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} options respectively. (@value{GDBN} reads the first argument
895 that does not have an associated option flag as equivalent to the
896 @samp{-se} option followed by that argument; and the second argument
897 that does not have an associated option flag, if any, as equivalent to
898 the @samp{-c} option followed by that argument.)
900 If @value{GDBN} has not been configured to included core file support,
901 such as for most embedded targets, then it will complain about a second
902 argument and ignore it.
904 Many options have both long and short forms; both are shown in the
905 following list. @value{GDBN} also recognizes the long forms if you truncate
906 them, so long as enough of the option is present to be unambiguous.
907 (If you prefer, you can flag option arguments with @samp{--} rather
908 than @samp{-}, though we illustrate the more usual convention.)
910 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
911 @c way, both those who look for -foo and --foo in the index, will find
915 @item -symbols @var{file}
917 @cindex @code{--symbols}
919 Read symbol table from file @var{file}.
921 @item -exec @var{file}
923 @cindex @code{--exec}
925 Use file @var{file} as the executable file to execute when appropriate,
926 and for examining pure data in conjunction with a core dump.
930 Read symbol table from file @var{file} and use it as the executable
933 @item -core @var{file}
935 @cindex @code{--core}
937 Use file @var{file} as a core dump to examine.
939 @item -c @var{number}
940 Connect to process ID @var{number}, as with the @code{attach} command
941 (unless there is a file in core-dump format named @var{number}, in which
942 case @samp{-c} specifies that file as a core dump to read).
944 @item -command @var{file}
946 @cindex @code{--command}
948 Execute @value{GDBN} commands from file @var{file}. @xref{Command
949 Files,, Command files}.
951 @item -directory @var{directory}
952 @itemx -d @var{directory}
953 @cindex @code{--directory}
955 Add @var{directory} to the path to search for source files.
959 @cindex @code{--mapped}
961 @emph{Warning: this option depends on operating system facilities that are not
962 supported on all systems.}@*
963 If memory-mapped files are available on your system through the @code{mmap}
964 system call, you can use this option
965 to have @value{GDBN} write the symbols from your
966 program into a reusable file in the current directory. If the program you are debugging is
967 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
968 Future @value{GDBN} debugging sessions notice the presence of this file,
969 and can quickly map in symbol information from it, rather than reading
970 the symbol table from the executable program.
972 The @file{.syms} file is specific to the host machine where @value{GDBN}
973 is run. It holds an exact image of the internal @value{GDBN} symbol
974 table. It cannot be shared across multiple host platforms.
978 @cindex @code{--readnow}
980 Read each symbol file's entire symbol table immediately, rather than
981 the default, which is to read it incrementally as it is needed.
982 This makes startup slower, but makes future operations faster.
986 You typically combine the @code{-mapped} and @code{-readnow} options in
987 order to build a @file{.syms} file that contains complete symbol
988 information. (@xref{Files,,Commands to specify files}, for information
989 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
990 but build a @file{.syms} file for future use is:
993 gdb -batch -nx -mapped -readnow programname
997 @subsection Choosing modes
999 You can run @value{GDBN} in various alternative modes---for example, in
1000 batch mode or quiet mode.
1007 Do not execute commands found in any initialization files. Normally,
1008 @value{GDBN} executes the commands in these files after all the command
1009 options and arguments have been processed. @xref{Command Files,,Command
1015 @cindex @code{--quiet}
1016 @cindex @code{--silent}
1018 ``Quiet''. Do not print the introductory and copyright messages. These
1019 messages are also suppressed in batch mode.
1022 @cindex @code{--batch}
1023 Run in batch mode. Exit with status @code{0} after processing all the
1024 command files specified with @samp{-x} (and all commands from
1025 initialization files, if not inhibited with @samp{-n}). Exit with
1026 nonzero status if an error occurs in executing the @value{GDBN} commands
1027 in the command files.
1029 Batch mode may be useful for running @value{GDBN} as a filter, for
1030 example to download and run a program on another computer; in order to
1031 make this more useful, the message
1034 Program exited normally.
1038 (which is ordinarily issued whenever a program running under
1039 @value{GDBN} control terminates) is not issued when running in batch
1044 @cindex @code{--nowindows}
1046 ``No windows''. If @value{GDBN} comes with a graphical user interface
1047 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1048 interface. If no GUI is available, this option has no effect.
1052 @cindex @code{--windows}
1054 If @value{GDBN} includes a GUI, then this option requires it to be
1057 @item -cd @var{directory}
1059 Run @value{GDBN} using @var{directory} as its working directory,
1060 instead of the current directory.
1064 @cindex @code{--fullname}
1066 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1067 subprocess. It tells @value{GDBN} to output the full file name and line
1068 number in a standard, recognizable fashion each time a stack frame is
1069 displayed (which includes each time your program stops). This
1070 recognizable format looks like two @samp{\032} characters, followed by
1071 the file name, line number and character position separated by colons,
1072 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1073 @samp{\032} characters as a signal to display the source code for the
1077 @cindex @code{--epoch}
1078 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1079 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1080 routines so as to allow Epoch to display values of expressions in a
1083 @item -annotate @var{level}
1084 @cindex @code{--annotate}
1085 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1086 effect is identical to using @samp{set annotate @var{level}}
1087 (@pxref{Annotations}).
1088 Annotation level controls how much information does @value{GDBN} print
1089 together with its prompt, values of expressions, source lines, and other
1090 types of output. Level 0 is the normal, level 1 is for use when
1091 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1092 maximum annotation suitable for programs that control @value{GDBN}.
1095 @cindex @code{--async}
1096 Use the asynchronous event loop for the command-line interface.
1097 @value{GDBN} processes all events, such as user keyboard input, via a
1098 special event loop. This allows @value{GDBN} to accept and process user
1099 commands in parallel with the debugged process being
1100 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1101 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1102 suspended when the debuggee runs.}, so you don't need to wait for
1103 control to return to @value{GDBN} before you type the next command.
1104 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1105 operation is not yet in place, so @samp{-async} does not work fully
1107 @c FIXME: when the target side of the event loop is done, the above NOTE
1108 @c should be removed.
1110 When the standard input is connected to a terminal device, @value{GDBN}
1111 uses the asynchronous event loop by default, unless disabled by the
1112 @samp{-noasync} option.
1115 @cindex @code{--noasync}
1116 Disable the asynchronous event loop for the command-line interface.
1119 @cindex @code{--args}
1120 Change interpretation of command line so that arguments following the
1121 executable file are passed as command line arguments to the inferior.
1122 This option stops option processing.
1124 @item -baud @var{bps}
1126 @cindex @code{--baud}
1128 Set the line speed (baud rate or bits per second) of any serial
1129 interface used by @value{GDBN} for remote debugging.
1131 @item -tty @var{device}
1132 @itemx -t @var{device}
1133 @cindex @code{--tty}
1135 Run using @var{device} for your program's standard input and output.
1136 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1138 @c resolve the situation of these eventually
1140 @cindex @code{--tui}
1141 Activate the Terminal User Interface when starting.
1142 The Terminal User Interface manages several text windows on the terminal,
1143 showing source, assembly, registers and @value{GDBN} command outputs
1144 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1145 Do not use this option if you run @value{GDBN} from Emacs
1146 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1149 @c @cindex @code{--xdb}
1150 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1151 @c For information, see the file @file{xdb_trans.html}, which is usually
1152 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1155 @item -interpreter @var{interp}
1156 @cindex @code{--interpreter}
1157 Use the interpreter @var{interp} for interface with the controlling
1158 program or device. This option is meant to be set by programs which
1159 communicate with @value{GDBN} using it as a back end.
1161 @samp{--interpreter=mi} (or @samp{--interpreter=mi1}) causes
1162 @value{GDBN} to use the @dfn{gdb/mi interface} (@pxref{GDB/MI, , The
1163 @sc{gdb/mi} Interface}). The older @sc{gdb/mi} interface, included in
1164 @value{GDBN} version 5.0 can be selected with @samp{--interpreter=mi0}.
1167 @cindex @code{--write}
1168 Open the executable and core files for both reading and writing. This
1169 is equivalent to the @samp{set write on} command inside @value{GDBN}
1173 @cindex @code{--statistics}
1174 This option causes @value{GDBN} to print statistics about time and
1175 memory usage after it completes each command and returns to the prompt.
1178 @cindex @code{--version}
1179 This option causes @value{GDBN} to print its version number and
1180 no-warranty blurb, and exit.
1185 @section Quitting @value{GDBN}
1186 @cindex exiting @value{GDBN}
1187 @cindex leaving @value{GDBN}
1190 @kindex quit @r{[}@var{expression}@r{]}
1191 @kindex q @r{(@code{quit})}
1192 @item quit @r{[}@var{expression}@r{]}
1194 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1195 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1196 do not supply @var{expression}, @value{GDBN} will terminate normally;
1197 otherwise it will terminate using the result of @var{expression} as the
1202 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1203 terminates the action of any @value{GDBN} command that is in progress and
1204 returns to @value{GDBN} command level. It is safe to type the interrupt
1205 character at any time because @value{GDBN} does not allow it to take effect
1206 until a time when it is safe.
1208 If you have been using @value{GDBN} to control an attached process or
1209 device, you can release it with the @code{detach} command
1210 (@pxref{Attach, ,Debugging an already-running process}).
1212 @node Shell Commands
1213 @section Shell commands
1215 If you need to execute occasional shell commands during your
1216 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1217 just use the @code{shell} command.
1221 @cindex shell escape
1222 @item shell @var{command string}
1223 Invoke a standard shell to execute @var{command string}.
1224 If it exists, the environment variable @code{SHELL} determines which
1225 shell to run. Otherwise @value{GDBN} uses the default shell
1226 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1229 The utility @code{make} is often needed in development environments.
1230 You do not have to use the @code{shell} command for this purpose in
1235 @cindex calling make
1236 @item make @var{make-args}
1237 Execute the @code{make} program with the specified
1238 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1242 @chapter @value{GDBN} Commands
1244 You can abbreviate a @value{GDBN} command to the first few letters of the command
1245 name, if that abbreviation is unambiguous; and you can repeat certain
1246 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1247 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1248 show you the alternatives available, if there is more than one possibility).
1251 * Command Syntax:: How to give commands to @value{GDBN}
1252 * Completion:: Command completion
1253 * Help:: How to ask @value{GDBN} for help
1256 @node Command Syntax
1257 @section Command syntax
1259 A @value{GDBN} command is a single line of input. There is no limit on
1260 how long it can be. It starts with a command name, which is followed by
1261 arguments whose meaning depends on the command name. For example, the
1262 command @code{step} accepts an argument which is the number of times to
1263 step, as in @samp{step 5}. You can also use the @code{step} command
1264 with no arguments. Some commands do not allow any arguments.
1266 @cindex abbreviation
1267 @value{GDBN} command names may always be truncated if that abbreviation is
1268 unambiguous. Other possible command abbreviations are listed in the
1269 documentation for individual commands. In some cases, even ambiguous
1270 abbreviations are allowed; for example, @code{s} is specially defined as
1271 equivalent to @code{step} even though there are other commands whose
1272 names start with @code{s}. You can test abbreviations by using them as
1273 arguments to the @code{help} command.
1275 @cindex repeating commands
1276 @kindex RET @r{(repeat last command)}
1277 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1278 repeat the previous command. Certain commands (for example, @code{run})
1279 will not repeat this way; these are commands whose unintentional
1280 repetition might cause trouble and which you are unlikely to want to
1283 The @code{list} and @code{x} commands, when you repeat them with
1284 @key{RET}, construct new arguments rather than repeating
1285 exactly as typed. This permits easy scanning of source or memory.
1287 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1288 output, in a way similar to the common utility @code{more}
1289 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1290 @key{RET} too many in this situation, @value{GDBN} disables command
1291 repetition after any command that generates this sort of display.
1293 @kindex # @r{(a comment)}
1295 Any text from a @kbd{#} to the end of the line is a comment; it does
1296 nothing. This is useful mainly in command files (@pxref{Command
1297 Files,,Command files}).
1299 @cindex repeating command sequences
1300 @kindex C-o @r{(operate-and-get-next)}
1301 The @kbd{C-o} binding is useful for repeating a complex sequence of
1302 commands. This command accepts the current line, like @kbd{RET}, and
1303 then fetches the next line relative to the current line from the history
1307 @section Command completion
1310 @cindex word completion
1311 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1312 only one possibility; it can also show you what the valid possibilities
1313 are for the next word in a command, at any time. This works for @value{GDBN}
1314 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1316 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1317 of a word. If there is only one possibility, @value{GDBN} fills in the
1318 word, and waits for you to finish the command (or press @key{RET} to
1319 enter it). For example, if you type
1321 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1322 @c complete accuracy in these examples; space introduced for clarity.
1323 @c If texinfo enhancements make it unnecessary, it would be nice to
1324 @c replace " @key" by "@key" in the following...
1326 (@value{GDBP}) info bre @key{TAB}
1330 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1331 the only @code{info} subcommand beginning with @samp{bre}:
1334 (@value{GDBP}) info breakpoints
1338 You can either press @key{RET} at this point, to run the @code{info
1339 breakpoints} command, or backspace and enter something else, if
1340 @samp{breakpoints} does not look like the command you expected. (If you
1341 were sure you wanted @code{info breakpoints} in the first place, you
1342 might as well just type @key{RET} immediately after @samp{info bre},
1343 to exploit command abbreviations rather than command completion).
1345 If there is more than one possibility for the next word when you press
1346 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1347 characters and try again, or just press @key{TAB} a second time;
1348 @value{GDBN} displays all the possible completions for that word. For
1349 example, you might want to set a breakpoint on a subroutine whose name
1350 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1351 just sounds the bell. Typing @key{TAB} again displays all the
1352 function names in your program that begin with those characters, for
1356 (@value{GDBP}) b make_ @key{TAB}
1357 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1358 make_a_section_from_file make_environ
1359 make_abs_section make_function_type
1360 make_blockvector make_pointer_type
1361 make_cleanup make_reference_type
1362 make_command make_symbol_completion_list
1363 (@value{GDBP}) b make_
1367 After displaying the available possibilities, @value{GDBN} copies your
1368 partial input (@samp{b make_} in the example) so you can finish the
1371 If you just want to see the list of alternatives in the first place, you
1372 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1373 means @kbd{@key{META} ?}. You can type this either by holding down a
1374 key designated as the @key{META} shift on your keyboard (if there is
1375 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1377 @cindex quotes in commands
1378 @cindex completion of quoted strings
1379 Sometimes the string you need, while logically a ``word'', may contain
1380 parentheses or other characters that @value{GDBN} normally excludes from
1381 its notion of a word. To permit word completion to work in this
1382 situation, you may enclose words in @code{'} (single quote marks) in
1383 @value{GDBN} commands.
1385 The most likely situation where you might need this is in typing the
1386 name of a C@t{++} function. This is because C@t{++} allows function
1387 overloading (multiple definitions of the same function, distinguished
1388 by argument type). For example, when you want to set a breakpoint you
1389 may need to distinguish whether you mean the version of @code{name}
1390 that takes an @code{int} parameter, @code{name(int)}, or the version
1391 that takes a @code{float} parameter, @code{name(float)}. To use the
1392 word-completion facilities in this situation, type a single quote
1393 @code{'} at the beginning of the function name. This alerts
1394 @value{GDBN} that it may need to consider more information than usual
1395 when you press @key{TAB} or @kbd{M-?} to request word completion:
1398 (@value{GDBP}) b 'bubble( @kbd{M-?}
1399 bubble(double,double) bubble(int,int)
1400 (@value{GDBP}) b 'bubble(
1403 In some cases, @value{GDBN} can tell that completing a name requires using
1404 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1405 completing as much as it can) if you do not type the quote in the first
1409 (@value{GDBP}) b bub @key{TAB}
1410 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1411 (@value{GDBP}) b 'bubble(
1415 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1416 you have not yet started typing the argument list when you ask for
1417 completion on an overloaded symbol.
1419 For more information about overloaded functions, see @ref{C plus plus
1420 expressions, ,C@t{++} expressions}. You can use the command @code{set
1421 overload-resolution off} to disable overload resolution;
1422 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1426 @section Getting help
1427 @cindex online documentation
1430 You can always ask @value{GDBN} itself for information on its commands,
1431 using the command @code{help}.
1434 @kindex h @r{(@code{help})}
1437 You can use @code{help} (abbreviated @code{h}) with no arguments to
1438 display a short list of named classes of commands:
1442 List of classes of commands:
1444 aliases -- Aliases of other commands
1445 breakpoints -- Making program stop at certain points
1446 data -- Examining data
1447 files -- Specifying and examining files
1448 internals -- Maintenance commands
1449 obscure -- Obscure features
1450 running -- Running the program
1451 stack -- Examining the stack
1452 status -- Status inquiries
1453 support -- Support facilities
1454 tracepoints -- Tracing of program execution without@*
1455 stopping the program
1456 user-defined -- User-defined commands
1458 Type "help" followed by a class name for a list of
1459 commands in that class.
1460 Type "help" followed by command name for full
1462 Command name abbreviations are allowed if unambiguous.
1465 @c the above line break eliminates huge line overfull...
1467 @item help @var{class}
1468 Using one of the general help classes as an argument, you can get a
1469 list of the individual commands in that class. For example, here is the
1470 help display for the class @code{status}:
1473 (@value{GDBP}) help status
1478 @c Line break in "show" line falsifies real output, but needed
1479 @c to fit in smallbook page size.
1480 info -- Generic command for showing things
1481 about the program being debugged
1482 show -- Generic command for showing things
1485 Type "help" followed by command name for full
1487 Command name abbreviations are allowed if unambiguous.
1491 @item help @var{command}
1492 With a command name as @code{help} argument, @value{GDBN} displays a
1493 short paragraph on how to use that command.
1496 @item apropos @var{args}
1497 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1498 commands, and their documentation, for the regular expression specified in
1499 @var{args}. It prints out all matches found. For example:
1510 set symbol-reloading -- Set dynamic symbol table reloading
1511 multiple times in one run
1512 show symbol-reloading -- Show dynamic symbol table reloading
1513 multiple times in one run
1518 @item complete @var{args}
1519 The @code{complete @var{args}} command lists all the possible completions
1520 for the beginning of a command. Use @var{args} to specify the beginning of the
1521 command you want completed. For example:
1527 @noindent results in:
1538 @noindent This is intended for use by @sc{gnu} Emacs.
1541 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1542 and @code{show} to inquire about the state of your program, or the state
1543 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1544 manual introduces each of them in the appropriate context. The listings
1545 under @code{info} and under @code{show} in the Index point to
1546 all the sub-commands. @xref{Index}.
1551 @kindex i @r{(@code{info})}
1553 This command (abbreviated @code{i}) is for describing the state of your
1554 program. For example, you can list the arguments given to your program
1555 with @code{info args}, list the registers currently in use with @code{info
1556 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1557 You can get a complete list of the @code{info} sub-commands with
1558 @w{@code{help info}}.
1562 You can assign the result of an expression to an environment variable with
1563 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1564 @code{set prompt $}.
1568 In contrast to @code{info}, @code{show} is for describing the state of
1569 @value{GDBN} itself.
1570 You can change most of the things you can @code{show}, by using the
1571 related command @code{set}; for example, you can control what number
1572 system is used for displays with @code{set radix}, or simply inquire
1573 which is currently in use with @code{show radix}.
1576 To display all the settable parameters and their current
1577 values, you can use @code{show} with no arguments; you may also use
1578 @code{info set}. Both commands produce the same display.
1579 @c FIXME: "info set" violates the rule that "info" is for state of
1580 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1581 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1585 Here are three miscellaneous @code{show} subcommands, all of which are
1586 exceptional in lacking corresponding @code{set} commands:
1589 @kindex show version
1590 @cindex version number
1592 Show what version of @value{GDBN} is running. You should include this
1593 information in @value{GDBN} bug-reports. If multiple versions of
1594 @value{GDBN} are in use at your site, you may need to determine which
1595 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1596 commands are introduced, and old ones may wither away. Also, many
1597 system vendors ship variant versions of @value{GDBN}, and there are
1598 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1599 The version number is the same as the one announced when you start
1602 @kindex show copying
1604 Display information about permission for copying @value{GDBN}.
1606 @kindex show warranty
1608 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1609 if your version of @value{GDBN} comes with one.
1614 @chapter Running Programs Under @value{GDBN}
1616 When you run a program under @value{GDBN}, you must first generate
1617 debugging information when you compile it.
1619 You may start @value{GDBN} with its arguments, if any, in an environment
1620 of your choice. If you are doing native debugging, you may redirect
1621 your program's input and output, debug an already running process, or
1622 kill a child process.
1625 * Compilation:: Compiling for debugging
1626 * Starting:: Starting your program
1627 * Arguments:: Your program's arguments
1628 * Environment:: Your program's environment
1630 * Working Directory:: Your program's working directory
1631 * Input/Output:: Your program's input and output
1632 * Attach:: Debugging an already-running process
1633 * Kill Process:: Killing the child process
1635 * Threads:: Debugging programs with multiple threads
1636 * Processes:: Debugging programs with multiple processes
1640 @section Compiling for debugging
1642 In order to debug a program effectively, you need to generate
1643 debugging information when you compile it. This debugging information
1644 is stored in the object file; it describes the data type of each
1645 variable or function and the correspondence between source line numbers
1646 and addresses in the executable code.
1648 To request debugging information, specify the @samp{-g} option when you run
1651 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1652 options together. Using those compilers, you cannot generate optimized
1653 executables containing debugging information.
1655 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1656 without @samp{-O}, making it possible to debug optimized code. We
1657 recommend that you @emph{always} use @samp{-g} whenever you compile a
1658 program. You may think your program is correct, but there is no sense
1659 in pushing your luck.
1661 @cindex optimized code, debugging
1662 @cindex debugging optimized code
1663 When you debug a program compiled with @samp{-g -O}, remember that the
1664 optimizer is rearranging your code; the debugger shows you what is
1665 really there. Do not be too surprised when the execution path does not
1666 exactly match your source file! An extreme example: if you define a
1667 variable, but never use it, @value{GDBN} never sees that
1668 variable---because the compiler optimizes it out of existence.
1670 Some things do not work as well with @samp{-g -O} as with just
1671 @samp{-g}, particularly on machines with instruction scheduling. If in
1672 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1673 please report it to us as a bug (including a test case!).
1675 Older versions of the @sc{gnu} C compiler permitted a variant option
1676 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1677 format; if your @sc{gnu} C compiler has this option, do not use it.
1681 @section Starting your program
1687 @kindex r @r{(@code{run})}
1690 Use the @code{run} command to start your program under @value{GDBN}.
1691 You must first specify the program name (except on VxWorks) with an
1692 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1693 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1694 (@pxref{Files, ,Commands to specify files}).
1698 If you are running your program in an execution environment that
1699 supports processes, @code{run} creates an inferior process and makes
1700 that process run your program. (In environments without processes,
1701 @code{run} jumps to the start of your program.)
1703 The execution of a program is affected by certain information it
1704 receives from its superior. @value{GDBN} provides ways to specify this
1705 information, which you must do @emph{before} starting your program. (You
1706 can change it after starting your program, but such changes only affect
1707 your program the next time you start it.) This information may be
1708 divided into four categories:
1711 @item The @emph{arguments.}
1712 Specify the arguments to give your program as the arguments of the
1713 @code{run} command. If a shell is available on your target, the shell
1714 is used to pass the arguments, so that you may use normal conventions
1715 (such as wildcard expansion or variable substitution) in describing
1717 In Unix systems, you can control which shell is used with the
1718 @code{SHELL} environment variable.
1719 @xref{Arguments, ,Your program's arguments}.
1721 @item The @emph{environment.}
1722 Your program normally inherits its environment from @value{GDBN}, but you can
1723 use the @value{GDBN} commands @code{set environment} and @code{unset
1724 environment} to change parts of the environment that affect
1725 your program. @xref{Environment, ,Your program's environment}.
1727 @item The @emph{working directory.}
1728 Your program inherits its working directory from @value{GDBN}. You can set
1729 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1730 @xref{Working Directory, ,Your program's working directory}.
1732 @item The @emph{standard input and output.}
1733 Your program normally uses the same device for standard input and
1734 standard output as @value{GDBN} is using. You can redirect input and output
1735 in the @code{run} command line, or you can use the @code{tty} command to
1736 set a different device for your program.
1737 @xref{Input/Output, ,Your program's input and output}.
1740 @emph{Warning:} While input and output redirection work, you cannot use
1741 pipes to pass the output of the program you are debugging to another
1742 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1746 When you issue the @code{run} command, your program begins to execute
1747 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1748 of how to arrange for your program to stop. Once your program has
1749 stopped, you may call functions in your program, using the @code{print}
1750 or @code{call} commands. @xref{Data, ,Examining Data}.
1752 If the modification time of your symbol file has changed since the last
1753 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1754 table, and reads it again. When it does this, @value{GDBN} tries to retain
1755 your current breakpoints.
1758 @section Your program's arguments
1760 @cindex arguments (to your program)
1761 The arguments to your program can be specified by the arguments of the
1763 They are passed to a shell, which expands wildcard characters and
1764 performs redirection of I/O, and thence to your program. Your
1765 @code{SHELL} environment variable (if it exists) specifies what shell
1766 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1767 the default shell (@file{/bin/sh} on Unix).
1769 On non-Unix systems, the program is usually invoked directly by
1770 @value{GDBN}, which emulates I/O redirection via the appropriate system
1771 calls, and the wildcard characters are expanded by the startup code of
1772 the program, not by the shell.
1774 @code{run} with no arguments uses the same arguments used by the previous
1775 @code{run}, or those set by the @code{set args} command.
1780 Specify the arguments to be used the next time your program is run. If
1781 @code{set args} has no arguments, @code{run} executes your program
1782 with no arguments. Once you have run your program with arguments,
1783 using @code{set args} before the next @code{run} is the only way to run
1784 it again without arguments.
1788 Show the arguments to give your program when it is started.
1792 @section Your program's environment
1794 @cindex environment (of your program)
1795 The @dfn{environment} consists of a set of environment variables and
1796 their values. Environment variables conventionally record such things as
1797 your user name, your home directory, your terminal type, and your search
1798 path for programs to run. Usually you set up environment variables with
1799 the shell and they are inherited by all the other programs you run. When
1800 debugging, it can be useful to try running your program with a modified
1801 environment without having to start @value{GDBN} over again.
1805 @item path @var{directory}
1806 Add @var{directory} to the front of the @code{PATH} environment variable
1807 (the search path for executables) that will be passed to your program.
1808 The value of @code{PATH} used by @value{GDBN} does not change.
1809 You may specify several directory names, separated by whitespace or by a
1810 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1811 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1812 is moved to the front, so it is searched sooner.
1814 You can use the string @samp{$cwd} to refer to whatever is the current
1815 working directory at the time @value{GDBN} searches the path. If you
1816 use @samp{.} instead, it refers to the directory where you executed the
1817 @code{path} command. @value{GDBN} replaces @samp{.} in the
1818 @var{directory} argument (with the current path) before adding
1819 @var{directory} to the search path.
1820 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1821 @c document that, since repeating it would be a no-op.
1825 Display the list of search paths for executables (the @code{PATH}
1826 environment variable).
1828 @kindex show environment
1829 @item show environment @r{[}@var{varname}@r{]}
1830 Print the value of environment variable @var{varname} to be given to
1831 your program when it starts. If you do not supply @var{varname},
1832 print the names and values of all environment variables to be given to
1833 your program. You can abbreviate @code{environment} as @code{env}.
1835 @kindex set environment
1836 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1837 Set environment variable @var{varname} to @var{value}. The value
1838 changes for your program only, not for @value{GDBN} itself. @var{value} may
1839 be any string; the values of environment variables are just strings, and
1840 any interpretation is supplied by your program itself. The @var{value}
1841 parameter is optional; if it is eliminated, the variable is set to a
1843 @c "any string" here does not include leading, trailing
1844 @c blanks. Gnu asks: does anyone care?
1846 For example, this command:
1853 tells the debugged program, when subsequently run, that its user is named
1854 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1855 are not actually required.)
1857 @kindex unset environment
1858 @item unset environment @var{varname}
1859 Remove variable @var{varname} from the environment to be passed to your
1860 program. This is different from @samp{set env @var{varname} =};
1861 @code{unset environment} removes the variable from the environment,
1862 rather than assigning it an empty value.
1865 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1867 by your @code{SHELL} environment variable if it exists (or
1868 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1869 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1870 @file{.bashrc} for BASH---any variables you set in that file affect
1871 your program. You may wish to move setting of environment variables to
1872 files that are only run when you sign on, such as @file{.login} or
1875 @node Working Directory
1876 @section Your program's working directory
1878 @cindex working directory (of your program)
1879 Each time you start your program with @code{run}, it inherits its
1880 working directory from the current working directory of @value{GDBN}.
1881 The @value{GDBN} working directory is initially whatever it inherited
1882 from its parent process (typically the shell), but you can specify a new
1883 working directory in @value{GDBN} with the @code{cd} command.
1885 The @value{GDBN} working directory also serves as a default for the commands
1886 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1891 @item cd @var{directory}
1892 Set the @value{GDBN} working directory to @var{directory}.
1896 Print the @value{GDBN} working directory.
1900 @section Your program's input and output
1905 By default, the program you run under @value{GDBN} does input and output to
1906 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1907 to its own terminal modes to interact with you, but it records the terminal
1908 modes your program was using and switches back to them when you continue
1909 running your program.
1912 @kindex info terminal
1914 Displays information recorded by @value{GDBN} about the terminal modes your
1918 You can redirect your program's input and/or output using shell
1919 redirection with the @code{run} command. For example,
1926 starts your program, diverting its output to the file @file{outfile}.
1929 @cindex controlling terminal
1930 Another way to specify where your program should do input and output is
1931 with the @code{tty} command. This command accepts a file name as
1932 argument, and causes this file to be the default for future @code{run}
1933 commands. It also resets the controlling terminal for the child
1934 process, for future @code{run} commands. For example,
1941 directs that processes started with subsequent @code{run} commands
1942 default to do input and output on the terminal @file{/dev/ttyb} and have
1943 that as their controlling terminal.
1945 An explicit redirection in @code{run} overrides the @code{tty} command's
1946 effect on the input/output device, but not its effect on the controlling
1949 When you use the @code{tty} command or redirect input in the @code{run}
1950 command, only the input @emph{for your program} is affected. The input
1951 for @value{GDBN} still comes from your terminal.
1954 @section Debugging an already-running process
1959 @item attach @var{process-id}
1960 This command attaches to a running process---one that was started
1961 outside @value{GDBN}. (@code{info files} shows your active
1962 targets.) The command takes as argument a process ID. The usual way to
1963 find out the process-id of a Unix process is with the @code{ps} utility,
1964 or with the @samp{jobs -l} shell command.
1966 @code{attach} does not repeat if you press @key{RET} a second time after
1967 executing the command.
1970 To use @code{attach}, your program must be running in an environment
1971 which supports processes; for example, @code{attach} does not work for
1972 programs on bare-board targets that lack an operating system. You must
1973 also have permission to send the process a signal.
1975 When you use @code{attach}, the debugger finds the program running in
1976 the process first by looking in the current working directory, then (if
1977 the program is not found) by using the source file search path
1978 (@pxref{Source Path, ,Specifying source directories}). You can also use
1979 the @code{file} command to load the program. @xref{Files, ,Commands to
1982 The first thing @value{GDBN} does after arranging to debug the specified
1983 process is to stop it. You can examine and modify an attached process
1984 with all the @value{GDBN} commands that are ordinarily available when
1985 you start processes with @code{run}. You can insert breakpoints; you
1986 can step and continue; you can modify storage. If you would rather the
1987 process continue running, you may use the @code{continue} command after
1988 attaching @value{GDBN} to the process.
1993 When you have finished debugging the attached process, you can use the
1994 @code{detach} command to release it from @value{GDBN} control. Detaching
1995 the process continues its execution. After the @code{detach} command,
1996 that process and @value{GDBN} become completely independent once more, and you
1997 are ready to @code{attach} another process or start one with @code{run}.
1998 @code{detach} does not repeat if you press @key{RET} again after
1999 executing the command.
2002 If you exit @value{GDBN} or use the @code{run} command while you have an
2003 attached process, you kill that process. By default, @value{GDBN} asks
2004 for confirmation if you try to do either of these things; you can
2005 control whether or not you need to confirm by using the @code{set
2006 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
2010 @section Killing the child process
2015 Kill the child process in which your program is running under @value{GDBN}.
2018 This command is useful if you wish to debug a core dump instead of a
2019 running process. @value{GDBN} ignores any core dump file while your program
2022 On some operating systems, a program cannot be executed outside @value{GDBN}
2023 while you have breakpoints set on it inside @value{GDBN}. You can use the
2024 @code{kill} command in this situation to permit running your program
2025 outside the debugger.
2027 The @code{kill} command is also useful if you wish to recompile and
2028 relink your program, since on many systems it is impossible to modify an
2029 executable file while it is running in a process. In this case, when you
2030 next type @code{run}, @value{GDBN} notices that the file has changed, and
2031 reads the symbol table again (while trying to preserve your current
2032 breakpoint settings).
2035 @section Debugging programs with multiple threads
2037 @cindex threads of execution
2038 @cindex multiple threads
2039 @cindex switching threads
2040 In some operating systems, such as HP-UX and Solaris, a single program
2041 may have more than one @dfn{thread} of execution. The precise semantics
2042 of threads differ from one operating system to another, but in general
2043 the threads of a single program are akin to multiple processes---except
2044 that they share one address space (that is, they can all examine and
2045 modify the same variables). On the other hand, each thread has its own
2046 registers and execution stack, and perhaps private memory.
2048 @value{GDBN} provides these facilities for debugging multi-thread
2052 @item automatic notification of new threads
2053 @item @samp{thread @var{threadno}}, a command to switch among threads
2054 @item @samp{info threads}, a command to inquire about existing threads
2055 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2056 a command to apply a command to a list of threads
2057 @item thread-specific breakpoints
2061 @emph{Warning:} These facilities are not yet available on every
2062 @value{GDBN} configuration where the operating system supports threads.
2063 If your @value{GDBN} does not support threads, these commands have no
2064 effect. For example, a system without thread support shows no output
2065 from @samp{info threads}, and always rejects the @code{thread} command,
2069 (@value{GDBP}) info threads
2070 (@value{GDBP}) thread 1
2071 Thread ID 1 not known. Use the "info threads" command to
2072 see the IDs of currently known threads.
2074 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2075 @c doesn't support threads"?
2078 @cindex focus of debugging
2079 @cindex current thread
2080 The @value{GDBN} thread debugging facility allows you to observe all
2081 threads while your program runs---but whenever @value{GDBN} takes
2082 control, one thread in particular is always the focus of debugging.
2083 This thread is called the @dfn{current thread}. Debugging commands show
2084 program information from the perspective of the current thread.
2086 @cindex @code{New} @var{systag} message
2087 @cindex thread identifier (system)
2088 @c FIXME-implementors!! It would be more helpful if the [New...] message
2089 @c included GDB's numeric thread handle, so you could just go to that
2090 @c thread without first checking `info threads'.
2091 Whenever @value{GDBN} detects a new thread in your program, it displays
2092 the target system's identification for the thread with a message in the
2093 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2094 whose form varies depending on the particular system. For example, on
2095 LynxOS, you might see
2098 [New process 35 thread 27]
2102 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2103 the @var{systag} is simply something like @samp{process 368}, with no
2106 @c FIXME!! (1) Does the [New...] message appear even for the very first
2107 @c thread of a program, or does it only appear for the
2108 @c second---i.e., when it becomes obvious we have a multithread
2110 @c (2) *Is* there necessarily a first thread always? Or do some
2111 @c multithread systems permit starting a program with multiple
2112 @c threads ab initio?
2114 @cindex thread number
2115 @cindex thread identifier (GDB)
2116 For debugging purposes, @value{GDBN} associates its own thread
2117 number---always a single integer---with each thread in your program.
2120 @kindex info threads
2122 Display a summary of all threads currently in your
2123 program. @value{GDBN} displays for each thread (in this order):
2126 @item the thread number assigned by @value{GDBN}
2128 @item the target system's thread identifier (@var{systag})
2130 @item the current stack frame summary for that thread
2134 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2135 indicates the current thread.
2139 @c end table here to get a little more width for example
2142 (@value{GDBP}) info threads
2143 3 process 35 thread 27 0x34e5 in sigpause ()
2144 2 process 35 thread 23 0x34e5 in sigpause ()
2145 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2151 @cindex thread number
2152 @cindex thread identifier (GDB)
2153 For debugging purposes, @value{GDBN} associates its own thread
2154 number---a small integer assigned in thread-creation order---with each
2155 thread in your program.
2157 @cindex @code{New} @var{systag} message, on HP-UX
2158 @cindex thread identifier (system), on HP-UX
2159 @c FIXME-implementors!! It would be more helpful if the [New...] message
2160 @c included GDB's numeric thread handle, so you could just go to that
2161 @c thread without first checking `info threads'.
2162 Whenever @value{GDBN} detects a new thread in your program, it displays
2163 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2164 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2165 whose form varies depending on the particular system. For example, on
2169 [New thread 2 (system thread 26594)]
2173 when @value{GDBN} notices a new thread.
2176 @kindex info threads
2178 Display a summary of all threads currently in your
2179 program. @value{GDBN} displays for each thread (in this order):
2182 @item the thread number assigned by @value{GDBN}
2184 @item the target system's thread identifier (@var{systag})
2186 @item the current stack frame summary for that thread
2190 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2191 indicates the current thread.
2195 @c end table here to get a little more width for example
2198 (@value{GDBP}) info threads
2199 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2201 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2202 from /usr/lib/libc.2
2203 1 system thread 27905 0x7b003498 in _brk () \@*
2204 from /usr/lib/libc.2
2208 @kindex thread @var{threadno}
2209 @item thread @var{threadno}
2210 Make thread number @var{threadno} the current thread. The command
2211 argument @var{threadno} is the internal @value{GDBN} thread number, as
2212 shown in the first field of the @samp{info threads} display.
2213 @value{GDBN} responds by displaying the system identifier of the thread
2214 you selected, and its current stack frame summary:
2217 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2218 (@value{GDBP}) thread 2
2219 [Switching to process 35 thread 23]
2220 0x34e5 in sigpause ()
2224 As with the @samp{[New @dots{}]} message, the form of the text after
2225 @samp{Switching to} depends on your system's conventions for identifying
2228 @kindex thread apply
2229 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2230 The @code{thread apply} command allows you to apply a command to one or
2231 more threads. Specify the numbers of the threads that you want affected
2232 with the command argument @var{threadno}. @var{threadno} is the internal
2233 @value{GDBN} thread number, as shown in the first field of the @samp{info
2234 threads} display. To apply a command to all threads, use
2235 @code{thread apply all} @var{args}.
2238 @cindex automatic thread selection
2239 @cindex switching threads automatically
2240 @cindex threads, automatic switching
2241 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2242 signal, it automatically selects the thread where that breakpoint or
2243 signal happened. @value{GDBN} alerts you to the context switch with a
2244 message of the form @samp{[Switching to @var{systag}]} to identify the
2247 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2248 more information about how @value{GDBN} behaves when you stop and start
2249 programs with multiple threads.
2251 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2252 watchpoints in programs with multiple threads.
2255 @section Debugging programs with multiple processes
2257 @cindex fork, debugging programs which call
2258 @cindex multiple processes
2259 @cindex processes, multiple
2260 On most systems, @value{GDBN} has no special support for debugging
2261 programs which create additional processes using the @code{fork}
2262 function. When a program forks, @value{GDBN} will continue to debug the
2263 parent process and the child process will run unimpeded. If you have
2264 set a breakpoint in any code which the child then executes, the child
2265 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2266 will cause it to terminate.
2268 However, if you want to debug the child process there is a workaround
2269 which isn't too painful. Put a call to @code{sleep} in the code which
2270 the child process executes after the fork. It may be useful to sleep
2271 only if a certain environment variable is set, or a certain file exists,
2272 so that the delay need not occur when you don't want to run @value{GDBN}
2273 on the child. While the child is sleeping, use the @code{ps} program to
2274 get its process ID. Then tell @value{GDBN} (a new invocation of
2275 @value{GDBN} if you are also debugging the parent process) to attach to
2276 the child process (@pxref{Attach}). From that point on you can debug
2277 the child process just like any other process which you attached to.
2279 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2280 debugging programs that create additional processes using the
2281 @code{fork} or @code{vfork} function.
2283 By default, when a program forks, @value{GDBN} will continue to debug
2284 the parent process and the child process will run unimpeded.
2286 If you want to follow the child process instead of the parent process,
2287 use the command @w{@code{set follow-fork-mode}}.
2290 @kindex set follow-fork-mode
2291 @item set follow-fork-mode @var{mode}
2292 Set the debugger response to a program call of @code{fork} or
2293 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2294 process. The @var{mode} can be:
2298 The original process is debugged after a fork. The child process runs
2299 unimpeded. This is the default.
2302 The new process is debugged after a fork. The parent process runs
2306 The debugger will ask for one of the above choices.
2309 @item show follow-fork-mode
2310 Display the current debugger response to a @code{fork} or @code{vfork} call.
2313 If you ask to debug a child process and a @code{vfork} is followed by an
2314 @code{exec}, @value{GDBN} executes the new target up to the first
2315 breakpoint in the new target. If you have a breakpoint set on
2316 @code{main} in your original program, the breakpoint will also be set on
2317 the child process's @code{main}.
2319 When a child process is spawned by @code{vfork}, you cannot debug the
2320 child or parent until an @code{exec} call completes.
2322 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2323 call executes, the new target restarts. To restart the parent process,
2324 use the @code{file} command with the parent executable name as its
2327 You can use the @code{catch} command to make @value{GDBN} stop whenever
2328 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2329 Catchpoints, ,Setting catchpoints}.
2332 @chapter Stopping and Continuing
2334 The principal purposes of using a debugger are so that you can stop your
2335 program before it terminates; or so that, if your program runs into
2336 trouble, you can investigate and find out why.
2338 Inside @value{GDBN}, your program may stop for any of several reasons,
2339 such as a signal, a breakpoint, or reaching a new line after a
2340 @value{GDBN} command such as @code{step}. You may then examine and
2341 change variables, set new breakpoints or remove old ones, and then
2342 continue execution. Usually, the messages shown by @value{GDBN} provide
2343 ample explanation of the status of your program---but you can also
2344 explicitly request this information at any time.
2347 @kindex info program
2349 Display information about the status of your program: whether it is
2350 running or not, what process it is, and why it stopped.
2354 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2355 * Continuing and Stepping:: Resuming execution
2357 * Thread Stops:: Stopping and starting multi-thread programs
2361 @section Breakpoints, watchpoints, and catchpoints
2364 A @dfn{breakpoint} makes your program stop whenever a certain point in
2365 the program is reached. For each breakpoint, you can add conditions to
2366 control in finer detail whether your program stops. You can set
2367 breakpoints with the @code{break} command and its variants (@pxref{Set
2368 Breaks, ,Setting breakpoints}), to specify the place where your program
2369 should stop by line number, function name or exact address in the
2372 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2373 breakpoints in shared libraries before the executable is run. There is
2374 a minor limitation on HP-UX systems: you must wait until the executable
2375 is run in order to set breakpoints in shared library routines that are
2376 not called directly by the program (for example, routines that are
2377 arguments in a @code{pthread_create} call).
2380 @cindex memory tracing
2381 @cindex breakpoint on memory address
2382 @cindex breakpoint on variable modification
2383 A @dfn{watchpoint} is a special breakpoint that stops your program
2384 when the value of an expression changes. You must use a different
2385 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2386 watchpoints}), but aside from that, you can manage a watchpoint like
2387 any other breakpoint: you enable, disable, and delete both breakpoints
2388 and watchpoints using the same commands.
2390 You can arrange to have values from your program displayed automatically
2391 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2395 @cindex breakpoint on events
2396 A @dfn{catchpoint} is another special breakpoint that stops your program
2397 when a certain kind of event occurs, such as the throwing of a C@t{++}
2398 exception or the loading of a library. As with watchpoints, you use a
2399 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2400 catchpoints}), but aside from that, you can manage a catchpoint like any
2401 other breakpoint. (To stop when your program receives a signal, use the
2402 @code{handle} command; see @ref{Signals, ,Signals}.)
2404 @cindex breakpoint numbers
2405 @cindex numbers for breakpoints
2406 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2407 catchpoint when you create it; these numbers are successive integers
2408 starting with one. In many of the commands for controlling various
2409 features of breakpoints you use the breakpoint number to say which
2410 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2411 @dfn{disabled}; if disabled, it has no effect on your program until you
2414 @cindex breakpoint ranges
2415 @cindex ranges of breakpoints
2416 Some @value{GDBN} commands accept a range of breakpoints on which to
2417 operate. A breakpoint range is either a single breakpoint number, like
2418 @samp{5}, or two such numbers, in increasing order, separated by a
2419 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2420 all breakpoint in that range are operated on.
2423 * Set Breaks:: Setting breakpoints
2424 * Set Watchpoints:: Setting watchpoints
2425 * Set Catchpoints:: Setting catchpoints
2426 * Delete Breaks:: Deleting breakpoints
2427 * Disabling:: Disabling breakpoints
2428 * Conditions:: Break conditions
2429 * Break Commands:: Breakpoint command lists
2430 * Breakpoint Menus:: Breakpoint menus
2431 * Error in Breakpoints:: ``Cannot insert breakpoints''
2435 @subsection Setting breakpoints
2437 @c FIXME LMB what does GDB do if no code on line of breakpt?
2438 @c consider in particular declaration with/without initialization.
2440 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2443 @kindex b @r{(@code{break})}
2444 @vindex $bpnum@r{, convenience variable}
2445 @cindex latest breakpoint
2446 Breakpoints are set with the @code{break} command (abbreviated
2447 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2448 number of the breakpoint you've set most recently; see @ref{Convenience
2449 Vars,, Convenience variables}, for a discussion of what you can do with
2450 convenience variables.
2452 You have several ways to say where the breakpoint should go.
2455 @item break @var{function}
2456 Set a breakpoint at entry to function @var{function}.
2457 When using source languages that permit overloading of symbols, such as
2458 C@t{++}, @var{function} may refer to more than one possible place to break.
2459 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2461 @item break +@var{offset}
2462 @itemx break -@var{offset}
2463 Set a breakpoint some number of lines forward or back from the position
2464 at which execution stopped in the currently selected @dfn{stack frame}.
2465 (@xref{Frames, ,Frames}, for a description of stack frames.)
2467 @item break @var{linenum}
2468 Set a breakpoint at line @var{linenum} in the current source file.
2469 The current source file is the last file whose source text was printed.
2470 The breakpoint will stop your program just before it executes any of the
2473 @item break @var{filename}:@var{linenum}
2474 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2476 @item break @var{filename}:@var{function}
2477 Set a breakpoint at entry to function @var{function} found in file
2478 @var{filename}. Specifying a file name as well as a function name is
2479 superfluous except when multiple files contain similarly named
2482 @item break *@var{address}
2483 Set a breakpoint at address @var{address}. You can use this to set
2484 breakpoints in parts of your program which do not have debugging
2485 information or source files.
2488 When called without any arguments, @code{break} sets a breakpoint at
2489 the next instruction to be executed in the selected stack frame
2490 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2491 innermost, this makes your program stop as soon as control
2492 returns to that frame. This is similar to the effect of a
2493 @code{finish} command in the frame inside the selected frame---except
2494 that @code{finish} does not leave an active breakpoint. If you use
2495 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2496 the next time it reaches the current location; this may be useful
2499 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2500 least one instruction has been executed. If it did not do this, you
2501 would be unable to proceed past a breakpoint without first disabling the
2502 breakpoint. This rule applies whether or not the breakpoint already
2503 existed when your program stopped.
2505 @item break @dots{} if @var{cond}
2506 Set a breakpoint with condition @var{cond}; evaluate the expression
2507 @var{cond} each time the breakpoint is reached, and stop only if the
2508 value is nonzero---that is, if @var{cond} evaluates as true.
2509 @samp{@dots{}} stands for one of the possible arguments described
2510 above (or no argument) specifying where to break. @xref{Conditions,
2511 ,Break conditions}, for more information on breakpoint conditions.
2514 @item tbreak @var{args}
2515 Set a breakpoint enabled only for one stop. @var{args} are the
2516 same as for the @code{break} command, and the breakpoint is set in the same
2517 way, but the breakpoint is automatically deleted after the first time your
2518 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2521 @item hbreak @var{args}
2522 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2523 @code{break} command and the breakpoint is set in the same way, but the
2524 breakpoint requires hardware support and some target hardware may not
2525 have this support. The main purpose of this is EPROM/ROM code
2526 debugging, so you can set a breakpoint at an instruction without
2527 changing the instruction. This can be used with the new trap-generation
2528 provided by SPARClite DSU and some x86-based targets. These targets
2529 will generate traps when a program accesses some data or instruction
2530 address that is assigned to the debug registers. However the hardware
2531 breakpoint registers can take a limited number of breakpoints. For
2532 example, on the DSU, only two data breakpoints can be set at a time, and
2533 @value{GDBN} will reject this command if more than two are used. Delete
2534 or disable unused hardware breakpoints before setting new ones
2535 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2538 @item thbreak @var{args}
2539 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2540 are the same as for the @code{hbreak} command and the breakpoint is set in
2541 the same way. However, like the @code{tbreak} command,
2542 the breakpoint is automatically deleted after the
2543 first time your program stops there. Also, like the @code{hbreak}
2544 command, the breakpoint requires hardware support and some target hardware
2545 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2546 See also @ref{Conditions, ,Break conditions}.
2549 @cindex regular expression
2550 @item rbreak @var{regex}
2551 Set breakpoints on all functions matching the regular expression
2552 @var{regex}. This command sets an unconditional breakpoint on all
2553 matches, printing a list of all breakpoints it set. Once these
2554 breakpoints are set, they are treated just like the breakpoints set with
2555 the @code{break} command. You can delete them, disable them, or make
2556 them conditional the same way as any other breakpoint.
2558 The syntax of the regular expression is the standard one used with tools
2559 like @file{grep}. Note that this is different from the syntax used by
2560 shells, so for instance @code{foo*} matches all functions that include
2561 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2562 @code{.*} leading and trailing the regular expression you supply, so to
2563 match only functions that begin with @code{foo}, use @code{^foo}.
2565 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2566 breakpoints on overloaded functions that are not members of any special
2569 @kindex info breakpoints
2570 @cindex @code{$_} and @code{info breakpoints}
2571 @item info breakpoints @r{[}@var{n}@r{]}
2572 @itemx info break @r{[}@var{n}@r{]}
2573 @itemx info watchpoints @r{[}@var{n}@r{]}
2574 Print a table of all breakpoints, watchpoints, and catchpoints set and
2575 not deleted, with the following columns for each breakpoint:
2578 @item Breakpoint Numbers
2580 Breakpoint, watchpoint, or catchpoint.
2582 Whether the breakpoint is marked to be disabled or deleted when hit.
2583 @item Enabled or Disabled
2584 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2585 that are not enabled.
2587 Where the breakpoint is in your program, as a memory address.
2589 Where the breakpoint is in the source for your program, as a file and
2594 If a breakpoint is conditional, @code{info break} shows the condition on
2595 the line following the affected breakpoint; breakpoint commands, if any,
2596 are listed after that.
2599 @code{info break} with a breakpoint
2600 number @var{n} as argument lists only that breakpoint. The
2601 convenience variable @code{$_} and the default examining-address for
2602 the @code{x} command are set to the address of the last breakpoint
2603 listed (@pxref{Memory, ,Examining memory}).
2606 @code{info break} displays a count of the number of times the breakpoint
2607 has been hit. This is especially useful in conjunction with the
2608 @code{ignore} command. You can ignore a large number of breakpoint
2609 hits, look at the breakpoint info to see how many times the breakpoint
2610 was hit, and then run again, ignoring one less than that number. This
2611 will get you quickly to the last hit of that breakpoint.
2614 @value{GDBN} allows you to set any number of breakpoints at the same place in
2615 your program. There is nothing silly or meaningless about this. When
2616 the breakpoints are conditional, this is even useful
2617 (@pxref{Conditions, ,Break conditions}).
2619 @cindex negative breakpoint numbers
2620 @cindex internal @value{GDBN} breakpoints
2621 @value{GDBN} itself sometimes sets breakpoints in your program for special
2622 purposes, such as proper handling of @code{longjmp} (in C programs).
2623 These internal breakpoints are assigned negative numbers, starting with
2624 @code{-1}; @samp{info breakpoints} does not display them.
2626 You can see these breakpoints with the @value{GDBN} maintenance command
2627 @samp{maint info breakpoints}.
2630 @kindex maint info breakpoints
2631 @item maint info breakpoints
2632 Using the same format as @samp{info breakpoints}, display both the
2633 breakpoints you've set explicitly, and those @value{GDBN} is using for
2634 internal purposes. Internal breakpoints are shown with negative
2635 breakpoint numbers. The type column identifies what kind of breakpoint
2640 Normal, explicitly set breakpoint.
2643 Normal, explicitly set watchpoint.
2646 Internal breakpoint, used to handle correctly stepping through
2647 @code{longjmp} calls.
2649 @item longjmp resume
2650 Internal breakpoint at the target of a @code{longjmp}.
2653 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2656 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2659 Shared library events.
2666 @node Set Watchpoints
2667 @subsection Setting watchpoints
2669 @cindex setting watchpoints
2670 @cindex software watchpoints
2671 @cindex hardware watchpoints
2672 You can use a watchpoint to stop execution whenever the value of an
2673 expression changes, without having to predict a particular place where
2676 Depending on your system, watchpoints may be implemented in software or
2677 hardware. @value{GDBN} does software watchpointing by single-stepping your
2678 program and testing the variable's value each time, which is hundreds of
2679 times slower than normal execution. (But this may still be worth it, to
2680 catch errors where you have no clue what part of your program is the
2683 On some systems, such as HP-UX, Linux and some other x86-based targets,
2684 @value{GDBN} includes support for
2685 hardware watchpoints, which do not slow down the running of your
2690 @item watch @var{expr}
2691 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2692 is written into by the program and its value changes.
2695 @item rwatch @var{expr}
2696 Set a watchpoint that will break when watch @var{expr} is read by the program.
2699 @item awatch @var{expr}
2700 Set a watchpoint that will break when @var{expr} is either read or written into
2703 @kindex info watchpoints
2704 @item info watchpoints
2705 This command prints a list of watchpoints, breakpoints, and catchpoints;
2706 it is the same as @code{info break}.
2709 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2710 watchpoints execute very quickly, and the debugger reports a change in
2711 value at the exact instruction where the change occurs. If @value{GDBN}
2712 cannot set a hardware watchpoint, it sets a software watchpoint, which
2713 executes more slowly and reports the change in value at the next
2714 statement, not the instruction, after the change occurs.
2716 When you issue the @code{watch} command, @value{GDBN} reports
2719 Hardware watchpoint @var{num}: @var{expr}
2723 if it was able to set a hardware watchpoint.
2725 Currently, the @code{awatch} and @code{rwatch} commands can only set
2726 hardware watchpoints, because accesses to data that don't change the
2727 value of the watched expression cannot be detected without examining
2728 every instruction as it is being executed, and @value{GDBN} does not do
2729 that currently. If @value{GDBN} finds that it is unable to set a
2730 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2731 will print a message like this:
2734 Expression cannot be implemented with read/access watchpoint.
2737 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2738 data type of the watched expression is wider than what a hardware
2739 watchpoint on the target machine can handle. For example, some systems
2740 can only watch regions that are up to 4 bytes wide; on such systems you
2741 cannot set hardware watchpoints for an expression that yields a
2742 double-precision floating-point number (which is typically 8 bytes
2743 wide). As a work-around, it might be possible to break the large region
2744 into a series of smaller ones and watch them with separate watchpoints.
2746 If you set too many hardware watchpoints, @value{GDBN} might be unable
2747 to insert all of them when you resume the execution of your program.
2748 Since the precise number of active watchpoints is unknown until such
2749 time as the program is about to be resumed, @value{GDBN} might not be
2750 able to warn you about this when you set the watchpoints, and the
2751 warning will be printed only when the program is resumed:
2754 Hardware watchpoint @var{num}: Could not insert watchpoint
2758 If this happens, delete or disable some of the watchpoints.
2760 The SPARClite DSU will generate traps when a program accesses some data
2761 or instruction address that is assigned to the debug registers. For the
2762 data addresses, DSU facilitates the @code{watch} command. However the
2763 hardware breakpoint registers can only take two data watchpoints, and
2764 both watchpoints must be the same kind. For example, you can set two
2765 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2766 @strong{or} two with @code{awatch} commands, but you cannot set one
2767 watchpoint with one command and the other with a different command.
2768 @value{GDBN} will reject the command if you try to mix watchpoints.
2769 Delete or disable unused watchpoint commands before setting new ones.
2771 If you call a function interactively using @code{print} or @code{call},
2772 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2773 kind of breakpoint or the call completes.
2775 @value{GDBN} automatically deletes watchpoints that watch local
2776 (automatic) variables, or expressions that involve such variables, when
2777 they go out of scope, that is, when the execution leaves the block in
2778 which these variables were defined. In particular, when the program
2779 being debugged terminates, @emph{all} local variables go out of scope,
2780 and so only watchpoints that watch global variables remain set. If you
2781 rerun the program, you will need to set all such watchpoints again. One
2782 way of doing that would be to set a code breakpoint at the entry to the
2783 @code{main} function and when it breaks, set all the watchpoints.
2786 @cindex watchpoints and threads
2787 @cindex threads and watchpoints
2788 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2789 usefulness. With the current watchpoint implementation, @value{GDBN}
2790 can only watch the value of an expression @emph{in a single thread}. If
2791 you are confident that the expression can only change due to the current
2792 thread's activity (and if you are also confident that no other thread
2793 can become current), then you can use watchpoints as usual. However,
2794 @value{GDBN} may not notice when a non-current thread's activity changes
2797 @c FIXME: this is almost identical to the previous paragraph.
2798 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2799 have only limited usefulness. If @value{GDBN} creates a software
2800 watchpoint, it can only watch the value of an expression @emph{in a
2801 single thread}. If you are confident that the expression can only
2802 change due to the current thread's activity (and if you are also
2803 confident that no other thread can become current), then you can use
2804 software watchpoints as usual. However, @value{GDBN} may not notice
2805 when a non-current thread's activity changes the expression. (Hardware
2806 watchpoints, in contrast, watch an expression in all threads.)
2809 @node Set Catchpoints
2810 @subsection Setting catchpoints
2811 @cindex catchpoints, setting
2812 @cindex exception handlers
2813 @cindex event handling
2815 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2816 kinds of program events, such as C@t{++} exceptions or the loading of a
2817 shared library. Use the @code{catch} command to set a catchpoint.
2821 @item catch @var{event}
2822 Stop when @var{event} occurs. @var{event} can be any of the following:
2826 The throwing of a C@t{++} exception.
2830 The catching of a C@t{++} exception.
2834 A call to @code{exec}. This is currently only available for HP-UX.
2838 A call to @code{fork}. This is currently only available for HP-UX.
2842 A call to @code{vfork}. This is currently only available for HP-UX.
2845 @itemx load @var{libname}
2847 The dynamic loading of any shared library, or the loading of the library
2848 @var{libname}. This is currently only available for HP-UX.
2851 @itemx unload @var{libname}
2852 @kindex catch unload
2853 The unloading of any dynamically loaded shared library, or the unloading
2854 of the library @var{libname}. This is currently only available for HP-UX.
2857 @item tcatch @var{event}
2858 Set a catchpoint that is enabled only for one stop. The catchpoint is
2859 automatically deleted after the first time the event is caught.
2863 Use the @code{info break} command to list the current catchpoints.
2865 There are currently some limitations to C@t{++} exception handling
2866 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2870 If you call a function interactively, @value{GDBN} normally returns
2871 control to you when the function has finished executing. If the call
2872 raises an exception, however, the call may bypass the mechanism that
2873 returns control to you and cause your program either to abort or to
2874 simply continue running until it hits a breakpoint, catches a signal
2875 that @value{GDBN} is listening for, or exits. This is the case even if
2876 you set a catchpoint for the exception; catchpoints on exceptions are
2877 disabled within interactive calls.
2880 You cannot raise an exception interactively.
2883 You cannot install an exception handler interactively.
2886 @cindex raise exceptions
2887 Sometimes @code{catch} is not the best way to debug exception handling:
2888 if you need to know exactly where an exception is raised, it is better to
2889 stop @emph{before} the exception handler is called, since that way you
2890 can see the stack before any unwinding takes place. If you set a
2891 breakpoint in an exception handler instead, it may not be easy to find
2892 out where the exception was raised.
2894 To stop just before an exception handler is called, you need some
2895 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2896 raised by calling a library function named @code{__raise_exception}
2897 which has the following ANSI C interface:
2900 /* @var{addr} is where the exception identifier is stored.
2901 @var{id} is the exception identifier. */
2902 void __raise_exception (void **addr, void *id);
2906 To make the debugger catch all exceptions before any stack
2907 unwinding takes place, set a breakpoint on @code{__raise_exception}
2908 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2910 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2911 that depends on the value of @var{id}, you can stop your program when
2912 a specific exception is raised. You can use multiple conditional
2913 breakpoints to stop your program when any of a number of exceptions are
2918 @subsection Deleting breakpoints
2920 @cindex clearing breakpoints, watchpoints, catchpoints
2921 @cindex deleting breakpoints, watchpoints, catchpoints
2922 It is often necessary to eliminate a breakpoint, watchpoint, or
2923 catchpoint once it has done its job and you no longer want your program
2924 to stop there. This is called @dfn{deleting} the breakpoint. A
2925 breakpoint that has been deleted no longer exists; it is forgotten.
2927 With the @code{clear} command you can delete breakpoints according to
2928 where they are in your program. With the @code{delete} command you can
2929 delete individual breakpoints, watchpoints, or catchpoints by specifying
2930 their breakpoint numbers.
2932 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2933 automatically ignores breakpoints on the first instruction to be executed
2934 when you continue execution without changing the execution address.
2939 Delete any breakpoints at the next instruction to be executed in the
2940 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2941 the innermost frame is selected, this is a good way to delete a
2942 breakpoint where your program just stopped.
2944 @item clear @var{function}
2945 @itemx clear @var{filename}:@var{function}
2946 Delete any breakpoints set at entry to the function @var{function}.
2948 @item clear @var{linenum}
2949 @itemx clear @var{filename}:@var{linenum}
2950 Delete any breakpoints set at or within the code of the specified line.
2952 @cindex delete breakpoints
2954 @kindex d @r{(@code{delete})}
2955 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2956 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2957 ranges specified as arguments. If no argument is specified, delete all
2958 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2959 confirm off}). You can abbreviate this command as @code{d}.
2963 @subsection Disabling breakpoints
2965 @kindex disable breakpoints
2966 @kindex enable breakpoints
2967 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2968 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2969 it had been deleted, but remembers the information on the breakpoint so
2970 that you can @dfn{enable} it again later.
2972 You disable and enable breakpoints, watchpoints, and catchpoints with
2973 the @code{enable} and @code{disable} commands, optionally specifying one
2974 or more breakpoint numbers as arguments. Use @code{info break} or
2975 @code{info watch} to print a list of breakpoints, watchpoints, and
2976 catchpoints if you do not know which numbers to use.
2978 A breakpoint, watchpoint, or catchpoint can have any of four different
2979 states of enablement:
2983 Enabled. The breakpoint stops your program. A breakpoint set
2984 with the @code{break} command starts out in this state.
2986 Disabled. The breakpoint has no effect on your program.
2988 Enabled once. The breakpoint stops your program, but then becomes
2991 Enabled for deletion. The breakpoint stops your program, but
2992 immediately after it does so it is deleted permanently. A breakpoint
2993 set with the @code{tbreak} command starts out in this state.
2996 You can use the following commands to enable or disable breakpoints,
2997 watchpoints, and catchpoints:
3000 @kindex disable breakpoints
3002 @kindex dis @r{(@code{disable})}
3003 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3004 Disable the specified breakpoints---or all breakpoints, if none are
3005 listed. A disabled breakpoint has no effect but is not forgotten. All
3006 options such as ignore-counts, conditions and commands are remembered in
3007 case the breakpoint is enabled again later. You may abbreviate
3008 @code{disable} as @code{dis}.
3010 @kindex enable breakpoints
3012 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3013 Enable the specified breakpoints (or all defined breakpoints). They
3014 become effective once again in stopping your program.
3016 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
3017 Enable the specified breakpoints temporarily. @value{GDBN} disables any
3018 of these breakpoints immediately after stopping your program.
3020 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
3021 Enable the specified breakpoints to work once, then die. @value{GDBN}
3022 deletes any of these breakpoints as soon as your program stops there.
3025 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
3026 @c confusing: tbreak is also initially enabled.
3027 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3028 ,Setting breakpoints}), breakpoints that you set are initially enabled;
3029 subsequently, they become disabled or enabled only when you use one of
3030 the commands above. (The command @code{until} can set and delete a
3031 breakpoint of its own, but it does not change the state of your other
3032 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3036 @subsection Break conditions
3037 @cindex conditional breakpoints
3038 @cindex breakpoint conditions
3040 @c FIXME what is scope of break condition expr? Context where wanted?
3041 @c in particular for a watchpoint?
3042 The simplest sort of breakpoint breaks every time your program reaches a
3043 specified place. You can also specify a @dfn{condition} for a
3044 breakpoint. A condition is just a Boolean expression in your
3045 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3046 a condition evaluates the expression each time your program reaches it,
3047 and your program stops only if the condition is @emph{true}.
3049 This is the converse of using assertions for program validation; in that
3050 situation, you want to stop when the assertion is violated---that is,
3051 when the condition is false. In C, if you want to test an assertion expressed
3052 by the condition @var{assert}, you should set the condition
3053 @samp{! @var{assert}} on the appropriate breakpoint.
3055 Conditions are also accepted for watchpoints; you may not need them,
3056 since a watchpoint is inspecting the value of an expression anyhow---but
3057 it might be simpler, say, to just set a watchpoint on a variable name,
3058 and specify a condition that tests whether the new value is an interesting
3061 Break conditions can have side effects, and may even call functions in
3062 your program. This can be useful, for example, to activate functions
3063 that log program progress, or to use your own print functions to
3064 format special data structures. The effects are completely predictable
3065 unless there is another enabled breakpoint at the same address. (In
3066 that case, @value{GDBN} might see the other breakpoint first and stop your
3067 program without checking the condition of this one.) Note that
3068 breakpoint commands are usually more convenient and flexible than break
3070 purpose of performing side effects when a breakpoint is reached
3071 (@pxref{Break Commands, ,Breakpoint command lists}).
3073 Break conditions can be specified when a breakpoint is set, by using
3074 @samp{if} in the arguments to the @code{break} command. @xref{Set
3075 Breaks, ,Setting breakpoints}. They can also be changed at any time
3076 with the @code{condition} command.
3078 You can also use the @code{if} keyword with the @code{watch} command.
3079 The @code{catch} command does not recognize the @code{if} keyword;
3080 @code{condition} is the only way to impose a further condition on a
3085 @item condition @var{bnum} @var{expression}
3086 Specify @var{expression} as the break condition for breakpoint,
3087 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3088 breakpoint @var{bnum} stops your program only if the value of
3089 @var{expression} is true (nonzero, in C). When you use
3090 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3091 syntactic correctness, and to determine whether symbols in it have
3092 referents in the context of your breakpoint. If @var{expression} uses
3093 symbols not referenced in the context of the breakpoint, @value{GDBN}
3094 prints an error message:
3097 No symbol "foo" in current context.
3102 not actually evaluate @var{expression} at the time the @code{condition}
3103 command (or a command that sets a breakpoint with a condition, like
3104 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3106 @item condition @var{bnum}
3107 Remove the condition from breakpoint number @var{bnum}. It becomes
3108 an ordinary unconditional breakpoint.
3111 @cindex ignore count (of breakpoint)
3112 A special case of a breakpoint condition is to stop only when the
3113 breakpoint has been reached a certain number of times. This is so
3114 useful that there is a special way to do it, using the @dfn{ignore
3115 count} of the breakpoint. Every breakpoint has an ignore count, which
3116 is an integer. Most of the time, the ignore count is zero, and
3117 therefore has no effect. But if your program reaches a breakpoint whose
3118 ignore count is positive, then instead of stopping, it just decrements
3119 the ignore count by one and continues. As a result, if the ignore count
3120 value is @var{n}, the breakpoint does not stop the next @var{n} times
3121 your program reaches it.
3125 @item ignore @var{bnum} @var{count}
3126 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3127 The next @var{count} times the breakpoint is reached, your program's
3128 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3131 To make the breakpoint stop the next time it is reached, specify
3134 When you use @code{continue} to resume execution of your program from a
3135 breakpoint, you can specify an ignore count directly as an argument to
3136 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3137 Stepping,,Continuing and stepping}.
3139 If a breakpoint has a positive ignore count and a condition, the
3140 condition is not checked. Once the ignore count reaches zero,
3141 @value{GDBN} resumes checking the condition.
3143 You could achieve the effect of the ignore count with a condition such
3144 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3145 is decremented each time. @xref{Convenience Vars, ,Convenience
3149 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3152 @node Break Commands
3153 @subsection Breakpoint command lists
3155 @cindex breakpoint commands
3156 You can give any breakpoint (or watchpoint or catchpoint) a series of
3157 commands to execute when your program stops due to that breakpoint. For
3158 example, you might want to print the values of certain expressions, or
3159 enable other breakpoints.
3164 @item commands @r{[}@var{bnum}@r{]}
3165 @itemx @dots{} @var{command-list} @dots{}
3167 Specify a list of commands for breakpoint number @var{bnum}. The commands
3168 themselves appear on the following lines. Type a line containing just
3169 @code{end} to terminate the commands.
3171 To remove all commands from a breakpoint, type @code{commands} and
3172 follow it immediately with @code{end}; that is, give no commands.
3174 With no @var{bnum} argument, @code{commands} refers to the last
3175 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3176 recently encountered).
3179 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3180 disabled within a @var{command-list}.
3182 You can use breakpoint commands to start your program up again. Simply
3183 use the @code{continue} command, or @code{step}, or any other command
3184 that resumes execution.
3186 Any other commands in the command list, after a command that resumes
3187 execution, are ignored. This is because any time you resume execution
3188 (even with a simple @code{next} or @code{step}), you may encounter
3189 another breakpoint---which could have its own command list, leading to
3190 ambiguities about which list to execute.
3193 If the first command you specify in a command list is @code{silent}, the
3194 usual message about stopping at a breakpoint is not printed. This may
3195 be desirable for breakpoints that are to print a specific message and
3196 then continue. If none of the remaining commands print anything, you
3197 see no sign that the breakpoint was reached. @code{silent} is
3198 meaningful only at the beginning of a breakpoint command list.
3200 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3201 print precisely controlled output, and are often useful in silent
3202 breakpoints. @xref{Output, ,Commands for controlled output}.
3204 For example, here is how you could use breakpoint commands to print the
3205 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3211 printf "x is %d\n",x
3216 One application for breakpoint commands is to compensate for one bug so
3217 you can test for another. Put a breakpoint just after the erroneous line
3218 of code, give it a condition to detect the case in which something
3219 erroneous has been done, and give it commands to assign correct values
3220 to any variables that need them. End with the @code{continue} command
3221 so that your program does not stop, and start with the @code{silent}
3222 command so that no output is produced. Here is an example:
3233 @node Breakpoint Menus
3234 @subsection Breakpoint menus
3236 @cindex symbol overloading
3238 Some programming languages (notably C@t{++}) permit a single function name
3239 to be defined several times, for application in different contexts.
3240 This is called @dfn{overloading}. When a function name is overloaded,
3241 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3242 a breakpoint. If you realize this is a problem, you can use
3243 something like @samp{break @var{function}(@var{types})} to specify which
3244 particular version of the function you want. Otherwise, @value{GDBN} offers
3245 you a menu of numbered choices for different possible breakpoints, and
3246 waits for your selection with the prompt @samp{>}. The first two
3247 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3248 sets a breakpoint at each definition of @var{function}, and typing
3249 @kbd{0} aborts the @code{break} command without setting any new
3252 For example, the following session excerpt shows an attempt to set a
3253 breakpoint at the overloaded symbol @code{String::after}.
3254 We choose three particular definitions of that function name:
3256 @c FIXME! This is likely to change to show arg type lists, at least
3259 (@value{GDBP}) b String::after
3262 [2] file:String.cc; line number:867
3263 [3] file:String.cc; line number:860
3264 [4] file:String.cc; line number:875
3265 [5] file:String.cc; line number:853
3266 [6] file:String.cc; line number:846
3267 [7] file:String.cc; line number:735
3269 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3270 Breakpoint 2 at 0xb344: file String.cc, line 875.
3271 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3272 Multiple breakpoints were set.
3273 Use the "delete" command to delete unwanted
3279 @c @ifclear BARETARGET
3280 @node Error in Breakpoints
3281 @subsection ``Cannot insert breakpoints''
3283 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3285 Under some operating systems, breakpoints cannot be used in a program if
3286 any other process is running that program. In this situation,
3287 attempting to run or continue a program with a breakpoint causes
3288 @value{GDBN} to print an error message:
3291 Cannot insert breakpoints.
3292 The same program may be running in another process.
3295 When this happens, you have three ways to proceed:
3299 Remove or disable the breakpoints, then continue.
3302 Suspend @value{GDBN}, and copy the file containing your program to a new
3303 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3304 that @value{GDBN} should run your program under that name.
3305 Then start your program again.
3308 Relink your program so that the text segment is nonsharable, using the
3309 linker option @samp{-N}. The operating system limitation may not apply
3310 to nonsharable executables.
3314 A similar message can be printed if you request too many active
3315 hardware-assisted breakpoints and watchpoints:
3317 @c FIXME: the precise wording of this message may change; the relevant
3318 @c source change is not committed yet (Sep 3, 1999).
3320 Stopped; cannot insert breakpoints.
3321 You may have requested too many hardware breakpoints and watchpoints.
3325 This message is printed when you attempt to resume the program, since
3326 only then @value{GDBN} knows exactly how many hardware breakpoints and
3327 watchpoints it needs to insert.
3329 When this message is printed, you need to disable or remove some of the
3330 hardware-assisted breakpoints and watchpoints, and then continue.
3333 @node Continuing and Stepping
3334 @section Continuing and stepping
3338 @cindex resuming execution
3339 @dfn{Continuing} means resuming program execution until your program
3340 completes normally. In contrast, @dfn{stepping} means executing just
3341 one more ``step'' of your program, where ``step'' may mean either one
3342 line of source code, or one machine instruction (depending on what
3343 particular command you use). Either when continuing or when stepping,
3344 your program may stop even sooner, due to a breakpoint or a signal. (If
3345 it stops due to a signal, you may want to use @code{handle}, or use
3346 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3350 @kindex c @r{(@code{continue})}
3351 @kindex fg @r{(resume foreground execution)}
3352 @item continue @r{[}@var{ignore-count}@r{]}
3353 @itemx c @r{[}@var{ignore-count}@r{]}
3354 @itemx fg @r{[}@var{ignore-count}@r{]}
3355 Resume program execution, at the address where your program last stopped;
3356 any breakpoints set at that address are bypassed. The optional argument
3357 @var{ignore-count} allows you to specify a further number of times to
3358 ignore a breakpoint at this location; its effect is like that of
3359 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3361 The argument @var{ignore-count} is meaningful only when your program
3362 stopped due to a breakpoint. At other times, the argument to
3363 @code{continue} is ignored.
3365 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3366 debugged program is deemed to be the foreground program) are provided
3367 purely for convenience, and have exactly the same behavior as
3371 To resume execution at a different place, you can use @code{return}
3372 (@pxref{Returning, ,Returning from a function}) to go back to the
3373 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3374 different address}) to go to an arbitrary location in your program.
3376 A typical technique for using stepping is to set a breakpoint
3377 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3378 beginning of the function or the section of your program where a problem
3379 is believed to lie, run your program until it stops at that breakpoint,
3380 and then step through the suspect area, examining the variables that are
3381 interesting, until you see the problem happen.
3385 @kindex s @r{(@code{step})}
3387 Continue running your program until control reaches a different source
3388 line, then stop it and return control to @value{GDBN}. This command is
3389 abbreviated @code{s}.
3392 @c "without debugging information" is imprecise; actually "without line
3393 @c numbers in the debugging information". (gcc -g1 has debugging info but
3394 @c not line numbers). But it seems complex to try to make that
3395 @c distinction here.
3396 @emph{Warning:} If you use the @code{step} command while control is
3397 within a function that was compiled without debugging information,
3398 execution proceeds until control reaches a function that does have
3399 debugging information. Likewise, it will not step into a function which
3400 is compiled without debugging information. To step through functions
3401 without debugging information, use the @code{stepi} command, described
3405 The @code{step} command only stops at the first instruction of a source
3406 line. This prevents the multiple stops that could otherwise occur in
3407 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3408 to stop if a function that has debugging information is called within
3409 the line. In other words, @code{step} @emph{steps inside} any functions
3410 called within the line.
3412 Also, the @code{step} command only enters a function if there is line
3413 number information for the function. Otherwise it acts like the
3414 @code{next} command. This avoids problems when using @code{cc -gl}
3415 on MIPS machines. Previously, @code{step} entered subroutines if there
3416 was any debugging information about the routine.
3418 @item step @var{count}
3419 Continue running as in @code{step}, but do so @var{count} times. If a
3420 breakpoint is reached, or a signal not related to stepping occurs before
3421 @var{count} steps, stepping stops right away.
3424 @kindex n @r{(@code{next})}
3425 @item next @r{[}@var{count}@r{]}
3426 Continue to the next source line in the current (innermost) stack frame.
3427 This is similar to @code{step}, but function calls that appear within
3428 the line of code are executed without stopping. Execution stops when
3429 control reaches a different line of code at the original stack level
3430 that was executing when you gave the @code{next} command. This command
3431 is abbreviated @code{n}.
3433 An argument @var{count} is a repeat count, as for @code{step}.
3436 @c FIX ME!! Do we delete this, or is there a way it fits in with
3437 @c the following paragraph? --- Vctoria
3439 @c @code{next} within a function that lacks debugging information acts like
3440 @c @code{step}, but any function calls appearing within the code of the
3441 @c function are executed without stopping.
3443 The @code{next} command only stops at the first instruction of a
3444 source line. This prevents multiple stops that could otherwise occur in
3445 @code{switch} statements, @code{for} loops, etc.
3447 @kindex set step-mode
3449 @cindex functions without line info, and stepping
3450 @cindex stepping into functions with no line info
3451 @itemx set step-mode on
3452 The @code{set step-mode on} command causes the @code{step} command to
3453 stop at the first instruction of a function which contains no debug line
3454 information rather than stepping over it.
3456 This is useful in cases where you may be interested in inspecting the
3457 machine instructions of a function which has no symbolic info and do not
3458 want @value{GDBN} to automatically skip over this function.
3460 @item set step-mode off
3461 Causes the @code{step} command to step over any functions which contains no
3462 debug information. This is the default.
3466 Continue running until just after function in the selected stack frame
3467 returns. Print the returned value (if any).
3469 Contrast this with the @code{return} command (@pxref{Returning,
3470 ,Returning from a function}).
3473 @kindex u @r{(@code{until})}
3476 Continue running until a source line past the current line, in the
3477 current stack frame, is reached. This command is used to avoid single
3478 stepping through a loop more than once. It is like the @code{next}
3479 command, except that when @code{until} encounters a jump, it
3480 automatically continues execution until the program counter is greater
3481 than the address of the jump.
3483 This means that when you reach the end of a loop after single stepping
3484 though it, @code{until} makes your program continue execution until it
3485 exits the loop. In contrast, a @code{next} command at the end of a loop
3486 simply steps back to the beginning of the loop, which forces you to step
3487 through the next iteration.
3489 @code{until} always stops your program if it attempts to exit the current
3492 @code{until} may produce somewhat counterintuitive results if the order
3493 of machine code does not match the order of the source lines. For
3494 example, in the following excerpt from a debugging session, the @code{f}
3495 (@code{frame}) command shows that execution is stopped at line
3496 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3500 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3502 (@value{GDBP}) until
3503 195 for ( ; argc > 0; NEXTARG) @{
3506 This happened because, for execution efficiency, the compiler had
3507 generated code for the loop closure test at the end, rather than the
3508 start, of the loop---even though the test in a C @code{for}-loop is
3509 written before the body of the loop. The @code{until} command appeared
3510 to step back to the beginning of the loop when it advanced to this
3511 expression; however, it has not really gone to an earlier
3512 statement---not in terms of the actual machine code.
3514 @code{until} with no argument works by means of single
3515 instruction stepping, and hence is slower than @code{until} with an
3518 @item until @var{location}
3519 @itemx u @var{location}
3520 Continue running your program until either the specified location is
3521 reached, or the current stack frame returns. @var{location} is any of
3522 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3523 ,Setting breakpoints}). This form of the command uses breakpoints,
3524 and hence is quicker than @code{until} without an argument.
3527 @kindex si @r{(@code{stepi})}
3529 @itemx stepi @var{arg}
3531 Execute one machine instruction, then stop and return to the debugger.
3533 It is often useful to do @samp{display/i $pc} when stepping by machine
3534 instructions. This makes @value{GDBN} automatically display the next
3535 instruction to be executed, each time your program stops. @xref{Auto
3536 Display,, Automatic display}.
3538 An argument is a repeat count, as in @code{step}.
3542 @kindex ni @r{(@code{nexti})}
3544 @itemx nexti @var{arg}
3546 Execute one machine instruction, but if it is a function call,
3547 proceed until the function returns.
3549 An argument is a repeat count, as in @code{next}.
3556 A signal is an asynchronous event that can happen in a program. The
3557 operating system defines the possible kinds of signals, and gives each
3558 kind a name and a number. For example, in Unix @code{SIGINT} is the
3559 signal a program gets when you type an interrupt character (often @kbd{C-c});
3560 @code{SIGSEGV} is the signal a program gets from referencing a place in
3561 memory far away from all the areas in use; @code{SIGALRM} occurs when
3562 the alarm clock timer goes off (which happens only if your program has
3563 requested an alarm).
3565 @cindex fatal signals
3566 Some signals, including @code{SIGALRM}, are a normal part of the
3567 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3568 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3569 program has not specified in advance some other way to handle the signal.
3570 @code{SIGINT} does not indicate an error in your program, but it is normally
3571 fatal so it can carry out the purpose of the interrupt: to kill the program.
3573 @value{GDBN} has the ability to detect any occurrence of a signal in your
3574 program. You can tell @value{GDBN} in advance what to do for each kind of
3577 @cindex handling signals
3578 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3579 @code{SIGALRM} be silently passed to your program
3580 (so as not to interfere with their role in the program's functioning)
3581 but to stop your program immediately whenever an error signal happens.
3582 You can change these settings with the @code{handle} command.
3585 @kindex info signals
3588 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3589 handle each one. You can use this to see the signal numbers of all
3590 the defined types of signals.
3592 @code{info handle} is an alias for @code{info signals}.
3595 @item handle @var{signal} @var{keywords}@dots{}
3596 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3597 can be the number of a signal or its name (with or without the
3598 @samp{SIG} at the beginning); a list of signal numbers of the form
3599 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3600 known signals. The @var{keywords} say what change to make.
3604 The keywords allowed by the @code{handle} command can be abbreviated.
3605 Their full names are:
3609 @value{GDBN} should not stop your program when this signal happens. It may
3610 still print a message telling you that the signal has come in.
3613 @value{GDBN} should stop your program when this signal happens. This implies
3614 the @code{print} keyword as well.
3617 @value{GDBN} should print a message when this signal happens.
3620 @value{GDBN} should not mention the occurrence of the signal at all. This
3621 implies the @code{nostop} keyword as well.
3625 @value{GDBN} should allow your program to see this signal; your program
3626 can handle the signal, or else it may terminate if the signal is fatal
3627 and not handled. @code{pass} and @code{noignore} are synonyms.
3631 @value{GDBN} should not allow your program to see this signal.
3632 @code{nopass} and @code{ignore} are synonyms.
3636 When a signal stops your program, the signal is not visible to the
3638 continue. Your program sees the signal then, if @code{pass} is in
3639 effect for the signal in question @emph{at that time}. In other words,
3640 after @value{GDBN} reports a signal, you can use the @code{handle}
3641 command with @code{pass} or @code{nopass} to control whether your
3642 program sees that signal when you continue.
3644 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3645 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3646 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3649 You can also use the @code{signal} command to prevent your program from
3650 seeing a signal, or cause it to see a signal it normally would not see,
3651 or to give it any signal at any time. For example, if your program stopped
3652 due to some sort of memory reference error, you might store correct
3653 values into the erroneous variables and continue, hoping to see more
3654 execution; but your program would probably terminate immediately as
3655 a result of the fatal signal once it saw the signal. To prevent this,
3656 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3660 @section Stopping and starting multi-thread programs
3662 When your program has multiple threads (@pxref{Threads,, Debugging
3663 programs with multiple threads}), you can choose whether to set
3664 breakpoints on all threads, or on a particular thread.
3667 @cindex breakpoints and threads
3668 @cindex thread breakpoints
3669 @kindex break @dots{} thread @var{threadno}
3670 @item break @var{linespec} thread @var{threadno}
3671 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3672 @var{linespec} specifies source lines; there are several ways of
3673 writing them, but the effect is always to specify some source line.
3675 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3676 to specify that you only want @value{GDBN} to stop the program when a
3677 particular thread reaches this breakpoint. @var{threadno} is one of the
3678 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3679 column of the @samp{info threads} display.
3681 If you do not specify @samp{thread @var{threadno}} when you set a
3682 breakpoint, the breakpoint applies to @emph{all} threads of your
3685 You can use the @code{thread} qualifier on conditional breakpoints as
3686 well; in this case, place @samp{thread @var{threadno}} before the
3687 breakpoint condition, like this:
3690 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3695 @cindex stopped threads
3696 @cindex threads, stopped
3697 Whenever your program stops under @value{GDBN} for any reason,
3698 @emph{all} threads of execution stop, not just the current thread. This
3699 allows you to examine the overall state of the program, including
3700 switching between threads, without worrying that things may change
3703 @cindex continuing threads
3704 @cindex threads, continuing
3705 Conversely, whenever you restart the program, @emph{all} threads start
3706 executing. @emph{This is true even when single-stepping} with commands
3707 like @code{step} or @code{next}.
3709 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3710 Since thread scheduling is up to your debugging target's operating
3711 system (not controlled by @value{GDBN}), other threads may
3712 execute more than one statement while the current thread completes a
3713 single step. Moreover, in general other threads stop in the middle of a
3714 statement, rather than at a clean statement boundary, when the program
3717 You might even find your program stopped in another thread after
3718 continuing or even single-stepping. This happens whenever some other
3719 thread runs into a breakpoint, a signal, or an exception before the
3720 first thread completes whatever you requested.
3722 On some OSes, you can lock the OS scheduler and thus allow only a single
3726 @item set scheduler-locking @var{mode}
3727 Set the scheduler locking mode. If it is @code{off}, then there is no
3728 locking and any thread may run at any time. If @code{on}, then only the
3729 current thread may run when the inferior is resumed. The @code{step}
3730 mode optimizes for single-stepping. It stops other threads from
3731 ``seizing the prompt'' by preempting the current thread while you are
3732 stepping. Other threads will only rarely (or never) get a chance to run
3733 when you step. They are more likely to run when you @samp{next} over a
3734 function call, and they are completely free to run when you use commands
3735 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3736 thread hits a breakpoint during its timeslice, they will never steal the
3737 @value{GDBN} prompt away from the thread that you are debugging.
3739 @item show scheduler-locking
3740 Display the current scheduler locking mode.
3745 @chapter Examining the Stack
3747 When your program has stopped, the first thing you need to know is where it
3748 stopped and how it got there.
3751 Each time your program performs a function call, information about the call
3753 That information includes the location of the call in your program,
3754 the arguments of the call,
3755 and the local variables of the function being called.
3756 The information is saved in a block of data called a @dfn{stack frame}.
3757 The stack frames are allocated in a region of memory called the @dfn{call
3760 When your program stops, the @value{GDBN} commands for examining the
3761 stack allow you to see all of this information.
3763 @cindex selected frame
3764 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3765 @value{GDBN} commands refer implicitly to the selected frame. In
3766 particular, whenever you ask @value{GDBN} for the value of a variable in
3767 your program, the value is found in the selected frame. There are
3768 special @value{GDBN} commands to select whichever frame you are
3769 interested in. @xref{Selection, ,Selecting a frame}.
3771 When your program stops, @value{GDBN} automatically selects the
3772 currently executing frame and describes it briefly, similar to the
3773 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3776 * Frames:: Stack frames
3777 * Backtrace:: Backtraces
3778 * Selection:: Selecting a frame
3779 * Frame Info:: Information on a frame
3784 @section Stack frames
3786 @cindex frame, definition
3788 The call stack is divided up into contiguous pieces called @dfn{stack
3789 frames}, or @dfn{frames} for short; each frame is the data associated
3790 with one call to one function. The frame contains the arguments given
3791 to the function, the function's local variables, and the address at
3792 which the function is executing.
3794 @cindex initial frame
3795 @cindex outermost frame
3796 @cindex innermost frame
3797 When your program is started, the stack has only one frame, that of the
3798 function @code{main}. This is called the @dfn{initial} frame or the
3799 @dfn{outermost} frame. Each time a function is called, a new frame is
3800 made. Each time a function returns, the frame for that function invocation
3801 is eliminated. If a function is recursive, there can be many frames for
3802 the same function. The frame for the function in which execution is
3803 actually occurring is called the @dfn{innermost} frame. This is the most
3804 recently created of all the stack frames that still exist.
3806 @cindex frame pointer
3807 Inside your program, stack frames are identified by their addresses. A
3808 stack frame consists of many bytes, each of which has its own address; each
3809 kind of computer has a convention for choosing one byte whose
3810 address serves as the address of the frame. Usually this address is kept
3811 in a register called the @dfn{frame pointer register} while execution is
3812 going on in that frame.
3814 @cindex frame number
3815 @value{GDBN} assigns numbers to all existing stack frames, starting with
3816 zero for the innermost frame, one for the frame that called it,
3817 and so on upward. These numbers do not really exist in your program;
3818 they are assigned by @value{GDBN} to give you a way of designating stack
3819 frames in @value{GDBN} commands.
3821 @c The -fomit-frame-pointer below perennially causes hbox overflow
3822 @c underflow problems.
3823 @cindex frameless execution
3824 Some compilers provide a way to compile functions so that they operate
3825 without stack frames. (For example, the @value{GCC} option
3827 @samp{-fomit-frame-pointer}
3829 generates functions without a frame.)
3830 This is occasionally done with heavily used library functions to save
3831 the frame setup time. @value{GDBN} has limited facilities for dealing
3832 with these function invocations. If the innermost function invocation
3833 has no stack frame, @value{GDBN} nevertheless regards it as though
3834 it had a separate frame, which is numbered zero as usual, allowing
3835 correct tracing of the function call chain. However, @value{GDBN} has
3836 no provision for frameless functions elsewhere in the stack.
3839 @kindex frame@r{, command}
3840 @cindex current stack frame
3841 @item frame @var{args}
3842 The @code{frame} command allows you to move from one stack frame to another,
3843 and to print the stack frame you select. @var{args} may be either the
3844 address of the frame or the stack frame number. Without an argument,
3845 @code{frame} prints the current stack frame.
3847 @kindex select-frame
3848 @cindex selecting frame silently
3850 The @code{select-frame} command allows you to move from one stack frame
3851 to another without printing the frame. This is the silent version of
3860 @cindex stack traces
3861 A backtrace is a summary of how your program got where it is. It shows one
3862 line per frame, for many frames, starting with the currently executing
3863 frame (frame zero), followed by its caller (frame one), and on up the
3868 @kindex bt @r{(@code{backtrace})}
3871 Print a backtrace of the entire stack: one line per frame for all
3872 frames in the stack.
3874 You can stop the backtrace at any time by typing the system interrupt
3875 character, normally @kbd{C-c}.
3877 @item backtrace @var{n}
3879 Similar, but print only the innermost @var{n} frames.
3881 @item backtrace -@var{n}
3883 Similar, but print only the outermost @var{n} frames.
3888 @kindex info s @r{(@code{info stack})}
3889 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3890 are additional aliases for @code{backtrace}.
3892 Each line in the backtrace shows the frame number and the function name.
3893 The program counter value is also shown---unless you use @code{set
3894 print address off}. The backtrace also shows the source file name and
3895 line number, as well as the arguments to the function. The program
3896 counter value is omitted if it is at the beginning of the code for that
3899 Here is an example of a backtrace. It was made with the command
3900 @samp{bt 3}, so it shows the innermost three frames.
3904 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3906 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3907 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3909 (More stack frames follow...)
3914 The display for frame zero does not begin with a program counter
3915 value, indicating that your program has stopped at the beginning of the
3916 code for line @code{993} of @code{builtin.c}.
3919 @section Selecting a frame
3921 Most commands for examining the stack and other data in your program work on
3922 whichever stack frame is selected at the moment. Here are the commands for
3923 selecting a stack frame; all of them finish by printing a brief description
3924 of the stack frame just selected.
3927 @kindex frame@r{, selecting}
3928 @kindex f @r{(@code{frame})}
3931 Select frame number @var{n}. Recall that frame zero is the innermost
3932 (currently executing) frame, frame one is the frame that called the
3933 innermost one, and so on. The highest-numbered frame is the one for
3936 @item frame @var{addr}
3938 Select the frame at address @var{addr}. This is useful mainly if the
3939 chaining of stack frames has been damaged by a bug, making it
3940 impossible for @value{GDBN} to assign numbers properly to all frames. In
3941 addition, this can be useful when your program has multiple stacks and
3942 switches between them.
3944 On the SPARC architecture, @code{frame} needs two addresses to
3945 select an arbitrary frame: a frame pointer and a stack pointer.
3947 On the MIPS and Alpha architecture, it needs two addresses: a stack
3948 pointer and a program counter.
3950 On the 29k architecture, it needs three addresses: a register stack
3951 pointer, a program counter, and a memory stack pointer.
3952 @c note to future updaters: this is conditioned on a flag
3953 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3954 @c as of 27 Jan 1994.
3958 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3959 advances toward the outermost frame, to higher frame numbers, to frames
3960 that have existed longer. @var{n} defaults to one.
3963 @kindex do @r{(@code{down})}
3965 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3966 advances toward the innermost frame, to lower frame numbers, to frames
3967 that were created more recently. @var{n} defaults to one. You may
3968 abbreviate @code{down} as @code{do}.
3971 All of these commands end by printing two lines of output describing the
3972 frame. The first line shows the frame number, the function name, the
3973 arguments, and the source file and line number of execution in that
3974 frame. The second line shows the text of that source line.
3982 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3984 10 read_input_file (argv[i]);
3988 After such a printout, the @code{list} command with no arguments
3989 prints ten lines centered on the point of execution in the frame.
3990 @xref{List, ,Printing source lines}.
3993 @kindex down-silently
3995 @item up-silently @var{n}
3996 @itemx down-silently @var{n}
3997 These two commands are variants of @code{up} and @code{down},
3998 respectively; they differ in that they do their work silently, without
3999 causing display of the new frame. They are intended primarily for use
4000 in @value{GDBN} command scripts, where the output might be unnecessary and
4005 @section Information about a frame
4007 There are several other commands to print information about the selected
4013 When used without any argument, this command does not change which
4014 frame is selected, but prints a brief description of the currently
4015 selected stack frame. It can be abbreviated @code{f}. With an
4016 argument, this command is used to select a stack frame.
4017 @xref{Selection, ,Selecting a frame}.
4020 @kindex info f @r{(@code{info frame})}
4023 This command prints a verbose description of the selected stack frame,
4028 the address of the frame
4030 the address of the next frame down (called by this frame)
4032 the address of the next frame up (caller of this frame)
4034 the language in which the source code corresponding to this frame is written
4036 the address of the frame's arguments
4038 the address of the frame's local variables
4040 the program counter saved in it (the address of execution in the caller frame)
4042 which registers were saved in the frame
4045 @noindent The verbose description is useful when
4046 something has gone wrong that has made the stack format fail to fit
4047 the usual conventions.
4049 @item info frame @var{addr}
4050 @itemx info f @var{addr}
4051 Print a verbose description of the frame at address @var{addr}, without
4052 selecting that frame. The selected frame remains unchanged by this
4053 command. This requires the same kind of address (more than one for some
4054 architectures) that you specify in the @code{frame} command.
4055 @xref{Selection, ,Selecting a frame}.
4059 Print the arguments of the selected frame, each on a separate line.
4063 Print the local variables of the selected frame, each on a separate
4064 line. These are all variables (declared either static or automatic)
4065 accessible at the point of execution of the selected frame.
4068 @cindex catch exceptions, list active handlers
4069 @cindex exception handlers, how to list
4071 Print a list of all the exception handlers that are active in the
4072 current stack frame at the current point of execution. To see other
4073 exception handlers, visit the associated frame (using the @code{up},
4074 @code{down}, or @code{frame} commands); then type @code{info catch}.
4075 @xref{Set Catchpoints, , Setting catchpoints}.
4081 @chapter Examining Source Files
4083 @value{GDBN} can print parts of your program's source, since the debugging
4084 information recorded in the program tells @value{GDBN} what source files were
4085 used to build it. When your program stops, @value{GDBN} spontaneously prints
4086 the line where it stopped. Likewise, when you select a stack frame
4087 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4088 execution in that frame has stopped. You can print other portions of
4089 source files by explicit command.
4091 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4092 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4093 @value{GDBN} under @sc{gnu} Emacs}.
4096 * List:: Printing source lines
4097 * Search:: Searching source files
4098 * Source Path:: Specifying source directories
4099 * Machine Code:: Source and machine code
4103 @section Printing source lines
4106 @kindex l @r{(@code{list})}
4107 To print lines from a source file, use the @code{list} command
4108 (abbreviated @code{l}). By default, ten lines are printed.
4109 There are several ways to specify what part of the file you want to print.
4111 Here are the forms of the @code{list} command most commonly used:
4114 @item list @var{linenum}
4115 Print lines centered around line number @var{linenum} in the
4116 current source file.
4118 @item list @var{function}
4119 Print lines centered around the beginning of function
4123 Print more lines. If the last lines printed were printed with a
4124 @code{list} command, this prints lines following the last lines
4125 printed; however, if the last line printed was a solitary line printed
4126 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4127 Stack}), this prints lines centered around that line.
4130 Print lines just before the lines last printed.
4133 By default, @value{GDBN} prints ten source lines with any of these forms of
4134 the @code{list} command. You can change this using @code{set listsize}:
4137 @kindex set listsize
4138 @item set listsize @var{count}
4139 Make the @code{list} command display @var{count} source lines (unless
4140 the @code{list} argument explicitly specifies some other number).
4142 @kindex show listsize
4144 Display the number of lines that @code{list} prints.
4147 Repeating a @code{list} command with @key{RET} discards the argument,
4148 so it is equivalent to typing just @code{list}. This is more useful
4149 than listing the same lines again. An exception is made for an
4150 argument of @samp{-}; that argument is preserved in repetition so that
4151 each repetition moves up in the source file.
4154 In general, the @code{list} command expects you to supply zero, one or two
4155 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4156 of writing them, but the effect is always to specify some source line.
4157 Here is a complete description of the possible arguments for @code{list}:
4160 @item list @var{linespec}
4161 Print lines centered around the line specified by @var{linespec}.
4163 @item list @var{first},@var{last}
4164 Print lines from @var{first} to @var{last}. Both arguments are
4167 @item list ,@var{last}
4168 Print lines ending with @var{last}.
4170 @item list @var{first},
4171 Print lines starting with @var{first}.
4174 Print lines just after the lines last printed.
4177 Print lines just before the lines last printed.
4180 As described in the preceding table.
4183 Here are the ways of specifying a single source line---all the
4188 Specifies line @var{number} of the current source file.
4189 When a @code{list} command has two linespecs, this refers to
4190 the same source file as the first linespec.
4193 Specifies the line @var{offset} lines after the last line printed.
4194 When used as the second linespec in a @code{list} command that has
4195 two, this specifies the line @var{offset} lines down from the
4199 Specifies the line @var{offset} lines before the last line printed.
4201 @item @var{filename}:@var{number}
4202 Specifies line @var{number} in the source file @var{filename}.
4204 @item @var{function}
4205 Specifies the line that begins the body of the function @var{function}.
4206 For example: in C, this is the line with the open brace.
4208 @item @var{filename}:@var{function}
4209 Specifies the line of the open-brace that begins the body of the
4210 function @var{function} in the file @var{filename}. You only need the
4211 file name with a function name to avoid ambiguity when there are
4212 identically named functions in different source files.
4214 @item *@var{address}
4215 Specifies the line containing the program address @var{address}.
4216 @var{address} may be any expression.
4220 @section Searching source files
4222 @kindex reverse-search
4224 There are two commands for searching through the current source file for a
4229 @kindex forward-search
4230 @item forward-search @var{regexp}
4231 @itemx search @var{regexp}
4232 The command @samp{forward-search @var{regexp}} checks each line,
4233 starting with the one following the last line listed, for a match for
4234 @var{regexp}. It lists the line that is found. You can use the
4235 synonym @samp{search @var{regexp}} or abbreviate the command name as
4238 @item reverse-search @var{regexp}
4239 The command @samp{reverse-search @var{regexp}} checks each line, starting
4240 with the one before the last line listed and going backward, for a match
4241 for @var{regexp}. It lists the line that is found. You can abbreviate
4242 this command as @code{rev}.
4246 @section Specifying source directories
4249 @cindex directories for source files
4250 Executable programs sometimes do not record the directories of the source
4251 files from which they were compiled, just the names. Even when they do,
4252 the directories could be moved between the compilation and your debugging
4253 session. @value{GDBN} has a list of directories to search for source files;
4254 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4255 it tries all the directories in the list, in the order they are present
4256 in the list, until it finds a file with the desired name. Note that
4257 the executable search path is @emph{not} used for this purpose. Neither is
4258 the current working directory, unless it happens to be in the source
4261 If @value{GDBN} cannot find a source file in the source path, and the
4262 object program records a directory, @value{GDBN} tries that directory
4263 too. If the source path is empty, and there is no record of the
4264 compilation directory, @value{GDBN} looks in the current directory as a
4267 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4268 any information it has cached about where source files are found and where
4269 each line is in the file.
4273 When you start @value{GDBN}, its source path includes only @samp{cdir}
4274 and @samp{cwd}, in that order.
4275 To add other directories, use the @code{directory} command.
4278 @item directory @var{dirname} @dots{}
4279 @item dir @var{dirname} @dots{}
4280 Add directory @var{dirname} to the front of the source path. Several
4281 directory names may be given to this command, separated by @samp{:}
4282 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4283 part of absolute file names) or
4284 whitespace. You may specify a directory that is already in the source
4285 path; this moves it forward, so @value{GDBN} searches it sooner.
4289 @vindex $cdir@r{, convenience variable}
4290 @vindex $cwdr@r{, convenience variable}
4291 @cindex compilation directory
4292 @cindex current directory
4293 @cindex working directory
4294 @cindex directory, current
4295 @cindex directory, compilation
4296 You can use the string @samp{$cdir} to refer to the compilation
4297 directory (if one is recorded), and @samp{$cwd} to refer to the current
4298 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4299 tracks the current working directory as it changes during your @value{GDBN}
4300 session, while the latter is immediately expanded to the current
4301 directory at the time you add an entry to the source path.
4304 Reset the source path to empty again. This requires confirmation.
4306 @c RET-repeat for @code{directory} is explicitly disabled, but since
4307 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4309 @item show directories
4310 @kindex show directories
4311 Print the source path: show which directories it contains.
4314 If your source path is cluttered with directories that are no longer of
4315 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4316 versions of source. You can correct the situation as follows:
4320 Use @code{directory} with no argument to reset the source path to empty.
4323 Use @code{directory} with suitable arguments to reinstall the
4324 directories you want in the source path. You can add all the
4325 directories in one command.
4329 @section Source and machine code
4331 You can use the command @code{info line} to map source lines to program
4332 addresses (and vice versa), and the command @code{disassemble} to display
4333 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4334 mode, the @code{info line} command causes the arrow to point to the
4335 line specified. Also, @code{info line} prints addresses in symbolic form as
4340 @item info line @var{linespec}
4341 Print the starting and ending addresses of the compiled code for
4342 source line @var{linespec}. You can specify source lines in any of
4343 the ways understood by the @code{list} command (@pxref{List, ,Printing
4347 For example, we can use @code{info line} to discover the location of
4348 the object code for the first line of function
4349 @code{m4_changequote}:
4351 @c FIXME: I think this example should also show the addresses in
4352 @c symbolic form, as they usually would be displayed.
4354 (@value{GDBP}) info line m4_changequote
4355 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4359 We can also inquire (using @code{*@var{addr}} as the form for
4360 @var{linespec}) what source line covers a particular address:
4362 (@value{GDBP}) info line *0x63ff
4363 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4366 @cindex @code{$_} and @code{info line}
4367 @kindex x@r{(examine), and} info line
4368 After @code{info line}, the default address for the @code{x} command
4369 is changed to the starting address of the line, so that @samp{x/i} is
4370 sufficient to begin examining the machine code (@pxref{Memory,
4371 ,Examining memory}). Also, this address is saved as the value of the
4372 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4377 @cindex assembly instructions
4378 @cindex instructions, assembly
4379 @cindex machine instructions
4380 @cindex listing machine instructions
4382 This specialized command dumps a range of memory as machine
4383 instructions. The default memory range is the function surrounding the
4384 program counter of the selected frame. A single argument to this
4385 command is a program counter value; @value{GDBN} dumps the function
4386 surrounding this value. Two arguments specify a range of addresses
4387 (first inclusive, second exclusive) to dump.
4390 The following example shows the disassembly of a range of addresses of
4391 HP PA-RISC 2.0 code:
4394 (@value{GDBP}) disas 0x32c4 0x32e4
4395 Dump of assembler code from 0x32c4 to 0x32e4:
4396 0x32c4 <main+204>: addil 0,dp
4397 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4398 0x32cc <main+212>: ldil 0x3000,r31
4399 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4400 0x32d4 <main+220>: ldo 0(r31),rp
4401 0x32d8 <main+224>: addil -0x800,dp
4402 0x32dc <main+228>: ldo 0x588(r1),r26
4403 0x32e0 <main+232>: ldil 0x3000,r31
4404 End of assembler dump.
4407 Some architectures have more than one commonly-used set of instruction
4408 mnemonics or other syntax.
4411 @kindex set disassembly-flavor
4412 @cindex assembly instructions
4413 @cindex instructions, assembly
4414 @cindex machine instructions
4415 @cindex listing machine instructions
4416 @cindex Intel disassembly flavor
4417 @cindex AT&T disassembly flavor
4418 @item set disassembly-flavor @var{instruction-set}
4419 Select the instruction set to use when disassembling the
4420 program via the @code{disassemble} or @code{x/i} commands.
4422 Currently this command is only defined for the Intel x86 family. You
4423 can set @var{instruction-set} to either @code{intel} or @code{att}.
4424 The default is @code{att}, the AT&T flavor used by default by Unix
4425 assemblers for x86-based targets.
4430 @chapter Examining Data
4432 @cindex printing data
4433 @cindex examining data
4436 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4437 @c document because it is nonstandard... Under Epoch it displays in a
4438 @c different window or something like that.
4439 The usual way to examine data in your program is with the @code{print}
4440 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4441 evaluates and prints the value of an expression of the language your
4442 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4443 Different Languages}).
4446 @item print @var{expr}
4447 @itemx print /@var{f} @var{expr}
4448 @var{expr} is an expression (in the source language). By default the
4449 value of @var{expr} is printed in a format appropriate to its data type;
4450 you can choose a different format by specifying @samp{/@var{f}}, where
4451 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4455 @itemx print /@var{f}
4456 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4457 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4458 conveniently inspect the same value in an alternative format.
4461 A more low-level way of examining data is with the @code{x} command.
4462 It examines data in memory at a specified address and prints it in a
4463 specified format. @xref{Memory, ,Examining memory}.
4465 If you are interested in information about types, or about how the
4466 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4467 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4471 * Expressions:: Expressions
4472 * Variables:: Program variables
4473 * Arrays:: Artificial arrays
4474 * Output Formats:: Output formats
4475 * Memory:: Examining memory
4476 * Auto Display:: Automatic display
4477 * Print Settings:: Print settings
4478 * Value History:: Value history
4479 * Convenience Vars:: Convenience variables
4480 * Registers:: Registers
4481 * Floating Point Hardware:: Floating point hardware
4482 * Memory Region Attributes:: Memory region attributes
4486 @section Expressions
4489 @code{print} and many other @value{GDBN} commands accept an expression and
4490 compute its value. Any kind of constant, variable or operator defined
4491 by the programming language you are using is valid in an expression in
4492 @value{GDBN}. This includes conditional expressions, function calls, casts
4493 and string constants. It unfortunately does not include symbols defined
4494 by preprocessor @code{#define} commands.
4496 @value{GDBN} supports array constants in expressions input by
4497 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4498 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4499 memory that is @code{malloc}ed in the target program.
4501 Because C is so widespread, most of the expressions shown in examples in
4502 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4503 Languages}, for information on how to use expressions in other
4506 In this section, we discuss operators that you can use in @value{GDBN}
4507 expressions regardless of your programming language.
4509 Casts are supported in all languages, not just in C, because it is so
4510 useful to cast a number into a pointer in order to examine a structure
4511 at that address in memory.
4512 @c FIXME: casts supported---Mod2 true?
4514 @value{GDBN} supports these operators, in addition to those common
4515 to programming languages:
4519 @samp{@@} is a binary operator for treating parts of memory as arrays.
4520 @xref{Arrays, ,Artificial arrays}, for more information.
4523 @samp{::} allows you to specify a variable in terms of the file or
4524 function where it is defined. @xref{Variables, ,Program variables}.
4526 @cindex @{@var{type}@}
4527 @cindex type casting memory
4528 @cindex memory, viewing as typed object
4529 @cindex casts, to view memory
4530 @item @{@var{type}@} @var{addr}
4531 Refers to an object of type @var{type} stored at address @var{addr} in
4532 memory. @var{addr} may be any expression whose value is an integer or
4533 pointer (but parentheses are required around binary operators, just as in
4534 a cast). This construct is allowed regardless of what kind of data is
4535 normally supposed to reside at @var{addr}.
4539 @section Program variables
4541 The most common kind of expression to use is the name of a variable
4544 Variables in expressions are understood in the selected stack frame
4545 (@pxref{Selection, ,Selecting a frame}); they must be either:
4549 global (or file-static)
4556 visible according to the scope rules of the
4557 programming language from the point of execution in that frame
4560 @noindent This means that in the function
4575 you can examine and use the variable @code{a} whenever your program is
4576 executing within the function @code{foo}, but you can only use or
4577 examine the variable @code{b} while your program is executing inside
4578 the block where @code{b} is declared.
4580 @cindex variable name conflict
4581 There is an exception: you can refer to a variable or function whose
4582 scope is a single source file even if the current execution point is not
4583 in this file. But it is possible to have more than one such variable or
4584 function with the same name (in different source files). If that
4585 happens, referring to that name has unpredictable effects. If you wish,
4586 you can specify a static variable in a particular function or file,
4587 using the colon-colon notation:
4589 @cindex colon-colon, context for variables/functions
4591 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4592 @cindex @code{::}, context for variables/functions
4595 @var{file}::@var{variable}
4596 @var{function}::@var{variable}
4600 Here @var{file} or @var{function} is the name of the context for the
4601 static @var{variable}. In the case of file names, you can use quotes to
4602 make sure @value{GDBN} parses the file name as a single word---for example,
4603 to print a global value of @code{x} defined in @file{f2.c}:
4606 (@value{GDBP}) p 'f2.c'::x
4609 @cindex C@t{++} scope resolution
4610 This use of @samp{::} is very rarely in conflict with the very similar
4611 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4612 scope resolution operator in @value{GDBN} expressions.
4613 @c FIXME: Um, so what happens in one of those rare cases where it's in
4616 @cindex wrong values
4617 @cindex variable values, wrong
4619 @emph{Warning:} Occasionally, a local variable may appear to have the
4620 wrong value at certain points in a function---just after entry to a new
4621 scope, and just before exit.
4623 You may see this problem when you are stepping by machine instructions.
4624 This is because, on most machines, it takes more than one instruction to
4625 set up a stack frame (including local variable definitions); if you are
4626 stepping by machine instructions, variables may appear to have the wrong
4627 values until the stack frame is completely built. On exit, it usually
4628 also takes more than one machine instruction to destroy a stack frame;
4629 after you begin stepping through that group of instructions, local
4630 variable definitions may be gone.
4632 This may also happen when the compiler does significant optimizations.
4633 To be sure of always seeing accurate values, turn off all optimization
4636 @cindex ``No symbol "foo" in current context''
4637 Another possible effect of compiler optimizations is to optimize
4638 unused variables out of existence, or assign variables to registers (as
4639 opposed to memory addresses). Depending on the support for such cases
4640 offered by the debug info format used by the compiler, @value{GDBN}
4641 might not be able to display values for such local variables. If that
4642 happens, @value{GDBN} will print a message like this:
4645 No symbol "foo" in current context.
4648 To solve such problems, either recompile without optimizations, or use a
4649 different debug info format, if the compiler supports several such
4650 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4651 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4652 in a format that is superior to formats such as COFF. You may be able
4653 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4654 debug info. See @ref{Debugging Options,,Options for Debugging Your
4655 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4660 @section Artificial arrays
4662 @cindex artificial array
4663 @kindex @@@r{, referencing memory as an array}
4664 It is often useful to print out several successive objects of the
4665 same type in memory; a section of an array, or an array of
4666 dynamically determined size for which only a pointer exists in the
4669 You can do this by referring to a contiguous span of memory as an
4670 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4671 operand of @samp{@@} should be the first element of the desired array
4672 and be an individual object. The right operand should be the desired length
4673 of the array. The result is an array value whose elements are all of
4674 the type of the left argument. The first element is actually the left
4675 argument; the second element comes from bytes of memory immediately
4676 following those that hold the first element, and so on. Here is an
4677 example. If a program says
4680 int *array = (int *) malloc (len * sizeof (int));
4684 you can print the contents of @code{array} with
4690 The left operand of @samp{@@} must reside in memory. Array values made
4691 with @samp{@@} in this way behave just like other arrays in terms of
4692 subscripting, and are coerced to pointers when used in expressions.
4693 Artificial arrays most often appear in expressions via the value history
4694 (@pxref{Value History, ,Value history}), after printing one out.
4696 Another way to create an artificial array is to use a cast.
4697 This re-interprets a value as if it were an array.
4698 The value need not be in memory:
4700 (@value{GDBP}) p/x (short[2])0x12345678
4701 $1 = @{0x1234, 0x5678@}
4704 As a convenience, if you leave the array length out (as in
4705 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4706 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4708 (@value{GDBP}) p/x (short[])0x12345678
4709 $2 = @{0x1234, 0x5678@}
4712 Sometimes the artificial array mechanism is not quite enough; in
4713 moderately complex data structures, the elements of interest may not
4714 actually be adjacent---for example, if you are interested in the values
4715 of pointers in an array. One useful work-around in this situation is
4716 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4717 variables}) as a counter in an expression that prints the first
4718 interesting value, and then repeat that expression via @key{RET}. For
4719 instance, suppose you have an array @code{dtab} of pointers to
4720 structures, and you are interested in the values of a field @code{fv}
4721 in each structure. Here is an example of what you might type:
4731 @node Output Formats
4732 @section Output formats
4734 @cindex formatted output
4735 @cindex output formats
4736 By default, @value{GDBN} prints a value according to its data type. Sometimes
4737 this is not what you want. For example, you might want to print a number
4738 in hex, or a pointer in decimal. Or you might want to view data in memory
4739 at a certain address as a character string or as an instruction. To do
4740 these things, specify an @dfn{output format} when you print a value.
4742 The simplest use of output formats is to say how to print a value
4743 already computed. This is done by starting the arguments of the
4744 @code{print} command with a slash and a format letter. The format
4745 letters supported are:
4749 Regard the bits of the value as an integer, and print the integer in
4753 Print as integer in signed decimal.
4756 Print as integer in unsigned decimal.
4759 Print as integer in octal.
4762 Print as integer in binary. The letter @samp{t} stands for ``two''.
4763 @footnote{@samp{b} cannot be used because these format letters are also
4764 used with the @code{x} command, where @samp{b} stands for ``byte'';
4765 see @ref{Memory,,Examining memory}.}
4768 @cindex unknown address, locating
4769 @cindex locate address
4770 Print as an address, both absolute in hexadecimal and as an offset from
4771 the nearest preceding symbol. You can use this format used to discover
4772 where (in what function) an unknown address is located:
4775 (@value{GDBP}) p/a 0x54320
4776 $3 = 0x54320 <_initialize_vx+396>
4780 The command @code{info symbol 0x54320} yields similar results.
4781 @xref{Symbols, info symbol}.
4784 Regard as an integer and print it as a character constant.
4787 Regard the bits of the value as a floating point number and print
4788 using typical floating point syntax.
4791 For example, to print the program counter in hex (@pxref{Registers}), type
4798 Note that no space is required before the slash; this is because command
4799 names in @value{GDBN} cannot contain a slash.
4801 To reprint the last value in the value history with a different format,
4802 you can use the @code{print} command with just a format and no
4803 expression. For example, @samp{p/x} reprints the last value in hex.
4806 @section Examining memory
4808 You can use the command @code{x} (for ``examine'') to examine memory in
4809 any of several formats, independently of your program's data types.
4811 @cindex examining memory
4813 @kindex x @r{(examine memory)}
4814 @item x/@var{nfu} @var{addr}
4817 Use the @code{x} command to examine memory.
4820 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4821 much memory to display and how to format it; @var{addr} is an
4822 expression giving the address where you want to start displaying memory.
4823 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4824 Several commands set convenient defaults for @var{addr}.
4827 @item @var{n}, the repeat count
4828 The repeat count is a decimal integer; the default is 1. It specifies
4829 how much memory (counting by units @var{u}) to display.
4830 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4833 @item @var{f}, the display format
4834 The display format is one of the formats used by @code{print},
4835 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4836 The default is @samp{x} (hexadecimal) initially.
4837 The default changes each time you use either @code{x} or @code{print}.
4839 @item @var{u}, the unit size
4840 The unit size is any of
4846 Halfwords (two bytes).
4848 Words (four bytes). This is the initial default.
4850 Giant words (eight bytes).
4853 Each time you specify a unit size with @code{x}, that size becomes the
4854 default unit the next time you use @code{x}. (For the @samp{s} and
4855 @samp{i} formats, the unit size is ignored and is normally not written.)
4857 @item @var{addr}, starting display address
4858 @var{addr} is the address where you want @value{GDBN} to begin displaying
4859 memory. The expression need not have a pointer value (though it may);
4860 it is always interpreted as an integer address of a byte of memory.
4861 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4862 @var{addr} is usually just after the last address examined---but several
4863 other commands also set the default address: @code{info breakpoints} (to
4864 the address of the last breakpoint listed), @code{info line} (to the
4865 starting address of a line), and @code{print} (if you use it to display
4866 a value from memory).
4869 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4870 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4871 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4872 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4873 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4875 Since the letters indicating unit sizes are all distinct from the
4876 letters specifying output formats, you do not have to remember whether
4877 unit size or format comes first; either order works. The output
4878 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4879 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4881 Even though the unit size @var{u} is ignored for the formats @samp{s}
4882 and @samp{i}, you might still want to use a count @var{n}; for example,
4883 @samp{3i} specifies that you want to see three machine instructions,
4884 including any operands. The command @code{disassemble} gives an
4885 alternative way of inspecting machine instructions; see @ref{Machine
4886 Code,,Source and machine code}.
4888 All the defaults for the arguments to @code{x} are designed to make it
4889 easy to continue scanning memory with minimal specifications each time
4890 you use @code{x}. For example, after you have inspected three machine
4891 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4892 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4893 the repeat count @var{n} is used again; the other arguments default as
4894 for successive uses of @code{x}.
4896 @cindex @code{$_}, @code{$__}, and value history
4897 The addresses and contents printed by the @code{x} command are not saved
4898 in the value history because there is often too much of them and they
4899 would get in the way. Instead, @value{GDBN} makes these values available for
4900 subsequent use in expressions as values of the convenience variables
4901 @code{$_} and @code{$__}. After an @code{x} command, the last address
4902 examined is available for use in expressions in the convenience variable
4903 @code{$_}. The contents of that address, as examined, are available in
4904 the convenience variable @code{$__}.
4906 If the @code{x} command has a repeat count, the address and contents saved
4907 are from the last memory unit printed; this is not the same as the last
4908 address printed if several units were printed on the last line of output.
4911 @section Automatic display
4912 @cindex automatic display
4913 @cindex display of expressions
4915 If you find that you want to print the value of an expression frequently
4916 (to see how it changes), you might want to add it to the @dfn{automatic
4917 display list} so that @value{GDBN} prints its value each time your program stops.
4918 Each expression added to the list is given a number to identify it;
4919 to remove an expression from the list, you specify that number.
4920 The automatic display looks like this:
4924 3: bar[5] = (struct hack *) 0x3804
4928 This display shows item numbers, expressions and their current values. As with
4929 displays you request manually using @code{x} or @code{print}, you can
4930 specify the output format you prefer; in fact, @code{display} decides
4931 whether to use @code{print} or @code{x} depending on how elaborate your
4932 format specification is---it uses @code{x} if you specify a unit size,
4933 or one of the two formats (@samp{i} and @samp{s}) that are only
4934 supported by @code{x}; otherwise it uses @code{print}.
4938 @item display @var{expr}
4939 Add the expression @var{expr} to the list of expressions to display
4940 each time your program stops. @xref{Expressions, ,Expressions}.
4942 @code{display} does not repeat if you press @key{RET} again after using it.
4944 @item display/@var{fmt} @var{expr}
4945 For @var{fmt} specifying only a display format and not a size or
4946 count, add the expression @var{expr} to the auto-display list but
4947 arrange to display it each time in the specified format @var{fmt}.
4948 @xref{Output Formats,,Output formats}.
4950 @item display/@var{fmt} @var{addr}
4951 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4952 number of units, add the expression @var{addr} as a memory address to
4953 be examined each time your program stops. Examining means in effect
4954 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4957 For example, @samp{display/i $pc} can be helpful, to see the machine
4958 instruction about to be executed each time execution stops (@samp{$pc}
4959 is a common name for the program counter; @pxref{Registers, ,Registers}).
4962 @kindex delete display
4964 @item undisplay @var{dnums}@dots{}
4965 @itemx delete display @var{dnums}@dots{}
4966 Remove item numbers @var{dnums} from the list of expressions to display.
4968 @code{undisplay} does not repeat if you press @key{RET} after using it.
4969 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4971 @kindex disable display
4972 @item disable display @var{dnums}@dots{}
4973 Disable the display of item numbers @var{dnums}. A disabled display
4974 item is not printed automatically, but is not forgotten. It may be
4975 enabled again later.
4977 @kindex enable display
4978 @item enable display @var{dnums}@dots{}
4979 Enable display of item numbers @var{dnums}. It becomes effective once
4980 again in auto display of its expression, until you specify otherwise.
4983 Display the current values of the expressions on the list, just as is
4984 done when your program stops.
4986 @kindex info display
4988 Print the list of expressions previously set up to display
4989 automatically, each one with its item number, but without showing the
4990 values. This includes disabled expressions, which are marked as such.
4991 It also includes expressions which would not be displayed right now
4992 because they refer to automatic variables not currently available.
4995 If a display expression refers to local variables, then it does not make
4996 sense outside the lexical context for which it was set up. Such an
4997 expression is disabled when execution enters a context where one of its
4998 variables is not defined. For example, if you give the command
4999 @code{display last_char} while inside a function with an argument
5000 @code{last_char}, @value{GDBN} displays this argument while your program
5001 continues to stop inside that function. When it stops elsewhere---where
5002 there is no variable @code{last_char}---the display is disabled
5003 automatically. The next time your program stops where @code{last_char}
5004 is meaningful, you can enable the display expression once again.
5006 @node Print Settings
5007 @section Print settings
5009 @cindex format options
5010 @cindex print settings
5011 @value{GDBN} provides the following ways to control how arrays, structures,
5012 and symbols are printed.
5015 These settings are useful for debugging programs in any language:
5018 @kindex set print address
5019 @item set print address
5020 @itemx set print address on
5021 @value{GDBN} prints memory addresses showing the location of stack
5022 traces, structure values, pointer values, breakpoints, and so forth,
5023 even when it also displays the contents of those addresses. The default
5024 is @code{on}. For example, this is what a stack frame display looks like with
5025 @code{set print address on}:
5030 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5032 530 if (lquote != def_lquote)
5036 @item set print address off
5037 Do not print addresses when displaying their contents. For example,
5038 this is the same stack frame displayed with @code{set print address off}:
5042 (@value{GDBP}) set print addr off
5044 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5045 530 if (lquote != def_lquote)
5049 You can use @samp{set print address off} to eliminate all machine
5050 dependent displays from the @value{GDBN} interface. For example, with
5051 @code{print address off}, you should get the same text for backtraces on
5052 all machines---whether or not they involve pointer arguments.
5054 @kindex show print address
5055 @item show print address
5056 Show whether or not addresses are to be printed.
5059 When @value{GDBN} prints a symbolic address, it normally prints the
5060 closest earlier symbol plus an offset. If that symbol does not uniquely
5061 identify the address (for example, it is a name whose scope is a single
5062 source file), you may need to clarify. One way to do this is with
5063 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5064 you can set @value{GDBN} to print the source file and line number when
5065 it prints a symbolic address:
5068 @kindex set print symbol-filename
5069 @item set print symbol-filename on
5070 Tell @value{GDBN} to print the source file name and line number of a
5071 symbol in the symbolic form of an address.
5073 @item set print symbol-filename off
5074 Do not print source file name and line number of a symbol. This is the
5077 @kindex show print symbol-filename
5078 @item show print symbol-filename
5079 Show whether or not @value{GDBN} will print the source file name and
5080 line number of a symbol in the symbolic form of an address.
5083 Another situation where it is helpful to show symbol filenames and line
5084 numbers is when disassembling code; @value{GDBN} shows you the line
5085 number and source file that corresponds to each instruction.
5087 Also, you may wish to see the symbolic form only if the address being
5088 printed is reasonably close to the closest earlier symbol:
5091 @kindex set print max-symbolic-offset
5092 @item set print max-symbolic-offset @var{max-offset}
5093 Tell @value{GDBN} to only display the symbolic form of an address if the
5094 offset between the closest earlier symbol and the address is less than
5095 @var{max-offset}. The default is 0, which tells @value{GDBN}
5096 to always print the symbolic form of an address if any symbol precedes it.
5098 @kindex show print max-symbolic-offset
5099 @item show print max-symbolic-offset
5100 Ask how large the maximum offset is that @value{GDBN} prints in a
5104 @cindex wild pointer, interpreting
5105 @cindex pointer, finding referent
5106 If you have a pointer and you are not sure where it points, try
5107 @samp{set print symbol-filename on}. Then you can determine the name
5108 and source file location of the variable where it points, using
5109 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5110 For example, here @value{GDBN} shows that a variable @code{ptt} points
5111 at another variable @code{t}, defined in @file{hi2.c}:
5114 (@value{GDBP}) set print symbol-filename on
5115 (@value{GDBP}) p/a ptt
5116 $4 = 0xe008 <t in hi2.c>
5120 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5121 does not show the symbol name and filename of the referent, even with
5122 the appropriate @code{set print} options turned on.
5125 Other settings control how different kinds of objects are printed:
5128 @kindex set print array
5129 @item set print array
5130 @itemx set print array on
5131 Pretty print arrays. This format is more convenient to read,
5132 but uses more space. The default is off.
5134 @item set print array off
5135 Return to compressed format for arrays.
5137 @kindex show print array
5138 @item show print array
5139 Show whether compressed or pretty format is selected for displaying
5142 @kindex set print elements
5143 @item set print elements @var{number-of-elements}
5144 Set a limit on how many elements of an array @value{GDBN} will print.
5145 If @value{GDBN} is printing a large array, it stops printing after it has
5146 printed the number of elements set by the @code{set print elements} command.
5147 This limit also applies to the display of strings.
5148 When @value{GDBN} starts, this limit is set to 200.
5149 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5151 @kindex show print elements
5152 @item show print elements
5153 Display the number of elements of a large array that @value{GDBN} will print.
5154 If the number is 0, then the printing is unlimited.
5156 @kindex set print null-stop
5157 @item set print null-stop
5158 Cause @value{GDBN} to stop printing the characters of an array when the first
5159 @sc{null} is encountered. This is useful when large arrays actually
5160 contain only short strings.
5163 @kindex set print pretty
5164 @item set print pretty on
5165 Cause @value{GDBN} to print structures in an indented format with one member
5166 per line, like this:
5181 @item set print pretty off
5182 Cause @value{GDBN} to print structures in a compact format, like this:
5186 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5187 meat = 0x54 "Pork"@}
5192 This is the default format.
5194 @kindex show print pretty
5195 @item show print pretty
5196 Show which format @value{GDBN} is using to print structures.
5198 @kindex set print sevenbit-strings
5199 @item set print sevenbit-strings on
5200 Print using only seven-bit characters; if this option is set,
5201 @value{GDBN} displays any eight-bit characters (in strings or
5202 character values) using the notation @code{\}@var{nnn}. This setting is
5203 best if you are working in English (@sc{ascii}) and you use the
5204 high-order bit of characters as a marker or ``meta'' bit.
5206 @item set print sevenbit-strings off
5207 Print full eight-bit characters. This allows the use of more
5208 international character sets, and is the default.
5210 @kindex show print sevenbit-strings
5211 @item show print sevenbit-strings
5212 Show whether or not @value{GDBN} is printing only seven-bit characters.
5214 @kindex set print union
5215 @item set print union on
5216 Tell @value{GDBN} to print unions which are contained in structures. This
5217 is the default setting.
5219 @item set print union off
5220 Tell @value{GDBN} not to print unions which are contained in structures.
5222 @kindex show print union
5223 @item show print union
5224 Ask @value{GDBN} whether or not it will print unions which are contained in
5227 For example, given the declarations
5230 typedef enum @{Tree, Bug@} Species;
5231 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5232 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5243 struct thing foo = @{Tree, @{Acorn@}@};
5247 with @code{set print union on} in effect @samp{p foo} would print
5250 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5254 and with @code{set print union off} in effect it would print
5257 $1 = @{it = Tree, form = @{...@}@}
5263 These settings are of interest when debugging C@t{++} programs:
5267 @kindex set print demangle
5268 @item set print demangle
5269 @itemx set print demangle on
5270 Print C@t{++} names in their source form rather than in the encoded
5271 (``mangled'') form passed to the assembler and linker for type-safe
5272 linkage. The default is on.
5274 @kindex show print demangle
5275 @item show print demangle
5276 Show whether C@t{++} names are printed in mangled or demangled form.
5278 @kindex set print asm-demangle
5279 @item set print asm-demangle
5280 @itemx set print asm-demangle on
5281 Print C@t{++} names in their source form rather than their mangled form, even
5282 in assembler code printouts such as instruction disassemblies.
5285 @kindex show print asm-demangle
5286 @item show print asm-demangle
5287 Show whether C@t{++} names in assembly listings are printed in mangled
5290 @kindex set demangle-style
5291 @cindex C@t{++} symbol decoding style
5292 @cindex symbol decoding style, C@t{++}
5293 @item set demangle-style @var{style}
5294 Choose among several encoding schemes used by different compilers to
5295 represent C@t{++} names. The choices for @var{style} are currently:
5299 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5302 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5303 This is the default.
5306 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5309 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5312 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5313 @strong{Warning:} this setting alone is not sufficient to allow
5314 debugging @code{cfront}-generated executables. @value{GDBN} would
5315 require further enhancement to permit that.
5318 If you omit @var{style}, you will see a list of possible formats.
5320 @kindex show demangle-style
5321 @item show demangle-style
5322 Display the encoding style currently in use for decoding C@t{++} symbols.
5324 @kindex set print object
5325 @item set print object
5326 @itemx set print object on
5327 When displaying a pointer to an object, identify the @emph{actual}
5328 (derived) type of the object rather than the @emph{declared} type, using
5329 the virtual function table.
5331 @item set print object off
5332 Display only the declared type of objects, without reference to the
5333 virtual function table. This is the default setting.
5335 @kindex show print object
5336 @item show print object
5337 Show whether actual, or declared, object types are displayed.
5339 @kindex set print static-members
5340 @item set print static-members
5341 @itemx set print static-members on
5342 Print static members when displaying a C@t{++} object. The default is on.
5344 @item set print static-members off
5345 Do not print static members when displaying a C@t{++} object.
5347 @kindex show print static-members
5348 @item show print static-members
5349 Show whether C@t{++} static members are printed, or not.
5351 @c These don't work with HP ANSI C++ yet.
5352 @kindex set print vtbl
5353 @item set print vtbl
5354 @itemx set print vtbl on
5355 Pretty print C@t{++} virtual function tables. The default is off.
5356 (The @code{vtbl} commands do not work on programs compiled with the HP
5357 ANSI C@t{++} compiler (@code{aCC}).)
5359 @item set print vtbl off
5360 Do not pretty print C@t{++} virtual function tables.
5362 @kindex show print vtbl
5363 @item show print vtbl
5364 Show whether C@t{++} virtual function tables are pretty printed, or not.
5368 @section Value history
5370 @cindex value history
5371 Values printed by the @code{print} command are saved in the @value{GDBN}
5372 @dfn{value history}. This allows you to refer to them in other expressions.
5373 Values are kept until the symbol table is re-read or discarded
5374 (for example with the @code{file} or @code{symbol-file} commands).
5375 When the symbol table changes, the value history is discarded,
5376 since the values may contain pointers back to the types defined in the
5381 @cindex history number
5382 The values printed are given @dfn{history numbers} by which you can
5383 refer to them. These are successive integers starting with one.
5384 @code{print} shows you the history number assigned to a value by
5385 printing @samp{$@var{num} = } before the value; here @var{num} is the
5388 To refer to any previous value, use @samp{$} followed by the value's
5389 history number. The way @code{print} labels its output is designed to
5390 remind you of this. Just @code{$} refers to the most recent value in
5391 the history, and @code{$$} refers to the value before that.
5392 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5393 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5394 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5396 For example, suppose you have just printed a pointer to a structure and
5397 want to see the contents of the structure. It suffices to type
5403 If you have a chain of structures where the component @code{next} points
5404 to the next one, you can print the contents of the next one with this:
5411 You can print successive links in the chain by repeating this
5412 command---which you can do by just typing @key{RET}.
5414 Note that the history records values, not expressions. If the value of
5415 @code{x} is 4 and you type these commands:
5423 then the value recorded in the value history by the @code{print} command
5424 remains 4 even though the value of @code{x} has changed.
5429 Print the last ten values in the value history, with their item numbers.
5430 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5431 values} does not change the history.
5433 @item show values @var{n}
5434 Print ten history values centered on history item number @var{n}.
5437 Print ten history values just after the values last printed. If no more
5438 values are available, @code{show values +} produces no display.
5441 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5442 same effect as @samp{show values +}.
5444 @node Convenience Vars
5445 @section Convenience variables
5447 @cindex convenience variables
5448 @value{GDBN} provides @dfn{convenience variables} that you can use within
5449 @value{GDBN} to hold on to a value and refer to it later. These variables
5450 exist entirely within @value{GDBN}; they are not part of your program, and
5451 setting a convenience variable has no direct effect on further execution
5452 of your program. That is why you can use them freely.
5454 Convenience variables are prefixed with @samp{$}. Any name preceded by
5455 @samp{$} can be used for a convenience variable, unless it is one of
5456 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5457 (Value history references, in contrast, are @emph{numbers} preceded
5458 by @samp{$}. @xref{Value History, ,Value history}.)
5460 You can save a value in a convenience variable with an assignment
5461 expression, just as you would set a variable in your program.
5465 set $foo = *object_ptr
5469 would save in @code{$foo} the value contained in the object pointed to by
5472 Using a convenience variable for the first time creates it, but its
5473 value is @code{void} until you assign a new value. You can alter the
5474 value with another assignment at any time.
5476 Convenience variables have no fixed types. You can assign a convenience
5477 variable any type of value, including structures and arrays, even if
5478 that variable already has a value of a different type. The convenience
5479 variable, when used as an expression, has the type of its current value.
5482 @kindex show convenience
5483 @item show convenience
5484 Print a list of convenience variables used so far, and their values.
5485 Abbreviated @code{show conv}.
5488 One of the ways to use a convenience variable is as a counter to be
5489 incremented or a pointer to be advanced. For example, to print
5490 a field from successive elements of an array of structures:
5494 print bar[$i++]->contents
5498 Repeat that command by typing @key{RET}.
5500 Some convenience variables are created automatically by @value{GDBN} and given
5501 values likely to be useful.
5504 @vindex $_@r{, convenience variable}
5506 The variable @code{$_} is automatically set by the @code{x} command to
5507 the last address examined (@pxref{Memory, ,Examining memory}). Other
5508 commands which provide a default address for @code{x} to examine also
5509 set @code{$_} to that address; these commands include @code{info line}
5510 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5511 except when set by the @code{x} command, in which case it is a pointer
5512 to the type of @code{$__}.
5514 @vindex $__@r{, convenience variable}
5516 The variable @code{$__} is automatically set by the @code{x} command
5517 to the value found in the last address examined. Its type is chosen
5518 to match the format in which the data was printed.
5521 @vindex $_exitcode@r{, convenience variable}
5522 The variable @code{$_exitcode} is automatically set to the exit code when
5523 the program being debugged terminates.
5526 On HP-UX systems, if you refer to a function or variable name that
5527 begins with a dollar sign, @value{GDBN} searches for a user or system
5528 name first, before it searches for a convenience variable.
5534 You can refer to machine register contents, in expressions, as variables
5535 with names starting with @samp{$}. The names of registers are different
5536 for each machine; use @code{info registers} to see the names used on
5540 @kindex info registers
5541 @item info registers
5542 Print the names and values of all registers except floating-point
5543 registers (in the selected stack frame).
5545 @kindex info all-registers
5546 @cindex floating point registers
5547 @item info all-registers
5548 Print the names and values of all registers, including floating-point
5551 @item info registers @var{regname} @dots{}
5552 Print the @dfn{relativized} value of each specified register @var{regname}.
5553 As discussed in detail below, register values are normally relative to
5554 the selected stack frame. @var{regname} may be any register name valid on
5555 the machine you are using, with or without the initial @samp{$}.
5558 @value{GDBN} has four ``standard'' register names that are available (in
5559 expressions) on most machines---whenever they do not conflict with an
5560 architecture's canonical mnemonics for registers. The register names
5561 @code{$pc} and @code{$sp} are used for the program counter register and
5562 the stack pointer. @code{$fp} is used for a register that contains a
5563 pointer to the current stack frame, and @code{$ps} is used for a
5564 register that contains the processor status. For example,
5565 you could print the program counter in hex with
5572 or print the instruction to be executed next with
5579 or add four to the stack pointer@footnote{This is a way of removing
5580 one word from the stack, on machines where stacks grow downward in
5581 memory (most machines, nowadays). This assumes that the innermost
5582 stack frame is selected; setting @code{$sp} is not allowed when other
5583 stack frames are selected. To pop entire frames off the stack,
5584 regardless of machine architecture, use @code{return};
5585 see @ref{Returning, ,Returning from a function}.} with
5591 Whenever possible, these four standard register names are available on
5592 your machine even though the machine has different canonical mnemonics,
5593 so long as there is no conflict. The @code{info registers} command
5594 shows the canonical names. For example, on the SPARC, @code{info
5595 registers} displays the processor status register as @code{$psr} but you
5596 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5597 is an alias for the @sc{eflags} register.
5599 @value{GDBN} always considers the contents of an ordinary register as an
5600 integer when the register is examined in this way. Some machines have
5601 special registers which can hold nothing but floating point; these
5602 registers are considered to have floating point values. There is no way
5603 to refer to the contents of an ordinary register as floating point value
5604 (although you can @emph{print} it as a floating point value with
5605 @samp{print/f $@var{regname}}).
5607 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5608 means that the data format in which the register contents are saved by
5609 the operating system is not the same one that your program normally
5610 sees. For example, the registers of the 68881 floating point
5611 coprocessor are always saved in ``extended'' (raw) format, but all C
5612 programs expect to work with ``double'' (virtual) format. In such
5613 cases, @value{GDBN} normally works with the virtual format only (the format
5614 that makes sense for your program), but the @code{info registers} command
5615 prints the data in both formats.
5617 Normally, register values are relative to the selected stack frame
5618 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5619 value that the register would contain if all stack frames farther in
5620 were exited and their saved registers restored. In order to see the
5621 true contents of hardware registers, you must select the innermost
5622 frame (with @samp{frame 0}).
5624 However, @value{GDBN} must deduce where registers are saved, from the machine
5625 code generated by your compiler. If some registers are not saved, or if
5626 @value{GDBN} is unable to locate the saved registers, the selected stack
5627 frame makes no difference.
5629 @node Floating Point Hardware
5630 @section Floating point hardware
5631 @cindex floating point
5633 Depending on the configuration, @value{GDBN} may be able to give
5634 you more information about the status of the floating point hardware.
5639 Display hardware-dependent information about the floating
5640 point unit. The exact contents and layout vary depending on the
5641 floating point chip. Currently, @samp{info float} is supported on
5642 the ARM and x86 machines.
5645 @node Memory Region Attributes
5646 @section Memory Region Attributes
5647 @cindex memory region attributes
5649 @dfn{Memory region attributes} allow you to describe special handling
5650 required by regions of your target's memory. @value{GDBN} uses attributes
5651 to determine whether to allow certain types of memory accesses; whether to
5652 use specific width accesses; and whether to cache target memory.
5654 Defined memory regions can be individually enabled and disabled. When a
5655 memory region is disabled, @value{GDBN} uses the default attributes when
5656 accessing memory in that region. Similarly, if no memory regions have
5657 been defined, @value{GDBN} uses the default attributes when accessing
5660 When a memory region is defined, it is given a number to identify it;
5661 to enable, disable, or remove a memory region, you specify that number.
5665 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5666 Define memory region bounded by @var{address1} and @var{address2}
5667 with attributes @var{attributes}@dots{}.
5670 @item delete mem @var{nums}@dots{}
5671 Remove memory region numbers @var{nums}.
5674 @item disable mem @var{nums}@dots{}
5675 Disable memory region numbers @var{nums}.
5676 A disabled memory region is not forgotten.
5677 It may be enabled again later.
5680 @item enable mem @var{nums}@dots{}
5681 Enable memory region numbers @var{nums}.
5685 Print a table of all defined memory regions, with the following columns
5689 @item Memory Region Number
5690 @item Enabled or Disabled.
5691 Enabled memory regions are marked with @samp{y}.
5692 Disabled memory regions are marked with @samp{n}.
5695 The address defining the inclusive lower bound of the memory region.
5698 The address defining the exclusive upper bound of the memory region.
5701 The list of attributes set for this memory region.
5706 @subsection Attributes
5708 @subsubsection Memory Access Mode
5709 The access mode attributes set whether @value{GDBN} may make read or
5710 write accesses to a memory region.
5712 While these attributes prevent @value{GDBN} from performing invalid
5713 memory accesses, they do nothing to prevent the target system, I/O DMA,
5714 etc. from accessing memory.
5718 Memory is read only.
5720 Memory is write only.
5722 Memory is read/write (default).
5725 @subsubsection Memory Access Size
5726 The acccess size attributes tells @value{GDBN} to use specific sized
5727 accesses in the memory region. Often memory mapped device registers
5728 require specific sized accesses. If no access size attribute is
5729 specified, @value{GDBN} may use accesses of any size.
5733 Use 8 bit memory accesses.
5735 Use 16 bit memory accesses.
5737 Use 32 bit memory accesses.
5739 Use 64 bit memory accesses.
5742 @c @subsubsection Hardware/Software Breakpoints
5743 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5744 @c will use hardware or software breakpoints for the internal breakpoints
5745 @c used by the step, next, finish, until, etc. commands.
5749 @c Always use hardware breakpoints
5750 @c @item swbreak (default)
5753 @subsubsection Data Cache
5754 The data cache attributes set whether @value{GDBN} will cache target
5755 memory. While this generally improves performance by reducing debug
5756 protocol overhead, it can lead to incorrect results because @value{GDBN}
5757 does not know about volatile variables or memory mapped device
5762 Enable @value{GDBN} to cache target memory.
5763 @item nocache (default)
5764 Disable @value{GDBN} from caching target memory.
5767 @c @subsubsection Memory Write Verification
5768 @c The memory write verification attributes set whether @value{GDBN}
5769 @c will re-reads data after each write to verify the write was successful.
5773 @c @item noverify (default)
5777 @chapter Tracepoints
5778 @c This chapter is based on the documentation written by Michael
5779 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5782 In some applications, it is not feasible for the debugger to interrupt
5783 the program's execution long enough for the developer to learn
5784 anything helpful about its behavior. If the program's correctness
5785 depends on its real-time behavior, delays introduced by a debugger
5786 might cause the program to change its behavior drastically, or perhaps
5787 fail, even when the code itself is correct. It is useful to be able
5788 to observe the program's behavior without interrupting it.
5790 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5791 specify locations in the program, called @dfn{tracepoints}, and
5792 arbitrary expressions to evaluate when those tracepoints are reached.
5793 Later, using the @code{tfind} command, you can examine the values
5794 those expressions had when the program hit the tracepoints. The
5795 expressions may also denote objects in memory---structures or arrays,
5796 for example---whose values @value{GDBN} should record; while visiting
5797 a particular tracepoint, you may inspect those objects as if they were
5798 in memory at that moment. However, because @value{GDBN} records these
5799 values without interacting with you, it can do so quickly and
5800 unobtrusively, hopefully not disturbing the program's behavior.
5802 The tracepoint facility is currently available only for remote
5803 targets. @xref{Targets}. In addition, your remote target must know how
5804 to collect trace data. This functionality is implemented in the remote
5805 stub; however, none of the stubs distributed with @value{GDBN} support
5806 tracepoints as of this writing.
5808 This chapter describes the tracepoint commands and features.
5812 * Analyze Collected Data::
5813 * Tracepoint Variables::
5816 @node Set Tracepoints
5817 @section Commands to Set Tracepoints
5819 Before running such a @dfn{trace experiment}, an arbitrary number of
5820 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5821 tracepoint has a number assigned to it by @value{GDBN}. Like with
5822 breakpoints, tracepoint numbers are successive integers starting from
5823 one. Many of the commands associated with tracepoints take the
5824 tracepoint number as their argument, to identify which tracepoint to
5827 For each tracepoint, you can specify, in advance, some arbitrary set
5828 of data that you want the target to collect in the trace buffer when
5829 it hits that tracepoint. The collected data can include registers,
5830 local variables, or global data. Later, you can use @value{GDBN}
5831 commands to examine the values these data had at the time the
5834 This section describes commands to set tracepoints and associated
5835 conditions and actions.
5838 * Create and Delete Tracepoints::
5839 * Enable and Disable Tracepoints::
5840 * Tracepoint Passcounts::
5841 * Tracepoint Actions::
5842 * Listing Tracepoints::
5843 * Starting and Stopping Trace Experiment::
5846 @node Create and Delete Tracepoints
5847 @subsection Create and Delete Tracepoints
5850 @cindex set tracepoint
5853 The @code{trace} command is very similar to the @code{break} command.
5854 Its argument can be a source line, a function name, or an address in
5855 the target program. @xref{Set Breaks}. The @code{trace} command
5856 defines a tracepoint, which is a point in the target program where the
5857 debugger will briefly stop, collect some data, and then allow the
5858 program to continue. Setting a tracepoint or changing its commands
5859 doesn't take effect until the next @code{tstart} command; thus, you
5860 cannot change the tracepoint attributes once a trace experiment is
5863 Here are some examples of using the @code{trace} command:
5866 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5868 (@value{GDBP}) @b{trace +2} // 2 lines forward
5870 (@value{GDBP}) @b{trace my_function} // first source line of function
5872 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5874 (@value{GDBP}) @b{trace *0x2117c4} // an address
5878 You can abbreviate @code{trace} as @code{tr}.
5881 @cindex last tracepoint number
5882 @cindex recent tracepoint number
5883 @cindex tracepoint number
5884 The convenience variable @code{$tpnum} records the tracepoint number
5885 of the most recently set tracepoint.
5887 @kindex delete tracepoint
5888 @cindex tracepoint deletion
5889 @item delete tracepoint @r{[}@var{num}@r{]}
5890 Permanently delete one or more tracepoints. With no argument, the
5891 default is to delete all tracepoints.
5896 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5898 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5902 You can abbreviate this command as @code{del tr}.
5905 @node Enable and Disable Tracepoints
5906 @subsection Enable and Disable Tracepoints
5909 @kindex disable tracepoint
5910 @item disable tracepoint @r{[}@var{num}@r{]}
5911 Disable tracepoint @var{num}, or all tracepoints if no argument
5912 @var{num} is given. A disabled tracepoint will have no effect during
5913 the next trace experiment, but it is not forgotten. You can re-enable
5914 a disabled tracepoint using the @code{enable tracepoint} command.
5916 @kindex enable tracepoint
5917 @item enable tracepoint @r{[}@var{num}@r{]}
5918 Enable tracepoint @var{num}, or all tracepoints. The enabled
5919 tracepoints will become effective the next time a trace experiment is
5923 @node Tracepoint Passcounts
5924 @subsection Tracepoint Passcounts
5928 @cindex tracepoint pass count
5929 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5930 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5931 automatically stop a trace experiment. If a tracepoint's passcount is
5932 @var{n}, then the trace experiment will be automatically stopped on
5933 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5934 @var{num} is not specified, the @code{passcount} command sets the
5935 passcount of the most recently defined tracepoint. If no passcount is
5936 given, the trace experiment will run until stopped explicitly by the
5942 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5944 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5945 // most recently defined tracepoint.
5946 (@value{GDBP}) @b{trace foo}
5947 (@value{GDBP}) @b{pass 3}
5948 (@value{GDBP}) @b{trace bar}
5949 (@value{GDBP}) @b{pass 2}
5950 (@value{GDBP}) @b{trace baz}
5951 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5952 // executed 3 times OR when bar has
5953 // been executed 2 times
5954 // OR when baz has been executed 1 time.
5958 @node Tracepoint Actions
5959 @subsection Tracepoint Action Lists
5963 @cindex tracepoint actions
5964 @item actions @r{[}@var{num}@r{]}
5965 This command will prompt for a list of actions to be taken when the
5966 tracepoint is hit. If the tracepoint number @var{num} is not
5967 specified, this command sets the actions for the one that was most
5968 recently defined (so that you can define a tracepoint and then say
5969 @code{actions} without bothering about its number). You specify the
5970 actions themselves on the following lines, one action at a time, and
5971 terminate the actions list with a line containing just @code{end}. So
5972 far, the only defined actions are @code{collect} and
5973 @code{while-stepping}.
5975 @cindex remove actions from a tracepoint
5976 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5977 and follow it immediately with @samp{end}.
5980 (@value{GDBP}) @b{collect @var{data}} // collect some data
5982 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5984 (@value{GDBP}) @b{end} // signals the end of actions.
5987 In the following example, the action list begins with @code{collect}
5988 commands indicating the things to be collected when the tracepoint is
5989 hit. Then, in order to single-step and collect additional data
5990 following the tracepoint, a @code{while-stepping} command is used,
5991 followed by the list of things to be collected while stepping. The
5992 @code{while-stepping} command is terminated by its own separate
5993 @code{end} command. Lastly, the action list is terminated by an
5997 (@value{GDBP}) @b{trace foo}
5998 (@value{GDBP}) @b{actions}
5999 Enter actions for tracepoint 1, one per line:
6008 @kindex collect @r{(tracepoints)}
6009 @item collect @var{expr1}, @var{expr2}, @dots{}
6010 Collect values of the given expressions when the tracepoint is hit.
6011 This command accepts a comma-separated list of any valid expressions.
6012 In addition to global, static, or local variables, the following
6013 special arguments are supported:
6017 collect all registers
6020 collect all function arguments
6023 collect all local variables.
6026 You can give several consecutive @code{collect} commands, each one
6027 with a single argument, or one @code{collect} command with several
6028 arguments separated by commas: the effect is the same.
6030 The command @code{info scope} (@pxref{Symbols, info scope}) is
6031 particularly useful for figuring out what data to collect.
6033 @kindex while-stepping @r{(tracepoints)}
6034 @item while-stepping @var{n}
6035 Perform @var{n} single-step traces after the tracepoint, collecting
6036 new data at each step. The @code{while-stepping} command is
6037 followed by the list of what to collect while stepping (followed by
6038 its own @code{end} command):
6042 > collect $regs, myglobal
6048 You may abbreviate @code{while-stepping} as @code{ws} or
6052 @node Listing Tracepoints
6053 @subsection Listing Tracepoints
6056 @kindex info tracepoints
6057 @cindex information about tracepoints
6058 @item info tracepoints @r{[}@var{num}@r{]}
6059 Display information the tracepoint @var{num}. If you don't specify a
6060 tracepoint number displays information about all the tracepoints
6061 defined so far. For each tracepoint, the following information is
6068 whether it is enabled or disabled
6072 its passcount as given by the @code{passcount @var{n}} command
6074 its step count as given by the @code{while-stepping @var{n}} command
6076 where in the source files is the tracepoint set
6078 its action list as given by the @code{actions} command
6082 (@value{GDBP}) @b{info trace}
6083 Num Enb Address PassC StepC What
6084 1 y 0x002117c4 0 0 <gdb_asm>
6085 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
6086 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
6091 This command can be abbreviated @code{info tp}.
6094 @node Starting and Stopping Trace Experiment
6095 @subsection Starting and Stopping Trace Experiment
6099 @cindex start a new trace experiment
6100 @cindex collected data discarded
6102 This command takes no arguments. It starts the trace experiment, and
6103 begins collecting data. This has the side effect of discarding all
6104 the data collected in the trace buffer during the previous trace
6108 @cindex stop a running trace experiment
6110 This command takes no arguments. It ends the trace experiment, and
6111 stops collecting data.
6113 @strong{Note:} a trace experiment and data collection may stop
6114 automatically if any tracepoint's passcount is reached
6115 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6118 @cindex status of trace data collection
6119 @cindex trace experiment, status of
6121 This command displays the status of the current trace data
6125 Here is an example of the commands we described so far:
6128 (@value{GDBP}) @b{trace gdb_c_test}
6129 (@value{GDBP}) @b{actions}
6130 Enter actions for tracepoint #1, one per line.
6131 > collect $regs,$locals,$args
6136 (@value{GDBP}) @b{tstart}
6137 [time passes @dots{}]
6138 (@value{GDBP}) @b{tstop}
6142 @node Analyze Collected Data
6143 @section Using the collected data
6145 After the tracepoint experiment ends, you use @value{GDBN} commands
6146 for examining the trace data. The basic idea is that each tracepoint
6147 collects a trace @dfn{snapshot} every time it is hit and another
6148 snapshot every time it single-steps. All these snapshots are
6149 consecutively numbered from zero and go into a buffer, and you can
6150 examine them later. The way you examine them is to @dfn{focus} on a
6151 specific trace snapshot. When the remote stub is focused on a trace
6152 snapshot, it will respond to all @value{GDBN} requests for memory and
6153 registers by reading from the buffer which belongs to that snapshot,
6154 rather than from @emph{real} memory or registers of the program being
6155 debugged. This means that @strong{all} @value{GDBN} commands
6156 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6157 behave as if we were currently debugging the program state as it was
6158 when the tracepoint occurred. Any requests for data that are not in
6159 the buffer will fail.
6162 * tfind:: How to select a trace snapshot
6163 * tdump:: How to display all data for a snapshot
6164 * save-tracepoints:: How to save tracepoints for a future run
6168 @subsection @code{tfind @var{n}}
6171 @cindex select trace snapshot
6172 @cindex find trace snapshot
6173 The basic command for selecting a trace snapshot from the buffer is
6174 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6175 counting from zero. If no argument @var{n} is given, the next
6176 snapshot is selected.
6178 Here are the various forms of using the @code{tfind} command.
6182 Find the first snapshot in the buffer. This is a synonym for
6183 @code{tfind 0} (since 0 is the number of the first snapshot).
6186 Stop debugging trace snapshots, resume @emph{live} debugging.
6189 Same as @samp{tfind none}.
6192 No argument means find the next trace snapshot.
6195 Find the previous trace snapshot before the current one. This permits
6196 retracing earlier steps.
6198 @item tfind tracepoint @var{num}
6199 Find the next snapshot associated with tracepoint @var{num}. Search
6200 proceeds forward from the last examined trace snapshot. If no
6201 argument @var{num} is given, it means find the next snapshot collected
6202 for the same tracepoint as the current snapshot.
6204 @item tfind pc @var{addr}
6205 Find the next snapshot associated with the value @var{addr} of the
6206 program counter. Search proceeds forward from the last examined trace
6207 snapshot. If no argument @var{addr} is given, it means find the next
6208 snapshot with the same value of PC as the current snapshot.
6210 @item tfind outside @var{addr1}, @var{addr2}
6211 Find the next snapshot whose PC is outside the given range of
6214 @item tfind range @var{addr1}, @var{addr2}
6215 Find the next snapshot whose PC is between @var{addr1} and
6216 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6218 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6219 Find the next snapshot associated with the source line @var{n}. If
6220 the optional argument @var{file} is given, refer to line @var{n} in
6221 that source file. Search proceeds forward from the last examined
6222 trace snapshot. If no argument @var{n} is given, it means find the
6223 next line other than the one currently being examined; thus saying
6224 @code{tfind line} repeatedly can appear to have the same effect as
6225 stepping from line to line in a @emph{live} debugging session.
6228 The default arguments for the @code{tfind} commands are specifically
6229 designed to make it easy to scan through the trace buffer. For
6230 instance, @code{tfind} with no argument selects the next trace
6231 snapshot, and @code{tfind -} with no argument selects the previous
6232 trace snapshot. So, by giving one @code{tfind} command, and then
6233 simply hitting @key{RET} repeatedly you can examine all the trace
6234 snapshots in order. Or, by saying @code{tfind -} and then hitting
6235 @key{RET} repeatedly you can examine the snapshots in reverse order.
6236 The @code{tfind line} command with no argument selects the snapshot
6237 for the next source line executed. The @code{tfind pc} command with
6238 no argument selects the next snapshot with the same program counter
6239 (PC) as the current frame. The @code{tfind tracepoint} command with
6240 no argument selects the next trace snapshot collected by the same
6241 tracepoint as the current one.
6243 In addition to letting you scan through the trace buffer manually,
6244 these commands make it easy to construct @value{GDBN} scripts that
6245 scan through the trace buffer and print out whatever collected data
6246 you are interested in. Thus, if we want to examine the PC, FP, and SP
6247 registers from each trace frame in the buffer, we can say this:
6250 (@value{GDBP}) @b{tfind start}
6251 (@value{GDBP}) @b{while ($trace_frame != -1)}
6252 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6253 $trace_frame, $pc, $sp, $fp
6257 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6258 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6259 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6260 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6261 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6262 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6263 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6264 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6265 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6266 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6267 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6270 Or, if we want to examine the variable @code{X} at each source line in
6274 (@value{GDBP}) @b{tfind start}
6275 (@value{GDBP}) @b{while ($trace_frame != -1)}
6276 > printf "Frame %d, X == %d\n", $trace_frame, X
6286 @subsection @code{tdump}
6288 @cindex dump all data collected at tracepoint
6289 @cindex tracepoint data, display
6291 This command takes no arguments. It prints all the data collected at
6292 the current trace snapshot.
6295 (@value{GDBP}) @b{trace 444}
6296 (@value{GDBP}) @b{actions}
6297 Enter actions for tracepoint #2, one per line:
6298 > collect $regs, $locals, $args, gdb_long_test
6301 (@value{GDBP}) @b{tstart}
6303 (@value{GDBP}) @b{tfind line 444}
6304 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6306 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6308 (@value{GDBP}) @b{tdump}
6309 Data collected at tracepoint 2, trace frame 1:
6310 d0 0xc4aa0085 -995491707
6314 d4 0x71aea3d 119204413
6319 a1 0x3000668 50333288
6322 a4 0x3000698 50333336
6324 fp 0x30bf3c 0x30bf3c
6325 sp 0x30bf34 0x30bf34
6327 pc 0x20b2c8 0x20b2c8
6331 p = 0x20e5b4 "gdb-test"
6338 gdb_long_test = 17 '\021'
6343 @node save-tracepoints
6344 @subsection @code{save-tracepoints @var{filename}}
6345 @kindex save-tracepoints
6346 @cindex save tracepoints for future sessions
6348 This command saves all current tracepoint definitions together with
6349 their actions and passcounts, into a file @file{@var{filename}}
6350 suitable for use in a later debugging session. To read the saved
6351 tracepoint definitions, use the @code{source} command (@pxref{Command
6354 @node Tracepoint Variables
6355 @section Convenience Variables for Tracepoints
6356 @cindex tracepoint variables
6357 @cindex convenience variables for tracepoints
6360 @vindex $trace_frame
6361 @item (int) $trace_frame
6362 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6363 snapshot is selected.
6366 @item (int) $tracepoint
6367 The tracepoint for the current trace snapshot.
6370 @item (int) $trace_line
6371 The line number for the current trace snapshot.
6374 @item (char []) $trace_file
6375 The source file for the current trace snapshot.
6378 @item (char []) $trace_func
6379 The name of the function containing @code{$tracepoint}.
6382 Note: @code{$trace_file} is not suitable for use in @code{printf},
6383 use @code{output} instead.
6385 Here's a simple example of using these convenience variables for
6386 stepping through all the trace snapshots and printing some of their
6390 (@value{GDBP}) @b{tfind start}
6392 (@value{GDBP}) @b{while $trace_frame != -1}
6393 > output $trace_file
6394 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6400 @chapter Debugging Programs That Use Overlays
6403 If your program is too large to fit completely in your target system's
6404 memory, you can sometimes use @dfn{overlays} to work around this
6405 problem. @value{GDBN} provides some support for debugging programs that
6409 * How Overlays Work:: A general explanation of overlays.
6410 * Overlay Commands:: Managing overlays in @value{GDBN}.
6411 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
6412 mapped by asking the inferior.
6413 * Overlay Sample Program:: A sample program using overlays.
6416 @node How Overlays Work
6417 @section How Overlays Work
6418 @cindex mapped overlays
6419 @cindex unmapped overlays
6420 @cindex load address, overlay's
6421 @cindex mapped address
6422 @cindex overlay area
6424 Suppose you have a computer whose instruction address space is only 64
6425 kilobytes long, but which has much more memory which can be accessed by
6426 other means: special instructions, segment registers, or memory
6427 management hardware, for example. Suppose further that you want to
6428 adapt a program which is larger than 64 kilobytes to run on this system.
6430 One solution is to identify modules of your program which are relatively
6431 independent, and need not call each other directly; call these modules
6432 @dfn{overlays}. Separate the overlays from the main program, and place
6433 their machine code in the larger memory. Place your main program in
6434 instruction memory, but leave at least enough space there to hold the
6435 largest overlay as well.
6437 Now, to call a function located in an overlay, you must first copy that
6438 overlay's machine code from the large memory into the space set aside
6439 for it in the instruction memory, and then jump to its entry point
6444 Data Instruction Larger
6445 Address Space Address Space Address Space
6446 +-----------+ +-----------+ +-----------+
6448 +-----------+ +-----------+ +-----------+<-- overlay 1
6449 | program | | main | | | load address
6450 | variables | | program | | overlay 1 |
6451 | and heap | | | ,---| |
6452 +-----------+ | | | | |
6453 | | +-----------+ | +-----------+
6454 +-----------+ | | | | |
6455 mapped --->+-----------+ / +-----------+<-- overlay 2
6456 address | overlay | <-' | overlay 2 | load address
6458 | | <---. +-----------+
6461 | | | +-----------+<-- overlay 3
6462 +-----------+ `--| | load address
6469 To map an overlay, copy its code from the larger address space
6470 to the instruction address space. Since the overlays shown here
6471 all use the same mapped address, only one may be mapped at a time.
6475 This diagram shows a system with separate data and instruction address
6476 spaces. For a system with a single address space for data and
6477 instructions, the diagram would be similar, except that the program
6478 variables and heap would share an address space with the main program
6479 and the overlay area.
6481 An overlay loaded into instruction memory and ready for use is called a
6482 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
6483 instruction memory. An overlay not present (or only partially present)
6484 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
6485 is its address in the larger memory. The mapped address is also called
6486 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
6487 called the @dfn{load memory address}, or @dfn{LMA}.
6489 Unfortunately, overlays are not a completely transparent way to adapt a
6490 program to limited instruction memory. They introduce a new set of
6491 global constraints you must keep in mind as you design your program:
6496 Before calling or returning to a function in an overlay, your program
6497 must make sure that overlay is actually mapped. Otherwise, the call or
6498 return will transfer control to the right address, but in the wrong
6499 overlay, and your program will probably crash.
6502 If the process of mapping an overlay is expensive on your system, you
6503 will need to choose your overlays carefully to minimize their effect on
6504 your program's performance.
6507 The executable file you load onto your system must contain each
6508 overlay's instructions, appearing at the overlay's load address, not its
6509 mapped address. However, each overlay's instructions must be relocated
6510 and its symbols defined as if the overlay were at its mapped address.
6511 You can use GNU linker scripts to specify different load and relocation
6512 addresses for pieces of your program; see @ref{Overlay Description,,,
6513 ld.info, Using ld: the GNU linker}.
6516 The procedure for loading executable files onto your system must be able
6517 to load their contents into the larger address space as well as the
6518 instruction and data spaces.
6522 The overlay system described above is rather simple, and could be
6523 improved in many ways:
6528 If your system has suitable bank switch registers or memory management
6529 hardware, you could use those facilities to make an overlay's load area
6530 contents simply appear at their mapped address in instruction space.
6531 This would probably be faster than copying the overlay to its mapped
6532 area in the usual way.
6535 If your overlays are small enough, you could set aside more than one
6536 overlay area, and have more than one overlay mapped at a time.
6539 You can use overlays to manage data, as well as instructions. In
6540 general, data overlays are even less transparent to your design than
6541 code overlays: whereas code overlays only require care when you call or
6542 return to functions, data overlays require care every time you access
6543 the data. Also, if you change the contents of a data overlay, you
6544 must copy its contents back out to its load address before you can copy a
6545 different data overlay into the same mapped area.
6550 @node Overlay Commands
6551 @section Overlay Commands
6553 To use @value{GDBN}'s overlay support, each overlay in your program must
6554 correspond to a separate section of the executable file. The section's
6555 virtual memory address and load memory address must be the overlay's
6556 mapped and load addresses. Identifying overlays with sections allows
6557 @value{GDBN} to determine the appropriate address of a function or
6558 variable, depending on whether the overlay is mapped or not.
6560 @value{GDBN}'s overlay commands all start with the word @code{overlay};
6561 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
6566 Disable @value{GDBN}'s overlay support. When overlay support is
6567 disabled, @value{GDBN} assumes that all functions and variables are
6568 always present at their mapped addresses. By default, @value{GDBN}'s
6569 overlay support is disabled.
6571 @item overlay manual
6572 @kindex overlay manual
6573 @cindex manual overlay debugging
6574 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
6575 relies on you to tell it which overlays are mapped, and which are not,
6576 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
6577 commands described below.
6579 @item overlay map-overlay @var{overlay}
6580 @itemx overlay map @var{overlay}
6581 @kindex overlay map-overlay
6582 @cindex map an overlay
6583 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
6584 be the name of the object file section containing the overlay. When an
6585 overlay is mapped, @value{GDBN} assumes it can find the overlay's
6586 functions and variables at their mapped addresses. @value{GDBN} assumes
6587 that any other overlays whose mapped ranges overlap that of
6588 @var{overlay} are now unmapped.
6590 @item overlay unmap-overlay @var{overlay}
6591 @itemx overlay unmap @var{overlay}
6592 @kindex overlay unmap-overlay
6593 @cindex unmap an overlay
6594 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
6595 must be the name of the object file section containing the overlay.
6596 When an overlay is unmapped, @value{GDBN} assumes it can find the
6597 overlay's functions and variables at their load addresses.
6600 @kindex overlay auto
6601 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
6602 consults a data structure the overlay manager maintains in the inferior
6603 to see which overlays are mapped. For details, see @ref{Automatic
6606 @item overlay load-target
6608 @kindex overlay load-target
6609 @cindex reloading the overlay table
6610 Re-read the overlay table from the inferior. Normally, @value{GDBN}
6611 re-reads the table @value{GDBN} automatically each time the inferior
6612 stops, so this command should only be necessary if you have changed the
6613 overlay mapping yourself using @value{GDBN}. This command is only
6614 useful when using automatic overlay debugging.
6616 @item overlay list-overlays
6618 @cindex listing mapped overlays
6619 Display a list of the overlays currently mapped, along with their mapped
6620 addresses, load addresses, and sizes.
6624 Normally, when @value{GDBN} prints a code address, it includes the name
6625 of the function the address falls in:
6629 $3 = @{int ()@} 0x11a0 <main>
6632 When overlay debugging is enabled, @value{GDBN} recognizes code in
6633 unmapped overlays, and prints the names of unmapped functions with
6634 asterisks around them. For example, if @code{foo} is a function in an
6635 unmapped overlay, @value{GDBN} prints it this way:
6639 No sections are mapped.
6641 $5 = @{int (int)@} 0x100000 <*foo*>
6644 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
6649 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
6650 mapped at 0x1016 - 0x104a
6652 $6 = @{int (int)@} 0x1016 <foo>
6655 When overlay debugging is enabled, @value{GDBN} can find the correct
6656 address for functions and variables in an overlay, whether or not the
6657 overlay is mapped. This allows most @value{GDBN} commands, like
6658 @code{break} and @code{disassemble}, to work normally, even on unmapped
6659 code. However, @value{GDBN}'s breakpoint support has some limitations:
6663 @cindex breakpoints in overlays
6664 @cindex overlays, setting breakpoints in
6665 You can set breakpoints in functions in unmapped overlays, as long as
6666 @value{GDBN} can write to the overlay at its load address.
6668 @value{GDBN} can not set hardware or simulator-based breakpoints in
6669 unmapped overlays. However, if you set a breakpoint at the end of your
6670 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
6671 you are using manual overlay management), @value{GDBN} will re-set its
6672 breakpoints properly.
6676 @node Automatic Overlay Debugging
6677 @section Automatic Overlay Debugging
6678 @cindex automatic overlay debugging
6680 @value{GDBN} can automatically track which overlays are mapped and which
6681 are not, given some simple co-operation from the overlay manager in the
6682 inferior. If you enable automatic overlay debugging with the
6683 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
6684 looks in the inferior's memory for certain variables describing the
6685 current state of the overlays.
6687 Here are the variables your overlay manager must define to support
6688 @value{GDBN}'s automatic overlay debugging:
6692 @item @code{_ovly_table}:
6693 This variable must be an array of the following structures:
6698 /* The overlay's mapped address. */
6701 /* The size of the overlay, in bytes. */
6704 /* The overlay's load address. */
6707 /* Non-zero if the overlay is currently mapped;
6709 unsigned long mapped;
6713 @item @code{_novlys}:
6714 This variable must be a four-byte signed integer, holding the total
6715 number of elements in @code{_ovly_table}.
6719 To decide whether a particular overlay is mapped or not, @value{GDBN}
6720 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
6721 @code{lma} members equal the VMA and LMA of the overlay's section in the
6722 executable file. When @value{GDBN} finds a matching entry, it consults
6723 the entry's @code{mapped} member to determine whether the overlay is
6727 @node Overlay Sample Program
6728 @section Overlay Sample Program
6729 @cindex overlay example program
6731 When linking a program which uses overlays, you must place the overlays
6732 at their load addresses, while relocating them to run at their mapped
6733 addresses. To do this, you must write a linker script (@pxref{Overlay
6734 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
6735 since linker scripts are specific to a particular host system, target
6736 architecture, and target memory layout, this manual cannot provide
6737 portable sample code demonstrating @value{GDBN}'s overlay support.
6739 However, the @value{GDBN} source distribution does contain an overlaid
6740 program, with linker scripts for a few systems, as part of its test
6741 suite. The program consists of the following files from
6742 @file{gdb/testsuite/gdb.base}:
6746 The main program file.
6748 A simple overlay manager, used by @file{overlays.c}.
6753 Overlay modules, loaded and used by @file{overlays.c}.
6756 Linker scripts for linking the test program on the @code{d10v-elf}
6757 and @code{m32r-elf} targets.
6760 You can build the test program using the @code{d10v-elf} GCC
6761 cross-compiler like this:
6764 $ d10v-elf-gcc -g -c overlays.c
6765 $ d10v-elf-gcc -g -c ovlymgr.c
6766 $ d10v-elf-gcc -g -c foo.c
6767 $ d10v-elf-gcc -g -c bar.c
6768 $ d10v-elf-gcc -g -c baz.c
6769 $ d10v-elf-gcc -g -c grbx.c
6770 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
6771 baz.o grbx.o -Wl,-Td10v.ld -o overlays
6774 The build process is identical for any other architecture, except that
6775 you must substitute the appropriate compiler and linker script for the
6776 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
6780 @chapter Using @value{GDBN} with Different Languages
6783 Although programming languages generally have common aspects, they are
6784 rarely expressed in the same manner. For instance, in ANSI C,
6785 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6786 Modula-2, it is accomplished by @code{p^}. Values can also be
6787 represented (and displayed) differently. Hex numbers in C appear as
6788 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6790 @cindex working language
6791 Language-specific information is built into @value{GDBN} for some languages,
6792 allowing you to express operations like the above in your program's
6793 native language, and allowing @value{GDBN} to output values in a manner
6794 consistent with the syntax of your program's native language. The
6795 language you use to build expressions is called the @dfn{working
6799 * Setting:: Switching between source languages
6800 * Show:: Displaying the language
6801 * Checks:: Type and range checks
6802 * Support:: Supported languages
6806 @section Switching between source languages
6808 There are two ways to control the working language---either have @value{GDBN}
6809 set it automatically, or select it manually yourself. You can use the
6810 @code{set language} command for either purpose. On startup, @value{GDBN}
6811 defaults to setting the language automatically. The working language is
6812 used to determine how expressions you type are interpreted, how values
6815 In addition to the working language, every source file that
6816 @value{GDBN} knows about has its own working language. For some object
6817 file formats, the compiler might indicate which language a particular
6818 source file is in. However, most of the time @value{GDBN} infers the
6819 language from the name of the file. The language of a source file
6820 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6821 show each frame appropriately for its own language. There is no way to
6822 set the language of a source file from within @value{GDBN}, but you can
6823 set the language associated with a filename extension. @xref{Show, ,
6824 Displaying the language}.
6826 This is most commonly a problem when you use a program, such
6827 as @code{cfront} or @code{f2c}, that generates C but is written in
6828 another language. In that case, make the
6829 program use @code{#line} directives in its C output; that way
6830 @value{GDBN} will know the correct language of the source code of the original
6831 program, and will display that source code, not the generated C code.
6834 * Filenames:: Filename extensions and languages.
6835 * Manually:: Setting the working language manually
6836 * Automatically:: Having @value{GDBN} infer the source language
6840 @subsection List of filename extensions and languages
6842 If a source file name ends in one of the following extensions, then
6843 @value{GDBN} infers that its language is the one indicated.
6868 Modula-2 source file
6872 Assembler source file. This actually behaves almost like C, but
6873 @value{GDBN} does not skip over function prologues when stepping.
6876 In addition, you may set the language associated with a filename
6877 extension. @xref{Show, , Displaying the language}.
6880 @subsection Setting the working language
6882 If you allow @value{GDBN} to set the language automatically,
6883 expressions are interpreted the same way in your debugging session and
6886 @kindex set language
6887 If you wish, you may set the language manually. To do this, issue the
6888 command @samp{set language @var{lang}}, where @var{lang} is the name of
6890 @code{c} or @code{modula-2}.
6891 For a list of the supported languages, type @samp{set language}.
6893 Setting the language manually prevents @value{GDBN} from updating the working
6894 language automatically. This can lead to confusion if you try
6895 to debug a program when the working language is not the same as the
6896 source language, when an expression is acceptable to both
6897 languages---but means different things. For instance, if the current
6898 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6906 might not have the effect you intended. In C, this means to add
6907 @code{b} and @code{c} and place the result in @code{a}. The result
6908 printed would be the value of @code{a}. In Modula-2, this means to compare
6909 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6912 @subsection Having @value{GDBN} infer the source language
6914 To have @value{GDBN} set the working language automatically, use
6915 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6916 then infers the working language. That is, when your program stops in a
6917 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6918 working language to the language recorded for the function in that
6919 frame. If the language for a frame is unknown (that is, if the function
6920 or block corresponding to the frame was defined in a source file that
6921 does not have a recognized extension), the current working language is
6922 not changed, and @value{GDBN} issues a warning.
6924 This may not seem necessary for most programs, which are written
6925 entirely in one source language. However, program modules and libraries
6926 written in one source language can be used by a main program written in
6927 a different source language. Using @samp{set language auto} in this
6928 case frees you from having to set the working language manually.
6931 @section Displaying the language
6933 The following commands help you find out which language is the
6934 working language, and also what language source files were written in.
6936 @kindex show language
6937 @kindex info frame@r{, show the source language}
6938 @kindex info source@r{, show the source language}
6941 Display the current working language. This is the
6942 language you can use with commands such as @code{print} to
6943 build and compute expressions that may involve variables in your program.
6946 Display the source language for this frame. This language becomes the
6947 working language if you use an identifier from this frame.
6948 @xref{Frame Info, ,Information about a frame}, to identify the other
6949 information listed here.
6952 Display the source language of this source file.
6953 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6954 information listed here.
6957 In unusual circumstances, you may have source files with extensions
6958 not in the standard list. You can then set the extension associated
6959 with a language explicitly:
6961 @kindex set extension-language
6962 @kindex info extensions
6964 @item set extension-language @var{.ext} @var{language}
6965 Set source files with extension @var{.ext} to be assumed to be in
6966 the source language @var{language}.
6968 @item info extensions
6969 List all the filename extensions and the associated languages.
6973 @section Type and range checking
6976 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6977 checking are included, but they do not yet have any effect. This
6978 section documents the intended facilities.
6980 @c FIXME remove warning when type/range code added
6982 Some languages are designed to guard you against making seemingly common
6983 errors through a series of compile- and run-time checks. These include
6984 checking the type of arguments to functions and operators, and making
6985 sure mathematical overflows are caught at run time. Checks such as
6986 these help to ensure a program's correctness once it has been compiled
6987 by eliminating type mismatches, and providing active checks for range
6988 errors when your program is running.
6990 @value{GDBN} can check for conditions like the above if you wish.
6991 Although @value{GDBN} does not check the statements in your program, it
6992 can check expressions entered directly into @value{GDBN} for evaluation via
6993 the @code{print} command, for example. As with the working language,
6994 @value{GDBN} can also decide whether or not to check automatically based on
6995 your program's source language. @xref{Support, ,Supported languages},
6996 for the default settings of supported languages.
6999 * Type Checking:: An overview of type checking
7000 * Range Checking:: An overview of range checking
7003 @cindex type checking
7004 @cindex checks, type
7006 @subsection An overview of type checking
7008 Some languages, such as Modula-2, are strongly typed, meaning that the
7009 arguments to operators and functions have to be of the correct type,
7010 otherwise an error occurs. These checks prevent type mismatch
7011 errors from ever causing any run-time problems. For example,
7019 The second example fails because the @code{CARDINAL} 1 is not
7020 type-compatible with the @code{REAL} 2.3.
7022 For the expressions you use in @value{GDBN} commands, you can tell the
7023 @value{GDBN} type checker to skip checking;
7024 to treat any mismatches as errors and abandon the expression;
7025 or to only issue warnings when type mismatches occur,
7026 but evaluate the expression anyway. When you choose the last of
7027 these, @value{GDBN} evaluates expressions like the second example above, but
7028 also issues a warning.
7030 Even if you turn type checking off, there may be other reasons
7031 related to type that prevent @value{GDBN} from evaluating an expression.
7032 For instance, @value{GDBN} does not know how to add an @code{int} and
7033 a @code{struct foo}. These particular type errors have nothing to do
7034 with the language in use, and usually arise from expressions, such as
7035 the one described above, which make little sense to evaluate anyway.
7037 Each language defines to what degree it is strict about type. For
7038 instance, both Modula-2 and C require the arguments to arithmetical
7039 operators to be numbers. In C, enumerated types and pointers can be
7040 represented as numbers, so that they are valid arguments to mathematical
7041 operators. @xref{Support, ,Supported languages}, for further
7042 details on specific languages.
7044 @value{GDBN} provides some additional commands for controlling the type checker:
7046 @kindex set check@r{, type}
7047 @kindex set check type
7048 @kindex show check type
7050 @item set check type auto
7051 Set type checking on or off based on the current working language.
7052 @xref{Support, ,Supported languages}, for the default settings for
7055 @item set check type on
7056 @itemx set check type off
7057 Set type checking on or off, overriding the default setting for the
7058 current working language. Issue a warning if the setting does not
7059 match the language default. If any type mismatches occur in
7060 evaluating an expression while type checking is on, @value{GDBN} prints a
7061 message and aborts evaluation of the expression.
7063 @item set check type warn
7064 Cause the type checker to issue warnings, but to always attempt to
7065 evaluate the expression. Evaluating the expression may still
7066 be impossible for other reasons. For example, @value{GDBN} cannot add
7067 numbers and structures.
7070 Show the current setting of the type checker, and whether or not @value{GDBN}
7071 is setting it automatically.
7074 @cindex range checking
7075 @cindex checks, range
7076 @node Range Checking
7077 @subsection An overview of range checking
7079 In some languages (such as Modula-2), it is an error to exceed the
7080 bounds of a type; this is enforced with run-time checks. Such range
7081 checking is meant to ensure program correctness by making sure
7082 computations do not overflow, or indices on an array element access do
7083 not exceed the bounds of the array.
7085 For expressions you use in @value{GDBN} commands, you can tell
7086 @value{GDBN} to treat range errors in one of three ways: ignore them,
7087 always treat them as errors and abandon the expression, or issue
7088 warnings but evaluate the expression anyway.
7090 A range error can result from numerical overflow, from exceeding an
7091 array index bound, or when you type a constant that is not a member
7092 of any type. Some languages, however, do not treat overflows as an
7093 error. In many implementations of C, mathematical overflow causes the
7094 result to ``wrap around'' to lower values---for example, if @var{m} is
7095 the largest integer value, and @var{s} is the smallest, then
7098 @var{m} + 1 @result{} @var{s}
7101 This, too, is specific to individual languages, and in some cases
7102 specific to individual compilers or machines. @xref{Support, ,
7103 Supported languages}, for further details on specific languages.
7105 @value{GDBN} provides some additional commands for controlling the range checker:
7107 @kindex set check@r{, range}
7108 @kindex set check range
7109 @kindex show check range
7111 @item set check range auto
7112 Set range checking on or off based on the current working language.
7113 @xref{Support, ,Supported languages}, for the default settings for
7116 @item set check range on
7117 @itemx set check range off
7118 Set range checking on or off, overriding the default setting for the
7119 current working language. A warning is issued if the setting does not
7120 match the language default. If a range error occurs and range checking is on,
7121 then a message is printed and evaluation of the expression is aborted.
7123 @item set check range warn
7124 Output messages when the @value{GDBN} range checker detects a range error,
7125 but attempt to evaluate the expression anyway. Evaluating the
7126 expression may still be impossible for other reasons, such as accessing
7127 memory that the process does not own (a typical example from many Unix
7131 Show the current setting of the range checker, and whether or not it is
7132 being set automatically by @value{GDBN}.
7136 @section Supported languages
7138 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
7139 @c This is false ...
7140 Some @value{GDBN} features may be used in expressions regardless of the
7141 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7142 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7143 ,Expressions}) can be used with the constructs of any supported
7146 The following sections detail to what degree each source language is
7147 supported by @value{GDBN}. These sections are not meant to be language
7148 tutorials or references, but serve only as a reference guide to what the
7149 @value{GDBN} expression parser accepts, and what input and output
7150 formats should look like for different languages. There are many good
7151 books written on each of these languages; please look to these for a
7152 language reference or tutorial.
7156 * Modula-2:: Modula-2
7161 @subsection C and C@t{++}
7163 @cindex C and C@t{++}
7164 @cindex expressions in C or C@t{++}
7166 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7167 to both languages. Whenever this is the case, we discuss those languages
7171 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7172 @cindex @sc{gnu} C@t{++}
7173 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7174 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7175 effectively, you must compile your C@t{++} programs with a supported
7176 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7177 compiler (@code{aCC}).
7179 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7180 format. You can select that format explicitly with the @code{g++}
7181 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7182 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7183 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7186 * C Operators:: C and C@t{++} operators
7187 * C Constants:: C and C@t{++} constants
7188 * C plus plus expressions:: C@t{++} expressions
7189 * C Defaults:: Default settings for C and C@t{++}
7190 * C Checks:: C and C@t{++} type and range checks
7191 * Debugging C:: @value{GDBN} and C
7192 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7196 @subsubsection C and C@t{++} operators
7198 @cindex C and C@t{++} operators
7200 Operators must be defined on values of specific types. For instance,
7201 @code{+} is defined on numbers, but not on structures. Operators are
7202 often defined on groups of types.
7204 For the purposes of C and C@t{++}, the following definitions hold:
7209 @emph{Integral types} include @code{int} with any of its storage-class
7210 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7213 @emph{Floating-point types} include @code{float}, @code{double}, and
7214 @code{long double} (if supported by the target platform).
7217 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7220 @emph{Scalar types} include all of the above.
7225 The following operators are supported. They are listed here
7226 in order of increasing precedence:
7230 The comma or sequencing operator. Expressions in a comma-separated list
7231 are evaluated from left to right, with the result of the entire
7232 expression being the last expression evaluated.
7235 Assignment. The value of an assignment expression is the value
7236 assigned. Defined on scalar types.
7239 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7240 and translated to @w{@code{@var{a} = @var{a op b}}}.
7241 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7242 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7243 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7246 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7247 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7251 Logical @sc{or}. Defined on integral types.
7254 Logical @sc{and}. Defined on integral types.
7257 Bitwise @sc{or}. Defined on integral types.
7260 Bitwise exclusive-@sc{or}. Defined on integral types.
7263 Bitwise @sc{and}. Defined on integral types.
7266 Equality and inequality. Defined on scalar types. The value of these
7267 expressions is 0 for false and non-zero for true.
7269 @item <@r{, }>@r{, }<=@r{, }>=
7270 Less than, greater than, less than or equal, greater than or equal.
7271 Defined on scalar types. The value of these expressions is 0 for false
7272 and non-zero for true.
7275 left shift, and right shift. Defined on integral types.
7278 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7281 Addition and subtraction. Defined on integral types, floating-point types and
7284 @item *@r{, }/@r{, }%
7285 Multiplication, division, and modulus. Multiplication and division are
7286 defined on integral and floating-point types. Modulus is defined on
7290 Increment and decrement. When appearing before a variable, the
7291 operation is performed before the variable is used in an expression;
7292 when appearing after it, the variable's value is used before the
7293 operation takes place.
7296 Pointer dereferencing. Defined on pointer types. Same precedence as
7300 Address operator. Defined on variables. Same precedence as @code{++}.
7302 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7303 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7304 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7305 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7309 Negative. Defined on integral and floating-point types. Same
7310 precedence as @code{++}.
7313 Logical negation. Defined on integral types. Same precedence as
7317 Bitwise complement operator. Defined on integral types. Same precedence as
7322 Structure member, and pointer-to-structure member. For convenience,
7323 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7324 pointer based on the stored type information.
7325 Defined on @code{struct} and @code{union} data.
7328 Dereferences of pointers to members.
7331 Array indexing. @code{@var{a}[@var{i}]} is defined as
7332 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7335 Function parameter list. Same precedence as @code{->}.
7338 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7339 and @code{class} types.
7342 Doubled colons also represent the @value{GDBN} scope operator
7343 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7347 If an operator is redefined in the user code, @value{GDBN} usually
7348 attempts to invoke the redefined version instead of using the operator's
7356 @subsubsection C and C@t{++} constants
7358 @cindex C and C@t{++} constants
7360 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7365 Integer constants are a sequence of digits. Octal constants are
7366 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
7367 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7368 @samp{l}, specifying that the constant should be treated as a
7372 Floating point constants are a sequence of digits, followed by a decimal
7373 point, followed by a sequence of digits, and optionally followed by an
7374 exponent. An exponent is of the form:
7375 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7376 sequence of digits. The @samp{+} is optional for positive exponents.
7377 A floating-point constant may also end with a letter @samp{f} or
7378 @samp{F}, specifying that the constant should be treated as being of
7379 the @code{float} (as opposed to the default @code{double}) type; or with
7380 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7384 Enumerated constants consist of enumerated identifiers, or their
7385 integral equivalents.
7388 Character constants are a single character surrounded by single quotes
7389 (@code{'}), or a number---the ordinal value of the corresponding character
7390 (usually its @sc{ascii} value). Within quotes, the single character may
7391 be represented by a letter or by @dfn{escape sequences}, which are of
7392 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
7393 of the character's ordinal value; or of the form @samp{\@var{x}}, where
7394 @samp{@var{x}} is a predefined special character---for example,
7395 @samp{\n} for newline.
7398 String constants are a sequence of character constants surrounded by
7399 double quotes (@code{"}). Any valid character constant (as described
7400 above) may appear. Double quotes within the string must be preceded by
7401 a backslash, so for instance @samp{"a\"b'c"} is a string of five
7405 Pointer constants are an integral value. You can also write pointers
7406 to constants using the C operator @samp{&}.
7409 Array constants are comma-separated lists surrounded by braces @samp{@{}
7410 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
7411 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
7412 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
7416 * C plus plus expressions::
7423 @node C plus plus expressions
7424 @subsubsection C@t{++} expressions
7426 @cindex expressions in C@t{++}
7427 @value{GDBN} expression handling can interpret most C@t{++} expressions.
7429 @cindex C@t{++} support, not in @sc{coff}
7430 @cindex @sc{coff} versus C@t{++}
7431 @cindex C@t{++} and object formats
7432 @cindex object formats and C@t{++}
7433 @cindex a.out and C@t{++}
7434 @cindex @sc{ecoff} and C@t{++}
7435 @cindex @sc{xcoff} and C@t{++}
7436 @cindex @sc{elf}/stabs and C@t{++}
7437 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
7438 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
7439 @c periodically whether this has happened...
7441 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
7442 proper compiler. Typically, C@t{++} debugging depends on the use of
7443 additional debugging information in the symbol table, and thus requires
7444 special support. In particular, if your compiler generates a.out, MIPS
7445 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
7446 symbol table, these facilities are all available. (With @sc{gnu} CC,
7447 you can use the @samp{-gstabs} option to request stabs debugging
7448 extensions explicitly.) Where the object code format is standard
7449 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
7450 support in @value{GDBN} does @emph{not} work.
7455 @cindex member functions
7457 Member function calls are allowed; you can use expressions like
7460 count = aml->GetOriginal(x, y)
7463 @vindex this@r{, inside C@t{++} member functions}
7464 @cindex namespace in C@t{++}
7466 While a member function is active (in the selected stack frame), your
7467 expressions have the same namespace available as the member function;
7468 that is, @value{GDBN} allows implicit references to the class instance
7469 pointer @code{this} following the same rules as C@t{++}.
7471 @cindex call overloaded functions
7472 @cindex overloaded functions, calling
7473 @cindex type conversions in C@t{++}
7475 You can call overloaded functions; @value{GDBN} resolves the function
7476 call to the right definition, with some restrictions. @value{GDBN} does not
7477 perform overload resolution involving user-defined type conversions,
7478 calls to constructors, or instantiations of templates that do not exist
7479 in the program. It also cannot handle ellipsis argument lists or
7482 It does perform integral conversions and promotions, floating-point
7483 promotions, arithmetic conversions, pointer conversions, conversions of
7484 class objects to base classes, and standard conversions such as those of
7485 functions or arrays to pointers; it requires an exact match on the
7486 number of function arguments.
7488 Overload resolution is always performed, unless you have specified
7489 @code{set overload-resolution off}. @xref{Debugging C plus plus,
7490 ,@value{GDBN} features for C@t{++}}.
7492 You must specify @code{set overload-resolution off} in order to use an
7493 explicit function signature to call an overloaded function, as in
7495 p 'foo(char,int)'('x', 13)
7498 The @value{GDBN} command-completion facility can simplify this;
7499 see @ref{Completion, ,Command completion}.
7501 @cindex reference declarations
7503 @value{GDBN} understands variables declared as C@t{++} references; you can use
7504 them in expressions just as you do in C@t{++} source---they are automatically
7507 In the parameter list shown when @value{GDBN} displays a frame, the values of
7508 reference variables are not displayed (unlike other variables); this
7509 avoids clutter, since references are often used for large structures.
7510 The @emph{address} of a reference variable is always shown, unless
7511 you have specified @samp{set print address off}.
7514 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7515 expressions can use it just as expressions in your program do. Since
7516 one scope may be defined in another, you can use @code{::} repeatedly if
7517 necessary, for example in an expression like
7518 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7519 resolving name scope by reference to source files, in both C and C@t{++}
7520 debugging (@pxref{Variables, ,Program variables}).
7523 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7524 calling virtual functions correctly, printing out virtual bases of
7525 objects, calling functions in a base subobject, casting objects, and
7526 invoking user-defined operators.
7529 @subsubsection C and C@t{++} defaults
7531 @cindex C and C@t{++} defaults
7533 If you allow @value{GDBN} to set type and range checking automatically, they
7534 both default to @code{off} whenever the working language changes to
7535 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7536 selects the working language.
7538 If you allow @value{GDBN} to set the language automatically, it
7539 recognizes source files whose names end with @file{.c}, @file{.C}, or
7540 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7541 these files, it sets the working language to C or C@t{++}.
7542 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7543 for further details.
7545 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7546 @c unimplemented. If (b) changes, it might make sense to let this node
7547 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7550 @subsubsection C and C@t{++} type and range checks
7552 @cindex C and C@t{++} checks
7554 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7555 is not used. However, if you turn type checking on, @value{GDBN}
7556 considers two variables type equivalent if:
7560 The two variables are structured and have the same structure, union, or
7564 The two variables have the same type name, or types that have been
7565 declared equivalent through @code{typedef}.
7568 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7571 The two @code{struct}, @code{union}, or @code{enum} variables are
7572 declared in the same declaration. (Note: this may not be true for all C
7577 Range checking, if turned on, is done on mathematical operations. Array
7578 indices are not checked, since they are often used to index a pointer
7579 that is not itself an array.
7582 @subsubsection @value{GDBN} and C
7584 The @code{set print union} and @code{show print union} commands apply to
7585 the @code{union} type. When set to @samp{on}, any @code{union} that is
7586 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7587 appears as @samp{@{...@}}.
7589 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7590 with pointers and a memory allocation function. @xref{Expressions,
7594 * Debugging C plus plus::
7597 @node Debugging C plus plus
7598 @subsubsection @value{GDBN} features for C@t{++}
7600 @cindex commands for C@t{++}
7602 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7603 designed specifically for use with C@t{++}. Here is a summary:
7606 @cindex break in overloaded functions
7607 @item @r{breakpoint menus}
7608 When you want a breakpoint in a function whose name is overloaded,
7609 @value{GDBN} breakpoint menus help you specify which function definition
7610 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7612 @cindex overloading in C@t{++}
7613 @item rbreak @var{regex}
7614 Setting breakpoints using regular expressions is helpful for setting
7615 breakpoints on overloaded functions that are not members of any special
7617 @xref{Set Breaks, ,Setting breakpoints}.
7619 @cindex C@t{++} exception handling
7622 Debug C@t{++} exception handling using these commands. @xref{Set
7623 Catchpoints, , Setting catchpoints}.
7626 @item ptype @var{typename}
7627 Print inheritance relationships as well as other information for type
7629 @xref{Symbols, ,Examining the Symbol Table}.
7631 @cindex C@t{++} symbol display
7632 @item set print demangle
7633 @itemx show print demangle
7634 @itemx set print asm-demangle
7635 @itemx show print asm-demangle
7636 Control whether C@t{++} symbols display in their source form, both when
7637 displaying code as C@t{++} source and when displaying disassemblies.
7638 @xref{Print Settings, ,Print settings}.
7640 @item set print object
7641 @itemx show print object
7642 Choose whether to print derived (actual) or declared types of objects.
7643 @xref{Print Settings, ,Print settings}.
7645 @item set print vtbl
7646 @itemx show print vtbl
7647 Control the format for printing virtual function tables.
7648 @xref{Print Settings, ,Print settings}.
7649 (The @code{vtbl} commands do not work on programs compiled with the HP
7650 ANSI C@t{++} compiler (@code{aCC}).)
7652 @kindex set overload-resolution
7653 @cindex overloaded functions, overload resolution
7654 @item set overload-resolution on
7655 Enable overload resolution for C@t{++} expression evaluation. The default
7656 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7657 and searches for a function whose signature matches the argument types,
7658 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7659 expressions}, for details). If it cannot find a match, it emits a
7662 @item set overload-resolution off
7663 Disable overload resolution for C@t{++} expression evaluation. For
7664 overloaded functions that are not class member functions, @value{GDBN}
7665 chooses the first function of the specified name that it finds in the
7666 symbol table, whether or not its arguments are of the correct type. For
7667 overloaded functions that are class member functions, @value{GDBN}
7668 searches for a function whose signature @emph{exactly} matches the
7671 @item @r{Overloaded symbol names}
7672 You can specify a particular definition of an overloaded symbol, using
7673 the same notation that is used to declare such symbols in C@t{++}: type
7674 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7675 also use the @value{GDBN} command-line word completion facilities to list the
7676 available choices, or to finish the type list for you.
7677 @xref{Completion,, Command completion}, for details on how to do this.
7681 @subsection Modula-2
7683 @cindex Modula-2, @value{GDBN} support
7685 The extensions made to @value{GDBN} to support Modula-2 only support
7686 output from the @sc{gnu} Modula-2 compiler (which is currently being
7687 developed). Other Modula-2 compilers are not currently supported, and
7688 attempting to debug executables produced by them is most likely
7689 to give an error as @value{GDBN} reads in the executable's symbol
7692 @cindex expressions in Modula-2
7694 * M2 Operators:: Built-in operators
7695 * Built-In Func/Proc:: Built-in functions and procedures
7696 * M2 Constants:: Modula-2 constants
7697 * M2 Defaults:: Default settings for Modula-2
7698 * Deviations:: Deviations from standard Modula-2
7699 * M2 Checks:: Modula-2 type and range checks
7700 * M2 Scope:: The scope operators @code{::} and @code{.}
7701 * GDB/M2:: @value{GDBN} and Modula-2
7705 @subsubsection Operators
7706 @cindex Modula-2 operators
7708 Operators must be defined on values of specific types. For instance,
7709 @code{+} is defined on numbers, but not on structures. Operators are
7710 often defined on groups of types. For the purposes of Modula-2, the
7711 following definitions hold:
7716 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7720 @emph{Character types} consist of @code{CHAR} and its subranges.
7723 @emph{Floating-point types} consist of @code{REAL}.
7726 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7730 @emph{Scalar types} consist of all of the above.
7733 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7736 @emph{Boolean types} consist of @code{BOOLEAN}.
7740 The following operators are supported, and appear in order of
7741 increasing precedence:
7745 Function argument or array index separator.
7748 Assignment. The value of @var{var} @code{:=} @var{value} is
7752 Less than, greater than on integral, floating-point, or enumerated
7756 Less than or equal to, greater than or equal to
7757 on integral, floating-point and enumerated types, or set inclusion on
7758 set types. Same precedence as @code{<}.
7760 @item =@r{, }<>@r{, }#
7761 Equality and two ways of expressing inequality, valid on scalar types.
7762 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7763 available for inequality, since @code{#} conflicts with the script
7767 Set membership. Defined on set types and the types of their members.
7768 Same precedence as @code{<}.
7771 Boolean disjunction. Defined on boolean types.
7774 Boolean conjunction. Defined on boolean types.
7777 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7780 Addition and subtraction on integral and floating-point types, or union
7781 and difference on set types.
7784 Multiplication on integral and floating-point types, or set intersection
7788 Division on floating-point types, or symmetric set difference on set
7789 types. Same precedence as @code{*}.
7792 Integer division and remainder. Defined on integral types. Same
7793 precedence as @code{*}.
7796 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7799 Pointer dereferencing. Defined on pointer types.
7802 Boolean negation. Defined on boolean types. Same precedence as
7806 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7807 precedence as @code{^}.
7810 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7813 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7817 @value{GDBN} and Modula-2 scope operators.
7821 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7822 treats the use of the operator @code{IN}, or the use of operators
7823 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7824 @code{<=}, and @code{>=} on sets as an error.
7828 @node Built-In Func/Proc
7829 @subsubsection Built-in functions and procedures
7830 @cindex Modula-2 built-ins
7832 Modula-2 also makes available several built-in procedures and functions.
7833 In describing these, the following metavariables are used:
7838 represents an @code{ARRAY} variable.
7841 represents a @code{CHAR} constant or variable.
7844 represents a variable or constant of integral type.
7847 represents an identifier that belongs to a set. Generally used in the
7848 same function with the metavariable @var{s}. The type of @var{s} should
7849 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7852 represents a variable or constant of integral or floating-point type.
7855 represents a variable or constant of floating-point type.
7861 represents a variable.
7864 represents a variable or constant of one of many types. See the
7865 explanation of the function for details.
7868 All Modula-2 built-in procedures also return a result, described below.
7872 Returns the absolute value of @var{n}.
7875 If @var{c} is a lower case letter, it returns its upper case
7876 equivalent, otherwise it returns its argument.
7879 Returns the character whose ordinal value is @var{i}.
7882 Decrements the value in the variable @var{v} by one. Returns the new value.
7884 @item DEC(@var{v},@var{i})
7885 Decrements the value in the variable @var{v} by @var{i}. Returns the
7888 @item EXCL(@var{m},@var{s})
7889 Removes the element @var{m} from the set @var{s}. Returns the new
7892 @item FLOAT(@var{i})
7893 Returns the floating point equivalent of the integer @var{i}.
7896 Returns the index of the last member of @var{a}.
7899 Increments the value in the variable @var{v} by one. Returns the new value.
7901 @item INC(@var{v},@var{i})
7902 Increments the value in the variable @var{v} by @var{i}. Returns the
7905 @item INCL(@var{m},@var{s})
7906 Adds the element @var{m} to the set @var{s} if it is not already
7907 there. Returns the new set.
7910 Returns the maximum value of the type @var{t}.
7913 Returns the minimum value of the type @var{t}.
7916 Returns boolean TRUE if @var{i} is an odd number.
7919 Returns the ordinal value of its argument. For example, the ordinal
7920 value of a character is its @sc{ascii} value (on machines supporting the
7921 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7922 integral, character and enumerated types.
7925 Returns the size of its argument. @var{x} can be a variable or a type.
7927 @item TRUNC(@var{r})
7928 Returns the integral part of @var{r}.
7930 @item VAL(@var{t},@var{i})
7931 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7935 @emph{Warning:} Sets and their operations are not yet supported, so
7936 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7940 @cindex Modula-2 constants
7942 @subsubsection Constants
7944 @value{GDBN} allows you to express the constants of Modula-2 in the following
7950 Integer constants are simply a sequence of digits. When used in an
7951 expression, a constant is interpreted to be type-compatible with the
7952 rest of the expression. Hexadecimal integers are specified by a
7953 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7956 Floating point constants appear as a sequence of digits, followed by a
7957 decimal point and another sequence of digits. An optional exponent can
7958 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7959 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7960 digits of the floating point constant must be valid decimal (base 10)
7964 Character constants consist of a single character enclosed by a pair of
7965 like quotes, either single (@code{'}) or double (@code{"}). They may
7966 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7967 followed by a @samp{C}.
7970 String constants consist of a sequence of characters enclosed by a
7971 pair of like quotes, either single (@code{'}) or double (@code{"}).
7972 Escape sequences in the style of C are also allowed. @xref{C
7973 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7977 Enumerated constants consist of an enumerated identifier.
7980 Boolean constants consist of the identifiers @code{TRUE} and
7984 Pointer constants consist of integral values only.
7987 Set constants are not yet supported.
7991 @subsubsection Modula-2 defaults
7992 @cindex Modula-2 defaults
7994 If type and range checking are set automatically by @value{GDBN}, they
7995 both default to @code{on} whenever the working language changes to
7996 Modula-2. This happens regardless of whether you or @value{GDBN}
7997 selected the working language.
7999 If you allow @value{GDBN} to set the language automatically, then entering
8000 code compiled from a file whose name ends with @file{.mod} sets the
8001 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8002 the language automatically}, for further details.
8005 @subsubsection Deviations from standard Modula-2
8006 @cindex Modula-2, deviations from
8008 A few changes have been made to make Modula-2 programs easier to debug.
8009 This is done primarily via loosening its type strictness:
8013 Unlike in standard Modula-2, pointer constants can be formed by
8014 integers. This allows you to modify pointer variables during
8015 debugging. (In standard Modula-2, the actual address contained in a
8016 pointer variable is hidden from you; it can only be modified
8017 through direct assignment to another pointer variable or expression that
8018 returned a pointer.)
8021 C escape sequences can be used in strings and characters to represent
8022 non-printable characters. @value{GDBN} prints out strings with these
8023 escape sequences embedded. Single non-printable characters are
8024 printed using the @samp{CHR(@var{nnn})} format.
8027 The assignment operator (@code{:=}) returns the value of its right-hand
8031 All built-in procedures both modify @emph{and} return their argument.
8035 @subsubsection Modula-2 type and range checks
8036 @cindex Modula-2 checks
8039 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8042 @c FIXME remove warning when type/range checks added
8044 @value{GDBN} considers two Modula-2 variables type equivalent if:
8048 They are of types that have been declared equivalent via a @code{TYPE
8049 @var{t1} = @var{t2}} statement
8052 They have been declared on the same line. (Note: This is true of the
8053 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8056 As long as type checking is enabled, any attempt to combine variables
8057 whose types are not equivalent is an error.
8059 Range checking is done on all mathematical operations, assignment, array
8060 index bounds, and all built-in functions and procedures.
8063 @subsubsection The scope operators @code{::} and @code{.}
8065 @cindex @code{.}, Modula-2 scope operator
8066 @cindex colon, doubled as scope operator
8068 @vindex colon-colon@r{, in Modula-2}
8069 @c Info cannot handle :: but TeX can.
8072 @vindex ::@r{, in Modula-2}
8075 There are a few subtle differences between the Modula-2 scope operator
8076 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8081 @var{module} . @var{id}
8082 @var{scope} :: @var{id}
8086 where @var{scope} is the name of a module or a procedure,
8087 @var{module} the name of a module, and @var{id} is any declared
8088 identifier within your program, except another module.
8090 Using the @code{::} operator makes @value{GDBN} search the scope
8091 specified by @var{scope} for the identifier @var{id}. If it is not
8092 found in the specified scope, then @value{GDBN} searches all scopes
8093 enclosing the one specified by @var{scope}.
8095 Using the @code{.} operator makes @value{GDBN} search the current scope for
8096 the identifier specified by @var{id} that was imported from the
8097 definition module specified by @var{module}. With this operator, it is
8098 an error if the identifier @var{id} was not imported from definition
8099 module @var{module}, or if @var{id} is not an identifier in
8103 @subsubsection @value{GDBN} and Modula-2
8105 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8106 Five subcommands of @code{set print} and @code{show print} apply
8107 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8108 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8109 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8110 analogue in Modula-2.
8112 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8113 with any language, is not useful with Modula-2. Its
8114 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8115 created in Modula-2 as they can in C or C@t{++}. However, because an
8116 address can be specified by an integral constant, the construct
8117 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8119 @cindex @code{#} in Modula-2
8120 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8121 interpreted as the beginning of a comment. Use @code{<>} instead.
8126 The extensions made to @value{GDBN} to support Chill only support output
8127 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
8128 supported, and attempting to debug executables produced by them is most
8129 likely to give an error as @value{GDBN} reads in the executable's symbol
8132 @c This used to say "... following Chill related topics ...", but since
8133 @c menus are not shown in the printed manual, it would look awkward.
8134 This section covers the Chill related topics and the features
8135 of @value{GDBN} which support these topics.
8138 * How modes are displayed:: How modes are displayed
8139 * Locations:: Locations and their accesses
8140 * Values and their Operations:: Values and their Operations
8141 * Chill type and range checks::
8145 @node How modes are displayed
8146 @subsubsection How modes are displayed
8148 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
8149 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
8150 slightly from the standard specification of the Chill language. The
8153 @c FIXME: this @table's contents effectively disable @code by using @r
8154 @c on every @item. So why does it need @code?
8156 @item @r{@emph{Discrete modes:}}
8159 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
8162 @emph{Boolean Mode} which is predefined by @code{BOOL},
8164 @emph{Character Mode} which is predefined by @code{CHAR},
8166 @emph{Set Mode} which is displayed by the keyword @code{SET}.
8168 (@value{GDBP}) ptype x
8169 type = SET (karli = 10, susi = 20, fritzi = 100)
8171 If the type is an unnumbered set the set element values are omitted.
8173 @emph{Range Mode} which is displayed by
8175 @code{type = <basemode>(<lower bound> : <upper bound>)}
8177 where @code{<lower bound>, <upper bound>} can be of any discrete literal
8178 expression (e.g. set element names).
8181 @item @r{@emph{Powerset Mode:}}
8182 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
8183 the member mode of the powerset. The member mode can be any discrete mode.
8185 (@value{GDBP}) ptype x
8186 type = POWERSET SET (egon, hugo, otto)
8189 @item @r{@emph{Reference Modes:}}
8192 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
8193 followed by the mode name to which the reference is bound.
8195 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
8198 @item @r{@emph{Procedure mode}}
8199 The procedure mode is displayed by @code{type = PROC(<parameter list>)
8200 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
8201 list>} is a list of the parameter modes. @code{<return mode>} indicates
8202 the mode of the result of the procedure if any. The exceptionlist lists
8203 all possible exceptions which can be raised by the procedure.
8206 @item @r{@emph{Instance mode}}
8207 The instance mode is represented by a structure, which has a static
8208 type, and is therefore not really of interest.
8211 @item @r{@emph{Synchronization Modes:}}
8214 @emph{Event Mode} which is displayed by
8216 @code{EVENT (<event length>)}
8218 where @code{(<event length>)} is optional.
8220 @emph{Buffer Mode} which is displayed by
8222 @code{BUFFER (<buffer length>)<buffer element mode>}
8224 where @code{(<buffer length>)} is optional.
8227 @item @r{@emph{Timing Modes:}}
8230 @emph{Duration Mode} which is predefined by @code{DURATION}
8232 @emph{Absolute Time Mode} which is predefined by @code{TIME}
8235 @item @r{@emph{Real Modes:}}
8236 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
8238 @item @r{@emph{String Modes:}}
8241 @emph{Character String Mode} which is displayed by
8243 @code{CHARS(<string length>)}
8245 followed by the keyword @code{VARYING} if the String Mode is a varying
8248 @emph{Bit String Mode} which is displayed by
8255 @item @r{@emph{Array Mode:}}
8256 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
8257 followed by the element mode (which may in turn be an array mode).
8259 (@value{GDBP}) ptype x
8262 SET (karli = 10, susi = 20, fritzi = 100)
8265 @item @r{@emph{Structure Mode}}
8266 The Structure mode is displayed by the keyword @code{STRUCT(<field
8267 list>)}. The @code{<field list>} consists of names and modes of fields
8268 of the structure. Variant structures have the keyword @code{CASE <field>
8269 OF <variant fields> ESAC} in their field list. Since the current version
8270 of the GNU Chill compiler doesn't implement tag processing (no runtime
8271 checks of variant fields, and therefore no debugging info), the output
8272 always displays all variant fields.
8274 (@value{GDBP}) ptype str
8289 @subsubsection Locations and their accesses
8291 A location in Chill is an object which can contain values.
8293 A value of a location is generally accessed by the (declared) name of
8294 the location. The output conforms to the specification of values in
8295 Chill programs. How values are specified
8296 is the topic of the next section, @ref{Values and their Operations}.
8298 The pseudo-location @code{RESULT} (or @code{result}) can be used to
8299 display or change the result of a currently-active procedure:
8306 This does the same as the Chill action @code{RESULT EXPR} (which
8307 is not available in @value{GDBN}).
8309 Values of reference mode locations are printed by @code{PTR(<hex
8310 value>)} in case of a free reference mode, and by @code{(REF <reference
8311 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
8312 represents the address where the reference points to. To access the
8313 value of the location referenced by the pointer, use the dereference
8316 Values of procedure mode locations are displayed by
8319 (<argument modes> ) <return mode> @} <address> <name of procedure
8322 @code{<argument modes>} is a list of modes according to the parameter
8323 specification of the procedure and @code{<address>} shows the address of
8327 Locations of instance modes are displayed just like a structure with two
8328 fields specifying the @emph{process type} and the @emph{copy number} of
8329 the investigated instance location@footnote{This comes from the current
8330 implementation of instances. They are implemented as a structure (no
8331 na). The output should be something like @code{[<name of the process>;
8332 <instance number>]}.}. The field names are @code{__proc_type} and
8335 Locations of synchronization modes are displayed like a structure with
8336 the field name @code{__event_data} in case of a event mode location, and
8337 like a structure with the field @code{__buffer_data} in case of a buffer
8338 mode location (refer to previous paragraph).
8340 Structure Mode locations are printed by @code{[.<field name>: <value>,
8341 ...]}. The @code{<field name>} corresponds to the structure mode
8342 definition and the layout of @code{<value>} varies depending of the mode
8343 of the field. If the investigated structure mode location is of variant
8344 structure mode, the variant parts of the structure are enclosed in curled
8345 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
8346 on the same memory location and represent the current values of the
8347 memory location in their specific modes. Since no tag processing is done
8348 all variants are displayed. A variant field is printed by
8349 @code{(<variant name>) = .<field name>: <value>}. (who implements the
8352 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
8353 [.cs: []], (susi) = [.ds: susi]}]
8357 Substructures of string mode-, array mode- or structure mode-values
8358 (e.g. array slices, fields of structure locations) are accessed using
8359 certain operations which are described in the next section, @ref{Values
8360 and their Operations}.
8362 A location value may be interpreted as having a different mode using the
8363 location conversion. This mode conversion is written as @code{<mode
8364 name>(<location>)}. The user has to consider that the sizes of the modes
8365 have to be equal otherwise an error occurs. Furthermore, no range
8366 checking of the location against the destination mode is performed, and
8367 therefore the result can be quite confusing.
8370 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
8373 @node Values and their Operations
8374 @subsubsection Values and their Operations
8376 Values are used to alter locations, to investigate complex structures in
8377 more detail or to filter relevant information out of a large amount of
8378 data. There are several (mode dependent) operations defined which enable
8379 such investigations. These operations are not only applicable to
8380 constant values but also to locations, which can become quite useful
8381 when debugging complex structures. During parsing the command line
8382 (e.g. evaluating an expression) @value{GDBN} treats location names as
8383 the values behind these locations.
8385 This section describes how values have to be specified and which
8386 operations are legal to be used with such values.
8389 @item Literal Values
8390 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
8391 For detailed specification refer to the @sc{gnu} Chill implementation Manual
8393 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
8394 @c be converted to a @ref.
8399 @emph{Integer Literals} are specified in the same manner as in Chill
8400 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
8402 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
8404 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
8407 @emph{Set Literals} are defined by a name which was specified in a set
8408 mode. The value delivered by a Set Literal is the set value. This is
8409 comparable to an enumeration in C/C@t{++} language.
8411 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
8412 emptiness literal delivers either the empty reference value, the empty
8413 procedure value or the empty instance value.
8416 @emph{Character String Literals} are defined by a sequence of characters
8417 enclosed in single- or double quotes. If a single- or double quote has
8418 to be part of the string literal it has to be stuffed (specified twice).
8420 @emph{Bitstring Literals} are specified in the same manner as in Chill
8421 programs (refer z200/88 chpt 5.2.4.8).
8423 @emph{Floating point literals} are specified in the same manner as in
8424 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
8429 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
8430 name>} can be omitted if the mode of the tuple is unambiguous. This
8431 unambiguity is derived from the context of a evaluated expression.
8432 @code{<tuple>} can be one of the following:
8435 @item @emph{Powerset Tuple}
8436 @item @emph{Array Tuple}
8437 @item @emph{Structure Tuple}
8438 Powerset tuples, array tuples and structure tuples are specified in the
8439 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
8442 @item String Element Value
8443 A string element value is specified by
8445 @code{<string value>(<index>)}
8447 where @code{<index>} is a integer expression. It delivers a character
8448 value which is equivalent to the character indexed by @code{<index>} in
8451 @item String Slice Value
8452 A string slice value is specified by @code{<string value>(<slice
8453 spec>)}, where @code{<slice spec>} can be either a range of integer
8454 expressions or specified by @code{<start expr> up <size>}.
8455 @code{<size>} denotes the number of elements which the slice contains.
8456 The delivered value is a string value, which is part of the specified
8459 @item Array Element Values
8460 An array element value is specified by @code{<array value>(<expr>)} and
8461 delivers a array element value of the mode of the specified array.
8463 @item Array Slice Values
8464 An array slice is specified by @code{<array value>(<slice spec>)}, where
8465 @code{<slice spec>} can be either a range specified by expressions or by
8466 @code{<start expr> up <size>}. @code{<size>} denotes the number of
8467 arrayelements the slice contains. The delivered value is an array value
8468 which is part of the specified array.
8470 @item Structure Field Values
8471 A structure field value is derived by @code{<structure value>.<field
8472 name>}, where @code{<field name>} indicates the name of a field specified
8473 in the mode definition of the structure. The mode of the delivered value
8474 corresponds to this mode definition in the structure definition.
8476 @item Procedure Call Value
8477 The procedure call value is derived from the return value of the
8478 procedure@footnote{If a procedure call is used for instance in an
8479 expression, then this procedure is called with all its side
8480 effects. This can lead to confusing results if used carelessly.}.
8482 Values of duration mode locations are represented by @code{ULONG} literals.
8484 Values of time mode locations appear as
8486 @code{TIME(<secs>:<nsecs>)}
8491 This is not implemented yet:
8492 @item Built-in Value
8494 The following built in functions are provided:
8506 @item @code{UPPER()}
8507 @item @code{LOWER()}
8508 @item @code{LENGTH()}
8512 @item @code{ARCSIN()}
8513 @item @code{ARCCOS()}
8514 @item @code{ARCTAN()}
8521 For a detailed description refer to the GNU Chill implementation manual
8525 @item Zero-adic Operator Value
8526 The zero-adic operator value is derived from the instance value for the
8527 current active process.
8529 @item Expression Values
8530 The value delivered by an expression is the result of the evaluation of
8531 the specified expression. If there are error conditions (mode
8532 incompatibility, etc.) the evaluation of expressions is aborted with a
8533 corresponding error message. Expressions may be parenthesised which
8534 causes the evaluation of this expression before any other expression
8535 which uses the result of the parenthesised expression. The following
8536 operators are supported by @value{GDBN}:
8539 @item @code{OR, ORIF, XOR}
8540 @itemx @code{AND, ANDIF}
8542 Logical operators defined over operands of boolean mode.
8545 Equality and inequality operators defined over all modes.
8549 Relational operators defined over predefined modes.
8552 @itemx @code{*, /, MOD, REM}
8553 Arithmetic operators defined over predefined modes.
8556 Change sign operator.
8559 String concatenation operator.
8562 String repetition operator.
8565 Referenced location operator which can be used either to take the
8566 address of a location (@code{->loc}), or to dereference a reference
8567 location (@code{loc->}).
8569 @item @code{OR, XOR}
8572 Powerset and bitstring operators.
8576 Powerset inclusion operators.
8579 Membership operator.
8583 @node Chill type and range checks
8584 @subsubsection Chill type and range checks
8586 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8587 of the two modes are equal. This rule applies recursively to more
8588 complex datatypes which means that complex modes are treated
8589 equivalent if all element modes (which also can be complex modes like
8590 structures, arrays, etc.) have the same size.
8592 Range checking is done on all mathematical operations, assignment, array
8593 index bounds and all built in procedures.
8595 Strong type checks are forced using the @value{GDBN} command @code{set
8596 check strong}. This enforces strong type and range checks on all
8597 operations where Chill constructs are used (expressions, built in
8598 functions, etc.) in respect to the semantics as defined in the z.200
8599 language specification.
8601 All checks can be disabled by the @value{GDBN} command @code{set check
8605 @c Deviations from the Chill Standard Z200/88
8606 see last paragraph ?
8609 @node Chill defaults
8610 @subsubsection Chill defaults
8612 If type and range checking are set automatically by @value{GDBN}, they
8613 both default to @code{on} whenever the working language changes to
8614 Chill. This happens regardless of whether you or @value{GDBN}
8615 selected the working language.
8617 If you allow @value{GDBN} to set the language automatically, then entering
8618 code compiled from a file whose name ends with @file{.ch} sets the
8619 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8620 the language automatically}, for further details.
8623 @chapter Examining the Symbol Table
8625 The commands described in this chapter allow you to inquire about the
8626 symbols (names of variables, functions and types) defined in your
8627 program. This information is inherent in the text of your program and
8628 does not change as your program executes. @value{GDBN} finds it in your
8629 program's symbol table, in the file indicated when you started @value{GDBN}
8630 (@pxref{File Options, ,Choosing files}), or by one of the
8631 file-management commands (@pxref{Files, ,Commands to specify files}).
8633 @cindex symbol names
8634 @cindex names of symbols
8635 @cindex quoting names
8636 Occasionally, you may need to refer to symbols that contain unusual
8637 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8638 most frequent case is in referring to static variables in other
8639 source files (@pxref{Variables,,Program variables}). File names
8640 are recorded in object files as debugging symbols, but @value{GDBN} would
8641 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8642 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8643 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8650 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8653 @kindex info address
8654 @cindex address of a symbol
8655 @item info address @var{symbol}
8656 Describe where the data for @var{symbol} is stored. For a register
8657 variable, this says which register it is kept in. For a non-register
8658 local variable, this prints the stack-frame offset at which the variable
8661 Note the contrast with @samp{print &@var{symbol}}, which does not work
8662 at all for a register variable, and for a stack local variable prints
8663 the exact address of the current instantiation of the variable.
8666 @cindex symbol from address
8667 @item info symbol @var{addr}
8668 Print the name of a symbol which is stored at the address @var{addr}.
8669 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8670 nearest symbol and an offset from it:
8673 (@value{GDBP}) info symbol 0x54320
8674 _initialize_vx + 396 in section .text
8678 This is the opposite of the @code{info address} command. You can use
8679 it to find out the name of a variable or a function given its address.
8682 @item whatis @var{expr}
8683 Print the data type of expression @var{expr}. @var{expr} is not
8684 actually evaluated, and any side-effecting operations (such as
8685 assignments or function calls) inside it do not take place.
8686 @xref{Expressions, ,Expressions}.
8689 Print the data type of @code{$}, the last value in the value history.
8692 @item ptype @var{typename}
8693 Print a description of data type @var{typename}. @var{typename} may be
8694 the name of a type, or for C code it may have the form @samp{class
8695 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8696 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8698 @item ptype @var{expr}
8700 Print a description of the type of expression @var{expr}. @code{ptype}
8701 differs from @code{whatis} by printing a detailed description, instead
8702 of just the name of the type.
8704 For example, for this variable declaration:
8707 struct complex @{double real; double imag;@} v;
8711 the two commands give this output:
8715 (@value{GDBP}) whatis v
8716 type = struct complex
8717 (@value{GDBP}) ptype v
8718 type = struct complex @{
8726 As with @code{whatis}, using @code{ptype} without an argument refers to
8727 the type of @code{$}, the last value in the value history.
8730 @item info types @var{regexp}
8732 Print a brief description of all types whose names match @var{regexp}
8733 (or all types in your program, if you supply no argument). Each
8734 complete typename is matched as though it were a complete line; thus,
8735 @samp{i type value} gives information on all types in your program whose
8736 names include the string @code{value}, but @samp{i type ^value$} gives
8737 information only on types whose complete name is @code{value}.
8739 This command differs from @code{ptype} in two ways: first, like
8740 @code{whatis}, it does not print a detailed description; second, it
8741 lists all source files where a type is defined.
8744 @cindex local variables
8745 @item info scope @var{addr}
8746 List all the variables local to a particular scope. This command
8747 accepts a location---a function name, a source line, or an address
8748 preceded by a @samp{*}, and prints all the variables local to the
8749 scope defined by that location. For example:
8752 (@value{GDBP}) @b{info scope command_line_handler}
8753 Scope for command_line_handler:
8754 Symbol rl is an argument at stack/frame offset 8, length 4.
8755 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8756 Symbol linelength is in static storage at address 0x150a1c, length 4.
8757 Symbol p is a local variable in register $esi, length 4.
8758 Symbol p1 is a local variable in register $ebx, length 4.
8759 Symbol nline is a local variable in register $edx, length 4.
8760 Symbol repeat is a local variable at frame offset -8, length 4.
8764 This command is especially useful for determining what data to collect
8765 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8770 Show the name of the current source file---that is, the source file for
8771 the function containing the current point of execution---and the language
8774 @kindex info sources
8776 Print the names of all source files in your program for which there is
8777 debugging information, organized into two lists: files whose symbols
8778 have already been read, and files whose symbols will be read when needed.
8780 @kindex info functions
8781 @item info functions
8782 Print the names and data types of all defined functions.
8784 @item info functions @var{regexp}
8785 Print the names and data types of all defined functions
8786 whose names contain a match for regular expression @var{regexp}.
8787 Thus, @samp{info fun step} finds all functions whose names
8788 include @code{step}; @samp{info fun ^step} finds those whose names
8789 start with @code{step}. If a function name contains characters
8790 that conflict with the regular expression language (eg.
8791 @samp{operator*()}), they may be quoted with a backslash.
8793 @kindex info variables
8794 @item info variables
8795 Print the names and data types of all variables that are declared
8796 outside of functions (i.e., excluding local variables).
8798 @item info variables @var{regexp}
8799 Print the names and data types of all variables (except for local
8800 variables) whose names contain a match for regular expression
8804 This was never implemented.
8805 @kindex info methods
8807 @itemx info methods @var{regexp}
8808 The @code{info methods} command permits the user to examine all defined
8809 methods within C@t{++} program, or (with the @var{regexp} argument) a
8810 specific set of methods found in the various C@t{++} classes. Many
8811 C@t{++} classes provide a large number of methods. Thus, the output
8812 from the @code{ptype} command can be overwhelming and hard to use. The
8813 @code{info-methods} command filters the methods, printing only those
8814 which match the regular-expression @var{regexp}.
8817 @cindex reloading symbols
8818 Some systems allow individual object files that make up your program to
8819 be replaced without stopping and restarting your program. For example,
8820 in VxWorks you can simply recompile a defective object file and keep on
8821 running. If you are running on one of these systems, you can allow
8822 @value{GDBN} to reload the symbols for automatically relinked modules:
8825 @kindex set symbol-reloading
8826 @item set symbol-reloading on
8827 Replace symbol definitions for the corresponding source file when an
8828 object file with a particular name is seen again.
8830 @item set symbol-reloading off
8831 Do not replace symbol definitions when encountering object files of the
8832 same name more than once. This is the default state; if you are not
8833 running on a system that permits automatic relinking of modules, you
8834 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8835 may discard symbols when linking large programs, that may contain
8836 several modules (from different directories or libraries) with the same
8839 @kindex show symbol-reloading
8840 @item show symbol-reloading
8841 Show the current @code{on} or @code{off} setting.
8844 @kindex set opaque-type-resolution
8845 @item set opaque-type-resolution on
8846 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8847 declared as a pointer to a @code{struct}, @code{class}, or
8848 @code{union}---for example, @code{struct MyType *}---that is used in one
8849 source file although the full declaration of @code{struct MyType} is in
8850 another source file. The default is on.
8852 A change in the setting of this subcommand will not take effect until
8853 the next time symbols for a file are loaded.
8855 @item set opaque-type-resolution off
8856 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8857 is printed as follows:
8859 @{<no data fields>@}
8862 @kindex show opaque-type-resolution
8863 @item show opaque-type-resolution
8864 Show whether opaque types are resolved or not.
8866 @kindex maint print symbols
8868 @kindex maint print psymbols
8869 @cindex partial symbol dump
8870 @item maint print symbols @var{filename}
8871 @itemx maint print psymbols @var{filename}
8872 @itemx maint print msymbols @var{filename}
8873 Write a dump of debugging symbol data into the file @var{filename}.
8874 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8875 symbols with debugging data are included. If you use @samp{maint print
8876 symbols}, @value{GDBN} includes all the symbols for which it has already
8877 collected full details: that is, @var{filename} reflects symbols for
8878 only those files whose symbols @value{GDBN} has read. You can use the
8879 command @code{info sources} to find out which files these are. If you
8880 use @samp{maint print psymbols} instead, the dump shows information about
8881 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8882 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8883 @samp{maint print msymbols} dumps just the minimal symbol information
8884 required for each object file from which @value{GDBN} has read some symbols.
8885 @xref{Files, ,Commands to specify files}, for a discussion of how
8886 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8890 @chapter Altering Execution
8892 Once you think you have found an error in your program, you might want to
8893 find out for certain whether correcting the apparent error would lead to
8894 correct results in the rest of the run. You can find the answer by
8895 experiment, using the @value{GDBN} features for altering execution of the
8898 For example, you can store new values into variables or memory
8899 locations, give your program a signal, restart it at a different
8900 address, or even return prematurely from a function.
8903 * Assignment:: Assignment to variables
8904 * Jumping:: Continuing at a different address
8905 * Signaling:: Giving your program a signal
8906 * Returning:: Returning from a function
8907 * Calling:: Calling your program's functions
8908 * Patching:: Patching your program
8912 @section Assignment to variables
8915 @cindex setting variables
8916 To alter the value of a variable, evaluate an assignment expression.
8917 @xref{Expressions, ,Expressions}. For example,
8924 stores the value 4 into the variable @code{x}, and then prints the
8925 value of the assignment expression (which is 4).
8926 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8927 information on operators in supported languages.
8929 @kindex set variable
8930 @cindex variables, setting
8931 If you are not interested in seeing the value of the assignment, use the
8932 @code{set} command instead of the @code{print} command. @code{set} is
8933 really the same as @code{print} except that the expression's value is
8934 not printed and is not put in the value history (@pxref{Value History,
8935 ,Value history}). The expression is evaluated only for its effects.
8937 If the beginning of the argument string of the @code{set} command
8938 appears identical to a @code{set} subcommand, use the @code{set
8939 variable} command instead of just @code{set}. This command is identical
8940 to @code{set} except for its lack of subcommands. For example, if your
8941 program has a variable @code{width}, you get an error if you try to set
8942 a new value with just @samp{set width=13}, because @value{GDBN} has the
8943 command @code{set width}:
8946 (@value{GDBP}) whatis width
8948 (@value{GDBP}) p width
8950 (@value{GDBP}) set width=47
8951 Invalid syntax in expression.
8955 The invalid expression, of course, is @samp{=47}. In
8956 order to actually set the program's variable @code{width}, use
8959 (@value{GDBP}) set var width=47
8962 Because the @code{set} command has many subcommands that can conflict
8963 with the names of program variables, it is a good idea to use the
8964 @code{set variable} command instead of just @code{set}. For example, if
8965 your program has a variable @code{g}, you run into problems if you try
8966 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8967 the command @code{set gnutarget}, abbreviated @code{set g}:
8971 (@value{GDBP}) whatis g
8975 (@value{GDBP}) set g=4
8979 The program being debugged has been started already.
8980 Start it from the beginning? (y or n) y
8981 Starting program: /home/smith/cc_progs/a.out
8982 "/home/smith/cc_progs/a.out": can't open to read symbols:
8984 (@value{GDBP}) show g
8985 The current BFD target is "=4".
8990 The program variable @code{g} did not change, and you silently set the
8991 @code{gnutarget} to an invalid value. In order to set the variable
8995 (@value{GDBP}) set var g=4
8998 @value{GDBN} allows more implicit conversions in assignments than C; you can
8999 freely store an integer value into a pointer variable or vice versa,
9000 and you can convert any structure to any other structure that is the
9001 same length or shorter.
9002 @comment FIXME: how do structs align/pad in these conversions?
9003 @comment /doc@cygnus.com 18dec1990
9005 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9006 construct to generate a value of specified type at a specified address
9007 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9008 to memory location @code{0x83040} as an integer (which implies a certain size
9009 and representation in memory), and
9012 set @{int@}0x83040 = 4
9016 stores the value 4 into that memory location.
9019 @section Continuing at a different address
9021 Ordinarily, when you continue your program, you do so at the place where
9022 it stopped, with the @code{continue} command. You can instead continue at
9023 an address of your own choosing, with the following commands:
9027 @item jump @var{linespec}
9028 Resume execution at line @var{linespec}. Execution stops again
9029 immediately if there is a breakpoint there. @xref{List, ,Printing
9030 source lines}, for a description of the different forms of
9031 @var{linespec}. It is common practice to use the @code{tbreak} command
9032 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9035 The @code{jump} command does not change the current stack frame, or
9036 the stack pointer, or the contents of any memory location or any
9037 register other than the program counter. If line @var{linespec} is in
9038 a different function from the one currently executing, the results may
9039 be bizarre if the two functions expect different patterns of arguments or
9040 of local variables. For this reason, the @code{jump} command requests
9041 confirmation if the specified line is not in the function currently
9042 executing. However, even bizarre results are predictable if you are
9043 well acquainted with the machine-language code of your program.
9045 @item jump *@var{address}
9046 Resume execution at the instruction at address @var{address}.
9049 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9050 On many systems, you can get much the same effect as the @code{jump}
9051 command by storing a new value into the register @code{$pc}. The
9052 difference is that this does not start your program running; it only
9053 changes the address of where it @emph{will} run when you continue. For
9061 makes the next @code{continue} command or stepping command execute at
9062 address @code{0x485}, rather than at the address where your program stopped.
9063 @xref{Continuing and Stepping, ,Continuing and stepping}.
9065 The most common occasion to use the @code{jump} command is to back
9066 up---perhaps with more breakpoints set---over a portion of a program
9067 that has already executed, in order to examine its execution in more
9072 @section Giving your program a signal
9076 @item signal @var{signal}
9077 Resume execution where your program stopped, but immediately give it the
9078 signal @var{signal}. @var{signal} can be the name or the number of a
9079 signal. For example, on many systems @code{signal 2} and @code{signal
9080 SIGINT} are both ways of sending an interrupt signal.
9082 Alternatively, if @var{signal} is zero, continue execution without
9083 giving a signal. This is useful when your program stopped on account of
9084 a signal and would ordinary see the signal when resumed with the
9085 @code{continue} command; @samp{signal 0} causes it to resume without a
9088 @code{signal} does not repeat when you press @key{RET} a second time
9089 after executing the command.
9093 Invoking the @code{signal} command is not the same as invoking the
9094 @code{kill} utility from the shell. Sending a signal with @code{kill}
9095 causes @value{GDBN} to decide what to do with the signal depending on
9096 the signal handling tables (@pxref{Signals}). The @code{signal} command
9097 passes the signal directly to your program.
9101 @section Returning from a function
9104 @cindex returning from a function
9107 @itemx return @var{expression}
9108 You can cancel execution of a function call with the @code{return}
9109 command. If you give an
9110 @var{expression} argument, its value is used as the function's return
9114 When you use @code{return}, @value{GDBN} discards the selected stack frame
9115 (and all frames within it). You can think of this as making the
9116 discarded frame return prematurely. If you wish to specify a value to
9117 be returned, give that value as the argument to @code{return}.
9119 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9120 frame}), and any other frames inside of it, leaving its caller as the
9121 innermost remaining frame. That frame becomes selected. The
9122 specified value is stored in the registers used for returning values
9125 The @code{return} command does not resume execution; it leaves the
9126 program stopped in the state that would exist if the function had just
9127 returned. In contrast, the @code{finish} command (@pxref{Continuing
9128 and Stepping, ,Continuing and stepping}) resumes execution until the
9129 selected stack frame returns naturally.
9132 @section Calling program functions
9134 @cindex calling functions
9137 @item call @var{expr}
9138 Evaluate the expression @var{expr} without displaying @code{void}
9142 You can use this variant of the @code{print} command if you want to
9143 execute a function from your program, but without cluttering the output
9144 with @code{void} returned values. If the result is not void, it
9145 is printed and saved in the value history.
9147 For the A29K, a user-controlled variable @code{call_scratch_address},
9148 specifies the location of a scratch area to be used when @value{GDBN}
9149 calls a function in the target. This is necessary because the usual
9150 method of putting the scratch area on the stack does not work in systems
9151 that have separate instruction and data spaces.
9154 @section Patching programs
9156 @cindex patching binaries
9157 @cindex writing into executables
9158 @cindex writing into corefiles
9160 By default, @value{GDBN} opens the file containing your program's
9161 executable code (or the corefile) read-only. This prevents accidental
9162 alterations to machine code; but it also prevents you from intentionally
9163 patching your program's binary.
9165 If you'd like to be able to patch the binary, you can specify that
9166 explicitly with the @code{set write} command. For example, you might
9167 want to turn on internal debugging flags, or even to make emergency
9173 @itemx set write off
9174 If you specify @samp{set write on}, @value{GDBN} opens executable and
9175 core files for both reading and writing; if you specify @samp{set write
9176 off} (the default), @value{GDBN} opens them read-only.
9178 If you have already loaded a file, you must load it again (using the
9179 @code{exec-file} or @code{core-file} command) after changing @code{set
9180 write}, for your new setting to take effect.
9184 Display whether executable files and core files are opened for writing
9189 @chapter @value{GDBN} Files
9191 @value{GDBN} needs to know the file name of the program to be debugged,
9192 both in order to read its symbol table and in order to start your
9193 program. To debug a core dump of a previous run, you must also tell
9194 @value{GDBN} the name of the core dump file.
9197 * Files:: Commands to specify files
9198 * Symbol Errors:: Errors reading symbol files
9202 @section Commands to specify files
9204 @cindex symbol table
9205 @cindex core dump file
9207 You may want to specify executable and core dump file names. The usual
9208 way to do this is at start-up time, using the arguments to
9209 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9210 Out of @value{GDBN}}).
9212 Occasionally it is necessary to change to a different file during a
9213 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9214 a file you want to use. In these situations the @value{GDBN} commands
9215 to specify new files are useful.
9218 @cindex executable file
9220 @item file @var{filename}
9221 Use @var{filename} as the program to be debugged. It is read for its
9222 symbols and for the contents of pure memory. It is also the program
9223 executed when you use the @code{run} command. If you do not specify a
9224 directory and the file is not found in the @value{GDBN} working directory,
9225 @value{GDBN} uses the environment variable @code{PATH} as a list of
9226 directories to search, just as the shell does when looking for a program
9227 to run. You can change the value of this variable, for both @value{GDBN}
9228 and your program, using the @code{path} command.
9230 On systems with memory-mapped files, an auxiliary file named
9231 @file{@var{filename}.syms} may hold symbol table information for
9232 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9233 @file{@var{filename}.syms}, starting up more quickly. See the
9234 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9235 (available on the command line, and with the commands @code{file},
9236 @code{symbol-file}, or @code{add-symbol-file}, described below),
9237 for more information.
9240 @code{file} with no argument makes @value{GDBN} discard any information it
9241 has on both executable file and the symbol table.
9244 @item exec-file @r{[} @var{filename} @r{]}
9245 Specify that the program to be run (but not the symbol table) is found
9246 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9247 if necessary to locate your program. Omitting @var{filename} means to
9248 discard information on the executable file.
9251 @item symbol-file @r{[} @var{filename} @r{]}
9252 Read symbol table information from file @var{filename}. @code{PATH} is
9253 searched when necessary. Use the @code{file} command to get both symbol
9254 table and program to run from the same file.
9256 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9257 program's symbol table.
9259 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9260 of its convenience variables, the value history, and all breakpoints and
9261 auto-display expressions. This is because they may contain pointers to
9262 the internal data recording symbols and data types, which are part of
9263 the old symbol table data being discarded inside @value{GDBN}.
9265 @code{symbol-file} does not repeat if you press @key{RET} again after
9268 When @value{GDBN} is configured for a particular environment, it
9269 understands debugging information in whatever format is the standard
9270 generated for that environment; you may use either a @sc{gnu} compiler, or
9271 other compilers that adhere to the local conventions.
9272 Best results are usually obtained from @sc{gnu} compilers; for example,
9273 using @code{@value{GCC}} you can generate debugging information for
9276 For most kinds of object files, with the exception of old SVR3 systems
9277 using COFF, the @code{symbol-file} command does not normally read the
9278 symbol table in full right away. Instead, it scans the symbol table
9279 quickly to find which source files and which symbols are present. The
9280 details are read later, one source file at a time, as they are needed.
9282 The purpose of this two-stage reading strategy is to make @value{GDBN}
9283 start up faster. For the most part, it is invisible except for
9284 occasional pauses while the symbol table details for a particular source
9285 file are being read. (The @code{set verbose} command can turn these
9286 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9287 warnings and messages}.)
9289 We have not implemented the two-stage strategy for COFF yet. When the
9290 symbol table is stored in COFF format, @code{symbol-file} reads the
9291 symbol table data in full right away. Note that ``stabs-in-COFF''
9292 still does the two-stage strategy, since the debug info is actually
9296 @cindex reading symbols immediately
9297 @cindex symbols, reading immediately
9299 @cindex memory-mapped symbol file
9300 @cindex saving symbol table
9301 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9302 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9303 You can override the @value{GDBN} two-stage strategy for reading symbol
9304 tables by using the @samp{-readnow} option with any of the commands that
9305 load symbol table information, if you want to be sure @value{GDBN} has the
9306 entire symbol table available.
9308 If memory-mapped files are available on your system through the
9309 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9310 cause @value{GDBN} to write the symbols for your program into a reusable
9311 file. Future @value{GDBN} debugging sessions map in symbol information
9312 from this auxiliary symbol file (if the program has not changed), rather
9313 than spending time reading the symbol table from the executable
9314 program. Using the @samp{-mapped} option has the same effect as
9315 starting @value{GDBN} with the @samp{-mapped} command-line option.
9317 You can use both options together, to make sure the auxiliary symbol
9318 file has all the symbol information for your program.
9320 The auxiliary symbol file for a program called @var{myprog} is called
9321 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9322 than the corresponding executable), @value{GDBN} always attempts to use
9323 it when you debug @var{myprog}; no special options or commands are
9326 The @file{.syms} file is specific to the host machine where you run
9327 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9328 symbol table. It cannot be shared across multiple host platforms.
9330 @c FIXME: for now no mention of directories, since this seems to be in
9331 @c flux. 13mar1992 status is that in theory GDB would look either in
9332 @c current dir or in same dir as myprog; but issues like competing
9333 @c GDB's, or clutter in system dirs, mean that in practice right now
9334 @c only current dir is used. FFish says maybe a special GDB hierarchy
9335 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9340 @item core-file @r{[} @var{filename} @r{]}
9341 Specify the whereabouts of a core dump file to be used as the ``contents
9342 of memory''. Traditionally, core files contain only some parts of the
9343 address space of the process that generated them; @value{GDBN} can access the
9344 executable file itself for other parts.
9346 @code{core-file} with no argument specifies that no core file is
9349 Note that the core file is ignored when your program is actually running
9350 under @value{GDBN}. So, if you have been running your program and you
9351 wish to debug a core file instead, you must kill the subprocess in which
9352 the program is running. To do this, use the @code{kill} command
9353 (@pxref{Kill Process, ,Killing the child process}).
9355 @kindex add-symbol-file
9356 @cindex dynamic linking
9357 @item add-symbol-file @var{filename} @var{address}
9358 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9359 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9360 The @code{add-symbol-file} command reads additional symbol table
9361 information from the file @var{filename}. You would use this command
9362 when @var{filename} has been dynamically loaded (by some other means)
9363 into the program that is running. @var{address} should be the memory
9364 address at which the file has been loaded; @value{GDBN} cannot figure
9365 this out for itself. You can additionally specify an arbitrary number
9366 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9367 section name and base address for that section. You can specify any
9368 @var{address} as an expression.
9370 The symbol table of the file @var{filename} is added to the symbol table
9371 originally read with the @code{symbol-file} command. You can use the
9372 @code{add-symbol-file} command any number of times; the new symbol data
9373 thus read keeps adding to the old. To discard all old symbol data
9374 instead, use the @code{symbol-file} command without any arguments.
9376 @cindex relocatable object files, reading symbols from
9377 @cindex object files, relocatable, reading symbols from
9378 @cindex reading symbols from relocatable object files
9379 @cindex symbols, reading from relocatable object files
9380 @cindex @file{.o} files, reading symbols from
9381 Although @var{filename} is typically a shared library file, an
9382 executable file, or some other object file which has been fully
9383 relocated for loading into a process, you can also load symbolic
9384 information from relocatable @file{.o} files, as long as:
9388 the file's symbolic information refers only to linker symbols defined in
9389 that file, not to symbols defined by other object files,
9391 every section the file's symbolic information refers to has actually
9392 been loaded into the inferior, as it appears in the file, and
9394 you can determine the address at which every section was loaded, and
9395 provide these to the @code{add-symbol-file} command.
9399 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9400 relocatable files into an already running program; such systems
9401 typically make the requirements above easy to meet. However, it's
9402 important to recognize that many native systems use complex link
9403 procedures (@code{.linkonce} section factoring and C++ constructor table
9404 assembly, for example) that make the requirements difficult to meet. In
9405 general, one cannot assume that using @code{add-symbol-file} to read a
9406 relocatable object file's symbolic information will have the same effect
9407 as linking the relocatable object file into the program in the normal
9410 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9412 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9413 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9414 table information for @var{filename}.
9416 @kindex add-shared-symbol-file
9417 @item add-shared-symbol-file
9418 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9419 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9420 shared libraries, however if @value{GDBN} does not find yours, you can run
9421 @code{add-shared-symbol-file}. It takes no arguments.
9425 The @code{section} command changes the base address of section SECTION of
9426 the exec file to ADDR. This can be used if the exec file does not contain
9427 section addresses, (such as in the a.out format), or when the addresses
9428 specified in the file itself are wrong. Each section must be changed
9429 separately. The @code{info files} command, described below, lists all
9430 the sections and their addresses.
9436 @code{info files} and @code{info target} are synonymous; both print the
9437 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9438 including the names of the executable and core dump files currently in
9439 use by @value{GDBN}, and the files from which symbols were loaded. The
9440 command @code{help target} lists all possible targets rather than
9443 @kindex maint info sections
9444 @item maint info sections
9445 Another command that can give you extra information about program sections
9446 is @code{maint info sections}. In addition to the section information
9447 displayed by @code{info files}, this command displays the flags and file
9448 offset of each section in the executable and core dump files. In addition,
9449 @code{maint info sections} provides the following command options (which
9450 may be arbitrarily combined):
9454 Display sections for all loaded object files, including shared libraries.
9455 @item @var{sections}
9456 Display info only for named @var{sections}.
9457 @item @var{section-flags}
9458 Display info only for sections for which @var{section-flags} are true.
9459 The section flags that @value{GDBN} currently knows about are:
9462 Section will have space allocated in the process when loaded.
9463 Set for all sections except those containing debug information.
9465 Section will be loaded from the file into the child process memory.
9466 Set for pre-initialized code and data, clear for @code{.bss} sections.
9468 Section needs to be relocated before loading.
9470 Section cannot be modified by the child process.
9472 Section contains executable code only.
9474 Section contains data only (no executable code).
9476 Section will reside in ROM.
9478 Section contains data for constructor/destructor lists.
9480 Section is not empty.
9482 An instruction to the linker to not output the section.
9483 @item COFF_SHARED_LIBRARY
9484 A notification to the linker that the section contains
9485 COFF shared library information.
9487 Section contains common symbols.
9492 All file-specifying commands allow both absolute and relative file names
9493 as arguments. @value{GDBN} always converts the file name to an absolute file
9494 name and remembers it that way.
9496 @cindex shared libraries
9497 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9500 @value{GDBN} automatically loads symbol definitions from shared libraries
9501 when you use the @code{run} command, or when you examine a core file.
9502 (Before you issue the @code{run} command, @value{GDBN} does not understand
9503 references to a function in a shared library, however---unless you are
9504 debugging a core file).
9506 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9507 automatically loads the symbols at the time of the @code{shl_load} call.
9509 @c FIXME: some @value{GDBN} release may permit some refs to undef
9510 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9511 @c FIXME...lib; check this from time to time when updating manual
9513 There are times, however, when you may wish to not automatically load
9514 symbol definitions from shared libraries, such as when they are
9515 particularly large or there are many of them.
9517 To control the automatic loading of shared library symbols, use the
9521 @kindex set auto-solib-add
9522 @item set auto-solib-add @var{mode}
9523 If @var{mode} is @code{on}, symbols from all shared object libraries
9524 will be loaded automatically when the inferior begins execution, you
9525 attach to an independently started inferior, or when the dynamic linker
9526 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9527 is @code{off}, symbols must be loaded manually, using the
9528 @code{sharedlibrary} command. The default value is @code{on}.
9530 @kindex show auto-solib-add
9531 @item show auto-solib-add
9532 Display the current autoloading mode.
9535 To explicitly load shared library symbols, use the @code{sharedlibrary}
9539 @kindex info sharedlibrary
9542 @itemx info sharedlibrary
9543 Print the names of the shared libraries which are currently loaded.
9545 @kindex sharedlibrary
9547 @item sharedlibrary @var{regex}
9548 @itemx share @var{regex}
9549 Load shared object library symbols for files matching a
9550 Unix regular expression.
9551 As with files loaded automatically, it only loads shared libraries
9552 required by your program for a core file or after typing @code{run}. If
9553 @var{regex} is omitted all shared libraries required by your program are
9557 On some systems, such as HP-UX systems, @value{GDBN} supports
9558 autoloading shared library symbols until a limiting threshold size is
9559 reached. This provides the benefit of allowing autoloading to remain on
9560 by default, but avoids autoloading excessively large shared libraries,
9561 up to a threshold that is initially set, but which you can modify if you
9564 Beyond that threshold, symbols from shared libraries must be explicitly
9565 loaded. To load these symbols, use the command @code{sharedlibrary
9566 @var{filename}}. The base address of the shared library is determined
9567 automatically by @value{GDBN} and need not be specified.
9569 To display or set the threshold, use the commands:
9572 @kindex set auto-solib-limit
9573 @item set auto-solib-limit @var{threshold}
9574 Set the autoloading size threshold, in an integral number of megabytes.
9575 If @var{threshold} is nonzero and shared library autoloading is enabled,
9576 symbols from all shared object libraries will be loaded until the total
9577 size of the loaded shared library symbols exceeds this threshold.
9578 Otherwise, symbols must be loaded manually, using the
9579 @code{sharedlibrary} command. The default threshold is 100 (i.e. 100
9582 @kindex show auto-solib-limit
9583 @item show auto-solib-limit
9584 Display the current autoloading size threshold, in megabytes.
9588 @section Errors reading symbol files
9590 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9591 such as symbol types it does not recognize, or known bugs in compiler
9592 output. By default, @value{GDBN} does not notify you of such problems, since
9593 they are relatively common and primarily of interest to people
9594 debugging compilers. If you are interested in seeing information
9595 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9596 only one message about each such type of problem, no matter how many
9597 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9598 to see how many times the problems occur, with the @code{set
9599 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9602 The messages currently printed, and their meanings, include:
9605 @item inner block not inside outer block in @var{symbol}
9607 The symbol information shows where symbol scopes begin and end
9608 (such as at the start of a function or a block of statements). This
9609 error indicates that an inner scope block is not fully contained
9610 in its outer scope blocks.
9612 @value{GDBN} circumvents the problem by treating the inner block as if it had
9613 the same scope as the outer block. In the error message, @var{symbol}
9614 may be shown as ``@code{(don't know)}'' if the outer block is not a
9617 @item block at @var{address} out of order
9619 The symbol information for symbol scope blocks should occur in
9620 order of increasing addresses. This error indicates that it does not
9623 @value{GDBN} does not circumvent this problem, and has trouble
9624 locating symbols in the source file whose symbols it is reading. (You
9625 can often determine what source file is affected by specifying
9626 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9629 @item bad block start address patched
9631 The symbol information for a symbol scope block has a start address
9632 smaller than the address of the preceding source line. This is known
9633 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9635 @value{GDBN} circumvents the problem by treating the symbol scope block as
9636 starting on the previous source line.
9638 @item bad string table offset in symbol @var{n}
9641 Symbol number @var{n} contains a pointer into the string table which is
9642 larger than the size of the string table.
9644 @value{GDBN} circumvents the problem by considering the symbol to have the
9645 name @code{foo}, which may cause other problems if many symbols end up
9648 @item unknown symbol type @code{0x@var{nn}}
9650 The symbol information contains new data types that @value{GDBN} does
9651 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9652 uncomprehended information, in hexadecimal.
9654 @value{GDBN} circumvents the error by ignoring this symbol information.
9655 This usually allows you to debug your program, though certain symbols
9656 are not accessible. If you encounter such a problem and feel like
9657 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9658 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9659 and examine @code{*bufp} to see the symbol.
9661 @item stub type has NULL name
9663 @value{GDBN} could not find the full definition for a struct or class.
9665 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9666 The symbol information for a C@t{++} member function is missing some
9667 information that recent versions of the compiler should have output for
9670 @item info mismatch between compiler and debugger
9672 @value{GDBN} could not parse a type specification output by the compiler.
9677 @chapter Specifying a Debugging Target
9679 @cindex debugging target
9682 A @dfn{target} is the execution environment occupied by your program.
9684 Often, @value{GDBN} runs in the same host environment as your program;
9685 in that case, the debugging target is specified as a side effect when
9686 you use the @code{file} or @code{core} commands. When you need more
9687 flexibility---for example, running @value{GDBN} on a physically separate
9688 host, or controlling a standalone system over a serial port or a
9689 realtime system over a TCP/IP connection---you can use the @code{target}
9690 command to specify one of the target types configured for @value{GDBN}
9691 (@pxref{Target Commands, ,Commands for managing targets}).
9694 * Active Targets:: Active targets
9695 * Target Commands:: Commands for managing targets
9696 * Byte Order:: Choosing target byte order
9697 * Remote:: Remote debugging
9698 * KOD:: Kernel Object Display
9702 @node Active Targets
9703 @section Active targets
9705 @cindex stacking targets
9706 @cindex active targets
9707 @cindex multiple targets
9709 There are three classes of targets: processes, core files, and
9710 executable files. @value{GDBN} can work concurrently on up to three
9711 active targets, one in each class. This allows you to (for example)
9712 start a process and inspect its activity without abandoning your work on
9715 For example, if you execute @samp{gdb a.out}, then the executable file
9716 @code{a.out} is the only active target. If you designate a core file as
9717 well---presumably from a prior run that crashed and coredumped---then
9718 @value{GDBN} has two active targets and uses them in tandem, looking
9719 first in the corefile target, then in the executable file, to satisfy
9720 requests for memory addresses. (Typically, these two classes of target
9721 are complementary, since core files contain only a program's
9722 read-write memory---variables and so on---plus machine status, while
9723 executable files contain only the program text and initialized data.)
9725 When you type @code{run}, your executable file becomes an active process
9726 target as well. When a process target is active, all @value{GDBN}
9727 commands requesting memory addresses refer to that target; addresses in
9728 an active core file or executable file target are obscured while the
9729 process target is active.
9731 Use the @code{core-file} and @code{exec-file} commands to select a new
9732 core file or executable target (@pxref{Files, ,Commands to specify
9733 files}). To specify as a target a process that is already running, use
9734 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9737 @node Target Commands
9738 @section Commands for managing targets
9741 @item target @var{type} @var{parameters}
9742 Connects the @value{GDBN} host environment to a target machine or
9743 process. A target is typically a protocol for talking to debugging
9744 facilities. You use the argument @var{type} to specify the type or
9745 protocol of the target machine.
9747 Further @var{parameters} are interpreted by the target protocol, but
9748 typically include things like device names or host names to connect
9749 with, process numbers, and baud rates.
9751 The @code{target} command does not repeat if you press @key{RET} again
9752 after executing the command.
9756 Displays the names of all targets available. To display targets
9757 currently selected, use either @code{info target} or @code{info files}
9758 (@pxref{Files, ,Commands to specify files}).
9760 @item help target @var{name}
9761 Describe a particular target, including any parameters necessary to
9764 @kindex set gnutarget
9765 @item set gnutarget @var{args}
9766 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9767 knows whether it is reading an @dfn{executable},
9768 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9769 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9770 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9773 @emph{Warning:} To specify a file format with @code{set gnutarget},
9774 you must know the actual BFD name.
9778 @xref{Files, , Commands to specify files}.
9780 @kindex show gnutarget
9781 @item show gnutarget
9782 Use the @code{show gnutarget} command to display what file format
9783 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9784 @value{GDBN} will determine the file format for each file automatically,
9785 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9788 Here are some common targets (available, or not, depending on the GDB
9793 @item target exec @var{program}
9794 An executable file. @samp{target exec @var{program}} is the same as
9795 @samp{exec-file @var{program}}.
9798 @item target core @var{filename}
9799 A core dump file. @samp{target core @var{filename}} is the same as
9800 @samp{core-file @var{filename}}.
9802 @kindex target remote
9803 @item target remote @var{dev}
9804 Remote serial target in GDB-specific protocol. The argument @var{dev}
9805 specifies what serial device to use for the connection (e.g.
9806 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9807 supports the @code{load} command. This is only useful if you have
9808 some other way of getting the stub to the target system, and you can put
9809 it somewhere in memory where it won't get clobbered by the download.
9813 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9821 works; however, you cannot assume that a specific memory map, device
9822 drivers, or even basic I/O is available, although some simulators do
9823 provide these. For info about any processor-specific simulator details,
9824 see the appropriate section in @ref{Embedded Processors, ,Embedded
9829 Some configurations may include these targets as well:
9834 @item target nrom @var{dev}
9835 NetROM ROM emulator. This target only supports downloading.
9839 Different targets are available on different configurations of @value{GDBN};
9840 your configuration may have more or fewer targets.
9842 Many remote targets require you to download the executable's code
9843 once you've successfully established a connection.
9847 @kindex load @var{filename}
9848 @item load @var{filename}
9849 Depending on what remote debugging facilities are configured into
9850 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9851 is meant to make @var{filename} (an executable) available for debugging
9852 on the remote system---by downloading, or dynamic linking, for example.
9853 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9854 the @code{add-symbol-file} command.
9856 If your @value{GDBN} does not have a @code{load} command, attempting to
9857 execute it gets the error message ``@code{You can't do that when your
9858 target is @dots{}}''
9860 The file is loaded at whatever address is specified in the executable.
9861 For some object file formats, you can specify the load address when you
9862 link the program; for other formats, like a.out, the object file format
9863 specifies a fixed address.
9864 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9866 @code{load} does not repeat if you press @key{RET} again after using it.
9870 @section Choosing target byte order
9872 @cindex choosing target byte order
9873 @cindex target byte order
9875 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9876 offer the ability to run either big-endian or little-endian byte
9877 orders. Usually the executable or symbol will include a bit to
9878 designate the endian-ness, and you will not need to worry about
9879 which to use. However, you may still find it useful to adjust
9880 @value{GDBN}'s idea of processor endian-ness manually.
9883 @kindex set endian big
9884 @item set endian big
9885 Instruct @value{GDBN} to assume the target is big-endian.
9887 @kindex set endian little
9888 @item set endian little
9889 Instruct @value{GDBN} to assume the target is little-endian.
9891 @kindex set endian auto
9892 @item set endian auto
9893 Instruct @value{GDBN} to use the byte order associated with the
9897 Display @value{GDBN}'s current idea of the target byte order.
9901 Note that these commands merely adjust interpretation of symbolic
9902 data on the host, and that they have absolutely no effect on the
9906 @section Remote debugging
9907 @cindex remote debugging
9909 If you are trying to debug a program running on a machine that cannot run
9910 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9911 For example, you might use remote debugging on an operating system kernel,
9912 or on a small system which does not have a general purpose operating system
9913 powerful enough to run a full-featured debugger.
9915 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9916 to make this work with particular debugging targets. In addition,
9917 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9918 but not specific to any particular target system) which you can use if you
9919 write the remote stubs---the code that runs on the remote system to
9920 communicate with @value{GDBN}.
9922 Other remote targets may be available in your
9923 configuration of @value{GDBN}; use @code{help target} to list them.
9926 * Remote Serial:: @value{GDBN} remote serial protocol
9930 @subsection The @value{GDBN} remote serial protocol
9932 @cindex remote serial debugging, overview
9933 To debug a program running on another machine (the debugging
9934 @dfn{target} machine), you must first arrange for all the usual
9935 prerequisites for the program to run by itself. For example, for a C
9940 A startup routine to set up the C runtime environment; these usually
9941 have a name like @file{crt0}. The startup routine may be supplied by
9942 your hardware supplier, or you may have to write your own.
9945 A C subroutine library to support your program's
9946 subroutine calls, notably managing input and output.
9949 A way of getting your program to the other machine---for example, a
9950 download program. These are often supplied by the hardware
9951 manufacturer, but you may have to write your own from hardware
9955 The next step is to arrange for your program to use a serial port to
9956 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9957 machine). In general terms, the scheme looks like this:
9961 @value{GDBN} already understands how to use this protocol; when everything
9962 else is set up, you can simply use the @samp{target remote} command
9963 (@pxref{Targets,,Specifying a Debugging Target}).
9965 @item On the target,
9966 you must link with your program a few special-purpose subroutines that
9967 implement the @value{GDBN} remote serial protocol. The file containing these
9968 subroutines is called a @dfn{debugging stub}.
9970 On certain remote targets, you can use an auxiliary program
9971 @code{gdbserver} instead of linking a stub into your program.
9972 @xref{Server,,Using the @code{gdbserver} program}, for details.
9975 The debugging stub is specific to the architecture of the remote
9976 machine; for example, use @file{sparc-stub.c} to debug programs on
9979 @cindex remote serial stub list
9980 These working remote stubs are distributed with @value{GDBN}:
9985 @cindex @file{i386-stub.c}
9988 For Intel 386 and compatible architectures.
9991 @cindex @file{m68k-stub.c}
9992 @cindex Motorola 680x0
9994 For Motorola 680x0 architectures.
9997 @cindex @file{sh-stub.c}
10000 For Hitachi SH architectures.
10003 @cindex @file{sparc-stub.c}
10005 For @sc{sparc} architectures.
10007 @item sparcl-stub.c
10008 @cindex @file{sparcl-stub.c}
10011 For Fujitsu @sc{sparclite} architectures.
10015 The @file{README} file in the @value{GDBN} distribution may list other
10016 recently added stubs.
10019 * Stub Contents:: What the stub can do for you
10020 * Bootstrapping:: What you must do for the stub
10021 * Debug Session:: Putting it all together
10022 * Protocol:: Definition of the communication protocol
10023 * Server:: Using the `gdbserver' program
10024 * NetWare:: Using the `gdbserve.nlm' program
10027 @node Stub Contents
10028 @subsubsection What the stub can do for you
10030 @cindex remote serial stub
10031 The debugging stub for your architecture supplies these three
10035 @item set_debug_traps
10036 @kindex set_debug_traps
10037 @cindex remote serial stub, initialization
10038 This routine arranges for @code{handle_exception} to run when your
10039 program stops. You must call this subroutine explicitly near the
10040 beginning of your program.
10042 @item handle_exception
10043 @kindex handle_exception
10044 @cindex remote serial stub, main routine
10045 This is the central workhorse, but your program never calls it
10046 explicitly---the setup code arranges for @code{handle_exception} to
10047 run when a trap is triggered.
10049 @code{handle_exception} takes control when your program stops during
10050 execution (for example, on a breakpoint), and mediates communications
10051 with @value{GDBN} on the host machine. This is where the communications
10052 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10053 representative on the target machine. It begins by sending summary
10054 information on the state of your program, then continues to execute,
10055 retrieving and transmitting any information @value{GDBN} needs, until you
10056 execute a @value{GDBN} command that makes your program resume; at that point,
10057 @code{handle_exception} returns control to your own code on the target
10061 @cindex @code{breakpoint} subroutine, remote
10062 Use this auxiliary subroutine to make your program contain a
10063 breakpoint. Depending on the particular situation, this may be the only
10064 way for @value{GDBN} to get control. For instance, if your target
10065 machine has some sort of interrupt button, you won't need to call this;
10066 pressing the interrupt button transfers control to
10067 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10068 simply receiving characters on the serial port may also trigger a trap;
10069 again, in that situation, you don't need to call @code{breakpoint} from
10070 your own program---simply running @samp{target remote} from the host
10071 @value{GDBN} session gets control.
10073 Call @code{breakpoint} if none of these is true, or if you simply want
10074 to make certain your program stops at a predetermined point for the
10075 start of your debugging session.
10078 @node Bootstrapping
10079 @subsubsection What you must do for the stub
10081 @cindex remote stub, support routines
10082 The debugging stubs that come with @value{GDBN} are set up for a particular
10083 chip architecture, but they have no information about the rest of your
10084 debugging target machine.
10086 First of all you need to tell the stub how to communicate with the
10090 @item int getDebugChar()
10091 @kindex getDebugChar
10092 Write this subroutine to read a single character from the serial port.
10093 It may be identical to @code{getchar} for your target system; a
10094 different name is used to allow you to distinguish the two if you wish.
10096 @item void putDebugChar(int)
10097 @kindex putDebugChar
10098 Write this subroutine to write a single character to the serial port.
10099 It may be identical to @code{putchar} for your target system; a
10100 different name is used to allow you to distinguish the two if you wish.
10103 @cindex control C, and remote debugging
10104 @cindex interrupting remote targets
10105 If you want @value{GDBN} to be able to stop your program while it is
10106 running, you need to use an interrupt-driven serial driver, and arrange
10107 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10108 character). That is the character which @value{GDBN} uses to tell the
10109 remote system to stop.
10111 Getting the debugging target to return the proper status to @value{GDBN}
10112 probably requires changes to the standard stub; one quick and dirty way
10113 is to just execute a breakpoint instruction (the ``dirty'' part is that
10114 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10116 Other routines you need to supply are:
10119 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10120 @kindex exceptionHandler
10121 Write this function to install @var{exception_address} in the exception
10122 handling tables. You need to do this because the stub does not have any
10123 way of knowing what the exception handling tables on your target system
10124 are like (for example, the processor's table might be in @sc{rom},
10125 containing entries which point to a table in @sc{ram}).
10126 @var{exception_number} is the exception number which should be changed;
10127 its meaning is architecture-dependent (for example, different numbers
10128 might represent divide by zero, misaligned access, etc). When this
10129 exception occurs, control should be transferred directly to
10130 @var{exception_address}, and the processor state (stack, registers,
10131 and so on) should be just as it is when a processor exception occurs. So if
10132 you want to use a jump instruction to reach @var{exception_address}, it
10133 should be a simple jump, not a jump to subroutine.
10135 For the 386, @var{exception_address} should be installed as an interrupt
10136 gate so that interrupts are masked while the handler runs. The gate
10137 should be at privilege level 0 (the most privileged level). The
10138 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10139 help from @code{exceptionHandler}.
10141 @item void flush_i_cache()
10142 @kindex flush_i_cache
10143 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10144 instruction cache, if any, on your target machine. If there is no
10145 instruction cache, this subroutine may be a no-op.
10147 On target machines that have instruction caches, @value{GDBN} requires this
10148 function to make certain that the state of your program is stable.
10152 You must also make sure this library routine is available:
10155 @item void *memset(void *, int, int)
10157 This is the standard library function @code{memset} that sets an area of
10158 memory to a known value. If you have one of the free versions of
10159 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10160 either obtain it from your hardware manufacturer, or write your own.
10163 If you do not use the GNU C compiler, you may need other standard
10164 library subroutines as well; this varies from one stub to another,
10165 but in general the stubs are likely to use any of the common library
10166 subroutines which @code{@value{GCC}} generates as inline code.
10169 @node Debug Session
10170 @subsubsection Putting it all together
10172 @cindex remote serial debugging summary
10173 In summary, when your program is ready to debug, you must follow these
10178 Make sure you have defined the supporting low-level routines
10179 (@pxref{Bootstrapping,,What you must do for the stub}):
10181 @code{getDebugChar}, @code{putDebugChar},
10182 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10186 Insert these lines near the top of your program:
10194 For the 680x0 stub only, you need to provide a variable called
10195 @code{exceptionHook}. Normally you just use:
10198 void (*exceptionHook)() = 0;
10202 but if before calling @code{set_debug_traps}, you set it to point to a
10203 function in your program, that function is called when
10204 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10205 error). The function indicated by @code{exceptionHook} is called with
10206 one parameter: an @code{int} which is the exception number.
10209 Compile and link together: your program, the @value{GDBN} debugging stub for
10210 your target architecture, and the supporting subroutines.
10213 Make sure you have a serial connection between your target machine and
10214 the @value{GDBN} host, and identify the serial port on the host.
10217 @c The "remote" target now provides a `load' command, so we should
10218 @c document that. FIXME.
10219 Download your program to your target machine (or get it there by
10220 whatever means the manufacturer provides), and start it.
10223 To start remote debugging, run @value{GDBN} on the host machine, and specify
10224 as an executable file the program that is running in the remote machine.
10225 This tells @value{GDBN} how to find your program's symbols and the contents
10229 @cindex serial line, @code{target remote}
10230 Establish communication using the @code{target remote} command.
10231 Its argument specifies how to communicate with the target
10232 machine---either via a devicename attached to a direct serial line, or a
10233 TCP port (usually to a terminal server which in turn has a serial line
10234 to the target). For example, to use a serial line connected to the
10235 device named @file{/dev/ttyb}:
10238 target remote /dev/ttyb
10241 @cindex TCP port, @code{target remote}
10242 To use a TCP connection, use an argument of the form
10243 @code{@var{host}:port}. For example, to connect to port 2828 on a
10244 terminal server named @code{manyfarms}:
10247 target remote manyfarms:2828
10250 If your remote target is actually running on the same machine as
10251 your debugger session (e.g.@: a simulator of your target running on
10252 the same host), you can omit the hostname. For example, to connect
10253 to port 1234 on your local machine:
10256 target remote :1234
10260 Note that the colon is still required here.
10263 Now you can use all the usual commands to examine and change data and to
10264 step and continue the remote program.
10266 To resume the remote program and stop debugging it, use the @code{detach}
10269 @cindex interrupting remote programs
10270 @cindex remote programs, interrupting
10271 Whenever @value{GDBN} is waiting for the remote program, if you type the
10272 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10273 program. This may or may not succeed, depending in part on the hardware
10274 and the serial drivers the remote system uses. If you type the
10275 interrupt character once again, @value{GDBN} displays this prompt:
10278 Interrupted while waiting for the program.
10279 Give up (and stop debugging it)? (y or n)
10282 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10283 (If you decide you want to try again later, you can use @samp{target
10284 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10285 goes back to waiting.
10288 @subsubsection Communication protocol
10290 @cindex debugging stub, example
10291 @cindex remote stub, example
10292 @cindex stub example, remote debugging
10293 The stub files provided with @value{GDBN} implement the target side of the
10294 communication protocol, and the @value{GDBN} side is implemented in the
10295 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10296 these subroutines to communicate, and ignore the details. (If you're
10297 implementing your own stub file, you can still ignore the details: start
10298 with one of the existing stub files. @file{sparc-stub.c} is the best
10299 organized, and therefore the easiest to read.)
10301 However, there may be occasions when you need to know something about
10302 the protocol---for example, if there is only one serial port to your
10303 target machine, you might want your program to do something special if
10304 it recognizes a packet meant for @value{GDBN}.
10306 In the examples below, @samp{<-} and @samp{->} are used to indicate
10307 transmitted and received data respectfully.
10309 @cindex protocol, @value{GDBN} remote serial
10310 @cindex serial protocol, @value{GDBN} remote
10311 @cindex remote serial protocol
10312 All @value{GDBN} commands and responses (other than acknowledgments) are
10313 sent as a @var{packet}. A @var{packet} is introduced with the character
10314 @samp{$}, the actual @var{packet-data}, and the terminating character
10315 @samp{#} followed by a two-digit @var{checksum}:
10318 @code{$}@var{packet-data}@code{#}@var{checksum}
10322 @cindex checksum, for @value{GDBN} remote
10324 The two-digit @var{checksum} is computed as the modulo 256 sum of all
10325 characters between the leading @samp{$} and the trailing @samp{#} (an
10326 eight bit unsigned checksum).
10328 Implementors should note that prior to @value{GDBN} 5.0 the protocol
10329 specification also included an optional two-digit @var{sequence-id}:
10332 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
10335 @cindex sequence-id, for @value{GDBN} remote
10337 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
10338 has never output @var{sequence-id}s. Stubs that handle packets added
10339 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
10341 @cindex acknowledgment, for @value{GDBN} remote
10342 When either the host or the target machine receives a packet, the first
10343 response expected is an acknowledgment: either @samp{+} (to indicate
10344 the package was received correctly) or @samp{-} (to request
10348 <- @code{$}@var{packet-data}@code{#}@var{checksum}
10353 The host (@value{GDBN}) sends @var{command}s, and the target (the
10354 debugging stub incorporated in your program) sends a @var{response}. In
10355 the case of step and continue @var{command}s, the response is only sent
10356 when the operation has completed (the target has again stopped).
10358 @var{packet-data} consists of a sequence of characters with the
10359 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
10362 Fields within the packet should be separated using @samp{,} @samp{;} or
10363 @samp{:}. Except where otherwise noted all numbers are represented in
10364 HEX with leading zeros suppressed.
10366 Implementors should note that prior to @value{GDBN} 5.0, the character
10367 @samp{:} could not appear as the third character in a packet (as it
10368 would potentially conflict with the @var{sequence-id}).
10370 Response @var{data} can be run-length encoded to save space. A @samp{*}
10371 means that the next character is an @sc{ascii} encoding giving a repeat count
10372 which stands for that many repetitions of the character preceding the
10373 @samp{*}. The encoding is @code{n+29}, yielding a printable character
10374 where @code{n >=3} (which is where rle starts to win). The printable
10375 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
10376 value greater than 126 should not be used.
10378 Some remote systems have used a different run-length encoding mechanism
10379 loosely refered to as the cisco encoding. Following the @samp{*}
10380 character are two hex digits that indicate the size of the packet.
10387 means the same as "0000".
10389 The error response returned for some packets includes a two character
10390 error number. That number is not well defined.
10392 For any @var{command} not supported by the stub, an empty response
10393 (@samp{$#00}) should be returned. That way it is possible to extend the
10394 protocol. A newer @value{GDBN} can tell if a packet is supported based
10397 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
10398 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
10401 Below is a complete list of all currently defined @var{command}s and
10402 their corresponding response @var{data}:
10404 @multitable @columnfractions .30 .30 .40
10409 @item extended mode
10412 Enable extended mode. In extended mode, the remote server is made
10413 persistent. The @samp{R} packet is used to restart the program being
10416 @tab reply @samp{OK}
10418 The remote target both supports and has enabled extended mode.
10423 Indicate the reason the target halted. The reply is the same as for step
10432 @tab Reserved for future use
10434 @item set program arguments @strong{(reserved)}
10435 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
10440 Initialized @samp{argv[]} array passed into program. @var{arglen}
10441 specifies the number of bytes in the hex encoded byte stream @var{arg}.
10442 See @file{gdbserver} for more details.
10444 @tab reply @code{OK}
10446 @tab reply @code{E}@var{NN}
10448 @item set baud @strong{(deprecated)}
10449 @tab @code{b}@var{baud}
10451 Change the serial line speed to @var{baud}. JTC: @emph{When does the
10452 transport layer state change? When it's received, or after the ACK is
10453 transmitted. In either case, there are problems if the command or the
10454 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
10455 to add something like this, and get it working for the first time, they
10456 ought to modify ser-unix.c to send some kind of out-of-band message to a
10457 specially-setup stub and have the switch happen "in between" packets, so
10458 that from remote protocol's point of view, nothing actually
10461 @item set breakpoint @strong{(deprecated)}
10462 @tab @code{B}@var{addr},@var{mode}
10464 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
10465 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
10469 @tab @code{c}@var{addr}
10471 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10477 @item continue with signal
10478 @tab @code{C}@var{sig}@code{;}@var{addr}
10480 Continue with signal @var{sig} (hex signal number). If
10481 @code{;}@var{addr} is omitted, resume at same address.
10486 @item toggle debug @strong{(deprecated)}
10494 Detach @value{GDBN} from the remote system. Sent to the remote target before
10495 @value{GDBN} disconnects.
10497 @tab reply @emph{no response}
10499 @value{GDBN} does not check for any response after sending this packet.
10503 @tab Reserved for future use
10507 @tab Reserved for future use
10511 @tab Reserved for future use
10515 @tab Reserved for future use
10517 @item read registers
10519 @tab Read general registers.
10521 @tab reply @var{XX...}
10523 Each byte of register data is described by two hex digits. The bytes
10524 with the register are transmitted in target byte order. The size of
10525 each register and their position within the @samp{g} @var{packet} are
10526 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
10527 @var{REGISTER_NAME} macros. The specification of several standard
10528 @code{g} packets is specified below.
10530 @tab @code{E}@var{NN}
10534 @tab @code{G}@var{XX...}
10536 See @samp{g} for a description of the @var{XX...} data.
10538 @tab reply @code{OK}
10541 @tab reply @code{E}@var{NN}
10546 @tab Reserved for future use
10549 @tab @code{H}@var{c}@var{t...}
10551 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
10552 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
10553 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
10554 thread used in other operations. If zero, pick a thread, any thread.
10556 @tab reply @code{OK}
10559 @tab reply @code{E}@var{NN}
10563 @c 'H': How restrictive (or permissive) is the thread model. If a
10564 @c thread is selected and stopped, are other threads allowed
10565 @c to continue to execute? As I mentioned above, I think the
10566 @c semantics of each command when a thread is selected must be
10567 @c described. For example:
10569 @c 'g': If the stub supports threads and a specific thread is
10570 @c selected, returns the register block from that thread;
10571 @c otherwise returns current registers.
10573 @c 'G' If the stub supports threads and a specific thread is
10574 @c selected, sets the registers of the register block of
10575 @c that thread; otherwise sets current registers.
10577 @item cycle step @strong{(draft)}
10578 @tab @code{i}@var{addr}@code{,}@var{nnn}
10580 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
10581 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
10582 step starting at that address.
10584 @item signal then cycle step @strong{(reserved)}
10587 See @samp{i} and @samp{S} for likely syntax and semantics.
10591 @tab Reserved for future use
10595 @tab Reserved for future use
10600 FIXME: @emph{There is no description of how operate when a specific
10601 thread context has been selected (ie. does 'k' kill only that thread?)}.
10605 @tab Reserved for future use
10609 @tab Reserved for future use
10612 @tab @code{m}@var{addr}@code{,}@var{length}
10614 Read @var{length} bytes of memory starting at address @var{addr}.
10615 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
10616 using word alligned accesses. FIXME: @emph{A word aligned memory
10617 transfer mechanism is needed.}
10619 @tab reply @var{XX...}
10621 @var{XX...} is mem contents. Can be fewer bytes than requested if able
10622 to read only part of the data. Neither @value{GDBN} nor the stub assume that
10623 sized memory transfers are assumed using word alligned accesses. FIXME:
10624 @emph{A word aligned memory transfer mechanism is needed.}
10626 @tab reply @code{E}@var{NN}
10627 @tab @var{NN} is errno
10630 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
10632 Write @var{length} bytes of memory starting at address @var{addr}.
10633 @var{XX...} is the data.
10635 @tab reply @code{OK}
10638 @tab reply @code{E}@var{NN}
10640 for an error (this includes the case where only part of the data was
10645 @tab Reserved for future use
10649 @tab Reserved for future use
10653 @tab Reserved for future use
10657 @tab Reserved for future use
10659 @item read reg @strong{(reserved)}
10660 @tab @code{p}@var{n...}
10662 See write register.
10664 @tab return @var{r....}
10665 @tab The hex encoded value of the register in target byte order.
10668 @tab @code{P}@var{n...}@code{=}@var{r...}
10670 Write register @var{n...} with value @var{r...}, which contains two hex
10671 digits for each byte in the register (target byte order).
10673 @tab reply @code{OK}
10676 @tab reply @code{E}@var{NN}
10679 @item general query
10680 @tab @code{q}@var{query}
10682 Request info about @var{query}. In general @value{GDBN} queries
10683 have a leading upper case letter. Custom vendor queries should use a
10684 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10685 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10686 must ensure that they match the full @var{query} name.
10688 @tab reply @code{XX...}
10689 @tab Hex encoded data from query. The reply can not be empty.
10691 @tab reply @code{E}@var{NN}
10695 @tab Indicating an unrecognized @var{query}.
10698 @tab @code{Q}@var{var}@code{=}@var{val}
10700 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10701 naming conventions.
10703 @item reset @strong{(deprecated)}
10706 Reset the entire system.
10708 @item remote restart
10709 @tab @code{R}@var{XX}
10711 Restart the program being debugged. @var{XX}, while needed, is ignored.
10712 This packet is only available in extended mode.
10717 The @samp{R} packet has no reply.
10720 @tab @code{s}@var{addr}
10722 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10728 @item step with signal
10729 @tab @code{S}@var{sig}@code{;}@var{addr}
10731 Like @samp{C} but step not continue.
10737 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10739 Search backwards starting at address @var{addr} for a match with pattern
10740 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10741 bytes. @var{addr} must be at least 3 digits.
10744 @tab @code{T}@var{XX}
10745 @tab Find out if the thread XX is alive.
10747 @tab reply @code{OK}
10748 @tab thread is still alive
10750 @tab reply @code{E}@var{NN}
10751 @tab thread is dead
10755 @tab Reserved for future use
10759 @tab Reserved for future use
10763 @tab Reserved for future use
10767 @tab Reserved for future use
10771 @tab Reserved for future use
10775 @tab Reserved for future use
10779 @tab Reserved for future use
10781 @item write mem (binary)
10782 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10784 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10785 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10786 escaped using @code{0x7d}.
10788 @tab reply @code{OK}
10791 @tab reply @code{E}@var{NN}
10796 @tab Reserved for future use
10800 @tab Reserved for future use
10802 @item remove break or watchpoint @strong{(draft)}
10803 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10807 @item insert break or watchpoint @strong{(draft)}
10808 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10810 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10811 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10812 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10813 bytes. For a software breakpoint, @var{length} specifies the size of
10814 the instruction to be patched. For hardware breakpoints and watchpoints
10815 @var{length} specifies the memory region to be monitored. To avoid
10816 potential problems with duplicate packets, the operations should be
10817 implemented in an idempotent way.
10819 @tab reply @code{E}@var{NN}
10822 @tab reply @code{OK}
10826 @tab If not supported.
10830 @tab Reserved for future use
10834 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10835 receive any of the below as a reply. In the case of the @samp{C},
10836 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10837 when the target halts. In the below the exact meaning of @samp{signal
10838 number} is poorly defined. In general one of the UNIX signal numbering
10839 conventions is used.
10841 @multitable @columnfractions .4 .6
10843 @item @code{S}@var{AA}
10844 @tab @var{AA} is the signal number
10846 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10848 @var{AA} = two hex digit signal number; @var{n...} = register number
10849 (hex), @var{r...} = target byte ordered register contents, size defined
10850 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10851 thread process ID, this is a hex integer; @var{n...} = other string not
10852 starting with valid hex digit. @value{GDBN} should ignore this
10853 @var{n...}, @var{r...} pair and go on to the next. This way we can
10854 extend the protocol.
10856 @item @code{W}@var{AA}
10858 The process exited, and @var{AA} is the exit status. This is only
10859 applicable for certains sorts of targets.
10861 @item @code{X}@var{AA}
10863 The process terminated with signal @var{AA}.
10865 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10867 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10868 @var{d...} = base of data section; @var{b...} = base of bss section.
10869 @emph{Note: only used by Cisco Systems targets. The difference between
10870 this reply and the "qOffsets" query is that the 'N' packet may arrive
10871 spontaneously whereas the 'qOffsets' is a query initiated by the host
10874 @item @code{O}@var{XX...}
10876 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10877 while the program is running and the debugger should continue to wait
10882 The following set and query packets have already been defined.
10884 @multitable @columnfractions .2 .2 .6
10886 @item current thread
10887 @tab @code{q}@code{C}
10888 @tab Return the current thread id.
10890 @tab reply @code{QC}@var{pid}
10892 Where @var{pid} is a HEX encoded 16 bit process id.
10895 @tab Any other reply implies the old pid.
10897 @item all thread ids
10898 @tab @code{q}@code{fThreadInfo}
10900 @tab @code{q}@code{sThreadInfo}
10902 Obtain a list of active thread ids from the target (OS). Since there
10903 may be too many active threads to fit into one reply packet, this query
10904 works iteratively: it may require more than one query/reply sequence to
10905 obtain the entire list of threads. The first query of the sequence will
10906 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10907 sequence will be the @code{qs}@code{ThreadInfo} query.
10910 @tab NOTE: replaces the @code{qL} query (see below).
10912 @tab reply @code{m}@var{<id>}
10913 @tab A single thread id
10915 @tab reply @code{m}@var{<id>},@var{<id>...}
10916 @tab a comma-separated list of thread ids
10918 @tab reply @code{l}
10919 @tab (lower case 'el') denotes end of list.
10923 In response to each query, the target will reply with a list of one
10924 or more thread ids, in big-endian hex, separated by commas. GDB will
10925 respond to each reply with a request for more thread ids (using the
10926 @code{qs} form of the query), until the target responds with @code{l}
10927 (lower-case el, for @code{'last'}).
10929 @item extra thread info
10930 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10935 Where @var{<id>} is a thread-id in big-endian hex.
10936 Obtain a printable string description of a thread's attributes from
10937 the target OS. This string may contain anything that the target OS
10938 thinks is interesting for @value{GDBN} to tell the user about the thread.
10939 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10940 Some examples of possible thread extra info strings are "Runnable", or
10941 "Blocked on Mutex".
10943 @tab reply @var{XX...}
10945 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10946 printable string containing the extra information about the thread's
10949 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10950 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10955 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10956 digit) is one to indicate the first query and zero to indicate a
10957 subsequent query; @var{threadcount} (two hex digits) is the maximum
10958 number of threads the response packet can contain; and @var{nextthread}
10959 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10960 returned in the response as @var{argthread}.
10963 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10966 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10971 Where: @var{count} (two hex digits) is the number of threads being
10972 returned; @var{done} (one hex digit) is zero to indicate more threads
10973 and one indicates no further threads; @var{argthreadid} (eight hex
10974 digits) is @var{nextthread} from the request packet; @var{thread...} is
10975 a sequence of thread IDs from the target. @var{threadid} (eight hex
10976 digits). See @code{remote.c:parse_threadlist_response()}.
10978 @item compute CRC of memory block
10979 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10982 @tab reply @code{E}@var{NN}
10983 @tab An error (such as memory fault)
10985 @tab reply @code{C}@var{CRC32}
10986 @tab A 32 bit cyclic redundancy check of the specified memory region.
10988 @item query sect offs
10989 @tab @code{q}@code{Offsets}
10991 Get section offsets that the target used when re-locating the downloaded
10992 image. @emph{Note: while a @code{Bss} offset is included in the
10993 response, @value{GDBN} ignores this and instead applies the @code{Data}
10994 offset to the @code{Bss} section.}
10996 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
10998 @item thread info request
10999 @tab @code{q}@code{P}@var{mode}@var{threadid}
11004 Returns information on @var{threadid}. Where: @var{mode} is a hex
11005 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
11009 See @code{remote.c:remote_unpack_thread_info_response()}.
11011 @item remote command
11012 @tab @code{q}@code{Rcmd,}@var{COMMAND}
11017 @var{COMMAND} (hex encoded) is passed to the local interpreter for
11018 execution. Invalid commands should be reported using the output string.
11019 Before the final result packet, the target may also respond with a
11020 number of intermediate @code{O}@var{OUTPUT} console output
11021 packets. @emph{Implementors should note that providing access to a
11022 stubs's interpreter may have security implications}.
11024 @tab reply @code{OK}
11026 A command response with no output.
11028 @tab reply @var{OUTPUT}
11030 A command response with the hex encoded output string @var{OUTPUT}.
11032 @tab reply @code{E}@var{NN}
11034 Indicate a badly formed request.
11039 When @samp{q}@samp{Rcmd} is not recognized.
11041 @item symbol lookup
11042 @tab @code{qSymbol::}
11044 Notify the target that @value{GDBN} is prepared to serve symbol lookup
11045 requests. Accept requests from the target for the values of symbols.
11050 @tab reply @code{OK}
11052 The target does not need to look up any (more) symbols.
11054 @tab reply @code{qSymbol:}@var{sym_name}
11056 The target requests the value of symbol @var{sym_name} (hex encoded).
11057 @value{GDBN} may provide the value by using the
11058 @code{qSymbol:}@var{sym_value}:@var{sym_name}
11059 message, described below.
11062 @tab @code{qSymbol:}@var{sym_value}:@var{sym_name}
11064 Set the value of SYM_NAME to SYM_VALUE.
11068 @var{sym_name} (hex encoded) is the name of a symbol whose value
11069 the target has previously requested.
11073 @var{sym_value} (hex) is the value for symbol @var{sym_name}.
11074 If @value{GDBN} cannot supply a value for @var{sym_name}, then this
11075 field will be empty.
11077 @tab reply @code{OK}
11079 The target does not need to look up any (more) symbols.
11081 @tab reply @code{qSymbol:}@var{sym_name}
11083 The target requests the value of a new symbol @var{sym_name} (hex encoded).
11084 @value{GDBN} will continue to supply the values of symbols (if available),
11085 until the target ceases to request them.
11089 The following @samp{g}/@samp{G} packets have previously been defined.
11090 In the below, some thirty-two bit registers are transferred as sixty-four
11091 bits. Those registers should be zero/sign extended (which?) to fill the
11092 space allocated. Register bytes are transfered in target byte order.
11093 The two nibbles within a register byte are transfered most-significant -
11096 @multitable @columnfractions .5 .5
11100 All registers are transfered as thirty-two bit quantities in the order:
11101 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
11102 registers; fsr; fir; fp.
11106 All registers are transfered as sixty-four bit quantities (including
11107 thirty-two bit registers such as @code{sr}). The ordering is the same
11112 Example sequence of a target being re-started. Notice how the restart
11113 does not get any direct output:
11118 @emph{target restarts}
11121 -> @code{T001:1234123412341234}
11125 Example sequence of a target being stepped by a single instruction:
11133 -> @code{T001:1234123412341234}
11142 @subsubsection Using the @code{gdbserver} program
11145 @cindex remote connection without stubs
11146 @code{gdbserver} is a control program for Unix-like systems, which
11147 allows you to connect your program with a remote @value{GDBN} via
11148 @code{target remote}---but without linking in the usual debugging stub.
11150 @code{gdbserver} is not a complete replacement for the debugging stubs,
11151 because it requires essentially the same operating-system facilities
11152 that @value{GDBN} itself does. In fact, a system that can run
11153 @code{gdbserver} to connect to a remote @value{GDBN} could also run
11154 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
11155 because it is a much smaller program than @value{GDBN} itself. It is
11156 also easier to port than all of @value{GDBN}, so you may be able to get
11157 started more quickly on a new system by using @code{gdbserver}.
11158 Finally, if you develop code for real-time systems, you may find that
11159 the tradeoffs involved in real-time operation make it more convenient to
11160 do as much development work as possible on another system, for example
11161 by cross-compiling. You can use @code{gdbserver} to make a similar
11162 choice for debugging.
11164 @value{GDBN} and @code{gdbserver} communicate via either a serial line
11165 or a TCP connection, using the standard @value{GDBN} remote serial
11169 @item On the target machine,
11170 you need to have a copy of the program you want to debug.
11171 @code{gdbserver} does not need your program's symbol table, so you can
11172 strip the program if necessary to save space. @value{GDBN} on the host
11173 system does all the symbol handling.
11175 To use the server, you must tell it how to communicate with @value{GDBN};
11176 the name of your program; and the arguments for your program. The
11180 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
11183 @var{comm} is either a device name (to use a serial line) or a TCP
11184 hostname and portnumber. For example, to debug Emacs with the argument
11185 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
11189 target> gdbserver /dev/com1 emacs foo.txt
11192 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
11195 To use a TCP connection instead of a serial line:
11198 target> gdbserver host:2345 emacs foo.txt
11201 The only difference from the previous example is the first argument,
11202 specifying that you are communicating with the host @value{GDBN} via
11203 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
11204 expect a TCP connection from machine @samp{host} to local TCP port 2345.
11205 (Currently, the @samp{host} part is ignored.) You can choose any number
11206 you want for the port number as long as it does not conflict with any
11207 TCP ports already in use on the target system (for example, @code{23} is
11208 reserved for @code{telnet}).@footnote{If you choose a port number that
11209 conflicts with another service, @code{gdbserver} prints an error message
11210 and exits.} You must use the same port number with the host @value{GDBN}
11211 @code{target remote} command.
11213 @item On the @value{GDBN} host machine,
11214 you need an unstripped copy of your program, since @value{GDBN} needs
11215 symbols and debugging information. Start up @value{GDBN} as usual,
11216 using the name of the local copy of your program as the first argument.
11217 (You may also need the @w{@samp{--baud}} option if the serial line is
11218 running at anything other than 9600@dmn{bps}.) After that, use @code{target
11219 remote} to establish communications with @code{gdbserver}. Its argument
11220 is either a device name (usually a serial device, like
11221 @file{/dev/ttyb}), or a TCP port descriptor in the form
11222 @code{@var{host}:@var{PORT}}. For example:
11225 (@value{GDBP}) target remote /dev/ttyb
11229 communicates with the server via serial line @file{/dev/ttyb}, and
11232 (@value{GDBP}) target remote the-target:2345
11236 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
11237 For TCP connections, you must start up @code{gdbserver} prior to using
11238 the @code{target remote} command. Otherwise you may get an error whose
11239 text depends on the host system, but which usually looks something like
11240 @samp{Connection refused}.
11244 @subsubsection Using the @code{gdbserve.nlm} program
11246 @kindex gdbserve.nlm
11247 @code{gdbserve.nlm} is a control program for NetWare systems, which
11248 allows you to connect your program with a remote @value{GDBN} via
11249 @code{target remote}.
11251 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
11252 using the standard @value{GDBN} remote serial protocol.
11255 @item On the target machine,
11256 you need to have a copy of the program you want to debug.
11257 @code{gdbserve.nlm} does not need your program's symbol table, so you
11258 can strip the program if necessary to save space. @value{GDBN} on the
11259 host system does all the symbol handling.
11261 To use the server, you must tell it how to communicate with
11262 @value{GDBN}; the name of your program; and the arguments for your
11263 program. The syntax is:
11266 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
11267 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
11270 @var{board} and @var{port} specify the serial line; @var{baud} specifies
11271 the baud rate used by the connection. @var{port} and @var{node} default
11272 to 0, @var{baud} defaults to 9600@dmn{bps}.
11274 For example, to debug Emacs with the argument @samp{foo.txt}and
11275 communicate with @value{GDBN} over serial port number 2 or board 1
11276 using a 19200@dmn{bps} connection:
11279 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
11282 @item On the @value{GDBN} host machine,
11283 you need an unstripped copy of your program, since @value{GDBN} needs
11284 symbols and debugging information. Start up @value{GDBN} as usual,
11285 using the name of the local copy of your program as the first argument.
11286 (You may also need the @w{@samp{--baud}} option if the serial line is
11287 running at anything other than 9600@dmn{bps}. After that, use @code{target
11288 remote} to establish communications with @code{gdbserve.nlm}. Its
11289 argument is a device name (usually a serial device, like
11290 @file{/dev/ttyb}). For example:
11293 (@value{GDBP}) target remote /dev/ttyb
11297 communications with the server via serial line @file{/dev/ttyb}.
11301 @section Kernel Object Display
11303 @cindex kernel object display
11304 @cindex kernel object
11307 Some targets support kernel object display. Using this facility,
11308 @value{GDBN} communicates specially with the underlying operating system
11309 and can display information about operating system-level objects such as
11310 mutexes and other synchronization objects. Exactly which objects can be
11311 displayed is determined on a per-OS basis.
11313 Use the @code{set os} command to set the operating system. This tells
11314 @value{GDBN} which kernel object display module to initialize:
11317 (@value{GDBP}) set os cisco
11320 If @code{set os} succeeds, @value{GDBN} will display some information
11321 about the operating system, and will create a new @code{info} command
11322 which can be used to query the target. The @code{info} command is named
11323 after the operating system:
11326 (@value{GDBP}) info cisco
11327 List of Cisco Kernel Objects
11329 any Any and all objects
11332 Further subcommands can be used to query about particular objects known
11335 There is currently no way to determine whether a given operating system
11336 is supported other than to try it.
11339 @node Configurations
11340 @chapter Configuration-Specific Information
11342 While nearly all @value{GDBN} commands are available for all native and
11343 cross versions of the debugger, there are some exceptions. This chapter
11344 describes things that are only available in certain configurations.
11346 There are three major categories of configurations: native
11347 configurations, where the host and target are the same, embedded
11348 operating system configurations, which are usually the same for several
11349 different processor architectures, and bare embedded processors, which
11350 are quite different from each other.
11355 * Embedded Processors::
11362 This section describes details specific to particular native
11367 * SVR4 Process Information:: SVR4 process information
11368 * DJGPP Native:: Features specific to the DJGPP port
11374 On HP-UX systems, if you refer to a function or variable name that
11375 begins with a dollar sign, @value{GDBN} searches for a user or system
11376 name first, before it searches for a convenience variable.
11378 @node SVR4 Process Information
11379 @subsection SVR4 process information
11382 @cindex process image
11384 Many versions of SVR4 provide a facility called @samp{/proc} that can be
11385 used to examine the image of a running process using file-system
11386 subroutines. If @value{GDBN} is configured for an operating system with
11387 this facility, the command @code{info proc} is available to report on
11388 several kinds of information about the process running your program.
11389 @code{info proc} works only on SVR4 systems that include the
11390 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
11391 and Unixware, but not HP-UX or Linux, for example.
11396 Summarize available information about the process.
11398 @kindex info proc mappings
11399 @item info proc mappings
11400 Report on the address ranges accessible in the program, with information
11401 on whether your program may read, write, or execute each range.
11403 @comment These sub-options of 'info proc' were not included when
11404 @comment procfs.c was re-written. Keep their descriptions around
11405 @comment against the day when someone finds the time to put them back in.
11406 @kindex info proc times
11407 @item info proc times
11408 Starting time, user CPU time, and system CPU time for your program and
11411 @kindex info proc id
11413 Report on the process IDs related to your program: its own process ID,
11414 the ID of its parent, the process group ID, and the session ID.
11416 @kindex info proc status
11417 @item info proc status
11418 General information on the state of the process. If the process is
11419 stopped, this report includes the reason for stopping, and any signal
11422 @item info proc all
11423 Show all the above information about the process.
11428 @subsection Features for Debugging @sc{djgpp} Programs
11429 @cindex @sc{djgpp} debugging
11430 @cindex native @sc{djgpp} debugging
11431 @cindex MS-DOS-specific commands
11433 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
11434 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
11435 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
11436 top of real-mode DOS systems and their emulations.
11438 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
11439 defines a few commands specific to the @sc{djgpp} port. This
11440 subsection describes those commands.
11445 This is a prefix of @sc{djgpp}-specific commands which print
11446 information about the target system and important OS structures.
11449 @cindex MS-DOS system info
11450 @cindex free memory information (MS-DOS)
11451 @item info dos sysinfo
11452 This command displays assorted information about the underlying
11453 platform: the CPU type and features, the OS version and flavor, the
11454 DPMI version, and the available conventional and DPMI memory.
11459 @cindex segment descriptor tables
11460 @cindex descriptor tables display
11462 @itemx info dos ldt
11463 @itemx info dos idt
11464 These 3 commands display entries from, respectively, Global, Local,
11465 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
11466 tables are data structures which store a descriptor for each segment
11467 that is currently in use. The segment's selector is an index into a
11468 descriptor table; the table entry for that index holds the
11469 descriptor's base address and limit, and its attributes and access
11472 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
11473 segment (used for both data and the stack), and a DOS segment (which
11474 allows access to DOS/BIOS data structures and absolute addresses in
11475 conventional memory). However, the DPMI host will usually define
11476 additional segments in order to support the DPMI environment.
11478 @cindex garbled pointers
11479 These commands allow to display entries from the descriptor tables.
11480 Without an argument, all entries from the specified table are
11481 displayed. An argument, which should be an integer expression, means
11482 display a single entry whose index is given by the argument. For
11483 example, here's a convenient way to display information about the
11484 debugged program's data segment:
11487 (@value{GDBP}) info dos ldt $ds
11488 0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)
11492 This comes in handy when you want to see whether a pointer is outside
11493 the data segment's limit (i.e.@: @dfn{garbled}).
11495 @cindex page tables display (MS-DOS)
11497 @itemx info dos pte
11498 These two commands display entries from, respectively, the Page
11499 Directory and the Page Tables. Page Directories and Page Tables are
11500 data structures which control how virtual memory addresses are mapped
11501 into physical addresses. A Page Table includes an entry for every
11502 page of memory that is mapped into the program's address space; there
11503 may be several Page Tables, each one holding up to 4096 entries. A
11504 Page Directory has up to 4096 entries, one each for every Page Table
11505 that is currently in use.
11507 Without an argument, @kbd{info dos pde} displays the entire Page
11508 Directory, and @kbd{info dos pte} displays all the entries in all of
11509 the Page Tables. An argument, an integer expression, given to the
11510 @kbd{info dos pde} command means display only that entry from the Page
11511 Directory table. An argument given to the @kbd{info dos pte} command
11512 means display entries from a single Page Table, the one pointed to by
11513 the specified entry in the Page Directory.
11515 These commands are useful when your program uses @dfn{DMA} (Direct
11516 Memory Access), which needs physical addresses to program the DMA
11519 These commands are supported only with some DPMI servers.
11521 @cindex physical address from linear address
11522 @item info dos address-pte
11523 This command displays the Page Table entry for a specified linear
11524 address. The argument linear address should already have the
11525 appropriate segment's base address added to it, because this command
11526 accepts addresses which may belong to @emph{any} segment. For
11527 example, here's how to display the Page Table entry for the page where
11528 the variable @code{i} is stored:
11531 (@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i
11532 Page Table entry for address 0x11a00d30:
11533 Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30
11537 This says that @code{i} is stored at offset @code{0xd30} from the page
11538 whose physical base address is @code{0x02698000}, and prints all the
11539 attributes of that page.
11541 Note that you must cast the addresses of variables to a @code{char *},
11542 since otherwise the value of @code{__djgpp_base_address}, the base
11543 address of all variables and functions in a @sc{djgpp} program, will
11544 be added using the rules of C pointer arithmetics: if @code{i} is
11545 declared an @code{int}, @value{GDBN} will add 4 times the value of
11546 @code{__djgpp_base_address} to the address of @code{i}.
11548 Here's another example, it displays the Page Table entry for the
11552 (@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)
11553 Page Table entry for address 0x29110:
11554 Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110
11558 (The @code{+ 3} offset is because the transfer buffer's address is the
11559 3rd member of the @code{_go32_info_block} structure.) The output of
11560 this command clearly shows that addresses in conventional memory are
11561 mapped 1:1, i.e.@: the physical and linear addresses are identical.
11563 This command is supported only with some DPMI servers.
11567 @section Embedded Operating Systems
11569 This section describes configurations involving the debugging of
11570 embedded operating systems that are available for several different
11574 * VxWorks:: Using @value{GDBN} with VxWorks
11577 @value{GDBN} includes the ability to debug programs running on
11578 various real-time operating systems.
11581 @subsection Using @value{GDBN} with VxWorks
11587 @kindex target vxworks
11588 @item target vxworks @var{machinename}
11589 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11590 is the target system's machine name or IP address.
11594 On VxWorks, @code{load} links @var{filename} dynamically on the
11595 current target system as well as adding its symbols in @value{GDBN}.
11597 @value{GDBN} enables developers to spawn and debug tasks running on networked
11598 VxWorks targets from a Unix host. Already-running tasks spawned from
11599 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11600 both the Unix host and on the VxWorks target. The program
11601 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11602 installed with the name @code{vxgdb}, to distinguish it from a
11603 @value{GDBN} for debugging programs on the host itself.)
11606 @item VxWorks-timeout @var{args}
11607 @kindex vxworks-timeout
11608 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11609 This option is set by the user, and @var{args} represents the number of
11610 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11611 your VxWorks target is a slow software simulator or is on the far side
11612 of a thin network line.
11615 The following information on connecting to VxWorks was current when
11616 this manual was produced; newer releases of VxWorks may use revised
11619 @kindex INCLUDE_RDB
11620 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11621 to include the remote debugging interface routines in the VxWorks
11622 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11623 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11624 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11625 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11626 information on configuring and remaking VxWorks, see the manufacturer's
11628 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11630 Once you have included @file{rdb.a} in your VxWorks system image and set
11631 your Unix execution search path to find @value{GDBN}, you are ready to
11632 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11633 @code{vxgdb}, depending on your installation).
11635 @value{GDBN} comes up showing the prompt:
11642 * VxWorks Connection:: Connecting to VxWorks
11643 * VxWorks Download:: VxWorks download
11644 * VxWorks Attach:: Running tasks
11647 @node VxWorks Connection
11648 @subsubsection Connecting to VxWorks
11650 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11651 network. To connect to a target whose host name is ``@code{tt}'', type:
11654 (vxgdb) target vxworks tt
11658 @value{GDBN} displays messages like these:
11661 Attaching remote machine across net...
11666 @value{GDBN} then attempts to read the symbol tables of any object modules
11667 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11668 these files by searching the directories listed in the command search
11669 path (@pxref{Environment, ,Your program's environment}); if it fails
11670 to find an object file, it displays a message such as:
11673 prog.o: No such file or directory.
11676 When this happens, add the appropriate directory to the search path with
11677 the @value{GDBN} command @code{path}, and execute the @code{target}
11680 @node VxWorks Download
11681 @subsubsection VxWorks download
11683 @cindex download to VxWorks
11684 If you have connected to the VxWorks target and you want to debug an
11685 object that has not yet been loaded, you can use the @value{GDBN}
11686 @code{load} command to download a file from Unix to VxWorks
11687 incrementally. The object file given as an argument to the @code{load}
11688 command is actually opened twice: first by the VxWorks target in order
11689 to download the code, then by @value{GDBN} in order to read the symbol
11690 table. This can lead to problems if the current working directories on
11691 the two systems differ. If both systems have NFS mounted the same
11692 filesystems, you can avoid these problems by using absolute paths.
11693 Otherwise, it is simplest to set the working directory on both systems
11694 to the directory in which the object file resides, and then to reference
11695 the file by its name, without any path. For instance, a program
11696 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11697 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11698 program, type this on VxWorks:
11701 -> cd "@var{vxpath}/vw/demo/rdb"
11705 Then, in @value{GDBN}, type:
11708 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11709 (vxgdb) load prog.o
11712 @value{GDBN} displays a response similar to this:
11715 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11718 You can also use the @code{load} command to reload an object module
11719 after editing and recompiling the corresponding source file. Note that
11720 this makes @value{GDBN} delete all currently-defined breakpoints,
11721 auto-displays, and convenience variables, and to clear the value
11722 history. (This is necessary in order to preserve the integrity of
11723 debugger's data structures that reference the target system's symbol
11726 @node VxWorks Attach
11727 @subsubsection Running tasks
11729 @cindex running VxWorks tasks
11730 You can also attach to an existing task using the @code{attach} command as
11734 (vxgdb) attach @var{task}
11738 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11739 or suspended when you attach to it. Running tasks are suspended at
11740 the time of attachment.
11742 @node Embedded Processors
11743 @section Embedded Processors
11745 This section goes into details specific to particular embedded
11749 * A29K Embedded:: AMD A29K Embedded
11751 * H8/300:: Hitachi H8/300
11752 * H8/500:: Hitachi H8/500
11753 * i960:: Intel i960
11754 * M32R/D:: Mitsubishi M32R/D
11755 * M68K:: Motorola M68K
11756 * M88K:: Motorola M88K
11757 * MIPS Embedded:: MIPS Embedded
11758 * PA:: HP PA Embedded
11761 * Sparclet:: Tsqware Sparclet
11762 * Sparclite:: Fujitsu Sparclite
11763 * ST2000:: Tandem ST2000
11764 * Z8000:: Zilog Z8000
11767 @node A29K Embedded
11768 @subsection AMD A29K Embedded
11773 * Comms (EB29K):: Communications setup
11774 * gdb-EB29K:: EB29K cross-debugging
11775 * Remote Log:: Remote log
11780 @kindex target adapt
11781 @item target adapt @var{dev}
11782 Adapt monitor for A29K.
11784 @kindex target amd-eb
11785 @item target amd-eb @var{dev} @var{speed} @var{PROG}
11787 Remote PC-resident AMD EB29K board, attached over serial lines.
11788 @var{dev} is the serial device, as for @code{target remote};
11789 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
11790 name of the program to be debugged, as it appears to DOS on the PC.
11791 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
11796 @subsubsection A29K UDI
11799 @cindex AMD29K via UDI
11801 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
11802 protocol for debugging the a29k processor family. To use this
11803 configuration with AMD targets running the MiniMON monitor, you need the
11804 program @code{MONTIP}, available from AMD at no charge. You can also
11805 use @value{GDBN} with the UDI-conformant a29k simulator program
11806 @code{ISSTIP}, also available from AMD.
11809 @item target udi @var{keyword}
11811 Select the UDI interface to a remote a29k board or simulator, where
11812 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
11813 This file contains keyword entries which specify parameters used to
11814 connect to a29k targets. If the @file{udi_soc} file is not in your
11815 working directory, you must set the environment variable @samp{UDICONF}
11820 @subsubsection EBMON protocol for AMD29K
11822 @cindex EB29K board
11823 @cindex running 29K programs
11825 AMD distributes a 29K development board meant to fit in a PC, together
11826 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
11827 term, this development system is called the ``EB29K''. To use
11828 @value{GDBN} from a Unix system to run programs on the EB29K board, you
11829 must first connect a serial cable between the PC (which hosts the EB29K
11830 board) and a serial port on the Unix system. In the following, we
11831 assume you've hooked the cable between the PC's @file{COM1} port and
11832 @file{/dev/ttya} on the Unix system.
11834 @node Comms (EB29K)
11835 @subsubsection Communications setup
11837 The next step is to set up the PC's port, by doing something like this
11841 C:\> MODE com1:9600,n,8,1,none
11845 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11846 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11847 you must match the communications parameters when establishing the Unix
11848 end of the connection as well.
11849 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11850 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11852 @c It's optional, but it's unwise to omit it: who knows what is the
11853 @c default value set when the DOS machines boots? "No retry" means that
11854 @c the DOS serial device driver won't retry the operation if it fails;
11855 @c I understand that this is needed because the GDB serial protocol
11856 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11858 To give control of the PC to the Unix side of the serial line, type
11859 the following at the DOS console:
11866 (Later, if you wish to return control to the DOS console, you can use
11867 the command @code{CTTY con}---but you must send it over the device that
11868 had control, in our example over the @file{COM1} serial line.)
11870 From the Unix host, use a communications program such as @code{tip} or
11871 @code{cu} to communicate with the PC; for example,
11874 cu -s 9600 -l /dev/ttya
11878 The @code{cu} options shown specify, respectively, the linespeed and the
11879 serial port to use. If you use @code{tip} instead, your command line
11880 may look something like the following:
11883 tip -9600 /dev/ttya
11887 Your system may require a different name where we show
11888 @file{/dev/ttya} as the argument to @code{tip}. The communications
11889 parameters, including which port to use, are associated with the
11890 @code{tip} argument in the ``remote'' descriptions file---normally the
11891 system table @file{/etc/remote}.
11892 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11893 @c the DOS side's comms setup? cu can support -o (odd
11894 @c parity), -e (even parity)---apparently no settings for no parity or
11895 @c for character size. Taken from stty maybe...? John points out tip
11896 @c can set these as internal variables, eg ~s parity=none; man stty
11897 @c suggests that it *might* work to stty these options with stdin or
11898 @c stdout redirected... ---doc@cygnus.com, 25feb91
11900 @c There's nothing to be done for the "none" part of the DOS MODE
11901 @c command. The rest of the parameters should be matched by the
11902 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11905 Using the @code{tip} or @code{cu} connection, change the DOS working
11906 directory to the directory containing a copy of your 29K program, then
11907 start the PC program @code{EBMON} (an EB29K control program supplied
11908 with your board by AMD). You should see an initial display from
11909 @code{EBMON} similar to the one that follows, ending with the
11910 @code{EBMON} prompt @samp{#}---
11915 G:\> CD \usr\joe\work29k
11917 G:\USR\JOE\WORK29K> EBMON
11918 Am29000 PC Coprocessor Board Monitor, version 3.0-18
11919 Copyright 1990 Advanced Micro Devices, Inc.
11920 Written by Gibbons and Associates, Inc.
11922 Enter '?' or 'H' for help
11924 PC Coprocessor Type = EB29K
11926 Memory Base = 0xd0000
11928 Data Memory Size = 2048KB
11929 Available I-RAM Range = 0x8000 to 0x1fffff
11930 Available D-RAM Range = 0x80002000 to 0x801fffff
11933 Register Stack Size = 0x800
11934 Memory Stack Size = 0x1800
11937 Am29027 Available = No
11938 Byte Write Available = Yes
11943 Then exit the @code{cu} or @code{tip} program (done in the example by
11944 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11945 running, ready for @value{GDBN} to take over.
11947 For this example, we've assumed what is probably the most convenient
11948 way to make sure the same 29K program is on both the PC and the Unix
11949 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11950 PC as a file system on the Unix host. If you do not have PC/NFS or
11951 something similar connecting the two systems, you must arrange some
11952 other way---perhaps floppy-disk transfer---of getting the 29K program
11953 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11957 @subsubsection EB29K cross-debugging
11959 Finally, @code{cd} to the directory containing an image of your 29K
11960 program on the Unix system, and start @value{GDBN}---specifying as argument the
11961 name of your 29K program:
11964 cd /usr/joe/work29k
11969 Now you can use the @code{target} command:
11972 target amd-eb /dev/ttya 9600 MYFOO
11973 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11974 @c emphasize that this is the name as seen by DOS (since I think DOS is
11975 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11979 In this example, we've assumed your program is in a file called
11980 @file{myfoo}. Note that the filename given as the last argument to
11981 @code{target amd-eb} should be the name of the program as it appears to DOS.
11982 In our example this is simply @code{MYFOO}, but in general it can include
11983 a DOS path, and depending on your transfer mechanism may not resemble
11984 the name on the Unix side.
11986 At this point, you can set any breakpoints you wish; when you are ready
11987 to see your program run on the 29K board, use the @value{GDBN} command
11990 To stop debugging the remote program, use the @value{GDBN} @code{detach}
11993 To return control of the PC to its console, use @code{tip} or @code{cu}
11994 once again, after your @value{GDBN} session has concluded, to attach to
11995 @code{EBMON}. You can then type the command @code{q} to shut down
11996 @code{EBMON}, returning control to the DOS command-line interpreter.
11997 Type @kbd{CTTY con} to return command input to the main DOS console,
11998 and type @kbd{~.} to leave @code{tip} or @code{cu}.
12001 @subsubsection Remote log
12002 @cindex @file{eb.log}, a log file for EB29K
12003 @cindex log file for EB29K
12005 The @code{target amd-eb} command creates a file @file{eb.log} in the
12006 current working directory, to help debug problems with the connection.
12007 @file{eb.log} records all the output from @code{EBMON}, including echoes
12008 of the commands sent to it. Running @samp{tail -f} on this file in
12009 another window often helps to understand trouble with @code{EBMON}, or
12010 unexpected events on the PC side of the connection.
12018 @item target rdi @var{dev}
12019 ARM Angel monitor, via RDI library interface to ADP protocol. You may
12020 use this target to communicate with both boards running the Angel
12021 monitor, or with the EmbeddedICE JTAG debug device.
12024 @item target rdp @var{dev}
12030 @subsection Hitachi H8/300
12034 @kindex target hms@r{, with H8/300}
12035 @item target hms @var{dev}
12036 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
12037 Use special commands @code{device} and @code{speed} to control the serial
12038 line and the communications speed used.
12040 @kindex target e7000@r{, with H8/300}
12041 @item target e7000 @var{dev}
12042 E7000 emulator for Hitachi H8 and SH.
12044 @kindex target sh3@r{, with H8/300}
12045 @kindex target sh3e@r{, with H8/300}
12046 @item target sh3 @var{dev}
12047 @itemx target sh3e @var{dev}
12048 Hitachi SH-3 and SH-3E target systems.
12052 @cindex download to H8/300 or H8/500
12053 @cindex H8/300 or H8/500 download
12054 @cindex download to Hitachi SH
12055 @cindex Hitachi SH download
12056 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
12057 board, the @code{load} command downloads your program to the Hitachi
12058 board and also opens it as the current executable target for
12059 @value{GDBN} on your host (like the @code{file} command).
12061 @value{GDBN} needs to know these things to talk to your
12062 Hitachi SH, H8/300, or H8/500:
12066 that you want to use @samp{target hms}, the remote debugging interface
12067 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
12068 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
12069 the default when @value{GDBN} is configured specifically for the Hitachi SH,
12070 H8/300, or H8/500.)
12073 what serial device connects your host to your Hitachi board (the first
12074 serial device available on your host is the default).
12077 what speed to use over the serial device.
12081 * Hitachi Boards:: Connecting to Hitachi boards.
12082 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
12083 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
12086 @node Hitachi Boards
12087 @subsubsection Connecting to Hitachi boards
12089 @c only for Unix hosts
12091 @cindex serial device, Hitachi micros
12092 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
12093 need to explicitly set the serial device. The default @var{port} is the
12094 first available port on your host. This is only necessary on Unix
12095 hosts, where it is typically something like @file{/dev/ttya}.
12098 @cindex serial line speed, Hitachi micros
12099 @code{@value{GDBN}} has another special command to set the communications
12100 speed: @samp{speed @var{bps}}. This command also is only used from Unix
12101 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
12102 the DOS @code{mode} command (for instance,
12103 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
12105 The @samp{device} and @samp{speed} commands are available only when you
12106 use a Unix host to debug your Hitachi microprocessor programs. If you
12108 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
12109 called @code{asynctsr} to communicate with the development board
12110 through a PC serial port. You must also use the DOS @code{mode} command
12111 to set up the serial port on the DOS side.
12113 The following sample session illustrates the steps needed to start a
12114 program under @value{GDBN} control on an H8/300. The example uses a
12115 sample H8/300 program called @file{t.x}. The procedure is the same for
12116 the Hitachi SH and the H8/500.
12118 First hook up your development board. In this example, we use a
12119 board attached to serial port @code{COM2}; if you use a different serial
12120 port, substitute its name in the argument of the @code{mode} command.
12121 When you call @code{asynctsr}, the auxiliary comms program used by the
12122 debugger, you give it just the numeric part of the serial port's name;
12123 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
12127 C:\H8300\TEST> asynctsr 2
12128 C:\H8300\TEST> mode com2:9600,n,8,1,p
12130 Resident portion of MODE loaded
12132 COM2: 9600, n, 8, 1, p
12137 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
12138 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
12139 disable it, or even boot without it, to use @code{asynctsr} to control
12140 your development board.
12143 @kindex target hms@r{, and serial protocol}
12144 Now that serial communications are set up, and the development board is
12145 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
12146 the name of your program as the argument. @code{@value{GDBN}} prompts
12147 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
12148 commands to begin your debugging session: @samp{target hms} to specify
12149 cross-debugging to the Hitachi board, and the @code{load} command to
12150 download your program to the board. @code{load} displays the names of
12151 the program's sections, and a @samp{*} for each 2K of data downloaded.
12152 (If you want to refresh @value{GDBN} data on symbols or on the
12153 executable file without downloading, use the @value{GDBN} commands
12154 @code{file} or @code{symbol-file}. These commands, and @code{load}
12155 itself, are described in @ref{Files,,Commands to specify files}.)
12158 (eg-C:\H8300\TEST) @value{GDBP} t.x
12159 @value{GDBN} is free software and you are welcome to distribute copies
12160 of it under certain conditions; type "show copying" to see
12162 There is absolutely no warranty for @value{GDBN}; type "show warranty"
12164 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
12165 (@value{GDBP}) target hms
12166 Connected to remote H8/300 HMS system.
12167 (@value{GDBP}) load t.x
12168 .text : 0x8000 .. 0xabde ***********
12169 .data : 0xabde .. 0xad30 *
12170 .stack : 0xf000 .. 0xf014 *
12173 At this point, you're ready to run or debug your program. From here on,
12174 you can use all the usual @value{GDBN} commands. The @code{break} command
12175 sets breakpoints; the @code{run} command starts your program;
12176 @code{print} or @code{x} display data; the @code{continue} command
12177 resumes execution after stopping at a breakpoint. You can use the
12178 @code{help} command at any time to find out more about @value{GDBN} commands.
12180 Remember, however, that @emph{operating system} facilities aren't
12181 available on your development board; for example, if your program hangs,
12182 you can't send an interrupt---but you can press the @sc{reset} switch!
12184 Use the @sc{reset} button on the development board
12187 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
12188 no way to pass an interrupt signal to the development board); and
12191 to return to the @value{GDBN} command prompt after your program finishes
12192 normally. The communications protocol provides no other way for @value{GDBN}
12193 to detect program completion.
12196 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
12197 development board as a ``normal exit'' of your program.
12200 @subsubsection Using the E7000 in-circuit emulator
12202 @kindex target e7000@r{, with Hitachi ICE}
12203 You can use the E7000 in-circuit emulator to develop code for either the
12204 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
12205 e7000} command to connect @value{GDBN} to your E7000:
12208 @item target e7000 @var{port} @var{speed}
12209 Use this form if your E7000 is connected to a serial port. The
12210 @var{port} argument identifies what serial port to use (for example,
12211 @samp{com2}). The third argument is the line speed in bits per second
12212 (for example, @samp{9600}).
12214 @item target e7000 @var{hostname}
12215 If your E7000 is installed as a host on a TCP/IP network, you can just
12216 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
12219 @node Hitachi Special
12220 @subsubsection Special @value{GDBN} commands for Hitachi micros
12222 Some @value{GDBN} commands are available only for the H8/300:
12226 @kindex set machine
12227 @kindex show machine
12228 @item set machine h8300
12229 @itemx set machine h8300h
12230 Condition @value{GDBN} for one of the two variants of the H8/300
12231 architecture with @samp{set machine}. You can use @samp{show machine}
12232 to check which variant is currently in effect.
12241 @kindex set memory @var{mod}
12242 @cindex memory models, H8/500
12243 @item set memory @var{mod}
12245 Specify which H8/500 memory model (@var{mod}) you are using with
12246 @samp{set memory}; check which memory model is in effect with @samp{show
12247 memory}. The accepted values for @var{mod} are @code{small},
12248 @code{big}, @code{medium}, and @code{compact}.
12253 @subsection Intel i960
12257 @kindex target mon960
12258 @item target mon960 @var{dev}
12259 MON960 monitor for Intel i960.
12261 @kindex target nindy
12262 @item target nindy @var{devicename}
12263 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
12264 the name of the serial device to use for the connection, e.g.
12271 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
12272 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
12273 tell @value{GDBN} how to connect to the 960 in several ways:
12277 Through command line options specifying serial port, version of the
12278 Nindy protocol, and communications speed;
12281 By responding to a prompt on startup;
12284 By using the @code{target} command at any point during your @value{GDBN}
12285 session. @xref{Target Commands, ,Commands for managing targets}.
12289 @cindex download to Nindy-960
12290 With the Nindy interface to an Intel 960 board, @code{load}
12291 downloads @var{filename} to the 960 as well as adding its symbols in
12295 * Nindy Startup:: Startup with Nindy
12296 * Nindy Options:: Options for Nindy
12297 * Nindy Reset:: Nindy reset command
12300 @node Nindy Startup
12301 @subsubsection Startup with Nindy
12303 If you simply start @code{@value{GDBP}} without using any command-line
12304 options, you are prompted for what serial port to use, @emph{before} you
12305 reach the ordinary @value{GDBN} prompt:
12308 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
12312 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
12313 identifies the serial port you want to use. You can, if you choose,
12314 simply start up with no Nindy connection by responding to the prompt
12315 with an empty line. If you do this and later wish to attach to Nindy,
12316 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
12318 @node Nindy Options
12319 @subsubsection Options for Nindy
12321 These are the startup options for beginning your @value{GDBN} session with a
12322 Nindy-960 board attached:
12325 @item -r @var{port}
12326 Specify the serial port name of a serial interface to be used to connect
12327 to the target system. This option is only available when @value{GDBN} is
12328 configured for the Intel 960 target architecture. You may specify
12329 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
12330 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
12331 suffix for a specific @code{tty} (e.g. @samp{-r a}).
12334 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
12335 the ``old'' Nindy monitor protocol to connect to the target system.
12336 This option is only available when @value{GDBN} is configured for the Intel 960
12337 target architecture.
12340 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
12341 connect to a target system that expects the newer protocol, the connection
12342 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
12343 attempts to reconnect at several different line speeds. You can abort
12344 this process with an interrupt.
12348 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
12349 system, in an attempt to reset it, before connecting to a Nindy target.
12352 @emph{Warning:} Many target systems do not have the hardware that this
12353 requires; it only works with a few boards.
12357 The standard @samp{-b} option controls the line speed used on the serial
12362 @subsubsection Nindy reset command
12367 For a Nindy target, this command sends a ``break'' to the remote target
12368 system; this is only useful if the target has been equipped with a
12369 circuit to perform a hard reset (or some other interesting action) when
12370 a break is detected.
12375 @subsection Mitsubishi M32R/D
12379 @kindex target m32r
12380 @item target m32r @var{dev}
12381 Mitsubishi M32R/D ROM monitor.
12388 The Motorola m68k configuration includes ColdFire support, and
12389 target command for the following ROM monitors.
12393 @kindex target abug
12394 @item target abug @var{dev}
12395 ABug ROM monitor for M68K.
12397 @kindex target cpu32bug
12398 @item target cpu32bug @var{dev}
12399 CPU32BUG monitor, running on a CPU32 (M68K) board.
12401 @kindex target dbug
12402 @item target dbug @var{dev}
12403 dBUG ROM monitor for Motorola ColdFire.
12406 @item target est @var{dev}
12407 EST-300 ICE monitor, running on a CPU32 (M68K) board.
12409 @kindex target rom68k
12410 @item target rom68k @var{dev}
12411 ROM 68K monitor, running on an M68K IDP board.
12415 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
12416 instead have only a single special target command:
12420 @kindex target es1800
12421 @item target es1800 @var{dev}
12422 ES-1800 emulator for M68K.
12430 @kindex target rombug
12431 @item target rombug @var{dev}
12432 ROMBUG ROM monitor for OS/9000.
12442 @item target bug @var{dev}
12443 BUG monitor, running on a MVME187 (m88k) board.
12447 @node MIPS Embedded
12448 @subsection MIPS Embedded
12450 @cindex MIPS boards
12451 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
12452 MIPS board attached to a serial line. This is available when
12453 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
12456 Use these @value{GDBN} commands to specify the connection to your target board:
12459 @item target mips @var{port}
12460 @kindex target mips @var{port}
12461 To run a program on the board, start up @code{@value{GDBP}} with the
12462 name of your program as the argument. To connect to the board, use the
12463 command @samp{target mips @var{port}}, where @var{port} is the name of
12464 the serial port connected to the board. If the program has not already
12465 been downloaded to the board, you may use the @code{load} command to
12466 download it. You can then use all the usual @value{GDBN} commands.
12468 For example, this sequence connects to the target board through a serial
12469 port, and loads and runs a program called @var{prog} through the
12473 host$ @value{GDBP} @var{prog}
12474 @value{GDBN} is free software and @dots{}
12475 (@value{GDBP}) target mips /dev/ttyb
12476 (@value{GDBP}) load @var{prog}
12480 @item target mips @var{hostname}:@var{portnumber}
12481 On some @value{GDBN} host configurations, you can specify a TCP
12482 connection (for instance, to a serial line managed by a terminal
12483 concentrator) instead of a serial port, using the syntax
12484 @samp{@var{hostname}:@var{portnumber}}.
12486 @item target pmon @var{port}
12487 @kindex target pmon @var{port}
12490 @item target ddb @var{port}
12491 @kindex target ddb @var{port}
12492 NEC's DDB variant of PMON for Vr4300.
12494 @item target lsi @var{port}
12495 @kindex target lsi @var{port}
12496 LSI variant of PMON.
12498 @kindex target r3900
12499 @item target r3900 @var{dev}
12500 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
12502 @kindex target array
12503 @item target array @var{dev}
12504 Array Tech LSI33K RAID controller board.
12510 @value{GDBN} also supports these special commands for MIPS targets:
12513 @item set processor @var{args}
12514 @itemx show processor
12515 @kindex set processor @var{args}
12516 @kindex show processor
12517 Use the @code{set processor} command to set the type of MIPS
12518 processor when you want to access processor-type-specific registers.
12519 For example, @code{set processor @var{r3041}} tells @value{GDBN}
12520 to use the CPU registers appropriate for the 3041 chip.
12521 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
12522 is using. Use the @code{info reg} command to see what registers
12523 @value{GDBN} is using.
12525 @item set mipsfpu double
12526 @itemx set mipsfpu single
12527 @itemx set mipsfpu none
12528 @itemx show mipsfpu
12529 @kindex set mipsfpu
12530 @kindex show mipsfpu
12531 @cindex MIPS remote floating point
12532 @cindex floating point, MIPS remote
12533 If your target board does not support the MIPS floating point
12534 coprocessor, you should use the command @samp{set mipsfpu none} (if you
12535 need this, you may wish to put the command in your @value{GDBN} init
12536 file). This tells @value{GDBN} how to find the return value of
12537 functions which return floating point values. It also allows
12538 @value{GDBN} to avoid saving the floating point registers when calling
12539 functions on the board. If you are using a floating point coprocessor
12540 with only single precision floating point support, as on the @sc{r4650}
12541 processor, use the command @samp{set mipsfpu single}. The default
12542 double precision floating point coprocessor may be selected using
12543 @samp{set mipsfpu double}.
12545 In previous versions the only choices were double precision or no
12546 floating point, so @samp{set mipsfpu on} will select double precision
12547 and @samp{set mipsfpu off} will select no floating point.
12549 As usual, you can inquire about the @code{mipsfpu} variable with
12550 @samp{show mipsfpu}.
12552 @item set remotedebug @var{n}
12553 @itemx show remotedebug
12554 @kindex set remotedebug@r{, MIPS protocol}
12555 @kindex show remotedebug@r{, MIPS protocol}
12556 @cindex @code{remotedebug}, MIPS protocol
12557 @cindex MIPS @code{remotedebug} protocol
12558 @c FIXME! For this to be useful, you must know something about the MIPS
12559 @c FIXME...protocol. Where is it described?
12560 You can see some debugging information about communications with the board
12561 by setting the @code{remotedebug} variable. If you set it to @code{1} using
12562 @samp{set remotedebug 1}, every packet is displayed. If you set it
12563 to @code{2}, every character is displayed. You can check the current value
12564 at any time with the command @samp{show remotedebug}.
12566 @item set timeout @var{seconds}
12567 @itemx set retransmit-timeout @var{seconds}
12568 @itemx show timeout
12569 @itemx show retransmit-timeout
12570 @cindex @code{timeout}, MIPS protocol
12571 @cindex @code{retransmit-timeout}, MIPS protocol
12572 @kindex set timeout
12573 @kindex show timeout
12574 @kindex set retransmit-timeout
12575 @kindex show retransmit-timeout
12576 You can control the timeout used while waiting for a packet, in the MIPS
12577 remote protocol, with the @code{set timeout @var{seconds}} command. The
12578 default is 5 seconds. Similarly, you can control the timeout used while
12579 waiting for an acknowledgement of a packet with the @code{set
12580 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
12581 You can inspect both values with @code{show timeout} and @code{show
12582 retransmit-timeout}. (These commands are @emph{only} available when
12583 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
12585 The timeout set by @code{set timeout} does not apply when @value{GDBN}
12586 is waiting for your program to stop. In that case, @value{GDBN} waits
12587 forever because it has no way of knowing how long the program is going
12588 to run before stopping.
12592 @subsection PowerPC
12596 @kindex target dink32
12597 @item target dink32 @var{dev}
12598 DINK32 ROM monitor.
12600 @kindex target ppcbug
12601 @item target ppcbug @var{dev}
12602 @kindex target ppcbug1
12603 @item target ppcbug1 @var{dev}
12604 PPCBUG ROM monitor for PowerPC.
12607 @item target sds @var{dev}
12608 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
12613 @subsection HP PA Embedded
12617 @kindex target op50n
12618 @item target op50n @var{dev}
12619 OP50N monitor, running on an OKI HPPA board.
12621 @kindex target w89k
12622 @item target w89k @var{dev}
12623 W89K monitor, running on a Winbond HPPA board.
12628 @subsection Hitachi SH
12632 @kindex target hms@r{, with Hitachi SH}
12633 @item target hms @var{dev}
12634 A Hitachi SH board attached via serial line to your host. Use special
12635 commands @code{device} and @code{speed} to control the serial line and
12636 the communications speed used.
12638 @kindex target e7000@r{, with Hitachi SH}
12639 @item target e7000 @var{dev}
12640 E7000 emulator for Hitachi SH.
12642 @kindex target sh3@r{, with SH}
12643 @kindex target sh3e@r{, with SH}
12644 @item target sh3 @var{dev}
12645 @item target sh3e @var{dev}
12646 Hitachi SH-3 and SH-3E target systems.
12651 @subsection Tsqware Sparclet
12655 @value{GDBN} enables developers to debug tasks running on
12656 Sparclet targets from a Unix host.
12657 @value{GDBN} uses code that runs on
12658 both the Unix host and on the Sparclet target. The program
12659 @code{@value{GDBP}} is installed and executed on the Unix host.
12662 @item remotetimeout @var{args}
12663 @kindex remotetimeout
12664 @value{GDBN} supports the option @code{remotetimeout}.
12665 This option is set by the user, and @var{args} represents the number of
12666 seconds @value{GDBN} waits for responses.
12669 @cindex compiling, on Sparclet
12670 When compiling for debugging, include the options @samp{-g} to get debug
12671 information and @samp{-Ttext} to relocate the program to where you wish to
12672 load it on the target. You may also want to add the options @samp{-n} or
12673 @samp{-N} in order to reduce the size of the sections. Example:
12676 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
12679 You can use @code{objdump} to verify that the addresses are what you intended:
12682 sparclet-aout-objdump --headers --syms prog
12685 @cindex running, on Sparclet
12687 your Unix execution search path to find @value{GDBN}, you are ready to
12688 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12689 (or @code{sparclet-aout-gdb}, depending on your installation).
12691 @value{GDBN} comes up showing the prompt:
12698 * Sparclet File:: Setting the file to debug
12699 * Sparclet Connection:: Connecting to Sparclet
12700 * Sparclet Download:: Sparclet download
12701 * Sparclet Execution:: Running and debugging
12704 @node Sparclet File
12705 @subsubsection Setting file to debug
12707 The @value{GDBN} command @code{file} lets you choose with program to debug.
12710 (gdbslet) file prog
12714 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12715 @value{GDBN} locates
12716 the file by searching the directories listed in the command search
12718 If the file was compiled with debug information (option "-g"), source
12719 files will be searched as well.
12720 @value{GDBN} locates
12721 the source files by searching the directories listed in the directory search
12722 path (@pxref{Environment, ,Your program's environment}).
12724 to find a file, it displays a message such as:
12727 prog: No such file or directory.
12730 When this happens, add the appropriate directories to the search paths with
12731 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12732 @code{target} command again.
12734 @node Sparclet Connection
12735 @subsubsection Connecting to Sparclet
12737 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12738 To connect to a target on serial port ``@code{ttya}'', type:
12741 (gdbslet) target sparclet /dev/ttya
12742 Remote target sparclet connected to /dev/ttya
12743 main () at ../prog.c:3
12747 @value{GDBN} displays messages like these:
12753 @node Sparclet Download
12754 @subsubsection Sparclet download
12756 @cindex download to Sparclet
12757 Once connected to the Sparclet target,
12758 you can use the @value{GDBN}
12759 @code{load} command to download the file from the host to the target.
12760 The file name and load offset should be given as arguments to the @code{load}
12762 Since the file format is aout, the program must be loaded to the starting
12763 address. You can use @code{objdump} to find out what this value is. The load
12764 offset is an offset which is added to the VMA (virtual memory address)
12765 of each of the file's sections.
12766 For instance, if the program
12767 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12768 and bss at 0x12010170, in @value{GDBN}, type:
12771 (gdbslet) load prog 0x12010000
12772 Loading section .text, size 0xdb0 vma 0x12010000
12775 If the code is loaded at a different address then what the program was linked
12776 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12777 to tell @value{GDBN} where to map the symbol table.
12779 @node Sparclet Execution
12780 @subsubsection Running and debugging
12782 @cindex running and debugging Sparclet programs
12783 You can now begin debugging the task using @value{GDBN}'s execution control
12784 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12785 manual for the list of commands.
12789 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12791 Starting program: prog
12792 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12793 3 char *symarg = 0;
12795 4 char *execarg = "hello!";
12800 @subsection Fujitsu Sparclite
12804 @kindex target sparclite
12805 @item target sparclite @var{dev}
12806 Fujitsu sparclite boards, used only for the purpose of loading.
12807 You must use an additional command to debug the program.
12808 For example: target remote @var{dev} using @value{GDBN} standard
12814 @subsection Tandem ST2000
12816 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12819 To connect your ST2000 to the host system, see the manufacturer's
12820 manual. Once the ST2000 is physically attached, you can run:
12823 target st2000 @var{dev} @var{speed}
12827 to establish it as your debugging environment. @var{dev} is normally
12828 the name of a serial device, such as @file{/dev/ttya}, connected to the
12829 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12830 connection (for example, to a serial line attached via a terminal
12831 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12833 The @code{load} and @code{attach} commands are @emph{not} defined for
12834 this target; you must load your program into the ST2000 as you normally
12835 would for standalone operation. @value{GDBN} reads debugging information
12836 (such as symbols) from a separate, debugging version of the program
12837 available on your host computer.
12838 @c FIXME!! This is terribly vague; what little content is here is
12839 @c basically hearsay.
12841 @cindex ST2000 auxiliary commands
12842 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12846 @item st2000 @var{command}
12847 @kindex st2000 @var{cmd}
12848 @cindex STDBUG commands (ST2000)
12849 @cindex commands to STDBUG (ST2000)
12850 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12851 manual for available commands.
12854 @cindex connect (to STDBUG)
12855 Connect the controlling terminal to the STDBUG command monitor. When
12856 you are done interacting with STDBUG, typing either of two character
12857 sequences gets you back to the @value{GDBN} command prompt:
12858 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12859 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12863 @subsection Zilog Z8000
12866 @cindex simulator, Z8000
12867 @cindex Zilog Z8000 simulator
12869 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12872 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12873 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12874 segmented variant). The simulator recognizes which architecture is
12875 appropriate by inspecting the object code.
12878 @item target sim @var{args}
12880 @kindex target sim@r{, with Z8000}
12881 Debug programs on a simulated CPU. If the simulator supports setup
12882 options, specify them via @var{args}.
12886 After specifying this target, you can debug programs for the simulated
12887 CPU in the same style as programs for your host computer; use the
12888 @code{file} command to load a new program image, the @code{run} command
12889 to run your program, and so on.
12891 As well as making available all the usual machine registers
12892 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12893 additional items of information as specially named registers:
12898 Counts clock-ticks in the simulator.
12901 Counts instructions run in the simulator.
12904 Execution time in 60ths of a second.
12908 You can refer to these values in @value{GDBN} expressions with the usual
12909 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12910 conditional breakpoint that suspends only after at least 5000
12911 simulated clock ticks.
12913 @node Architectures
12914 @section Architectures
12916 This section describes characteristics of architectures that affect
12917 all uses of @value{GDBN} with the architecture, both native and cross.
12930 @kindex set rstack_high_address
12931 @cindex AMD 29K register stack
12932 @cindex register stack, AMD29K
12933 @item set rstack_high_address @var{address}
12934 On AMD 29000 family processors, registers are saved in a separate
12935 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12936 extent of this stack. Normally, @value{GDBN} just assumes that the
12937 stack is ``large enough''. This may result in @value{GDBN} referencing
12938 memory locations that do not exist. If necessary, you can get around
12939 this problem by specifying the ending address of the register stack with
12940 the @code{set rstack_high_address} command. The argument should be an
12941 address, which you probably want to precede with @samp{0x} to specify in
12944 @kindex show rstack_high_address
12945 @item show rstack_high_address
12946 Display the current limit of the register stack, on AMD 29000 family
12954 See the following section.
12959 @cindex stack on Alpha
12960 @cindex stack on MIPS
12961 @cindex Alpha stack
12963 Alpha- and MIPS-based computers use an unusual stack frame, which
12964 sometimes requires @value{GDBN} to search backward in the object code to
12965 find the beginning of a function.
12967 @cindex response time, MIPS debugging
12968 To improve response time (especially for embedded applications, where
12969 @value{GDBN} may be restricted to a slow serial line for this search)
12970 you may want to limit the size of this search, using one of these
12974 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12975 @item set heuristic-fence-post @var{limit}
12976 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12977 search for the beginning of a function. A value of @var{0} (the
12978 default) means there is no limit. However, except for @var{0}, the
12979 larger the limit the more bytes @code{heuristic-fence-post} must search
12980 and therefore the longer it takes to run.
12982 @item show heuristic-fence-post
12983 Display the current limit.
12987 These commands are available @emph{only} when @value{GDBN} is configured
12988 for debugging programs on Alpha or MIPS processors.
12991 @node Controlling GDB
12992 @chapter Controlling @value{GDBN}
12994 You can alter the way @value{GDBN} interacts with you by using the
12995 @code{set} command. For commands controlling how @value{GDBN} displays
12996 data, see @ref{Print Settings, ,Print settings}. Other settings are
13001 * Editing:: Command editing
13002 * History:: Command history
13003 * Screen Size:: Screen size
13004 * Numbers:: Numbers
13005 * Messages/Warnings:: Optional warnings and messages
13006 * Debugging Output:: Optional messages about internal happenings
13014 @value{GDBN} indicates its readiness to read a command by printing a string
13015 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
13016 can change the prompt string with the @code{set prompt} command. For
13017 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
13018 the prompt in one of the @value{GDBN} sessions so that you can always tell
13019 which one you are talking to.
13021 @emph{Note:} @code{set prompt} does not add a space for you after the
13022 prompt you set. This allows you to set a prompt which ends in a space
13023 or a prompt that does not.
13027 @item set prompt @var{newprompt}
13028 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
13030 @kindex show prompt
13032 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
13036 @section Command editing
13038 @cindex command line editing
13040 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
13041 @sc{gnu} library provides consistent behavior for programs which provide a
13042 command line interface to the user. Advantages are @sc{gnu} Emacs-style
13043 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
13044 substitution, and a storage and recall of command history across
13045 debugging sessions.
13047 You may control the behavior of command line editing in @value{GDBN} with the
13048 command @code{set}.
13051 @kindex set editing
13054 @itemx set editing on
13055 Enable command line editing (enabled by default).
13057 @item set editing off
13058 Disable command line editing.
13060 @kindex show editing
13062 Show whether command line editing is enabled.
13066 @section Command history
13068 @value{GDBN} can keep track of the commands you type during your
13069 debugging sessions, so that you can be certain of precisely what
13070 happened. Use these commands to manage the @value{GDBN} command
13074 @cindex history substitution
13075 @cindex history file
13076 @kindex set history filename
13077 @kindex GDBHISTFILE
13078 @item set history filename @var{fname}
13079 Set the name of the @value{GDBN} command history file to @var{fname}.
13080 This is the file where @value{GDBN} reads an initial command history
13081 list, and where it writes the command history from this session when it
13082 exits. You can access this list through history expansion or through
13083 the history command editing characters listed below. This file defaults
13084 to the value of the environment variable @code{GDBHISTFILE}, or to
13085 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
13088 @cindex history save
13089 @kindex set history save
13090 @item set history save
13091 @itemx set history save on
13092 Record command history in a file, whose name may be specified with the
13093 @code{set history filename} command. By default, this option is disabled.
13095 @item set history save off
13096 Stop recording command history in a file.
13098 @cindex history size
13099 @kindex set history size
13100 @item set history size @var{size}
13101 Set the number of commands which @value{GDBN} keeps in its history list.
13102 This defaults to the value of the environment variable
13103 @code{HISTSIZE}, or to 256 if this variable is not set.
13106 @cindex history expansion
13107 History expansion assigns special meaning to the character @kbd{!}.
13108 @ifset have-readline-appendices
13109 @xref{Event Designators}.
13112 Since @kbd{!} is also the logical not operator in C, history expansion
13113 is off by default. If you decide to enable history expansion with the
13114 @code{set history expansion on} command, you may sometimes need to
13115 follow @kbd{!} (when it is used as logical not, in an expression) with
13116 a space or a tab to prevent it from being expanded. The readline
13117 history facilities do not attempt substitution on the strings
13118 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
13120 The commands to control history expansion are:
13123 @kindex set history expansion
13124 @item set history expansion on
13125 @itemx set history expansion
13126 Enable history expansion. History expansion is off by default.
13128 @item set history expansion off
13129 Disable history expansion.
13131 The readline code comes with more complete documentation of
13132 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
13133 or @code{vi} may wish to read it.
13134 @ifset have-readline-appendices
13135 @xref{Command Line Editing}.
13139 @kindex show history
13141 @itemx show history filename
13142 @itemx show history save
13143 @itemx show history size
13144 @itemx show history expansion
13145 These commands display the state of the @value{GDBN} history parameters.
13146 @code{show history} by itself displays all four states.
13152 @item show commands
13153 Display the last ten commands in the command history.
13155 @item show commands @var{n}
13156 Print ten commands centered on command number @var{n}.
13158 @item show commands +
13159 Print ten commands just after the commands last printed.
13163 @section Screen size
13164 @cindex size of screen
13165 @cindex pauses in output
13167 Certain commands to @value{GDBN} may produce large amounts of
13168 information output to the screen. To help you read all of it,
13169 @value{GDBN} pauses and asks you for input at the end of each page of
13170 output. Type @key{RET} when you want to continue the output, or @kbd{q}
13171 to discard the remaining output. Also, the screen width setting
13172 determines when to wrap lines of output. Depending on what is being
13173 printed, @value{GDBN} tries to break the line at a readable place,
13174 rather than simply letting it overflow onto the following line.
13176 Normally @value{GDBN} knows the size of the screen from the terminal
13177 driver software. For example, on Unix @value{GDBN} uses the termcap data base
13178 together with the value of the @code{TERM} environment variable and the
13179 @code{stty rows} and @code{stty cols} settings. If this is not correct,
13180 you can override it with the @code{set height} and @code{set
13187 @kindex show height
13188 @item set height @var{lpp}
13190 @itemx set width @var{cpl}
13192 These @code{set} commands specify a screen height of @var{lpp} lines and
13193 a screen width of @var{cpl} characters. The associated @code{show}
13194 commands display the current settings.
13196 If you specify a height of zero lines, @value{GDBN} does not pause during
13197 output no matter how long the output is. This is useful if output is to a
13198 file or to an editor buffer.
13200 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
13201 from wrapping its output.
13206 @cindex number representation
13207 @cindex entering numbers
13209 You can always enter numbers in octal, decimal, or hexadecimal in
13210 @value{GDBN} by the usual conventions: octal numbers begin with
13211 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
13212 begin with @samp{0x}. Numbers that begin with none of these are, by
13213 default, entered in base 10; likewise, the default display for
13214 numbers---when no particular format is specified---is base 10. You can
13215 change the default base for both input and output with the @code{set
13219 @kindex set input-radix
13220 @item set input-radix @var{base}
13221 Set the default base for numeric input. Supported choices
13222 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
13223 specified either unambiguously or using the current default radix; for
13233 sets the base to decimal. On the other hand, @samp{set radix 10}
13234 leaves the radix unchanged no matter what it was.
13236 @kindex set output-radix
13237 @item set output-radix @var{base}
13238 Set the default base for numeric display. Supported choices
13239 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
13240 specified either unambiguously or using the current default radix.
13242 @kindex show input-radix
13243 @item show input-radix
13244 Display the current default base for numeric input.
13246 @kindex show output-radix
13247 @item show output-radix
13248 Display the current default base for numeric display.
13251 @node Messages/Warnings
13252 @section Optional warnings and messages
13254 By default, @value{GDBN} is silent about its inner workings. If you are
13255 running on a slow machine, you may want to use the @code{set verbose}
13256 command. This makes @value{GDBN} tell you when it does a lengthy
13257 internal operation, so you will not think it has crashed.
13259 Currently, the messages controlled by @code{set verbose} are those
13260 which announce that the symbol table for a source file is being read;
13261 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
13264 @kindex set verbose
13265 @item set verbose on
13266 Enables @value{GDBN} output of certain informational messages.
13268 @item set verbose off
13269 Disables @value{GDBN} output of certain informational messages.
13271 @kindex show verbose
13273 Displays whether @code{set verbose} is on or off.
13276 By default, if @value{GDBN} encounters bugs in the symbol table of an
13277 object file, it is silent; but if you are debugging a compiler, you may
13278 find this information useful (@pxref{Symbol Errors, ,Errors reading
13283 @kindex set complaints
13284 @item set complaints @var{limit}
13285 Permits @value{GDBN} to output @var{limit} complaints about each type of
13286 unusual symbols before becoming silent about the problem. Set
13287 @var{limit} to zero to suppress all complaints; set it to a large number
13288 to prevent complaints from being suppressed.
13290 @kindex show complaints
13291 @item show complaints
13292 Displays how many symbol complaints @value{GDBN} is permitted to produce.
13296 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
13297 lot of stupid questions to confirm certain commands. For example, if
13298 you try to run a program which is already running:
13302 The program being debugged has been started already.
13303 Start it from the beginning? (y or n)
13306 If you are willing to unflinchingly face the consequences of your own
13307 commands, you can disable this ``feature'':
13311 @kindex set confirm
13313 @cindex confirmation
13314 @cindex stupid questions
13315 @item set confirm off
13316 Disables confirmation requests.
13318 @item set confirm on
13319 Enables confirmation requests (the default).
13321 @kindex show confirm
13323 Displays state of confirmation requests.
13327 @node Debugging Output
13328 @section Optional messages about internal happenings
13330 @kindex set debug arch
13331 @item set debug arch
13332 Turns on or off display of gdbarch debugging info. The default is off
13333 @kindex show debug arch
13334 @item show debug arch
13335 Displays the current state of displaying gdbarch debugging info.
13336 @kindex set debug event
13337 @item set debug event
13338 Turns on or off display of @value{GDBN} event debugging info. The
13340 @kindex show debug event
13341 @item show debug event
13342 Displays the current state of displaying @value{GDBN} event debugging
13344 @kindex set debug expression
13345 @item set debug expression
13346 Turns on or off display of @value{GDBN} expression debugging info. The
13348 @kindex show debug expression
13349 @item show debug expression
13350 Displays the current state of displaying @value{GDBN} expression
13352 @kindex set debug overload
13353 @item set debug overload
13354 Turns on or off display of @value{GDBN} C@t{++} overload debugging
13355 info. This includes info such as ranking of functions, etc. The default
13357 @kindex show debug overload
13358 @item show debug overload
13359 Displays the current state of displaying @value{GDBN} C@t{++} overload
13361 @kindex set debug remote
13362 @cindex packets, reporting on stdout
13363 @cindex serial connections, debugging
13364 @item set debug remote
13365 Turns on or off display of reports on all packets sent back and forth across
13366 the serial line to the remote machine. The info is printed on the
13367 @value{GDBN} standard output stream. The default is off.
13368 @kindex show debug remote
13369 @item show debug remote
13370 Displays the state of display of remote packets.
13371 @kindex set debug serial
13372 @item set debug serial
13373 Turns on or off display of @value{GDBN} serial debugging info. The
13375 @kindex show debug serial
13376 @item show debug serial
13377 Displays the current state of displaying @value{GDBN} serial debugging
13379 @kindex set debug target
13380 @item set debug target
13381 Turns on or off display of @value{GDBN} target debugging info. This info
13382 includes what is going on at the target level of GDB, as it happens. The
13384 @kindex show debug target
13385 @item show debug target
13386 Displays the current state of displaying @value{GDBN} target debugging
13388 @kindex set debug varobj
13389 @item set debug varobj
13390 Turns on or off display of @value{GDBN} variable object debugging
13391 info. The default is off.
13392 @kindex show debug varobj
13393 @item show debug varobj
13394 Displays the current state of displaying @value{GDBN} variable object
13399 @chapter Canned Sequences of Commands
13401 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
13402 command lists}), @value{GDBN} provides two ways to store sequences of
13403 commands for execution as a unit: user-defined commands and command
13407 * Define:: User-defined commands
13408 * Hooks:: User-defined command hooks
13409 * Command Files:: Command files
13410 * Output:: Commands for controlled output
13414 @section User-defined commands
13416 @cindex user-defined command
13417 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
13418 which you assign a new name as a command. This is done with the
13419 @code{define} command. User commands may accept up to 10 arguments
13420 separated by whitespace. Arguments are accessed within the user command
13421 via @var{$arg0@dots{}$arg9}. A trivial example:
13425 print $arg0 + $arg1 + $arg2
13429 To execute the command use:
13436 This defines the command @code{adder}, which prints the sum of
13437 its three arguments. Note the arguments are text substitutions, so they may
13438 reference variables, use complex expressions, or even perform inferior
13444 @item define @var{commandname}
13445 Define a command named @var{commandname}. If there is already a command
13446 by that name, you are asked to confirm that you want to redefine it.
13448 The definition of the command is made up of other @value{GDBN} command lines,
13449 which are given following the @code{define} command. The end of these
13450 commands is marked by a line containing @code{end}.
13455 Takes a single argument, which is an expression to evaluate.
13456 It is followed by a series of commands that are executed
13457 only if the expression is true (nonzero).
13458 There can then optionally be a line @code{else}, followed
13459 by a series of commands that are only executed if the expression
13460 was false. The end of the list is marked by a line containing @code{end}.
13464 The syntax is similar to @code{if}: the command takes a single argument,
13465 which is an expression to evaluate, and must be followed by the commands to
13466 execute, one per line, terminated by an @code{end}.
13467 The commands are executed repeatedly as long as the expression
13471 @item document @var{commandname}
13472 Document the user-defined command @var{commandname}, so that it can be
13473 accessed by @code{help}. The command @var{commandname} must already be
13474 defined. This command reads lines of documentation just as @code{define}
13475 reads the lines of the command definition, ending with @code{end}.
13476 After the @code{document} command is finished, @code{help} on command
13477 @var{commandname} displays the documentation you have written.
13479 You may use the @code{document} command again to change the
13480 documentation of a command. Redefining the command with @code{define}
13481 does not change the documentation.
13483 @kindex help user-defined
13484 @item help user-defined
13485 List all user-defined commands, with the first line of the documentation
13490 @itemx show user @var{commandname}
13491 Display the @value{GDBN} commands used to define @var{commandname} (but
13492 not its documentation). If no @var{commandname} is given, display the
13493 definitions for all user-defined commands.
13497 When user-defined commands are executed, the
13498 commands of the definition are not printed. An error in any command
13499 stops execution of the user-defined command.
13501 If used interactively, commands that would ask for confirmation proceed
13502 without asking when used inside a user-defined command. Many @value{GDBN}
13503 commands that normally print messages to say what they are doing omit the
13504 messages when used in a user-defined command.
13507 @section User-defined command hooks
13508 @cindex command hooks
13509 @cindex hooks, for commands
13510 @cindex hooks, pre-command
13514 You may define @dfn{hooks}, which are a special kind of user-defined
13515 command. Whenever you run the command @samp{foo}, if the user-defined
13516 command @samp{hook-foo} exists, it is executed (with no arguments)
13517 before that command.
13519 @cindex hooks, post-command
13522 A hook may also be defined which is run after the command you executed.
13523 Whenever you run the command @samp{foo}, if the user-defined command
13524 @samp{hookpost-foo} exists, it is executed (with no arguments) after
13525 that command. Post-execution hooks may exist simultaneously with
13526 pre-execution hooks, for the same command.
13528 It is valid for a hook to call the command which it hooks. If this
13529 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
13531 @c It would be nice if hookpost could be passed a parameter indicating
13532 @c if the command it hooks executed properly or not. FIXME!
13534 @kindex stop@r{, a pseudo-command}
13535 In addition, a pseudo-command, @samp{stop} exists. Defining
13536 (@samp{hook-stop}) makes the associated commands execute every time
13537 execution stops in your program: before breakpoint commands are run,
13538 displays are printed, or the stack frame is printed.
13540 For example, to ignore @code{SIGALRM} signals while
13541 single-stepping, but treat them normally during normal execution,
13546 handle SIGALRM nopass
13550 handle SIGALRM pass
13553 define hook-continue
13554 handle SIGLARM pass
13558 As a further example, to hook at the begining and end of the @code{echo}
13559 command, and to add extra text to the beginning and end of the message,
13567 define hookpost-echo
13571 (@value{GDBP}) echo Hello World
13572 <<<---Hello World--->>>
13577 You can define a hook for any single-word command in @value{GDBN}, but
13578 not for command aliases; you should define a hook for the basic command
13579 name, e.g. @code{backtrace} rather than @code{bt}.
13580 @c FIXME! So how does Joe User discover whether a command is an alias
13582 If an error occurs during the execution of your hook, execution of
13583 @value{GDBN} commands stops and @value{GDBN} issues a prompt
13584 (before the command that you actually typed had a chance to run).
13586 If you try to define a hook which does not match any known command, you
13587 get a warning from the @code{define} command.
13589 @node Command Files
13590 @section Command files
13592 @cindex command files
13593 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
13594 commands. Comments (lines starting with @kbd{#}) may also be included.
13595 An empty line in a command file does nothing; it does not mean to repeat
13596 the last command, as it would from the terminal.
13599 @cindex @file{.gdbinit}
13600 @cindex @file{gdb.ini}
13601 When you start @value{GDBN}, it automatically executes commands from its
13602 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
13603 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
13604 limitations of file names imposed by DOS filesystems.}.
13605 During startup, @value{GDBN} does the following:
13609 Reads the init file (if any) in your home directory@footnote{On
13610 DOS/Windows systems, the home directory is the one pointed to by the
13611 @code{HOME} environment variable.}.
13614 Processes command line options and operands.
13617 Reads the init file (if any) in the current working directory.
13620 Reads command files specified by the @samp{-x} option.
13623 The init file in your home directory can set options (such as @samp{set
13624 complaints}) that affect subsequent processing of command line options
13625 and operands. Init files are not executed if you use the @samp{-nx}
13626 option (@pxref{Mode Options, ,Choosing modes}).
13628 @cindex init file name
13629 On some configurations of @value{GDBN}, the init file is known by a
13630 different name (these are typically environments where a specialized
13631 form of @value{GDBN} may need to coexist with other forms, hence a
13632 different name for the specialized version's init file). These are the
13633 environments with special init file names:
13635 @cindex @file{.vxgdbinit}
13638 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13640 @cindex @file{.os68gdbinit}
13642 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13644 @cindex @file{.esgdbinit}
13646 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13649 You can also request the execution of a command file with the
13650 @code{source} command:
13654 @item source @var{filename}
13655 Execute the command file @var{filename}.
13658 The lines in a command file are executed sequentially. They are not
13659 printed as they are executed. An error in any command terminates execution
13660 of the command file.
13662 Commands that would ask for confirmation if used interactively proceed
13663 without asking when used in a command file. Many @value{GDBN} commands that
13664 normally print messages to say what they are doing omit the messages
13665 when called from command files.
13667 @value{GDBN} also accepts command input from standard input. In this
13668 mode, normal output goes to standard output and error output goes to
13669 standard error. Errors in a command file supplied on standard input do
13670 not terminate execution of the command file --- execution continues with
13674 gdb < cmds > log 2>&1
13677 (The syntax above will vary depending on the shell used.) This example
13678 will execute commands from the file @file{cmds}. All output and errors
13679 would be directed to @file{log}.
13682 @section Commands for controlled output
13684 During the execution of a command file or a user-defined command, normal
13685 @value{GDBN} output is suppressed; the only output that appears is what is
13686 explicitly printed by the commands in the definition. This section
13687 describes three commands useful for generating exactly the output you
13692 @item echo @var{text}
13693 @c I do not consider backslash-space a standard C escape sequence
13694 @c because it is not in ANSI.
13695 Print @var{text}. Nonprinting characters can be included in
13696 @var{text} using C escape sequences, such as @samp{\n} to print a
13697 newline. @strong{No newline is printed unless you specify one.}
13698 In addition to the standard C escape sequences, a backslash followed
13699 by a space stands for a space. This is useful for displaying a
13700 string with spaces at the beginning or the end, since leading and
13701 trailing spaces are otherwise trimmed from all arguments.
13702 To print @samp{@w{ }and foo =@w{ }}, use the command
13703 @samp{echo \@w{ }and foo = \@w{ }}.
13705 A backslash at the end of @var{text} can be used, as in C, to continue
13706 the command onto subsequent lines. For example,
13709 echo This is some text\n\
13710 which is continued\n\
13711 onto several lines.\n
13714 produces the same output as
13717 echo This is some text\n
13718 echo which is continued\n
13719 echo onto several lines.\n
13723 @item output @var{expression}
13724 Print the value of @var{expression} and nothing but that value: no
13725 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13726 value history either. @xref{Expressions, ,Expressions}, for more information
13729 @item output/@var{fmt} @var{expression}
13730 Print the value of @var{expression} in format @var{fmt}. You can use
13731 the same formats as for @code{print}. @xref{Output Formats,,Output
13732 formats}, for more information.
13735 @item printf @var{string}, @var{expressions}@dots{}
13736 Print the values of the @var{expressions} under the control of
13737 @var{string}. The @var{expressions} are separated by commas and may be
13738 either numbers or pointers. Their values are printed as specified by
13739 @var{string}, exactly as if your program were to execute the C
13741 @c FIXME: the above implies that at least all ANSI C formats are
13742 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13743 @c Either this is a bug, or the manual should document what formats are
13747 printf (@var{string}, @var{expressions}@dots{});
13750 For example, you can print two values in hex like this:
13753 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13756 The only backslash-escape sequences that you can use in the format
13757 string are the simple ones that consist of backslash followed by a
13762 @chapter @value{GDBN} Text User Interface
13766 * TUI Overview:: TUI overview
13767 * TUI Keys:: TUI key bindings
13768 * TUI Commands:: TUI specific commands
13769 * TUI Configuration:: TUI configuration variables
13772 The @value{GDBN} Text User Interface, TUI in short,
13773 is a terminal interface which uses the @code{curses} library
13774 to show the source file, the assembly output, the program registers
13775 and @value{GDBN} commands in separate text windows.
13776 The TUI is available only when @value{GDBN} is configured
13777 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13780 @section TUI overview
13782 The TUI has two display modes that can be switched while
13787 A curses (or TUI) mode in which it displays several text
13788 windows on the terminal.
13791 A standard mode which corresponds to the @value{GDBN} configured without
13795 In the TUI mode, @value{GDBN} can display several text window
13800 This window is the @value{GDBN} command window with the @value{GDBN}
13801 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13802 managed using readline but through the TUI. The @emph{command}
13803 window is always visible.
13806 The source window shows the source file of the program. The current
13807 line as well as active breakpoints are displayed in this window.
13808 The current program position is shown with the @samp{>} marker and
13809 active breakpoints are shown with @samp{*} markers.
13812 The assembly window shows the disassembly output of the program.
13815 This window shows the processor registers. It detects when
13816 a register is changed and when this is the case, registers that have
13817 changed are highlighted.
13821 The source, assembly and register windows are attached to the thread
13822 and the frame position. They are updated when the current thread
13823 changes, when the frame changes or when the program counter changes.
13824 These three windows are arranged by the TUI according to several
13825 layouts. The layout defines which of these three windows are visible.
13826 The following layouts are available:
13836 source and assembly
13839 source and registers
13842 assembly and registers
13847 @section TUI Key Bindings
13848 @cindex TUI key bindings
13850 The TUI installs several key bindings in the readline keymaps
13851 (@pxref{Command Line Editing}).
13852 They allow to leave or enter in the TUI mode or they operate
13853 directly on the TUI layout and windows. The following key bindings
13854 are installed for both TUI mode and the @value{GDBN} standard mode.
13863 Enter or leave the TUI mode. When the TUI mode is left,
13864 the curses window management is left and @value{GDBN} operates using
13865 its standard mode writing on the terminal directly. When the TUI
13866 mode is entered, the control is given back to the curses windows.
13867 The screen is then refreshed.
13871 Use a TUI layout with only one window. The layout will
13872 either be @samp{source} or @samp{assembly}. When the TUI mode
13873 is not active, it will switch to the TUI mode.
13875 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13879 Use a TUI layout with at least two windows. When the current
13880 layout shows already two windows, a next layout with two windows is used.
13881 When a new layout is chosen, one window will always be common to the
13882 previous layout and the new one.
13884 Think of it as the Emacs @kbd{C-x 2} binding.
13888 The following key bindings are handled only by the TUI mode:
13893 Scroll the active window one page up.
13897 Scroll the active window one page down.
13901 Scroll the active window one line up.
13905 Scroll the active window one line down.
13909 Scroll the active window one column left.
13913 Scroll the active window one column right.
13917 Refresh the screen.
13921 In the TUI mode, the arrow keys are used by the active window
13922 for scrolling. This means they are not available for readline. It is
13923 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13924 @key{C-b} and @key{C-f}.
13927 @section TUI specific commands
13928 @cindex TUI commands
13930 The TUI has specific commands to control the text windows.
13931 These commands are always available, that is they do not depend on
13932 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13933 is in the standard mode, using these commands will automatically switch
13938 @kindex layout next
13939 Display the next layout.
13942 @kindex layout prev
13943 Display the previous layout.
13947 Display the source window only.
13951 Display the assembly window only.
13954 @kindex layout split
13955 Display the source and assembly window.
13958 @kindex layout regs
13959 Display the register window together with the source or assembly window.
13961 @item focus next | prev | src | asm | regs | split
13963 Set the focus to the named window.
13964 This command allows to change the active window so that scrolling keys
13965 can be affected to another window.
13969 Refresh the screen. This is similar to using @key{C-L} key.
13973 Update the source window and the current execution point.
13975 @item winheight @var{name} +@var{count}
13976 @itemx winheight @var{name} -@var{count}
13978 Change the height of the window @var{name} by @var{count}
13979 lines. Positive counts increase the height, while negative counts
13984 @node TUI Configuration
13985 @section TUI configuration variables
13986 @cindex TUI configuration variables
13988 The TUI has several configuration variables that control the
13989 appearance of windows on the terminal.
13992 @item set tui border-kind @var{kind}
13993 @kindex set tui border-kind
13994 Select the border appearance for the source, assembly and register windows.
13995 The possible values are the following:
13998 Use a space character to draw the border.
14001 Use ascii characters + - and | to draw the border.
14004 Use the Alternate Character Set to draw the border. The border is
14005 drawn using character line graphics if the terminal supports them.
14009 @item set tui active-border-mode @var{mode}
14010 @kindex set tui active-border-mode
14011 Select the attributes to display the border of the active window.
14012 The possible values are @code{normal}, @code{standout}, @code{reverse},
14013 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
14015 @item set tui border-mode @var{mode}
14016 @kindex set tui border-mode
14017 Select the attributes to display the border of other windows.
14018 The @var{mode} can be one of the following:
14021 Use normal attributes to display the border.
14027 Use reverse video mode.
14030 Use half bright mode.
14032 @item half-standout
14033 Use half bright and standout mode.
14036 Use extra bright or bold mode.
14038 @item bold-standout
14039 Use extra bright or bold and standout mode.
14046 @chapter Using @value{GDBN} under @sc{gnu} Emacs
14049 @cindex @sc{gnu} Emacs
14050 A special interface allows you to use @sc{gnu} Emacs to view (and
14051 edit) the source files for the program you are debugging with
14054 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
14055 executable file you want to debug as an argument. This command starts
14056 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
14057 created Emacs buffer.
14058 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
14060 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
14065 All ``terminal'' input and output goes through the Emacs buffer.
14068 This applies both to @value{GDBN} commands and their output, and to the input
14069 and output done by the program you are debugging.
14071 This is useful because it means that you can copy the text of previous
14072 commands and input them again; you can even use parts of the output
14075 All the facilities of Emacs' Shell mode are available for interacting
14076 with your program. In particular, you can send signals the usual
14077 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
14082 @value{GDBN} displays source code through Emacs.
14085 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
14086 source file for that frame and puts an arrow (@samp{=>}) at the
14087 left margin of the current line. Emacs uses a separate buffer for
14088 source display, and splits the screen to show both your @value{GDBN} session
14091 Explicit @value{GDBN} @code{list} or search commands still produce output as
14092 usual, but you probably have no reason to use them from Emacs.
14095 @emph{Warning:} If the directory where your program resides is not your
14096 current directory, it can be easy to confuse Emacs about the location of
14097 the source files, in which case the auxiliary display buffer does not
14098 appear to show your source. @value{GDBN} can find programs by searching your
14099 environment's @code{PATH} variable, so the @value{GDBN} input and output
14100 session proceeds normally; but Emacs does not get enough information
14101 back from @value{GDBN} to locate the source files in this situation. To
14102 avoid this problem, either start @value{GDBN} mode from the directory where
14103 your program resides, or specify an absolute file name when prompted for the
14104 @kbd{M-x gdb} argument.
14106 A similar confusion can result if you use the @value{GDBN} @code{file} command to
14107 switch to debugging a program in some other location, from an existing
14108 @value{GDBN} buffer in Emacs.
14111 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
14112 you need to call @value{GDBN} by a different name (for example, if you keep
14113 several configurations around, with different names) you can set the
14114 Emacs variable @code{gdb-command-name}; for example,
14117 (setq gdb-command-name "mygdb")
14121 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
14122 in your @file{.emacs} file) makes Emacs call the program named
14123 ``@code{mygdb}'' instead.
14125 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
14126 addition to the standard Shell mode commands:
14130 Describe the features of Emacs' @value{GDBN} Mode.
14133 Execute to another source line, like the @value{GDBN} @code{step} command; also
14134 update the display window to show the current file and location.
14137 Execute to next source line in this function, skipping all function
14138 calls, like the @value{GDBN} @code{next} command. Then update the display window
14139 to show the current file and location.
14142 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
14143 display window accordingly.
14145 @item M-x gdb-nexti
14146 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
14147 display window accordingly.
14150 Execute until exit from the selected stack frame, like the @value{GDBN}
14151 @code{finish} command.
14154 Continue execution of your program, like the @value{GDBN} @code{continue}
14157 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
14160 Go up the number of frames indicated by the numeric argument
14161 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
14162 like the @value{GDBN} @code{up} command.
14164 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
14167 Go down the number of frames indicated by the numeric argument, like the
14168 @value{GDBN} @code{down} command.
14170 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
14173 Read the number where the cursor is positioned, and insert it at the end
14174 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
14175 around an address that was displayed earlier, type @kbd{disassemble};
14176 then move the cursor to the address display, and pick up the
14177 argument for @code{disassemble} by typing @kbd{C-x &}.
14179 You can customize this further by defining elements of the list
14180 @code{gdb-print-command}; once it is defined, you can format or
14181 otherwise process numbers picked up by @kbd{C-x &} before they are
14182 inserted. A numeric argument to @kbd{C-x &} indicates that you
14183 wish special formatting, and also acts as an index to pick an element of the
14184 list. If the list element is a string, the number to be inserted is
14185 formatted using the Emacs function @code{format}; otherwise the number
14186 is passed as an argument to the corresponding list element.
14189 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
14190 tells @value{GDBN} to set a breakpoint on the source line point is on.
14192 If you accidentally delete the source-display buffer, an easy way to get
14193 it back is to type the command @code{f} in the @value{GDBN} buffer, to
14194 request a frame display; when you run under Emacs, this recreates
14195 the source buffer if necessary to show you the context of the current
14198 The source files displayed in Emacs are in ordinary Emacs buffers
14199 which are visiting the source files in the usual way. You can edit
14200 the files with these buffers if you wish; but keep in mind that @value{GDBN}
14201 communicates with Emacs in terms of line numbers. If you add or
14202 delete lines from the text, the line numbers that @value{GDBN} knows cease
14203 to correspond properly with the code.
14205 @c The following dropped because Epoch is nonstandard. Reactivate
14206 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
14208 @kindex Emacs Epoch environment
14212 Version 18 of @sc{gnu} Emacs has a built-in window system
14213 called the @code{epoch}
14214 environment. Users of this environment can use a new command,
14215 @code{inspect} which performs identically to @code{print} except that
14216 each value is printed in its own window.
14219 @include annotate.texi
14220 @include gdbmi.texinfo
14223 @chapter Reporting Bugs in @value{GDBN}
14224 @cindex bugs in @value{GDBN}
14225 @cindex reporting bugs in @value{GDBN}
14227 Your bug reports play an essential role in making @value{GDBN} reliable.
14229 Reporting a bug may help you by bringing a solution to your problem, or it
14230 may not. But in any case the principal function of a bug report is to help
14231 the entire community by making the next version of @value{GDBN} work better. Bug
14232 reports are your contribution to the maintenance of @value{GDBN}.
14234 In order for a bug report to serve its purpose, you must include the
14235 information that enables us to fix the bug.
14238 * Bug Criteria:: Have you found a bug?
14239 * Bug Reporting:: How to report bugs
14243 @section Have you found a bug?
14244 @cindex bug criteria
14246 If you are not sure whether you have found a bug, here are some guidelines:
14249 @cindex fatal signal
14250 @cindex debugger crash
14251 @cindex crash of debugger
14253 If the debugger gets a fatal signal, for any input whatever, that is a
14254 @value{GDBN} bug. Reliable debuggers never crash.
14256 @cindex error on valid input
14258 If @value{GDBN} produces an error message for valid input, that is a
14259 bug. (Note that if you're cross debugging, the problem may also be
14260 somewhere in the connection to the target.)
14262 @cindex invalid input
14264 If @value{GDBN} does not produce an error message for invalid input,
14265 that is a bug. However, you should note that your idea of
14266 ``invalid input'' might be our idea of ``an extension'' or ``support
14267 for traditional practice''.
14270 If you are an experienced user of debugging tools, your suggestions
14271 for improvement of @value{GDBN} are welcome in any case.
14274 @node Bug Reporting
14275 @section How to report bugs
14276 @cindex bug reports
14277 @cindex @value{GDBN} bugs, reporting
14279 A number of companies and individuals offer support for @sc{gnu} products.
14280 If you obtained @value{GDBN} from a support organization, we recommend you
14281 contact that organization first.
14283 You can find contact information for many support companies and
14284 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
14286 @c should add a web page ref...
14288 In any event, we also recommend that you send bug reports for
14289 @value{GDBN} to this addresses:
14295 @strong{Do not send bug reports to @samp{info-gdb}, or to
14296 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
14297 not want to receive bug reports. Those that do have arranged to receive
14300 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
14301 serves as a repeater. The mailing list and the newsgroup carry exactly
14302 the same messages. Often people think of posting bug reports to the
14303 newsgroup instead of mailing them. This appears to work, but it has one
14304 problem which can be crucial: a newsgroup posting often lacks a mail
14305 path back to the sender. Thus, if we need to ask for more information,
14306 we may be unable to reach you. For this reason, it is better to send
14307 bug reports to the mailing list.
14309 As a last resort, send bug reports on paper to:
14312 @sc{gnu} Debugger Bugs
14313 Free Software Foundation Inc.
14314 59 Temple Place - Suite 330
14315 Boston, MA 02111-1307
14319 The fundamental principle of reporting bugs usefully is this:
14320 @strong{report all the facts}. If you are not sure whether to state a
14321 fact or leave it out, state it!
14323 Often people omit facts because they think they know what causes the
14324 problem and assume that some details do not matter. Thus, you might
14325 assume that the name of the variable you use in an example does not matter.
14326 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
14327 stray memory reference which happens to fetch from the location where that
14328 name is stored in memory; perhaps, if the name were different, the contents
14329 of that location would fool the debugger into doing the right thing despite
14330 the bug. Play it safe and give a specific, complete example. That is the
14331 easiest thing for you to do, and the most helpful.
14333 Keep in mind that the purpose of a bug report is to enable us to fix the
14334 bug. It may be that the bug has been reported previously, but neither
14335 you nor we can know that unless your bug report is complete and
14338 Sometimes people give a few sketchy facts and ask, ``Does this ring a
14339 bell?'' Those bug reports are useless, and we urge everyone to
14340 @emph{refuse to respond to them} except to chide the sender to report
14343 To enable us to fix the bug, you should include all these things:
14347 The version of @value{GDBN}. @value{GDBN} announces it if you start
14348 with no arguments; you can also print it at any time using @code{show
14351 Without this, we will not know whether there is any point in looking for
14352 the bug in the current version of @value{GDBN}.
14355 The type of machine you are using, and the operating system name and
14359 What compiler (and its version) was used to compile @value{GDBN}---e.g.
14360 ``@value{GCC}--2.8.1''.
14363 What compiler (and its version) was used to compile the program you are
14364 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
14365 C Compiler''. For GCC, you can say @code{gcc --version} to get this
14366 information; for other compilers, see the documentation for those
14370 The command arguments you gave the compiler to compile your example and
14371 observe the bug. For example, did you use @samp{-O}? To guarantee
14372 you will not omit something important, list them all. A copy of the
14373 Makefile (or the output from make) is sufficient.
14375 If we were to try to guess the arguments, we would probably guess wrong
14376 and then we might not encounter the bug.
14379 A complete input script, and all necessary source files, that will
14383 A description of what behavior you observe that you believe is
14384 incorrect. For example, ``It gets a fatal signal.''
14386 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
14387 will certainly notice it. But if the bug is incorrect output, we might
14388 not notice unless it is glaringly wrong. You might as well not give us
14389 a chance to make a mistake.
14391 Even if the problem you experience is a fatal signal, you should still
14392 say so explicitly. Suppose something strange is going on, such as, your
14393 copy of @value{GDBN} is out of synch, or you have encountered a bug in
14394 the C library on your system. (This has happened!) Your copy might
14395 crash and ours would not. If you told us to expect a crash, then when
14396 ours fails to crash, we would know that the bug was not happening for
14397 us. If you had not told us to expect a crash, then we would not be able
14398 to draw any conclusion from our observations.
14401 If you wish to suggest changes to the @value{GDBN} source, send us context
14402 diffs. If you even discuss something in the @value{GDBN} source, refer to
14403 it by context, not by line number.
14405 The line numbers in our development sources will not match those in your
14406 sources. Your line numbers would convey no useful information to us.
14410 Here are some things that are not necessary:
14414 A description of the envelope of the bug.
14416 Often people who encounter a bug spend a lot of time investigating
14417 which changes to the input file will make the bug go away and which
14418 changes will not affect it.
14420 This is often time consuming and not very useful, because the way we
14421 will find the bug is by running a single example under the debugger
14422 with breakpoints, not by pure deduction from a series of examples.
14423 We recommend that you save your time for something else.
14425 Of course, if you can find a simpler example to report @emph{instead}
14426 of the original one, that is a convenience for us. Errors in the
14427 output will be easier to spot, running under the debugger will take
14428 less time, and so on.
14430 However, simplification is not vital; if you do not want to do this,
14431 report the bug anyway and send us the entire test case you used.
14434 A patch for the bug.
14436 A patch for the bug does help us if it is a good one. But do not omit
14437 the necessary information, such as the test case, on the assumption that
14438 a patch is all we need. We might see problems with your patch and decide
14439 to fix the problem another way, or we might not understand it at all.
14441 Sometimes with a program as complicated as @value{GDBN} it is very hard to
14442 construct an example that will make the program follow a certain path
14443 through the code. If you do not send us the example, we will not be able
14444 to construct one, so we will not be able to verify that the bug is fixed.
14446 And if we cannot understand what bug you are trying to fix, or why your
14447 patch should be an improvement, we will not install it. A test case will
14448 help us to understand.
14451 A guess about what the bug is or what it depends on.
14453 Such guesses are usually wrong. Even we cannot guess right about such
14454 things without first using the debugger to find the facts.
14457 @c The readline documentation is distributed with the readline code
14458 @c and consists of the two following files:
14460 @c inc-hist.texinfo
14461 @c Use -I with makeinfo to point to the appropriate directory,
14462 @c environment var TEXINPUTS with TeX.
14463 @include rluser.texinfo
14464 @include inc-hist.texinfo
14467 @node Formatting Documentation
14468 @appendix Formatting Documentation
14470 @cindex @value{GDBN} reference card
14471 @cindex reference card
14472 The @value{GDBN} 4 release includes an already-formatted reference card, ready
14473 for printing with PostScript or Ghostscript, in the @file{gdb}
14474 subdirectory of the main source directory@footnote{In
14475 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
14476 release.}. If you can use PostScript or Ghostscript with your printer,
14477 you can print the reference card immediately with @file{refcard.ps}.
14479 The release also includes the source for the reference card. You
14480 can format it, using @TeX{}, by typing:
14486 The @value{GDBN} reference card is designed to print in @dfn{landscape}
14487 mode on US ``letter'' size paper;
14488 that is, on a sheet 11 inches wide by 8.5 inches
14489 high. You will need to specify this form of printing as an option to
14490 your @sc{dvi} output program.
14492 @cindex documentation
14494 All the documentation for @value{GDBN} comes as part of the machine-readable
14495 distribution. The documentation is written in Texinfo format, which is
14496 a documentation system that uses a single source file to produce both
14497 on-line information and a printed manual. You can use one of the Info
14498 formatting commands to create the on-line version of the documentation
14499 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
14501 @value{GDBN} includes an already formatted copy of the on-line Info
14502 version of this manual in the @file{gdb} subdirectory. The main Info
14503 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
14504 subordinate files matching @samp{gdb.info*} in the same directory. If
14505 necessary, you can print out these files, or read them with any editor;
14506 but they are easier to read using the @code{info} subsystem in @sc{gnu}
14507 Emacs or the standalone @code{info} program, available as part of the
14508 @sc{gnu} Texinfo distribution.
14510 If you want to format these Info files yourself, you need one of the
14511 Info formatting programs, such as @code{texinfo-format-buffer} or
14514 If you have @code{makeinfo} installed, and are in the top level
14515 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
14516 version @value{GDBVN}), you can make the Info file by typing:
14523 If you want to typeset and print copies of this manual, you need @TeX{},
14524 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
14525 Texinfo definitions file.
14527 @TeX{} is a typesetting program; it does not print files directly, but
14528 produces output files called @sc{dvi} files. To print a typeset
14529 document, you need a program to print @sc{dvi} files. If your system
14530 has @TeX{} installed, chances are it has such a program. The precise
14531 command to use depends on your system; @kbd{lpr -d} is common; another
14532 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14533 require a file name without any extension or a @samp{.dvi} extension.
14535 @TeX{} also requires a macro definitions file called
14536 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14537 written in Texinfo format. On its own, @TeX{} cannot either read or
14538 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14539 and is located in the @file{gdb-@var{version-number}/texinfo}
14542 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14543 typeset and print this manual. First switch to the the @file{gdb}
14544 subdirectory of the main source directory (for example, to
14545 @file{gdb-@value{GDBVN}/gdb}) and type:
14551 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14553 @node Installing GDB
14554 @appendix Installing @value{GDBN}
14555 @cindex configuring @value{GDBN}
14556 @cindex installation
14558 @value{GDBN} comes with a @code{configure} script that automates the process
14559 of preparing @value{GDBN} for installation; you can then use @code{make} to
14560 build the @code{gdb} program.
14562 @c irrelevant in info file; it's as current as the code it lives with.
14563 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14564 look at the @file{README} file in the sources; we may have improved the
14565 installation procedures since publishing this manual.}
14568 The @value{GDBN} distribution includes all the source code you need for
14569 @value{GDBN} in a single directory, whose name is usually composed by
14570 appending the version number to @samp{gdb}.
14572 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14573 @file{gdb-@value{GDBVN}} directory. That directory contains:
14576 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14577 script for configuring @value{GDBN} and all its supporting libraries
14579 @item gdb-@value{GDBVN}/gdb
14580 the source specific to @value{GDBN} itself
14582 @item gdb-@value{GDBVN}/bfd
14583 source for the Binary File Descriptor library
14585 @item gdb-@value{GDBVN}/include
14586 @sc{gnu} include files
14588 @item gdb-@value{GDBVN}/libiberty
14589 source for the @samp{-liberty} free software library
14591 @item gdb-@value{GDBVN}/opcodes
14592 source for the library of opcode tables and disassemblers
14594 @item gdb-@value{GDBVN}/readline
14595 source for the @sc{gnu} command-line interface
14597 @item gdb-@value{GDBVN}/glob
14598 source for the @sc{gnu} filename pattern-matching subroutine
14600 @item gdb-@value{GDBVN}/mmalloc
14601 source for the @sc{gnu} memory-mapped malloc package
14604 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14605 from the @file{gdb-@var{version-number}} source directory, which in
14606 this example is the @file{gdb-@value{GDBVN}} directory.
14608 First switch to the @file{gdb-@var{version-number}} source directory
14609 if you are not already in it; then run @code{configure}. Pass the
14610 identifier for the platform on which @value{GDBN} will run as an
14616 cd gdb-@value{GDBVN}
14617 ./configure @var{host}
14622 where @var{host} is an identifier such as @samp{sun4} or
14623 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14624 (You can often leave off @var{host}; @code{configure} tries to guess the
14625 correct value by examining your system.)
14627 Running @samp{configure @var{host}} and then running @code{make} builds the
14628 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14629 libraries, then @code{gdb} itself. The configured source files, and the
14630 binaries, are left in the corresponding source directories.
14633 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14634 system does not recognize this automatically when you run a different
14635 shell, you may need to run @code{sh} on it explicitly:
14638 sh configure @var{host}
14641 If you run @code{configure} from a directory that contains source
14642 directories for multiple libraries or programs, such as the
14643 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14644 creates configuration files for every directory level underneath (unless
14645 you tell it not to, with the @samp{--norecursion} option).
14647 You can run the @code{configure} script from any of the
14648 subordinate directories in the @value{GDBN} distribution if you only want to
14649 configure that subdirectory, but be sure to specify a path to it.
14651 For example, with version @value{GDBVN}, type the following to configure only
14652 the @code{bfd} subdirectory:
14656 cd gdb-@value{GDBVN}/bfd
14657 ../configure @var{host}
14661 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14662 However, you should make sure that the shell on your path (named by
14663 the @samp{SHELL} environment variable) is publicly readable. Remember
14664 that @value{GDBN} uses the shell to start your program---some systems refuse to
14665 let @value{GDBN} debug child processes whose programs are not readable.
14668 * Separate Objdir:: Compiling @value{GDBN} in another directory
14669 * Config Names:: Specifying names for hosts and targets
14670 * Configure Options:: Summary of options for configure
14673 @node Separate Objdir
14674 @section Compiling @value{GDBN} in another directory
14676 If you want to run @value{GDBN} versions for several host or target machines,
14677 you need a different @code{gdb} compiled for each combination of
14678 host and target. @code{configure} is designed to make this easy by
14679 allowing you to generate each configuration in a separate subdirectory,
14680 rather than in the source directory. If your @code{make} program
14681 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14682 @code{make} in each of these directories builds the @code{gdb}
14683 program specified there.
14685 To build @code{gdb} in a separate directory, run @code{configure}
14686 with the @samp{--srcdir} option to specify where to find the source.
14687 (You also need to specify a path to find @code{configure}
14688 itself from your working directory. If the path to @code{configure}
14689 would be the same as the argument to @samp{--srcdir}, you can leave out
14690 the @samp{--srcdir} option; it is assumed.)
14692 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14693 separate directory for a Sun 4 like this:
14697 cd gdb-@value{GDBVN}
14700 ../gdb-@value{GDBVN}/configure sun4
14705 When @code{configure} builds a configuration using a remote source
14706 directory, it creates a tree for the binaries with the same structure
14707 (and using the same names) as the tree under the source directory. In
14708 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14709 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14710 @file{gdb-sun4/gdb}.
14712 One popular reason to build several @value{GDBN} configurations in separate
14713 directories is to configure @value{GDBN} for cross-compiling (where
14714 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14715 programs that run on another machine---the @dfn{target}).
14716 You specify a cross-debugging target by
14717 giving the @samp{--target=@var{target}} option to @code{configure}.
14719 When you run @code{make} to build a program or library, you must run
14720 it in a configured directory---whatever directory you were in when you
14721 called @code{configure} (or one of its subdirectories).
14723 The @code{Makefile} that @code{configure} generates in each source
14724 directory also runs recursively. If you type @code{make} in a source
14725 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14726 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14727 will build all the required libraries, and then build GDB.
14729 When you have multiple hosts or targets configured in separate
14730 directories, you can run @code{make} on them in parallel (for example,
14731 if they are NFS-mounted on each of the hosts); they will not interfere
14735 @section Specifying names for hosts and targets
14737 The specifications used for hosts and targets in the @code{configure}
14738 script are based on a three-part naming scheme, but some short predefined
14739 aliases are also supported. The full naming scheme encodes three pieces
14740 of information in the following pattern:
14743 @var{architecture}-@var{vendor}-@var{os}
14746 For example, you can use the alias @code{sun4} as a @var{host} argument,
14747 or as the value for @var{target} in a @code{--target=@var{target}}
14748 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14750 The @code{configure} script accompanying @value{GDBN} does not provide
14751 any query facility to list all supported host and target names or
14752 aliases. @code{configure} calls the Bourne shell script
14753 @code{config.sub} to map abbreviations to full names; you can read the
14754 script, if you wish, or you can use it to test your guesses on
14755 abbreviations---for example:
14758 % sh config.sub i386-linux
14760 % sh config.sub alpha-linux
14761 alpha-unknown-linux-gnu
14762 % sh config.sub hp9k700
14764 % sh config.sub sun4
14765 sparc-sun-sunos4.1.1
14766 % sh config.sub sun3
14767 m68k-sun-sunos4.1.1
14768 % sh config.sub i986v
14769 Invalid configuration `i986v': machine `i986v' not recognized
14773 @code{config.sub} is also distributed in the @value{GDBN} source
14774 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14776 @node Configure Options
14777 @section @code{configure} options
14779 Here is a summary of the @code{configure} options and arguments that
14780 are most often useful for building @value{GDBN}. @code{configure} also has
14781 several other options not listed here. @inforef{What Configure
14782 Does,,configure.info}, for a full explanation of @code{configure}.
14785 configure @r{[}--help@r{]}
14786 @r{[}--prefix=@var{dir}@r{]}
14787 @r{[}--exec-prefix=@var{dir}@r{]}
14788 @r{[}--srcdir=@var{dirname}@r{]}
14789 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14790 @r{[}--target=@var{target}@r{]}
14795 You may introduce options with a single @samp{-} rather than
14796 @samp{--} if you prefer; but you may abbreviate option names if you use
14801 Display a quick summary of how to invoke @code{configure}.
14803 @item --prefix=@var{dir}
14804 Configure the source to install programs and files under directory
14807 @item --exec-prefix=@var{dir}
14808 Configure the source to install programs under directory
14811 @c avoid splitting the warning from the explanation:
14813 @item --srcdir=@var{dirname}
14814 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14815 @code{make} that implements the @code{VPATH} feature.}@*
14816 Use this option to make configurations in directories separate from the
14817 @value{GDBN} source directories. Among other things, you can use this to
14818 build (or maintain) several configurations simultaneously, in separate
14819 directories. @code{configure} writes configuration specific files in
14820 the current directory, but arranges for them to use the source in the
14821 directory @var{dirname}. @code{configure} creates directories under
14822 the working directory in parallel to the source directories below
14825 @item --norecursion
14826 Configure only the directory level where @code{configure} is executed; do not
14827 propagate configuration to subdirectories.
14829 @item --target=@var{target}
14830 Configure @value{GDBN} for cross-debugging programs running on the specified
14831 @var{target}. Without this option, @value{GDBN} is configured to debug
14832 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14834 There is no convenient way to generate a list of all available targets.
14836 @item @var{host} @dots{}
14837 Configure @value{GDBN} to run on the specified @var{host}.
14839 There is no convenient way to generate a list of all available hosts.
14842 There are many other options available as well, but they are generally
14843 needed for special purposes only.
14851 % I think something like @colophon should be in texinfo. In the
14853 \long\def\colophon{\hbox to0pt{}\vfill
14854 \centerline{The body of this manual is set in}
14855 \centerline{\fontname\tenrm,}
14856 \centerline{with headings in {\bf\fontname\tenbf}}
14857 \centerline{and examples in {\tt\fontname\tentt}.}
14858 \centerline{{\it\fontname\tenit\/},}
14859 \centerline{{\bf\fontname\tenbf}, and}
14860 \centerline{{\sl\fontname\tensl\/}}
14861 \centerline{are used for emphasis.}\vfill}
14863 % Blame: doc@cygnus.com, 1991.
14866 @c TeX can handle the contents at the start but makeinfo 3.12 can not