments separated by commas: the effect is the same.
6039 The command @code{info scope} (@pxref{Symbols, info scope}) is
6040 particularly useful for figuring out what data to collect.
6042 @kindex while-stepping @r{(tracepoints)}
6043 @item while-stepping @var{n}
6044 Perform @var{n} single-step traces after the tracepoint, collecting
6045 new data at each step. The @code{while-stepping} command is
6046 followed by the list of what to collect while stepping (followed by
6047 its own @code{end} command):
6051 > collect $regs, myglobal
6057 You may abbreviate @code{while-stepping} as @code{ws} or
6061 @node Listing Tracepoints
6062 @subsection Listing Tracepoints
6065 @kindex info tracepoints
6066 @cindex information about tracepoints
6067 @item info tracepoints @r{[}@var{num}@r{]}
6068 Display information the tracepoint @var{num}. If you don't specify a
6069 tracepoint number displays information about all the tracepoints
6070 defined so far. For each tracepoint, the following information is
6077 whether it is enabled or disabled
6081 its passcount as given by the @code{passcount @var{n}} command
6083 its step count as given by the @code{while-stepping @var{n}} command
6085 where in the source files is the tracepoint set
6087 its action list as given by the @code{actions} command
6091 (@value{GDBP}) @b{info trace}
6092 Num Enb Address PassC StepC What
6093 1 y 0x002117c4 0 0 <gdb_asm>
6094 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
6095 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
6100 This command can be abbreviated @code{info tp}.
6103 @node Starting and Stopping Trace Experiment
6104 @subsection Starting and Stopping Trace Experiment
6108 @cindex start a new trace experiment
6109 @cindex collected data discarded
6111 This command takes no arguments. It starts the trace experiment, and
6112 begins collecting data. This has the side effect of discarding all
6113 the data collected in the trace buffer during the previous trace
6117 @cindex stop a running trace experiment
6119 This command takes no arguments. It ends the trace experiment, and
6120 stops collecting data.
6122 @strong{Note:} a trace experiment and data collection may stop
6123 automatically if any tracepoint's passcount is reached
6124 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6127 @cindex status of trace data collection
6128 @cindex trace experiment, status of
6130 This command displays the status of the current trace data
6134 Here is an example of the commands we described so far:
6137 (@value{GDBP}) @b{trace gdb_c_test}
6138 (@value{GDBP}) @b{actions}
6139 Enter actions for tracepoint #1, one per line.
6140 > collect $regs,$locals,$args
6145 (@value{GDBP}) @b{tstart}
6146 [time passes @dots{}]
6147 (@value{GDBP}) @b{tstop}
6151 @node Analyze Collected Data
6152 @section Using the collected data
6154 After the tracepoint experiment ends, you use @value{GDBN} commands
6155 for examining the trace data. The basic idea is that each tracepoint
6156 collects a trace @dfn{snapshot} every time it is hit and another
6157 snapshot every time it single-steps. All these snapshots are
6158 consecutively numbered from zero and go into a buffer, and you can
6159 examine them later. The way you examine them is to @dfn{focus} on a
6160 specific trace snapshot. When the remote stub is focused on a trace
6161 snapshot, it will respond to all @value{GDBN} requests for memory and
6162 registers by reading from the buffer which belongs to that snapshot,
6163 rather than from @emph{real} memory or registers of the program being
6164 debugged. This means that @strong{all} @value{GDBN} commands
6165 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6166 behave as if we were currently debugging the program state as it was
6167 when the tracepoint occurred. Any requests for data that are not in
6168 the buffer will fail.
6171 * tfind:: How to select a trace snapshot
6172 * tdump:: How to display all data for a snapshot
6173 * save-tracepoints:: How to save tracepoints for a future run
6177 @subsection @code{tfind @var{n}}
6180 @cindex select trace snapshot
6181 @cindex find trace snapshot
6182 The basic command for selecting a trace snapshot from the buffer is
6183 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6184 counting from zero. If no argument @var{n} is given, the next
6185 snapshot is selected.
6187 Here are the various forms of using the @code{tfind} command.
6191 Find the first snapshot in the buffer. This is a synonym for
6192 @code{tfind 0} (since 0 is the number of the first snapshot).
6195 Stop debugging trace snapshots, resume @emph{live} debugging.
6198 Same as @samp{tfind none}.
6201 No argument means find the next trace snapshot.
6204 Find the previous trace snapshot before the current one. This permits
6205 retracing earlier steps.
6207 @item tfind tracepoint @var{num}
6208 Find the next snapshot associated with tracepoint @var{num}. Search
6209 proceeds forward from the last examined trace snapshot. If no
6210 argument @var{num} is given, it means find the next snapshot collected
6211 for the same tracepoint as the current snapshot.
6213 @item tfind pc @var{addr}
6214 Find the next snapshot associated with the value @var{addr} of the
6215 program counter. Search proceeds forward from the last examined trace
6216 snapshot. If no argument @var{addr} is given, it means find the next
6217 snapshot with the same value of PC as the current snapshot.
6219 @item tfind outside @var{addr1}, @var{addr2}
6220 Find the next snapshot whose PC is outside the given range of
6223 @item tfind range @var{addr1}, @var{addr2}
6224 Find the next snapshot whose PC is between @var{addr1} and
6225 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6227 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6228 Find the next snapshot associated with the source line @var{n}. If
6229 the optional argument @var{file} is given, refer to line @var{n} in
6230 that source file. Search proceeds forward from the last examined
6231 trace snapshot. If no argument @var{n} is given, it means find the
6232 next line other than the one currently being examined; thus saying
6233 @code{tfind line} repeatedly can appear to have the same effect as
6234 stepping from line to line in a @emph{live} debugging session.
6237 The default arguments for the @code{tfind} commands are specifically
6238 designed to make it easy to scan through the trace buffer. For
6239 instance, @code{tfind} with no argument selects the next trace
6240 snapshot, and @code{tfind -} with no argument selects the previous
6241 trace snapshot. So, by giving one @code{tfind} command, and then
6242 simply hitting @key{RET} repeatedly you can examine all the trace
6243 snapshots in order. Or, by saying @code{tfind -} and then hitting
6244 @key{RET} repeatedly you can examine the snapshots in reverse order.
6245 The @code{tfind line} command with no argument selects the snapshot
6246 for the next source line executed. The @code{tfind pc} command with
6247 no argument selects the next snapshot with the same program counter
6248 (PC) as the current frame. The @code{tfind tracepoint} command with
6249 no argument selects the next trace snapshot collected by the same
6250 tracepoint as the current one.
6252 In addition to letting you scan through the trace buffer manually,
6253 these commands make it easy to construct @value{GDBN} scripts that
6254 scan through the trace buffer and print out whatever collected data
6255 you are interested in. Thus, if we want to examine the PC, FP, and SP
6256 registers from each trace frame in the buffer, we can say this:
6259 (@value{GDBP}) @b{tfind start}
6260 (@value{GDBP}) @b{while ($trace_frame != -1)}
6261 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6262 $trace_frame, $pc, $sp, $fp
6266 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6267 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6268 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6269 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6270 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6271 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6272 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6273 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6274 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6275 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6276 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6279 Or, if we want to examine the variable @code{X} at each source line in
6283 (@value{GDBP}) @b{tfind start}
6284 (@value{GDBP}) @b{while ($trace_frame != -1)}
6285 > printf "Frame %d, X == %d\n", $trace_frame, X
6295 @subsection @code{tdump}
6297 @cindex dump all data collected at tracepoint
6298 @cindex tracepoint data, display
6300 This command takes no arguments. It prints all the data collected at
6301 the current trace snapshot.
6304 (@value{GDBP}) @b{trace 444}
6305 (@value{GDBP}) @b{actions}
6306 Enter actions for tracepoint #2, one per line:
6307 > collect $regs, $locals, $args, gdb_long_test
6310 (@value{GDBP}) @b{tstart}
6312 (@value{GDBP}) @b{tfind line 444}
6313 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6315 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6317 (@value{GDBP}) @b{tdump}
6318 Data collected at tracepoint 2, trace frame 1:
6319 d0 0xc4aa0085 -995491707
6323 d4 0x71aea3d 119204413
6328 a1 0x3000668 50333288
6331 a4 0x3000698 50333336
6333 fp 0x30bf3c 0x30bf3c
6334 sp 0x30bf34 0x30bf34
6336 pc 0x20b2c8 0x20b2c8
6340 p = 0x20e5b4 "gdb-test"
6347 gdb_long_test = 17 '\021'
6352 @node save-tracepoints
6353 @subsection @code{save-tracepoints @var{filename}}
6354 @kindex save-tracepoints
6355 @cindex save tracepoints for future sessions
6357 This command saves all current tracepoint definitions together with
6358 their actions and passcounts, into a file @file{@var{filename}}
6359 suitable for use in a later debugging session. To read the saved
6360 tracepoint definitions, use the @code{source} command (@pxref{Command
6363 @node Tracepoint Variables
6364 @section Convenience Variables for Tracepoints
6365 @cindex tracepoint variables
6366 @cindex convenience variables for tracepoints
6369 @vindex $trace_frame
6370 @item (int) $trace_frame
6371 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6372 snapshot is selected.
6375 @item (int) $tracepoint
6376 The tracepoint for the current trace snapshot.
6379 @item (int) $trace_line
6380 The line number for the current trace snapshot.
6383 @item (char []) $trace_file
6384 The source file for the current trace snapshot.
6387 @item (char []) $trace_func
6388 The name of the function containing @code{$tracepoint}.
6391 Note: @code{$trace_file} is not suitable for use in @code{printf},
6392 use @code{output} instead.
6394 Here's a simple example of using these convenience variables for
6395 stepping through all the trace snapshots and printing some of their
6399 (@value{GDBP}) @b{tfind start}
6401 (@value{GDBP}) @b{while $trace_frame != -1}
6402 > output $trace_file
6403 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6409 @chapter Debugging Programs That Use Overlays
6412 If your program is too large to fit completely in your target system's
6413 memory, you can sometimes use @dfn{overlays} to work around this
6414 problem. @value{GDBN} provides some support for debugging programs that
6418 * How Overlays Work:: A general explanation of overlays.
6419 * Overlay Commands:: Managing overlays in @value{GDBN}.
6420 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6421 mapped by asking the inferior.
6422 * Overlay Sample Program:: A sample program using overlays.
6425 @node How Overlays Work
6426 @section How Overlays Work
6427 @cindex mapped overlays
6428 @cindex unmapped overlays
6429 @cindex load address, overlay's
6430 @cindex mapped address
6431 @cindex overlay area
6433 Suppose you have a computer whose instruction address space is only 64
6434 kilobytes long, but which has much more memory which can be accessed by
6435 other means: special instructions, segment registers, or memory
6436 management hardware, for example. Suppose further that you want to
6437 adapt a program which is larger than 64 kilobytes to run on this system.
6439 One solution is to identify modules of your program which are relatively
6440 independent, and need not call each other directly; call these modules
6441 @dfn{overlays}. Separate the overlays from the main program, and place
6442 their machine code in the larger memory. Place your main program in
6443 instruction memory, but leave at least enough space there to hold the
6444 largest overlay as well.
6446 Now, to call a function located in an overlay, you must first copy that
6447 overlay's machine code from the large memory into the space set aside
6448 for it in the instruction memory, and then jump to its entry point
6453 Data Instruction Larger
6454 Address Space Address Space Address Space
6455 +-----------+ +-----------+ +-----------+
6457 +-----------+ +-----------+ +-----------+<-- overlay 1
6458 | program | | main | | | load address
6459 | variables | | program | | overlay 1 |
6460 | and heap | | | ,---| |
6461 +-----------+ | | | | |
6462 | | +-----------+ | +-----------+
6463 +-----------+ | | | | |
6464 mapped --->+-----------+ / +-----------+<-- overlay 2
6465 address | overlay | <-' | overlay 2 | load address
6467 | | <---. +-----------+
6470 | | | +-----------+<-- overlay 3
6471 +-----------+ `--| | load address
6478 To map an overlay, copy its code from the larger address space
6479 to the instruction address space. Since the overlays shown here
6480 all use the same mapped address, only one may be mapped at a time.
6484 This diagram shows a system with separate data and instruction address
6485 spaces. For a system with a single address space for data and
6486 instructions, the diagram would be similar, except that the program
6487 variables and heap would share an address space with the main program
6488 and the overlay area.
6490 An overlay loaded into instruction memory and ready for use is called a
6491 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6492 instruction memory. An overlay not present (or only partially present)
6493 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6494 is its address in the larger memory. The mapped address is also called
6495 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6496 called the @dfn{load memory address}, or @dfn{LMA}.
6498 Unfortunately, overlays are not a completely transparent way to adapt a
6499 program to limited instruction memory. They introduce a new set of
6500 global constraints you must keep in mind as you design your program:
6505 Before calling or returning to a function in an overlay, your program
6506 must make sure that overlay is actually mapped. Otherwise, the call or
6507 return will transfer control to the right address, but in the wrong
6508 overlay, and your program will probably crash.
6511 If the process of mapping an overlay is expensive on your system, you
6512 will need to choose your overlays carefully to minimize their effect on
6513 your program's performance.
6516 The executable file you load onto your system must contain each
6517 overlay's instructions, appearing at the overlay's load address, not its
6518 mapped address. However, each overlay's instructions must be relocated
6519 and its symbols defined as if the overlay were at its mapped address.
6520 You can use GNU linker scripts to specify different load and relocation
6521 addresses for pieces of your program; see @ref{Overlay Description,,,
6522 ld.info, Using ld: the GNU linker}.
6525 The procedure for loading executable files onto your system must be able
6526 to load their contents into the larger address space as well as the
6527 instruction and data spaces.
6531 The overlay system described above is rather simple, and could be
6532 improved in many ways:
6537 If your system has suitable bank switch registers or memory management
6538 hardware, you could use those facilities to make an overlay's load area
6539 contents simply appear at their mapped address in instruction space.
6540 This would probably be faster than copying the overlay to its mapped
6541 area in the usual way.
6544 If your overlays are small enough, you could set aside more than one
6545 overlay area, and have more than one overlay mapped at a time.
6548 You can use overlays to manage data, as well as instructions. In
6549 general, data overlays are even less transparent to your design than
6550 code overlays: whereas code overlays only require care when you call or
6551 return to functions, data overlays require care every time you access
6552 the data. Also, if you change the contents of a data overlay, you
6553 must copy its contents back out to its load address before you can copy a
6554 different data overlay into the same mapped area.
6559 @node Overlay Commands
6560 @section Overlay Commands
6562 To use @value{GDBN}'s overlay support, each overlay in your program must
6563 correspond to a separate section of the executable file. The section's
6564 virtual memory address and load memory address must be the overlay's
6565 mapped and load addresses. Identifying overlays with sections allows
6566 @value{GDBN} to determine the appropriate address of a function or
6567 variable, depending on whether the overlay is mapped or not.
6569 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6570 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6575 Disable @value{GDBN}'s overlay support. When overlay support is
6576 disabled, @value{GDBN} assumes that all functions and variables are
6577 always present at their mapped addresses. By default, @value{GDBN}'s
6578 overlay support is disabled.
6580 @item overlay manual
6581 @kindex overlay manual
6582 @cindex manual overlay debugging
6583 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6584 relies on you to tell it which overlays are mapped, and which are not,
6585 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6586 commands described below.
6588 @item overlay map-overlay @var{overlay}
6589 @itemx overlay map @var{overlay}
6590 @kindex overlay map-overlay
6591 @cindex map an overlay
6592 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6593 be the name of the object file section containing the overlay. When an
6594 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6595 functions and variables at their mapped addresses. @value{GDBN} assumes
6596 that any other overlays whose mapped ranges overlap that of
6597 @var{overlay} are now unmapped.
6599 @item overlay unmap-overlay @var{overlay}
6600 @itemx overlay unmap @var{overlay}
6601 @kindex overlay unmap-overlay
6602 @cindex unmap an overlay
6603 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6604 must be the name of the object file section containing the overlay.
6605 When an overlay is unmapped, @value{GDBN} assumes it can find the
6606 overlay's functions and variables at their load addresses.
6609 @kindex overlay auto
6610 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6611 consults a data structure the overlay manager maintains in the inferior
6612 to see which overlays are mapped. For details, see @ref{Automatic
6615 @item overlay load-target
6617 @kindex overlay load-target
6618 @cindex reloading the overlay table
6619 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6620 re-reads the table @value{GDBN} automatically each time the inferior
6621 stops, so this command should only be necessary if you have changed the
6622 overlay mapping yourself using @value{GDBN}. This command is only
6623 useful when using automatic overlay debugging.
6625 @item overlay list-overlays
6627 @cindex listing mapped overlays
6628 Display a list of the overlays currently mapped, along with their mapped
6629 addresses, load addresses, and sizes.
6633 Normally, when @value{GDBN} prints a code address, it includes the name
6634 of the function the address falls in:
6638 $3 = @{int ()@} 0x11a0 <main>
6641 When overlay debugging is enabled, @value{GDBN} recognizes code in
6642 unmapped overlays, and prints the names of unmapped functions with
6643 asterisks around them. For example, if @code{foo} is a function in an
6644 unmapped overlay, @value{GDBN} prints it this way:
6648 No sections are mapped.
6650 $5 = @{int (int)@} 0x100000 <*foo*>
6653 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6658 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6659 mapped at 0x1016 - 0x104a
6661 $6 = @{int (int)@} 0x1016 <foo>
6664 When overlay debugging is enabled, @value{GDBN} can find the correct
6665 address for functions and variables in an overlay, whether or not the
6666 overlay is mapped. This allows most @value{GDBN} commands, like
6667 @code{break} and @code{disassemble}, to work normally, even on unmapped
6668 code. However, @value{GDBN}'s breakpoint support has some limitations:
6672 @cindex breakpoints in overlays
6673 @cindex overlays, setting breakpoints in
6674 You can set breakpoints in functions in unmapped overlays, as long as
6675 @value{GDBN} can write to the overlay at its load address.
6677 @value{GDBN} can not set hardware or simulator-based breakpoints in
6678 unmapped overlays. However, if you set a breakpoint at the end of your
6679 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6680 you are using manual overlay management), @value{GDBN} will re-set its
6681 breakpoints properly.
6685 @node Automatic Overlay Debugging
6686 @section Automatic Overlay Debugging
6687 @cindex automatic overlay debugging
6689 @value{GDBN} can automatically track which overlays are mapped and which
6690 are not, given some simple co-operation from the overlay manager in the
6691 inferior. If you enable automatic overlay debugging with the
6692 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6693 looks in the inferior's memory for certain variables describing the
6694 current state of the overlays.
6696 Here are the variables your overlay manager must define to support
6697 @value{GDBN}'s automatic overlay debugging:
6701 @item @code{_ovly_table}:
6702 This variable must be an array of the following structures:
6707 /* The overlay's mapped address. */
6710 /* The size of the overlay, in bytes. */
6713 /* The overlay's load address. */
6716 /* Non-zero if the overlay is currently mapped;
6718 unsigned long mapped;
6722 @item @code{_novlys}:
6723 This variable must be a four-byte signed integer, holding the total
6724 number of elements in @code{_ovly_table}.
6728 To decide whether a particular overlay is mapped or not, @value{GDBN}
6729 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6730 @code{lma} members equal the VMA and LMA of the overlay's section in the
6731 executable file. When @value{GDBN} finds a matching entry, it consults
6732 the entry's @code{mapped} member to determine whether the overlay is
6736 @node Overlay Sample Program
6737 @section Overlay Sample Program
6738 @cindex overlay example program
6740 When linking a program which uses overlays, you must place the overlays
6741 at their load addresses, while relocating them to run at their mapped
6742 addresses. To do this, you must write a linker script (@pxref{Overlay
6743 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
6744 since linker scripts are specific to a particular host system, target
6745 architecture, and target memory layout, this manual cannot provide
6746 portable sample code demonstrating @value{GDBN}'s overlay support.
6748 However, the @value{GDBN} source distribution does contain an overlaid
6749 program, with linker scripts for a few systems, as part of its test
6750 suite. The program consists of the following files from
6751 @file{gdb/testsuite/gdb.base}:
6755 The main program file.
6757 A simple overlay manager, used by @file{overlays.c}.
6762 Overlay modules, loaded and used by @file{overlays.c}.
6765 Linker scripts for linking the test program on the @code{d10v-elf}
6766 and @code{m32r-elf} targets.
6769 You can build the test program using the @code{d10v-elf} GCC
6770 cross-compiler like this:
6773 $ d10v-elf-gcc -g -c overlays.c
6774 $ d10v-elf-gcc -g -c ovlymgr.c
6775 $ d10v-elf-gcc -g -c foo.c
6776 $ d10v-elf-gcc -g -c bar.c
6777 $ d10v-elf-gcc -g -c baz.c
6778 $ d10v-elf-gcc -g -c grbx.c
6779 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
6780 baz.o grbx.o -Wl,-Td10v.ld -o overlays
6783 The build process is identical for any other architecture, except that
6784 you must substitute the appropriate compiler and linker script for the
6785 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
6789 @chapter Using @value{GDBN} with Different Languages
6792 Although programming languages generally have common aspects, they are
6793 rarely expressed in the same manner. For instance, in ANSI C,
6794 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6795 Modula-2, it is accomplished by @code{p^}. Values can also be
6796 represented (and displayed) differently. Hex numbers in C appear as
6797 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6799 @cindex working language
6800 Language-specific information is built into @value{GDBN} for some languages,
6801 allowing you to express operations like the above in your program's
6802 native language, and allowing @value{GDBN} to output values in a manner
6803 consistent with the syntax of your program's native language. The
6804 language you use to build expressions is called the @dfn{working
6808 * Setting:: Switching between source languages
6809 * Show:: Displaying the language
6810 * Checks:: Type and range checks
6811 * Support:: Supported languages
6815 @section Switching between source languages
6817 There are two ways to control the working language---either have @value{GDBN}
6818 set it automatically, or select it manually yourself. You can use the
6819 @code{set language} command for either purpose. On startup, @value{GDBN}
6820 defaults to setting the language automatically. The working language is
6821 used to determine how expressions you type are interpreted, how values
6824 In addition to the working language, every source file that
6825 @value{GDBN} knows about has its own working language. For some object
6826 file formats, the compiler might indicate which language a particular
6827 source file is in. However, most of the time @value{GDBN} infers the
6828 language from the name of the file. The language of a source file
6829 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6830 show each frame appropriately for its own language. There is no way to
6831 set the language of a source file from within @value{GDBN}, but you can
6832 set the language associated with a filename extension. @xref{Show, ,
6833 Displaying the language}.
6835 This is most commonly a problem when you use a program, such
6836 as @code{cfront} or @code{f2c}, that generates C but is written in
6837 another language. In that case, make the
6838 program use @code{#line} directives in its C output; that way
6839 @value{GDBN} will know the correct language of the source code of the original
6840 program, and will display that source code, not the generated C code.
6843 * Filenames:: Filename extensions and languages.
6844 * Manually:: Setting the working language manually
6845 * Automatically:: Having @value{GDBN} infer the source language
6849 @subsection List of filename extensions and languages
6851 If a source file name ends in one of the following extensions, then
6852 @value{GDBN} infers that its language is the one indicated.
6877 Modula-2 source file
6881 Assembler source file. This actually behaves almost like C, but
6882 @value{GDBN} does not skip over function prologues when stepping.
6885 In addition, you may set the language associated with a filename
6886 extension. @xref{Show, , Displaying the language}.
6889 @subsection Setting the working language
6891 If you allow @value{GDBN} to set the language automatically,
6892 expressions are interpreted the same way in your debugging session and
6895 @kindex set language
6896 If you wish, you may set the language manually. To do this, issue the
6897 command @samp{set language @var{lang}}, where @var{lang} is the name of
6899 @code{c} or @code{modula-2}.
6900 For a list of the supported languages, type @samp{set language}.
6902 Setting the language manually prevents @value{GDBN} from updating the working
6903 language automatically. This can lead to confusion if you try
6904 to debug a program when the working language is not the same as the
6905 source language, when an expression is acceptable to both
6906 languages---but means different things. For instance, if the current
6907 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6915 might not have the effect you intended. In C, this means to add
6916 @code{b} and @code{c} and place the result in @code{a}. The result
6917 printed would be the value of @code{a}. In Modula-2, this means to compare
6918 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6921 @subsection Having @value{GDBN} infer the source language
6923 To have @value{GDBN} set the working language automatically, use
6924 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6925 then infers the working language. That is, when your program stops in a
6926 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6927 working language to the language recorded for the function in that
6928 frame. If the language for a frame is unknown (that is, if the function
6929 or block corresponding to the frame was defined in a source file that
6930 does not have a recognized extension), the current working language is
6931 not changed, and @value{GDBN} issues a warning.
6933 This may not seem necessary for most programs, which are written
6934 entirely in one source language. However, program modules and libraries
6935 written in one source language can be used by a main program written in
6936 a different source language. Using @samp{set language auto} in this
6937 case frees you from having to set the working language manually.
6940 @section Displaying the language
6942 The following commands help you find out which language is the
6943 working language, and also what language source files were written in.
6945 @kindex show language
6946 @kindex info frame@r{, show the source language}
6947 @kindex info source@r{, show the source language}
6950 Display the current working language. This is the
6951 language you can use with commands such as @code{print} to
6952 build and compute expressions that may involve variables in your program.
6955 Display the source language for this frame. This language becomes the
6956 working language if you use an identifier from this frame.
6957 @xref{Frame Info, ,Information about a frame}, to identify the other
6958 information listed here.
6961 Display the source language of this source file.
6962 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6963 information listed here.
6966 In unusual circumstances, you may have source files with extensions
6967 not in the standard list. You can then set the extension associated
6968 with a language explicitly:
6970 @kindex set extension-language
6971 @kindex info extensions
6973 @item set extension-language @var{.ext} @var{language}
6974 Set source files with extension @var{.ext} to be assumed to be in
6975 the source language @var{language}.
6977 @item info extensions
6978 List all the filename extensions and the associated languages.
6982 @section Type and range checking
6985 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6986 checking are included, but they do not yet have any effect. This
6987 section documents the intended facilities.
6989 @c FIXME remove warning when type/range code added
6991 Some languages are designed to guard you against making seemingly common
6992 errors through a series of compile- and run-time checks. These include
6993 checking the type of arguments to functions and operators, and making
6994 sure mathematical overflows are caught at run time. Checks such as
6995 these help to ensure a program's correctness once it has been compiled
6996 by eliminating type mismatches, and providing active checks for range
6997 errors when your program is running.
6999 @value{GDBN} can check for conditions like the above if you wish.
7000 Although @value{GDBN} does not check the statements in your program, it
7001 can check expressions entered directly into @value{GDBN} for evaluation via
7002 the @code{print} command, for example. As with the working language,
7003 @value{GDBN} can also decide whether or not to check automatically based on
7004 your program's source language. @xref{Support, ,Supported languages},
7005 for the default settings of supported languages.
7008 * Type Checking:: An overview of type checking
7009 * Range Checking:: An overview of range checking
7012 @cindex type checking
7013 @cindex checks, type
7015 @subsection An overview of type checking
7017 Some languages, such as Modula-2, are strongly typed, meaning that the
7018 arguments to operators and functions have to be of the correct type,
7019 otherwise an error occurs. These checks prevent type mismatch
7020 errors from ever causing any run-time problems. For example,
7028 The second example fails because the @code{CARDINAL} 1 is not
7029 type-compatible with the @code{REAL} 2.3.
7031 For the expressions you use in @value{GDBN} commands, you can tell the
7032 @value{GDBN} type checker to skip checking;
7033 to treat any mismatches as errors and abandon the expression;
7034 or to only issue warnings when type mismatches occur,
7035 but evaluate the expression anyway. When you choose the last of
7036 these, @value{GDBN} evaluates expressions like the second example above, but
7037 also issues a warning.
7039 Even if you turn type checking off, there may be other reasons
7040 related to type that prevent @value{GDBN} from evaluating an expression.
7041 For instance, @value{GDBN} does not know how to add an @code{int} and
7042 a @code{struct foo}. These particular type errors have nothing to do
7043 with the language in use, and usually arise from expressions, such as
7044 the one described above, which make little sense to evaluate anyway.
7046 Each language defines to what degree it is strict about type. For
7047 instance, both Modula-2 and C require the arguments to arithmetical
7048 operators to be numbers. In C, enumerated types and pointers can be
7049 represented as numbers, so that they are valid arguments to mathematical
7050 operators. @xref{Support, ,Supported languages}, for further
7051 details on specific languages.
7053 @value{GDBN} provides some additional commands for controlling the type checker:
7055 @kindex set check@r{, type}
7056 @kindex set check type
7057 @kindex show check type
7059 @item set check type auto
7060 Set type checking on or off based on the current working language.
7061 @xref{Support, ,Supported languages}, for the default settings for
7064 @item set check type on
7065 @itemx set check type off
7066 Set type checking on or off, overriding the default setting for the
7067 current working language. Issue a warning if the setting does not
7068 match the language default. If any type mismatches occur in
7069 evaluating an expression while type checking is on, @value{GDBN} prints a
7070 message and aborts evaluation of the expression.
7072 @item set check type warn
7073 Cause the type checker to issue warnings, but to always attempt to
7074 evaluate the expression. Evaluating the expression may still
7075 be impossible for other reasons. For example, @value{GDBN} cannot add
7076 numbers and structures.
7079 Show the current setting of the type checker, and whether or not @value{GDBN}
7080 is setting it automatically.
7083 @cindex range checking
7084 @cindex checks, range
7085 @node Range Checking
7086 @subsection An overview of range checking
7088 In some languages (such as Modula-2), it is an error to exceed the
7089 bounds of a type; this is enforced with run-time checks. Such range
7090 checking is meant to ensure program correctness by making sure
7091 computations do not overflow, or indices on an array element access do
7092 not exceed the bounds of the array.
7094 For expressions you use in @value{GDBN} commands, you can tell
7095 @value{GDBN} to treat range errors in one of three ways: ignore them,
7096 always treat them as errors and abandon the expression, or issue
7097 warnings but evaluate the expression anyway.
7099 A range error can result from numerical overflow, from exceeding an
7100 array index bound, or when you type a constant that is not a member
7101 of any type. Some languages, however, do not treat overflows as an
7102 error. In many implementations of C, mathematical overflow causes the
7103 result to ``wrap around'' to lower values---for example, if @var{m} is
7104 the largest integer value, and @var{s} is the smallest, then
7107 @var{m} + 1 @result{} @var{s}
7110 This, too, is specific to individual languages, and in some cases
7111 specific to individual compilers or machines. @xref{Support, ,
7112 Supported languages}, for further details on specific languages.
7114 @value{GDBN} provides some additional commands for controlling the range checker:
7116 @kindex set check@r{, range}
7117 @kindex set check range
7118 @kindex show check range
7120 @item set check range auto
7121 Set range checking on or off based on the current working language.
7122 @xref{Support, ,Supported languages}, for the default settings for
7125 @item set check range on
7126 @itemx set check range off
7127 Set range checking on or off, overriding the default setting for the
7128 current working language. A warning is issued if the setting does not
7129 match the language default. If a range error occurs and range checking is on,
7130 then a message is printed and evaluation of the expression is aborted.
7132 @item set check range warn
7133 Output messages when the @value{GDBN} range checker detects a range error,
7134 but attempt to evaluate the expression anyway. Evaluating the
7135 expression may still be impossible for other reasons, such as accessing
7136 memory that the process does not own (a typical example from many Unix
7140 Show the current setting of the range checker, and whether or not it is
7141 being set automatically by @value{GDBN}.
7145 @section Supported languages
7147 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
7148 @c This is false ...
7149 Some @value{GDBN} features may be used in expressions regardless of the
7150 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7151 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7152 ,Expressions}) can be used with the constructs of any supported
7155 The following sections detail to what degree each source language is
7156 supported by @value{GDBN}. These sections are not meant to be language
7157 tutorials or references, but serve only as a reference guide to what the
7158 @value{GDBN} expression parser accepts, and what input and output
7159 formats should look like for different languages. There are many good
7160 books written on each of these languages; please look to these for a
7161 language reference or tutorial.
7165 * Modula-2:: Modula-2
7170 @subsection C and C@t{++}
7172 @cindex C and C@t{++}
7173 @cindex expressions in C or C@t{++}
7175 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7176 to both languages. Whenever this is the case, we discuss those languages
7180 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7181 @cindex @sc{gnu} C@t{++}
7182 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7183 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7184 effectively, you must compile your C@t{++} programs with a supported
7185 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7186 compiler (@code{aCC}).
7188 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7189 format. You can select that format explicitly with the @code{g++}
7190 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7191 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7192 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7195 * C Operators:: C and C@t{++} operators
7196 * C Constants:: C and C@t{++} constants
7197 * C plus plus expressions:: C@t{++} expressions
7198 * C Defaults:: Default settings for C and C@t{++}
7199 * C Checks:: C and C@t{++} type and range checks
7200 * Debugging C:: @value{GDBN} and C
7201 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7205 @subsubsection C and C@t{++} operators
7207 @cindex C and C@t{++} operators
7209 Operators must be defined on values of specific types. For instance,
7210 @code{+} is defined on numbers, but not on structures. Operators are
7211 often defined on groups of types.
7213 For the purposes of C and C@t{++}, the following definitions hold:
7218 @emph{Integral types} include @code{int} with any of its storage-class
7219 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7222 @emph{Floating-point types} include @code{float}, @code{double}, and
7223 @code{long double} (if supported by the target platform).
7226 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7229 @emph{Scalar types} include all of the above.
7234 The following operators are supported. They are listed here
7235 in order of increasing precedence:
7239 The comma or sequencing operator. Expressions in a comma-separated list
7240 are evaluated from left to right, with the result of the entire
7241 expression being the last expression evaluated.
7244 Assignment. The value of an assignment expression is the value
7245 assigned. Defined on scalar types.
7248 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7249 and translated to @w{@code{@var{a} = @var{a op b}}}.
7250 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7251 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7252 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7255 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7256 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7260 Logical @sc{or}. Defined on integral types.
7263 Logical @sc{and}. Defined on integral types.
7266 Bitwise @sc{or}. Defined on integral types.
7269 Bitwise exclusive-@sc{or}. Defined on integral types.
7272 Bitwise @sc{and}. Defined on integral types.
7275 Equality and inequality. Defined on scalar types. The value of these
7276 expressions is 0 for false and non-zero for true.
7278 @item <@r{, }>@r{, }<=@r{, }>=
7279 Less than, greater than, less than or equal, greater than or equal.
7280 Defined on scalar types. The value of these expressions is 0 for false
7281 and non-zero for true.
7284 left shift, and right shift. Defined on integral types.
7287 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7290 Addition and subtraction. Defined on integral types, floating-point types and
7293 @item *@r{, }/@r{, }%
7294 Multiplication, division, and modulus. Multiplication and division are
7295 defined on integral and floating-point types. Modulus is defined on
7299 Increment and decrement. When appearing before a variable, the
7300 operation is performed before the variable is used in an expression;
7301 when appearing after it, the variable's value is used before the
7302 operation takes place.
7305 Pointer dereferencing. Defined on pointer types. Same precedence as
7309 Address operator. Defined on variables. Same precedence as @code{++}.
7311 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7312 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7313 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7314 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7318 Negative. Defined on integral and floating-point types. Same
7319 precedence as @code{++}.
7322 Logical negation. Defined on integral types. Same precedence as
7326 Bitwise complement operator. Defined on integral types. Same precedence as
7331 Structure member, and pointer-to-structure member. For convenience,
7332 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7333 pointer based on the stored type information.
7334 Defined on @code{struct} and @code{union} data.
7337 Dereferences of pointers to members.
7340 Array indexing. @code{@var{a}[@var{i}]} is defined as
7341 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7344 Function parameter list. Same precedence as @code{->}.
7347 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7348 and @code{class} types.
7351 Doubled colons also represent the @value{GDBN} scope operator
7352 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7356 If an operator is redefined in the user code, @value{GDBN} usually
7357 attempts to invoke the redefined version instead of using the operator's
7365 @subsubsection C and C@t{++} constants
7367 @cindex C and C@t{++} constants
7369 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7374 Integer constants are a sequence of digits. Octal constants are
7375 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
7376 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7377 @samp{l}, specifying that the constant should be treated as a
7381 Floating point constants are a sequence of digits, followed by a decimal
7382 point, followed by a sequence of digits, and optionally followed by an
7383 exponent. An exponent is of the form:
7384 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7385 sequence of digits. The @samp{+} is optional for positive exponents.
7386 A floating-point constant may also end with a letter @samp{f} or
7387 @samp{F}, specifying that the constant should be treated as being of
7388 the @code{float} (as opposed to the default @code{double}) type; or with
7389 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7393 Enumerated constants consist of enumerated identifiers, or their
7394 integral equivalents.
7397 Character constants are a single character surrounded by single quotes
7398 (@code{'}), or a number---the ordinal value of the corresponding character
7399 (usually its @sc{ascii} value). Within quotes, the single character may
7400 be represented by a letter or by @dfn{escape sequences}, which are of
7401 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7402 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7403 @samp{@var{x}} is a predefined special character---for example,
7404 @samp{\n} for newline.
7407 String constants are a sequence of character constants surrounded by
7408 double quotes (@code{"}). Any valid character constant (as described
7409 above) may appear. Double quotes within the string must be preceded by
7410 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7414 Pointer constants are an integral value. You can also write pointers
7415 to constants using the C operator @samp{&}.
7418 Array constants are comma-separated lists surrounded by braces @samp{@{}
7419 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7420 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7421 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7425 * C plus plus expressions::
7432 @node C plus plus expressions
7433 @subsubsection C@t{++} expressions
7435 @cindex expressions in C@t{++}
7436 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7438 @cindex C@t{++} support, not in @sc{coff}
7439 @cindex @sc{coff} versus C@t{++}
7440 @cindex C@t{++} and object formats
7441 @cindex object formats and C@t{++}
7442 @cindex a.out and C@t{++}
7443 @cindex @sc{ecoff} and C@t{++}
7444 @cindex @sc{xcoff} and C@t{++}
7445 @cindex @sc{elf}/stabs and C@t{++}
7446 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7447 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7448 @c periodically whether this has happened...
7450 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7451 proper compiler. Typically, C@t{++} debugging depends on the use of
7452 additional debugging information in the symbol table, and thus requires
7453 special support. In particular, if your compiler generates a.out, MIPS
7454 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7455 symbol table, these facilities are all available. (With @sc{gnu} CC,
7456 you can use the @samp{-gstabs} option to request stabs debugging
7457 extensions explicitly.) Where the object code format is standard
7458 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7459 support in @value{GDBN} does @emph{not} work.
7464 @cindex member functions
7466 Member function calls are allowed; you can use expressions like
7469 count = aml->GetOriginal(x, y)
7472 @vindex this@r{, inside C@t{++} member functions}
7473 @cindex namespace in C@t{++}
7475 While a member function is active (in the selected stack frame), your
7476 expressions have the same namespace available as the member function;
7477 that is, @value{GDBN} allows implicit references to the class instance
7478 pointer @code{this} following the same rules as C@t{++}.
7480 @cindex call overloaded functions
7481 @cindex overloaded functions, calling
7482 @cindex type conversions in C@t{++}
7484 You can call overloaded functions; @value{GDBN} resolves the function
7485 call to the right definition, with some restrictions. @value{GDBN} does not
7486 perform overload resolution involving user-defined type conversions,
7487 calls to constructors, or instantiations of templates that do not exist
7488 in the program. It also cannot handle ellipsis argument lists or
7491 It does perform integral conversions and promotions, floating-point
7492 promotions, arithmetic conversions, pointer conversions, conversions of
7493 class objects to base classes, and standard conversions such as those of
7494 functions or arrays to pointers; it requires an exact match on the
7495 number of function arguments.
7497 Overload resolution is always performed, unless you have specified
7498 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7499 ,@value{GDBN} features for C@t{++}}.
7501 You must specify @code{set overload-resolution off} in order to use an
7502 explicit function signature to call an overloaded function, as in
7504 p 'foo(char,int)'('x', 13)
7507 The @value{GDBN} command-completion facility can simplify this;
7508 see @ref{Completion, ,Command completion}.
7510 @cindex reference declarations
7512 @value{GDBN} understands variables declared as C@t{++} references; you can use
7513 them in expressions just as you do in C@t{++} source---they are automatically
7516 In the parameter list shown when @value{GDBN} displays a frame, the values of
7517 reference variables are not displayed (unlike other variables); this
7518 avoids clutter, since references are often used for large structures.
7519 The @emph{address} of a reference variable is always shown, unless
7520 you have specified @samp{set print address off}.
7523 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7524 expressions can use it just as expressions in your program do. Since
7525 one scope may be defined in another, you can use @code{::} repeatedly if
7526 necessary, for example in an expression like
7527 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7528 resolving name scope by reference to source files, in both C and C@t{++}
7529 debugging (@pxref{Variables, ,Program variables}).
7532 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7533 calling virtual functions correctly, printing out virtual bases of
7534 objects, calling functions in a base subobject, casting objects, and
7535 invoking user-defined operators.
7538 @subsubsection C and C@t{++} defaults
7540 @cindex C and C@t{++} defaults
7542 If you allow @value{GDBN} to set type and range checking automatically, they
7543 both default to @code{off} whenever the working language changes to
7544 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7545 selects the working language.
7547 If you allow @value{GDBN} to set the language automatically, it
7548 recognizes source files whose names end with @file{.c}, @file{.C}, or
7549 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7550 these files, it sets the working language to C or C@t{++}.
7551 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7552 for further details.
7554 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7555 @c unimplemented. If (b) changes, it might make sense to let this node
7556 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7559 @subsubsection C and C@t{++} type and range checks
7561 @cindex C and C@t{++} checks
7563 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7564 is not used. However, if you turn type checking on, @value{GDBN}
7565 considers two variables type equivalent if:
7569 The two variables are structured and have the same structure, union, or
7573 The two variables have the same type name, or types that have been
7574 declared equivalent through @code{typedef}.
7577 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7580 The two @code{struct}, @code{union}, or @code{enum} variables are
7581 declared in the same declaration. (Note: this may not be true for all C
7586 Range checking, if turned on, is done on mathematical operations. Array
7587 indices are not checked, since they are often used to index a pointer
7588 that is not itself an array.
7591 @subsubsection @value{GDBN} and C
7593 The @code{set print union} and @code{show print union} commands apply to
7594 the @code{union} type. When set to @samp{on}, any @code{union} that is
7595 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7596 appears as @samp{@{...@}}.
7598 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7599 with pointers and a memory allocation function. @xref{Expressions,
7603 * Debugging C plus plus::
7606 @node Debugging C plus plus
7607 @subsubsection @value{GDBN} features for C@t{++}
7609 @cindex commands for C@t{++}
7611 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7612 designed specifically for use with C@t{++}. Here is a summary:
7615 @cindex break in overloaded functions
7616 @item @r{breakpoint menus}
7617 When you want a breakpoint in a function whose name is overloaded,
7618 @value{GDBN} breakpoint menus help you specify which function definition
7619 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7621 @cindex overloading in C@t{++}
7622 @item rbreak @var{regex}
7623 Setting breakpoints using regular expressions is helpful for setting
7624 breakpoints on overloaded functions that are not members of any special
7626 @xref{Set Breaks, ,Setting breakpoints}.
7628 @cindex C@t{++} exception handling
7631 Debug C@t{++} exception handling using these commands. @xref{Set
7632 Catchpoints, , Setting catchpoints}.
7635 @item ptype @var{typename}
7636 Print inheritance relationships as well as other information for type
7638 @xref{Symbols, ,Examining the Symbol Table}.
7640 @cindex C@t{++} symbol display
7641 @item set print demangle
7642 @itemx show print demangle
7643 @itemx set print asm-demangle
7644 @itemx show print asm-demangle
7645 Control whether C@t{++} symbols display in their source form, both when
7646 displaying code as C@t{++} source and when displaying disassemblies.
7647 @xref{Print Settings, ,Print settings}.
7649 @item set print object
7650 @itemx show print object
7651 Choose whether to print derived (actual) or declared types of objects.
7652 @xref{Print Settings, ,Print settings}.
7654 @item set print vtbl
7655 @itemx show print vtbl
7656 Control the format for printing virtual function tables.
7657 @xref{Print Settings, ,Print settings}.
7658 (The @code{vtbl} commands do not work on programs compiled with the HP
7659 ANSI C@t{++} compiler (@code{aCC}).)
7661 @kindex set overload-resolution
7662 @cindex overloaded functions, overload resolution
7663 @item set overload-resolution on
7664 Enable overload resolution for C@t{++} expression evaluation. The default
7665 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7666 and searches for a function whose signature matches the argument types,
7667 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7668 expressions}, for details). If it cannot find a match, it emits a
7671 @item set overload-resolution off
7672 Disable overload resolution for C@t{++} expression evaluation. For
7673 overloaded functions that are not class member functions, @value{GDBN}
7674 chooses the first function of the specified name that it finds in the
7675 symbol table, whether or not its arguments are of the correct type. For
7676 overloaded functions that are class member functions, @value{GDBN}
7677 searches for a function whose signature @emph{exactly} matches the
7680 @item @r{Overloaded symbol names}
7681 You can specify a particular definition of an overloaded symbol, using
7682 the same notation that is used to declare such symbols in C@t{++}: type
7683 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7684 also use the @value{GDBN} command-line word completion facilities to list the
7685 available choices, or to finish the type list for you.
7686 @xref{Completion,, Command completion}, for details on how to do this.
7690 @subsection Modula-2
7692 @cindex Modula-2, @value{GDBN} support
7694 The extensions made to @value{GDBN} to support Modula-2 only support
7695 output from the @sc{gnu} Modula-2 compiler (which is currently being
7696 developed). Other Modula-2 compilers are not currently supported, and
7697 attempting to debug executables produced by them is most likely
7698 to give an error as @value{GDBN} reads in the executable's symbol
7701 @cindex expressions in Modula-2
7703 * M2 Operators:: Built-in operators
7704 * Built-In Func/Proc:: Built-in functions and procedures
7705 * M2 Constants:: Modula-2 constants
7706 * M2 Defaults:: Default settings for Modula-2
7707 * Deviations:: Deviations from standard Modula-2
7708 * M2 Checks:: Modula-2 type and range checks
7709 * M2 Scope:: The scope operators @code{::} and @code{.}
7710 * GDB/M2:: @value{GDBN} and Modula-2
7714 @subsubsection Operators
7715 @cindex Modula-2 operators
7717 Operators must be defined on values of specific types. For instance,
7718 @code{+} is defined on numbers, but not on structures. Operators are
7719 often defined on groups of types. For the purposes of Modula-2, the
7720 following definitions hold:
7725 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7729 @emph{Character types} consist of @code{CHAR} and its subranges.
7732 @emph{Floating-point types} consist of @code{REAL}.
7735 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7739 @emph{Scalar types} consist of all of the above.
7742 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7745 @emph{Boolean types} consist of @code{BOOLEAN}.
7749 The following operators are supported, and appear in order of
7750 increasing precedence:
7754 Function argument or array index separator.
7757 Assignment. The value of @var{var} @code{:=} @var{value} is
7761 Less than, greater than on integral, floating-point, or enumerated
7765 Less than or equal to, greater than or equal to
7766 on integral, floating-point and enumerated types, or set inclusion on
7767 set types. Same precedence as @code{<}.
7769 @item =@r{, }<>@r{, }#
7770 Equality and two ways of expressing inequality, valid on scalar types.
7771 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7772 available for inequality, since @code{#} conflicts with the script
7776 Set membership. Defined on set types and the types of their members.
7777 Same precedence as @code{<}.
7780 Boolean disjunction. Defined on boolean types.
7783 Boolean conjunction. Defined on boolean types.
7786 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7789 Addition and subtraction on integral and floating-point types, or union
7790 and difference on set types.
7793 Multiplication on integral and floating-point types, or set intersection
7797 Division on floating-point types, or symmetric set difference on set
7798 types. Same precedence as @code{*}.
7801 Integer division and remainder. Defined on integral types. Same
7802 precedence as @code{*}.
7805 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7808 Pointer dereferencing. Defined on pointer types.
7811 Boolean negation. Defined on boolean types. Same precedence as
7815 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7816 precedence as @code{^}.
7819 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7822 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7826 @value{GDBN} and Modula-2 scope operators.
7830 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7831 treats the use of the operator @code{IN}, or the use of operators
7832 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7833 @code{<=}, and @code{>=} on sets as an error.
7837 @node Built-In Func/Proc
7838 @subsubsection Built-in functions and procedures
7839 @cindex Modula-2 built-ins
7841 Modula-2 also makes available several built-in procedures and functions.
7842 In describing these, the following metavariables are used:
7847 represents an @code{ARRAY} variable.
7850 represents a @code{CHAR} constant or variable.
7853 represents a variable or constant of integral type.
7856 represents an identifier that belongs to a set. Generally used in the
7857 same function with the metavariable @var{s}. The type of @var{s} should
7858 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7861 represents a variable or constant of integral or floating-point type.
7864 represents a variable or constant of floating-point type.
7870 represents a variable.
7873 represents a variable or constant of one of many types. See the
7874 explanation of the function for details.
7877 All Modula-2 built-in procedures also return a result, described below.
7881 Returns the absolute value of @var{n}.
7884 If @var{c} is a lower case letter, it returns its upper case
7885 equivalent, otherwise it returns its argument.
7888 Returns the character whose ordinal value is @var{i}.
7891 Decrements the value in the variable @var{v} by one. Returns the new value.
7893 @item DEC(@var{v},@var{i})
7894 Decrements the value in the variable @var{v} by @var{i}. Returns the
7897 @item EXCL(@var{m},@var{s})
7898 Removes the element @var{m} from the set @var{s}. Returns the new
7901 @item FLOAT(@var{i})
7902 Returns the floating point equivalent of the integer @var{i}.
7905 Returns the index of the last member of @var{a}.
7908 Increments the value in the variable @var{v} by one. Returns the new value.
7910 @item INC(@var{v},@var{i})
7911 Increments the value in the variable @var{v} by @var{i}. Returns the
7914 @item INCL(@var{m},@var{s})
7915 Adds the element @var{m} to the set @var{s} if it is not already
7916 there. Returns the new set.
7919 Returns the maximum value of the type @var{t}.
7922 Returns the minimum value of the type @var{t}.
7925 Returns boolean TRUE if @var{i} is an odd number.
7928 Returns the ordinal value of its argument. For example, the ordinal
7929 value of a character is its @sc{ascii} value (on machines supporting the
7930 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7931 integral, character and enumerated types.
7934 Returns the size of its argument. @var{x} can be a variable or a type.
7936 @item TRUNC(@var{r})
7937 Returns the integral part of @var{r}.
7939 @item VAL(@var{t},@var{i})
7940 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7944 @emph{Warning:} Sets and their operations are not yet supported, so
7945 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7949 @cindex Modula-2 constants
7951 @subsubsection Constants
7953 @value{GDBN} allows you to express the constants of Modula-2 in the following
7959 Integer constants are simply a sequence of digits. When used in an
7960 expression, a constant is interpreted to be type-compatible with the
7961 rest of the expression. Hexadecimal integers are specified by a
7962 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7965 Floating point constants appear as a sequence of digits, followed by a
7966 decimal point and another sequence of digits. An optional exponent can
7967 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7968 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7969 digits of the floating point constant must be valid decimal (base 10)
7973 Character constants consist of a single character enclosed by a pair of
7974 like quotes, either single (@code{'}) or double (@code{"}). They may
7975 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7976 followed by a @samp{C}.
7979 String constants consist of a sequence of characters enclosed by a
7980 pair of like quotes, either single (@code{'}) or double (@code{"}).
7981 Escape sequences in the style of C are also allowed. @xref{C
7982 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7986 Enumerated constants consist of an enumerated identifier.
7989 Boolean constants consist of the identifiers @code{TRUE} and
7993 Pointer constants consist of integral values only.
7996 Set constants are not yet supported.
8000 @subsubsection Modula-2 defaults
8001 @cindex Modula-2 defaults
8003 If type and range checking are set automatically by @value{GDBN}, they
8004 both default to @code{on} whenever the working language changes to
8005 Modula-2. This happens regardless of whether you or @value{GDBN}
8006 selected the working language.
8008 If you allow @value{GDBN} to set the language automatically, then entering
8009 code compiled from a file whose name ends with @file{.mod} sets the
8010 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8011 the language automatically}, for further details.
8014 @subsubsection Deviations from standard Modula-2
8015 @cindex Modula-2, deviations from
8017 A few changes have been made to make Modula-2 programs easier to debug.
8018 This is done primarily via loosening its type strictness:
8022 Unlike in standard Modula-2, pointer constants can be formed by
8023 integers. This allows you to modify pointer variables during
8024 debugging. (In standard Modula-2, the actual address contained in a
8025 pointer variable is hidden from you; it can only be modified
8026 through direct assignment to another pointer variable or expression that
8027 returned a pointer.)
8030 C escape sequences can be used in strings and characters to represent
8031 non-printable characters. @value{GDBN} prints out strings with these
8032 escape sequences embedded. Single non-printable characters are
8033 printed using the @samp{CHR(@var{nnn})} format.
8036 The assignment operator (@code{:=}) returns the value of its right-hand
8040 All built-in procedures both modify @emph{and} return their argument.
8044 @subsubsection Modula-2 type and range checks
8045 @cindex Modula-2 checks
8048 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8051 @c FIXME remove warning when type/range checks added
8053 @value{GDBN} considers two Modula-2 variables type equivalent if:
8057 They are of types that have been declared equivalent via a @code{TYPE
8058 @var{t1} = @var{t2}} statement
8061 They have been declared on the same line. (Note: This is true of the
8062 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8065 As long as type checking is enabled, any attempt to combine variables
8066 whose types are not equivalent is an error.
8068 Range checking is done on all mathematical operations, assignment, array
8069 index bounds, and all built-in functions and procedures.
8072 @subsubsection The scope operators @code{::} and @code{.}
8074 @cindex @code{.}, Modula-2 scope operator
8075 @cindex colon, doubled as scope operator
8077 @vindex colon-colon@r{, in Modula-2}
8078 @c Info cannot handle :: but TeX can.
8081 @vindex ::@r{, in Modula-2}
8084 There are a few subtle differences between the Modula-2 scope operator
8085 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8090 @var{module} . @var{id}
8091 @var{scope} :: @var{id}
8095 where @var{scope} is the name of a module or a procedure,
8096 @var{module} the name of a module, and @var{id} is any declared
8097 identifier within your program, except another module.
8099 Using the @code{::} operator makes @value{GDBN} search the scope
8100 specified by @var{scope} for the identifier @var{id}. If it is not
8101 found in the specified scope, then @value{GDBN} searches all scopes
8102 enclosing the one specified by @var{scope}.
8104 Using the @code{.} operator makes @value{GDBN} search the current scope for
8105 the identifier specified by @var{id} that was imported from the
8106 definition module specified by @var{module}. With this operator, it is
8107 an error if the identifier @var{id} was not imported from definition
8108 module @var{module}, or if @var{id} is not an identifier in
8112 @subsubsection @value{GDBN} and Modula-2
8114 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8115 Five subcommands of @code{set print} and @code{show print} apply
8116 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8117 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8118 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8119 analogue in Modula-2.
8121 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8122 with any language, is not useful with Modula-2. Its
8123 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8124 created in Modula-2 as they can in C or C@t{++}. However, because an
8125 address can be specified by an integral constant, the construct
8126 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8128 @cindex @code{#} in Modula-2
8129 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8130 interpreted as the beginning of a comment. Use @code{<>} instead.
8135 The extensions made to @value{GDBN} to support Chill only support output
8136 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8137 supported, and attempting to debug executables produced by them is most
8138 likely to give an error as @value{GDBN} reads in the executable's symbol
8141 @c This used to say "... following Chill related topics ...", but since
8142 @c menus are not shown in the printed manual, it would look awkward.
8143 This section covers the Chill related topics and the features
8144 of @value{GDBN} which support these topics.
8147 * How modes are displayed:: How modes are displayed
8148 * Locations:: Locations and their accesses
8149 * Values and their Operations:: Values and their Operations
8150 * Chill type and range checks::
8154 @node How modes are displayed
8155 @subsubsection How modes are displayed
8157 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8158 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8159 slightly from the standard specification of the Chill language. The
8162 @c FIXME: this @table's contents effectively disable @code by using @r
8163 @c on every @item. So why does it need @code?
8165 @item @r{@emph{Discrete modes:}}
8168 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8171 @emph{Boolean Mode} which is predefined by @code{BOOL},
8173 @emph{Character Mode} which is predefined by @code{CHAR},
8175 @emph{Set Mode} which is displayed by the keyword @code{SET}.
8177 (@value{GDBP}) ptype x
8178 type = SET (karli = 10, susi = 20, fritzi = 100)
8180 If the type is an unnumbered set the set element values are omitted.
8182 @emph{Range Mode} which is displayed by
8184 @code{type = <basemode>(<lower bound> : <upper bound>)}
8186 where @code{<lower bound>, <upper bound>} can be of any discrete literal
8187 expression (e.g. set element names).
8190 @item @r{@emph{Powerset Mode:}}
8191 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8192 the member mode of the powerset. The member mode can be any discrete mode.
8194 (@value{GDBP}) ptype x
8195 type = POWERSET SET (egon, hugo, otto)
8198 @item @r{@emph{Reference Modes:}}
8201 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8202 followed by the mode name to which the reference is bound.
8204 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8207 @item @r{@emph{Procedure mode}}
8208 The procedure mode is displayed by @code{type = PROC(<parameter list>)
8209 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8210 list>} is a list of the parameter modes. @code{<return mode>} indicates
8211 the mode of the result of the procedure if any. The exceptionlist lists
8212 all possible exceptions which can be raised by the procedure.
8215 @item @r{@emph{Instance mode}}
8216 The instance mode is represented by a structure, which has a static
8217 type, and is therefore not really of interest.
8220 @item @r{@emph{Synchronization Modes:}}
8223 @emph{Event Mode} which is displayed by
8225 @code{EVENT (<event length>)}
8227 where @code{(<event length>)} is optional.
8229 @emph{Buffer Mode} which is displayed by
8231 @code{BUFFER (<buffer length>)<buffer element mode>}
8233 where @code{(<buffer length>)} is optional.
8236 @item @r{@emph{Timing Modes:}}
8239 @emph{Duration Mode} which is predefined by @code{DURATION}
8241 @emph{Absolute Time Mode} which is predefined by @code{TIME}
8244 @item @r{@emph{Real Modes:}}
8245 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8247 @item @r{@emph{String Modes:}}
8250 @emph{Character String Mode} which is displayed by
8252 @code{CHARS(<string length>)}
8254 followed by the keyword @code{VARYING} if the String Mode is a varying
8257 @emph{Bit String Mode} which is displayed by
8264 @item @r{@emph{Array Mode:}}
8265 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8266 followed by the element mode (which may in turn be an array mode).
8268 (@value{GDBP}) ptype x
8271 SET (karli = 10, susi = 20, fritzi = 100)
8274 @item @r{@emph{Structure Mode}}
8275 The Structure mode is displayed by the keyword @code{STRUCT(<field
8276 list>)}. The @code{<field list>} consists of names and modes of fields
8277 of the structure. Variant structures have the keyword @code{CASE <field>
8278 OF <variant fields> ESAC} in their field list. Since the current version
8279 of the GNU Chill compiler doesn't implement tag processing (no runtime
8280 checks of variant fields, and therefore no debugging info), the output
8281 always displays all variant fields.
8283 (@value{GDBP}) ptype str
8298 @subsubsection Locations and their accesses
8300 A location in Chill is an object which can contain values.
8302 A value of a location is generally accessed by the (declared) name of
8303 the location. The output conforms to the specification of values in
8304 Chill programs. How values are specified
8305 is the topic of the next section, @ref{Values and their Operations}.
8307 The pseudo-location @code{RESULT} (or @code{result}) can be used to
8308 display or change the result of a currently-active procedure:
8315 This does the same as the Chill action @code{RESULT EXPR} (which
8316 is not available in @value{GDBN}).
8318 Values of reference mode locations are printed by @code{PTR(<hex
8319 value>)} in case of a free reference mode, and by @code{(REF <reference
8320 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8321 represents the address where the reference points to. To access the
8322 value of the location referenced by the pointer, use the dereference
8325 Values of procedure mode locations are displayed by
8328 (<argument modes> ) <return mode> @} <address> <name of procedure
8331 @code{<argument modes>} is a list of modes according to the parameter
8332 specification of the procedure and @code{<address>} shows the address of
8336 Locations of instance modes are displayed just like a structure with two
8337 fields specifying the @emph{process type} and the @emph{copy number} of
8338 the investigated instance location@footnote{This comes from the current
8339 implementation of instances. They are implemented as a structure (no
8340 na). The output should be something like @code{[<name of the process>;
8341 <instance number>]}.}. The field names are @code{__proc_type} and
8344 Locations of synchronization modes are displayed like a structure with
8345 the field name @code{__event_data} in case of a event mode location, and
8346 like a structure with the field @code{__buffer_data} in case of a buffer
8347 mode location (refer to previous paragraph).
8349 Structure Mode locations are printed by @code{[.<field name>: <value>,
8350 ...]}. The @code{<field name>} corresponds to the structure mode
8351 definition and the layout of @code{<value>} varies depending of the mode
8352 of the field. If the investigated structure mode location is of variant
8353 structure mode, the variant parts of the structure are enclosed in curled
8354 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8355 on the same memory location and represent the current values of the
8356 memory location in their specific modes. Since no tag processing is done
8357 all variants are displayed. A variant field is printed by
8358 @code{(<variant name>) = .<field name>: <value>}. (who implements the
8361 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8362 [.cs: []], (susi) = [.ds: susi]}]
8366 Substructures of string mode-, array mode- or structure mode-values
8367 (e.g. array slices, fields of structure locations) are accessed using
8368 certain operations which are described in the next section, @ref{Values
8369 and their Operations}.
8371 A location value may be interpreted as having a different mode using the
8372 location conversion. This mode conversion is written as @code{<mode
8373 name>(<location>)}. The user has to consider that the sizes of the modes
8374 have to be equal otherwise an error occurs. Furthermore, no range
8375 checking of the location against the destination mode is performed, and
8376 therefore the result can be quite confusing.
8379 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8382 @node Values and their Operations
8383 @subsubsection Values and their Operations
8385 Values are used to alter locations, to investigate complex structures in
8386 more detail or to filter relevant information out of a large amount of
8387 data. There are several (mode dependent) operations defined which enable
8388 such investigations. These operations are not only applicable to
8389 constant values but also to locations, which can become quite useful
8390 when debugging complex structures. During parsing the command line
8391 (e.g. evaluating an expression) @value{GDBN} treats location names as
8392 the values behind these locations.
8394 This section describes how values have to be specified and which
8395 operations are legal to be used with such values.
8398 @item Literal Values
8399 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8400 For detailed specification refer to the @sc{gnu} Chill implementation Manual
8402 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8403 @c be converted to a @ref.
8408 @emph{Integer Literals} are specified in the same manner as in Chill
8409 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8411 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8413 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8416 @emph{Set Literals} are defined by a name which was specified in a set
8417 mode. The value delivered by a Set Literal is the set value. This is
8418 comparable to an enumeration in C/C@t{++} language.
8420 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8421 emptiness literal delivers either the empty reference value, the empty
8422 procedure value or the empty instance value.
8425 @emph{Character String Literals} are defined by a sequence of characters
8426 enclosed in single- or double quotes. If a single- or double quote has
8427 to be part of the string literal it has to be stuffed (specified twice).
8429 @emph{Bitstring Literals} are specified in the same manner as in Chill
8430 programs (refer z200/88 chpt 5.2.4.8).
8432 @emph{Floating point literals} are specified in the same manner as in
8433 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8438 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8439 name>} can be omitted if the mode of the tuple is unambiguous. This
8440 unambiguity is derived from the context of a evaluated expression.
8441 @code{<tuple>} can be one of the following:
8444 @item @emph{Powerset Tuple}
8445 @item @emph{Array Tuple}
8446 @item @emph{Structure Tuple}
8447 Powerset tuples, array tuples and structure tuples are specified in the
8448 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8451 @item String Element Value
8452 A string element value is specified by
8454 @code{<string value>(<index>)}
8456 where @code{<index>} is a integer expression. It delivers a character
8457 value which is equivalent to the character indexed by @code{<index>} in
8460 @item String Slice Value
8461 A string slice value is specified by @code{<string value>(<slice
8462 spec>)}, where @code{<slice spec>} can be either a range of integer
8463 expressions or specified by @code{<start expr> up <size>}.
8464 @code{<size>} denotes the number of elements which the slice contains.
8465 The delivered value is a string value, which is part of the specified
8468 @item Array Element Values
8469 An array element value is specified by @code{<array value>(<expr>)} and
8470 delivers a array element value of the mode of the specified array.
8472 @item Array Slice Values
8473 An array slice is specified by @code{<array value>(<slice spec>)}, where
8474 @code{<slice spec>} can be either a range specified by expressions or by
8475 @code{<start expr> up <size>}. @code{<size>} denotes the number of
8476 arrayelements the slice contains. The delivered value is an array value
8477 which is part of the specified array.
8479 @item Structure Field Values
8480 A structure field value is derived by @code{<structure value>.<field
8481 name>}, where @code{<field name>} indicates the name of a field specified
8482 in the mode definition of the structure. The mode of the delivered value
8483 corresponds to this mode definition in the structure definition.
8485 @item Procedure Call Value
8486 The procedure call value is derived from the return value of the
8487 procedure@footnote{If a procedure call is used for instance in an
8488 expression, then this procedure is called with all its side
8489 effects. This can lead to confusing results if used carelessly.}.
8491 Values of duration mode locations are represented by @code{ULONG} literals.
8493 Values of time mode locations appear as
8495 @code{TIME(<secs>:<nsecs>)}
8500 This is not implemented yet:
8501 @item Built-in Value
8503 The following built in functions are provided:
8515 @item @code{UPPER()}
8516 @item @code{LOWER()}
8517 @item @code{LENGTH()}
8521 @item @code{ARCSIN()}
8522 @item @code{ARCCOS()}
8523 @item @code{ARCTAN()}
8530 For a detailed description refer to the GNU Chill implementation manual
8534 @item Zero-adic Operator Value
8535 The zero-adic operator value is derived from the instance value for the
8536 current active process.
8538 @item Expression Values
8539 The value delivered by an expression is the result of the evaluation of
8540 the specified expression. If there are error conditions (mode
8541 incompatibility, etc.) the evaluation of expressions is aborted with a
8542 corresponding error message. Expressions may be parenthesised which
8543 causes the evaluation of this expression before any other expression
8544 which uses the result of the parenthesised expression. The following
8545 operators are supported by @value{GDBN}:
8548 @item @code{OR, ORIF, XOR}
8549 @itemx @code{AND, ANDIF}
8551 Logical operators defined over operands of boolean mode.
8554 Equality and inequality operators defined over all modes.
8558 Relational operators defined over predefined modes.
8561 @itemx @code{*, /, MOD, REM}
8562 Arithmetic operators defined over predefined modes.
8565 Change sign operator.
8568 String concatenation operator.
8571 String repetition operator.
8574 Referenced location operator which can be used either to take the
8575 address of a location (@code{->loc}), or to dereference a reference
8576 location (@code{loc->}).
8578 @item @code{OR, XOR}
8581 Powerset and bitstring operators.
8585 Powerset inclusion operators.
8588 Membership operator.
8592 @node Chill type and range checks
8593 @subsubsection Chill type and range checks
8595 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8596 of the two modes are equal. This rule applies recursively to more
8597 complex datatypes which means that complex modes are treated
8598 equivalent if all element modes (which also can be complex modes like
8599 structures, arrays, etc.) have the same size.
8601 Range checking is done on all mathematical operations, assignment, array
8602 index bounds and all built in procedures.
8604 Strong type checks are forced using the @value{GDBN} command @code{set
8605 check strong}. This enforces strong type and range checks on all
8606 operations where Chill constructs are used (expressions, built in
8607 functions, etc.) in respect to the semantics as defined in the z.200
8608 language specification.
8610 All checks can be disabled by the @value{GDBN} command @code{set check
8614 @c Deviations from the Chill Standard Z200/88
8615 see last paragraph ?
8618 @node Chill defaults
8619 @subsubsection Chill defaults
8621 If type and range checking are set automatically by @value{GDBN}, they
8622 both default to @code{on} whenever the working language changes to
8623 Chill. This happens regardless of whether you or @value{GDBN}
8624 selected the working language.
8626 If you allow @value{GDBN} to set the language automatically, then entering
8627 code compiled from a file whose name ends with @file{.ch} sets the
8628 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8629 the language automatically}, for further details.
8632 @chapter Examining the Symbol Table
8634 The commands described in this chapter allow you to inquire about the
8635 symbols (names of variables, functions and types) defined in your
8636 program. This information is inherent in the text of your program and
8637 does not change as your program executes. @value{GDBN} finds it in your
8638 program's symbol table, in the file indicated when you started @value{GDBN}
8639 (@pxref{File Options, ,Choosing files}), or by one of the
8640 file-management commands (@pxref{Files, ,Commands to specify files}).
8642 @cindex symbol names
8643 @cindex names of symbols
8644 @cindex quoting names
8645 Occasionally, you may need to refer to symbols that contain unusual
8646 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8647 most frequent case is in referring to static variables in other
8648 source files (@pxref{Variables,,Program variables}). File names
8649 are recorded in object files as debugging symbols, but @value{GDBN} would
8650 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8651 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8652 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8659 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8662 @kindex info address
8663 @cindex address of a symbol
8664 @item info address @var{symbol}
8665 Describe where the data for @var{symbol} is stored. For a register
8666 variable, this says which register it is kept in. For a non-register
8667 local variable, this prints the stack-frame offset at which the variable
8670 Note the contrast with @samp{print &@var{symbol}}, which does not work
8671 at all for a register variable, and for a stack local variable prints
8672 the exact address of the current instantiation of the variable.
8675 @cindex symbol from address
8676 @item info symbol @var{addr}
8677 Print the name of a symbol which is stored at the address @var{addr}.
8678 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8679 nearest symbol and an offset from it:
8682 (@value{GDBP}) info symbol 0x54320
8683 _initialize_vx + 396 in section .text
8687 This is the opposite of the @code{info address} command. You can use
8688 it to find out the name of a variable or a function given its address.
8691 @item whatis @var{expr}
8692 Print the data type of expression @var{expr}. @var{expr} is not
8693 actually evaluated, and any side-effecting operations (such as
8694 assignments or function calls) inside it do not take place.
8695 @xref{Expressions, ,Expressions}.
8698 Print the data type of @code{$}, the last value in the value history.
8701 @item ptype @var{typename}
8702 Print a description of data type @var{typename}. @var{typename} may be
8703 the name of a type, or for C code it may have the form @samp{class
8704 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8705 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8707 @item ptype @var{expr}
8709 Print a description of the type of expression @var{expr}. @code{ptype}
8710 differs from @code{whatis} by printing a detailed description, instead
8711 of just the name of the type.
8713 For example, for this variable declaration:
8716 struct complex @{double real; double imag;@} v;
8720 the two commands give this output:
8724 (@value{GDBP}) whatis v
8725 type = struct complex
8726 (@value{GDBP}) ptype v
8727 type = struct complex @{
8735 As with @code{whatis}, using @code{ptype} without an argument refers to
8736 the type of @code{$}, the last value in the value history.
8739 @item info types @var{regexp}
8741 Print a brief description of all types whose names match @var{regexp}
8742 (or all types in your program, if you supply no argument). Each
8743 complete typename is matched as though it were a complete line; thus,
8744 @samp{i type value} gives information on all types in your program whose
8745 names include the string @code{value}, but @samp{i type ^value$} gives
8746 information only on types whose complete name is @code{value}.
8748 This command differs from @code{ptype} in two ways: first, like
8749 @code{whatis}, it does not print a detailed description; second, it
8750 lists all source files where a type is defined.
8753 @cindex local variables
8754 @item info scope @var{addr}
8755 List all the variables local to a particular scope. This command
8756 accepts a location---a function name, a source line, or an address
8757 preceded by a @samp{*}, and prints all the variables local to the
8758 scope defined by that location. For example:
8761 (@value{GDBP}) @b{info scope command_line_handler}
8762 Scope for command_line_handler:
8763 Symbol rl is an argument at stack/frame offset 8, length 4.
8764 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8765 Symbol linelength is in static storage at address 0x150a1c, length 4.
8766 Symbol p is a local variable in register $esi, length 4.
8767 Symbol p1 is a local variable in register $ebx, length 4.
8768 Symbol nline is a local variable in register $edx, length 4.
8769 Symbol repeat is a local variable at frame offset -8, length 4.
8773 This command is especially useful for determining what data to collect
8774 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8779 Show the name of the current source file---that is, the source file for
8780 the function containing the current point of execution---and the language
8783 @kindex info sources
8785 Print the names of all source files in your program for which there is
8786 debugging information, organized into two lists: files whose symbols
8787 have already been read, and files whose symbols will be read when needed.
8789 @kindex info functions
8790 @item info functions
8791 Print the names and data types of all defined functions.
8793 @item info functions @var{regexp}
8794 Print the names and data types of all defined functions
8795 whose names contain a match for regular expression @var{regexp}.
8796 Thus, @samp{info fun step} finds all functions whose names
8797 include @code{step}; @samp{info fun ^step} finds those whose names
8798 start with @code{step}. If a function name contains characters
8799 that conflict with the regular expression language (eg.
8800 @samp{operator*()}), they may be quoted with a backslash.
8802 @kindex info variables
8803 @item info variables
8804 Print the names and data types of all variables that are declared
8805 outside of functions (i.e., excluding local variables).
8807 @item info variables @var{regexp}
8808 Print the names and data types of all variables (except for local
8809 variables) whose names contain a match for regular expression
8813 This was never implemented.
8814 @kindex info methods
8816 @itemx info methods @var{regexp}
8817 The @code{info methods} command permits the user to examine all defined
8818 methods within C@t{++} program, or (with the @var{regexp} argument) a
8819 specific set of methods found in the various C@t{++} classes. Many
8820 C@t{++} classes provide a large number of methods. Thus, the output
8821 from the @code{ptype} command can be overwhelming and hard to use. The
8822 @code{info-methods} command filters the methods, printing only those
8823 which match the regular-expression @var{regexp}.
8826 @cindex reloading symbols
8827 Some systems allow individual object files that make up your program to
8828 be replaced without stopping and restarting your program. For example,
8829 in VxWorks you can simply recompile a defective object file and keep on
8830 running. If you are running on one of these systems, you can allow
8831 @value{GDBN} to reload the symbols for automatically relinked modules:
8834 @kindex set symbol-reloading
8835 @item set symbol-reloading on
8836 Replace symbol definitions for the corresponding source file when an
8837 object file with a particular name is seen again.
8839 @item set symbol-reloading off
8840 Do not replace symbol definitions when encountering object files of the
8841 same name more than once. This is the default state; if you are not
8842 running on a system that permits automatic relinking of modules, you
8843 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8844 may discard symbols when linking large programs, that may contain
8845 several modules (from different directories or libraries) with the same
8848 @kindex show symbol-reloading
8849 @item show symbol-reloading
8850 Show the current @code{on} or @code{off} setting.
8853 @kindex set opaque-type-resolution
8854 @item set opaque-type-resolution on
8855 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8856 declared as a pointer to a @code{struct}, @code{class}, or
8857 @code{union}---for example, @code{struct MyType *}---that is used in one
8858 source file although the full declaration of @code{struct MyType} is in
8859 another source file. The default is on.
8861 A change in the setting of this subcommand will not take effect until
8862 the next time symbols for a file are loaded.
8864 @item set opaque-type-resolution off
8865 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8866 is printed as follows:
8868 @{<no data fields>@}
8871 @kindex show opaque-type-resolution
8872 @item show opaque-type-resolution
8873 Show whether opaque types are resolved or not.
8875 @kindex maint print symbols
8877 @kindex maint print psymbols
8878 @cindex partial symbol dump
8879 @item maint print symbols @var{filename}
8880 @itemx maint print psymbols @var{filename}
8881 @itemx maint print msymbols @var{filename}
8882 Write a dump of debugging symbol data into the file @var{filename}.
8883 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8884 symbols with debugging data are included. If you use @samp{maint print
8885 symbols}, @value{GDBN} includes all the symbols for which it has already
8886 collected full details: that is, @var{filename} reflects symbols for
8887 only those files whose symbols @value{GDBN} has read. You can use the
8888 command @code{info sources} to find out which files these are. If you
8889 use @samp{maint print psymbols} instead, the dump shows information about
8890 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8891 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8892 @samp{maint print msymbols} dumps just the minimal symbol information
8893 required for each object file from which @value{GDBN} has read some symbols.
8894 @xref{Files, ,Commands to specify files}, for a discussion of how
8895 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8899 @chapter Altering Execution
8901 Once you think you have found an error in your program, you might want to
8902 find out for certain whether correcting the apparent error would lead to
8903 correct results in the rest of the run. You can find the answer by
8904 experiment, using the @value{GDBN} features for altering execution of the
8907 For example, you can store new values into variables or memory
8908 locations, give your program a signal, restart it at a different
8909 address, or even return prematurely from a function.
8912 * Assignment:: Assignment to variables
8913 * Jumping:: Continuing at a different address
8914 * Signaling:: Giving your program a signal
8915 * Returning:: Returning from a function
8916 * Calling:: Calling your program's functions
8917 * Patching:: Patching your program
8921 @section Assignment to variables
8924 @cindex setting variables
8925 To alter the value of a variable, evaluate an assignment expression.
8926 @xref{Expressions, ,Expressions}. For example,
8933 stores the value 4 into the variable @code{x}, and then prints the
8934 value of the assignment expression (which is 4).
8935 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8936 information on operators in supported languages.
8938 @kindex set variable
8939 @cindex variables, setting
8940 If you are not interested in seeing the value of the assignment, use the
8941 @code{set} command instead of the @code{print} command. @code{set} is
8942 really the same as @code{print} except that the expression's value is
8943 not printed and is not put in the value history (@pxref{Value History,
8944 ,Value history}). The expression is evaluated only for its effects.
8946 If the beginning of the argument string of the @code{set} command
8947 appears identical to a @code{set} subcommand, use the @code{set
8948 variable} command instead of just @code{set}. This command is identical
8949 to @code{set} except for its lack of subcommands. For example, if your
8950 program has a variable @code{width}, you get an error if you try to set
8951 a new value with just @samp{set width=13}, because @value{GDBN} has the
8952 command @code{set width}:
8955 (@value{GDBP}) whatis width
8957 (@value{GDBP}) p width
8959 (@value{GDBP}) set width=47
8960 Invalid syntax in expression.
8964 The invalid expression, of course, is @samp{=47}. In
8965 order to actually set the program's variable @code{width}, use
8968 (@value{GDBP}) set var width=47
8971 Because the @code{set} command has many subcommands that can conflict
8972 with the names of program variables, it is a good idea to use the
8973 @code{set variable} command instead of just @code{set}. For example, if
8974 your program has a variable @code{g}, you run into problems if you try
8975 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8976 the command @code{set gnutarget}, abbreviated @code{set g}:
8980 (@value{GDBP}) whatis g
8984 (@value{GDBP}) set g=4
8988 The program being debugged has been started already.
8989 Start it from the beginning? (y or n) y
8990 Starting program: /home/smith/cc_progs/a.out
8991 "/home/smith/cc_progs/a.out": can't open to read symbols:
8993 (@value{GDBP}) show g
8994 The current BFD target is "=4".
8999 The program variable @code{g} did not change, and you silently set the
9000 @code{gnutarget} to an invalid value. In order to set the variable
9004 (@value{GDBP}) set var g=4
9007 @value{GDBN} allows more implicit conversions in assignments than C; you can
9008 freely store an integer value into a pointer variable or vice versa,
9009 and you can convert any structure to any other structure that is the
9010 same length or shorter.
9011 @comment FIXME: how do structs align/pad in these conversions?
9012 @comment /doc@cygnus.com 18dec1990
9014 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9015 construct to generate a value of specified type at a specified address
9016 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9017 to memory location @code{0x83040} as an integer (which implies a certain size
9018 and representation in memory), and
9021 set @{int@}0x83040 = 4
9025 stores the value 4 into that memory location.
9028 @section Continuing at a different address
9030 Ordinarily, when you continue your program, you do so at the place where
9031 it stopped, with the @code{continue} command. You can instead continue at
9032 an address of your own choosing, with the following commands:
9036 @item jump @var{linespec}
9037 Resume execution at line @var{linespec}. Execution stops again
9038 immediately if there is a breakpoint there. @xref{List, ,Printing
9039 source lines}, for a description of the different forms of
9040 @var{linespec}. It is common practice to use the @code{tbreak} command
9041 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9044 The @code{jump} command does not change the current stack frame, or
9045 the stack pointer, or the contents of any memory location or any
9046 register other than the program counter. If line @var{linespec} is in
9047 a different function from the one currently executing, the results may
9048 be bizarre if the two functions expect different patterns of arguments or
9049 of local variables. For this reason, the @code{jump} command requests
9050 confirmation if the specified line is not in the function currently
9051 executing. However, even bizarre results are predictable if you are
9052 well acquainted with the machine-language code of your program.
9054 @item jump *@var{address}
9055 Resume execution at the instruction at address @var{address}.
9058 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9059 On many systems, you can get much the same effect as the @code{jump}
9060 command by storing a new value into the register @code{$pc}. The
9061 difference is that this does not start your program running; it only
9062 changes the address of where it @emph{will} run when you continue. For
9070 makes the next @code{continue} command or stepping command execute at
9071 address @code{0x485}, rather than at the address where your program stopped.
9072 @xref{Continuing and Stepping, ,Continuing and stepping}.
9074 The most common occasion to use the @code{jump} command is to back
9075 up---perhaps with more breakpoints set---over a portion of a program
9076 that has already executed, in order to examine its execution in more
9081 @section Giving your program a signal
9085 @item signal @var{signal}
9086 Resume execution where your program stopped, but immediately give it the
9087 signal @var{signal}. @var{signal} can be the name or the number of a
9088 signal. For example, on many systems @code{signal 2} and @code{signal
9089 SIGINT} are both ways of sending an interrupt signal.
9091 Alternatively, if @var{signal} is zero, continue execution without
9092 giving a signal. This is useful when your program stopped on account of
9093 a signal and would ordinary see the signal when resumed with the
9094 @code{continue} command; @samp{signal 0} causes it to resume without a
9097 @code{signal} does not repeat when you press @key{RET} a second time
9098 after executing the command.
9102 Invoking the @code{signal} command is not the same as invoking the
9103 @code{kill} utility from the shell. Sending a signal with @code{kill}
9104 causes @value{GDBN} to decide what to do with the signal depending on
9105 the signal handling tables (@pxref{Signals}). The @code{signal} command
9106 passes the signal directly to your program.
9110 @section Returning from a function
9113 @cindex returning from a function
9116 @itemx return @var{expression}
9117 You can cancel execution of a function call with the @code{return}
9118 command. If you give an
9119 @var{expression} argument, its value is used as the function's return
9123 When you use @code{return}, @value{GDBN} discards the selected stack frame
9124 (and all frames within it). You can think of this as making the
9125 discarded frame return prematurely. If you wish to specify a value to
9126 be returned, give that value as the argument to @code{return}.
9128 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9129 frame}), and any other frames inside of it, leaving its caller as the
9130 innermost remaining frame. That frame becomes selected. The
9131 specified value is stored in the registers used for returning values
9134 The @code{return} command does not resume execution; it leaves the
9135 program stopped in the state that would exist if the function had just
9136 returned. In contrast, the @code{finish} command (@pxref{Continuing
9137 and Stepping, ,Continuing and stepping}) resumes execution until the
9138 selected stack frame returns naturally.
9141 @section Calling program functions
9143 @cindex calling functions
9146 @item call @var{expr}
9147 Evaluate the expression @var{expr} without displaying @code{void}
9151 You can use this variant of the @code{print} command if you want to
9152 execute a function from your program, but without cluttering the output
9153 with @code{void} returned values. If the result is not void, it
9154 is printed and saved in the value history.
9156 @c OBSOLETE For the A29K, a user-controlled variable @code{call_scratch_address},
9157 @c OBSOLETE specifies the location of a scratch area to be used when @value{GDBN}
9158 @c OBSOLETE calls a function in the target. This is necessary because the usual
9159 @c OBSOLETE method of putting the scratch area on the stack does not work in systems
9160 @c OBSOLETE that have separate instruction and data spaces.
9163 @section Patching programs
9165 @cindex patching binaries
9166 @cindex writing into executables
9167 @cindex writing into corefiles
9169 By default, @value{GDBN} opens the file containing your program's
9170 executable code (or the corefile) read-only. This prevents accidental
9171 alterations to machine code; but it also prevents you from intentionally
9172 patching your program's binary.
9174 If you'd like to be able to patch the binary, you can specify that
9175 explicitly with the @code{set write} command. For example, you might
9176 want to turn on internal debugging flags, or even to make emergency
9182 @itemx set write off
9183 If you specify @samp{set write on}, @value{GDBN} opens executable and
9184 core files for both reading and writing; if you specify @samp{set write
9185 off} (the default), @value{GDBN} opens them read-only.
9187 If you have already loaded a file, you must load it again (using the
9188 @code{exec-file} or @code{core-file} command) after changing @code{set
9189 write}, for your new setting to take effect.
9193 Display whether executable files and core files are opened for writing
9198 @chapter @value{GDBN} Files
9200 @value{GDBN} needs to know the file name of the program to be debugged,
9201 both in order to read its symbol table and in order to start your
9202 program. To debug a core dump of a previous run, you must also tell
9203 @value{GDBN} the name of the core dump file.
9206 * Files:: Commands to specify files
9207 * Symbol Errors:: Errors reading symbol files
9211 @section Commands to specify files
9213 @cindex symbol table
9214 @cindex core dump file
9216 You may want to specify executable and core dump file names. The usual
9217 way to do this is at start-up time, using the arguments to
9218 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9219 Out of @value{GDBN}}).
9221 Occasionally it is necessary to change to a different file during a
9222 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9223 a file you want to use. In these situations the @value{GDBN} commands
9224 to specify new files are useful.
9227 @cindex executable file
9229 @item file @var{filename}
9230 Use @var{filename} as the program to be debugged. It is read for its
9231 symbols and for the contents of pure memory. It is also the program
9232 executed when you use the @code{run} command. If you do not specify a
9233 directory and the file is not found in the @value{GDBN} working directory,
9234 @value{GDBN} uses the environment variable @code{PATH} as a list of
9235 directories to search, just as the shell does when looking for a program
9236 to run. You can change the value of this variable, for both @value{GDBN}
9237 and your program, using the @code{path} command.
9239 On systems with memory-mapped files, an auxiliary file named
9240 @file{@var{filename}.syms} may hold symbol table information for
9241 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9242 @file{@var{filename}.syms}, starting up more quickly. See the
9243 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9244 (available on the command line, and with the commands @code{file},
9245 @code{symbol-file}, or @code{add-symbol-file}, described below),
9246 for more information.
9249 @code{file} with no argument makes @value{GDBN} discard any information it
9250 has on both executable file and the symbol table.
9253 @item exec-file @r{[} @var{filename} @r{]}
9254 Specify that the program to be run (but not the symbol table) is found
9255 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9256 if necessary to locate your program. Omitting @var{filename} means to
9257 discard information on the executable file.
9260 @item symbol-file @r{[} @var{filename} @r{]}
9261 Read symbol table information from file @var{filename}. @code{PATH} is
9262 searched when necessary. Use the @code{file} command to get both symbol
9263 table and program to run from the same file.
9265 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9266 program's symbol table.
9268 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9269 of its convenience variables, the value history, and all breakpoints and
9270 auto-display expressions. This is because they may contain pointers to
9271 the internal data recording symbols and data types, which are part of
9272 the old symbol table data being discarded inside @value{GDBN}.
9274 @code{symbol-file} does not repeat if you press @key{RET} again after
9277 When @value{GDBN} is configured for a particular environment, it
9278 understands debugging information in whatever format is the standard
9279 generated for that environment; you may use either a @sc{gnu} compiler, or
9280 other compilers that adhere to the local conventions.
9281 Best results are usually obtained from @sc{gnu} compilers; for example,
9282 using @code{@value{GCC}} you can generate debugging information for
9285 For most kinds of object files, with the exception of old SVR3 systems
9286 using COFF, the @code{symbol-file} command does not normally read the
9287 symbol table in full right away. Instead, it scans the symbol table
9288 quickly to find which source files and which symbols are present. The
9289 details are read later, one source file at a time, as they are needed.
9291 The purpose of this two-stage reading strategy is to make @value{GDBN}
9292 start up faster. For the most part, it is invisible except for
9293 occasional pauses while the symbol table details for a particular source
9294 file are being read. (The @code{set verbose} command can turn these
9295 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9296 warnings and messages}.)
9298 We have not implemented the two-stage strategy for COFF yet. When the
9299 symbol table is stored in COFF format, @code{symbol-file} reads the
9300 symbol table data in full right away. Note that ``stabs-in-COFF''
9301 still does the two-stage strategy, since the debug info is actually
9305 @cindex reading symbols immediately
9306 @cindex symbols, reading immediately
9308 @cindex memory-mapped symbol file
9309 @cindex saving symbol table
9310 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9311 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9312 You can override the @value{GDBN} two-stage strategy for reading symbol
9313 tables by using the @samp{-readnow} option with any of the commands that
9314 load symbol table information, if you want to be sure @value{GDBN} has the
9315 entire symbol table available.
9317 If memory-mapped files are available on your system through the
9318 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9319 cause @value{GDBN} to write the symbols for your program into a reusable
9320 file. Future @value{GDBN} debugging sessions map in symbol information
9321 from this auxiliary symbol file (if the program has not changed), rather
9322 than spending time reading the symbol table from the executable
9323 program. Using the @samp{-mapped} option has the same effect as
9324 starting @value{GDBN} with the @samp{-mapped} command-line option.
9326 You can use both options together, to make sure the auxiliary symbol
9327 file has all the symbol information for your program.
9329 The auxiliary symbol file for a program called @var{myprog} is called
9330 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9331 than the corresponding executable), @value{GDBN} always attempts to use
9332 it when you debug @var{myprog}; no special options or commands are
9335 The @file{.syms} file is specific to the host machine where you run
9336 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9337 symbol table. It cannot be shared across multiple host platforms.
9339 @c FIXME: for now no mention of directories, since this seems to be in
9340 @c flux. 13mar1992 status is that in theory GDB would look either in
9341 @c current dir or in same dir as myprog; but issues like competing
9342 @c GDB's, or clutter in system dirs, mean that in practice right now
9343 @c only current dir is used. FFish says maybe a special GDB hierarchy
9344 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9349 @item core-file @r{[} @var{filename} @r{]}
9350 Specify the whereabouts of a core dump file to be used as the ``contents
9351 of memory''. Traditionally, core files contain only some parts of the
9352 address space of the process that generated them; @value{GDBN} can access the
9353 executable file itself for other parts.
9355 @code{core-file} with no argument specifies that no core file is
9358 Note that the core file is ignored when your program is actually running
9359 under @value{GDBN}. So, if you have been running your program and you
9360 wish to debug a core file instead, you must kill the subprocess in which
9361 the program is running. To do this, use the @code{kill} command
9362 (@pxref{Kill Process, ,Killing the child process}).
9364 @kindex add-symbol-file
9365 @cindex dynamic linking
9366 @item add-symbol-file @var{filename} @var{address}
9367 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9368 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9369 The @code{add-symbol-file} command reads additional symbol table
9370 information from the file @var{filename}. You would use this command
9371 when @var{filename} has been dynamically loaded (by some other means)
9372 into the program that is running. @var{address} should be the memory
9373 address at which the file has been loaded; @value{GDBN} cannot figure
9374 this out for itself. You can additionally specify an arbitrary number
9375 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9376 section name and base address for that section. You can specify any
9377 @var{address} as an expression.
9379 The symbol table of the file @var{filename} is added to the symbol table
9380 originally read with the @code{symbol-file} command. You can use the
9381 @code{add-symbol-file} command any number of times; the new symbol data
9382 thus read keeps adding to the old. To discard all old symbol data
9383 instead, use the @code{symbol-file} command without any arguments.
9385 @cindex relocatable object files, reading symbols from
9386 @cindex object files, relocatable, reading symbols from
9387 @cindex reading symbols from relocatable object files
9388 @cindex symbols, reading from relocatable object files
9389 @cindex @file{.o} files, reading symbols from
9390 Although @var{filename} is typically a shared library file, an
9391 executable file, or some other object file which has been fully
9392 relocated for loading into a process, you can also load symbolic
9393 information from relocatable @file{.o} files, as long as:
9397 the file's symbolic information refers only to linker symbols defined in
9398 that file, not to symbols defined by other object files,
9400 every section the file's symbolic information refers to has actually
9401 been loaded into the inferior, as it appears in the file, and
9403 you can determine the address at which every section was loaded, and
9404 provide these to the @code{add-symbol-file} command.
9408 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9409 relocatable files into an already running program; such systems
9410 typically make the requirements above easy to meet. However, it's
9411 important to recognize that many native systems use complex link
9412 procedures (@code{.linkonce} section factoring and C++ constructor table
9413 assembly, for example) that make the requirements difficult to meet. In
9414 general, one cannot assume that using @code{add-symbol-file} to read a
9415 relocatable object file's symbolic information will have the same effect
9416 as linking the relocatable object file into the program in the normal
9419 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9421 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9422 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9423 table information for @var{filename}.
9425 @kindex add-shared-symbol-file
9426 @item add-shared-symbol-file
9427 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9428 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9429 shared libraries, however if @value{GDBN} does not find yours, you can run
9430 @code{add-shared-symbol-file}. It takes no arguments.
9434 The @code{section} command changes the base address of section SECTION of
9435 the exec file to ADDR. This can be used if the exec file does not contain
9436 section addresses, (such as in the a.out format), or when the addresses
9437 specified in the file itself are wrong. Each section must be changed
9438 separately. The @code{info files} command, described below, lists all
9439 the sections and their addresses.
9445 @code{info files} and @code{info target} are synonymous; both print the
9446 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9447 including the names of the executable and core dump files currently in
9448 use by @value{GDBN}, and the files from which symbols were loaded. The
9449 command @code{help target} lists all possible targets rather than
9452 @kindex maint info sections
9453 @item maint info sections
9454 Another command that can give you extra information about program sections
9455 is @code{maint info sections}. In addition to the section information
9456 displayed by @code{info files}, this command displays the flags and file
9457 offset of each section in the executable and core dump files. In addition,
9458 @code{maint info sections} provides the following command options (which
9459 may be arbitrarily combined):
9463 Display sections for all loaded object files, including shared libraries.
9464 @item @var{sections}
9465 Display info only for named @var{sections}.
9466 @item @var{section-flags}
9467 Display info only for sections for which @var{section-flags} are true.
9468 The section flags that @value{GDBN} currently knows about are:
9471 Section will have space allocated in the process when loaded.
9472 Set for all sections except those containing debug information.
9474 Section will be loaded from the file into the child process memory.
9475 Set for pre-initialized code and data, clear for @code{.bss} sections.
9477 Section needs to be relocated before loading.
9479 Section cannot be modified by the child process.
9481 Section contains executable code only.
9483 Section contains data only (no executable code).
9485 Section will reside in ROM.
9487 Section contains data for constructor/destructor lists.
9489 Section is not empty.
9491 An instruction to the linker to not output the section.
9492 @item COFF_SHARED_LIBRARY
9493 A notification to the linker that the section contains
9494 COFF shared library information.
9496 Section contains common symbols.
9501 All file-specifying commands allow both absolute and relative file names
9502 as arguments. @value{GDBN} always converts the file name to an absolute file
9503 name and remembers it that way.
9505 @cindex shared libraries
9506 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9509 @value{GDBN} automatically loads symbol definitions from shared libraries
9510 when you use the @code{run} command, or when you examine a core file.
9511 (Before you issue the @code{run} command, @value{GDBN} does not understand
9512 references to a function in a shared library, however---unless you are
9513 debugging a core file).
9515 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9516 automatically loads the symbols at the time of the @code{shl_load} call.
9518 @c FIXME: some @value{GDBN} release may permit some refs to undef
9519 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9520 @c FIXME...lib; check this from time to time when updating manual
9522 There are times, however, when you may wish to not automatically load
9523 symbol definitions from shared libraries, such as when they are
9524 particularly large or there are many of them.
9526 To control the automatic loading of shared library symbols, use the
9530 @kindex set auto-solib-add
9531 @item set auto-solib-add @var{mode}
9532 If @var{mode} is @code{on}, symbols from all shared object libraries
9533 will be loaded automatically when the inferior begins execution, you
9534 attach to an independently started inferior, or when the dynamic linker
9535 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9536 is @code{off}, symbols must be loaded manually, using the
9537 @code{sharedlibrary} command. The default value is @code{on}.
9539 @kindex show auto-solib-add
9540 @item show auto-solib-add
9541 Display the current autoloading mode.
9544 To explicitly load shared library symbols, use the @code{sharedlibrary}
9548 @kindex info sharedlibrary
9551 @itemx info sharedlibrary
9552 Print the names of the shared libraries which are currently loaded.
9554 @kindex sharedlibrary
9556 @item sharedlibrary @var{regex}
9557 @itemx share @var{regex}
9558 Load shared object library symbols for files matching a
9559 Unix regular expression.
9560 As with files loaded automatically, it only loads shared libraries
9561 required by your program for a core file or after typing @code{run}. If
9562 @var{regex} is omitted all shared libraries required by your program are
9566 On some systems, such as HP-UX systems, @value{GDBN} supports
9567 autoloading shared library symbols until a limiting threshold size is
9568 reached. This provides the benefit of allowing autoloading to remain on
9569 by default, but avoids autoloading excessively large shared libraries,
9570 up to a threshold that is initially set, but which you can modify if you
9573 Beyond that threshold, symbols from shared libraries must be explicitly
9574 loaded. To load these symbols, use the command @code{sharedlibrary
9575 @var{filename}}. The base address of the shared library is determined
9576 automatically by @value{GDBN} and need not be specified.
9578 To display or set the threshold, use the commands:
9581 @kindex set auto-solib-limit
9582 @item set auto-solib-limit @var{threshold}
9583 Set the autoloading size threshold, in an integral number of megabytes.
9584 If @var{threshold} is nonzero and shared library autoloading is enabled,
9585 symbols from all shared object libraries will be loaded until the total
9586 size of the loaded shared library symbols exceeds this threshold.
9587 Otherwise, symbols must be loaded manually, using the
9588 @code{sharedlibrary} command. The default threshold is 100 (i.e. 100
9591 @kindex show auto-solib-limit
9592 @item show auto-solib-limit
9593 Display the current autoloading size threshold, in megabytes.
9597 @section Errors reading symbol files
9599 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9600 such as symbol types it does not recognize, or known bugs in compiler
9601 output. By default, @value{GDBN} does not notify you of such problems, since
9602 they are relatively common and primarily of interest to people
9603 debugging compilers. If you are interested in seeing information
9604 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9605 only one message about each such type of problem, no matter how many
9606 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9607 to see how many times the problems occur, with the @code{set
9608 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9611 The messages currently printed, and their meanings, include:
9614 @item inner block not inside outer block in @var{symbol}
9616 The symbol information shows where symbol scopes begin and end
9617 (such as at the start of a function or a block of statements). This
9618 error indicates that an inner scope block is not fully contained
9619 in its outer scope blocks.
9621 @value{GDBN} circumvents the problem by treating the inner block as if it had
9622 the same scope as the outer block. In the error message, @var{symbol}
9623 may be shown as ``@code{(don't know)}'' if the outer block is not a
9626 @item block at @var{address} out of order
9628 The symbol information for symbol scope blocks should occur in
9629 order of increasing addresses. This error indicates that it does not
9632 @value{GDBN} does not circumvent this problem, and has trouble
9633 locating symbols in the source file whose symbols it is reading. (You
9634 can often determine what source file is affected by specifying
9635 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9638 @item bad block start address patched
9640 The symbol information for a symbol scope block has a start address
9641 smaller than the address of the preceding source line. This is known
9642 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9644 @value{GDBN} circumvents the problem by treating the symbol scope block as
9645 starting on the previous source line.
9647 @item bad string table offset in symbol @var{n}
9650 Symbol number @var{n} contains a pointer into the string table which is
9651 larger than the size of the string table.
9653 @value{GDBN} circumvents the problem by considering the symbol to have the
9654 name @code{foo}, which may cause other problems if many symbols end up
9657 @item unknown symbol type @code{0x@var{nn}}
9659 The symbol information contains new data types that @value{GDBN} does
9660 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9661 uncomprehended information, in hexadecimal.
9663 @value{GDBN} circumvents the error by ignoring this symbol information.
9664 This usually allows you to debug your program, though certain symbols
9665 are not accessible. If you encounter such a problem and feel like
9666 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9667 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9668 and examine @code{*bufp} to see the symbol.
9670 @item stub type has NULL name
9672 @value{GDBN} could not find the full definition for a struct or class.
9674 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9675 The symbol information for a C@t{++} member function is missing some
9676 information that recent versions of the compiler should have output for
9679 @item info mismatch between compiler and debugger
9681 @value{GDBN} could not parse a type specification output by the compiler.
9686 @chapter Specifying a Debugging Target
9688 @cindex debugging target
9691 A @dfn{target} is the execution environment occupied by your program.
9693 Often, @value{GDBN} runs in the same host environment as your program;
9694 in that case, the debugging target is specified as a side effect when
9695 you use the @code{file} or @code{core} commands. When you need more
9696 flexibility---for example, running @value{GDBN} on a physically separate
9697 host, or controlling a standalone system over a serial port or a
9698 realtime system over a TCP/IP connection---you can use the @code{target}
9699 command to specify one of the target types configured for @value{GDBN}
9700 (@pxref{Target Commands, ,Commands for managing targets}).
9703 * Active Targets:: Active targets
9704 * Target Commands:: Commands for managing targets
9705 * Byte Order:: Choosing target byte order
9706 * Remote:: Remote debugging
9707 * KOD:: Kernel Object Display
9711 @node Active Targets
9712 @section Active targets
9714 @cindex stacking targets
9715 @cindex active targets
9716 @cindex multiple targets
9718 There are three classes of targets: processes, core files, and
9719 executable files. @value{GDBN} can work concurrently on up to three
9720 active targets, one in each class. This allows you to (for example)
9721 start a process and inspect its activity without abandoning your work on
9724 For example, if you execute @samp{gdb a.out}, then the executable file
9725 @code{a.out} is the only active target. If you designate a core file as
9726 well---presumably from a prior run that crashed and coredumped---then
9727 @value{GDBN} has two active targets and uses them in tandem, looking
9728 first in the corefile target, then in the executable file, to satisfy
9729 requests for memory addresses. (Typically, these two classes of target
9730 are complementary, since core files contain only a program's
9731 read-write memory---variables and so on---plus machine status, while
9732 executable files contain only the program text and initialized data.)
9734 When you type @code{run}, your executable file becomes an active process
9735 target as well. When a process target is active, all @value{GDBN}
9736 commands requesting memory addresses refer to that target; addresses in
9737 an active core file or executable file target are obscured while the
9738 process target is active.
9740 Use the @code{core-file} and @code{exec-file} commands to select a new
9741 core file or executable target (@pxref{Files, ,Commands to specify
9742 files}). To specify as a target a process that is already running, use
9743 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9746 @node Target Commands
9747 @section Commands for managing targets
9750 @item target @var{type} @var{parameters}
9751 Connects the @value{GDBN} host environment to a target machine or
9752 process. A target is typically a protocol for talking to debugging
9753 facilities. You use the argument @var{type} to specify the type or
9754 protocol of the target machine.
9756 Further @var{parameters} are interpreted by the target protocol, but
9757 typically include things like device names or host names to connect
9758 with, process numbers, and baud rates.
9760 The @code{target} command does not repeat if you press @key{RET} again
9761 after executing the command.
9765 Displays the names of all targets available. To display targets
9766 currently selected, use either @code{info target} or @code{info files}
9767 (@pxref{Files, ,Commands to specify files}).
9769 @item help target @var{name}
9770 Describe a particular target, including any parameters necessary to
9773 @kindex set gnutarget
9774 @item set gnutarget @var{args}
9775 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9776 knows whether it is reading an @dfn{executable},
9777 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9778 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9779 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9782 @emph{Warning:} To specify a file format with @code{set gnutarget},
9783 you must know the actual BFD name.
9787 @xref{Files, , Commands to specify files}.
9789 @kindex show gnutarget
9790 @item show gnutarget
9791 Use the @code{show gnutarget} command to display what file format
9792 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9793 @value{GDBN} will determine the file format for each file automatically,
9794 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9797 Here are some common targets (available, or not, depending on the GDB
9802 @item target exec @var{program}
9803 An executable file. @samp{target exec @var{program}} is the same as
9804 @samp{exec-file @var{program}}.
9807 @item target core @var{filename}
9808 A core dump file. @samp{target core @var{filename}} is the same as
9809 @samp{core-file @var{filename}}.
9811 @kindex target remote
9812 @item target remote @var{dev}
9813 Remote serial target in GDB-specific protocol. The argument @var{dev}
9814 specifies what serial device to use for the connection (e.g.
9815 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9816 supports the @code{load} command. This is only useful if you have
9817 some other way of getting the stub to the target system, and you can put
9818 it somewhere in memory where it won't get clobbered by the download.
9822 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9830 works; however, you cannot assume that a specific memory map, device
9831 drivers, or even basic I/O is available, although some simulators do
9832 provide these. For info about any processor-specific simulator details,
9833 see the appropriate section in @ref{Embedded Processors, ,Embedded
9838 Some configurations may include these targets as well:
9843 @item target nrom @var{dev}
9844 NetROM ROM emulator. This target only supports downloading.
9848 Different targets are available on different configurations of @value{GDBN};
9849 your configuration may have more or fewer targets.
9851 Many remote targets require you to download the executable's code
9852 once you've successfully established a connection.
9856 @kindex load @var{filename}
9857 @item load @var{filename}
9858 Depending on what remote debugging facilities are configured into
9859 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9860 is meant to make @var{filename} (an executable) available for debugging
9861 on the remote system---by downloading, or dynamic linking, for example.
9862 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9863 the @code{add-symbol-file} command.
9865 If your @value{GDBN} does not have a @code{load} command, attempting to
9866 execute it gets the error message ``@code{You can't do that when your
9867 target is @dots{}}''
9869 The file is loaded at whatever address is specified in the executable.
9870 For some object file formats, you can specify the load address when you
9871 link the program; for other formats, like a.out, the object file format
9872 specifies a fixed address.
9873 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9875 @code{load} does not repeat if you press @key{RET} again after using it.
9879 @section Choosing target byte order
9881 @cindex choosing target byte order
9882 @cindex target byte order
9884 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9885 offer the ability to run either big-endian or little-endian byte
9886 orders. Usually the executable or symbol will include a bit to
9887 designate the endian-ness, and you will not need to worry about
9888 which to use. However, you may still find it useful to adjust
9889 @value{GDBN}'s idea of processor endian-ness manually.
9892 @kindex set endian big
9893 @item set endian big
9894 Instruct @value{GDBN} to assume the target is big-endian.
9896 @kindex set endian little
9897 @item set endian little
9898 Instruct @value{GDBN} to assume the target is little-endian.
9900 @kindex set endian auto
9901 @item set endian auto
9902 Instruct @value{GDBN} to use the byte order associated with the
9906 Display @value{GDBN}'s current idea of the target byte order.
9910 Note that these commands merely adjust interpretation of symbolic
9911 data on the host, and that they have absolutely no effect on the
9915 @section Remote debugging
9916 @cindex remote debugging
9918 If you are trying to debug a program running on a machine that cannot run
9919 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9920 For example, you might use remote debugging on an operating system kernel,
9921 or on a small system which does not have a general purpose operating system
9922 powerful enough to run a full-featured debugger.
9924 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9925 to make this work with particular debugging targets. In addition,
9926 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9927 but not specific to any particular target system) which you can use if you
9928 write the remote stubs---the code that runs on the remote system to
9929 communicate with @value{GDBN}.
9931 Other remote targets may be available in your
9932 configuration of @value{GDBN}; use @code{help target} to list them.
9935 * Remote Serial:: @value{GDBN} remote serial protocol
9939 @subsection The @value{GDBN} remote serial protocol
9941 @cindex remote serial debugging, overview
9942 To debug a program running on another machine (the debugging
9943 @dfn{target} machine), you must first arrange for all the usual
9944 prerequisites for the program to run by itself. For example, for a C
9949 A startup routine to set up the C runtime environment; these usually
9950 have a name like @file{crt0}. The startup routine may be supplied by
9951 your hardware supplier, or you may have to write your own.
9954 A C subroutine library to support your program's
9955 subroutine calls, notably managing input and output.
9958 A way of getting your program to the other machine---for example, a
9959 download program. These are often supplied by the hardware
9960 manufacturer, but you may have to write your own from hardware
9964 The next step is to arrange for your program to use a serial port to
9965 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9966 machine). In general terms, the scheme looks like this:
9970 @value{GDBN} already understands how to use this protocol; when everything
9971 else is set up, you can simply use the @samp{target remote} command
9972 (@pxref{Targets,,Specifying a Debugging Target}).
9974 @item On the target,
9975 you must link with your program a few special-purpose subroutines that
9976 implement the @value{GDBN} remote serial protocol. The file containing these
9977 subroutines is called a @dfn{debugging stub}.
9979 On certain remote targets, you can use an auxiliary program
9980 @code{gdbserver} instead of linking a stub into your program.
9981 @xref{Server,,Using the @code{gdbserver} program}, for details.
9984 The debugging stub is specific to the architecture of the remote
9985 machine; for example, use @file{sparc-stub.c} to debug programs on
9988 @cindex remote serial stub list
9989 These working remote stubs are distributed with @value{GDBN}:
9994 @cindex @file{i386-stub.c}
9997 For Intel 386 and compatible architectures.
10000 @cindex @file{m68k-stub.c}
10001 @cindex Motorola 680x0
10003 For Motorola 680x0 architectures.
10006 @cindex @file{sh-stub.c}
10009 For Hitachi SH architectures.
10012 @cindex @file{sparc-stub.c}
10014 For @sc{sparc} architectures.
10016 @item sparcl-stub.c
10017 @cindex @file{sparcl-stub.c}
10020 For Fujitsu @sc{sparclite} architectures.
10024 The @file{README} file in the @value{GDBN} distribution may list other
10025 recently added stubs.
10028 * Stub Contents:: What the stub can do for you
10029 * Bootstrapping:: What you must do for the stub
10030 * Debug Session:: Putting it all together
10031 * Protocol:: Definition of the communication protocol
10032 * Server:: Using the `gdbserver' program
10033 * NetWare:: Using the `gdbserve.nlm' program
10036 @node Stub Contents
10037 @subsubsection What the stub can do for you
10039 @cindex remote serial stub
10040 The debugging stub for your architecture supplies these three
10044 @item set_debug_traps
10045 @kindex set_debug_traps
10046 @cindex remote serial stub, initialization
10047 This routine arranges for @code{handle_exception} to run when your
10048 program stops. You must call this subroutine explicitly near the
10049 beginning of your program.
10051 @item handle_exception
10052 @kindex handle_exception
10053 @cindex remote serial stub, main routine
10054 This is the central workhorse, but your program never calls it
10055 explicitly---the setup code arranges for @code{handle_exception} to
10056 run when a trap is triggered.
10058 @code{handle_exception} takes control when your program stops during
10059 execution (for example, on a breakpoint), and mediates communications
10060 with @value{GDBN} on the host machine. This is where the communications
10061 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10062 representative on the target machine. It begins by sending summary
10063 information on the state of your program, then continues to execute,
10064 retrieving and transmitting any information @value{GDBN} needs, until you
10065 execute a @value{GDBN} command that makes your program resume; at that point,
10066 @code{handle_exception} returns control to your own code on the target
10070 @cindex @code{breakpoint} subroutine, remote
10071 Use this auxiliary subroutine to make your program contain a
10072 breakpoint. Depending on the particular situation, this may be the only
10073 way for @value{GDBN} to get control. For instance, if your target
10074 machine has some sort of interrupt button, you won't need to call this;
10075 pressing the interrupt button transfers control to
10076 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10077 simply receiving characters on the serial port may also trigger a trap;
10078 again, in that situation, you don't need to call @code{breakpoint} from
10079 your own program---simply running @samp{target remote} from the host
10080 @value{GDBN} session gets control.
10082 Call @code{breakpoint} if none of these is true, or if you simply want
10083 to make certain your program stops at a predetermined point for the
10084 start of your debugging session.
10087 @node Bootstrapping
10088 @subsubsection What you must do for the stub
10090 @cindex remote stub, support routines
10091 The debugging stubs that come with @value{GDBN} are set up for a particular
10092 chip architecture, but they have no information about the rest of your
10093 debugging target machine.
10095 First of all you need to tell the stub how to communicate with the
10099 @item int getDebugChar()
10100 @kindex getDebugChar
10101 Write this subroutine to read a single character from the serial port.
10102 It may be identical to @code{getchar} for your target system; a
10103 different name is used to allow you to distinguish the two if you wish.
10105 @item void putDebugChar(int)
10106 @kindex putDebugChar
10107 Write this subroutine to write a single character to the serial port.
10108 It may be identical to @code{putchar} for your target system; a
10109 different name is used to allow you to distinguish the two if you wish.
10112 @cindex control C, and remote debugging
10113 @cindex interrupting remote targets
10114 If you want @value{GDBN} to be able to stop your program while it is
10115 running, you need to use an interrupt-driven serial driver, and arrange
10116 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10117 character). That is the character which @value{GDBN} uses to tell the
10118 remote system to stop.
10120 Getting the debugging target to return the proper status to @value{GDBN}
10121 probably requires changes to the standard stub; one quick and dirty way
10122 is to just execute a breakpoint instruction (the ``dirty'' part is that
10123 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10125 Other routines you need to supply are:
10128 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10129 @kindex exceptionHandler
10130 Write this function to install @var{exception_address} in the exception
10131 handling tables. You need to do this because the stub does not have any
10132 way of knowing what the exception handling tables on your target system
10133 are like (for example, the processor's table might be in @sc{rom},
10134 containing entries which point to a table in @sc{ram}).
10135 @var{exception_number} is the exception number which should be changed;
10136 its meaning is architecture-dependent (for example, different numbers
10137 might represent divide by zero, misaligned access, etc). When this
10138 exception occurs, control should be transferred directly to
10139 @var{exception_address}, and the processor state (stack, registers,
10140 and so on) should be just as it is when a processor exception occurs. So if
10141 you want to use a jump instruction to reach @var{exception_address}, it
10142 should be a simple jump, not a jump to subroutine.
10144 For the 386, @var{exception_address} should be installed as an interrupt
10145 gate so that interrupts are masked while the handler runs. The gate
10146 should be at privilege level 0 (the most privileged level). The
10147 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10148 help from @code{exceptionHandler}.
10150 @item void flush_i_cache()
10151 @kindex flush_i_cache
10152 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10153 instruction cache, if any, on your target machine. If there is no
10154 instruction cache, this subroutine may be a no-op.
10156 On target machines that have instruction caches, @value{GDBN} requires this
10157 function to make certain that the state of your program is stable.
10161 You must also make sure this library routine is available:
10164 @item void *memset(void *, int, int)
10166 This is the standard library function @code{memset} that sets an area of
10167 memory to a known value. If you have one of the free versions of
10168 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10169 either obtain it from your hardware manufacturer, or write your own.
10172 If you do not use the GNU C compiler, you may need other standard
10173 library subroutines as well; this varies from one stub to another,
10174 but in general the stubs are likely to use any of the common library
10175 subroutines which @code{@value{GCC}} generates as inline code.
10178 @node Debug Session
10179 @subsubsection Putting it all together
10181 @cindex remote serial debugging summary
10182 In summary, when your program is ready to debug, you must follow these
10187 Make sure you have defined the supporting low-level routines
10188 (@pxref{Bootstrapping,,What you must do for the stub}):
10190 @code{getDebugChar}, @code{putDebugChar},
10191 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10195 Insert these lines near the top of your program:
10203 For the 680x0 stub only, you need to provide a variable called
10204 @code{exceptionHook}. Normally you just use:
10207 void (*exceptionHook)() = 0;
10211 but if before calling @code{set_debug_traps}, you set it to point to a
10212 function in your program, that function is called when
10213 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10214 error). The function indicated by @code{exceptionHook} is called with
10215 one parameter: an @code{int} which is the exception number.
10218 Compile and link together: your program, the @value{GDBN} debugging stub for
10219 your target architecture, and the supporting subroutines.
10222 Make sure you have a serial connection between your target machine and
10223 the @value{GDBN} host, and identify the serial port on the host.
10226 @c The "remote" target now provides a `load' command, so we should
10227 @c document that. FIXME.
10228 Download your program to your target machine (or get it there by
10229 whatever means the manufacturer provides), and start it.
10232 To start remote debugging, run @value{GDBN} on the host machine, and specify
10233 as an executable file the program that is running in the remote machine.
10234 This tells @value{GDBN} how to find your program's symbols and the contents
10238 @cindex serial line, @code{target remote}
10239 Establish communication using the @code{target remote} command.
10240 Its argument specifies how to communicate with the target
10241 machine---either via a devicename attached to a direct serial line, or a
10242 TCP port (usually to a terminal server which in turn has a serial line
10243 to the target). For example, to use a serial line connected to the
10244 device named @file{/dev/ttyb}:
10247 target remote /dev/ttyb
10250 @cindex TCP port, @code{target remote}
10251 To use a TCP connection, use an argument of the form
10252 @code{@var{host}:port}. For example, to connect to port 2828 on a
10253 terminal server named @code{manyfarms}:
10256 target remote manyfarms:2828
10259 If your remote target is actually running on the same machine as
10260 your debugger session (e.g.@: a simulator of your target running on
10261 the same host), you can omit the hostname. For example, to connect
10262 to port 1234 on your local machine:
10265 target remote :1234
10269 Note that the colon is still required here.
10272 Now you can use all the usual commands to examine and change data and to
10273 step and continue the remote program.
10275 To resume the remote program and stop debugging it, use the @code{detach}
10278 @cindex interrupting remote programs
10279 @cindex remote programs, interrupting
10280 Whenever @value{GDBN} is waiting for the remote program, if you type the
10281 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10282 program. This may or may not succeed, depending in part on the hardware
10283 and the serial drivers the remote system uses. If you type the
10284 interrupt character once again, @value{GDBN} displays this prompt:
10287 Interrupted while waiting for the program.
10288 Give up (and stop debugging it)? (y or n)
10291 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10292 (If you decide you want to try again later, you can use @samp{target
10293 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10294 goes back to waiting.
10297 @subsubsection Communication protocol
10299 @cindex debugging stub, example
10300 @cindex remote stub, example
10301 @cindex stub example, remote debugging
10302 The stub files provided with @value{GDBN} implement the target side of the
10303 communication protocol, and the @value{GDBN} side is implemented in the
10304 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10305 these subroutines to communicate, and ignore the details. (If you're
10306 implementing your own stub file, you can still ignore the details: start
10307 with one of the existing stub files. @file{sparc-stub.c} is the best
10308 organized, and therefore the easiest to read.)
10310 However, there may be occasions when you need to know something about
10311 the protocol---for example, if there is only one serial port to your
10312 target machine, you might want your program to do something special if
10313 it recognizes a packet meant for @value{GDBN}.
10315 In the examples below, @samp{<-} and @samp{->} are used to indicate
10316 transmitted and received data respectfully.
10318 @cindex protocol, @value{GDBN} remote serial
10319 @cindex serial protocol, @value{GDBN} remote
10320 @cindex remote serial protocol
10321 All @value{GDBN} commands and responses (other than acknowledgments) are
10322 sent as a @var{packet}. A @var{packet} is introduced with the character
10323 @samp{$}, the actual @var{packet-data}, and the terminating character
10324 @samp{#} followed by a two-digit @var{checksum}:
10327 @code{$}@var{packet-data}@code{#}@var{checksum}
10331 @cindex checksum, for @value{GDBN} remote
10333 The two-digit @var{checksum} is computed as the modulo 256 sum of all
10334 characters between the leading @samp{$} and the trailing @samp{#} (an
10335 eight bit unsigned checksum).
10337 Implementors should note that prior to @value{GDBN} 5.0 the protocol
10338 specification also included an optional two-digit @var{sequence-id}:
10341 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
10344 @cindex sequence-id, for @value{GDBN} remote
10346 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
10347 has never output @var{sequence-id}s. Stubs that handle packets added
10348 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
10350 @cindex acknowledgment, for @value{GDBN} remote
10351 When either the host or the target machine receives a packet, the first
10352 response expected is an acknowledgment: either @samp{+} (to indicate
10353 the package was received correctly) or @samp{-} (to request
10357 <- @code{$}@var{packet-data}@code{#}@var{checksum}
10362 The host (@value{GDBN}) sends @var{command}s, and the target (the
10363 debugging stub incorporated in your program) sends a @var{response}. In
10364 the case of step and continue @var{command}s, the response is only sent
10365 when the operation has completed (the target has again stopped).
10367 @var{packet-data} consists of a sequence of characters with the
10368 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
10371 Fields within the packet should be separated using @samp{,} @samp{;} or
10372 @samp{:}. Except where otherwise noted all numbers are represented in
10373 HEX with leading zeros suppressed.
10375 Implementors should note that prior to @value{GDBN} 5.0, the character
10376 @samp{:} could not appear as the third character in a packet (as it
10377 would potentially conflict with the @var{sequence-id}).
10379 Response @var{data} can be run-length encoded to save space. A @samp{*}
10380 means that the next character is an @sc{ascii} encoding giving a repeat count
10381 which stands for that many repetitions of the character preceding the
10382 @samp{*}. The encoding is @code{n+29}, yielding a printable character
10383 where @code{n >=3} (which is where rle starts to win). The printable
10384 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
10385 value greater than 126 should not be used.
10387 Some remote systems have used a different run-length encoding mechanism
10388 loosely refered to as the cisco encoding. Following the @samp{*}
10389 character are two hex digits that indicate the size of the packet.
10396 means the same as "0000".
10398 The error response returned for some packets includes a two character
10399 error number. That number is not well defined.
10401 For any @var{command} not supported by the stub, an empty response
10402 (@samp{$#00}) should be returned. That way it is possible to extend the
10403 protocol. A newer @value{GDBN} can tell if a packet is supported based
10406 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
10407 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
10410 Below is a complete list of all currently defined @var{command}s and
10411 their corresponding response @var{data}:
10413 @multitable @columnfractions .30 .30 .40
10418 @item extended mode
10421 Enable extended mode. In extended mode, the remote server is made
10422 persistent. The @samp{R} packet is used to restart the program being
10425 @tab reply @samp{OK}
10427 The remote target both supports and has enabled extended mode.
10432 Indicate the reason the target halted. The reply is the same as for step
10441 @tab Reserved for future use
10443 @item set program arguments @strong{(reserved)}
10444 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
10449 Initialized @samp{argv[]} array passed into program. @var{arglen}
10450 specifies the number of bytes in the hex encoded byte stream @var{arg}.
10451 See @file{gdbserver} for more details.
10453 @tab reply @code{OK}
10455 @tab reply @code{E}@var{NN}
10457 @item set baud @strong{(deprecated)}
10458 @tab @code{b}@var{baud}
10460 Change the serial line speed to @var{baud}. JTC: @emph{When does the
10461 transport layer state change? When it's received, or after the ACK is
10462 transmitted. In either case, there are problems if the command or the
10463 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
10464 to add something like this, and get it working for the first time, they
10465 ought to modify ser-unix.c to send some kind of out-of-band message to a
10466 specially-setup stub and have the switch happen "in between" packets, so
10467 that from remote protocol's point of view, nothing actually
10470 @item set breakpoint @strong{(deprecated)}
10471 @tab @code{B}@var{addr},@var{mode}
10473 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
10474 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
10478 @tab @code{c}@var{addr}
10480 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10486 @item continue with signal
10487 @tab @code{C}@var{sig}@code{;}@var{addr}
10489 Continue with signal @var{sig} (hex signal number). If
10490 @code{;}@var{addr} is omitted, resume at same address.
10495 @item toggle debug @strong{(deprecated)}
10503 Detach @value{GDBN} from the remote system. Sent to the remote target before
10504 @value{GDBN} disconnects.
10506 @tab reply @emph{no response}
10508 @value{GDBN} does not check for any response after sending this packet.
10512 @tab Reserved for future use
10516 @tab Reserved for future use
10520 @tab Reserved for future use
10524 @tab Reserved for future use
10526 @item read registers
10528 @tab Read general registers.
10530 @tab reply @var{XX...}
10532 Each byte of register data is described by two hex digits. The bytes
10533 with the register are transmitted in target byte order. The size of
10534 each register and their position within the @samp{g} @var{packet} are
10535 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
10536 @var{REGISTER_NAME} macros. The specification of several standard
10537 @code{g} packets is specified below.
10539 @tab @code{E}@var{NN}
10543 @tab @code{G}@var{XX...}
10545 See @samp{g} for a description of the @var{XX...} data.
10547 @tab reply @code{OK}
10550 @tab reply @code{E}@var{NN}
10555 @tab Reserved for future use
10558 @tab @code{H}@var{c}@var{t...}
10560 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
10561 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
10562 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
10563 thread used in other operations. If zero, pick a thread, any thread.
10565 @tab reply @code{OK}
10568 @tab reply @code{E}@var{NN}
10572 @c 'H': How restrictive (or permissive) is the thread model. If a
10573 @c thread is selected and stopped, are other threads allowed
10574 @c to continue to execute? As I mentioned above, I think the
10575 @c semantics of each command when a thread is selected must be
10576 @c described. For example:
10578 @c 'g': If the stub supports threads and a specific thread is
10579 @c selected, returns the register block from that thread;
10580 @c otherwise returns current registers.
10582 @c 'G' If the stub supports threads and a specific thread is
10583 @c selected, sets the registers of the register block of
10584 @c that thread; otherwise sets current registers.
10586 @item cycle step @strong{(draft)}
10587 @tab @code{i}@var{addr}@code{,}@var{nnn}
10589 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
10590 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
10591 step starting at that address.
10593 @item signal then cycle step @strong{(reserved)}
10596 See @samp{i} and @samp{S} for likely syntax and semantics.
10600 @tab Reserved for future use
10604 @tab Reserved for future use
10609 FIXME: @emph{There is no description of how operate when a specific
10610 thread context has been selected (ie. does 'k' kill only that thread?)}.
10614 @tab Reserved for future use
10618 @tab Reserved for future use
10621 @tab @code{m}@var{addr}@code{,}@var{length}
10623 Read @var{length} bytes of memory starting at address @var{addr}.
10624 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
10625 using word alligned accesses. FIXME: @emph{A word aligned memory
10626 transfer mechanism is needed.}
10628 @tab reply @var{XX...}
10630 @var{XX...} is mem contents. Can be fewer bytes than requested if able
10631 to read only part of the data. Neither @value{GDBN} nor the stub assume that
10632 sized memory transfers are assumed using word alligned accesses. FIXME:
10633 @emph{A word aligned memory transfer mechanism is needed.}
10635 @tab reply @code{E}@var{NN}
10636 @tab @var{NN} is errno
10639 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
10641 Write @var{length} bytes of memory starting at address @var{addr}.
10642 @var{XX...} is the data.
10644 @tab reply @code{OK}
10647 @tab reply @code{E}@var{NN}
10649 for an error (this includes the case where only part of the data was
10654 @tab Reserved for future use
10658 @tab Reserved for future use
10662 @tab Reserved for future use
10666 @tab Reserved for future use
10668 @item read reg @strong{(reserved)}
10669 @tab @code{p}@var{n...}
10671 See write register.
10673 @tab return @var{r....}
10674 @tab The hex encoded value of the register in target byte order.
10677 @tab @code{P}@var{n...}@code{=}@var{r...}
10679 Write register @var{n...} with value @var{r...}, which contains two hex
10680 digits for each byte in the register (target byte order).
10682 @tab reply @code{OK}
10685 @tab reply @code{E}@var{NN}
10688 @item general query
10689 @tab @code{q}@var{query}
10691 Request info about @var{query}. In general @value{GDBN} queries
10692 have a leading upper case letter. Custom vendor queries should use a
10693 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10694 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10695 must ensure that they match the full @var{query} name.
10697 @tab reply @code{XX...}
10698 @tab Hex encoded data from query. The reply can not be empty.
10700 @tab reply @code{E}@var{NN}
10704 @tab Indicating an unrecognized @var{query}.
10707 @tab @code{Q}@var{var}@code{=}@var{val}
10709 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10710 naming conventions.
10712 @item reset @strong{(deprecated)}
10715 Reset the entire system.
10717 @item remote restart
10718 @tab @code{R}@var{XX}
10720 Restart the program being debugged. @var{XX}, while needed, is ignored.
10721 This packet is only available in extended mode.
10726 The @samp{R} packet has no reply.
10729 @tab @code{s}@var{addr}
10731 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10737 @item step with signal
10738 @tab @code{S}@var{sig}@code{;}@var{addr}
10740 Like @samp{C} but step not continue.
10746 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10748 Search backwards starting at address @var{addr} for a match with pattern
10749 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10750 bytes. @var{addr} must be at least 3 digits.
10753 @tab @code{T}@var{XX}
10754 @tab Find out if the thread XX is alive.
10756 @tab reply @code{OK}
10757 @tab thread is still alive
10759 @tab reply @code{E}@var{NN}
10760 @tab thread is dead
10764 @tab Reserved for future use
10768 @tab Reserved for future use
10772 @tab Reserved for future use
10776 @tab Reserved for future use
10780 @tab Reserved for future use
10784 @tab Reserved for future use
10788 @tab Reserved for future use
10790 @item write mem (binary)
10791 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10793 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10794 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10795 escaped using @code{0x7d}.
10797 @tab reply @code{OK}
10800 @tab reply @code{E}@var{NN}
10805 @tab Reserved for future use
10809 @tab Reserved for future use
10811 @item remove break or watchpoint @strong{(draft)}
10812 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10816 @item insert break or watchpoint @strong{(draft)}
10817 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10819 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10820 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10821 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10822 bytes. For a software breakpoint, @var{length} specifies the size of
10823 the instruction to be patched. For hardware breakpoints and watchpoints
10824 @var{length} specifies the memory region to be monitored. To avoid
10825 potential problems with duplicate packets, the operations should be
10826 implemented in an idempotent way.
10828 @tab reply @code{E}@var{NN}
10831 @tab reply @code{OK}
10835 @tab If not supported.
10839 @tab Reserved for future use
10843 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10844 receive any of the below as a reply. In the case of the @samp{C},
10845 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10846 when the target halts. In the below the exact meaning of @samp{signal
10847 number} is poorly defined. In general one of the UNIX signal numbering
10848 conventions is used.
10850 @multitable @columnfractions .4 .6
10852 @item @code{S}@var{AA}
10853 @tab @var{AA} is the signal number
10855 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10857 @var{AA} = two hex digit signal number; @var{n...} = register number
10858 (hex), @var{r...} = target byte ordered register contents, size defined
10859 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10860 thread process ID, this is a hex integer; @var{n...} = other string not
10861 starting with valid hex digit. @value{GDBN} should ignore this
10862 @var{n...}, @var{r...} pair and go on to the next. This way we can
10863 extend the protocol.
10865 @item @code{W}@var{AA}
10867 The process exited, and @var{AA} is the exit status. This is only
10868 applicable for certains sorts of targets.
10870 @item @code{X}@var{AA}
10872 The process terminated with signal @var{AA}.
10874 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10876 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10877 @var{d...} = base of data section; @var{b...} = base of bss section.
10878 @emph{Note: only used by Cisco Systems targets. The difference between
10879 this reply and the "qOffsets" query is that the 'N' packet may arrive
10880 spontaneously whereas the 'qOffsets' is a query initiated by the host
10883 @item @code{O}@var{XX...}
10885 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10886 while the program is running and the debugger should continue to wait
10891 The following set and query packets have already been defined.
10893 @multitable @columnfractions .2 .2 .6
10895 @item current thread
10896 @tab @code{q}@code{C}
10897 @tab Return the current thread id.
10899 @tab reply @code{QC}@var{pid}
10901 Where @var{pid} is a HEX encoded 16 bit process id.
10904 @tab Any other reply implies the old pid.
10906 @item all thread ids
10907 @tab @code{q}@code{fThreadInfo}
10909 @tab @code{q}@code{sThreadInfo}
10911 Obtain a list of active thread ids from the target (OS). Since there
10912 may be too many active threads to fit into one reply packet, this query
10913 works iteratively: it may require more than one query/reply sequence to
10914 obtain the entire list of threads. The first query of the sequence will
10915 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10916 sequence will be the @code{qs}@code{ThreadInfo} query.
10919 @tab NOTE: replaces the @code{qL} query (see below).
10921 @tab reply @code{m}@var{<id>}
10922 @tab A single thread id
10924 @tab reply @code{m}@var{<id>},@var{<id>...}
10925 @tab a comma-separated list of thread ids
10927 @tab reply @code{l}
10928 @tab (lower case 'el') denotes end of list.
10932 In response to each query, the target will reply with a list of one
10933 or more thread ids, in big-endian hex, separated by commas. GDB will
10934 respond to each reply with a request for more thread ids (using the
10935 @code{qs} form of the query), until the target responds with @code{l}
10936 (lower-case el, for @code{'last'}).
10938 @item extra thread info
10939 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10944 Where @var{<id>} is a thread-id in big-endian hex.
10945 Obtain a printable string description of a thread's attributes from
10946 the target OS. This string may contain anything that the target OS
10947 thinks is interesting for @value{GDBN} to tell the user about the thread.
10948 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10949 Some examples of possible thread extra info strings are "Runnable", or
10950 "Blocked on Mutex".
10952 @tab reply @var{XX...}
10954 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10955 printable string containing the extra information about the thread's
10958 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10959 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10964 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10965 digit) is one to indicate the first query and zero to indicate a
10966 subsequent query; @var{threadcount} (two hex digits) is the maximum
10967 number of threads the response packet can contain; and @var{nextthread}
10968 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10969 returned in the response as @var{argthread}.
10972 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10975 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10980 Where: @var{count} (two hex digits) is the number of threads being
10981 returned; @var{done} (one hex digit) is zero to indicate more threads
10982 and one indicates no further threads; @var{argthreadid} (eight hex
10983 digits) is @var{nextthread} from the request packet; @var{thread...} is
10984 a sequence of thread IDs from the target. @var{threadid} (eight hex
10985 digits). See @code{remote.c:parse_threadlist_response()}.
10987 @item compute CRC of memory block
10988 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10991 @tab reply @code{E}@var{NN}
10992 @tab An error (such as memory fault)
10994 @tab reply @code{C}@var{CRC32}
10995 @tab A 32 bit cyclic redundancy check of the specified memory region.
10997 @item query sect offs
10998 @tab @code{q}@code{Offsets}
11000 Get section offsets that the target used when re-locating the downloaded
11001 image. @emph{Note: while a @code{Bss} offset is included in the
11002 response, @value{GDBN} ignores this and instead applies the @code{Data}
11003 offset to the @code{Bss} section.}
11005 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
11007 @item thread info request
11008 @tab @code{q}@code{P}@var{mode}@var{threadid}
11013 Returns information on @var{threadid}. Where: @var{mode} is a hex
11014 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
11018 See @code{remote.c:remote_unpack_thread_info_response()}.
11020 @item remote command
11021 @tab @code{q}@code{Rcmd,}@var{COMMAND}
11026 @var{COMMAND} (hex encoded) is passed to the local interpreter for
11027 execution. Invalid commands should be reported using the output string.
11028 Before the final result packet, the target may also respond with a
11029 number of intermediate @code{O}@var{OUTPUT} console output
11030 packets. @emph{Implementors should note that providing access to a
11031 stubs's interpreter may have security implications}.
11033 @tab reply @code{OK}
11035 A command response with no output.
11037 @tab reply @var{OUTPUT}
11039 A command response with the hex encoded output string @var{OUTPUT}.
11041 @tab reply @code{E}@var{NN}
11043 Indicate a badly formed request.
11048 When @samp{q}@samp{Rcmd} is not recognized.
11050 @item symbol lookup
11051 @tab @code{qSymbol::}
11053 Notify the target that @value{GDBN} is prepared to serve symbol lookup
11054 requests. Accept requests from the target for the values of symbols.
11059 @tab reply @code{OK}
11061 The target does not need to look up any (more) symbols.
11063 @tab reply @code{qSymbol:}@var{sym_name}
11065 The target requests the value of symbol @var{sym_name} (hex encoded).
11066 @value{GDBN} may provide the value by using the
11067 @code{qSymbol:}@var{sym_value}:@var{sym_name}
11068 message, described below.
11071 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
11073 Set the value of SYM_NAME to SYM_VALUE.
11077 @var{sym_name} (hex encoded) is the name of a symbol whose value
11078 the target has previously requested.
11082 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
11083 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
11084 field will be empty.
11086 @tab reply @code{OK}
11088 The target does not need to look up any (more) symbols.
11090 @tab reply @code{qSymbol:}@var{sym_name}
11092 The target requests the value of a new symbol @var{sym_name} (hex encoded).
11093 @value{GDBN} will continue to supply the values of symbols (if available),
11094 until the target ceases to request them.
11098 The following @samp{g}/@samp{G} packets have previously been defined.
11099 In the below, some thirty-two bit registers are transferred as sixty-four
11100 bits. Those registers should be zero/sign extended (which?) to fill the
11101 space allocated. Register bytes are transfered in target byte order.
11102 The two nibbles within a register byte are transfered most-significant -
11105 @multitable @columnfractions .5 .5
11109 All registers are transfered as thirty-two bit quantities in the order:
11110 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
11111 registers; fsr; fir; fp.
11115 All registers are transfered as sixty-four bit quantities (including
11116 thirty-two bit registers such as @code{sr}). The ordering is the same
11121 Example sequence of a target being re-started. Notice how the restart
11122 does not get any direct output:
11127 @emph{target restarts}
11130 -> @code{T001:1234123412341234}
11134 Example sequence of a target being stepped by a single instruction:
11142 -> @code{T001:1234123412341234}
11151 @subsubsection Using the @code{gdbserver} program
11154 @cindex remote connection without stubs
11155 @code{gdbserver} is a control program for Unix-like systems, which
11156 allows you to connect your program with a remote @value{GDBN} via
11157 @code{target remote}---but without linking in the usual debugging stub.
11159 @code{gdbserver} is not a complete replacement for the debugging stubs,
11160 because it requires essentially the same operating-system facilities
11161 that @value{GDBN} itself does. In fact, a system that can run
11162 @code{gdbserver} to connect to a remote @value{GDBN} could also run
11163 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
11164 because it is a much smaller program than @value{GDBN} itself. It is
11165 also easier to port than all of @value{GDBN}, so you may be able to get
11166 started more quickly on a new system by using @code{gdbserver}.
11167 Finally, if you develop code for real-time systems, you may find that
11168 the tradeoffs involved in real-time operation make it more convenient to
11169 do as much development work as possible on another system, for example
11170 by cross-compiling. You can use @code{gdbserver} to make a similar
11171 choice for debugging.
11173 @value{GDBN} and @code{gdbserver} communicate via either a serial line
11174 or a TCP connection, using the standard @value{GDBN} remote serial
11178 @item On the target machine,
11179 you need to have a copy of the program you want to debug.
11180 @code{gdbserver} does not need your program's symbol table, so you can
11181 strip the program if necessary to save space. @value{GDBN} on the host
11182 system does all the symbol handling.
11184 To use the server, you must tell it how to communicate with @value{GDBN};
11185 the name of your program; and the arguments for your program. The
11189 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
11192 @var{comm} is either a device name (to use a serial line) or a TCP
11193 hostname and portnumber. For example, to debug Emacs with the argument
11194 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
11198 target> gdbserver /dev/com1 emacs foo.txt
11201 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
11204 To use a TCP connection instead of a serial line:
11207 target> gdbserver host:2345 emacs foo.txt
11210 The only difference from the previous example is the first argument,
11211 specifying that you are communicating with the host @value{GDBN} via
11212 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
11213 expect a TCP connection from machine @samp{host} to local TCP port 2345.
11214 (Currently, the @samp{host} part is ignored.) You can choose any number
11215 you want for the port number as long as it does not conflict with any
11216 TCP ports already in use on the target system (for example, @code{23} is
11217 reserved for @code{telnet}).@footnote{If you choose a port number that
11218 conflicts with another service, @code{gdbserver} prints an error message
11219 and exits.} You must use the same port number with the host @value{GDBN}
11220 @code{target remote} command.
11222 @item On the @value{GDBN} host machine,
11223 you need an unstripped copy of your program, since @value{GDBN} needs
11224 symbols and debugging information. Start up @value{GDBN} as usual,
11225 using the name of the local copy of your program as the first argument.
11226 (You may also need the @w{@samp{--baud}} option if the serial line is
11227 running at anything other than 9600@dmn{bps}.) After that, use @code{target
11228 remote} to establish communications with @code{gdbserver}. Its argument
11229 is either a device name (usually a serial device, like
11230 @file{/dev/ttyb}), or a TCP port descriptor in the form
11231 @code{@var{host}:@var{PORT}}. For example:
11234 (@value{GDBP}) target remote /dev/ttyb
11238 communicates with the server via serial line @file{/dev/ttyb}, and
11241 (@value{GDBP}) target remote the-target:2345
11245 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
11246 For TCP connections, you must start up @code{gdbserver} prior to using
11247 the @code{target remote} command. Otherwise you may get an error whose
11248 text depends on the host system, but which usually looks something like
11249 @samp{Connection refused}.
11253 @subsubsection Using the @code{gdbserve.nlm} program
11255 @kindex gdbserve.nlm
11256 @code{gdbserve.nlm} is a control program for NetWare systems, which
11257 allows you to connect your program with a remote @value{GDBN} via
11258 @code{target remote}.
11260 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
11261 using the standard @value{GDBN} remote serial protocol.
11264 @item On the target machine,
11265 you need to have a copy of the program you want to debug.
11266 @code{gdbserve.nlm} does not need your program's symbol table, so you
11267 can strip the program if necessary to save space. @value{GDBN} on the
11268 host system does all the symbol handling.
11270 To use the server, you must tell it how to communicate with
11271 @value{GDBN}; the name of your program; and the arguments for your
11272 program. The syntax is:
11275 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
11276 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
11279 @var{board} and @var{port} specify the serial line; @var{baud} specifies
11280 the baud rate used by the connection. @var{port} and @var{node} default
11281 to 0, @var{baud} defaults to 9600@dmn{bps}.
11283 For example, to debug Emacs with the argument @samp{foo.txt}and
11284 communicate with @value{GDBN} over serial port number 2 or board 1
11285 using a 19200@dmn{bps} connection:
11288 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
11291 @item On the @value{GDBN} host machine,
11292 you need an unstripped copy of your program, since @value{GDBN} needs
11293 symbols and debugging information. Start up @value{GDBN} as usual,
11294 using the name of the local copy of your program as the first argument.
11295 (You may also need the @w{@samp{--baud}} option if the serial line is
11296 running at anything other than 9600@dmn{bps}. After that, use @code{target
11297 remote} to establish communications with @code{gdbserve.nlm}. Its
11298 argument is a device name (usually a serial device, like
11299 @file{/dev/ttyb}). For example:
11302 (@value{GDBP}) target remote /dev/ttyb
11306 communications with the server via serial line @file{/dev/ttyb}.
11310 @section Kernel Object Display
11312 @cindex kernel object display
11313 @cindex kernel object
11316 Some targets support kernel object display. Using this facility,
11317 @value{GDBN} communicates specially with the underlying operating system
11318 and can display information about operating system-level objects such as
11319 mutexes and other synchronization objects. Exactly which objects can be
11320 displayed is determined on a per-OS basis.
11322 Use the @code{set os} command to set the operating system. This tells
11323 @value{GDBN} which kernel object display module to initialize:
11326 (@value{GDBP}) set os cisco
11329 If @code{set os} succeeds, @value{GDBN} will display some information
11330 about the operating system, and will create a new @code{info} command
11331 which can be used to query the target. The @code{info} command is named
11332 after the operating system:
11335 (@value{GDBP}) info cisco
11336 List of Cisco Kernel Objects
11338 any Any and all objects
11341 Further subcommands can be used to query about particular objects known
11344 There is currently no way to determine whether a given operating system
11345 is supported other than to try it.
11348 @node Configurations
11349 @chapter Configuration-Specific Information
11351 While nearly all @value{GDBN} commands are available for all native and
11352 cross versions of the debugger, there are some exceptions. This chapter
11353 describes things that are only available in certain configurations.
11355 There are three major categories of configurations: native
11356 configurations, where the host and target are the same, embedded
11357 operating system configurations, which are usually the same for several
11358 different processor architectures, and bare embedded processors, which
11359 are quite different from each other.
11364 * Embedded Processors::
11371 This section describes details specific to particular native
11376 * SVR4 Process Information:: SVR4 process information
11377 * DJGPP Native:: Features specific to the DJGPP port
11383 On HP-UX systems, if you refer to a function or variable name that
11384 begins with a dollar sign, @value{GDBN} searches for a user or system
11385 name first, before it searches for a convenience variable.
11387 @node SVR4 Process Information
11388 @subsection SVR4 process information
11391 @cindex process image
11393 Many versions of SVR4 provide a facility called @samp{/proc} that can be
11394 used to examine the image of a running process using file-system
11395 subroutines. If @value{GDBN} is configured for an operating system with
11396 this facility, the command @code{info proc} is available to report on
11397 several kinds of information about the process running your program.
11398 @code{info proc} works only on SVR4 systems that include the
11399 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
11400 and Unixware, but not HP-UX or Linux, for example.
11405 Summarize available information about the process.
11407 @kindex info proc mappings
11408 @item info proc mappings
11409 Report on the address ranges accessible in the program, with information
11410 on whether your program may read, write, or execute each range.
11412 @comment These sub-options of 'info proc' were not included when
11413 @comment procfs.c was re-written. Keep their descriptions around
11414 @comment against the day when someone finds the time to put them back in.
11415 @kindex info proc times
11416 @item info proc times
11417 Starting time, user CPU time, and system CPU time for your program and
11420 @kindex info proc id
11422 Report on the process IDs related to your program: its own process ID,
11423 the ID of its parent, the process group ID, and the session ID.
11425 @kindex info proc status
11426 @item info proc status
11427 General information on the state of the process. If the process is
11428 stopped, this report includes the reason for stopping, and any signal
11431 @item info proc all
11432 Show all the above information about the process.
11437 @subsection Features for Debugging @sc{djgpp} Programs
11438 @cindex @sc{djgpp} debugging
11439 @cindex native @sc{djgpp} debugging
11440 @cindex MS-DOS-specific commands
11442 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
11443 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
11444 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
11445 top of real-mode DOS systems and their emulations.
11447 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
11448 defines a few commands specific to the @sc{djgpp} port. This
11449 subsection describes those commands.
11454 This is a prefix of @sc{djgpp}-specific commands which print
11455 information about the target system and important OS structures.
11458 @cindex MS-DOS system info
11459 @cindex free memory information (MS-DOS)
11460 @item info dos sysinfo
11461 This command displays assorted information about the underlying
11462 platform: the CPU type and features, the OS version and flavor, the
11463 DPMI version, and the available conventional and DPMI memory.
11468 @cindex segment descriptor tables
11469 @cindex descriptor tables display
11471 @itemx info dos ldt
11472 @itemx info dos idt
11473 These 3 commands display entries from, respectively, Global, Local,
11474 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
11475 tables are data structures which store a descriptor for each segment
11476 that is currently in use. The segment's selector is an index into a
11477 descriptor table; the table entry for that index holds the
11478 descriptor's base address and limit, and its attributes and access
11481 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
11482 segment (used for both data and the stack), and a DOS segment (which
11483 allows access to DOS/BIOS data structures and absolute addresses in
11484 conventional memory). However, the DPMI host will usually define
11485 additional segments in order to support the DPMI environment.
11487 @cindex garbled pointers
11488 These commands allow to display entries from the descriptor tables.
11489 Without an argument, all entries from the specified table are
11490 displayed. An argument, which should be an integer expression, means
11491 display a single entry whose index is given by the argument. For
11492 example, here's a convenient way to display information about the
11493 debugged program's data segment:
11496 (@value{GDBP}) info dos ldt $ds
11497 0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
11501 This comes in handy when you want to see whether a pointer is outside
11502 the data segment's limit (i.e.@: @dfn{garbled}).
11504 @cindex page tables display (MS-DOS)
11506 @itemx info dos pte
11507 These two commands display entries from, respectively, the Page
11508 Directory and the Page Tables. Page Directories and Page Tables are
11509 data structures which control how virtual memory addresses are mapped
11510 into physical addresses. A Page Table includes an entry for every
11511 page of memory that is mapped into the program's address space; there
11512 may be several Page Tables, each one holding up to 4096 entries. A
11513 Page Directory has up to 4096 entries, one each for every Page Table
11514 that is currently in use.
11516 Without an argument, @kbd{info dos pde} displays the entire Page
11517 Directory, and @kbd{info dos pte} displays all the entries in all of
11518 the Page Tables. An argument, an integer expression, given to the
11519 @kbd{info dos pde} command means display only that entry from the Page
11520 Directory table. An argument given to the @kbd{info dos pte} command
11521 means display entries from a single Page Table, the one pointed to by
11522 the specified entry in the Page Directory.
11524 These commands are useful when your program uses @dfn{DMA} (Direct
11525 Memory Access), which needs physical addresses to program the DMA
11528 These commands are supported only with some DPMI servers.
11530 @cindex physical address from linear address
11531 @item info dos address-pte
11532 This command displays the Page Table entry for a specified linear
11533 address. The argument linear address should already have the
11534 appropriate segment's base address added to it, because this command
11535 accepts addresses which may belong to @emph{any} segment. For
11536 example, here's how to display the Page Table entry for the page where
11537 the variable @code{i} is stored:
11540 (@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i
11541 Page Table entry for address 0x11a00d30:
11542 Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
11546 This says that @code{i} is stored at offset @code{0xd30} from the page
11547 whose physical base address is @code{0x02698000}, and prints all the
11548 attributes of that page.
11550 Note that you must cast the addresses of variables to a @code{char *},
11551 since otherwise the value of @code{__djgpp_base_address}, the base
11552 address of all variables and functions in a @sc{djgpp} program, will
11553 be added using the rules of C pointer arithmetics: if @code{i} is
11554 declared an @code{int}, @value{GDBN} will add 4 times the value of
11555 @code{__djgpp_base_address} to the address of @code{i}.
11557 Here's another example, it displays the Page Table entry for the
11561 (@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)
11562 Page Table entry for address 0x29110:
11563 Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
11567 (The @code{+ 3} offset is because the transfer buffer's address is the
11568 3rd member of the @code{_go32_info_block} structure.) The output of
11569 this command clearly shows that addresses in conventional memory are
11570 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11572 This command is supported only with some DPMI servers.
11576 @section Embedded Operating Systems
11578 This section describes configurations involving the debugging of
11579 embedded operating systems that are available for several different
11583 * VxWorks:: Using @value{GDBN} with VxWorks
11586 @value{GDBN} includes the ability to debug programs running on
11587 various real-time operating systems.
11590 @subsection Using @value{GDBN} with VxWorks
11596 @kindex target vxworks
11597 @item target vxworks @var{machinename}
11598 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11599 is the target system's machine name or IP address.
11603 On VxWorks, @code{load} links @var{filename} dynamically on the
11604 current target system as well as adding its symbols in @value{GDBN}.
11606 @value{GDBN} enables developers to spawn and debug tasks running on networked
11607 VxWorks targets from a Unix host. Already-running tasks spawned from
11608 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11609 both the Unix host and on the VxWorks target. The program
11610 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11611 installed with the name @code{vxgdb}, to distinguish it from a
11612 @value{GDBN} for debugging programs on the host itself.)
11615 @item VxWorks-timeout @var{args}
11616 @kindex vxworks-timeout
11617 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11618 This option is set by the user, and @var{args} represents the number of
11619 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11620 your VxWorks target is a slow software simulator or is on the far side
11621 of a thin network line.
11624 The following information on connecting to VxWorks was current when
11625 this manual was produced; newer releases of VxWorks may use revised
11628 @kindex INCLUDE_RDB
11629 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11630 to include the remote debugging interface routines in the VxWorks
11631 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11632 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11633 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11634 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11635 information on configuring and remaking VxWorks, see the manufacturer's
11637 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11639 Once you have included @file{rdb.a} in your VxWorks system image and set
11640 your Unix execution search path to find @value{GDBN}, you are ready to
11641 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11642 @code{vxgdb}, depending on your installation).
11644 @value{GDBN} comes up showing the prompt:
11651 * VxWorks Connection:: Connecting to VxWorks
11652 * VxWorks Download:: VxWorks download
11653 * VxWorks Attach:: Running tasks
11656 @node VxWorks Connection
11657 @subsubsection Connecting to VxWorks
11659 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11660 network. To connect to a target whose host name is ``@code{tt}'', type:
11663 (vxgdb) target vxworks tt
11667 @value{GDBN} displays messages like these:
11670 Attaching remote machine across net...
11675 @value{GDBN} then attempts to read the symbol tables of any object modules
11676 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11677 these files by searching the directories listed in the command search
11678 path (@pxref{Environment, ,Your program's environment}); if it fails
11679 to find an object file, it displays a message such as:
11682 prog.o: No such file or directory.
11685 When this happens, add the appropriate directory to the search path with
11686 the @value{GDBN} command @code{path}, and execute the @code{target}
11689 @node VxWorks Download
11690 @subsubsection VxWorks download
11692 @cindex download to VxWorks
11693 If you have connected to the VxWorks target and you want to debug an
11694 object that has not yet been loaded, you can use the @value{GDBN}
11695 @code{load} command to download a file from Unix to VxWorks
11696 incrementally. The object file given as an argument to the @code{load}
11697 command is actually opened twice: first by the VxWorks target in order
11698 to download the code, then by @value{GDBN} in order to read the symbol
11699 table. This can lead to problems if the current working directories on
11700 the two systems differ. If both systems have NFS mounted the same
11701 filesystems, you can avoid these problems by using absolute paths.
11702 Otherwise, it is simplest to set the working directory on both systems
11703 to the directory in which the object file resides, and then to reference
11704 the file by its name, without any path. For instance, a program
11705 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11706 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11707 program, type this on VxWorks:
11710 -> cd "@var{vxpath}/vw/demo/rdb"
11714 Then, in @value{GDBN}, type:
11717 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11718 (vxgdb) load prog.o
11721 @value{GDBN} displays a response similar to this:
11724 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11727 You can also use the @code{load} command to reload an object module
11728 after editing and recompiling the corresponding source file. Note that
11729 this makes @value{GDBN} delete all currently-defined breakpoints,
11730 auto-displays, and convenience variables, and to clear the value
11731 history. (This is necessary in order to preserve the integrity of
11732 debugger's data structures that reference the target system's symbol
11735 @node VxWorks Attach
11736 @subsubsection Running tasks
11738 @cindex running VxWorks tasks
11739 You can also attach to an existing task using the @code{attach} command as
11743 (vxgdb) attach @var{task}
11747 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11748 or suspended when you attach to it. Running tasks are suspended at
11749 the time of attachment.
11751 @node Embedded Processors
11752 @section Embedded Processors
11754 This section goes into details specific to particular embedded
11758 @c OBSOLETE * A29K Embedded:: AMD A29K Embedded
11761 * H8/300:: Hitachi H8/300
11762 * H8/500:: Hitachi H8/500
11763 * i960:: Intel i960
11764 * M32R/D:: Mitsubishi M32R/D
11765 * M68K:: Motorola M68K
11766 * M88K:: Motorola M88K
11767 * MIPS Embedded:: MIPS Embedded
11768 * PA:: HP PA Embedded
11771 * Sparclet:: Tsqware Sparclet
11772 * Sparclite:: Fujitsu Sparclite
11773 * ST2000:: Tandem ST2000
11774 * Z8000:: Zilog Z8000
11777 @c OBSOLETE @node A29K Embedded
11778 @c OBSOLETE @subsection AMD A29K Embedded
11781 @c OBSOLETE * A29K UDI::
11782 @c OBSOLETE * A29K EB29K::
11783 @c OBSOLETE * Comms (EB29K):: Communications setup
11784 @c OBSOLETE * gdb-EB29K:: EB29K cross-debugging
11785 @c OBSOLETE * Remote Log:: Remote log
11786 @c OBSOLETE @end menu
11788 @c OBSOLETE @table @code
11790 @c OBSOLETE @kindex target adapt
11791 @c OBSOLETE @item target adapt @var{dev}
11792 @c OBSOLETE Adapt monitor for A29K.
11794 @c OBSOLETE @kindex target amd-eb
11795 @c OBSOLETE @item target amd-eb @var{dev} @var{speed} @var{PROG}
11796 @c OBSOLETE @cindex AMD EB29K
11797 @c OBSOLETE Remote PC-resident AMD EB29K board, attached over serial lines.
11798 @c OBSOLETE @var{dev} is the serial device, as for @code{target remote};
11799 @c OBSOLETE @var{speed} allows you to specify the linespeed; and @var{PROG} is the
11800 @c OBSOLETE name of the program to be debugged, as it appears to DOS on the PC.
11801 @c OBSOLETE @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
11803 @c OBSOLETE @end table
11805 @c OBSOLETE @node A29K UDI
11806 @c OBSOLETE @subsubsection A29K UDI
11808 @c OBSOLETE @cindex UDI
11809 @c OBSOLETE @cindex AMD29K via UDI
11811 @c OBSOLETE @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
11812 @c OBSOLETE protocol for debugging the a29k processor family. To use this
11813 @c OBSOLETE configuration with AMD targets running the MiniMON monitor, you need the
11814 @c OBSOLETE program @code{MONTIP}, available from AMD at no charge. You can also
11815 @c OBSOLETE use @value{GDBN} with the UDI-conformant a29k simulator program
11816 @c OBSOLETE @code{ISSTIP}, also available from AMD.
11818 @c OBSOLETE @table @code
11819 @c OBSOLETE @item target udi @var{keyword}
11820 @c OBSOLETE @kindex udi
11821 @c OBSOLETE Select the UDI interface to a remote a29k board or simulator, where
11822 @c OBSOLETE @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
11823 @c OBSOLETE This file contains keyword entries which specify parameters used to
11824 @c OBSOLETE connect to a29k targets. If the @file{udi_soc} file is not in your
11825 @c OBSOLETE working directory, you must set the environment variable @samp{UDICONF}
11826 @c OBSOLETE to its pathname.
11827 @c OBSOLETE @end table
11829 @c OBSOLETE @node A29K EB29K
11830 @c OBSOLETE @subsubsection EBMON protocol for AMD29K
11832 @c OBSOLETE @cindex EB29K board
11833 @c OBSOLETE @cindex running 29K programs
11835 @c OBSOLETE AMD distributes a 29K development board meant to fit in a PC, together
11836 @c OBSOLETE with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
11837 @c OBSOLETE term, this development system is called the ``EB29K''. To use
11838 @c OBSOLETE @value{GDBN} from a Unix system to run programs on the EB29K board, you
11839 @c OBSOLETE must first connect a serial cable between the PC (which hosts the EB29K
11840 @c OBSOLETE board) and a serial port on the Unix system. In the following, we
11841 @c OBSOLETE assume you've hooked the cable between the PC's @file{COM1} port and
11842 @c OBSOLETE @file{/dev/ttya} on the Unix system.
11844 @c OBSOLETE @node Comms (EB29K)
11845 @c OBSOLETE @subsubsection Communications setup
11847 @c OBSOLETE The next step is to set up the PC's port, by doing something like this
11848 @c OBSOLETE in DOS on the PC:
11850 @c OBSOLETE @example
11851 @c OBSOLETE C:\> MODE com1:9600,n,8,1,none
11852 @c OBSOLETE @end example
11854 @c OBSOLETE @noindent
11855 @c OBSOLETE This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11856 @c OBSOLETE bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11857 @c OBSOLETE you must match the communications parameters when establishing the Unix
11858 @c OBSOLETE end of the connection as well.
11859 @c OBSOLETE @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11860 @c OBSOLETE @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11862 @c OBSOLETE @c It's optional, but it's unwise to omit it: who knows what is the
11863 @c OBSOLETE @c default value set when the DOS machines boots? "No retry" means that
11864 @c OBSOLETE @c the DOS serial device driver won't retry the operation if it fails;
11865 @c OBSOLETE @c I understand that this is needed because the GDB serial protocol
11866 @c OBSOLETE @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11868 @c OBSOLETE To give control of the PC to the Unix side of the serial line, type
11869 @c OBSOLETE the following at the DOS console:
11871 @c OBSOLETE @example
11872 @c OBSOLETE C:\> CTTY com1
11873 @c OBSOLETE @end example
11875 @c OBSOLETE @noindent
11876 @c OBSOLETE (Later, if you wish to return control to the DOS console, you can use
11877 @c OBSOLETE the command @code{CTTY con}---but you must send it over the device that
11878 @c OBSOLETE had control, in our example over the @file{COM1} serial line.)
11880 @c OBSOLETE From the Unix host, use a communications program such as @code{tip} or
11881 @c OBSOLETE @code{cu} to communicate with the PC; for example,
11883 @c OBSOLETE @example
11884 @c OBSOLETE cu -s 9600 -l /dev/ttya
11885 @c OBSOLETE @end example
11887 @c OBSOLETE @noindent
11888 @c OBSOLETE The @code{cu} options shown specify, respectively, the linespeed and the
11889 @c OBSOLETE serial port to use. If you use @code{tip} instead, your command line
11890 @c OBSOLETE may look something like the following:
11892 @c OBSOLETE @example
11893 @c OBSOLETE tip -9600 /dev/ttya
11894 @c OBSOLETE @end example
11896 @c OBSOLETE @noindent
11897 @c OBSOLETE Your system may require a different name where we show
11898 @c OBSOLETE @file{/dev/ttya} as the argument to @code{tip}. The communications
11899 @c OBSOLETE parameters, including which port to use, are associated with the
11900 @c OBSOLETE @code{tip} argument in the ``remote'' descriptions file---normally the
11901 @c OBSOLETE system table @file{/etc/remote}.
11902 @c OBSOLETE @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11903 @c OBSOLETE @c the DOS side's comms setup? cu can support -o (odd
11904 @c OBSOLETE @c parity), -e (even parity)---apparently no settings for no parity or
11905 @c OBSOLETE @c for character size. Taken from stty maybe...? John points out tip
11906 @c OBSOLETE @c can set these as internal variables, eg ~s parity=none; man stty
11907 @c OBSOLETE @c suggests that it *might* work to stty these options with stdin or
11908 @c OBSOLETE @c stdout redirected... ---doc@cygnus.com, 25feb91
11910 @c OBSOLETE @c There's nothing to be done for the "none" part of the DOS MODE
11911 @c OBSOLETE @c command. The rest of the parameters should be matched by the
11912 @c OBSOLETE @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11914 @c OBSOLETE @kindex EBMON
11915 @c OBSOLETE Using the @code{tip} or @code{cu} connection, change the DOS working
11916 @c OBSOLETE directory to the directory containing a copy of your 29K program, then
11917 @c OBSOLETE start the PC program @code{EBMON} (an EB29K control program supplied
11918 @c OBSOLETE with your board by AMD). You should see an initial display from
11919 @c OBSOLETE @code{EBMON} similar to the one that follows, ending with the
11920 @c OBSOLETE @code{EBMON} prompt @samp{#}---
11922 @c OBSOLETE @example
11923 @c OBSOLETE C:\> G:
11925 @c OBSOLETE G:\> CD \usr\joe\work29k
11927 @c OBSOLETE G:\USR\JOE\WORK29K> EBMON
11928 @c OBSOLETE Am29000 PC Coprocessor Board Monitor, version 3.0-18
11929 @c OBSOLETE Copyright 1990 Advanced Micro Devices, Inc.
11930 @c OBSOLETE Written by Gibbons and Associates, Inc.
11932 @c OBSOLETE Enter '?' or 'H' for help
11934 @c OBSOLETE PC Coprocessor Type = EB29K
11935 @c OBSOLETE I/O Base = 0x208
11936 @c OBSOLETE Memory Base = 0xd0000
11938 @c OBSOLETE Data Memory Size = 2048KB
11939 @c OBSOLETE Available I-RAM Range = 0x8000 to 0x1fffff
11940 @c OBSOLETE Available D-RAM Range = 0x80002000 to 0x801fffff
11942 @c OBSOLETE PageSize = 0x400
11943 @c OBSOLETE Register Stack Size = 0x800
11944 @c OBSOLETE Memory Stack Size = 0x1800
11946 @c OBSOLETE CPU PRL = 0x3
11947 @c OBSOLETE Am29027 Available = No
11948 @c OBSOLETE Byte Write Available = Yes
11951 @c OBSOLETE @end example
11953 @c OBSOLETE Then exit the @code{cu} or @code{tip} program (done in the example by
11954 @c OBSOLETE typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11955 @c OBSOLETE running, ready for @value{GDBN} to take over.
11957 @c OBSOLETE For this example, we've assumed what is probably the most convenient
11958 @c OBSOLETE way to make sure the same 29K program is on both the PC and the Unix
11959 @c OBSOLETE system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11960 @c OBSOLETE PC as a file system on the Unix host. If you do not have PC/NFS or
11961 @c OBSOLETE something similar connecting the two systems, you must arrange some
11962 @c OBSOLETE other way---perhaps floppy-disk transfer---of getting the 29K program
11963 @c OBSOLETE from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11964 @c OBSOLETE serial line.
11966 @c OBSOLETE @node gdb-EB29K
11967 @c OBSOLETE @subsubsection EB29K cross-debugging
11969 @c OBSOLETE Finally, @code{cd} to the directory containing an image of your 29K
11970 @c OBSOLETE program on the Unix system, and start @value{GDBN}---specifying as argument the
11971 @c OBSOLETE name of your 29K program:
11973 @c OBSOLETE @example
11974 @c OBSOLETE cd /usr/joe/work29k
11975 @c OBSOLETE @value{GDBP} myfoo
11976 @c OBSOLETE @end example
11978 @c OBSOLETE @need 500
11979 @c OBSOLETE Now you can use the @code{target} command:
11981 @c OBSOLETE @example
11982 @c OBSOLETE target amd-eb /dev/ttya 9600 MYFOO
11983 @c OBSOLETE @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11984 @c OBSOLETE @c emphasize that this is the name as seen by DOS (since I think DOS is
11985 @c OBSOLETE @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11986 @c OBSOLETE @end example
11988 @c OBSOLETE @noindent
11989 @c OBSOLETE In this example, we've assumed your program is in a file called
11990 @c OBSOLETE @file{myfoo}. Note that the filename given as the last argument to
11991 @c OBSOLETE @code{target amd-eb} should be the name of the program as it appears to DOS.
11992 @c OBSOLETE In our example this is simply @code{MYFOO}, but in general it can include
11993 @c OBSOLETE a DOS path, and depending on your transfer mechanism may not resemble
11994 @c OBSOLETE the name on the Unix side.
11996 @c OBSOLETE At this point, you can set any breakpoints you wish; when you are ready
11997 @c OBSOLETE to see your program run on the 29K board, use the @value{GDBN} command
11998 @c OBSOLETE @code{run}.
12000 @c OBSOLETE To stop debugging the remote program, use the @value{GDBN} @code{detach}
12001 @c OBSOLETE command.
12003 @c OBSOLETE To return control of the PC to its console, use @code{tip} or @code{cu}
12004 @c OBSOLETE once again, after your @value{GDBN} session has concluded, to attach to
12005 @c OBSOLETE @code{EBMON}. You can then type the command @code{q} to shut down
12006 @c OBSOLETE @code{EBMON}, returning control to the DOS command-line interpreter.
12007 @c OBSOLETE Type @kbd{CTTY con} to return command input to the main DOS console,
12008 @c OBSOLETE and type @kbd{~.} to leave @code{tip} or @code{cu}.
12010 @c OBSOLETE @node Remote Log
12011 @c OBSOLETE @subsubsection Remote log
12012 @c OBSOLETE @cindex @file{eb.log}, a log file for EB29K
12013 @c OBSOLETE @cindex log file for EB29K
12015 @c OBSOLETE The @code{target amd-eb} command creates a file @file{eb.log} in the
12016 @c OBSOLETE current working directory, to help debug problems with the connection.
12017 @c OBSOLETE @file{eb.log} records all the output from @code{EBMON}, including echoes
12018 @c OBSOLETE of the commands sent to it. Running @samp{tail -f} on this file in
12019 @c OBSOLETE another window often helps to understand trouble with @code{EBMON}, or
12020 @c OBSOLETE unexpected events on the PC side of the connection.
12028 @item target rdi @var{dev}
12029 ARM Angel monitor, via RDI library interface to ADP protocol. You may
12030 use this target to communicate with both boards running the Angel
12031 monitor, or with the EmbeddedICE JTAG debug device.
12034 @item target rdp @var{dev}
12040 @subsection Hitachi H8/300
12044 @kindex target hms@r{, with H8/300}
12045 @item target hms @var{dev}
12046 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
12047 Use special commands @code{device} and @code{speed} to control the serial
12048 line and the communications speed used.
12050 @kindex target e7000@r{, with H8/300}
12051 @item target e7000 @var{dev}
12052 E7000 emulator for Hitachi H8 and SH.
12054 @kindex target sh3@r{, with H8/300}
12055 @kindex target sh3e@r{, with H8/300}
12056 @item target sh3 @var{dev}
12057 @itemx target sh3e @var{dev}
12058 Hitachi SH-3 and SH-3E target systems.
12062 @cindex download to H8/300 or H8/500
12063 @cindex H8/300 or H8/500 download
12064 @cindex download to Hitachi SH
12065 @cindex Hitachi SH download
12066 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
12067 board, the @code{load} command downloads your program to the Hitachi
12068 board and also opens it as the current executable target for
12069 @value{GDBN} on your host (like the @code{file} command).
12071 @value{GDBN} needs to know these things to talk to your
12072 Hitachi SH, H8/300, or H8/500:
12076 that you want to use @samp{target hms}, the remote debugging interface
12077 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
12078 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
12079 the default when @value{GDBN} is configured specifically for the Hitachi SH,
12080 H8/300, or H8/500.)
12083 what serial device connects your host to your Hitachi board (the first
12084 serial device available on your host is the default).
12087 what speed to use over the serial device.
12091 * Hitachi Boards:: Connecting to Hitachi boards.
12092 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
12093 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
12096 @node Hitachi Boards
12097 @subsubsection Connecting to Hitachi boards
12099 @c only for Unix hosts
12101 @cindex serial device, Hitachi micros
12102 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
12103 need to explicitly set the serial device. The default @var{port} is the
12104 first available port on your host. This is only necessary on Unix
12105 hosts, where it is typically something like @file{/dev/ttya}.
12108 @cindex serial line speed, Hitachi micros
12109 @code{@value{GDBN}} has another special command to set the communications
12110 speed: @samp{speed @var{bps}}. This command also is only used from Unix
12111 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
12112 the DOS @code{mode} command (for instance,
12113 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
12115 The @samp{device} and @samp{speed} commands are available only when you
12116 use a Unix host to debug your Hitachi microprocessor programs. If you
12118 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
12119 called @code{asynctsr} to communicate with the development board
12120 through a PC serial port. You must also use the DOS @code{mode} command
12121 to set up the serial port on the DOS side.
12123 The following sample session illustrates the steps needed to start a
12124 program under @value{GDBN} control on an H8/300. The example uses a
12125 sample H8/300 program called @file{t.x}. The procedure is the same for
12126 the Hitachi SH and the H8/500.
12128 First hook up your development board. In this example, we use a
12129 board attached to serial port @code{COM2}; if you use a different serial
12130 port, substitute its name in the argument of the @code{mode} command.
12131 When you call @code{asynctsr}, the auxiliary comms program used by the
12132 debugger, you give it just the numeric part of the serial port's name;
12133 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
12137 C:\H8300\TEST> asynctsr 2
12138 C:\H8300\TEST> mode com2:9600,n,8,1,p
12140 Resident portion of MODE loaded
12142 COM2: 9600, n, 8, 1, p
12147 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
12148 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
12149 disable it, or even boot without it, to use @code{asynctsr} to control
12150 your development board.
12153 @kindex target hms@r{, and serial protocol}
12154 Now that serial communications are set up, and the development board is
12155 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
12156 the name of your program as the argument. @code{@value{GDBN}} prompts
12157 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
12158 commands to begin your debugging session: @samp{target hms} to specify
12159 cross-debugging to the Hitachi board, and the @code{load} command to
12160 download your program to the board. @code{load} displays the names of
12161 the program's sections, and a @samp{*} for each 2K of data downloaded.
12162 (If you want to refresh @value{GDBN} data on symbols or on the
12163 executable file without downloading, use the @value{GDBN} commands
12164 @code{file} or @code{symbol-file}. These commands, and @code{load}
12165 itself, are described in @ref{Files,,Commands to specify files}.)
12168 (eg-C:\H8300\TEST) @value{GDBP} t.x
12169 @value{GDBN} is free software and you are welcome to distribute copies
12170 of it under certain conditions; type "show copying" to see
12172 There is absolutely no warranty for @value{GDBN}; type "show warranty"
12174 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
12175 (@value{GDBP}) target hms
12176 Connected to remote H8/300 HMS system.
12177 (@value{GDBP}) load t.x
12178 .text : 0x8000 .. 0xabde ***********
12179 .data : 0xabde .. 0xad30 *
12180 .stack : 0xf000 .. 0xf014 *
12183 At this point, you're ready to run or debug your program. From here on,
12184 you can use all the usual @value{GDBN} commands. The @code{break} command
12185 sets breakpoints; the @code{run} command starts your program;
12186 @code{print} or @code{x} display data; the @code{continue} command
12187 resumes execution after stopping at a breakpoint. You can use the
12188 @code{help} command at any time to find out more about @value{GDBN} commands.
12190 Remember, however, that @emph{operating system} facilities aren't
12191 available on your development board; for example, if your program hangs,
12192 you can't send an interrupt---but you can press the @sc{reset} switch!
12194 Use the @sc{reset} button on the development board
12197 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
12198 no way to pass an interrupt signal to the development board); and
12201 to return to the @value{GDBN} command prompt after your program finishes
12202 normally. The communications protocol provides no other way for @value{GDBN}
12203 to detect program completion.
12206 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
12207 development board as a ``normal exit'' of your program.
12210 @subsubsection Using the E7000 in-circuit emulator
12212 @kindex target e7000@r{, with Hitachi ICE}
12213 You can use the E7000 in-circuit emulator to develop code for either the
12214 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
12215 e7000} command to connect @value{GDBN} to your E7000:
12218 @item target e7000 @var{port} @var{speed}
12219 Use this form if your E7000 is connected to a serial port. The
12220 @var{port} argument identifies what serial port to use (for example,
12221 @samp{com2}). The third argument is the line speed in bits per second
12222 (for example, @samp{9600}).
12224 @item target e7000 @var{hostname}
12225 If your E7000 is installed as a host on a TCP/IP network, you can just
12226 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
12229 @node Hitachi Special
12230 @subsubsection Special @value{GDBN} commands for Hitachi micros
12232 Some @value{GDBN} commands are available only for the H8/300:
12236 @kindex set machine
12237 @kindex show machine
12238 @item set machine h8300
12239 @itemx set machine h8300h
12240 Condition @value{GDBN} for one of the two variants of the H8/300
12241 architecture with @samp{set machine}. You can use @samp{show machine}
12242 to check which variant is currently in effect.
12251 @kindex set memory @var{mod}
12252 @cindex memory models, H8/500
12253 @item set memory @var{mod}
12255 Specify which H8/500 memory model (@var{mod}) you are using with
12256 @samp{set memory}; check which memory model is in effect with @samp{show
12257 memory}. The accepted values for @var{mod} are @code{small},
12258 @code{big}, @code{medium}, and @code{compact}.
12263 @subsection Intel i960
12267 @kindex target mon960
12268 @item target mon960 @var{dev}
12269 MON960 monitor for Intel i960.
12271 @kindex target nindy
12272 @item target nindy @var{devicename}
12273 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
12274 the name of the serial device to use for the connection, e.g.
12281 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
12282 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
12283 tell @value{GDBN} how to connect to the 960 in several ways:
12287 Through command line options specifying serial port, version of the
12288 Nindy protocol, and communications speed;
12291 By responding to a prompt on startup;
12294 By using the @code{target} command at any point during your @value{GDBN}
12295 session. @xref{Target Commands, ,Commands for managing targets}.
12299 @cindex download to Nindy-960
12300 With the Nindy interface to an Intel 960 board, @code{load}
12301 downloads @var{filename} to the 960 as well as adding its symbols in
12305 * Nindy Startup:: Startup with Nindy
12306 * Nindy Options:: Options for Nindy
12307 * Nindy Reset:: Nindy reset command
12310 @node Nindy Startup
12311 @subsubsection Startup with Nindy
12313 If you simply start @code{@value{GDBP}} without using any command-line
12314 options, you are prompted for what serial port to use, @emph{before} you
12315 reach the ordinary @value{GDBN} prompt:
12318 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
12322 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
12323 identifies the serial port you want to use. You can, if you choose,
12324 simply start up with no Nindy connection by responding to the prompt
12325 with an empty line. If you do this and later wish to attach to Nindy,
12326 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
12328 @node Nindy Options
12329 @subsubsection Options for Nindy
12331 These are the startup options for beginning your @value{GDBN} session with a
12332 Nindy-960 board attached:
12335 @item -r @var{port}
12336 Specify the serial port name of a serial interface to be used to connect
12337 to the target system. This option is only available when @value{GDBN} is
12338 configured for the Intel 960 target architecture. You may specify
12339 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
12340 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
12341 suffix for a specific @code{tty} (e.g. @samp{-r a}).
12344 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
12345 the ``old'' Nindy monitor protocol to connect to the target system.
12346 This option is only available when @value{GDBN} is configured for the Intel 960
12347 target architecture.
12350 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
12351 connect to a target system that expects the newer protocol, the connection
12352 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
12353 attempts to reconnect at several different line speeds. You can abort
12354 this process with an interrupt.
12358 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
12359 system, in an attempt to reset it, before connecting to a Nindy target.
12362 @emph{Warning:} Many target systems do not have the hardware that this
12363 requires; it only works with a few boards.
12367 The standard @samp{-b} option controls the line speed used on the serial
12372 @subsubsection Nindy reset command
12377 For a Nindy target, this command sends a ``break'' to the remote target
12378 system; this is only useful if the target has been equipped with a
12379 circuit to perform a hard reset (or some other interesting action) when
12380 a break is detected.
12385 @subsection Mitsubishi M32R/D
12389 @kindex target m32r
12390 @item target m32r @var{dev}
12391 Mitsubishi M32R/D ROM monitor.
12398 The Motorola m68k configuration includes ColdFire support, and
12399 target command for the following ROM monitors.
12403 @kindex target abug
12404 @item target abug @var{dev}
12405 ABug ROM monitor for M68K.
12407 @kindex target cpu32bug
12408 @item target cpu32bug @var{dev}
12409 CPU32BUG monitor, running on a CPU32 (M68K) board.
12411 @kindex target dbug
12412 @item target dbug @var{dev}
12413 dBUG ROM monitor for Motorola ColdFire.
12416 @item target est @var{dev}
12417 EST-300 ICE monitor, running on a CPU32 (M68K) board.
12419 @kindex target rom68k
12420 @item target rom68k @var{dev}
12421 ROM 68K monitor, running on an M68K IDP board.
12425 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
12426 instead have only a single special target command:
12430 @kindex target es1800
12431 @item target es1800 @var{dev}
12432 ES-1800 emulator for M68K.
12440 @kindex target rombug
12441 @item target rombug @var{dev}
12442 ROMBUG ROM monitor for OS/9000.
12452 @item target bug @var{dev}
12453 BUG monitor, running on a MVME187 (m88k) board.
12457 @node MIPS Embedded
12458 @subsection MIPS Embedded
12460 @cindex MIPS boards
12461 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
12462 MIPS board attached to a serial line. This is available when
12463 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
12466 Use these @value{GDBN} commands to specify the connection to your target board:
12469 @item target mips @var{port}
12470 @kindex target mips @var{port}
12471 To run a program on the board, start up @code{@value{GDBP}} with the
12472 name of your program as the argument. To connect to the board, use the
12473 command @samp{target mips @var{port}}, where @var{port} is the name of
12474 the serial port connected to the board. If the program has not already
12475 been downloaded to the board, you may use the @code{load} command to
12476 download it. You can then use all the usual @value{GDBN} commands.
12478 For example, this sequence connects to the target board through a serial
12479 port, and loads and runs a program called @var{prog} through the
12483 host$ @value{GDBP} @var{prog}
12484 @value{GDBN} is free software and @dots{}
12485 (@value{GDBP}) target mips /dev/ttyb
12486 (@value{GDBP}) load @var{prog}
12490 @item target mips @var{hostname}:@var{portnumber}
12491 On some @value{GDBN} host configurations, you can specify a TCP
12492 connection (for instance, to a serial line managed by a terminal
12493 concentrator) instead of a serial port, using the syntax
12494 @samp{@var{hostname}:@var{portnumber}}.
12496 @item target pmon @var{port}
12497 @kindex target pmon @var{port}
12500 @item target ddb @var{port}
12501 @kindex target ddb @var{port}
12502 NEC's DDB variant of PMON for Vr4300.
12504 @item target lsi @var{port}
12505 @kindex target lsi @var{port}
12506 LSI variant of PMON.
12508 @kindex target r3900
12509 @item target r3900 @var{dev}
12510 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
12512 @kindex target array
12513 @item target array @var{dev}
12514 Array Tech LSI33K RAID controller board.
12520 @value{GDBN} also supports these special commands for MIPS targets:
12523 @item set processor @var{args}
12524 @itemx show processor
12525 @kindex set processor @var{args}
12526 @kindex show processor
12527 Use the @code{set processor} command to set the type of MIPS
12528 processor when you want to access processor-type-specific registers.
12529 For example, @code{set processor @var{r3041}} tells @value{GDBN}
12530 to use the CPU registers appropriate for the 3041 chip.
12531 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
12532 is using. Use the @code{info reg} command to see what registers
12533 @value{GDBN} is using.
12535 @item set mipsfpu double
12536 @itemx set mipsfpu single
12537 @itemx set mipsfpu none
12538 @itemx show mipsfpu
12539 @kindex set mipsfpu
12540 @kindex show mipsfpu
12541 @cindex MIPS remote floating point
12542 @cindex floating point, MIPS remote
12543 If your target board does not support the MIPS floating point
12544 coprocessor, you should use the command @samp{set mipsfpu none} (if you
12545 need this, you may wish to put the command in your @value{GDBN} init
12546 file). This tells @value{GDBN} how to find the return value of
12547 functions which return floating point values. It also allows
12548 @value{GDBN} to avoid saving the floating point registers when calling
12549 functions on the board. If you are using a floating point coprocessor
12550 with only single precision floating point support, as on the @sc{r4650}
12551 processor, use the command @samp{set mipsfpu single}. The default
12552 double precision floating point coprocessor may be selected using
12553 @samp{set mipsfpu double}.
12555 In previous versions the only choices were double precision or no
12556 floating point, so @samp{set mipsfpu on} will select double precision
12557 and @samp{set mipsfpu off} will select no floating point.
12559 As usual, you can inquire about the @code{mipsfpu} variable with
12560 @samp{show mipsfpu}.
12562 @item set remotedebug @var{n}
12563 @itemx show remotedebug
12564 @kindex set remotedebug@r{, MIPS protocol}
12565 @kindex show remotedebug@r{, MIPS protocol}
12566 @cindex @code{remotedebug}, MIPS protocol
12567 @cindex MIPS @code{remotedebug} protocol
12568 @c FIXME! For this to be useful, you must know something about the MIPS
12569 @c FIXME...protocol. Where is it described?
12570 You can see some debugging information about communications with the board
12571 by setting the @code{remotedebug} variable. If you set it to @code{1} using
12572 @samp{set remotedebug 1}, every packet is displayed. If you set it
12573 to @code{2}, every character is displayed. You can check the current value
12574 at any time with the command @samp{show remotedebug}.
12576 @item set timeout @var{seconds}
12577 @itemx set retransmit-timeout @var{seconds}
12578 @itemx show timeout
12579 @itemx show retransmit-timeout
12580 @cindex @code{timeout}, MIPS protocol
12581 @cindex @code{retransmit-timeout}, MIPS protocol
12582 @kindex set timeout
12583 @kindex show timeout
12584 @kindex set retransmit-timeout
12585 @kindex show retransmit-timeout
12586 You can control the timeout used while waiting for a packet, in the MIPS
12587 remote protocol, with the @code{set timeout @var{seconds}} command. The
12588 default is 5 seconds. Similarly, you can control the timeout used while
12589 waiting for an acknowledgement of a packet with the @code{set
12590 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
12591 You can inspect both values with @code{show timeout} and @code{show
12592 retransmit-timeout}. (These commands are @emph{only} available when
12593 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
12595 The timeout set by @code{set timeout} does not apply when @value{GDBN}
12596 is waiting for your program to stop. In that case, @value{GDBN} waits
12597 forever because it has no way of knowing how long the program is going
12598 to run before stopping.
12602 @subsection PowerPC
12606 @kindex target dink32
12607 @item target dink32 @var{dev}
12608 DINK32 ROM monitor.
12610 @kindex target ppcbug
12611 @item target ppcbug @var{dev}
12612 @kindex target ppcbug1
12613 @item target ppcbug1 @var{dev}
12614 PPCBUG ROM monitor for PowerPC.
12617 @item target sds @var{dev}
12618 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
12623 @subsection HP PA Embedded
12627 @kindex target op50n
12628 @item target op50n @var{dev}
12629 OP50N monitor, running on an OKI HPPA board.
12631 @kindex target w89k
12632 @item target w89k @var{dev}
12633 W89K monitor, running on a Winbond HPPA board.
12638 @subsection Hitachi SH
12642 @kindex target hms@r{, with Hitachi SH}
12643 @item target hms @var{dev}
12644 A Hitachi SH board attached via serial line to your host. Use special
12645 commands @code{device} and @code{speed} to control the serial line and
12646 the communications speed used.
12648 @kindex target e7000@r{, with Hitachi SH}
12649 @item target e7000 @var{dev}
12650 E7000 emulator for Hitachi SH.
12652 @kindex target sh3@r{, with SH}
12653 @kindex target sh3e@r{, with SH}
12654 @item target sh3 @var{dev}
12655 @item target sh3e @var{dev}
12656 Hitachi SH-3 and SH-3E target systems.
12661 @subsection Tsqware Sparclet
12665 @value{GDBN} enables developers to debug tasks running on
12666 Sparclet targets from a Unix host.
12667 @value{GDBN} uses code that runs on
12668 both the Unix host and on the Sparclet target. The program
12669 @code{@value{GDBP}} is installed and executed on the Unix host.
12672 @item remotetimeout @var{args}
12673 @kindex remotetimeout
12674 @value{GDBN} supports the option @code{remotetimeout}.
12675 This option is set by the user, and @var{args} represents the number of
12676 seconds @value{GDBN} waits for responses.
12679 @cindex compiling, on Sparclet
12680 When compiling for debugging, include the options @samp{-g} to get debug
12681 information and @samp{-Ttext} to relocate the program to where you wish to
12682 load it on the target. You may also want to add the options @samp{-n} or
12683 @samp{-N} in order to reduce the size of the sections. Example:
12686 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12689 You can use @code{objdump} to verify that the addresses are what you intended:
12692 sparclet-aout-objdump --headers --syms prog
12695 @cindex running, on Sparclet
12697 your Unix execution search path to find @value{GDBN}, you are ready to
12698 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12699 (or @code{sparclet-aout-gdb}, depending on your installation).
12701 @value{GDBN} comes up showing the prompt:
12708 * Sparclet File:: Setting the file to debug
12709 * Sparclet Connection:: Connecting to Sparclet
12710 * Sparclet Download:: Sparclet download
12711 * Sparclet Execution:: Running and debugging
12714 @node Sparclet File
12715 @subsubsection Setting file to debug
12717 The @value{GDBN} command @code{file} lets you choose with program to debug.
12720 (gdbslet) file prog
12724 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12725 @value{GDBN} locates
12726 the file by searching the directories listed in the command search
12728 If the file was compiled with debug information (option "-g"), source
12729 files will be searched as well.
12730 @value{GDBN} locates
12731 the source files by searching the directories listed in the directory search
12732 path (@pxref{Environment, ,Your program's environment}).
12734 to find a file, it displays a message such as:
12737 prog: No such file or directory.
12740 When this happens, add the appropriate directories to the search paths with
12741 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12742 @code{target} command again.
12744 @node Sparclet Connection
12745 @subsubsection Connecting to Sparclet
12747 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12748 To connect to a target on serial port ``@code{ttya}'', type:
12751 (gdbslet) target sparclet /dev/ttya
12752 Remote target sparclet connected to /dev/ttya
12753 main () at ../prog.c:3
12757 @value{GDBN} displays messages like these:
12763 @node Sparclet Download
12764 @subsubsection Sparclet download
12766 @cindex download to Sparclet
12767 Once connected to the Sparclet target,
12768 you can use the @value{GDBN}
12769 @code{load} command to download the file from the host to the target.
12770 The file name and load offset should be given as arguments to the @code{load}
12772 Since the file format is aout, the program must be loaded to the starting
12773 address. You can use @code{objdump} to find out what this value is. The load
12774 offset is an offset which is added to the VMA (virtual memory address)
12775 of each of the file's sections.
12776 For instance, if the program
12777 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12778 and bss at 0x12010170, in @value{GDBN}, type:
12781 (gdbslet) load prog 0x12010000
12782 Loading section .text, size 0xdb0 vma 0x12010000
12785 If the code is loaded at a different address then what the program was linked
12786 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12787 to tell @value{GDBN} where to map the symbol table.
12789 @node Sparclet Execution
12790 @subsubsection Running and debugging
12792 @cindex running and debugging Sparclet programs
12793 You can now begin debugging the task using @value{GDBN}'s execution control
12794 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12795 manual for the list of commands.
12799 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12801 Starting program: prog
12802 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12803 3 char *symarg = 0;
12805 4 char *execarg = "hello!";
12810 @subsection Fujitsu Sparclite
12814 @kindex target sparclite
12815 @item target sparclite @var{dev}
12816 Fujitsu sparclite boards, used only for the purpose of loading.
12817 You must use an additional command to debug the program.
12818 For example: target remote @var{dev} using @value{GDBN} standard
12824 @subsection Tandem ST2000
12826 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12829 To connect your ST2000 to the host system, see the manufacturer's
12830 manual. Once the ST2000 is physically attached, you can run:
12833 target st2000 @var{dev} @var{speed}
12837 to establish it as your debugging environment. @var{dev} is normally
12838 the name of a serial device, such as @file{/dev/ttya}, connected to the
12839 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12840 connection (for example, to a serial line attached via a terminal
12841 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12843 The @code{load} and @code{attach} commands are @emph{not} defined for
12844 this target; you must load your program into the ST2000 as you normally
12845 would for standalone operation. @value{GDBN} reads debugging information
12846 (such as symbols) from a separate, debugging version of the program
12847 available on your host computer.
12848 @c FIXME!! This is terribly vague; what little content is here is
12849 @c basically hearsay.
12851 @cindex ST2000 auxiliary commands
12852 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12856 @item st2000 @var{command}
12857 @kindex st2000 @var{cmd}
12858 @cindex STDBUG commands (ST2000)
12859 @cindex commands to STDBUG (ST2000)
12860 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12861 manual for available commands.
12864 @cindex connect (to STDBUG)
12865 Connect the controlling terminal to the STDBUG command monitor. When
12866 you are done interacting with STDBUG, typing either of two character
12867 sequences gets you back to the @value{GDBN} command prompt:
12868 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12869 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12873 @subsection Zilog Z8000
12876 @cindex simulator, Z8000
12877 @cindex Zilog Z8000 simulator
12879 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12882 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12883 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12884 segmented variant). The simulator recognizes which architecture is
12885 appropriate by inspecting the object code.
12888 @item target sim @var{args}
12890 @kindex target sim@r{, with Z8000}
12891 Debug programs on a simulated CPU. If the simulator supports setup
12892 options, specify them via @var{args}.
12896 After specifying this target, you can debug programs for the simulated
12897 CPU in the same style as programs for your host computer; use the
12898 @code{file} command to load a new program image, the @code{run} command
12899 to run your program, and so on.
12901 As well as making available all the usual machine registers
12902 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12903 additional items of information as specially named registers:
12908 Counts clock-ticks in the simulator.
12911 Counts instructions run in the simulator.
12914 Execution time in 60ths of a second.
12918 You can refer to these values in @value{GDBN} expressions with the usual
12919 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12920 conditional breakpoint that suspends only after at least 5000
12921 simulated clock ticks.
12923 @node Architectures
12924 @section Architectures
12926 This section describes characteristics of architectures that affect
12927 all uses of @value{GDBN} with the architecture, both native and cross.
12940 @kindex set rstack_high_address
12941 @cindex AMD 29K register stack
12942 @cindex register stack, AMD29K
12943 @item set rstack_high_address @var{address}
12944 On AMD 29000 family processors, registers are saved in a separate
12945 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12946 extent of this stack. Normally, @value{GDBN} just assumes that the
12947 stack is ``large enough''. This may result in @value{GDBN} referencing
12948 memory locations that do not exist. If necessary, you can get around
12949 this problem by specifying the ending address of the register stack with
12950 the @code{set rstack_high_address} command. The argument should be an
12951 address, which you probably want to precede with @samp{0x} to specify in
12954 @kindex show rstack_high_address
12955 @item show rstack_high_address
12956 Display the current limit of the register stack, on AMD 29000 family
12964 See the following section.
12969 @cindex stack on Alpha
12970 @cindex stack on MIPS
12971 @cindex Alpha stack
12973 Alpha- and MIPS-based computers use an unusual stack frame, which
12974 sometimes requires @value{GDBN} to search backward in the object code to
12975 find the beginning of a function.
12977 @cindex response time, MIPS debugging
12978 To improve response time (especially for embedded applications, where
12979 @value{GDBN} may be restricted to a slow serial line for this search)
12980 you may want to limit the size of this search, using one of these
12984 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12985 @item set heuristic-fence-post @var{limit}
12986 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12987 search for the beginning of a function. A value of @var{0} (the
12988 default) means there is no limit. However, except for @var{0}, the
12989 larger the limit the more bytes @code{heuristic-fence-post} must search
12990 and therefore the longer it takes to run.
12992 @item show heuristic-fence-post
12993 Display the current limit.
12997 These commands are available @emph{only} when @value{GDBN} is configured
12998 for debugging programs on Alpha or MIPS processors.
13001 @node Controlling GDB
13002 @chapter Controlling @value{GDBN}
13004 You can alter the way @value{GDBN} interacts with you by using the
13005 @code{set} command. For commands controlling how @value{GDBN} displays
13006 data, see @ref{Print Settings, ,Print settings}. Other settings are
13011 * Editing:: Command editing
13012 * History:: Command history
13013 * Screen Size:: Screen size
13014 * Numbers:: Numbers
13015 * Messages/Warnings:: Optional warnings and messages
13016 * Debugging Output:: Optional messages about internal happenings
13024 @value{GDBN} indicates its readiness to read a command by printing a string
13025 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
13026 can change the prompt string with the @code{set prompt} command. For
13027 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
13028 the prompt in one of the @value{GDBN} sessions so that you can always tell
13029 which one you are talking to.
13031 @emph{Note:} @code{set prompt} does not add a space for you after the
13032 prompt you set. This allows you to set a prompt which ends in a space
13033 or a prompt that does not.
13037 @item set prompt @var{newprompt}
13038 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
13040 @kindex show prompt
13042 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
13046 @section Command editing
13048 @cindex command line editing
13050 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
13051 @sc{gnu} library provides consistent behavior for programs which provide a
13052 command line interface to the user. Advantages are @sc{gnu} Emacs-style
13053 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
13054 substitution, and a storage and recall of command history across
13055 debugging sessions.
13057 You may control the behavior of command line editing in @value{GDBN} with the
13058 command @code{set}.
13061 @kindex set editing
13064 @itemx set editing on
13065 Enable command line editing (enabled by default).
13067 @item set editing off
13068 Disable command line editing.
13070 @kindex show editing
13072 Show whether command line editing is enabled.
13076 @section Command history
13078 @value{GDBN} can keep track of the commands you type during your
13079 debugging sessions, so that you can be certain of precisely what
13080 happened. Use these commands to manage the @value{GDBN} command
13084 @cindex history substitution
13085 @cindex history file
13086 @kindex set history filename
13087 @kindex GDBHISTFILE
13088 @item set history filename @var{fname}
13089 Set the name of the @value{GDBN} command history file to @var{fname}.
13090 This is the file where @value{GDBN} reads an initial command history
13091 list, and where it writes the command history from this session when it
13092 exits. You can access this list through history expansion or through
13093 the history command editing characters listed below. This file defaults
13094 to the value of the environment variable @code{GDBHISTFILE}, or to
13095 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
13098 @cindex history save
13099 @kindex set history save
13100 @item set history save
13101 @itemx set history save on
13102 Record command history in a file, whose name may be specified with the
13103 @code{set history filename} command. By default, this option is disabled.
13105 @item set history save off
13106 Stop recording command history in a file.
13108 @cindex history size
13109 @kindex set history size
13110 @item set history size @var{size}
13111 Set the number of commands which @value{GDBN} keeps in its history list.
13112 This defaults to the value of the environment variable
13113 @code{HISTSIZE}, or to 256 if this variable is not set.
13116 @cindex history expansion
13117 History expansion assigns special meaning to the character @kbd{!}.
13118 @ifset have-readline-appendices
13119 @xref{Event Designators}.
13122 Since @kbd{!} is also the logical not operator in C, history expansion
13123 is off by default. If you decide to enable history expansion with the
13124 @code{set history expansion on} command, you may sometimes need to
13125 follow @kbd{!} (when it is used as logical not, in an expression) with
13126 a space or a tab to prevent it from being expanded. The readline
13127 history facilities do not attempt substitution on the strings
13128 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
13130 The commands to control history expansion are:
13133 @kindex set history expansion
13134 @item set history expansion on
13135 @itemx set history expansion
13136 Enable history expansion. History expansion is off by default.
13138 @item set history expansion off
13139 Disable history expansion.
13141 The readline code comes with more complete documentation of
13142 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
13143 or @code{vi} may wish to read it.
13144 @ifset have-readline-appendices
13145 @xref{Command Line Editing}.
13149 @kindex show history
13151 @itemx show history filename
13152 @itemx show history save
13153 @itemx show history size
13154 @itemx show history expansion
13155 These commands display the state of the @value{GDBN} history parameters.
13156 @code{show history} by itself displays all four states.
13162 @item show commands
13163 Display the last ten commands in the command history.
13165 @item show commands @var{n}
13166 Print ten commands centered on command number @var{n}.
13168 @item show commands +
13169 Print ten commands just after the commands last printed.
13173 @section Screen size
13174 @cindex size of screen
13175 @cindex pauses in output
13177 Certain commands to @value{GDBN} may produce large amounts of
13178 information output to the screen. To help you read all of it,
13179 @value{GDBN} pauses and asks you for input at the end of each page of
13180 output. Type @key{RET} when you want to continue the output, or @kbd{q}
13181 to discard the remaining output. Also, the screen width setting
13182 determines when to wrap lines of output. Depending on what is being
13183 printed, @value{GDBN} tries to break the line at a readable place,
13184 rather than simply letting it overflow onto the following line.
13186 Normally @value{GDBN} knows the size of the screen from the terminal
13187 driver software. For example, on Unix @value{GDBN} uses the termcap data base
13188 together with the value of the @code{TERM} environment variable and the
13189 @code{stty rows} and @code{stty cols} settings. If this is not correct,
13190 you can override it with the @code{set height} and @code{set
13197 @kindex show height
13198 @item set height @var{lpp}
13200 @itemx set width @var{cpl}
13202 These @code{set} commands specify a screen height of @var{lpp} lines and
13203 a screen width of @var{cpl} characters. The associated @code{show}
13204 commands display the current settings.
13206 If you specify a height of zero lines, @value{GDBN} does not pause during
13207 output no matter how long the output is. This is useful if output is to a
13208 file or to an editor buffer.
13210 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
13211 from wrapping its output.
13216 @cindex number representation
13217 @cindex entering numbers
13219 You can always enter numbers in octal, decimal, or hexadecimal in
13220 @value{GDBN} by the usual conventions: octal numbers begin with
13221 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
13222 begin with @samp{0x}. Numbers that begin with none of these are, by
13223 default, entered in base 10; likewise, the default display for
13224 numbers---when no particular format is specified---is base 10. You can
13225 change the default base for both input and output with the @code{set
13229 @kindex set input-radix
13230 @item set input-radix @var{base}
13231 Set the default base for numeric input. Supported choices
13232 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
13233 specified either unambiguously or using the current default radix; for
13243 sets the base to decimal. On the other hand, @samp{set radix 10}
13244 leaves the radix unchanged no matter what it was.
13246 @kindex set output-radix
13247 @item set output-radix @var{base}
13248 Set the default base for numeric display. Supported choices
13249 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
13250 specified either unambiguously or using the current default radix.
13252 @kindex show input-radix
13253 @item show input-radix
13254 Display the current default base for numeric input.
13256 @kindex show output-radix
13257 @item show output-radix
13258 Display the current default base for numeric display.
13261 @node Messages/Warnings
13262 @section Optional warnings and messages
13264 By default, @value{GDBN} is silent about its inner workings. If you are
13265 running on a slow machine, you may want to use the @code{set verbose}
13266 command. This makes @value{GDBN} tell you when it does a lengthy
13267 internal operation, so you will not think it has crashed.
13269 Currently, the messages controlled by @code{set verbose} are those
13270 which announce that the symbol table for a source file is being read;
13271 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
13274 @kindex set verbose
13275 @item set verbose on
13276 Enables @value{GDBN} output of certain informational messages.
13278 @item set verbose off
13279 Disables @value{GDBN} output of certain informational messages.
13281 @kindex show verbose
13283 Displays whether @code{set verbose} is on or off.
13286 By default, if @value{GDBN} encounters bugs in the symbol table of an
13287 object file, it is silent; but if you are debugging a compiler, you may
13288 find this information useful (@pxref{Symbol Errors, ,Errors reading
13293 @kindex set complaints
13294 @item set complaints @var{limit}
13295 Permits @value{GDBN} to output @var{limit} complaints about each type of
13296 unusual symbols before becoming silent about the problem. Set
13297 @var{limit} to zero to suppress all complaints; set it to a large number
13298 to prevent complaints from being suppressed.
13300 @kindex show complaints
13301 @item show complaints
13302 Displays how many symbol complaints @value{GDBN} is permitted to produce.
13306 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
13307 lot of stupid questions to confirm certain commands. For example, if
13308 you try to run a program which is already running:
13312 The program being debugged has been started already.
13313 Start it from the beginning? (y or n)
13316 If you are willing to unflinchingly face the consequences of your own
13317 commands, you can disable this ``feature'':
13321 @kindex set confirm
13323 @cindex confirmation
13324 @cindex stupid questions
13325 @item set confirm off
13326 Disables confirmation requests.
13328 @item set confirm on
13329 Enables confirmation requests (the default).
13331 @kindex show confirm
13333 Displays state of confirmation requests.
13337 @node Debugging Output
13338 @section Optional messages about internal happenings
13340 @kindex set debug arch
13341 @item set debug arch
13342 Turns on or off display of gdbarch debugging info. The default is off
13343 @kindex show debug arch
13344 @item show debug arch
13345 Displays the current state of displaying gdbarch debugging info.
13346 @kindex set debug event
13347 @item set debug event
13348 Turns on or off display of @value{GDBN} event debugging info. The
13350 @kindex show debug event
13351 @item show debug event
13352 Displays the current state of displaying @value{GDBN} event debugging
13354 @kindex set debug expression
13355 @item set debug expression
13356 Turns on or off display of @value{GDBN} expression debugging info. The
13358 @kindex show debug expression
13359 @item show debug expression
13360 Displays the current state of displaying @value{GDBN} expression
13362 @kindex set debug overload
13363 @item set debug overload
13364 Turns on or off display of @value{GDBN} C@t{++} overload debugging
13365 info. This includes info such as ranking of functions, etc. The default
13367 @kindex show debug overload
13368 @item show debug overload
13369 Displays the current state of displaying @value{GDBN} C@t{++} overload
13371 @kindex set debug remote
13372 @cindex packets, reporting on stdout
13373 @cindex serial connections, debugging
13374 @item set debug remote
13375 Turns on or off display of reports on all packets sent back and forth across
13376 the serial line to the remote machine. The info is printed on the
13377 @value{GDBN} standard output stream. The default is off.
13378 @kindex show debug remote
13379 @item show debug remote
13380 Displays the state of display of remote packets.
13381 @kindex set debug serial
13382 @item set debug serial
13383 Turns on or off display of @value{GDBN} serial debugging info. The
13385 @kindex show debug serial
13386 @item show debug serial
13387 Displays the current state of displaying @value{GDBN} serial debugging
13389 @kindex set debug target
13390 @item set debug target
13391 Turns on or off display of @value{GDBN} target debugging info. This info
13392 includes what is going on at the target level of GDB, as it happens. The
13394 @kindex show debug target
13395 @item show debug target
13396 Displays the current state of displaying @value{GDBN} target debugging
13398 @kindex set debug varobj
13399 @item set debug varobj
13400 Turns on or off display of @value{GDBN} variable object debugging
13401 info. The default is off.
13402 @kindex show debug varobj
13403 @item show debug varobj
13404 Displays the current state of displaying @value{GDBN} variable object
13409 @chapter Canned Sequences of Commands
13411 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
13412 command lists}), @value{GDBN} provides two ways to store sequences of
13413 commands for execution as a unit: user-defined commands and command
13417 * Define:: User-defined commands
13418 * Hooks:: User-defined command hooks
13419 * Command Files:: Command files
13420 * Output:: Commands for controlled output
13424 @section User-defined commands
13426 @cindex user-defined command
13427 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
13428 which you assign a new name as a command. This is done with the
13429 @code{define} command. User commands may accept up to 10 arguments
13430 separated by whitespace. Arguments are accessed within the user command
13431 via @var{$arg0@dots{}$arg9}. A trivial example:
13435 print $arg0 + $arg1 + $arg2
13439 To execute the command use:
13446 This defines the command @code{adder}, which prints the sum of
13447 its three arguments. Note the arguments are text substitutions, so they may
13448 reference variables, use complex expressions, or even perform inferior
13454 @item define @var{commandname}
13455 Define a command named @var{commandname}. If there is already a command
13456 by that name, you are asked to confirm that you want to redefine it.
13458 The definition of the command is made up of other @value{GDBN} command lines,
13459 which are given following the @code{define} command. The end of these
13460 commands is marked by a line containing @code{end}.
13465 Takes a single argument, which is an expression to evaluate.
13466 It is followed by a series of commands that are executed
13467 only if the expression is true (nonzero).
13468 There can then optionally be a line @code{else}, followed
13469 by a series of commands that are only executed if the expression
13470 was false. The end of the list is marked by a line containing @code{end}.
13474 The syntax is similar to @code{if}: the command takes a single argument,
13475 which is an expression to evaluate, and must be followed by the commands to
13476 execute, one per line, terminated by an @code{end}.
13477 The commands are executed repeatedly as long as the expression
13481 @item document @var{commandname}
13482 Document the user-defined command @var{commandname}, so that it can be
13483 accessed by @code{help}. The command @var{commandname} must already be
13484 defined. This command reads lines of documentation just as @code{define}
13485 reads the lines of the command definition, ending with @code{end}.
13486 After the @code{document} command is finished, @code{help} on command
13487 @var{commandname} displays the documentation you have written.
13489 You may use the @code{document} command again to change the
13490 documentation of a command. Redefining the command with @code{define}
13491 does not change the documentation.
13493 @kindex help user-defined
13494 @item help user-defined
13495 List all user-defined commands, with the first line of the documentation
13500 @itemx show user @var{commandname}
13501 Display the @value{GDBN} commands used to define @var{commandname} (but
13502 not its documentation). If no @var{commandname} is given, display the
13503 definitions for all user-defined commands.
13507 When user-defined commands are executed, the
13508 commands of the definition are not printed. An error in any command
13509 stops execution of the user-defined command.
13511 If used interactively, commands that would ask for confirmation proceed
13512 without asking when used inside a user-defined command. Many @value{GDBN}
13513 commands that normally print messages to say what they are doing omit the
13514 messages when used in a user-defined command.
13517 @section User-defined command hooks
13518 @cindex command hooks
13519 @cindex hooks, for commands
13520 @cindex hooks, pre-command
13524 You may define @dfn{hooks}, which are a special kind of user-defined
13525 command. Whenever you run the command @samp{foo}, if the user-defined
13526 command @samp{hook-foo} exists, it is executed (with no arguments)
13527 before that command.
13529 @cindex hooks, post-command
13532 A hook may also be defined which is run after the command you executed.
13533 Whenever you run the command @samp{foo}, if the user-defined command
13534 @samp{hookpost-foo} exists, it is executed (with no arguments) after
13535 that command. Post-execution hooks may exist simultaneously with
13536 pre-execution hooks, for the same command.
13538 It is valid for a hook to call the command which it hooks. If this
13539 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
13541 @c It would be nice if hookpost could be passed a parameter indicating
13542 @c if the command it hooks executed properly or not. FIXME!
13544 @kindex stop@r{, a pseudo-command}
13545 In addition, a pseudo-command, @samp{stop} exists. Defining
13546 (@samp{hook-stop}) makes the associated commands execute every time
13547 execution stops in your program: before breakpoint commands are run,
13548 displays are printed, or the stack frame is printed.
13550 For example, to ignore @code{SIGALRM} signals while
13551 single-stepping, but treat them normally during normal execution,
13556 handle SIGALRM nopass
13560 handle SIGALRM pass
13563 define hook-continue
13564 handle SIGLARM pass
13568 As a further example, to hook at the begining and end of the @code{echo}
13569 command, and to add extra text to the beginning and end of the message,
13577 define hookpost-echo
13581 (@value{GDBP}) echo Hello World
13582 <<<---Hello World--->>>
13587 You can define a hook for any single-word command in @value{GDBN}, but
13588 not for command aliases; you should define a hook for the basic command
13589 name, e.g. @code{backtrace} rather than @code{bt}.
13590 @c FIXME! So how does Joe User discover whether a command is an alias
13592 If an error occurs during the execution of your hook, execution of
13593 @value{GDBN} commands stops and @value{GDBN} issues a prompt
13594 (before the command that you actually typed had a chance to run).
13596 If you try to define a hook which does not match any known command, you
13597 get a warning from the @code{define} command.
13599 @node Command Files
13600 @section Command files
13602 @cindex command files
13603 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13604 commands. Comments (lines starting with @kbd{#}) may also be included.
13605 An empty line in a command file does nothing; it does not mean to repeat
13606 the last command, as it would from the terminal.
13609 @cindex @file{.gdbinit}
13610 @cindex @file{gdb.ini}
13611 When you start @value{GDBN}, it automatically executes commands from its
13612 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
13613 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
13614 limitations of file names imposed by DOS filesystems.}.
13615 During startup, @value{GDBN} does the following:
13619 Reads the init file (if any) in your home directory@footnote{On
13620 DOS/Windows systems, the home directory is the one pointed to by the
13621 @code{HOME} environment variable.}.
13624 Processes command line options and operands.
13627 Reads the init file (if any) in the current working directory.
13630 Reads command files specified by the @samp{-x} option.
13633 The init file in your home directory can set options (such as @samp{set
13634 complaints}) that affect subsequent processing of command line options
13635 and operands. Init files are not executed if you use the @samp{-nx}
13636 option (@pxref{Mode Options, ,Choosing modes}).
13638 @cindex init file name
13639 On some configurations of @value{GDBN}, the init file is known by a
13640 different name (these are typically environments where a specialized
13641 form of @value{GDBN} may need to coexist with other forms, hence a
13642 different name for the specialized version's init file). These are the
13643 environments with special init file names:
13645 @cindex @file{.vxgdbinit}
13648 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13650 @cindex @file{.os68gdbinit}
13652 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13654 @cindex @file{.esgdbinit}
13656 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13659 You can also request the execution of a command file with the
13660 @code{source} command:
13664 @item source @var{filename}
13665 Execute the command file @var{filename}.
13668 The lines in a command file are executed sequentially. They are not
13669 printed as they are executed. An error in any command terminates execution
13670 of the command file.
13672 Commands that would ask for confirmation if used interactively proceed
13673 without asking when used in a command file. Many @value{GDBN} commands that
13674 normally print messages to say what they are doing omit the messages
13675 when called from command files.
13677 @value{GDBN} also accepts command input from standard input. In this
13678 mode, normal output goes to standard output and error output goes to
13679 standard error. Errors in a command file supplied on standard input do
13680 not terminate execution of the command file --- execution continues with
13684 gdb < cmds > log 2>&1
13687 (The syntax above will vary depending on the shell used.) This example
13688 will execute commands from the file @file{cmds}. All output and errors
13689 would be directed to @file{log}.
13692 @section Commands for controlled output
13694 During the execution of a command file or a user-defined command, normal
13695 @value{GDBN} output is suppressed; the only output that appears is what is
13696 explicitly printed by the commands in the definition. This section
13697 describes three commands useful for generating exactly the output you
13702 @item echo @var{text}
13703 @c I do not consider backslash-space a standard C escape sequence
13704 @c because it is not in ANSI.
13705 Print @var{text}. Nonprinting characters can be included in
13706 @var{text} using C escape sequences, such as @samp{\n} to print a
13707 newline. @strong{No newline is printed unless you specify one.}
13708 In addition to the standard C escape sequences, a backslash followed
13709 by a space stands for a space. This is useful for displaying a
13710 string with spaces at the beginning or the end, since leading and
13711 trailing spaces are otherwise trimmed from all arguments.
13712 To print @samp{@w{ }and foo =@w{ }}, use the command
13713 @samp{echo \@w{ }and foo = \@w{ }}.
13715 A backslash at the end of @var{text} can be used, as in C, to continue
13716 the command onto subsequent lines. For example,
13719 echo This is some text\n\
13720 which is continued\n\
13721 onto several lines.\n
13724 produces the same output as
13727 echo This is some text\n
13728 echo which is continued\n
13729 echo onto several lines.\n
13733 @item output @var{expression}
13734 Print the value of @var{expression} and nothing but that value: no
13735 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13736 value history either. @xref{Expressions, ,Expressions}, for more information
13739 @item output/@var{fmt} @var{expression}
13740 Print the value of @var{expression} in format @var{fmt}. You can use
13741 the same formats as for @code{print}. @xref{Output Formats,,Output
13742 formats}, for more information.
13745 @item printf @var{string}, @var{expressions}@dots{}
13746 Print the values of the @var{expressions} under the control of
13747 @var{string}. The @var{expressions} are separated by commas and may be
13748 either numbers or pointers. Their values are printed as specified by
13749 @var{string}, exactly as if your program were to execute the C
13751 @c FIXME: the above implies that at least all ANSI C formats are
13752 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13753 @c Either this is a bug, or the manual should document what formats are
13757 printf (@var{string}, @var{expressions}@dots{});
13760 For example, you can print two values in hex like this:
13763 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13766 The only backslash-escape sequences that you can use in the format
13767 string are the simple ones that consist of backslash followed by a
13772 @chapter @value{GDBN} Text User Interface
13776 * TUI Overview:: TUI overview
13777 * TUI Keys:: TUI key bindings
13778 * TUI Commands:: TUI specific commands
13779 * TUI Configuration:: TUI configuration variables
13782 The @value{GDBN} Text User Interface, TUI in short,
13783 is a terminal interface which uses the @code{curses} library
13784 to show the source file, the assembly output, the program registers
13785 and @value{GDBN} commands in separate text windows.
13786 The TUI is available only when @value{GDBN} is configured
13787 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13790 @section TUI overview
13792 The TUI has two display modes that can be switched while
13797 A curses (or TUI) mode in which it displays several text
13798 windows on the terminal.
13801 A standard mode which corresponds to the @value{GDBN} configured without
13805 In the TUI mode, @value{GDBN} can display several text window
13810 This window is the @value{GDBN} command window with the @value{GDBN}
13811 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13812 managed using readline but through the TUI. The @emph{command}
13813 window is always visible.
13816 The source window shows the source file of the program. The current
13817 line as well as active breakpoints are displayed in this window.
13818 The current program position is shown with the @samp{>} marker and
13819 active breakpoints are shown with @samp{*} markers.
13822 The assembly window shows the disassembly output of the program.
13825 This window shows the processor registers. It detects when
13826 a register is changed and when this is the case, registers that have
13827 changed are highlighted.
13831 The source, assembly and register windows are attached to the thread
13832 and the frame position. They are updated when the current thread
13833 changes, when the frame changes or when the program counter changes.
13834 These three windows are arranged by the TUI according to several
13835 layouts. The layout defines which of these three windows are visible.
13836 The following layouts are available:
13846 source and assembly
13849 source and registers
13852 assembly and registers
13857 @section TUI Key Bindings
13858 @cindex TUI key bindings
13860 The TUI installs several key bindings in the readline keymaps
13861 (@pxref{Command Line Editing}).
13862 They allow to leave or enter in the TUI mode or they operate
13863 directly on the TUI layout and windows. The following key bindings
13864 are installed for both TUI mode and the @value{GDBN} standard mode.
13873 Enter or leave the TUI mode. When the TUI mode is left,
13874 the curses window management is left and @value{GDBN} operates using
13875 its standard mode writing on the terminal directly. When the TUI
13876 mode is entered, the control is given back to the curses windows.
13877 The screen is then refreshed.
13881 Use a TUI layout with only one window. The layout will
13882 either be @samp{source} or @samp{assembly}. When the TUI mode
13883 is not active, it will switch to the TUI mode.
13885 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13889 Use a TUI layout with at least two windows. When the current
13890 layout shows already two windows, a next layout with two windows is used.
13891 When a new layout is chosen, one window will always be common to the
13892 previous layout and the new one.
13894 Think of it as the Emacs @kbd{C-x 2} binding.
13898 The following key bindings are handled only by the TUI mode:
13903 Scroll the active window one page up.
13907 Scroll the active window one page down.
13911 Scroll the active window one line up.
13915 Scroll the active window one line down.
13919 Scroll the active window one column left.
13923 Scroll the active window one column right.
13927 Refresh the screen.
13931 In the TUI mode, the arrow keys are used by the active window
13932 for scrolling. This means they are not available for readline. It is
13933 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13934 @key{C-b} and @key{C-f}.
13937 @section TUI specific commands
13938 @cindex TUI commands
13940 The TUI has specific commands to control the text windows.
13941 These commands are always available, that is they do not depend on
13942 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13943 is in the standard mode, using these commands will automatically switch
13948 @kindex layout next
13949 Display the next layout.
13952 @kindex layout prev
13953 Display the previous layout.
13957 Display the source window only.
13961 Display the assembly window only.
13964 @kindex layout split
13965 Display the source and assembly window.
13968 @kindex layout regs
13969 Display the register window together with the source or assembly window.
13971 @item focus next | prev | src | asm | regs | split
13973 Set the focus to the named window.
13974 This command allows to change the active window so that scrolling keys
13975 can be affected to another window.
13979 Refresh the screen. This is similar to using @key{C-L} key.
13983 Update the source window and the current execution point.
13985 @item winheight @var{name} +@var{count}
13986 @itemx winheight @var{name} -@var{count}
13988 Change the height of the window @var{name} by @var{count}
13989 lines. Positive counts increase the height, while negative counts
13994 @node TUI Configuration
13995 @section TUI configuration variables
13996 @cindex TUI configuration variables
13998 The TUI has several configuration variables that control the
13999 appearance of windows on the terminal.
14002 @item set tui border-kind @var{kind}
14003 @kindex set tui border-kind
14004 Select the border appearance for the source, assembly and register windows.
14005 The possible values are the following:
14008 Use a space character to draw the border.
14011 Use ascii characters + - and | to draw the border.
14014 Use the Alternate Character Set to draw the border. The border is
14015 drawn using character line graphics if the terminal supports them.
14019 @item set tui active-border-mode @var{mode}
14020 @kindex set tui active-border-mode
14021 Select the attributes to display the border of the active window.
14022 The possible values are @code{normal}, @code{standout}, @code{reverse},
14023 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
14025 @item set tui border-mode @var{mode}
14026 @kindex set tui border-mode
14027 Select the attributes to display the border of other windows.
14028 The @var{mode} can be one of the following:
14031 Use normal attributes to display the border.
14037 Use reverse video mode.
14040 Use half bright mode.
14042 @item half-standout
14043 Use half bright and standout mode.
14046 Use extra bright or bold mode.
14048 @item bold-standout
14049 Use extra bright or bold and standout mode.
14056 @chapter Using @value{GDBN} under @sc{gnu} Emacs
14059 @cindex @sc{gnu} Emacs
14060 A special interface allows you to use @sc{gnu} Emacs to view (and
14061 edit) the source files for the program you are debugging with
14064 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
14065 executable file you want to debug as an argument. This command starts
14066 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
14067 created Emacs buffer.
14068 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
14070 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
14075 All ``terminal'' input and output goes through the Emacs buffer.
14078 This applies both to @value{GDBN} commands and their output, and to the input
14079 and output done by the program you are debugging.
14081 This is useful because it means that you can copy the text of previous
14082 commands and input them again; you can even use parts of the output
14085 All the facilities of Emacs' Shell mode are available for interacting
14086 with your program. In particular, you can send signals the usual
14087 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
14092 @value{GDBN} displays source code through Emacs.
14095 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
14096 source file for that frame and puts an arrow (@samp{=>}) at the
14097 left margin of the current line. Emacs uses a separate buffer for
14098 source display, and splits the screen to show both your @value{GDBN} session
14101 Explicit @value{GDBN} @code{list} or search commands still produce output as
14102 usual, but you probably have no reason to use them from Emacs.
14105 @emph{Warning:} If the directory where your program resides is not your
14106 current directory, it can be easy to confuse Emacs about the location of
14107 the source files, in which case the auxiliary display buffer does not
14108 appear to show your source. @value{GDBN} can find programs by searching your
14109 environment's @code{PATH} variable, so the @value{GDBN} input and output
14110 session proceeds normally; but Emacs does not get enough information
14111 back from @value{GDBN} to locate the source files in this situation. To
14112 avoid this problem, either start @value{GDBN} mode from the directory where
14113 your program resides, or specify an absolute file name when prompted for the
14114 @kbd{M-x gdb} argument.
14116 A similar confusion can result if you use the @value{GDBN} @code{file} command to
14117 switch to debugging a program in some other location, from an existing
14118 @value{GDBN} buffer in Emacs.
14121 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
14122 you need to call @value{GDBN} by a different name (for example, if you keep
14123 several configurations around, with different names) you can set the
14124 Emacs variable @code{gdb-command-name}; for example,
14127 (setq gdb-command-name "mygdb")
14131 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
14132 in your @file{.emacs} file) makes Emacs call the program named
14133 ``@code{mygdb}'' instead.
14135 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
14136 addition to the standard Shell mode commands:
14140 Describe the features of Emacs' @value{GDBN} Mode.
14143 Execute to another source line, like the @value{GDBN} @code{step} command; also
14144 update the display window to show the current file and location.
14147 Execute to next source line in this function, skipping all function
14148 calls, like the @value{GDBN} @code{next} command. Then update the display window
14149 to show the current file and location.
14152 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
14153 display window accordingly.
14155 @item M-x gdb-nexti
14156 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
14157 display window accordingly.
14160 Execute until exit from the selected stack frame, like the @value{GDBN}
14161 @code{finish} command.
14164 Continue execution of your program, like the @value{GDBN} @code{continue}
14167 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
14170 Go up the number of frames indicated by the numeric argument
14171 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
14172 like the @value{GDBN} @code{up} command.
14174 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
14177 Go down the number of frames indicated by the numeric argument, like the
14178 @value{GDBN} @code{down} command.
14180 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
14183 Read the number where the cursor is positioned, and insert it at the end
14184 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
14185 around an address that was displayed earlier, type @kbd{disassemble};
14186 then move the cursor to the address display, and pick up the
14187 argument for @code{disassemble} by typing @kbd{C-x &}.
14189 You can customize this further by defining elements of the list
14190 @code{gdb-print-command}; once it is defined, you can format or
14191 otherwise process numbers picked up by @kbd{C-x &} before they are
14192 inserted. A numeric argument to @kbd{C-x &} indicates that you
14193 wish special formatting, and also acts as an index to pick an element of the
14194 list. If the list element is a string, the number to be inserted is
14195 formatted using the Emacs function @code{format}; otherwise the number
14196 is passed as an argument to the corresponding list element.
14199 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
14200 tells @value{GDBN} to set a breakpoint on the source line point is on.
14202 If you accidentally delete the source-display buffer, an easy way to get
14203 it back is to type the command @code{f} in the @value{GDBN} buffer, to
14204 request a frame display; when you run under Emacs, this recreates
14205 the source buffer if necessary to show you the context of the current
14208 The source files displayed in Emacs are in ordinary Emacs buffers
14209 which are visiting the source files in the usual way. You can edit
14210 the files with these buffers if you wish; but keep in mind that @value{GDBN}
14211 communicates with Emacs in terms of line numbers. If you add or
14212 delete lines from the text, the line numbers that @value{GDBN} knows cease
14213 to correspond properly with the code.
14215 @c The following dropped because Epoch is nonstandard. Reactivate
14216 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
14218 @kindex Emacs Epoch environment
14222 Version 18 of @sc{gnu} Emacs has a built-in window system
14223 called the @code{epoch}
14224 environment. Users of this environment can use a new command,
14225 @code{inspect} which performs identically to @code{print} except that
14226 each value is printed in its own window.
14229 @include annotate.texi
14230 @include gdbmi.texinfo
14233 @chapter Reporting Bugs in @value{GDBN}
14234 @cindex bugs in @value{GDBN}
14235 @cindex reporting bugs in @value{GDBN}
14237 Your bug reports play an essential role in making @value{GDBN} reliable.
14239 Reporting a bug may help you by bringing a solution to your problem, or it
14240 may not. But in any case the principal function of a bug report is to help
14241 the entire community by making the next version of @value{GDBN} work better. Bug
14242 reports are your contribution to the maintenance of @value{GDBN}.
14244 In order for a bug report to serve its purpose, you must include the
14245 information that enables us to fix the bug.
14248 * Bug Criteria:: Have you found a bug?
14249 * Bug Reporting:: How to report bugs
14253 @section Have you found a bug?
14254 @cindex bug criteria
14256 If you are not sure whether you have found a bug, here are some guidelines:
14259 @cindex fatal signal
14260 @cindex debugger crash
14261 @cindex crash of debugger
14263 If the debugger gets a fatal signal, for any input whatever, that is a
14264 @value{GDBN} bug. Reliable debuggers never crash.
14266 @cindex error on valid input
14268 If @value{GDBN} produces an error message for valid input, that is a
14269 bug. (Note that if you're cross debugging, the problem may also be
14270 somewhere in the connection to the target.)
14272 @cindex invalid input
14274 If @value{GDBN} does not produce an error message for invalid input,
14275 that is a bug. However, you should note that your idea of
14276 ``invalid input'' might be our idea of ``an extension'' or ``support
14277 for traditional practice''.
14280 If you are an experienced user of debugging tools, your suggestions
14281 for improvement of @value{GDBN} are welcome in any case.
14284 @node Bug Reporting
14285 @section How to report bugs
14286 @cindex bug reports
14287 @cindex @value{GDBN} bugs, reporting
14289 A number of companies and individuals offer support for @sc{gnu} products.
14290 If you obtained @value{GDBN} from a support organization, we recommend you
14291 contact that organization first.
14293 You can find contact information for many support companies and
14294 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
14296 @c should add a web page ref...
14298 In any event, we also recommend that you send bug reports for
14299 @value{GDBN} to this addresses:
14305 @strong{Do not send bug reports to @samp{info-gdb}, or to
14306 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
14307 not want to receive bug reports. Those that do have arranged to receive
14310 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
14311 serves as a repeater. The mailing list and the newsgroup carry exactly
14312 the same messages. Often people think of posting bug reports to the
14313 newsgroup instead of mailing them. This appears to work, but it has one
14314 problem which can be crucial: a newsgroup posting often lacks a mail
14315 path back to the sender. Thus, if we need to ask for more information,
14316 we may be unable to reach you. For this reason, it is better to send
14317 bug reports to the mailing list.
14319 As a last resort, send bug reports on paper to:
14322 @sc{gnu} Debugger Bugs
14323 Free Software Foundation Inc.
14324 59 Temple Place - Suite 330
14325 Boston, MA 02111-1307
14329 The fundamental principle of reporting bugs usefully is this:
14330 @strong{report all the facts}. If you are not sure whether to state a
14331 fact or leave it out, state it!
14333 Often people omit facts because they think they know what causes the
14334 problem and assume that some details do not matter. Thus, you might
14335 assume that the name of the variable you use in an example does not matter.
14336 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
14337 stray memory reference which happens to fetch from the location where that
14338 name is stored in memory; perhaps, if the name were different, the contents
14339 of that location would fool the debugger into doing the right thing despite
14340 the bug. Play it safe and give a specific, complete example. That is the
14341 easiest thing for you to do, and the most helpful.
14343 Keep in mind that the purpose of a bug report is to enable us to fix the
14344 bug. It may be that the bug has been reported previously, but neither
14345 you nor we can know that unless your bug report is complete and
14348 Sometimes people give a few sketchy facts and ask, ``Does this ring a
14349 bell?'' Those bug reports are useless, and we urge everyone to
14350 @emph{refuse to respond to them} except to chide the sender to report
14353 To enable us to fix the bug, you should include all these things:
14357 The version of @value{GDBN}. @value{GDBN} announces it if you start
14358 with no arguments; you can also print it at any time using @code{show
14361 Without this, we will not know whether there is any point in looking for
14362 the bug in the current version of @value{GDBN}.
14365 The type of machine you are using, and the operating system name and
14369 What compiler (and its version) was used to compile @value{GDBN}---e.g.
14370 ``@value{GCC}--2.8.1''.
14373 What compiler (and its version) was used to compile the program you are
14374 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
14375 C Compiler''. For GCC, you can say @code{gcc --version} to get this
14376 information; for other compilers, see the documentation for those
14380 The command arguments you gave the compiler to compile your example and
14381 observe the bug. For example, did you use @samp{-O}? To guarantee
14382 you will not omit something important, list them all. A copy of the
14383 Makefile (or the output from make) is sufficient.
14385 If we were to try to guess the arguments, we would probably guess wrong
14386 and then we might not encounter the bug.
14389 A complete input script, and all necessary source files, that will
14393 A description of what behavior you observe that you believe is
14394 incorrect. For example, ``It gets a fatal signal.''
14396 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
14397 will certainly notice it. But if the bug is incorrect output, we might
14398 not notice unless it is glaringly wrong. You might as well not give us
14399 a chance to make a mistake.
14401 Even if the problem you experience is a fatal signal, you should still
14402 say so explicitly. Suppose something strange is going on, such as, your
14403 copy of @value{GDBN} is out of synch, or you have encountered a bug in
14404 the C library on your system. (This has happened!) Your copy might
14405 crash and ours would not. If you told us to expect a crash, then when
14406 ours fails to crash, we would know that the bug was not happening for
14407 us. If you had not told us to expect a crash, then we would not be able
14408 to draw any conclusion from our observations.
14411 If you wish to suggest changes to the @value{GDBN} source, send us context
14412 diffs. If you even discuss something in the @value{GDBN} source, refer to
14413 it by context, not by line number.
14415 The line numbers in our development sources will not match those in your
14416 sources. Your line numbers would convey no useful information to us.
14420 Here are some things that are not necessary:
14424 A description of the envelope of the bug.
14426 Often people who encounter a bug spend a lot of time investigating
14427 which changes to the input file will make the bug go away and which
14428 changes will not affect it.
14430 This is often time consuming and not very useful, because the way we
14431 will find the bug is by running a single example under the debugger
14432 with breakpoints, not by pure deduction from a series of examples.
14433 We recommend that you save your time for something else.
14435 Of course, if you can find a simpler example to report @emph{instead}
14436 of the original one, that is a convenience for us. Errors in the
14437 output will be easier to spot, running under the debugger will take
14438 less time, and so on.
14440 However, simplification is not vital; if you do not want to do this,
14441 report the bug anyway and send us the entire test case you used.
14444 A patch for the bug.
14446 A patch for the bug does help us if it is a good one. But do not omit
14447 the necessary information, such as the test case, on the assumption that
14448 a patch is all we need. We might see problems with your patch and decide
14449 to fix the problem another way, or we might not understand it at all.
14451 Sometimes with a program as complicated as @value{GDBN} it is very hard to
14452 construct an example that will make the program follow a certain path
14453 through the code. If you do not send us the example, we will not be able
14454 to construct one, so we will not be able to verify that the bug is fixed.
14456 And if we cannot understand what bug you are trying to fix, or why your
14457 patch should be an improvement, we will not install it. A test case will
14458 help us to understand.
14461 A guess about what the bug is or what it depends on.
14463 Such guesses are usually wrong. Even we cannot guess right about such
14464 things without first using the debugger to find the facts.
14467 @c The readline documentation is distributed with the readline code
14468 @c and consists of the two following files:
14470 @c inc-hist.texinfo
14471 @c Use -I with makeinfo to point to the appropriate directory,
14472 @c environment var TEXINPUTS with TeX.
14473 @include rluser.texinfo
14474 @include inc-hist.texinfo
14477 @node Formatting Documentation
14478 @appendix Formatting Documentation
14480 @cindex @value{GDBN} reference card
14481 @cindex reference card
14482 The @value{GDBN} 4 release includes an already-formatted reference card, ready
14483 for printing with PostScript or Ghostscript, in the @file{gdb}
14484 subdirectory of the main source directory@footnote{In
14485 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
14486 release.}. If you can use PostScript or Ghostscript with your printer,
14487 you can print the reference card immediately with @file{refcard.ps}.
14489 The release also includes the source for the reference card. You
14490 can format it, using @TeX{}, by typing:
14496 The @value{GDBN} reference card is designed to print in @dfn{landscape}
14497 mode on US ``letter'' size paper;
14498 that is, on a sheet 11 inches wide by 8.5 inches
14499 high. You will need to specify this form of printing as an option to
14500 your @sc{dvi} output program.
14502 @cindex documentation
14504 All the documentation for @value{GDBN} comes as part of the machine-readable
14505 distribution. The documentation is written in Texinfo format, which is
14506 a documentation system that uses a single source file to produce both
14507 on-line information and a printed manual. You can use one of the Info
14508 formatting commands to create the on-line version of the documentation
14509 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
14511 @value{GDBN} includes an already formatted copy of the on-line Info
14512 version of this manual in the @file{gdb} subdirectory. The main Info
14513 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
14514 subordinate files matching @samp{gdb.info*} in the same directory. If
14515 necessary, you can print out these files, or read them with any editor;
14516 but they are easier to read using the @code{info} subsystem in @sc{gnu}
14517 Emacs or the standalone @code{info} program, available as part of the
14518 @sc{gnu} Texinfo distribution.
14520 If you want to format these Info files yourself, you need one of the
14521 Info formatting programs, such as @code{texinfo-format-buffer} or
14524 If you have @code{makeinfo} installed, and are in the top level
14525 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
14526 version @value{GDBVN}), you can make the Info file by typing:
14533 If you want to typeset and print copies of this manual, you need @TeX{},
14534 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
14535 Texinfo definitions file.
14537 @TeX{} is a typesetting program; it does not print files directly, but
14538 produces output files called @sc{dvi} files. To print a typeset
14539 document, you need a program to print @sc{dvi} files. If your system
14540 has @TeX{} installed, chances are it has such a program. The precise
14541 command to use depends on your system; @kbd{lpr -d} is common; another
14542 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14543 require a file name without any extension or a @samp{.dvi} extension.
14545 @TeX{} also requires a macro definitions file called
14546 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14547 written in Texinfo format. On its own, @TeX{} cannot either read or
14548 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14549 and is located in the @file{gdb-@var{version-number}/texinfo}
14552 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14553 typeset and print this manual. First switch to the the @file{gdb}
14554 subdirectory of the main source directory (for example, to
14555 @file{gdb-@value{GDBVN}/gdb}) and type:
14561 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14563 @node Installing GDB
14564 @appendix Installing @value{GDBN}
14565 @cindex configuring @value{GDBN}
14566 @cindex installation
14568 @value{GDBN} comes with a @code{configure} script that automates the process
14569 of preparing @value{GDBN} for installation; you can then use @code{make} to
14570 build the @code{gdb} program.
14572 @c irrelevant in info file; it's as current as the code it lives with.
14573 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14574 look at the @file{README} file in the sources; we may have improved the
14575 installation procedures since publishing this manual.}
14578 The @value{GDBN} distribution includes all the source code you need for
14579 @value{GDBN} in a single directory, whose name is usually composed by
14580 appending the version number to @samp{gdb}.
14582 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14583 @file{gdb-@value{GDBVN}} directory. That directory contains:
14586 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14587 script for configuring @value{GDBN} and all its supporting libraries
14589 @item gdb-@value{GDBVN}/gdb
14590 the source specific to @value{GDBN} itself
14592 @item gdb-@value{GDBVN}/bfd
14593 source for the Binary File Descriptor library
14595 @item gdb-@value{GDBVN}/include
14596 @sc{gnu} include files
14598 @item gdb-@value{GDBVN}/libiberty
14599 source for the @samp{-liberty} free software library
14601 @item gdb-@value{GDBVN}/opcodes
14602 source for the library of opcode tables and disassemblers
14604 @item gdb-@value{GDBVN}/readline
14605 source for the @sc{gnu} command-line interface
14607 @item gdb-@value{GDBVN}/glob
14608 source for the @sc{gnu} filename pattern-matching subroutine
14610 @item gdb-@value{GDBVN}/mmalloc
14611 source for the @sc{gnu} memory-mapped malloc package
14614 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14615 from the @file{gdb-@var{version-number}} source directory, which in
14616 this example is the @file{gdb-@value{GDBVN}} directory.
14618 First switch to the @file{gdb-@var{version-number}} source directory
14619 if you are not already in it; then run @code{configure}. Pass the
14620 identifier for the platform on which @value{GDBN} will run as an
14626 cd gdb-@value{GDBVN}
14627 ./configure @var{host}
14632 where @var{host} is an identifier such as @samp{sun4} or
14633 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14634 (You can often leave off @var{host}; @code{configure} tries to guess the
14635 correct value by examining your system.)
14637 Running @samp{configure @var{host}} and then running @code{make} builds the
14638 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14639 libraries, then @code{gdb} itself. The configured source files, and the
14640 binaries, are left in the corresponding source directories.
14643 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14644 system does not recognize this automatically when you run a different
14645 shell, you may need to run @code{sh} on it explicitly:
14648 sh configure @var{host}
14651 If you run @code{configure} from a directory that contains source
14652 directories for multiple libraries or programs, such as the
14653 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14654 creates configuration files for every directory level underneath (unless
14655 you tell it not to, with the @samp{--norecursion} option).
14657 You can run the @code{configure} script from any of the
14658 subordinate directories in the @value{GDBN} distribution if you only want to
14659 configure that subdirectory, but be sure to specify a path to it.
14661 For example, with version @value{GDBVN}, type the following to configure only
14662 the @code{bfd} subdirectory:
14666 cd gdb-@value{GDBVN}/bfd
14667 ../configure @var{host}
14671 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14672 However, you should make sure that the shell on your path (named by
14673 the @samp{SHELL} environment variable) is publicly readable. Remember
14674 that @value{GDBN} uses the shell to start your program---some systems refuse to
14675 let @value{GDBN} debug child processes whose programs are not readable.
14678 * Separate Objdir:: Compiling @value{GDBN} in another directory
14679 * Config Names:: Specifying names for hosts and targets
14680 * Configure Options:: Summary of options for configure
14683 @node Separate Objdir
14684 @section Compiling @value{GDBN} in another directory
14686 If you want to run @value{GDBN} versions for several host or target machines,
14687 you need a different @code{gdb} compiled for each combination of
14688 host and target. @code{configure} is designed to make this easy by
14689 allowing you to generate each configuration in a separate subdirectory,
14690 rather than in the source directory. If your @code{make} program
14691 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14692 @code{make} in each of these directories builds the @code{gdb}
14693 program specified there.
14695 To build @code{gdb} in a separate directory, run @code{configure}
14696 with the @samp{--srcdir} option to specify where to find the source.
14697 (You also need to specify a path to find @code{configure}
14698 itself from your working directory. If the path to @code{configure}
14699 would be the same as the argument to @samp{--srcdir}, you can leave out
14700 the @samp{--srcdir} option; it is assumed.)
14702 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14703 separate directory for a Sun 4 like this:
14707 cd gdb-@value{GDBVN}
14710 ../gdb-@value{GDBVN}/configure sun4
14715 When @code{configure} builds a configuration using a remote source
14716 directory, it creates a tree for the binaries with the same structure
14717 (and using the same names) as the tree under the source directory. In
14718 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14719 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14720 @file{gdb-sun4/gdb}.
14722 One popular reason to build several @value{GDBN} configurations in separate
14723 directories is to configure @value{GDBN} for cross-compiling (where
14724 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14725 programs that run on another machine---the @dfn{target}).
14726 You specify a cross-debugging target by
14727 giving the @samp{--target=@var{target}} option to @code{configure}.
14729 When you run @code{make} to build a program or library, you must run
14730 it in a configured directory---whatever directory you were in when you
14731 called @code{configure} (or one of its subdirectories).
14733 The @code{Makefile} that @code{configure} generates in each source
14734 directory also runs recursively. If you type @code{make} in a source
14735 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14736 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14737 will build all the required libraries, and then build GDB.
14739 When you have multiple hosts or targets configured in separate
14740 directories, you can run @code{make} on them in parallel (for example,
14741 if they are NFS-mounted on each of the hosts); they will not interfere
14745 @section Specifying names for hosts and targets
14747 The specifications used for hosts and targets in the @code{configure}
14748 script are based on a three-part naming scheme, but some short predefined
14749 aliases are also supported. The full naming scheme encodes three pieces
14750 of information in the following pattern:
14753 @var{architecture}-@var{vendor}-@var{os}
14756 For example, you can use the alias @code{sun4} as a @var{host} argument,
14757 or as the value for @var{target} in a @code{--target=@var{target}}
14758 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14760 The @code{configure} script accompanying @value{GDBN} does not provide
14761 any query facility to list all supported host and target names or
14762 aliases. @code{configure} calls the Bourne shell script
14763 @code{config.sub} to map abbreviations to full names; you can read the
14764 script, if you wish, or you can use it to test your guesses on
14765 abbreviations---for example:
14768 % sh config.sub i386-linux
14770 % sh config.sub alpha-linux
14771 alpha-unknown-linux-gnu
14772 % sh config.sub hp9k700
14774 % sh config.sub sun4
14775 sparc-sun-sunos4.1.1
14776 % sh config.sub sun3
14777 m68k-sun-sunos4.1.1
14778 % sh config.sub i986v
14779 Invalid configuration `i986v': machine `i986v' not recognized
14783 @code{config.sub} is also distributed in the @value{GDBN} source
14784 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14786 @node Configure Options
14787 @section @code{configure} options
14789 Here is a summary of the @code{configure} options and arguments that
14790 are most often useful for building @value{GDBN}. @code{configure} also has
14791 several other options not listed here. @inforef{What Configure
14792 Does,,configure.info}, for a full explanation of @code{configure}.
14795 configure @r{[}--help@r{]}
14796 @r{[}--prefix=@var{dir}@r{]}
14797 @r{[}--exec-prefix=@var{dir}@r{]}
14798 @r{[}--srcdir=@var{dirname}@r{]}
14799 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14800 @r{[}--target=@var{target}@r{]}
14805 You may introduce options with a single @samp{-} rather than
14806 @samp{--} if you prefer; but you may abbreviate option names if you use
14811 Display a quick summary of how to invoke @code{configure}.
14813 @item --prefix=@var{dir}
14814 Configure the source to install programs and files under directory
14817 @item --exec-prefix=@var{dir}
14818 Configure the source to install programs under directory
14821 @c avoid splitting the warning from the explanation:
14823 @item --srcdir=@var{dirname}
14824 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14825 @code{make} that implements the @code{VPATH} feature.}@*
14826 Use this option to make configurations in directories separate from the
14827 @value{GDBN} source directories. Among other things, you can use this to
14828 build (or maintain) several configurations simultaneously, in separate
14829 directories. @code{configure} writes configuration specific files in
14830 the current directory, but arranges for them to use the source in the
14831 directory @var{dirname}. @code{configure} creates directories under
14832 the working directory in parallel to the source directories below
14835 @item --norecursion
14836 Configure only the directory level where @code{configure} is executed; do not
14837 propagate configuration to subdirectories.
14839 @item --target=@var{target}
14840 Configure @value{GDBN} for cross-debugging programs running on the specified
14841 @var{target}. Without this option, @value{GDBN} is configured to debug
14842 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14844 There is no convenient way to generate a list of all available targets.
14846 @item @var{host} @dots{}
14847 Configure @value{GDBN} to run on the specified @var{host}.
14849 There is no convenient way to generate a list of all available hosts.
14852 There are many other options available as well, but they are generally
14853 needed for special purposes only.
14861 % I think something like @colophon should be in texinfo. In the
14863 \long\def\colophon{\hbox to0pt{}\vfill
14864 \centerline{The body of this manual is set in}
14865 \centerline{\fontname\tenrm,}
14866 \centerline{with headings in {\bf\fontname\tenbf}}
14867 \centerline{and examples in {\tt\fontname\tentt}.}
14868 \centerline{{\it\fontname\tenit\/},}
14869 \centerline{{\bf\fontname\tenbf}, and}
14870 \centerline{{\sl\fontname\tensl\/}}
14871 \centerline{are used for emphasis.}\vfill}
14873 % Blame: doc@cygnus.com, 1991.
14876 @c TeX can handle the contents at the start but makeinfo 3.12 can not