1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
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
26 @c readline appendices use @vindex, @findex and @ftable,
27 @c annotate.texi and gdbmi use @findex.
31 @c !!set GDB manual's edition---not the same as GDB version!
32 @c This is updated by GNU Press.
35 @c !!set GDB edit command default editor
38 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
40 @c This is a dir.info fragment to support semi-automated addition of
41 @c manuals to an info tree.
42 @dircategory Software development
44 * Gdb: (gdb). The GNU debugger.
48 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996,
49 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
50 Free Software Foundation, Inc.
52 Permission is granted to copy, distribute and/or modify this document
53 under the terms of the GNU Free Documentation License, Version 1.1 or
54 any later version published by the Free Software Foundation; with the
55 Invariant Sections being ``Free Software'' and ``Free Software Needs
56 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
57 and with the Back-Cover Texts as in (a) below.
59 (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
60 this GNU Manual. Buying copies from GNU Press supports the FSF in
61 developing GNU and promoting software freedom.''
65 This file documents the @sc{gnu} debugger @value{GDBN}.
67 This is the @value{EDITION} Edition, of @cite{Debugging with
68 @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN}
69 @ifset VERSION_PACKAGE
70 @value{VERSION_PACKAGE}
72 Version @value{GDBVN}.
78 @title Debugging with @value{GDBN}
79 @subtitle The @sc{gnu} Source-Level Debugger
81 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
82 @ifset VERSION_PACKAGE
84 @subtitle @value{VERSION_PACKAGE}
86 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
90 \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par
91 \hfill {\it Debugging with @value{GDBN}}\par
92 \hfill \TeX{}info \texinfoversion\par
96 @vskip 0pt plus 1filll
97 Published by the Free Software Foundation @*
98 51 Franklin Street, Fifth Floor,
99 Boston, MA 02110-1301, USA@*
100 ISBN 1-882114-77-9 @*
104 This edition of the GDB manual is dedicated to the memory of Fred
105 Fish. Fred was a long-standing contributor to GDB and to Free
106 software in general. We will miss him.
111 @node Top, Summary, (dir), (dir)
113 @top Debugging with @value{GDBN}
115 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
117 This is the @value{EDITION} Edition, for @value{GDBN}
118 @ifset VERSION_PACKAGE
119 @value{VERSION_PACKAGE}
121 Version @value{GDBVN}.
123 Copyright (C) 1988-2009 Free Software Foundation, Inc.
125 This edition of the GDB manual is dedicated to the memory of Fred
126 Fish. Fred was a long-standing contributor to GDB and to Free
127 software in general. We will miss him.
130 * Summary:: Summary of @value{GDBN}
131 * Sample Session:: A sample @value{GDBN} session
133 * Invocation:: Getting in and out of @value{GDBN}
134 * Commands:: @value{GDBN} commands
135 * Running:: Running programs under @value{GDBN}
136 * Stopping:: Stopping and continuing
137 * Reverse Execution:: Running programs backward
138 * Process Record and Replay:: Recording inferior's execution and replaying it
139 * Stack:: Examining the stack
140 * Source:: Examining source files
141 * Data:: Examining data
142 * Optimized Code:: Debugging optimized code
143 * Macros:: Preprocessor Macros
144 * Tracepoints:: Debugging remote targets non-intrusively
145 * Overlays:: Debugging programs that use overlays
147 * Languages:: Using @value{GDBN} with different languages
149 * Symbols:: Examining the symbol table
150 * Altering:: Altering execution
151 * GDB Files:: @value{GDBN} files
152 * Targets:: Specifying a debugging target
153 * Remote Debugging:: Debugging remote programs
154 * Configurations:: Configuration-specific information
155 * Controlling GDB:: Controlling @value{GDBN}
156 * Extending GDB:: Extending @value{GDBN}
157 * Interpreters:: Command Interpreters
158 * TUI:: @value{GDBN} Text User Interface
159 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
160 * GDB/MI:: @value{GDBN}'s Machine Interface.
161 * Annotations:: @value{GDBN}'s annotation interface.
162 * JIT Interface:: Using the JIT debugging interface.
164 * GDB Bugs:: Reporting bugs in @value{GDBN}
166 * Command Line Editing:: Command Line Editing
167 * Using History Interactively:: Using History Interactively
168 * Formatting Documentation:: How to format and print @value{GDBN} documentation
169 * Installing GDB:: Installing GDB
170 * Maintenance Commands:: Maintenance Commands
171 * Remote Protocol:: GDB Remote Serial Protocol
172 * Agent Expressions:: The GDB Agent Expression Mechanism
173 * Target Descriptions:: How targets can describe themselves to
175 * Operating System Information:: Getting additional information from
177 * Copying:: GNU General Public License says
178 how you can copy and share GDB
179 * GNU Free Documentation License:: The license for this documentation
188 @unnumbered Summary of @value{GDBN}
190 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
191 going on ``inside'' another program while it executes---or what another
192 program was doing at the moment it crashed.
194 @value{GDBN} can do four main kinds of things (plus other things in support of
195 these) to help you catch bugs in the act:
199 Start your program, specifying anything that might affect its behavior.
202 Make your program stop on specified conditions.
205 Examine what has happened, when your program has stopped.
208 Change things in your program, so you can experiment with correcting the
209 effects of one bug and go on to learn about another.
212 You can use @value{GDBN} to debug programs written in C and C@t{++}.
213 For more information, see @ref{Supported Languages,,Supported Languages}.
214 For more information, see @ref{C,,C and C++}.
217 Support for Modula-2 is partial. For information on Modula-2, see
218 @ref{Modula-2,,Modula-2}.
221 Debugging Pascal programs which use sets, subranges, file variables, or
222 nested functions does not currently work. @value{GDBN} does not support
223 entering expressions, printing values, or similar features using Pascal
227 @value{GDBN} can be used to debug programs written in Fortran, although
228 it may be necessary to refer to some variables with a trailing
231 @value{GDBN} can be used to debug programs written in Objective-C,
232 using either the Apple/NeXT or the GNU Objective-C runtime.
235 * Free Software:: Freely redistributable software
236 * Contributors:: Contributors to GDB
240 @unnumberedsec Free Software
242 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
243 General Public License
244 (GPL). The GPL gives you the freedom to copy or adapt a licensed
245 program---but every person getting a copy also gets with it the
246 freedom to modify that copy (which means that they must get access to
247 the source code), and the freedom to distribute further copies.
248 Typical software companies use copyrights to limit your freedoms; the
249 Free Software Foundation uses the GPL to preserve these freedoms.
251 Fundamentally, the General Public License is a license which says that
252 you have these freedoms and that you cannot take these freedoms away
255 @unnumberedsec Free Software Needs Free Documentation
257 The biggest deficiency in the free software community today is not in
258 the software---it is the lack of good free documentation that we can
259 include with the free software. Many of our most important
260 programs do not come with free reference manuals and free introductory
261 texts. Documentation is an essential part of any software package;
262 when an important free software package does not come with a free
263 manual and a free tutorial, that is a major gap. We have many such
266 Consider Perl, for instance. The tutorial manuals that people
267 normally use are non-free. How did this come about? Because the
268 authors of those manuals published them with restrictive terms---no
269 copying, no modification, source files not available---which exclude
270 them from the free software world.
272 That wasn't the first time this sort of thing happened, and it was far
273 from the last. Many times we have heard a GNU user eagerly describe a
274 manual that he is writing, his intended contribution to the community,
275 only to learn that he had ruined everything by signing a publication
276 contract to make it non-free.
278 Free documentation, like free software, is a matter of freedom, not
279 price. The problem with the non-free manual is not that publishers
280 charge a price for printed copies---that in itself is fine. (The Free
281 Software Foundation sells printed copies of manuals, too.) The
282 problem is the restrictions on the use of the manual. Free manuals
283 are available in source code form, and give you permission to copy and
284 modify. Non-free manuals do not allow this.
286 The criteria of freedom for a free manual are roughly the same as for
287 free software. Redistribution (including the normal kinds of
288 commercial redistribution) must be permitted, so that the manual can
289 accompany every copy of the program, both on-line and on paper.
291 Permission for modification of the technical content is crucial too.
292 When people modify the software, adding or changing features, if they
293 are conscientious they will change the manual too---so they can
294 provide accurate and clear documentation for the modified program. A
295 manual that leaves you no choice but to write a new manual to document
296 a changed version of the program is not really available to our
299 Some kinds of limits on the way modification is handled are
300 acceptable. For example, requirements to preserve the original
301 author's copyright notice, the distribution terms, or the list of
302 authors, are ok. It is also no problem to require modified versions
303 to include notice that they were modified. Even entire sections that
304 may not be deleted or changed are acceptable, as long as they deal
305 with nontechnical topics (like this one). These kinds of restrictions
306 are acceptable because they don't obstruct the community's normal use
309 However, it must be possible to modify all the @emph{technical}
310 content of the manual, and then distribute the result in all the usual
311 media, through all the usual channels. Otherwise, the restrictions
312 obstruct the use of the manual, it is not free, and we need another
313 manual to replace it.
315 Please spread the word about this issue. Our community continues to
316 lose manuals to proprietary publishing. If we spread the word that
317 free software needs free reference manuals and free tutorials, perhaps
318 the next person who wants to contribute by writing documentation will
319 realize, before it is too late, that only free manuals contribute to
320 the free software community.
322 If you are writing documentation, please insist on publishing it under
323 the GNU Free Documentation License or another free documentation
324 license. Remember that this decision requires your approval---you
325 don't have to let the publisher decide. Some commercial publishers
326 will use a free license if you insist, but they will not propose the
327 option; it is up to you to raise the issue and say firmly that this is
328 what you want. If the publisher you are dealing with refuses, please
329 try other publishers. If you're not sure whether a proposed license
330 is free, write to @email{licensing@@gnu.org}.
332 You can encourage commercial publishers to sell more free, copylefted
333 manuals and tutorials by buying them, and particularly by buying
334 copies from the publishers that paid for their writing or for major
335 improvements. Meanwhile, try to avoid buying non-free documentation
336 at all. Check the distribution terms of a manual before you buy it,
337 and insist that whoever seeks your business must respect your freedom.
338 Check the history of the book, and try to reward the publishers that
339 have paid or pay the authors to work on it.
341 The Free Software Foundation maintains a list of free documentation
342 published by other publishers, at
343 @url{http://www.fsf.org/doc/other-free-books.html}.
346 @unnumberedsec Contributors to @value{GDBN}
348 Richard Stallman was the original author of @value{GDBN}, and of many
349 other @sc{gnu} programs. Many others have contributed to its
350 development. This section attempts to credit major contributors. One
351 of the virtues of free software is that everyone is free to contribute
352 to it; with regret, we cannot actually acknowledge everyone here. The
353 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
354 blow-by-blow account.
356 Changes much prior to version 2.0 are lost in the mists of time.
359 @emph{Plea:} Additions to this section are particularly welcome. If you
360 or your friends (or enemies, to be evenhanded) have been unfairly
361 omitted from this list, we would like to add your names!
364 So that they may not regard their many labors as thankless, we
365 particularly thank those who shepherded @value{GDBN} through major
367 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
368 Jim Blandy (release 4.18);
369 Jason Molenda (release 4.17);
370 Stan Shebs (release 4.14);
371 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
372 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
373 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
374 Jim Kingdon (releases 3.5, 3.4, and 3.3);
375 and Randy Smith (releases 3.2, 3.1, and 3.0).
377 Richard Stallman, assisted at various times by Peter TerMaat, Chris
378 Hanson, and Richard Mlynarik, handled releases through 2.8.
380 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
381 in @value{GDBN}, with significant additional contributions from Per
382 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
383 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
384 much general update work leading to release 3.0).
386 @value{GDBN} uses the BFD subroutine library to examine multiple
387 object-file formats; BFD was a joint project of David V.
388 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
390 David Johnson wrote the original COFF support; Pace Willison did
391 the original support for encapsulated COFF.
393 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
395 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
396 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
398 Jean-Daniel Fekete contributed Sun 386i support.
399 Chris Hanson improved the HP9000 support.
400 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
401 David Johnson contributed Encore Umax support.
402 Jyrki Kuoppala contributed Altos 3068 support.
403 Jeff Law contributed HP PA and SOM support.
404 Keith Packard contributed NS32K support.
405 Doug Rabson contributed Acorn Risc Machine support.
406 Bob Rusk contributed Harris Nighthawk CX-UX support.
407 Chris Smith contributed Convex support (and Fortran debugging).
408 Jonathan Stone contributed Pyramid support.
409 Michael Tiemann contributed SPARC support.
410 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
411 Pace Willison contributed Intel 386 support.
412 Jay Vosburgh contributed Symmetry support.
413 Marko Mlinar contributed OpenRISC 1000 support.
415 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
417 Rich Schaefer and Peter Schauer helped with support of SunOS shared
420 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
421 about several machine instruction sets.
423 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
424 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
425 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
426 and RDI targets, respectively.
428 Brian Fox is the author of the readline libraries providing
429 command-line editing and command history.
431 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
432 Modula-2 support, and contributed the Languages chapter of this manual.
434 Fred Fish wrote most of the support for Unix System Vr4.
435 He also enhanced the command-completion support to cover C@t{++} overloaded
438 Hitachi America (now Renesas America), Ltd. sponsored the support for
439 H8/300, H8/500, and Super-H processors.
441 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
443 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
446 Toshiba sponsored the support for the TX39 Mips processor.
448 Matsushita sponsored the support for the MN10200 and MN10300 processors.
450 Fujitsu sponsored the support for SPARClite and FR30 processors.
452 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
455 Michael Snyder added support for tracepoints.
457 Stu Grossman wrote gdbserver.
459 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
460 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
462 The following people at the Hewlett-Packard Company contributed
463 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
464 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
465 compiler, and the Text User Interface (nee Terminal User Interface):
466 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
467 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
468 provided HP-specific information in this manual.
470 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
471 Robert Hoehne made significant contributions to the DJGPP port.
473 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
474 development since 1991. Cygnus engineers who have worked on @value{GDBN}
475 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
476 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
477 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
478 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
479 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
480 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
481 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
482 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
483 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
484 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
485 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
486 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
487 Zuhn have made contributions both large and small.
489 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
490 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
492 Jim Blandy added support for preprocessor macros, while working for Red
495 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
496 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
497 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
498 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
499 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
500 with the migration of old architectures to this new framework.
502 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
503 unwinder framework, this consisting of a fresh new design featuring
504 frame IDs, independent frame sniffers, and the sentinel frame. Mark
505 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
506 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
507 trad unwinders. The architecture-specific changes, each involving a
508 complete rewrite of the architecture's frame code, were carried out by
509 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
510 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
511 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
512 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
515 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
516 Tensilica, Inc.@: contributed support for Xtensa processors. Others
517 who have worked on the Xtensa port of @value{GDBN} in the past include
518 Steve Tjiang, John Newlin, and Scott Foehner.
520 Michael Eager and staff of Xilinx, Inc., contributed support for the
521 Xilinx MicroBlaze architecture.
524 @chapter A Sample @value{GDBN} Session
526 You can use this manual at your leisure to read all about @value{GDBN}.
527 However, a handful of commands are enough to get started using the
528 debugger. This chapter illustrates those commands.
531 In this sample session, we emphasize user input like this: @b{input},
532 to make it easier to pick out from the surrounding output.
535 @c FIXME: this example may not be appropriate for some configs, where
536 @c FIXME...primary interest is in remote use.
538 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
539 processor) exhibits the following bug: sometimes, when we change its
540 quote strings from the default, the commands used to capture one macro
541 definition within another stop working. In the following short @code{m4}
542 session, we define a macro @code{foo} which expands to @code{0000}; we
543 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
544 same thing. However, when we change the open quote string to
545 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
546 procedure fails to define a new synonym @code{baz}:
555 @b{define(bar,defn(`foo'))}
559 @b{changequote(<QUOTE>,<UNQUOTE>)}
561 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
564 m4: End of input: 0: fatal error: EOF in string
568 Let us use @value{GDBN} to try to see what is going on.
571 $ @b{@value{GDBP} m4}
572 @c FIXME: this falsifies the exact text played out, to permit smallbook
573 @c FIXME... format to come out better.
574 @value{GDBN} is free software and you are welcome to distribute copies
575 of it under certain conditions; type "show copying" to see
577 There is absolutely no warranty for @value{GDBN}; type "show warranty"
580 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
585 @value{GDBN} reads only enough symbol data to know where to find the
586 rest when needed; as a result, the first prompt comes up very quickly.
587 We now tell @value{GDBN} to use a narrower display width than usual, so
588 that examples fit in this manual.
591 (@value{GDBP}) @b{set width 70}
595 We need to see how the @code{m4} built-in @code{changequote} works.
596 Having looked at the source, we know the relevant subroutine is
597 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
598 @code{break} command.
601 (@value{GDBP}) @b{break m4_changequote}
602 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
606 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
607 control; as long as control does not reach the @code{m4_changequote}
608 subroutine, the program runs as usual:
611 (@value{GDBP}) @b{run}
612 Starting program: /work/Editorial/gdb/gnu/m4/m4
620 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
621 suspends execution of @code{m4}, displaying information about the
622 context where it stops.
625 @b{changequote(<QUOTE>,<UNQUOTE>)}
627 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
629 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
633 Now we use the command @code{n} (@code{next}) to advance execution to
634 the next line of the current function.
638 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
643 @code{set_quotes} looks like a promising subroutine. We can go into it
644 by using the command @code{s} (@code{step}) instead of @code{next}.
645 @code{step} goes to the next line to be executed in @emph{any}
646 subroutine, so it steps into @code{set_quotes}.
650 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
652 530 if (lquote != def_lquote)
656 The display that shows the subroutine where @code{m4} is now
657 suspended (and its arguments) is called a stack frame display. It
658 shows a summary of the stack. We can use the @code{backtrace}
659 command (which can also be spelled @code{bt}), to see where we are
660 in the stack as a whole: the @code{backtrace} command displays a
661 stack frame for each active subroutine.
664 (@value{GDBP}) @b{bt}
665 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
667 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
669 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
670 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
672 #4 0x79dc in expand_input () at macro.c:40
673 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
677 We step through a few more lines to see what happens. The first two
678 times, we can use @samp{s}; the next two times we use @code{n} to avoid
679 falling into the @code{xstrdup} subroutine.
683 0x3b5c 532 if (rquote != def_rquote)
685 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
686 def_lquote : xstrdup(lq);
688 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
691 538 len_lquote = strlen(rquote);
695 The last line displayed looks a little odd; we can examine the variables
696 @code{lquote} and @code{rquote} to see if they are in fact the new left
697 and right quotes we specified. We use the command @code{p}
698 (@code{print}) to see their values.
701 (@value{GDBP}) @b{p lquote}
702 $1 = 0x35d40 "<QUOTE>"
703 (@value{GDBP}) @b{p rquote}
704 $2 = 0x35d50 "<UNQUOTE>"
708 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
709 To look at some context, we can display ten lines of source
710 surrounding the current line with the @code{l} (@code{list}) command.
716 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
718 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
721 538 len_lquote = strlen(rquote);
722 539 len_rquote = strlen(lquote);
729 Let us step past the two lines that set @code{len_lquote} and
730 @code{len_rquote}, and then examine the values of those variables.
734 539 len_rquote = strlen(lquote);
737 (@value{GDBP}) @b{p len_lquote}
739 (@value{GDBP}) @b{p len_rquote}
744 That certainly looks wrong, assuming @code{len_lquote} and
745 @code{len_rquote} are meant to be the lengths of @code{lquote} and
746 @code{rquote} respectively. We can set them to better values using
747 the @code{p} command, since it can print the value of
748 any expression---and that expression can include subroutine calls and
752 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
754 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
759 Is that enough to fix the problem of using the new quotes with the
760 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
761 executing with the @code{c} (@code{continue}) command, and then try the
762 example that caused trouble initially:
768 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
775 Success! The new quotes now work just as well as the default ones. The
776 problem seems to have been just the two typos defining the wrong
777 lengths. We allow @code{m4} exit by giving it an EOF as input:
781 Program exited normally.
785 The message @samp{Program exited normally.} is from @value{GDBN}; it
786 indicates @code{m4} has finished executing. We can end our @value{GDBN}
787 session with the @value{GDBN} @code{quit} command.
790 (@value{GDBP}) @b{quit}
794 @chapter Getting In and Out of @value{GDBN}
796 This chapter discusses how to start @value{GDBN}, and how to get out of it.
800 type @samp{@value{GDBP}} to start @value{GDBN}.
802 type @kbd{quit} or @kbd{Ctrl-d} to exit.
806 * Invoking GDB:: How to start @value{GDBN}
807 * Quitting GDB:: How to quit @value{GDBN}
808 * Shell Commands:: How to use shell commands inside @value{GDBN}
809 * Logging Output:: How to log @value{GDBN}'s output to a file
813 @section Invoking @value{GDBN}
815 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
816 @value{GDBN} reads commands from the terminal until you tell it to exit.
818 You can also run @code{@value{GDBP}} with a variety of arguments and options,
819 to specify more of your debugging environment at the outset.
821 The command-line options described here are designed
822 to cover a variety of situations; in some environments, some of these
823 options may effectively be unavailable.
825 The most usual way to start @value{GDBN} is with one argument,
826 specifying an executable program:
829 @value{GDBP} @var{program}
833 You can also start with both an executable program and a core file
837 @value{GDBP} @var{program} @var{core}
840 You can, instead, specify a process ID as a second argument, if you want
841 to debug a running process:
844 @value{GDBP} @var{program} 1234
848 would attach @value{GDBN} to process @code{1234} (unless you also have a file
849 named @file{1234}; @value{GDBN} does check for a core file first).
851 Taking advantage of the second command-line argument requires a fairly
852 complete operating system; when you use @value{GDBN} as a remote
853 debugger attached to a bare board, there may not be any notion of
854 ``process'', and there is often no way to get a core dump. @value{GDBN}
855 will warn you if it is unable to attach or to read core dumps.
857 You can optionally have @code{@value{GDBP}} pass any arguments after the
858 executable file to the inferior using @code{--args}. This option stops
861 @value{GDBP} --args gcc -O2 -c foo.c
863 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
864 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
866 You can run @code{@value{GDBP}} without printing the front material, which describes
867 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
874 You can further control how @value{GDBN} starts up by using command-line
875 options. @value{GDBN} itself can remind you of the options available.
885 to display all available options and briefly describe their use
886 (@samp{@value{GDBP} -h} is a shorter equivalent).
888 All options and command line arguments you give are processed
889 in sequential order. The order makes a difference when the
890 @samp{-x} option is used.
894 * File Options:: Choosing files
895 * Mode Options:: Choosing modes
896 * Startup:: What @value{GDBN} does during startup
900 @subsection Choosing Files
902 When @value{GDBN} starts, it reads any arguments other than options as
903 specifying an executable file and core file (or process ID). This is
904 the same as if the arguments were specified by the @samp{-se} and
905 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
906 first argument that does not have an associated option flag as
907 equivalent to the @samp{-se} option followed by that argument; and the
908 second argument that does not have an associated option flag, if any, as
909 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
910 If the second argument begins with a decimal digit, @value{GDBN} will
911 first attempt to attach to it as a process, and if that fails, attempt
912 to open it as a corefile. If you have a corefile whose name begins with
913 a digit, you can prevent @value{GDBN} from treating it as a pid by
914 prefixing it with @file{./}, e.g.@: @file{./12345}.
916 If @value{GDBN} has not been configured to included core file support,
917 such as for most embedded targets, then it will complain about a second
918 argument and ignore it.
920 Many options have both long and short forms; both are shown in the
921 following list. @value{GDBN} also recognizes the long forms if you truncate
922 them, so long as enough of the option is present to be unambiguous.
923 (If you prefer, you can flag option arguments with @samp{--} rather
924 than @samp{-}, though we illustrate the more usual convention.)
926 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
927 @c way, both those who look for -foo and --foo in the index, will find
931 @item -symbols @var{file}
933 @cindex @code{--symbols}
935 Read symbol table from file @var{file}.
937 @item -exec @var{file}
939 @cindex @code{--exec}
941 Use file @var{file} as the executable file to execute when appropriate,
942 and for examining pure data in conjunction with a core dump.
946 Read symbol table from file @var{file} and use it as the executable
949 @item -core @var{file}
951 @cindex @code{--core}
953 Use file @var{file} as a core dump to examine.
955 @item -pid @var{number}
956 @itemx -p @var{number}
959 Connect to process ID @var{number}, as with the @code{attach} command.
961 @item -command @var{file}
963 @cindex @code{--command}
965 Execute @value{GDBN} commands from file @var{file}. @xref{Command
966 Files,, Command files}.
968 @item -eval-command @var{command}
969 @itemx -ex @var{command}
970 @cindex @code{--eval-command}
972 Execute a single @value{GDBN} command.
974 This option may be used multiple times to call multiple commands. It may
975 also be interleaved with @samp{-command} as required.
978 @value{GDBP} -ex 'target sim' -ex 'load' \
979 -x setbreakpoints -ex 'run' a.out
982 @item -directory @var{directory}
983 @itemx -d @var{directory}
984 @cindex @code{--directory}
986 Add @var{directory} to the path to search for source and script files.
990 @cindex @code{--readnow}
992 Read each symbol file's entire symbol table immediately, rather than
993 the default, which is to read it incrementally as it is needed.
994 This makes startup slower, but makes future operations faster.
999 @subsection Choosing Modes
1001 You can run @value{GDBN} in various alternative modes---for example, in
1002 batch mode or quiet mode.
1009 Do not execute commands found in any initialization files. Normally,
1010 @value{GDBN} executes the commands in these files after all the command
1011 options and arguments have been processed. @xref{Command Files,,Command
1017 @cindex @code{--quiet}
1018 @cindex @code{--silent}
1020 ``Quiet''. Do not print the introductory and copyright messages. These
1021 messages are also suppressed in batch mode.
1024 @cindex @code{--batch}
1025 Run in batch mode. Exit with status @code{0} after processing all the
1026 command files specified with @samp{-x} (and all commands from
1027 initialization files, if not inhibited with @samp{-n}). Exit with
1028 nonzero status if an error occurs in executing the @value{GDBN} commands
1029 in the command files.
1031 Batch mode may be useful for running @value{GDBN} as a filter, for
1032 example to download and run a program on another computer; in order to
1033 make this more useful, the message
1036 Program exited normally.
1040 (which is ordinarily issued whenever a program running under
1041 @value{GDBN} control terminates) is not issued when running in batch
1045 @cindex @code{--batch-silent}
1046 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1047 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1048 unaffected). This is much quieter than @samp{-silent} and would be useless
1049 for an interactive session.
1051 This is particularly useful when using targets that give @samp{Loading section}
1052 messages, for example.
1054 Note that targets that give their output via @value{GDBN}, as opposed to
1055 writing directly to @code{stdout}, will also be made silent.
1057 @item -return-child-result
1058 @cindex @code{--return-child-result}
1059 The return code from @value{GDBN} will be the return code from the child
1060 process (the process being debugged), with the following exceptions:
1064 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1065 internal error. In this case the exit code is the same as it would have been
1066 without @samp{-return-child-result}.
1068 The user quits with an explicit value. E.g., @samp{quit 1}.
1070 The child process never runs, or is not allowed to terminate, in which case
1071 the exit code will be -1.
1074 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1075 when @value{GDBN} is being used as a remote program loader or simulator
1080 @cindex @code{--nowindows}
1082 ``No windows''. If @value{GDBN} comes with a graphical user interface
1083 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1084 interface. If no GUI is available, this option has no effect.
1088 @cindex @code{--windows}
1090 If @value{GDBN} includes a GUI, then this option requires it to be
1093 @item -cd @var{directory}
1095 Run @value{GDBN} using @var{directory} as its working directory,
1096 instead of the current directory.
1100 @cindex @code{--fullname}
1102 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1103 subprocess. It tells @value{GDBN} to output the full file name and line
1104 number in a standard, recognizable fashion each time a stack frame is
1105 displayed (which includes each time your program stops). This
1106 recognizable format looks like two @samp{\032} characters, followed by
1107 the file name, line number and character position separated by colons,
1108 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1109 @samp{\032} characters as a signal to display the source code for the
1113 @cindex @code{--epoch}
1114 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1115 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1116 routines so as to allow Epoch to display values of expressions in a
1119 @item -annotate @var{level}
1120 @cindex @code{--annotate}
1121 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1122 effect is identical to using @samp{set annotate @var{level}}
1123 (@pxref{Annotations}). The annotation @var{level} controls how much
1124 information @value{GDBN} prints together with its prompt, values of
1125 expressions, source lines, and other types of output. Level 0 is the
1126 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1127 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1128 that control @value{GDBN}, and level 2 has been deprecated.
1130 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1134 @cindex @code{--args}
1135 Change interpretation of command line so that arguments following the
1136 executable file are passed as command line arguments to the inferior.
1137 This option stops option processing.
1139 @item -baud @var{bps}
1141 @cindex @code{--baud}
1143 Set the line speed (baud rate or bits per second) of any serial
1144 interface used by @value{GDBN} for remote debugging.
1146 @item -l @var{timeout}
1148 Set the timeout (in seconds) of any communication used by @value{GDBN}
1149 for remote debugging.
1151 @item -tty @var{device}
1152 @itemx -t @var{device}
1153 @cindex @code{--tty}
1155 Run using @var{device} for your program's standard input and output.
1156 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1158 @c resolve the situation of these eventually
1160 @cindex @code{--tui}
1161 Activate the @dfn{Text User Interface} when starting. The Text User
1162 Interface manages several text windows on the terminal, showing
1163 source, assembly, registers and @value{GDBN} command outputs
1164 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Alternatively, the
1165 Text User Interface can be enabled by invoking the program
1166 @samp{@value{GDBTUI}}. Do not use this option if you run @value{GDBN} from
1167 Emacs (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1170 @c @cindex @code{--xdb}
1171 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1172 @c For information, see the file @file{xdb_trans.html}, which is usually
1173 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1176 @item -interpreter @var{interp}
1177 @cindex @code{--interpreter}
1178 Use the interpreter @var{interp} for interface with the controlling
1179 program or device. This option is meant to be set by programs which
1180 communicate with @value{GDBN} using it as a back end.
1181 @xref{Interpreters, , Command Interpreters}.
1183 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1184 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1185 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1186 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1187 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1188 @sc{gdb/mi} interfaces are no longer supported.
1191 @cindex @code{--write}
1192 Open the executable and core files for both reading and writing. This
1193 is equivalent to the @samp{set write on} command inside @value{GDBN}
1197 @cindex @code{--statistics}
1198 This option causes @value{GDBN} to print statistics about time and
1199 memory usage after it completes each command and returns to the prompt.
1202 @cindex @code{--version}
1203 This option causes @value{GDBN} to print its version number and
1204 no-warranty blurb, and exit.
1209 @subsection What @value{GDBN} Does During Startup
1210 @cindex @value{GDBN} startup
1212 Here's the description of what @value{GDBN} does during session startup:
1216 Sets up the command interpreter as specified by the command line
1217 (@pxref{Mode Options, interpreter}).
1221 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1222 used when building @value{GDBN}; @pxref{System-wide configuration,
1223 ,System-wide configuration and settings}) and executes all the commands in
1227 Reads the init file (if any) in your home directory@footnote{On
1228 DOS/Windows systems, the home directory is the one pointed to by the
1229 @code{HOME} environment variable.} and executes all the commands in
1233 Processes command line options and operands.
1236 Reads and executes the commands from init file (if any) in the current
1237 working directory. This is only done if the current directory is
1238 different from your home directory. Thus, you can have more than one
1239 init file, one generic in your home directory, and another, specific
1240 to the program you are debugging, in the directory where you invoke
1244 Reads command files specified by the @samp{-x} option. @xref{Command
1245 Files}, for more details about @value{GDBN} command files.
1248 Reads the command history recorded in the @dfn{history file}.
1249 @xref{Command History}, for more details about the command history and the
1250 files where @value{GDBN} records it.
1253 Init files use the same syntax as @dfn{command files} (@pxref{Command
1254 Files}) and are processed by @value{GDBN} in the same way. The init
1255 file in your home directory can set options (such as @samp{set
1256 complaints}) that affect subsequent processing of command line options
1257 and operands. Init files are not executed if you use the @samp{-nx}
1258 option (@pxref{Mode Options, ,Choosing Modes}).
1260 To display the list of init files loaded by gdb at startup, you
1261 can use @kbd{gdb --help}.
1263 @cindex init file name
1264 @cindex @file{.gdbinit}
1265 @cindex @file{gdb.ini}
1266 The @value{GDBN} init files are normally called @file{.gdbinit}.
1267 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1268 the limitations of file names imposed by DOS filesystems. The Windows
1269 ports of @value{GDBN} use the standard name, but if they find a
1270 @file{gdb.ini} file, they warn you about that and suggest to rename
1271 the file to the standard name.
1275 @section Quitting @value{GDBN}
1276 @cindex exiting @value{GDBN}
1277 @cindex leaving @value{GDBN}
1280 @kindex quit @r{[}@var{expression}@r{]}
1281 @kindex q @r{(@code{quit})}
1282 @item quit @r{[}@var{expression}@r{]}
1284 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1285 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1286 do not supply @var{expression}, @value{GDBN} will terminate normally;
1287 otherwise it will terminate using the result of @var{expression} as the
1292 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1293 terminates the action of any @value{GDBN} command that is in progress and
1294 returns to @value{GDBN} command level. It is safe to type the interrupt
1295 character at any time because @value{GDBN} does not allow it to take effect
1296 until a time when it is safe.
1298 If you have been using @value{GDBN} to control an attached process or
1299 device, you can release it with the @code{detach} command
1300 (@pxref{Attach, ,Debugging an Already-running Process}).
1302 @node Shell Commands
1303 @section Shell Commands
1305 If you need to execute occasional shell commands during your
1306 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1307 just use the @code{shell} command.
1311 @cindex shell escape
1312 @item shell @var{command string}
1313 Invoke a standard shell to execute @var{command string}.
1314 If it exists, the environment variable @code{SHELL} determines which
1315 shell to run. Otherwise @value{GDBN} uses the default shell
1316 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1319 The utility @code{make} is often needed in development environments.
1320 You do not have to use the @code{shell} command for this purpose in
1325 @cindex calling make
1326 @item make @var{make-args}
1327 Execute the @code{make} program with the specified
1328 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1331 @node Logging Output
1332 @section Logging Output
1333 @cindex logging @value{GDBN} output
1334 @cindex save @value{GDBN} output to a file
1336 You may want to save the output of @value{GDBN} commands to a file.
1337 There are several commands to control @value{GDBN}'s logging.
1341 @item set logging on
1343 @item set logging off
1345 @cindex logging file name
1346 @item set logging file @var{file}
1347 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1348 @item set logging overwrite [on|off]
1349 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1350 you want @code{set logging on} to overwrite the logfile instead.
1351 @item set logging redirect [on|off]
1352 By default, @value{GDBN} output will go to both the terminal and the logfile.
1353 Set @code{redirect} if you want output to go only to the log file.
1354 @kindex show logging
1356 Show the current values of the logging settings.
1360 @chapter @value{GDBN} Commands
1362 You can abbreviate a @value{GDBN} command to the first few letters of the command
1363 name, if that abbreviation is unambiguous; and you can repeat certain
1364 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1365 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1366 show you the alternatives available, if there is more than one possibility).
1369 * Command Syntax:: How to give commands to @value{GDBN}
1370 * Completion:: Command completion
1371 * Help:: How to ask @value{GDBN} for help
1374 @node Command Syntax
1375 @section Command Syntax
1377 A @value{GDBN} command is a single line of input. There is no limit on
1378 how long it can be. It starts with a command name, which is followed by
1379 arguments whose meaning depends on the command name. For example, the
1380 command @code{step} accepts an argument which is the number of times to
1381 step, as in @samp{step 5}. You can also use the @code{step} command
1382 with no arguments. Some commands do not allow any arguments.
1384 @cindex abbreviation
1385 @value{GDBN} command names may always be truncated if that abbreviation is
1386 unambiguous. Other possible command abbreviations are listed in the
1387 documentation for individual commands. In some cases, even ambiguous
1388 abbreviations are allowed; for example, @code{s} is specially defined as
1389 equivalent to @code{step} even though there are other commands whose
1390 names start with @code{s}. You can test abbreviations by using them as
1391 arguments to the @code{help} command.
1393 @cindex repeating commands
1394 @kindex RET @r{(repeat last command)}
1395 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1396 repeat the previous command. Certain commands (for example, @code{run})
1397 will not repeat this way; these are commands whose unintentional
1398 repetition might cause trouble and which you are unlikely to want to
1399 repeat. User-defined commands can disable this feature; see
1400 @ref{Define, dont-repeat}.
1402 The @code{list} and @code{x} commands, when you repeat them with
1403 @key{RET}, construct new arguments rather than repeating
1404 exactly as typed. This permits easy scanning of source or memory.
1406 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1407 output, in a way similar to the common utility @code{more}
1408 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1409 @key{RET} too many in this situation, @value{GDBN} disables command
1410 repetition after any command that generates this sort of display.
1412 @kindex # @r{(a comment)}
1414 Any text from a @kbd{#} to the end of the line is a comment; it does
1415 nothing. This is useful mainly in command files (@pxref{Command
1416 Files,,Command Files}).
1418 @cindex repeating command sequences
1419 @kindex Ctrl-o @r{(operate-and-get-next)}
1420 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1421 commands. This command accepts the current line, like @key{RET}, and
1422 then fetches the next line relative to the current line from the history
1426 @section Command Completion
1429 @cindex word completion
1430 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1431 only one possibility; it can also show you what the valid possibilities
1432 are for the next word in a command, at any time. This works for @value{GDBN}
1433 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1435 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1436 of a word. If there is only one possibility, @value{GDBN} fills in the
1437 word, and waits for you to finish the command (or press @key{RET} to
1438 enter it). For example, if you type
1440 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1441 @c complete accuracy in these examples; space introduced for clarity.
1442 @c If texinfo enhancements make it unnecessary, it would be nice to
1443 @c replace " @key" by "@key" in the following...
1445 (@value{GDBP}) info bre @key{TAB}
1449 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1450 the only @code{info} subcommand beginning with @samp{bre}:
1453 (@value{GDBP}) info breakpoints
1457 You can either press @key{RET} at this point, to run the @code{info
1458 breakpoints} command, or backspace and enter something else, if
1459 @samp{breakpoints} does not look like the command you expected. (If you
1460 were sure you wanted @code{info breakpoints} in the first place, you
1461 might as well just type @key{RET} immediately after @samp{info bre},
1462 to exploit command abbreviations rather than command completion).
1464 If there is more than one possibility for the next word when you press
1465 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1466 characters and try again, or just press @key{TAB} a second time;
1467 @value{GDBN} displays all the possible completions for that word. For
1468 example, you might want to set a breakpoint on a subroutine whose name
1469 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1470 just sounds the bell. Typing @key{TAB} again displays all the
1471 function names in your program that begin with those characters, for
1475 (@value{GDBP}) b make_ @key{TAB}
1476 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1477 make_a_section_from_file make_environ
1478 make_abs_section make_function_type
1479 make_blockvector make_pointer_type
1480 make_cleanup make_reference_type
1481 make_command make_symbol_completion_list
1482 (@value{GDBP}) b make_
1486 After displaying the available possibilities, @value{GDBN} copies your
1487 partial input (@samp{b make_} in the example) so you can finish the
1490 If you just want to see the list of alternatives in the first place, you
1491 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1492 means @kbd{@key{META} ?}. You can type this either by holding down a
1493 key designated as the @key{META} shift on your keyboard (if there is
1494 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1496 @cindex quotes in commands
1497 @cindex completion of quoted strings
1498 Sometimes the string you need, while logically a ``word'', may contain
1499 parentheses or other characters that @value{GDBN} normally excludes from
1500 its notion of a word. To permit word completion to work in this
1501 situation, you may enclose words in @code{'} (single quote marks) in
1502 @value{GDBN} commands.
1504 The most likely situation where you might need this is in typing the
1505 name of a C@t{++} function. This is because C@t{++} allows function
1506 overloading (multiple definitions of the same function, distinguished
1507 by argument type). For example, when you want to set a breakpoint you
1508 may need to distinguish whether you mean the version of @code{name}
1509 that takes an @code{int} parameter, @code{name(int)}, or the version
1510 that takes a @code{float} parameter, @code{name(float)}. To use the
1511 word-completion facilities in this situation, type a single quote
1512 @code{'} at the beginning of the function name. This alerts
1513 @value{GDBN} that it may need to consider more information than usual
1514 when you press @key{TAB} or @kbd{M-?} to request word completion:
1517 (@value{GDBP}) b 'bubble( @kbd{M-?}
1518 bubble(double,double) bubble(int,int)
1519 (@value{GDBP}) b 'bubble(
1522 In some cases, @value{GDBN} can tell that completing a name requires using
1523 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1524 completing as much as it can) if you do not type the quote in the first
1528 (@value{GDBP}) b bub @key{TAB}
1529 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1530 (@value{GDBP}) b 'bubble(
1534 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1535 you have not yet started typing the argument list when you ask for
1536 completion on an overloaded symbol.
1538 For more information about overloaded functions, see @ref{C Plus Plus
1539 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1540 overload-resolution off} to disable overload resolution;
1541 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1543 @cindex completion of structure field names
1544 @cindex structure field name completion
1545 @cindex completion of union field names
1546 @cindex union field name completion
1547 When completing in an expression which looks up a field in a
1548 structure, @value{GDBN} also tries@footnote{The completer can be
1549 confused by certain kinds of invalid expressions. Also, it only
1550 examines the static type of the expression, not the dynamic type.} to
1551 limit completions to the field names available in the type of the
1555 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1556 magic to_delete to_fputs to_put to_rewind
1557 to_data to_flush to_isatty to_read to_write
1561 This is because the @code{gdb_stdout} is a variable of the type
1562 @code{struct ui_file} that is defined in @value{GDBN} sources as
1569 ui_file_flush_ftype *to_flush;
1570 ui_file_write_ftype *to_write;
1571 ui_file_fputs_ftype *to_fputs;
1572 ui_file_read_ftype *to_read;
1573 ui_file_delete_ftype *to_delete;
1574 ui_file_isatty_ftype *to_isatty;
1575 ui_file_rewind_ftype *to_rewind;
1576 ui_file_put_ftype *to_put;
1583 @section Getting Help
1584 @cindex online documentation
1587 You can always ask @value{GDBN} itself for information on its commands,
1588 using the command @code{help}.
1591 @kindex h @r{(@code{help})}
1594 You can use @code{help} (abbreviated @code{h}) with no arguments to
1595 display a short list of named classes of commands:
1599 List of classes of commands:
1601 aliases -- Aliases of other commands
1602 breakpoints -- Making program stop at certain points
1603 data -- Examining data
1604 files -- Specifying and examining files
1605 internals -- Maintenance commands
1606 obscure -- Obscure features
1607 running -- Running the program
1608 stack -- Examining the stack
1609 status -- Status inquiries
1610 support -- Support facilities
1611 tracepoints -- Tracing of program execution without
1612 stopping the program
1613 user-defined -- User-defined commands
1615 Type "help" followed by a class name for a list of
1616 commands in that class.
1617 Type "help" followed by command name for full
1619 Command name abbreviations are allowed if unambiguous.
1622 @c the above line break eliminates huge line overfull...
1624 @item help @var{class}
1625 Using one of the general help classes as an argument, you can get a
1626 list of the individual commands in that class. For example, here is the
1627 help display for the class @code{status}:
1630 (@value{GDBP}) help status
1635 @c Line break in "show" line falsifies real output, but needed
1636 @c to fit in smallbook page size.
1637 info -- Generic command for showing things
1638 about the program being debugged
1639 show -- Generic command for showing things
1642 Type "help" followed by command name for full
1644 Command name abbreviations are allowed if unambiguous.
1648 @item help @var{command}
1649 With a command name as @code{help} argument, @value{GDBN} displays a
1650 short paragraph on how to use that command.
1653 @item apropos @var{args}
1654 The @code{apropos} command searches through all of the @value{GDBN}
1655 commands, and their documentation, for the regular expression specified in
1656 @var{args}. It prints out all matches found. For example:
1667 set symbol-reloading -- Set dynamic symbol table reloading
1668 multiple times in one run
1669 show symbol-reloading -- Show dynamic symbol table reloading
1670 multiple times in one run
1675 @item complete @var{args}
1676 The @code{complete @var{args}} command lists all the possible completions
1677 for the beginning of a command. Use @var{args} to specify the beginning of the
1678 command you want completed. For example:
1684 @noindent results in:
1695 @noindent This is intended for use by @sc{gnu} Emacs.
1698 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1699 and @code{show} to inquire about the state of your program, or the state
1700 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1701 manual introduces each of them in the appropriate context. The listings
1702 under @code{info} and under @code{show} in the Index point to
1703 all the sub-commands. @xref{Index}.
1708 @kindex i @r{(@code{info})}
1710 This command (abbreviated @code{i}) is for describing the state of your
1711 program. For example, you can show the arguments passed to a function
1712 with @code{info args}, list the registers currently in use with @code{info
1713 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1714 You can get a complete list of the @code{info} sub-commands with
1715 @w{@code{help info}}.
1719 You can assign the result of an expression to an environment variable with
1720 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1721 @code{set prompt $}.
1725 In contrast to @code{info}, @code{show} is for describing the state of
1726 @value{GDBN} itself.
1727 You can change most of the things you can @code{show}, by using the
1728 related command @code{set}; for example, you can control what number
1729 system is used for displays with @code{set radix}, or simply inquire
1730 which is currently in use with @code{show radix}.
1733 To display all the settable parameters and their current
1734 values, you can use @code{show} with no arguments; you may also use
1735 @code{info set}. Both commands produce the same display.
1736 @c FIXME: "info set" violates the rule that "info" is for state of
1737 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1738 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1742 Here are three miscellaneous @code{show} subcommands, all of which are
1743 exceptional in lacking corresponding @code{set} commands:
1746 @kindex show version
1747 @cindex @value{GDBN} version number
1749 Show what version of @value{GDBN} is running. You should include this
1750 information in @value{GDBN} bug-reports. If multiple versions of
1751 @value{GDBN} are in use at your site, you may need to determine which
1752 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1753 commands are introduced, and old ones may wither away. Also, many
1754 system vendors ship variant versions of @value{GDBN}, and there are
1755 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1756 The version number is the same as the one announced when you start
1759 @kindex show copying
1760 @kindex info copying
1761 @cindex display @value{GDBN} copyright
1764 Display information about permission for copying @value{GDBN}.
1766 @kindex show warranty
1767 @kindex info warranty
1769 @itemx info warranty
1770 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1771 if your version of @value{GDBN} comes with one.
1776 @chapter Running Programs Under @value{GDBN}
1778 When you run a program under @value{GDBN}, you must first generate
1779 debugging information when you compile it.
1781 You may start @value{GDBN} with its arguments, if any, in an environment
1782 of your choice. If you are doing native debugging, you may redirect
1783 your program's input and output, debug an already running process, or
1784 kill a child process.
1787 * Compilation:: Compiling for debugging
1788 * Starting:: Starting your program
1789 * Arguments:: Your program's arguments
1790 * Environment:: Your program's environment
1792 * Working Directory:: Your program's working directory
1793 * Input/Output:: Your program's input and output
1794 * Attach:: Debugging an already-running process
1795 * Kill Process:: Killing the child process
1797 * Inferiors:: Debugging multiple inferiors
1798 * Threads:: Debugging programs with multiple threads
1799 * Processes:: Debugging programs with multiple processes
1800 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1804 @section Compiling for Debugging
1806 In order to debug a program effectively, you need to generate
1807 debugging information when you compile it. This debugging information
1808 is stored in the object file; it describes the data type of each
1809 variable or function and the correspondence between source line numbers
1810 and addresses in the executable code.
1812 To request debugging information, specify the @samp{-g} option when you run
1815 Programs that are to be shipped to your customers are compiled with
1816 optimizations, using the @samp{-O} compiler option. However, some
1817 compilers are unable to handle the @samp{-g} and @samp{-O} options
1818 together. Using those compilers, you cannot generate optimized
1819 executables containing debugging information.
1821 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1822 without @samp{-O}, making it possible to debug optimized code. We
1823 recommend that you @emph{always} use @samp{-g} whenever you compile a
1824 program. You may think your program is correct, but there is no sense
1825 in pushing your luck. For more information, see @ref{Optimized Code}.
1827 Older versions of the @sc{gnu} C compiler permitted a variant option
1828 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1829 format; if your @sc{gnu} C compiler has this option, do not use it.
1831 @value{GDBN} knows about preprocessor macros and can show you their
1832 expansion (@pxref{Macros}). Most compilers do not include information
1833 about preprocessor macros in the debugging information if you specify
1834 the @option{-g} flag alone, because this information is rather large.
1835 Version 3.1 and later of @value{NGCC}, the @sc{gnu} C compiler,
1836 provides macro information if you specify the options
1837 @option{-gdwarf-2} and @option{-g3}; the former option requests
1838 debugging information in the Dwarf 2 format, and the latter requests
1839 ``extra information''. In the future, we hope to find more compact
1840 ways to represent macro information, so that it can be included with
1845 @section Starting your Program
1851 @kindex r @r{(@code{run})}
1854 Use the @code{run} command to start your program under @value{GDBN}.
1855 You must first specify the program name (except on VxWorks) with an
1856 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1857 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1858 (@pxref{Files, ,Commands to Specify Files}).
1862 If you are running your program in an execution environment that
1863 supports processes, @code{run} creates an inferior process and makes
1864 that process run your program. In some environments without processes,
1865 @code{run} jumps to the start of your program. Other targets,
1866 like @samp{remote}, are always running. If you get an error
1867 message like this one:
1870 The "remote" target does not support "run".
1871 Try "help target" or "continue".
1875 then use @code{continue} to run your program. You may need @code{load}
1876 first (@pxref{load}).
1878 The execution of a program is affected by certain information it
1879 receives from its superior. @value{GDBN} provides ways to specify this
1880 information, which you must do @emph{before} starting your program. (You
1881 can change it after starting your program, but such changes only affect
1882 your program the next time you start it.) This information may be
1883 divided into four categories:
1886 @item The @emph{arguments.}
1887 Specify the arguments to give your program as the arguments of the
1888 @code{run} command. If a shell is available on your target, the shell
1889 is used to pass the arguments, so that you may use normal conventions
1890 (such as wildcard expansion or variable substitution) in describing
1892 In Unix systems, you can control which shell is used with the
1893 @code{SHELL} environment variable.
1894 @xref{Arguments, ,Your Program's Arguments}.
1896 @item The @emph{environment.}
1897 Your program normally inherits its environment from @value{GDBN}, but you can
1898 use the @value{GDBN} commands @code{set environment} and @code{unset
1899 environment} to change parts of the environment that affect
1900 your program. @xref{Environment, ,Your Program's Environment}.
1902 @item The @emph{working directory.}
1903 Your program inherits its working directory from @value{GDBN}. You can set
1904 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1905 @xref{Working Directory, ,Your Program's Working Directory}.
1907 @item The @emph{standard input and output.}
1908 Your program normally uses the same device for standard input and
1909 standard output as @value{GDBN} is using. You can redirect input and output
1910 in the @code{run} command line, or you can use the @code{tty} command to
1911 set a different device for your program.
1912 @xref{Input/Output, ,Your Program's Input and Output}.
1915 @emph{Warning:} While input and output redirection work, you cannot use
1916 pipes to pass the output of the program you are debugging to another
1917 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1921 When you issue the @code{run} command, your program begins to execute
1922 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
1923 of how to arrange for your program to stop. Once your program has
1924 stopped, you may call functions in your program, using the @code{print}
1925 or @code{call} commands. @xref{Data, ,Examining Data}.
1927 If the modification time of your symbol file has changed since the last
1928 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1929 table, and reads it again. When it does this, @value{GDBN} tries to retain
1930 your current breakpoints.
1935 @cindex run to main procedure
1936 The name of the main procedure can vary from language to language.
1937 With C or C@t{++}, the main procedure name is always @code{main}, but
1938 other languages such as Ada do not require a specific name for their
1939 main procedure. The debugger provides a convenient way to start the
1940 execution of the program and to stop at the beginning of the main
1941 procedure, depending on the language used.
1943 The @samp{start} command does the equivalent of setting a temporary
1944 breakpoint at the beginning of the main procedure and then invoking
1945 the @samp{run} command.
1947 @cindex elaboration phase
1948 Some programs contain an @dfn{elaboration} phase where some startup code is
1949 executed before the main procedure is called. This depends on the
1950 languages used to write your program. In C@t{++}, for instance,
1951 constructors for static and global objects are executed before
1952 @code{main} is called. It is therefore possible that the debugger stops
1953 before reaching the main procedure. However, the temporary breakpoint
1954 will remain to halt execution.
1956 Specify the arguments to give to your program as arguments to the
1957 @samp{start} command. These arguments will be given verbatim to the
1958 underlying @samp{run} command. Note that the same arguments will be
1959 reused if no argument is provided during subsequent calls to
1960 @samp{start} or @samp{run}.
1962 It is sometimes necessary to debug the program during elaboration. In
1963 these cases, using the @code{start} command would stop the execution of
1964 your program too late, as the program would have already completed the
1965 elaboration phase. Under these circumstances, insert breakpoints in your
1966 elaboration code before running your program.
1968 @kindex set exec-wrapper
1969 @item set exec-wrapper @var{wrapper}
1970 @itemx show exec-wrapper
1971 @itemx unset exec-wrapper
1972 When @samp{exec-wrapper} is set, the specified wrapper is used to
1973 launch programs for debugging. @value{GDBN} starts your program
1974 with a shell command of the form @kbd{exec @var{wrapper}
1975 @var{program}}. Quoting is added to @var{program} and its
1976 arguments, but not to @var{wrapper}, so you should add quotes if
1977 appropriate for your shell. The wrapper runs until it executes
1978 your program, and then @value{GDBN} takes control.
1980 You can use any program that eventually calls @code{execve} with
1981 its arguments as a wrapper. Several standard Unix utilities do
1982 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
1983 with @code{exec "$@@"} will also work.
1985 For example, you can use @code{env} to pass an environment variable to
1986 the debugged program, without setting the variable in your shell's
1990 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
1994 This command is available when debugging locally on most targets, excluding
1995 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
1997 @kindex set disable-randomization
1998 @item set disable-randomization
1999 @itemx set disable-randomization on
2000 This option (enabled by default in @value{GDBN}) will turn off the native
2001 randomization of the virtual address space of the started program. This option
2002 is useful for multiple debugging sessions to make the execution better
2003 reproducible and memory addresses reusable across debugging sessions.
2005 This feature is implemented only on @sc{gnu}/Linux. You can get the same
2009 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2012 @item set disable-randomization off
2013 Leave the behavior of the started executable unchanged. Some bugs rear their
2014 ugly heads only when the program is loaded at certain addresses. If your bug
2015 disappears when you run the program under @value{GDBN}, that might be because
2016 @value{GDBN} by default disables the address randomization on platforms, such
2017 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2018 disable-randomization off} to try to reproduce such elusive bugs.
2020 The virtual address space randomization is implemented only on @sc{gnu}/Linux.
2021 It protects the programs against some kinds of security attacks. In these
2022 cases the attacker needs to know the exact location of a concrete executable
2023 code. Randomizing its location makes it impossible to inject jumps misusing
2024 a code at its expected addresses.
2026 Prelinking shared libraries provides a startup performance advantage but it
2027 makes addresses in these libraries predictable for privileged processes by
2028 having just unprivileged access at the target system. Reading the shared
2029 library binary gives enough information for assembling the malicious code
2030 misusing it. Still even a prelinked shared library can get loaded at a new
2031 random address just requiring the regular relocation process during the
2032 startup. Shared libraries not already prelinked are always loaded at
2033 a randomly chosen address.
2035 Position independent executables (PIE) contain position independent code
2036 similar to the shared libraries and therefore such executables get loaded at
2037 a randomly chosen address upon startup. PIE executables always load even
2038 already prelinked shared libraries at a random address. You can build such
2039 executable using @command{gcc -fPIE -pie}.
2041 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2042 (as long as the randomization is enabled).
2044 @item show disable-randomization
2045 Show the current setting of the explicit disable of the native randomization of
2046 the virtual address space of the started program.
2051 @section Your Program's Arguments
2053 @cindex arguments (to your program)
2054 The arguments to your program can be specified by the arguments of the
2056 They are passed to a shell, which expands wildcard characters and
2057 performs redirection of I/O, and thence to your program. Your
2058 @code{SHELL} environment variable (if it exists) specifies what shell
2059 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2060 the default shell (@file{/bin/sh} on Unix).
2062 On non-Unix systems, the program is usually invoked directly by
2063 @value{GDBN}, which emulates I/O redirection via the appropriate system
2064 calls, and the wildcard characters are expanded by the startup code of
2065 the program, not by the shell.
2067 @code{run} with no arguments uses the same arguments used by the previous
2068 @code{run}, or those set by the @code{set args} command.
2073 Specify the arguments to be used the next time your program is run. If
2074 @code{set args} has no arguments, @code{run} executes your program
2075 with no arguments. Once you have run your program with arguments,
2076 using @code{set args} before the next @code{run} is the only way to run
2077 it again without arguments.
2081 Show the arguments to give your program when it is started.
2085 @section Your Program's Environment
2087 @cindex environment (of your program)
2088 The @dfn{environment} consists of a set of environment variables and
2089 their values. Environment variables conventionally record such things as
2090 your user name, your home directory, your terminal type, and your search
2091 path for programs to run. Usually you set up environment variables with
2092 the shell and they are inherited by all the other programs you run. When
2093 debugging, it can be useful to try running your program with a modified
2094 environment without having to start @value{GDBN} over again.
2098 @item path @var{directory}
2099 Add @var{directory} to the front of the @code{PATH} environment variable
2100 (the search path for executables) that will be passed to your program.
2101 The value of @code{PATH} used by @value{GDBN} does not change.
2102 You may specify several directory names, separated by whitespace or by a
2103 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2104 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2105 is moved to the front, so it is searched sooner.
2107 You can use the string @samp{$cwd} to refer to whatever is the current
2108 working directory at the time @value{GDBN} searches the path. If you
2109 use @samp{.} instead, it refers to the directory where you executed the
2110 @code{path} command. @value{GDBN} replaces @samp{.} in the
2111 @var{directory} argument (with the current path) before adding
2112 @var{directory} to the search path.
2113 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2114 @c document that, since repeating it would be a no-op.
2118 Display the list of search paths for executables (the @code{PATH}
2119 environment variable).
2121 @kindex show environment
2122 @item show environment @r{[}@var{varname}@r{]}
2123 Print the value of environment variable @var{varname} to be given to
2124 your program when it starts. If you do not supply @var{varname},
2125 print the names and values of all environment variables to be given to
2126 your program. You can abbreviate @code{environment} as @code{env}.
2128 @kindex set environment
2129 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2130 Set environment variable @var{varname} to @var{value}. The value
2131 changes for your program only, not for @value{GDBN} itself. @var{value} may
2132 be any string; the values of environment variables are just strings, and
2133 any interpretation is supplied by your program itself. The @var{value}
2134 parameter is optional; if it is eliminated, the variable is set to a
2136 @c "any string" here does not include leading, trailing
2137 @c blanks. Gnu asks: does anyone care?
2139 For example, this command:
2146 tells the debugged program, when subsequently run, that its user is named
2147 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2148 are not actually required.)
2150 @kindex unset environment
2151 @item unset environment @var{varname}
2152 Remove variable @var{varname} from the environment to be passed to your
2153 program. This is different from @samp{set env @var{varname} =};
2154 @code{unset environment} removes the variable from the environment,
2155 rather than assigning it an empty value.
2158 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2160 by your @code{SHELL} environment variable if it exists (or
2161 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
2162 that runs an initialization file---such as @file{.cshrc} for C-shell, or
2163 @file{.bashrc} for BASH---any variables you set in that file affect
2164 your program. You may wish to move setting of environment variables to
2165 files that are only run when you sign on, such as @file{.login} or
2168 @node Working Directory
2169 @section Your Program's Working Directory
2171 @cindex working directory (of your program)
2172 Each time you start your program with @code{run}, it inherits its
2173 working directory from the current working directory of @value{GDBN}.
2174 The @value{GDBN} working directory is initially whatever it inherited
2175 from its parent process (typically the shell), but you can specify a new
2176 working directory in @value{GDBN} with the @code{cd} command.
2178 The @value{GDBN} working directory also serves as a default for the commands
2179 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
2184 @cindex change working directory
2185 @item cd @var{directory}
2186 Set the @value{GDBN} working directory to @var{directory}.
2190 Print the @value{GDBN} working directory.
2193 It is generally impossible to find the current working directory of
2194 the process being debugged (since a program can change its directory
2195 during its run). If you work on a system where @value{GDBN} is
2196 configured with the @file{/proc} support, you can use the @code{info
2197 proc} command (@pxref{SVR4 Process Information}) to find out the
2198 current working directory of the debuggee.
2201 @section Your Program's Input and Output
2206 By default, the program you run under @value{GDBN} does input and output to
2207 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2208 to its own terminal modes to interact with you, but it records the terminal
2209 modes your program was using and switches back to them when you continue
2210 running your program.
2213 @kindex info terminal
2215 Displays information recorded by @value{GDBN} about the terminal modes your
2219 You can redirect your program's input and/or output using shell
2220 redirection with the @code{run} command. For example,
2227 starts your program, diverting its output to the file @file{outfile}.
2230 @cindex controlling terminal
2231 Another way to specify where your program should do input and output is
2232 with the @code{tty} command. This command accepts a file name as
2233 argument, and causes this file to be the default for future @code{run}
2234 commands. It also resets the controlling terminal for the child
2235 process, for future @code{run} commands. For example,
2242 directs that processes started with subsequent @code{run} commands
2243 default to do input and output on the terminal @file{/dev/ttyb} and have
2244 that as their controlling terminal.
2246 An explicit redirection in @code{run} overrides the @code{tty} command's
2247 effect on the input/output device, but not its effect on the controlling
2250 When you use the @code{tty} command or redirect input in the @code{run}
2251 command, only the input @emph{for your program} is affected. The input
2252 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2253 for @code{set inferior-tty}.
2255 @cindex inferior tty
2256 @cindex set inferior controlling terminal
2257 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2258 display the name of the terminal that will be used for future runs of your
2262 @item set inferior-tty /dev/ttyb
2263 @kindex set inferior-tty
2264 Set the tty for the program being debugged to /dev/ttyb.
2266 @item show inferior-tty
2267 @kindex show inferior-tty
2268 Show the current tty for the program being debugged.
2272 @section Debugging an Already-running Process
2277 @item attach @var{process-id}
2278 This command attaches to a running process---one that was started
2279 outside @value{GDBN}. (@code{info files} shows your active
2280 targets.) The command takes as argument a process ID. The usual way to
2281 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2282 or with the @samp{jobs -l} shell command.
2284 @code{attach} does not repeat if you press @key{RET} a second time after
2285 executing the command.
2288 To use @code{attach}, your program must be running in an environment
2289 which supports processes; for example, @code{attach} does not work for
2290 programs on bare-board targets that lack an operating system. You must
2291 also have permission to send the process a signal.
2293 When you use @code{attach}, the debugger finds the program running in
2294 the process first by looking in the current working directory, then (if
2295 the program is not found) by using the source file search path
2296 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2297 the @code{file} command to load the program. @xref{Files, ,Commands to
2300 The first thing @value{GDBN} does after arranging to debug the specified
2301 process is to stop it. You can examine and modify an attached process
2302 with all the @value{GDBN} commands that are ordinarily available when
2303 you start processes with @code{run}. You can insert breakpoints; you
2304 can step and continue; you can modify storage. If you would rather the
2305 process continue running, you may use the @code{continue} command after
2306 attaching @value{GDBN} to the process.
2311 When you have finished debugging the attached process, you can use the
2312 @code{detach} command to release it from @value{GDBN} control. Detaching
2313 the process continues its execution. After the @code{detach} command,
2314 that process and @value{GDBN} become completely independent once more, and you
2315 are ready to @code{attach} another process or start one with @code{run}.
2316 @code{detach} does not repeat if you press @key{RET} again after
2317 executing the command.
2320 If you exit @value{GDBN} while you have an attached process, you detach
2321 that process. If you use the @code{run} command, you kill that process.
2322 By default, @value{GDBN} asks for confirmation if you try to do either of these
2323 things; you can control whether or not you need to confirm by using the
2324 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2328 @section Killing the Child Process
2333 Kill the child process in which your program is running under @value{GDBN}.
2336 This command is useful if you wish to debug a core dump instead of a
2337 running process. @value{GDBN} ignores any core dump file while your program
2340 On some operating systems, a program cannot be executed outside @value{GDBN}
2341 while you have breakpoints set on it inside @value{GDBN}. You can use the
2342 @code{kill} command in this situation to permit running your program
2343 outside the debugger.
2345 The @code{kill} command is also useful if you wish to recompile and
2346 relink your program, since on many systems it is impossible to modify an
2347 executable file while it is running in a process. In this case, when you
2348 next type @code{run}, @value{GDBN} notices that the file has changed, and
2349 reads the symbol table again (while trying to preserve your current
2350 breakpoint settings).
2353 @section Debugging Multiple Inferiors
2355 Some @value{GDBN} targets are able to run multiple processes created
2356 from a single executable. This can happen, for instance, with an
2357 embedded system reporting back several processes via the remote
2361 @value{GDBN} represents the state of each program execution with an
2362 object called an @dfn{inferior}. An inferior typically corresponds to
2363 a process, but is more general and applies also to targets that do not
2364 have processes. Inferiors may be created before a process runs, and
2365 may (in future) be retained after a process exits. Each run of an
2366 executable creates a new inferior, as does each attachment to an
2367 existing process. Inferiors have unique identifiers that are
2368 different from process ids, and may optionally be named as well.
2369 Usually each inferior will also have its own distinct address space,
2370 although some embedded targets may have several inferiors running in
2371 different parts of a single space.
2373 Each inferior may in turn have multiple threads running in it.
2375 To find out what inferiors exist at any moment, use @code{info inferiors}:
2378 @kindex info inferiors
2379 @item info inferiors
2380 Print a list of all inferiors currently being managed by @value{GDBN}.
2382 @value{GDBN} displays for each inferior (in this order):
2386 the inferior number assigned by @value{GDBN}
2389 the target system's inferior identifier
2393 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2394 indicates the current inferior.
2398 @c end table here to get a little more width for example
2401 (@value{GDBP}) info inferiors
2407 To switch focus between inferiors, use the @code{inferior} command:
2410 @kindex inferior @var{infno}
2411 @item inferior @var{infno}
2412 Make inferior number @var{infno} the current inferior. The argument
2413 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2414 in the first field of the @samp{info inferiors} display.
2417 To quit debugging one of the inferiors, you can either detach from it
2418 by using the @w{@code{detach inferior}} command (allowing it to run
2419 independently), or kill it using the @w{@code{kill inferior}} command:
2422 @kindex detach inferior @var{infno}
2423 @item detach inferior @var{infno}
2424 Detach from the inferior identified by @value{GDBN} inferior number
2425 @var{infno}, and remove it from the inferior list.
2427 @kindex kill inferior @var{infno}
2428 @item kill inferior @var{infno}
2429 Kill the inferior identified by @value{GDBN} inferior number
2430 @var{infno}, and remove it from the inferior list.
2433 To be notified when inferiors are started or exit under @value{GDBN}'s
2434 control use @w{@code{set print inferior-events}}:
2437 @kindex set print inferior-events
2438 @cindex print messages on inferior start and exit
2439 @item set print inferior-events
2440 @itemx set print inferior-events on
2441 @itemx set print inferior-events off
2442 The @code{set print inferior-events} command allows you to enable or
2443 disable printing of messages when @value{GDBN} notices that new
2444 inferiors have started or that inferiors have exited or have been
2445 detached. By default, these messages will not be printed.
2447 @kindex show print inferior-events
2448 @item show print inferior-events
2449 Show whether messages will be printed when @value{GDBN} detects that
2450 inferiors have started, exited or have been detached.
2454 @section Debugging Programs with Multiple Threads
2456 @cindex threads of execution
2457 @cindex multiple threads
2458 @cindex switching threads
2459 In some operating systems, such as HP-UX and Solaris, a single program
2460 may have more than one @dfn{thread} of execution. The precise semantics
2461 of threads differ from one operating system to another, but in general
2462 the threads of a single program are akin to multiple processes---except
2463 that they share one address space (that is, they can all examine and
2464 modify the same variables). On the other hand, each thread has its own
2465 registers and execution stack, and perhaps private memory.
2467 @value{GDBN} provides these facilities for debugging multi-thread
2471 @item automatic notification of new threads
2472 @item @samp{thread @var{threadno}}, a command to switch among threads
2473 @item @samp{info threads}, a command to inquire about existing threads
2474 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2475 a command to apply a command to a list of threads
2476 @item thread-specific breakpoints
2477 @item @samp{set print thread-events}, which controls printing of
2478 messages on thread start and exit.
2479 @item @samp{set libthread-db-search-path @var{path}}, which lets
2480 the user specify which @code{libthread_db} to use if the default choice
2481 isn't compatible with the program.
2485 @emph{Warning:} These facilities are not yet available on every
2486 @value{GDBN} configuration where the operating system supports threads.
2487 If your @value{GDBN} does not support threads, these commands have no
2488 effect. For example, a system without thread support shows no output
2489 from @samp{info threads}, and always rejects the @code{thread} command,
2493 (@value{GDBP}) info threads
2494 (@value{GDBP}) thread 1
2495 Thread ID 1 not known. Use the "info threads" command to
2496 see the IDs of currently known threads.
2498 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2499 @c doesn't support threads"?
2502 @cindex focus of debugging
2503 @cindex current thread
2504 The @value{GDBN} thread debugging facility allows you to observe all
2505 threads while your program runs---but whenever @value{GDBN} takes
2506 control, one thread in particular is always the focus of debugging.
2507 This thread is called the @dfn{current thread}. Debugging commands show
2508 program information from the perspective of the current thread.
2510 @cindex @code{New} @var{systag} message
2511 @cindex thread identifier (system)
2512 @c FIXME-implementors!! It would be more helpful if the [New...] message
2513 @c included GDB's numeric thread handle, so you could just go to that
2514 @c thread without first checking `info threads'.
2515 Whenever @value{GDBN} detects a new thread in your program, it displays
2516 the target system's identification for the thread with a message in the
2517 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2518 whose form varies depending on the particular system. For example, on
2519 @sc{gnu}/Linux, you might see
2522 [New Thread 46912507313328 (LWP 25582)]
2526 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2527 the @var{systag} is simply something like @samp{process 368}, with no
2530 @c FIXME!! (1) Does the [New...] message appear even for the very first
2531 @c thread of a program, or does it only appear for the
2532 @c second---i.e.@: when it becomes obvious we have a multithread
2534 @c (2) *Is* there necessarily a first thread always? Or do some
2535 @c multithread systems permit starting a program with multiple
2536 @c threads ab initio?
2538 @cindex thread number
2539 @cindex thread identifier (GDB)
2540 For debugging purposes, @value{GDBN} associates its own thread
2541 number---always a single integer---with each thread in your program.
2544 @kindex info threads
2546 Display a summary of all threads currently in your
2547 program. @value{GDBN} displays for each thread (in this order):
2551 the thread number assigned by @value{GDBN}
2554 the target system's thread identifier (@var{systag})
2557 the current stack frame summary for that thread
2561 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2562 indicates the current thread.
2566 @c end table here to get a little more width for example
2569 (@value{GDBP}) info threads
2570 3 process 35 thread 27 0x34e5 in sigpause ()
2571 2 process 35 thread 23 0x34e5 in sigpause ()
2572 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2578 @cindex debugging multithreaded programs (on HP-UX)
2579 @cindex thread identifier (GDB), on HP-UX
2580 For debugging purposes, @value{GDBN} associates its own thread
2581 number---a small integer assigned in thread-creation order---with each
2582 thread in your program.
2584 @cindex @code{New} @var{systag} message, on HP-UX
2585 @cindex thread identifier (system), on HP-UX
2586 @c FIXME-implementors!! It would be more helpful if the [New...] message
2587 @c included GDB's numeric thread handle, so you could just go to that
2588 @c thread without first checking `info threads'.
2589 Whenever @value{GDBN} detects a new thread in your program, it displays
2590 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2591 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2592 whose form varies depending on the particular system. For example, on
2596 [New thread 2 (system thread 26594)]
2600 when @value{GDBN} notices a new thread.
2603 @kindex info threads (HP-UX)
2605 Display a summary of all threads currently in your
2606 program. @value{GDBN} displays for each thread (in this order):
2609 @item the thread number assigned by @value{GDBN}
2611 @item the target system's thread identifier (@var{systag})
2613 @item the current stack frame summary for that thread
2617 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2618 indicates the current thread.
2622 @c end table here to get a little more width for example
2625 (@value{GDBP}) info threads
2626 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2628 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2629 from /usr/lib/libc.2
2630 1 system thread 27905 0x7b003498 in _brk () \@*
2631 from /usr/lib/libc.2
2634 On Solaris, you can display more information about user threads with a
2635 Solaris-specific command:
2638 @item maint info sol-threads
2639 @kindex maint info sol-threads
2640 @cindex thread info (Solaris)
2641 Display info on Solaris user threads.
2645 @kindex thread @var{threadno}
2646 @item thread @var{threadno}
2647 Make thread number @var{threadno} the current thread. The command
2648 argument @var{threadno} is the internal @value{GDBN} thread number, as
2649 shown in the first field of the @samp{info threads} display.
2650 @value{GDBN} responds by displaying the system identifier of the thread
2651 you selected, and its current stack frame summary:
2654 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2655 (@value{GDBP}) thread 2
2656 [Switching to process 35 thread 23]
2657 0x34e5 in sigpause ()
2661 As with the @samp{[New @dots{}]} message, the form of the text after
2662 @samp{Switching to} depends on your system's conventions for identifying
2665 @kindex thread apply
2666 @cindex apply command to several threads
2667 @item thread apply [@var{threadno}] [@var{all}] @var{command}
2668 The @code{thread apply} command allows you to apply the named
2669 @var{command} to one or more threads. Specify the numbers of the
2670 threads that you want affected with the command argument
2671 @var{threadno}. It can be a single thread number, one of the numbers
2672 shown in the first field of the @samp{info threads} display; or it
2673 could be a range of thread numbers, as in @code{2-4}. To apply a
2674 command to all threads, type @kbd{thread apply all @var{command}}.
2676 @kindex set print thread-events
2677 @cindex print messages on thread start and exit
2678 @item set print thread-events
2679 @itemx set print thread-events on
2680 @itemx set print thread-events off
2681 The @code{set print thread-events} command allows you to enable or
2682 disable printing of messages when @value{GDBN} notices that new threads have
2683 started or that threads have exited. By default, these messages will
2684 be printed if detection of these events is supported by the target.
2685 Note that these messages cannot be disabled on all targets.
2687 @kindex show print thread-events
2688 @item show print thread-events
2689 Show whether messages will be printed when @value{GDBN} detects that threads
2690 have started and exited.
2693 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
2694 more information about how @value{GDBN} behaves when you stop and start
2695 programs with multiple threads.
2697 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
2698 watchpoints in programs with multiple threads.
2701 @kindex set libthread-db-search-path
2702 @cindex search path for @code{libthread_db}
2703 @item set libthread-db-search-path @r{[}@var{path}@r{]}
2704 If this variable is set, @var{path} is a colon-separated list of
2705 directories @value{GDBN} will use to search for @code{libthread_db}.
2706 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
2709 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
2710 @code{libthread_db} library to obtain information about threads in the
2711 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
2712 to find @code{libthread_db}. If that fails, @value{GDBN} will continue
2713 with default system shared library directories, and finally the directory
2714 from which @code{libpthread} was loaded in the inferior process.
2716 For any @code{libthread_db} library @value{GDBN} finds in above directories,
2717 @value{GDBN} attempts to initialize it with the current inferior process.
2718 If this initialization fails (which could happen because of a version
2719 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
2720 will unload @code{libthread_db}, and continue with the next directory.
2721 If none of @code{libthread_db} libraries initialize successfully,
2722 @value{GDBN} will issue a warning and thread debugging will be disabled.
2724 Setting @code{libthread-db-search-path} is currently implemented
2725 only on some platforms.
2727 @kindex show libthread-db-search-path
2728 @item show libthread-db-search-path
2729 Display current libthread_db search path.
2733 @section Debugging Programs with Multiple Processes
2735 @cindex fork, debugging programs which call
2736 @cindex multiple processes
2737 @cindex processes, multiple
2738 On most systems, @value{GDBN} has no special support for debugging
2739 programs which create additional processes using the @code{fork}
2740 function. When a program forks, @value{GDBN} will continue to debug the
2741 parent process and the child process will run unimpeded. If you have
2742 set a breakpoint in any code which the child then executes, the child
2743 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2744 will cause it to terminate.
2746 However, if you want to debug the child process there is a workaround
2747 which isn't too painful. Put a call to @code{sleep} in the code which
2748 the child process executes after the fork. It may be useful to sleep
2749 only if a certain environment variable is set, or a certain file exists,
2750 so that the delay need not occur when you don't want to run @value{GDBN}
2751 on the child. While the child is sleeping, use the @code{ps} program to
2752 get its process ID. Then tell @value{GDBN} (a new invocation of
2753 @value{GDBN} if you are also debugging the parent process) to attach to
2754 the child process (@pxref{Attach}). From that point on you can debug
2755 the child process just like any other process which you attached to.
2757 On some systems, @value{GDBN} provides support for debugging programs that
2758 create additional processes using the @code{fork} or @code{vfork} functions.
2759 Currently, the only platforms with this feature are HP-UX (11.x and later
2760 only?) and @sc{gnu}/Linux (kernel version 2.5.60 and later).
2762 By default, when a program forks, @value{GDBN} will continue to debug
2763 the parent process and the child process will run unimpeded.
2765 If you want to follow the child process instead of the parent process,
2766 use the command @w{@code{set follow-fork-mode}}.
2769 @kindex set follow-fork-mode
2770 @item set follow-fork-mode @var{mode}
2771 Set the debugger response to a program call of @code{fork} or
2772 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2773 process. The @var{mode} argument can be:
2777 The original process is debugged after a fork. The child process runs
2778 unimpeded. This is the default.
2781 The new process is debugged after a fork. The parent process runs
2786 @kindex show follow-fork-mode
2787 @item show follow-fork-mode
2788 Display the current debugger response to a @code{fork} or @code{vfork} call.
2791 @cindex debugging multiple processes
2792 On Linux, if you want to debug both the parent and child processes, use the
2793 command @w{@code{set detach-on-fork}}.
2796 @kindex set detach-on-fork
2797 @item set detach-on-fork @var{mode}
2798 Tells gdb whether to detach one of the processes after a fork, or
2799 retain debugger control over them both.
2803 The child process (or parent process, depending on the value of
2804 @code{follow-fork-mode}) will be detached and allowed to run
2805 independently. This is the default.
2808 Both processes will be held under the control of @value{GDBN}.
2809 One process (child or parent, depending on the value of
2810 @code{follow-fork-mode}) is debugged as usual, while the other
2815 @kindex show detach-on-fork
2816 @item show detach-on-fork
2817 Show whether detach-on-fork mode is on/off.
2820 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
2821 will retain control of all forked processes (including nested forks).
2822 You can list the forked processes under the control of @value{GDBN} by
2823 using the @w{@code{info inferiors}} command, and switch from one fork
2824 to another by using the @code{inferior} command (@pxref{Inferiors,
2825 ,Debugging Multiple Inferiors}).
2827 To quit debugging one of the forked processes, you can either detach
2828 from it by using the @w{@code{detach inferior}} command (allowing it
2829 to run independently), or kill it using the @w{@code{kill inferior}}
2830 command. @xref{Inferiors, ,Debugging Multiple Inferiors}.
2832 If you ask to debug a child process and a @code{vfork} is followed by an
2833 @code{exec}, @value{GDBN} executes the new target up to the first
2834 breakpoint in the new target. If you have a breakpoint set on
2835 @code{main} in your original program, the breakpoint will also be set on
2836 the child process's @code{main}.
2838 On some systems, when a child process is spawned by @code{vfork}, you
2839 cannot debug the child or parent until an @code{exec} call completes.
2841 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2842 call executes, the new target restarts. To restart the parent process,
2843 use the @code{file} command with the parent executable name as its
2846 You can use the @code{catch} command to make @value{GDBN} stop whenever
2847 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2848 Catchpoints, ,Setting Catchpoints}.
2850 @node Checkpoint/Restart
2851 @section Setting a @emph{Bookmark} to Return to Later
2856 @cindex snapshot of a process
2857 @cindex rewind program state
2859 On certain operating systems@footnote{Currently, only
2860 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
2861 program's state, called a @dfn{checkpoint}, and come back to it
2864 Returning to a checkpoint effectively undoes everything that has
2865 happened in the program since the @code{checkpoint} was saved. This
2866 includes changes in memory, registers, and even (within some limits)
2867 system state. Effectively, it is like going back in time to the
2868 moment when the checkpoint was saved.
2870 Thus, if you're stepping thru a program and you think you're
2871 getting close to the point where things go wrong, you can save
2872 a checkpoint. Then, if you accidentally go too far and miss
2873 the critical statement, instead of having to restart your program
2874 from the beginning, you can just go back to the checkpoint and
2875 start again from there.
2877 This can be especially useful if it takes a lot of time or
2878 steps to reach the point where you think the bug occurs.
2880 To use the @code{checkpoint}/@code{restart} method of debugging:
2885 Save a snapshot of the debugged program's current execution state.
2886 The @code{checkpoint} command takes no arguments, but each checkpoint
2887 is assigned a small integer id, similar to a breakpoint id.
2889 @kindex info checkpoints
2890 @item info checkpoints
2891 List the checkpoints that have been saved in the current debugging
2892 session. For each checkpoint, the following information will be
2899 @item Source line, or label
2902 @kindex restart @var{checkpoint-id}
2903 @item restart @var{checkpoint-id}
2904 Restore the program state that was saved as checkpoint number
2905 @var{checkpoint-id}. All program variables, registers, stack frames
2906 etc.@: will be returned to the values that they had when the checkpoint
2907 was saved. In essence, gdb will ``wind back the clock'' to the point
2908 in time when the checkpoint was saved.
2910 Note that breakpoints, @value{GDBN} variables, command history etc.
2911 are not affected by restoring a checkpoint. In general, a checkpoint
2912 only restores things that reside in the program being debugged, not in
2915 @kindex delete checkpoint @var{checkpoint-id}
2916 @item delete checkpoint @var{checkpoint-id}
2917 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
2921 Returning to a previously saved checkpoint will restore the user state
2922 of the program being debugged, plus a significant subset of the system
2923 (OS) state, including file pointers. It won't ``un-write'' data from
2924 a file, but it will rewind the file pointer to the previous location,
2925 so that the previously written data can be overwritten. For files
2926 opened in read mode, the pointer will also be restored so that the
2927 previously read data can be read again.
2929 Of course, characters that have been sent to a printer (or other
2930 external device) cannot be ``snatched back'', and characters received
2931 from eg.@: a serial device can be removed from internal program buffers,
2932 but they cannot be ``pushed back'' into the serial pipeline, ready to
2933 be received again. Similarly, the actual contents of files that have
2934 been changed cannot be restored (at this time).
2936 However, within those constraints, you actually can ``rewind'' your
2937 program to a previously saved point in time, and begin debugging it
2938 again --- and you can change the course of events so as to debug a
2939 different execution path this time.
2941 @cindex checkpoints and process id
2942 Finally, there is one bit of internal program state that will be
2943 different when you return to a checkpoint --- the program's process
2944 id. Each checkpoint will have a unique process id (or @var{pid}),
2945 and each will be different from the program's original @var{pid}.
2946 If your program has saved a local copy of its process id, this could
2947 potentially pose a problem.
2949 @subsection A Non-obvious Benefit of Using Checkpoints
2951 On some systems such as @sc{gnu}/Linux, address space randomization
2952 is performed on new processes for security reasons. This makes it
2953 difficult or impossible to set a breakpoint, or watchpoint, on an
2954 absolute address if you have to restart the program, since the
2955 absolute location of a symbol will change from one execution to the
2958 A checkpoint, however, is an @emph{identical} copy of a process.
2959 Therefore if you create a checkpoint at (eg.@:) the start of main,
2960 and simply return to that checkpoint instead of restarting the
2961 process, you can avoid the effects of address randomization and
2962 your symbols will all stay in the same place.
2965 @chapter Stopping and Continuing
2967 The principal purposes of using a debugger are so that you can stop your
2968 program before it terminates; or so that, if your program runs into
2969 trouble, you can investigate and find out why.
2971 Inside @value{GDBN}, your program may stop for any of several reasons,
2972 such as a signal, a breakpoint, or reaching a new line after a
2973 @value{GDBN} command such as @code{step}. You may then examine and
2974 change variables, set new breakpoints or remove old ones, and then
2975 continue execution. Usually, the messages shown by @value{GDBN} provide
2976 ample explanation of the status of your program---but you can also
2977 explicitly request this information at any time.
2980 @kindex info program
2982 Display information about the status of your program: whether it is
2983 running or not, what process it is, and why it stopped.
2987 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2988 * Continuing and Stepping:: Resuming execution
2990 * Thread Stops:: Stopping and starting multi-thread programs
2994 @section Breakpoints, Watchpoints, and Catchpoints
2997 A @dfn{breakpoint} makes your program stop whenever a certain point in
2998 the program is reached. For each breakpoint, you can add conditions to
2999 control in finer detail whether your program stops. You can set
3000 breakpoints with the @code{break} command and its variants (@pxref{Set
3001 Breaks, ,Setting Breakpoints}), to specify the place where your program
3002 should stop by line number, function name or exact address in the
3005 On some systems, you can set breakpoints in shared libraries before
3006 the executable is run. There is a minor limitation on HP-UX systems:
3007 you must wait until the executable is run in order to set breakpoints
3008 in shared library routines that are not called directly by the program
3009 (for example, routines that are arguments in a @code{pthread_create}
3013 @cindex data breakpoints
3014 @cindex memory tracing
3015 @cindex breakpoint on memory address
3016 @cindex breakpoint on variable modification
3017 A @dfn{watchpoint} is a special breakpoint that stops your program
3018 when the value of an expression changes. The expression may be a value
3019 of a variable, or it could involve values of one or more variables
3020 combined by operators, such as @samp{a + b}. This is sometimes called
3021 @dfn{data breakpoints}. You must use a different command to set
3022 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3023 from that, you can manage a watchpoint like any other breakpoint: you
3024 enable, disable, and delete both breakpoints and watchpoints using the
3027 You can arrange to have values from your program displayed automatically
3028 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3032 @cindex breakpoint on events
3033 A @dfn{catchpoint} is another special breakpoint that stops your program
3034 when a certain kind of event occurs, such as the throwing of a C@t{++}
3035 exception or the loading of a library. As with watchpoints, you use a
3036 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3037 Catchpoints}), but aside from that, you can manage a catchpoint like any
3038 other breakpoint. (To stop when your program receives a signal, use the
3039 @code{handle} command; see @ref{Signals, ,Signals}.)
3041 @cindex breakpoint numbers
3042 @cindex numbers for breakpoints
3043 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3044 catchpoint when you create it; these numbers are successive integers
3045 starting with one. In many of the commands for controlling various
3046 features of breakpoints you use the breakpoint number to say which
3047 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3048 @dfn{disabled}; if disabled, it has no effect on your program until you
3051 @cindex breakpoint ranges
3052 @cindex ranges of breakpoints
3053 Some @value{GDBN} commands accept a range of breakpoints on which to
3054 operate. A breakpoint range is either a single breakpoint number, like
3055 @samp{5}, or two such numbers, in increasing order, separated by a
3056 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
3057 all breakpoints in that range are operated on.
3060 * Set Breaks:: Setting breakpoints
3061 * Set Watchpoints:: Setting watchpoints
3062 * Set Catchpoints:: Setting catchpoints
3063 * Delete Breaks:: Deleting breakpoints
3064 * Disabling:: Disabling breakpoints
3065 * Conditions:: Break conditions
3066 * Break Commands:: Breakpoint command lists
3067 * Error in Breakpoints:: ``Cannot insert breakpoints''
3068 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3072 @subsection Setting Breakpoints
3074 @c FIXME LMB what does GDB do if no code on line of breakpt?
3075 @c consider in particular declaration with/without initialization.
3077 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3080 @kindex b @r{(@code{break})}
3081 @vindex $bpnum@r{, convenience variable}
3082 @cindex latest breakpoint
3083 Breakpoints are set with the @code{break} command (abbreviated
3084 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3085 number of the breakpoint you've set most recently; see @ref{Convenience
3086 Vars,, Convenience Variables}, for a discussion of what you can do with
3087 convenience variables.
3090 @item break @var{location}
3091 Set a breakpoint at the given @var{location}, which can specify a
3092 function name, a line number, or an address of an instruction.
3093 (@xref{Specify Location}, for a list of all the possible ways to
3094 specify a @var{location}.) The breakpoint will stop your program just
3095 before it executes any of the code in the specified @var{location}.
3097 When using source languages that permit overloading of symbols, such as
3098 C@t{++}, a function name may refer to more than one possible place to break.
3099 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3102 It is also possible to insert a breakpoint that will stop the program
3103 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3104 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3107 When called without any arguments, @code{break} sets a breakpoint at
3108 the next instruction to be executed in the selected stack frame
3109 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3110 innermost, this makes your program stop as soon as control
3111 returns to that frame. This is similar to the effect of a
3112 @code{finish} command in the frame inside the selected frame---except
3113 that @code{finish} does not leave an active breakpoint. If you use
3114 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3115 the next time it reaches the current location; this may be useful
3118 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3119 least one instruction has been executed. If it did not do this, you
3120 would be unable to proceed past a breakpoint without first disabling the
3121 breakpoint. This rule applies whether or not the breakpoint already
3122 existed when your program stopped.
3124 @item break @dots{} if @var{cond}
3125 Set a breakpoint with condition @var{cond}; evaluate the expression
3126 @var{cond} each time the breakpoint is reached, and stop only if the
3127 value is nonzero---that is, if @var{cond} evaluates as true.
3128 @samp{@dots{}} stands for one of the possible arguments described
3129 above (or no argument) specifying where to break. @xref{Conditions,
3130 ,Break Conditions}, for more information on breakpoint conditions.
3133 @item tbreak @var{args}
3134 Set a breakpoint enabled only for one stop. @var{args} are the
3135 same as for the @code{break} command, and the breakpoint is set in the same
3136 way, but the breakpoint is automatically deleted after the first time your
3137 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3140 @cindex hardware breakpoints
3141 @item hbreak @var{args}
3142 Set a hardware-assisted breakpoint. @var{args} are the same as for the
3143 @code{break} command and the breakpoint is set in the same way, but the
3144 breakpoint requires hardware support and some target hardware may not
3145 have this support. The main purpose of this is EPROM/ROM code
3146 debugging, so you can set a breakpoint at an instruction without
3147 changing the instruction. This can be used with the new trap-generation
3148 provided by SPARClite DSU and most x86-based targets. These targets
3149 will generate traps when a program accesses some data or instruction
3150 address that is assigned to the debug registers. However the hardware
3151 breakpoint registers can take a limited number of breakpoints. For
3152 example, on the DSU, only two data breakpoints can be set at a time, and
3153 @value{GDBN} will reject this command if more than two are used. Delete
3154 or disable unused hardware breakpoints before setting new ones
3155 (@pxref{Disabling, ,Disabling Breakpoints}).
3156 @xref{Conditions, ,Break Conditions}.
3157 For remote targets, you can restrict the number of hardware
3158 breakpoints @value{GDBN} will use, see @ref{set remote
3159 hardware-breakpoint-limit}.
3162 @item thbreak @var{args}
3163 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
3164 are the same as for the @code{hbreak} command and the breakpoint is set in
3165 the same way. However, like the @code{tbreak} command,
3166 the breakpoint is automatically deleted after the
3167 first time your program stops there. Also, like the @code{hbreak}
3168 command, the breakpoint requires hardware support and some target hardware
3169 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3170 See also @ref{Conditions, ,Break Conditions}.
3173 @cindex regular expression
3174 @cindex breakpoints in functions matching a regexp
3175 @cindex set breakpoints in many functions
3176 @item rbreak @var{regex}
3177 Set breakpoints on all functions matching the regular expression
3178 @var{regex}. This command sets an unconditional breakpoint on all
3179 matches, printing a list of all breakpoints it set. Once these
3180 breakpoints are set, they are treated just like the breakpoints set with
3181 the @code{break} command. You can delete them, disable them, or make
3182 them conditional the same way as any other breakpoint.
3184 The syntax of the regular expression is the standard one used with tools
3185 like @file{grep}. Note that this is different from the syntax used by
3186 shells, so for instance @code{foo*} matches all functions that include
3187 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3188 @code{.*} leading and trailing the regular expression you supply, so to
3189 match only functions that begin with @code{foo}, use @code{^foo}.
3191 @cindex non-member C@t{++} functions, set breakpoint in
3192 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3193 breakpoints on overloaded functions that are not members of any special
3196 @cindex set breakpoints on all functions
3197 The @code{rbreak} command can be used to set breakpoints in
3198 @strong{all} the functions in a program, like this:
3201 (@value{GDBP}) rbreak .
3204 @kindex info breakpoints
3205 @cindex @code{$_} and @code{info breakpoints}
3206 @item info breakpoints @r{[}@var{n}@r{]}
3207 @itemx info break @r{[}@var{n}@r{]}
3208 @itemx info watchpoints @r{[}@var{n}@r{]}
3209 Print a table of all breakpoints, watchpoints, and catchpoints set and
3210 not deleted. Optional argument @var{n} means print information only
3211 about the specified breakpoint (or watchpoint or catchpoint). For
3212 each breakpoint, following columns are printed:
3215 @item Breakpoint Numbers
3217 Breakpoint, watchpoint, or catchpoint.
3219 Whether the breakpoint is marked to be disabled or deleted when hit.
3220 @item Enabled or Disabled
3221 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3222 that are not enabled.
3224 Where the breakpoint is in your program, as a memory address. For a
3225 pending breakpoint whose address is not yet known, this field will
3226 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3227 library that has the symbol or line referred by breakpoint is loaded.
3228 See below for details. A breakpoint with several locations will
3229 have @samp{<MULTIPLE>} in this field---see below for details.
3231 Where the breakpoint is in the source for your program, as a file and
3232 line number. For a pending breakpoint, the original string passed to
3233 the breakpoint command will be listed as it cannot be resolved until
3234 the appropriate shared library is loaded in the future.
3238 If a breakpoint is conditional, @code{info break} shows the condition on
3239 the line following the affected breakpoint; breakpoint commands, if any,
3240 are listed after that. A pending breakpoint is allowed to have a condition
3241 specified for it. The condition is not parsed for validity until a shared
3242 library is loaded that allows the pending breakpoint to resolve to a
3246 @code{info break} with a breakpoint
3247 number @var{n} as argument lists only that breakpoint. The
3248 convenience variable @code{$_} and the default examining-address for
3249 the @code{x} command are set to the address of the last breakpoint
3250 listed (@pxref{Memory, ,Examining Memory}).
3253 @code{info break} displays a count of the number of times the breakpoint
3254 has been hit. This is especially useful in conjunction with the
3255 @code{ignore} command. You can ignore a large number of breakpoint
3256 hits, look at the breakpoint info to see how many times the breakpoint
3257 was hit, and then run again, ignoring one less than that number. This
3258 will get you quickly to the last hit of that breakpoint.
3261 @value{GDBN} allows you to set any number of breakpoints at the same place in
3262 your program. There is nothing silly or meaningless about this. When
3263 the breakpoints are conditional, this is even useful
3264 (@pxref{Conditions, ,Break Conditions}).
3266 @cindex multiple locations, breakpoints
3267 @cindex breakpoints, multiple locations
3268 It is possible that a breakpoint corresponds to several locations
3269 in your program. Examples of this situation are:
3273 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3274 instances of the function body, used in different cases.
3277 For a C@t{++} template function, a given line in the function can
3278 correspond to any number of instantiations.
3281 For an inlined function, a given source line can correspond to
3282 several places where that function is inlined.
3285 In all those cases, @value{GDBN} will insert a breakpoint at all
3286 the relevant locations@footnote{
3287 As of this writing, multiple-location breakpoints work only if there's
3288 line number information for all the locations. This means that they
3289 will generally not work in system libraries, unless you have debug
3290 info with line numbers for them.}.
3292 A breakpoint with multiple locations is displayed in the breakpoint
3293 table using several rows---one header row, followed by one row for
3294 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3295 address column. The rows for individual locations contain the actual
3296 addresses for locations, and show the functions to which those
3297 locations belong. The number column for a location is of the form
3298 @var{breakpoint-number}.@var{location-number}.
3303 Num Type Disp Enb Address What
3304 1 breakpoint keep y <MULTIPLE>
3306 breakpoint already hit 1 time
3307 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3308 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3311 Each location can be individually enabled or disabled by passing
3312 @var{breakpoint-number}.@var{location-number} as argument to the
3313 @code{enable} and @code{disable} commands. Note that you cannot
3314 delete the individual locations from the list, you can only delete the
3315 entire list of locations that belong to their parent breakpoint (with
3316 the @kbd{delete @var{num}} command, where @var{num} is the number of
3317 the parent breakpoint, 1 in the above example). Disabling or enabling
3318 the parent breakpoint (@pxref{Disabling}) affects all of the locations
3319 that belong to that breakpoint.
3321 @cindex pending breakpoints
3322 It's quite common to have a breakpoint inside a shared library.
3323 Shared libraries can be loaded and unloaded explicitly,
3324 and possibly repeatedly, as the program is executed. To support
3325 this use case, @value{GDBN} updates breakpoint locations whenever
3326 any shared library is loaded or unloaded. Typically, you would
3327 set a breakpoint in a shared library at the beginning of your
3328 debugging session, when the library is not loaded, and when the
3329 symbols from the library are not available. When you try to set
3330 breakpoint, @value{GDBN} will ask you if you want to set
3331 a so called @dfn{pending breakpoint}---breakpoint whose address
3332 is not yet resolved.
3334 After the program is run, whenever a new shared library is loaded,
3335 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3336 shared library contains the symbol or line referred to by some
3337 pending breakpoint, that breakpoint is resolved and becomes an
3338 ordinary breakpoint. When a library is unloaded, all breakpoints
3339 that refer to its symbols or source lines become pending again.
3341 This logic works for breakpoints with multiple locations, too. For
3342 example, if you have a breakpoint in a C@t{++} template function, and
3343 a newly loaded shared library has an instantiation of that template,
3344 a new location is added to the list of locations for the breakpoint.
3346 Except for having unresolved address, pending breakpoints do not
3347 differ from regular breakpoints. You can set conditions or commands,
3348 enable and disable them and perform other breakpoint operations.
3350 @value{GDBN} provides some additional commands for controlling what
3351 happens when the @samp{break} command cannot resolve breakpoint
3352 address specification to an address:
3354 @kindex set breakpoint pending
3355 @kindex show breakpoint pending
3357 @item set breakpoint pending auto
3358 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3359 location, it queries you whether a pending breakpoint should be created.
3361 @item set breakpoint pending on
3362 This indicates that an unrecognized breakpoint location should automatically
3363 result in a pending breakpoint being created.
3365 @item set breakpoint pending off
3366 This indicates that pending breakpoints are not to be created. Any
3367 unrecognized breakpoint location results in an error. This setting does
3368 not affect any pending breakpoints previously created.
3370 @item show breakpoint pending
3371 Show the current behavior setting for creating pending breakpoints.
3374 The settings above only affect the @code{break} command and its
3375 variants. Once breakpoint is set, it will be automatically updated
3376 as shared libraries are loaded and unloaded.
3378 @cindex automatic hardware breakpoints
3379 For some targets, @value{GDBN} can automatically decide if hardware or
3380 software breakpoints should be used, depending on whether the
3381 breakpoint address is read-only or read-write. This applies to
3382 breakpoints set with the @code{break} command as well as to internal
3383 breakpoints set by commands like @code{next} and @code{finish}. For
3384 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
3387 You can control this automatic behaviour with the following commands::
3389 @kindex set breakpoint auto-hw
3390 @kindex show breakpoint auto-hw
3392 @item set breakpoint auto-hw on
3393 This is the default behavior. When @value{GDBN} sets a breakpoint, it
3394 will try to use the target memory map to decide if software or hardware
3395 breakpoint must be used.
3397 @item set breakpoint auto-hw off
3398 This indicates @value{GDBN} should not automatically select breakpoint
3399 type. If the target provides a memory map, @value{GDBN} will warn when
3400 trying to set software breakpoint at a read-only address.
3403 @value{GDBN} normally implements breakpoints by replacing the program code
3404 at the breakpoint address with a special instruction, which, when
3405 executed, given control to the debugger. By default, the program
3406 code is so modified only when the program is resumed. As soon as
3407 the program stops, @value{GDBN} restores the original instructions. This
3408 behaviour guards against leaving breakpoints inserted in the
3409 target should gdb abrubptly disconnect. However, with slow remote
3410 targets, inserting and removing breakpoint can reduce the performance.
3411 This behavior can be controlled with the following commands::
3413 @kindex set breakpoint always-inserted
3414 @kindex show breakpoint always-inserted
3416 @item set breakpoint always-inserted off
3417 All breakpoints, including newly added by the user, are inserted in
3418 the target only when the target is resumed. All breakpoints are
3419 removed from the target when it stops.
3421 @item set breakpoint always-inserted on
3422 Causes all breakpoints to be inserted in the target at all times. If
3423 the user adds a new breakpoint, or changes an existing breakpoint, the
3424 breakpoints in the target are updated immediately. A breakpoint is
3425 removed from the target only when breakpoint itself is removed.
3427 @cindex non-stop mode, and @code{breakpoint always-inserted}
3428 @item set breakpoint always-inserted auto
3429 This is the default mode. If @value{GDBN} is controlling the inferior
3430 in non-stop mode (@pxref{Non-Stop Mode}), gdb behaves as if
3431 @code{breakpoint always-inserted} mode is on. If @value{GDBN} is
3432 controlling the inferior in all-stop mode, @value{GDBN} behaves as if
3433 @code{breakpoint always-inserted} mode is off.
3436 @cindex negative breakpoint numbers
3437 @cindex internal @value{GDBN} breakpoints
3438 @value{GDBN} itself sometimes sets breakpoints in your program for
3439 special purposes, such as proper handling of @code{longjmp} (in C
3440 programs). These internal breakpoints are assigned negative numbers,
3441 starting with @code{-1}; @samp{info breakpoints} does not display them.
3442 You can see these breakpoints with the @value{GDBN} maintenance command
3443 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
3446 @node Set Watchpoints
3447 @subsection Setting Watchpoints
3449 @cindex setting watchpoints
3450 You can use a watchpoint to stop execution whenever the value of an
3451 expression changes, without having to predict a particular place where
3452 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
3453 The expression may be as simple as the value of a single variable, or
3454 as complex as many variables combined by operators. Examples include:
3458 A reference to the value of a single variable.
3461 An address cast to an appropriate data type. For example,
3462 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
3463 address (assuming an @code{int} occupies 4 bytes).
3466 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
3467 expression can use any operators valid in the program's native
3468 language (@pxref{Languages}).
3471 You can set a watchpoint on an expression even if the expression can
3472 not be evaluated yet. For instance, you can set a watchpoint on
3473 @samp{*global_ptr} before @samp{global_ptr} is initialized.
3474 @value{GDBN} will stop when your program sets @samp{global_ptr} and
3475 the expression produces a valid value. If the expression becomes
3476 valid in some other way than changing a variable (e.g.@: if the memory
3477 pointed to by @samp{*global_ptr} becomes readable as the result of a
3478 @code{malloc} call), @value{GDBN} may not stop until the next time
3479 the expression changes.
3481 @cindex software watchpoints
3482 @cindex hardware watchpoints
3483 Depending on your system, watchpoints may be implemented in software or
3484 hardware. @value{GDBN} does software watchpointing by single-stepping your
3485 program and testing the variable's value each time, which is hundreds of
3486 times slower than normal execution. (But this may still be worth it, to
3487 catch errors where you have no clue what part of your program is the
3490 On some systems, such as HP-UX, PowerPC, @sc{gnu}/Linux and most other
3491 x86-based targets, @value{GDBN} includes support for hardware
3492 watchpoints, which do not slow down the running of your program.
3496 @item watch @var{expr} @r{[}thread @var{threadnum}@r{]}
3497 Set a watchpoint for an expression. @value{GDBN} will break when the
3498 expression @var{expr} is written into by the program and its value
3499 changes. The simplest (and the most popular) use of this command is
3500 to watch the value of a single variable:
3503 (@value{GDBP}) watch foo
3506 If the command includes a @code{@r{[}thread @var{threadnum}@r{]}}
3507 clause, @value{GDBN} breaks only when the thread identified by
3508 @var{threadnum} changes the value of @var{expr}. If any other threads
3509 change the value of @var{expr}, @value{GDBN} will not break. Note
3510 that watchpoints restricted to a single thread in this way only work
3511 with Hardware Watchpoints.
3514 @item rwatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3515 Set a watchpoint that will break when the value of @var{expr} is read
3519 @item awatch @var{expr} @r{[}thread @var{threadnum}@r{]}
3520 Set a watchpoint that will break when @var{expr} is either read from
3521 or written into by the program.
3523 @kindex info watchpoints @r{[}@var{n}@r{]}
3524 @item info watchpoints
3525 This command prints a list of watchpoints, breakpoints, and catchpoints;
3526 it is the same as @code{info break} (@pxref{Set Breaks}).
3529 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
3530 watchpoints execute very quickly, and the debugger reports a change in
3531 value at the exact instruction where the change occurs. If @value{GDBN}
3532 cannot set a hardware watchpoint, it sets a software watchpoint, which
3533 executes more slowly and reports the change in value at the next
3534 @emph{statement}, not the instruction, after the change occurs.
3536 @cindex use only software watchpoints
3537 You can force @value{GDBN} to use only software watchpoints with the
3538 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
3539 zero, @value{GDBN} will never try to use hardware watchpoints, even if
3540 the underlying system supports them. (Note that hardware-assisted
3541 watchpoints that were set @emph{before} setting
3542 @code{can-use-hw-watchpoints} to zero will still use the hardware
3543 mechanism of watching expression values.)
3546 @item set can-use-hw-watchpoints
3547 @kindex set can-use-hw-watchpoints
3548 Set whether or not to use hardware watchpoints.
3550 @item show can-use-hw-watchpoints
3551 @kindex show can-use-hw-watchpoints
3552 Show the current mode of using hardware watchpoints.
3555 For remote targets, you can restrict the number of hardware
3556 watchpoints @value{GDBN} will use, see @ref{set remote
3557 hardware-breakpoint-limit}.
3559 When you issue the @code{watch} command, @value{GDBN} reports
3562 Hardware watchpoint @var{num}: @var{expr}
3566 if it was able to set a hardware watchpoint.
3568 Currently, the @code{awatch} and @code{rwatch} commands can only set
3569 hardware watchpoints, because accesses to data that don't change the
3570 value of the watched expression cannot be detected without examining
3571 every instruction as it is being executed, and @value{GDBN} does not do
3572 that currently. If @value{GDBN} finds that it is unable to set a
3573 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
3574 will print a message like this:
3577 Expression cannot be implemented with read/access watchpoint.
3580 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
3581 data type of the watched expression is wider than what a hardware
3582 watchpoint on the target machine can handle. For example, some systems
3583 can only watch regions that are up to 4 bytes wide; on such systems you
3584 cannot set hardware watchpoints for an expression that yields a
3585 double-precision floating-point number (which is typically 8 bytes
3586 wide). As a work-around, it might be possible to break the large region
3587 into a series of smaller ones and watch them with separate watchpoints.
3589 If you set too many hardware watchpoints, @value{GDBN} might be unable
3590 to insert all of them when you resume the execution of your program.
3591 Since the precise number of active watchpoints is unknown until such
3592 time as the program is about to be resumed, @value{GDBN} might not be
3593 able to warn you about this when you set the watchpoints, and the
3594 warning will be printed only when the program is resumed:
3597 Hardware watchpoint @var{num}: Could not insert watchpoint
3601 If this happens, delete or disable some of the watchpoints.
3603 Watching complex expressions that reference many variables can also
3604 exhaust the resources available for hardware-assisted watchpoints.
3605 That's because @value{GDBN} needs to watch every variable in the
3606 expression with separately allocated resources.
3608 If you call a function interactively using @code{print} or @code{call},
3609 any watchpoints you have set will be inactive until @value{GDBN} reaches another
3610 kind of breakpoint or the call completes.
3612 @value{GDBN} automatically deletes watchpoints that watch local
3613 (automatic) variables, or expressions that involve such variables, when
3614 they go out of scope, that is, when the execution leaves the block in
3615 which these variables were defined. In particular, when the program
3616 being debugged terminates, @emph{all} local variables go out of scope,
3617 and so only watchpoints that watch global variables remain set. If you
3618 rerun the program, you will need to set all such watchpoints again. One
3619 way of doing that would be to set a code breakpoint at the entry to the
3620 @code{main} function and when it breaks, set all the watchpoints.
3622 @cindex watchpoints and threads
3623 @cindex threads and watchpoints
3624 In multi-threaded programs, watchpoints will detect changes to the
3625 watched expression from every thread.
3628 @emph{Warning:} In multi-threaded programs, software watchpoints
3629 have only limited usefulness. If @value{GDBN} creates a software
3630 watchpoint, it can only watch the value of an expression @emph{in a
3631 single thread}. If you are confident that the expression can only
3632 change due to the current thread's activity (and if you are also
3633 confident that no other thread can become current), then you can use
3634 software watchpoints as usual. However, @value{GDBN} may not notice
3635 when a non-current thread's activity changes the expression. (Hardware
3636 watchpoints, in contrast, watch an expression in all threads.)
3639 @xref{set remote hardware-watchpoint-limit}.
3641 @node Set Catchpoints
3642 @subsection Setting Catchpoints
3643 @cindex catchpoints, setting
3644 @cindex exception handlers
3645 @cindex event handling
3647 You can use @dfn{catchpoints} to cause the debugger to stop for certain
3648 kinds of program events, such as C@t{++} exceptions or the loading of a
3649 shared library. Use the @code{catch} command to set a catchpoint.
3653 @item catch @var{event}
3654 Stop when @var{event} occurs. @var{event} can be any of the following:
3657 @cindex stop on C@t{++} exceptions
3658 The throwing of a C@t{++} exception.
3661 The catching of a C@t{++} exception.
3664 @cindex Ada exception catching
3665 @cindex catch Ada exceptions
3666 An Ada exception being raised. If an exception name is specified
3667 at the end of the command (eg @code{catch exception Program_Error}),
3668 the debugger will stop only when this specific exception is raised.
3669 Otherwise, the debugger stops execution when any Ada exception is raised.
3671 When inserting an exception catchpoint on a user-defined exception whose
3672 name is identical to one of the exceptions defined by the language, the
3673 fully qualified name must be used as the exception name. Otherwise,
3674 @value{GDBN} will assume that it should stop on the pre-defined exception
3675 rather than the user-defined one. For instance, assuming an exception
3676 called @code{Constraint_Error} is defined in package @code{Pck}, then
3677 the command to use to catch such exceptions is @kbd{catch exception
3678 Pck.Constraint_Error}.
3680 @item exception unhandled
3681 An exception that was raised but is not handled by the program.
3684 A failed Ada assertion.
3687 @cindex break on fork/exec
3688 A call to @code{exec}. This is currently only available for HP-UX
3692 @itemx syscall @r{[}@var{name} @r{|} @var{number}@r{]} @r{...}
3693 @cindex break on a system call.
3694 A call to or return from a system call, a.k.a.@: @dfn{syscall}. A
3695 syscall is a mechanism for application programs to request a service
3696 from the operating system (OS) or one of the OS system services.
3697 @value{GDBN} can catch some or all of the syscalls issued by the
3698 debuggee, and show the related information for each syscall. If no
3699 argument is specified, calls to and returns from all system calls
3702 @var{name} can be any system call name that is valid for the
3703 underlying OS. Just what syscalls are valid depends on the OS. On
3704 GNU and Unix systems, you can find the full list of valid syscall
3705 names on @file{/usr/include/asm/unistd.h}.
3707 @c For MS-Windows, the syscall names and the corresponding numbers
3708 @c can be found, e.g., on this URL:
3709 @c http://www.metasploit.com/users/opcode/syscalls.html
3710 @c but we don't support Windows syscalls yet.
3712 Normally, @value{GDBN} knows in advance which syscalls are valid for
3713 each OS, so you can use the @value{GDBN} command-line completion
3714 facilities (@pxref{Completion,, command completion}) to list the
3717 You may also specify the system call numerically. A syscall's
3718 number is the value passed to the OS's syscall dispatcher to
3719 identify the requested service. When you specify the syscall by its
3720 name, @value{GDBN} uses its database of syscalls to convert the name
3721 into the corresponding numeric code, but using the number directly
3722 may be useful if @value{GDBN}'s database does not have the complete
3723 list of syscalls on your system (e.g., because @value{GDBN} lags
3724 behind the OS upgrades).
3726 The example below illustrates how this command works if you don't provide
3730 (@value{GDBP}) catch syscall
3731 Catchpoint 1 (syscall)
3733 Starting program: /tmp/catch-syscall
3735 Catchpoint 1 (call to syscall 'close'), \
3736 0xffffe424 in __kernel_vsyscall ()
3740 Catchpoint 1 (returned from syscall 'close'), \
3741 0xffffe424 in __kernel_vsyscall ()
3745 Here is an example of catching a system call by name:
3748 (@value{GDBP}) catch syscall chroot
3749 Catchpoint 1 (syscall 'chroot' [61])
3751 Starting program: /tmp/catch-syscall
3753 Catchpoint 1 (call to syscall 'chroot'), \
3754 0xffffe424 in __kernel_vsyscall ()
3758 Catchpoint 1 (returned from syscall 'chroot'), \
3759 0xffffe424 in __kernel_vsyscall ()
3763 An example of specifying a system call numerically. In the case
3764 below, the syscall number has a corresponding entry in the XML
3765 file, so @value{GDBN} finds its name and prints it:
3768 (@value{GDBP}) catch syscall 252
3769 Catchpoint 1 (syscall(s) 'exit_group')
3771 Starting program: /tmp/catch-syscall
3773 Catchpoint 1 (call to syscall 'exit_group'), \
3774 0xffffe424 in __kernel_vsyscall ()
3778 Program exited normally.
3782 However, there can be situations when there is no corresponding name
3783 in XML file for that syscall number. In this case, @value{GDBN} prints
3784 a warning message saying that it was not able to find the syscall name,
3785 but the catchpoint will be set anyway. See the example below:
3788 (@value{GDBP}) catch syscall 764
3789 warning: The number '764' does not represent a known syscall.
3790 Catchpoint 2 (syscall 764)
3794 If you configure @value{GDBN} using the @samp{--without-expat} option,
3795 it will not be able to display syscall names. Also, if your
3796 architecture does not have an XML file describing its system calls,
3797 you will not be able to see the syscall names. It is important to
3798 notice that these two features are used for accessing the syscall
3799 name database. In either case, you will see a warning like this:
3802 (@value{GDBP}) catch syscall
3803 warning: Could not open "syscalls/i386-linux.xml"
3804 warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
3805 GDB will not be able to display syscall names.
3806 Catchpoint 1 (syscall)
3810 Of course, the file name will change depending on your architecture and system.
3812 Still using the example above, you can also try to catch a syscall by its
3813 number. In this case, you would see something like:
3816 (@value{GDBP}) catch syscall 252
3817 Catchpoint 1 (syscall(s) 252)
3820 Again, in this case @value{GDBN} would not be able to display syscall's names.
3823 A call to @code{fork}. This is currently only available for HP-UX
3827 A call to @code{vfork}. This is currently only available for HP-UX
3832 @item tcatch @var{event}
3833 Set a catchpoint that is enabled only for one stop. The catchpoint is
3834 automatically deleted after the first time the event is caught.
3838 Use the @code{info break} command to list the current catchpoints.
3840 There are currently some limitations to C@t{++} exception handling
3841 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
3845 If you call a function interactively, @value{GDBN} normally returns
3846 control to you when the function has finished executing. If the call
3847 raises an exception, however, the call may bypass the mechanism that
3848 returns control to you and cause your program either to abort or to
3849 simply continue running until it hits a breakpoint, catches a signal
3850 that @value{GDBN} is listening for, or exits. This is the case even if
3851 you set a catchpoint for the exception; catchpoints on exceptions are
3852 disabled within interactive calls.
3855 You cannot raise an exception interactively.
3858 You cannot install an exception handler interactively.
3861 @cindex raise exceptions
3862 Sometimes @code{catch} is not the best way to debug exception handling:
3863 if you need to know exactly where an exception is raised, it is better to
3864 stop @emph{before} the exception handler is called, since that way you
3865 can see the stack before any unwinding takes place. If you set a
3866 breakpoint in an exception handler instead, it may not be easy to find
3867 out where the exception was raised.
3869 To stop just before an exception handler is called, you need some
3870 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
3871 raised by calling a library function named @code{__raise_exception}
3872 which has the following ANSI C interface:
3875 /* @var{addr} is where the exception identifier is stored.
3876 @var{id} is the exception identifier. */
3877 void __raise_exception (void **addr, void *id);
3881 To make the debugger catch all exceptions before any stack
3882 unwinding takes place, set a breakpoint on @code{__raise_exception}
3883 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Exceptions}).
3885 With a conditional breakpoint (@pxref{Conditions, ,Break Conditions})
3886 that depends on the value of @var{id}, you can stop your program when
3887 a specific exception is raised. You can use multiple conditional
3888 breakpoints to stop your program when any of a number of exceptions are
3893 @subsection Deleting Breakpoints
3895 @cindex clearing breakpoints, watchpoints, catchpoints
3896 @cindex deleting breakpoints, watchpoints, catchpoints
3897 It is often necessary to eliminate a breakpoint, watchpoint, or
3898 catchpoint once it has done its job and you no longer want your program
3899 to stop there. This is called @dfn{deleting} the breakpoint. A
3900 breakpoint that has been deleted no longer exists; it is forgotten.
3902 With the @code{clear} command you can delete breakpoints according to
3903 where they are in your program. With the @code{delete} command you can
3904 delete individual breakpoints, watchpoints, or catchpoints by specifying
3905 their breakpoint numbers.
3907 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
3908 automatically ignores breakpoints on the first instruction to be executed
3909 when you continue execution without changing the execution address.
3914 Delete any breakpoints at the next instruction to be executed in the
3915 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
3916 the innermost frame is selected, this is a good way to delete a
3917 breakpoint where your program just stopped.
3919 @item clear @var{location}
3920 Delete any breakpoints set at the specified @var{location}.
3921 @xref{Specify Location}, for the various forms of @var{location}; the
3922 most useful ones are listed below:
3925 @item clear @var{function}
3926 @itemx clear @var{filename}:@var{function}
3927 Delete any breakpoints set at entry to the named @var{function}.
3929 @item clear @var{linenum}
3930 @itemx clear @var{filename}:@var{linenum}
3931 Delete any breakpoints set at or within the code of the specified
3932 @var{linenum} of the specified @var{filename}.
3935 @cindex delete breakpoints
3937 @kindex d @r{(@code{delete})}
3938 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3939 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
3940 ranges specified as arguments. If no argument is specified, delete all
3941 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
3942 confirm off}). You can abbreviate this command as @code{d}.
3946 @subsection Disabling Breakpoints
3948 @cindex enable/disable a breakpoint
3949 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
3950 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
3951 it had been deleted, but remembers the information on the breakpoint so
3952 that you can @dfn{enable} it again later.
3954 You disable and enable breakpoints, watchpoints, and catchpoints with
3955 the @code{enable} and @code{disable} commands, optionally specifying one
3956 or more breakpoint numbers as arguments. Use @code{info break} or
3957 @code{info watch} to print a list of breakpoints, watchpoints, and
3958 catchpoints if you do not know which numbers to use.
3960 Disabling and enabling a breakpoint that has multiple locations
3961 affects all of its locations.
3963 A breakpoint, watchpoint, or catchpoint can have any of four different
3964 states of enablement:
3968 Enabled. The breakpoint stops your program. A breakpoint set
3969 with the @code{break} command starts out in this state.
3971 Disabled. The breakpoint has no effect on your program.
3973 Enabled once. The breakpoint stops your program, but then becomes
3976 Enabled for deletion. The breakpoint stops your program, but
3977 immediately after it does so it is deleted permanently. A breakpoint
3978 set with the @code{tbreak} command starts out in this state.
3981 You can use the following commands to enable or disable breakpoints,
3982 watchpoints, and catchpoints:
3986 @kindex dis @r{(@code{disable})}
3987 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3988 Disable the specified breakpoints---or all breakpoints, if none are
3989 listed. A disabled breakpoint has no effect but is not forgotten. All
3990 options such as ignore-counts, conditions and commands are remembered in
3991 case the breakpoint is enabled again later. You may abbreviate
3992 @code{disable} as @code{dis}.
3995 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
3996 Enable the specified breakpoints (or all defined breakpoints). They
3997 become effective once again in stopping your program.
3999 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
4000 Enable the specified breakpoints temporarily. @value{GDBN} disables any
4001 of these breakpoints immediately after stopping your program.
4003 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
4004 Enable the specified breakpoints to work once, then die. @value{GDBN}
4005 deletes any of these breakpoints as soon as your program stops there.
4006 Breakpoints set by the @code{tbreak} command start out in this state.
4009 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
4010 @c confusing: tbreak is also initially enabled.
4011 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
4012 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
4013 subsequently, they become disabled or enabled only when you use one of
4014 the commands above. (The command @code{until} can set and delete a
4015 breakpoint of its own, but it does not change the state of your other
4016 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
4020 @subsection Break Conditions
4021 @cindex conditional breakpoints
4022 @cindex breakpoint conditions
4024 @c FIXME what is scope of break condition expr? Context where wanted?
4025 @c in particular for a watchpoint?
4026 The simplest sort of breakpoint breaks every time your program reaches a
4027 specified place. You can also specify a @dfn{condition} for a
4028 breakpoint. A condition is just a Boolean expression in your
4029 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
4030 a condition evaluates the expression each time your program reaches it,
4031 and your program stops only if the condition is @emph{true}.
4033 This is the converse of using assertions for program validation; in that
4034 situation, you want to stop when the assertion is violated---that is,
4035 when the condition is false. In C, if you want to test an assertion expressed
4036 by the condition @var{assert}, you should set the condition
4037 @samp{! @var{assert}} on the appropriate breakpoint.
4039 Conditions are also accepted for watchpoints; you may not need them,
4040 since a watchpoint is inspecting the value of an expression anyhow---but
4041 it might be simpler, say, to just set a watchpoint on a variable name,
4042 and specify a condition that tests whether the new value is an interesting
4045 Break conditions can have side effects, and may even call functions in
4046 your program. This can be useful, for example, to activate functions
4047 that log program progress, or to use your own print functions to
4048 format special data structures. The effects are completely predictable
4049 unless there is another enabled breakpoint at the same address. (In
4050 that case, @value{GDBN} might see the other breakpoint first and stop your
4051 program without checking the condition of this one.) Note that
4052 breakpoint commands are usually more convenient and flexible than break
4054 purpose of performing side effects when a breakpoint is reached
4055 (@pxref{Break Commands, ,Breakpoint Command Lists}).
4057 Break conditions can be specified when a breakpoint is set, by using
4058 @samp{if} in the arguments to the @code{break} command. @xref{Set
4059 Breaks, ,Setting Breakpoints}. They can also be changed at any time
4060 with the @code{condition} command.
4062 You can also use the @code{if} keyword with the @code{watch} command.
4063 The @code{catch} command does not recognize the @code{if} keyword;
4064 @code{condition} is the only way to impose a further condition on a
4069 @item condition @var{bnum} @var{expression}
4070 Specify @var{expression} as the break condition for breakpoint,
4071 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
4072 breakpoint @var{bnum} stops your program only if the value of
4073 @var{expression} is true (nonzero, in C). When you use
4074 @code{condition}, @value{GDBN} checks @var{expression} immediately for
4075 syntactic correctness, and to determine whether symbols in it have
4076 referents in the context of your breakpoint. If @var{expression} uses
4077 symbols not referenced in the context of the breakpoint, @value{GDBN}
4078 prints an error message:
4081 No symbol "foo" in current context.
4086 not actually evaluate @var{expression} at the time the @code{condition}
4087 command (or a command that sets a breakpoint with a condition, like
4088 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
4090 @item condition @var{bnum}
4091 Remove the condition from breakpoint number @var{bnum}. It becomes
4092 an ordinary unconditional breakpoint.
4095 @cindex ignore count (of breakpoint)
4096 A special case of a breakpoint condition is to stop only when the
4097 breakpoint has been reached a certain number of times. This is so
4098 useful that there is a special way to do it, using the @dfn{ignore
4099 count} of the breakpoint. Every breakpoint has an ignore count, which
4100 is an integer. Most of the time, the ignore count is zero, and
4101 therefore has no effect. But if your program reaches a breakpoint whose
4102 ignore count is positive, then instead of stopping, it just decrements
4103 the ignore count by one and continues. As a result, if the ignore count
4104 value is @var{n}, the breakpoint does not stop the next @var{n} times
4105 your program reaches it.
4109 @item ignore @var{bnum} @var{count}
4110 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
4111 The next @var{count} times the breakpoint is reached, your program's
4112 execution does not stop; other than to decrement the ignore count, @value{GDBN}
4115 To make the breakpoint stop the next time it is reached, specify
4118 When you use @code{continue} to resume execution of your program from a
4119 breakpoint, you can specify an ignore count directly as an argument to
4120 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
4121 Stepping,,Continuing and Stepping}.
4123 If a breakpoint has a positive ignore count and a condition, the
4124 condition is not checked. Once the ignore count reaches zero,
4125 @value{GDBN} resumes checking the condition.
4127 You could achieve the effect of the ignore count with a condition such
4128 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
4129 is decremented each time. @xref{Convenience Vars, ,Convenience
4133 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4136 @node Break Commands
4137 @subsection Breakpoint Command Lists
4139 @cindex breakpoint commands
4140 You can give any breakpoint (or watchpoint or catchpoint) a series of
4141 commands to execute when your program stops due to that breakpoint. For
4142 example, you might want to print the values of certain expressions, or
4143 enable other breakpoints.
4147 @kindex end@r{ (breakpoint commands)}
4148 @item commands @r{[}@var{bnum}@r{]}
4149 @itemx @dots{} @var{command-list} @dots{}
4151 Specify a list of commands for breakpoint number @var{bnum}. The commands
4152 themselves appear on the following lines. Type a line containing just
4153 @code{end} to terminate the commands.
4155 To remove all commands from a breakpoint, type @code{commands} and
4156 follow it immediately with @code{end}; that is, give no commands.
4158 With no @var{bnum} argument, @code{commands} refers to the last
4159 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
4160 recently encountered).
4163 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4164 disabled within a @var{command-list}.
4166 You can use breakpoint commands to start your program up again. Simply
4167 use the @code{continue} command, or @code{step}, or any other command
4168 that resumes execution.
4170 Any other commands in the command list, after a command that resumes
4171 execution, are ignored. This is because any time you resume execution
4172 (even with a simple @code{next} or @code{step}), you may encounter
4173 another breakpoint---which could have its own command list, leading to
4174 ambiguities about which list to execute.
4177 If the first command you specify in a command list is @code{silent}, the
4178 usual message about stopping at a breakpoint is not printed. This may
4179 be desirable for breakpoints that are to print a specific message and
4180 then continue. If none of the remaining commands print anything, you
4181 see no sign that the breakpoint was reached. @code{silent} is
4182 meaningful only at the beginning of a breakpoint command list.
4184 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4185 print precisely controlled output, and are often useful in silent
4186 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4188 For example, here is how you could use breakpoint commands to print the
4189 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4195 printf "x is %d\n",x
4200 One application for breakpoint commands is to compensate for one bug so
4201 you can test for another. Put a breakpoint just after the erroneous line
4202 of code, give it a condition to detect the case in which something
4203 erroneous has been done, and give it commands to assign correct values
4204 to any variables that need them. End with the @code{continue} command
4205 so that your program does not stop, and start with the @code{silent}
4206 command so that no output is produced. Here is an example:
4217 @c @ifclear BARETARGET
4218 @node Error in Breakpoints
4219 @subsection ``Cannot insert breakpoints''
4221 If you request too many active hardware-assisted breakpoints and
4222 watchpoints, you will see this error message:
4224 @c FIXME: the precise wording of this message may change; the relevant
4225 @c source change is not committed yet (Sep 3, 1999).
4227 Stopped; cannot insert breakpoints.
4228 You may have requested too many hardware breakpoints and watchpoints.
4232 This message is printed when you attempt to resume the program, since
4233 only then @value{GDBN} knows exactly how many hardware breakpoints and
4234 watchpoints it needs to insert.
4236 When this message is printed, you need to disable or remove some of the
4237 hardware-assisted breakpoints and watchpoints, and then continue.
4239 @node Breakpoint-related Warnings
4240 @subsection ``Breakpoint address adjusted...''
4241 @cindex breakpoint address adjusted
4243 Some processor architectures place constraints on the addresses at
4244 which breakpoints may be placed. For architectures thus constrained,
4245 @value{GDBN} will attempt to adjust the breakpoint's address to comply
4246 with the constraints dictated by the architecture.
4248 One example of such an architecture is the Fujitsu FR-V. The FR-V is
4249 a VLIW architecture in which a number of RISC-like instructions may be
4250 bundled together for parallel execution. The FR-V architecture
4251 constrains the location of a breakpoint instruction within such a
4252 bundle to the instruction with the lowest address. @value{GDBN}
4253 honors this constraint by adjusting a breakpoint's address to the
4254 first in the bundle.
4256 It is not uncommon for optimized code to have bundles which contain
4257 instructions from different source statements, thus it may happen that
4258 a breakpoint's address will be adjusted from one source statement to
4259 another. Since this adjustment may significantly alter @value{GDBN}'s
4260 breakpoint related behavior from what the user expects, a warning is
4261 printed when the breakpoint is first set and also when the breakpoint
4264 A warning like the one below is printed when setting a breakpoint
4265 that's been subject to address adjustment:
4268 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
4271 Such warnings are printed both for user settable and @value{GDBN}'s
4272 internal breakpoints. If you see one of these warnings, you should
4273 verify that a breakpoint set at the adjusted address will have the
4274 desired affect. If not, the breakpoint in question may be removed and
4275 other breakpoints may be set which will have the desired behavior.
4276 E.g., it may be sufficient to place the breakpoint at a later
4277 instruction. A conditional breakpoint may also be useful in some
4278 cases to prevent the breakpoint from triggering too often.
4280 @value{GDBN} will also issue a warning when stopping at one of these
4281 adjusted breakpoints:
4284 warning: Breakpoint 1 address previously adjusted from 0x00010414
4288 When this warning is encountered, it may be too late to take remedial
4289 action except in cases where the breakpoint is hit earlier or more
4290 frequently than expected.
4292 @node Continuing and Stepping
4293 @section Continuing and Stepping
4297 @cindex resuming execution
4298 @dfn{Continuing} means resuming program execution until your program
4299 completes normally. In contrast, @dfn{stepping} means executing just
4300 one more ``step'' of your program, where ``step'' may mean either one
4301 line of source code, or one machine instruction (depending on what
4302 particular command you use). Either when continuing or when stepping,
4303 your program may stop even sooner, due to a breakpoint or a signal. (If
4304 it stops due to a signal, you may want to use @code{handle}, or use
4305 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
4309 @kindex c @r{(@code{continue})}
4310 @kindex fg @r{(resume foreground execution)}
4311 @item continue @r{[}@var{ignore-count}@r{]}
4312 @itemx c @r{[}@var{ignore-count}@r{]}
4313 @itemx fg @r{[}@var{ignore-count}@r{]}
4314 Resume program execution, at the address where your program last stopped;
4315 any breakpoints set at that address are bypassed. The optional argument
4316 @var{ignore-count} allows you to specify a further number of times to
4317 ignore a breakpoint at this location; its effect is like that of
4318 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
4320 The argument @var{ignore-count} is meaningful only when your program
4321 stopped due to a breakpoint. At other times, the argument to
4322 @code{continue} is ignored.
4324 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
4325 debugged program is deemed to be the foreground program) are provided
4326 purely for convenience, and have exactly the same behavior as
4330 To resume execution at a different place, you can use @code{return}
4331 (@pxref{Returning, ,Returning from a Function}) to go back to the
4332 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
4333 Different Address}) to go to an arbitrary location in your program.
4335 A typical technique for using stepping is to set a breakpoint
4336 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
4337 beginning of the function or the section of your program where a problem
4338 is believed to lie, run your program until it stops at that breakpoint,
4339 and then step through the suspect area, examining the variables that are
4340 interesting, until you see the problem happen.
4344 @kindex s @r{(@code{step})}
4346 Continue running your program until control reaches a different source
4347 line, then stop it and return control to @value{GDBN}. This command is
4348 abbreviated @code{s}.
4351 @c "without debugging information" is imprecise; actually "without line
4352 @c numbers in the debugging information". (gcc -g1 has debugging info but
4353 @c not line numbers). But it seems complex to try to make that
4354 @c distinction here.
4355 @emph{Warning:} If you use the @code{step} command while control is
4356 within a function that was compiled without debugging information,
4357 execution proceeds until control reaches a function that does have
4358 debugging information. Likewise, it will not step into a function which
4359 is compiled without debugging information. To step through functions
4360 without debugging information, use the @code{stepi} command, described
4364 The @code{step} command only stops at the first instruction of a source
4365 line. This prevents the multiple stops that could otherwise occur in
4366 @code{switch} statements, @code{for} loops, etc. @code{step} continues
4367 to stop if a function that has debugging information is called within
4368 the line. In other words, @code{step} @emph{steps inside} any functions
4369 called within the line.
4371 Also, the @code{step} command only enters a function if there is line
4372 number information for the function. Otherwise it acts like the
4373 @code{next} command. This avoids problems when using @code{cc -gl}
4374 on MIPS machines. Previously, @code{step} entered subroutines if there
4375 was any debugging information about the routine.
4377 @item step @var{count}
4378 Continue running as in @code{step}, but do so @var{count} times. If a
4379 breakpoint is reached, or a signal not related to stepping occurs before
4380 @var{count} steps, stepping stops right away.
4383 @kindex n @r{(@code{next})}
4384 @item next @r{[}@var{count}@r{]}
4385 Continue to the next source line in the current (innermost) stack frame.
4386 This is similar to @code{step}, but function calls that appear within
4387 the line of code are executed without stopping. Execution stops when
4388 control reaches a different line of code at the original stack level
4389 that was executing when you gave the @code{next} command. This command
4390 is abbreviated @code{n}.
4392 An argument @var{count} is a repeat count, as for @code{step}.
4395 @c FIX ME!! Do we delete this, or is there a way it fits in with
4396 @c the following paragraph? --- Vctoria
4398 @c @code{next} within a function that lacks debugging information acts like
4399 @c @code{step}, but any function calls appearing within the code of the
4400 @c function are executed without stopping.
4402 The @code{next} command only stops at the first instruction of a
4403 source line. This prevents multiple stops that could otherwise occur in
4404 @code{switch} statements, @code{for} loops, etc.
4406 @kindex set step-mode
4408 @cindex functions without line info, and stepping
4409 @cindex stepping into functions with no line info
4410 @itemx set step-mode on
4411 The @code{set step-mode on} command causes the @code{step} command to
4412 stop at the first instruction of a function which contains no debug line
4413 information rather than stepping over it.
4415 This is useful in cases where you may be interested in inspecting the
4416 machine instructions of a function which has no symbolic info and do not
4417 want @value{GDBN} to automatically skip over this function.
4419 @item set step-mode off
4420 Causes the @code{step} command to step over any functions which contains no
4421 debug information. This is the default.
4423 @item show step-mode
4424 Show whether @value{GDBN} will stop in or step over functions without
4425 source line debug information.
4428 @kindex fin @r{(@code{finish})}
4430 Continue running until just after function in the selected stack frame
4431 returns. Print the returned value (if any). This command can be
4432 abbreviated as @code{fin}.
4434 Contrast this with the @code{return} command (@pxref{Returning,
4435 ,Returning from a Function}).
4438 @kindex u @r{(@code{until})}
4439 @cindex run until specified location
4442 Continue running until a source line past the current line, in the
4443 current stack frame, is reached. This command is used to avoid single
4444 stepping through a loop more than once. It is like the @code{next}
4445 command, except that when @code{until} encounters a jump, it
4446 automatically continues execution until the program counter is greater
4447 than the address of the jump.
4449 This means that when you reach the end of a loop after single stepping
4450 though it, @code{until} makes your program continue execution until it
4451 exits the loop. In contrast, a @code{next} command at the end of a loop
4452 simply steps back to the beginning of the loop, which forces you to step
4453 through the next iteration.
4455 @code{until} always stops your program if it attempts to exit the current
4458 @code{until} may produce somewhat counterintuitive results if the order
4459 of machine code does not match the order of the source lines. For
4460 example, in the following excerpt from a debugging session, the @code{f}
4461 (@code{frame}) command shows that execution is stopped at line
4462 @code{206}; yet when we use @code{until}, we get to line @code{195}:
4466 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
4468 (@value{GDBP}) until
4469 195 for ( ; argc > 0; NEXTARG) @{
4472 This happened because, for execution efficiency, the compiler had
4473 generated code for the loop closure test at the end, rather than the
4474 start, of the loop---even though the test in a C @code{for}-loop is
4475 written before the body of the loop. The @code{until} command appeared
4476 to step back to the beginning of the loop when it advanced to this
4477 expression; however, it has not really gone to an earlier
4478 statement---not in terms of the actual machine code.
4480 @code{until} with no argument works by means of single
4481 instruction stepping, and hence is slower than @code{until} with an
4484 @item until @var{location}
4485 @itemx u @var{location}
4486 Continue running your program until either the specified location is
4487 reached, or the current stack frame returns. @var{location} is any of
4488 the forms described in @ref{Specify Location}.
4489 This form of the command uses temporary breakpoints, and
4490 hence is quicker than @code{until} without an argument. The specified
4491 location is actually reached only if it is in the current frame. This
4492 implies that @code{until} can be used to skip over recursive function
4493 invocations. For instance in the code below, if the current location is
4494 line @code{96}, issuing @code{until 99} will execute the program up to
4495 line @code{99} in the same invocation of factorial, i.e., after the inner
4496 invocations have returned.
4499 94 int factorial (int value)
4501 96 if (value > 1) @{
4502 97 value *= factorial (value - 1);
4509 @kindex advance @var{location}
4510 @itemx advance @var{location}
4511 Continue running the program up to the given @var{location}. An argument is
4512 required, which should be of one of the forms described in
4513 @ref{Specify Location}.
4514 Execution will also stop upon exit from the current stack
4515 frame. This command is similar to @code{until}, but @code{advance} will
4516 not skip over recursive function calls, and the target location doesn't
4517 have to be in the same frame as the current one.
4521 @kindex si @r{(@code{stepi})}
4523 @itemx stepi @var{arg}
4525 Execute one machine instruction, then stop and return to the debugger.
4527 It is often useful to do @samp{display/i $pc} when stepping by machine
4528 instructions. This makes @value{GDBN} automatically display the next
4529 instruction to be executed, each time your program stops. @xref{Auto
4530 Display,, Automatic Display}.
4532 An argument is a repeat count, as in @code{step}.
4536 @kindex ni @r{(@code{nexti})}
4538 @itemx nexti @var{arg}
4540 Execute one machine instruction, but if it is a function call,
4541 proceed until the function returns.
4543 An argument is a repeat count, as in @code{next}.
4550 A signal is an asynchronous event that can happen in a program. The
4551 operating system defines the possible kinds of signals, and gives each
4552 kind a name and a number. For example, in Unix @code{SIGINT} is the
4553 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
4554 @code{SIGSEGV} is the signal a program gets from referencing a place in
4555 memory far away from all the areas in use; @code{SIGALRM} occurs when
4556 the alarm clock timer goes off (which happens only if your program has
4557 requested an alarm).
4559 @cindex fatal signals
4560 Some signals, including @code{SIGALRM}, are a normal part of the
4561 functioning of your program. Others, such as @code{SIGSEGV}, indicate
4562 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
4563 program has not specified in advance some other way to handle the signal.
4564 @code{SIGINT} does not indicate an error in your program, but it is normally
4565 fatal so it can carry out the purpose of the interrupt: to kill the program.
4567 @value{GDBN} has the ability to detect any occurrence of a signal in your
4568 program. You can tell @value{GDBN} in advance what to do for each kind of
4571 @cindex handling signals
4572 Normally, @value{GDBN} is set up to let the non-erroneous signals like
4573 @code{SIGALRM} be silently passed to your program
4574 (so as not to interfere with their role in the program's functioning)
4575 but to stop your program immediately whenever an error signal happens.
4576 You can change these settings with the @code{handle} command.
4579 @kindex info signals
4583 Print a table of all the kinds of signals and how @value{GDBN} has been told to
4584 handle each one. You can use this to see the signal numbers of all
4585 the defined types of signals.
4587 @item info signals @var{sig}
4588 Similar, but print information only about the specified signal number.
4590 @code{info handle} is an alias for @code{info signals}.
4593 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
4594 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
4595 can be the number of a signal or its name (with or without the
4596 @samp{SIG} at the beginning); a list of signal numbers of the form
4597 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
4598 known signals. Optional arguments @var{keywords}, described below,
4599 say what change to make.
4603 The keywords allowed by the @code{handle} command can be abbreviated.
4604 Their full names are:
4608 @value{GDBN} should not stop your program when this signal happens. It may
4609 still print a message telling you that the signal has come in.
4612 @value{GDBN} should stop your program when this signal happens. This implies
4613 the @code{print} keyword as well.
4616 @value{GDBN} should print a message when this signal happens.
4619 @value{GDBN} should not mention the occurrence of the signal at all. This
4620 implies the @code{nostop} keyword as well.
4624 @value{GDBN} should allow your program to see this signal; your program
4625 can handle the signal, or else it may terminate if the signal is fatal
4626 and not handled. @code{pass} and @code{noignore} are synonyms.
4630 @value{GDBN} should not allow your program to see this signal.
4631 @code{nopass} and @code{ignore} are synonyms.
4635 When a signal stops your program, the signal is not visible to the
4637 continue. Your program sees the signal then, if @code{pass} is in
4638 effect for the signal in question @emph{at that time}. In other words,
4639 after @value{GDBN} reports a signal, you can use the @code{handle}
4640 command with @code{pass} or @code{nopass} to control whether your
4641 program sees that signal when you continue.
4643 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
4644 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
4645 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
4648 You can also use the @code{signal} command to prevent your program from
4649 seeing a signal, or cause it to see a signal it normally would not see,
4650 or to give it any signal at any time. For example, if your program stopped
4651 due to some sort of memory reference error, you might store correct
4652 values into the erroneous variables and continue, hoping to see more
4653 execution; but your program would probably terminate immediately as
4654 a result of the fatal signal once it saw the signal. To prevent this,
4655 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
4658 @cindex extra signal information
4659 @anchor{extra signal information}
4661 On some targets, @value{GDBN} can inspect extra signal information
4662 associated with the intercepted signal, before it is actually
4663 delivered to the program being debugged. This information is exported
4664 by the convenience variable @code{$_siginfo}, and consists of data
4665 that is passed by the kernel to the signal handler at the time of the
4666 receipt of a signal. The data type of the information itself is
4667 target dependent. You can see the data type using the @code{ptype
4668 $_siginfo} command. On Unix systems, it typically corresponds to the
4669 standard @code{siginfo_t} type, as defined in the @file{signal.h}
4672 Here's an example, on a @sc{gnu}/Linux system, printing the stray
4673 referenced address that raised a segmentation fault.
4677 (@value{GDBP}) continue
4678 Program received signal SIGSEGV, Segmentation fault.
4679 0x0000000000400766 in main ()
4681 (@value{GDBP}) ptype $_siginfo
4688 struct @{...@} _kill;
4689 struct @{...@} _timer;
4691 struct @{...@} _sigchld;
4692 struct @{...@} _sigfault;
4693 struct @{...@} _sigpoll;
4696 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
4700 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
4701 $1 = (void *) 0x7ffff7ff7000
4705 Depending on target support, @code{$_siginfo} may also be writable.
4708 @section Stopping and Starting Multi-thread Programs
4710 @cindex stopped threads
4711 @cindex threads, stopped
4713 @cindex continuing threads
4714 @cindex threads, continuing
4716 @value{GDBN} supports debugging programs with multiple threads
4717 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
4718 are two modes of controlling execution of your program within the
4719 debugger. In the default mode, referred to as @dfn{all-stop mode},
4720 when any thread in your program stops (for example, at a breakpoint
4721 or while being stepped), all other threads in the program are also stopped by
4722 @value{GDBN}. On some targets, @value{GDBN} also supports
4723 @dfn{non-stop mode}, in which other threads can continue to run freely while
4724 you examine the stopped thread in the debugger.
4727 * All-Stop Mode:: All threads stop when GDB takes control
4728 * Non-Stop Mode:: Other threads continue to execute
4729 * Background Execution:: Running your program asynchronously
4730 * Thread-Specific Breakpoints:: Controlling breakpoints
4731 * Interrupted System Calls:: GDB may interfere with system calls
4735 @subsection All-Stop Mode
4737 @cindex all-stop mode
4739 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
4740 @emph{all} threads of execution stop, not just the current thread. This
4741 allows you to examine the overall state of the program, including
4742 switching between threads, without worrying that things may change
4745 Conversely, whenever you restart the program, @emph{all} threads start
4746 executing. @emph{This is true even when single-stepping} with commands
4747 like @code{step} or @code{next}.
4749 In particular, @value{GDBN} cannot single-step all threads in lockstep.
4750 Since thread scheduling is up to your debugging target's operating
4751 system (not controlled by @value{GDBN}), other threads may
4752 execute more than one statement while the current thread completes a
4753 single step. Moreover, in general other threads stop in the middle of a
4754 statement, rather than at a clean statement boundary, when the program
4757 You might even find your program stopped in another thread after
4758 continuing or even single-stepping. This happens whenever some other
4759 thread runs into a breakpoint, a signal, or an exception before the
4760 first thread completes whatever you requested.
4762 @cindex automatic thread selection
4763 @cindex switching threads automatically
4764 @cindex threads, automatic switching
4765 Whenever @value{GDBN} stops your program, due to a breakpoint or a
4766 signal, it automatically selects the thread where that breakpoint or
4767 signal happened. @value{GDBN} alerts you to the context switch with a
4768 message such as @samp{[Switching to Thread @var{n}]} to identify the
4771 On some OSes, you can modify @value{GDBN}'s default behavior by
4772 locking the OS scheduler to allow only a single thread to run.
4775 @item set scheduler-locking @var{mode}
4776 @cindex scheduler locking mode
4777 @cindex lock scheduler
4778 Set the scheduler locking mode. If it is @code{off}, then there is no
4779 locking and any thread may run at any time. If @code{on}, then only the
4780 current thread may run when the inferior is resumed. The @code{step}
4781 mode optimizes for single-stepping; it prevents other threads
4782 from preempting the current thread while you are stepping, so that
4783 the focus of debugging does not change unexpectedly.
4784 Other threads only rarely (or never) get a chance to run
4785 when you step. They are more likely to run when you @samp{next} over a
4786 function call, and they are completely free to run when you use commands
4787 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
4788 thread hits a breakpoint during its timeslice, @value{GDBN} does not change
4789 the current thread away from the thread that you are debugging.
4791 @item show scheduler-locking
4792 Display the current scheduler locking mode.
4795 @cindex resume threads of multiple processes simultaneously
4796 By default, when you issue one of the execution commands such as
4797 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
4798 threads of the current inferior to run. For example, if @value{GDBN}
4799 is attached to two inferiors, each with two threads, the
4800 @code{continue} command resumes only the two threads of the current
4801 inferior. This is useful, for example, when you debug a program that
4802 forks and you want to hold the parent stopped (so that, for instance,
4803 it doesn't run to exit), while you debug the child. In other
4804 situations, you may not be interested in inspecting the current state
4805 of any of the processes @value{GDBN} is attached to, and you may want
4806 to resume them all until some breakpoint is hit. In the latter case,
4807 you can instruct @value{GDBN} to allow all threads of all the
4808 inferiors to run with the @w{@code{set schedule-multiple}} command.
4811 @kindex set schedule-multiple
4812 @item set schedule-multiple
4813 Set the mode for allowing threads of multiple processes to be resumed
4814 when an execution command is issued. When @code{on}, all threads of
4815 all processes are allowed to run. When @code{off}, only the threads
4816 of the current process are resumed. The default is @code{off}. The
4817 @code{scheduler-locking} mode takes precedence when set to @code{on},
4818 or while you are stepping and set to @code{step}.
4820 @item show schedule-multiple
4821 Display the current mode for resuming the execution of threads of
4826 @subsection Non-Stop Mode
4828 @cindex non-stop mode
4830 @c This section is really only a place-holder, and needs to be expanded
4831 @c with more details.
4833 For some multi-threaded targets, @value{GDBN} supports an optional
4834 mode of operation in which you can examine stopped program threads in
4835 the debugger while other threads continue to execute freely. This
4836 minimizes intrusion when debugging live systems, such as programs
4837 where some threads have real-time constraints or must continue to
4838 respond to external events. This is referred to as @dfn{non-stop} mode.
4840 In non-stop mode, when a thread stops to report a debugging event,
4841 @emph{only} that thread is stopped; @value{GDBN} does not stop other
4842 threads as well, in contrast to the all-stop mode behavior. Additionally,
4843 execution commands such as @code{continue} and @code{step} apply by default
4844 only to the current thread in non-stop mode, rather than all threads as
4845 in all-stop mode. This allows you to control threads explicitly in
4846 ways that are not possible in all-stop mode --- for example, stepping
4847 one thread while allowing others to run freely, stepping
4848 one thread while holding all others stopped, or stepping several threads
4849 independently and simultaneously.
4851 To enter non-stop mode, use this sequence of commands before you run
4852 or attach to your program:
4855 # Enable the async interface.
4858 # If using the CLI, pagination breaks non-stop.
4861 # Finally, turn it on!
4865 You can use these commands to manipulate the non-stop mode setting:
4868 @kindex set non-stop
4869 @item set non-stop on
4870 Enable selection of non-stop mode.
4871 @item set non-stop off
4872 Disable selection of non-stop mode.
4873 @kindex show non-stop
4875 Show the current non-stop enablement setting.
4878 Note these commands only reflect whether non-stop mode is enabled,
4879 not whether the currently-executing program is being run in non-stop mode.
4880 In particular, the @code{set non-stop} preference is only consulted when
4881 @value{GDBN} starts or connects to the target program, and it is generally
4882 not possible to switch modes once debugging has started. Furthermore,
4883 since not all targets support non-stop mode, even when you have enabled
4884 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
4887 In non-stop mode, all execution commands apply only to the current thread
4888 by default. That is, @code{continue} only continues one thread.
4889 To continue all threads, issue @code{continue -a} or @code{c -a}.
4891 You can use @value{GDBN}'s background execution commands
4892 (@pxref{Background Execution}) to run some threads in the background
4893 while you continue to examine or step others from @value{GDBN}.
4894 The MI execution commands (@pxref{GDB/MI Program Execution}) are
4895 always executed asynchronously in non-stop mode.
4897 Suspending execution is done with the @code{interrupt} command when
4898 running in the background, or @kbd{Ctrl-c} during foreground execution.
4899 In all-stop mode, this stops the whole process;
4900 but in non-stop mode the interrupt applies only to the current thread.
4901 To stop the whole program, use @code{interrupt -a}.
4903 Other execution commands do not currently support the @code{-a} option.
4905 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
4906 that thread current, as it does in all-stop mode. This is because the
4907 thread stop notifications are asynchronous with respect to @value{GDBN}'s
4908 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
4909 changed to a different thread just as you entered a command to operate on the
4910 previously current thread.
4912 @node Background Execution
4913 @subsection Background Execution
4915 @cindex foreground execution
4916 @cindex background execution
4917 @cindex asynchronous execution
4918 @cindex execution, foreground, background and asynchronous
4920 @value{GDBN}'s execution commands have two variants: the normal
4921 foreground (synchronous) behavior, and a background
4922 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
4923 the program to report that some thread has stopped before prompting for
4924 another command. In background execution, @value{GDBN} immediately gives
4925 a command prompt so that you can issue other commands while your program runs.
4927 You need to explicitly enable asynchronous mode before you can use
4928 background execution commands. You can use these commands to
4929 manipulate the asynchronous mode setting:
4932 @kindex set target-async
4933 @item set target-async on
4934 Enable asynchronous mode.
4935 @item set target-async off
4936 Disable asynchronous mode.
4937 @kindex show target-async
4938 @item show target-async
4939 Show the current target-async setting.
4942 If the target doesn't support async mode, @value{GDBN} issues an error
4943 message if you attempt to use the background execution commands.
4945 To specify background execution, add a @code{&} to the command. For example,
4946 the background form of the @code{continue} command is @code{continue&}, or
4947 just @code{c&}. The execution commands that accept background execution
4953 @xref{Starting, , Starting your Program}.
4957 @xref{Attach, , Debugging an Already-running Process}.
4961 @xref{Continuing and Stepping, step}.
4965 @xref{Continuing and Stepping, stepi}.
4969 @xref{Continuing and Stepping, next}.
4973 @xref{Continuing and Stepping, nexti}.
4977 @xref{Continuing and Stepping, continue}.
4981 @xref{Continuing and Stepping, finish}.
4985 @xref{Continuing and Stepping, until}.
4989 Background execution is especially useful in conjunction with non-stop
4990 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
4991 However, you can also use these commands in the normal all-stop mode with
4992 the restriction that you cannot issue another execution command until the
4993 previous one finishes. Examples of commands that are valid in all-stop
4994 mode while the program is running include @code{help} and @code{info break}.
4996 You can interrupt your program while it is running in the background by
4997 using the @code{interrupt} command.
5004 Suspend execution of the running program. In all-stop mode,
5005 @code{interrupt} stops the whole process, but in non-stop mode, it stops
5006 only the current thread. To stop the whole program in non-stop mode,
5007 use @code{interrupt -a}.
5010 @node Thread-Specific Breakpoints
5011 @subsection Thread-Specific Breakpoints
5013 When your program has multiple threads (@pxref{Threads,, Debugging
5014 Programs with Multiple Threads}), you can choose whether to set
5015 breakpoints on all threads, or on a particular thread.
5018 @cindex breakpoints and threads
5019 @cindex thread breakpoints
5020 @kindex break @dots{} thread @var{threadno}
5021 @item break @var{linespec} thread @var{threadno}
5022 @itemx break @var{linespec} thread @var{threadno} if @dots{}
5023 @var{linespec} specifies source lines; there are several ways of
5024 writing them (@pxref{Specify Location}), but the effect is always to
5025 specify some source line.
5027 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
5028 to specify that you only want @value{GDBN} to stop the program when a
5029 particular thread reaches this breakpoint. @var{threadno} is one of the
5030 numeric thread identifiers assigned by @value{GDBN}, shown in the first
5031 column of the @samp{info threads} display.
5033 If you do not specify @samp{thread @var{threadno}} when you set a
5034 breakpoint, the breakpoint applies to @emph{all} threads of your
5037 You can use the @code{thread} qualifier on conditional breakpoints as
5038 well; in this case, place @samp{thread @var{threadno}} before the
5039 breakpoint condition, like this:
5042 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
5047 @node Interrupted System Calls
5048 @subsection Interrupted System Calls
5050 @cindex thread breakpoints and system calls
5051 @cindex system calls and thread breakpoints
5052 @cindex premature return from system calls
5053 There is an unfortunate side effect when using @value{GDBN} to debug
5054 multi-threaded programs. If one thread stops for a
5055 breakpoint, or for some other reason, and another thread is blocked in a
5056 system call, then the system call may return prematurely. This is a
5057 consequence of the interaction between multiple threads and the signals
5058 that @value{GDBN} uses to implement breakpoints and other events that
5061 To handle this problem, your program should check the return value of
5062 each system call and react appropriately. This is good programming
5065 For example, do not write code like this:
5071 The call to @code{sleep} will return early if a different thread stops
5072 at a breakpoint or for some other reason.
5074 Instead, write this:
5079 unslept = sleep (unslept);
5082 A system call is allowed to return early, so the system is still
5083 conforming to its specification. But @value{GDBN} does cause your
5084 multi-threaded program to behave differently than it would without
5087 Also, @value{GDBN} uses internal breakpoints in the thread library to
5088 monitor certain events such as thread creation and thread destruction.
5089 When such an event happens, a system call in another thread may return
5090 prematurely, even though your program does not appear to stop.
5093 @node Reverse Execution
5094 @chapter Running programs backward
5095 @cindex reverse execution
5096 @cindex running programs backward
5098 When you are debugging a program, it is not unusual to realize that
5099 you have gone too far, and some event of interest has already happened.
5100 If the target environment supports it, @value{GDBN} can allow you to
5101 ``rewind'' the program by running it backward.
5103 A target environment that supports reverse execution should be able
5104 to ``undo'' the changes in machine state that have taken place as the
5105 program was executing normally. Variables, registers etc.@: should
5106 revert to their previous values. Obviously this requires a great
5107 deal of sophistication on the part of the target environment; not
5108 all target environments can support reverse execution.
5110 When a program is executed in reverse, the instructions that
5111 have most recently been executed are ``un-executed'', in reverse
5112 order. The program counter runs backward, following the previous
5113 thread of execution in reverse. As each instruction is ``un-executed'',
5114 the values of memory and/or registers that were changed by that
5115 instruction are reverted to their previous states. After executing
5116 a piece of source code in reverse, all side effects of that code
5117 should be ``undone'', and all variables should be returned to their
5118 prior values@footnote{
5119 Note that some side effects are easier to undo than others. For instance,
5120 memory and registers are relatively easy, but device I/O is hard. Some
5121 targets may be able undo things like device I/O, and some may not.
5123 The contract between @value{GDBN} and the reverse executing target
5124 requires only that the target do something reasonable when
5125 @value{GDBN} tells it to execute backwards, and then report the
5126 results back to @value{GDBN}. Whatever the target reports back to
5127 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
5128 assumes that the memory and registers that the target reports are in a
5129 consistant state, but @value{GDBN} accepts whatever it is given.
5132 If you are debugging in a target environment that supports
5133 reverse execution, @value{GDBN} provides the following commands.
5136 @kindex reverse-continue
5137 @kindex rc @r{(@code{reverse-continue})}
5138 @item reverse-continue @r{[}@var{ignore-count}@r{]}
5139 @itemx rc @r{[}@var{ignore-count}@r{]}
5140 Beginning at the point where your program last stopped, start executing
5141 in reverse. Reverse execution will stop for breakpoints and synchronous
5142 exceptions (signals), just like normal execution. Behavior of
5143 asynchronous signals depends on the target environment.
5145 @kindex reverse-step
5146 @kindex rs @r{(@code{step})}
5147 @item reverse-step @r{[}@var{count}@r{]}
5148 Run the program backward until control reaches the start of a
5149 different source line; then stop it, and return control to @value{GDBN}.
5151 Like the @code{step} command, @code{reverse-step} will only stop
5152 at the beginning of a source line. It ``un-executes'' the previously
5153 executed source line. If the previous source line included calls to
5154 debuggable functions, @code{reverse-step} will step (backward) into
5155 the called function, stopping at the beginning of the @emph{last}
5156 statement in the called function (typically a return statement).
5158 Also, as with the @code{step} command, if non-debuggable functions are
5159 called, @code{reverse-step} will run thru them backward without stopping.
5161 @kindex reverse-stepi
5162 @kindex rsi @r{(@code{reverse-stepi})}
5163 @item reverse-stepi @r{[}@var{count}@r{]}
5164 Reverse-execute one machine instruction. Note that the instruction
5165 to be reverse-executed is @emph{not} the one pointed to by the program
5166 counter, but the instruction executed prior to that one. For instance,
5167 if the last instruction was a jump, @code{reverse-stepi} will take you
5168 back from the destination of the jump to the jump instruction itself.
5170 @kindex reverse-next
5171 @kindex rn @r{(@code{reverse-next})}
5172 @item reverse-next @r{[}@var{count}@r{]}
5173 Run backward to the beginning of the previous line executed in
5174 the current (innermost) stack frame. If the line contains function
5175 calls, they will be ``un-executed'' without stopping. Starting from
5176 the first line of a function, @code{reverse-next} will take you back
5177 to the caller of that function, @emph{before} the function was called,
5178 just as the normal @code{next} command would take you from the last
5179 line of a function back to its return to its caller
5180 @footnote{Unles the code is too heavily optimized.}.
5182 @kindex reverse-nexti
5183 @kindex rni @r{(@code{reverse-nexti})}
5184 @item reverse-nexti @r{[}@var{count}@r{]}
5185 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
5186 in reverse, except that called functions are ``un-executed'' atomically.
5187 That is, if the previously executed instruction was a return from
5188 another instruction, @code{reverse-nexti} will continue to execute
5189 in reverse until the call to that function (from the current stack
5192 @kindex reverse-finish
5193 @item reverse-finish
5194 Just as the @code{finish} command takes you to the point where the
5195 current function returns, @code{reverse-finish} takes you to the point
5196 where it was called. Instead of ending up at the end of the current
5197 function invocation, you end up at the beginning.
5199 @kindex set exec-direction
5200 @item set exec-direction
5201 Set the direction of target execution.
5202 @itemx set exec-direction reverse
5203 @cindex execute forward or backward in time
5204 @value{GDBN} will perform all execution commands in reverse, until the
5205 exec-direction mode is changed to ``forward''. Affected commands include
5206 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
5207 command cannot be used in reverse mode.
5208 @item set exec-direction forward
5209 @value{GDBN} will perform all execution commands in the normal fashion.
5210 This is the default.
5214 @node Process Record and Replay
5215 @chapter Recording Inferior's Execution and Replaying It
5216 @cindex process record and replay
5217 @cindex recording inferior's execution and replaying it
5219 On some platforms, @value{GDBN} provides a special @dfn{process record
5220 and replay} target that can record a log of the process execution, and
5221 replay it later with both forward and reverse execution commands.
5224 When this target is in use, if the execution log includes the record
5225 for the next instruction, @value{GDBN} will debug in @dfn{replay
5226 mode}. In the replay mode, the inferior does not really execute code
5227 instructions. Instead, all the events that normally happen during
5228 code execution are taken from the execution log. While code is not
5229 really executed in replay mode, the values of registers (including the
5230 program counter register) and the memory of the inferior are still
5231 changed as they normally would. Their contents are taken from the
5235 If the record for the next instruction is not in the execution log,
5236 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
5237 inferior executes normally, and @value{GDBN} records the execution log
5240 The process record and replay target supports reverse execution
5241 (@pxref{Reverse Execution}), even if the platform on which the
5242 inferior runs does not. However, the reverse execution is limited in
5243 this case by the range of the instructions recorded in the execution
5244 log. In other words, reverse execution on platforms that don't
5245 support it directly can only be done in the replay mode.
5247 When debugging in the reverse direction, @value{GDBN} will work in
5248 replay mode as long as the execution log includes the record for the
5249 previous instruction; otherwise, it will work in record mode, if the
5250 platform supports reverse execution, or stop if not.
5252 For architecture environments that support process record and replay,
5253 @value{GDBN} provides the following commands:
5256 @kindex target record
5260 This command starts the process record and replay target. The process
5261 record and replay target can only debug a process that is already
5262 running. Therefore, you need first to start the process with the
5263 @kbd{run} or @kbd{start} commands, and then start the recording with
5264 the @kbd{target record} command.
5266 Both @code{record} and @code{rec} are aliases of @code{target record}.
5268 @cindex displaced stepping, and process record and replay
5269 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
5270 will be automatically disabled when process record and replay target
5271 is started. That's because the process record and replay target
5272 doesn't support displaced stepping.
5274 @cindex non-stop mode, and process record and replay
5275 @cindex asynchronous execution, and process record and replay
5276 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
5277 the asynchronous execution mode (@pxref{Background Execution}), the
5278 process record and replay target cannot be started because it doesn't
5279 support these two modes.
5284 Stop the process record and replay target. When process record and
5285 replay target stops, the entire execution log will be deleted and the
5286 inferior will either be terminated, or will remain in its final state.
5288 When you stop the process record and replay target in record mode (at
5289 the end of the execution log), the inferior will be stopped at the
5290 next instruction that would have been recorded. In other words, if
5291 you record for a while and then stop recording, the inferior process
5292 will be left in the same state as if the recording never happened.
5294 On the other hand, if the process record and replay target is stopped
5295 while in replay mode (that is, not at the end of the execution log,
5296 but at some earlier point), the inferior process will become ``live''
5297 at that earlier state, and it will then be possible to continue the
5298 usual ``live'' debugging of the process from that state.
5300 When the inferior process exits, or @value{GDBN} detaches from it,
5301 process record and replay target will automatically stop itself.
5303 @kindex set record insn-number-max
5304 @item set record insn-number-max @var{limit}
5305 Set the limit of instructions to be recorded. Default value is 200000.
5307 If @var{limit} is a positive number, then @value{GDBN} will start
5308 deleting instructions from the log once the number of the record
5309 instructions becomes greater than @var{limit}. For every new recorded
5310 instruction, @value{GDBN} will delete the earliest recorded
5311 instruction to keep the number of recorded instructions at the limit.
5312 (Since deleting recorded instructions loses information, @value{GDBN}
5313 lets you control what happens when the limit is reached, by means of
5314 the @code{stop-at-limit} option, described below.)
5316 If @var{limit} is zero, @value{GDBN} will never delete recorded
5317 instructions from the execution log. The number of recorded
5318 instructions is unlimited in this case.
5320 @kindex show record insn-number-max
5321 @item show record insn-number-max
5322 Show the limit of instructions to be recorded.
5324 @kindex set record stop-at-limit
5325 @item set record stop-at-limit
5326 Control the behavior when the number of recorded instructions reaches
5327 the limit. If ON (the default), @value{GDBN} will stop when the limit
5328 is reached for the first time and ask you whether you want to stop the
5329 inferior or continue running it and recording the execution log. If
5330 you decide to continue recording, each new recorded instruction will
5331 cause the oldest one to be deleted.
5333 If this option is OFF, @value{GDBN} will automatically delete the
5334 oldest record to make room for each new one, without asking.
5336 @kindex show record stop-at-limit
5337 @item show record stop-at-limit
5338 Show the current setting of @code{stop-at-limit}.
5340 @kindex info record insn-number
5341 @item info record insn-number
5342 Show the current number of recorded instructions.
5344 @kindex record delete
5347 When record target runs in replay mode (``in the past''), delete the
5348 subsequent execution log and begin to record a new execution log starting
5349 from the current address. This means you will abandon the previously
5350 recorded ``future'' and begin recording a new ``future''.
5355 @chapter Examining the Stack
5357 When your program has stopped, the first thing you need to know is where it
5358 stopped and how it got there.
5361 Each time your program performs a function call, information about the call
5363 That information includes the location of the call in your program,
5364 the arguments of the call,
5365 and the local variables of the function being called.
5366 The information is saved in a block of data called a @dfn{stack frame}.
5367 The stack frames are allocated in a region of memory called the @dfn{call
5370 When your program stops, the @value{GDBN} commands for examining the
5371 stack allow you to see all of this information.
5373 @cindex selected frame
5374 One of the stack frames is @dfn{selected} by @value{GDBN} and many
5375 @value{GDBN} commands refer implicitly to the selected frame. In
5376 particular, whenever you ask @value{GDBN} for the value of a variable in
5377 your program, the value is found in the selected frame. There are
5378 special @value{GDBN} commands to select whichever frame you are
5379 interested in. @xref{Selection, ,Selecting a Frame}.
5381 When your program stops, @value{GDBN} automatically selects the
5382 currently executing frame and describes it briefly, similar to the
5383 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
5386 * Frames:: Stack frames
5387 * Backtrace:: Backtraces
5388 * Selection:: Selecting a frame
5389 * Frame Info:: Information on a frame
5394 @section Stack Frames
5396 @cindex frame, definition
5398 The call stack is divided up into contiguous pieces called @dfn{stack
5399 frames}, or @dfn{frames} for short; each frame is the data associated
5400 with one call to one function. The frame contains the arguments given
5401 to the function, the function's local variables, and the address at
5402 which the function is executing.
5404 @cindex initial frame
5405 @cindex outermost frame
5406 @cindex innermost frame
5407 When your program is started, the stack has only one frame, that of the
5408 function @code{main}. This is called the @dfn{initial} frame or the
5409 @dfn{outermost} frame. Each time a function is called, a new frame is
5410 made. Each time a function returns, the frame for that function invocation
5411 is eliminated. If a function is recursive, there can be many frames for
5412 the same function. The frame for the function in which execution is
5413 actually occurring is called the @dfn{innermost} frame. This is the most
5414 recently created of all the stack frames that still exist.
5416 @cindex frame pointer
5417 Inside your program, stack frames are identified by their addresses. A
5418 stack frame consists of many bytes, each of which has its own address; each
5419 kind of computer has a convention for choosing one byte whose
5420 address serves as the address of the frame. Usually this address is kept
5421 in a register called the @dfn{frame pointer register}
5422 (@pxref{Registers, $fp}) while execution is going on in that frame.
5424 @cindex frame number
5425 @value{GDBN} assigns numbers to all existing stack frames, starting with
5426 zero for the innermost frame, one for the frame that called it,
5427 and so on upward. These numbers do not really exist in your program;
5428 they are assigned by @value{GDBN} to give you a way of designating stack
5429 frames in @value{GDBN} commands.
5431 @c The -fomit-frame-pointer below perennially causes hbox overflow
5432 @c underflow problems.
5433 @cindex frameless execution
5434 Some compilers provide a way to compile functions so that they operate
5435 without stack frames. (For example, the @value{NGCC} option
5437 @samp{-fomit-frame-pointer}
5439 generates functions without a frame.)
5440 This is occasionally done with heavily used library functions to save
5441 the frame setup time. @value{GDBN} has limited facilities for dealing
5442 with these function invocations. If the innermost function invocation
5443 has no stack frame, @value{GDBN} nevertheless regards it as though
5444 it had a separate frame, which is numbered zero as usual, allowing
5445 correct tracing of the function call chain. However, @value{GDBN} has
5446 no provision for frameless functions elsewhere in the stack.
5449 @kindex frame@r{, command}
5450 @cindex current stack frame
5451 @item frame @var{args}
5452 The @code{frame} command allows you to move from one stack frame to another,
5453 and to print the stack frame you select. @var{args} may be either the
5454 address of the frame or the stack frame number. Without an argument,
5455 @code{frame} prints the current stack frame.
5457 @kindex select-frame
5458 @cindex selecting frame silently
5460 The @code{select-frame} command allows you to move from one stack frame
5461 to another without printing the frame. This is the silent version of
5469 @cindex call stack traces
5470 A backtrace is a summary of how your program got where it is. It shows one
5471 line per frame, for many frames, starting with the currently executing
5472 frame (frame zero), followed by its caller (frame one), and on up the
5477 @kindex bt @r{(@code{backtrace})}
5480 Print a backtrace of the entire stack: one line per frame for all
5481 frames in the stack.
5483 You can stop the backtrace at any time by typing the system interrupt
5484 character, normally @kbd{Ctrl-c}.
5486 @item backtrace @var{n}
5488 Similar, but print only the innermost @var{n} frames.
5490 @item backtrace -@var{n}
5492 Similar, but print only the outermost @var{n} frames.
5494 @item backtrace full
5496 @itemx bt full @var{n}
5497 @itemx bt full -@var{n}
5498 Print the values of the local variables also. @var{n} specifies the
5499 number of frames to print, as described above.
5504 The names @code{where} and @code{info stack} (abbreviated @code{info s})
5505 are additional aliases for @code{backtrace}.
5507 @cindex multiple threads, backtrace
5508 In a multi-threaded program, @value{GDBN} by default shows the
5509 backtrace only for the current thread. To display the backtrace for
5510 several or all of the threads, use the command @code{thread apply}
5511 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
5512 apply all backtrace}, @value{GDBN} will display the backtrace for all
5513 the threads; this is handy when you debug a core dump of a
5514 multi-threaded program.
5516 Each line in the backtrace shows the frame number and the function name.
5517 The program counter value is also shown---unless you use @code{set
5518 print address off}. The backtrace also shows the source file name and
5519 line number, as well as the arguments to the function. The program
5520 counter value is omitted if it is at the beginning of the code for that
5523 Here is an example of a backtrace. It was made with the command
5524 @samp{bt 3}, so it shows the innermost three frames.
5528 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5530 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
5531 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
5533 (More stack frames follow...)
5538 The display for frame zero does not begin with a program counter
5539 value, indicating that your program has stopped at the beginning of the
5540 code for line @code{993} of @code{builtin.c}.
5543 The value of parameter @code{data} in frame 1 has been replaced by
5544 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
5545 only if it is a scalar (integer, pointer, enumeration, etc). See command
5546 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
5547 on how to configure the way function parameter values are printed.
5549 @cindex value optimized out, in backtrace
5550 @cindex function call arguments, optimized out
5551 If your program was compiled with optimizations, some compilers will
5552 optimize away arguments passed to functions if those arguments are
5553 never used after the call. Such optimizations generate code that
5554 passes arguments through registers, but doesn't store those arguments
5555 in the stack frame. @value{GDBN} has no way of displaying such
5556 arguments in stack frames other than the innermost one. Here's what
5557 such a backtrace might look like:
5561 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
5563 #1 0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
5564 #2 0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
5566 (More stack frames follow...)
5571 The values of arguments that were not saved in their stack frames are
5572 shown as @samp{<value optimized out>}.
5574 If you need to display the values of such optimized-out arguments,
5575 either deduce that from other variables whose values depend on the one
5576 you are interested in, or recompile without optimizations.
5578 @cindex backtrace beyond @code{main} function
5579 @cindex program entry point
5580 @cindex startup code, and backtrace
5581 Most programs have a standard user entry point---a place where system
5582 libraries and startup code transition into user code. For C this is
5583 @code{main}@footnote{
5584 Note that embedded programs (the so-called ``free-standing''
5585 environment) are not required to have a @code{main} function as the
5586 entry point. They could even have multiple entry points.}.
5587 When @value{GDBN} finds the entry function in a backtrace
5588 it will terminate the backtrace, to avoid tracing into highly
5589 system-specific (and generally uninteresting) code.
5591 If you need to examine the startup code, or limit the number of levels
5592 in a backtrace, you can change this behavior:
5595 @item set backtrace past-main
5596 @itemx set backtrace past-main on
5597 @kindex set backtrace
5598 Backtraces will continue past the user entry point.
5600 @item set backtrace past-main off
5601 Backtraces will stop when they encounter the user entry point. This is the
5604 @item show backtrace past-main
5605 @kindex show backtrace
5606 Display the current user entry point backtrace policy.
5608 @item set backtrace past-entry
5609 @itemx set backtrace past-entry on
5610 Backtraces will continue past the internal entry point of an application.
5611 This entry point is encoded by the linker when the application is built,
5612 and is likely before the user entry point @code{main} (or equivalent) is called.
5614 @item set backtrace past-entry off
5615 Backtraces will stop when they encounter the internal entry point of an
5616 application. This is the default.
5618 @item show backtrace past-entry
5619 Display the current internal entry point backtrace policy.
5621 @item set backtrace limit @var{n}
5622 @itemx set backtrace limit 0
5623 @cindex backtrace limit
5624 Limit the backtrace to @var{n} levels. A value of zero means
5627 @item show backtrace limit
5628 Display the current limit on backtrace levels.
5632 @section Selecting a Frame
5634 Most commands for examining the stack and other data in your program work on
5635 whichever stack frame is selected at the moment. Here are the commands for
5636 selecting a stack frame; all of them finish by printing a brief description
5637 of the stack frame just selected.
5640 @kindex frame@r{, selecting}
5641 @kindex f @r{(@code{frame})}
5644 Select frame number @var{n}. Recall that frame zero is the innermost
5645 (currently executing) frame, frame one is the frame that called the
5646 innermost one, and so on. The highest-numbered frame is the one for
5649 @item frame @var{addr}
5651 Select the frame at address @var{addr}. This is useful mainly if the
5652 chaining of stack frames has been damaged by a bug, making it
5653 impossible for @value{GDBN} to assign numbers properly to all frames. In
5654 addition, this can be useful when your program has multiple stacks and
5655 switches between them.
5657 On the SPARC architecture, @code{frame} needs two addresses to
5658 select an arbitrary frame: a frame pointer and a stack pointer.
5660 On the MIPS and Alpha architecture, it needs two addresses: a stack
5661 pointer and a program counter.
5663 On the 29k architecture, it needs three addresses: a register stack
5664 pointer, a program counter, and a memory stack pointer.
5668 Move @var{n} frames up the stack. For positive numbers @var{n}, this
5669 advances toward the outermost frame, to higher frame numbers, to frames
5670 that have existed longer. @var{n} defaults to one.
5673 @kindex do @r{(@code{down})}
5675 Move @var{n} frames down the stack. For positive numbers @var{n}, this
5676 advances toward the innermost frame, to lower frame numbers, to frames
5677 that were created more recently. @var{n} defaults to one. You may
5678 abbreviate @code{down} as @code{do}.
5681 All of these commands end by printing two lines of output describing the
5682 frame. The first line shows the frame number, the function name, the
5683 arguments, and the source file and line number of execution in that
5684 frame. The second line shows the text of that source line.
5692 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
5694 10 read_input_file (argv[i]);
5698 After such a printout, the @code{list} command with no arguments
5699 prints ten lines centered on the point of execution in the frame.
5700 You can also edit the program at the point of execution with your favorite
5701 editing program by typing @code{edit}.
5702 @xref{List, ,Printing Source Lines},
5706 @kindex down-silently
5708 @item up-silently @var{n}
5709 @itemx down-silently @var{n}
5710 These two commands are variants of @code{up} and @code{down},
5711 respectively; they differ in that they do their work silently, without
5712 causing display of the new frame. They are intended primarily for use
5713 in @value{GDBN} command scripts, where the output might be unnecessary and
5718 @section Information About a Frame
5720 There are several other commands to print information about the selected
5726 When used without any argument, this command does not change which
5727 frame is selected, but prints a brief description of the currently
5728 selected stack frame. It can be abbreviated @code{f}. With an
5729 argument, this command is used to select a stack frame.
5730 @xref{Selection, ,Selecting a Frame}.
5733 @kindex info f @r{(@code{info frame})}
5736 This command prints a verbose description of the selected stack frame,
5741 the address of the frame
5743 the address of the next frame down (called by this frame)
5745 the address of the next frame up (caller of this frame)
5747 the language in which the source code corresponding to this frame is written
5749 the address of the frame's arguments
5751 the address of the frame's local variables
5753 the program counter saved in it (the address of execution in the caller frame)
5755 which registers were saved in the frame
5758 @noindent The verbose description is useful when
5759 something has gone wrong that has made the stack format fail to fit
5760 the usual conventions.
5762 @item info frame @var{addr}
5763 @itemx info f @var{addr}
5764 Print a verbose description of the frame at address @var{addr}, without
5765 selecting that frame. The selected frame remains unchanged by this
5766 command. This requires the same kind of address (more than one for some
5767 architectures) that you specify in the @code{frame} command.
5768 @xref{Selection, ,Selecting a Frame}.
5772 Print the arguments of the selected frame, each on a separate line.
5776 Print the local variables of the selected frame, each on a separate
5777 line. These are all variables (declared either static or automatic)
5778 accessible at the point of execution of the selected frame.
5781 @cindex catch exceptions, list active handlers
5782 @cindex exception handlers, how to list
5784 Print a list of all the exception handlers that are active in the
5785 current stack frame at the current point of execution. To see other
5786 exception handlers, visit the associated frame (using the @code{up},
5787 @code{down}, or @code{frame} commands); then type @code{info catch}.
5788 @xref{Set Catchpoints, , Setting Catchpoints}.
5794 @chapter Examining Source Files
5796 @value{GDBN} can print parts of your program's source, since the debugging
5797 information recorded in the program tells @value{GDBN} what source files were
5798 used to build it. When your program stops, @value{GDBN} spontaneously prints
5799 the line where it stopped. Likewise, when you select a stack frame
5800 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
5801 execution in that frame has stopped. You can print other portions of
5802 source files by explicit command.
5804 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
5805 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
5806 @value{GDBN} under @sc{gnu} Emacs}.
5809 * List:: Printing source lines
5810 * Specify Location:: How to specify code locations
5811 * Edit:: Editing source files
5812 * Search:: Searching source files
5813 * Source Path:: Specifying source directories
5814 * Machine Code:: Source and machine code
5818 @section Printing Source Lines
5821 @kindex l @r{(@code{list})}
5822 To print lines from a source file, use the @code{list} command
5823 (abbreviated @code{l}). By default, ten lines are printed.
5824 There are several ways to specify what part of the file you want to
5825 print; see @ref{Specify Location}, for the full list.
5827 Here are the forms of the @code{list} command most commonly used:
5830 @item list @var{linenum}
5831 Print lines centered around line number @var{linenum} in the
5832 current source file.
5834 @item list @var{function}
5835 Print lines centered around the beginning of function
5839 Print more lines. If the last lines printed were printed with a
5840 @code{list} command, this prints lines following the last lines
5841 printed; however, if the last line printed was a solitary line printed
5842 as part of displaying a stack frame (@pxref{Stack, ,Examining the
5843 Stack}), this prints lines centered around that line.
5846 Print lines just before the lines last printed.
5849 @cindex @code{list}, how many lines to display
5850 By default, @value{GDBN} prints ten source lines with any of these forms of
5851 the @code{list} command. You can change this using @code{set listsize}:
5854 @kindex set listsize
5855 @item set listsize @var{count}
5856 Make the @code{list} command display @var{count} source lines (unless
5857 the @code{list} argument explicitly specifies some other number).
5859 @kindex show listsize
5861 Display the number of lines that @code{list} prints.
5864 Repeating a @code{list} command with @key{RET} discards the argument,
5865 so it is equivalent to typing just @code{list}. This is more useful
5866 than listing the same lines again. An exception is made for an
5867 argument of @samp{-}; that argument is preserved in repetition so that
5868 each repetition moves up in the source file.
5870 In general, the @code{list} command expects you to supply zero, one or two
5871 @dfn{linespecs}. Linespecs specify source lines; there are several ways
5872 of writing them (@pxref{Specify Location}), but the effect is always
5873 to specify some source line.
5875 Here is a complete description of the possible arguments for @code{list}:
5878 @item list @var{linespec}
5879 Print lines centered around the line specified by @var{linespec}.
5881 @item list @var{first},@var{last}
5882 Print lines from @var{first} to @var{last}. Both arguments are
5883 linespecs. When a @code{list} command has two linespecs, and the
5884 source file of the second linespec is omitted, this refers to
5885 the same source file as the first linespec.
5887 @item list ,@var{last}
5888 Print lines ending with @var{last}.
5890 @item list @var{first},
5891 Print lines starting with @var{first}.
5894 Print lines just after the lines last printed.
5897 Print lines just before the lines last printed.
5900 As described in the preceding table.
5903 @node Specify Location
5904 @section Specifying a Location
5905 @cindex specifying location
5908 Several @value{GDBN} commands accept arguments that specify a location
5909 of your program's code. Since @value{GDBN} is a source-level
5910 debugger, a location usually specifies some line in the source code;
5911 for that reason, locations are also known as @dfn{linespecs}.
5913 Here are all the different ways of specifying a code location that
5914 @value{GDBN} understands:
5918 Specifies the line number @var{linenum} of the current source file.
5921 @itemx +@var{offset}
5922 Specifies the line @var{offset} lines before or after the @dfn{current
5923 line}. For the @code{list} command, the current line is the last one
5924 printed; for the breakpoint commands, this is the line at which
5925 execution stopped in the currently selected @dfn{stack frame}
5926 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
5927 used as the second of the two linespecs in a @code{list} command,
5928 this specifies the line @var{offset} lines up or down from the first
5931 @item @var{filename}:@var{linenum}
5932 Specifies the line @var{linenum} in the source file @var{filename}.
5934 @item @var{function}
5935 Specifies the line that begins the body of the function @var{function}.
5936 For example, in C, this is the line with the open brace.
5938 @item @var{filename}:@var{function}
5939 Specifies the line that begins the body of the function @var{function}
5940 in the file @var{filename}. You only need the file name with a
5941 function name to avoid ambiguity when there are identically named
5942 functions in different source files.
5944 @item *@var{address}
5945 Specifies the program address @var{address}. For line-oriented
5946 commands, such as @code{list} and @code{edit}, this specifies a source
5947 line that contains @var{address}. For @code{break} and other
5948 breakpoint oriented commands, this can be used to set breakpoints in
5949 parts of your program which do not have debugging information or
5952 Here @var{address} may be any expression valid in the current working
5953 language (@pxref{Languages, working language}) that specifies a code
5954 address. In addition, as a convenience, @value{GDBN} extends the
5955 semantics of expressions used in locations to cover the situations
5956 that frequently happen during debugging. Here are the various forms
5960 @item @var{expression}
5961 Any expression valid in the current working language.
5963 @item @var{funcaddr}
5964 An address of a function or procedure derived from its name. In C,
5965 C@t{++}, Java, Objective-C, Fortran, minimal, and assembly, this is
5966 simply the function's name @var{function} (and actually a special case
5967 of a valid expression). In Pascal and Modula-2, this is
5968 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
5969 (although the Pascal form also works).
5971 This form specifies the address of the function's first instruction,
5972 before the stack frame and arguments have been set up.
5974 @item '@var{filename}'::@var{funcaddr}
5975 Like @var{funcaddr} above, but also specifies the name of the source
5976 file explicitly. This is useful if the name of the function does not
5977 specify the function unambiguously, e.g., if there are several
5978 functions with identical names in different source files.
5985 @section Editing Source Files
5986 @cindex editing source files
5989 @kindex e @r{(@code{edit})}
5990 To edit the lines in a source file, use the @code{edit} command.
5991 The editing program of your choice
5992 is invoked with the current line set to
5993 the active line in the program.
5994 Alternatively, there are several ways to specify what part of the file you
5995 want to print if you want to see other parts of the program:
5998 @item edit @var{location}
5999 Edit the source file specified by @code{location}. Editing starts at
6000 that @var{location}, e.g., at the specified source line of the
6001 specified file. @xref{Specify Location}, for all the possible forms
6002 of the @var{location} argument; here are the forms of the @code{edit}
6003 command most commonly used:
6006 @item edit @var{number}
6007 Edit the current source file with @var{number} as the active line number.
6009 @item edit @var{function}
6010 Edit the file containing @var{function} at the beginning of its definition.
6015 @subsection Choosing your Editor
6016 You can customize @value{GDBN} to use any editor you want
6018 The only restriction is that your editor (say @code{ex}), recognizes the
6019 following command-line syntax:
6021 ex +@var{number} file
6023 The optional numeric value +@var{number} specifies the number of the line in
6024 the file where to start editing.}.
6025 By default, it is @file{@value{EDITOR}}, but you can change this
6026 by setting the environment variable @code{EDITOR} before using
6027 @value{GDBN}. For example, to configure @value{GDBN} to use the
6028 @code{vi} editor, you could use these commands with the @code{sh} shell:
6034 or in the @code{csh} shell,
6036 setenv EDITOR /usr/bin/vi
6041 @section Searching Source Files
6042 @cindex searching source files
6044 There are two commands for searching through the current source file for a
6049 @kindex forward-search
6050 @item forward-search @var{regexp}
6051 @itemx search @var{regexp}
6052 The command @samp{forward-search @var{regexp}} checks each line,
6053 starting with the one following the last line listed, for a match for
6054 @var{regexp}. It lists the line that is found. You can use the
6055 synonym @samp{search @var{regexp}} or abbreviate the command name as
6058 @kindex reverse-search
6059 @item reverse-search @var{regexp}
6060 The command @samp{reverse-search @var{regexp}} checks each line, starting
6061 with the one before the last line listed and going backward, for a match
6062 for @var{regexp}. It lists the line that is found. You can abbreviate
6063 this command as @code{rev}.
6067 @section Specifying Source Directories
6070 @cindex directories for source files
6071 Executable programs sometimes do not record the directories of the source
6072 files from which they were compiled, just the names. Even when they do,
6073 the directories could be moved between the compilation and your debugging
6074 session. @value{GDBN} has a list of directories to search for source files;
6075 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
6076 it tries all the directories in the list, in the order they are present
6077 in the list, until it finds a file with the desired name.
6079 For example, suppose an executable references the file
6080 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
6081 @file{/mnt/cross}. The file is first looked up literally; if this
6082 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
6083 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
6084 message is printed. @value{GDBN} does not look up the parts of the
6085 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
6086 Likewise, the subdirectories of the source path are not searched: if
6087 the source path is @file{/mnt/cross}, and the binary refers to
6088 @file{foo.c}, @value{GDBN} would not find it under
6089 @file{/mnt/cross/usr/src/foo-1.0/lib}.
6091 Plain file names, relative file names with leading directories, file
6092 names containing dots, etc.@: are all treated as described above; for
6093 instance, if the source path is @file{/mnt/cross}, and the source file
6094 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
6095 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
6096 that---@file{/mnt/cross/foo.c}.
6098 Note that the executable search path is @emph{not} used to locate the
6101 Whenever you reset or rearrange the source path, @value{GDBN} clears out
6102 any information it has cached about where source files are found and where
6103 each line is in the file.
6107 When you start @value{GDBN}, its source path includes only @samp{cdir}
6108 and @samp{cwd}, in that order.
6109 To add other directories, use the @code{directory} command.
6111 The search path is used to find both program source files and @value{GDBN}
6112 script files (read using the @samp{-command} option and @samp{source} command).
6114 In addition to the source path, @value{GDBN} provides a set of commands
6115 that manage a list of source path substitution rules. A @dfn{substitution
6116 rule} specifies how to rewrite source directories stored in the program's
6117 debug information in case the sources were moved to a different
6118 directory between compilation and debugging. A rule is made of
6119 two strings, the first specifying what needs to be rewritten in
6120 the path, and the second specifying how it should be rewritten.
6121 In @ref{set substitute-path}, we name these two parts @var{from} and
6122 @var{to} respectively. @value{GDBN} does a simple string replacement
6123 of @var{from} with @var{to} at the start of the directory part of the
6124 source file name, and uses that result instead of the original file
6125 name to look up the sources.
6127 Using the previous example, suppose the @file{foo-1.0} tree has been
6128 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
6129 @value{GDBN} to replace @file{/usr/src} in all source path names with
6130 @file{/mnt/cross}. The first lookup will then be
6131 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
6132 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
6133 substitution rule, use the @code{set substitute-path} command
6134 (@pxref{set substitute-path}).
6136 To avoid unexpected substitution results, a rule is applied only if the
6137 @var{from} part of the directory name ends at a directory separator.
6138 For instance, a rule substituting @file{/usr/source} into
6139 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
6140 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
6141 is applied only at the beginning of the directory name, this rule will
6142 not be applied to @file{/root/usr/source/baz.c} either.
6144 In many cases, you can achieve the same result using the @code{directory}
6145 command. However, @code{set substitute-path} can be more efficient in
6146 the case where the sources are organized in a complex tree with multiple
6147 subdirectories. With the @code{directory} command, you need to add each
6148 subdirectory of your project. If you moved the entire tree while
6149 preserving its internal organization, then @code{set substitute-path}
6150 allows you to direct the debugger to all the sources with one single
6153 @code{set substitute-path} is also more than just a shortcut command.
6154 The source path is only used if the file at the original location no
6155 longer exists. On the other hand, @code{set substitute-path} modifies
6156 the debugger behavior to look at the rewritten location instead. So, if
6157 for any reason a source file that is not relevant to your executable is
6158 located at the original location, a substitution rule is the only
6159 method available to point @value{GDBN} at the new location.
6161 @cindex @samp{--with-relocated-sources}
6162 @cindex default source path substitution
6163 You can configure a default source path substitution rule by
6164 configuring @value{GDBN} with the
6165 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
6166 should be the name of a directory under @value{GDBN}'s configured
6167 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
6168 directory names in debug information under @var{dir} will be adjusted
6169 automatically if the installed @value{GDBN} is moved to a new
6170 location. This is useful if @value{GDBN}, libraries or executables
6171 with debug information and corresponding source code are being moved
6175 @item directory @var{dirname} @dots{}
6176 @item dir @var{dirname} @dots{}
6177 Add directory @var{dirname} to the front of the source path. Several
6178 directory names may be given to this command, separated by @samp{:}
6179 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
6180 part of absolute file names) or
6181 whitespace. You may specify a directory that is already in the source
6182 path; this moves it forward, so @value{GDBN} searches it sooner.
6186 @vindex $cdir@r{, convenience variable}
6187 @vindex $cwd@r{, convenience variable}
6188 @cindex compilation directory
6189 @cindex current directory
6190 @cindex working directory
6191 @cindex directory, current
6192 @cindex directory, compilation
6193 You can use the string @samp{$cdir} to refer to the compilation
6194 directory (if one is recorded), and @samp{$cwd} to refer to the current
6195 working directory. @samp{$cwd} is not the same as @samp{.}---the former
6196 tracks the current working directory as it changes during your @value{GDBN}
6197 session, while the latter is immediately expanded to the current
6198 directory at the time you add an entry to the source path.
6201 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
6203 @c RET-repeat for @code{directory} is explicitly disabled, but since
6204 @c repeating it would be a no-op we do not say that. (thanks to RMS)
6206 @item show directories
6207 @kindex show directories
6208 Print the source path: show which directories it contains.
6210 @anchor{set substitute-path}
6211 @item set substitute-path @var{from} @var{to}
6212 @kindex set substitute-path
6213 Define a source path substitution rule, and add it at the end of the
6214 current list of existing substitution rules. If a rule with the same
6215 @var{from} was already defined, then the old rule is also deleted.
6217 For example, if the file @file{/foo/bar/baz.c} was moved to
6218 @file{/mnt/cross/baz.c}, then the command
6221 (@value{GDBP}) set substitute-path /usr/src /mnt/cross
6225 will tell @value{GDBN} to replace @samp{/usr/src} with
6226 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
6227 @file{baz.c} even though it was moved.
6229 In the case when more than one substitution rule have been defined,
6230 the rules are evaluated one by one in the order where they have been
6231 defined. The first one matching, if any, is selected to perform
6234 For instance, if we had entered the following commands:
6237 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
6238 (@value{GDBP}) set substitute-path /usr/src /mnt/src
6242 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
6243 @file{/mnt/include/defs.h} by using the first rule. However, it would
6244 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
6245 @file{/mnt/src/lib/foo.c}.
6248 @item unset substitute-path [path]
6249 @kindex unset substitute-path
6250 If a path is specified, search the current list of substitution rules
6251 for a rule that would rewrite that path. Delete that rule if found.
6252 A warning is emitted by the debugger if no rule could be found.
6254 If no path is specified, then all substitution rules are deleted.
6256 @item show substitute-path [path]
6257 @kindex show substitute-path
6258 If a path is specified, then print the source path substitution rule
6259 which would rewrite that path, if any.
6261 If no path is specified, then print all existing source path substitution
6266 If your source path is cluttered with directories that are no longer of
6267 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
6268 versions of source. You can correct the situation as follows:
6272 Use @code{directory} with no argument to reset the source path to its default value.
6275 Use @code{directory} with suitable arguments to reinstall the
6276 directories you want in the source path. You can add all the
6277 directories in one command.
6281 @section Source and Machine Code
6282 @cindex source line and its code address
6284 You can use the command @code{info line} to map source lines to program
6285 addresses (and vice versa), and the command @code{disassemble} to display
6286 a range of addresses as machine instructions. You can use the command
6287 @code{set disassemble-next-line} to set whether to disassemble next
6288 source line when execution stops. When run under @sc{gnu} Emacs
6289 mode, the @code{info line} command causes the arrow to point to the
6290 line specified. Also, @code{info line} prints addresses in symbolic form as
6295 @item info line @var{linespec}
6296 Print the starting and ending addresses of the compiled code for
6297 source line @var{linespec}. You can specify source lines in any of
6298 the ways documented in @ref{Specify Location}.
6301 For example, we can use @code{info line} to discover the location of
6302 the object code for the first line of function
6303 @code{m4_changequote}:
6305 @c FIXME: I think this example should also show the addresses in
6306 @c symbolic form, as they usually would be displayed.
6308 (@value{GDBP}) info line m4_changequote
6309 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
6313 @cindex code address and its source line
6314 We can also inquire (using @code{*@var{addr}} as the form for
6315 @var{linespec}) what source line covers a particular address:
6317 (@value{GDBP}) info line *0x63ff
6318 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
6321 @cindex @code{$_} and @code{info line}
6322 @cindex @code{x} command, default address
6323 @kindex x@r{(examine), and} info line
6324 After @code{info line}, the default address for the @code{x} command
6325 is changed to the starting address of the line, so that @samp{x/i} is
6326 sufficient to begin examining the machine code (@pxref{Memory,
6327 ,Examining Memory}). Also, this address is saved as the value of the
6328 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
6333 @cindex assembly instructions
6334 @cindex instructions, assembly
6335 @cindex machine instructions
6336 @cindex listing machine instructions
6338 @itemx disassemble /m
6339 @itemx disassemble /r
6340 This specialized command dumps a range of memory as machine
6341 instructions. It can also print mixed source+disassembly by specifying
6342 the @code{/m} modifier and print the raw instructions in hex as well as
6343 in symbolic form by specifying the @code{/r}.
6344 The default memory range is the function surrounding the
6345 program counter of the selected frame. A single argument to this
6346 command is a program counter value; @value{GDBN} dumps the function
6347 surrounding this value. Two arguments specify a range of addresses
6348 (first inclusive, second exclusive) to dump.
6351 The following example shows the disassembly of a range of addresses of
6352 HP PA-RISC 2.0 code:
6355 (@value{GDBP}) disas 0x32c4 0x32e4
6356 Dump of assembler code from 0x32c4 to 0x32e4:
6357 0x32c4 <main+204>: addil 0,dp
6358 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
6359 0x32cc <main+212>: ldil 0x3000,r31
6360 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
6361 0x32d4 <main+220>: ldo 0(r31),rp
6362 0x32d8 <main+224>: addil -0x800,dp
6363 0x32dc <main+228>: ldo 0x588(r1),r26
6364 0x32e0 <main+232>: ldil 0x3000,r31
6365 End of assembler dump.
6368 Here is an example showing mixed source+assembly for Intel x86:
6371 (@value{GDBP}) disas /m main
6372 Dump of assembler code for function main:
6374 0x08048330 <main+0>: push %ebp
6375 0x08048331 <main+1>: mov %esp,%ebp
6376 0x08048333 <main+3>: sub $0x8,%esp
6377 0x08048336 <main+6>: and $0xfffffff0,%esp
6378 0x08048339 <main+9>: sub $0x10,%esp
6380 6 printf ("Hello.\n");
6381 0x0804833c <main+12>: movl $0x8048440,(%esp)
6382 0x08048343 <main+19>: call 0x8048284 <puts@@plt>
6386 0x08048348 <main+24>: mov $0x0,%eax
6387 0x0804834d <main+29>: leave
6388 0x0804834e <main+30>: ret
6390 End of assembler dump.
6393 Some architectures have more than one commonly-used set of instruction
6394 mnemonics or other syntax.
6396 For programs that were dynamically linked and use shared libraries,
6397 instructions that call functions or branch to locations in the shared
6398 libraries might show a seemingly bogus location---it's actually a
6399 location of the relocation table. On some architectures, @value{GDBN}
6400 might be able to resolve these to actual function names.
6403 @kindex set disassembly-flavor
6404 @cindex Intel disassembly flavor
6405 @cindex AT&T disassembly flavor
6406 @item set disassembly-flavor @var{instruction-set}
6407 Select the instruction set to use when disassembling the
6408 program via the @code{disassemble} or @code{x/i} commands.
6410 Currently this command is only defined for the Intel x86 family. You
6411 can set @var{instruction-set} to either @code{intel} or @code{att}.
6412 The default is @code{att}, the AT&T flavor used by default by Unix
6413 assemblers for x86-based targets.
6415 @kindex show disassembly-flavor
6416 @item show disassembly-flavor
6417 Show the current setting of the disassembly flavor.
6421 @kindex set disassemble-next-line
6422 @kindex show disassemble-next-line
6423 @item set disassemble-next-line
6424 @itemx show disassemble-next-line
6425 Control whether or not @value{GDBN} will disassemble the next source
6426 line or instruction when execution stops. If ON, @value{GDBN} will
6427 display disassembly of the next source line when execution of the
6428 program being debugged stops. This is @emph{in addition} to
6429 displaying the source line itself, which @value{GDBN} always does if
6430 possible. If the next source line cannot be displayed for some reason
6431 (e.g., if @value{GDBN} cannot find the source file, or there's no line
6432 info in the debug info), @value{GDBN} will display disassembly of the
6433 next @emph{instruction} instead of showing the next source line. If
6434 AUTO, @value{GDBN} will display disassembly of next instruction only
6435 if the source line cannot be displayed. This setting causes
6436 @value{GDBN} to display some feedback when you step through a function
6437 with no line info or whose source file is unavailable. The default is
6438 OFF, which means never display the disassembly of the next line or
6444 @chapter Examining Data
6446 @cindex printing data
6447 @cindex examining data
6450 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
6451 @c document because it is nonstandard... Under Epoch it displays in a
6452 @c different window or something like that.
6453 The usual way to examine data in your program is with the @code{print}
6454 command (abbreviated @code{p}), or its synonym @code{inspect}. It
6455 evaluates and prints the value of an expression of the language your
6456 program is written in (@pxref{Languages, ,Using @value{GDBN} with
6457 Different Languages}).
6460 @item print @var{expr}
6461 @itemx print /@var{f} @var{expr}
6462 @var{expr} is an expression (in the source language). By default the
6463 value of @var{expr} is printed in a format appropriate to its data type;
6464 you can choose a different format by specifying @samp{/@var{f}}, where
6465 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
6469 @itemx print /@var{f}
6470 @cindex reprint the last value
6471 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
6472 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
6473 conveniently inspect the same value in an alternative format.
6476 A more low-level way of examining data is with the @code{x} command.
6477 It examines data in memory at a specified address and prints it in a
6478 specified format. @xref{Memory, ,Examining Memory}.
6480 If you are interested in information about types, or about how the
6481 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
6482 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
6486 * Expressions:: Expressions
6487 * Ambiguous Expressions:: Ambiguous Expressions
6488 * Variables:: Program variables
6489 * Arrays:: Artificial arrays
6490 * Output Formats:: Output formats
6491 * Memory:: Examining memory
6492 * Auto Display:: Automatic display
6493 * Print Settings:: Print settings
6494 * Value History:: Value history
6495 * Convenience Vars:: Convenience variables
6496 * Registers:: Registers
6497 * Floating Point Hardware:: Floating point hardware
6498 * Vector Unit:: Vector Unit
6499 * OS Information:: Auxiliary data provided by operating system
6500 * Memory Region Attributes:: Memory region attributes
6501 * Dump/Restore Files:: Copy between memory and a file
6502 * Core File Generation:: Cause a program dump its core
6503 * Character Sets:: Debugging programs that use a different
6504 character set than GDB does
6505 * Caching Remote Data:: Data caching for remote targets
6506 * Searching Memory:: Searching memory for a sequence of bytes
6510 @section Expressions
6513 @code{print} and many other @value{GDBN} commands accept an expression and
6514 compute its value. Any kind of constant, variable or operator defined
6515 by the programming language you are using is valid in an expression in
6516 @value{GDBN}. This includes conditional expressions, function calls,
6517 casts, and string constants. It also includes preprocessor macros, if
6518 you compiled your program to include this information; see
6521 @cindex arrays in expressions
6522 @value{GDBN} supports array constants in expressions input by
6523 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
6524 you can use the command @code{print @{1, 2, 3@}} to create an array
6525 of three integers. If you pass an array to a function or assign it
6526 to a program variable, @value{GDBN} copies the array to memory that
6527 is @code{malloc}ed in the target program.
6529 Because C is so widespread, most of the expressions shown in examples in
6530 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
6531 Languages}, for information on how to use expressions in other
6534 In this section, we discuss operators that you can use in @value{GDBN}
6535 expressions regardless of your programming language.
6537 @cindex casts, in expressions
6538 Casts are supported in all languages, not just in C, because it is so
6539 useful to cast a number into a pointer in order to examine a structure
6540 at that address in memory.
6541 @c FIXME: casts supported---Mod2 true?
6543 @value{GDBN} supports these operators, in addition to those common
6544 to programming languages:
6548 @samp{@@} is a binary operator for treating parts of memory as arrays.
6549 @xref{Arrays, ,Artificial Arrays}, for more information.
6552 @samp{::} allows you to specify a variable in terms of the file or
6553 function where it is defined. @xref{Variables, ,Program Variables}.
6555 @cindex @{@var{type}@}
6556 @cindex type casting memory
6557 @cindex memory, viewing as typed object
6558 @cindex casts, to view memory
6559 @item @{@var{type}@} @var{addr}
6560 Refers to an object of type @var{type} stored at address @var{addr} in
6561 memory. @var{addr} may be any expression whose value is an integer or
6562 pointer (but parentheses are required around binary operators, just as in
6563 a cast). This construct is allowed regardless of what kind of data is
6564 normally supposed to reside at @var{addr}.
6567 @node Ambiguous Expressions
6568 @section Ambiguous Expressions
6569 @cindex ambiguous expressions
6571 Expressions can sometimes contain some ambiguous elements. For instance,
6572 some programming languages (notably Ada, C@t{++} and Objective-C) permit
6573 a single function name to be defined several times, for application in
6574 different contexts. This is called @dfn{overloading}. Another example
6575 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
6576 templates and is typically instantiated several times, resulting in
6577 the same function name being defined in different contexts.
6579 In some cases and depending on the language, it is possible to adjust
6580 the expression to remove the ambiguity. For instance in C@t{++}, you
6581 can specify the signature of the function you want to break on, as in
6582 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
6583 qualified name of your function often makes the expression unambiguous
6586 When an ambiguity that needs to be resolved is detected, the debugger
6587 has the capability to display a menu of numbered choices for each
6588 possibility, and then waits for the selection with the prompt @samp{>}.
6589 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
6590 aborts the current command. If the command in which the expression was
6591 used allows more than one choice to be selected, the next option in the
6592 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
6595 For example, the following session excerpt shows an attempt to set a
6596 breakpoint at the overloaded symbol @code{String::after}.
6597 We choose three particular definitions of that function name:
6599 @c FIXME! This is likely to change to show arg type lists, at least
6602 (@value{GDBP}) b String::after
6605 [2] file:String.cc; line number:867
6606 [3] file:String.cc; line number:860
6607 [4] file:String.cc; line number:875
6608 [5] file:String.cc; line number:853
6609 [6] file:String.cc; line number:846
6610 [7] file:String.cc; line number:735
6612 Breakpoint 1 at 0xb26c: file String.cc, line 867.
6613 Breakpoint 2 at 0xb344: file String.cc, line 875.
6614 Breakpoint 3 at 0xafcc: file String.cc, line 846.
6615 Multiple breakpoints were set.
6616 Use the "delete" command to delete unwanted
6623 @kindex set multiple-symbols
6624 @item set multiple-symbols @var{mode}
6625 @cindex multiple-symbols menu
6627 This option allows you to adjust the debugger behavior when an expression
6630 By default, @var{mode} is set to @code{all}. If the command with which
6631 the expression is used allows more than one choice, then @value{GDBN}
6632 automatically selects all possible choices. For instance, inserting
6633 a breakpoint on a function using an ambiguous name results in a breakpoint
6634 inserted on each possible match. However, if a unique choice must be made,
6635 then @value{GDBN} uses the menu to help you disambiguate the expression.
6636 For instance, printing the address of an overloaded function will result
6637 in the use of the menu.
6639 When @var{mode} is set to @code{ask}, the debugger always uses the menu
6640 when an ambiguity is detected.
6642 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
6643 an error due to the ambiguity and the command is aborted.
6645 @kindex show multiple-symbols
6646 @item show multiple-symbols
6647 Show the current value of the @code{multiple-symbols} setting.
6651 @section Program Variables
6653 The most common kind of expression to use is the name of a variable
6656 Variables in expressions are understood in the selected stack frame
6657 (@pxref{Selection, ,Selecting a Frame}); they must be either:
6661 global (or file-static)
6668 visible according to the scope rules of the
6669 programming language from the point of execution in that frame
6672 @noindent This means that in the function
6687 you can examine and use the variable @code{a} whenever your program is
6688 executing within the function @code{foo}, but you can only use or
6689 examine the variable @code{b} while your program is executing inside
6690 the block where @code{b} is declared.
6692 @cindex variable name conflict
6693 There is an exception: you can refer to a variable or function whose
6694 scope is a single source file even if the current execution point is not
6695 in this file. But it is possible to have more than one such variable or
6696 function with the same name (in different source files). If that
6697 happens, referring to that name has unpredictable effects. If you wish,
6698 you can specify a static variable in a particular function or file,
6699 using the colon-colon (@code{::}) notation:
6701 @cindex colon-colon, context for variables/functions
6703 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
6704 @cindex @code{::}, context for variables/functions
6707 @var{file}::@var{variable}
6708 @var{function}::@var{variable}
6712 Here @var{file} or @var{function} is the name of the context for the
6713 static @var{variable}. In the case of file names, you can use quotes to
6714 make sure @value{GDBN} parses the file name as a single word---for example,
6715 to print a global value of @code{x} defined in @file{f2.c}:
6718 (@value{GDBP}) p 'f2.c'::x
6721 @cindex C@t{++} scope resolution
6722 This use of @samp{::} is very rarely in conflict with the very similar
6723 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
6724 scope resolution operator in @value{GDBN} expressions.
6725 @c FIXME: Um, so what happens in one of those rare cases where it's in
6728 @cindex wrong values
6729 @cindex variable values, wrong
6730 @cindex function entry/exit, wrong values of variables
6731 @cindex optimized code, wrong values of variables
6733 @emph{Warning:} Occasionally, a local variable may appear to have the
6734 wrong value at certain points in a function---just after entry to a new
6735 scope, and just before exit.
6737 You may see this problem when you are stepping by machine instructions.
6738 This is because, on most machines, it takes more than one instruction to
6739 set up a stack frame (including local variable definitions); if you are
6740 stepping by machine instructions, variables may appear to have the wrong
6741 values until the stack frame is completely built. On exit, it usually
6742 also takes more than one machine instruction to destroy a stack frame;
6743 after you begin stepping through that group of instructions, local
6744 variable definitions may be gone.
6746 This may also happen when the compiler does significant optimizations.
6747 To be sure of always seeing accurate values, turn off all optimization
6750 @cindex ``No symbol "foo" in current context''
6751 Another possible effect of compiler optimizations is to optimize
6752 unused variables out of existence, or assign variables to registers (as
6753 opposed to memory addresses). Depending on the support for such cases
6754 offered by the debug info format used by the compiler, @value{GDBN}
6755 might not be able to display values for such local variables. If that
6756 happens, @value{GDBN} will print a message like this:
6759 No symbol "foo" in current context.
6762 To solve such problems, either recompile without optimizations, or use a
6763 different debug info format, if the compiler supports several such
6764 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler,
6765 usually supports the @option{-gstabs+} option. @option{-gstabs+}
6766 produces debug info in a format that is superior to formats such as
6767 COFF. You may be able to use DWARF 2 (@option{-gdwarf-2}), which is also
6768 an effective form for debug info. @xref{Debugging Options,,Options
6769 for Debugging Your Program or GCC, gcc.info, Using the @sc{gnu}
6770 Compiler Collection (GCC)}.
6771 @xref{C, ,C and C@t{++}}, for more information about debug info formats
6772 that are best suited to C@t{++} programs.
6774 If you ask to print an object whose contents are unknown to
6775 @value{GDBN}, e.g., because its data type is not completely specified
6776 by the debug information, @value{GDBN} will say @samp{<incomplete
6777 type>}. @xref{Symbols, incomplete type}, for more about this.
6779 Strings are identified as arrays of @code{char} values without specified
6780 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
6781 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
6782 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
6783 defines literal string type @code{"char"} as @code{char} without a sign.
6788 signed char var1[] = "A";
6791 You get during debugging
6796 $2 = @{65 'A', 0 '\0'@}
6800 @section Artificial Arrays
6802 @cindex artificial array
6804 @kindex @@@r{, referencing memory as an array}
6805 It is often useful to print out several successive objects of the
6806 same type in memory; a section of an array, or an array of
6807 dynamically determined size for which only a pointer exists in the
6810 You can do this by referring to a contiguous span of memory as an
6811 @dfn{artificial array}, using the binary operator @samp{@@}. The left
6812 operand of @samp{@@} should be the first element of the desired array
6813 and be an individual object. The right operand should be the desired length
6814 of the array. The result is an array value whose elements are all of
6815 the type of the left argument. The first element is actually the left
6816 argument; the second element comes from bytes of memory immediately
6817 following those that hold the first element, and so on. Here is an
6818 example. If a program says
6821 int *array = (int *) malloc (len * sizeof (int));
6825 you can print the contents of @code{array} with
6831 The left operand of @samp{@@} must reside in memory. Array values made
6832 with @samp{@@} in this way behave just like other arrays in terms of
6833 subscripting, and are coerced to pointers when used in expressions.
6834 Artificial arrays most often appear in expressions via the value history
6835 (@pxref{Value History, ,Value History}), after printing one out.
6837 Another way to create an artificial array is to use a cast.
6838 This re-interprets a value as if it were an array.
6839 The value need not be in memory:
6841 (@value{GDBP}) p/x (short[2])0x12345678
6842 $1 = @{0x1234, 0x5678@}
6845 As a convenience, if you leave the array length out (as in
6846 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
6847 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
6849 (@value{GDBP}) p/x (short[])0x12345678
6850 $2 = @{0x1234, 0x5678@}
6853 Sometimes the artificial array mechanism is not quite enough; in
6854 moderately complex data structures, the elements of interest may not
6855 actually be adjacent---for example, if you are interested in the values
6856 of pointers in an array. One useful work-around in this situation is
6857 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
6858 Variables}) as a counter in an expression that prints the first
6859 interesting value, and then repeat that expression via @key{RET}. For
6860 instance, suppose you have an array @code{dtab} of pointers to
6861 structures, and you are interested in the values of a field @code{fv}
6862 in each structure. Here is an example of what you might type:
6872 @node Output Formats
6873 @section Output Formats
6875 @cindex formatted output
6876 @cindex output formats
6877 By default, @value{GDBN} prints a value according to its data type. Sometimes
6878 this is not what you want. For example, you might want to print a number
6879 in hex, or a pointer in decimal. Or you might want to view data in memory
6880 at a certain address as a character string or as an instruction. To do
6881 these things, specify an @dfn{output format} when you print a value.
6883 The simplest use of output formats is to say how to print a value
6884 already computed. This is done by starting the arguments of the
6885 @code{print} command with a slash and a format letter. The format
6886 letters supported are:
6890 Regard the bits of the value as an integer, and print the integer in
6894 Print as integer in signed decimal.
6897 Print as integer in unsigned decimal.
6900 Print as integer in octal.
6903 Print as integer in binary. The letter @samp{t} stands for ``two''.
6904 @footnote{@samp{b} cannot be used because these format letters are also
6905 used with the @code{x} command, where @samp{b} stands for ``byte'';
6906 see @ref{Memory,,Examining Memory}.}
6909 @cindex unknown address, locating
6910 @cindex locate address
6911 Print as an address, both absolute in hexadecimal and as an offset from
6912 the nearest preceding symbol. You can use this format used to discover
6913 where (in what function) an unknown address is located:
6916 (@value{GDBP}) p/a 0x54320
6917 $3 = 0x54320 <_initialize_vx+396>
6921 The command @code{info symbol 0x54320} yields similar results.
6922 @xref{Symbols, info symbol}.
6925 Regard as an integer and print it as a character constant. This
6926 prints both the numerical value and its character representation. The
6927 character representation is replaced with the octal escape @samp{\nnn}
6928 for characters outside the 7-bit @sc{ascii} range.
6930 Without this format, @value{GDBN} displays @code{char},
6931 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
6932 constants. Single-byte members of vectors are displayed as integer
6936 Regard the bits of the value as a floating point number and print
6937 using typical floating point syntax.
6940 @cindex printing strings
6941 @cindex printing byte arrays
6942 Regard as a string, if possible. With this format, pointers to single-byte
6943 data are displayed as null-terminated strings and arrays of single-byte data
6944 are displayed as fixed-length strings. Other values are displayed in their
6947 Without this format, @value{GDBN} displays pointers to and arrays of
6948 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
6949 strings. Single-byte members of a vector are displayed as an integer
6953 @cindex raw printing
6954 Print using the @samp{raw} formatting. By default, @value{GDBN} will
6955 use a type-specific pretty-printer. The @samp{r} format bypasses any
6956 pretty-printer which might exist for the value's type.
6959 For example, to print the program counter in hex (@pxref{Registers}), type
6966 Note that no space is required before the slash; this is because command
6967 names in @value{GDBN} cannot contain a slash.
6969 To reprint the last value in the value history with a different format,
6970 you can use the @code{print} command with just a format and no
6971 expression. For example, @samp{p/x} reprints the last value in hex.
6974 @section Examining Memory
6976 You can use the command @code{x} (for ``examine'') to examine memory in
6977 any of several formats, independently of your program's data types.
6979 @cindex examining memory
6981 @kindex x @r{(examine memory)}
6982 @item x/@var{nfu} @var{addr}
6985 Use the @code{x} command to examine memory.
6988 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
6989 much memory to display and how to format it; @var{addr} is an
6990 expression giving the address where you want to start displaying memory.
6991 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
6992 Several commands set convenient defaults for @var{addr}.
6995 @item @var{n}, the repeat count
6996 The repeat count is a decimal integer; the default is 1. It specifies
6997 how much memory (counting by units @var{u}) to display.
6998 @c This really is **decimal**; unaffected by 'set radix' as of GDB
7001 @item @var{f}, the display format
7002 The display format is one of the formats used by @code{print}
7003 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
7004 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
7005 The default is @samp{x} (hexadecimal) initially. The default changes
7006 each time you use either @code{x} or @code{print}.
7008 @item @var{u}, the unit size
7009 The unit size is any of
7015 Halfwords (two bytes).
7017 Words (four bytes). This is the initial default.
7019 Giant words (eight bytes).
7022 Each time you specify a unit size with @code{x}, that size becomes the
7023 default unit the next time you use @code{x}. (For the @samp{s} and
7024 @samp{i} formats, the unit size is ignored and is normally not written.)
7026 @item @var{addr}, starting display address
7027 @var{addr} is the address where you want @value{GDBN} to begin displaying
7028 memory. The expression need not have a pointer value (though it may);
7029 it is always interpreted as an integer address of a byte of memory.
7030 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
7031 @var{addr} is usually just after the last address examined---but several
7032 other commands also set the default address: @code{info breakpoints} (to
7033 the address of the last breakpoint listed), @code{info line} (to the
7034 starting address of a line), and @code{print} (if you use it to display
7035 a value from memory).
7038 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
7039 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
7040 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
7041 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
7042 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
7044 Since the letters indicating unit sizes are all distinct from the
7045 letters specifying output formats, you do not have to remember whether
7046 unit size or format comes first; either order works. The output
7047 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
7048 (However, the count @var{n} must come first; @samp{wx4} does not work.)
7050 Even though the unit size @var{u} is ignored for the formats @samp{s}
7051 and @samp{i}, you might still want to use a count @var{n}; for example,
7052 @samp{3i} specifies that you want to see three machine instructions,
7053 including any operands. For convenience, especially when used with
7054 the @code{display} command, the @samp{i} format also prints branch delay
7055 slot instructions, if any, beyond the count specified, which immediately
7056 follow the last instruction that is within the count. The command
7057 @code{disassemble} gives an alternative way of inspecting machine
7058 instructions; see @ref{Machine Code,,Source and Machine Code}.
7060 All the defaults for the arguments to @code{x} are designed to make it
7061 easy to continue scanning memory with minimal specifications each time
7062 you use @code{x}. For example, after you have inspected three machine
7063 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
7064 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
7065 the repeat count @var{n} is used again; the other arguments default as
7066 for successive uses of @code{x}.
7068 @cindex @code{$_}, @code{$__}, and value history
7069 The addresses and contents printed by the @code{x} command are not saved
7070 in the value history because there is often too much of them and they
7071 would get in the way. Instead, @value{GDBN} makes these values available for
7072 subsequent use in expressions as values of the convenience variables
7073 @code{$_} and @code{$__}. After an @code{x} command, the last address
7074 examined is available for use in expressions in the convenience variable
7075 @code{$_}. The contents of that address, as examined, are available in
7076 the convenience variable @code{$__}.
7078 If the @code{x} command has a repeat count, the address and contents saved
7079 are from the last memory unit printed; this is not the same as the last
7080 address printed if several units were printed on the last line of output.
7082 @cindex remote memory comparison
7083 @cindex verify remote memory image
7084 When you are debugging a program running on a remote target machine
7085 (@pxref{Remote Debugging}), you may wish to verify the program's image in the
7086 remote machine's memory against the executable file you downloaded to
7087 the target. The @code{compare-sections} command is provided for such
7091 @kindex compare-sections
7092 @item compare-sections @r{[}@var{section-name}@r{]}
7093 Compare the data of a loadable section @var{section-name} in the
7094 executable file of the program being debugged with the same section in
7095 the remote machine's memory, and report any mismatches. With no
7096 arguments, compares all loadable sections. This command's
7097 availability depends on the target's support for the @code{"qCRC"}
7102 @section Automatic Display
7103 @cindex automatic display
7104 @cindex display of expressions
7106 If you find that you want to print the value of an expression frequently
7107 (to see how it changes), you might want to add it to the @dfn{automatic
7108 display list} so that @value{GDBN} prints its value each time your program stops.
7109 Each expression added to the list is given a number to identify it;
7110 to remove an expression from the list, you specify that number.
7111 The automatic display looks like this:
7115 3: bar[5] = (struct hack *) 0x3804
7119 This display shows item numbers, expressions and their current values. As with
7120 displays you request manually using @code{x} or @code{print}, you can
7121 specify the output format you prefer; in fact, @code{display} decides
7122 whether to use @code{print} or @code{x} depending your format
7123 specification---it uses @code{x} if you specify either the @samp{i}
7124 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
7128 @item display @var{expr}
7129 Add the expression @var{expr} to the list of expressions to display
7130 each time your program stops. @xref{Expressions, ,Expressions}.
7132 @code{display} does not repeat if you press @key{RET} again after using it.
7134 @item display/@var{fmt} @var{expr}
7135 For @var{fmt} specifying only a display format and not a size or
7136 count, add the expression @var{expr} to the auto-display list but
7137 arrange to display it each time in the specified format @var{fmt}.
7138 @xref{Output Formats,,Output Formats}.
7140 @item display/@var{fmt} @var{addr}
7141 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
7142 number of units, add the expression @var{addr} as a memory address to
7143 be examined each time your program stops. Examining means in effect
7144 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
7147 For example, @samp{display/i $pc} can be helpful, to see the machine
7148 instruction about to be executed each time execution stops (@samp{$pc}
7149 is a common name for the program counter; @pxref{Registers, ,Registers}).
7152 @kindex delete display
7154 @item undisplay @var{dnums}@dots{}
7155 @itemx delete display @var{dnums}@dots{}
7156 Remove item numbers @var{dnums} from the list of expressions to display.
7158 @code{undisplay} does not repeat if you press @key{RET} after using it.
7159 (Otherwise you would just get the error @samp{No display number @dots{}}.)
7161 @kindex disable display
7162 @item disable display @var{dnums}@dots{}
7163 Disable the display of item numbers @var{dnums}. A disabled display
7164 item is not printed automatically, but is not forgotten. It may be
7165 enabled again later.
7167 @kindex enable display
7168 @item enable display @var{dnums}@dots{}
7169 Enable display of item numbers @var{dnums}. It becomes effective once
7170 again in auto display of its expression, until you specify otherwise.
7173 Display the current values of the expressions on the list, just as is
7174 done when your program stops.
7176 @kindex info display
7178 Print the list of expressions previously set up to display
7179 automatically, each one with its item number, but without showing the
7180 values. This includes disabled expressions, which are marked as such.
7181 It also includes expressions which would not be displayed right now
7182 because they refer to automatic variables not currently available.
7185 @cindex display disabled out of scope
7186 If a display expression refers to local variables, then it does not make
7187 sense outside the lexical context for which it was set up. Such an
7188 expression is disabled when execution enters a context where one of its
7189 variables is not defined. For example, if you give the command
7190 @code{display last_char} while inside a function with an argument
7191 @code{last_char}, @value{GDBN} displays this argument while your program
7192 continues to stop inside that function. When it stops elsewhere---where
7193 there is no variable @code{last_char}---the display is disabled
7194 automatically. The next time your program stops where @code{last_char}
7195 is meaningful, you can enable the display expression once again.
7197 @node Print Settings
7198 @section Print Settings
7200 @cindex format options
7201 @cindex print settings
7202 @value{GDBN} provides the following ways to control how arrays, structures,
7203 and symbols are printed.
7206 These settings are useful for debugging programs in any language:
7210 @item set print address
7211 @itemx set print address on
7212 @cindex print/don't print memory addresses
7213 @value{GDBN} prints memory addresses showing the location of stack
7214 traces, structure values, pointer values, breakpoints, and so forth,
7215 even when it also displays the contents of those addresses. The default
7216 is @code{on}. For example, this is what a stack frame display looks like with
7217 @code{set print address on}:
7222 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
7224 530 if (lquote != def_lquote)
7228 @item set print address off
7229 Do not print addresses when displaying their contents. For example,
7230 this is the same stack frame displayed with @code{set print address off}:
7234 (@value{GDBP}) set print addr off
7236 #0 set_quotes (lq="<<", rq=">>") at input.c:530
7237 530 if (lquote != def_lquote)
7241 You can use @samp{set print address off} to eliminate all machine
7242 dependent displays from the @value{GDBN} interface. For example, with
7243 @code{print address off}, you should get the same text for backtraces on
7244 all machines---whether or not they involve pointer arguments.
7247 @item show print address
7248 Show whether or not addresses are to be printed.
7251 When @value{GDBN} prints a symbolic address, it normally prints the
7252 closest earlier symbol plus an offset. If that symbol does not uniquely
7253 identify the address (for example, it is a name whose scope is a single
7254 source file), you may need to clarify. One way to do this is with
7255 @code{info line}, for example @samp{info line *0x4537}. Alternately,
7256 you can set @value{GDBN} to print the source file and line number when
7257 it prints a symbolic address:
7260 @item set print symbol-filename on
7261 @cindex source file and line of a symbol
7262 @cindex symbol, source file and line
7263 Tell @value{GDBN} to print the source file name and line number of a
7264 symbol in the symbolic form of an address.
7266 @item set print symbol-filename off
7267 Do not print source file name and line number of a symbol. This is the
7270 @item show print symbol-filename
7271 Show whether or not @value{GDBN} will print the source file name and
7272 line number of a symbol in the symbolic form of an address.
7275 Another situation where it is helpful to show symbol filenames and line
7276 numbers is when disassembling code; @value{GDBN} shows you the line
7277 number and source file that corresponds to each instruction.
7279 Also, you may wish to see the symbolic form only if the address being
7280 printed is reasonably close to the closest earlier symbol:
7283 @item set print max-symbolic-offset @var{max-offset}
7284 @cindex maximum value for offset of closest symbol
7285 Tell @value{GDBN} to only display the symbolic form of an address if the
7286 offset between the closest earlier symbol and the address is less than
7287 @var{max-offset}. The default is 0, which tells @value{GDBN}
7288 to always print the symbolic form of an address if any symbol precedes it.
7290 @item show print max-symbolic-offset
7291 Ask how large the maximum offset is that @value{GDBN} prints in a
7295 @cindex wild pointer, interpreting
7296 @cindex pointer, finding referent
7297 If you have a pointer and you are not sure where it points, try
7298 @samp{set print symbol-filename on}. Then you can determine the name
7299 and source file location of the variable where it points, using
7300 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
7301 For example, here @value{GDBN} shows that a variable @code{ptt} points
7302 at another variable @code{t}, defined in @file{hi2.c}:
7305 (@value{GDBP}) set print symbol-filename on
7306 (@value{GDBP}) p/a ptt
7307 $4 = 0xe008 <t in hi2.c>
7311 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
7312 does not show the symbol name and filename of the referent, even with
7313 the appropriate @code{set print} options turned on.
7316 Other settings control how different kinds of objects are printed:
7319 @item set print array
7320 @itemx set print array on
7321 @cindex pretty print arrays
7322 Pretty print arrays. This format is more convenient to read,
7323 but uses more space. The default is off.
7325 @item set print array off
7326 Return to compressed format for arrays.
7328 @item show print array
7329 Show whether compressed or pretty format is selected for displaying
7332 @cindex print array indexes
7333 @item set print array-indexes
7334 @itemx set print array-indexes on
7335 Print the index of each element when displaying arrays. May be more
7336 convenient to locate a given element in the array or quickly find the
7337 index of a given element in that printed array. The default is off.
7339 @item set print array-indexes off
7340 Stop printing element indexes when displaying arrays.
7342 @item show print array-indexes
7343 Show whether the index of each element is printed when displaying
7346 @item set print elements @var{number-of-elements}
7347 @cindex number of array elements to print
7348 @cindex limit on number of printed array elements
7349 Set a limit on how many elements of an array @value{GDBN} will print.
7350 If @value{GDBN} is printing a large array, it stops printing after it has
7351 printed the number of elements set by the @code{set print elements} command.
7352 This limit also applies to the display of strings.
7353 When @value{GDBN} starts, this limit is set to 200.
7354 Setting @var{number-of-elements} to zero means that the printing is unlimited.
7356 @item show print elements
7357 Display the number of elements of a large array that @value{GDBN} will print.
7358 If the number is 0, then the printing is unlimited.
7360 @item set print frame-arguments @var{value}
7361 @kindex set print frame-arguments
7362 @cindex printing frame argument values
7363 @cindex print all frame argument values
7364 @cindex print frame argument values for scalars only
7365 @cindex do not print frame argument values
7366 This command allows to control how the values of arguments are printed
7367 when the debugger prints a frame (@pxref{Frames}). The possible
7372 The values of all arguments are printed.
7375 Print the value of an argument only if it is a scalar. The value of more
7376 complex arguments such as arrays, structures, unions, etc, is replaced
7377 by @code{@dots{}}. This is the default. Here is an example where
7378 only scalar arguments are shown:
7381 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
7386 None of the argument values are printed. Instead, the value of each argument
7387 is replaced by @code{@dots{}}. In this case, the example above now becomes:
7390 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
7395 By default, only scalar arguments are printed. This command can be used
7396 to configure the debugger to print the value of all arguments, regardless
7397 of their type. However, it is often advantageous to not print the value
7398 of more complex parameters. For instance, it reduces the amount of
7399 information printed in each frame, making the backtrace more readable.
7400 Also, it improves performance when displaying Ada frames, because
7401 the computation of large arguments can sometimes be CPU-intensive,
7402 especially in large applications. Setting @code{print frame-arguments}
7403 to @code{scalars} (the default) or @code{none} avoids this computation,
7404 thus speeding up the display of each Ada frame.
7406 @item show print frame-arguments
7407 Show how the value of arguments should be displayed when printing a frame.
7409 @item set print repeats
7410 @cindex repeated array elements
7411 Set the threshold for suppressing display of repeated array
7412 elements. When the number of consecutive identical elements of an
7413 array exceeds the threshold, @value{GDBN} prints the string
7414 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
7415 identical repetitions, instead of displaying the identical elements
7416 themselves. Setting the threshold to zero will cause all elements to
7417 be individually printed. The default threshold is 10.
7419 @item show print repeats
7420 Display the current threshold for printing repeated identical
7423 @item set print null-stop
7424 @cindex @sc{null} elements in arrays
7425 Cause @value{GDBN} to stop printing the characters of an array when the first
7426 @sc{null} is encountered. This is useful when large arrays actually
7427 contain only short strings.
7430 @item show print null-stop
7431 Show whether @value{GDBN} stops printing an array on the first
7432 @sc{null} character.
7434 @item set print pretty on
7435 @cindex print structures in indented form
7436 @cindex indentation in structure display
7437 Cause @value{GDBN} to print structures in an indented format with one member
7438 per line, like this:
7453 @item set print pretty off
7454 Cause @value{GDBN} to print structures in a compact format, like this:
7458 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
7459 meat = 0x54 "Pork"@}
7464 This is the default format.
7466 @item show print pretty
7467 Show which format @value{GDBN} is using to print structures.
7469 @item set print sevenbit-strings on
7470 @cindex eight-bit characters in strings
7471 @cindex octal escapes in strings
7472 Print using only seven-bit characters; if this option is set,
7473 @value{GDBN} displays any eight-bit characters (in strings or
7474 character values) using the notation @code{\}@var{nnn}. This setting is
7475 best if you are working in English (@sc{ascii}) and you use the
7476 high-order bit of characters as a marker or ``meta'' bit.
7478 @item set print sevenbit-strings off
7479 Print full eight-bit characters. This allows the use of more
7480 international character sets, and is the default.
7482 @item show print sevenbit-strings
7483 Show whether or not @value{GDBN} is printing only seven-bit characters.
7485 @item set print union on
7486 @cindex unions in structures, printing
7487 Tell @value{GDBN} to print unions which are contained in structures
7488 and other unions. This is the default setting.
7490 @item set print union off
7491 Tell @value{GDBN} not to print unions which are contained in
7492 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
7495 @item show print union
7496 Ask @value{GDBN} whether or not it will print unions which are contained in
7497 structures and other unions.
7499 For example, given the declarations
7502 typedef enum @{Tree, Bug@} Species;
7503 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
7504 typedef enum @{Caterpillar, Cocoon, Butterfly@}
7515 struct thing foo = @{Tree, @{Acorn@}@};
7519 with @code{set print union on} in effect @samp{p foo} would print
7522 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
7526 and with @code{set print union off} in effect it would print
7529 $1 = @{it = Tree, form = @{...@}@}
7533 @code{set print union} affects programs written in C-like languages
7539 These settings are of interest when debugging C@t{++} programs:
7542 @cindex demangling C@t{++} names
7543 @item set print demangle
7544 @itemx set print demangle on
7545 Print C@t{++} names in their source form rather than in the encoded
7546 (``mangled'') form passed to the assembler and linker for type-safe
7547 linkage. The default is on.
7549 @item show print demangle
7550 Show whether C@t{++} names are printed in mangled or demangled form.
7552 @item set print asm-demangle
7553 @itemx set print asm-demangle on
7554 Print C@t{++} names in their source form rather than their mangled form, even
7555 in assembler code printouts such as instruction disassemblies.
7558 @item show print asm-demangle
7559 Show whether C@t{++} names in assembly listings are printed in mangled
7562 @cindex C@t{++} symbol decoding style
7563 @cindex symbol decoding style, C@t{++}
7564 @kindex set demangle-style
7565 @item set demangle-style @var{style}
7566 Choose among several encoding schemes used by different compilers to
7567 represent C@t{++} names. The choices for @var{style} are currently:
7571 Allow @value{GDBN} to choose a decoding style by inspecting your program.
7574 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
7575 This is the default.
7578 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
7581 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
7584 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
7585 @strong{Warning:} this setting alone is not sufficient to allow
7586 debugging @code{cfront}-generated executables. @value{GDBN} would
7587 require further enhancement to permit that.
7590 If you omit @var{style}, you will see a list of possible formats.
7592 @item show demangle-style
7593 Display the encoding style currently in use for decoding C@t{++} symbols.
7595 @item set print object
7596 @itemx set print object on
7597 @cindex derived type of an object, printing
7598 @cindex display derived types
7599 When displaying a pointer to an object, identify the @emph{actual}
7600 (derived) type of the object rather than the @emph{declared} type, using
7601 the virtual function table.
7603 @item set print object off
7604 Display only the declared type of objects, without reference to the
7605 virtual function table. This is the default setting.
7607 @item show print object
7608 Show whether actual, or declared, object types are displayed.
7610 @item set print static-members
7611 @itemx set print static-members on
7612 @cindex static members of C@t{++} objects
7613 Print static members when displaying a C@t{++} object. The default is on.
7615 @item set print static-members off
7616 Do not print static members when displaying a C@t{++} object.
7618 @item show print static-members
7619 Show whether C@t{++} static members are printed or not.
7621 @item set print pascal_static-members
7622 @itemx set print pascal_static-members on
7623 @cindex static members of Pascal objects
7624 @cindex Pascal objects, static members display
7625 Print static members when displaying a Pascal object. The default is on.
7627 @item set print pascal_static-members off
7628 Do not print static members when displaying a Pascal object.
7630 @item show print pascal_static-members
7631 Show whether Pascal static members are printed or not.
7633 @c These don't work with HP ANSI C++ yet.
7634 @item set print vtbl
7635 @itemx set print vtbl on
7636 @cindex pretty print C@t{++} virtual function tables
7637 @cindex virtual functions (C@t{++}) display
7638 @cindex VTBL display
7639 Pretty print C@t{++} virtual function tables. The default is off.
7640 (The @code{vtbl} commands do not work on programs compiled with the HP
7641 ANSI C@t{++} compiler (@code{aCC}).)
7643 @item set print vtbl off
7644 Do not pretty print C@t{++} virtual function tables.
7646 @item show print vtbl
7647 Show whether C@t{++} virtual function tables are pretty printed, or not.
7651 @section Value History
7653 @cindex value history
7654 @cindex history of values printed by @value{GDBN}
7655 Values printed by the @code{print} command are saved in the @value{GDBN}
7656 @dfn{value history}. This allows you to refer to them in other expressions.
7657 Values are kept until the symbol table is re-read or discarded
7658 (for example with the @code{file} or @code{symbol-file} commands).
7659 When the symbol table changes, the value history is discarded,
7660 since the values may contain pointers back to the types defined in the
7665 @cindex history number
7666 The values printed are given @dfn{history numbers} by which you can
7667 refer to them. These are successive integers starting with one.
7668 @code{print} shows you the history number assigned to a value by
7669 printing @samp{$@var{num} = } before the value; here @var{num} is the
7672 To refer to any previous value, use @samp{$} followed by the value's
7673 history number. The way @code{print} labels its output is designed to
7674 remind you of this. Just @code{$} refers to the most recent value in
7675 the history, and @code{$$} refers to the value before that.
7676 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
7677 is the value just prior to @code{$$}, @code{$$1} is equivalent to
7678 @code{$$}, and @code{$$0} is equivalent to @code{$}.
7680 For example, suppose you have just printed a pointer to a structure and
7681 want to see the contents of the structure. It suffices to type
7687 If you have a chain of structures where the component @code{next} points
7688 to the next one, you can print the contents of the next one with this:
7695 You can print successive links in the chain by repeating this
7696 command---which you can do by just typing @key{RET}.
7698 Note that the history records values, not expressions. If the value of
7699 @code{x} is 4 and you type these commands:
7707 then the value recorded in the value history by the @code{print} command
7708 remains 4 even though the value of @code{x} has changed.
7713 Print the last ten values in the value history, with their item numbers.
7714 This is like @samp{p@ $$9} repeated ten times, except that @code{show
7715 values} does not change the history.
7717 @item show values @var{n}
7718 Print ten history values centered on history item number @var{n}.
7721 Print ten history values just after the values last printed. If no more
7722 values are available, @code{show values +} produces no display.
7725 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
7726 same effect as @samp{show values +}.
7728 @node Convenience Vars
7729 @section Convenience Variables
7731 @cindex convenience variables
7732 @cindex user-defined variables
7733 @value{GDBN} provides @dfn{convenience variables} that you can use within
7734 @value{GDBN} to hold on to a value and refer to it later. These variables
7735 exist entirely within @value{GDBN}; they are not part of your program, and
7736 setting a convenience variable has no direct effect on further execution
7737 of your program. That is why you can use them freely.
7739 Convenience variables are prefixed with @samp{$}. Any name preceded by
7740 @samp{$} can be used for a convenience variable, unless it is one of
7741 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
7742 (Value history references, in contrast, are @emph{numbers} preceded
7743 by @samp{$}. @xref{Value History, ,Value History}.)
7745 You can save a value in a convenience variable with an assignment
7746 expression, just as you would set a variable in your program.
7750 set $foo = *object_ptr
7754 would save in @code{$foo} the value contained in the object pointed to by
7757 Using a convenience variable for the first time creates it, but its
7758 value is @code{void} until you assign a new value. You can alter the
7759 value with another assignment at any time.
7761 Convenience variables have no fixed types. You can assign a convenience
7762 variable any type of value, including structures and arrays, even if
7763 that variable already has a value of a different type. The convenience
7764 variable, when used as an expression, has the type of its current value.
7767 @kindex show convenience
7768 @cindex show all user variables
7769 @item show convenience
7770 Print a list of convenience variables used so far, and their values.
7771 Abbreviated @code{show conv}.
7773 @kindex init-if-undefined
7774 @cindex convenience variables, initializing
7775 @item init-if-undefined $@var{variable} = @var{expression}
7776 Set a convenience variable if it has not already been set. This is useful
7777 for user-defined commands that keep some state. It is similar, in concept,
7778 to using local static variables with initializers in C (except that
7779 convenience variables are global). It can also be used to allow users to
7780 override default values used in a command script.
7782 If the variable is already defined then the expression is not evaluated so
7783 any side-effects do not occur.
7786 One of the ways to use a convenience variable is as a counter to be
7787 incremented or a pointer to be advanced. For example, to print
7788 a field from successive elements of an array of structures:
7792 print bar[$i++]->contents
7796 Repeat that command by typing @key{RET}.
7798 Some convenience variables are created automatically by @value{GDBN} and given
7799 values likely to be useful.
7802 @vindex $_@r{, convenience variable}
7804 The variable @code{$_} is automatically set by the @code{x} command to
7805 the last address examined (@pxref{Memory, ,Examining Memory}). Other
7806 commands which provide a default address for @code{x} to examine also
7807 set @code{$_} to that address; these commands include @code{info line}
7808 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
7809 except when set by the @code{x} command, in which case it is a pointer
7810 to the type of @code{$__}.
7812 @vindex $__@r{, convenience variable}
7814 The variable @code{$__} is automatically set by the @code{x} command
7815 to the value found in the last address examined. Its type is chosen
7816 to match the format in which the data was printed.
7819 @vindex $_exitcode@r{, convenience variable}
7820 The variable @code{$_exitcode} is automatically set to the exit code when
7821 the program being debugged terminates.
7824 @vindex $_siginfo@r{, convenience variable}
7825 The variable @code{$_siginfo} contains extra signal information
7826 (@pxref{extra signal information}). Note that @code{$_siginfo}
7827 could be empty, if the application has not yet received any signals.
7828 For example, it will be empty before you execute the @code{run} command.
7831 On HP-UX systems, if you refer to a function or variable name that
7832 begins with a dollar sign, @value{GDBN} searches for a user or system
7833 name first, before it searches for a convenience variable.
7835 @cindex convenience functions
7836 @value{GDBN} also supplies some @dfn{convenience functions}. These
7837 have a syntax similar to convenience variables. A convenience
7838 function can be used in an expression just like an ordinary function;
7839 however, a convenience function is implemented internally to
7844 @kindex help function
7845 @cindex show all convenience functions
7846 Print a list of all convenience functions.
7853 You can refer to machine register contents, in expressions, as variables
7854 with names starting with @samp{$}. The names of registers are different
7855 for each machine; use @code{info registers} to see the names used on
7859 @kindex info registers
7860 @item info registers
7861 Print the names and values of all registers except floating-point
7862 and vector registers (in the selected stack frame).
7864 @kindex info all-registers
7865 @cindex floating point registers
7866 @item info all-registers
7867 Print the names and values of all registers, including floating-point
7868 and vector registers (in the selected stack frame).
7870 @item info registers @var{regname} @dots{}
7871 Print the @dfn{relativized} value of each specified register @var{regname}.
7872 As discussed in detail below, register values are normally relative to
7873 the selected stack frame. @var{regname} may be any register name valid on
7874 the machine you are using, with or without the initial @samp{$}.
7877 @cindex stack pointer register
7878 @cindex program counter register
7879 @cindex process status register
7880 @cindex frame pointer register
7881 @cindex standard registers
7882 @value{GDBN} has four ``standard'' register names that are available (in
7883 expressions) on most machines---whenever they do not conflict with an
7884 architecture's canonical mnemonics for registers. The register names
7885 @code{$pc} and @code{$sp} are used for the program counter register and
7886 the stack pointer. @code{$fp} is used for a register that contains a
7887 pointer to the current stack frame, and @code{$ps} is used for a
7888 register that contains the processor status. For example,
7889 you could print the program counter in hex with
7896 or print the instruction to be executed next with
7903 or add four to the stack pointer@footnote{This is a way of removing
7904 one word from the stack, on machines where stacks grow downward in
7905 memory (most machines, nowadays). This assumes that the innermost
7906 stack frame is selected; setting @code{$sp} is not allowed when other
7907 stack frames are selected. To pop entire frames off the stack,
7908 regardless of machine architecture, use @code{return};
7909 see @ref{Returning, ,Returning from a Function}.} with
7915 Whenever possible, these four standard register names are available on
7916 your machine even though the machine has different canonical mnemonics,
7917 so long as there is no conflict. The @code{info registers} command
7918 shows the canonical names. For example, on the SPARC, @code{info
7919 registers} displays the processor status register as @code{$psr} but you
7920 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
7921 is an alias for the @sc{eflags} register.
7923 @value{GDBN} always considers the contents of an ordinary register as an
7924 integer when the register is examined in this way. Some machines have
7925 special registers which can hold nothing but floating point; these
7926 registers are considered to have floating point values. There is no way
7927 to refer to the contents of an ordinary register as floating point value
7928 (although you can @emph{print} it as a floating point value with
7929 @samp{print/f $@var{regname}}).
7931 Some registers have distinct ``raw'' and ``virtual'' data formats. This
7932 means that the data format in which the register contents are saved by
7933 the operating system is not the same one that your program normally
7934 sees. For example, the registers of the 68881 floating point
7935 coprocessor are always saved in ``extended'' (raw) format, but all C
7936 programs expect to work with ``double'' (virtual) format. In such
7937 cases, @value{GDBN} normally works with the virtual format only (the format
7938 that makes sense for your program), but the @code{info registers} command
7939 prints the data in both formats.
7941 @cindex SSE registers (x86)
7942 @cindex MMX registers (x86)
7943 Some machines have special registers whose contents can be interpreted
7944 in several different ways. For example, modern x86-based machines
7945 have SSE and MMX registers that can hold several values packed
7946 together in several different formats. @value{GDBN} refers to such
7947 registers in @code{struct} notation:
7950 (@value{GDBP}) print $xmm1
7952 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
7953 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
7954 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
7955 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
7956 v4_int32 = @{0, 20657912, 11, 13@},
7957 v2_int64 = @{88725056443645952, 55834574859@},
7958 uint128 = 0x0000000d0000000b013b36f800000000
7963 To set values of such registers, you need to tell @value{GDBN} which
7964 view of the register you wish to change, as if you were assigning
7965 value to a @code{struct} member:
7968 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
7971 Normally, register values are relative to the selected stack frame
7972 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
7973 value that the register would contain if all stack frames farther in
7974 were exited and their saved registers restored. In order to see the
7975 true contents of hardware registers, you must select the innermost
7976 frame (with @samp{frame 0}).
7978 However, @value{GDBN} must deduce where registers are saved, from the machine
7979 code generated by your compiler. If some registers are not saved, or if
7980 @value{GDBN} is unable to locate the saved registers, the selected stack
7981 frame makes no difference.
7983 @node Floating Point Hardware
7984 @section Floating Point Hardware
7985 @cindex floating point
7987 Depending on the configuration, @value{GDBN} may be able to give
7988 you more information about the status of the floating point hardware.
7993 Display hardware-dependent information about the floating
7994 point unit. The exact contents and layout vary depending on the
7995 floating point chip. Currently, @samp{info float} is supported on
7996 the ARM and x86 machines.
8000 @section Vector Unit
8003 Depending on the configuration, @value{GDBN} may be able to give you
8004 more information about the status of the vector unit.
8009 Display information about the vector unit. The exact contents and
8010 layout vary depending on the hardware.
8013 @node OS Information
8014 @section Operating System Auxiliary Information
8015 @cindex OS information
8017 @value{GDBN} provides interfaces to useful OS facilities that can help
8018 you debug your program.
8020 @cindex @code{ptrace} system call
8021 @cindex @code{struct user} contents
8022 When @value{GDBN} runs on a @dfn{Posix system} (such as GNU or Unix
8023 machines), it interfaces with the inferior via the @code{ptrace}
8024 system call. The operating system creates a special sata structure,
8025 called @code{struct user}, for this interface. You can use the
8026 command @code{info udot} to display the contents of this data
8032 Display the contents of the @code{struct user} maintained by the OS
8033 kernel for the program being debugged. @value{GDBN} displays the
8034 contents of @code{struct user} as a list of hex numbers, similar to
8035 the @code{examine} command.
8038 @cindex auxiliary vector
8039 @cindex vector, auxiliary
8040 Some operating systems supply an @dfn{auxiliary vector} to programs at
8041 startup. This is akin to the arguments and environment that you
8042 specify for a program, but contains a system-dependent variety of
8043 binary values that tell system libraries important details about the
8044 hardware, operating system, and process. Each value's purpose is
8045 identified by an integer tag; the meanings are well-known but system-specific.
8046 Depending on the configuration and operating system facilities,
8047 @value{GDBN} may be able to show you this information. For remote
8048 targets, this functionality may further depend on the remote stub's
8049 support of the @samp{qXfer:auxv:read} packet, see
8050 @ref{qXfer auxiliary vector read}.
8055 Display the auxiliary vector of the inferior, which can be either a
8056 live process or a core dump file. @value{GDBN} prints each tag value
8057 numerically, and also shows names and text descriptions for recognized
8058 tags. Some values in the vector are numbers, some bit masks, and some
8059 pointers to strings or other data. @value{GDBN} displays each value in the
8060 most appropriate form for a recognized tag, and in hexadecimal for
8061 an unrecognized tag.
8064 On some targets, @value{GDBN} can access operating-system-specific information
8065 and display it to user, without interpretation. For remote targets,
8066 this functionality depends on the remote stub's support of the
8067 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
8070 @kindex info os processes
8071 @item info os processes
8072 Display the list of processes on the target. For each process,
8073 @value{GDBN} prints the process identifier, the name of the user, and
8074 the command corresponding to the process.
8077 @node Memory Region Attributes
8078 @section Memory Region Attributes
8079 @cindex memory region attributes
8081 @dfn{Memory region attributes} allow you to describe special handling
8082 required by regions of your target's memory. @value{GDBN} uses
8083 attributes to determine whether to allow certain types of memory
8084 accesses; whether to use specific width accesses; and whether to cache
8085 target memory. By default the description of memory regions is
8086 fetched from the target (if the current target supports this), but the
8087 user can override the fetched regions.
8089 Defined memory regions can be individually enabled and disabled. When a
8090 memory region is disabled, @value{GDBN} uses the default attributes when
8091 accessing memory in that region. Similarly, if no memory regions have
8092 been defined, @value{GDBN} uses the default attributes when accessing
8095 When a memory region is defined, it is given a number to identify it;
8096 to enable, disable, or remove a memory region, you specify that number.
8100 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
8101 Define a memory region bounded by @var{lower} and @var{upper} with
8102 attributes @var{attributes}@dots{}, and add it to the list of regions
8103 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
8104 case: it is treated as the target's maximum memory address.
8105 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
8108 Discard any user changes to the memory regions and use target-supplied
8109 regions, if available, or no regions if the target does not support.
8112 @item delete mem @var{nums}@dots{}
8113 Remove memory regions @var{nums}@dots{} from the list of regions
8114 monitored by @value{GDBN}.
8117 @item disable mem @var{nums}@dots{}
8118 Disable monitoring of memory regions @var{nums}@dots{}.
8119 A disabled memory region is not forgotten.
8120 It may be enabled again later.
8123 @item enable mem @var{nums}@dots{}
8124 Enable monitoring of memory regions @var{nums}@dots{}.
8128 Print a table of all defined memory regions, with the following columns
8132 @item Memory Region Number
8133 @item Enabled or Disabled.
8134 Enabled memory regions are marked with @samp{y}.
8135 Disabled memory regions are marked with @samp{n}.
8138 The address defining the inclusive lower bound of the memory region.
8141 The address defining the exclusive upper bound of the memory region.
8144 The list of attributes set for this memory region.
8149 @subsection Attributes
8151 @subsubsection Memory Access Mode
8152 The access mode attributes set whether @value{GDBN} may make read or
8153 write accesses to a memory region.
8155 While these attributes prevent @value{GDBN} from performing invalid
8156 memory accesses, they do nothing to prevent the target system, I/O DMA,
8157 etc.@: from accessing memory.
8161 Memory is read only.
8163 Memory is write only.
8165 Memory is read/write. This is the default.
8168 @subsubsection Memory Access Size
8169 The access size attribute tells @value{GDBN} to use specific sized
8170 accesses in the memory region. Often memory mapped device registers
8171 require specific sized accesses. If no access size attribute is
8172 specified, @value{GDBN} may use accesses of any size.
8176 Use 8 bit memory accesses.
8178 Use 16 bit memory accesses.
8180 Use 32 bit memory accesses.
8182 Use 64 bit memory accesses.
8185 @c @subsubsection Hardware/Software Breakpoints
8186 @c The hardware/software breakpoint attributes set whether @value{GDBN}
8187 @c will use hardware or software breakpoints for the internal breakpoints
8188 @c used by the step, next, finish, until, etc. commands.
8192 @c Always use hardware breakpoints
8193 @c @item swbreak (default)
8196 @subsubsection Data Cache
8197 The data cache attributes set whether @value{GDBN} will cache target
8198 memory. While this generally improves performance by reducing debug
8199 protocol overhead, it can lead to incorrect results because @value{GDBN}
8200 does not know about volatile variables or memory mapped device
8205 Enable @value{GDBN} to cache target memory.
8207 Disable @value{GDBN} from caching target memory. This is the default.
8210 @subsection Memory Access Checking
8211 @value{GDBN} can be instructed to refuse accesses to memory that is
8212 not explicitly described. This can be useful if accessing such
8213 regions has undesired effects for a specific target, or to provide
8214 better error checking. The following commands control this behaviour.
8217 @kindex set mem inaccessible-by-default
8218 @item set mem inaccessible-by-default [on|off]
8219 If @code{on} is specified, make @value{GDBN} treat memory not
8220 explicitly described by the memory ranges as non-existent and refuse accesses
8221 to such memory. The checks are only performed if there's at least one
8222 memory range defined. If @code{off} is specified, make @value{GDBN}
8223 treat the memory not explicitly described by the memory ranges as RAM.
8224 The default value is @code{on}.
8225 @kindex show mem inaccessible-by-default
8226 @item show mem inaccessible-by-default
8227 Show the current handling of accesses to unknown memory.
8231 @c @subsubsection Memory Write Verification
8232 @c The memory write verification attributes set whether @value{GDBN}
8233 @c will re-reads data after each write to verify the write was successful.
8237 @c @item noverify (default)
8240 @node Dump/Restore Files
8241 @section Copy Between Memory and a File
8242 @cindex dump/restore files
8243 @cindex append data to a file
8244 @cindex dump data to a file
8245 @cindex restore data from a file
8247 You can use the commands @code{dump}, @code{append}, and
8248 @code{restore} to copy data between target memory and a file. The
8249 @code{dump} and @code{append} commands write data to a file, and the
8250 @code{restore} command reads data from a file back into the inferior's
8251 memory. Files may be in binary, Motorola S-record, Intel hex, or
8252 Tektronix Hex format; however, @value{GDBN} can only append to binary
8258 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8259 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
8260 Dump the contents of memory from @var{start_addr} to @var{end_addr},
8261 or the value of @var{expr}, to @var{filename} in the given format.
8263 The @var{format} parameter may be any one of:
8270 Motorola S-record format.
8272 Tektronix Hex format.
8275 @value{GDBN} uses the same definitions of these formats as the
8276 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
8277 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
8281 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
8282 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
8283 Append the contents of memory from @var{start_addr} to @var{end_addr},
8284 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
8285 (@value{GDBN} can only append data to files in raw binary form.)
8288 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
8289 Restore the contents of file @var{filename} into memory. The
8290 @code{restore} command can automatically recognize any known @sc{bfd}
8291 file format, except for raw binary. To restore a raw binary file you
8292 must specify the optional keyword @code{binary} after the filename.
8294 If @var{bias} is non-zero, its value will be added to the addresses
8295 contained in the file. Binary files always start at address zero, so
8296 they will be restored at address @var{bias}. Other bfd files have
8297 a built-in location; they will be restored at offset @var{bias}
8300 If @var{start} and/or @var{end} are non-zero, then only data between
8301 file offset @var{start} and file offset @var{end} will be restored.
8302 These offsets are relative to the addresses in the file, before
8303 the @var{bias} argument is applied.
8307 @node Core File Generation
8308 @section How to Produce a Core File from Your Program
8309 @cindex dump core from inferior
8311 A @dfn{core file} or @dfn{core dump} is a file that records the memory
8312 image of a running process and its process status (register values
8313 etc.). Its primary use is post-mortem debugging of a program that
8314 crashed while it ran outside a debugger. A program that crashes
8315 automatically produces a core file, unless this feature is disabled by
8316 the user. @xref{Files}, for information on invoking @value{GDBN} in
8317 the post-mortem debugging mode.
8319 Occasionally, you may wish to produce a core file of the program you
8320 are debugging in order to preserve a snapshot of its state.
8321 @value{GDBN} has a special command for that.
8325 @kindex generate-core-file
8326 @item generate-core-file [@var{file}]
8327 @itemx gcore [@var{file}]
8328 Produce a core dump of the inferior process. The optional argument
8329 @var{file} specifies the file name where to put the core dump. If not
8330 specified, the file name defaults to @file{core.@var{pid}}, where
8331 @var{pid} is the inferior process ID.
8333 Note that this command is implemented only for some systems (as of
8334 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, Unixware, and S390).
8337 @node Character Sets
8338 @section Character Sets
8339 @cindex character sets
8341 @cindex translating between character sets
8342 @cindex host character set
8343 @cindex target character set
8345 If the program you are debugging uses a different character set to
8346 represent characters and strings than the one @value{GDBN} uses itself,
8347 @value{GDBN} can automatically translate between the character sets for
8348 you. The character set @value{GDBN} uses we call the @dfn{host
8349 character set}; the one the inferior program uses we call the
8350 @dfn{target character set}.
8352 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
8353 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
8354 remote protocol (@pxref{Remote Debugging}) to debug a program
8355 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
8356 then the host character set is Latin-1, and the target character set is
8357 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
8358 target-charset EBCDIC-US}, then @value{GDBN} translates between
8359 @sc{ebcdic} and Latin 1 as you print character or string values, or use
8360 character and string literals in expressions.
8362 @value{GDBN} has no way to automatically recognize which character set
8363 the inferior program uses; you must tell it, using the @code{set
8364 target-charset} command, described below.
8366 Here are the commands for controlling @value{GDBN}'s character set
8370 @item set target-charset @var{charset}
8371 @kindex set target-charset
8372 Set the current target character set to @var{charset}. To display the
8373 list of supported target character sets, type
8374 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
8376 @item set host-charset @var{charset}
8377 @kindex set host-charset
8378 Set the current host character set to @var{charset}.
8380 By default, @value{GDBN} uses a host character set appropriate to the
8381 system it is running on; you can override that default using the
8382 @code{set host-charset} command. On some systems, @value{GDBN} cannot
8383 automatically determine the appropriate host character set. In this
8384 case, @value{GDBN} uses @samp{UTF-8}.
8386 @value{GDBN} can only use certain character sets as its host character
8387 set. If you type @kbd{@w{set target-charset @key{TAB}@key{TAB}}},
8388 @value{GDBN} will list the host character sets it supports.
8390 @item set charset @var{charset}
8392 Set the current host and target character sets to @var{charset}. As
8393 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
8394 @value{GDBN} will list the names of the character sets that can be used
8395 for both host and target.
8398 @kindex show charset
8399 Show the names of the current host and target character sets.
8401 @item show host-charset
8402 @kindex show host-charset
8403 Show the name of the current host character set.
8405 @item show target-charset
8406 @kindex show target-charset
8407 Show the name of the current target character set.
8409 @item set target-wide-charset @var{charset}
8410 @kindex set target-wide-charset
8411 Set the current target's wide character set to @var{charset}. This is
8412 the character set used by the target's @code{wchar_t} type. To
8413 display the list of supported wide character sets, type
8414 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
8416 @item show target-wide-charset
8417 @kindex show target-wide-charset
8418 Show the name of the current target's wide character set.
8421 Here is an example of @value{GDBN}'s character set support in action.
8422 Assume that the following source code has been placed in the file
8423 @file{charset-test.c}:
8429 = @{72, 101, 108, 108, 111, 44, 32, 119,
8430 111, 114, 108, 100, 33, 10, 0@};
8431 char ibm1047_hello[]
8432 = @{200, 133, 147, 147, 150, 107, 64, 166,
8433 150, 153, 147, 132, 90, 37, 0@};
8437 printf ("Hello, world!\n");
8441 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
8442 containing the string @samp{Hello, world!} followed by a newline,
8443 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
8445 We compile the program, and invoke the debugger on it:
8448 $ gcc -g charset-test.c -o charset-test
8449 $ gdb -nw charset-test
8450 GNU gdb 2001-12-19-cvs
8451 Copyright 2001 Free Software Foundation, Inc.
8456 We can use the @code{show charset} command to see what character sets
8457 @value{GDBN} is currently using to interpret and display characters and
8461 (@value{GDBP}) show charset
8462 The current host and target character set is `ISO-8859-1'.
8466 For the sake of printing this manual, let's use @sc{ascii} as our
8467 initial character set:
8469 (@value{GDBP}) set charset ASCII
8470 (@value{GDBP}) show charset
8471 The current host and target character set is `ASCII'.
8475 Let's assume that @sc{ascii} is indeed the correct character set for our
8476 host system --- in other words, let's assume that if @value{GDBN} prints
8477 characters using the @sc{ascii} character set, our terminal will display
8478 them properly. Since our current target character set is also
8479 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
8482 (@value{GDBP}) print ascii_hello
8483 $1 = 0x401698 "Hello, world!\n"
8484 (@value{GDBP}) print ascii_hello[0]
8489 @value{GDBN} uses the target character set for character and string
8490 literals you use in expressions:
8493 (@value{GDBP}) print '+'
8498 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
8501 @value{GDBN} relies on the user to tell it which character set the
8502 target program uses. If we print @code{ibm1047_hello} while our target
8503 character set is still @sc{ascii}, we get jibberish:
8506 (@value{GDBP}) print ibm1047_hello
8507 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
8508 (@value{GDBP}) print ibm1047_hello[0]
8513 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
8514 @value{GDBN} tells us the character sets it supports:
8517 (@value{GDBP}) set target-charset
8518 ASCII EBCDIC-US IBM1047 ISO-8859-1
8519 (@value{GDBP}) set target-charset
8522 We can select @sc{ibm1047} as our target character set, and examine the
8523 program's strings again. Now the @sc{ascii} string is wrong, but
8524 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
8525 target character set, @sc{ibm1047}, to the host character set,
8526 @sc{ascii}, and they display correctly:
8529 (@value{GDBP}) set target-charset IBM1047
8530 (@value{GDBP}) show charset
8531 The current host character set is `ASCII'.
8532 The current target character set is `IBM1047'.
8533 (@value{GDBP}) print ascii_hello
8534 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
8535 (@value{GDBP}) print ascii_hello[0]
8537 (@value{GDBP}) print ibm1047_hello
8538 $8 = 0x4016a8 "Hello, world!\n"
8539 (@value{GDBP}) print ibm1047_hello[0]
8544 As above, @value{GDBN} uses the target character set for character and
8545 string literals you use in expressions:
8548 (@value{GDBP}) print '+'
8553 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
8556 @node Caching Remote Data
8557 @section Caching Data of Remote Targets
8558 @cindex caching data of remote targets
8560 @value{GDBN} caches data exchanged between the debugger and a
8561 remote target (@pxref{Remote Debugging}). Such caching generally improves
8562 performance, because it reduces the overhead of the remote protocol by
8563 bundling memory reads and writes into large chunks. Unfortunately, simply
8564 caching everything would lead to incorrect results, since @value{GDBN}
8565 does not necessarily know anything about volatile values, memory-mapped I/O
8566 addresses, etc. Furthermore, in non-stop mode (@pxref{Non-Stop Mode})
8567 memory can be changed @emph{while} a gdb command is executing.
8568 Therefore, by default, @value{GDBN} only caches data
8569 known to be on the stack@footnote{In non-stop mode, it is moderately
8570 rare for a running thread to modify the stack of a stopped thread
8571 in a way that would interfere with a backtrace, and caching of
8572 stack reads provides a significant speed up of remote backtraces.}.
8573 Other regions of memory can be explicitly marked as
8574 cacheable; see @pxref{Memory Region Attributes}.
8577 @kindex set remotecache
8578 @item set remotecache on
8579 @itemx set remotecache off
8580 This option no longer does anything; it exists for compatibility
8583 @kindex show remotecache
8584 @item show remotecache
8585 Show the current state of the obsolete remotecache flag.
8587 @kindex set stack-cache
8588 @item set stack-cache on
8589 @itemx set stack-cache off
8590 Enable or disable caching of stack accesses. When @code{ON}, use
8591 caching. By default, this option is @code{ON}.
8593 @kindex show stack-cache
8594 @item show stack-cache
8595 Show the current state of data caching for memory accesses.
8598 @item info dcache @r{[}line@r{]}
8599 Print the information about the data cache performance. The
8600 information displayed includes the dcache width and depth, and for
8601 each cache line, its number, address, and how many times it was
8602 referenced. This command is useful for debugging the data cache
8605 If a line number is specified, the contents of that line will be
8609 @node Searching Memory
8610 @section Search Memory
8611 @cindex searching memory
8613 Memory can be searched for a particular sequence of bytes with the
8614 @code{find} command.
8618 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8619 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
8620 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
8621 etc. The search begins at address @var{start_addr} and continues for either
8622 @var{len} bytes or through to @var{end_addr} inclusive.
8625 @var{s} and @var{n} are optional parameters.
8626 They may be specified in either order, apart or together.
8629 @item @var{s}, search query size
8630 The size of each search query value.
8636 halfwords (two bytes)
8640 giant words (eight bytes)
8643 All values are interpreted in the current language.
8644 This means, for example, that if the current source language is C/C@t{++}
8645 then searching for the string ``hello'' includes the trailing '\0'.
8647 If the value size is not specified, it is taken from the
8648 value's type in the current language.
8649 This is useful when one wants to specify the search
8650 pattern as a mixture of types.
8651 Note that this means, for example, that in the case of C-like languages
8652 a search for an untyped 0x42 will search for @samp{(int) 0x42}
8653 which is typically four bytes.
8655 @item @var{n}, maximum number of finds
8656 The maximum number of matches to print. The default is to print all finds.
8659 You can use strings as search values. Quote them with double-quotes
8661 The string value is copied into the search pattern byte by byte,
8662 regardless of the endianness of the target and the size specification.
8664 The address of each match found is printed as well as a count of the
8665 number of matches found.
8667 The address of the last value found is stored in convenience variable
8669 A count of the number of matches is stored in @samp{$numfound}.
8671 For example, if stopped at the @code{printf} in this function:
8677 static char hello[] = "hello-hello";
8678 static struct @{ char c; short s; int i; @}
8679 __attribute__ ((packed)) mixed
8680 = @{ 'c', 0x1234, 0x87654321 @};
8681 printf ("%s\n", hello);
8686 you get during debugging:
8689 (gdb) find &hello[0], +sizeof(hello), "hello"
8690 0x804956d <hello.1620+6>
8692 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
8693 0x8049567 <hello.1620>
8694 0x804956d <hello.1620+6>
8696 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
8697 0x8049567 <hello.1620>
8699 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
8700 0x8049560 <mixed.1625>
8702 (gdb) print $numfound
8705 $2 = (void *) 0x8049560
8708 @node Optimized Code
8709 @chapter Debugging Optimized Code
8710 @cindex optimized code, debugging
8711 @cindex debugging optimized code
8713 Almost all compilers support optimization. With optimization
8714 disabled, the compiler generates assembly code that corresponds
8715 directly to your source code, in a simplistic way. As the compiler
8716 applies more powerful optimizations, the generated assembly code
8717 diverges from your original source code. With help from debugging
8718 information generated by the compiler, @value{GDBN} can map from
8719 the running program back to constructs from your original source.
8721 @value{GDBN} is more accurate with optimization disabled. If you
8722 can recompile without optimization, it is easier to follow the
8723 progress of your program during debugging. But, there are many cases
8724 where you may need to debug an optimized version.
8726 When you debug a program compiled with @samp{-g -O}, remember that the
8727 optimizer has rearranged your code; the debugger shows you what is
8728 really there. Do not be too surprised when the execution path does not
8729 exactly match your source file! An extreme example: if you define a
8730 variable, but never use it, @value{GDBN} never sees that
8731 variable---because the compiler optimizes it out of existence.
8733 Some things do not work as well with @samp{-g -O} as with just
8734 @samp{-g}, particularly on machines with instruction scheduling. If in
8735 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
8736 please report it to us as a bug (including a test case!).
8737 @xref{Variables}, for more information about debugging optimized code.
8740 * Inline Functions:: How @value{GDBN} presents inlining
8743 @node Inline Functions
8744 @section Inline Functions
8745 @cindex inline functions, debugging
8747 @dfn{Inlining} is an optimization that inserts a copy of the function
8748 body directly at each call site, instead of jumping to a shared
8749 routine. @value{GDBN} displays inlined functions just like
8750 non-inlined functions. They appear in backtraces. You can view their
8751 arguments and local variables, step into them with @code{step}, skip
8752 them with @code{next}, and escape from them with @code{finish}.
8753 You can check whether a function was inlined by using the
8754 @code{info frame} command.
8756 For @value{GDBN} to support inlined functions, the compiler must
8757 record information about inlining in the debug information ---
8758 @value{NGCC} using the @sc{dwarf 2} format does this, and several
8759 other compilers do also. @value{GDBN} only supports inlined functions
8760 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
8761 do not emit two required attributes (@samp{DW_AT_call_file} and
8762 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
8763 function calls with earlier versions of @value{NGCC}. It instead
8764 displays the arguments and local variables of inlined functions as
8765 local variables in the caller.
8767 The body of an inlined function is directly included at its call site;
8768 unlike a non-inlined function, there are no instructions devoted to
8769 the call. @value{GDBN} still pretends that the call site and the
8770 start of the inlined function are different instructions. Stepping to
8771 the call site shows the call site, and then stepping again shows
8772 the first line of the inlined function, even though no additional
8773 instructions are executed.
8775 This makes source-level debugging much clearer; you can see both the
8776 context of the call and then the effect of the call. Only stepping by
8777 a single instruction using @code{stepi} or @code{nexti} does not do
8778 this; single instruction steps always show the inlined body.
8780 There are some ways that @value{GDBN} does not pretend that inlined
8781 function calls are the same as normal calls:
8785 You cannot set breakpoints on inlined functions. @value{GDBN}
8786 either reports that there is no symbol with that name, or else sets the
8787 breakpoint only on non-inlined copies of the function. This limitation
8788 will be removed in a future version of @value{GDBN}; until then,
8789 set a breakpoint by line number on the first line of the inlined
8793 Setting breakpoints at the call site of an inlined function may not
8794 work, because the call site does not contain any code. @value{GDBN}
8795 may incorrectly move the breakpoint to the next line of the enclosing
8796 function, after the call. This limitation will be removed in a future
8797 version of @value{GDBN}; until then, set a breakpoint on an earlier line
8798 or inside the inlined function instead.
8801 @value{GDBN} cannot locate the return value of inlined calls after
8802 using the @code{finish} command. This is a limitation of compiler-generated
8803 debugging information; after @code{finish}, you can step to the next line
8804 and print a variable where your program stored the return value.
8810 @chapter C Preprocessor Macros
8812 Some languages, such as C and C@t{++}, provide a way to define and invoke
8813 ``preprocessor macros'' which expand into strings of tokens.
8814 @value{GDBN} can evaluate expressions containing macro invocations, show
8815 the result of macro expansion, and show a macro's definition, including
8816 where it was defined.
8818 You may need to compile your program specially to provide @value{GDBN}
8819 with information about preprocessor macros. Most compilers do not
8820 include macros in their debugging information, even when you compile
8821 with the @option{-g} flag. @xref{Compilation}.
8823 A program may define a macro at one point, remove that definition later,
8824 and then provide a different definition after that. Thus, at different
8825 points in the program, a macro may have different definitions, or have
8826 no definition at all. If there is a current stack frame, @value{GDBN}
8827 uses the macros in scope at that frame's source code line. Otherwise,
8828 @value{GDBN} uses the macros in scope at the current listing location;
8831 Whenever @value{GDBN} evaluates an expression, it always expands any
8832 macro invocations present in the expression. @value{GDBN} also provides
8833 the following commands for working with macros explicitly.
8837 @kindex macro expand
8838 @cindex macro expansion, showing the results of preprocessor
8839 @cindex preprocessor macro expansion, showing the results of
8840 @cindex expanding preprocessor macros
8841 @item macro expand @var{expression}
8842 @itemx macro exp @var{expression}
8843 Show the results of expanding all preprocessor macro invocations in
8844 @var{expression}. Since @value{GDBN} simply expands macros, but does
8845 not parse the result, @var{expression} need not be a valid expression;
8846 it can be any string of tokens.
8849 @item macro expand-once @var{expression}
8850 @itemx macro exp1 @var{expression}
8851 @cindex expand macro once
8852 @i{(This command is not yet implemented.)} Show the results of
8853 expanding those preprocessor macro invocations that appear explicitly in
8854 @var{expression}. Macro invocations appearing in that expansion are
8855 left unchanged. This command allows you to see the effect of a
8856 particular macro more clearly, without being confused by further
8857 expansions. Since @value{GDBN} simply expands macros, but does not
8858 parse the result, @var{expression} need not be a valid expression; it
8859 can be any string of tokens.
8862 @cindex macro definition, showing
8863 @cindex definition, showing a macro's
8864 @item info macro @var{macro}
8865 Show the definition of the macro named @var{macro}, and describe the
8866 source location or compiler command-line where that definition was established.
8868 @kindex macro define
8869 @cindex user-defined macros
8870 @cindex defining macros interactively
8871 @cindex macros, user-defined
8872 @item macro define @var{macro} @var{replacement-list}
8873 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
8874 Introduce a definition for a preprocessor macro named @var{macro},
8875 invocations of which are replaced by the tokens given in
8876 @var{replacement-list}. The first form of this command defines an
8877 ``object-like'' macro, which takes no arguments; the second form
8878 defines a ``function-like'' macro, which takes the arguments given in
8881 A definition introduced by this command is in scope in every
8882 expression evaluated in @value{GDBN}, until it is removed with the
8883 @code{macro undef} command, described below. The definition overrides
8884 all definitions for @var{macro} present in the program being debugged,
8885 as well as any previous user-supplied definition.
8888 @item macro undef @var{macro}
8889 Remove any user-supplied definition for the macro named @var{macro}.
8890 This command only affects definitions provided with the @code{macro
8891 define} command, described above; it cannot remove definitions present
8892 in the program being debugged.
8896 List all the macros defined using the @code{macro define} command.
8899 @cindex macros, example of debugging with
8900 Here is a transcript showing the above commands in action. First, we
8901 show our source files:
8909 #define ADD(x) (M + x)
8914 printf ("Hello, world!\n");
8916 printf ("We're so creative.\n");
8918 printf ("Goodbye, world!\n");
8925 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
8926 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
8927 compiler includes information about preprocessor macros in the debugging
8931 $ gcc -gdwarf-2 -g3 sample.c -o sample
8935 Now, we start @value{GDBN} on our sample program:
8939 GNU gdb 2002-05-06-cvs
8940 Copyright 2002 Free Software Foundation, Inc.
8941 GDB is free software, @dots{}
8945 We can expand macros and examine their definitions, even when the
8946 program is not running. @value{GDBN} uses the current listing position
8947 to decide which macro definitions are in scope:
8950 (@value{GDBP}) list main
8953 5 #define ADD(x) (M + x)
8958 10 printf ("Hello, world!\n");
8960 12 printf ("We're so creative.\n");
8961 (@value{GDBP}) info macro ADD
8962 Defined at /home/jimb/gdb/macros/play/sample.c:5
8963 #define ADD(x) (M + x)
8964 (@value{GDBP}) info macro Q
8965 Defined at /home/jimb/gdb/macros/play/sample.h:1
8966 included at /home/jimb/gdb/macros/play/sample.c:2
8968 (@value{GDBP}) macro expand ADD(1)
8969 expands to: (42 + 1)
8970 (@value{GDBP}) macro expand-once ADD(1)
8971 expands to: once (M + 1)
8975 In the example above, note that @code{macro expand-once} expands only
8976 the macro invocation explicit in the original text --- the invocation of
8977 @code{ADD} --- but does not expand the invocation of the macro @code{M},
8978 which was introduced by @code{ADD}.
8980 Once the program is running, @value{GDBN} uses the macro definitions in
8981 force at the source line of the current stack frame:
8984 (@value{GDBP}) break main
8985 Breakpoint 1 at 0x8048370: file sample.c, line 10.
8987 Starting program: /home/jimb/gdb/macros/play/sample
8989 Breakpoint 1, main () at sample.c:10
8990 10 printf ("Hello, world!\n");
8994 At line 10, the definition of the macro @code{N} at line 9 is in force:
8997 (@value{GDBP}) info macro N
8998 Defined at /home/jimb/gdb/macros/play/sample.c:9
9000 (@value{GDBP}) macro expand N Q M
9002 (@value{GDBP}) print N Q M
9007 As we step over directives that remove @code{N}'s definition, and then
9008 give it a new definition, @value{GDBN} finds the definition (or lack
9009 thereof) in force at each point:
9014 12 printf ("We're so creative.\n");
9015 (@value{GDBP}) info macro N
9016 The symbol `N' has no definition as a C/C++ preprocessor macro
9017 at /home/jimb/gdb/macros/play/sample.c:12
9020 14 printf ("Goodbye, world!\n");
9021 (@value{GDBP}) info macro N
9022 Defined at /home/jimb/gdb/macros/play/sample.c:13
9024 (@value{GDBP}) macro expand N Q M
9025 expands to: 1729 < 42
9026 (@value{GDBP}) print N Q M
9031 In addition to source files, macros can be defined on the compilation command
9032 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
9033 such a way, @value{GDBN} displays the location of their definition as line zero
9034 of the source file submitted to the compiler.
9037 (@value{GDBP}) info macro __STDC__
9038 Defined at /home/jimb/gdb/macros/play/sample.c:0
9045 @chapter Tracepoints
9046 @c This chapter is based on the documentation written by Michael
9047 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
9050 In some applications, it is not feasible for the debugger to interrupt
9051 the program's execution long enough for the developer to learn
9052 anything helpful about its behavior. If the program's correctness
9053 depends on its real-time behavior, delays introduced by a debugger
9054 might cause the program to change its behavior drastically, or perhaps
9055 fail, even when the code itself is correct. It is useful to be able
9056 to observe the program's behavior without interrupting it.
9058 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
9059 specify locations in the program, called @dfn{tracepoints}, and
9060 arbitrary expressions to evaluate when those tracepoints are reached.
9061 Later, using the @code{tfind} command, you can examine the values
9062 those expressions had when the program hit the tracepoints. The
9063 expressions may also denote objects in memory---structures or arrays,
9064 for example---whose values @value{GDBN} should record; while visiting
9065 a particular tracepoint, you may inspect those objects as if they were
9066 in memory at that moment. However, because @value{GDBN} records these
9067 values without interacting with you, it can do so quickly and
9068 unobtrusively, hopefully not disturbing the program's behavior.
9070 The tracepoint facility is currently available only for remote
9071 targets. @xref{Targets}. In addition, your remote target must know
9072 how to collect trace data. This functionality is implemented in the
9073 remote stub; however, none of the stubs distributed with @value{GDBN}
9074 support tracepoints as of this writing. The format of the remote
9075 packets used to implement tracepoints are described in @ref{Tracepoint
9078 This chapter describes the tracepoint commands and features.
9082 * Analyze Collected Data::
9083 * Tracepoint Variables::
9086 @node Set Tracepoints
9087 @section Commands to Set Tracepoints
9089 Before running such a @dfn{trace experiment}, an arbitrary number of
9090 tracepoints can be set. A tracepoint is actually a special type of
9091 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
9092 standard breakpoint commands. For instance, as with breakpoints,
9093 tracepoint numbers are successive integers starting from one, and many
9094 of the commands associated with tracepoints take the tracepoint number
9095 as their argument, to identify which tracepoint to work on.
9097 For each tracepoint, you can specify, in advance, some arbitrary set
9098 of data that you want the target to collect in the trace buffer when
9099 it hits that tracepoint. The collected data can include registers,
9100 local variables, or global data. Later, you can use @value{GDBN}
9101 commands to examine the values these data had at the time the
9104 Tracepoints do not support every breakpoint feature. Conditional
9105 expressions and ignore counts on tracepoints have no effect, and
9106 tracepoints cannot run @value{GDBN} commands when they are
9107 hit. Tracepoints may not be thread-specific either.
9109 This section describes commands to set tracepoints and associated
9110 conditions and actions.
9113 * Create and Delete Tracepoints::
9114 * Enable and Disable Tracepoints::
9115 * Tracepoint Passcounts::
9116 * Tracepoint Conditions::
9117 * Tracepoint Actions::
9118 * Listing Tracepoints::
9119 * Starting and Stopping Trace Experiments::
9122 @node Create and Delete Tracepoints
9123 @subsection Create and Delete Tracepoints
9126 @cindex set tracepoint
9128 @item trace @var{location}
9129 The @code{trace} command is very similar to the @code{break} command.
9130 Its argument @var{location} can be a source line, a function name, or
9131 an address in the target program. @xref{Specify Location}. The
9132 @code{trace} command defines a tracepoint, which is a point in the
9133 target program where the debugger will briefly stop, collect some
9134 data, and then allow the program to continue. Setting a tracepoint or
9135 changing its actions doesn't take effect until the next @code{tstart}
9136 command, and once a trace experiment is running, further changes will
9137 not have any effect until the next trace experiment starts.
9139 Here are some examples of using the @code{trace} command:
9142 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
9144 (@value{GDBP}) @b{trace +2} // 2 lines forward
9146 (@value{GDBP}) @b{trace my_function} // first source line of function
9148 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
9150 (@value{GDBP}) @b{trace *0x2117c4} // an address
9154 You can abbreviate @code{trace} as @code{tr}.
9156 @item trace @var{location} if @var{cond}
9157 Set a tracepoint with condition @var{cond}; evaluate the expression
9158 @var{cond} each time the tracepoint is reached, and collect data only
9159 if the value is nonzero---that is, if @var{cond} evaluates as true.
9160 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
9161 information on tracepoint conditions.
9164 @cindex last tracepoint number
9165 @cindex recent tracepoint number
9166 @cindex tracepoint number
9167 The convenience variable @code{$tpnum} records the tracepoint number
9168 of the most recently set tracepoint.
9170 @kindex delete tracepoint
9171 @cindex tracepoint deletion
9172 @item delete tracepoint @r{[}@var{num}@r{]}
9173 Permanently delete one or more tracepoints. With no argument, the
9174 default is to delete all tracepoints. Note that the regular
9175 @code{delete} command can remove tracepoints also.
9180 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
9182 (@value{GDBP}) @b{delete trace} // remove all tracepoints
9186 You can abbreviate this command as @code{del tr}.
9189 @node Enable and Disable Tracepoints
9190 @subsection Enable and Disable Tracepoints
9192 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
9195 @kindex disable tracepoint
9196 @item disable tracepoint @r{[}@var{num}@r{]}
9197 Disable tracepoint @var{num}, or all tracepoints if no argument
9198 @var{num} is given. A disabled tracepoint will have no effect during
9199 the next trace experiment, but it is not forgotten. You can re-enable
9200 a disabled tracepoint using the @code{enable tracepoint} command.
9202 @kindex enable tracepoint
9203 @item enable tracepoint @r{[}@var{num}@r{]}
9204 Enable tracepoint @var{num}, or all tracepoints. The enabled
9205 tracepoints will become effective the next time a trace experiment is
9209 @node Tracepoint Passcounts
9210 @subsection Tracepoint Passcounts
9214 @cindex tracepoint pass count
9215 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
9216 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
9217 automatically stop a trace experiment. If a tracepoint's passcount is
9218 @var{n}, then the trace experiment will be automatically stopped on
9219 the @var{n}'th time that tracepoint is hit. If the tracepoint number
9220 @var{num} is not specified, the @code{passcount} command sets the
9221 passcount of the most recently defined tracepoint. If no passcount is
9222 given, the trace experiment will run until stopped explicitly by the
9228 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
9229 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
9231 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
9232 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
9233 (@value{GDBP}) @b{trace foo}
9234 (@value{GDBP}) @b{pass 3}
9235 (@value{GDBP}) @b{trace bar}
9236 (@value{GDBP}) @b{pass 2}
9237 (@value{GDBP}) @b{trace baz}
9238 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
9239 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
9240 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
9241 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
9245 @node Tracepoint Conditions
9246 @subsection Tracepoint Conditions
9247 @cindex conditional tracepoints
9248 @cindex tracepoint conditions
9250 The simplest sort of tracepoint collects data every time your program
9251 reaches a specified place. You can also specify a @dfn{condition} for
9252 a tracepoint. A condition is just a Boolean expression in your
9253 programming language (@pxref{Expressions, ,Expressions}). A
9254 tracepoint with a condition evaluates the expression each time your
9255 program reaches it, and data collection happens only if the condition
9258 Tracepoint conditions can be specified when a tracepoint is set, by
9259 using @samp{if} in the arguments to the @code{trace} command.
9260 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
9261 also be set or changed at any time with the @code{condition} command,
9262 just as with breakpoints.
9264 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
9265 the conditional expression itself. Instead, @value{GDBN} encodes the
9266 expression into an agent expression (@pxref{Agent Expressions}
9267 suitable for execution on the target, independently of @value{GDBN}.
9268 Global variables become raw memory locations, locals become stack
9269 accesses, and so forth.
9271 For instance, suppose you have a function that is usually called
9272 frequently, but should not be called after an error has occurred. You
9273 could use the following tracepoint command to collect data about calls
9274 of that function that happen while the error code is propagating
9275 through the program; an unconditional tracepoint could end up
9276 collecting thousands of useless trace frames that you would have to
9280 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
9283 @node Tracepoint Actions
9284 @subsection Tracepoint Action Lists
9288 @cindex tracepoint actions
9289 @item actions @r{[}@var{num}@r{]}
9290 This command will prompt for a list of actions to be taken when the
9291 tracepoint is hit. If the tracepoint number @var{num} is not
9292 specified, this command sets the actions for the one that was most
9293 recently defined (so that you can define a tracepoint and then say
9294 @code{actions} without bothering about its number). You specify the
9295 actions themselves on the following lines, one action at a time, and
9296 terminate the actions list with a line containing just @code{end}. So
9297 far, the only defined actions are @code{collect} and
9298 @code{while-stepping}.
9300 @cindex remove actions from a tracepoint
9301 To remove all actions from a tracepoint, type @samp{actions @var{num}}
9302 and follow it immediately with @samp{end}.
9305 (@value{GDBP}) @b{collect @var{data}} // collect some data
9307 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
9309 (@value{GDBP}) @b{end} // signals the end of actions.
9312 In the following example, the action list begins with @code{collect}
9313 commands indicating the things to be collected when the tracepoint is
9314 hit. Then, in order to single-step and collect additional data
9315 following the tracepoint, a @code{while-stepping} command is used,
9316 followed by the list of things to be collected while stepping. The
9317 @code{while-stepping} command is terminated by its own separate
9318 @code{end} command. Lastly, the action list is terminated by an
9322 (@value{GDBP}) @b{trace foo}
9323 (@value{GDBP}) @b{actions}
9324 Enter actions for tracepoint 1, one per line:
9333 @kindex collect @r{(tracepoints)}
9334 @item collect @var{expr1}, @var{expr2}, @dots{}
9335 Collect values of the given expressions when the tracepoint is hit.
9336 This command accepts a comma-separated list of any valid expressions.
9337 In addition to global, static, or local variables, the following
9338 special arguments are supported:
9342 collect all registers
9345 collect all function arguments
9348 collect all local variables.
9351 You can give several consecutive @code{collect} commands, each one
9352 with a single argument, or one @code{collect} command with several
9353 arguments separated by commas: the effect is the same.
9355 The command @code{info scope} (@pxref{Symbols, info scope}) is
9356 particularly useful for figuring out what data to collect.
9358 @kindex while-stepping @r{(tracepoints)}
9359 @item while-stepping @var{n}
9360 Perform @var{n} single-step traces after the tracepoint, collecting
9361 new data at each step. The @code{while-stepping} command is
9362 followed by the list of what to collect while stepping (followed by
9363 its own @code{end} command):
9367 > collect $regs, myglobal
9373 You may abbreviate @code{while-stepping} as @code{ws} or
9377 @node Listing Tracepoints
9378 @subsection Listing Tracepoints
9381 @kindex info tracepoints
9383 @cindex information about tracepoints
9384 @item info tracepoints @r{[}@var{num}@r{]}
9385 Display information about the tracepoint @var{num}. If you don't
9386 specify a tracepoint number, displays information about all the
9387 tracepoints defined so far. The format is similar to that used for
9388 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
9389 command, simply restricting itself to tracepoints.
9391 A tracepoint's listing may include additional information specific to
9396 its passcount as given by the @code{passcount @var{n}} command
9398 its step count as given by the @code{while-stepping @var{n}} command
9400 its action list as given by the @code{actions} command. The actions
9401 are prefixed with an @samp{A} so as to distinguish them from commands.
9405 (@value{GDBP}) @b{info trace}
9406 Num Type Disp Enb Address What
9407 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
9411 A collect globfoo, $regs
9419 This command can be abbreviated @code{info tp}.
9422 @node Starting and Stopping Trace Experiments
9423 @subsection Starting and Stopping Trace Experiments
9427 @cindex start a new trace experiment
9428 @cindex collected data discarded
9430 This command takes no arguments. It starts the trace experiment, and
9431 begins collecting data. This has the side effect of discarding all
9432 the data collected in the trace buffer during the previous trace
9436 @cindex stop a running trace experiment
9438 This command takes no arguments. It ends the trace experiment, and
9439 stops collecting data.
9441 @strong{Note}: a trace experiment and data collection may stop
9442 automatically if any tracepoint's passcount is reached
9443 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
9446 @cindex status of trace data collection
9447 @cindex trace experiment, status of
9449 This command displays the status of the current trace data
9453 Here is an example of the commands we described so far:
9456 (@value{GDBP}) @b{trace gdb_c_test}
9457 (@value{GDBP}) @b{actions}
9458 Enter actions for tracepoint #1, one per line.
9459 > collect $regs,$locals,$args
9464 (@value{GDBP}) @b{tstart}
9465 [time passes @dots{}]
9466 (@value{GDBP}) @b{tstop}
9470 @node Analyze Collected Data
9471 @section Using the Collected Data
9473 After the tracepoint experiment ends, you use @value{GDBN} commands
9474 for examining the trace data. The basic idea is that each tracepoint
9475 collects a trace @dfn{snapshot} every time it is hit and another
9476 snapshot every time it single-steps. All these snapshots are
9477 consecutively numbered from zero and go into a buffer, and you can
9478 examine them later. The way you examine them is to @dfn{focus} on a
9479 specific trace snapshot. When the remote stub is focused on a trace
9480 snapshot, it will respond to all @value{GDBN} requests for memory and
9481 registers by reading from the buffer which belongs to that snapshot,
9482 rather than from @emph{real} memory or registers of the program being
9483 debugged. This means that @strong{all} @value{GDBN} commands
9484 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
9485 behave as if we were currently debugging the program state as it was
9486 when the tracepoint occurred. Any requests for data that are not in
9487 the buffer will fail.
9490 * tfind:: How to select a trace snapshot
9491 * tdump:: How to display all data for a snapshot
9492 * save-tracepoints:: How to save tracepoints for a future run
9496 @subsection @code{tfind @var{n}}
9499 @cindex select trace snapshot
9500 @cindex find trace snapshot
9501 The basic command for selecting a trace snapshot from the buffer is
9502 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
9503 counting from zero. If no argument @var{n} is given, the next
9504 snapshot is selected.
9506 Here are the various forms of using the @code{tfind} command.
9510 Find the first snapshot in the buffer. This is a synonym for
9511 @code{tfind 0} (since 0 is the number of the first snapshot).
9514 Stop debugging trace snapshots, resume @emph{live} debugging.
9517 Same as @samp{tfind none}.
9520 No argument means find the next trace snapshot.
9523 Find the previous trace snapshot before the current one. This permits
9524 retracing earlier steps.
9526 @item tfind tracepoint @var{num}
9527 Find the next snapshot associated with tracepoint @var{num}. Search
9528 proceeds forward from the last examined trace snapshot. If no
9529 argument @var{num} is given, it means find the next snapshot collected
9530 for the same tracepoint as the current snapshot.
9532 @item tfind pc @var{addr}
9533 Find the next snapshot associated with the value @var{addr} of the
9534 program counter. Search proceeds forward from the last examined trace
9535 snapshot. If no argument @var{addr} is given, it means find the next
9536 snapshot with the same value of PC as the current snapshot.
9538 @item tfind outside @var{addr1}, @var{addr2}
9539 Find the next snapshot whose PC is outside the given range of
9542 @item tfind range @var{addr1}, @var{addr2}
9543 Find the next snapshot whose PC is between @var{addr1} and
9544 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
9546 @item tfind line @r{[}@var{file}:@r{]}@var{n}
9547 Find the next snapshot associated with the source line @var{n}. If
9548 the optional argument @var{file} is given, refer to line @var{n} in
9549 that source file. Search proceeds forward from the last examined
9550 trace snapshot. If no argument @var{n} is given, it means find the
9551 next line other than the one currently being examined; thus saying
9552 @code{tfind line} repeatedly can appear to have the same effect as
9553 stepping from line to line in a @emph{live} debugging session.
9556 The default arguments for the @code{tfind} commands are specifically
9557 designed to make it easy to scan through the trace buffer. For
9558 instance, @code{tfind} with no argument selects the next trace
9559 snapshot, and @code{tfind -} with no argument selects the previous
9560 trace snapshot. So, by giving one @code{tfind} command, and then
9561 simply hitting @key{RET} repeatedly you can examine all the trace
9562 snapshots in order. Or, by saying @code{tfind -} and then hitting
9563 @key{RET} repeatedly you can examine the snapshots in reverse order.
9564 The @code{tfind line} command with no argument selects the snapshot
9565 for the next source line executed. The @code{tfind pc} command with
9566 no argument selects the next snapshot with the same program counter
9567 (PC) as the current frame. The @code{tfind tracepoint} command with
9568 no argument selects the next trace snapshot collected by the same
9569 tracepoint as the current one.
9571 In addition to letting you scan through the trace buffer manually,
9572 these commands make it easy to construct @value{GDBN} scripts that
9573 scan through the trace buffer and print out whatever collected data
9574 you are interested in. Thus, if we want to examine the PC, FP, and SP
9575 registers from each trace frame in the buffer, we can say this:
9578 (@value{GDBP}) @b{tfind start}
9579 (@value{GDBP}) @b{while ($trace_frame != -1)}
9580 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
9581 $trace_frame, $pc, $sp, $fp
9585 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
9586 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
9587 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
9588 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
9589 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
9590 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
9591 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
9592 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
9593 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
9594 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
9595 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
9598 Or, if we want to examine the variable @code{X} at each source line in
9602 (@value{GDBP}) @b{tfind start}
9603 (@value{GDBP}) @b{while ($trace_frame != -1)}
9604 > printf "Frame %d, X == %d\n", $trace_frame, X
9614 @subsection @code{tdump}
9616 @cindex dump all data collected at tracepoint
9617 @cindex tracepoint data, display
9619 This command takes no arguments. It prints all the data collected at
9620 the current trace snapshot.
9623 (@value{GDBP}) @b{trace 444}
9624 (@value{GDBP}) @b{actions}
9625 Enter actions for tracepoint #2, one per line:
9626 > collect $regs, $locals, $args, gdb_long_test
9629 (@value{GDBP}) @b{tstart}
9631 (@value{GDBP}) @b{tfind line 444}
9632 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
9634 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
9636 (@value{GDBP}) @b{tdump}
9637 Data collected at tracepoint 2, trace frame 1:
9638 d0 0xc4aa0085 -995491707
9642 d4 0x71aea3d 119204413
9647 a1 0x3000668 50333288
9650 a4 0x3000698 50333336
9652 fp 0x30bf3c 0x30bf3c
9653 sp 0x30bf34 0x30bf34
9655 pc 0x20b2c8 0x20b2c8
9659 p = 0x20e5b4 "gdb-test"
9666 gdb_long_test = 17 '\021'
9671 @node save-tracepoints
9672 @subsection @code{save-tracepoints @var{filename}}
9673 @kindex save-tracepoints
9674 @cindex save tracepoints for future sessions
9676 This command saves all current tracepoint definitions together with
9677 their actions and passcounts, into a file @file{@var{filename}}
9678 suitable for use in a later debugging session. To read the saved
9679 tracepoint definitions, use the @code{source} command (@pxref{Command
9682 @node Tracepoint Variables
9683 @section Convenience Variables for Tracepoints
9684 @cindex tracepoint variables
9685 @cindex convenience variables for tracepoints
9688 @vindex $trace_frame
9689 @item (int) $trace_frame
9690 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
9691 snapshot is selected.
9694 @item (int) $tracepoint
9695 The tracepoint for the current trace snapshot.
9698 @item (int) $trace_line
9699 The line number for the current trace snapshot.
9702 @item (char []) $trace_file
9703 The source file for the current trace snapshot.
9706 @item (char []) $trace_func
9707 The name of the function containing @code{$tracepoint}.
9710 Note: @code{$trace_file} is not suitable for use in @code{printf},
9711 use @code{output} instead.
9713 Here's a simple example of using these convenience variables for
9714 stepping through all the trace snapshots and printing some of their
9718 (@value{GDBP}) @b{tfind start}
9720 (@value{GDBP}) @b{while $trace_frame != -1}
9721 > output $trace_file
9722 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
9728 @chapter Debugging Programs That Use Overlays
9731 If your program is too large to fit completely in your target system's
9732 memory, you can sometimes use @dfn{overlays} to work around this
9733 problem. @value{GDBN} provides some support for debugging programs that
9737 * How Overlays Work:: A general explanation of overlays.
9738 * Overlay Commands:: Managing overlays in @value{GDBN}.
9739 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
9740 mapped by asking the inferior.
9741 * Overlay Sample Program:: A sample program using overlays.
9744 @node How Overlays Work
9745 @section How Overlays Work
9746 @cindex mapped overlays
9747 @cindex unmapped overlays
9748 @cindex load address, overlay's
9749 @cindex mapped address
9750 @cindex overlay area
9752 Suppose you have a computer whose instruction address space is only 64
9753 kilobytes long, but which has much more memory which can be accessed by
9754 other means: special instructions, segment registers, or memory
9755 management hardware, for example. Suppose further that you want to
9756 adapt a program which is larger than 64 kilobytes to run on this system.
9758 One solution is to identify modules of your program which are relatively
9759 independent, and need not call each other directly; call these modules
9760 @dfn{overlays}. Separate the overlays from the main program, and place
9761 their machine code in the larger memory. Place your main program in
9762 instruction memory, but leave at least enough space there to hold the
9763 largest overlay as well.
9765 Now, to call a function located in an overlay, you must first copy that
9766 overlay's machine code from the large memory into the space set aside
9767 for it in the instruction memory, and then jump to its entry point
9770 @c NB: In the below the mapped area's size is greater or equal to the
9771 @c size of all overlays. This is intentional to remind the developer
9772 @c that overlays don't necessarily need to be the same size.
9776 Data Instruction Larger
9777 Address Space Address Space Address Space
9778 +-----------+ +-----------+ +-----------+
9780 +-----------+ +-----------+ +-----------+<-- overlay 1
9781 | program | | main | .----| overlay 1 | load address
9782 | variables | | program | | +-----------+
9783 | and heap | | | | | |
9784 +-----------+ | | | +-----------+<-- overlay 2
9785 | | +-----------+ | | | load address
9786 +-----------+ | | | .-| overlay 2 |
9788 mapped --->+-----------+ | | +-----------+
9790 | overlay | <-' | | |
9791 | area | <---' +-----------+<-- overlay 3
9792 | | <---. | | load address
9793 +-----------+ `--| overlay 3 |
9800 @anchor{A code overlay}A code overlay
9804 The diagram (@pxref{A code overlay}) shows a system with separate data
9805 and instruction address spaces. To map an overlay, the program copies
9806 its code from the larger address space to the instruction address space.
9807 Since the overlays shown here all use the same mapped address, only one
9808 may be mapped at a time. For a system with a single address space for
9809 data and instructions, the diagram would be similar, except that the
9810 program variables and heap would share an address space with the main
9811 program and the overlay area.
9813 An overlay loaded into instruction memory and ready for use is called a
9814 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
9815 instruction memory. An overlay not present (or only partially present)
9816 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
9817 is its address in the larger memory. The mapped address is also called
9818 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
9819 called the @dfn{load memory address}, or @dfn{LMA}.
9821 Unfortunately, overlays are not a completely transparent way to adapt a
9822 program to limited instruction memory. They introduce a new set of
9823 global constraints you must keep in mind as you design your program:
9828 Before calling or returning to a function in an overlay, your program
9829 must make sure that overlay is actually mapped. Otherwise, the call or
9830 return will transfer control to the right address, but in the wrong
9831 overlay, and your program will probably crash.
9834 If the process of mapping an overlay is expensive on your system, you
9835 will need to choose your overlays carefully to minimize their effect on
9836 your program's performance.
9839 The executable file you load onto your system must contain each
9840 overlay's instructions, appearing at the overlay's load address, not its
9841 mapped address. However, each overlay's instructions must be relocated
9842 and its symbols defined as if the overlay were at its mapped address.
9843 You can use GNU linker scripts to specify different load and relocation
9844 addresses for pieces of your program; see @ref{Overlay Description,,,
9845 ld.info, Using ld: the GNU linker}.
9848 The procedure for loading executable files onto your system must be able
9849 to load their contents into the larger address space as well as the
9850 instruction and data spaces.
9854 The overlay system described above is rather simple, and could be
9855 improved in many ways:
9860 If your system has suitable bank switch registers or memory management
9861 hardware, you could use those facilities to make an overlay's load area
9862 contents simply appear at their mapped address in instruction space.
9863 This would probably be faster than copying the overlay to its mapped
9864 area in the usual way.
9867 If your overlays are small enough, you could set aside more than one
9868 overlay area, and have more than one overlay mapped at a time.
9871 You can use overlays to manage data, as well as instructions. In
9872 general, data overlays are even less transparent to your design than
9873 code overlays: whereas code overlays only require care when you call or
9874 return to functions, data overlays require care every time you access
9875 the data. Also, if you change the contents of a data overlay, you
9876 must copy its contents back out to its load address before you can copy a
9877 different data overlay into the same mapped area.
9882 @node Overlay Commands
9883 @section Overlay Commands
9885 To use @value{GDBN}'s overlay support, each overlay in your program must
9886 correspond to a separate section of the executable file. The section's
9887 virtual memory address and load memory address must be the overlay's
9888 mapped and load addresses. Identifying overlays with sections allows
9889 @value{GDBN} to determine the appropriate address of a function or
9890 variable, depending on whether the overlay is mapped or not.
9892 @value{GDBN}'s overlay commands all start with the word @code{overlay};
9893 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
9898 Disable @value{GDBN}'s overlay support. When overlay support is
9899 disabled, @value{GDBN} assumes that all functions and variables are
9900 always present at their mapped addresses. By default, @value{GDBN}'s
9901 overlay support is disabled.
9903 @item overlay manual
9904 @cindex manual overlay debugging
9905 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
9906 relies on you to tell it which overlays are mapped, and which are not,
9907 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
9908 commands described below.
9910 @item overlay map-overlay @var{overlay}
9911 @itemx overlay map @var{overlay}
9912 @cindex map an overlay
9913 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
9914 be the name of the object file section containing the overlay. When an
9915 overlay is mapped, @value{GDBN} assumes it can find the overlay's
9916 functions and variables at their mapped addresses. @value{GDBN} assumes
9917 that any other overlays whose mapped ranges overlap that of
9918 @var{overlay} are now unmapped.
9920 @item overlay unmap-overlay @var{overlay}
9921 @itemx overlay unmap @var{overlay}
9922 @cindex unmap an overlay
9923 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
9924 must be the name of the object file section containing the overlay.
9925 When an overlay is unmapped, @value{GDBN} assumes it can find the
9926 overlay's functions and variables at their load addresses.
9929 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
9930 consults a data structure the overlay manager maintains in the inferior
9931 to see which overlays are mapped. For details, see @ref{Automatic
9934 @item overlay load-target
9936 @cindex reloading the overlay table
9937 Re-read the overlay table from the inferior. Normally, @value{GDBN}
9938 re-reads the table @value{GDBN} automatically each time the inferior
9939 stops, so this command should only be necessary if you have changed the
9940 overlay mapping yourself using @value{GDBN}. This command is only
9941 useful when using automatic overlay debugging.
9943 @item overlay list-overlays
9945 @cindex listing mapped overlays
9946 Display a list of the overlays currently mapped, along with their mapped
9947 addresses, load addresses, and sizes.
9951 Normally, when @value{GDBN} prints a code address, it includes the name
9952 of the function the address falls in:
9955 (@value{GDBP}) print main
9956 $3 = @{int ()@} 0x11a0 <main>
9959 When overlay debugging is enabled, @value{GDBN} recognizes code in
9960 unmapped overlays, and prints the names of unmapped functions with
9961 asterisks around them. For example, if @code{foo} is a function in an
9962 unmapped overlay, @value{GDBN} prints it this way:
9965 (@value{GDBP}) overlay list
9966 No sections are mapped.
9967 (@value{GDBP}) print foo
9968 $5 = @{int (int)@} 0x100000 <*foo*>
9971 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
9975 (@value{GDBP}) overlay list
9976 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
9977 mapped at 0x1016 - 0x104a
9978 (@value{GDBP}) print foo
9979 $6 = @{int (int)@} 0x1016 <foo>
9982 When overlay debugging is enabled, @value{GDBN} can find the correct
9983 address for functions and variables in an overlay, whether or not the
9984 overlay is mapped. This allows most @value{GDBN} commands, like
9985 @code{break} and @code{disassemble}, to work normally, even on unmapped
9986 code. However, @value{GDBN}'s breakpoint support has some limitations:
9990 @cindex breakpoints in overlays
9991 @cindex overlays, setting breakpoints in
9992 You can set breakpoints in functions in unmapped overlays, as long as
9993 @value{GDBN} can write to the overlay at its load address.
9995 @value{GDBN} can not set hardware or simulator-based breakpoints in
9996 unmapped overlays. However, if you set a breakpoint at the end of your
9997 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
9998 you are using manual overlay management), @value{GDBN} will re-set its
9999 breakpoints properly.
10003 @node Automatic Overlay Debugging
10004 @section Automatic Overlay Debugging
10005 @cindex automatic overlay debugging
10007 @value{GDBN} can automatically track which overlays are mapped and which
10008 are not, given some simple co-operation from the overlay manager in the
10009 inferior. If you enable automatic overlay debugging with the
10010 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
10011 looks in the inferior's memory for certain variables describing the
10012 current state of the overlays.
10014 Here are the variables your overlay manager must define to support
10015 @value{GDBN}'s automatic overlay debugging:
10019 @item @code{_ovly_table}:
10020 This variable must be an array of the following structures:
10025 /* The overlay's mapped address. */
10028 /* The size of the overlay, in bytes. */
10029 unsigned long size;
10031 /* The overlay's load address. */
10034 /* Non-zero if the overlay is currently mapped;
10036 unsigned long mapped;
10040 @item @code{_novlys}:
10041 This variable must be a four-byte signed integer, holding the total
10042 number of elements in @code{_ovly_table}.
10046 To decide whether a particular overlay is mapped or not, @value{GDBN}
10047 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
10048 @code{lma} members equal the VMA and LMA of the overlay's section in the
10049 executable file. When @value{GDBN} finds a matching entry, it consults
10050 the entry's @code{mapped} member to determine whether the overlay is
10053 In addition, your overlay manager may define a function called
10054 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
10055 will silently set a breakpoint there. If the overlay manager then
10056 calls this function whenever it has changed the overlay table, this
10057 will enable @value{GDBN} to accurately keep track of which overlays
10058 are in program memory, and update any breakpoints that may be set
10059 in overlays. This will allow breakpoints to work even if the
10060 overlays are kept in ROM or other non-writable memory while they
10061 are not being executed.
10063 @node Overlay Sample Program
10064 @section Overlay Sample Program
10065 @cindex overlay example program
10067 When linking a program which uses overlays, you must place the overlays
10068 at their load addresses, while relocating them to run at their mapped
10069 addresses. To do this, you must write a linker script (@pxref{Overlay
10070 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
10071 since linker scripts are specific to a particular host system, target
10072 architecture, and target memory layout, this manual cannot provide
10073 portable sample code demonstrating @value{GDBN}'s overlay support.
10075 However, the @value{GDBN} source distribution does contain an overlaid
10076 program, with linker scripts for a few systems, as part of its test
10077 suite. The program consists of the following files from
10078 @file{gdb/testsuite/gdb.base}:
10082 The main program file.
10084 A simple overlay manager, used by @file{overlays.c}.
10089 Overlay modules, loaded and used by @file{overlays.c}.
10092 Linker scripts for linking the test program on the @code{d10v-elf}
10093 and @code{m32r-elf} targets.
10096 You can build the test program using the @code{d10v-elf} GCC
10097 cross-compiler like this:
10100 $ d10v-elf-gcc -g -c overlays.c
10101 $ d10v-elf-gcc -g -c ovlymgr.c
10102 $ d10v-elf-gcc -g -c foo.c
10103 $ d10v-elf-gcc -g -c bar.c
10104 $ d10v-elf-gcc -g -c baz.c
10105 $ d10v-elf-gcc -g -c grbx.c
10106 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
10107 baz.o grbx.o -Wl,-Td10v.ld -o overlays
10110 The build process is identical for any other architecture, except that
10111 you must substitute the appropriate compiler and linker script for the
10112 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
10116 @chapter Using @value{GDBN} with Different Languages
10119 Although programming languages generally have common aspects, they are
10120 rarely expressed in the same manner. For instance, in ANSI C,
10121 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
10122 Modula-2, it is accomplished by @code{p^}. Values can also be
10123 represented (and displayed) differently. Hex numbers in C appear as
10124 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
10126 @cindex working language
10127 Language-specific information is built into @value{GDBN} for some languages,
10128 allowing you to express operations like the above in your program's
10129 native language, and allowing @value{GDBN} to output values in a manner
10130 consistent with the syntax of your program's native language. The
10131 language you use to build expressions is called the @dfn{working
10135 * Setting:: Switching between source languages
10136 * Show:: Displaying the language
10137 * Checks:: Type and range checks
10138 * Supported Languages:: Supported languages
10139 * Unsupported Languages:: Unsupported languages
10143 @section Switching Between Source Languages
10145 There are two ways to control the working language---either have @value{GDBN}
10146 set it automatically, or select it manually yourself. You can use the
10147 @code{set language} command for either purpose. On startup, @value{GDBN}
10148 defaults to setting the language automatically. The working language is
10149 used to determine how expressions you type are interpreted, how values
10152 In addition to the working language, every source file that
10153 @value{GDBN} knows about has its own working language. For some object
10154 file formats, the compiler might indicate which language a particular
10155 source file is in. However, most of the time @value{GDBN} infers the
10156 language from the name of the file. The language of a source file
10157 controls whether C@t{++} names are demangled---this way @code{backtrace} can
10158 show each frame appropriately for its own language. There is no way to
10159 set the language of a source file from within @value{GDBN}, but you can
10160 set the language associated with a filename extension. @xref{Show, ,
10161 Displaying the Language}.
10163 This is most commonly a problem when you use a program, such
10164 as @code{cfront} or @code{f2c}, that generates C but is written in
10165 another language. In that case, make the
10166 program use @code{#line} directives in its C output; that way
10167 @value{GDBN} will know the correct language of the source code of the original
10168 program, and will display that source code, not the generated C code.
10171 * Filenames:: Filename extensions and languages.
10172 * Manually:: Setting the working language manually
10173 * Automatically:: Having @value{GDBN} infer the source language
10177 @subsection List of Filename Extensions and Languages
10179 If a source file name ends in one of the following extensions, then
10180 @value{GDBN} infers that its language is the one indicated.
10198 C@t{++} source file
10201 Objective-C source file
10205 Fortran source file
10208 Modula-2 source file
10212 Assembler source file. This actually behaves almost like C, but
10213 @value{GDBN} does not skip over function prologues when stepping.
10216 In addition, you may set the language associated with a filename
10217 extension. @xref{Show, , Displaying the Language}.
10220 @subsection Setting the Working Language
10222 If you allow @value{GDBN} to set the language automatically,
10223 expressions are interpreted the same way in your debugging session and
10226 @kindex set language
10227 If you wish, you may set the language manually. To do this, issue the
10228 command @samp{set language @var{lang}}, where @var{lang} is the name of
10229 a language, such as
10230 @code{c} or @code{modula-2}.
10231 For a list of the supported languages, type @samp{set language}.
10233 Setting the language manually prevents @value{GDBN} from updating the working
10234 language automatically. This can lead to confusion if you try
10235 to debug a program when the working language is not the same as the
10236 source language, when an expression is acceptable to both
10237 languages---but means different things. For instance, if the current
10238 source file were written in C, and @value{GDBN} was parsing Modula-2, a
10246 might not have the effect you intended. In C, this means to add
10247 @code{b} and @code{c} and place the result in @code{a}. The result
10248 printed would be the value of @code{a}. In Modula-2, this means to compare
10249 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
10251 @node Automatically
10252 @subsection Having @value{GDBN} Infer the Source Language
10254 To have @value{GDBN} set the working language automatically, use
10255 @samp{set language local} or @samp{set language auto}. @value{GDBN}
10256 then infers the working language. That is, when your program stops in a
10257 frame (usually by encountering a breakpoint), @value{GDBN} sets the
10258 working language to the language recorded for the function in that
10259 frame. If the language for a frame is unknown (that is, if the function
10260 or block corresponding to the frame was defined in a source file that
10261 does not have a recognized extension), the current working language is
10262 not changed, and @value{GDBN} issues a warning.
10264 This may not seem necessary for most programs, which are written
10265 entirely in one source language. However, program modules and libraries
10266 written in one source language can be used by a main program written in
10267 a different source language. Using @samp{set language auto} in this
10268 case frees you from having to set the working language manually.
10271 @section Displaying the Language
10273 The following commands help you find out which language is the
10274 working language, and also what language source files were written in.
10277 @item show language
10278 @kindex show language
10279 Display the current working language. This is the
10280 language you can use with commands such as @code{print} to
10281 build and compute expressions that may involve variables in your program.
10284 @kindex info frame@r{, show the source language}
10285 Display the source language for this frame. This language becomes the
10286 working language if you use an identifier from this frame.
10287 @xref{Frame Info, ,Information about a Frame}, to identify the other
10288 information listed here.
10291 @kindex info source@r{, show the source language}
10292 Display the source language of this source file.
10293 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
10294 information listed here.
10297 In unusual circumstances, you may have source files with extensions
10298 not in the standard list. You can then set the extension associated
10299 with a language explicitly:
10302 @item set extension-language @var{ext} @var{language}
10303 @kindex set extension-language
10304 Tell @value{GDBN} that source files with extension @var{ext} are to be
10305 assumed as written in the source language @var{language}.
10307 @item info extensions
10308 @kindex info extensions
10309 List all the filename extensions and the associated languages.
10313 @section Type and Range Checking
10316 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
10317 checking are included, but they do not yet have any effect. This
10318 section documents the intended facilities.
10320 @c FIXME remove warning when type/range code added
10322 Some languages are designed to guard you against making seemingly common
10323 errors through a series of compile- and run-time checks. These include
10324 checking the type of arguments to functions and operators, and making
10325 sure mathematical overflows are caught at run time. Checks such as
10326 these help to ensure a program's correctness once it has been compiled
10327 by eliminating type mismatches, and providing active checks for range
10328 errors when your program is running.
10330 @value{GDBN} can check for conditions like the above if you wish.
10331 Although @value{GDBN} does not check the statements in your program,
10332 it can check expressions entered directly into @value{GDBN} for
10333 evaluation via the @code{print} command, for example. As with the
10334 working language, @value{GDBN} can also decide whether or not to check
10335 automatically based on your program's source language.
10336 @xref{Supported Languages, ,Supported Languages}, for the default
10337 settings of supported languages.
10340 * Type Checking:: An overview of type checking
10341 * Range Checking:: An overview of range checking
10344 @cindex type checking
10345 @cindex checks, type
10346 @node Type Checking
10347 @subsection An Overview of Type Checking
10349 Some languages, such as Modula-2, are strongly typed, meaning that the
10350 arguments to operators and functions have to be of the correct type,
10351 otherwise an error occurs. These checks prevent type mismatch
10352 errors from ever causing any run-time problems. For example,
10360 The second example fails because the @code{CARDINAL} 1 is not
10361 type-compatible with the @code{REAL} 2.3.
10363 For the expressions you use in @value{GDBN} commands, you can tell the
10364 @value{GDBN} type checker to skip checking;
10365 to treat any mismatches as errors and abandon the expression;
10366 or to only issue warnings when type mismatches occur,
10367 but evaluate the expression anyway. When you choose the last of
10368 these, @value{GDBN} evaluates expressions like the second example above, but
10369 also issues a warning.
10371 Even if you turn type checking off, there may be other reasons
10372 related to type that prevent @value{GDBN} from evaluating an expression.
10373 For instance, @value{GDBN} does not know how to add an @code{int} and
10374 a @code{struct foo}. These particular type errors have nothing to do
10375 with the language in use, and usually arise from expressions, such as
10376 the one described above, which make little sense to evaluate anyway.
10378 Each language defines to what degree it is strict about type. For
10379 instance, both Modula-2 and C require the arguments to arithmetical
10380 operators to be numbers. In C, enumerated types and pointers can be
10381 represented as numbers, so that they are valid arguments to mathematical
10382 operators. @xref{Supported Languages, ,Supported Languages}, for further
10383 details on specific languages.
10385 @value{GDBN} provides some additional commands for controlling the type checker:
10387 @kindex set check type
10388 @kindex show check type
10390 @item set check type auto
10391 Set type checking on or off based on the current working language.
10392 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10395 @item set check type on
10396 @itemx set check type off
10397 Set type checking on or off, overriding the default setting for the
10398 current working language. Issue a warning if the setting does not
10399 match the language default. If any type mismatches occur in
10400 evaluating an expression while type checking is on, @value{GDBN} prints a
10401 message and aborts evaluation of the expression.
10403 @item set check type warn
10404 Cause the type checker to issue warnings, but to always attempt to
10405 evaluate the expression. Evaluating the expression may still
10406 be impossible for other reasons. For example, @value{GDBN} cannot add
10407 numbers and structures.
10410 Show the current setting of the type checker, and whether or not @value{GDBN}
10411 is setting it automatically.
10414 @cindex range checking
10415 @cindex checks, range
10416 @node Range Checking
10417 @subsection An Overview of Range Checking
10419 In some languages (such as Modula-2), it is an error to exceed the
10420 bounds of a type; this is enforced with run-time checks. Such range
10421 checking is meant to ensure program correctness by making sure
10422 computations do not overflow, or indices on an array element access do
10423 not exceed the bounds of the array.
10425 For expressions you use in @value{GDBN} commands, you can tell
10426 @value{GDBN} to treat range errors in one of three ways: ignore them,
10427 always treat them as errors and abandon the expression, or issue
10428 warnings but evaluate the expression anyway.
10430 A range error can result from numerical overflow, from exceeding an
10431 array index bound, or when you type a constant that is not a member
10432 of any type. Some languages, however, do not treat overflows as an
10433 error. In many implementations of C, mathematical overflow causes the
10434 result to ``wrap around'' to lower values---for example, if @var{m} is
10435 the largest integer value, and @var{s} is the smallest, then
10438 @var{m} + 1 @result{} @var{s}
10441 This, too, is specific to individual languages, and in some cases
10442 specific to individual compilers or machines. @xref{Supported Languages, ,
10443 Supported Languages}, for further details on specific languages.
10445 @value{GDBN} provides some additional commands for controlling the range checker:
10447 @kindex set check range
10448 @kindex show check range
10450 @item set check range auto
10451 Set range checking on or off based on the current working language.
10452 @xref{Supported Languages, ,Supported Languages}, for the default settings for
10455 @item set check range on
10456 @itemx set check range off
10457 Set range checking on or off, overriding the default setting for the
10458 current working language. A warning is issued if the setting does not
10459 match the language default. If a range error occurs and range checking is on,
10460 then a message is printed and evaluation of the expression is aborted.
10462 @item set check range warn
10463 Output messages when the @value{GDBN} range checker detects a range error,
10464 but attempt to evaluate the expression anyway. Evaluating the
10465 expression may still be impossible for other reasons, such as accessing
10466 memory that the process does not own (a typical example from many Unix
10470 Show the current setting of the range checker, and whether or not it is
10471 being set automatically by @value{GDBN}.
10474 @node Supported Languages
10475 @section Supported Languages
10477 @value{GDBN} supports C, C@t{++}, Objective-C, Fortran, Java, Pascal,
10478 assembly, Modula-2, and Ada.
10479 @c This is false ...
10480 Some @value{GDBN} features may be used in expressions regardless of the
10481 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
10482 and the @samp{@{type@}addr} construct (@pxref{Expressions,
10483 ,Expressions}) can be used with the constructs of any supported
10486 The following sections detail to what degree each source language is
10487 supported by @value{GDBN}. These sections are not meant to be language
10488 tutorials or references, but serve only as a reference guide to what the
10489 @value{GDBN} expression parser accepts, and what input and output
10490 formats should look like for different languages. There are many good
10491 books written on each of these languages; please look to these for a
10492 language reference or tutorial.
10495 * C:: C and C@t{++}
10496 * Objective-C:: Objective-C
10497 * Fortran:: Fortran
10499 * Modula-2:: Modula-2
10504 @subsection C and C@t{++}
10506 @cindex C and C@t{++}
10507 @cindex expressions in C or C@t{++}
10509 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
10510 to both languages. Whenever this is the case, we discuss those languages
10514 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
10515 @cindex @sc{gnu} C@t{++}
10516 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
10517 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
10518 effectively, you must compile your C@t{++} programs with a supported
10519 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
10520 compiler (@code{aCC}).
10522 For best results when using @sc{gnu} C@t{++}, use the DWARF 2 debugging
10523 format; if it doesn't work on your system, try the stabs+ debugging
10524 format. You can select those formats explicitly with the @code{g++}
10525 command-line options @option{-gdwarf-2} and @option{-gstabs+}.
10526 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
10527 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}.
10530 * C Operators:: C and C@t{++} operators
10531 * C Constants:: C and C@t{++} constants
10532 * C Plus Plus Expressions:: C@t{++} expressions
10533 * C Defaults:: Default settings for C and C@t{++}
10534 * C Checks:: C and C@t{++} type and range checks
10535 * Debugging C:: @value{GDBN} and C
10536 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
10537 * Decimal Floating Point:: Numbers in Decimal Floating Point format
10541 @subsubsection C and C@t{++} Operators
10543 @cindex C and C@t{++} operators
10545 Operators must be defined on values of specific types. For instance,
10546 @code{+} is defined on numbers, but not on structures. Operators are
10547 often defined on groups of types.
10549 For the purposes of C and C@t{++}, the following definitions hold:
10554 @emph{Integral types} include @code{int} with any of its storage-class
10555 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
10558 @emph{Floating-point types} include @code{float}, @code{double}, and
10559 @code{long double} (if supported by the target platform).
10562 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
10565 @emph{Scalar types} include all of the above.
10570 The following operators are supported. They are listed here
10571 in order of increasing precedence:
10575 The comma or sequencing operator. Expressions in a comma-separated list
10576 are evaluated from left to right, with the result of the entire
10577 expression being the last expression evaluated.
10580 Assignment. The value of an assignment expression is the value
10581 assigned. Defined on scalar types.
10584 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
10585 and translated to @w{@code{@var{a} = @var{a op b}}}.
10586 @w{@code{@var{op}=}} and @code{=} have the same precedence.
10587 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
10588 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
10591 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
10592 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
10596 Logical @sc{or}. Defined on integral types.
10599 Logical @sc{and}. Defined on integral types.
10602 Bitwise @sc{or}. Defined on integral types.
10605 Bitwise exclusive-@sc{or}. Defined on integral types.
10608 Bitwise @sc{and}. Defined on integral types.
10611 Equality and inequality. Defined on scalar types. The value of these
10612 expressions is 0 for false and non-zero for true.
10614 @item <@r{, }>@r{, }<=@r{, }>=
10615 Less than, greater than, less than or equal, greater than or equal.
10616 Defined on scalar types. The value of these expressions is 0 for false
10617 and non-zero for true.
10620 left shift, and right shift. Defined on integral types.
10623 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
10626 Addition and subtraction. Defined on integral types, floating-point types and
10629 @item *@r{, }/@r{, }%
10630 Multiplication, division, and modulus. Multiplication and division are
10631 defined on integral and floating-point types. Modulus is defined on
10635 Increment and decrement. When appearing before a variable, the
10636 operation is performed before the variable is used in an expression;
10637 when appearing after it, the variable's value is used before the
10638 operation takes place.
10641 Pointer dereferencing. Defined on pointer types. Same precedence as
10645 Address operator. Defined on variables. Same precedence as @code{++}.
10647 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
10648 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
10649 to examine the address
10650 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
10654 Negative. Defined on integral and floating-point types. Same
10655 precedence as @code{++}.
10658 Logical negation. Defined on integral types. Same precedence as
10662 Bitwise complement operator. Defined on integral types. Same precedence as
10667 Structure member, and pointer-to-structure member. For convenience,
10668 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
10669 pointer based on the stored type information.
10670 Defined on @code{struct} and @code{union} data.
10673 Dereferences of pointers to members.
10676 Array indexing. @code{@var{a}[@var{i}]} is defined as
10677 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
10680 Function parameter list. Same precedence as @code{->}.
10683 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
10684 and @code{class} types.
10687 Doubled colons also represent the @value{GDBN} scope operator
10688 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
10692 If an operator is redefined in the user code, @value{GDBN} usually
10693 attempts to invoke the redefined version instead of using the operator's
10694 predefined meaning.
10697 @subsubsection C and C@t{++} Constants
10699 @cindex C and C@t{++} constants
10701 @value{GDBN} allows you to express the constants of C and C@t{++} in the
10706 Integer constants are a sequence of digits. Octal constants are
10707 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
10708 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
10709 @samp{l}, specifying that the constant should be treated as a
10713 Floating point constants are a sequence of digits, followed by a decimal
10714 point, followed by a sequence of digits, and optionally followed by an
10715 exponent. An exponent is of the form:
10716 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
10717 sequence of digits. The @samp{+} is optional for positive exponents.
10718 A floating-point constant may also end with a letter @samp{f} or
10719 @samp{F}, specifying that the constant should be treated as being of
10720 the @code{float} (as opposed to the default @code{double}) type; or with
10721 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
10725 Enumerated constants consist of enumerated identifiers, or their
10726 integral equivalents.
10729 Character constants are a single character surrounded by single quotes
10730 (@code{'}), or a number---the ordinal value of the corresponding character
10731 (usually its @sc{ascii} value). Within quotes, the single character may
10732 be represented by a letter or by @dfn{escape sequences}, which are of
10733 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
10734 of the character's ordinal value; or of the form @samp{\@var{x}}, where
10735 @samp{@var{x}} is a predefined special character---for example,
10736 @samp{\n} for newline.
10739 String constants are a sequence of character constants surrounded by
10740 double quotes (@code{"}). Any valid character constant (as described
10741 above) may appear. Double quotes within the string must be preceded by
10742 a backslash, so for instance @samp{"a\"b'c"} is a string of five
10746 Pointer constants are an integral value. You can also write pointers
10747 to constants using the C operator @samp{&}.
10750 Array constants are comma-separated lists surrounded by braces @samp{@{}
10751 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
10752 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
10753 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
10756 @node C Plus Plus Expressions
10757 @subsubsection C@t{++} Expressions
10759 @cindex expressions in C@t{++}
10760 @value{GDBN} expression handling can interpret most C@t{++} expressions.
10762 @cindex debugging C@t{++} programs
10763 @cindex C@t{++} compilers
10764 @cindex debug formats and C@t{++}
10765 @cindex @value{NGCC} and C@t{++}
10767 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
10768 proper compiler and the proper debug format. Currently, @value{GDBN}
10769 works best when debugging C@t{++} code that is compiled with
10770 @value{NGCC} 2.95.3 or with @value{NGCC} 3.1 or newer, using the options
10771 @option{-gdwarf-2} or @option{-gstabs+}. DWARF 2 is preferred over
10772 stabs+. Most configurations of @value{NGCC} emit either DWARF 2 or
10773 stabs+ as their default debug format, so you usually don't need to
10774 specify a debug format explicitly. Other compilers and/or debug formats
10775 are likely to work badly or not at all when using @value{GDBN} to debug
10781 @cindex member functions
10783 Member function calls are allowed; you can use expressions like
10786 count = aml->GetOriginal(x, y)
10789 @vindex this@r{, inside C@t{++} member functions}
10790 @cindex namespace in C@t{++}
10792 While a member function is active (in the selected stack frame), your
10793 expressions have the same namespace available as the member function;
10794 that is, @value{GDBN} allows implicit references to the class instance
10795 pointer @code{this} following the same rules as C@t{++}.
10797 @cindex call overloaded functions
10798 @cindex overloaded functions, calling
10799 @cindex type conversions in C@t{++}
10801 You can call overloaded functions; @value{GDBN} resolves the function
10802 call to the right definition, with some restrictions. @value{GDBN} does not
10803 perform overload resolution involving user-defined type conversions,
10804 calls to constructors, or instantiations of templates that do not exist
10805 in the program. It also cannot handle ellipsis argument lists or
10808 It does perform integral conversions and promotions, floating-point
10809 promotions, arithmetic conversions, pointer conversions, conversions of
10810 class objects to base classes, and standard conversions such as those of
10811 functions or arrays to pointers; it requires an exact match on the
10812 number of function arguments.
10814 Overload resolution is always performed, unless you have specified
10815 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
10816 ,@value{GDBN} Features for C@t{++}}.
10818 You must specify @code{set overload-resolution off} in order to use an
10819 explicit function signature to call an overloaded function, as in
10821 p 'foo(char,int)'('x', 13)
10824 The @value{GDBN} command-completion facility can simplify this;
10825 see @ref{Completion, ,Command Completion}.
10827 @cindex reference declarations
10829 @value{GDBN} understands variables declared as C@t{++} references; you can use
10830 them in expressions just as you do in C@t{++} source---they are automatically
10833 In the parameter list shown when @value{GDBN} displays a frame, the values of
10834 reference variables are not displayed (unlike other variables); this
10835 avoids clutter, since references are often used for large structures.
10836 The @emph{address} of a reference variable is always shown, unless
10837 you have specified @samp{set print address off}.
10840 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
10841 expressions can use it just as expressions in your program do. Since
10842 one scope may be defined in another, you can use @code{::} repeatedly if
10843 necessary, for example in an expression like
10844 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
10845 resolving name scope by reference to source files, in both C and C@t{++}
10846 debugging (@pxref{Variables, ,Program Variables}).
10849 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
10850 calling virtual functions correctly, printing out virtual bases of
10851 objects, calling functions in a base subobject, casting objects, and
10852 invoking user-defined operators.
10855 @subsubsection C and C@t{++} Defaults
10857 @cindex C and C@t{++} defaults
10859 If you allow @value{GDBN} to set type and range checking automatically, they
10860 both default to @code{off} whenever the working language changes to
10861 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
10862 selects the working language.
10864 If you allow @value{GDBN} to set the language automatically, it
10865 recognizes source files whose names end with @file{.c}, @file{.C}, or
10866 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
10867 these files, it sets the working language to C or C@t{++}.
10868 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
10869 for further details.
10871 @c Type checking is (a) primarily motivated by Modula-2, and (b)
10872 @c unimplemented. If (b) changes, it might make sense to let this node
10873 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
10876 @subsubsection C and C@t{++} Type and Range Checks
10878 @cindex C and C@t{++} checks
10880 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
10881 is not used. However, if you turn type checking on, @value{GDBN}
10882 considers two variables type equivalent if:
10886 The two variables are structured and have the same structure, union, or
10890 The two variables have the same type name, or types that have been
10891 declared equivalent through @code{typedef}.
10894 @c leaving this out because neither J Gilmore nor R Pesch understand it.
10897 The two @code{struct}, @code{union}, or @code{enum} variables are
10898 declared in the same declaration. (Note: this may not be true for all C
10903 Range checking, if turned on, is done on mathematical operations. Array
10904 indices are not checked, since they are often used to index a pointer
10905 that is not itself an array.
10908 @subsubsection @value{GDBN} and C
10910 The @code{set print union} and @code{show print union} commands apply to
10911 the @code{union} type. When set to @samp{on}, any @code{union} that is
10912 inside a @code{struct} or @code{class} is also printed. Otherwise, it
10913 appears as @samp{@{...@}}.
10915 The @code{@@} operator aids in the debugging of dynamic arrays, formed
10916 with pointers and a memory allocation function. @xref{Expressions,
10919 @node Debugging C Plus Plus
10920 @subsubsection @value{GDBN} Features for C@t{++}
10922 @cindex commands for C@t{++}
10924 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
10925 designed specifically for use with C@t{++}. Here is a summary:
10928 @cindex break in overloaded functions
10929 @item @r{breakpoint menus}
10930 When you want a breakpoint in a function whose name is overloaded,
10931 @value{GDBN} has the capability to display a menu of possible breakpoint
10932 locations to help you specify which function definition you want.
10933 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
10935 @cindex overloading in C@t{++}
10936 @item rbreak @var{regex}
10937 Setting breakpoints using regular expressions is helpful for setting
10938 breakpoints on overloaded functions that are not members of any special
10940 @xref{Set Breaks, ,Setting Breakpoints}.
10942 @cindex C@t{++} exception handling
10945 Debug C@t{++} exception handling using these commands. @xref{Set
10946 Catchpoints, , Setting Catchpoints}.
10948 @cindex inheritance
10949 @item ptype @var{typename}
10950 Print inheritance relationships as well as other information for type
10952 @xref{Symbols, ,Examining the Symbol Table}.
10954 @cindex C@t{++} symbol display
10955 @item set print demangle
10956 @itemx show print demangle
10957 @itemx set print asm-demangle
10958 @itemx show print asm-demangle
10959 Control whether C@t{++} symbols display in their source form, both when
10960 displaying code as C@t{++} source and when displaying disassemblies.
10961 @xref{Print Settings, ,Print Settings}.
10963 @item set print object
10964 @itemx show print object
10965 Choose whether to print derived (actual) or declared types of objects.
10966 @xref{Print Settings, ,Print Settings}.
10968 @item set print vtbl
10969 @itemx show print vtbl
10970 Control the format for printing virtual function tables.
10971 @xref{Print Settings, ,Print Settings}.
10972 (The @code{vtbl} commands do not work on programs compiled with the HP
10973 ANSI C@t{++} compiler (@code{aCC}).)
10975 @kindex set overload-resolution
10976 @cindex overloaded functions, overload resolution
10977 @item set overload-resolution on
10978 Enable overload resolution for C@t{++} expression evaluation. The default
10979 is on. For overloaded functions, @value{GDBN} evaluates the arguments
10980 and searches for a function whose signature matches the argument types,
10981 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
10982 Expressions, ,C@t{++} Expressions}, for details).
10983 If it cannot find a match, it emits a message.
10985 @item set overload-resolution off
10986 Disable overload resolution for C@t{++} expression evaluation. For
10987 overloaded functions that are not class member functions, @value{GDBN}
10988 chooses the first function of the specified name that it finds in the
10989 symbol table, whether or not its arguments are of the correct type. For
10990 overloaded functions that are class member functions, @value{GDBN}
10991 searches for a function whose signature @emph{exactly} matches the
10994 @kindex show overload-resolution
10995 @item show overload-resolution
10996 Show the current setting of overload resolution.
10998 @item @r{Overloaded symbol names}
10999 You can specify a particular definition of an overloaded symbol, using
11000 the same notation that is used to declare such symbols in C@t{++}: type
11001 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
11002 also use the @value{GDBN} command-line word completion facilities to list the
11003 available choices, or to finish the type list for you.
11004 @xref{Completion,, Command Completion}, for details on how to do this.
11007 @node Decimal Floating Point
11008 @subsubsection Decimal Floating Point format
11009 @cindex decimal floating point format
11011 @value{GDBN} can examine, set and perform computations with numbers in
11012 decimal floating point format, which in the C language correspond to the
11013 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
11014 specified by the extension to support decimal floating-point arithmetic.
11016 There are two encodings in use, depending on the architecture: BID (Binary
11017 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
11018 PowerPC. @value{GDBN} will use the appropriate encoding for the configured
11021 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
11022 to manipulate decimal floating point numbers, it is not possible to convert
11023 (using a cast, for example) integers wider than 32-bit to decimal float.
11025 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
11026 point computations, error checking in decimal float operations ignores
11027 underflow, overflow and divide by zero exceptions.
11029 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
11030 to inspect @code{_Decimal128} values stored in floating point registers.
11031 See @ref{PowerPC,,PowerPC} for more details.
11034 @subsection Objective-C
11036 @cindex Objective-C
11037 This section provides information about some commands and command
11038 options that are useful for debugging Objective-C code. See also
11039 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
11040 few more commands specific to Objective-C support.
11043 * Method Names in Commands::
11044 * The Print Command with Objective-C::
11047 @node Method Names in Commands
11048 @subsubsection Method Names in Commands
11050 The following commands have been extended to accept Objective-C method
11051 names as line specifications:
11053 @kindex clear@r{, and Objective-C}
11054 @kindex break@r{, and Objective-C}
11055 @kindex info line@r{, and Objective-C}
11056 @kindex jump@r{, and Objective-C}
11057 @kindex list@r{, and Objective-C}
11061 @item @code{info line}
11066 A fully qualified Objective-C method name is specified as
11069 -[@var{Class} @var{methodName}]
11072 where the minus sign is used to indicate an instance method and a
11073 plus sign (not shown) is used to indicate a class method. The class
11074 name @var{Class} and method name @var{methodName} are enclosed in
11075 brackets, similar to the way messages are specified in Objective-C
11076 source code. For example, to set a breakpoint at the @code{create}
11077 instance method of class @code{Fruit} in the program currently being
11081 break -[Fruit create]
11084 To list ten program lines around the @code{initialize} class method,
11088 list +[NSText initialize]
11091 In the current version of @value{GDBN}, the plus or minus sign is
11092 required. In future versions of @value{GDBN}, the plus or minus
11093 sign will be optional, but you can use it to narrow the search. It
11094 is also possible to specify just a method name:
11100 You must specify the complete method name, including any colons. If
11101 your program's source files contain more than one @code{create} method,
11102 you'll be presented with a numbered list of classes that implement that
11103 method. Indicate your choice by number, or type @samp{0} to exit if
11106 As another example, to clear a breakpoint established at the
11107 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
11110 clear -[NSWindow makeKeyAndOrderFront:]
11113 @node The Print Command with Objective-C
11114 @subsubsection The Print Command With Objective-C
11115 @cindex Objective-C, print objects
11116 @kindex print-object
11117 @kindex po @r{(@code{print-object})}
11119 The print command has also been extended to accept methods. For example:
11122 print -[@var{object} hash]
11125 @cindex print an Objective-C object description
11126 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
11128 will tell @value{GDBN} to send the @code{hash} message to @var{object}
11129 and print the result. Also, an additional command has been added,
11130 @code{print-object} or @code{po} for short, which is meant to print
11131 the description of an object. However, this command may only work
11132 with certain Objective-C libraries that have a particular hook
11133 function, @code{_NSPrintForDebugger}, defined.
11136 @subsection Fortran
11137 @cindex Fortran-specific support in @value{GDBN}
11139 @value{GDBN} can be used to debug programs written in Fortran, but it
11140 currently supports only the features of Fortran 77 language.
11142 @cindex trailing underscore, in Fortran symbols
11143 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
11144 among them) append an underscore to the names of variables and
11145 functions. When you debug programs compiled by those compilers, you
11146 will need to refer to variables and functions with a trailing
11150 * Fortran Operators:: Fortran operators and expressions
11151 * Fortran Defaults:: Default settings for Fortran
11152 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
11155 @node Fortran Operators
11156 @subsubsection Fortran Operators and Expressions
11158 @cindex Fortran operators and expressions
11160 Operators must be defined on values of specific types. For instance,
11161 @code{+} is defined on numbers, but not on characters or other non-
11162 arithmetic types. Operators are often defined on groups of types.
11166 The exponentiation operator. It raises the first operand to the power
11170 The range operator. Normally used in the form of array(low:high) to
11171 represent a section of array.
11174 The access component operator. Normally used to access elements in derived
11175 types. Also suitable for unions. As unions aren't part of regular Fortran,
11176 this can only happen when accessing a register that uses a gdbarch-defined
11180 @node Fortran Defaults
11181 @subsubsection Fortran Defaults
11183 @cindex Fortran Defaults
11185 Fortran symbols are usually case-insensitive, so @value{GDBN} by
11186 default uses case-insensitive matches for Fortran symbols. You can
11187 change that with the @samp{set case-insensitive} command, see
11188 @ref{Symbols}, for the details.
11190 @node Special Fortran Commands
11191 @subsubsection Special Fortran Commands
11193 @cindex Special Fortran commands
11195 @value{GDBN} has some commands to support Fortran-specific features,
11196 such as displaying common blocks.
11199 @cindex @code{COMMON} blocks, Fortran
11200 @kindex info common
11201 @item info common @r{[}@var{common-name}@r{]}
11202 This command prints the values contained in the Fortran @code{COMMON}
11203 block whose name is @var{common-name}. With no argument, the names of
11204 all @code{COMMON} blocks visible at the current program location are
11211 @cindex Pascal support in @value{GDBN}, limitations
11212 Debugging Pascal programs which use sets, subranges, file variables, or
11213 nested functions does not currently work. @value{GDBN} does not support
11214 entering expressions, printing values, or similar features using Pascal
11217 The Pascal-specific command @code{set print pascal_static-members}
11218 controls whether static members of Pascal objects are displayed.
11219 @xref{Print Settings, pascal_static-members}.
11222 @subsection Modula-2
11224 @cindex Modula-2, @value{GDBN} support
11226 The extensions made to @value{GDBN} to support Modula-2 only support
11227 output from the @sc{gnu} Modula-2 compiler (which is currently being
11228 developed). Other Modula-2 compilers are not currently supported, and
11229 attempting to debug executables produced by them is most likely
11230 to give an error as @value{GDBN} reads in the executable's symbol
11233 @cindex expressions in Modula-2
11235 * M2 Operators:: Built-in operators
11236 * Built-In Func/Proc:: Built-in functions and procedures
11237 * M2 Constants:: Modula-2 constants
11238 * M2 Types:: Modula-2 types
11239 * M2 Defaults:: Default settings for Modula-2
11240 * Deviations:: Deviations from standard Modula-2
11241 * M2 Checks:: Modula-2 type and range checks
11242 * M2 Scope:: The scope operators @code{::} and @code{.}
11243 * GDB/M2:: @value{GDBN} and Modula-2
11247 @subsubsection Operators
11248 @cindex Modula-2 operators
11250 Operators must be defined on values of specific types. For instance,
11251 @code{+} is defined on numbers, but not on structures. Operators are
11252 often defined on groups of types. For the purposes of Modula-2, the
11253 following definitions hold:
11258 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
11262 @emph{Character types} consist of @code{CHAR} and its subranges.
11265 @emph{Floating-point types} consist of @code{REAL}.
11268 @emph{Pointer types} consist of anything declared as @code{POINTER TO
11272 @emph{Scalar types} consist of all of the above.
11275 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
11278 @emph{Boolean types} consist of @code{BOOLEAN}.
11282 The following operators are supported, and appear in order of
11283 increasing precedence:
11287 Function argument or array index separator.
11290 Assignment. The value of @var{var} @code{:=} @var{value} is
11294 Less than, greater than on integral, floating-point, or enumerated
11298 Less than or equal to, greater than or equal to
11299 on integral, floating-point and enumerated types, or set inclusion on
11300 set types. Same precedence as @code{<}.
11302 @item =@r{, }<>@r{, }#
11303 Equality and two ways of expressing inequality, valid on scalar types.
11304 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
11305 available for inequality, since @code{#} conflicts with the script
11309 Set membership. Defined on set types and the types of their members.
11310 Same precedence as @code{<}.
11313 Boolean disjunction. Defined on boolean types.
11316 Boolean conjunction. Defined on boolean types.
11319 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
11322 Addition and subtraction on integral and floating-point types, or union
11323 and difference on set types.
11326 Multiplication on integral and floating-point types, or set intersection
11330 Division on floating-point types, or symmetric set difference on set
11331 types. Same precedence as @code{*}.
11334 Integer division and remainder. Defined on integral types. Same
11335 precedence as @code{*}.
11338 Negative. Defined on @code{INTEGER} and @code{REAL} data.
11341 Pointer dereferencing. Defined on pointer types.
11344 Boolean negation. Defined on boolean types. Same precedence as
11348 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
11349 precedence as @code{^}.
11352 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
11355 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
11359 @value{GDBN} and Modula-2 scope operators.
11363 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
11364 treats the use of the operator @code{IN}, or the use of operators
11365 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
11366 @code{<=}, and @code{>=} on sets as an error.
11370 @node Built-In Func/Proc
11371 @subsubsection Built-in Functions and Procedures
11372 @cindex Modula-2 built-ins
11374 Modula-2 also makes available several built-in procedures and functions.
11375 In describing these, the following metavariables are used:
11380 represents an @code{ARRAY} variable.
11383 represents a @code{CHAR} constant or variable.
11386 represents a variable or constant of integral type.
11389 represents an identifier that belongs to a set. Generally used in the
11390 same function with the metavariable @var{s}. The type of @var{s} should
11391 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
11394 represents a variable or constant of integral or floating-point type.
11397 represents a variable or constant of floating-point type.
11403 represents a variable.
11406 represents a variable or constant of one of many types. See the
11407 explanation of the function for details.
11410 All Modula-2 built-in procedures also return a result, described below.
11414 Returns the absolute value of @var{n}.
11417 If @var{c} is a lower case letter, it returns its upper case
11418 equivalent, otherwise it returns its argument.
11421 Returns the character whose ordinal value is @var{i}.
11424 Decrements the value in the variable @var{v} by one. Returns the new value.
11426 @item DEC(@var{v},@var{i})
11427 Decrements the value in the variable @var{v} by @var{i}. Returns the
11430 @item EXCL(@var{m},@var{s})
11431 Removes the element @var{m} from the set @var{s}. Returns the new
11434 @item FLOAT(@var{i})
11435 Returns the floating point equivalent of the integer @var{i}.
11437 @item HIGH(@var{a})
11438 Returns the index of the last member of @var{a}.
11441 Increments the value in the variable @var{v} by one. Returns the new value.
11443 @item INC(@var{v},@var{i})
11444 Increments the value in the variable @var{v} by @var{i}. Returns the
11447 @item INCL(@var{m},@var{s})
11448 Adds the element @var{m} to the set @var{s} if it is not already
11449 there. Returns the new set.
11452 Returns the maximum value of the type @var{t}.
11455 Returns the minimum value of the type @var{t}.
11458 Returns boolean TRUE if @var{i} is an odd number.
11461 Returns the ordinal value of its argument. For example, the ordinal
11462 value of a character is its @sc{ascii} value (on machines supporting the
11463 @sc{ascii} character set). @var{x} must be of an ordered type, which include
11464 integral, character and enumerated types.
11466 @item SIZE(@var{x})
11467 Returns the size of its argument. @var{x} can be a variable or a type.
11469 @item TRUNC(@var{r})
11470 Returns the integral part of @var{r}.
11472 @item TSIZE(@var{x})
11473 Returns the size of its argument. @var{x} can be a variable or a type.
11475 @item VAL(@var{t},@var{i})
11476 Returns the member of the type @var{t} whose ordinal value is @var{i}.
11480 @emph{Warning:} Sets and their operations are not yet supported, so
11481 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
11485 @cindex Modula-2 constants
11487 @subsubsection Constants
11489 @value{GDBN} allows you to express the constants of Modula-2 in the following
11495 Integer constants are simply a sequence of digits. When used in an
11496 expression, a constant is interpreted to be type-compatible with the
11497 rest of the expression. Hexadecimal integers are specified by a
11498 trailing @samp{H}, and octal integers by a trailing @samp{B}.
11501 Floating point constants appear as a sequence of digits, followed by a
11502 decimal point and another sequence of digits. An optional exponent can
11503 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
11504 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
11505 digits of the floating point constant must be valid decimal (base 10)
11509 Character constants consist of a single character enclosed by a pair of
11510 like quotes, either single (@code{'}) or double (@code{"}). They may
11511 also be expressed by their ordinal value (their @sc{ascii} value, usually)
11512 followed by a @samp{C}.
11515 String constants consist of a sequence of characters enclosed by a
11516 pair of like quotes, either single (@code{'}) or double (@code{"}).
11517 Escape sequences in the style of C are also allowed. @xref{C
11518 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
11522 Enumerated constants consist of an enumerated identifier.
11525 Boolean constants consist of the identifiers @code{TRUE} and
11529 Pointer constants consist of integral values only.
11532 Set constants are not yet supported.
11536 @subsubsection Modula-2 Types
11537 @cindex Modula-2 types
11539 Currently @value{GDBN} can print the following data types in Modula-2
11540 syntax: array types, record types, set types, pointer types, procedure
11541 types, enumerated types, subrange types and base types. You can also
11542 print the contents of variables declared using these type.
11543 This section gives a number of simple source code examples together with
11544 sample @value{GDBN} sessions.
11546 The first example contains the following section of code:
11555 and you can request @value{GDBN} to interrogate the type and value of
11556 @code{r} and @code{s}.
11559 (@value{GDBP}) print s
11561 (@value{GDBP}) ptype s
11563 (@value{GDBP}) print r
11565 (@value{GDBP}) ptype r
11570 Likewise if your source code declares @code{s} as:
11574 s: SET ['A'..'Z'] ;
11578 then you may query the type of @code{s} by:
11581 (@value{GDBP}) ptype s
11582 type = SET ['A'..'Z']
11586 Note that at present you cannot interactively manipulate set
11587 expressions using the debugger.
11589 The following example shows how you might declare an array in Modula-2
11590 and how you can interact with @value{GDBN} to print its type and contents:
11594 s: ARRAY [-10..10] OF CHAR ;
11598 (@value{GDBP}) ptype s
11599 ARRAY [-10..10] OF CHAR
11602 Note that the array handling is not yet complete and although the type
11603 is printed correctly, expression handling still assumes that all
11604 arrays have a lower bound of zero and not @code{-10} as in the example
11607 Here are some more type related Modula-2 examples:
11611 colour = (blue, red, yellow, green) ;
11612 t = [blue..yellow] ;
11620 The @value{GDBN} interaction shows how you can query the data type
11621 and value of a variable.
11624 (@value{GDBP}) print s
11626 (@value{GDBP}) ptype t
11627 type = [blue..yellow]
11631 In this example a Modula-2 array is declared and its contents
11632 displayed. Observe that the contents are written in the same way as
11633 their @code{C} counterparts.
11637 s: ARRAY [1..5] OF CARDINAL ;
11643 (@value{GDBP}) print s
11644 $1 = @{1, 0, 0, 0, 0@}
11645 (@value{GDBP}) ptype s
11646 type = ARRAY [1..5] OF CARDINAL
11649 The Modula-2 language interface to @value{GDBN} also understands
11650 pointer types as shown in this example:
11654 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
11661 and you can request that @value{GDBN} describes the type of @code{s}.
11664 (@value{GDBP}) ptype s
11665 type = POINTER TO ARRAY [1..5] OF CARDINAL
11668 @value{GDBN} handles compound types as we can see in this example.
11669 Here we combine array types, record types, pointer types and subrange
11680 myarray = ARRAY myrange OF CARDINAL ;
11681 myrange = [-2..2] ;
11683 s: POINTER TO ARRAY myrange OF foo ;
11687 and you can ask @value{GDBN} to describe the type of @code{s} as shown
11691 (@value{GDBP}) ptype s
11692 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
11695 f3 : ARRAY [-2..2] OF CARDINAL;
11700 @subsubsection Modula-2 Defaults
11701 @cindex Modula-2 defaults
11703 If type and range checking are set automatically by @value{GDBN}, they
11704 both default to @code{on} whenever the working language changes to
11705 Modula-2. This happens regardless of whether you or @value{GDBN}
11706 selected the working language.
11708 If you allow @value{GDBN} to set the language automatically, then entering
11709 code compiled from a file whose name ends with @file{.mod} sets the
11710 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
11711 Infer the Source Language}, for further details.
11714 @subsubsection Deviations from Standard Modula-2
11715 @cindex Modula-2, deviations from
11717 A few changes have been made to make Modula-2 programs easier to debug.
11718 This is done primarily via loosening its type strictness:
11722 Unlike in standard Modula-2, pointer constants can be formed by
11723 integers. This allows you to modify pointer variables during
11724 debugging. (In standard Modula-2, the actual address contained in a
11725 pointer variable is hidden from you; it can only be modified
11726 through direct assignment to another pointer variable or expression that
11727 returned a pointer.)
11730 C escape sequences can be used in strings and characters to represent
11731 non-printable characters. @value{GDBN} prints out strings with these
11732 escape sequences embedded. Single non-printable characters are
11733 printed using the @samp{CHR(@var{nnn})} format.
11736 The assignment operator (@code{:=}) returns the value of its right-hand
11740 All built-in procedures both modify @emph{and} return their argument.
11744 @subsubsection Modula-2 Type and Range Checks
11745 @cindex Modula-2 checks
11748 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
11751 @c FIXME remove warning when type/range checks added
11753 @value{GDBN} considers two Modula-2 variables type equivalent if:
11757 They are of types that have been declared equivalent via a @code{TYPE
11758 @var{t1} = @var{t2}} statement
11761 They have been declared on the same line. (Note: This is true of the
11762 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
11765 As long as type checking is enabled, any attempt to combine variables
11766 whose types are not equivalent is an error.
11768 Range checking is done on all mathematical operations, assignment, array
11769 index bounds, and all built-in functions and procedures.
11772 @subsubsection The Scope Operators @code{::} and @code{.}
11774 @cindex @code{.}, Modula-2 scope operator
11775 @cindex colon, doubled as scope operator
11777 @vindex colon-colon@r{, in Modula-2}
11778 @c Info cannot handle :: but TeX can.
11781 @vindex ::@r{, in Modula-2}
11784 There are a few subtle differences between the Modula-2 scope operator
11785 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
11790 @var{module} . @var{id}
11791 @var{scope} :: @var{id}
11795 where @var{scope} is the name of a module or a procedure,
11796 @var{module} the name of a module, and @var{id} is any declared
11797 identifier within your program, except another module.
11799 Using the @code{::} operator makes @value{GDBN} search the scope
11800 specified by @var{scope} for the identifier @var{id}. If it is not
11801 found in the specified scope, then @value{GDBN} searches all scopes
11802 enclosing the one specified by @var{scope}.
11804 Using the @code{.} operator makes @value{GDBN} search the current scope for
11805 the identifier specified by @var{id} that was imported from the
11806 definition module specified by @var{module}. With this operator, it is
11807 an error if the identifier @var{id} was not imported from definition
11808 module @var{module}, or if @var{id} is not an identifier in
11812 @subsubsection @value{GDBN} and Modula-2
11814 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
11815 Five subcommands of @code{set print} and @code{show print} apply
11816 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
11817 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
11818 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
11819 analogue in Modula-2.
11821 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
11822 with any language, is not useful with Modula-2. Its
11823 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
11824 created in Modula-2 as they can in C or C@t{++}. However, because an
11825 address can be specified by an integral constant, the construct
11826 @samp{@{@var{type}@}@var{adrexp}} is still useful.
11828 @cindex @code{#} in Modula-2
11829 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
11830 interpreted as the beginning of a comment. Use @code{<>} instead.
11836 The extensions made to @value{GDBN} for Ada only support
11837 output from the @sc{gnu} Ada (GNAT) compiler.
11838 Other Ada compilers are not currently supported, and
11839 attempting to debug executables produced by them is most likely
11843 @cindex expressions in Ada
11845 * Ada Mode Intro:: General remarks on the Ada syntax
11846 and semantics supported by Ada mode
11848 * Omissions from Ada:: Restrictions on the Ada expression syntax.
11849 * Additions to Ada:: Extensions of the Ada expression syntax.
11850 * Stopping Before Main Program:: Debugging the program during elaboration.
11851 * Ada Tasks:: Listing and setting breakpoints in tasks.
11852 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
11853 * Ada Glitches:: Known peculiarities of Ada mode.
11856 @node Ada Mode Intro
11857 @subsubsection Introduction
11858 @cindex Ada mode, general
11860 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
11861 syntax, with some extensions.
11862 The philosophy behind the design of this subset is
11866 That @value{GDBN} should provide basic literals and access to operations for
11867 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
11868 leaving more sophisticated computations to subprograms written into the
11869 program (which therefore may be called from @value{GDBN}).
11872 That type safety and strict adherence to Ada language restrictions
11873 are not particularly important to the @value{GDBN} user.
11876 That brevity is important to the @value{GDBN} user.
11879 Thus, for brevity, the debugger acts as if all names declared in
11880 user-written packages are directly visible, even if they are not visible
11881 according to Ada rules, thus making it unnecessary to fully qualify most
11882 names with their packages, regardless of context. Where this causes
11883 ambiguity, @value{GDBN} asks the user's intent.
11885 The debugger will start in Ada mode if it detects an Ada main program.
11886 As for other languages, it will enter Ada mode when stopped in a program that
11887 was translated from an Ada source file.
11889 While in Ada mode, you may use `@t{--}' for comments. This is useful
11890 mostly for documenting command files. The standard @value{GDBN} comment
11891 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
11892 middle (to allow based literals).
11894 The debugger supports limited overloading. Given a subprogram call in which
11895 the function symbol has multiple definitions, it will use the number of
11896 actual parameters and some information about their types to attempt to narrow
11897 the set of definitions. It also makes very limited use of context, preferring
11898 procedures to functions in the context of the @code{call} command, and
11899 functions to procedures elsewhere.
11901 @node Omissions from Ada
11902 @subsubsection Omissions from Ada
11903 @cindex Ada, omissions from
11905 Here are the notable omissions from the subset:
11909 Only a subset of the attributes are supported:
11913 @t{'First}, @t{'Last}, and @t{'Length}
11914 on array objects (not on types and subtypes).
11917 @t{'Min} and @t{'Max}.
11920 @t{'Pos} and @t{'Val}.
11926 @t{'Range} on array objects (not subtypes), but only as the right
11927 operand of the membership (@code{in}) operator.
11930 @t{'Access}, @t{'Unchecked_Access}, and
11931 @t{'Unrestricted_Access} (a GNAT extension).
11939 @code{Characters.Latin_1} are not available and
11940 concatenation is not implemented. Thus, escape characters in strings are
11941 not currently available.
11944 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
11945 equality of representations. They will generally work correctly
11946 for strings and arrays whose elements have integer or enumeration types.
11947 They may not work correctly for arrays whose element
11948 types have user-defined equality, for arrays of real values
11949 (in particular, IEEE-conformant floating point, because of negative
11950 zeroes and NaNs), and for arrays whose elements contain unused bits with
11951 indeterminate values.
11954 The other component-by-component array operations (@code{and}, @code{or},
11955 @code{xor}, @code{not}, and relational tests other than equality)
11956 are not implemented.
11959 @cindex array aggregates (Ada)
11960 @cindex record aggregates (Ada)
11961 @cindex aggregates (Ada)
11962 There is limited support for array and record aggregates. They are
11963 permitted only on the right sides of assignments, as in these examples:
11966 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
11967 (@value{GDBP}) set An_Array := (1, others => 0)
11968 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
11969 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
11970 (@value{GDBP}) set A_Record := (1, "Peter", True);
11971 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
11975 discriminant's value by assigning an aggregate has an
11976 undefined effect if that discriminant is used within the record.
11977 However, you can first modify discriminants by directly assigning to
11978 them (which normally would not be allowed in Ada), and then performing an
11979 aggregate assignment. For example, given a variable @code{A_Rec}
11980 declared to have a type such as:
11983 type Rec (Len : Small_Integer := 0) is record
11985 Vals : IntArray (1 .. Len);
11989 you can assign a value with a different size of @code{Vals} with two
11993 (@value{GDBP}) set A_Rec.Len := 4
11994 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
11997 As this example also illustrates, @value{GDBN} is very loose about the usual
11998 rules concerning aggregates. You may leave out some of the
11999 components of an array or record aggregate (such as the @code{Len}
12000 component in the assignment to @code{A_Rec} above); they will retain their
12001 original values upon assignment. You may freely use dynamic values as
12002 indices in component associations. You may even use overlapping or
12003 redundant component associations, although which component values are
12004 assigned in such cases is not defined.
12007 Calls to dispatching subprograms are not implemented.
12010 The overloading algorithm is much more limited (i.e., less selective)
12011 than that of real Ada. It makes only limited use of the context in
12012 which a subexpression appears to resolve its meaning, and it is much
12013 looser in its rules for allowing type matches. As a result, some
12014 function calls will be ambiguous, and the user will be asked to choose
12015 the proper resolution.
12018 The @code{new} operator is not implemented.
12021 Entry calls are not implemented.
12024 Aside from printing, arithmetic operations on the native VAX floating-point
12025 formats are not supported.
12028 It is not possible to slice a packed array.
12031 The names @code{True} and @code{False}, when not part of a qualified name,
12032 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
12034 Should your program
12035 redefine these names in a package or procedure (at best a dubious practice),
12036 you will have to use fully qualified names to access their new definitions.
12039 @node Additions to Ada
12040 @subsubsection Additions to Ada
12041 @cindex Ada, deviations from
12043 As it does for other languages, @value{GDBN} makes certain generic
12044 extensions to Ada (@pxref{Expressions}):
12048 If the expression @var{E} is a variable residing in memory (typically
12049 a local variable or array element) and @var{N} is a positive integer,
12050 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
12051 @var{N}-1 adjacent variables following it in memory as an array. In
12052 Ada, this operator is generally not necessary, since its prime use is
12053 in displaying parts of an array, and slicing will usually do this in
12054 Ada. However, there are occasional uses when debugging programs in
12055 which certain debugging information has been optimized away.
12058 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
12059 appears in function or file @var{B}.'' When @var{B} is a file name,
12060 you must typically surround it in single quotes.
12063 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
12064 @var{type} that appears at address @var{addr}.''
12067 A name starting with @samp{$} is a convenience variable
12068 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
12071 In addition, @value{GDBN} provides a few other shortcuts and outright
12072 additions specific to Ada:
12076 The assignment statement is allowed as an expression, returning
12077 its right-hand operand as its value. Thus, you may enter
12080 (@value{GDBP}) set x := y + 3
12081 (@value{GDBP}) print A(tmp := y + 1)
12085 The semicolon is allowed as an ``operator,'' returning as its value
12086 the value of its right-hand operand.
12087 This allows, for example,
12088 complex conditional breaks:
12091 (@value{GDBP}) break f
12092 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
12096 Rather than use catenation and symbolic character names to introduce special
12097 characters into strings, one may instead use a special bracket notation,
12098 which is also used to print strings. A sequence of characters of the form
12099 @samp{["@var{XX}"]} within a string or character literal denotes the
12100 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
12101 sequence of characters @samp{["""]} also denotes a single quotation mark
12102 in strings. For example,
12104 "One line.["0a"]Next line.["0a"]"
12107 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
12111 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
12112 @t{'Max} is optional (and is ignored in any case). For example, it is valid
12116 (@value{GDBP}) print 'max(x, y)
12120 When printing arrays, @value{GDBN} uses positional notation when the
12121 array has a lower bound of 1, and uses a modified named notation otherwise.
12122 For example, a one-dimensional array of three integers with a lower bound
12123 of 3 might print as
12130 That is, in contrast to valid Ada, only the first component has a @code{=>}
12134 You may abbreviate attributes in expressions with any unique,
12135 multi-character subsequence of
12136 their names (an exact match gets preference).
12137 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
12138 in place of @t{a'length}.
12141 @cindex quoting Ada internal identifiers
12142 Since Ada is case-insensitive, the debugger normally maps identifiers you type
12143 to lower case. The GNAT compiler uses upper-case characters for
12144 some of its internal identifiers, which are normally of no interest to users.
12145 For the rare occasions when you actually have to look at them,
12146 enclose them in angle brackets to avoid the lower-case mapping.
12149 (@value{GDBP}) print <JMPBUF_SAVE>[0]
12153 Printing an object of class-wide type or dereferencing an
12154 access-to-class-wide value will display all the components of the object's
12155 specific type (as indicated by its run-time tag). Likewise, component
12156 selection on such a value will operate on the specific type of the
12161 @node Stopping Before Main Program
12162 @subsubsection Stopping at the Very Beginning
12164 @cindex breakpointing Ada elaboration code
12165 It is sometimes necessary to debug the program during elaboration, and
12166 before reaching the main procedure.
12167 As defined in the Ada Reference
12168 Manual, the elaboration code is invoked from a procedure called
12169 @code{adainit}. To run your program up to the beginning of
12170 elaboration, simply use the following two commands:
12171 @code{tbreak adainit} and @code{run}.
12174 @subsubsection Extensions for Ada Tasks
12175 @cindex Ada, tasking
12177 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
12178 @value{GDBN} provides the following task-related commands:
12183 This command shows a list of current Ada tasks, as in the following example:
12190 (@value{GDBP}) info tasks
12191 ID TID P-ID Pri State Name
12192 1 8088000 0 15 Child Activation Wait main_task
12193 2 80a4000 1 15 Accept Statement b
12194 3 809a800 1 15 Child Activation Wait a
12195 * 4 80ae800 3 15 Runnable c
12200 In this listing, the asterisk before the last task indicates it to be the
12201 task currently being inspected.
12205 Represents @value{GDBN}'s internal task number.
12211 The parent's task ID (@value{GDBN}'s internal task number).
12214 The base priority of the task.
12217 Current state of the task.
12221 The task has been created but has not been activated. It cannot be
12225 The task is not blocked for any reason known to Ada. (It may be waiting
12226 for a mutex, though.) It is conceptually "executing" in normal mode.
12229 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
12230 that were waiting on terminate alternatives have been awakened and have
12231 terminated themselves.
12233 @item Child Activation Wait
12234 The task is waiting for created tasks to complete activation.
12236 @item Accept Statement
12237 The task is waiting on an accept or selective wait statement.
12239 @item Waiting on entry call
12240 The task is waiting on an entry call.
12242 @item Async Select Wait
12243 The task is waiting to start the abortable part of an asynchronous
12247 The task is waiting on a select statement with only a delay
12250 @item Child Termination Wait
12251 The task is sleeping having completed a master within itself, and is
12252 waiting for the tasks dependent on that master to become terminated or
12253 waiting on a terminate Phase.
12255 @item Wait Child in Term Alt
12256 The task is sleeping waiting for tasks on terminate alternatives to
12257 finish terminating.
12259 @item Accepting RV with @var{taskno}
12260 The task is accepting a rendez-vous with the task @var{taskno}.
12264 Name of the task in the program.
12268 @kindex info task @var{taskno}
12269 @item info task @var{taskno}
12270 This command shows detailled informations on the specified task, as in
12271 the following example:
12276 (@value{GDBP}) info tasks
12277 ID TID P-ID Pri State Name
12278 1 8077880 0 15 Child Activation Wait main_task
12279 * 2 807c468 1 15 Runnable task_1
12280 (@value{GDBP}) info task 2
12281 Ada Task: 0x807c468
12284 Parent: 1 (main_task)
12290 @kindex task@r{ (Ada)}
12291 @cindex current Ada task ID
12292 This command prints the ID of the current task.
12298 (@value{GDBP}) info tasks
12299 ID TID P-ID Pri State Name
12300 1 8077870 0 15 Child Activation Wait main_task
12301 * 2 807c458 1 15 Runnable t
12302 (@value{GDBP}) task
12303 [Current task is 2]
12306 @item task @var{taskno}
12307 @cindex Ada task switching
12308 This command is like the @code{thread @var{threadno}}
12309 command (@pxref{Threads}). It switches the context of debugging
12310 from the current task to the given task.
12316 (@value{GDBP}) info tasks
12317 ID TID P-ID Pri State Name
12318 1 8077870 0 15 Child Activation Wait main_task
12319 * 2 807c458 1 15 Runnable t
12320 (@value{GDBP}) task 1
12321 [Switching to task 1]
12322 #0 0x8067726 in pthread_cond_wait ()
12324 #0 0x8067726 in pthread_cond_wait ()
12325 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
12326 #2 0x805cb63 in system.task_primitives.operations.sleep ()
12327 #3 0x806153e in system.tasking.stages.activate_tasks ()
12328 #4 0x804aacc in un () at un.adb:5
12331 @item break @var{linespec} task @var{taskno}
12332 @itemx break @var{linespec} task @var{taskno} if @dots{}
12333 @cindex breakpoints and tasks, in Ada
12334 @cindex task breakpoints, in Ada
12335 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
12336 These commands are like the @code{break @dots{} thread @dots{}}
12337 command (@pxref{Thread Stops}).
12338 @var{linespec} specifies source lines, as described
12339 in @ref{Specify Location}.
12341 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
12342 to specify that you only want @value{GDBN} to stop the program when a
12343 particular Ada task reaches this breakpoint. @var{taskno} is one of the
12344 numeric task identifiers assigned by @value{GDBN}, shown in the first
12345 column of the @samp{info tasks} display.
12347 If you do not specify @samp{task @var{taskno}} when you set a
12348 breakpoint, the breakpoint applies to @emph{all} tasks of your
12351 You can use the @code{task} qualifier on conditional breakpoints as
12352 well; in this case, place @samp{task @var{taskno}} before the
12353 breakpoint condition (before the @code{if}).
12361 (@value{GDBP}) info tasks
12362 ID TID P-ID Pri State Name
12363 1 140022020 0 15 Child Activation Wait main_task
12364 2 140045060 1 15 Accept/Select Wait t2
12365 3 140044840 1 15 Runnable t1
12366 * 4 140056040 1 15 Runnable t3
12367 (@value{GDBP}) b 15 task 2
12368 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
12369 (@value{GDBP}) cont
12374 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
12376 (@value{GDBP}) info tasks
12377 ID TID P-ID Pri State Name
12378 1 140022020 0 15 Child Activation Wait main_task
12379 * 2 140045060 1 15 Runnable t2
12380 3 140044840 1 15 Runnable t1
12381 4 140056040 1 15 Delay Sleep t3
12385 @node Ada Tasks and Core Files
12386 @subsubsection Tasking Support when Debugging Core Files
12387 @cindex Ada tasking and core file debugging
12389 When inspecting a core file, as opposed to debugging a live program,
12390 tasking support may be limited or even unavailable, depending on
12391 the platform being used.
12392 For instance, on x86-linux, the list of tasks is available, but task
12393 switching is not supported. On Tru64, however, task switching will work
12396 On certain platforms, including Tru64, the debugger needs to perform some
12397 memory writes in order to provide Ada tasking support. When inspecting
12398 a core file, this means that the core file must be opened with read-write
12399 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
12400 Under these circumstances, you should make a backup copy of the core
12401 file before inspecting it with @value{GDBN}.
12404 @subsubsection Known Peculiarities of Ada Mode
12405 @cindex Ada, problems
12407 Besides the omissions listed previously (@pxref{Omissions from Ada}),
12408 we know of several problems with and limitations of Ada mode in
12410 some of which will be fixed with planned future releases of the debugger
12411 and the GNU Ada compiler.
12415 Currently, the debugger
12416 has insufficient information to determine whether certain pointers represent
12417 pointers to objects or the objects themselves.
12418 Thus, the user may have to tack an extra @code{.all} after an expression
12419 to get it printed properly.
12422 Static constants that the compiler chooses not to materialize as objects in
12423 storage are invisible to the debugger.
12426 Named parameter associations in function argument lists are ignored (the
12427 argument lists are treated as positional).
12430 Many useful library packages are currently invisible to the debugger.
12433 Fixed-point arithmetic, conversions, input, and output is carried out using
12434 floating-point arithmetic, and may give results that only approximate those on
12438 The GNAT compiler never generates the prefix @code{Standard} for any of
12439 the standard symbols defined by the Ada language. @value{GDBN} knows about
12440 this: it will strip the prefix from names when you use it, and will never
12441 look for a name you have so qualified among local symbols, nor match against
12442 symbols in other packages or subprograms. If you have
12443 defined entities anywhere in your program other than parameters and
12444 local variables whose simple names match names in @code{Standard},
12445 GNAT's lack of qualification here can cause confusion. When this happens,
12446 you can usually resolve the confusion
12447 by qualifying the problematic names with package
12448 @code{Standard} explicitly.
12451 @node Unsupported Languages
12452 @section Unsupported Languages
12454 @cindex unsupported languages
12455 @cindex minimal language
12456 In addition to the other fully-supported programming languages,
12457 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
12458 It does not represent a real programming language, but provides a set
12459 of capabilities close to what the C or assembly languages provide.
12460 This should allow most simple operations to be performed while debugging
12461 an application that uses a language currently not supported by @value{GDBN}.
12463 If the language is set to @code{auto}, @value{GDBN} will automatically
12464 select this language if the current frame corresponds to an unsupported
12468 @chapter Examining the Symbol Table
12470 The commands described in this chapter allow you to inquire about the
12471 symbols (names of variables, functions and types) defined in your
12472 program. This information is inherent in the text of your program and
12473 does not change as your program executes. @value{GDBN} finds it in your
12474 program's symbol table, in the file indicated when you started @value{GDBN}
12475 (@pxref{File Options, ,Choosing Files}), or by one of the
12476 file-management commands (@pxref{Files, ,Commands to Specify Files}).
12478 @cindex symbol names
12479 @cindex names of symbols
12480 @cindex quoting names
12481 Occasionally, you may need to refer to symbols that contain unusual
12482 characters, which @value{GDBN} ordinarily treats as word delimiters. The
12483 most frequent case is in referring to static variables in other
12484 source files (@pxref{Variables,,Program Variables}). File names
12485 are recorded in object files as debugging symbols, but @value{GDBN} would
12486 ordinarily parse a typical file name, like @file{foo.c}, as the three words
12487 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
12488 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
12495 looks up the value of @code{x} in the scope of the file @file{foo.c}.
12498 @cindex case-insensitive symbol names
12499 @cindex case sensitivity in symbol names
12500 @kindex set case-sensitive
12501 @item set case-sensitive on
12502 @itemx set case-sensitive off
12503 @itemx set case-sensitive auto
12504 Normally, when @value{GDBN} looks up symbols, it matches their names
12505 with case sensitivity determined by the current source language.
12506 Occasionally, you may wish to control that. The command @code{set
12507 case-sensitive} lets you do that by specifying @code{on} for
12508 case-sensitive matches or @code{off} for case-insensitive ones. If
12509 you specify @code{auto}, case sensitivity is reset to the default
12510 suitable for the source language. The default is case-sensitive
12511 matches for all languages except for Fortran, for which the default is
12512 case-insensitive matches.
12514 @kindex show case-sensitive
12515 @item show case-sensitive
12516 This command shows the current setting of case sensitivity for symbols
12519 @kindex info address
12520 @cindex address of a symbol
12521 @item info address @var{symbol}
12522 Describe where the data for @var{symbol} is stored. For a register
12523 variable, this says which register it is kept in. For a non-register
12524 local variable, this prints the stack-frame offset at which the variable
12527 Note the contrast with @samp{print &@var{symbol}}, which does not work
12528 at all for a register variable, and for a stack local variable prints
12529 the exact address of the current instantiation of the variable.
12531 @kindex info symbol
12532 @cindex symbol from address
12533 @cindex closest symbol and offset for an address
12534 @item info symbol @var{addr}
12535 Print the name of a symbol which is stored at the address @var{addr}.
12536 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
12537 nearest symbol and an offset from it:
12540 (@value{GDBP}) info symbol 0x54320
12541 _initialize_vx + 396 in section .text
12545 This is the opposite of the @code{info address} command. You can use
12546 it to find out the name of a variable or a function given its address.
12548 For dynamically linked executables, the name of executable or shared
12549 library containing the symbol is also printed:
12552 (@value{GDBP}) info symbol 0x400225
12553 _start + 5 in section .text of /tmp/a.out
12554 (@value{GDBP}) info symbol 0x2aaaac2811cf
12555 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
12559 @item whatis [@var{arg}]
12560 Print the data type of @var{arg}, which can be either an expression or
12561 a data type. With no argument, print the data type of @code{$}, the
12562 last value in the value history. If @var{arg} is an expression, it is
12563 not actually evaluated, and any side-effecting operations (such as
12564 assignments or function calls) inside it do not take place. If
12565 @var{arg} is a type name, it may be the name of a type or typedef, or
12566 for C code it may have the form @samp{class @var{class-name}},
12567 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
12568 @samp{enum @var{enum-tag}}.
12569 @xref{Expressions, ,Expressions}.
12572 @item ptype [@var{arg}]
12573 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
12574 detailed description of the type, instead of just the name of the type.
12575 @xref{Expressions, ,Expressions}.
12577 For example, for this variable declaration:
12580 struct complex @{double real; double imag;@} v;
12584 the two commands give this output:
12588 (@value{GDBP}) whatis v
12589 type = struct complex
12590 (@value{GDBP}) ptype v
12591 type = struct complex @{
12599 As with @code{whatis}, using @code{ptype} without an argument refers to
12600 the type of @code{$}, the last value in the value history.
12602 @cindex incomplete type
12603 Sometimes, programs use opaque data types or incomplete specifications
12604 of complex data structure. If the debug information included in the
12605 program does not allow @value{GDBN} to display a full declaration of
12606 the data type, it will say @samp{<incomplete type>}. For example,
12607 given these declarations:
12611 struct foo *fooptr;
12615 but no definition for @code{struct foo} itself, @value{GDBN} will say:
12618 (@value{GDBP}) ptype foo
12619 $1 = <incomplete type>
12623 ``Incomplete type'' is C terminology for data types that are not
12624 completely specified.
12627 @item info types @var{regexp}
12629 Print a brief description of all types whose names match the regular
12630 expression @var{regexp} (or all types in your program, if you supply
12631 no argument). Each complete typename is matched as though it were a
12632 complete line; thus, @samp{i type value} gives information on all
12633 types in your program whose names include the string @code{value}, but
12634 @samp{i type ^value$} gives information only on types whose complete
12635 name is @code{value}.
12637 This command differs from @code{ptype} in two ways: first, like
12638 @code{whatis}, it does not print a detailed description; second, it
12639 lists all source files where a type is defined.
12642 @cindex local variables
12643 @item info scope @var{location}
12644 List all the variables local to a particular scope. This command
12645 accepts a @var{location} argument---a function name, a source line, or
12646 an address preceded by a @samp{*}, and prints all the variables local
12647 to the scope defined by that location. (@xref{Specify Location}, for
12648 details about supported forms of @var{location}.) For example:
12651 (@value{GDBP}) @b{info scope command_line_handler}
12652 Scope for command_line_handler:
12653 Symbol rl is an argument at stack/frame offset 8, length 4.
12654 Symbol linebuffer is in static storage at address 0x150a18, length 4.
12655 Symbol linelength is in static storage at address 0x150a1c, length 4.
12656 Symbol p is a local variable in register $esi, length 4.
12657 Symbol p1 is a local variable in register $ebx, length 4.
12658 Symbol nline is a local variable in register $edx, length 4.
12659 Symbol repeat is a local variable at frame offset -8, length 4.
12663 This command is especially useful for determining what data to collect
12664 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
12667 @kindex info source
12669 Show information about the current source file---that is, the source file for
12670 the function containing the current point of execution:
12673 the name of the source file, and the directory containing it,
12675 the directory it was compiled in,
12677 its length, in lines,
12679 which programming language it is written in,
12681 whether the executable includes debugging information for that file, and
12682 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
12684 whether the debugging information includes information about
12685 preprocessor macros.
12689 @kindex info sources
12691 Print the names of all source files in your program for which there is
12692 debugging information, organized into two lists: files whose symbols
12693 have already been read, and files whose symbols will be read when needed.
12695 @kindex info functions
12696 @item info functions
12697 Print the names and data types of all defined functions.
12699 @item info functions @var{regexp}
12700 Print the names and data types of all defined functions
12701 whose names contain a match for regular expression @var{regexp}.
12702 Thus, @samp{info fun step} finds all functions whose names
12703 include @code{step}; @samp{info fun ^step} finds those whose names
12704 start with @code{step}. If a function name contains characters
12705 that conflict with the regular expression language (e.g.@:
12706 @samp{operator*()}), they may be quoted with a backslash.
12708 @kindex info variables
12709 @item info variables
12710 Print the names and data types of all variables that are declared
12711 outside of functions (i.e.@: excluding local variables).
12713 @item info variables @var{regexp}
12714 Print the names and data types of all variables (except for local
12715 variables) whose names contain a match for regular expression
12718 @kindex info classes
12719 @cindex Objective-C, classes and selectors
12721 @itemx info classes @var{regexp}
12722 Display all Objective-C classes in your program, or
12723 (with the @var{regexp} argument) all those matching a particular regular
12726 @kindex info selectors
12727 @item info selectors
12728 @itemx info selectors @var{regexp}
12729 Display all Objective-C selectors in your program, or
12730 (with the @var{regexp} argument) all those matching a particular regular
12734 This was never implemented.
12735 @kindex info methods
12737 @itemx info methods @var{regexp}
12738 The @code{info methods} command permits the user to examine all defined
12739 methods within C@t{++} program, or (with the @var{regexp} argument) a
12740 specific set of methods found in the various C@t{++} classes. Many
12741 C@t{++} classes provide a large number of methods. Thus, the output
12742 from the @code{ptype} command can be overwhelming and hard to use. The
12743 @code{info-methods} command filters the methods, printing only those
12744 which match the regular-expression @var{regexp}.
12747 @cindex reloading symbols
12748 Some systems allow individual object files that make up your program to
12749 be replaced without stopping and restarting your program. For example,
12750 in VxWorks you can simply recompile a defective object file and keep on
12751 running. If you are running on one of these systems, you can allow
12752 @value{GDBN} to reload the symbols for automatically relinked modules:
12755 @kindex set symbol-reloading
12756 @item set symbol-reloading on
12757 Replace symbol definitions for the corresponding source file when an
12758 object file with a particular name is seen again.
12760 @item set symbol-reloading off
12761 Do not replace symbol definitions when encountering object files of the
12762 same name more than once. This is the default state; if you are not
12763 running on a system that permits automatic relinking of modules, you
12764 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
12765 may discard symbols when linking large programs, that may contain
12766 several modules (from different directories or libraries) with the same
12769 @kindex show symbol-reloading
12770 @item show symbol-reloading
12771 Show the current @code{on} or @code{off} setting.
12774 @cindex opaque data types
12775 @kindex set opaque-type-resolution
12776 @item set opaque-type-resolution on
12777 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
12778 declared as a pointer to a @code{struct}, @code{class}, or
12779 @code{union}---for example, @code{struct MyType *}---that is used in one
12780 source file although the full declaration of @code{struct MyType} is in
12781 another source file. The default is on.
12783 A change in the setting of this subcommand will not take effect until
12784 the next time symbols for a file are loaded.
12786 @item set opaque-type-resolution off
12787 Tell @value{GDBN} not to resolve opaque types. In this case, the type
12788 is printed as follows:
12790 @{<no data fields>@}
12793 @kindex show opaque-type-resolution
12794 @item show opaque-type-resolution
12795 Show whether opaque types are resolved or not.
12797 @kindex maint print symbols
12798 @cindex symbol dump
12799 @kindex maint print psymbols
12800 @cindex partial symbol dump
12801 @item maint print symbols @var{filename}
12802 @itemx maint print psymbols @var{filename}
12803 @itemx maint print msymbols @var{filename}
12804 Write a dump of debugging symbol data into the file @var{filename}.
12805 These commands are used to debug the @value{GDBN} symbol-reading code. Only
12806 symbols with debugging data are included. If you use @samp{maint print
12807 symbols}, @value{GDBN} includes all the symbols for which it has already
12808 collected full details: that is, @var{filename} reflects symbols for
12809 only those files whose symbols @value{GDBN} has read. You can use the
12810 command @code{info sources} to find out which files these are. If you
12811 use @samp{maint print psymbols} instead, the dump shows information about
12812 symbols that @value{GDBN} only knows partially---that is, symbols defined in
12813 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
12814 @samp{maint print msymbols} dumps just the minimal symbol information
12815 required for each object file from which @value{GDBN} has read some symbols.
12816 @xref{Files, ,Commands to Specify Files}, for a discussion of how
12817 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
12819 @kindex maint info symtabs
12820 @kindex maint info psymtabs
12821 @cindex listing @value{GDBN}'s internal symbol tables
12822 @cindex symbol tables, listing @value{GDBN}'s internal
12823 @cindex full symbol tables, listing @value{GDBN}'s internal
12824 @cindex partial symbol tables, listing @value{GDBN}'s internal
12825 @item maint info symtabs @r{[} @var{regexp} @r{]}
12826 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
12828 List the @code{struct symtab} or @code{struct partial_symtab}
12829 structures whose names match @var{regexp}. If @var{regexp} is not
12830 given, list them all. The output includes expressions which you can
12831 copy into a @value{GDBN} debugging this one to examine a particular
12832 structure in more detail. For example:
12835 (@value{GDBP}) maint info psymtabs dwarf2read
12836 @{ objfile /home/gnu/build/gdb/gdb
12837 ((struct objfile *) 0x82e69d0)
12838 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
12839 ((struct partial_symtab *) 0x8474b10)
12842 text addresses 0x814d3c8 -- 0x8158074
12843 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
12844 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
12845 dependencies (none)
12848 (@value{GDBP}) maint info symtabs
12852 We see that there is one partial symbol table whose filename contains
12853 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
12854 and we see that @value{GDBN} has not read in any symtabs yet at all.
12855 If we set a breakpoint on a function, that will cause @value{GDBN} to
12856 read the symtab for the compilation unit containing that function:
12859 (@value{GDBP}) break dwarf2_psymtab_to_symtab
12860 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
12862 (@value{GDBP}) maint info symtabs
12863 @{ objfile /home/gnu/build/gdb/gdb
12864 ((struct objfile *) 0x82e69d0)
12865 @{ symtab /home/gnu/src/gdb/dwarf2read.c
12866 ((struct symtab *) 0x86c1f38)
12869 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
12870 linetable ((struct linetable *) 0x8370fa0)
12871 debugformat DWARF 2
12880 @chapter Altering Execution
12882 Once you think you have found an error in your program, you might want to
12883 find out for certain whether correcting the apparent error would lead to
12884 correct results in the rest of the run. You can find the answer by
12885 experiment, using the @value{GDBN} features for altering execution of the
12888 For example, you can store new values into variables or memory
12889 locations, give your program a signal, restart it at a different
12890 address, or even return prematurely from a function.
12893 * Assignment:: Assignment to variables
12894 * Jumping:: Continuing at a different address
12895 * Signaling:: Giving your program a signal
12896 * Returning:: Returning from a function
12897 * Calling:: Calling your program's functions
12898 * Patching:: Patching your program
12902 @section Assignment to Variables
12905 @cindex setting variables
12906 To alter the value of a variable, evaluate an assignment expression.
12907 @xref{Expressions, ,Expressions}. For example,
12914 stores the value 4 into the variable @code{x}, and then prints the
12915 value of the assignment expression (which is 4).
12916 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
12917 information on operators in supported languages.
12919 @kindex set variable
12920 @cindex variables, setting
12921 If you are not interested in seeing the value of the assignment, use the
12922 @code{set} command instead of the @code{print} command. @code{set} is
12923 really the same as @code{print} except that the expression's value is
12924 not printed and is not put in the value history (@pxref{Value History,
12925 ,Value History}). The expression is evaluated only for its effects.
12927 If the beginning of the argument string of the @code{set} command
12928 appears identical to a @code{set} subcommand, use the @code{set
12929 variable} command instead of just @code{set}. This command is identical
12930 to @code{set} except for its lack of subcommands. For example, if your
12931 program has a variable @code{width}, you get an error if you try to set
12932 a new value with just @samp{set width=13}, because @value{GDBN} has the
12933 command @code{set width}:
12936 (@value{GDBP}) whatis width
12938 (@value{GDBP}) p width
12940 (@value{GDBP}) set width=47
12941 Invalid syntax in expression.
12945 The invalid expression, of course, is @samp{=47}. In
12946 order to actually set the program's variable @code{width}, use
12949 (@value{GDBP}) set var width=47
12952 Because the @code{set} command has many subcommands that can conflict
12953 with the names of program variables, it is a good idea to use the
12954 @code{set variable} command instead of just @code{set}. For example, if
12955 your program has a variable @code{g}, you run into problems if you try
12956 to set a new value with just @samp{set g=4}, because @value{GDBN} has
12957 the command @code{set gnutarget}, abbreviated @code{set g}:
12961 (@value{GDBP}) whatis g
12965 (@value{GDBP}) set g=4
12969 The program being debugged has been started already.
12970 Start it from the beginning? (y or n) y
12971 Starting program: /home/smith/cc_progs/a.out
12972 "/home/smith/cc_progs/a.out": can't open to read symbols:
12973 Invalid bfd target.
12974 (@value{GDBP}) show g
12975 The current BFD target is "=4".
12980 The program variable @code{g} did not change, and you silently set the
12981 @code{gnutarget} to an invalid value. In order to set the variable
12985 (@value{GDBP}) set var g=4
12988 @value{GDBN} allows more implicit conversions in assignments than C; you can
12989 freely store an integer value into a pointer variable or vice versa,
12990 and you can convert any structure to any other structure that is the
12991 same length or shorter.
12992 @comment FIXME: how do structs align/pad in these conversions?
12993 @comment /doc@cygnus.com 18dec1990
12995 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
12996 construct to generate a value of specified type at a specified address
12997 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
12998 to memory location @code{0x83040} as an integer (which implies a certain size
12999 and representation in memory), and
13002 set @{int@}0x83040 = 4
13006 stores the value 4 into that memory location.
13009 @section Continuing at a Different Address
13011 Ordinarily, when you continue your program, you do so at the place where
13012 it stopped, with the @code{continue} command. You can instead continue at
13013 an address of your own choosing, with the following commands:
13017 @item jump @var{linespec}
13018 @itemx jump @var{location}
13019 Resume execution at line @var{linespec} or at address given by
13020 @var{location}. Execution stops again immediately if there is a
13021 breakpoint there. @xref{Specify Location}, for a description of the
13022 different forms of @var{linespec} and @var{location}. It is common
13023 practice to use the @code{tbreak} command in conjunction with
13024 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
13026 The @code{jump} command does not change the current stack frame, or
13027 the stack pointer, or the contents of any memory location or any
13028 register other than the program counter. If line @var{linespec} is in
13029 a different function from the one currently executing, the results may
13030 be bizarre if the two functions expect different patterns of arguments or
13031 of local variables. For this reason, the @code{jump} command requests
13032 confirmation if the specified line is not in the function currently
13033 executing. However, even bizarre results are predictable if you are
13034 well acquainted with the machine-language code of your program.
13037 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
13038 On many systems, you can get much the same effect as the @code{jump}
13039 command by storing a new value into the register @code{$pc}. The
13040 difference is that this does not start your program running; it only
13041 changes the address of where it @emph{will} run when you continue. For
13049 makes the next @code{continue} command or stepping command execute at
13050 address @code{0x485}, rather than at the address where your program stopped.
13051 @xref{Continuing and Stepping, ,Continuing and Stepping}.
13053 The most common occasion to use the @code{jump} command is to back
13054 up---perhaps with more breakpoints set---over a portion of a program
13055 that has already executed, in order to examine its execution in more
13060 @section Giving your Program a Signal
13061 @cindex deliver a signal to a program
13065 @item signal @var{signal}
13066 Resume execution where your program stopped, but immediately give it the
13067 signal @var{signal}. @var{signal} can be the name or the number of a
13068 signal. For example, on many systems @code{signal 2} and @code{signal
13069 SIGINT} are both ways of sending an interrupt signal.
13071 Alternatively, if @var{signal} is zero, continue execution without
13072 giving a signal. This is useful when your program stopped on account of
13073 a signal and would ordinary see the signal when resumed with the
13074 @code{continue} command; @samp{signal 0} causes it to resume without a
13077 @code{signal} does not repeat when you press @key{RET} a second time
13078 after executing the command.
13082 Invoking the @code{signal} command is not the same as invoking the
13083 @code{kill} utility from the shell. Sending a signal with @code{kill}
13084 causes @value{GDBN} to decide what to do with the signal depending on
13085 the signal handling tables (@pxref{Signals}). The @code{signal} command
13086 passes the signal directly to your program.
13090 @section Returning from a Function
13093 @cindex returning from a function
13096 @itemx return @var{expression}
13097 You can cancel execution of a function call with the @code{return}
13098 command. If you give an
13099 @var{expression} argument, its value is used as the function's return
13103 When you use @code{return}, @value{GDBN} discards the selected stack frame
13104 (and all frames within it). You can think of this as making the
13105 discarded frame return prematurely. If you wish to specify a value to
13106 be returned, give that value as the argument to @code{return}.
13108 This pops the selected stack frame (@pxref{Selection, ,Selecting a
13109 Frame}), and any other frames inside of it, leaving its caller as the
13110 innermost remaining frame. That frame becomes selected. The
13111 specified value is stored in the registers used for returning values
13114 The @code{return} command does not resume execution; it leaves the
13115 program stopped in the state that would exist if the function had just
13116 returned. In contrast, the @code{finish} command (@pxref{Continuing
13117 and Stepping, ,Continuing and Stepping}) resumes execution until the
13118 selected stack frame returns naturally.
13120 @value{GDBN} needs to know how the @var{expression} argument should be set for
13121 the inferior. The concrete registers assignment depends on the OS ABI and the
13122 type being returned by the selected stack frame. For example it is common for
13123 OS ABI to return floating point values in FPU registers while integer values in
13124 CPU registers. Still some ABIs return even floating point values in CPU
13125 registers. Larger integer widths (such as @code{long long int}) also have
13126 specific placement rules. @value{GDBN} already knows the OS ABI from its
13127 current target so it needs to find out also the type being returned to make the
13128 assignment into the right register(s).
13130 Normally, the selected stack frame has debug info. @value{GDBN} will always
13131 use the debug info instead of the implicit type of @var{expression} when the
13132 debug info is available. For example, if you type @kbd{return -1}, and the
13133 function in the current stack frame is declared to return a @code{long long
13134 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
13135 into a @code{long long int}:
13138 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
13140 (@value{GDBP}) return -1
13141 Make func return now? (y or n) y
13142 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
13143 43 printf ("result=%lld\n", func ());
13147 However, if the selected stack frame does not have a debug info, e.g., if the
13148 function was compiled without debug info, @value{GDBN} has to find out the type
13149 to return from user. Specifying a different type by mistake may set the value
13150 in different inferior registers than the caller code expects. For example,
13151 typing @kbd{return -1} with its implicit type @code{int} would set only a part
13152 of a @code{long long int} result for a debug info less function (on 32-bit
13153 architectures). Therefore the user is required to specify the return type by
13154 an appropriate cast explicitly:
13157 Breakpoint 2, 0x0040050b in func ()
13158 (@value{GDBP}) return -1
13159 Return value type not available for selected stack frame.
13160 Please use an explicit cast of the value to return.
13161 (@value{GDBP}) return (long long int) -1
13162 Make selected stack frame return now? (y or n) y
13163 #0 0x00400526 in main ()
13168 @section Calling Program Functions
13171 @cindex calling functions
13172 @cindex inferior functions, calling
13173 @item print @var{expr}
13174 Evaluate the expression @var{expr} and display the resulting value.
13175 @var{expr} may include calls to functions in the program being
13179 @item call @var{expr}
13180 Evaluate the expression @var{expr} without displaying @code{void}
13183 You can use this variant of the @code{print} command if you want to
13184 execute a function from your program that does not return anything
13185 (a.k.a.@: @dfn{a void function}), but without cluttering the output
13186 with @code{void} returned values that @value{GDBN} will otherwise
13187 print. If the result is not void, it is printed and saved in the
13191 It is possible for the function you call via the @code{print} or
13192 @code{call} command to generate a signal (e.g., if there's a bug in
13193 the function, or if you passed it incorrect arguments). What happens
13194 in that case is controlled by the @code{set unwindonsignal} command.
13196 Similarly, with a C@t{++} program it is possible for the function you
13197 call via the @code{print} or @code{call} command to generate an
13198 exception that is not handled due to the constraints of the dummy
13199 frame. In this case, any exception that is raised in the frame, but has
13200 an out-of-frame exception handler will not be found. GDB builds a
13201 dummy-frame for the inferior function call, and the unwinder cannot
13202 seek for exception handlers outside of this dummy-frame. What happens
13203 in that case is controlled by the
13204 @code{set unwind-on-terminating-exception} command.
13207 @item set unwindonsignal
13208 @kindex set unwindonsignal
13209 @cindex unwind stack in called functions
13210 @cindex call dummy stack unwinding
13211 Set unwinding of the stack if a signal is received while in a function
13212 that @value{GDBN} called in the program being debugged. If set to on,
13213 @value{GDBN} unwinds the stack it created for the call and restores
13214 the context to what it was before the call. If set to off (the
13215 default), @value{GDBN} stops in the frame where the signal was
13218 @item show unwindonsignal
13219 @kindex show unwindonsignal
13220 Show the current setting of stack unwinding in the functions called by
13223 @item set unwind-on-terminating-exception
13224 @kindex set unwind-on-terminating-exception
13225 @cindex unwind stack in called functions with unhandled exceptions
13226 @cindex call dummy stack unwinding on unhandled exception.
13227 Set unwinding of the stack if a C@t{++} exception is raised, but left
13228 unhandled while in a function that @value{GDBN} called in the program being
13229 debugged. If set to on (the default), @value{GDBN} unwinds the stack
13230 it created for the call and restores the context to what it was before
13231 the call. If set to off, @value{GDBN} the exception is delivered to
13232 the default C@t{++} exception handler and the inferior terminated.
13234 @item show unwind-on-terminating-exception
13235 @kindex show unwind-on-terminating-exception
13236 Show the current setting of stack unwinding in the functions called by
13241 @cindex weak alias functions
13242 Sometimes, a function you wish to call is actually a @dfn{weak alias}
13243 for another function. In such case, @value{GDBN} might not pick up
13244 the type information, including the types of the function arguments,
13245 which causes @value{GDBN} to call the inferior function incorrectly.
13246 As a result, the called function will function erroneously and may
13247 even crash. A solution to that is to use the name of the aliased
13251 @section Patching Programs
13253 @cindex patching binaries
13254 @cindex writing into executables
13255 @cindex writing into corefiles
13257 By default, @value{GDBN} opens the file containing your program's
13258 executable code (or the corefile) read-only. This prevents accidental
13259 alterations to machine code; but it also prevents you from intentionally
13260 patching your program's binary.
13262 If you'd like to be able to patch the binary, you can specify that
13263 explicitly with the @code{set write} command. For example, you might
13264 want to turn on internal debugging flags, or even to make emergency
13270 @itemx set write off
13271 If you specify @samp{set write on}, @value{GDBN} opens executable and
13272 core files for both reading and writing; if you specify @kbd{set write
13273 off} (the default), @value{GDBN} opens them read-only.
13275 If you have already loaded a file, you must load it again (using the
13276 @code{exec-file} or @code{core-file} command) after changing @code{set
13277 write}, for your new setting to take effect.
13281 Display whether executable files and core files are opened for writing
13282 as well as reading.
13286 @chapter @value{GDBN} Files
13288 @value{GDBN} needs to know the file name of the program to be debugged,
13289 both in order to read its symbol table and in order to start your
13290 program. To debug a core dump of a previous run, you must also tell
13291 @value{GDBN} the name of the core dump file.
13294 * Files:: Commands to specify files
13295 * Separate Debug Files:: Debugging information in separate files
13296 * Symbol Errors:: Errors reading symbol files
13297 * Data Files:: GDB data files
13301 @section Commands to Specify Files
13303 @cindex symbol table
13304 @cindex core dump file
13306 You may want to specify executable and core dump file names. The usual
13307 way to do this is at start-up time, using the arguments to
13308 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
13309 Out of @value{GDBN}}).
13311 Occasionally it is necessary to change to a different file during a
13312 @value{GDBN} session. Or you may run @value{GDBN} and forget to
13313 specify a file you want to use. Or you are debugging a remote target
13314 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
13315 Program}). In these situations the @value{GDBN} commands to specify
13316 new files are useful.
13319 @cindex executable file
13321 @item file @var{filename}
13322 Use @var{filename} as the program to be debugged. It is read for its
13323 symbols and for the contents of pure memory. It is also the program
13324 executed when you use the @code{run} command. If you do not specify a
13325 directory and the file is not found in the @value{GDBN} working directory,
13326 @value{GDBN} uses the environment variable @code{PATH} as a list of
13327 directories to search, just as the shell does when looking for a program
13328 to run. You can change the value of this variable, for both @value{GDBN}
13329 and your program, using the @code{path} command.
13331 @cindex unlinked object files
13332 @cindex patching object files
13333 You can load unlinked object @file{.o} files into @value{GDBN} using
13334 the @code{file} command. You will not be able to ``run'' an object
13335 file, but you can disassemble functions and inspect variables. Also,
13336 if the underlying BFD functionality supports it, you could use
13337 @kbd{gdb -write} to patch object files using this technique. Note
13338 that @value{GDBN} can neither interpret nor modify relocations in this
13339 case, so branches and some initialized variables will appear to go to
13340 the wrong place. But this feature is still handy from time to time.
13343 @code{file} with no argument makes @value{GDBN} discard any information it
13344 has on both executable file and the symbol table.
13347 @item exec-file @r{[} @var{filename} @r{]}
13348 Specify that the program to be run (but not the symbol table) is found
13349 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
13350 if necessary to locate your program. Omitting @var{filename} means to
13351 discard information on the executable file.
13353 @kindex symbol-file
13354 @item symbol-file @r{[} @var{filename} @r{]}
13355 Read symbol table information from file @var{filename}. @code{PATH} is
13356 searched when necessary. Use the @code{file} command to get both symbol
13357 table and program to run from the same file.
13359 @code{symbol-file} with no argument clears out @value{GDBN} information on your
13360 program's symbol table.
13362 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
13363 some breakpoints and auto-display expressions. This is because they may
13364 contain pointers to the internal data recording symbols and data types,
13365 which are part of the old symbol table data being discarded inside
13368 @code{symbol-file} does not repeat if you press @key{RET} again after
13371 When @value{GDBN} is configured for a particular environment, it
13372 understands debugging information in whatever format is the standard
13373 generated for that environment; you may use either a @sc{gnu} compiler, or
13374 other compilers that adhere to the local conventions.
13375 Best results are usually obtained from @sc{gnu} compilers; for example,
13376 using @code{@value{NGCC}} you can generate debugging information for
13379 For most kinds of object files, with the exception of old SVR3 systems
13380 using COFF, the @code{symbol-file} command does not normally read the
13381 symbol table in full right away. Instead, it scans the symbol table
13382 quickly to find which source files and which symbols are present. The
13383 details are read later, one source file at a time, as they are needed.
13385 The purpose of this two-stage reading strategy is to make @value{GDBN}
13386 start up faster. For the most part, it is invisible except for
13387 occasional pauses while the symbol table details for a particular source
13388 file are being read. (The @code{set verbose} command can turn these
13389 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
13390 Warnings and Messages}.)
13392 We have not implemented the two-stage strategy for COFF yet. When the
13393 symbol table is stored in COFF format, @code{symbol-file} reads the
13394 symbol table data in full right away. Note that ``stabs-in-COFF''
13395 still does the two-stage strategy, since the debug info is actually
13399 @cindex reading symbols immediately
13400 @cindex symbols, reading immediately
13401 @item symbol-file @var{filename} @r{[} -readnow @r{]}
13402 @itemx file @var{filename} @r{[} -readnow @r{]}
13403 You can override the @value{GDBN} two-stage strategy for reading symbol
13404 tables by using the @samp{-readnow} option with any of the commands that
13405 load symbol table information, if you want to be sure @value{GDBN} has the
13406 entire symbol table available.
13408 @c FIXME: for now no mention of directories, since this seems to be in
13409 @c flux. 13mar1992 status is that in theory GDB would look either in
13410 @c current dir or in same dir as myprog; but issues like competing
13411 @c GDB's, or clutter in system dirs, mean that in practice right now
13412 @c only current dir is used. FFish says maybe a special GDB hierarchy
13413 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
13417 @item core-file @r{[}@var{filename}@r{]}
13419 Specify the whereabouts of a core dump file to be used as the ``contents
13420 of memory''. Traditionally, core files contain only some parts of the
13421 address space of the process that generated them; @value{GDBN} can access the
13422 executable file itself for other parts.
13424 @code{core-file} with no argument specifies that no core file is
13427 Note that the core file is ignored when your program is actually running
13428 under @value{GDBN}. So, if you have been running your program and you
13429 wish to debug a core file instead, you must kill the subprocess in which
13430 the program is running. To do this, use the @code{kill} command
13431 (@pxref{Kill Process, ,Killing the Child Process}).
13433 @kindex add-symbol-file
13434 @cindex dynamic linking
13435 @item add-symbol-file @var{filename} @var{address}
13436 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
13437 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
13438 The @code{add-symbol-file} command reads additional symbol table
13439 information from the file @var{filename}. You would use this command
13440 when @var{filename} has been dynamically loaded (by some other means)
13441 into the program that is running. @var{address} should be the memory
13442 address at which the file has been loaded; @value{GDBN} cannot figure
13443 this out for itself. You can additionally specify an arbitrary number
13444 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
13445 section name and base address for that section. You can specify any
13446 @var{address} as an expression.
13448 The symbol table of the file @var{filename} is added to the symbol table
13449 originally read with the @code{symbol-file} command. You can use the
13450 @code{add-symbol-file} command any number of times; the new symbol data
13451 thus read keeps adding to the old. To discard all old symbol data
13452 instead, use the @code{symbol-file} command without any arguments.
13454 @cindex relocatable object files, reading symbols from
13455 @cindex object files, relocatable, reading symbols from
13456 @cindex reading symbols from relocatable object files
13457 @cindex symbols, reading from relocatable object files
13458 @cindex @file{.o} files, reading symbols from
13459 Although @var{filename} is typically a shared library file, an
13460 executable file, or some other object file which has been fully
13461 relocated for loading into a process, you can also load symbolic
13462 information from relocatable @file{.o} files, as long as:
13466 the file's symbolic information refers only to linker symbols defined in
13467 that file, not to symbols defined by other object files,
13469 every section the file's symbolic information refers to has actually
13470 been loaded into the inferior, as it appears in the file, and
13472 you can determine the address at which every section was loaded, and
13473 provide these to the @code{add-symbol-file} command.
13477 Some embedded operating systems, like Sun Chorus and VxWorks, can load
13478 relocatable files into an already running program; such systems
13479 typically make the requirements above easy to meet. However, it's
13480 important to recognize that many native systems use complex link
13481 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
13482 assembly, for example) that make the requirements difficult to meet. In
13483 general, one cannot assume that using @code{add-symbol-file} to read a
13484 relocatable object file's symbolic information will have the same effect
13485 as linking the relocatable object file into the program in the normal
13488 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
13490 @kindex add-symbol-file-from-memory
13491 @cindex @code{syscall DSO}
13492 @cindex load symbols from memory
13493 @item add-symbol-file-from-memory @var{address}
13494 Load symbols from the given @var{address} in a dynamically loaded
13495 object file whose image is mapped directly into the inferior's memory.
13496 For example, the Linux kernel maps a @code{syscall DSO} into each
13497 process's address space; this DSO provides kernel-specific code for
13498 some system calls. The argument can be any expression whose
13499 evaluation yields the address of the file's shared object file header.
13500 For this command to work, you must have used @code{symbol-file} or
13501 @code{exec-file} commands in advance.
13503 @kindex add-shared-symbol-files
13505 @item add-shared-symbol-files @var{library-file}
13506 @itemx assf @var{library-file}
13507 The @code{add-shared-symbol-files} command can currently be used only
13508 in the Cygwin build of @value{GDBN} on MS-Windows OS, where it is an
13509 alias for the @code{dll-symbols} command (@pxref{Cygwin Native}).
13510 @value{GDBN} automatically looks for shared libraries, however if
13511 @value{GDBN} does not find yours, you can invoke
13512 @code{add-shared-symbol-files}. It takes one argument: the shared
13513 library's file name. @code{assf} is a shorthand alias for
13514 @code{add-shared-symbol-files}.
13517 @item section @var{section} @var{addr}
13518 The @code{section} command changes the base address of the named
13519 @var{section} of the exec file to @var{addr}. This can be used if the
13520 exec file does not contain section addresses, (such as in the
13521 @code{a.out} format), or when the addresses specified in the file
13522 itself are wrong. Each section must be changed separately. The
13523 @code{info files} command, described below, lists all the sections and
13527 @kindex info target
13530 @code{info files} and @code{info target} are synonymous; both print the
13531 current target (@pxref{Targets, ,Specifying a Debugging Target}),
13532 including the names of the executable and core dump files currently in
13533 use by @value{GDBN}, and the files from which symbols were loaded. The
13534 command @code{help target} lists all possible targets rather than
13537 @kindex maint info sections
13538 @item maint info sections
13539 Another command that can give you extra information about program sections
13540 is @code{maint info sections}. In addition to the section information
13541 displayed by @code{info files}, this command displays the flags and file
13542 offset of each section in the executable and core dump files. In addition,
13543 @code{maint info sections} provides the following command options (which
13544 may be arbitrarily combined):
13548 Display sections for all loaded object files, including shared libraries.
13549 @item @var{sections}
13550 Display info only for named @var{sections}.
13551 @item @var{section-flags}
13552 Display info only for sections for which @var{section-flags} are true.
13553 The section flags that @value{GDBN} currently knows about are:
13556 Section will have space allocated in the process when loaded.
13557 Set for all sections except those containing debug information.
13559 Section will be loaded from the file into the child process memory.
13560 Set for pre-initialized code and data, clear for @code{.bss} sections.
13562 Section needs to be relocated before loading.
13564 Section cannot be modified by the child process.
13566 Section contains executable code only.
13568 Section contains data only (no executable code).
13570 Section will reside in ROM.
13572 Section contains data for constructor/destructor lists.
13574 Section is not empty.
13576 An instruction to the linker to not output the section.
13577 @item COFF_SHARED_LIBRARY
13578 A notification to the linker that the section contains
13579 COFF shared library information.
13581 Section contains common symbols.
13584 @kindex set trust-readonly-sections
13585 @cindex read-only sections
13586 @item set trust-readonly-sections on
13587 Tell @value{GDBN} that readonly sections in your object file
13588 really are read-only (i.e.@: that their contents will not change).
13589 In that case, @value{GDBN} can fetch values from these sections
13590 out of the object file, rather than from the target program.
13591 For some targets (notably embedded ones), this can be a significant
13592 enhancement to debugging performance.
13594 The default is off.
13596 @item set trust-readonly-sections off
13597 Tell @value{GDBN} not to trust readonly sections. This means that
13598 the contents of the section might change while the program is running,
13599 and must therefore be fetched from the target when needed.
13601 @item show trust-readonly-sections
13602 Show the current setting of trusting readonly sections.
13605 All file-specifying commands allow both absolute and relative file names
13606 as arguments. @value{GDBN} always converts the file name to an absolute file
13607 name and remembers it that way.
13609 @cindex shared libraries
13610 @anchor{Shared Libraries}
13611 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix,
13612 and IBM RS/6000 AIX shared libraries.
13614 On MS-Windows @value{GDBN} must be linked with the Expat library to support
13615 shared libraries. @xref{Expat}.
13617 @value{GDBN} automatically loads symbol definitions from shared libraries
13618 when you use the @code{run} command, or when you examine a core file.
13619 (Before you issue the @code{run} command, @value{GDBN} does not understand
13620 references to a function in a shared library, however---unless you are
13621 debugging a core file).
13623 On HP-UX, if the program loads a library explicitly, @value{GDBN}
13624 automatically loads the symbols at the time of the @code{shl_load} call.
13626 @c FIXME: some @value{GDBN} release may permit some refs to undef
13627 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
13628 @c FIXME...lib; check this from time to time when updating manual
13630 There are times, however, when you may wish to not automatically load
13631 symbol definitions from shared libraries, such as when they are
13632 particularly large or there are many of them.
13634 To control the automatic loading of shared library symbols, use the
13638 @kindex set auto-solib-add
13639 @item set auto-solib-add @var{mode}
13640 If @var{mode} is @code{on}, symbols from all shared object libraries
13641 will be loaded automatically when the inferior begins execution, you
13642 attach to an independently started inferior, or when the dynamic linker
13643 informs @value{GDBN} that a new library has been loaded. If @var{mode}
13644 is @code{off}, symbols must be loaded manually, using the
13645 @code{sharedlibrary} command. The default value is @code{on}.
13647 @cindex memory used for symbol tables
13648 If your program uses lots of shared libraries with debug info that
13649 takes large amounts of memory, you can decrease the @value{GDBN}
13650 memory footprint by preventing it from automatically loading the
13651 symbols from shared libraries. To that end, type @kbd{set
13652 auto-solib-add off} before running the inferior, then load each
13653 library whose debug symbols you do need with @kbd{sharedlibrary
13654 @var{regexp}}, where @var{regexp} is a regular expression that matches
13655 the libraries whose symbols you want to be loaded.
13657 @kindex show auto-solib-add
13658 @item show auto-solib-add
13659 Display the current autoloading mode.
13662 @cindex load shared library
13663 To explicitly load shared library symbols, use the @code{sharedlibrary}
13667 @kindex info sharedlibrary
13669 @item info share @var{regex}
13670 @itemx info sharedlibrary @var{regex}
13671 Print the names of the shared libraries which are currently loaded
13672 that match @var{regex}. If @var{regex} is omitted then print
13673 all shared libraries that are loaded.
13675 @kindex sharedlibrary
13677 @item sharedlibrary @var{regex}
13678 @itemx share @var{regex}
13679 Load shared object library symbols for files matching a
13680 Unix regular expression.
13681 As with files loaded automatically, it only loads shared libraries
13682 required by your program for a core file or after typing @code{run}. If
13683 @var{regex} is omitted all shared libraries required by your program are
13686 @item nosharedlibrary
13687 @kindex nosharedlibrary
13688 @cindex unload symbols from shared libraries
13689 Unload all shared object library symbols. This discards all symbols
13690 that have been loaded from all shared libraries. Symbols from shared
13691 libraries that were loaded by explicit user requests are not
13695 Sometimes you may wish that @value{GDBN} stops and gives you control
13696 when any of shared library events happen. Use the @code{set
13697 stop-on-solib-events} command for this:
13700 @item set stop-on-solib-events
13701 @kindex set stop-on-solib-events
13702 This command controls whether @value{GDBN} should give you control
13703 when the dynamic linker notifies it about some shared library event.
13704 The most common event of interest is loading or unloading of a new
13707 @item show stop-on-solib-events
13708 @kindex show stop-on-solib-events
13709 Show whether @value{GDBN} stops and gives you control when shared
13710 library events happen.
13713 Shared libraries are also supported in many cross or remote debugging
13714 configurations. @value{GDBN} needs to have access to the target's libraries;
13715 this can be accomplished either by providing copies of the libraries
13716 on the host system, or by asking @value{GDBN} to automatically retrieve the
13717 libraries from the target. If copies of the target libraries are
13718 provided, they need to be the same as the target libraries, although the
13719 copies on the target can be stripped as long as the copies on the host are
13722 @cindex where to look for shared libraries
13723 For remote debugging, you need to tell @value{GDBN} where the target
13724 libraries are, so that it can load the correct copies---otherwise, it
13725 may try to load the host's libraries. @value{GDBN} has two variables
13726 to specify the search directories for target libraries.
13729 @cindex prefix for shared library file names
13730 @cindex system root, alternate
13731 @kindex set solib-absolute-prefix
13732 @kindex set sysroot
13733 @item set sysroot @var{path}
13734 Use @var{path} as the system root for the program being debugged. Any
13735 absolute shared library paths will be prefixed with @var{path}; many
13736 runtime loaders store the absolute paths to the shared library in the
13737 target program's memory. If you use @code{set sysroot} to find shared
13738 libraries, they need to be laid out in the same way that they are on
13739 the target, with e.g.@: a @file{/lib} and @file{/usr/lib} hierarchy
13742 If @var{path} starts with the sequence @file{remote:}, @value{GDBN} will
13743 retrieve the target libraries from the remote system. This is only
13744 supported when using a remote target that supports the @code{remote get}
13745 command (@pxref{File Transfer,,Sending files to a remote system}).
13746 The part of @var{path} following the initial @file{remote:}
13747 (if present) is used as system root prefix on the remote file system.
13748 @footnote{If you want to specify a local system root using a directory
13749 that happens to be named @file{remote:}, you need to use some equivalent
13750 variant of the name like @file{./remote:}.}
13752 The @code{set solib-absolute-prefix} command is an alias for @code{set
13755 @cindex default system root
13756 @cindex @samp{--with-sysroot}
13757 You can set the default system root by using the configure-time
13758 @samp{--with-sysroot} option. If the system root is inside
13759 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
13760 @samp{--exec-prefix}), then the default system root will be updated
13761 automatically if the installed @value{GDBN} is moved to a new
13764 @kindex show sysroot
13766 Display the current shared library prefix.
13768 @kindex set solib-search-path
13769 @item set solib-search-path @var{path}
13770 If this variable is set, @var{path} is a colon-separated list of
13771 directories to search for shared libraries. @samp{solib-search-path}
13772 is used after @samp{sysroot} fails to locate the library, or if the
13773 path to the library is relative instead of absolute. If you want to
13774 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
13775 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
13776 finding your host's libraries. @samp{sysroot} is preferred; setting
13777 it to a nonexistent directory may interfere with automatic loading
13778 of shared library symbols.
13780 @kindex show solib-search-path
13781 @item show solib-search-path
13782 Display the current shared library search path.
13786 @node Separate Debug Files
13787 @section Debugging Information in Separate Files
13788 @cindex separate debugging information files
13789 @cindex debugging information in separate files
13790 @cindex @file{.debug} subdirectories
13791 @cindex debugging information directory, global
13792 @cindex global debugging information directory
13793 @cindex build ID, and separate debugging files
13794 @cindex @file{.build-id} directory
13796 @value{GDBN} allows you to put a program's debugging information in a
13797 file separate from the executable itself, in a way that allows
13798 @value{GDBN} to find and load the debugging information automatically.
13799 Since debugging information can be very large---sometimes larger
13800 than the executable code itself---some systems distribute debugging
13801 information for their executables in separate files, which users can
13802 install only when they need to debug a problem.
13804 @value{GDBN} supports two ways of specifying the separate debug info
13809 The executable contains a @dfn{debug link} that specifies the name of
13810 the separate debug info file. The separate debug file's name is
13811 usually @file{@var{executable}.debug}, where @var{executable} is the
13812 name of the corresponding executable file without leading directories
13813 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
13814 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
13815 checksum for the debug file, which @value{GDBN} uses to validate that
13816 the executable and the debug file came from the same build.
13819 The executable contains a @dfn{build ID}, a unique bit string that is
13820 also present in the corresponding debug info file. (This is supported
13821 only on some operating systems, notably those which use the ELF format
13822 for binary files and the @sc{gnu} Binutils.) For more details about
13823 this feature, see the description of the @option{--build-id}
13824 command-line option in @ref{Options, , Command Line Options, ld.info,
13825 The GNU Linker}. The debug info file's name is not specified
13826 explicitly by the build ID, but can be computed from the build ID, see
13830 Depending on the way the debug info file is specified, @value{GDBN}
13831 uses two different methods of looking for the debug file:
13835 For the ``debug link'' method, @value{GDBN} looks up the named file in
13836 the directory of the executable file, then in a subdirectory of that
13837 directory named @file{.debug}, and finally under the global debug
13838 directory, in a subdirectory whose name is identical to the leading
13839 directories of the executable's absolute file name.
13842 For the ``build ID'' method, @value{GDBN} looks in the
13843 @file{.build-id} subdirectory of the global debug directory for a file
13844 named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
13845 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
13846 are the rest of the bit string. (Real build ID strings are 32 or more
13847 hex characters, not 10.)
13850 So, for example, suppose you ask @value{GDBN} to debug
13851 @file{/usr/bin/ls}, which has a debug link that specifies the
13852 file @file{ls.debug}, and a build ID whose value in hex is
13853 @code{abcdef1234}. If the global debug directory is
13854 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
13855 debug information files, in the indicated order:
13859 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
13861 @file{/usr/bin/ls.debug}
13863 @file{/usr/bin/.debug/ls.debug}
13865 @file{/usr/lib/debug/usr/bin/ls.debug}.
13868 You can set the global debugging info directory's name, and view the
13869 name @value{GDBN} is currently using.
13873 @kindex set debug-file-directory
13874 @item set debug-file-directory @var{directory}
13875 Set the directory which @value{GDBN} searches for separate debugging
13876 information files to @var{directory}.
13878 @kindex show debug-file-directory
13879 @item show debug-file-directory
13880 Show the directory @value{GDBN} searches for separate debugging
13885 @cindex @code{.gnu_debuglink} sections
13886 @cindex debug link sections
13887 A debug link is a special section of the executable file named
13888 @code{.gnu_debuglink}. The section must contain:
13892 A filename, with any leading directory components removed, followed by
13895 zero to three bytes of padding, as needed to reach the next four-byte
13896 boundary within the section, and
13898 a four-byte CRC checksum, stored in the same endianness used for the
13899 executable file itself. The checksum is computed on the debugging
13900 information file's full contents by the function given below, passing
13901 zero as the @var{crc} argument.
13904 Any executable file format can carry a debug link, as long as it can
13905 contain a section named @code{.gnu_debuglink} with the contents
13908 @cindex @code{.note.gnu.build-id} sections
13909 @cindex build ID sections
13910 The build ID is a special section in the executable file (and in other
13911 ELF binary files that @value{GDBN} may consider). This section is
13912 often named @code{.note.gnu.build-id}, but that name is not mandatory.
13913 It contains unique identification for the built files---the ID remains
13914 the same across multiple builds of the same build tree. The default
13915 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
13916 content for the build ID string. The same section with an identical
13917 value is present in the original built binary with symbols, in its
13918 stripped variant, and in the separate debugging information file.
13920 The debugging information file itself should be an ordinary
13921 executable, containing a full set of linker symbols, sections, and
13922 debugging information. The sections of the debugging information file
13923 should have the same names, addresses, and sizes as the original file,
13924 but they need not contain any data---much like a @code{.bss} section
13925 in an ordinary executable.
13927 The @sc{gnu} binary utilities (Binutils) package includes the
13928 @samp{objcopy} utility that can produce
13929 the separated executable / debugging information file pairs using the
13930 following commands:
13933 @kbd{objcopy --only-keep-debug foo foo.debug}
13938 These commands remove the debugging
13939 information from the executable file @file{foo} and place it in the file
13940 @file{foo.debug}. You can use the first, second or both methods to link the
13945 The debug link method needs the following additional command to also leave
13946 behind a debug link in @file{foo}:
13949 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
13952 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
13953 a version of the @code{strip} command such that the command @kbd{strip foo -f
13954 foo.debug} has the same functionality as the two @code{objcopy} commands and
13955 the @code{ln -s} command above, together.
13958 Build ID gets embedded into the main executable using @code{ld --build-id} or
13959 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
13960 compatibility fixes for debug files separation are present in @sc{gnu} binary
13961 utilities (Binutils) package since version 2.18.
13966 @cindex CRC algorithm definition
13967 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
13968 IEEE 802.3 using the polynomial:
13970 @c TexInfo requires naked braces for multi-digit exponents for Tex
13971 @c output, but this causes HTML output to barf. HTML has to be set using
13972 @c raw commands. So we end up having to specify this equation in 2
13977 <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup>
13978 + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1
13984 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
13985 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
13989 The function is computed byte at a time, taking the least
13990 significant bit of each byte first. The initial pattern
13991 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
13992 the final result is inverted to ensure trailing zeros also affect the
13995 @emph{Note:} This is the same CRC polynomial as used in handling the
13996 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{Remote Protocol,
13997 , @value{GDBN} Remote Serial Protocol}). However in the
13998 case of the Remote Serial Protocol, the CRC is computed @emph{most}
13999 significant bit first, and the result is not inverted, so trailing
14000 zeros have no effect on the CRC value.
14002 To complete the description, we show below the code of the function
14003 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
14004 initially supplied @code{crc} argument means that an initial call to
14005 this function passing in zero will start computing the CRC using
14008 @kindex gnu_debuglink_crc32
14011 gnu_debuglink_crc32 (unsigned long crc,
14012 unsigned char *buf, size_t len)
14014 static const unsigned long crc32_table[256] =
14016 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
14017 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
14018 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
14019 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
14020 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
14021 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
14022 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
14023 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
14024 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
14025 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
14026 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
14027 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
14028 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
14029 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
14030 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
14031 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
14032 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
14033 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
14034 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
14035 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
14036 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
14037 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
14038 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
14039 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
14040 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
14041 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
14042 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
14043 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
14044 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
14045 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
14046 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
14047 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
14048 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
14049 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
14050 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
14051 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
14052 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
14053 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
14054 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
14055 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
14056 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
14057 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
14058 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
14059 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
14060 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
14061 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
14062 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
14063 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
14064 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
14065 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
14066 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
14069 unsigned char *end;
14071 crc = ~crc & 0xffffffff;
14072 for (end = buf + len; buf < end; ++buf)
14073 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
14074 return ~crc & 0xffffffff;
14079 This computation does not apply to the ``build ID'' method.
14082 @node Symbol Errors
14083 @section Errors Reading Symbol Files
14085 While reading a symbol file, @value{GDBN} occasionally encounters problems,
14086 such as symbol types it does not recognize, or known bugs in compiler
14087 output. By default, @value{GDBN} does not notify you of such problems, since
14088 they are relatively common and primarily of interest to people
14089 debugging compilers. If you are interested in seeing information
14090 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
14091 only one message about each such type of problem, no matter how many
14092 times the problem occurs; or you can ask @value{GDBN} to print more messages,
14093 to see how many times the problems occur, with the @code{set
14094 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
14097 The messages currently printed, and their meanings, include:
14100 @item inner block not inside outer block in @var{symbol}
14102 The symbol information shows where symbol scopes begin and end
14103 (such as at the start of a function or a block of statements). This
14104 error indicates that an inner scope block is not fully contained
14105 in its outer scope blocks.
14107 @value{GDBN} circumvents the problem by treating the inner block as if it had
14108 the same scope as the outer block. In the error message, @var{symbol}
14109 may be shown as ``@code{(don't know)}'' if the outer block is not a
14112 @item block at @var{address} out of order
14114 The symbol information for symbol scope blocks should occur in
14115 order of increasing addresses. This error indicates that it does not
14118 @value{GDBN} does not circumvent this problem, and has trouble
14119 locating symbols in the source file whose symbols it is reading. (You
14120 can often determine what source file is affected by specifying
14121 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
14124 @item bad block start address patched
14126 The symbol information for a symbol scope block has a start address
14127 smaller than the address of the preceding source line. This is known
14128 to occur in the SunOS 4.1.1 (and earlier) C compiler.
14130 @value{GDBN} circumvents the problem by treating the symbol scope block as
14131 starting on the previous source line.
14133 @item bad string table offset in symbol @var{n}
14136 Symbol number @var{n} contains a pointer into the string table which is
14137 larger than the size of the string table.
14139 @value{GDBN} circumvents the problem by considering the symbol to have the
14140 name @code{foo}, which may cause other problems if many symbols end up
14143 @item unknown symbol type @code{0x@var{nn}}
14145 The symbol information contains new data types that @value{GDBN} does
14146 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
14147 uncomprehended information, in hexadecimal.
14149 @value{GDBN} circumvents the error by ignoring this symbol information.
14150 This usually allows you to debug your program, though certain symbols
14151 are not accessible. If you encounter such a problem and feel like
14152 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
14153 on @code{complain}, then go up to the function @code{read_dbx_symtab}
14154 and examine @code{*bufp} to see the symbol.
14156 @item stub type has NULL name
14158 @value{GDBN} could not find the full definition for a struct or class.
14160 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
14161 The symbol information for a C@t{++} member function is missing some
14162 information that recent versions of the compiler should have output for
14165 @item info mismatch between compiler and debugger
14167 @value{GDBN} could not parse a type specification output by the compiler.
14172 @section GDB Data Files
14174 @cindex prefix for data files
14175 @value{GDBN} will sometimes read an auxiliary data file. These files
14176 are kept in a directory known as the @dfn{data directory}.
14178 You can set the data directory's name, and view the name @value{GDBN}
14179 is currently using.
14182 @kindex set data-directory
14183 @item set data-directory @var{directory}
14184 Set the directory which @value{GDBN} searches for auxiliary data files
14185 to @var{directory}.
14187 @kindex show data-directory
14188 @item show data-directory
14189 Show the directory @value{GDBN} searches for auxiliary data files.
14192 @cindex default data directory
14193 @cindex @samp{--with-gdb-datadir}
14194 You can set the default data directory by using the configure-time
14195 @samp{--with-gdb-datadir} option. If the data directory is inside
14196 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
14197 @samp{--exec-prefix}), then the default data directory will be updated
14198 automatically if the installed @value{GDBN} is moved to a new
14202 @chapter Specifying a Debugging Target
14204 @cindex debugging target
14205 A @dfn{target} is the execution environment occupied by your program.
14207 Often, @value{GDBN} runs in the same host environment as your program;
14208 in that case, the debugging target is specified as a side effect when
14209 you use the @code{file} or @code{core} commands. When you need more
14210 flexibility---for example, running @value{GDBN} on a physically separate
14211 host, or controlling a standalone system over a serial port or a
14212 realtime system over a TCP/IP connection---you can use the @code{target}
14213 command to specify one of the target types configured for @value{GDBN}
14214 (@pxref{Target Commands, ,Commands for Managing Targets}).
14216 @cindex target architecture
14217 It is possible to build @value{GDBN} for several different @dfn{target
14218 architectures}. When @value{GDBN} is built like that, you can choose
14219 one of the available architectures with the @kbd{set architecture}
14223 @kindex set architecture
14224 @kindex show architecture
14225 @item set architecture @var{arch}
14226 This command sets the current target architecture to @var{arch}. The
14227 value of @var{arch} can be @code{"auto"}, in addition to one of the
14228 supported architectures.
14230 @item show architecture
14231 Show the current target architecture.
14233 @item set processor
14235 @kindex set processor
14236 @kindex show processor
14237 These are alias commands for, respectively, @code{set architecture}
14238 and @code{show architecture}.
14242 * Active Targets:: Active targets
14243 * Target Commands:: Commands for managing targets
14244 * Byte Order:: Choosing target byte order
14247 @node Active Targets
14248 @section Active Targets
14250 @cindex stacking targets
14251 @cindex active targets
14252 @cindex multiple targets
14254 There are three classes of targets: processes, core files, and
14255 executable files. @value{GDBN} can work concurrently on up to three
14256 active targets, one in each class. This allows you to (for example)
14257 start a process and inspect its activity without abandoning your work on
14260 For example, if you execute @samp{gdb a.out}, then the executable file
14261 @code{a.out} is the only active target. If you designate a core file as
14262 well---presumably from a prior run that crashed and coredumped---then
14263 @value{GDBN} has two active targets and uses them in tandem, looking
14264 first in the corefile target, then in the executable file, to satisfy
14265 requests for memory addresses. (Typically, these two classes of target
14266 are complementary, since core files contain only a program's
14267 read-write memory---variables and so on---plus machine status, while
14268 executable files contain only the program text and initialized data.)
14270 When you type @code{run}, your executable file becomes an active process
14271 target as well. When a process target is active, all @value{GDBN}
14272 commands requesting memory addresses refer to that target; addresses in
14273 an active core file or executable file target are obscured while the
14274 process target is active.
14276 Use the @code{core-file} and @code{exec-file} commands to select a new
14277 core file or executable target (@pxref{Files, ,Commands to Specify
14278 Files}). To specify as a target a process that is already running, use
14279 the @code{attach} command (@pxref{Attach, ,Debugging an Already-running
14282 @node Target Commands
14283 @section Commands for Managing Targets
14286 @item target @var{type} @var{parameters}
14287 Connects the @value{GDBN} host environment to a target machine or
14288 process. A target is typically a protocol for talking to debugging
14289 facilities. You use the argument @var{type} to specify the type or
14290 protocol of the target machine.
14292 Further @var{parameters} are interpreted by the target protocol, but
14293 typically include things like device names or host names to connect
14294 with, process numbers, and baud rates.
14296 The @code{target} command does not repeat if you press @key{RET} again
14297 after executing the command.
14299 @kindex help target
14301 Displays the names of all targets available. To display targets
14302 currently selected, use either @code{info target} or @code{info files}
14303 (@pxref{Files, ,Commands to Specify Files}).
14305 @item help target @var{name}
14306 Describe a particular target, including any parameters necessary to
14309 @kindex set gnutarget
14310 @item set gnutarget @var{args}
14311 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
14312 knows whether it is reading an @dfn{executable},
14313 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
14314 with the @code{set gnutarget} command. Unlike most @code{target} commands,
14315 with @code{gnutarget} the @code{target} refers to a program, not a machine.
14318 @emph{Warning:} To specify a file format with @code{set gnutarget},
14319 you must know the actual BFD name.
14323 @xref{Files, , Commands to Specify Files}.
14325 @kindex show gnutarget
14326 @item show gnutarget
14327 Use the @code{show gnutarget} command to display what file format
14328 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
14329 @value{GDBN} will determine the file format for each file automatically,
14330 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
14333 @cindex common targets
14334 Here are some common targets (available, or not, depending on the GDB
14339 @item target exec @var{program}
14340 @cindex executable file target
14341 An executable file. @samp{target exec @var{program}} is the same as
14342 @samp{exec-file @var{program}}.
14344 @item target core @var{filename}
14345 @cindex core dump file target
14346 A core dump file. @samp{target core @var{filename}} is the same as
14347 @samp{core-file @var{filename}}.
14349 @item target remote @var{medium}
14350 @cindex remote target
14351 A remote system connected to @value{GDBN} via a serial line or network
14352 connection. This command tells @value{GDBN} to use its own remote
14353 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
14355 For example, if you have a board connected to @file{/dev/ttya} on the
14356 machine running @value{GDBN}, you could say:
14359 target remote /dev/ttya
14362 @code{target remote} supports the @code{load} command. This is only
14363 useful if you have some other way of getting the stub to the target
14364 system, and you can put it somewhere in memory where it won't get
14365 clobbered by the download.
14368 @cindex built-in simulator target
14369 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
14377 works; however, you cannot assume that a specific memory map, device
14378 drivers, or even basic I/O is available, although some simulators do
14379 provide these. For info about any processor-specific simulator details,
14380 see the appropriate section in @ref{Embedded Processors, ,Embedded
14385 Some configurations may include these targets as well:
14389 @item target nrom @var{dev}
14390 @cindex NetROM ROM emulator target
14391 NetROM ROM emulator. This target only supports downloading.
14395 Different targets are available on different configurations of @value{GDBN};
14396 your configuration may have more or fewer targets.
14398 Many remote targets require you to download the executable's code once
14399 you've successfully established a connection. You may wish to control
14400 various aspects of this process.
14405 @kindex set hash@r{, for remote monitors}
14406 @cindex hash mark while downloading
14407 This command controls whether a hash mark @samp{#} is displayed while
14408 downloading a file to the remote monitor. If on, a hash mark is
14409 displayed after each S-record is successfully downloaded to the
14413 @kindex show hash@r{, for remote monitors}
14414 Show the current status of displaying the hash mark.
14416 @item set debug monitor
14417 @kindex set debug monitor
14418 @cindex display remote monitor communications
14419 Enable or disable display of communications messages between
14420 @value{GDBN} and the remote monitor.
14422 @item show debug monitor
14423 @kindex show debug monitor
14424 Show the current status of displaying communications between
14425 @value{GDBN} and the remote monitor.
14430 @kindex load @var{filename}
14431 @item load @var{filename}
14433 Depending on what remote debugging facilities are configured into
14434 @value{GDBN}, the @code{load} command may be available. Where it exists, it
14435 is meant to make @var{filename} (an executable) available for debugging
14436 on the remote system---by downloading, or dynamic linking, for example.
14437 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
14438 the @code{add-symbol-file} command.
14440 If your @value{GDBN} does not have a @code{load} command, attempting to
14441 execute it gets the error message ``@code{You can't do that when your
14442 target is @dots{}}''
14444 The file is loaded at whatever address is specified in the executable.
14445 For some object file formats, you can specify the load address when you
14446 link the program; for other formats, like a.out, the object file format
14447 specifies a fixed address.
14448 @c FIXME! This would be a good place for an xref to the GNU linker doc.
14450 Depending on the remote side capabilities, @value{GDBN} may be able to
14451 load programs into flash memory.
14453 @code{load} does not repeat if you press @key{RET} again after using it.
14457 @section Choosing Target Byte Order
14459 @cindex choosing target byte order
14460 @cindex target byte order
14462 Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
14463 offer the ability to run either big-endian or little-endian byte
14464 orders. Usually the executable or symbol will include a bit to
14465 designate the endian-ness, and you will not need to worry about
14466 which to use. However, you may still find it useful to adjust
14467 @value{GDBN}'s idea of processor endian-ness manually.
14471 @item set endian big
14472 Instruct @value{GDBN} to assume the target is big-endian.
14474 @item set endian little
14475 Instruct @value{GDBN} to assume the target is little-endian.
14477 @item set endian auto
14478 Instruct @value{GDBN} to use the byte order associated with the
14482 Display @value{GDBN}'s current idea of the target byte order.
14486 Note that these commands merely adjust interpretation of symbolic
14487 data on the host, and that they have absolutely no effect on the
14491 @node Remote Debugging
14492 @chapter Debugging Remote Programs
14493 @cindex remote debugging
14495 If you are trying to debug a program running on a machine that cannot run
14496 @value{GDBN} in the usual way, it is often useful to use remote debugging.
14497 For example, you might use remote debugging on an operating system kernel,
14498 or on a small system which does not have a general purpose operating system
14499 powerful enough to run a full-featured debugger.
14501 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
14502 to make this work with particular debugging targets. In addition,
14503 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
14504 but not specific to any particular target system) which you can use if you
14505 write the remote stubs---the code that runs on the remote system to
14506 communicate with @value{GDBN}.
14508 Other remote targets may be available in your
14509 configuration of @value{GDBN}; use @code{help target} to list them.
14512 * Connecting:: Connecting to a remote target
14513 * File Transfer:: Sending files to a remote system
14514 * Server:: Using the gdbserver program
14515 * Remote Configuration:: Remote configuration
14516 * Remote Stub:: Implementing a remote stub
14520 @section Connecting to a Remote Target
14522 On the @value{GDBN} host machine, you will need an unstripped copy of
14523 your program, since @value{GDBN} needs symbol and debugging information.
14524 Start up @value{GDBN} as usual, using the name of the local copy of your
14525 program as the first argument.
14527 @cindex @code{target remote}
14528 @value{GDBN} can communicate with the target over a serial line, or
14529 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
14530 each case, @value{GDBN} uses the same protocol for debugging your
14531 program; only the medium carrying the debugging packets varies. The
14532 @code{target remote} command establishes a connection to the target.
14533 Its arguments indicate which medium to use:
14537 @item target remote @var{serial-device}
14538 @cindex serial line, @code{target remote}
14539 Use @var{serial-device} to communicate with the target. For example,
14540 to use a serial line connected to the device named @file{/dev/ttyb}:
14543 target remote /dev/ttyb
14546 If you're using a serial line, you may want to give @value{GDBN} the
14547 @w{@samp{--baud}} option, or use the @code{set remotebaud} command
14548 (@pxref{Remote Configuration, set remotebaud}) before the
14549 @code{target} command.
14551 @item target remote @code{@var{host}:@var{port}}
14552 @itemx target remote @code{tcp:@var{host}:@var{port}}
14553 @cindex @acronym{TCP} port, @code{target remote}
14554 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
14555 The @var{host} may be either a host name or a numeric @acronym{IP}
14556 address; @var{port} must be a decimal number. The @var{host} could be
14557 the target machine itself, if it is directly connected to the net, or
14558 it might be a terminal server which in turn has a serial line to the
14561 For example, to connect to port 2828 on a terminal server named
14565 target remote manyfarms:2828
14568 If your remote target is actually running on the same machine as your
14569 debugger session (e.g.@: a simulator for your target running on the
14570 same host), you can omit the hostname. For example, to connect to
14571 port 1234 on your local machine:
14574 target remote :1234
14578 Note that the colon is still required here.
14580 @item target remote @code{udp:@var{host}:@var{port}}
14581 @cindex @acronym{UDP} port, @code{target remote}
14582 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
14583 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
14586 target remote udp:manyfarms:2828
14589 When using a @acronym{UDP} connection for remote debugging, you should
14590 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
14591 can silently drop packets on busy or unreliable networks, which will
14592 cause havoc with your debugging session.
14594 @item target remote | @var{command}
14595 @cindex pipe, @code{target remote} to
14596 Run @var{command} in the background and communicate with it using a
14597 pipe. The @var{command} is a shell command, to be parsed and expanded
14598 by the system's command shell, @code{/bin/sh}; it should expect remote
14599 protocol packets on its standard input, and send replies on its
14600 standard output. You could use this to run a stand-alone simulator
14601 that speaks the remote debugging protocol, to make net connections
14602 using programs like @code{ssh}, or for other similar tricks.
14604 If @var{command} closes its standard output (perhaps by exiting),
14605 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
14606 program has already exited, this will have no effect.)
14610 Once the connection has been established, you can use all the usual
14611 commands to examine and change data. The remote program is already
14612 running; you can use @kbd{step} and @kbd{continue}, and you do not
14613 need to use @kbd{run}.
14615 @cindex interrupting remote programs
14616 @cindex remote programs, interrupting
14617 Whenever @value{GDBN} is waiting for the remote program, if you type the
14618 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
14619 program. This may or may not succeed, depending in part on the hardware
14620 and the serial drivers the remote system uses. If you type the
14621 interrupt character once again, @value{GDBN} displays this prompt:
14624 Interrupted while waiting for the program.
14625 Give up (and stop debugging it)? (y or n)
14628 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
14629 (If you decide you want to try again later, you can use @samp{target
14630 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
14631 goes back to waiting.
14634 @kindex detach (remote)
14636 When you have finished debugging the remote program, you can use the
14637 @code{detach} command to release it from @value{GDBN} control.
14638 Detaching from the target normally resumes its execution, but the results
14639 will depend on your particular remote stub. After the @code{detach}
14640 command, @value{GDBN} is free to connect to another target.
14644 The @code{disconnect} command behaves like @code{detach}, except that
14645 the target is generally not resumed. It will wait for @value{GDBN}
14646 (this instance or another one) to connect and continue debugging. After
14647 the @code{disconnect} command, @value{GDBN} is again free to connect to
14650 @cindex send command to remote monitor
14651 @cindex extend @value{GDBN} for remote targets
14652 @cindex add new commands for external monitor
14654 @item monitor @var{cmd}
14655 This command allows you to send arbitrary commands directly to the
14656 remote monitor. Since @value{GDBN} doesn't care about the commands it
14657 sends like this, this command is the way to extend @value{GDBN}---you
14658 can add new commands that only the external monitor will understand
14662 @node File Transfer
14663 @section Sending files to a remote system
14664 @cindex remote target, file transfer
14665 @cindex file transfer
14666 @cindex sending files to remote systems
14668 Some remote targets offer the ability to transfer files over the same
14669 connection used to communicate with @value{GDBN}. This is convenient
14670 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
14671 running @code{gdbserver} over a network interface. For other targets,
14672 e.g.@: embedded devices with only a single serial port, this may be
14673 the only way to upload or download files.
14675 Not all remote targets support these commands.
14679 @item remote put @var{hostfile} @var{targetfile}
14680 Copy file @var{hostfile} from the host system (the machine running
14681 @value{GDBN}) to @var{targetfile} on the target system.
14684 @item remote get @var{targetfile} @var{hostfile}
14685 Copy file @var{targetfile} from the target system to @var{hostfile}
14686 on the host system.
14688 @kindex remote delete
14689 @item remote delete @var{targetfile}
14690 Delete @var{targetfile} from the target system.
14695 @section Using the @code{gdbserver} Program
14698 @cindex remote connection without stubs
14699 @code{gdbserver} is a control program for Unix-like systems, which
14700 allows you to connect your program with a remote @value{GDBN} via
14701 @code{target remote}---but without linking in the usual debugging stub.
14703 @code{gdbserver} is not a complete replacement for the debugging stubs,
14704 because it requires essentially the same operating-system facilities
14705 that @value{GDBN} itself does. In fact, a system that can run
14706 @code{gdbserver} to connect to a remote @value{GDBN} could also run
14707 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
14708 because it is a much smaller program than @value{GDBN} itself. It is
14709 also easier to port than all of @value{GDBN}, so you may be able to get
14710 started more quickly on a new system by using @code{gdbserver}.
14711 Finally, if you develop code for real-time systems, you may find that
14712 the tradeoffs involved in real-time operation make it more convenient to
14713 do as much development work as possible on another system, for example
14714 by cross-compiling. You can use @code{gdbserver} to make a similar
14715 choice for debugging.
14717 @value{GDBN} and @code{gdbserver} communicate via either a serial line
14718 or a TCP connection, using the standard @value{GDBN} remote serial
14722 @emph{Warning:} @code{gdbserver} does not have any built-in security.
14723 Do not run @code{gdbserver} connected to any public network; a
14724 @value{GDBN} connection to @code{gdbserver} provides access to the
14725 target system with the same privileges as the user running
14729 @subsection Running @code{gdbserver}
14730 @cindex arguments, to @code{gdbserver}
14732 Run @code{gdbserver} on the target system. You need a copy of the
14733 program you want to debug, including any libraries it requires.
14734 @code{gdbserver} does not need your program's symbol table, so you can
14735 strip the program if necessary to save space. @value{GDBN} on the host
14736 system does all the symbol handling.
14738 To use the server, you must tell it how to communicate with @value{GDBN};
14739 the name of your program; and the arguments for your program. The usual
14743 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
14746 @var{comm} is either a device name (to use a serial line) or a TCP
14747 hostname and portnumber. For example, to debug Emacs with the argument
14748 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
14752 target> gdbserver /dev/com1 emacs foo.txt
14755 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
14758 To use a TCP connection instead of a serial line:
14761 target> gdbserver host:2345 emacs foo.txt
14764 The only difference from the previous example is the first argument,
14765 specifying that you are communicating with the host @value{GDBN} via
14766 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
14767 expect a TCP connection from machine @samp{host} to local TCP port 2345.
14768 (Currently, the @samp{host} part is ignored.) You can choose any number
14769 you want for the port number as long as it does not conflict with any
14770 TCP ports already in use on the target system (for example, @code{23} is
14771 reserved for @code{telnet}).@footnote{If you choose a port number that
14772 conflicts with another service, @code{gdbserver} prints an error message
14773 and exits.} You must use the same port number with the host @value{GDBN}
14774 @code{target remote} command.
14776 @subsubsection Attaching to a Running Program
14778 On some targets, @code{gdbserver} can also attach to running programs.
14779 This is accomplished via the @code{--attach} argument. The syntax is:
14782 target> gdbserver --attach @var{comm} @var{pid}
14785 @var{pid} is the process ID of a currently running process. It isn't necessary
14786 to point @code{gdbserver} at a binary for the running process.
14789 @cindex attach to a program by name
14790 You can debug processes by name instead of process ID if your target has the
14791 @code{pidof} utility:
14794 target> gdbserver --attach @var{comm} `pidof @var{program}`
14797 In case more than one copy of @var{program} is running, or @var{program}
14798 has multiple threads, most versions of @code{pidof} support the
14799 @code{-s} option to only return the first process ID.
14801 @subsubsection Multi-Process Mode for @code{gdbserver}
14802 @cindex gdbserver, multiple processes
14803 @cindex multiple processes with gdbserver
14805 When you connect to @code{gdbserver} using @code{target remote},
14806 @code{gdbserver} debugs the specified program only once. When the
14807 program exits, or you detach from it, @value{GDBN} closes the connection
14808 and @code{gdbserver} exits.
14810 If you connect using @kbd{target extended-remote}, @code{gdbserver}
14811 enters multi-process mode. When the debugged program exits, or you
14812 detach from it, @value{GDBN} stays connected to @code{gdbserver} even
14813 though no program is running. The @code{run} and @code{attach}
14814 commands instruct @code{gdbserver} to run or attach to a new program.
14815 The @code{run} command uses @code{set remote exec-file} (@pxref{set
14816 remote exec-file}) to select the program to run. Command line
14817 arguments are supported, except for wildcard expansion and I/O
14818 redirection (@pxref{Arguments}).
14820 To start @code{gdbserver} without supplying an initial command to run
14821 or process ID to attach, use the @option{--multi} command line option.
14822 Then you can connect using @kbd{target extended-remote} and start
14823 the program you want to debug.
14825 @code{gdbserver} does not automatically exit in multi-process mode.
14826 You can terminate it by using @code{monitor exit}
14827 (@pxref{Monitor Commands for gdbserver}).
14829 @subsubsection Other Command-Line Arguments for @code{gdbserver}
14831 The @option{--debug} option tells @code{gdbserver} to display extra
14832 status information about the debugging process. The
14833 @option{--remote-debug} option tells @code{gdbserver} to display
14834 remote protocol debug output. These options are intended for
14835 @code{gdbserver} development and for bug reports to the developers.
14837 The @option{--wrapper} option specifies a wrapper to launch programs
14838 for debugging. The option should be followed by the name of the
14839 wrapper, then any command-line arguments to pass to the wrapper, then
14840 @kbd{--} indicating the end of the wrapper arguments.
14842 @code{gdbserver} runs the specified wrapper program with a combined
14843 command line including the wrapper arguments, then the name of the
14844 program to debug, then any arguments to the program. The wrapper
14845 runs until it executes your program, and then @value{GDBN} gains control.
14847 You can use any program that eventually calls @code{execve} with
14848 its arguments as a wrapper. Several standard Unix utilities do
14849 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
14850 with @code{exec "$@@"} will also work.
14852 For example, you can use @code{env} to pass an environment variable to
14853 the debugged program, without setting the variable in @code{gdbserver}'s
14857 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
14860 @subsection Connecting to @code{gdbserver}
14862 Run @value{GDBN} on the host system.
14864 First make sure you have the necessary symbol files. Load symbols for
14865 your application using the @code{file} command before you connect. Use
14866 @code{set sysroot} to locate target libraries (unless your @value{GDBN}
14867 was compiled with the correct sysroot using @code{--with-sysroot}).
14869 The symbol file and target libraries must exactly match the executable
14870 and libraries on the target, with one exception: the files on the host
14871 system should not be stripped, even if the files on the target system
14872 are. Mismatched or missing files will lead to confusing results
14873 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
14874 files may also prevent @code{gdbserver} from debugging multi-threaded
14877 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
14878 For TCP connections, you must start up @code{gdbserver} prior to using
14879 the @code{target remote} command. Otherwise you may get an error whose
14880 text depends on the host system, but which usually looks something like
14881 @samp{Connection refused}. Don't use the @code{load}
14882 command in @value{GDBN} when using @code{gdbserver}, since the program is
14883 already on the target.
14885 @subsection Monitor Commands for @code{gdbserver}
14886 @cindex monitor commands, for @code{gdbserver}
14887 @anchor{Monitor Commands for gdbserver}
14889 During a @value{GDBN} session using @code{gdbserver}, you can use the
14890 @code{monitor} command to send special requests to @code{gdbserver}.
14891 Here are the available commands.
14895 List the available monitor commands.
14897 @item monitor set debug 0
14898 @itemx monitor set debug 1
14899 Disable or enable general debugging messages.
14901 @item monitor set remote-debug 0
14902 @itemx monitor set remote-debug 1
14903 Disable or enable specific debugging messages associated with the remote
14904 protocol (@pxref{Remote Protocol}).
14906 @item monitor set libthread-db-search-path [PATH]
14907 @cindex gdbserver, search path for @code{libthread_db}
14908 When this command is issued, @var{path} is a colon-separated list of
14909 directories to search for @code{libthread_db} (@pxref{Threads,,set
14910 libthread-db-search-path}). If you omit @var{path},
14911 @samp{libthread-db-search-path} will be reset to an empty list.
14914 Tell gdbserver to exit immediately. This command should be followed by
14915 @code{disconnect} to close the debugging session. @code{gdbserver} will
14916 detach from any attached processes and kill any processes it created.
14917 Use @code{monitor exit} to terminate @code{gdbserver} at the end
14918 of a multi-process mode debug session.
14922 @node Remote Configuration
14923 @section Remote Configuration
14926 @kindex show remote
14927 This section documents the configuration options available when
14928 debugging remote programs. For the options related to the File I/O
14929 extensions of the remote protocol, see @ref{system,
14930 system-call-allowed}.
14933 @item set remoteaddresssize @var{bits}
14934 @cindex address size for remote targets
14935 @cindex bits in remote address
14936 Set the maximum size of address in a memory packet to the specified
14937 number of bits. @value{GDBN} will mask off the address bits above
14938 that number, when it passes addresses to the remote target. The
14939 default value is the number of bits in the target's address.
14941 @item show remoteaddresssize
14942 Show the current value of remote address size in bits.
14944 @item set remotebaud @var{n}
14945 @cindex baud rate for remote targets
14946 Set the baud rate for the remote serial I/O to @var{n} baud. The
14947 value is used to set the speed of the serial port used for debugging
14950 @item show remotebaud
14951 Show the current speed of the remote connection.
14953 @item set remotebreak
14954 @cindex interrupt remote programs
14955 @cindex BREAK signal instead of Ctrl-C
14956 @anchor{set remotebreak}
14957 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
14958 when you type @kbd{Ctrl-c} to interrupt the program running
14959 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
14960 character instead. The default is off, since most remote systems
14961 expect to see @samp{Ctrl-C} as the interrupt signal.
14963 @item show remotebreak
14964 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
14965 interrupt the remote program.
14967 @item set remoteflow on
14968 @itemx set remoteflow off
14969 @kindex set remoteflow
14970 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
14971 on the serial port used to communicate to the remote target.
14973 @item show remoteflow
14974 @kindex show remoteflow
14975 Show the current setting of hardware flow control.
14977 @item set remotelogbase @var{base}
14978 Set the base (a.k.a.@: radix) of logging serial protocol
14979 communications to @var{base}. Supported values of @var{base} are:
14980 @code{ascii}, @code{octal}, and @code{hex}. The default is
14983 @item show remotelogbase
14984 Show the current setting of the radix for logging remote serial
14987 @item set remotelogfile @var{file}
14988 @cindex record serial communications on file
14989 Record remote serial communications on the named @var{file}. The
14990 default is not to record at all.
14992 @item show remotelogfile.
14993 Show the current setting of the file name on which to record the
14994 serial communications.
14996 @item set remotetimeout @var{num}
14997 @cindex timeout for serial communications
14998 @cindex remote timeout
14999 Set the timeout limit to wait for the remote target to respond to
15000 @var{num} seconds. The default is 2 seconds.
15002 @item show remotetimeout
15003 Show the current number of seconds to wait for the remote target
15006 @cindex limit hardware breakpoints and watchpoints
15007 @cindex remote target, limit break- and watchpoints
15008 @anchor{set remote hardware-watchpoint-limit}
15009 @anchor{set remote hardware-breakpoint-limit}
15010 @item set remote hardware-watchpoint-limit @var{limit}
15011 @itemx set remote hardware-breakpoint-limit @var{limit}
15012 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
15013 watchpoints. A limit of -1, the default, is treated as unlimited.
15015 @item set remote exec-file @var{filename}
15016 @itemx show remote exec-file
15017 @anchor{set remote exec-file}
15018 @cindex executable file, for remote target
15019 Select the file used for @code{run} with @code{target
15020 extended-remote}. This should be set to a filename valid on the
15021 target system. If it is not set, the target will use a default
15022 filename (e.g.@: the last program run).
15026 @item set tcp auto-retry on
15027 @cindex auto-retry, for remote TCP target
15028 Enable auto-retry for remote TCP connections. This is useful if the remote
15029 debugging agent is launched in parallel with @value{GDBN}; there is a race
15030 condition because the agent may not become ready to accept the connection
15031 before @value{GDBN} attempts to connect. When auto-retry is
15032 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
15033 to establish the connection using the timeout specified by
15034 @code{set tcp connect-timeout}.
15036 @item set tcp auto-retry off
15037 Do not auto-retry failed TCP connections.
15039 @item show tcp auto-retry
15040 Show the current auto-retry setting.
15042 @item set tcp connect-timeout @var{seconds}
15043 @cindex connection timeout, for remote TCP target
15044 @cindex timeout, for remote target connection
15045 Set the timeout for establishing a TCP connection to the remote target to
15046 @var{seconds}. The timeout affects both polling to retry failed connections
15047 (enabled by @code{set tcp auto-retry on}) and waiting for connections
15048 that are merely slow to complete, and represents an approximate cumulative
15051 @item show tcp connect-timeout
15052 Show the current connection timeout setting.
15055 @cindex remote packets, enabling and disabling
15056 The @value{GDBN} remote protocol autodetects the packets supported by
15057 your debugging stub. If you need to override the autodetection, you
15058 can use these commands to enable or disable individual packets. Each
15059 packet can be set to @samp{on} (the remote target supports this
15060 packet), @samp{off} (the remote target does not support this packet),
15061 or @samp{auto} (detect remote target support for this packet). They
15062 all default to @samp{auto}. For more information about each packet,
15063 see @ref{Remote Protocol}.
15065 During normal use, you should not have to use any of these commands.
15066 If you do, that may be a bug in your remote debugging stub, or a bug
15067 in @value{GDBN}. You may want to report the problem to the
15068 @value{GDBN} developers.
15070 For each packet @var{name}, the command to enable or disable the
15071 packet is @code{set remote @var{name}-packet}. The available settings
15074 @multitable @columnfractions 0.28 0.32 0.25
15077 @tab Related Features
15079 @item @code{fetch-register}
15081 @tab @code{info registers}
15083 @item @code{set-register}
15087 @item @code{binary-download}
15089 @tab @code{load}, @code{set}
15091 @item @code{read-aux-vector}
15092 @tab @code{qXfer:auxv:read}
15093 @tab @code{info auxv}
15095 @item @code{symbol-lookup}
15096 @tab @code{qSymbol}
15097 @tab Detecting multiple threads
15099 @item @code{attach}
15100 @tab @code{vAttach}
15103 @item @code{verbose-resume}
15105 @tab Stepping or resuming multiple threads
15111 @item @code{software-breakpoint}
15115 @item @code{hardware-breakpoint}
15119 @item @code{write-watchpoint}
15123 @item @code{read-watchpoint}
15127 @item @code{access-watchpoint}
15131 @item @code{target-features}
15132 @tab @code{qXfer:features:read}
15133 @tab @code{set architecture}
15135 @item @code{library-info}
15136 @tab @code{qXfer:libraries:read}
15137 @tab @code{info sharedlibrary}
15139 @item @code{memory-map}
15140 @tab @code{qXfer:memory-map:read}
15141 @tab @code{info mem}
15143 @item @code{read-spu-object}
15144 @tab @code{qXfer:spu:read}
15145 @tab @code{info spu}
15147 @item @code{write-spu-object}
15148 @tab @code{qXfer:spu:write}
15149 @tab @code{info spu}
15151 @item @code{read-siginfo-object}
15152 @tab @code{qXfer:siginfo:read}
15153 @tab @code{print $_siginfo}
15155 @item @code{write-siginfo-object}
15156 @tab @code{qXfer:siginfo:write}
15157 @tab @code{set $_siginfo}
15159 @item @code{get-thread-local-@*storage-address}
15160 @tab @code{qGetTLSAddr}
15161 @tab Displaying @code{__thread} variables
15163 @item @code{search-memory}
15164 @tab @code{qSearch:memory}
15167 @item @code{supported-packets}
15168 @tab @code{qSupported}
15169 @tab Remote communications parameters
15171 @item @code{pass-signals}
15172 @tab @code{QPassSignals}
15173 @tab @code{handle @var{signal}}
15175 @item @code{hostio-close-packet}
15176 @tab @code{vFile:close}
15177 @tab @code{remote get}, @code{remote put}
15179 @item @code{hostio-open-packet}
15180 @tab @code{vFile:open}
15181 @tab @code{remote get}, @code{remote put}
15183 @item @code{hostio-pread-packet}
15184 @tab @code{vFile:pread}
15185 @tab @code{remote get}, @code{remote put}
15187 @item @code{hostio-pwrite-packet}
15188 @tab @code{vFile:pwrite}
15189 @tab @code{remote get}, @code{remote put}
15191 @item @code{hostio-unlink-packet}
15192 @tab @code{vFile:unlink}
15193 @tab @code{remote delete}
15195 @item @code{noack-packet}
15196 @tab @code{QStartNoAckMode}
15197 @tab Packet acknowledgment
15199 @item @code{osdata}
15200 @tab @code{qXfer:osdata:read}
15201 @tab @code{info os}
15203 @item @code{query-attached}
15204 @tab @code{qAttached}
15205 @tab Querying remote process attach state.
15209 @section Implementing a Remote Stub
15211 @cindex debugging stub, example
15212 @cindex remote stub, example
15213 @cindex stub example, remote debugging
15214 The stub files provided with @value{GDBN} implement the target side of the
15215 communication protocol, and the @value{GDBN} side is implemented in the
15216 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
15217 these subroutines to communicate, and ignore the details. (If you're
15218 implementing your own stub file, you can still ignore the details: start
15219 with one of the existing stub files. @file{sparc-stub.c} is the best
15220 organized, and therefore the easiest to read.)
15222 @cindex remote serial debugging, overview
15223 To debug a program running on another machine (the debugging
15224 @dfn{target} machine), you must first arrange for all the usual
15225 prerequisites for the program to run by itself. For example, for a C
15230 A startup routine to set up the C runtime environment; these usually
15231 have a name like @file{crt0}. The startup routine may be supplied by
15232 your hardware supplier, or you may have to write your own.
15235 A C subroutine library to support your program's
15236 subroutine calls, notably managing input and output.
15239 A way of getting your program to the other machine---for example, a
15240 download program. These are often supplied by the hardware
15241 manufacturer, but you may have to write your own from hardware
15245 The next step is to arrange for your program to use a serial port to
15246 communicate with the machine where @value{GDBN} is running (the @dfn{host}
15247 machine). In general terms, the scheme looks like this:
15251 @value{GDBN} already understands how to use this protocol; when everything
15252 else is set up, you can simply use the @samp{target remote} command
15253 (@pxref{Targets,,Specifying a Debugging Target}).
15255 @item On the target,
15256 you must link with your program a few special-purpose subroutines that
15257 implement the @value{GDBN} remote serial protocol. The file containing these
15258 subroutines is called a @dfn{debugging stub}.
15260 On certain remote targets, you can use an auxiliary program
15261 @code{gdbserver} instead of linking a stub into your program.
15262 @xref{Server,,Using the @code{gdbserver} Program}, for details.
15265 The debugging stub is specific to the architecture of the remote
15266 machine; for example, use @file{sparc-stub.c} to debug programs on
15269 @cindex remote serial stub list
15270 These working remote stubs are distributed with @value{GDBN}:
15275 @cindex @file{i386-stub.c}
15278 For Intel 386 and compatible architectures.
15281 @cindex @file{m68k-stub.c}
15282 @cindex Motorola 680x0
15284 For Motorola 680x0 architectures.
15287 @cindex @file{sh-stub.c}
15290 For Renesas SH architectures.
15293 @cindex @file{sparc-stub.c}
15295 For @sc{sparc} architectures.
15297 @item sparcl-stub.c
15298 @cindex @file{sparcl-stub.c}
15301 For Fujitsu @sc{sparclite} architectures.
15305 The @file{README} file in the @value{GDBN} distribution may list other
15306 recently added stubs.
15309 * Stub Contents:: What the stub can do for you
15310 * Bootstrapping:: What you must do for the stub
15311 * Debug Session:: Putting it all together
15314 @node Stub Contents
15315 @subsection What the Stub Can Do for You
15317 @cindex remote serial stub
15318 The debugging stub for your architecture supplies these three
15322 @item set_debug_traps
15323 @findex set_debug_traps
15324 @cindex remote serial stub, initialization
15325 This routine arranges for @code{handle_exception} to run when your
15326 program stops. You must call this subroutine explicitly near the
15327 beginning of your program.
15329 @item handle_exception
15330 @findex handle_exception
15331 @cindex remote serial stub, main routine
15332 This is the central workhorse, but your program never calls it
15333 explicitly---the setup code arranges for @code{handle_exception} to
15334 run when a trap is triggered.
15336 @code{handle_exception} takes control when your program stops during
15337 execution (for example, on a breakpoint), and mediates communications
15338 with @value{GDBN} on the host machine. This is where the communications
15339 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
15340 representative on the target machine. It begins by sending summary
15341 information on the state of your program, then continues to execute,
15342 retrieving and transmitting any information @value{GDBN} needs, until you
15343 execute a @value{GDBN} command that makes your program resume; at that point,
15344 @code{handle_exception} returns control to your own code on the target
15348 @cindex @code{breakpoint} subroutine, remote
15349 Use this auxiliary subroutine to make your program contain a
15350 breakpoint. Depending on the particular situation, this may be the only
15351 way for @value{GDBN} to get control. For instance, if your target
15352 machine has some sort of interrupt button, you won't need to call this;
15353 pressing the interrupt button transfers control to
15354 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
15355 simply receiving characters on the serial port may also trigger a trap;
15356 again, in that situation, you don't need to call @code{breakpoint} from
15357 your own program---simply running @samp{target remote} from the host
15358 @value{GDBN} session gets control.
15360 Call @code{breakpoint} if none of these is true, or if you simply want
15361 to make certain your program stops at a predetermined point for the
15362 start of your debugging session.
15365 @node Bootstrapping
15366 @subsection What You Must Do for the Stub
15368 @cindex remote stub, support routines
15369 The debugging stubs that come with @value{GDBN} are set up for a particular
15370 chip architecture, but they have no information about the rest of your
15371 debugging target machine.
15373 First of all you need to tell the stub how to communicate with the
15377 @item int getDebugChar()
15378 @findex getDebugChar
15379 Write this subroutine to read a single character from the serial port.
15380 It may be identical to @code{getchar} for your target system; a
15381 different name is used to allow you to distinguish the two if you wish.
15383 @item void putDebugChar(int)
15384 @findex putDebugChar
15385 Write this subroutine to write a single character to the serial port.
15386 It may be identical to @code{putchar} for your target system; a
15387 different name is used to allow you to distinguish the two if you wish.
15390 @cindex control C, and remote debugging
15391 @cindex interrupting remote targets
15392 If you want @value{GDBN} to be able to stop your program while it is
15393 running, you need to use an interrupt-driven serial driver, and arrange
15394 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
15395 character). That is the character which @value{GDBN} uses to tell the
15396 remote system to stop.
15398 Getting the debugging target to return the proper status to @value{GDBN}
15399 probably requires changes to the standard stub; one quick and dirty way
15400 is to just execute a breakpoint instruction (the ``dirty'' part is that
15401 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
15403 Other routines you need to supply are:
15406 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
15407 @findex exceptionHandler
15408 Write this function to install @var{exception_address} in the exception
15409 handling tables. You need to do this because the stub does not have any
15410 way of knowing what the exception handling tables on your target system
15411 are like (for example, the processor's table might be in @sc{rom},
15412 containing entries which point to a table in @sc{ram}).
15413 @var{exception_number} is the exception number which should be changed;
15414 its meaning is architecture-dependent (for example, different numbers
15415 might represent divide by zero, misaligned access, etc). When this
15416 exception occurs, control should be transferred directly to
15417 @var{exception_address}, and the processor state (stack, registers,
15418 and so on) should be just as it is when a processor exception occurs. So if
15419 you want to use a jump instruction to reach @var{exception_address}, it
15420 should be a simple jump, not a jump to subroutine.
15422 For the 386, @var{exception_address} should be installed as an interrupt
15423 gate so that interrupts are masked while the handler runs. The gate
15424 should be at privilege level 0 (the most privileged level). The
15425 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
15426 help from @code{exceptionHandler}.
15428 @item void flush_i_cache()
15429 @findex flush_i_cache
15430 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
15431 instruction cache, if any, on your target machine. If there is no
15432 instruction cache, this subroutine may be a no-op.
15434 On target machines that have instruction caches, @value{GDBN} requires this
15435 function to make certain that the state of your program is stable.
15439 You must also make sure this library routine is available:
15442 @item void *memset(void *, int, int)
15444 This is the standard library function @code{memset} that sets an area of
15445 memory to a known value. If you have one of the free versions of
15446 @code{libc.a}, @code{memset} can be found there; otherwise, you must
15447 either obtain it from your hardware manufacturer, or write your own.
15450 If you do not use the GNU C compiler, you may need other standard
15451 library subroutines as well; this varies from one stub to another,
15452 but in general the stubs are likely to use any of the common library
15453 subroutines which @code{@value{NGCC}} generates as inline code.
15456 @node Debug Session
15457 @subsection Putting it All Together
15459 @cindex remote serial debugging summary
15460 In summary, when your program is ready to debug, you must follow these
15465 Make sure you have defined the supporting low-level routines
15466 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
15468 @code{getDebugChar}, @code{putDebugChar},
15469 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
15473 Insert these lines near the top of your program:
15481 For the 680x0 stub only, you need to provide a variable called
15482 @code{exceptionHook}. Normally you just use:
15485 void (*exceptionHook)() = 0;
15489 but if before calling @code{set_debug_traps}, you set it to point to a
15490 function in your program, that function is called when
15491 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
15492 error). The function indicated by @code{exceptionHook} is called with
15493 one parameter: an @code{int} which is the exception number.
15496 Compile and link together: your program, the @value{GDBN} debugging stub for
15497 your target architecture, and the supporting subroutines.
15500 Make sure you have a serial connection between your target machine and
15501 the @value{GDBN} host, and identify the serial port on the host.
15504 @c The "remote" target now provides a `load' command, so we should
15505 @c document that. FIXME.
15506 Download your program to your target machine (or get it there by
15507 whatever means the manufacturer provides), and start it.
15510 Start @value{GDBN} on the host, and connect to the target
15511 (@pxref{Connecting,,Connecting to a Remote Target}).
15515 @node Configurations
15516 @chapter Configuration-Specific Information
15518 While nearly all @value{GDBN} commands are available for all native and
15519 cross versions of the debugger, there are some exceptions. This chapter
15520 describes things that are only available in certain configurations.
15522 There are three major categories of configurations: native
15523 configurations, where the host and target are the same, embedded
15524 operating system configurations, which are usually the same for several
15525 different processor architectures, and bare embedded processors, which
15526 are quite different from each other.
15531 * Embedded Processors::
15538 This section describes details specific to particular native
15543 * BSD libkvm Interface:: Debugging BSD kernel memory images
15544 * SVR4 Process Information:: SVR4 process information
15545 * DJGPP Native:: Features specific to the DJGPP port
15546 * Cygwin Native:: Features specific to the Cygwin port
15547 * Hurd Native:: Features specific to @sc{gnu} Hurd
15548 * Neutrino:: Features specific to QNX Neutrino
15549 * Darwin:: Features specific to Darwin
15555 On HP-UX systems, if you refer to a function or variable name that
15556 begins with a dollar sign, @value{GDBN} searches for a user or system
15557 name first, before it searches for a convenience variable.
15560 @node BSD libkvm Interface
15561 @subsection BSD libkvm Interface
15564 @cindex kernel memory image
15565 @cindex kernel crash dump
15567 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
15568 interface that provides a uniform interface for accessing kernel virtual
15569 memory images, including live systems and crash dumps. @value{GDBN}
15570 uses this interface to allow you to debug live kernels and kernel crash
15571 dumps on many native BSD configurations. This is implemented as a
15572 special @code{kvm} debugging target. For debugging a live system, load
15573 the currently running kernel into @value{GDBN} and connect to the
15577 (@value{GDBP}) @b{target kvm}
15580 For debugging crash dumps, provide the file name of the crash dump as an
15584 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
15587 Once connected to the @code{kvm} target, the following commands are
15593 Set current context from the @dfn{Process Control Block} (PCB) address.
15596 Set current context from proc address. This command isn't available on
15597 modern FreeBSD systems.
15600 @node SVR4 Process Information
15601 @subsection SVR4 Process Information
15603 @cindex examine process image
15604 @cindex process info via @file{/proc}
15606 Many versions of SVR4 and compatible systems provide a facility called
15607 @samp{/proc} that can be used to examine the image of a running
15608 process using file-system subroutines. If @value{GDBN} is configured
15609 for an operating system with this facility, the command @code{info
15610 proc} is available to report information about the process running
15611 your program, or about any process running on your system. @code{info
15612 proc} works only on SVR4 systems that include the @code{procfs} code.
15613 This includes, as of this writing, @sc{gnu}/Linux, OSF/1 (Digital
15614 Unix), Solaris, Irix, and Unixware, but not HP-UX, for example.
15620 @itemx info proc @var{process-id}
15621 Summarize available information about any running process. If a
15622 process ID is specified by @var{process-id}, display information about
15623 that process; otherwise display information about the program being
15624 debugged. The summary includes the debugged process ID, the command
15625 line used to invoke it, its current working directory, and its
15626 executable file's absolute file name.
15628 On some systems, @var{process-id} can be of the form
15629 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
15630 within a process. If the optional @var{pid} part is missing, it means
15631 a thread from the process being debugged (the leading @samp{/} still
15632 needs to be present, or else @value{GDBN} will interpret the number as
15633 a process ID rather than a thread ID).
15635 @item info proc mappings
15636 @cindex memory address space mappings
15637 Report the memory address space ranges accessible in the program, with
15638 information on whether the process has read, write, or execute access
15639 rights to each range. On @sc{gnu}/Linux systems, each memory range
15640 includes the object file which is mapped to that range, instead of the
15641 memory access rights to that range.
15643 @item info proc stat
15644 @itemx info proc status
15645 @cindex process detailed status information
15646 These subcommands are specific to @sc{gnu}/Linux systems. They show
15647 the process-related information, including the user ID and group ID;
15648 how many threads are there in the process; its virtual memory usage;
15649 the signals that are pending, blocked, and ignored; its TTY; its
15650 consumption of system and user time; its stack size; its @samp{nice}
15651 value; etc. For more information, see the @samp{proc} man page
15652 (type @kbd{man 5 proc} from your shell prompt).
15654 @item info proc all
15655 Show all the information about the process described under all of the
15656 above @code{info proc} subcommands.
15659 @comment These sub-options of 'info proc' were not included when
15660 @comment procfs.c was re-written. Keep their descriptions around
15661 @comment against the day when someone finds the time to put them back in.
15662 @kindex info proc times
15663 @item info proc times
15664 Starting time, user CPU time, and system CPU time for your program and
15667 @kindex info proc id
15669 Report on the process IDs related to your program: its own process ID,
15670 the ID of its parent, the process group ID, and the session ID.
15673 @item set procfs-trace
15674 @kindex set procfs-trace
15675 @cindex @code{procfs} API calls
15676 This command enables and disables tracing of @code{procfs} API calls.
15678 @item show procfs-trace
15679 @kindex show procfs-trace
15680 Show the current state of @code{procfs} API call tracing.
15682 @item set procfs-file @var{file}
15683 @kindex set procfs-file
15684 Tell @value{GDBN} to write @code{procfs} API trace to the named
15685 @var{file}. @value{GDBN} appends the trace info to the previous
15686 contents of the file. The default is to display the trace on the
15689 @item show procfs-file
15690 @kindex show procfs-file
15691 Show the file to which @code{procfs} API trace is written.
15693 @item proc-trace-entry
15694 @itemx proc-trace-exit
15695 @itemx proc-untrace-entry
15696 @itemx proc-untrace-exit
15697 @kindex proc-trace-entry
15698 @kindex proc-trace-exit
15699 @kindex proc-untrace-entry
15700 @kindex proc-untrace-exit
15701 These commands enable and disable tracing of entries into and exits
15702 from the @code{syscall} interface.
15705 @kindex info pidlist
15706 @cindex process list, QNX Neutrino
15707 For QNX Neutrino only, this command displays the list of all the
15708 processes and all the threads within each process.
15711 @kindex info meminfo
15712 @cindex mapinfo list, QNX Neutrino
15713 For QNX Neutrino only, this command displays the list of all mapinfos.
15717 @subsection Features for Debugging @sc{djgpp} Programs
15718 @cindex @sc{djgpp} debugging
15719 @cindex native @sc{djgpp} debugging
15720 @cindex MS-DOS-specific commands
15723 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
15724 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
15725 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
15726 top of real-mode DOS systems and their emulations.
15728 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
15729 defines a few commands specific to the @sc{djgpp} port. This
15730 subsection describes those commands.
15735 This is a prefix of @sc{djgpp}-specific commands which print
15736 information about the target system and important OS structures.
15739 @cindex MS-DOS system info
15740 @cindex free memory information (MS-DOS)
15741 @item info dos sysinfo
15742 This command displays assorted information about the underlying
15743 platform: the CPU type and features, the OS version and flavor, the
15744 DPMI version, and the available conventional and DPMI memory.
15749 @cindex segment descriptor tables
15750 @cindex descriptor tables display
15752 @itemx info dos ldt
15753 @itemx info dos idt
15754 These 3 commands display entries from, respectively, Global, Local,
15755 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
15756 tables are data structures which store a descriptor for each segment
15757 that is currently in use. The segment's selector is an index into a
15758 descriptor table; the table entry for that index holds the
15759 descriptor's base address and limit, and its attributes and access
15762 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
15763 segment (used for both data and the stack), and a DOS segment (which
15764 allows access to DOS/BIOS data structures and absolute addresses in
15765 conventional memory). However, the DPMI host will usually define
15766 additional segments in order to support the DPMI environment.
15768 @cindex garbled pointers
15769 These commands allow to display entries from the descriptor tables.
15770 Without an argument, all entries from the specified table are
15771 displayed. An argument, which should be an integer expression, means
15772 display a single entry whose index is given by the argument. For
15773 example, here's a convenient way to display information about the
15774 debugged program's data segment:
15777 @exdent @code{(@value{GDBP}) info dos ldt $ds}
15778 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
15782 This comes in handy when you want to see whether a pointer is outside
15783 the data segment's limit (i.e.@: @dfn{garbled}).
15785 @cindex page tables display (MS-DOS)
15787 @itemx info dos pte
15788 These two commands display entries from, respectively, the Page
15789 Directory and the Page Tables. Page Directories and Page Tables are
15790 data structures which control how virtual memory addresses are mapped
15791 into physical addresses. A Page Table includes an entry for every
15792 page of memory that is mapped into the program's address space; there
15793 may be several Page Tables, each one holding up to 4096 entries. A
15794 Page Directory has up to 4096 entries, one each for every Page Table
15795 that is currently in use.
15797 Without an argument, @kbd{info dos pde} displays the entire Page
15798 Directory, and @kbd{info dos pte} displays all the entries in all of
15799 the Page Tables. An argument, an integer expression, given to the
15800 @kbd{info dos pde} command means display only that entry from the Page
15801 Directory table. An argument given to the @kbd{info dos pte} command
15802 means display entries from a single Page Table, the one pointed to by
15803 the specified entry in the Page Directory.
15805 @cindex direct memory access (DMA) on MS-DOS
15806 These commands are useful when your program uses @dfn{DMA} (Direct
15807 Memory Access), which needs physical addresses to program the DMA
15810 These commands are supported only with some DPMI servers.
15812 @cindex physical address from linear address
15813 @item info dos address-pte @var{addr}
15814 This command displays the Page Table entry for a specified linear
15815 address. The argument @var{addr} is a linear address which should
15816 already have the appropriate segment's base address added to it,
15817 because this command accepts addresses which may belong to @emph{any}
15818 segment. For example, here's how to display the Page Table entry for
15819 the page where a variable @code{i} is stored:
15822 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
15823 @exdent @code{Page Table entry for address 0x11a00d30:}
15824 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
15828 This says that @code{i} is stored at offset @code{0xd30} from the page
15829 whose physical base address is @code{0x02698000}, and shows all the
15830 attributes of that page.
15832 Note that you must cast the addresses of variables to a @code{char *},
15833 since otherwise the value of @code{__djgpp_base_address}, the base
15834 address of all variables and functions in a @sc{djgpp} program, will
15835 be added using the rules of C pointer arithmetics: if @code{i} is
15836 declared an @code{int}, @value{GDBN} will add 4 times the value of
15837 @code{__djgpp_base_address} to the address of @code{i}.
15839 Here's another example, it displays the Page Table entry for the
15843 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
15844 @exdent @code{Page Table entry for address 0x29110:}
15845 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
15849 (The @code{+ 3} offset is because the transfer buffer's address is the
15850 3rd member of the @code{_go32_info_block} structure.) The output
15851 clearly shows that this DPMI server maps the addresses in conventional
15852 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
15853 linear (@code{0x29110}) addresses are identical.
15855 This command is supported only with some DPMI servers.
15858 @cindex DOS serial data link, remote debugging
15859 In addition to native debugging, the DJGPP port supports remote
15860 debugging via a serial data link. The following commands are specific
15861 to remote serial debugging in the DJGPP port of @value{GDBN}.
15864 @kindex set com1base
15865 @kindex set com1irq
15866 @kindex set com2base
15867 @kindex set com2irq
15868 @kindex set com3base
15869 @kindex set com3irq
15870 @kindex set com4base
15871 @kindex set com4irq
15872 @item set com1base @var{addr}
15873 This command sets the base I/O port address of the @file{COM1} serial
15876 @item set com1irq @var{irq}
15877 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
15878 for the @file{COM1} serial port.
15880 There are similar commands @samp{set com2base}, @samp{set com3irq},
15881 etc.@: for setting the port address and the @code{IRQ} lines for the
15884 @kindex show com1base
15885 @kindex show com1irq
15886 @kindex show com2base
15887 @kindex show com2irq
15888 @kindex show com3base
15889 @kindex show com3irq
15890 @kindex show com4base
15891 @kindex show com4irq
15892 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
15893 display the current settings of the base address and the @code{IRQ}
15894 lines used by the COM ports.
15897 @kindex info serial
15898 @cindex DOS serial port status
15899 This command prints the status of the 4 DOS serial ports. For each
15900 port, it prints whether it's active or not, its I/O base address and
15901 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
15902 counts of various errors encountered so far.
15906 @node Cygwin Native
15907 @subsection Features for Debugging MS Windows PE Executables
15908 @cindex MS Windows debugging
15909 @cindex native Cygwin debugging
15910 @cindex Cygwin-specific commands
15912 @value{GDBN} supports native debugging of MS Windows programs, including
15913 DLLs with and without symbolic debugging information.
15915 @cindex Ctrl-BREAK, MS-Windows
15916 @cindex interrupt debuggee on MS-Windows
15917 MS-Windows programs that call @code{SetConsoleMode} to switch off the
15918 special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted
15919 by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows
15920 supports @kbd{C-@key{BREAK}} as an alternative interrupt key
15921 sequence, which can be used to interrupt the debuggee even if it
15924 There are various additional Cygwin-specific commands, described in
15925 this section. Working with DLLs that have no debugging symbols is
15926 described in @ref{Non-debug DLL Symbols}.
15931 This is a prefix of MS Windows-specific commands which print
15932 information about the target system and important OS structures.
15934 @item info w32 selector
15935 This command displays information returned by
15936 the Win32 API @code{GetThreadSelectorEntry} function.
15937 It takes an optional argument that is evaluated to
15938 a long value to give the information about this given selector.
15939 Without argument, this command displays information
15940 about the six segment registers.
15944 This is a Cygwin-specific alias of @code{info shared}.
15946 @kindex dll-symbols
15948 This command loads symbols from a dll similarly to
15949 add-sym command but without the need to specify a base address.
15951 @kindex set cygwin-exceptions
15952 @cindex debugging the Cygwin DLL
15953 @cindex Cygwin DLL, debugging
15954 @item set cygwin-exceptions @var{mode}
15955 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
15956 happen inside the Cygwin DLL. If @var{mode} is @code{off},
15957 @value{GDBN} will delay recognition of exceptions, and may ignore some
15958 exceptions which seem to be caused by internal Cygwin DLL
15959 ``bookkeeping''. This option is meant primarily for debugging the
15960 Cygwin DLL itself; the default value is @code{off} to avoid annoying
15961 @value{GDBN} users with false @code{SIGSEGV} signals.
15963 @kindex show cygwin-exceptions
15964 @item show cygwin-exceptions
15965 Displays whether @value{GDBN} will break on exceptions that happen
15966 inside the Cygwin DLL itself.
15968 @kindex set new-console
15969 @item set new-console @var{mode}
15970 If @var{mode} is @code{on} the debuggee will
15971 be started in a new console on next start.
15972 If @var{mode} is @code{off}i, the debuggee will
15973 be started in the same console as the debugger.
15975 @kindex show new-console
15976 @item show new-console
15977 Displays whether a new console is used
15978 when the debuggee is started.
15980 @kindex set new-group
15981 @item set new-group @var{mode}
15982 This boolean value controls whether the debuggee should
15983 start a new group or stay in the same group as the debugger.
15984 This affects the way the Windows OS handles
15987 @kindex show new-group
15988 @item show new-group
15989 Displays current value of new-group boolean.
15991 @kindex set debugevents
15992 @item set debugevents
15993 This boolean value adds debug output concerning kernel events related
15994 to the debuggee seen by the debugger. This includes events that
15995 signal thread and process creation and exit, DLL loading and
15996 unloading, console interrupts, and debugging messages produced by the
15997 Windows @code{OutputDebugString} API call.
15999 @kindex set debugexec
16000 @item set debugexec
16001 This boolean value adds debug output concerning execute events
16002 (such as resume thread) seen by the debugger.
16004 @kindex set debugexceptions
16005 @item set debugexceptions
16006 This boolean value adds debug output concerning exceptions in the
16007 debuggee seen by the debugger.
16009 @kindex set debugmemory
16010 @item set debugmemory
16011 This boolean value adds debug output concerning debuggee memory reads
16012 and writes by the debugger.
16016 This boolean values specifies whether the debuggee is called
16017 via a shell or directly (default value is on).
16021 Displays if the debuggee will be started with a shell.
16026 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
16029 @node Non-debug DLL Symbols
16030 @subsubsection Support for DLLs without Debugging Symbols
16031 @cindex DLLs with no debugging symbols
16032 @cindex Minimal symbols and DLLs
16034 Very often on windows, some of the DLLs that your program relies on do
16035 not include symbolic debugging information (for example,
16036 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
16037 symbols in a DLL, it relies on the minimal amount of symbolic
16038 information contained in the DLL's export table. This section
16039 describes working with such symbols, known internally to @value{GDBN} as
16040 ``minimal symbols''.
16042 Note that before the debugged program has started execution, no DLLs
16043 will have been loaded. The easiest way around this problem is simply to
16044 start the program --- either by setting a breakpoint or letting the
16045 program run once to completion. It is also possible to force
16046 @value{GDBN} to load a particular DLL before starting the executable ---
16047 see the shared library information in @ref{Files}, or the
16048 @code{dll-symbols} command in @ref{Cygwin Native}. Currently,
16049 explicitly loading symbols from a DLL with no debugging information will
16050 cause the symbol names to be duplicated in @value{GDBN}'s lookup table,
16051 which may adversely affect symbol lookup performance.
16053 @subsubsection DLL Name Prefixes
16055 In keeping with the naming conventions used by the Microsoft debugging
16056 tools, DLL export symbols are made available with a prefix based on the
16057 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
16058 also entered into the symbol table, so @code{CreateFileA} is often
16059 sufficient. In some cases there will be name clashes within a program
16060 (particularly if the executable itself includes full debugging symbols)
16061 necessitating the use of the fully qualified name when referring to the
16062 contents of the DLL. Use single-quotes around the name to avoid the
16063 exclamation mark (``!'') being interpreted as a language operator.
16065 Note that the internal name of the DLL may be all upper-case, even
16066 though the file name of the DLL is lower-case, or vice-versa. Since
16067 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
16068 some confusion. If in doubt, try the @code{info functions} and
16069 @code{info variables} commands or even @code{maint print msymbols}
16070 (@pxref{Symbols}). Here's an example:
16073 (@value{GDBP}) info function CreateFileA
16074 All functions matching regular expression "CreateFileA":
16076 Non-debugging symbols:
16077 0x77e885f4 CreateFileA
16078 0x77e885f4 KERNEL32!CreateFileA
16082 (@value{GDBP}) info function !
16083 All functions matching regular expression "!":
16085 Non-debugging symbols:
16086 0x6100114c cygwin1!__assert
16087 0x61004034 cygwin1!_dll_crt0@@0
16088 0x61004240 cygwin1!dll_crt0(per_process *)
16092 @subsubsection Working with Minimal Symbols
16094 Symbols extracted from a DLL's export table do not contain very much
16095 type information. All that @value{GDBN} can do is guess whether a symbol
16096 refers to a function or variable depending on the linker section that
16097 contains the symbol. Also note that the actual contents of the memory
16098 contained in a DLL are not available unless the program is running. This
16099 means that you cannot examine the contents of a variable or disassemble
16100 a function within a DLL without a running program.
16102 Variables are generally treated as pointers and dereferenced
16103 automatically. For this reason, it is often necessary to prefix a
16104 variable name with the address-of operator (``&'') and provide explicit
16105 type information in the command. Here's an example of the type of
16109 (@value{GDBP}) print 'cygwin1!__argv'
16114 (@value{GDBP}) x 'cygwin1!__argv'
16115 0x10021610: "\230y\""
16118 And two possible solutions:
16121 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
16122 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
16126 (@value{GDBP}) x/2x &'cygwin1!__argv'
16127 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
16128 (@value{GDBP}) x/x 0x10021608
16129 0x10021608: 0x0022fd98
16130 (@value{GDBP}) x/s 0x0022fd98
16131 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
16134 Setting a break point within a DLL is possible even before the program
16135 starts execution. However, under these circumstances, @value{GDBN} can't
16136 examine the initial instructions of the function in order to skip the
16137 function's frame set-up code. You can work around this by using ``*&''
16138 to set the breakpoint at a raw memory address:
16141 (@value{GDBP}) break *&'python22!PyOS_Readline'
16142 Breakpoint 1 at 0x1e04eff0
16145 The author of these extensions is not entirely convinced that setting a
16146 break point within a shared DLL like @file{kernel32.dll} is completely
16150 @subsection Commands Specific to @sc{gnu} Hurd Systems
16151 @cindex @sc{gnu} Hurd debugging
16153 This subsection describes @value{GDBN} commands specific to the
16154 @sc{gnu} Hurd native debugging.
16159 @kindex set signals@r{, Hurd command}
16160 @kindex set sigs@r{, Hurd command}
16161 This command toggles the state of inferior signal interception by
16162 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
16163 affected by this command. @code{sigs} is a shorthand alias for
16168 @kindex show signals@r{, Hurd command}
16169 @kindex show sigs@r{, Hurd command}
16170 Show the current state of intercepting inferior's signals.
16172 @item set signal-thread
16173 @itemx set sigthread
16174 @kindex set signal-thread
16175 @kindex set sigthread
16176 This command tells @value{GDBN} which thread is the @code{libc} signal
16177 thread. That thread is run when a signal is delivered to a running
16178 process. @code{set sigthread} is the shorthand alias of @code{set
16181 @item show signal-thread
16182 @itemx show sigthread
16183 @kindex show signal-thread
16184 @kindex show sigthread
16185 These two commands show which thread will run when the inferior is
16186 delivered a signal.
16189 @kindex set stopped@r{, Hurd command}
16190 This commands tells @value{GDBN} that the inferior process is stopped,
16191 as with the @code{SIGSTOP} signal. The stopped process can be
16192 continued by delivering a signal to it.
16195 @kindex show stopped@r{, Hurd command}
16196 This command shows whether @value{GDBN} thinks the debuggee is
16199 @item set exceptions
16200 @kindex set exceptions@r{, Hurd command}
16201 Use this command to turn off trapping of exceptions in the inferior.
16202 When exception trapping is off, neither breakpoints nor
16203 single-stepping will work. To restore the default, set exception
16206 @item show exceptions
16207 @kindex show exceptions@r{, Hurd command}
16208 Show the current state of trapping exceptions in the inferior.
16210 @item set task pause
16211 @kindex set task@r{, Hurd commands}
16212 @cindex task attributes (@sc{gnu} Hurd)
16213 @cindex pause current task (@sc{gnu} Hurd)
16214 This command toggles task suspension when @value{GDBN} has control.
16215 Setting it to on takes effect immediately, and the task is suspended
16216 whenever @value{GDBN} gets control. Setting it to off will take
16217 effect the next time the inferior is continued. If this option is set
16218 to off, you can use @code{set thread default pause on} or @code{set
16219 thread pause on} (see below) to pause individual threads.
16221 @item show task pause
16222 @kindex show task@r{, Hurd commands}
16223 Show the current state of task suspension.
16225 @item set task detach-suspend-count
16226 @cindex task suspend count
16227 @cindex detach from task, @sc{gnu} Hurd
16228 This command sets the suspend count the task will be left with when
16229 @value{GDBN} detaches from it.
16231 @item show task detach-suspend-count
16232 Show the suspend count the task will be left with when detaching.
16234 @item set task exception-port
16235 @itemx set task excp
16236 @cindex task exception port, @sc{gnu} Hurd
16237 This command sets the task exception port to which @value{GDBN} will
16238 forward exceptions. The argument should be the value of the @dfn{send
16239 rights} of the task. @code{set task excp} is a shorthand alias.
16241 @item set noninvasive
16242 @cindex noninvasive task options
16243 This command switches @value{GDBN} to a mode that is the least
16244 invasive as far as interfering with the inferior is concerned. This
16245 is the same as using @code{set task pause}, @code{set exceptions}, and
16246 @code{set signals} to values opposite to the defaults.
16248 @item info send-rights
16249 @itemx info receive-rights
16250 @itemx info port-rights
16251 @itemx info port-sets
16252 @itemx info dead-names
16255 @cindex send rights, @sc{gnu} Hurd
16256 @cindex receive rights, @sc{gnu} Hurd
16257 @cindex port rights, @sc{gnu} Hurd
16258 @cindex port sets, @sc{gnu} Hurd
16259 @cindex dead names, @sc{gnu} Hurd
16260 These commands display information about, respectively, send rights,
16261 receive rights, port rights, port sets, and dead names of a task.
16262 There are also shorthand aliases: @code{info ports} for @code{info
16263 port-rights} and @code{info psets} for @code{info port-sets}.
16265 @item set thread pause
16266 @kindex set thread@r{, Hurd command}
16267 @cindex thread properties, @sc{gnu} Hurd
16268 @cindex pause current thread (@sc{gnu} Hurd)
16269 This command toggles current thread suspension when @value{GDBN} has
16270 control. Setting it to on takes effect immediately, and the current
16271 thread is suspended whenever @value{GDBN} gets control. Setting it to
16272 off will take effect the next time the inferior is continued.
16273 Normally, this command has no effect, since when @value{GDBN} has
16274 control, the whole task is suspended. However, if you used @code{set
16275 task pause off} (see above), this command comes in handy to suspend
16276 only the current thread.
16278 @item show thread pause
16279 @kindex show thread@r{, Hurd command}
16280 This command shows the state of current thread suspension.
16282 @item set thread run
16283 This command sets whether the current thread is allowed to run.
16285 @item show thread run
16286 Show whether the current thread is allowed to run.
16288 @item set thread detach-suspend-count
16289 @cindex thread suspend count, @sc{gnu} Hurd
16290 @cindex detach from thread, @sc{gnu} Hurd
16291 This command sets the suspend count @value{GDBN} will leave on a
16292 thread when detaching. This number is relative to the suspend count
16293 found by @value{GDBN} when it notices the thread; use @code{set thread
16294 takeover-suspend-count} to force it to an absolute value.
16296 @item show thread detach-suspend-count
16297 Show the suspend count @value{GDBN} will leave on the thread when
16300 @item set thread exception-port
16301 @itemx set thread excp
16302 Set the thread exception port to which to forward exceptions. This
16303 overrides the port set by @code{set task exception-port} (see above).
16304 @code{set thread excp} is the shorthand alias.
16306 @item set thread takeover-suspend-count
16307 Normally, @value{GDBN}'s thread suspend counts are relative to the
16308 value @value{GDBN} finds when it notices each thread. This command
16309 changes the suspend counts to be absolute instead.
16311 @item set thread default
16312 @itemx show thread default
16313 @cindex thread default settings, @sc{gnu} Hurd
16314 Each of the above @code{set thread} commands has a @code{set thread
16315 default} counterpart (e.g., @code{set thread default pause}, @code{set
16316 thread default exception-port}, etc.). The @code{thread default}
16317 variety of commands sets the default thread properties for all
16318 threads; you can then change the properties of individual threads with
16319 the non-default commands.
16324 @subsection QNX Neutrino
16325 @cindex QNX Neutrino
16327 @value{GDBN} provides the following commands specific to the QNX
16331 @item set debug nto-debug
16332 @kindex set debug nto-debug
16333 When set to on, enables debugging messages specific to the QNX
16336 @item show debug nto-debug
16337 @kindex show debug nto-debug
16338 Show the current state of QNX Neutrino messages.
16345 @value{GDBN} provides the following commands specific to the Darwin target:
16348 @item set debug darwin @var{num}
16349 @kindex set debug darwin
16350 When set to a non zero value, enables debugging messages specific to
16351 the Darwin support. Higher values produce more verbose output.
16353 @item show debug darwin
16354 @kindex show debug darwin
16355 Show the current state of Darwin messages.
16357 @item set debug mach-o @var{num}
16358 @kindex set debug mach-o
16359 When set to a non zero value, enables debugging messages while
16360 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
16361 file format used on Darwin for object and executable files.) Higher
16362 values produce more verbose output. This is a command to diagnose
16363 problems internal to @value{GDBN} and should not be needed in normal
16366 @item show debug mach-o
16367 @kindex show debug mach-o
16368 Show the current state of Mach-O file messages.
16370 @item set mach-exceptions on
16371 @itemx set mach-exceptions off
16372 @kindex set mach-exceptions
16373 On Darwin, faults are first reported as a Mach exception and are then
16374 mapped to a Posix signal. Use this command to turn on trapping of
16375 Mach exceptions in the inferior. This might be sometimes useful to
16376 better understand the cause of a fault. The default is off.
16378 @item show mach-exceptions
16379 @kindex show mach-exceptions
16380 Show the current state of exceptions trapping.
16385 @section Embedded Operating Systems
16387 This section describes configurations involving the debugging of
16388 embedded operating systems that are available for several different
16392 * VxWorks:: Using @value{GDBN} with VxWorks
16395 @value{GDBN} includes the ability to debug programs running on
16396 various real-time operating systems.
16399 @subsection Using @value{GDBN} with VxWorks
16405 @kindex target vxworks
16406 @item target vxworks @var{machinename}
16407 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
16408 is the target system's machine name or IP address.
16412 On VxWorks, @code{load} links @var{filename} dynamically on the
16413 current target system as well as adding its symbols in @value{GDBN}.
16415 @value{GDBN} enables developers to spawn and debug tasks running on networked
16416 VxWorks targets from a Unix host. Already-running tasks spawned from
16417 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
16418 both the Unix host and on the VxWorks target. The program
16419 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
16420 installed with the name @code{vxgdb}, to distinguish it from a
16421 @value{GDBN} for debugging programs on the host itself.)
16424 @item VxWorks-timeout @var{args}
16425 @kindex vxworks-timeout
16426 All VxWorks-based targets now support the option @code{vxworks-timeout}.
16427 This option is set by the user, and @var{args} represents the number of
16428 seconds @value{GDBN} waits for responses to rpc's. You might use this if
16429 your VxWorks target is a slow software simulator or is on the far side
16430 of a thin network line.
16433 The following information on connecting to VxWorks was current when
16434 this manual was produced; newer releases of VxWorks may use revised
16437 @findex INCLUDE_RDB
16438 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
16439 to include the remote debugging interface routines in the VxWorks
16440 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
16441 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
16442 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
16443 source debugging task @code{tRdbTask} when VxWorks is booted. For more
16444 information on configuring and remaking VxWorks, see the manufacturer's
16446 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
16448 Once you have included @file{rdb.a} in your VxWorks system image and set
16449 your Unix execution search path to find @value{GDBN}, you are ready to
16450 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
16451 @code{vxgdb}, depending on your installation).
16453 @value{GDBN} comes up showing the prompt:
16460 * VxWorks Connection:: Connecting to VxWorks
16461 * VxWorks Download:: VxWorks download
16462 * VxWorks Attach:: Running tasks
16465 @node VxWorks Connection
16466 @subsubsection Connecting to VxWorks
16468 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
16469 network. To connect to a target whose host name is ``@code{tt}'', type:
16472 (vxgdb) target vxworks tt
16476 @value{GDBN} displays messages like these:
16479 Attaching remote machine across net...
16484 @value{GDBN} then attempts to read the symbol tables of any object modules
16485 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
16486 these files by searching the directories listed in the command search
16487 path (@pxref{Environment, ,Your Program's Environment}); if it fails
16488 to find an object file, it displays a message such as:
16491 prog.o: No such file or directory.
16494 When this happens, add the appropriate directory to the search path with
16495 the @value{GDBN} command @code{path}, and execute the @code{target}
16498 @node VxWorks Download
16499 @subsubsection VxWorks Download
16501 @cindex download to VxWorks
16502 If you have connected to the VxWorks target and you want to debug an
16503 object that has not yet been loaded, you can use the @value{GDBN}
16504 @code{load} command to download a file from Unix to VxWorks
16505 incrementally. The object file given as an argument to the @code{load}
16506 command is actually opened twice: first by the VxWorks target in order
16507 to download the code, then by @value{GDBN} in order to read the symbol
16508 table. This can lead to problems if the current working directories on
16509 the two systems differ. If both systems have NFS mounted the same
16510 filesystems, you can avoid these problems by using absolute paths.
16511 Otherwise, it is simplest to set the working directory on both systems
16512 to the directory in which the object file resides, and then to reference
16513 the file by its name, without any path. For instance, a program
16514 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
16515 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
16516 program, type this on VxWorks:
16519 -> cd "@var{vxpath}/vw/demo/rdb"
16523 Then, in @value{GDBN}, type:
16526 (vxgdb) cd @var{hostpath}/vw/demo/rdb
16527 (vxgdb) load prog.o
16530 @value{GDBN} displays a response similar to this:
16533 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
16536 You can also use the @code{load} command to reload an object module
16537 after editing and recompiling the corresponding source file. Note that
16538 this makes @value{GDBN} delete all currently-defined breakpoints,
16539 auto-displays, and convenience variables, and to clear the value
16540 history. (This is necessary in order to preserve the integrity of
16541 debugger's data structures that reference the target system's symbol
16544 @node VxWorks Attach
16545 @subsubsection Running Tasks
16547 @cindex running VxWorks tasks
16548 You can also attach to an existing task using the @code{attach} command as
16552 (vxgdb) attach @var{task}
16556 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
16557 or suspended when you attach to it. Running tasks are suspended at
16558 the time of attachment.
16560 @node Embedded Processors
16561 @section Embedded Processors
16563 This section goes into details specific to particular embedded
16566 @cindex send command to simulator
16567 Whenever a specific embedded processor has a simulator, @value{GDBN}
16568 allows to send an arbitrary command to the simulator.
16571 @item sim @var{command}
16572 @kindex sim@r{, a command}
16573 Send an arbitrary @var{command} string to the simulator. Consult the
16574 documentation for the specific simulator in use for information about
16575 acceptable commands.
16581 * M32R/D:: Renesas M32R/D
16582 * M68K:: Motorola M68K
16583 * MicroBlaze:: Xilinx MicroBlaze
16584 * MIPS Embedded:: MIPS Embedded
16585 * OpenRISC 1000:: OpenRisc 1000
16586 * PA:: HP PA Embedded
16587 * PowerPC Embedded:: PowerPC Embedded
16588 * Sparclet:: Tsqware Sparclet
16589 * Sparclite:: Fujitsu Sparclite
16590 * Z8000:: Zilog Z8000
16593 * Super-H:: Renesas Super-H
16602 @item target rdi @var{dev}
16603 ARM Angel monitor, via RDI library interface to ADP protocol. You may
16604 use this target to communicate with both boards running the Angel
16605 monitor, or with the EmbeddedICE JTAG debug device.
16608 @item target rdp @var{dev}
16613 @value{GDBN} provides the following ARM-specific commands:
16616 @item set arm disassembler
16618 This commands selects from a list of disassembly styles. The
16619 @code{"std"} style is the standard style.
16621 @item show arm disassembler
16623 Show the current disassembly style.
16625 @item set arm apcs32
16626 @cindex ARM 32-bit mode
16627 This command toggles ARM operation mode between 32-bit and 26-bit.
16629 @item show arm apcs32
16630 Display the current usage of the ARM 32-bit mode.
16632 @item set arm fpu @var{fputype}
16633 This command sets the ARM floating-point unit (FPU) type. The
16634 argument @var{fputype} can be one of these:
16638 Determine the FPU type by querying the OS ABI.
16640 Software FPU, with mixed-endian doubles on little-endian ARM
16643 GCC-compiled FPA co-processor.
16645 Software FPU with pure-endian doubles.
16651 Show the current type of the FPU.
16654 This command forces @value{GDBN} to use the specified ABI.
16657 Show the currently used ABI.
16659 @item set arm fallback-mode (arm|thumb|auto)
16660 @value{GDBN} uses the symbol table, when available, to determine
16661 whether instructions are ARM or Thumb. This command controls
16662 @value{GDBN}'s default behavior when the symbol table is not
16663 available. The default is @samp{auto}, which causes @value{GDBN} to
16664 use the current execution mode (from the @code{T} bit in the @code{CPSR}
16667 @item show arm fallback-mode
16668 Show the current fallback instruction mode.
16670 @item set arm force-mode (arm|thumb|auto)
16671 This command overrides use of the symbol table to determine whether
16672 instructions are ARM or Thumb. The default is @samp{auto}, which
16673 causes @value{GDBN} to use the symbol table and then the setting
16674 of @samp{set arm fallback-mode}.
16676 @item show arm force-mode
16677 Show the current forced instruction mode.
16679 @item set debug arm
16680 Toggle whether to display ARM-specific debugging messages from the ARM
16681 target support subsystem.
16683 @item show debug arm
16684 Show whether ARM-specific debugging messages are enabled.
16687 The following commands are available when an ARM target is debugged
16688 using the RDI interface:
16691 @item rdilogfile @r{[}@var{file}@r{]}
16693 @cindex ADP (Angel Debugger Protocol) logging
16694 Set the filename for the ADP (Angel Debugger Protocol) packet log.
16695 With an argument, sets the log file to the specified @var{file}. With
16696 no argument, show the current log file name. The default log file is
16699 @item rdilogenable @r{[}@var{arg}@r{]}
16700 @kindex rdilogenable
16701 Control logging of ADP packets. With an argument of 1 or @code{"yes"}
16702 enables logging, with an argument 0 or @code{"no"} disables it. With
16703 no arguments displays the current setting. When logging is enabled,
16704 ADP packets exchanged between @value{GDBN} and the RDI target device
16705 are logged to a file.
16707 @item set rdiromatzero
16708 @kindex set rdiromatzero
16709 @cindex ROM at zero address, RDI
16710 Tell @value{GDBN} whether the target has ROM at address 0. If on,
16711 vector catching is disabled, so that zero address can be used. If off
16712 (the default), vector catching is enabled. For this command to take
16713 effect, it needs to be invoked prior to the @code{target rdi} command.
16715 @item show rdiromatzero
16716 @kindex show rdiromatzero
16717 Show the current setting of ROM at zero address.
16719 @item set rdiheartbeat
16720 @kindex set rdiheartbeat
16721 @cindex RDI heartbeat
16722 Enable or disable RDI heartbeat packets. It is not recommended to
16723 turn on this option, since it confuses ARM and EPI JTAG interface, as
16724 well as the Angel monitor.
16726 @item show rdiheartbeat
16727 @kindex show rdiheartbeat
16728 Show the setting of RDI heartbeat packets.
16733 @subsection Renesas M32R/D and M32R/SDI
16736 @kindex target m32r
16737 @item target m32r @var{dev}
16738 Renesas M32R/D ROM monitor.
16740 @kindex target m32rsdi
16741 @item target m32rsdi @var{dev}
16742 Renesas M32R SDI server, connected via parallel port to the board.
16745 The following @value{GDBN} commands are specific to the M32R monitor:
16748 @item set download-path @var{path}
16749 @kindex set download-path
16750 @cindex find downloadable @sc{srec} files (M32R)
16751 Set the default path for finding downloadable @sc{srec} files.
16753 @item show download-path
16754 @kindex show download-path
16755 Show the default path for downloadable @sc{srec} files.
16757 @item set board-address @var{addr}
16758 @kindex set board-address
16759 @cindex M32-EVA target board address
16760 Set the IP address for the M32R-EVA target board.
16762 @item show board-address
16763 @kindex show board-address
16764 Show the current IP address of the target board.
16766 @item set server-address @var{addr}
16767 @kindex set server-address
16768 @cindex download server address (M32R)
16769 Set the IP address for the download server, which is the @value{GDBN}'s
16772 @item show server-address
16773 @kindex show server-address
16774 Display the IP address of the download server.
16776 @item upload @r{[}@var{file}@r{]}
16777 @kindex upload@r{, M32R}
16778 Upload the specified @sc{srec} @var{file} via the monitor's Ethernet
16779 upload capability. If no @var{file} argument is given, the current
16780 executable file is uploaded.
16782 @item tload @r{[}@var{file}@r{]}
16783 @kindex tload@r{, M32R}
16784 Test the @code{upload} command.
16787 The following commands are available for M32R/SDI:
16792 @cindex reset SDI connection, M32R
16793 This command resets the SDI connection.
16797 This command shows the SDI connection status.
16800 @kindex debug_chaos
16801 @cindex M32R/Chaos debugging
16802 Instructs the remote that M32R/Chaos debugging is to be used.
16804 @item use_debug_dma
16805 @kindex use_debug_dma
16806 Instructs the remote to use the DEBUG_DMA method of accessing memory.
16809 @kindex use_mon_code
16810 Instructs the remote to use the MON_CODE method of accessing memory.
16813 @kindex use_ib_break
16814 Instructs the remote to set breakpoints by IB break.
16816 @item use_dbt_break
16817 @kindex use_dbt_break
16818 Instructs the remote to set breakpoints by DBT.
16824 The Motorola m68k configuration includes ColdFire support, and a
16825 target command for the following ROM monitor.
16829 @kindex target dbug
16830 @item target dbug @var{dev}
16831 dBUG ROM monitor for Motorola ColdFire.
16836 @subsection MicroBlaze
16837 @cindex Xilinx MicroBlaze
16838 @cindex XMD, Xilinx Microprocessor Debugger
16840 The MicroBlaze is a soft-core processor supported on various Xilinx
16841 FPGAs, such as Spartan or Virtex series. Boards with these processors
16842 usually have JTAG ports which connect to a host system running the Xilinx
16843 Embedded Development Kit (EDK) or Software Development Kit (SDK).
16844 This host system is used to download the configuration bitstream to
16845 the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
16846 communicates with the target board using the JTAG interface and
16847 presents a @code{gdbserver} interface to the board. By default
16848 @code{xmd} uses port @code{1234}. (While it is possible to change
16849 this default port, it requires the use of undocumented @code{xmd}
16850 commands. Contact Xilinx support if you need to do this.)
16852 Use these GDB commands to connect to the MicroBlaze target processor.
16855 @item target remote :1234
16856 Use this command to connect to the target if you are running @value{GDBN}
16857 on the same system as @code{xmd}.
16859 @item target remote @var{xmd-host}:1234
16860 Use this command to connect to the target if it is connected to @code{xmd}
16861 running on a different system named @var{xmd-host}.
16864 Use this command to download a program to the MicroBlaze target.
16866 @item set debug microblaze @var{n}
16867 Enable MicroBlaze-specific debugging messages if non-zero.
16869 @item show debug microblaze @var{n}
16870 Show MicroBlaze-specific debugging level.
16873 @node MIPS Embedded
16874 @subsection MIPS Embedded
16876 @cindex MIPS boards
16877 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
16878 MIPS board attached to a serial line. This is available when
16879 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
16882 Use these @value{GDBN} commands to specify the connection to your target board:
16885 @item target mips @var{port}
16886 @kindex target mips @var{port}
16887 To run a program on the board, start up @code{@value{GDBP}} with the
16888 name of your program as the argument. To connect to the board, use the
16889 command @samp{target mips @var{port}}, where @var{port} is the name of
16890 the serial port connected to the board. If the program has not already
16891 been downloaded to the board, you may use the @code{load} command to
16892 download it. You can then use all the usual @value{GDBN} commands.
16894 For example, this sequence connects to the target board through a serial
16895 port, and loads and runs a program called @var{prog} through the
16899 host$ @value{GDBP} @var{prog}
16900 @value{GDBN} is free software and @dots{}
16901 (@value{GDBP}) target mips /dev/ttyb
16902 (@value{GDBP}) load @var{prog}
16906 @item target mips @var{hostname}:@var{portnumber}
16907 On some @value{GDBN} host configurations, you can specify a TCP
16908 connection (for instance, to a serial line managed by a terminal
16909 concentrator) instead of a serial port, using the syntax
16910 @samp{@var{hostname}:@var{portnumber}}.
16912 @item target pmon @var{port}
16913 @kindex target pmon @var{port}
16916 @item target ddb @var{port}
16917 @kindex target ddb @var{port}
16918 NEC's DDB variant of PMON for Vr4300.
16920 @item target lsi @var{port}
16921 @kindex target lsi @var{port}
16922 LSI variant of PMON.
16924 @kindex target r3900
16925 @item target r3900 @var{dev}
16926 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
16928 @kindex target array
16929 @item target array @var{dev}
16930 Array Tech LSI33K RAID controller board.
16936 @value{GDBN} also supports these special commands for MIPS targets:
16939 @item set mipsfpu double
16940 @itemx set mipsfpu single
16941 @itemx set mipsfpu none
16942 @itemx set mipsfpu auto
16943 @itemx show mipsfpu
16944 @kindex set mipsfpu
16945 @kindex show mipsfpu
16946 @cindex MIPS remote floating point
16947 @cindex floating point, MIPS remote
16948 If your target board does not support the MIPS floating point
16949 coprocessor, you should use the command @samp{set mipsfpu none} (if you
16950 need this, you may wish to put the command in your @value{GDBN} init
16951 file). This tells @value{GDBN} how to find the return value of
16952 functions which return floating point values. It also allows
16953 @value{GDBN} to avoid saving the floating point registers when calling
16954 functions on the board. If you are using a floating point coprocessor
16955 with only single precision floating point support, as on the @sc{r4650}
16956 processor, use the command @samp{set mipsfpu single}. The default
16957 double precision floating point coprocessor may be selected using
16958 @samp{set mipsfpu double}.
16960 In previous versions the only choices were double precision or no
16961 floating point, so @samp{set mipsfpu on} will select double precision
16962 and @samp{set mipsfpu off} will select no floating point.
16964 As usual, you can inquire about the @code{mipsfpu} variable with
16965 @samp{show mipsfpu}.
16967 @item set timeout @var{seconds}
16968 @itemx set retransmit-timeout @var{seconds}
16969 @itemx show timeout
16970 @itemx show retransmit-timeout
16971 @cindex @code{timeout}, MIPS protocol
16972 @cindex @code{retransmit-timeout}, MIPS protocol
16973 @kindex set timeout
16974 @kindex show timeout
16975 @kindex set retransmit-timeout
16976 @kindex show retransmit-timeout
16977 You can control the timeout used while waiting for a packet, in the MIPS
16978 remote protocol, with the @code{set timeout @var{seconds}} command. The
16979 default is 5 seconds. Similarly, you can control the timeout used while
16980 waiting for an acknowledgment of a packet with the @code{set
16981 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
16982 You can inspect both values with @code{show timeout} and @code{show
16983 retransmit-timeout}. (These commands are @emph{only} available when
16984 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
16986 The timeout set by @code{set timeout} does not apply when @value{GDBN}
16987 is waiting for your program to stop. In that case, @value{GDBN} waits
16988 forever because it has no way of knowing how long the program is going
16989 to run before stopping.
16991 @item set syn-garbage-limit @var{num}
16992 @kindex set syn-garbage-limit@r{, MIPS remote}
16993 @cindex synchronize with remote MIPS target
16994 Limit the maximum number of characters @value{GDBN} should ignore when
16995 it tries to synchronize with the remote target. The default is 10
16996 characters. Setting the limit to -1 means there's no limit.
16998 @item show syn-garbage-limit
16999 @kindex show syn-garbage-limit@r{, MIPS remote}
17000 Show the current limit on the number of characters to ignore when
17001 trying to synchronize with the remote system.
17003 @item set monitor-prompt @var{prompt}
17004 @kindex set monitor-prompt@r{, MIPS remote}
17005 @cindex remote monitor prompt
17006 Tell @value{GDBN} to expect the specified @var{prompt} string from the
17007 remote monitor. The default depends on the target:
17017 @item show monitor-prompt
17018 @kindex show monitor-prompt@r{, MIPS remote}
17019 Show the current strings @value{GDBN} expects as the prompt from the
17022 @item set monitor-warnings
17023 @kindex set monitor-warnings@r{, MIPS remote}
17024 Enable or disable monitor warnings about hardware breakpoints. This
17025 has effect only for the @code{lsi} target. When on, @value{GDBN} will
17026 display warning messages whose codes are returned by the @code{lsi}
17027 PMON monitor for breakpoint commands.
17029 @item show monitor-warnings
17030 @kindex show monitor-warnings@r{, MIPS remote}
17031 Show the current setting of printing monitor warnings.
17033 @item pmon @var{command}
17034 @kindex pmon@r{, MIPS remote}
17035 @cindex send PMON command
17036 This command allows sending an arbitrary @var{command} string to the
17037 monitor. The monitor must be in debug mode for this to work.
17040 @node OpenRISC 1000
17041 @subsection OpenRISC 1000
17042 @cindex OpenRISC 1000
17044 @cindex or1k boards
17045 See OR1k Architecture document (@uref{www.opencores.org}) for more information
17046 about platform and commands.
17050 @kindex target jtag
17051 @item target jtag jtag://@var{host}:@var{port}
17053 Connects to remote JTAG server.
17054 JTAG remote server can be either an or1ksim or JTAG server,
17055 connected via parallel port to the board.
17057 Example: @code{target jtag jtag://localhost:9999}
17060 @item or1ksim @var{command}
17061 If connected to @code{or1ksim} OpenRISC 1000 Architectural
17062 Simulator, proprietary commands can be executed.
17064 @kindex info or1k spr
17065 @item info or1k spr
17066 Displays spr groups.
17068 @item info or1k spr @var{group}
17069 @itemx info or1k spr @var{groupno}
17070 Displays register names in selected group.
17072 @item info or1k spr @var{group} @var{register}
17073 @itemx info or1k spr @var{register}
17074 @itemx info or1k spr @var{groupno} @var{registerno}
17075 @itemx info or1k spr @var{registerno}
17076 Shows information about specified spr register.
17079 @item spr @var{group} @var{register} @var{value}
17080 @itemx spr @var{register @var{value}}
17081 @itemx spr @var{groupno} @var{registerno @var{value}}
17082 @itemx spr @var{registerno @var{value}}
17083 Writes @var{value} to specified spr register.
17086 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
17087 It is very similar to @value{GDBN} trace, except it does not interfere with normal
17088 program execution and is thus much faster. Hardware breakpoints/watchpoint
17089 triggers can be set using:
17092 Load effective address/data
17094 Store effective address/data
17096 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
17101 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
17102 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
17104 @code{htrace} commands:
17105 @cindex OpenRISC 1000 htrace
17108 @item hwatch @var{conditional}
17109 Set hardware watchpoint on combination of Load/Store Effective Address(es)
17110 or Data. For example:
17112 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
17114 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
17118 Display information about current HW trace configuration.
17120 @item htrace trigger @var{conditional}
17121 Set starting criteria for HW trace.
17123 @item htrace qualifier @var{conditional}
17124 Set acquisition qualifier for HW trace.
17126 @item htrace stop @var{conditional}
17127 Set HW trace stopping criteria.
17129 @item htrace record [@var{data}]*
17130 Selects the data to be recorded, when qualifier is met and HW trace was
17133 @item htrace enable
17134 @itemx htrace disable
17135 Enables/disables the HW trace.
17137 @item htrace rewind [@var{filename}]
17138 Clears currently recorded trace data.
17140 If filename is specified, new trace file is made and any newly collected data
17141 will be written there.
17143 @item htrace print [@var{start} [@var{len}]]
17144 Prints trace buffer, using current record configuration.
17146 @item htrace mode continuous
17147 Set continuous trace mode.
17149 @item htrace mode suspend
17150 Set suspend trace mode.
17154 @node PowerPC Embedded
17155 @subsection PowerPC Embedded
17157 @value{GDBN} provides the following PowerPC-specific commands:
17160 @kindex set powerpc
17161 @item set powerpc soft-float
17162 @itemx show powerpc soft-float
17163 Force @value{GDBN} to use (or not use) a software floating point calling
17164 convention. By default, @value{GDBN} selects the calling convention based
17165 on the selected architecture and the provided executable file.
17167 @item set powerpc vector-abi
17168 @itemx show powerpc vector-abi
17169 Force @value{GDBN} to use the specified calling convention for vector
17170 arguments and return values. The valid options are @samp{auto};
17171 @samp{generic}, to avoid vector registers even if they are present;
17172 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
17173 registers. By default, @value{GDBN} selects the calling convention
17174 based on the selected architecture and the provided executable file.
17176 @kindex target dink32
17177 @item target dink32 @var{dev}
17178 DINK32 ROM monitor.
17180 @kindex target ppcbug
17181 @item target ppcbug @var{dev}
17182 @kindex target ppcbug1
17183 @item target ppcbug1 @var{dev}
17184 PPCBUG ROM monitor for PowerPC.
17187 @item target sds @var{dev}
17188 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
17191 @cindex SDS protocol
17192 The following commands specific to the SDS protocol are supported
17196 @item set sdstimeout @var{nsec}
17197 @kindex set sdstimeout
17198 Set the timeout for SDS protocol reads to be @var{nsec} seconds. The
17199 default is 2 seconds.
17201 @item show sdstimeout
17202 @kindex show sdstimeout
17203 Show the current value of the SDS timeout.
17205 @item sds @var{command}
17206 @kindex sds@r{, a command}
17207 Send the specified @var{command} string to the SDS monitor.
17212 @subsection HP PA Embedded
17216 @kindex target op50n
17217 @item target op50n @var{dev}
17218 OP50N monitor, running on an OKI HPPA board.
17220 @kindex target w89k
17221 @item target w89k @var{dev}
17222 W89K monitor, running on a Winbond HPPA board.
17227 @subsection Tsqware Sparclet
17231 @value{GDBN} enables developers to debug tasks running on
17232 Sparclet targets from a Unix host.
17233 @value{GDBN} uses code that runs on
17234 both the Unix host and on the Sparclet target. The program
17235 @code{@value{GDBP}} is installed and executed on the Unix host.
17238 @item remotetimeout @var{args}
17239 @kindex remotetimeout
17240 @value{GDBN} supports the option @code{remotetimeout}.
17241 This option is set by the user, and @var{args} represents the number of
17242 seconds @value{GDBN} waits for responses.
17245 @cindex compiling, on Sparclet
17246 When compiling for debugging, include the options @samp{-g} to get debug
17247 information and @samp{-Ttext} to relocate the program to where you wish to
17248 load it on the target. You may also want to add the options @samp{-n} or
17249 @samp{-N} in order to reduce the size of the sections. Example:
17252 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
17255 You can use @code{objdump} to verify that the addresses are what you intended:
17258 sparclet-aout-objdump --headers --syms prog
17261 @cindex running, on Sparclet
17263 your Unix execution search path to find @value{GDBN}, you are ready to
17264 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
17265 (or @code{sparclet-aout-gdb}, depending on your installation).
17267 @value{GDBN} comes up showing the prompt:
17274 * Sparclet File:: Setting the file to debug
17275 * Sparclet Connection:: Connecting to Sparclet
17276 * Sparclet Download:: Sparclet download
17277 * Sparclet Execution:: Running and debugging
17280 @node Sparclet File
17281 @subsubsection Setting File to Debug
17283 The @value{GDBN} command @code{file} lets you choose with program to debug.
17286 (gdbslet) file prog
17290 @value{GDBN} then attempts to read the symbol table of @file{prog}.
17291 @value{GDBN} locates
17292 the file by searching the directories listed in the command search
17294 If the file was compiled with debug information (option @samp{-g}), source
17295 files will be searched as well.
17296 @value{GDBN} locates
17297 the source files by searching the directories listed in the directory search
17298 path (@pxref{Environment, ,Your Program's Environment}).
17300 to find a file, it displays a message such as:
17303 prog: No such file or directory.
17306 When this happens, add the appropriate directories to the search paths with
17307 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
17308 @code{target} command again.
17310 @node Sparclet Connection
17311 @subsubsection Connecting to Sparclet
17313 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
17314 To connect to a target on serial port ``@code{ttya}'', type:
17317 (gdbslet) target sparclet /dev/ttya
17318 Remote target sparclet connected to /dev/ttya
17319 main () at ../prog.c:3
17323 @value{GDBN} displays messages like these:
17329 @node Sparclet Download
17330 @subsubsection Sparclet Download
17332 @cindex download to Sparclet
17333 Once connected to the Sparclet target,
17334 you can use the @value{GDBN}
17335 @code{load} command to download the file from the host to the target.
17336 The file name and load offset should be given as arguments to the @code{load}
17338 Since the file format is aout, the program must be loaded to the starting
17339 address. You can use @code{objdump} to find out what this value is. The load
17340 offset is an offset which is added to the VMA (virtual memory address)
17341 of each of the file's sections.
17342 For instance, if the program
17343 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
17344 and bss at 0x12010170, in @value{GDBN}, type:
17347 (gdbslet) load prog 0x12010000
17348 Loading section .text, size 0xdb0 vma 0x12010000
17351 If the code is loaded at a different address then what the program was linked
17352 to, you may need to use the @code{section} and @code{add-symbol-file} commands
17353 to tell @value{GDBN} where to map the symbol table.
17355 @node Sparclet Execution
17356 @subsubsection Running and Debugging
17358 @cindex running and debugging Sparclet programs
17359 You can now begin debugging the task using @value{GDBN}'s execution control
17360 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
17361 manual for the list of commands.
17365 Breakpoint 1 at 0x12010000: file prog.c, line 3.
17367 Starting program: prog
17368 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
17369 3 char *symarg = 0;
17371 4 char *execarg = "hello!";
17376 @subsection Fujitsu Sparclite
17380 @kindex target sparclite
17381 @item target sparclite @var{dev}
17382 Fujitsu sparclite boards, used only for the purpose of loading.
17383 You must use an additional command to debug the program.
17384 For example: target remote @var{dev} using @value{GDBN} standard
17390 @subsection Zilog Z8000
17393 @cindex simulator, Z8000
17394 @cindex Zilog Z8000 simulator
17396 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
17399 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
17400 unsegmented variant of the Z8000 architecture) or the Z8001 (the
17401 segmented variant). The simulator recognizes which architecture is
17402 appropriate by inspecting the object code.
17405 @item target sim @var{args}
17407 @kindex target sim@r{, with Z8000}
17408 Debug programs on a simulated CPU. If the simulator supports setup
17409 options, specify them via @var{args}.
17413 After specifying this target, you can debug programs for the simulated
17414 CPU in the same style as programs for your host computer; use the
17415 @code{file} command to load a new program image, the @code{run} command
17416 to run your program, and so on.
17418 As well as making available all the usual machine registers
17419 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
17420 additional items of information as specially named registers:
17425 Counts clock-ticks in the simulator.
17428 Counts instructions run in the simulator.
17431 Execution time in 60ths of a second.
17435 You can refer to these values in @value{GDBN} expressions with the usual
17436 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
17437 conditional breakpoint that suspends only after at least 5000
17438 simulated clock ticks.
17441 @subsection Atmel AVR
17444 When configured for debugging the Atmel AVR, @value{GDBN} supports the
17445 following AVR-specific commands:
17448 @item info io_registers
17449 @kindex info io_registers@r{, AVR}
17450 @cindex I/O registers (Atmel AVR)
17451 This command displays information about the AVR I/O registers. For
17452 each register, @value{GDBN} prints its number and value.
17459 When configured for debugging CRIS, @value{GDBN} provides the
17460 following CRIS-specific commands:
17463 @item set cris-version @var{ver}
17464 @cindex CRIS version
17465 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
17466 The CRIS version affects register names and sizes. This command is useful in
17467 case autodetection of the CRIS version fails.
17469 @item show cris-version
17470 Show the current CRIS version.
17472 @item set cris-dwarf2-cfi
17473 @cindex DWARF-2 CFI and CRIS
17474 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
17475 Change to @samp{off} when using @code{gcc-cris} whose version is below
17478 @item show cris-dwarf2-cfi
17479 Show the current state of using DWARF-2 CFI.
17481 @item set cris-mode @var{mode}
17483 Set the current CRIS mode to @var{mode}. It should only be changed when
17484 debugging in guru mode, in which case it should be set to
17485 @samp{guru} (the default is @samp{normal}).
17487 @item show cris-mode
17488 Show the current CRIS mode.
17492 @subsection Renesas Super-H
17495 For the Renesas Super-H processor, @value{GDBN} provides these
17500 @kindex regs@r{, Super-H}
17501 Show the values of all Super-H registers.
17503 @item set sh calling-convention @var{convention}
17504 @kindex set sh calling-convention
17505 Set the calling-convention used when calling functions from @value{GDBN}.
17506 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
17507 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
17508 convention. If the DWARF-2 information of the called function specifies
17509 that the function follows the Renesas calling convention, the function
17510 is called using the Renesas calling convention. If the calling convention
17511 is set to @samp{renesas}, the Renesas calling convention is always used,
17512 regardless of the DWARF-2 information. This can be used to override the
17513 default of @samp{gcc} if debug information is missing, or the compiler
17514 does not emit the DWARF-2 calling convention entry for a function.
17516 @item show sh calling-convention
17517 @kindex show sh calling-convention
17518 Show the current calling convention setting.
17523 @node Architectures
17524 @section Architectures
17526 This section describes characteristics of architectures that affect
17527 all uses of @value{GDBN} with the architecture, both native and cross.
17534 * HPPA:: HP PA architecture
17535 * SPU:: Cell Broadband Engine SPU architecture
17540 @subsection x86 Architecture-specific Issues
17543 @item set struct-convention @var{mode}
17544 @kindex set struct-convention
17545 @cindex struct return convention
17546 @cindex struct/union returned in registers
17547 Set the convention used by the inferior to return @code{struct}s and
17548 @code{union}s from functions to @var{mode}. Possible values of
17549 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
17550 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
17551 are returned on the stack, while @code{"reg"} means that a
17552 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
17553 be returned in a register.
17555 @item show struct-convention
17556 @kindex show struct-convention
17557 Show the current setting of the convention to return @code{struct}s
17566 @kindex set rstack_high_address
17567 @cindex AMD 29K register stack
17568 @cindex register stack, AMD29K
17569 @item set rstack_high_address @var{address}
17570 On AMD 29000 family processors, registers are saved in a separate
17571 @dfn{register stack}. There is no way for @value{GDBN} to determine the
17572 extent of this stack. Normally, @value{GDBN} just assumes that the
17573 stack is ``large enough''. This may result in @value{GDBN} referencing
17574 memory locations that do not exist. If necessary, you can get around
17575 this problem by specifying the ending address of the register stack with
17576 the @code{set rstack_high_address} command. The argument should be an
17577 address, which you probably want to precede with @samp{0x} to specify in
17580 @kindex show rstack_high_address
17581 @item show rstack_high_address
17582 Display the current limit of the register stack, on AMD 29000 family
17590 See the following section.
17595 @cindex stack on Alpha
17596 @cindex stack on MIPS
17597 @cindex Alpha stack
17599 Alpha- and MIPS-based computers use an unusual stack frame, which
17600 sometimes requires @value{GDBN} to search backward in the object code to
17601 find the beginning of a function.
17603 @cindex response time, MIPS debugging
17604 To improve response time (especially for embedded applications, where
17605 @value{GDBN} may be restricted to a slow serial line for this search)
17606 you may want to limit the size of this search, using one of these
17610 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
17611 @item set heuristic-fence-post @var{limit}
17612 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
17613 search for the beginning of a function. A value of @var{0} (the
17614 default) means there is no limit. However, except for @var{0}, the
17615 larger the limit the more bytes @code{heuristic-fence-post} must search
17616 and therefore the longer it takes to run. You should only need to use
17617 this command when debugging a stripped executable.
17619 @item show heuristic-fence-post
17620 Display the current limit.
17624 These commands are available @emph{only} when @value{GDBN} is configured
17625 for debugging programs on Alpha or MIPS processors.
17627 Several MIPS-specific commands are available when debugging MIPS
17631 @item set mips abi @var{arg}
17632 @kindex set mips abi
17633 @cindex set ABI for MIPS
17634 Tell @value{GDBN} which MIPS ABI is used by the inferior. Possible
17635 values of @var{arg} are:
17639 The default ABI associated with the current binary (this is the
17650 @item show mips abi
17651 @kindex show mips abi
17652 Show the MIPS ABI used by @value{GDBN} to debug the inferior.
17655 @itemx show mipsfpu
17656 @xref{MIPS Embedded, set mipsfpu}.
17658 @item set mips mask-address @var{arg}
17659 @kindex set mips mask-address
17660 @cindex MIPS addresses, masking
17661 This command determines whether the most-significant 32 bits of 64-bit
17662 MIPS addresses are masked off. The argument @var{arg} can be
17663 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
17664 setting, which lets @value{GDBN} determine the correct value.
17666 @item show mips mask-address
17667 @kindex show mips mask-address
17668 Show whether the upper 32 bits of MIPS addresses are masked off or
17671 @item set remote-mips64-transfers-32bit-regs
17672 @kindex set remote-mips64-transfers-32bit-regs
17673 This command controls compatibility with 64-bit MIPS targets that
17674 transfer data in 32-bit quantities. If you have an old MIPS 64 target
17675 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
17676 and 64 bits for other registers, set this option to @samp{on}.
17678 @item show remote-mips64-transfers-32bit-regs
17679 @kindex show remote-mips64-transfers-32bit-regs
17680 Show the current setting of compatibility with older MIPS 64 targets.
17682 @item set debug mips
17683 @kindex set debug mips
17684 This command turns on and off debugging messages for the MIPS-specific
17685 target code in @value{GDBN}.
17687 @item show debug mips
17688 @kindex show debug mips
17689 Show the current setting of MIPS debugging messages.
17695 @cindex HPPA support
17697 When @value{GDBN} is debugging the HP PA architecture, it provides the
17698 following special commands:
17701 @item set debug hppa
17702 @kindex set debug hppa
17703 This command determines whether HPPA architecture-specific debugging
17704 messages are to be displayed.
17706 @item show debug hppa
17707 Show whether HPPA debugging messages are displayed.
17709 @item maint print unwind @var{address}
17710 @kindex maint print unwind@r{, HPPA}
17711 This command displays the contents of the unwind table entry at the
17712 given @var{address}.
17718 @subsection Cell Broadband Engine SPU architecture
17719 @cindex Cell Broadband Engine
17722 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
17723 it provides the following special commands:
17726 @item info spu event
17728 Display SPU event facility status. Shows current event mask
17729 and pending event status.
17731 @item info spu signal
17732 Display SPU signal notification facility status. Shows pending
17733 signal-control word and signal notification mode of both signal
17734 notification channels.
17736 @item info spu mailbox
17737 Display SPU mailbox facility status. Shows all pending entries,
17738 in order of processing, in each of the SPU Write Outbound,
17739 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
17742 Display MFC DMA status. Shows all pending commands in the MFC
17743 DMA queue. For each entry, opcode, tag, class IDs, effective
17744 and local store addresses and transfer size are shown.
17746 @item info spu proxydma
17747 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
17748 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
17749 and local store addresses and transfer size are shown.
17753 When @value{GDBN} is debugging a combined PowerPC/SPU application
17754 on the Cell Broadband Engine, it provides in addition the following
17758 @item set spu stop-on-load @var{arg}
17760 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
17761 will give control to the user when a new SPE thread enters its @code{main}
17762 function. The default is @code{off}.
17764 @item show spu stop-on-load
17766 Show whether to stop for new SPE threads.
17768 @item set spu auto-flush-cache @var{arg}
17769 Set whether to automatically flush the software-managed cache. When set to
17770 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
17771 cache to be flushed whenever SPE execution stops. This provides a consistent
17772 view of PowerPC memory that is accessed via the cache. If an application
17773 does not use the software-managed cache, this option has no effect.
17775 @item show spu auto-flush-cache
17776 Show whether to automatically flush the software-managed cache.
17781 @subsection PowerPC
17782 @cindex PowerPC architecture
17784 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
17785 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
17786 numbers stored in the floating point registers. These values must be stored
17787 in two consecutive registers, always starting at an even register like
17788 @code{f0} or @code{f2}.
17790 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
17791 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
17792 @code{f2} and @code{f3} for @code{$dl1} and so on.
17794 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
17795 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
17798 @node Controlling GDB
17799 @chapter Controlling @value{GDBN}
17801 You can alter the way @value{GDBN} interacts with you by using the
17802 @code{set} command. For commands controlling how @value{GDBN} displays
17803 data, see @ref{Print Settings, ,Print Settings}. Other settings are
17808 * Editing:: Command editing
17809 * Command History:: Command history
17810 * Screen Size:: Screen size
17811 * Numbers:: Numbers
17812 * ABI:: Configuring the current ABI
17813 * Messages/Warnings:: Optional warnings and messages
17814 * Debugging Output:: Optional messages about internal happenings
17815 * Other Misc Settings:: Other Miscellaneous Settings
17823 @value{GDBN} indicates its readiness to read a command by printing a string
17824 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
17825 can change the prompt string with the @code{set prompt} command. For
17826 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
17827 the prompt in one of the @value{GDBN} sessions so that you can always tell
17828 which one you are talking to.
17830 @emph{Note:} @code{set prompt} does not add a space for you after the
17831 prompt you set. This allows you to set a prompt which ends in a space
17832 or a prompt that does not.
17836 @item set prompt @var{newprompt}
17837 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
17839 @kindex show prompt
17841 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
17845 @section Command Editing
17847 @cindex command line editing
17849 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
17850 @sc{gnu} library provides consistent behavior for programs which provide a
17851 command line interface to the user. Advantages are @sc{gnu} Emacs-style
17852 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
17853 substitution, and a storage and recall of command history across
17854 debugging sessions.
17856 You may control the behavior of command line editing in @value{GDBN} with the
17857 command @code{set}.
17860 @kindex set editing
17863 @itemx set editing on
17864 Enable command line editing (enabled by default).
17866 @item set editing off
17867 Disable command line editing.
17869 @kindex show editing
17871 Show whether command line editing is enabled.
17874 @xref{Command Line Editing}, for more details about the Readline
17875 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
17876 encouraged to read that chapter.
17878 @node Command History
17879 @section Command History
17880 @cindex command history
17882 @value{GDBN} can keep track of the commands you type during your
17883 debugging sessions, so that you can be certain of precisely what
17884 happened. Use these commands to manage the @value{GDBN} command
17887 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
17888 package, to provide the history facility. @xref{Using History
17889 Interactively}, for the detailed description of the History library.
17891 To issue a command to @value{GDBN} without affecting certain aspects of
17892 the state which is seen by users, prefix it with @samp{server }
17893 (@pxref{Server Prefix}). This
17894 means that this command will not affect the command history, nor will it
17895 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
17896 pressed on a line by itself.
17898 @cindex @code{server}, command prefix
17899 The server prefix does not affect the recording of values into the value
17900 history; to print a value without recording it into the value history,
17901 use the @code{output} command instead of the @code{print} command.
17903 Here is the description of @value{GDBN} commands related to command
17907 @cindex history substitution
17908 @cindex history file
17909 @kindex set history filename
17910 @cindex @env{GDBHISTFILE}, environment variable
17911 @item set history filename @var{fname}
17912 Set the name of the @value{GDBN} command history file to @var{fname}.
17913 This is the file where @value{GDBN} reads an initial command history
17914 list, and where it writes the command history from this session when it
17915 exits. You can access this list through history expansion or through
17916 the history command editing characters listed below. This file defaults
17917 to the value of the environment variable @code{GDBHISTFILE}, or to
17918 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
17921 @cindex save command history
17922 @kindex set history save
17923 @item set history save
17924 @itemx set history save on
17925 Record command history in a file, whose name may be specified with the
17926 @code{set history filename} command. By default, this option is disabled.
17928 @item set history save off
17929 Stop recording command history in a file.
17931 @cindex history size
17932 @kindex set history size
17933 @cindex @env{HISTSIZE}, environment variable
17934 @item set history size @var{size}
17935 Set the number of commands which @value{GDBN} keeps in its history list.
17936 This defaults to the value of the environment variable
17937 @code{HISTSIZE}, or to 256 if this variable is not set.
17940 History expansion assigns special meaning to the character @kbd{!}.
17941 @xref{Event Designators}, for more details.
17943 @cindex history expansion, turn on/off
17944 Since @kbd{!} is also the logical not operator in C, history expansion
17945 is off by default. If you decide to enable history expansion with the
17946 @code{set history expansion on} command, you may sometimes need to
17947 follow @kbd{!} (when it is used as logical not, in an expression) with
17948 a space or a tab to prevent it from being expanded. The readline
17949 history facilities do not attempt substitution on the strings
17950 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
17952 The commands to control history expansion are:
17955 @item set history expansion on
17956 @itemx set history expansion
17957 @kindex set history expansion
17958 Enable history expansion. History expansion is off by default.
17960 @item set history expansion off
17961 Disable history expansion.
17964 @kindex show history
17966 @itemx show history filename
17967 @itemx show history save
17968 @itemx show history size
17969 @itemx show history expansion
17970 These commands display the state of the @value{GDBN} history parameters.
17971 @code{show history} by itself displays all four states.
17976 @kindex show commands
17977 @cindex show last commands
17978 @cindex display command history
17979 @item show commands
17980 Display the last ten commands in the command history.
17982 @item show commands @var{n}
17983 Print ten commands centered on command number @var{n}.
17985 @item show commands +
17986 Print ten commands just after the commands last printed.
17990 @section Screen Size
17991 @cindex size of screen
17992 @cindex pauses in output
17994 Certain commands to @value{GDBN} may produce large amounts of
17995 information output to the screen. To help you read all of it,
17996 @value{GDBN} pauses and asks you for input at the end of each page of
17997 output. Type @key{RET} when you want to continue the output, or @kbd{q}
17998 to discard the remaining output. Also, the screen width setting
17999 determines when to wrap lines of output. Depending on what is being
18000 printed, @value{GDBN} tries to break the line at a readable place,
18001 rather than simply letting it overflow onto the following line.
18003 Normally @value{GDBN} knows the size of the screen from the terminal
18004 driver software. For example, on Unix @value{GDBN} uses the termcap data base
18005 together with the value of the @code{TERM} environment variable and the
18006 @code{stty rows} and @code{stty cols} settings. If this is not correct,
18007 you can override it with the @code{set height} and @code{set
18014 @kindex show height
18015 @item set height @var{lpp}
18017 @itemx set width @var{cpl}
18019 These @code{set} commands specify a screen height of @var{lpp} lines and
18020 a screen width of @var{cpl} characters. The associated @code{show}
18021 commands display the current settings.
18023 If you specify a height of zero lines, @value{GDBN} does not pause during
18024 output no matter how long the output is. This is useful if output is to a
18025 file or to an editor buffer.
18027 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
18028 from wrapping its output.
18030 @item set pagination on
18031 @itemx set pagination off
18032 @kindex set pagination
18033 Turn the output pagination on or off; the default is on. Turning
18034 pagination off is the alternative to @code{set height 0}.
18036 @item show pagination
18037 @kindex show pagination
18038 Show the current pagination mode.
18043 @cindex number representation
18044 @cindex entering numbers
18046 You can always enter numbers in octal, decimal, or hexadecimal in
18047 @value{GDBN} by the usual conventions: octal numbers begin with
18048 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
18049 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
18050 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
18051 10; likewise, the default display for numbers---when no particular
18052 format is specified---is base 10. You can change the default base for
18053 both input and output with the commands described below.
18056 @kindex set input-radix
18057 @item set input-radix @var{base}
18058 Set the default base for numeric input. Supported choices
18059 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
18060 specified either unambiguously or using the current input radix; for
18064 set input-radix 012
18065 set input-radix 10.
18066 set input-radix 0xa
18070 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
18071 leaves the input radix unchanged, no matter what it was, since
18072 @samp{10}, being without any leading or trailing signs of its base, is
18073 interpreted in the current radix. Thus, if the current radix is 16,
18074 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
18077 @kindex set output-radix
18078 @item set output-radix @var{base}
18079 Set the default base for numeric display. Supported choices
18080 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
18081 specified either unambiguously or using the current input radix.
18083 @kindex show input-radix
18084 @item show input-radix
18085 Display the current default base for numeric input.
18087 @kindex show output-radix
18088 @item show output-radix
18089 Display the current default base for numeric display.
18091 @item set radix @r{[}@var{base}@r{]}
18095 These commands set and show the default base for both input and output
18096 of numbers. @code{set radix} sets the radix of input and output to
18097 the same base; without an argument, it resets the radix back to its
18098 default value of 10.
18103 @section Configuring the Current ABI
18105 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
18106 application automatically. However, sometimes you need to override its
18107 conclusions. Use these commands to manage @value{GDBN}'s view of the
18114 One @value{GDBN} configuration can debug binaries for multiple operating
18115 system targets, either via remote debugging or native emulation.
18116 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
18117 but you can override its conclusion using the @code{set osabi} command.
18118 One example where this is useful is in debugging of binaries which use
18119 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
18120 not have the same identifying marks that the standard C library for your
18125 Show the OS ABI currently in use.
18128 With no argument, show the list of registered available OS ABI's.
18130 @item set osabi @var{abi}
18131 Set the current OS ABI to @var{abi}.
18134 @cindex float promotion
18136 Generally, the way that an argument of type @code{float} is passed to a
18137 function depends on whether the function is prototyped. For a prototyped
18138 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
18139 according to the architecture's convention for @code{float}. For unprototyped
18140 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
18141 @code{double} and then passed.
18143 Unfortunately, some forms of debug information do not reliably indicate whether
18144 a function is prototyped. If @value{GDBN} calls a function that is not marked
18145 as prototyped, it consults @kbd{set coerce-float-to-double}.
18148 @kindex set coerce-float-to-double
18149 @item set coerce-float-to-double
18150 @itemx set coerce-float-to-double on
18151 Arguments of type @code{float} will be promoted to @code{double} when passed
18152 to an unprototyped function. This is the default setting.
18154 @item set coerce-float-to-double off
18155 Arguments of type @code{float} will be passed directly to unprototyped
18158 @kindex show coerce-float-to-double
18159 @item show coerce-float-to-double
18160 Show the current setting of promoting @code{float} to @code{double}.
18164 @kindex show cp-abi
18165 @value{GDBN} needs to know the ABI used for your program's C@t{++}
18166 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
18167 used to build your application. @value{GDBN} only fully supports
18168 programs with a single C@t{++} ABI; if your program contains code using
18169 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
18170 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
18171 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
18172 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
18173 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
18174 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
18179 Show the C@t{++} ABI currently in use.
18182 With no argument, show the list of supported C@t{++} ABI's.
18184 @item set cp-abi @var{abi}
18185 @itemx set cp-abi auto
18186 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
18189 @node Messages/Warnings
18190 @section Optional Warnings and Messages
18192 @cindex verbose operation
18193 @cindex optional warnings
18194 By default, @value{GDBN} is silent about its inner workings. If you are
18195 running on a slow machine, you may want to use the @code{set verbose}
18196 command. This makes @value{GDBN} tell you when it does a lengthy
18197 internal operation, so you will not think it has crashed.
18199 Currently, the messages controlled by @code{set verbose} are those
18200 which announce that the symbol table for a source file is being read;
18201 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
18204 @kindex set verbose
18205 @item set verbose on
18206 Enables @value{GDBN} output of certain informational messages.
18208 @item set verbose off
18209 Disables @value{GDBN} output of certain informational messages.
18211 @kindex show verbose
18213 Displays whether @code{set verbose} is on or off.
18216 By default, if @value{GDBN} encounters bugs in the symbol table of an
18217 object file, it is silent; but if you are debugging a compiler, you may
18218 find this information useful (@pxref{Symbol Errors, ,Errors Reading
18223 @kindex set complaints
18224 @item set complaints @var{limit}
18225 Permits @value{GDBN} to output @var{limit} complaints about each type of
18226 unusual symbols before becoming silent about the problem. Set
18227 @var{limit} to zero to suppress all complaints; set it to a large number
18228 to prevent complaints from being suppressed.
18230 @kindex show complaints
18231 @item show complaints
18232 Displays how many symbol complaints @value{GDBN} is permitted to produce.
18236 @anchor{confirmation requests}
18237 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
18238 lot of stupid questions to confirm certain commands. For example, if
18239 you try to run a program which is already running:
18243 The program being debugged has been started already.
18244 Start it from the beginning? (y or n)
18247 If you are willing to unflinchingly face the consequences of your own
18248 commands, you can disable this ``feature'':
18252 @kindex set confirm
18254 @cindex confirmation
18255 @cindex stupid questions
18256 @item set confirm off
18257 Disables confirmation requests.
18259 @item set confirm on
18260 Enables confirmation requests (the default).
18262 @kindex show confirm
18264 Displays state of confirmation requests.
18268 @cindex command tracing
18269 If you need to debug user-defined commands or sourced files you may find it
18270 useful to enable @dfn{command tracing}. In this mode each command will be
18271 printed as it is executed, prefixed with one or more @samp{+} symbols, the
18272 quantity denoting the call depth of each command.
18275 @kindex set trace-commands
18276 @cindex command scripts, debugging
18277 @item set trace-commands on
18278 Enable command tracing.
18279 @item set trace-commands off
18280 Disable command tracing.
18281 @item show trace-commands
18282 Display the current state of command tracing.
18285 @node Debugging Output
18286 @section Optional Messages about Internal Happenings
18287 @cindex optional debugging messages
18289 @value{GDBN} has commands that enable optional debugging messages from
18290 various @value{GDBN} subsystems; normally these commands are of
18291 interest to @value{GDBN} maintainers, or when reporting a bug. This
18292 section documents those commands.
18295 @kindex set exec-done-display
18296 @item set exec-done-display
18297 Turns on or off the notification of asynchronous commands'
18298 completion. When on, @value{GDBN} will print a message when an
18299 asynchronous command finishes its execution. The default is off.
18300 @kindex show exec-done-display
18301 @item show exec-done-display
18302 Displays the current setting of asynchronous command completion
18305 @cindex gdbarch debugging info
18306 @cindex architecture debugging info
18307 @item set debug arch
18308 Turns on or off display of gdbarch debugging info. The default is off
18310 @item show debug arch
18311 Displays the current state of displaying gdbarch debugging info.
18312 @item set debug aix-thread
18313 @cindex AIX threads
18314 Display debugging messages about inner workings of the AIX thread
18316 @item show debug aix-thread
18317 Show the current state of AIX thread debugging info display.
18318 @item set debug dwarf2-die
18319 @cindex DWARF2 DIEs
18320 Dump DWARF2 DIEs after they are read in.
18321 The value is the number of nesting levels to print.
18322 A value of zero turns off the display.
18323 @item show debug dwarf2-die
18324 Show the current state of DWARF2 DIE debugging.
18325 @item set debug displaced
18326 @cindex displaced stepping debugging info
18327 Turns on or off display of @value{GDBN} debugging info for the
18328 displaced stepping support. The default is off.
18329 @item show debug displaced
18330 Displays the current state of displaying @value{GDBN} debugging info
18331 related to displaced stepping.
18332 @item set debug event
18333 @cindex event debugging info
18334 Turns on or off display of @value{GDBN} event debugging info. The
18336 @item show debug event
18337 Displays the current state of displaying @value{GDBN} event debugging
18339 @item set debug expression
18340 @cindex expression debugging info
18341 Turns on or off display of debugging info about @value{GDBN}
18342 expression parsing. The default is off.
18343 @item show debug expression
18344 Displays the current state of displaying debugging info about
18345 @value{GDBN} expression parsing.
18346 @item set debug frame
18347 @cindex frame debugging info
18348 Turns on or off display of @value{GDBN} frame debugging info. The
18350 @item show debug frame
18351 Displays the current state of displaying @value{GDBN} frame debugging
18353 @item set debug gnu-nat
18354 @cindex @sc{gnu}/Hurd debug messages
18355 Turns on or off debugging messages from the @sc{gnu}/Hurd debug support.
18356 @item show debug gnu-nat
18357 Show the current state of @sc{gnu}/Hurd debugging messages.
18358 @item set debug infrun
18359 @cindex inferior debugging info
18360 Turns on or off display of @value{GDBN} debugging info for running the inferior.
18361 The default is off. @file{infrun.c} contains GDB's runtime state machine used
18362 for implementing operations such as single-stepping the inferior.
18363 @item show debug infrun
18364 Displays the current state of @value{GDBN} inferior debugging.
18365 @item set debug lin-lwp
18366 @cindex @sc{gnu}/Linux LWP debug messages
18367 @cindex Linux lightweight processes
18368 Turns on or off debugging messages from the Linux LWP debug support.
18369 @item show debug lin-lwp
18370 Show the current state of Linux LWP debugging messages.
18371 @item set debug lin-lwp-async
18372 @cindex @sc{gnu}/Linux LWP async debug messages
18373 @cindex Linux lightweight processes
18374 Turns on or off debugging messages from the Linux LWP async debug support.
18375 @item show debug lin-lwp-async
18376 Show the current state of Linux LWP async debugging messages.
18377 @item set debug observer
18378 @cindex observer debugging info
18379 Turns on or off display of @value{GDBN} observer debugging. This
18380 includes info such as the notification of observable events.
18381 @item show debug observer
18382 Displays the current state of observer debugging.
18383 @item set debug overload
18384 @cindex C@t{++} overload debugging info
18385 Turns on or off display of @value{GDBN} C@t{++} overload debugging
18386 info. This includes info such as ranking of functions, etc. The default
18388 @item show debug overload
18389 Displays the current state of displaying @value{GDBN} C@t{++} overload
18391 @cindex packets, reporting on stdout
18392 @cindex serial connections, debugging
18393 @cindex debug remote protocol
18394 @cindex remote protocol debugging
18395 @cindex display remote packets
18396 @item set debug remote
18397 Turns on or off display of reports on all packets sent back and forth across
18398 the serial line to the remote machine. The info is printed on the
18399 @value{GDBN} standard output stream. The default is off.
18400 @item show debug remote
18401 Displays the state of display of remote packets.
18402 @item set debug serial
18403 Turns on or off display of @value{GDBN} serial debugging info. The
18405 @item show debug serial
18406 Displays the current state of displaying @value{GDBN} serial debugging
18408 @item set debug solib-frv
18409 @cindex FR-V shared-library debugging
18410 Turns on or off debugging messages for FR-V shared-library code.
18411 @item show debug solib-frv
18412 Display the current state of FR-V shared-library code debugging
18414 @item set debug target
18415 @cindex target debugging info
18416 Turns on or off display of @value{GDBN} target debugging info. This info
18417 includes what is going on at the target level of GDB, as it happens. The
18418 default is 0. Set it to 1 to track events, and to 2 to also track the
18419 value of large memory transfers. Changes to this flag do not take effect
18420 until the next time you connect to a target or use the @code{run} command.
18421 @item show debug target
18422 Displays the current state of displaying @value{GDBN} target debugging
18424 @item set debug timestamp
18425 @cindex timestampping debugging info
18426 Turns on or off display of timestamps with @value{GDBN} debugging info.
18427 When enabled, seconds and microseconds are displayed before each debugging
18429 @item show debug timestamp
18430 Displays the current state of displaying timestamps with @value{GDBN}
18432 @item set debugvarobj
18433 @cindex variable object debugging info
18434 Turns on or off display of @value{GDBN} variable object debugging
18435 info. The default is off.
18436 @item show debugvarobj
18437 Displays the current state of displaying @value{GDBN} variable object
18439 @item set debug xml
18440 @cindex XML parser debugging
18441 Turns on or off debugging messages for built-in XML parsers.
18442 @item show debug xml
18443 Displays the current state of XML debugging messages.
18446 @node Other Misc Settings
18447 @section Other Miscellaneous Settings
18448 @cindex miscellaneous settings
18451 @kindex set interactive-mode
18452 @item set interactive-mode
18453 If @code{on}, forces @value{GDBN} to operate interactively.
18454 If @code{off}, forces @value{GDBN} to operate non-interactively,
18455 If @code{auto} (the default), @value{GDBN} guesses which mode to use,
18456 based on whether the debugger was started in a terminal or not.
18458 In the vast majority of cases, the debugger should be able to guess
18459 correctly which mode should be used. But this setting can be useful
18460 in certain specific cases, such as running a MinGW @value{GDBN}
18461 inside a cygwin window.
18463 @kindex show interactive-mode
18464 @item show interactive-mode
18465 Displays whether the debugger is operating in interactive mode or not.
18468 @node Extending GDB
18469 @chapter Extending @value{GDBN}
18470 @cindex extending GDB
18472 @value{GDBN} provides two mechanisms for extension. The first is based
18473 on composition of @value{GDBN} commands, and the second is based on the
18474 Python scripting language.
18477 * Sequences:: Canned Sequences of Commands
18478 * Python:: Scripting @value{GDBN} using Python
18482 @section Canned Sequences of Commands
18484 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
18485 Command Lists}), @value{GDBN} provides two ways to store sequences of
18486 commands for execution as a unit: user-defined commands and command
18490 * Define:: How to define your own commands
18491 * Hooks:: Hooks for user-defined commands
18492 * Command Files:: How to write scripts of commands to be stored in a file
18493 * Output:: Commands for controlled output
18497 @subsection User-defined Commands
18499 @cindex user-defined command
18500 @cindex arguments, to user-defined commands
18501 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
18502 which you assign a new name as a command. This is done with the
18503 @code{define} command. User commands may accept up to 10 arguments
18504 separated by whitespace. Arguments are accessed within the user command
18505 via @code{$arg0@dots{}$arg9}. A trivial example:
18509 print $arg0 + $arg1 + $arg2
18514 To execute the command use:
18521 This defines the command @code{adder}, which prints the sum of
18522 its three arguments. Note the arguments are text substitutions, so they may
18523 reference variables, use complex expressions, or even perform inferior
18526 @cindex argument count in user-defined commands
18527 @cindex how many arguments (user-defined commands)
18528 In addition, @code{$argc} may be used to find out how many arguments have
18529 been passed. This expands to a number in the range 0@dots{}10.
18534 print $arg0 + $arg1
18537 print $arg0 + $arg1 + $arg2
18545 @item define @var{commandname}
18546 Define a command named @var{commandname}. If there is already a command
18547 by that name, you are asked to confirm that you want to redefine it.
18548 @var{commandname} may be a bare command name consisting of letters,
18549 numbers, dashes, and underscores. It may also start with any predefined
18550 prefix command. For example, @samp{define target my-target} creates
18551 a user-defined @samp{target my-target} command.
18553 The definition of the command is made up of other @value{GDBN} command lines,
18554 which are given following the @code{define} command. The end of these
18555 commands is marked by a line containing @code{end}.
18558 @kindex end@r{ (user-defined commands)}
18559 @item document @var{commandname}
18560 Document the user-defined command @var{commandname}, so that it can be
18561 accessed by @code{help}. The command @var{commandname} must already be
18562 defined. This command reads lines of documentation just as @code{define}
18563 reads the lines of the command definition, ending with @code{end}.
18564 After the @code{document} command is finished, @code{help} on command
18565 @var{commandname} displays the documentation you have written.
18567 You may use the @code{document} command again to change the
18568 documentation of a command. Redefining the command with @code{define}
18569 does not change the documentation.
18571 @kindex dont-repeat
18572 @cindex don't repeat command
18574 Used inside a user-defined command, this tells @value{GDBN} that this
18575 command should not be repeated when the user hits @key{RET}
18576 (@pxref{Command Syntax, repeat last command}).
18578 @kindex help user-defined
18579 @item help user-defined
18580 List all user-defined commands, with the first line of the documentation
18585 @itemx show user @var{commandname}
18586 Display the @value{GDBN} commands used to define @var{commandname} (but
18587 not its documentation). If no @var{commandname} is given, display the
18588 definitions for all user-defined commands.
18590 @cindex infinite recursion in user-defined commands
18591 @kindex show max-user-call-depth
18592 @kindex set max-user-call-depth
18593 @item show max-user-call-depth
18594 @itemx set max-user-call-depth
18595 The value of @code{max-user-call-depth} controls how many recursion
18596 levels are allowed in user-defined commands before @value{GDBN} suspects an
18597 infinite recursion and aborts the command.
18600 In addition to the above commands, user-defined commands frequently
18601 use control flow commands, described in @ref{Command Files}.
18603 When user-defined commands are executed, the
18604 commands of the definition are not printed. An error in any command
18605 stops execution of the user-defined command.
18607 If used interactively, commands that would ask for confirmation proceed
18608 without asking when used inside a user-defined command. Many @value{GDBN}
18609 commands that normally print messages to say what they are doing omit the
18610 messages when used in a user-defined command.
18613 @subsection User-defined Command Hooks
18614 @cindex command hooks
18615 @cindex hooks, for commands
18616 @cindex hooks, pre-command
18619 You may define @dfn{hooks}, which are a special kind of user-defined
18620 command. Whenever you run the command @samp{foo}, if the user-defined
18621 command @samp{hook-foo} exists, it is executed (with no arguments)
18622 before that command.
18624 @cindex hooks, post-command
18626 A hook may also be defined which is run after the command you executed.
18627 Whenever you run the command @samp{foo}, if the user-defined command
18628 @samp{hookpost-foo} exists, it is executed (with no arguments) after
18629 that command. Post-execution hooks may exist simultaneously with
18630 pre-execution hooks, for the same command.
18632 It is valid for a hook to call the command which it hooks. If this
18633 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
18635 @c It would be nice if hookpost could be passed a parameter indicating
18636 @c if the command it hooks executed properly or not. FIXME!
18638 @kindex stop@r{, a pseudo-command}
18639 In addition, a pseudo-command, @samp{stop} exists. Defining
18640 (@samp{hook-stop}) makes the associated commands execute every time
18641 execution stops in your program: before breakpoint commands are run,
18642 displays are printed, or the stack frame is printed.
18644 For example, to ignore @code{SIGALRM} signals while
18645 single-stepping, but treat them normally during normal execution,
18650 handle SIGALRM nopass
18654 handle SIGALRM pass
18657 define hook-continue
18658 handle SIGALRM pass
18662 As a further example, to hook at the beginning and end of the @code{echo}
18663 command, and to add extra text to the beginning and end of the message,
18671 define hookpost-echo
18675 (@value{GDBP}) echo Hello World
18676 <<<---Hello World--->>>
18681 You can define a hook for any single-word command in @value{GDBN}, but
18682 not for command aliases; you should define a hook for the basic command
18683 name, e.g.@: @code{backtrace} rather than @code{bt}.
18684 @c FIXME! So how does Joe User discover whether a command is an alias
18686 You can hook a multi-word command by adding @code{hook-} or
18687 @code{hookpost-} to the last word of the command, e.g.@:
18688 @samp{define target hook-remote} to add a hook to @samp{target remote}.
18690 If an error occurs during the execution of your hook, execution of
18691 @value{GDBN} commands stops and @value{GDBN} issues a prompt
18692 (before the command that you actually typed had a chance to run).
18694 If you try to define a hook which does not match any known command, you
18695 get a warning from the @code{define} command.
18697 @node Command Files
18698 @subsection Command Files
18700 @cindex command files
18701 @cindex scripting commands
18702 A command file for @value{GDBN} is a text file made of lines that are
18703 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
18704 also be included. An empty line in a command file does nothing; it
18705 does not mean to repeat the last command, as it would from the
18708 You can request the execution of a command file with the @code{source}
18713 @cindex execute commands from a file
18714 @item source [@code{-v}] @var{filename}
18715 Execute the command file @var{filename}.
18718 The lines in a command file are generally executed sequentially,
18719 unless the order of execution is changed by one of the
18720 @emph{flow-control commands} described below. The commands are not
18721 printed as they are executed. An error in any command terminates
18722 execution of the command file and control is returned to the console.
18724 @value{GDBN} searches for @var{filename} in the current directory and then
18725 on the search path (specified with the @samp{directory} command).
18727 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
18728 each command as it is executed. The option must be given before
18729 @var{filename}, and is interpreted as part of the filename anywhere else.
18731 Commands that would ask for confirmation if used interactively proceed
18732 without asking when used in a command file. Many @value{GDBN} commands that
18733 normally print messages to say what they are doing omit the messages
18734 when called from command files.
18736 @value{GDBN} also accepts command input from standard input. In this
18737 mode, normal output goes to standard output and error output goes to
18738 standard error. Errors in a command file supplied on standard input do
18739 not terminate execution of the command file---execution continues with
18743 gdb < cmds > log 2>&1
18746 (The syntax above will vary depending on the shell used.) This example
18747 will execute commands from the file @file{cmds}. All output and errors
18748 would be directed to @file{log}.
18750 Since commands stored on command files tend to be more general than
18751 commands typed interactively, they frequently need to deal with
18752 complicated situations, such as different or unexpected values of
18753 variables and symbols, changes in how the program being debugged is
18754 built, etc. @value{GDBN} provides a set of flow-control commands to
18755 deal with these complexities. Using these commands, you can write
18756 complex scripts that loop over data structures, execute commands
18757 conditionally, etc.
18764 This command allows to include in your script conditionally executed
18765 commands. The @code{if} command takes a single argument, which is an
18766 expression to evaluate. It is followed by a series of commands that
18767 are executed only if the expression is true (its value is nonzero).
18768 There can then optionally be an @code{else} line, followed by a series
18769 of commands that are only executed if the expression was false. The
18770 end of the list is marked by a line containing @code{end}.
18774 This command allows to write loops. Its syntax is similar to
18775 @code{if}: the command takes a single argument, which is an expression
18776 to evaluate, and must be followed by the commands to execute, one per
18777 line, terminated by an @code{end}. These commands are called the
18778 @dfn{body} of the loop. The commands in the body of @code{while} are
18779 executed repeatedly as long as the expression evaluates to true.
18783 This command exits the @code{while} loop in whose body it is included.
18784 Execution of the script continues after that @code{while}s @code{end}
18787 @kindex loop_continue
18788 @item loop_continue
18789 This command skips the execution of the rest of the body of commands
18790 in the @code{while} loop in whose body it is included. Execution
18791 branches to the beginning of the @code{while} loop, where it evaluates
18792 the controlling expression.
18794 @kindex end@r{ (if/else/while commands)}
18796 Terminate the block of commands that are the body of @code{if},
18797 @code{else}, or @code{while} flow-control commands.
18802 @subsection Commands for Controlled Output
18804 During the execution of a command file or a user-defined command, normal
18805 @value{GDBN} output is suppressed; the only output that appears is what is
18806 explicitly printed by the commands in the definition. This section
18807 describes three commands useful for generating exactly the output you
18812 @item echo @var{text}
18813 @c I do not consider backslash-space a standard C escape sequence
18814 @c because it is not in ANSI.
18815 Print @var{text}. Nonprinting characters can be included in
18816 @var{text} using C escape sequences, such as @samp{\n} to print a
18817 newline. @strong{No newline is printed unless you specify one.}
18818 In addition to the standard C escape sequences, a backslash followed
18819 by a space stands for a space. This is useful for displaying a
18820 string with spaces at the beginning or the end, since leading and
18821 trailing spaces are otherwise trimmed from all arguments.
18822 To print @samp{@w{ }and foo =@w{ }}, use the command
18823 @samp{echo \@w{ }and foo = \@w{ }}.
18825 A backslash at the end of @var{text} can be used, as in C, to continue
18826 the command onto subsequent lines. For example,
18829 echo This is some text\n\
18830 which is continued\n\
18831 onto several lines.\n
18834 produces the same output as
18837 echo This is some text\n
18838 echo which is continued\n
18839 echo onto several lines.\n
18843 @item output @var{expression}
18844 Print the value of @var{expression} and nothing but that value: no
18845 newlines, no @samp{$@var{nn} = }. The value is not entered in the
18846 value history either. @xref{Expressions, ,Expressions}, for more information
18849 @item output/@var{fmt} @var{expression}
18850 Print the value of @var{expression} in format @var{fmt}. You can use
18851 the same formats as for @code{print}. @xref{Output Formats,,Output
18852 Formats}, for more information.
18855 @item printf @var{template}, @var{expressions}@dots{}
18856 Print the values of one or more @var{expressions} under the control of
18857 the string @var{template}. To print several values, make
18858 @var{expressions} be a comma-separated list of individual expressions,
18859 which may be either numbers or pointers. Their values are printed as
18860 specified by @var{template}, exactly as a C program would do by
18861 executing the code below:
18864 printf (@var{template}, @var{expressions}@dots{});
18867 As in @code{C} @code{printf}, ordinary characters in @var{template}
18868 are printed verbatim, while @dfn{conversion specification} introduced
18869 by the @samp{%} character cause subsequent @var{expressions} to be
18870 evaluated, their values converted and formatted according to type and
18871 style information encoded in the conversion specifications, and then
18874 For example, you can print two values in hex like this:
18877 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
18880 @code{printf} supports all the standard @code{C} conversion
18881 specifications, including the flags and modifiers between the @samp{%}
18882 character and the conversion letter, with the following exceptions:
18886 The argument-ordering modifiers, such as @samp{2$}, are not supported.
18889 The modifier @samp{*} is not supported for specifying precision or
18893 The @samp{'} flag (for separation of digits into groups according to
18894 @code{LC_NUMERIC'}) is not supported.
18897 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
18901 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
18904 The conversion letters @samp{a} and @samp{A} are not supported.
18908 Note that the @samp{ll} type modifier is supported only if the
18909 underlying @code{C} implementation used to build @value{GDBN} supports
18910 the @code{long long int} type, and the @samp{L} type modifier is
18911 supported only if @code{long double} type is available.
18913 As in @code{C}, @code{printf} supports simple backslash-escape
18914 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
18915 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
18916 single character. Octal and hexadecimal escape sequences are not
18919 Additionally, @code{printf} supports conversion specifications for DFP
18920 (@dfn{Decimal Floating Point}) types using the following length modifiers
18921 together with a floating point specifier.
18926 @samp{H} for printing @code{Decimal32} types.
18929 @samp{D} for printing @code{Decimal64} types.
18932 @samp{DD} for printing @code{Decimal128} types.
18935 If the underlying @code{C} implementation used to build @value{GDBN} has
18936 support for the three length modifiers for DFP types, other modifiers
18937 such as width and precision will also be available for @value{GDBN} to use.
18939 In case there is no such @code{C} support, no additional modifiers will be
18940 available and the value will be printed in the standard way.
18942 Here's an example of printing DFP types using the above conversion letters:
18944 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
18950 @section Scripting @value{GDBN} using Python
18951 @cindex python scripting
18952 @cindex scripting with python
18954 You can script @value{GDBN} using the @uref{http://www.python.org/,
18955 Python programming language}. This feature is available only if
18956 @value{GDBN} was configured using @option{--with-python}.
18959 * Python Commands:: Accessing Python from @value{GDBN}.
18960 * Python API:: Accessing @value{GDBN} from Python.
18963 @node Python Commands
18964 @subsection Python Commands
18965 @cindex python commands
18966 @cindex commands to access python
18968 @value{GDBN} provides one command for accessing the Python interpreter,
18969 and one related setting:
18973 @item python @r{[}@var{code}@r{]}
18974 The @code{python} command can be used to evaluate Python code.
18976 If given an argument, the @code{python} command will evaluate the
18977 argument as a Python command. For example:
18980 (@value{GDBP}) python print 23
18984 If you do not provide an argument to @code{python}, it will act as a
18985 multi-line command, like @code{define}. In this case, the Python
18986 script is made up of subsequent command lines, given after the
18987 @code{python} command. This command list is terminated using a line
18988 containing @code{end}. For example:
18991 (@value{GDBP}) python
18993 End with a line saying just "end".
18999 @kindex maint set python print-stack
19000 @item maint set python print-stack
19001 By default, @value{GDBN} will print a stack trace when an error occurs
19002 in a Python script. This can be controlled using @code{maint set
19003 python print-stack}: if @code{on}, the default, then Python stack
19004 printing is enabled; if @code{off}, then Python stack printing is
19009 @subsection Python API
19011 @cindex programming in python
19013 @cindex python stdout
19014 @cindex python pagination
19015 At startup, @value{GDBN} overrides Python's @code{sys.stdout} and
19016 @code{sys.stderr} to print using @value{GDBN}'s output-paging streams.
19017 A Python program which outputs to one of these streams may have its
19018 output interrupted by the user (@pxref{Screen Size}). In this
19019 situation, a Python @code{KeyboardInterrupt} exception is thrown.
19022 * Basic Python:: Basic Python Functions.
19023 * Exception Handling::
19024 * Auto-loading:: Automatically loading Python code.
19025 * Values From Inferior::
19026 * Types In Python:: Python representation of types.
19027 * Pretty Printing:: Pretty-printing values.
19028 * Selecting Pretty-Printers:: How GDB chooses a pretty-printer.
19029 * Commands In Python:: Implementing new commands in Python.
19030 * Functions In Python:: Writing new convenience functions.
19031 * Objfiles In Python:: Object files.
19032 * Frames In Python:: Acessing inferior stack frames from Python.
19036 @subsubsection Basic Python
19038 @cindex python functions
19039 @cindex python module
19041 @value{GDBN} introduces a new Python module, named @code{gdb}. All
19042 methods and classes added by @value{GDBN} are placed in this module.
19043 @value{GDBN} automatically @code{import}s the @code{gdb} module for
19044 use in all scripts evaluated by the @code{python} command.
19046 @findex gdb.execute
19047 @defun execute command [from_tty]
19048 Evaluate @var{command}, a string, as a @value{GDBN} CLI command.
19049 If a GDB exception happens while @var{command} runs, it is
19050 translated as described in @ref{Exception Handling,,Exception Handling}.
19051 If no exceptions occur, this function returns @code{None}.
19053 @var{from_tty} specifies whether @value{GDBN} ought to consider this
19054 command as having originated from the user invoking it interactively.
19055 It must be a boolean value. If omitted, it defaults to @code{False}.
19058 @findex gdb.parameter
19059 @defun parameter parameter
19060 Return the value of a @value{GDBN} parameter. @var{parameter} is a
19061 string naming the parameter to look up; @var{parameter} may contain
19062 spaces if the parameter has a multi-part name. For example,
19063 @samp{print object} is a valid parameter name.
19065 If the named parameter does not exist, this function throws a
19066 @code{RuntimeError}. Otherwise, the parameter's value is converted to
19067 a Python value of the appropriate type, and returned.
19070 @findex gdb.history
19071 @defun history number
19072 Return a value from @value{GDBN}'s value history (@pxref{Value
19073 History}). @var{number} indicates which history element to return.
19074 If @var{number} is negative, then @value{GDBN} will take its absolute value
19075 and count backward from the last element (i.e., the most recent element) to
19076 find the value to return. If @var{number} is zero, then @value{GDBN} will
19077 return the most recent element. If the element specified by @var{number}
19078 doesn't exist in the value history, a @code{RuntimeError} exception will be
19081 If no exception is raised, the return value is always an instance of
19082 @code{gdb.Value} (@pxref{Values From Inferior}).
19086 @defun write string
19087 Print a string to @value{GDBN}'s paginated standard output stream.
19088 Writing to @code{sys.stdout} or @code{sys.stderr} will automatically
19089 call this function.
19094 Flush @value{GDBN}'s paginated standard output stream. Flushing
19095 @code{sys.stdout} or @code{sys.stderr} will automatically call this
19099 @node Exception Handling
19100 @subsubsection Exception Handling
19101 @cindex python exceptions
19102 @cindex exceptions, python
19104 When executing the @code{python} command, Python exceptions
19105 uncaught within the Python code are translated to calls to
19106 @value{GDBN} error-reporting mechanism. If the command that called
19107 @code{python} does not handle the error, @value{GDBN} will
19108 terminate it and print an error message containing the Python
19109 exception name, the associated value, and the Python call stack
19110 backtrace at the point where the exception was raised. Example:
19113 (@value{GDBP}) python print foo
19114 Traceback (most recent call last):
19115 File "<string>", line 1, in <module>
19116 NameError: name 'foo' is not defined
19119 @value{GDBN} errors that happen in @value{GDBN} commands invoked by Python
19120 code are converted to Python @code{RuntimeError} exceptions. User
19121 interrupt (via @kbd{C-c} or by typing @kbd{q} at a pagination
19122 prompt) is translated to a Python @code{KeyboardInterrupt}
19123 exception. If you catch these exceptions in your Python code, your
19124 exception handler will see @code{RuntimeError} or
19125 @code{KeyboardInterrupt} as the exception type, the @value{GDBN} error
19126 message as its value, and the Python call stack backtrace at the
19127 Python statement closest to where the @value{GDBN} error occured as the
19131 @subsubsection Auto-loading
19132 @cindex auto-loading, Python
19134 When a new object file is read (for example, due to the @code{file}
19135 command, or because the inferior has loaded a shared library),
19136 @value{GDBN} will look for a file named @file{@var{objfile}-gdb.py},
19137 where @var{objfile} is the object file's real name, formed by ensuring
19138 that the file name is absolute, following all symlinks, and resolving
19139 @code{.} and @code{..} components. If this file exists and is
19140 readable, @value{GDBN} will evaluate it as a Python script.
19142 If this file does not exist, and if the parameter
19143 @code{debug-file-directory} is set (@pxref{Separate Debug Files}),
19144 then @value{GDBN} will use the file named
19145 @file{@var{debug-file-directory}/@var{real-name}}, where
19146 @var{real-name} is the object file's real name, as described above.
19148 Finally, if this file does not exist, then @value{GDBN} will look for
19149 a file named @file{@var{data-directory}/python/auto-load/@var{real-name}}, where
19150 @var{data-directory} is @value{GDBN}'s data directory (available via
19151 @code{show data-directory}, @pxref{Data Files}), and @var{real-name}
19152 is the object file's real name, as described above.
19154 When reading an auto-loaded file, @value{GDBN} sets the ``current
19155 objfile''. This is available via the @code{gdb.current_objfile}
19156 function (@pxref{Objfiles In Python}). This can be useful for
19157 registering objfile-specific pretty-printers.
19159 The auto-loading feature is useful for supplying application-specific
19160 debugging commands and scripts. You can enable or disable this
19161 feature, and view its current state.
19164 @kindex maint set python auto-load
19165 @item maint set python auto-load [yes|no]
19166 Enable or disable the Python auto-loading feature.
19168 @kindex show python auto-load
19169 @item show python auto-load
19170 Show whether Python auto-loading is enabled or disabled.
19173 @value{GDBN} does not track which files it has already auto-loaded.
19174 So, your @samp{-gdb.py} file should take care to ensure that it may be
19175 evaluated multiple times without error.
19177 @node Values From Inferior
19178 @subsubsection Values From Inferior
19179 @cindex values from inferior, with Python
19180 @cindex python, working with values from inferior
19182 @cindex @code{gdb.Value}
19183 @value{GDBN} provides values it obtains from the inferior program in
19184 an object of type @code{gdb.Value}. @value{GDBN} uses this object
19185 for its internal bookkeeping of the inferior's values, and for
19186 fetching values when necessary.
19188 Inferior values that are simple scalars can be used directly in
19189 Python expressions that are valid for the value's data type. Here's
19190 an example for an integer or floating-point value @code{some_val}:
19197 As result of this, @code{bar} will also be a @code{gdb.Value} object
19198 whose values are of the same type as those of @code{some_val}.
19200 Inferior values that are structures or instances of some class can
19201 be accessed using the Python @dfn{dictionary syntax}. For example, if
19202 @code{some_val} is a @code{gdb.Value} instance holding a structure, you
19203 can access its @code{foo} element with:
19206 bar = some_val['foo']
19209 Again, @code{bar} will also be a @code{gdb.Value} object.
19211 The following attributes are provided:
19214 @defivar Value address
19215 If this object is addressable, this read-only attribute holds a
19216 @code{gdb.Value} object representing the address. Otherwise,
19217 this attribute holds @code{None}.
19220 @cindex optimized out value in Python
19221 @defivar Value is_optimized_out
19222 This read-only boolean attribute is true if the compiler optimized out
19223 this value, thus it is not available for fetching from the inferior.
19226 @defivar Value type
19227 The type of this @code{gdb.Value}. The value of this attribute is a
19228 @code{gdb.Type} object.
19232 The following methods are provided:
19235 @defmethod Value dereference
19236 For pointer data types, this method returns a new @code{gdb.Value} object
19237 whose contents is the object pointed to by the pointer. For example, if
19238 @code{foo} is a C pointer to an @code{int}, declared in your C program as
19245 then you can use the corresponding @code{gdb.Value} to access what
19246 @code{foo} points to like this:
19249 bar = foo.dereference ()
19252 The result @code{bar} will be a @code{gdb.Value} object holding the
19253 value pointed to by @code{foo}.
19256 @defmethod Value string @r{[}encoding@r{]} @r{[}errors@r{]} @r{[}length@r{]}
19257 If this @code{gdb.Value} represents a string, then this method
19258 converts the contents to a Python string. Otherwise, this method will
19259 throw an exception.
19261 Strings are recognized in a language-specific way; whether a given
19262 @code{gdb.Value} represents a string is determined by the current
19265 For C-like languages, a value is a string if it is a pointer to or an
19266 array of characters or ints. The string is assumed to be terminated
19267 by a zero of the appropriate width. However if the optional length
19268 argument is given, the string will be converted to that given length,
19269 ignoring any embedded zeros that the string may contain.
19271 If the optional @var{encoding} argument is given, it must be a string
19272 naming the encoding of the string in the @code{gdb.Value}, such as
19273 @code{"ascii"}, @code{"iso-8859-6"} or @code{"utf-8"}. It accepts
19274 the same encodings as the corresponding argument to Python's
19275 @code{string.decode} method, and the Python codec machinery will be used
19276 to convert the string. If @var{encoding} is not given, or if
19277 @var{encoding} is the empty string, then either the @code{target-charset}
19278 (@pxref{Character Sets}) will be used, or a language-specific encoding
19279 will be used, if the current language is able to supply one.
19281 The optional @var{errors} argument is the same as the corresponding
19282 argument to Python's @code{string.decode} method.
19284 If the optional @var{length} argument is given, the string will be
19285 fetched and converted to the given length.
19289 @node Types In Python
19290 @subsubsection Types In Python
19291 @cindex types in Python
19292 @cindex Python, working with types
19295 @value{GDBN} represents types from the inferior using the class
19298 The following type-related functions are available in the @code{gdb}
19301 @findex gdb.lookup_type
19302 @defun lookup_type name [block]
19303 This function looks up a type by name. @var{name} is the name of the
19304 type to look up. It must be a string.
19306 Ordinarily, this function will return an instance of @code{gdb.Type}.
19307 If the named type cannot be found, it will throw an exception.
19310 An instance of @code{Type} has the following attributes:
19314 The type code for this type. The type code will be one of the
19315 @code{TYPE_CODE_} constants defined below.
19318 @defivar Type sizeof
19319 The size of this type, in target @code{char} units. Usually, a
19320 target's @code{char} type will be an 8-bit byte. However, on some
19321 unusual platforms, this type may have a different size.
19325 The tag name for this type. The tag name is the name after
19326 @code{struct}, @code{union}, or @code{enum} in C and C@t{++}; not all
19327 languages have this concept. If this type has no tag name, then
19328 @code{None} is returned.
19332 The following methods are provided:
19335 @defmethod Type fields
19336 For structure and union types, this method returns the fields. Range
19337 types have two fields, the minimum and maximum values. Enum types
19338 have one field per enum constant. Function and method types have one
19339 field per parameter. The base types of C@t{++} classes are also
19340 represented as fields. If the type has no fields, or does not fit
19341 into one of these categories, an empty sequence will be returned.
19343 Each field is an object, with some pre-defined attributes:
19346 This attribute is not available for @code{static} fields (as in
19347 C@t{++} or Java). For non-@code{static} fields, the value is the bit
19348 position of the field.
19351 The name of the field, or @code{None} for anonymous fields.
19354 This is @code{True} if the field is artificial, usually meaning that
19355 it was provided by the compiler and not the user. This attribute is
19356 always provided, and is @code{False} if the field is not artificial.
19359 If the field is packed, or is a bitfield, then this will have a
19360 non-zero value, which is the size of the field in bits. Otherwise,
19361 this will be zero; in this case the field's size is given by its type.
19364 The type of the field. This is usually an instance of @code{Type},
19365 but it can be @code{None} in some situations.
19369 @defmethod Type const
19370 Return a new @code{gdb.Type} object which represents a
19371 @code{const}-qualified variant of this type.
19374 @defmethod Type volatile
19375 Return a new @code{gdb.Type} object which represents a
19376 @code{volatile}-qualified variant of this type.
19379 @defmethod Type unqualified
19380 Return a new @code{gdb.Type} object which represents an unqualified
19381 variant of this type. That is, the result is neither @code{const} nor
19385 @defmethod Type reference
19386 Return a new @code{gdb.Type} object which represents a reference to this
19390 @defmethod Type strip_typedefs
19391 Return a new @code{gdb.Type} that represents the real type,
19392 after removing all layers of typedefs.
19395 @defmethod Type target
19396 Return a new @code{gdb.Type} object which represents the target type
19399 For a pointer type, the target type is the type of the pointed-to
19400 object. For an array type (meaning C-like arrays), the target type is
19401 the type of the elements of the array. For a function or method type,
19402 the target type is the type of the return value. For a complex type,
19403 the target type is the type of the elements. For a typedef, the
19404 target type is the aliased type.
19406 If the type does not have a target, this method will throw an
19410 @defmethod Type template_argument n
19411 If this @code{gdb.Type} is an instantiation of a template, this will
19412 return a new @code{gdb.Type} which represents the type of the
19413 @var{n}th template argument.
19415 If this @code{gdb.Type} is not a template type, this will throw an
19416 exception. Ordinarily, only C@t{++} code will have template types.
19418 @var{name} is searched for globally.
19423 Each type has a code, which indicates what category this type falls
19424 into. The available type categories are represented by constants
19425 defined in the @code{gdb} module:
19428 @findex TYPE_CODE_PTR
19429 @findex gdb.TYPE_CODE_PTR
19430 @item TYPE_CODE_PTR
19431 The type is a pointer.
19433 @findex TYPE_CODE_ARRAY
19434 @findex gdb.TYPE_CODE_ARRAY
19435 @item TYPE_CODE_ARRAY
19436 The type is an array.
19438 @findex TYPE_CODE_STRUCT
19439 @findex gdb.TYPE_CODE_STRUCT
19440 @item TYPE_CODE_STRUCT
19441 The type is a structure.
19443 @findex TYPE_CODE_UNION
19444 @findex gdb.TYPE_CODE_UNION
19445 @item TYPE_CODE_UNION
19446 The type is a union.
19448 @findex TYPE_CODE_ENUM
19449 @findex gdb.TYPE_CODE_ENUM
19450 @item TYPE_CODE_ENUM
19451 The type is an enum.
19453 @findex TYPE_CODE_FLAGS
19454 @findex gdb.TYPE_CODE_FLAGS
19455 @item TYPE_CODE_FLAGS
19456 A bit flags type, used for things such as status registers.
19458 @findex TYPE_CODE_FUNC
19459 @findex gdb.TYPE_CODE_FUNC
19460 @item TYPE_CODE_FUNC
19461 The type is a function.
19463 @findex TYPE_CODE_INT
19464 @findex gdb.TYPE_CODE_INT
19465 @item TYPE_CODE_INT
19466 The type is an integer type.
19468 @findex TYPE_CODE_FLT
19469 @findex gdb.TYPE_CODE_FLT
19470 @item TYPE_CODE_FLT
19471 A floating point type.
19473 @findex TYPE_CODE_VOID
19474 @findex gdb.TYPE_CODE_VOID
19475 @item TYPE_CODE_VOID
19476 The special type @code{void}.
19478 @findex TYPE_CODE_SET
19479 @findex gdb.TYPE_CODE_SET
19480 @item TYPE_CODE_SET
19483 @findex TYPE_CODE_RANGE
19484 @findex gdb.TYPE_CODE_RANGE
19485 @item TYPE_CODE_RANGE
19486 A range type, that is, an integer type with bounds.
19488 @findex TYPE_CODE_STRING
19489 @findex gdb.TYPE_CODE_STRING
19490 @item TYPE_CODE_STRING
19491 A string type. Note that this is only used for certain languages with
19492 language-defined string types; C strings are not represented this way.
19494 @findex TYPE_CODE_BITSTRING
19495 @findex gdb.TYPE_CODE_BITSTRING
19496 @item TYPE_CODE_BITSTRING
19499 @findex TYPE_CODE_ERROR
19500 @findex gdb.TYPE_CODE_ERROR
19501 @item TYPE_CODE_ERROR
19502 An unknown or erroneous type.
19504 @findex TYPE_CODE_METHOD
19505 @findex gdb.TYPE_CODE_METHOD
19506 @item TYPE_CODE_METHOD
19507 A method type, as found in C@t{++} or Java.
19509 @findex TYPE_CODE_METHODPTR
19510 @findex gdb.TYPE_CODE_METHODPTR
19511 @item TYPE_CODE_METHODPTR
19512 A pointer-to-member-function.
19514 @findex TYPE_CODE_MEMBERPTR
19515 @findex gdb.TYPE_CODE_MEMBERPTR
19516 @item TYPE_CODE_MEMBERPTR
19517 A pointer-to-member.
19519 @findex TYPE_CODE_REF
19520 @findex gdb.TYPE_CODE_REF
19521 @item TYPE_CODE_REF
19524 @findex TYPE_CODE_CHAR
19525 @findex gdb.TYPE_CODE_CHAR
19526 @item TYPE_CODE_CHAR
19529 @findex TYPE_CODE_BOOL
19530 @findex gdb.TYPE_CODE_BOOL
19531 @item TYPE_CODE_BOOL
19534 @findex TYPE_CODE_COMPLEX
19535 @findex gdb.TYPE_CODE_COMPLEX
19536 @item TYPE_CODE_COMPLEX
19537 A complex float type.
19539 @findex TYPE_CODE_TYPEDEF
19540 @findex gdb.TYPE_CODE_TYPEDEF
19541 @item TYPE_CODE_TYPEDEF
19542 A typedef to some other type.
19544 @findex TYPE_CODE_NAMESPACE
19545 @findex gdb.TYPE_CODE_NAMESPACE
19546 @item TYPE_CODE_NAMESPACE
19547 A C@t{++} namespace.
19549 @findex TYPE_CODE_DECFLOAT
19550 @findex gdb.TYPE_CODE_DECFLOAT
19551 @item TYPE_CODE_DECFLOAT
19552 A decimal floating point type.
19554 @findex TYPE_CODE_INTERNAL_FUNCTION
19555 @findex gdb.TYPE_CODE_INTERNAL_FUNCTION
19556 @item TYPE_CODE_INTERNAL_FUNCTION
19557 A function internal to @value{GDBN}. This is the type used to represent
19558 convenience functions.
19561 @node Pretty Printing
19562 @subsubsection Pretty Printing
19564 @value{GDBN} provides a mechanism to allow pretty-printing of values
19565 using Python code. The pretty-printer API allows application-specific
19566 code to greatly simplify the display of complex objects. This
19567 mechanism works for both MI and the CLI.
19569 For example, here is how a C@t{++} @code{std::string} looks without a
19573 (@value{GDBP}) print s
19575 static npos = 4294967295,
19577 <std::allocator<char>> = @{
19578 <__gnu_cxx::new_allocator<char>> = @{<No data fields>@}, <No data fields>@},
19579 members of std::basic_string<char, std::char_traits<char>, std::allocator<char> >::_Alloc_hider:
19580 _M_p = 0x804a014 "abcd"
19585 After a pretty-printer for @code{std::string} has been installed, only
19586 the contents are printed:
19589 (@value{GDBP}) print s
19593 A pretty-printer is just an object that holds a value and implements a
19594 specific interface, defined here.
19596 @defop Operation {pretty printer} children (self)
19597 @value{GDBN} will call this method on a pretty-printer to compute the
19598 children of the pretty-printer's value.
19600 This method must return an object conforming to the Python iterator
19601 protocol. Each item returned by the iterator must be a tuple holding
19602 two elements. The first element is the ``name'' of the child; the
19603 second element is the child's value. The value can be any Python
19604 object which is convertible to a @value{GDBN} value.
19606 This method is optional. If it does not exist, @value{GDBN} will act
19607 as though the value has no children.
19610 @defop Operation {pretty printer} display_hint (self)
19611 The CLI may call this method and use its result to change the
19612 formatting of a value. The result will also be supplied to an MI
19613 consumer as a @samp{displayhint} attribute of the variable being
19616 This method is optional. If it does exist, this method must return a
19619 Some display hints are predefined by @value{GDBN}:
19623 Indicate that the object being printed is ``array-like''. The CLI
19624 uses this to respect parameters such as @code{set print elements} and
19625 @code{set print array}.
19628 Indicate that the object being printed is ``map-like'', and that the
19629 children of this value can be assumed to alternate between keys and
19633 Indicate that the object being printed is ``string-like''. If the
19634 printer's @code{to_string} method returns a Python string of some
19635 kind, then @value{GDBN} will call its internal language-specific
19636 string-printing function to format the string. For the CLI this means
19637 adding quotation marks, possibly escaping some characters, respecting
19638 @code{set print elements}, and the like.
19642 @defop Operation {pretty printer} to_string (self)
19643 @value{GDBN} will call this method to display the string
19644 representation of the value passed to the object's constructor.
19646 When printing from the CLI, if the @code{to_string} method exists,
19647 then @value{GDBN} will prepend its result to the values returned by
19648 @code{children}. Exactly how this formatting is done is dependent on
19649 the display hint, and may change as more hints are added. Also,
19650 depending on the print settings (@pxref{Print Settings}), the CLI may
19651 print just the result of @code{to_string} in a stack trace, omitting
19652 the result of @code{children}.
19654 If this method returns a string, it is printed verbatim.
19656 Otherwise, if this method returns an instance of @code{gdb.Value},
19657 then @value{GDBN} prints this value. This may result in a call to
19658 another pretty-printer.
19660 If instead the method returns a Python value which is convertible to a
19661 @code{gdb.Value}, then @value{GDBN} performs the conversion and prints
19662 the resulting value. Again, this may result in a call to another
19663 pretty-printer. Python scalars (integers, floats, and booleans) and
19664 strings are convertible to @code{gdb.Value}; other types are not.
19666 If the result is not one of these types, an exception is raised.
19669 @node Selecting Pretty-Printers
19670 @subsubsection Selecting Pretty-Printers
19672 The Python list @code{gdb.pretty_printers} contains an array of
19673 functions that have been registered via addition as a pretty-printer.
19674 Each @code{gdb.Objfile} also contains a @code{pretty_printers}
19677 A function on one of these lists is passed a single @code{gdb.Value}
19678 argument and should return a pretty-printer object conforming to the
19679 interface definition above (@pxref{Pretty Printing}). If a function
19680 cannot create a pretty-printer for the value, it should return
19683 @value{GDBN} first checks the @code{pretty_printers} attribute of each
19684 @code{gdb.Objfile} and iteratively calls each function in the list for
19685 that @code{gdb.Objfile} until it receives a pretty-printer object.
19686 After these lists have been exhausted, it tries the global
19687 @code{gdb.pretty-printers} list, again calling each function until an
19688 object is returned.
19690 The order in which the objfiles are searched is not specified. For a
19691 given list, functions are always invoked from the head of the list,
19692 and iterated over sequentially until the end of the list, or a printer
19693 object is returned.
19695 Here is an example showing how a @code{std::string} printer might be
19699 class StdStringPrinter:
19700 "Print a std::string"
19702 def __init__ (self, val):
19705 def to_string (self):
19706 return self.val['_M_dataplus']['_M_p']
19708 def display_hint (self):
19712 And here is an example showing how a lookup function for the printer
19713 example above might be written.
19716 def str_lookup_function (val):
19718 lookup_tag = val.type.tag
19719 regex = re.compile ("^std::basic_string<char,.*>$")
19720 if lookup_tag == None:
19722 if regex.match (lookup_tag):
19723 return StdStringPrinter (val)
19728 The example lookup function extracts the value's type, and attempts to
19729 match it to a type that it can pretty-print. If it is a type the
19730 printer can pretty-print, it will return a printer object. If not, it
19731 returns @code{None}.
19733 We recommend that you put your core pretty-printers into a Python
19734 package. If your pretty-printers are for use with a library, we
19735 further recommend embedding a version number into the package name.
19736 This practice will enable @value{GDBN} to load multiple versions of
19737 your pretty-printers at the same time, because they will have
19740 You should write auto-loaded code (@pxref{Auto-loading}) such that it
19741 can be evaluated multiple times without changing its meaning. An
19742 ideal auto-load file will consist solely of @code{import}s of your
19743 printer modules, followed by a call to a register pretty-printers with
19744 the current objfile.
19746 Taken as a whole, this approach will scale nicely to multiple
19747 inferiors, each potentially using a different library version.
19748 Embedding a version number in the Python package name will ensure that
19749 @value{GDBN} is able to load both sets of printers simultaneously.
19750 Then, because the search for pretty-printers is done by objfile, and
19751 because your auto-loaded code took care to register your library's
19752 printers with a specific objfile, @value{GDBN} will find the correct
19753 printers for the specific version of the library used by each
19756 To continue the @code{std::string} example (@pxref{Pretty Printing}),
19757 this code might appear in @code{gdb.libstdcxx.v6}:
19760 def register_printers (objfile):
19761 objfile.pretty_printers.add (str_lookup_function)
19765 And then the corresponding contents of the auto-load file would be:
19768 import gdb.libstdcxx.v6
19769 gdb.libstdcxx.v6.register_printers (gdb.current_objfile ())
19772 @node Commands In Python
19773 @subsubsection Commands In Python
19775 @cindex commands in python
19776 @cindex python commands
19777 You can implement new @value{GDBN} CLI commands in Python. A CLI
19778 command is implemented using an instance of the @code{gdb.Command}
19779 class, most commonly using a subclass.
19781 @defmethod Command __init__ name @var{command_class} @r{[}@var{completer_class}@r{]} @r{[}@var{prefix}@r{]}
19782 The object initializer for @code{Command} registers the new command
19783 with @value{GDBN}. This initializer is normally invoked from the
19784 subclass' own @code{__init__} method.
19786 @var{name} is the name of the command. If @var{name} consists of
19787 multiple words, then the initial words are looked for as prefix
19788 commands. In this case, if one of the prefix commands does not exist,
19789 an exception is raised.
19791 There is no support for multi-line commands.
19793 @var{command_class} should be one of the @samp{COMMAND_} constants
19794 defined below. This argument tells @value{GDBN} how to categorize the
19795 new command in the help system.
19797 @var{completer_class} is an optional argument. If given, it should be
19798 one of the @samp{COMPLETE_} constants defined below. This argument
19799 tells @value{GDBN} how to perform completion for this command. If not
19800 given, @value{GDBN} will attempt to complete using the object's
19801 @code{complete} method (see below); if no such method is found, an
19802 error will occur when completion is attempted.
19804 @var{prefix} is an optional argument. If @code{True}, then the new
19805 command is a prefix command; sub-commands of this command may be
19808 The help text for the new command is taken from the Python
19809 documentation string for the command's class, if there is one. If no
19810 documentation string is provided, the default value ``This command is
19811 not documented.'' is used.
19814 @cindex don't repeat Python command
19815 @defmethod Command dont_repeat
19816 By default, a @value{GDBN} command is repeated when the user enters a
19817 blank line at the command prompt. A command can suppress this
19818 behavior by invoking the @code{dont_repeat} method. This is similar
19819 to the user command @code{dont-repeat}, see @ref{Define, dont-repeat}.
19822 @defmethod Command invoke argument from_tty
19823 This method is called by @value{GDBN} when this command is invoked.
19825 @var{argument} is a string. It is the argument to the command, after
19826 leading and trailing whitespace has been stripped.
19828 @var{from_tty} is a boolean argument. When true, this means that the
19829 command was entered by the user at the terminal; when false it means
19830 that the command came from elsewhere.
19832 If this method throws an exception, it is turned into a @value{GDBN}
19833 @code{error} call. Otherwise, the return value is ignored.
19836 @cindex completion of Python commands
19837 @defmethod Command complete text word
19838 This method is called by @value{GDBN} when the user attempts
19839 completion on this command. All forms of completion are handled by
19840 this method, that is, the @key{TAB} and @key{M-?} key bindings
19841 (@pxref{Completion}), and the @code{complete} command (@pxref{Help,
19844 The arguments @var{text} and @var{word} are both strings. @var{text}
19845 holds the complete command line up to the cursor's location.
19846 @var{word} holds the last word of the command line; this is computed
19847 using a word-breaking heuristic.
19849 The @code{complete} method can return several values:
19852 If the return value is a sequence, the contents of the sequence are
19853 used as the completions. It is up to @code{complete} to ensure that the
19854 contents actually do complete the word. A zero-length sequence is
19855 allowed, it means that there were no completions available. Only
19856 string elements of the sequence are used; other elements in the
19857 sequence are ignored.
19860 If the return value is one of the @samp{COMPLETE_} constants defined
19861 below, then the corresponding @value{GDBN}-internal completion
19862 function is invoked, and its result is used.
19865 All other results are treated as though there were no available
19870 When a new command is registered, it must be declared as a member of
19871 some general class of commands. This is used to classify top-level
19872 commands in the on-line help system; note that prefix commands are not
19873 listed under their own category but rather that of their top-level
19874 command. The available classifications are represented by constants
19875 defined in the @code{gdb} module:
19878 @findex COMMAND_NONE
19879 @findex gdb.COMMAND_NONE
19881 The command does not belong to any particular class. A command in
19882 this category will not be displayed in any of the help categories.
19884 @findex COMMAND_RUNNING
19885 @findex gdb.COMMAND_RUNNING
19886 @item COMMAND_RUNNING
19887 The command is related to running the inferior. For example,
19888 @code{start}, @code{step}, and @code{continue} are in this category.
19889 Type @kbd{help running} at the @value{GDBN} prompt to see a list of
19890 commands in this category.
19892 @findex COMMAND_DATA
19893 @findex gdb.COMMAND_DATA
19895 The command is related to data or variables. For example,
19896 @code{call}, @code{find}, and @code{print} are in this category. Type
19897 @kbd{help data} at the @value{GDBN} prompt to see a list of commands
19900 @findex COMMAND_STACK
19901 @findex gdb.COMMAND_STACK
19902 @item COMMAND_STACK
19903 The command has to do with manipulation of the stack. For example,
19904 @code{backtrace}, @code{frame}, and @code{return} are in this
19905 category. Type @kbd{help stack} at the @value{GDBN} prompt to see a
19906 list of commands in this category.
19908 @findex COMMAND_FILES
19909 @findex gdb.COMMAND_FILES
19910 @item COMMAND_FILES
19911 This class is used for file-related commands. For example,
19912 @code{file}, @code{list} and @code{section} are in this category.
19913 Type @kbd{help files} at the @value{GDBN} prompt to see a list of
19914 commands in this category.
19916 @findex COMMAND_SUPPORT
19917 @findex gdb.COMMAND_SUPPORT
19918 @item COMMAND_SUPPORT
19919 This should be used for ``support facilities'', generally meaning
19920 things that are useful to the user when interacting with @value{GDBN},
19921 but not related to the state of the inferior. For example,
19922 @code{help}, @code{make}, and @code{shell} are in this category. Type
19923 @kbd{help support} at the @value{GDBN} prompt to see a list of
19924 commands in this category.
19926 @findex COMMAND_STATUS
19927 @findex gdb.COMMAND_STATUS
19928 @item COMMAND_STATUS
19929 The command is an @samp{info}-related command, that is, related to the
19930 state of @value{GDBN} itself. For example, @code{info}, @code{macro},
19931 and @code{show} are in this category. Type @kbd{help status} at the
19932 @value{GDBN} prompt to see a list of commands in this category.
19934 @findex COMMAND_BREAKPOINTS
19935 @findex gdb.COMMAND_BREAKPOINTS
19936 @item COMMAND_BREAKPOINTS
19937 The command has to do with breakpoints. For example, @code{break},
19938 @code{clear}, and @code{delete} are in this category. Type @kbd{help
19939 breakpoints} at the @value{GDBN} prompt to see a list of commands in
19942 @findex COMMAND_TRACEPOINTS
19943 @findex gdb.COMMAND_TRACEPOINTS
19944 @item COMMAND_TRACEPOINTS
19945 The command has to do with tracepoints. For example, @code{trace},
19946 @code{actions}, and @code{tfind} are in this category. Type
19947 @kbd{help tracepoints} at the @value{GDBN} prompt to see a list of
19948 commands in this category.
19950 @findex COMMAND_OBSCURE
19951 @findex gdb.COMMAND_OBSCURE
19952 @item COMMAND_OBSCURE
19953 The command is only used in unusual circumstances, or is not of
19954 general interest to users. For example, @code{checkpoint},
19955 @code{fork}, and @code{stop} are in this category. Type @kbd{help
19956 obscure} at the @value{GDBN} prompt to see a list of commands in this
19959 @findex COMMAND_MAINTENANCE
19960 @findex gdb.COMMAND_MAINTENANCE
19961 @item COMMAND_MAINTENANCE
19962 The command is only useful to @value{GDBN} maintainers. The
19963 @code{maintenance} and @code{flushregs} commands are in this category.
19964 Type @kbd{help internals} at the @value{GDBN} prompt to see a list of
19965 commands in this category.
19968 A new command can use a predefined completion function, either by
19969 specifying it via an argument at initialization, or by returning it
19970 from the @code{complete} method. These predefined completion
19971 constants are all defined in the @code{gdb} module:
19974 @findex COMPLETE_NONE
19975 @findex gdb.COMPLETE_NONE
19976 @item COMPLETE_NONE
19977 This constant means that no completion should be done.
19979 @findex COMPLETE_FILENAME
19980 @findex gdb.COMPLETE_FILENAME
19981 @item COMPLETE_FILENAME
19982 This constant means that filename completion should be performed.
19984 @findex COMPLETE_LOCATION
19985 @findex gdb.COMPLETE_LOCATION
19986 @item COMPLETE_LOCATION
19987 This constant means that location completion should be done.
19988 @xref{Specify Location}.
19990 @findex COMPLETE_COMMAND
19991 @findex gdb.COMPLETE_COMMAND
19992 @item COMPLETE_COMMAND
19993 This constant means that completion should examine @value{GDBN}
19996 @findex COMPLETE_SYMBOL
19997 @findex gdb.COMPLETE_SYMBOL
19998 @item COMPLETE_SYMBOL
19999 This constant means that completion should be done using symbol names
20003 The following code snippet shows how a trivial CLI command can be
20004 implemented in Python:
20007 class HelloWorld (gdb.Command):
20008 """Greet the whole world."""
20010 def __init__ (self):
20011 super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
20013 def invoke (self, arg, from_tty):
20014 print "Hello, World!"
20019 The last line instantiates the class, and is necessary to trigger the
20020 registration of the command with @value{GDBN}. Depending on how the
20021 Python code is read into @value{GDBN}, you may need to import the
20022 @code{gdb} module explicitly.
20024 @node Functions In Python
20025 @subsubsection Writing new convenience functions
20027 @cindex writing convenience functions
20028 @cindex convenience functions in python
20029 @cindex python convenience functions
20030 @tindex gdb.Function
20032 You can implement new convenience functions (@pxref{Convenience Vars})
20033 in Python. A convenience function is an instance of a subclass of the
20034 class @code{gdb.Function}.
20036 @defmethod Function __init__ name
20037 The initializer for @code{Function} registers the new function with
20038 @value{GDBN}. The argument @var{name} is the name of the function,
20039 a string. The function will be visible to the user as a convenience
20040 variable of type @code{internal function}, whose name is the same as
20041 the given @var{name}.
20043 The documentation for the new function is taken from the documentation
20044 string for the new class.
20047 @defmethod Function invoke @var{*args}
20048 When a convenience function is evaluated, its arguments are converted
20049 to instances of @code{gdb.Value}, and then the function's
20050 @code{invoke} method is called. Note that @value{GDBN} does not
20051 predetermine the arity of convenience functions. Instead, all
20052 available arguments are passed to @code{invoke}, following the
20053 standard Python calling convention. In particular, a convenience
20054 function can have default values for parameters without ill effect.
20056 The return value of this method is used as its value in the enclosing
20057 expression. If an ordinary Python value is returned, it is converted
20058 to a @code{gdb.Value} following the usual rules.
20061 The following code snippet shows how a trivial convenience function can
20062 be implemented in Python:
20065 class Greet (gdb.Function):
20066 """Return string to greet someone.
20067 Takes a name as argument."""
20069 def __init__ (self):
20070 super (Greet, self).__init__ ("greet")
20072 def invoke (self, name):
20073 return "Hello, %s!" % name.string ()
20078 The last line instantiates the class, and is necessary to trigger the
20079 registration of the function with @value{GDBN}. Depending on how the
20080 Python code is read into @value{GDBN}, you may need to import the
20081 @code{gdb} module explicitly.
20083 @node Objfiles In Python
20084 @subsubsection Objfiles In Python
20086 @cindex objfiles in python
20087 @tindex gdb.Objfile
20089 @value{GDBN} loads symbols for an inferior from various
20090 symbol-containing files (@pxref{Files}). These include the primary
20091 executable file, any shared libraries used by the inferior, and any
20092 separate debug info files (@pxref{Separate Debug Files}).
20093 @value{GDBN} calls these symbol-containing files @dfn{objfiles}.
20095 The following objfile-related functions are available in the
20098 @findex gdb.current_objfile
20099 @defun current_objfile
20100 When auto-loading a Python script (@pxref{Auto-loading}), @value{GDBN}
20101 sets the ``current objfile'' to the corresponding objfile. This
20102 function returns the current objfile. If there is no current objfile,
20103 this function returns @code{None}.
20106 @findex gdb.objfiles
20108 Return a sequence of all the objfiles current known to @value{GDBN}.
20109 @xref{Objfiles In Python}.
20112 Each objfile is represented by an instance of the @code{gdb.Objfile}
20115 @defivar Objfile filename
20116 The file name of the objfile as a string.
20119 @defivar Objfile pretty_printers
20120 The @code{pretty_printers} attribute is a list of functions. It is
20121 used to look up pretty-printers. A @code{Value} is passed to each
20122 function in order; if the function returns @code{None}, then the
20123 search continues. Otherwise, the return value should be an object
20124 which is used to format the value. @xref{Pretty Printing}, for more
20128 @node Frames In Python
20129 @subsubsection Acessing inferior stack frames from Python.
20131 @cindex frames in python
20132 When the debugged program stops, @value{GDBN} is able to analyze its call
20133 stack (@pxref{Frames,,Stack frames}). The @code{gdb.Frame} class
20134 represents a frame in the stack. A @code{gdb.Frame} object is only valid
20135 while its corresponding frame exists in the inferior's stack. If you try
20136 to use an invalid frame object, @value{GDBN} will throw a @code{RuntimeError}
20139 Two @code{gdb.Frame} objects can be compared for equality with the @code{==}
20143 (@value{GDBP}) python print gdb.newest_frame() == gdb.selected_frame ()
20147 The following frame-related functions are available in the @code{gdb} module:
20149 @findex gdb.selected_frame
20150 @defun selected_frame
20151 Return the selected frame object. (@pxref{Selection,,Selecting a Frame}).
20154 @defun frame_stop_reason_string reason
20155 Return a string explaining the reason why @value{GDBN} stopped unwinding
20156 frames, as expressed by the given @var{reason} code (an integer, see the
20157 @code{unwind_stop_reason} method further down in this section).
20160 A @code{gdb.Frame} object has the following methods:
20163 @defmethod Frame is_valid
20164 Returns true if the @code{gdb.Frame} object is valid, false if not.
20165 A frame object can become invalid if the frame it refers to doesn't
20166 exist anymore in the inferior. All @code{gdb.Frame} methods will throw
20167 an exception if it is invalid at the time the method is called.
20170 @defmethod Frame name
20171 Returns the function name of the frame, or @code{None} if it can't be
20175 @defmethod Frame type
20176 Returns the type of the frame. The value can be one of
20177 @code{gdb.NORMAL_FRAME}, @code{gdb.DUMMY_FRAME}, @code{gdb.SIGTRAMP_FRAME}
20178 or @code{gdb.SENTINEL_FRAME}.
20181 @defmethod Frame unwind_stop_reason
20182 Return an integer representing the reason why it's not possible to find
20183 more frames toward the outermost frame. Use
20184 @code{gdb.frame_stop_reason_string} to convert the value returned by this
20185 function to a string.
20188 @defmethod Frame pc
20189 Returns the frame's resume address.
20192 @defmethod Frame older
20193 Return the frame that called this frame.
20196 @defmethod Frame newer
20197 Return the frame called by this frame.
20200 @defmethod Frame read_var variable
20201 Return the value of the given variable in this frame. @var{variable} must
20207 @chapter Command Interpreters
20208 @cindex command interpreters
20210 @value{GDBN} supports multiple command interpreters, and some command
20211 infrastructure to allow users or user interface writers to switch
20212 between interpreters or run commands in other interpreters.
20214 @value{GDBN} currently supports two command interpreters, the console
20215 interpreter (sometimes called the command-line interpreter or @sc{cli})
20216 and the machine interface interpreter (or @sc{gdb/mi}). This manual
20217 describes both of these interfaces in great detail.
20219 By default, @value{GDBN} will start with the console interpreter.
20220 However, the user may choose to start @value{GDBN} with another
20221 interpreter by specifying the @option{-i} or @option{--interpreter}
20222 startup options. Defined interpreters include:
20226 @cindex console interpreter
20227 The traditional console or command-line interpreter. This is the most often
20228 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
20229 @value{GDBN} will use this interpreter.
20232 @cindex mi interpreter
20233 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
20234 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
20235 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
20239 @cindex mi2 interpreter
20240 The current @sc{gdb/mi} interface.
20243 @cindex mi1 interpreter
20244 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
20248 @cindex invoke another interpreter
20249 The interpreter being used by @value{GDBN} may not be dynamically
20250 switched at runtime. Although possible, this could lead to a very
20251 precarious situation. Consider an IDE using @sc{gdb/mi}. If a user
20252 enters the command "interpreter-set console" in a console view,
20253 @value{GDBN} would switch to using the console interpreter, rendering
20254 the IDE inoperable!
20256 @kindex interpreter-exec
20257 Although you may only choose a single interpreter at startup, you may execute
20258 commands in any interpreter from the current interpreter using the appropriate
20259 command. If you are running the console interpreter, simply use the
20260 @code{interpreter-exec} command:
20263 interpreter-exec mi "-data-list-register-names"
20266 @sc{gdb/mi} has a similar command, although it is only available in versions of
20267 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
20270 @chapter @value{GDBN} Text User Interface
20272 @cindex Text User Interface
20275 * TUI Overview:: TUI overview
20276 * TUI Keys:: TUI key bindings
20277 * TUI Single Key Mode:: TUI single key mode
20278 * TUI Commands:: TUI-specific commands
20279 * TUI Configuration:: TUI configuration variables
20282 The @value{GDBN} Text User Interface (TUI) is a terminal
20283 interface which uses the @code{curses} library to show the source
20284 file, the assembly output, the program registers and @value{GDBN}
20285 commands in separate text windows. The TUI mode is supported only
20286 on platforms where a suitable version of the @code{curses} library
20289 @pindex @value{GDBTUI}
20290 The TUI mode is enabled by default when you invoke @value{GDBN} as
20291 either @samp{@value{GDBTUI}} or @samp{@value{GDBP} -tui}.
20292 You can also switch in and out of TUI mode while @value{GDBN} runs by
20293 using various TUI commands and key bindings, such as @kbd{C-x C-a}.
20294 @xref{TUI Keys, ,TUI Key Bindings}.
20297 @section TUI Overview
20299 In TUI mode, @value{GDBN} can display several text windows:
20303 This window is the @value{GDBN} command window with the @value{GDBN}
20304 prompt and the @value{GDBN} output. The @value{GDBN} input is still
20305 managed using readline.
20308 The source window shows the source file of the program. The current
20309 line and active breakpoints are displayed in this window.
20312 The assembly window shows the disassembly output of the program.
20315 This window shows the processor registers. Registers are highlighted
20316 when their values change.
20319 The source and assembly windows show the current program position
20320 by highlighting the current line and marking it with a @samp{>} marker.
20321 Breakpoints are indicated with two markers. The first marker
20322 indicates the breakpoint type:
20326 Breakpoint which was hit at least once.
20329 Breakpoint which was never hit.
20332 Hardware breakpoint which was hit at least once.
20335 Hardware breakpoint which was never hit.
20338 The second marker indicates whether the breakpoint is enabled or not:
20342 Breakpoint is enabled.
20345 Breakpoint is disabled.
20348 The source, assembly and register windows are updated when the current
20349 thread changes, when the frame changes, or when the program counter
20352 These windows are not all visible at the same time. The command
20353 window is always visible. The others can be arranged in several
20364 source and assembly,
20367 source and registers, or
20370 assembly and registers.
20373 A status line above the command window shows the following information:
20377 Indicates the current @value{GDBN} target.
20378 (@pxref{Targets, ,Specifying a Debugging Target}).
20381 Gives the current process or thread number.
20382 When no process is being debugged, this field is set to @code{No process}.
20385 Gives the current function name for the selected frame.
20386 The name is demangled if demangling is turned on (@pxref{Print Settings}).
20387 When there is no symbol corresponding to the current program counter,
20388 the string @code{??} is displayed.
20391 Indicates the current line number for the selected frame.
20392 When the current line number is not known, the string @code{??} is displayed.
20395 Indicates the current program counter address.
20399 @section TUI Key Bindings
20400 @cindex TUI key bindings
20402 The TUI installs several key bindings in the readline keymaps
20403 (@pxref{Command Line Editing}). The following key bindings
20404 are installed for both TUI mode and the @value{GDBN} standard mode.
20413 Enter or leave the TUI mode. When leaving the TUI mode,
20414 the curses window management stops and @value{GDBN} operates using
20415 its standard mode, writing on the terminal directly. When reentering
20416 the TUI mode, control is given back to the curses windows.
20417 The screen is then refreshed.
20421 Use a TUI layout with only one window. The layout will
20422 either be @samp{source} or @samp{assembly}. When the TUI mode
20423 is not active, it will switch to the TUI mode.
20425 Think of this key binding as the Emacs @kbd{C-x 1} binding.
20429 Use a TUI layout with at least two windows. When the current
20430 layout already has two windows, the next layout with two windows is used.
20431 When a new layout is chosen, one window will always be common to the
20432 previous layout and the new one.
20434 Think of it as the Emacs @kbd{C-x 2} binding.
20438 Change the active window. The TUI associates several key bindings
20439 (like scrolling and arrow keys) with the active window. This command
20440 gives the focus to the next TUI window.
20442 Think of it as the Emacs @kbd{C-x o} binding.
20446 Switch in and out of the TUI SingleKey mode that binds single
20447 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
20450 The following key bindings only work in the TUI mode:
20455 Scroll the active window one page up.
20459 Scroll the active window one page down.
20463 Scroll the active window one line up.
20467 Scroll the active window one line down.
20471 Scroll the active window one column left.
20475 Scroll the active window one column right.
20479 Refresh the screen.
20482 Because the arrow keys scroll the active window in the TUI mode, they
20483 are not available for their normal use by readline unless the command
20484 window has the focus. When another window is active, you must use
20485 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
20486 and @kbd{C-f} to control the command window.
20488 @node TUI Single Key Mode
20489 @section TUI Single Key Mode
20490 @cindex TUI single key mode
20492 The TUI also provides a @dfn{SingleKey} mode, which binds several
20493 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
20494 switch into this mode, where the following key bindings are used:
20497 @kindex c @r{(SingleKey TUI key)}
20501 @kindex d @r{(SingleKey TUI key)}
20505 @kindex f @r{(SingleKey TUI key)}
20509 @kindex n @r{(SingleKey TUI key)}
20513 @kindex q @r{(SingleKey TUI key)}
20515 exit the SingleKey mode.
20517 @kindex r @r{(SingleKey TUI key)}
20521 @kindex s @r{(SingleKey TUI key)}
20525 @kindex u @r{(SingleKey TUI key)}
20529 @kindex v @r{(SingleKey TUI key)}
20533 @kindex w @r{(SingleKey TUI key)}
20538 Other keys temporarily switch to the @value{GDBN} command prompt.
20539 The key that was pressed is inserted in the editing buffer so that
20540 it is possible to type most @value{GDBN} commands without interaction
20541 with the TUI SingleKey mode. Once the command is entered the TUI
20542 SingleKey mode is restored. The only way to permanently leave
20543 this mode is by typing @kbd{q} or @kbd{C-x s}.
20547 @section TUI-specific Commands
20548 @cindex TUI commands
20550 The TUI has specific commands to control the text windows.
20551 These commands are always available, even when @value{GDBN} is not in
20552 the TUI mode. When @value{GDBN} is in the standard mode, most
20553 of these commands will automatically switch to the TUI mode.
20558 List and give the size of all displayed windows.
20562 Display the next layout.
20565 Display the previous layout.
20568 Display the source window only.
20571 Display the assembly window only.
20574 Display the source and assembly window.
20577 Display the register window together with the source or assembly window.
20581 Make the next window active for scrolling.
20584 Make the previous window active for scrolling.
20587 Make the source window active for scrolling.
20590 Make the assembly window active for scrolling.
20593 Make the register window active for scrolling.
20596 Make the command window active for scrolling.
20600 Refresh the screen. This is similar to typing @kbd{C-L}.
20602 @item tui reg float
20604 Show the floating point registers in the register window.
20606 @item tui reg general
20607 Show the general registers in the register window.
20610 Show the next register group. The list of register groups as well as
20611 their order is target specific. The predefined register groups are the
20612 following: @code{general}, @code{float}, @code{system}, @code{vector},
20613 @code{all}, @code{save}, @code{restore}.
20615 @item tui reg system
20616 Show the system registers in the register window.
20620 Update the source window and the current execution point.
20622 @item winheight @var{name} +@var{count}
20623 @itemx winheight @var{name} -@var{count}
20625 Change the height of the window @var{name} by @var{count}
20626 lines. Positive counts increase the height, while negative counts
20629 @item tabset @var{nchars}
20631 Set the width of tab stops to be @var{nchars} characters.
20634 @node TUI Configuration
20635 @section TUI Configuration Variables
20636 @cindex TUI configuration variables
20638 Several configuration variables control the appearance of TUI windows.
20641 @item set tui border-kind @var{kind}
20642 @kindex set tui border-kind
20643 Select the border appearance for the source, assembly and register windows.
20644 The possible values are the following:
20647 Use a space character to draw the border.
20650 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
20653 Use the Alternate Character Set to draw the border. The border is
20654 drawn using character line graphics if the terminal supports them.
20657 @item set tui border-mode @var{mode}
20658 @kindex set tui border-mode
20659 @itemx set tui active-border-mode @var{mode}
20660 @kindex set tui active-border-mode
20661 Select the display attributes for the borders of the inactive windows
20662 or the active window. The @var{mode} can be one of the following:
20665 Use normal attributes to display the border.
20671 Use reverse video mode.
20674 Use half bright mode.
20676 @item half-standout
20677 Use half bright and standout mode.
20680 Use extra bright or bold mode.
20682 @item bold-standout
20683 Use extra bright or bold and standout mode.
20688 @chapter Using @value{GDBN} under @sc{gnu} Emacs
20691 @cindex @sc{gnu} Emacs
20692 A special interface allows you to use @sc{gnu} Emacs to view (and
20693 edit) the source files for the program you are debugging with
20696 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
20697 executable file you want to debug as an argument. This command starts
20698 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
20699 created Emacs buffer.
20700 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
20702 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
20707 All ``terminal'' input and output goes through an Emacs buffer, called
20710 This applies both to @value{GDBN} commands and their output, and to the input
20711 and output done by the program you are debugging.
20713 This is useful because it means that you can copy the text of previous
20714 commands and input them again; you can even use parts of the output
20717 All the facilities of Emacs' Shell mode are available for interacting
20718 with your program. In particular, you can send signals the usual
20719 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
20723 @value{GDBN} displays source code through Emacs.
20725 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
20726 source file for that frame and puts an arrow (@samp{=>}) at the
20727 left margin of the current line. Emacs uses a separate buffer for
20728 source display, and splits the screen to show both your @value{GDBN} session
20731 Explicit @value{GDBN} @code{list} or search commands still produce output as
20732 usual, but you probably have no reason to use them from Emacs.
20735 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
20736 a graphical mode, enabled by default, which provides further buffers
20737 that can control the execution and describe the state of your program.
20738 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
20740 If you specify an absolute file name when prompted for the @kbd{M-x
20741 gdb} argument, then Emacs sets your current working directory to where
20742 your program resides. If you only specify the file name, then Emacs
20743 sets your current working directory to to the directory associated
20744 with the previous buffer. In this case, @value{GDBN} may find your
20745 program by searching your environment's @code{PATH} variable, but on
20746 some operating systems it might not find the source. So, although the
20747 @value{GDBN} input and output session proceeds normally, the auxiliary
20748 buffer does not display the current source and line of execution.
20750 The initial working directory of @value{GDBN} is printed on the top
20751 line of the GUD buffer and this serves as a default for the commands
20752 that specify files for @value{GDBN} to operate on. @xref{Files,
20753 ,Commands to Specify Files}.
20755 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
20756 need to call @value{GDBN} by a different name (for example, if you
20757 keep several configurations around, with different names) you can
20758 customize the Emacs variable @code{gud-gdb-command-name} to run the
20761 In the GUD buffer, you can use these special Emacs commands in
20762 addition to the standard Shell mode commands:
20766 Describe the features of Emacs' GUD Mode.
20769 Execute to another source line, like the @value{GDBN} @code{step} command; also
20770 update the display window to show the current file and location.
20773 Execute to next source line in this function, skipping all function
20774 calls, like the @value{GDBN} @code{next} command. Then update the display window
20775 to show the current file and location.
20778 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
20779 display window accordingly.
20782 Execute until exit from the selected stack frame, like the @value{GDBN}
20783 @code{finish} command.
20786 Continue execution of your program, like the @value{GDBN} @code{continue}
20790 Go up the number of frames indicated by the numeric argument
20791 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
20792 like the @value{GDBN} @code{up} command.
20795 Go down the number of frames indicated by the numeric argument, like the
20796 @value{GDBN} @code{down} command.
20799 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
20800 tells @value{GDBN} to set a breakpoint on the source line point is on.
20802 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
20803 separate frame which shows a backtrace when the GUD buffer is current.
20804 Move point to any frame in the stack and type @key{RET} to make it
20805 become the current frame and display the associated source in the
20806 source buffer. Alternatively, click @kbd{Mouse-2} to make the
20807 selected frame become the current one. In graphical mode, the
20808 speedbar displays watch expressions.
20810 If you accidentally delete the source-display buffer, an easy way to get
20811 it back is to type the command @code{f} in the @value{GDBN} buffer, to
20812 request a frame display; when you run under Emacs, this recreates
20813 the source buffer if necessary to show you the context of the current
20816 The source files displayed in Emacs are in ordinary Emacs buffers
20817 which are visiting the source files in the usual way. You can edit
20818 the files with these buffers if you wish; but keep in mind that @value{GDBN}
20819 communicates with Emacs in terms of line numbers. If you add or
20820 delete lines from the text, the line numbers that @value{GDBN} knows cease
20821 to correspond properly with the code.
20823 A more detailed description of Emacs' interaction with @value{GDBN} is
20824 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
20827 @c The following dropped because Epoch is nonstandard. Reactivate
20828 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
20830 @kindex Emacs Epoch environment
20834 Version 18 of @sc{gnu} Emacs has a built-in window system
20835 called the @code{epoch}
20836 environment. Users of this environment can use a new command,
20837 @code{inspect} which performs identically to @code{print} except that
20838 each value is printed in its own window.
20843 @chapter The @sc{gdb/mi} Interface
20845 @unnumberedsec Function and Purpose
20847 @cindex @sc{gdb/mi}, its purpose
20848 @sc{gdb/mi} is a line based machine oriented text interface to
20849 @value{GDBN} and is activated by specifying using the
20850 @option{--interpreter} command line option (@pxref{Mode Options}). It
20851 is specifically intended to support the development of systems which
20852 use the debugger as just one small component of a larger system.
20854 This chapter is a specification of the @sc{gdb/mi} interface. It is written
20855 in the form of a reference manual.
20857 Note that @sc{gdb/mi} is still under construction, so some of the
20858 features described below are incomplete and subject to change
20859 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
20861 @unnumberedsec Notation and Terminology
20863 @cindex notational conventions, for @sc{gdb/mi}
20864 This chapter uses the following notation:
20868 @code{|} separates two alternatives.
20871 @code{[ @var{something} ]} indicates that @var{something} is optional:
20872 it may or may not be given.
20875 @code{( @var{group} )*} means that @var{group} inside the parentheses
20876 may repeat zero or more times.
20879 @code{( @var{group} )+} means that @var{group} inside the parentheses
20880 may repeat one or more times.
20883 @code{"@var{string}"} means a literal @var{string}.
20887 @heading Dependencies
20891 * GDB/MI General Design::
20892 * GDB/MI Command Syntax::
20893 * GDB/MI Compatibility with CLI::
20894 * GDB/MI Development and Front Ends::
20895 * GDB/MI Output Records::
20896 * GDB/MI Simple Examples::
20897 * GDB/MI Command Description Format::
20898 * GDB/MI Breakpoint Commands::
20899 * GDB/MI Program Context::
20900 * GDB/MI Thread Commands::
20901 * GDB/MI Program Execution::
20902 * GDB/MI Stack Manipulation::
20903 * GDB/MI Variable Objects::
20904 * GDB/MI Data Manipulation::
20905 * GDB/MI Tracepoint Commands::
20906 * GDB/MI Symbol Query::
20907 * GDB/MI File Commands::
20909 * GDB/MI Kod Commands::
20910 * GDB/MI Memory Overlay Commands::
20911 * GDB/MI Signal Handling Commands::
20913 * GDB/MI Target Manipulation::
20914 * GDB/MI File Transfer Commands::
20915 * GDB/MI Miscellaneous Commands::
20918 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
20919 @node GDB/MI General Design
20920 @section @sc{gdb/mi} General Design
20921 @cindex GDB/MI General Design
20923 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
20924 parts---commands sent to @value{GDBN}, responses to those commands
20925 and notifications. Each command results in exactly one response,
20926 indicating either successful completion of the command, or an error.
20927 For the commands that do not resume the target, the response contains the
20928 requested information. For the commands that resume the target, the
20929 response only indicates whether the target was successfully resumed.
20930 Notifications is the mechanism for reporting changes in the state of the
20931 target, or in @value{GDBN} state, that cannot conveniently be associated with
20932 a command and reported as part of that command response.
20934 The important examples of notifications are:
20938 Exec notifications. These are used to report changes in
20939 target state---when a target is resumed, or stopped. It would not
20940 be feasible to include this information in response of resuming
20941 commands, because one resume commands can result in multiple events in
20942 different threads. Also, quite some time may pass before any event
20943 happens in the target, while a frontend needs to know whether the resuming
20944 command itself was successfully executed.
20947 Console output, and status notifications. Console output
20948 notifications are used to report output of CLI commands, as well as
20949 diagnostics for other commands. Status notifications are used to
20950 report the progress of a long-running operation. Naturally, including
20951 this information in command response would mean no output is produced
20952 until the command is finished, which is undesirable.
20955 General notifications. Commands may have various side effects on
20956 the @value{GDBN} or target state beyond their official purpose. For example,
20957 a command may change the selected thread. Although such changes can
20958 be included in command response, using notification allows for more
20959 orthogonal frontend design.
20963 There's no guarantee that whenever an MI command reports an error,
20964 @value{GDBN} or the target are in any specific state, and especially,
20965 the state is not reverted to the state before the MI command was
20966 processed. Therefore, whenever an MI command results in an error,
20967 we recommend that the frontend refreshes all the information shown in
20968 the user interface.
20972 * Context management::
20973 * Asynchronous and non-stop modes::
20977 @node Context management
20978 @subsection Context management
20980 In most cases when @value{GDBN} accesses the target, this access is
20981 done in context of a specific thread and frame (@pxref{Frames}).
20982 Often, even when accessing global data, the target requires that a thread
20983 be specified. The CLI interface maintains the selected thread and frame,
20984 and supplies them to target on each command. This is convenient,
20985 because a command line user would not want to specify that information
20986 explicitly on each command, and because user interacts with
20987 @value{GDBN} via a single terminal, so no confusion is possible as
20988 to what thread and frame are the current ones.
20990 In the case of MI, the concept of selected thread and frame is less
20991 useful. First, a frontend can easily remember this information
20992 itself. Second, a graphical frontend can have more than one window,
20993 each one used for debugging a different thread, and the frontend might
20994 want to access additional threads for internal purposes. This
20995 increases the risk that by relying on implicitly selected thread, the
20996 frontend may be operating on a wrong one. Therefore, each MI command
20997 should explicitly specify which thread and frame to operate on. To
20998 make it possible, each MI command accepts the @samp{--thread} and
20999 @samp{--frame} options, the value to each is @value{GDBN} identifier
21000 for thread and frame to operate on.
21002 Usually, each top-level window in a frontend allows the user to select
21003 a thread and a frame, and remembers the user selection for further
21004 operations. However, in some cases @value{GDBN} may suggest that the
21005 current thread be changed. For example, when stopping on a breakpoint
21006 it is reasonable to switch to the thread where breakpoint is hit. For
21007 another example, if the user issues the CLI @samp{thread} command via
21008 the frontend, it is desirable to change the frontend's selected thread to the
21009 one specified by user. @value{GDBN} communicates the suggestion to
21010 change current thread using the @samp{=thread-selected} notification.
21011 No such notification is available for the selected frame at the moment.
21013 Note that historically, MI shares the selected thread with CLI, so
21014 frontends used the @code{-thread-select} to execute commands in the
21015 right context. However, getting this to work right is cumbersome. The
21016 simplest way is for frontend to emit @code{-thread-select} command
21017 before every command. This doubles the number of commands that need
21018 to be sent. The alternative approach is to suppress @code{-thread-select}
21019 if the selected thread in @value{GDBN} is supposed to be identical to the
21020 thread the frontend wants to operate on. However, getting this
21021 optimization right can be tricky. In particular, if the frontend
21022 sends several commands to @value{GDBN}, and one of the commands changes the
21023 selected thread, then the behaviour of subsequent commands will
21024 change. So, a frontend should either wait for response from such
21025 problematic commands, or explicitly add @code{-thread-select} for
21026 all subsequent commands. No frontend is known to do this exactly
21027 right, so it is suggested to just always pass the @samp{--thread} and
21028 @samp{--frame} options.
21030 @node Asynchronous and non-stop modes
21031 @subsection Asynchronous command execution and non-stop mode
21033 On some targets, @value{GDBN} is capable of processing MI commands
21034 even while the target is running. This is called @dfn{asynchronous
21035 command execution} (@pxref{Background Execution}). The frontend may
21036 specify a preferrence for asynchronous execution using the
21037 @code{-gdb-set target-async 1} command, which should be emitted before
21038 either running the executable or attaching to the target. After the
21039 frontend has started the executable or attached to the target, it can
21040 find if asynchronous execution is enabled using the
21041 @code{-list-target-features} command.
21043 Even if @value{GDBN} can accept a command while target is running,
21044 many commands that access the target do not work when the target is
21045 running. Therefore, asynchronous command execution is most useful
21046 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
21047 it is possible to examine the state of one thread, while other threads
21050 When a given thread is running, MI commands that try to access the
21051 target in the context of that thread may not work, or may work only on
21052 some targets. In particular, commands that try to operate on thread's
21053 stack will not work, on any target. Commands that read memory, or
21054 modify breakpoints, may work or not work, depending on the target. Note
21055 that even commands that operate on global state, such as @code{print},
21056 @code{set}, and breakpoint commands, still access the target in the
21057 context of a specific thread, so frontend should try to find a
21058 stopped thread and perform the operation on that thread (using the
21059 @samp{--thread} option).
21061 Which commands will work in the context of a running thread is
21062 highly target dependent. However, the two commands
21063 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
21064 to find the state of a thread, will always work.
21066 @node Thread groups
21067 @subsection Thread groups
21068 @value{GDBN} may be used to debug several processes at the same time.
21069 On some platfroms, @value{GDBN} may support debugging of several
21070 hardware systems, each one having several cores with several different
21071 processes running on each core. This section describes the MI
21072 mechanism to support such debugging scenarios.
21074 The key observation is that regardless of the structure of the
21075 target, MI can have a global list of threads, because most commands that
21076 accept the @samp{--thread} option do not need to know what process that
21077 thread belongs to. Therefore, it is not necessary to introduce
21078 neither additional @samp{--process} option, nor an notion of the
21079 current process in the MI interface. The only strictly new feature
21080 that is required is the ability to find how the threads are grouped
21083 To allow the user to discover such grouping, and to support arbitrary
21084 hierarchy of machines/cores/processes, MI introduces the concept of a
21085 @dfn{thread group}. Thread group is a collection of threads and other
21086 thread groups. A thread group always has a string identifier, a type,
21087 and may have additional attributes specific to the type. A new
21088 command, @code{-list-thread-groups}, returns the list of top-level
21089 thread groups, which correspond to processes that @value{GDBN} is
21090 debugging at the moment. By passing an identifier of a thread group
21091 to the @code{-list-thread-groups} command, it is possible to obtain
21092 the members of specific thread group.
21094 To allow the user to easily discover processes, and other objects, he
21095 wishes to debug, a concept of @dfn{available thread group} is
21096 introduced. Available thread group is an thread group that
21097 @value{GDBN} is not debugging, but that can be attached to, using the
21098 @code{-target-attach} command. The list of available top-level thread
21099 groups can be obtained using @samp{-list-thread-groups --available}.
21100 In general, the content of a thread group may be only retrieved only
21101 after attaching to that thread group.
21103 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21104 @node GDB/MI Command Syntax
21105 @section @sc{gdb/mi} Command Syntax
21108 * GDB/MI Input Syntax::
21109 * GDB/MI Output Syntax::
21112 @node GDB/MI Input Syntax
21113 @subsection @sc{gdb/mi} Input Syntax
21115 @cindex input syntax for @sc{gdb/mi}
21116 @cindex @sc{gdb/mi}, input syntax
21118 @item @var{command} @expansion{}
21119 @code{@var{cli-command} | @var{mi-command}}
21121 @item @var{cli-command} @expansion{}
21122 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
21123 @var{cli-command} is any existing @value{GDBN} CLI command.
21125 @item @var{mi-command} @expansion{}
21126 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
21127 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
21129 @item @var{token} @expansion{}
21130 "any sequence of digits"
21132 @item @var{option} @expansion{}
21133 @code{"-" @var{parameter} [ " " @var{parameter} ]}
21135 @item @var{parameter} @expansion{}
21136 @code{@var{non-blank-sequence} | @var{c-string}}
21138 @item @var{operation} @expansion{}
21139 @emph{any of the operations described in this chapter}
21141 @item @var{non-blank-sequence} @expansion{}
21142 @emph{anything, provided it doesn't contain special characters such as
21143 "-", @var{nl}, """ and of course " "}
21145 @item @var{c-string} @expansion{}
21146 @code{""" @var{seven-bit-iso-c-string-content} """}
21148 @item @var{nl} @expansion{}
21157 The CLI commands are still handled by the @sc{mi} interpreter; their
21158 output is described below.
21161 The @code{@var{token}}, when present, is passed back when the command
21165 Some @sc{mi} commands accept optional arguments as part of the parameter
21166 list. Each option is identified by a leading @samp{-} (dash) and may be
21167 followed by an optional argument parameter. Options occur first in the
21168 parameter list and can be delimited from normal parameters using
21169 @samp{--} (this is useful when some parameters begin with a dash).
21176 We want easy access to the existing CLI syntax (for debugging).
21179 We want it to be easy to spot a @sc{mi} operation.
21182 @node GDB/MI Output Syntax
21183 @subsection @sc{gdb/mi} Output Syntax
21185 @cindex output syntax of @sc{gdb/mi}
21186 @cindex @sc{gdb/mi}, output syntax
21187 The output from @sc{gdb/mi} consists of zero or more out-of-band records
21188 followed, optionally, by a single result record. This result record
21189 is for the most recent command. The sequence of output records is
21190 terminated by @samp{(gdb)}.
21192 If an input command was prefixed with a @code{@var{token}} then the
21193 corresponding output for that command will also be prefixed by that same
21197 @item @var{output} @expansion{}
21198 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
21200 @item @var{result-record} @expansion{}
21201 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
21203 @item @var{out-of-band-record} @expansion{}
21204 @code{@var{async-record} | @var{stream-record}}
21206 @item @var{async-record} @expansion{}
21207 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
21209 @item @var{exec-async-output} @expansion{}
21210 @code{[ @var{token} ] "*" @var{async-output}}
21212 @item @var{status-async-output} @expansion{}
21213 @code{[ @var{token} ] "+" @var{async-output}}
21215 @item @var{notify-async-output} @expansion{}
21216 @code{[ @var{token} ] "=" @var{async-output}}
21218 @item @var{async-output} @expansion{}
21219 @code{@var{async-class} ( "," @var{result} )* @var{nl}}
21221 @item @var{result-class} @expansion{}
21222 @code{"done" | "running" | "connected" | "error" | "exit"}
21224 @item @var{async-class} @expansion{}
21225 @code{"stopped" | @var{others}} (where @var{others} will be added
21226 depending on the needs---this is still in development).
21228 @item @var{result} @expansion{}
21229 @code{ @var{variable} "=" @var{value}}
21231 @item @var{variable} @expansion{}
21232 @code{ @var{string} }
21234 @item @var{value} @expansion{}
21235 @code{ @var{const} | @var{tuple} | @var{list} }
21237 @item @var{const} @expansion{}
21238 @code{@var{c-string}}
21240 @item @var{tuple} @expansion{}
21241 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
21243 @item @var{list} @expansion{}
21244 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
21245 @var{result} ( "," @var{result} )* "]" }
21247 @item @var{stream-record} @expansion{}
21248 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
21250 @item @var{console-stream-output} @expansion{}
21251 @code{"~" @var{c-string}}
21253 @item @var{target-stream-output} @expansion{}
21254 @code{"@@" @var{c-string}}
21256 @item @var{log-stream-output} @expansion{}
21257 @code{"&" @var{c-string}}
21259 @item @var{nl} @expansion{}
21262 @item @var{token} @expansion{}
21263 @emph{any sequence of digits}.
21271 All output sequences end in a single line containing a period.
21274 The @code{@var{token}} is from the corresponding request. Note that
21275 for all async output, while the token is allowed by the grammar and
21276 may be output by future versions of @value{GDBN} for select async
21277 output messages, it is generally omitted. Frontends should treat
21278 all async output as reporting general changes in the state of the
21279 target and there should be no need to associate async output to any
21283 @cindex status output in @sc{gdb/mi}
21284 @var{status-async-output} contains on-going status information about the
21285 progress of a slow operation. It can be discarded. All status output is
21286 prefixed by @samp{+}.
21289 @cindex async output in @sc{gdb/mi}
21290 @var{exec-async-output} contains asynchronous state change on the target
21291 (stopped, started, disappeared). All async output is prefixed by
21295 @cindex notify output in @sc{gdb/mi}
21296 @var{notify-async-output} contains supplementary information that the
21297 client should handle (e.g., a new breakpoint information). All notify
21298 output is prefixed by @samp{=}.
21301 @cindex console output in @sc{gdb/mi}
21302 @var{console-stream-output} is output that should be displayed as is in the
21303 console. It is the textual response to a CLI command. All the console
21304 output is prefixed by @samp{~}.
21307 @cindex target output in @sc{gdb/mi}
21308 @var{target-stream-output} is the output produced by the target program.
21309 All the target output is prefixed by @samp{@@}.
21312 @cindex log output in @sc{gdb/mi}
21313 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
21314 instance messages that should be displayed as part of an error log. All
21315 the log output is prefixed by @samp{&}.
21318 @cindex list output in @sc{gdb/mi}
21319 New @sc{gdb/mi} commands should only output @var{lists} containing
21325 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
21326 details about the various output records.
21328 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21329 @node GDB/MI Compatibility with CLI
21330 @section @sc{gdb/mi} Compatibility with CLI
21332 @cindex compatibility, @sc{gdb/mi} and CLI
21333 @cindex @sc{gdb/mi}, compatibility with CLI
21335 For the developers convenience CLI commands can be entered directly,
21336 but there may be some unexpected behaviour. For example, commands
21337 that query the user will behave as if the user replied yes, breakpoint
21338 command lists are not executed and some CLI commands, such as
21339 @code{if}, @code{when} and @code{define}, prompt for further input with
21340 @samp{>}, which is not valid MI output.
21342 This feature may be removed at some stage in the future and it is
21343 recommended that front ends use the @code{-interpreter-exec} command
21344 (@pxref{-interpreter-exec}).
21346 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21347 @node GDB/MI Development and Front Ends
21348 @section @sc{gdb/mi} Development and Front Ends
21349 @cindex @sc{gdb/mi} development
21351 The application which takes the MI output and presents the state of the
21352 program being debugged to the user is called a @dfn{front end}.
21354 Although @sc{gdb/mi} is still incomplete, it is currently being used
21355 by a variety of front ends to @value{GDBN}. This makes it difficult
21356 to introduce new functionality without breaking existing usage. This
21357 section tries to minimize the problems by describing how the protocol
21360 Some changes in MI need not break a carefully designed front end, and
21361 for these the MI version will remain unchanged. The following is a
21362 list of changes that may occur within one level, so front ends should
21363 parse MI output in a way that can handle them:
21367 New MI commands may be added.
21370 New fields may be added to the output of any MI command.
21373 The range of values for fields with specified values, e.g.,
21374 @code{in_scope} (@pxref{-var-update}) may be extended.
21376 @c The format of field's content e.g type prefix, may change so parse it
21377 @c at your own risk. Yes, in general?
21379 @c The order of fields may change? Shouldn't really matter but it might
21380 @c resolve inconsistencies.
21383 If the changes are likely to break front ends, the MI version level
21384 will be increased by one. This will allow the front end to parse the
21385 output according to the MI version. Apart from mi0, new versions of
21386 @value{GDBN} will not support old versions of MI and it will be the
21387 responsibility of the front end to work with the new one.
21389 @c Starting with mi3, add a new command -mi-version that prints the MI
21392 The best way to avoid unexpected changes in MI that might break your front
21393 end is to make your project known to @value{GDBN} developers and
21394 follow development on @email{gdb@@sourceware.org} and
21395 @email{gdb-patches@@sourceware.org}.
21396 @cindex mailing lists
21398 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21399 @node GDB/MI Output Records
21400 @section @sc{gdb/mi} Output Records
21403 * GDB/MI Result Records::
21404 * GDB/MI Stream Records::
21405 * GDB/MI Async Records::
21406 * GDB/MI Frame Information::
21409 @node GDB/MI Result Records
21410 @subsection @sc{gdb/mi} Result Records
21412 @cindex result records in @sc{gdb/mi}
21413 @cindex @sc{gdb/mi}, result records
21414 In addition to a number of out-of-band notifications, the response to a
21415 @sc{gdb/mi} command includes one of the following result indications:
21419 @item "^done" [ "," @var{results} ]
21420 The synchronous operation was successful, @code{@var{results}} are the return
21425 @c Is this one correct? Should it be an out-of-band notification?
21426 The asynchronous operation was successfully started. The target is
21431 @value{GDBN} has connected to a remote target.
21433 @item "^error" "," @var{c-string}
21435 The operation failed. The @code{@var{c-string}} contains the corresponding
21440 @value{GDBN} has terminated.
21444 @node GDB/MI Stream Records
21445 @subsection @sc{gdb/mi} Stream Records
21447 @cindex @sc{gdb/mi}, stream records
21448 @cindex stream records in @sc{gdb/mi}
21449 @value{GDBN} internally maintains a number of output streams: the console, the
21450 target, and the log. The output intended for each of these streams is
21451 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
21453 Each stream record begins with a unique @dfn{prefix character} which
21454 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
21455 Syntax}). In addition to the prefix, each stream record contains a
21456 @code{@var{string-output}}. This is either raw text (with an implicit new
21457 line) or a quoted C string (which does not contain an implicit newline).
21460 @item "~" @var{string-output}
21461 The console output stream contains text that should be displayed in the
21462 CLI console window. It contains the textual responses to CLI commands.
21464 @item "@@" @var{string-output}
21465 The target output stream contains any textual output from the running
21466 target. This is only present when GDB's event loop is truly
21467 asynchronous, which is currently only the case for remote targets.
21469 @item "&" @var{string-output}
21470 The log stream contains debugging messages being produced by @value{GDBN}'s
21474 @node GDB/MI Async Records
21475 @subsection @sc{gdb/mi} Async Records
21477 @cindex async records in @sc{gdb/mi}
21478 @cindex @sc{gdb/mi}, async records
21479 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
21480 additional changes that have occurred. Those changes can either be a
21481 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
21482 target activity (e.g., target stopped).
21484 The following is the list of possible async records:
21488 @item *running,thread-id="@var{thread}"
21489 The target is now running. The @var{thread} field tells which
21490 specific thread is now running, and can be @samp{all} if all threads
21491 are running. The frontend should assume that no interaction with a
21492 running thread is possible after this notification is produced.
21493 The frontend should not assume that this notification is output
21494 only once for any command. @value{GDBN} may emit this notification
21495 several times, either for different threads, because it cannot resume
21496 all threads together, or even for a single thread, if the thread must
21497 be stepped though some code before letting it run freely.
21499 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}"
21500 The target has stopped. The @var{reason} field can have one of the
21504 @item breakpoint-hit
21505 A breakpoint was reached.
21506 @item watchpoint-trigger
21507 A watchpoint was triggered.
21508 @item read-watchpoint-trigger
21509 A read watchpoint was triggered.
21510 @item access-watchpoint-trigger
21511 An access watchpoint was triggered.
21512 @item function-finished
21513 An -exec-finish or similar CLI command was accomplished.
21514 @item location-reached
21515 An -exec-until or similar CLI command was accomplished.
21516 @item watchpoint-scope
21517 A watchpoint has gone out of scope.
21518 @item end-stepping-range
21519 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
21520 similar CLI command was accomplished.
21521 @item exited-signalled
21522 The inferior exited because of a signal.
21524 The inferior exited.
21525 @item exited-normally
21526 The inferior exited normally.
21527 @item signal-received
21528 A signal was received by the inferior.
21531 The @var{id} field identifies the thread that directly caused the stop
21532 -- for example by hitting a breakpoint. Depending on whether all-stop
21533 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
21534 stop all threads, or only the thread that directly triggered the stop.
21535 If all threads are stopped, the @var{stopped} field will have the
21536 value of @code{"all"}. Otherwise, the value of the @var{stopped}
21537 field will be a list of thread identifiers. Presently, this list will
21538 always include a single thread, but frontend should be prepared to see
21539 several threads in the list.
21541 @item =thread-group-created,id="@var{id}"
21542 @itemx =thread-group-exited,id="@var{id}"
21543 A thread thread group either was attached to, or has exited/detached
21544 from. The @var{id} field contains the @value{GDBN} identifier of the
21547 @item =thread-created,id="@var{id}",group-id="@var{gid}"
21548 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
21549 A thread either was created, or has exited. The @var{id} field
21550 contains the @value{GDBN} identifier of the thread. The @var{gid}
21551 field identifies the thread group this thread belongs to.
21553 @item =thread-selected,id="@var{id}"
21554 Informs that the selected thread was changed as result of the last
21555 command. This notification is not emitted as result of @code{-thread-select}
21556 command but is emitted whenever an MI command that is not documented
21557 to change the selected thread actually changes it. In particular,
21558 invoking, directly or indirectly (via user-defined command), the CLI
21559 @code{thread} command, will generate this notification.
21561 We suggest that in response to this notification, front ends
21562 highlight the selected thread and cause subsequent commands to apply to
21565 @item =library-loaded,...
21566 Reports that a new library file was loaded by the program. This
21567 notification has 4 fields---@var{id}, @var{target-name},
21568 @var{host-name}, and @var{symbols-loaded}. The @var{id} field is an
21569 opaque identifier of the library. For remote debugging case,
21570 @var{target-name} and @var{host-name} fields give the name of the
21571 library file on the target, and on the host respectively. For native
21572 debugging, both those fields have the same value. The
21573 @var{symbols-loaded} field reports if the debug symbols for this
21574 library are loaded.
21576 @item =library-unloaded,...
21577 Reports that a library was unloaded by the program. This notification
21578 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
21579 the same meaning as for the @code{=library-loaded} notification
21583 @node GDB/MI Frame Information
21584 @subsection @sc{gdb/mi} Frame Information
21586 Response from many MI commands includes an information about stack
21587 frame. This information is a tuple that may have the following
21592 The level of the stack frame. The innermost frame has the level of
21593 zero. This field is always present.
21596 The name of the function corresponding to the frame. This field may
21597 be absent if @value{GDBN} is unable to determine the function name.
21600 The code address for the frame. This field is always present.
21603 The name of the source files that correspond to the frame's code
21604 address. This field may be absent.
21607 The source line corresponding to the frames' code address. This field
21611 The name of the binary file (either executable or shared library) the
21612 corresponds to the frame's code address. This field may be absent.
21617 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21618 @node GDB/MI Simple Examples
21619 @section Simple Examples of @sc{gdb/mi} Interaction
21620 @cindex @sc{gdb/mi}, simple examples
21622 This subsection presents several simple examples of interaction using
21623 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
21624 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
21625 the output received from @sc{gdb/mi}.
21627 Note the line breaks shown in the examples are here only for
21628 readability, they don't appear in the real output.
21630 @subheading Setting a Breakpoint
21632 Setting a breakpoint generates synchronous output which contains detailed
21633 information of the breakpoint.
21636 -> -break-insert main
21637 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21638 enabled="y",addr="0x08048564",func="main",file="myprog.c",
21639 fullname="/home/nickrob/myprog.c",line="68",times="0"@}
21643 @subheading Program Execution
21645 Program execution generates asynchronous records and MI gives the
21646 reason that execution stopped.
21652 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
21653 frame=@{addr="0x08048564",func="main",
21654 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
21655 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
21660 <- *stopped,reason="exited-normally"
21664 @subheading Quitting @value{GDBN}
21666 Quitting @value{GDBN} just prints the result class @samp{^exit}.
21674 @subheading A Bad Command
21676 Here's what happens if you pass a non-existent command:
21680 <- ^error,msg="Undefined MI command: rubbish"
21685 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21686 @node GDB/MI Command Description Format
21687 @section @sc{gdb/mi} Command Description Format
21689 The remaining sections describe blocks of commands. Each block of
21690 commands is laid out in a fashion similar to this section.
21692 @subheading Motivation
21694 The motivation for this collection of commands.
21696 @subheading Introduction
21698 A brief introduction to this collection of commands as a whole.
21700 @subheading Commands
21702 For each command in the block, the following is described:
21704 @subsubheading Synopsis
21707 -command @var{args}@dots{}
21710 @subsubheading Result
21712 @subsubheading @value{GDBN} Command
21714 The corresponding @value{GDBN} CLI command(s), if any.
21716 @subsubheading Example
21718 Example(s) formatted for readability. Some of the described commands have
21719 not been implemented yet and these are labeled N.A.@: (not available).
21722 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
21723 @node GDB/MI Breakpoint Commands
21724 @section @sc{gdb/mi} Breakpoint Commands
21726 @cindex breakpoint commands for @sc{gdb/mi}
21727 @cindex @sc{gdb/mi}, breakpoint commands
21728 This section documents @sc{gdb/mi} commands for manipulating
21731 @subheading The @code{-break-after} Command
21732 @findex -break-after
21734 @subsubheading Synopsis
21737 -break-after @var{number} @var{count}
21740 The breakpoint number @var{number} is not in effect until it has been
21741 hit @var{count} times. To see how this is reflected in the output of
21742 the @samp{-break-list} command, see the description of the
21743 @samp{-break-list} command below.
21745 @subsubheading @value{GDBN} Command
21747 The corresponding @value{GDBN} command is @samp{ignore}.
21749 @subsubheading Example
21754 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21755 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21756 fullname="/home/foo/hello.c",line="5",times="0"@}
21763 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21764 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21765 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21766 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21767 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21768 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21769 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21770 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21771 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21772 line="5",times="0",ignore="3"@}]@}
21777 @subheading The @code{-break-catch} Command
21778 @findex -break-catch
21781 @subheading The @code{-break-commands} Command
21782 @findex -break-commands
21784 @subsubheading Synopsis
21787 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
21790 Specifies the CLI commands that should be executed when breakpoint
21791 @var{number} is hit. The parameters @var{command1} to @var{commandN}
21792 are the commands. If no command is specified, any previously-set
21793 commands are cleared. @xref{Break Commands}. Typical use of this
21794 functionality is tracing a program, that is, printing of values of
21795 some variables whenever breakpoint is hit and then continuing.
21797 @subsubheading @value{GDBN} Command
21799 The corresponding @value{GDBN} command is @samp{commands}.
21801 @subsubheading Example
21806 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
21807 enabled="y",addr="0x000100d0",func="main",file="hello.c",
21808 fullname="/home/foo/hello.c",line="5",times="0"@}
21810 -break-commands 1 "print v" "continue"
21815 @subheading The @code{-break-condition} Command
21816 @findex -break-condition
21818 @subsubheading Synopsis
21821 -break-condition @var{number} @var{expr}
21824 Breakpoint @var{number} will stop the program only if the condition in
21825 @var{expr} is true. The condition becomes part of the
21826 @samp{-break-list} output (see the description of the @samp{-break-list}
21829 @subsubheading @value{GDBN} Command
21831 The corresponding @value{GDBN} command is @samp{condition}.
21833 @subsubheading Example
21837 -break-condition 1 1
21841 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21842 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21843 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21844 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21845 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21846 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21847 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21848 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
21849 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21850 line="5",cond="1",times="0",ignore="3"@}]@}
21854 @subheading The @code{-break-delete} Command
21855 @findex -break-delete
21857 @subsubheading Synopsis
21860 -break-delete ( @var{breakpoint} )+
21863 Delete the breakpoint(s) whose number(s) are specified in the argument
21864 list. This is obviously reflected in the breakpoint list.
21866 @subsubheading @value{GDBN} Command
21868 The corresponding @value{GDBN} command is @samp{delete}.
21870 @subsubheading Example
21878 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
21879 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21880 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21881 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21882 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21883 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21884 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21889 @subheading The @code{-break-disable} Command
21890 @findex -break-disable
21892 @subsubheading Synopsis
21895 -break-disable ( @var{breakpoint} )+
21898 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
21899 break list is now set to @samp{n} for the named @var{breakpoint}(s).
21901 @subsubheading @value{GDBN} Command
21903 The corresponding @value{GDBN} command is @samp{disable}.
21905 @subsubheading Example
21913 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21914 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21915 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21916 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21917 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21918 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21919 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21920 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
21921 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21922 line="5",times="0"@}]@}
21926 @subheading The @code{-break-enable} Command
21927 @findex -break-enable
21929 @subsubheading Synopsis
21932 -break-enable ( @var{breakpoint} )+
21935 Enable (previously disabled) @var{breakpoint}(s).
21937 @subsubheading @value{GDBN} Command
21939 The corresponding @value{GDBN} command is @samp{enable}.
21941 @subsubheading Example
21949 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
21950 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
21951 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
21952 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
21953 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
21954 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
21955 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
21956 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
21957 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
21958 line="5",times="0"@}]@}
21962 @subheading The @code{-break-info} Command
21963 @findex -break-info
21965 @subsubheading Synopsis
21968 -break-info @var{breakpoint}
21972 Get information about a single breakpoint.
21974 @subsubheading @value{GDBN} Command
21976 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
21978 @subsubheading Example
21981 @subheading The @code{-break-insert} Command
21982 @findex -break-insert
21984 @subsubheading Synopsis
21987 -break-insert [ -t ] [ -h ] [ -f ] [ -d ]
21988 [ -c @var{condition} ] [ -i @var{ignore-count} ]
21989 [ -p @var{thread} ] [ @var{location} ]
21993 If specified, @var{location}, can be one of:
22000 @item filename:linenum
22001 @item filename:function
22005 The possible optional parameters of this command are:
22009 Insert a temporary breakpoint.
22011 Insert a hardware breakpoint.
22012 @item -c @var{condition}
22013 Make the breakpoint conditional on @var{condition}.
22014 @item -i @var{ignore-count}
22015 Initialize the @var{ignore-count}.
22017 If @var{location} cannot be parsed (for example if it
22018 refers to unknown files or functions), create a pending
22019 breakpoint. Without this flag, @value{GDBN} will report
22020 an error, and won't create a breakpoint, if @var{location}
22023 Create a disabled breakpoint.
22026 @subsubheading Result
22028 The result is in the form:
22031 ^done,bkpt=@{number="@var{number}",type="@var{type}",disp="del"|"keep",
22032 enabled="y"|"n",addr="@var{hex}",func="@var{funcname}",file="@var{filename}",
22033 fullname="@var{full_filename}",line="@var{lineno}",[thread="@var{threadno},]
22034 times="@var{times}"@}
22038 where @var{number} is the @value{GDBN} number for this breakpoint,
22039 @var{funcname} is the name of the function where the breakpoint was
22040 inserted, @var{filename} is the name of the source file which contains
22041 this function, @var{lineno} is the source line number within that file
22042 and @var{times} the number of times that the breakpoint has been hit
22043 (always 0 for -break-insert but may be greater for -break-info or -break-list
22044 which use the same output).
22046 Note: this format is open to change.
22047 @c An out-of-band breakpoint instead of part of the result?
22049 @subsubheading @value{GDBN} Command
22051 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
22052 @samp{hbreak}, @samp{thbreak}, and @samp{rbreak}.
22054 @subsubheading Example
22059 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
22060 fullname="/home/foo/recursive2.c,line="4",times="0"@}
22062 -break-insert -t foo
22063 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
22064 fullname="/home/foo/recursive2.c,line="11",times="0"@}
22067 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22068 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22069 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22070 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22071 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22072 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22073 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22074 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22075 addr="0x0001072c", func="main",file="recursive2.c",
22076 fullname="/home/foo/recursive2.c,"line="4",times="0"@},
22077 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
22078 addr="0x00010774",func="foo",file="recursive2.c",
22079 fullname="/home/foo/recursive2.c",line="11",times="0"@}]@}
22081 -break-insert -r foo.*
22082 ~int foo(int, int);
22083 ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
22084 "fullname="/home/foo/recursive2.c",line="11",times="0"@}
22088 @subheading The @code{-break-list} Command
22089 @findex -break-list
22091 @subsubheading Synopsis
22097 Displays the list of inserted breakpoints, showing the following fields:
22101 number of the breakpoint
22103 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
22105 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
22108 is the breakpoint enabled or no: @samp{y} or @samp{n}
22110 memory location at which the breakpoint is set
22112 logical location of the breakpoint, expressed by function name, file
22115 number of times the breakpoint has been hit
22118 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
22119 @code{body} field is an empty list.
22121 @subsubheading @value{GDBN} Command
22123 The corresponding @value{GDBN} command is @samp{info break}.
22125 @subsubheading Example
22130 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22131 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22132 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22133 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22134 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22135 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22136 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22137 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22138 addr="0x000100d0",func="main",file="hello.c",line="5",times="0"@},
22139 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
22140 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
22141 line="13",times="0"@}]@}
22145 Here's an example of the result when there are no breakpoints:
22150 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
22151 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22152 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22153 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22154 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22155 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22156 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22161 @subheading The @code{-break-watch} Command
22162 @findex -break-watch
22164 @subsubheading Synopsis
22167 -break-watch [ -a | -r ]
22170 Create a watchpoint. With the @samp{-a} option it will create an
22171 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
22172 read from or on a write to the memory location. With the @samp{-r}
22173 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
22174 trigger only when the memory location is accessed for reading. Without
22175 either of the options, the watchpoint created is a regular watchpoint,
22176 i.e., it will trigger when the memory location is accessed for writing.
22177 @xref{Set Watchpoints, , Setting Watchpoints}.
22179 Note that @samp{-break-list} will report a single list of watchpoints and
22180 breakpoints inserted.
22182 @subsubheading @value{GDBN} Command
22184 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
22187 @subsubheading Example
22189 Setting a watchpoint on a variable in the @code{main} function:
22194 ^done,wpt=@{number="2",exp="x"@}
22199 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
22200 value=@{old="-268439212",new="55"@},
22201 frame=@{func="main",args=[],file="recursive2.c",
22202 fullname="/home/foo/bar/recursive2.c",line="5"@}
22206 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
22207 the program execution twice: first for the variable changing value, then
22208 for the watchpoint going out of scope.
22213 ^done,wpt=@{number="5",exp="C"@}
22218 *stopped,reason="watchpoint-trigger",
22219 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
22220 frame=@{func="callee4",args=[],
22221 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22222 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
22227 *stopped,reason="watchpoint-scope",wpnum="5",
22228 frame=@{func="callee3",args=[@{name="strarg",
22229 value="0x11940 \"A string argument.\""@}],
22230 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22231 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22235 Listing breakpoints and watchpoints, at different points in the program
22236 execution. Note that once the watchpoint goes out of scope, it is
22242 ^done,wpt=@{number="2",exp="C"@}
22245 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22246 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22247 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22248 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22249 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22250 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22251 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22252 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22253 addr="0x00010734",func="callee4",
22254 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22255 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"@},
22256 bkpt=@{number="2",type="watchpoint",disp="keep",
22257 enabled="y",addr="",what="C",times="0"@}]@}
22262 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
22263 value=@{old="-276895068",new="3"@},
22264 frame=@{func="callee4",args=[],
22265 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22266 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
22269 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
22270 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22271 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22272 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22273 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22274 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22275 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22276 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22277 addr="0x00010734",func="callee4",
22278 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22279 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"@},
22280 bkpt=@{number="2",type="watchpoint",disp="keep",
22281 enabled="y",addr="",what="C",times="-5"@}]@}
22285 ^done,reason="watchpoint-scope",wpnum="2",
22286 frame=@{func="callee3",args=[@{name="strarg",
22287 value="0x11940 \"A string argument.\""@}],
22288 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22289 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22292 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
22293 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
22294 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
22295 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
22296 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
22297 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
22298 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
22299 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
22300 addr="0x00010734",func="callee4",
22301 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22302 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
22307 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22308 @node GDB/MI Program Context
22309 @section @sc{gdb/mi} Program Context
22311 @subheading The @code{-exec-arguments} Command
22312 @findex -exec-arguments
22315 @subsubheading Synopsis
22318 -exec-arguments @var{args}
22321 Set the inferior program arguments, to be used in the next
22324 @subsubheading @value{GDBN} Command
22326 The corresponding @value{GDBN} command is @samp{set args}.
22328 @subsubheading Example
22332 -exec-arguments -v word
22339 @subheading The @code{-exec-show-arguments} Command
22340 @findex -exec-show-arguments
22342 @subsubheading Synopsis
22345 -exec-show-arguments
22348 Print the arguments of the program.
22350 @subsubheading @value{GDBN} Command
22352 The corresponding @value{GDBN} command is @samp{show args}.
22354 @subsubheading Example
22359 @subheading The @code{-environment-cd} Command
22360 @findex -environment-cd
22362 @subsubheading Synopsis
22365 -environment-cd @var{pathdir}
22368 Set @value{GDBN}'s working directory.
22370 @subsubheading @value{GDBN} Command
22372 The corresponding @value{GDBN} command is @samp{cd}.
22374 @subsubheading Example
22378 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22384 @subheading The @code{-environment-directory} Command
22385 @findex -environment-directory
22387 @subsubheading Synopsis
22390 -environment-directory [ -r ] [ @var{pathdir} ]+
22393 Add directories @var{pathdir} to beginning of search path for source files.
22394 If the @samp{-r} option is used, the search path is reset to the default
22395 search path. If directories @var{pathdir} are supplied in addition to the
22396 @samp{-r} option, the search path is first reset and then addition
22398 Multiple directories may be specified, separated by blanks. Specifying
22399 multiple directories in a single command
22400 results in the directories added to the beginning of the
22401 search path in the same order they were presented in the command.
22402 If blanks are needed as
22403 part of a directory name, double-quotes should be used around
22404 the name. In the command output, the path will show up separated
22405 by the system directory-separator character. The directory-separator
22406 character must not be used
22407 in any directory name.
22408 If no directories are specified, the current search path is displayed.
22410 @subsubheading @value{GDBN} Command
22412 The corresponding @value{GDBN} command is @samp{dir}.
22414 @subsubheading Example
22418 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
22419 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22421 -environment-directory ""
22422 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
22424 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
22425 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
22427 -environment-directory -r
22428 ^done,source-path="$cdir:$cwd"
22433 @subheading The @code{-environment-path} Command
22434 @findex -environment-path
22436 @subsubheading Synopsis
22439 -environment-path [ -r ] [ @var{pathdir} ]+
22442 Add directories @var{pathdir} to beginning of search path for object files.
22443 If the @samp{-r} option is used, the search path is reset to the original
22444 search path that existed at gdb start-up. If directories @var{pathdir} are
22445 supplied in addition to the
22446 @samp{-r} option, the search path is first reset and then addition
22448 Multiple directories may be specified, separated by blanks. Specifying
22449 multiple directories in a single command
22450 results in the directories added to the beginning of the
22451 search path in the same order they were presented in the command.
22452 If blanks are needed as
22453 part of a directory name, double-quotes should be used around
22454 the name. In the command output, the path will show up separated
22455 by the system directory-separator character. The directory-separator
22456 character must not be used
22457 in any directory name.
22458 If no directories are specified, the current path is displayed.
22461 @subsubheading @value{GDBN} Command
22463 The corresponding @value{GDBN} command is @samp{path}.
22465 @subsubheading Example
22470 ^done,path="/usr/bin"
22472 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
22473 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
22475 -environment-path -r /usr/local/bin
22476 ^done,path="/usr/local/bin:/usr/bin"
22481 @subheading The @code{-environment-pwd} Command
22482 @findex -environment-pwd
22484 @subsubheading Synopsis
22490 Show the current working directory.
22492 @subsubheading @value{GDBN} Command
22494 The corresponding @value{GDBN} command is @samp{pwd}.
22496 @subsubheading Example
22501 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
22505 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22506 @node GDB/MI Thread Commands
22507 @section @sc{gdb/mi} Thread Commands
22510 @subheading The @code{-thread-info} Command
22511 @findex -thread-info
22513 @subsubheading Synopsis
22516 -thread-info [ @var{thread-id} ]
22519 Reports information about either a specific thread, if
22520 the @var{thread-id} parameter is present, or about all
22521 threads. When printing information about all threads,
22522 also reports the current thread.
22524 @subsubheading @value{GDBN} Command
22526 The @samp{info thread} command prints the same information
22529 @subsubheading Example
22534 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
22535 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
22536 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
22537 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
22538 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}],
22539 current-thread-id="1"
22543 The @samp{state} field may have the following values:
22547 The thread is stopped. Frame information is available for stopped
22551 The thread is running. There's no frame information for running
22556 @subheading The @code{-thread-list-ids} Command
22557 @findex -thread-list-ids
22559 @subsubheading Synopsis
22565 Produces a list of the currently known @value{GDBN} thread ids. At the
22566 end of the list it also prints the total number of such threads.
22568 This command is retained for historical reasons, the
22569 @code{-thread-info} command should be used instead.
22571 @subsubheading @value{GDBN} Command
22573 Part of @samp{info threads} supplies the same information.
22575 @subsubheading Example
22580 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22581 current-thread-id="1",number-of-threads="3"
22586 @subheading The @code{-thread-select} Command
22587 @findex -thread-select
22589 @subsubheading Synopsis
22592 -thread-select @var{threadnum}
22595 Make @var{threadnum} the current thread. It prints the number of the new
22596 current thread, and the topmost frame for that thread.
22598 This command is deprecated in favor of explicitly using the
22599 @samp{--thread} option to each command.
22601 @subsubheading @value{GDBN} Command
22603 The corresponding @value{GDBN} command is @samp{thread}.
22605 @subsubheading Example
22612 *stopped,reason="end-stepping-range",thread-id="2",line="187",
22613 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
22617 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
22618 number-of-threads="3"
22621 ^done,new-thread-id="3",
22622 frame=@{level="0",func="vprintf",
22623 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
22624 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
22628 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
22629 @node GDB/MI Program Execution
22630 @section @sc{gdb/mi} Program Execution
22632 These are the asynchronous commands which generate the out-of-band
22633 record @samp{*stopped}. Currently @value{GDBN} only really executes
22634 asynchronously with remote targets and this interaction is mimicked in
22637 @subheading The @code{-exec-continue} Command
22638 @findex -exec-continue
22640 @subsubheading Synopsis
22643 -exec-continue [--all|--thread-group N]
22646 Resumes the execution of the inferior program until a breakpoint is
22647 encountered, or until the inferior exits. In all-stop mode
22648 (@pxref{All-Stop Mode}), may resume only one thread, or all threads,
22649 depending on the value of the @samp{scheduler-locking} variable. In
22650 non-stop mode (@pxref{Non-Stop Mode}), if the @samp{--all} is not
22651 specified, only the thread specified with the @samp{--thread} option
22652 (or current thread, if no @samp{--thread} is provided) is resumed. If
22653 @samp{--all} is specified, all threads will be resumed. The
22654 @samp{--all} option is ignored in all-stop mode. If the
22655 @samp{--thread-group} options is specified, then all threads in that
22656 thread group are resumed.
22658 @subsubheading @value{GDBN} Command
22660 The corresponding @value{GDBN} corresponding is @samp{continue}.
22662 @subsubheading Example
22669 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
22670 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
22676 @subheading The @code{-exec-finish} Command
22677 @findex -exec-finish
22679 @subsubheading Synopsis
22685 Resumes the execution of the inferior program until the current
22686 function is exited. Displays the results returned by the function.
22688 @subsubheading @value{GDBN} Command
22690 The corresponding @value{GDBN} command is @samp{finish}.
22692 @subsubheading Example
22694 Function returning @code{void}.
22701 *stopped,reason="function-finished",frame=@{func="main",args=[],
22702 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
22706 Function returning other than @code{void}. The name of the internal
22707 @value{GDBN} variable storing the result is printed, together with the
22714 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
22715 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
22716 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
22717 gdb-result-var="$1",return-value="0"
22722 @subheading The @code{-exec-interrupt} Command
22723 @findex -exec-interrupt
22725 @subsubheading Synopsis
22728 -exec-interrupt [--all|--thread-group N]
22731 Interrupts the background execution of the target. Note how the token
22732 associated with the stop message is the one for the execution command
22733 that has been interrupted. The token for the interrupt itself only
22734 appears in the @samp{^done} output. If the user is trying to
22735 interrupt a non-running program, an error message will be printed.
22737 Note that when asynchronous execution is enabled, this command is
22738 asynchronous just like other execution commands. That is, first the
22739 @samp{^done} response will be printed, and the target stop will be
22740 reported after that using the @samp{*stopped} notification.
22742 In non-stop mode, only the context thread is interrupted by default.
22743 All threads will be interrupted if the @samp{--all} option is
22744 specified. If the @samp{--thread-group} option is specified, all
22745 threads in that group will be interrupted.
22747 @subsubheading @value{GDBN} Command
22749 The corresponding @value{GDBN} command is @samp{interrupt}.
22751 @subsubheading Example
22762 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
22763 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
22764 fullname="/home/foo/bar/try.c",line="13"@}
22769 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
22773 @subheading The @code{-exec-jump} Command
22776 @subsubheading Synopsis
22779 -exec-jump @var{location}
22782 Resumes execution of the inferior program at the location specified by
22783 parameter. @xref{Specify Location}, for a description of the
22784 different forms of @var{location}.
22786 @subsubheading @value{GDBN} Command
22788 The corresponding @value{GDBN} command is @samp{jump}.
22790 @subsubheading Example
22793 -exec-jump foo.c:10
22794 *running,thread-id="all"
22799 @subheading The @code{-exec-next} Command
22802 @subsubheading Synopsis
22808 Resumes execution of the inferior program, stopping when the beginning
22809 of the next source line is reached.
22811 @subsubheading @value{GDBN} Command
22813 The corresponding @value{GDBN} command is @samp{next}.
22815 @subsubheading Example
22821 *stopped,reason="end-stepping-range",line="8",file="hello.c"
22826 @subheading The @code{-exec-next-instruction} Command
22827 @findex -exec-next-instruction
22829 @subsubheading Synopsis
22832 -exec-next-instruction
22835 Executes one machine instruction. If the instruction is a function
22836 call, continues until the function returns. If the program stops at an
22837 instruction in the middle of a source line, the address will be
22840 @subsubheading @value{GDBN} Command
22842 The corresponding @value{GDBN} command is @samp{nexti}.
22844 @subsubheading Example
22848 -exec-next-instruction
22852 *stopped,reason="end-stepping-range",
22853 addr="0x000100d4",line="5",file="hello.c"
22858 @subheading The @code{-exec-return} Command
22859 @findex -exec-return
22861 @subsubheading Synopsis
22867 Makes current function return immediately. Doesn't execute the inferior.
22868 Displays the new current frame.
22870 @subsubheading @value{GDBN} Command
22872 The corresponding @value{GDBN} command is @samp{return}.
22874 @subsubheading Example
22878 200-break-insert callee4
22879 200^done,bkpt=@{number="1",addr="0x00010734",
22880 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22885 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22886 frame=@{func="callee4",args=[],
22887 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22888 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
22894 111^done,frame=@{level="0",func="callee3",
22895 args=[@{name="strarg",
22896 value="0x11940 \"A string argument.\""@}],
22897 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
22898 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
22903 @subheading The @code{-exec-run} Command
22906 @subsubheading Synopsis
22912 Starts execution of the inferior from the beginning. The inferior
22913 executes until either a breakpoint is encountered or the program
22914 exits. In the latter case the output will include an exit code, if
22915 the program has exited exceptionally.
22917 @subsubheading @value{GDBN} Command
22919 The corresponding @value{GDBN} command is @samp{run}.
22921 @subsubheading Examples
22926 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
22931 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
22932 frame=@{func="main",args=[],file="recursive2.c",
22933 fullname="/home/foo/bar/recursive2.c",line="4"@}
22938 Program exited normally:
22946 *stopped,reason="exited-normally"
22951 Program exited exceptionally:
22959 *stopped,reason="exited",exit-code="01"
22963 Another way the program can terminate is if it receives a signal such as
22964 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
22968 *stopped,reason="exited-signalled",signal-name="SIGINT",
22969 signal-meaning="Interrupt"
22973 @c @subheading -exec-signal
22976 @subheading The @code{-exec-step} Command
22979 @subsubheading Synopsis
22985 Resumes execution of the inferior program, stopping when the beginning
22986 of the next source line is reached, if the next source line is not a
22987 function call. If it is, stop at the first instruction of the called
22990 @subsubheading @value{GDBN} Command
22992 The corresponding @value{GDBN} command is @samp{step}.
22994 @subsubheading Example
22996 Stepping into a function:
23002 *stopped,reason="end-stepping-range",
23003 frame=@{func="foo",args=[@{name="a",value="10"@},
23004 @{name="b",value="0"@}],file="recursive2.c",
23005 fullname="/home/foo/bar/recursive2.c",line="11"@}
23015 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
23020 @subheading The @code{-exec-step-instruction} Command
23021 @findex -exec-step-instruction
23023 @subsubheading Synopsis
23026 -exec-step-instruction
23029 Resumes the inferior which executes one machine instruction. The
23030 output, once @value{GDBN} has stopped, will vary depending on whether
23031 we have stopped in the middle of a source line or not. In the former
23032 case, the address at which the program stopped will be printed as
23035 @subsubheading @value{GDBN} Command
23037 The corresponding @value{GDBN} command is @samp{stepi}.
23039 @subsubheading Example
23043 -exec-step-instruction
23047 *stopped,reason="end-stepping-range",
23048 frame=@{func="foo",args=[],file="try.c",
23049 fullname="/home/foo/bar/try.c",line="10"@}
23051 -exec-step-instruction
23055 *stopped,reason="end-stepping-range",
23056 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
23057 fullname="/home/foo/bar/try.c",line="10"@}
23062 @subheading The @code{-exec-until} Command
23063 @findex -exec-until
23065 @subsubheading Synopsis
23068 -exec-until [ @var{location} ]
23071 Executes the inferior until the @var{location} specified in the
23072 argument is reached. If there is no argument, the inferior executes
23073 until a source line greater than the current one is reached. The
23074 reason for stopping in this case will be @samp{location-reached}.
23076 @subsubheading @value{GDBN} Command
23078 The corresponding @value{GDBN} command is @samp{until}.
23080 @subsubheading Example
23084 -exec-until recursive2.c:6
23088 *stopped,reason="location-reached",frame=@{func="main",args=[],
23089 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
23094 @subheading -file-clear
23095 Is this going away????
23098 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23099 @node GDB/MI Stack Manipulation
23100 @section @sc{gdb/mi} Stack Manipulation Commands
23103 @subheading The @code{-stack-info-frame} Command
23104 @findex -stack-info-frame
23106 @subsubheading Synopsis
23112 Get info on the selected frame.
23114 @subsubheading @value{GDBN} Command
23116 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
23117 (without arguments).
23119 @subsubheading Example
23124 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
23125 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23126 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
23130 @subheading The @code{-stack-info-depth} Command
23131 @findex -stack-info-depth
23133 @subsubheading Synopsis
23136 -stack-info-depth [ @var{max-depth} ]
23139 Return the depth of the stack. If the integer argument @var{max-depth}
23140 is specified, do not count beyond @var{max-depth} frames.
23142 @subsubheading @value{GDBN} Command
23144 There's no equivalent @value{GDBN} command.
23146 @subsubheading Example
23148 For a stack with frame levels 0 through 11:
23155 -stack-info-depth 4
23158 -stack-info-depth 12
23161 -stack-info-depth 11
23164 -stack-info-depth 13
23169 @subheading The @code{-stack-list-arguments} Command
23170 @findex -stack-list-arguments
23172 @subsubheading Synopsis
23175 -stack-list-arguments @var{show-values}
23176 [ @var{low-frame} @var{high-frame} ]
23179 Display a list of the arguments for the frames between @var{low-frame}
23180 and @var{high-frame} (inclusive). If @var{low-frame} and
23181 @var{high-frame} are not provided, list the arguments for the whole
23182 call stack. If the two arguments are equal, show the single frame
23183 at the corresponding level. It is an error if @var{low-frame} is
23184 larger than the actual number of frames. On the other hand,
23185 @var{high-frame} may be larger than the actual number of frames, in
23186 which case only existing frames will be returned.
23188 The @var{show-values} argument must have a value of 0 or 1. A value of
23189 0 means that only the names of the arguments are listed, a value of 1
23190 means that both names and values of the arguments are printed.
23192 Use of this command to obtain arguments in a single frame is
23193 deprecated in favor of the @samp{-stack-list-variables} command.
23195 @subsubheading @value{GDBN} Command
23197 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
23198 @samp{gdb_get_args} command which partially overlaps with the
23199 functionality of @samp{-stack-list-arguments}.
23201 @subsubheading Example
23208 frame=@{level="0",addr="0x00010734",func="callee4",
23209 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23210 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
23211 frame=@{level="1",addr="0x0001076c",func="callee3",
23212 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23213 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
23214 frame=@{level="2",addr="0x0001078c",func="callee2",
23215 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23216 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
23217 frame=@{level="3",addr="0x000107b4",func="callee1",
23218 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23219 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
23220 frame=@{level="4",addr="0x000107e0",func="main",
23221 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
23222 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
23224 -stack-list-arguments 0
23227 frame=@{level="0",args=[]@},
23228 frame=@{level="1",args=[name="strarg"]@},
23229 frame=@{level="2",args=[name="intarg",name="strarg"]@},
23230 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
23231 frame=@{level="4",args=[]@}]
23233 -stack-list-arguments 1
23236 frame=@{level="0",args=[]@},
23238 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
23239 frame=@{level="2",args=[
23240 @{name="intarg",value="2"@},
23241 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
23242 @{frame=@{level="3",args=[
23243 @{name="intarg",value="2"@},
23244 @{name="strarg",value="0x11940 \"A string argument.\""@},
23245 @{name="fltarg",value="3.5"@}]@},
23246 frame=@{level="4",args=[]@}]
23248 -stack-list-arguments 0 2 2
23249 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
23251 -stack-list-arguments 1 2 2
23252 ^done,stack-args=[frame=@{level="2",
23253 args=[@{name="intarg",value="2"@},
23254 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
23258 @c @subheading -stack-list-exception-handlers
23261 @subheading The @code{-stack-list-frames} Command
23262 @findex -stack-list-frames
23264 @subsubheading Synopsis
23267 -stack-list-frames [ @var{low-frame} @var{high-frame} ]
23270 List the frames currently on the stack. For each frame it displays the
23275 The frame number, 0 being the topmost frame, i.e., the innermost function.
23277 The @code{$pc} value for that frame.
23281 File name of the source file where the function lives.
23283 Line number corresponding to the @code{$pc}.
23286 If invoked without arguments, this command prints a backtrace for the
23287 whole stack. If given two integer arguments, it shows the frames whose
23288 levels are between the two arguments (inclusive). If the two arguments
23289 are equal, it shows the single frame at the corresponding level. It is
23290 an error if @var{low-frame} is larger than the actual number of
23291 frames. On the other hand, @var{high-frame} may be larger than the
23292 actual number of frames, in which case only existing frames will be returned.
23294 @subsubheading @value{GDBN} Command
23296 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
23298 @subsubheading Example
23300 Full stack backtrace:
23306 [frame=@{level="0",addr="0x0001076c",func="foo",
23307 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
23308 frame=@{level="1",addr="0x000107a4",func="foo",
23309 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23310 frame=@{level="2",addr="0x000107a4",func="foo",
23311 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23312 frame=@{level="3",addr="0x000107a4",func="foo",
23313 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23314 frame=@{level="4",addr="0x000107a4",func="foo",
23315 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23316 frame=@{level="5",addr="0x000107a4",func="foo",
23317 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23318 frame=@{level="6",addr="0x000107a4",func="foo",
23319 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23320 frame=@{level="7",addr="0x000107a4",func="foo",
23321 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23322 frame=@{level="8",addr="0x000107a4",func="foo",
23323 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23324 frame=@{level="9",addr="0x000107a4",func="foo",
23325 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23326 frame=@{level="10",addr="0x000107a4",func="foo",
23327 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23328 frame=@{level="11",addr="0x00010738",func="main",
23329 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
23333 Show frames between @var{low_frame} and @var{high_frame}:
23337 -stack-list-frames 3 5
23339 [frame=@{level="3",addr="0x000107a4",func="foo",
23340 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23341 frame=@{level="4",addr="0x000107a4",func="foo",
23342 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
23343 frame=@{level="5",addr="0x000107a4",func="foo",
23344 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23348 Show a single frame:
23352 -stack-list-frames 3 3
23354 [frame=@{level="3",addr="0x000107a4",func="foo",
23355 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
23360 @subheading The @code{-stack-list-locals} Command
23361 @findex -stack-list-locals
23363 @subsubheading Synopsis
23366 -stack-list-locals @var{print-values}
23369 Display the local variable names for the selected frame. If
23370 @var{print-values} is 0 or @code{--no-values}, print only the names of
23371 the variables; if it is 1 or @code{--all-values}, print also their
23372 values; and if it is 2 or @code{--simple-values}, print the name,
23373 type and value for simple data types and the name and type for arrays,
23374 structures and unions. In this last case, a frontend can immediately
23375 display the value of simple data types and create variable objects for
23376 other data types when the user wishes to explore their values in
23379 This command is deprecated in favor of the
23380 @samp{-stack-list-variables} command.
23382 @subsubheading @value{GDBN} Command
23384 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
23386 @subsubheading Example
23390 -stack-list-locals 0
23391 ^done,locals=[name="A",name="B",name="C"]
23393 -stack-list-locals --all-values
23394 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
23395 @{name="C",value="@{1, 2, 3@}"@}]
23396 -stack-list-locals --simple-values
23397 ^done,locals=[@{name="A",type="int",value="1"@},
23398 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
23402 @subheading The @code{-stack-list-variables} Command
23403 @findex -stack-list-variables
23405 @subsubheading Synopsis
23408 -stack-list-variables @var{print-values}
23411 Display the names of local variables and function arguments for the selected frame. If
23412 @var{print-values} is 0 or @code{--no-values}, print only the names of
23413 the variables; if it is 1 or @code{--all-values}, print also their
23414 values; and if it is 2 or @code{--simple-values}, print the name,
23415 type and value for simple data types and the name and type for arrays,
23416 structures and unions.
23418 @subsubheading Example
23422 -stack-list-variables --thread 1 --frame 0 --all-values
23423 ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}]
23428 @subheading The @code{-stack-select-frame} Command
23429 @findex -stack-select-frame
23431 @subsubheading Synopsis
23434 -stack-select-frame @var{framenum}
23437 Change the selected frame. Select a different frame @var{framenum} on
23440 This command in deprecated in favor of passing the @samp{--frame}
23441 option to every command.
23443 @subsubheading @value{GDBN} Command
23445 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
23446 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
23448 @subsubheading Example
23452 -stack-select-frame 2
23457 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
23458 @node GDB/MI Variable Objects
23459 @section @sc{gdb/mi} Variable Objects
23463 @subheading Motivation for Variable Objects in @sc{gdb/mi}
23465 For the implementation of a variable debugger window (locals, watched
23466 expressions, etc.), we are proposing the adaptation of the existing code
23467 used by @code{Insight}.
23469 The two main reasons for that are:
23473 It has been proven in practice (it is already on its second generation).
23476 It will shorten development time (needless to say how important it is
23480 The original interface was designed to be used by Tcl code, so it was
23481 slightly changed so it could be used through @sc{gdb/mi}. This section
23482 describes the @sc{gdb/mi} operations that will be available and gives some
23483 hints about their use.
23485 @emph{Note}: In addition to the set of operations described here, we
23486 expect the @sc{gui} implementation of a variable window to require, at
23487 least, the following operations:
23490 @item @code{-gdb-show} @code{output-radix}
23491 @item @code{-stack-list-arguments}
23492 @item @code{-stack-list-locals}
23493 @item @code{-stack-select-frame}
23498 @subheading Introduction to Variable Objects
23500 @cindex variable objects in @sc{gdb/mi}
23502 Variable objects are "object-oriented" MI interface for examining and
23503 changing values of expressions. Unlike some other MI interfaces that
23504 work with expressions, variable objects are specifically designed for
23505 simple and efficient presentation in the frontend. A variable object
23506 is identified by string name. When a variable object is created, the
23507 frontend specifies the expression for that variable object. The
23508 expression can be a simple variable, or it can be an arbitrary complex
23509 expression, and can even involve CPU registers. After creating a
23510 variable object, the frontend can invoke other variable object
23511 operations---for example to obtain or change the value of a variable
23512 object, or to change display format.
23514 Variable objects have hierarchical tree structure. Any variable object
23515 that corresponds to a composite type, such as structure in C, has
23516 a number of child variable objects, for example corresponding to each
23517 element of a structure. A child variable object can itself have
23518 children, recursively. Recursion ends when we reach
23519 leaf variable objects, which always have built-in types. Child variable
23520 objects are created only by explicit request, so if a frontend
23521 is not interested in the children of a particular variable object, no
23522 child will be created.
23524 For a leaf variable object it is possible to obtain its value as a
23525 string, or set the value from a string. String value can be also
23526 obtained for a non-leaf variable object, but it's generally a string
23527 that only indicates the type of the object, and does not list its
23528 contents. Assignment to a non-leaf variable object is not allowed.
23530 A frontend does not need to read the values of all variable objects each time
23531 the program stops. Instead, MI provides an update command that lists all
23532 variable objects whose values has changed since the last update
23533 operation. This considerably reduces the amount of data that must
23534 be transferred to the frontend. As noted above, children variable
23535 objects are created on demand, and only leaf variable objects have a
23536 real value. As result, gdb will read target memory only for leaf
23537 variables that frontend has created.
23539 The automatic update is not always desirable. For example, a frontend
23540 might want to keep a value of some expression for future reference,
23541 and never update it. For another example, fetching memory is
23542 relatively slow for embedded targets, so a frontend might want
23543 to disable automatic update for the variables that are either not
23544 visible on the screen, or ``closed''. This is possible using so
23545 called ``frozen variable objects''. Such variable objects are never
23546 implicitly updated.
23548 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
23549 fixed variable object, the expression is parsed when the variable
23550 object is created, including associating identifiers to specific
23551 variables. The meaning of expression never changes. For a floating
23552 variable object the values of variables whose names appear in the
23553 expressions are re-evaluated every time in the context of the current
23554 frame. Consider this example:
23559 struct work_state state;
23566 If a fixed variable object for the @code{state} variable is created in
23567 this function, and we enter the recursive call, the the variable
23568 object will report the value of @code{state} in the top-level
23569 @code{do_work} invocation. On the other hand, a floating variable
23570 object will report the value of @code{state} in the current frame.
23572 If an expression specified when creating a fixed variable object
23573 refers to a local variable, the variable object becomes bound to the
23574 thread and frame in which the variable object is created. When such
23575 variable object is updated, @value{GDBN} makes sure that the
23576 thread/frame combination the variable object is bound to still exists,
23577 and re-evaluates the variable object in context of that thread/frame.
23579 The following is the complete set of @sc{gdb/mi} operations defined to
23580 access this functionality:
23582 @multitable @columnfractions .4 .6
23583 @item @strong{Operation}
23584 @tab @strong{Description}
23586 @item @code{-enable-pretty-printing}
23587 @tab enable Python-based pretty-printing
23588 @item @code{-var-create}
23589 @tab create a variable object
23590 @item @code{-var-delete}
23591 @tab delete the variable object and/or its children
23592 @item @code{-var-set-format}
23593 @tab set the display format of this variable
23594 @item @code{-var-show-format}
23595 @tab show the display format of this variable
23596 @item @code{-var-info-num-children}
23597 @tab tells how many children this object has
23598 @item @code{-var-list-children}
23599 @tab return a list of the object's children
23600 @item @code{-var-info-type}
23601 @tab show the type of this variable object
23602 @item @code{-var-info-expression}
23603 @tab print parent-relative expression that this variable object represents
23604 @item @code{-var-info-path-expression}
23605 @tab print full expression that this variable object represents
23606 @item @code{-var-show-attributes}
23607 @tab is this variable editable? does it exist here?
23608 @item @code{-var-evaluate-expression}
23609 @tab get the value of this variable
23610 @item @code{-var-assign}
23611 @tab set the value of this variable
23612 @item @code{-var-update}
23613 @tab update the variable and its children
23614 @item @code{-var-set-frozen}
23615 @tab set frozeness attribute
23616 @item @code{-var-set-update-range}
23617 @tab set range of children to display on update
23620 In the next subsection we describe each operation in detail and suggest
23621 how it can be used.
23623 @subheading Description And Use of Operations on Variable Objects
23625 @subheading The @code{-enable-pretty-printing} Command
23626 @findex -enable-pretty-printing
23629 -enable-pretty-printing
23632 @value{GDBN} allows Python-based visualizers to affect the output of the
23633 MI variable object commands. However, because there was no way to
23634 implement this in a fully backward-compatible way, a front end must
23635 request that this functionality be enabled.
23637 Once enabled, this feature cannot be disabled.
23639 Note that if Python support has not been compiled into @value{GDBN},
23640 this command will still succeed (and do nothing).
23642 This feature is currently (as of @value{GDBN} 7.0) experimental, and
23643 may work differently in future versions of @value{GDBN}.
23645 @subheading The @code{-var-create} Command
23646 @findex -var-create
23648 @subsubheading Synopsis
23651 -var-create @{@var{name} | "-"@}
23652 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
23655 This operation creates a variable object, which allows the monitoring of
23656 a variable, the result of an expression, a memory cell or a CPU
23659 The @var{name} parameter is the string by which the object can be
23660 referenced. It must be unique. If @samp{-} is specified, the varobj
23661 system will generate a string ``varNNNNNN'' automatically. It will be
23662 unique provided that one does not specify @var{name} of that format.
23663 The command fails if a duplicate name is found.
23665 The frame under which the expression should be evaluated can be
23666 specified by @var{frame-addr}. A @samp{*} indicates that the current
23667 frame should be used. A @samp{@@} indicates that a floating variable
23668 object must be created.
23670 @var{expression} is any expression valid on the current language set (must not
23671 begin with a @samp{*}), or one of the following:
23675 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
23678 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
23681 @samp{$@var{regname}} --- a CPU register name
23684 @cindex dynamic varobj
23685 A varobj's contents may be provided by a Python-based pretty-printer. In this
23686 case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs
23687 have slightly different semantics in some cases. If the
23688 @code{-enable-pretty-printing} command is not sent, then @value{GDBN}
23689 will never create a dynamic varobj. This ensures backward
23690 compatibility for existing clients.
23692 @subsubheading Result
23694 This operation returns attributes of the newly-created varobj. These
23699 The name of the varobj.
23702 The number of children of the varobj. This number is not necessarily
23703 reliable for a dynamic varobj. Instead, you must examine the
23704 @samp{has_more} attribute.
23707 The varobj's scalar value. For a varobj whose type is some sort of
23708 aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value
23709 will not be interesting.
23712 The varobj's type. This is a string representation of the type, as
23713 would be printed by the @value{GDBN} CLI.
23716 If a variable object is bound to a specific thread, then this is the
23717 thread's identifier.
23720 For a dynamic varobj, this indicates whether there appear to be any
23721 children available. For a non-dynamic varobj, this will be 0.
23724 This attribute will be present and have the value @samp{1} if the
23725 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
23726 then this attribute will not be present.
23729 A dynamic varobj can supply a display hint to the front end. The
23730 value comes directly from the Python pretty-printer object's
23731 @code{display_hint} method. @xref{Pretty Printing}.
23734 Typical output will look like this:
23737 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}",
23738 has_more="@var{has_more}"
23742 @subheading The @code{-var-delete} Command
23743 @findex -var-delete
23745 @subsubheading Synopsis
23748 -var-delete [ -c ] @var{name}
23751 Deletes a previously created variable object and all of its children.
23752 With the @samp{-c} option, just deletes the children.
23754 Returns an error if the object @var{name} is not found.
23757 @subheading The @code{-var-set-format} Command
23758 @findex -var-set-format
23760 @subsubheading Synopsis
23763 -var-set-format @var{name} @var{format-spec}
23766 Sets the output format for the value of the object @var{name} to be
23769 @anchor{-var-set-format}
23770 The syntax for the @var{format-spec} is as follows:
23773 @var{format-spec} @expansion{}
23774 @{binary | decimal | hexadecimal | octal | natural@}
23777 The natural format is the default format choosen automatically
23778 based on the variable type (like decimal for an @code{int}, hex
23779 for pointers, etc.).
23781 For a variable with children, the format is set only on the
23782 variable itself, and the children are not affected.
23784 @subheading The @code{-var-show-format} Command
23785 @findex -var-show-format
23787 @subsubheading Synopsis
23790 -var-show-format @var{name}
23793 Returns the format used to display the value of the object @var{name}.
23796 @var{format} @expansion{}
23801 @subheading The @code{-var-info-num-children} Command
23802 @findex -var-info-num-children
23804 @subsubheading Synopsis
23807 -var-info-num-children @var{name}
23810 Returns the number of children of a variable object @var{name}:
23816 Note that this number is not completely reliable for a dynamic varobj.
23817 It will return the current number of children, but more children may
23821 @subheading The @code{-var-list-children} Command
23822 @findex -var-list-children
23824 @subsubheading Synopsis
23827 -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}]
23829 @anchor{-var-list-children}
23831 Return a list of the children of the specified variable object and
23832 create variable objects for them, if they do not already exist. With
23833 a single argument or if @var{print-values} has a value for of 0 or
23834 @code{--no-values}, print only the names of the variables; if
23835 @var{print-values} is 1 or @code{--all-values}, also print their
23836 values; and if it is 2 or @code{--simple-values} print the name and
23837 value for simple data types and just the name for arrays, structures
23840 @var{from} and @var{to}, if specified, indicate the range of children
23841 to report. If @var{from} or @var{to} is less than zero, the range is
23842 reset and all children will be reported. Otherwise, children starting
23843 at @var{from} (zero-based) and up to and excluding @var{to} will be
23846 If a child range is requested, it will only affect the current call to
23847 @code{-var-list-children}, but not future calls to @code{-var-update}.
23848 For this, you must instead use @code{-var-set-update-range}. The
23849 intent of this approach is to enable a front end to implement any
23850 update approach it likes; for example, scrolling a view may cause the
23851 front end to request more children with @code{-var-list-children}, and
23852 then the front end could call @code{-var-set-update-range} with a
23853 different range to ensure that future updates are restricted to just
23856 For each child the following results are returned:
23861 Name of the variable object created for this child.
23864 The expression to be shown to the user by the front end to designate this child.
23865 For example this may be the name of a structure member.
23867 For a dynamic varobj, this value cannot be used to form an
23868 expression. There is no way to do this at all with a dynamic varobj.
23870 For C/C@t{++} structures there are several pseudo children returned to
23871 designate access qualifiers. For these pseudo children @var{exp} is
23872 @samp{public}, @samp{private}, or @samp{protected}. In this case the
23873 type and value are not present.
23875 A dynamic varobj will not report the access qualifying
23876 pseudo-children, regardless of the language. This information is not
23877 available at all with a dynamic varobj.
23880 Number of children this child has. For a dynamic varobj, this will be
23884 The type of the child.
23887 If values were requested, this is the value.
23890 If this variable object is associated with a thread, this is the thread id.
23891 Otherwise this result is not present.
23894 If the variable object is frozen, this variable will be present with a value of 1.
23897 The result may have its own attributes:
23901 A dynamic varobj can supply a display hint to the front end. The
23902 value comes directly from the Python pretty-printer object's
23903 @code{display_hint} method. @xref{Pretty Printing}.
23906 This is an integer attribute which is nonzero if there are children
23907 remaining after the end of the selected range.
23910 @subsubheading Example
23914 -var-list-children n
23915 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23916 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
23918 -var-list-children --all-values n
23919 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
23920 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
23924 @subheading The @code{-var-info-type} Command
23925 @findex -var-info-type
23927 @subsubheading Synopsis
23930 -var-info-type @var{name}
23933 Returns the type of the specified variable @var{name}. The type is
23934 returned as a string in the same format as it is output by the
23938 type=@var{typename}
23942 @subheading The @code{-var-info-expression} Command
23943 @findex -var-info-expression
23945 @subsubheading Synopsis
23948 -var-info-expression @var{name}
23951 Returns a string that is suitable for presenting this
23952 variable object in user interface. The string is generally
23953 not valid expression in the current language, and cannot be evaluated.
23955 For example, if @code{a} is an array, and variable object
23956 @code{A} was created for @code{a}, then we'll get this output:
23959 (gdb) -var-info-expression A.1
23960 ^done,lang="C",exp="1"
23964 Here, the values of @code{lang} can be @code{@{"C" | "C++" | "Java"@}}.
23966 Note that the output of the @code{-var-list-children} command also
23967 includes those expressions, so the @code{-var-info-expression} command
23970 @subheading The @code{-var-info-path-expression} Command
23971 @findex -var-info-path-expression
23973 @subsubheading Synopsis
23976 -var-info-path-expression @var{name}
23979 Returns an expression that can be evaluated in the current
23980 context and will yield the same value that a variable object has.
23981 Compare this with the @code{-var-info-expression} command, which
23982 result can be used only for UI presentation. Typical use of
23983 the @code{-var-info-path-expression} command is creating a
23984 watchpoint from a variable object.
23986 This command is currently not valid for children of a dynamic varobj,
23987 and will give an error when invoked on one.
23989 For example, suppose @code{C} is a C@t{++} class, derived from class
23990 @code{Base}, and that the @code{Base} class has a member called
23991 @code{m_size}. Assume a variable @code{c} is has the type of
23992 @code{C} and a variable object @code{C} was created for variable
23993 @code{c}. Then, we'll get this output:
23995 (gdb) -var-info-path-expression C.Base.public.m_size
23996 ^done,path_expr=((Base)c).m_size)
23999 @subheading The @code{-var-show-attributes} Command
24000 @findex -var-show-attributes
24002 @subsubheading Synopsis
24005 -var-show-attributes @var{name}
24008 List attributes of the specified variable object @var{name}:
24011 status=@var{attr} [ ( ,@var{attr} )* ]
24015 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
24017 @subheading The @code{-var-evaluate-expression} Command
24018 @findex -var-evaluate-expression
24020 @subsubheading Synopsis
24023 -var-evaluate-expression [-f @var{format-spec}] @var{name}
24026 Evaluates the expression that is represented by the specified variable
24027 object and returns its value as a string. The format of the string
24028 can be specified with the @samp{-f} option. The possible values of
24029 this option are the same as for @code{-var-set-format}
24030 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
24031 the current display format will be used. The current display format
24032 can be changed using the @code{-var-set-format} command.
24038 Note that one must invoke @code{-var-list-children} for a variable
24039 before the value of a child variable can be evaluated.
24041 @subheading The @code{-var-assign} Command
24042 @findex -var-assign
24044 @subsubheading Synopsis
24047 -var-assign @var{name} @var{expression}
24050 Assigns the value of @var{expression} to the variable object specified
24051 by @var{name}. The object must be @samp{editable}. If the variable's
24052 value is altered by the assign, the variable will show up in any
24053 subsequent @code{-var-update} list.
24055 @subsubheading Example
24063 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
24067 @subheading The @code{-var-update} Command
24068 @findex -var-update
24070 @subsubheading Synopsis
24073 -var-update [@var{print-values}] @{@var{name} | "*"@}
24076 Reevaluate the expressions corresponding to the variable object
24077 @var{name} and all its direct and indirect children, and return the
24078 list of variable objects whose values have changed; @var{name} must
24079 be a root variable object. Here, ``changed'' means that the result of
24080 @code{-var-evaluate-expression} before and after the
24081 @code{-var-update} is different. If @samp{*} is used as the variable
24082 object names, all existing variable objects are updated, except
24083 for frozen ones (@pxref{-var-set-frozen}). The option
24084 @var{print-values} determines whether both names and values, or just
24085 names are printed. The possible values of this option are the same
24086 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
24087 recommended to use the @samp{--all-values} option, to reduce the
24088 number of MI commands needed on each program stop.
24090 With the @samp{*} parameter, if a variable object is bound to a
24091 currently running thread, it will not be updated, without any
24094 If @code{-var-set-update-range} was previously used on a varobj, then
24095 only the selected range of children will be reported.
24097 @code{-var-update} reports all the changed varobjs in a tuple named
24100 Each item in the change list is itself a tuple holding:
24104 The name of the varobj.
24107 If values were requested for this update, then this field will be
24108 present and will hold the value of the varobj.
24111 @anchor{-var-update}
24112 This field is a string which may take one of three values:
24116 The variable object's current value is valid.
24119 The variable object does not currently hold a valid value but it may
24120 hold one in the future if its associated expression comes back into
24124 The variable object no longer holds a valid value.
24125 This can occur when the executable file being debugged has changed,
24126 either through recompilation or by using the @value{GDBN} @code{file}
24127 command. The front end should normally choose to delete these variable
24131 In the future new values may be added to this list so the front should
24132 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
24135 This is only present if the varobj is still valid. If the type
24136 changed, then this will be the string @samp{true}; otherwise it will
24140 If the varobj's type changed, then this field will be present and will
24143 @item new_num_children
24144 For a dynamic varobj, if the number of children changed, or if the
24145 type changed, this will be the new number of children.
24147 The @samp{numchild} field in other varobj responses is generally not
24148 valid for a dynamic varobj -- it will show the number of children that
24149 @value{GDBN} knows about, but because dynamic varobjs lazily
24150 instantiate their children, this will not reflect the number of
24151 children which may be available.
24153 The @samp{new_num_children} attribute only reports changes to the
24154 number of children known by @value{GDBN}. This is the only way to
24155 detect whether an update has removed children (which necessarily can
24156 only happen at the end of the update range).
24159 The display hint, if any.
24162 This is an integer value, which will be 1 if there are more children
24163 available outside the varobj's update range.
24166 This attribute will be present and have the value @samp{1} if the
24167 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
24168 then this attribute will not be present.
24171 If new children were added to a dynamic varobj within the selected
24172 update range (as set by @code{-var-set-update-range}), then they will
24173 be listed in this attribute.
24176 @subsubheading Example
24183 -var-update --all-values var1
24184 ^done,changelist=[@{name="var1",value="3",in_scope="true",
24185 type_changed="false"@}]
24189 @subheading The @code{-var-set-frozen} Command
24190 @findex -var-set-frozen
24191 @anchor{-var-set-frozen}
24193 @subsubheading Synopsis
24196 -var-set-frozen @var{name} @var{flag}
24199 Set the frozenness flag on the variable object @var{name}. The
24200 @var{flag} parameter should be either @samp{1} to make the variable
24201 frozen or @samp{0} to make it unfrozen. If a variable object is
24202 frozen, then neither itself, nor any of its children, are
24203 implicitly updated by @code{-var-update} of
24204 a parent variable or by @code{-var-update *}. Only
24205 @code{-var-update} of the variable itself will update its value and
24206 values of its children. After a variable object is unfrozen, it is
24207 implicitly updated by all subsequent @code{-var-update} operations.
24208 Unfreezing a variable does not update it, only subsequent
24209 @code{-var-update} does.
24211 @subsubheading Example
24215 -var-set-frozen V 1
24220 @subheading The @code{-var-set-update-range} command
24221 @findex -var-set-update-range
24222 @anchor{-var-set-update-range}
24224 @subsubheading Synopsis
24227 -var-set-update-range @var{name} @var{from} @var{to}
24230 Set the range of children to be returned by future invocations of
24231 @code{-var-update}.
24233 @var{from} and @var{to} indicate the range of children to report. If
24234 @var{from} or @var{to} is less than zero, the range is reset and all
24235 children will be reported. Otherwise, children starting at @var{from}
24236 (zero-based) and up to and excluding @var{to} will be reported.
24238 @subsubheading Example
24242 -var-set-update-range V 1 2
24246 @subheading The @code{-var-set-visualizer} command
24247 @findex -var-set-visualizer
24248 @anchor{-var-set-visualizer}
24250 @subsubheading Synopsis
24253 -var-set-visualizer @var{name} @var{visualizer}
24256 Set a visualizer for the variable object @var{name}.
24258 @var{visualizer} is the visualizer to use. The special value
24259 @samp{None} means to disable any visualizer in use.
24261 If not @samp{None}, @var{visualizer} must be a Python expression.
24262 This expression must evaluate to a callable object which accepts a
24263 single argument. @value{GDBN} will call this object with the value of
24264 the varobj @var{name} as an argument (this is done so that the same
24265 Python pretty-printing code can be used for both the CLI and MI).
24266 When called, this object must return an object which conforms to the
24267 pretty-printing interface (@pxref{Pretty Printing}).
24269 The pre-defined function @code{gdb.default_visualizer} may be used to
24270 select a visualizer by following the built-in process
24271 (@pxref{Selecting Pretty-Printers}). This is done automatically when
24272 a varobj is created, and so ordinarily is not needed.
24274 This feature is only available if Python support is enabled. The MI
24275 command @code{-list-features} (@pxref{GDB/MI Miscellaneous Commands})
24276 can be used to check this.
24278 @subsubheading Example
24280 Resetting the visualizer:
24284 -var-set-visualizer V None
24288 Reselecting the default (type-based) visualizer:
24292 -var-set-visualizer V gdb.default_visualizer
24296 Suppose @code{SomeClass} is a visualizer class. A lambda expression
24297 can be used to instantiate this class for a varobj:
24301 -var-set-visualizer V "lambda val: SomeClass()"
24305 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24306 @node GDB/MI Data Manipulation
24307 @section @sc{gdb/mi} Data Manipulation
24309 @cindex data manipulation, in @sc{gdb/mi}
24310 @cindex @sc{gdb/mi}, data manipulation
24311 This section describes the @sc{gdb/mi} commands that manipulate data:
24312 examine memory and registers, evaluate expressions, etc.
24314 @c REMOVED FROM THE INTERFACE.
24315 @c @subheading -data-assign
24316 @c Change the value of a program variable. Plenty of side effects.
24317 @c @subsubheading GDB Command
24319 @c @subsubheading Example
24322 @subheading The @code{-data-disassemble} Command
24323 @findex -data-disassemble
24325 @subsubheading Synopsis
24329 [ -s @var{start-addr} -e @var{end-addr} ]
24330 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
24338 @item @var{start-addr}
24339 is the beginning address (or @code{$pc})
24340 @item @var{end-addr}
24342 @item @var{filename}
24343 is the name of the file to disassemble
24344 @item @var{linenum}
24345 is the line number to disassemble around
24347 is the number of disassembly lines to be produced. If it is -1,
24348 the whole function will be disassembled, in case no @var{end-addr} is
24349 specified. If @var{end-addr} is specified as a non-zero value, and
24350 @var{lines} is lower than the number of disassembly lines between
24351 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
24352 displayed; if @var{lines} is higher than the number of lines between
24353 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
24356 is either 0 (meaning only disassembly) or 1 (meaning mixed source and
24360 @subsubheading Result
24362 The output for each instruction is composed of four fields:
24371 Note that whatever included in the instruction field, is not manipulated
24372 directly by @sc{gdb/mi}, i.e., it is not possible to adjust its format.
24374 @subsubheading @value{GDBN} Command
24376 There's no direct mapping from this command to the CLI.
24378 @subsubheading Example
24380 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
24384 -data-disassemble -s $pc -e "$pc + 20" -- 0
24387 @{address="0x000107c0",func-name="main",offset="4",
24388 inst="mov 2, %o0"@},
24389 @{address="0x000107c4",func-name="main",offset="8",
24390 inst="sethi %hi(0x11800), %o2"@},
24391 @{address="0x000107c8",func-name="main",offset="12",
24392 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
24393 @{address="0x000107cc",func-name="main",offset="16",
24394 inst="sethi %hi(0x11800), %o2"@},
24395 @{address="0x000107d0",func-name="main",offset="20",
24396 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
24400 Disassemble the whole @code{main} function. Line 32 is part of
24404 -data-disassemble -f basics.c -l 32 -- 0
24406 @{address="0x000107bc",func-name="main",offset="0",
24407 inst="save %sp, -112, %sp"@},
24408 @{address="0x000107c0",func-name="main",offset="4",
24409 inst="mov 2, %o0"@},
24410 @{address="0x000107c4",func-name="main",offset="8",
24411 inst="sethi %hi(0x11800), %o2"@},
24413 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
24414 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
24418 Disassemble 3 instructions from the start of @code{main}:
24422 -data-disassemble -f basics.c -l 32 -n 3 -- 0
24424 @{address="0x000107bc",func-name="main",offset="0",
24425 inst="save %sp, -112, %sp"@},
24426 @{address="0x000107c0",func-name="main",offset="4",
24427 inst="mov 2, %o0"@},
24428 @{address="0x000107c4",func-name="main",offset="8",
24429 inst="sethi %hi(0x11800), %o2"@}]
24433 Disassemble 3 instructions from the start of @code{main} in mixed mode:
24437 -data-disassemble -f basics.c -l 32 -n 3 -- 1
24439 src_and_asm_line=@{line="31",
24440 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
24441 testsuite/gdb.mi/basics.c",line_asm_insn=[
24442 @{address="0x000107bc",func-name="main",offset="0",
24443 inst="save %sp, -112, %sp"@}]@},
24444 src_and_asm_line=@{line="32",
24445 file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \
24446 testsuite/gdb.mi/basics.c",line_asm_insn=[
24447 @{address="0x000107c0",func-name="main",offset="4",
24448 inst="mov 2, %o0"@},
24449 @{address="0x000107c4",func-name="main",offset="8",
24450 inst="sethi %hi(0x11800), %o2"@}]@}]
24455 @subheading The @code{-data-evaluate-expression} Command
24456 @findex -data-evaluate-expression
24458 @subsubheading Synopsis
24461 -data-evaluate-expression @var{expr}
24464 Evaluate @var{expr} as an expression. The expression could contain an
24465 inferior function call. The function call will execute synchronously.
24466 If the expression contains spaces, it must be enclosed in double quotes.
24468 @subsubheading @value{GDBN} Command
24470 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
24471 @samp{call}. In @code{gdbtk} only, there's a corresponding
24472 @samp{gdb_eval} command.
24474 @subsubheading Example
24476 In the following example, the numbers that precede the commands are the
24477 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
24478 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
24482 211-data-evaluate-expression A
24485 311-data-evaluate-expression &A
24486 311^done,value="0xefffeb7c"
24488 411-data-evaluate-expression A+3
24491 511-data-evaluate-expression "A + 3"
24497 @subheading The @code{-data-list-changed-registers} Command
24498 @findex -data-list-changed-registers
24500 @subsubheading Synopsis
24503 -data-list-changed-registers
24506 Display a list of the registers that have changed.
24508 @subsubheading @value{GDBN} Command
24510 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
24511 has the corresponding command @samp{gdb_changed_register_list}.
24513 @subsubheading Example
24515 On a PPC MBX board:
24523 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
24524 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
24527 -data-list-changed-registers
24528 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
24529 "10","11","13","14","15","16","17","18","19","20","21","22","23",
24530 "24","25","26","27","28","30","31","64","65","66","67","69"]
24535 @subheading The @code{-data-list-register-names} Command
24536 @findex -data-list-register-names
24538 @subsubheading Synopsis
24541 -data-list-register-names [ ( @var{regno} )+ ]
24544 Show a list of register names for the current target. If no arguments
24545 are given, it shows a list of the names of all the registers. If
24546 integer numbers are given as arguments, it will print a list of the
24547 names of the registers corresponding to the arguments. To ensure
24548 consistency between a register name and its number, the output list may
24549 include empty register names.
24551 @subsubheading @value{GDBN} Command
24553 @value{GDBN} does not have a command which corresponds to
24554 @samp{-data-list-register-names}. In @code{gdbtk} there is a
24555 corresponding command @samp{gdb_regnames}.
24557 @subsubheading Example
24559 For the PPC MBX board:
24562 -data-list-register-names
24563 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
24564 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
24565 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
24566 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
24567 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
24568 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
24569 "", "pc","ps","cr","lr","ctr","xer"]
24571 -data-list-register-names 1 2 3
24572 ^done,register-names=["r1","r2","r3"]
24576 @subheading The @code{-data-list-register-values} Command
24577 @findex -data-list-register-values
24579 @subsubheading Synopsis
24582 -data-list-register-values @var{fmt} [ ( @var{regno} )*]
24585 Display the registers' contents. @var{fmt} is the format according to
24586 which the registers' contents are to be returned, followed by an optional
24587 list of numbers specifying the registers to display. A missing list of
24588 numbers indicates that the contents of all the registers must be returned.
24590 Allowed formats for @var{fmt} are:
24607 @subsubheading @value{GDBN} Command
24609 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
24610 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
24612 @subsubheading Example
24614 For a PPC MBX board (note: line breaks are for readability only, they
24615 don't appear in the actual output):
24619 -data-list-register-values r 64 65
24620 ^done,register-values=[@{number="64",value="0xfe00a300"@},
24621 @{number="65",value="0x00029002"@}]
24623 -data-list-register-values x
24624 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
24625 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
24626 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
24627 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
24628 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
24629 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
24630 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
24631 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
24632 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
24633 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
24634 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
24635 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
24636 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
24637 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
24638 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
24639 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
24640 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
24641 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
24642 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
24643 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
24644 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
24645 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
24646 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
24647 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
24648 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
24649 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
24650 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
24651 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
24652 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
24653 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
24654 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
24655 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
24656 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
24657 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
24658 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
24659 @{number="69",value="0x20002b03"@}]
24664 @subheading The @code{-data-read-memory} Command
24665 @findex -data-read-memory
24667 @subsubheading Synopsis
24670 -data-read-memory [ -o @var{byte-offset} ]
24671 @var{address} @var{word-format} @var{word-size}
24672 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
24679 @item @var{address}
24680 An expression specifying the address of the first memory word to be
24681 read. Complex expressions containing embedded white space should be
24682 quoted using the C convention.
24684 @item @var{word-format}
24685 The format to be used to print the memory words. The notation is the
24686 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
24689 @item @var{word-size}
24690 The size of each memory word in bytes.
24692 @item @var{nr-rows}
24693 The number of rows in the output table.
24695 @item @var{nr-cols}
24696 The number of columns in the output table.
24699 If present, indicates that each row should include an @sc{ascii} dump. The
24700 value of @var{aschar} is used as a padding character when a byte is not a
24701 member of the printable @sc{ascii} character set (printable @sc{ascii}
24702 characters are those whose code is between 32 and 126, inclusively).
24704 @item @var{byte-offset}
24705 An offset to add to the @var{address} before fetching memory.
24708 This command displays memory contents as a table of @var{nr-rows} by
24709 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
24710 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
24711 (returned as @samp{total-bytes}). Should less than the requested number
24712 of bytes be returned by the target, the missing words are identified
24713 using @samp{N/A}. The number of bytes read from the target is returned
24714 in @samp{nr-bytes} and the starting address used to read memory in
24717 The address of the next/previous row or page is available in
24718 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
24721 @subsubheading @value{GDBN} Command
24723 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
24724 @samp{gdb_get_mem} memory read command.
24726 @subsubheading Example
24728 Read six bytes of memory starting at @code{bytes+6} but then offset by
24729 @code{-6} bytes. Format as three rows of two columns. One byte per
24730 word. Display each word in hex.
24734 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
24735 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
24736 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
24737 prev-page="0x0000138a",memory=[
24738 @{addr="0x00001390",data=["0x00","0x01"]@},
24739 @{addr="0x00001392",data=["0x02","0x03"]@},
24740 @{addr="0x00001394",data=["0x04","0x05"]@}]
24744 Read two bytes of memory starting at address @code{shorts + 64} and
24745 display as a single word formatted in decimal.
24749 5-data-read-memory shorts+64 d 2 1 1
24750 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
24751 next-row="0x00001512",prev-row="0x0000150e",
24752 next-page="0x00001512",prev-page="0x0000150e",memory=[
24753 @{addr="0x00001510",data=["128"]@}]
24757 Read thirty two bytes of memory starting at @code{bytes+16} and format
24758 as eight rows of four columns. Include a string encoding with @samp{x}
24759 used as the non-printable character.
24763 4-data-read-memory bytes+16 x 1 8 4 x
24764 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
24765 next-row="0x000013c0",prev-row="0x0000139c",
24766 next-page="0x000013c0",prev-page="0x00001380",memory=[
24767 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
24768 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
24769 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
24770 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
24771 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
24772 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
24773 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
24774 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
24778 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24779 @node GDB/MI Tracepoint Commands
24780 @section @sc{gdb/mi} Tracepoint Commands
24782 The tracepoint commands are not yet implemented.
24784 @c @subheading -trace-actions
24786 @c @subheading -trace-delete
24788 @c @subheading -trace-disable
24790 @c @subheading -trace-dump
24792 @c @subheading -trace-enable
24794 @c @subheading -trace-exists
24796 @c @subheading -trace-find
24798 @c @subheading -trace-frame-number
24800 @c @subheading -trace-info
24802 @c @subheading -trace-insert
24804 @c @subheading -trace-list
24806 @c @subheading -trace-pass-count
24808 @c @subheading -trace-save
24810 @c @subheading -trace-start
24812 @c @subheading -trace-stop
24815 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
24816 @node GDB/MI Symbol Query
24817 @section @sc{gdb/mi} Symbol Query Commands
24821 @subheading The @code{-symbol-info-address} Command
24822 @findex -symbol-info-address
24824 @subsubheading Synopsis
24827 -symbol-info-address @var{symbol}
24830 Describe where @var{symbol} is stored.
24832 @subsubheading @value{GDBN} Command
24834 The corresponding @value{GDBN} command is @samp{info address}.
24836 @subsubheading Example
24840 @subheading The @code{-symbol-info-file} Command
24841 @findex -symbol-info-file
24843 @subsubheading Synopsis
24849 Show the file for the symbol.
24851 @subsubheading @value{GDBN} Command
24853 There's no equivalent @value{GDBN} command. @code{gdbtk} has
24854 @samp{gdb_find_file}.
24856 @subsubheading Example
24860 @subheading The @code{-symbol-info-function} Command
24861 @findex -symbol-info-function
24863 @subsubheading Synopsis
24866 -symbol-info-function
24869 Show which function the symbol lives in.
24871 @subsubheading @value{GDBN} Command
24873 @samp{gdb_get_function} in @code{gdbtk}.
24875 @subsubheading Example
24879 @subheading The @code{-symbol-info-line} Command
24880 @findex -symbol-info-line
24882 @subsubheading Synopsis
24888 Show the core addresses of the code for a source line.
24890 @subsubheading @value{GDBN} Command
24892 The corresponding @value{GDBN} command is @samp{info line}.
24893 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
24895 @subsubheading Example
24899 @subheading The @code{-symbol-info-symbol} Command
24900 @findex -symbol-info-symbol
24902 @subsubheading Synopsis
24905 -symbol-info-symbol @var{addr}
24908 Describe what symbol is at location @var{addr}.
24910 @subsubheading @value{GDBN} Command
24912 The corresponding @value{GDBN} command is @samp{info symbol}.
24914 @subsubheading Example
24918 @subheading The @code{-symbol-list-functions} Command
24919 @findex -symbol-list-functions
24921 @subsubheading Synopsis
24924 -symbol-list-functions
24927 List the functions in the executable.
24929 @subsubheading @value{GDBN} Command
24931 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
24932 @samp{gdb_search} in @code{gdbtk}.
24934 @subsubheading Example
24939 @subheading The @code{-symbol-list-lines} Command
24940 @findex -symbol-list-lines
24942 @subsubheading Synopsis
24945 -symbol-list-lines @var{filename}
24948 Print the list of lines that contain code and their associated program
24949 addresses for the given source filename. The entries are sorted in
24950 ascending PC order.
24952 @subsubheading @value{GDBN} Command
24954 There is no corresponding @value{GDBN} command.
24956 @subsubheading Example
24959 -symbol-list-lines basics.c
24960 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
24966 @subheading The @code{-symbol-list-types} Command
24967 @findex -symbol-list-types
24969 @subsubheading Synopsis
24975 List all the type names.
24977 @subsubheading @value{GDBN} Command
24979 The corresponding commands are @samp{info types} in @value{GDBN},
24980 @samp{gdb_search} in @code{gdbtk}.
24982 @subsubheading Example
24986 @subheading The @code{-symbol-list-variables} Command
24987 @findex -symbol-list-variables
24989 @subsubheading Synopsis
24992 -symbol-list-variables
24995 List all the global and static variable names.
24997 @subsubheading @value{GDBN} Command
24999 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
25001 @subsubheading Example
25005 @subheading The @code{-symbol-locate} Command
25006 @findex -symbol-locate
25008 @subsubheading Synopsis
25014 @subsubheading @value{GDBN} Command
25016 @samp{gdb_loc} in @code{gdbtk}.
25018 @subsubheading Example
25022 @subheading The @code{-symbol-type} Command
25023 @findex -symbol-type
25025 @subsubheading Synopsis
25028 -symbol-type @var{variable}
25031 Show type of @var{variable}.
25033 @subsubheading @value{GDBN} Command
25035 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
25036 @samp{gdb_obj_variable}.
25038 @subsubheading Example
25043 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25044 @node GDB/MI File Commands
25045 @section @sc{gdb/mi} File Commands
25047 This section describes the GDB/MI commands to specify executable file names
25048 and to read in and obtain symbol table information.
25050 @subheading The @code{-file-exec-and-symbols} Command
25051 @findex -file-exec-and-symbols
25053 @subsubheading Synopsis
25056 -file-exec-and-symbols @var{file}
25059 Specify the executable file to be debugged. This file is the one from
25060 which the symbol table is also read. If no file is specified, the
25061 command clears the executable and symbol information. If breakpoints
25062 are set when using this command with no arguments, @value{GDBN} will produce
25063 error messages. Otherwise, no output is produced, except a completion
25066 @subsubheading @value{GDBN} Command
25068 The corresponding @value{GDBN} command is @samp{file}.
25070 @subsubheading Example
25074 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
25080 @subheading The @code{-file-exec-file} Command
25081 @findex -file-exec-file
25083 @subsubheading Synopsis
25086 -file-exec-file @var{file}
25089 Specify the executable file to be debugged. Unlike
25090 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
25091 from this file. If used without argument, @value{GDBN} clears the information
25092 about the executable file. No output is produced, except a completion
25095 @subsubheading @value{GDBN} Command
25097 The corresponding @value{GDBN} command is @samp{exec-file}.
25099 @subsubheading Example
25103 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
25110 @subheading The @code{-file-list-exec-sections} Command
25111 @findex -file-list-exec-sections
25113 @subsubheading Synopsis
25116 -file-list-exec-sections
25119 List the sections of the current executable file.
25121 @subsubheading @value{GDBN} Command
25123 The @value{GDBN} command @samp{info file} shows, among the rest, the same
25124 information as this command. @code{gdbtk} has a corresponding command
25125 @samp{gdb_load_info}.
25127 @subsubheading Example
25132 @subheading The @code{-file-list-exec-source-file} Command
25133 @findex -file-list-exec-source-file
25135 @subsubheading Synopsis
25138 -file-list-exec-source-file
25141 List the line number, the current source file, and the absolute path
25142 to the current source file for the current executable. The macro
25143 information field has a value of @samp{1} or @samp{0} depending on
25144 whether or not the file includes preprocessor macro information.
25146 @subsubheading @value{GDBN} Command
25148 The @value{GDBN} equivalent is @samp{info source}
25150 @subsubheading Example
25154 123-file-list-exec-source-file
25155 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
25160 @subheading The @code{-file-list-exec-source-files} Command
25161 @findex -file-list-exec-source-files
25163 @subsubheading Synopsis
25166 -file-list-exec-source-files
25169 List the source files for the current executable.
25171 It will always output the filename, but only when @value{GDBN} can find
25172 the absolute file name of a source file, will it output the fullname.
25174 @subsubheading @value{GDBN} Command
25176 The @value{GDBN} equivalent is @samp{info sources}.
25177 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
25179 @subsubheading Example
25182 -file-list-exec-source-files
25184 @{file=foo.c,fullname=/home/foo.c@},
25185 @{file=/home/bar.c,fullname=/home/bar.c@},
25186 @{file=gdb_could_not_find_fullpath.c@}]
25191 @subheading The @code{-file-list-shared-libraries} Command
25192 @findex -file-list-shared-libraries
25194 @subsubheading Synopsis
25197 -file-list-shared-libraries
25200 List the shared libraries in the program.
25202 @subsubheading @value{GDBN} Command
25204 The corresponding @value{GDBN} command is @samp{info shared}.
25206 @subsubheading Example
25210 @subheading The @code{-file-list-symbol-files} Command
25211 @findex -file-list-symbol-files
25213 @subsubheading Synopsis
25216 -file-list-symbol-files
25221 @subsubheading @value{GDBN} Command
25223 The corresponding @value{GDBN} command is @samp{info file} (part of it).
25225 @subsubheading Example
25230 @subheading The @code{-file-symbol-file} Command
25231 @findex -file-symbol-file
25233 @subsubheading Synopsis
25236 -file-symbol-file @var{file}
25239 Read symbol table info from the specified @var{file} argument. When
25240 used without arguments, clears @value{GDBN}'s symbol table info. No output is
25241 produced, except for a completion notification.
25243 @subsubheading @value{GDBN} Command
25245 The corresponding @value{GDBN} command is @samp{symbol-file}.
25247 @subsubheading Example
25251 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
25257 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25258 @node GDB/MI Memory Overlay Commands
25259 @section @sc{gdb/mi} Memory Overlay Commands
25261 The memory overlay commands are not implemented.
25263 @c @subheading -overlay-auto
25265 @c @subheading -overlay-list-mapping-state
25267 @c @subheading -overlay-list-overlays
25269 @c @subheading -overlay-map
25271 @c @subheading -overlay-off
25273 @c @subheading -overlay-on
25275 @c @subheading -overlay-unmap
25277 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25278 @node GDB/MI Signal Handling Commands
25279 @section @sc{gdb/mi} Signal Handling Commands
25281 Signal handling commands are not implemented.
25283 @c @subheading -signal-handle
25285 @c @subheading -signal-list-handle-actions
25287 @c @subheading -signal-list-signal-types
25291 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25292 @node GDB/MI Target Manipulation
25293 @section @sc{gdb/mi} Target Manipulation Commands
25296 @subheading The @code{-target-attach} Command
25297 @findex -target-attach
25299 @subsubheading Synopsis
25302 -target-attach @var{pid} | @var{gid} | @var{file}
25305 Attach to a process @var{pid} or a file @var{file} outside of
25306 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
25307 group, the id previously returned by
25308 @samp{-list-thread-groups --available} must be used.
25310 @subsubheading @value{GDBN} Command
25312 The corresponding @value{GDBN} command is @samp{attach}.
25314 @subsubheading Example
25318 =thread-created,id="1"
25319 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
25325 @subheading The @code{-target-compare-sections} Command
25326 @findex -target-compare-sections
25328 @subsubheading Synopsis
25331 -target-compare-sections [ @var{section} ]
25334 Compare data of section @var{section} on target to the exec file.
25335 Without the argument, all sections are compared.
25337 @subsubheading @value{GDBN} Command
25339 The @value{GDBN} equivalent is @samp{compare-sections}.
25341 @subsubheading Example
25346 @subheading The @code{-target-detach} Command
25347 @findex -target-detach
25349 @subsubheading Synopsis
25352 -target-detach [ @var{pid} | @var{gid} ]
25355 Detach from the remote target which normally resumes its execution.
25356 If either @var{pid} or @var{gid} is specified, detaches from either
25357 the specified process, or specified thread group. There's no output.
25359 @subsubheading @value{GDBN} Command
25361 The corresponding @value{GDBN} command is @samp{detach}.
25363 @subsubheading Example
25373 @subheading The @code{-target-disconnect} Command
25374 @findex -target-disconnect
25376 @subsubheading Synopsis
25382 Disconnect from the remote target. There's no output and the target is
25383 generally not resumed.
25385 @subsubheading @value{GDBN} Command
25387 The corresponding @value{GDBN} command is @samp{disconnect}.
25389 @subsubheading Example
25399 @subheading The @code{-target-download} Command
25400 @findex -target-download
25402 @subsubheading Synopsis
25408 Loads the executable onto the remote target.
25409 It prints out an update message every half second, which includes the fields:
25413 The name of the section.
25415 The size of what has been sent so far for that section.
25417 The size of the section.
25419 The total size of what was sent so far (the current and the previous sections).
25421 The size of the overall executable to download.
25425 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
25426 @sc{gdb/mi} Output Syntax}).
25428 In addition, it prints the name and size of the sections, as they are
25429 downloaded. These messages include the following fields:
25433 The name of the section.
25435 The size of the section.
25437 The size of the overall executable to download.
25441 At the end, a summary is printed.
25443 @subsubheading @value{GDBN} Command
25445 The corresponding @value{GDBN} command is @samp{load}.
25447 @subsubheading Example
25449 Note: each status message appears on a single line. Here the messages
25450 have been broken down so that they can fit onto a page.
25455 +download,@{section=".text",section-size="6668",total-size="9880"@}
25456 +download,@{section=".text",section-sent="512",section-size="6668",
25457 total-sent="512",total-size="9880"@}
25458 +download,@{section=".text",section-sent="1024",section-size="6668",
25459 total-sent="1024",total-size="9880"@}
25460 +download,@{section=".text",section-sent="1536",section-size="6668",
25461 total-sent="1536",total-size="9880"@}
25462 +download,@{section=".text",section-sent="2048",section-size="6668",
25463 total-sent="2048",total-size="9880"@}
25464 +download,@{section=".text",section-sent="2560",section-size="6668",
25465 total-sent="2560",total-size="9880"@}
25466 +download,@{section=".text",section-sent="3072",section-size="6668",
25467 total-sent="3072",total-size="9880"@}
25468 +download,@{section=".text",section-sent="3584",section-size="6668",
25469 total-sent="3584",total-size="9880"@}
25470 +download,@{section=".text",section-sent="4096",section-size="6668",
25471 total-sent="4096",total-size="9880"@}
25472 +download,@{section=".text",section-sent="4608",section-size="6668",
25473 total-sent="4608",total-size="9880"@}
25474 +download,@{section=".text",section-sent="5120",section-size="6668",
25475 total-sent="5120",total-size="9880"@}
25476 +download,@{section=".text",section-sent="5632",section-size="6668",
25477 total-sent="5632",total-size="9880"@}
25478 +download,@{section=".text",section-sent="6144",section-size="6668",
25479 total-sent="6144",total-size="9880"@}
25480 +download,@{section=".text",section-sent="6656",section-size="6668",
25481 total-sent="6656",total-size="9880"@}
25482 +download,@{section=".init",section-size="28",total-size="9880"@}
25483 +download,@{section=".fini",section-size="28",total-size="9880"@}
25484 +download,@{section=".data",section-size="3156",total-size="9880"@}
25485 +download,@{section=".data",section-sent="512",section-size="3156",
25486 total-sent="7236",total-size="9880"@}
25487 +download,@{section=".data",section-sent="1024",section-size="3156",
25488 total-sent="7748",total-size="9880"@}
25489 +download,@{section=".data",section-sent="1536",section-size="3156",
25490 total-sent="8260",total-size="9880"@}
25491 +download,@{section=".data",section-sent="2048",section-size="3156",
25492 total-sent="8772",total-size="9880"@}
25493 +download,@{section=".data",section-sent="2560",section-size="3156",
25494 total-sent="9284",total-size="9880"@}
25495 +download,@{section=".data",section-sent="3072",section-size="3156",
25496 total-sent="9796",total-size="9880"@}
25497 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
25504 @subheading The @code{-target-exec-status} Command
25505 @findex -target-exec-status
25507 @subsubheading Synopsis
25510 -target-exec-status
25513 Provide information on the state of the target (whether it is running or
25514 not, for instance).
25516 @subsubheading @value{GDBN} Command
25518 There's no equivalent @value{GDBN} command.
25520 @subsubheading Example
25524 @subheading The @code{-target-list-available-targets} Command
25525 @findex -target-list-available-targets
25527 @subsubheading Synopsis
25530 -target-list-available-targets
25533 List the possible targets to connect to.
25535 @subsubheading @value{GDBN} Command
25537 The corresponding @value{GDBN} command is @samp{help target}.
25539 @subsubheading Example
25543 @subheading The @code{-target-list-current-targets} Command
25544 @findex -target-list-current-targets
25546 @subsubheading Synopsis
25549 -target-list-current-targets
25552 Describe the current target.
25554 @subsubheading @value{GDBN} Command
25556 The corresponding information is printed by @samp{info file} (among
25559 @subsubheading Example
25563 @subheading The @code{-target-list-parameters} Command
25564 @findex -target-list-parameters
25566 @subsubheading Synopsis
25569 -target-list-parameters
25575 @subsubheading @value{GDBN} Command
25579 @subsubheading Example
25583 @subheading The @code{-target-select} Command
25584 @findex -target-select
25586 @subsubheading Synopsis
25589 -target-select @var{type} @var{parameters @dots{}}
25592 Connect @value{GDBN} to the remote target. This command takes two args:
25596 The type of target, for instance @samp{remote}, etc.
25597 @item @var{parameters}
25598 Device names, host names and the like. @xref{Target Commands, ,
25599 Commands for Managing Targets}, for more details.
25602 The output is a connection notification, followed by the address at
25603 which the target program is, in the following form:
25606 ^connected,addr="@var{address}",func="@var{function name}",
25607 args=[@var{arg list}]
25610 @subsubheading @value{GDBN} Command
25612 The corresponding @value{GDBN} command is @samp{target}.
25614 @subsubheading Example
25618 -target-select remote /dev/ttya
25619 ^connected,addr="0xfe00a300",func="??",args=[]
25623 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25624 @node GDB/MI File Transfer Commands
25625 @section @sc{gdb/mi} File Transfer Commands
25628 @subheading The @code{-target-file-put} Command
25629 @findex -target-file-put
25631 @subsubheading Synopsis
25634 -target-file-put @var{hostfile} @var{targetfile}
25637 Copy file @var{hostfile} from the host system (the machine running
25638 @value{GDBN}) to @var{targetfile} on the target system.
25640 @subsubheading @value{GDBN} Command
25642 The corresponding @value{GDBN} command is @samp{remote put}.
25644 @subsubheading Example
25648 -target-file-put localfile remotefile
25654 @subheading The @code{-target-file-get} Command
25655 @findex -target-file-get
25657 @subsubheading Synopsis
25660 -target-file-get @var{targetfile} @var{hostfile}
25663 Copy file @var{targetfile} from the target system to @var{hostfile}
25664 on the host system.
25666 @subsubheading @value{GDBN} Command
25668 The corresponding @value{GDBN} command is @samp{remote get}.
25670 @subsubheading Example
25674 -target-file-get remotefile localfile
25680 @subheading The @code{-target-file-delete} Command
25681 @findex -target-file-delete
25683 @subsubheading Synopsis
25686 -target-file-delete @var{targetfile}
25689 Delete @var{targetfile} from the target system.
25691 @subsubheading @value{GDBN} Command
25693 The corresponding @value{GDBN} command is @samp{remote delete}.
25695 @subsubheading Example
25699 -target-file-delete remotefile
25705 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25706 @node GDB/MI Miscellaneous Commands
25707 @section Miscellaneous @sc{gdb/mi} Commands
25709 @c @subheading -gdb-complete
25711 @subheading The @code{-gdb-exit} Command
25714 @subsubheading Synopsis
25720 Exit @value{GDBN} immediately.
25722 @subsubheading @value{GDBN} Command
25724 Approximately corresponds to @samp{quit}.
25726 @subsubheading Example
25736 @subheading The @code{-exec-abort} Command
25737 @findex -exec-abort
25739 @subsubheading Synopsis
25745 Kill the inferior running program.
25747 @subsubheading @value{GDBN} Command
25749 The corresponding @value{GDBN} command is @samp{kill}.
25751 @subsubheading Example
25756 @subheading The @code{-gdb-set} Command
25759 @subsubheading Synopsis
25765 Set an internal @value{GDBN} variable.
25766 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
25768 @subsubheading @value{GDBN} Command
25770 The corresponding @value{GDBN} command is @samp{set}.
25772 @subsubheading Example
25782 @subheading The @code{-gdb-show} Command
25785 @subsubheading Synopsis
25791 Show the current value of a @value{GDBN} variable.
25793 @subsubheading @value{GDBN} Command
25795 The corresponding @value{GDBN} command is @samp{show}.
25797 @subsubheading Example
25806 @c @subheading -gdb-source
25809 @subheading The @code{-gdb-version} Command
25810 @findex -gdb-version
25812 @subsubheading Synopsis
25818 Show version information for @value{GDBN}. Used mostly in testing.
25820 @subsubheading @value{GDBN} Command
25822 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
25823 default shows this information when you start an interactive session.
25825 @subsubheading Example
25827 @c This example modifies the actual output from GDB to avoid overfull
25833 ~Copyright 2000 Free Software Foundation, Inc.
25834 ~GDB is free software, covered by the GNU General Public License, and
25835 ~you are welcome to change it and/or distribute copies of it under
25836 ~ certain conditions.
25837 ~Type "show copying" to see the conditions.
25838 ~There is absolutely no warranty for GDB. Type "show warranty" for
25840 ~This GDB was configured as
25841 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
25846 @subheading The @code{-list-features} Command
25847 @findex -list-features
25849 Returns a list of particular features of the MI protocol that
25850 this version of gdb implements. A feature can be a command,
25851 or a new field in an output of some command, or even an
25852 important bugfix. While a frontend can sometimes detect presence
25853 of a feature at runtime, it is easier to perform detection at debugger
25856 The command returns a list of strings, with each string naming an
25857 available feature. Each returned string is just a name, it does not
25858 have any internal structure. The list of possible feature names
25864 (gdb) -list-features
25865 ^done,result=["feature1","feature2"]
25868 The current list of features is:
25871 @item frozen-varobjs
25872 Indicates presence of the @code{-var-set-frozen} command, as well
25873 as possible presense of the @code{frozen} field in the output
25874 of @code{-varobj-create}.
25875 @item pending-breakpoints
25876 Indicates presence of the @option{-f} option to the @code{-break-insert} command.
25878 Indicates presence of Python scripting support, Python-based
25879 pretty-printing commands, and possible presence of the
25880 @samp{display_hint} field in the output of @code{-var-list-children}
25882 Indicates presence of the @code{-thread-info} command.
25886 @subheading The @code{-list-target-features} Command
25887 @findex -list-target-features
25889 Returns a list of particular features that are supported by the
25890 target. Those features affect the permitted MI commands, but
25891 unlike the features reported by the @code{-list-features} command, the
25892 features depend on which target GDB is using at the moment. Whenever
25893 a target can change, due to commands such as @code{-target-select},
25894 @code{-target-attach} or @code{-exec-run}, the list of target features
25895 may change, and the frontend should obtain it again.
25899 (gdb) -list-features
25900 ^done,result=["async"]
25903 The current list of features is:
25907 Indicates that the target is capable of asynchronous command
25908 execution, which means that @value{GDBN} will accept further commands
25909 while the target is running.
25913 @subheading The @code{-list-thread-groups} Command
25914 @findex -list-thread-groups
25916 @subheading Synopsis
25919 -list-thread-groups [ --available ] [ @var{group} ]
25922 When used without the @var{group} parameter, lists top-level thread
25923 groups that are being debugged. When used with the @var{group}
25924 parameter, the children of the specified group are listed. The
25925 children can be either threads, or other groups. At present,
25926 @value{GDBN} will not report both threads and groups as children at
25927 the same time, but it may change in future.
25929 With the @samp{--available} option, instead of reporting groups that
25930 are been debugged, GDB will report all thread groups available on the
25931 target. Using the @samp{--available} option together with @var{group}
25934 @subheading Example
25938 -list-thread-groups
25939 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
25940 -list-thread-groups 17
25941 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
25942 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
25943 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
25944 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
25945 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
25948 @subheading The @code{-interpreter-exec} Command
25949 @findex -interpreter-exec
25951 @subheading Synopsis
25954 -interpreter-exec @var{interpreter} @var{command}
25956 @anchor{-interpreter-exec}
25958 Execute the specified @var{command} in the given @var{interpreter}.
25960 @subheading @value{GDBN} Command
25962 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
25964 @subheading Example
25968 -interpreter-exec console "break main"
25969 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
25970 &"During symbol reading, bad structure-type format.\n"
25971 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
25976 @subheading The @code{-inferior-tty-set} Command
25977 @findex -inferior-tty-set
25979 @subheading Synopsis
25982 -inferior-tty-set /dev/pts/1
25985 Set terminal for future runs of the program being debugged.
25987 @subheading @value{GDBN} Command
25989 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
25991 @subheading Example
25995 -inferior-tty-set /dev/pts/1
26000 @subheading The @code{-inferior-tty-show} Command
26001 @findex -inferior-tty-show
26003 @subheading Synopsis
26009 Show terminal for future runs of program being debugged.
26011 @subheading @value{GDBN} Command
26013 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
26015 @subheading Example
26019 -inferior-tty-set /dev/pts/1
26023 ^done,inferior_tty_terminal="/dev/pts/1"
26027 @subheading The @code{-enable-timings} Command
26028 @findex -enable-timings
26030 @subheading Synopsis
26033 -enable-timings [yes | no]
26036 Toggle the printing of the wallclock, user and system times for an MI
26037 command as a field in its output. This command is to help frontend
26038 developers optimize the performance of their code. No argument is
26039 equivalent to @samp{yes}.
26041 @subheading @value{GDBN} Command
26045 @subheading Example
26053 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
26054 addr="0x080484ed",func="main",file="myprog.c",
26055 fullname="/home/nickrob/myprog.c",line="73",times="0"@},
26056 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
26064 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
26065 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
26066 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
26067 fullname="/home/nickrob/myprog.c",line="73"@}
26072 @chapter @value{GDBN} Annotations
26074 This chapter describes annotations in @value{GDBN}. Annotations were
26075 designed to interface @value{GDBN} to graphical user interfaces or other
26076 similar programs which want to interact with @value{GDBN} at a
26077 relatively high level.
26079 The annotation mechanism has largely been superseded by @sc{gdb/mi}
26083 This is Edition @value{EDITION}, @value{DATE}.
26087 * Annotations Overview:: What annotations are; the general syntax.
26088 * Server Prefix:: Issuing a command without affecting user state.
26089 * Prompting:: Annotations marking @value{GDBN}'s need for input.
26090 * Errors:: Annotations for error messages.
26091 * Invalidation:: Some annotations describe things now invalid.
26092 * Annotations for Running::
26093 Whether the program is running, how it stopped, etc.
26094 * Source Annotations:: Annotations describing source code.
26097 @node Annotations Overview
26098 @section What is an Annotation?
26099 @cindex annotations
26101 Annotations start with a newline character, two @samp{control-z}
26102 characters, and the name of the annotation. If there is no additional
26103 information associated with this annotation, the name of the annotation
26104 is followed immediately by a newline. If there is additional
26105 information, the name of the annotation is followed by a space, the
26106 additional information, and a newline. The additional information
26107 cannot contain newline characters.
26109 Any output not beginning with a newline and two @samp{control-z}
26110 characters denotes literal output from @value{GDBN}. Currently there is
26111 no need for @value{GDBN} to output a newline followed by two
26112 @samp{control-z} characters, but if there was such a need, the
26113 annotations could be extended with an @samp{escape} annotation which
26114 means those three characters as output.
26116 The annotation @var{level}, which is specified using the
26117 @option{--annotate} command line option (@pxref{Mode Options}), controls
26118 how much information @value{GDBN} prints together with its prompt,
26119 values of expressions, source lines, and other types of output. Level 0
26120 is for no annotations, level 1 is for use when @value{GDBN} is run as a
26121 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
26122 for programs that control @value{GDBN}, and level 2 annotations have
26123 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
26124 Interface, annotate, GDB's Obsolete Annotations}).
26127 @kindex set annotate
26128 @item set annotate @var{level}
26129 The @value{GDBN} command @code{set annotate} sets the level of
26130 annotations to the specified @var{level}.
26132 @item show annotate
26133 @kindex show annotate
26134 Show the current annotation level.
26137 This chapter describes level 3 annotations.
26139 A simple example of starting up @value{GDBN} with annotations is:
26142 $ @kbd{gdb --annotate=3}
26144 Copyright 2003 Free Software Foundation, Inc.
26145 GDB is free software, covered by the GNU General Public License,
26146 and you are welcome to change it and/or distribute copies of it
26147 under certain conditions.
26148 Type "show copying" to see the conditions.
26149 There is absolutely no warranty for GDB. Type "show warranty"
26151 This GDB was configured as "i386-pc-linux-gnu"
26162 Here @samp{quit} is input to @value{GDBN}; the rest is output from
26163 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
26164 denotes a @samp{control-z} character) are annotations; the rest is
26165 output from @value{GDBN}.
26167 @node Server Prefix
26168 @section The Server Prefix
26169 @cindex server prefix
26171 If you prefix a command with @samp{server } then it will not affect
26172 the command history, nor will it affect @value{GDBN}'s notion of which
26173 command to repeat if @key{RET} is pressed on a line by itself. This
26174 means that commands can be run behind a user's back by a front-end in
26175 a transparent manner.
26177 The @code{server } prefix does not affect the recording of values into
26178 the value history; to print a value without recording it into the
26179 value history, use the @code{output} command instead of the
26180 @code{print} command.
26182 Using this prefix also disables confirmation requests
26183 (@pxref{confirmation requests}).
26186 @section Annotation for @value{GDBN} Input
26188 @cindex annotations for prompts
26189 When @value{GDBN} prompts for input, it annotates this fact so it is possible
26190 to know when to send output, when the output from a given command is
26193 Different kinds of input each have a different @dfn{input type}. Each
26194 input type has three annotations: a @code{pre-} annotation, which
26195 denotes the beginning of any prompt which is being output, a plain
26196 annotation, which denotes the end of the prompt, and then a @code{post-}
26197 annotation which denotes the end of any echo which may (or may not) be
26198 associated with the input. For example, the @code{prompt} input type
26199 features the following annotations:
26207 The input types are
26210 @findex pre-prompt annotation
26211 @findex prompt annotation
26212 @findex post-prompt annotation
26214 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
26216 @findex pre-commands annotation
26217 @findex commands annotation
26218 @findex post-commands annotation
26220 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
26221 command. The annotations are repeated for each command which is input.
26223 @findex pre-overload-choice annotation
26224 @findex overload-choice annotation
26225 @findex post-overload-choice annotation
26226 @item overload-choice
26227 When @value{GDBN} wants the user to select between various overloaded functions.
26229 @findex pre-query annotation
26230 @findex query annotation
26231 @findex post-query annotation
26233 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
26235 @findex pre-prompt-for-continue annotation
26236 @findex prompt-for-continue annotation
26237 @findex post-prompt-for-continue annotation
26238 @item prompt-for-continue
26239 When @value{GDBN} is asking the user to press return to continue. Note: Don't
26240 expect this to work well; instead use @code{set height 0} to disable
26241 prompting. This is because the counting of lines is buggy in the
26242 presence of annotations.
26247 @cindex annotations for errors, warnings and interrupts
26249 @findex quit annotation
26254 This annotation occurs right before @value{GDBN} responds to an interrupt.
26256 @findex error annotation
26261 This annotation occurs right before @value{GDBN} responds to an error.
26263 Quit and error annotations indicate that any annotations which @value{GDBN} was
26264 in the middle of may end abruptly. For example, if a
26265 @code{value-history-begin} annotation is followed by a @code{error}, one
26266 cannot expect to receive the matching @code{value-history-end}. One
26267 cannot expect not to receive it either, however; an error annotation
26268 does not necessarily mean that @value{GDBN} is immediately returning all the way
26271 @findex error-begin annotation
26272 A quit or error annotation may be preceded by
26278 Any output between that and the quit or error annotation is the error
26281 Warning messages are not yet annotated.
26282 @c If we want to change that, need to fix warning(), type_error(),
26283 @c range_error(), and possibly other places.
26286 @section Invalidation Notices
26288 @cindex annotations for invalidation messages
26289 The following annotations say that certain pieces of state may have
26293 @findex frames-invalid annotation
26294 @item ^Z^Zframes-invalid
26296 The frames (for example, output from the @code{backtrace} command) may
26299 @findex breakpoints-invalid annotation
26300 @item ^Z^Zbreakpoints-invalid
26302 The breakpoints may have changed. For example, the user just added or
26303 deleted a breakpoint.
26306 @node Annotations for Running
26307 @section Running the Program
26308 @cindex annotations for running programs
26310 @findex starting annotation
26311 @findex stopping annotation
26312 When the program starts executing due to a @value{GDBN} command such as
26313 @code{step} or @code{continue},
26319 is output. When the program stops,
26325 is output. Before the @code{stopped} annotation, a variety of
26326 annotations describe how the program stopped.
26329 @findex exited annotation
26330 @item ^Z^Zexited @var{exit-status}
26331 The program exited, and @var{exit-status} is the exit status (zero for
26332 successful exit, otherwise nonzero).
26334 @findex signalled annotation
26335 @findex signal-name annotation
26336 @findex signal-name-end annotation
26337 @findex signal-string annotation
26338 @findex signal-string-end annotation
26339 @item ^Z^Zsignalled
26340 The program exited with a signal. After the @code{^Z^Zsignalled}, the
26341 annotation continues:
26347 ^Z^Zsignal-name-end
26351 ^Z^Zsignal-string-end
26356 where @var{name} is the name of the signal, such as @code{SIGILL} or
26357 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
26358 as @code{Illegal Instruction} or @code{Segmentation fault}.
26359 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
26360 user's benefit and have no particular format.
26362 @findex signal annotation
26364 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
26365 just saying that the program received the signal, not that it was
26366 terminated with it.
26368 @findex breakpoint annotation
26369 @item ^Z^Zbreakpoint @var{number}
26370 The program hit breakpoint number @var{number}.
26372 @findex watchpoint annotation
26373 @item ^Z^Zwatchpoint @var{number}
26374 The program hit watchpoint number @var{number}.
26377 @node Source Annotations
26378 @section Displaying Source
26379 @cindex annotations for source display
26381 @findex source annotation
26382 The following annotation is used instead of displaying source code:
26385 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
26388 where @var{filename} is an absolute file name indicating which source
26389 file, @var{line} is the line number within that file (where 1 is the
26390 first line in the file), @var{character} is the character position
26391 within the file (where 0 is the first character in the file) (for most
26392 debug formats this will necessarily point to the beginning of a line),
26393 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
26394 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
26395 @var{addr} is the address in the target program associated with the
26396 source which is being displayed. @var{addr} is in the form @samp{0x}
26397 followed by one or more lowercase hex digits (note that this does not
26398 depend on the language).
26400 @node JIT Interface
26401 @chapter JIT Compilation Interface
26402 @cindex just-in-time compilation
26403 @cindex JIT compilation interface
26405 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
26406 interface. A JIT compiler is a program or library that generates native
26407 executable code at runtime and executes it, usually in order to achieve good
26408 performance while maintaining platform independence.
26410 Programs that use JIT compilation are normally difficult to debug because
26411 portions of their code are generated at runtime, instead of being loaded from
26412 object files, which is where @value{GDBN} normally finds the program's symbols
26413 and debug information. In order to debug programs that use JIT compilation,
26414 @value{GDBN} has an interface that allows the program to register in-memory
26415 symbol files with @value{GDBN} at runtime.
26417 If you are using @value{GDBN} to debug a program that uses this interface, then
26418 it should work transparently so long as you have not stripped the binary. If
26419 you are developing a JIT compiler, then the interface is documented in the rest
26420 of this chapter. At this time, the only known client of this interface is the
26423 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
26424 JIT compiler communicates with @value{GDBN} by writing data into a global
26425 variable and calling a fuction at a well-known symbol. When @value{GDBN}
26426 attaches, it reads a linked list of symbol files from the global variable to
26427 find existing code, and puts a breakpoint in the function so that it can find
26428 out about additional code.
26431 * Declarations:: Relevant C struct declarations
26432 * Registering Code:: Steps to register code
26433 * Unregistering Code:: Steps to unregister code
26437 @section JIT Declarations
26439 These are the relevant struct declarations that a C program should include to
26440 implement the interface:
26450 struct jit_code_entry
26452 struct jit_code_entry *next_entry;
26453 struct jit_code_entry *prev_entry;
26454 const char *symfile_addr;
26455 uint64_t symfile_size;
26458 struct jit_descriptor
26461 /* This type should be jit_actions_t, but we use uint32_t
26462 to be explicit about the bitwidth. */
26463 uint32_t action_flag;
26464 struct jit_code_entry *relevant_entry;
26465 struct jit_code_entry *first_entry;
26468 /* GDB puts a breakpoint in this function. */
26469 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
26471 /* Make sure to specify the version statically, because the
26472 debugger may check the version before we can set it. */
26473 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
26476 If the JIT is multi-threaded, then it is important that the JIT synchronize any
26477 modifications to this global data properly, which can easily be done by putting
26478 a global mutex around modifications to these structures.
26480 @node Registering Code
26481 @section Registering Code
26483 To register code with @value{GDBN}, the JIT should follow this protocol:
26487 Generate an object file in memory with symbols and other desired debug
26488 information. The file must include the virtual addresses of the sections.
26491 Create a code entry for the file, which gives the start and size of the symbol
26495 Add it to the linked list in the JIT descriptor.
26498 Point the relevant_entry field of the descriptor at the entry.
26501 Set @code{action_flag} to @code{JIT_REGISTER} and call
26502 @code{__jit_debug_register_code}.
26505 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
26506 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
26507 new code. However, the linked list must still be maintained in order to allow
26508 @value{GDBN} to attach to a running process and still find the symbol files.
26510 @node Unregistering Code
26511 @section Unregistering Code
26513 If code is freed, then the JIT should use the following protocol:
26517 Remove the code entry corresponding to the code from the linked list.
26520 Point the @code{relevant_entry} field of the descriptor at the code entry.
26523 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
26524 @code{__jit_debug_register_code}.
26527 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
26528 and the JIT will leak the memory used for the associated symbol files.
26531 @chapter Reporting Bugs in @value{GDBN}
26532 @cindex bugs in @value{GDBN}
26533 @cindex reporting bugs in @value{GDBN}
26535 Your bug reports play an essential role in making @value{GDBN} reliable.
26537 Reporting a bug may help you by bringing a solution to your problem, or it
26538 may not. But in any case the principal function of a bug report is to help
26539 the entire community by making the next version of @value{GDBN} work better. Bug
26540 reports are your contribution to the maintenance of @value{GDBN}.
26542 In order for a bug report to serve its purpose, you must include the
26543 information that enables us to fix the bug.
26546 * Bug Criteria:: Have you found a bug?
26547 * Bug Reporting:: How to report bugs
26551 @section Have You Found a Bug?
26552 @cindex bug criteria
26554 If you are not sure whether you have found a bug, here are some guidelines:
26557 @cindex fatal signal
26558 @cindex debugger crash
26559 @cindex crash of debugger
26561 If the debugger gets a fatal signal, for any input whatever, that is a
26562 @value{GDBN} bug. Reliable debuggers never crash.
26564 @cindex error on valid input
26566 If @value{GDBN} produces an error message for valid input, that is a
26567 bug. (Note that if you're cross debugging, the problem may also be
26568 somewhere in the connection to the target.)
26570 @cindex invalid input
26572 If @value{GDBN} does not produce an error message for invalid input,
26573 that is a bug. However, you should note that your idea of
26574 ``invalid input'' might be our idea of ``an extension'' or ``support
26575 for traditional practice''.
26578 If you are an experienced user of debugging tools, your suggestions
26579 for improvement of @value{GDBN} are welcome in any case.
26582 @node Bug Reporting
26583 @section How to Report Bugs
26584 @cindex bug reports
26585 @cindex @value{GDBN} bugs, reporting
26587 A number of companies and individuals offer support for @sc{gnu} products.
26588 If you obtained @value{GDBN} from a support organization, we recommend you
26589 contact that organization first.
26591 You can find contact information for many support companies and
26592 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
26594 @c should add a web page ref...
26597 @ifset BUGURL_DEFAULT
26598 In any event, we also recommend that you submit bug reports for
26599 @value{GDBN}. The preferred method is to submit them directly using
26600 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
26601 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
26604 @strong{Do not send bug reports to @samp{info-gdb}, or to
26605 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
26606 not want to receive bug reports. Those that do have arranged to receive
26609 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
26610 serves as a repeater. The mailing list and the newsgroup carry exactly
26611 the same messages. Often people think of posting bug reports to the
26612 newsgroup instead of mailing them. This appears to work, but it has one
26613 problem which can be crucial: a newsgroup posting often lacks a mail
26614 path back to the sender. Thus, if we need to ask for more information,
26615 we may be unable to reach you. For this reason, it is better to send
26616 bug reports to the mailing list.
26618 @ifclear BUGURL_DEFAULT
26619 In any event, we also recommend that you submit bug reports for
26620 @value{GDBN} to @value{BUGURL}.
26624 The fundamental principle of reporting bugs usefully is this:
26625 @strong{report all the facts}. If you are not sure whether to state a
26626 fact or leave it out, state it!
26628 Often people omit facts because they think they know what causes the
26629 problem and assume that some details do not matter. Thus, you might
26630 assume that the name of the variable you use in an example does not matter.
26631 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
26632 stray memory reference which happens to fetch from the location where that
26633 name is stored in memory; perhaps, if the name were different, the contents
26634 of that location would fool the debugger into doing the right thing despite
26635 the bug. Play it safe and give a specific, complete example. That is the
26636 easiest thing for you to do, and the most helpful.
26638 Keep in mind that the purpose of a bug report is to enable us to fix the
26639 bug. It may be that the bug has been reported previously, but neither
26640 you nor we can know that unless your bug report is complete and
26643 Sometimes people give a few sketchy facts and ask, ``Does this ring a
26644 bell?'' Those bug reports are useless, and we urge everyone to
26645 @emph{refuse to respond to them} except to chide the sender to report
26648 To enable us to fix the bug, you should include all these things:
26652 The version of @value{GDBN}. @value{GDBN} announces it if you start
26653 with no arguments; you can also print it at any time using @code{show
26656 Without this, we will not know whether there is any point in looking for
26657 the bug in the current version of @value{GDBN}.
26660 The type of machine you are using, and the operating system name and
26664 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
26665 ``@value{GCC}--2.8.1''.
26668 What compiler (and its version) was used to compile the program you are
26669 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
26670 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
26671 to get this information; for other compilers, see the documentation for
26675 The command arguments you gave the compiler to compile your example and
26676 observe the bug. For example, did you use @samp{-O}? To guarantee
26677 you will not omit something important, list them all. A copy of the
26678 Makefile (or the output from make) is sufficient.
26680 If we were to try to guess the arguments, we would probably guess wrong
26681 and then we might not encounter the bug.
26684 A complete input script, and all necessary source files, that will
26688 A description of what behavior you observe that you believe is
26689 incorrect. For example, ``It gets a fatal signal.''
26691 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
26692 will certainly notice it. But if the bug is incorrect output, we might
26693 not notice unless it is glaringly wrong. You might as well not give us
26694 a chance to make a mistake.
26696 Even if the problem you experience is a fatal signal, you should still
26697 say so explicitly. Suppose something strange is going on, such as, your
26698 copy of @value{GDBN} is out of synch, or you have encountered a bug in
26699 the C library on your system. (This has happened!) Your copy might
26700 crash and ours would not. If you told us to expect a crash, then when
26701 ours fails to crash, we would know that the bug was not happening for
26702 us. If you had not told us to expect a crash, then we would not be able
26703 to draw any conclusion from our observations.
26706 @cindex recording a session script
26707 To collect all this information, you can use a session recording program
26708 such as @command{script}, which is available on many Unix systems.
26709 Just run your @value{GDBN} session inside @command{script} and then
26710 include the @file{typescript} file with your bug report.
26712 Another way to record a @value{GDBN} session is to run @value{GDBN}
26713 inside Emacs and then save the entire buffer to a file.
26716 If you wish to suggest changes to the @value{GDBN} source, send us context
26717 diffs. If you even discuss something in the @value{GDBN} source, refer to
26718 it by context, not by line number.
26720 The line numbers in our development sources will not match those in your
26721 sources. Your line numbers would convey no useful information to us.
26725 Here are some things that are not necessary:
26729 A description of the envelope of the bug.
26731 Often people who encounter a bug spend a lot of time investigating
26732 which changes to the input file will make the bug go away and which
26733 changes will not affect it.
26735 This is often time consuming and not very useful, because the way we
26736 will find the bug is by running a single example under the debugger
26737 with breakpoints, not by pure deduction from a series of examples.
26738 We recommend that you save your time for something else.
26740 Of course, if you can find a simpler example to report @emph{instead}
26741 of the original one, that is a convenience for us. Errors in the
26742 output will be easier to spot, running under the debugger will take
26743 less time, and so on.
26745 However, simplification is not vital; if you do not want to do this,
26746 report the bug anyway and send us the entire test case you used.
26749 A patch for the bug.
26751 A patch for the bug does help us if it is a good one. But do not omit
26752 the necessary information, such as the test case, on the assumption that
26753 a patch is all we need. We might see problems with your patch and decide
26754 to fix the problem another way, or we might not understand it at all.
26756 Sometimes with a program as complicated as @value{GDBN} it is very hard to
26757 construct an example that will make the program follow a certain path
26758 through the code. If you do not send us the example, we will not be able
26759 to construct one, so we will not be able to verify that the bug is fixed.
26761 And if we cannot understand what bug you are trying to fix, or why your
26762 patch should be an improvement, we will not install it. A test case will
26763 help us to understand.
26766 A guess about what the bug is or what it depends on.
26768 Such guesses are usually wrong. Even we cannot guess right about such
26769 things without first using the debugger to find the facts.
26772 @c The readline documentation is distributed with the readline code
26773 @c and consists of the two following files:
26775 @c inc-hist.texinfo
26776 @c Use -I with makeinfo to point to the appropriate directory,
26777 @c environment var TEXINPUTS with TeX.
26778 @include rluser.texi
26779 @include inc-hist.texinfo
26782 @node Formatting Documentation
26783 @appendix Formatting Documentation
26785 @cindex @value{GDBN} reference card
26786 @cindex reference card
26787 The @value{GDBN} 4 release includes an already-formatted reference card, ready
26788 for printing with PostScript or Ghostscript, in the @file{gdb}
26789 subdirectory of the main source directory@footnote{In
26790 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
26791 release.}. If you can use PostScript or Ghostscript with your printer,
26792 you can print the reference card immediately with @file{refcard.ps}.
26794 The release also includes the source for the reference card. You
26795 can format it, using @TeX{}, by typing:
26801 The @value{GDBN} reference card is designed to print in @dfn{landscape}
26802 mode on US ``letter'' size paper;
26803 that is, on a sheet 11 inches wide by 8.5 inches
26804 high. You will need to specify this form of printing as an option to
26805 your @sc{dvi} output program.
26807 @cindex documentation
26809 All the documentation for @value{GDBN} comes as part of the machine-readable
26810 distribution. The documentation is written in Texinfo format, which is
26811 a documentation system that uses a single source file to produce both
26812 on-line information and a printed manual. You can use one of the Info
26813 formatting commands to create the on-line version of the documentation
26814 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
26816 @value{GDBN} includes an already formatted copy of the on-line Info
26817 version of this manual in the @file{gdb} subdirectory. The main Info
26818 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
26819 subordinate files matching @samp{gdb.info*} in the same directory. If
26820 necessary, you can print out these files, or read them with any editor;
26821 but they are easier to read using the @code{info} subsystem in @sc{gnu}
26822 Emacs or the standalone @code{info} program, available as part of the
26823 @sc{gnu} Texinfo distribution.
26825 If you want to format these Info files yourself, you need one of the
26826 Info formatting programs, such as @code{texinfo-format-buffer} or
26829 If you have @code{makeinfo} installed, and are in the top level
26830 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
26831 version @value{GDBVN}), you can make the Info file by typing:
26838 If you want to typeset and print copies of this manual, you need @TeX{},
26839 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
26840 Texinfo definitions file.
26842 @TeX{} is a typesetting program; it does not print files directly, but
26843 produces output files called @sc{dvi} files. To print a typeset
26844 document, you need a program to print @sc{dvi} files. If your system
26845 has @TeX{} installed, chances are it has such a program. The precise
26846 command to use depends on your system; @kbd{lpr -d} is common; another
26847 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
26848 require a file name without any extension or a @samp{.dvi} extension.
26850 @TeX{} also requires a macro definitions file called
26851 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
26852 written in Texinfo format. On its own, @TeX{} cannot either read or
26853 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
26854 and is located in the @file{gdb-@var{version-number}/texinfo}
26857 If you have @TeX{} and a @sc{dvi} printer program installed, you can
26858 typeset and print this manual. First switch to the @file{gdb}
26859 subdirectory of the main source directory (for example, to
26860 @file{gdb-@value{GDBVN}/gdb}) and type:
26866 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
26868 @node Installing GDB
26869 @appendix Installing @value{GDBN}
26870 @cindex installation
26873 * Requirements:: Requirements for building @value{GDBN}
26874 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
26875 * Separate Objdir:: Compiling @value{GDBN} in another directory
26876 * Config Names:: Specifying names for hosts and targets
26877 * Configure Options:: Summary of options for configure
26878 * System-wide configuration:: Having a system-wide init file
26882 @section Requirements for Building @value{GDBN}
26883 @cindex building @value{GDBN}, requirements for
26885 Building @value{GDBN} requires various tools and packages to be available.
26886 Other packages will be used only if they are found.
26888 @heading Tools/Packages Necessary for Building @value{GDBN}
26890 @item ISO C90 compiler
26891 @value{GDBN} is written in ISO C90. It should be buildable with any
26892 working C90 compiler, e.g.@: GCC.
26896 @heading Tools/Packages Optional for Building @value{GDBN}
26900 @value{GDBN} can use the Expat XML parsing library. This library may be
26901 included with your operating system distribution; if it is not, you
26902 can get the latest version from @url{http://expat.sourceforge.net}.
26903 The @file{configure} script will search for this library in several
26904 standard locations; if it is installed in an unusual path, you can
26905 use the @option{--with-libexpat-prefix} option to specify its location.
26911 Remote protocol memory maps (@pxref{Memory Map Format})
26913 Target descriptions (@pxref{Target Descriptions})
26915 Remote shared library lists (@pxref{Library List Format})
26917 MS-Windows shared libraries (@pxref{Shared Libraries})
26921 @cindex compressed debug sections
26922 @value{GDBN} will use the @samp{zlib} library, if available, to read
26923 compressed debug sections. Some linkers, such as GNU gold, are capable
26924 of producing binaries with compressed debug sections. If @value{GDBN}
26925 is compiled with @samp{zlib}, it will be able to read the debug
26926 information in such binaries.
26928 The @samp{zlib} library is likely included with your operating system
26929 distribution; if it is not, you can get the latest version from
26930 @url{http://zlib.net}.
26933 @value{GDBN}'s features related to character sets (@pxref{Character
26934 Sets}) require a functioning @code{iconv} implementation. If you are
26935 on a GNU system, then this is provided by the GNU C Library. Some
26936 other systems also provide a working @code{iconv}.
26938 On systems with @code{iconv}, you can install GNU Libiconv. If you
26939 have previously installed Libiconv, you can use the
26940 @option{--with-libiconv-prefix} option to configure.
26942 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
26943 arrange to build Libiconv if a directory named @file{libiconv} appears
26944 in the top-most source directory. If Libiconv is built this way, and
26945 if the operating system does not provide a suitable @code{iconv}
26946 implementation, then the just-built library will automatically be used
26947 by @value{GDBN}. One easy way to set this up is to download GNU
26948 Libiconv, unpack it, and then rename the directory holding the
26949 Libiconv source code to @samp{libiconv}.
26952 @node Running Configure
26953 @section Invoking the @value{GDBN} @file{configure} Script
26954 @cindex configuring @value{GDBN}
26955 @value{GDBN} comes with a @file{configure} script that automates the process
26956 of preparing @value{GDBN} for installation; you can then use @code{make} to
26957 build the @code{gdb} program.
26959 @c irrelevant in info file; it's as current as the code it lives with.
26960 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
26961 look at the @file{README} file in the sources; we may have improved the
26962 installation procedures since publishing this manual.}
26965 The @value{GDBN} distribution includes all the source code you need for
26966 @value{GDBN} in a single directory, whose name is usually composed by
26967 appending the version number to @samp{gdb}.
26969 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
26970 @file{gdb-@value{GDBVN}} directory. That directory contains:
26973 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
26974 script for configuring @value{GDBN} and all its supporting libraries
26976 @item gdb-@value{GDBVN}/gdb
26977 the source specific to @value{GDBN} itself
26979 @item gdb-@value{GDBVN}/bfd
26980 source for the Binary File Descriptor library
26982 @item gdb-@value{GDBVN}/include
26983 @sc{gnu} include files
26985 @item gdb-@value{GDBVN}/libiberty
26986 source for the @samp{-liberty} free software library
26988 @item gdb-@value{GDBVN}/opcodes
26989 source for the library of opcode tables and disassemblers
26991 @item gdb-@value{GDBVN}/readline
26992 source for the @sc{gnu} command-line interface
26994 @item gdb-@value{GDBVN}/glob
26995 source for the @sc{gnu} filename pattern-matching subroutine
26997 @item gdb-@value{GDBVN}/mmalloc
26998 source for the @sc{gnu} memory-mapped malloc package
27001 The simplest way to configure and build @value{GDBN} is to run @file{configure}
27002 from the @file{gdb-@var{version-number}} source directory, which in
27003 this example is the @file{gdb-@value{GDBVN}} directory.
27005 First switch to the @file{gdb-@var{version-number}} source directory
27006 if you are not already in it; then run @file{configure}. Pass the
27007 identifier for the platform on which @value{GDBN} will run as an
27013 cd gdb-@value{GDBVN}
27014 ./configure @var{host}
27019 where @var{host} is an identifier such as @samp{sun4} or
27020 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
27021 (You can often leave off @var{host}; @file{configure} tries to guess the
27022 correct value by examining your system.)
27024 Running @samp{configure @var{host}} and then running @code{make} builds the
27025 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
27026 libraries, then @code{gdb} itself. The configured source files, and the
27027 binaries, are left in the corresponding source directories.
27030 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
27031 system does not recognize this automatically when you run a different
27032 shell, you may need to run @code{sh} on it explicitly:
27035 sh configure @var{host}
27038 If you run @file{configure} from a directory that contains source
27039 directories for multiple libraries or programs, such as the
27040 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
27042 creates configuration files for every directory level underneath (unless
27043 you tell it not to, with the @samp{--norecursion} option).
27045 You should run the @file{configure} script from the top directory in the
27046 source tree, the @file{gdb-@var{version-number}} directory. If you run
27047 @file{configure} from one of the subdirectories, you will configure only
27048 that subdirectory. That is usually not what you want. In particular,
27049 if you run the first @file{configure} from the @file{gdb} subdirectory
27050 of the @file{gdb-@var{version-number}} directory, you will omit the
27051 configuration of @file{bfd}, @file{readline}, and other sibling
27052 directories of the @file{gdb} subdirectory. This leads to build errors
27053 about missing include files such as @file{bfd/bfd.h}.
27055 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
27056 However, you should make sure that the shell on your path (named by
27057 the @samp{SHELL} environment variable) is publicly readable. Remember
27058 that @value{GDBN} uses the shell to start your program---some systems refuse to
27059 let @value{GDBN} debug child processes whose programs are not readable.
27061 @node Separate Objdir
27062 @section Compiling @value{GDBN} in Another Directory
27064 If you want to run @value{GDBN} versions for several host or target machines,
27065 you need a different @code{gdb} compiled for each combination of
27066 host and target. @file{configure} is designed to make this easy by
27067 allowing you to generate each configuration in a separate subdirectory,
27068 rather than in the source directory. If your @code{make} program
27069 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
27070 @code{make} in each of these directories builds the @code{gdb}
27071 program specified there.
27073 To build @code{gdb} in a separate directory, run @file{configure}
27074 with the @samp{--srcdir} option to specify where to find the source.
27075 (You also need to specify a path to find @file{configure}
27076 itself from your working directory. If the path to @file{configure}
27077 would be the same as the argument to @samp{--srcdir}, you can leave out
27078 the @samp{--srcdir} option; it is assumed.)
27080 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
27081 separate directory for a Sun 4 like this:
27085 cd gdb-@value{GDBVN}
27088 ../gdb-@value{GDBVN}/configure sun4
27093 When @file{configure} builds a configuration using a remote source
27094 directory, it creates a tree for the binaries with the same structure
27095 (and using the same names) as the tree under the source directory. In
27096 the example, you'd find the Sun 4 library @file{libiberty.a} in the
27097 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
27098 @file{gdb-sun4/gdb}.
27100 Make sure that your path to the @file{configure} script has just one
27101 instance of @file{gdb} in it. If your path to @file{configure} looks
27102 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
27103 one subdirectory of @value{GDBN}, not the whole package. This leads to
27104 build errors about missing include files such as @file{bfd/bfd.h}.
27106 One popular reason to build several @value{GDBN} configurations in separate
27107 directories is to configure @value{GDBN} for cross-compiling (where
27108 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
27109 programs that run on another machine---the @dfn{target}).
27110 You specify a cross-debugging target by
27111 giving the @samp{--target=@var{target}} option to @file{configure}.
27113 When you run @code{make} to build a program or library, you must run
27114 it in a configured directory---whatever directory you were in when you
27115 called @file{configure} (or one of its subdirectories).
27117 The @code{Makefile} that @file{configure} generates in each source
27118 directory also runs recursively. If you type @code{make} in a source
27119 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
27120 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
27121 will build all the required libraries, and then build GDB.
27123 When you have multiple hosts or targets configured in separate
27124 directories, you can run @code{make} on them in parallel (for example,
27125 if they are NFS-mounted on each of the hosts); they will not interfere
27129 @section Specifying Names for Hosts and Targets
27131 The specifications used for hosts and targets in the @file{configure}
27132 script are based on a three-part naming scheme, but some short predefined
27133 aliases are also supported. The full naming scheme encodes three pieces
27134 of information in the following pattern:
27137 @var{architecture}-@var{vendor}-@var{os}
27140 For example, you can use the alias @code{sun4} as a @var{host} argument,
27141 or as the value for @var{target} in a @code{--target=@var{target}}
27142 option. The equivalent full name is @samp{sparc-sun-sunos4}.
27144 The @file{configure} script accompanying @value{GDBN} does not provide
27145 any query facility to list all supported host and target names or
27146 aliases. @file{configure} calls the Bourne shell script
27147 @code{config.sub} to map abbreviations to full names; you can read the
27148 script, if you wish, or you can use it to test your guesses on
27149 abbreviations---for example:
27152 % sh config.sub i386-linux
27154 % sh config.sub alpha-linux
27155 alpha-unknown-linux-gnu
27156 % sh config.sub hp9k700
27158 % sh config.sub sun4
27159 sparc-sun-sunos4.1.1
27160 % sh config.sub sun3
27161 m68k-sun-sunos4.1.1
27162 % sh config.sub i986v
27163 Invalid configuration `i986v': machine `i986v' not recognized
27167 @code{config.sub} is also distributed in the @value{GDBN} source
27168 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
27170 @node Configure Options
27171 @section @file{configure} Options
27173 Here is a summary of the @file{configure} options and arguments that
27174 are most often useful for building @value{GDBN}. @file{configure} also has
27175 several other options not listed here. @inforef{What Configure
27176 Does,,configure.info}, for a full explanation of @file{configure}.
27179 configure @r{[}--help@r{]}
27180 @r{[}--prefix=@var{dir}@r{]}
27181 @r{[}--exec-prefix=@var{dir}@r{]}
27182 @r{[}--srcdir=@var{dirname}@r{]}
27183 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
27184 @r{[}--target=@var{target}@r{]}
27189 You may introduce options with a single @samp{-} rather than
27190 @samp{--} if you prefer; but you may abbreviate option names if you use
27195 Display a quick summary of how to invoke @file{configure}.
27197 @item --prefix=@var{dir}
27198 Configure the source to install programs and files under directory
27201 @item --exec-prefix=@var{dir}
27202 Configure the source to install programs under directory
27205 @c avoid splitting the warning from the explanation:
27207 @item --srcdir=@var{dirname}
27208 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
27209 @code{make} that implements the @code{VPATH} feature.}@*
27210 Use this option to make configurations in directories separate from the
27211 @value{GDBN} source directories. Among other things, you can use this to
27212 build (or maintain) several configurations simultaneously, in separate
27213 directories. @file{configure} writes configuration-specific files in
27214 the current directory, but arranges for them to use the source in the
27215 directory @var{dirname}. @file{configure} creates directories under
27216 the working directory in parallel to the source directories below
27219 @item --norecursion
27220 Configure only the directory level where @file{configure} is executed; do not
27221 propagate configuration to subdirectories.
27223 @item --target=@var{target}
27224 Configure @value{GDBN} for cross-debugging programs running on the specified
27225 @var{target}. Without this option, @value{GDBN} is configured to debug
27226 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
27228 There is no convenient way to generate a list of all available targets.
27230 @item @var{host} @dots{}
27231 Configure @value{GDBN} to run on the specified @var{host}.
27233 There is no convenient way to generate a list of all available hosts.
27236 There are many other options available as well, but they are generally
27237 needed for special purposes only.
27239 @node System-wide configuration
27240 @section System-wide configuration and settings
27241 @cindex system-wide init file
27243 @value{GDBN} can be configured to have a system-wide init file;
27244 this file will be read and executed at startup (@pxref{Startup, , What
27245 @value{GDBN} does during startup}).
27247 Here is the corresponding configure option:
27250 @item --with-system-gdbinit=@var{file}
27251 Specify that the default location of the system-wide init file is
27255 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
27256 it may be subject to relocation. Two possible cases:
27260 If the default location of this init file contains @file{$prefix},
27261 it will be subject to relocation. Suppose that the configure options
27262 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
27263 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
27264 init file is looked for as @file{$install/etc/gdbinit} instead of
27265 @file{$prefix/etc/gdbinit}.
27268 By contrast, if the default location does not contain the prefix,
27269 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
27270 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
27271 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
27272 wherever @value{GDBN} is installed.
27275 @node Maintenance Commands
27276 @appendix Maintenance Commands
27277 @cindex maintenance commands
27278 @cindex internal commands
27280 In addition to commands intended for @value{GDBN} users, @value{GDBN}
27281 includes a number of commands intended for @value{GDBN} developers,
27282 that are not documented elsewhere in this manual. These commands are
27283 provided here for reference. (For commands that turn on debugging
27284 messages, see @ref{Debugging Output}.)
27287 @kindex maint agent
27288 @kindex maint agent-eval
27289 @item maint agent @var{expression}
27290 @itemx maint agent-eval @var{expression}
27291 Translate the given @var{expression} into remote agent bytecodes.
27292 This command is useful for debugging the Agent Expression mechanism
27293 (@pxref{Agent Expressions}). The @samp{agent} version produces an
27294 expression useful for data collection, such as by tracepoints, while
27295 @samp{maint agent-eval} produces an expression that evaluates directly
27296 to a result. For instance, a collection expression for @code{globa +
27297 globb} will include bytecodes to record four bytes of memory at each
27298 of the addresses of @code{globa} and @code{globb}, while discarding
27299 the result of the addition, while an evaluation expression will do the
27300 addition and return the sum.
27302 @kindex maint info breakpoints
27303 @item @anchor{maint info breakpoints}maint info breakpoints
27304 Using the same format as @samp{info breakpoints}, display both the
27305 breakpoints you've set explicitly, and those @value{GDBN} is using for
27306 internal purposes. Internal breakpoints are shown with negative
27307 breakpoint numbers. The type column identifies what kind of breakpoint
27312 Normal, explicitly set breakpoint.
27315 Normal, explicitly set watchpoint.
27318 Internal breakpoint, used to handle correctly stepping through
27319 @code{longjmp} calls.
27321 @item longjmp resume
27322 Internal breakpoint at the target of a @code{longjmp}.
27325 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
27328 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
27331 Shared library events.
27335 @kindex set displaced-stepping
27336 @kindex show displaced-stepping
27337 @cindex displaced stepping support
27338 @cindex out-of-line single-stepping
27339 @item set displaced-stepping
27340 @itemx show displaced-stepping
27341 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
27342 if the target supports it. Displaced stepping is a way to single-step
27343 over breakpoints without removing them from the inferior, by executing
27344 an out-of-line copy of the instruction that was originally at the
27345 breakpoint location. It is also known as out-of-line single-stepping.
27348 @item set displaced-stepping on
27349 If the target architecture supports it, @value{GDBN} will use
27350 displaced stepping to step over breakpoints.
27352 @item set displaced-stepping off
27353 @value{GDBN} will not use displaced stepping to step over breakpoints,
27354 even if such is supported by the target architecture.
27356 @cindex non-stop mode, and @samp{set displaced-stepping}
27357 @item set displaced-stepping auto
27358 This is the default mode. @value{GDBN} will use displaced stepping
27359 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
27360 architecture supports displaced stepping.
27363 @kindex maint check-symtabs
27364 @item maint check-symtabs
27365 Check the consistency of psymtabs and symtabs.
27367 @kindex maint cplus first_component
27368 @item maint cplus first_component @var{name}
27369 Print the first C@t{++} class/namespace component of @var{name}.
27371 @kindex maint cplus namespace
27372 @item maint cplus namespace
27373 Print the list of possible C@t{++} namespaces.
27375 @kindex maint demangle
27376 @item maint demangle @var{name}
27377 Demangle a C@t{++} or Objective-C mangled @var{name}.
27379 @kindex maint deprecate
27380 @kindex maint undeprecate
27381 @cindex deprecated commands
27382 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
27383 @itemx maint undeprecate @var{command}
27384 Deprecate or undeprecate the named @var{command}. Deprecated commands
27385 cause @value{GDBN} to issue a warning when you use them. The optional
27386 argument @var{replacement} says which newer command should be used in
27387 favor of the deprecated one; if it is given, @value{GDBN} will mention
27388 the replacement as part of the warning.
27390 @kindex maint dump-me
27391 @item maint dump-me
27392 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
27393 Cause a fatal signal in the debugger and force it to dump its core.
27394 This is supported only on systems which support aborting a program
27395 with the @code{SIGQUIT} signal.
27397 @kindex maint internal-error
27398 @kindex maint internal-warning
27399 @item maint internal-error @r{[}@var{message-text}@r{]}
27400 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
27401 Cause @value{GDBN} to call the internal function @code{internal_error}
27402 or @code{internal_warning} and hence behave as though an internal error
27403 or internal warning has been detected. In addition to reporting the
27404 internal problem, these functions give the user the opportunity to
27405 either quit @value{GDBN} or create a core file of the current
27406 @value{GDBN} session.
27408 These commands take an optional parameter @var{message-text} that is
27409 used as the text of the error or warning message.
27411 Here's an example of using @code{internal-error}:
27414 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
27415 @dots{}/maint.c:121: internal-error: testing, 1, 2
27416 A problem internal to GDB has been detected. Further
27417 debugging may prove unreliable.
27418 Quit this debugging session? (y or n) @kbd{n}
27419 Create a core file? (y or n) @kbd{n}
27423 @cindex @value{GDBN} internal error
27424 @cindex internal errors, control of @value{GDBN} behavior
27426 @kindex maint set internal-error
27427 @kindex maint show internal-error
27428 @kindex maint set internal-warning
27429 @kindex maint show internal-warning
27430 @item maint set internal-error @var{action} [ask|yes|no]
27431 @itemx maint show internal-error @var{action}
27432 @itemx maint set internal-warning @var{action} [ask|yes|no]
27433 @itemx maint show internal-warning @var{action}
27434 When @value{GDBN} reports an internal problem (error or warning) it
27435 gives the user the opportunity to both quit @value{GDBN} and create a
27436 core file of the current @value{GDBN} session. These commands let you
27437 override the default behaviour for each particular @var{action},
27438 described in the table below.
27442 You can specify that @value{GDBN} should always (yes) or never (no)
27443 quit. The default is to ask the user what to do.
27446 You can specify that @value{GDBN} should always (yes) or never (no)
27447 create a core file. The default is to ask the user what to do.
27450 @kindex maint packet
27451 @item maint packet @var{text}
27452 If @value{GDBN} is talking to an inferior via the serial protocol,
27453 then this command sends the string @var{text} to the inferior, and
27454 displays the response packet. @value{GDBN} supplies the initial
27455 @samp{$} character, the terminating @samp{#} character, and the
27458 @kindex maint print architecture
27459 @item maint print architecture @r{[}@var{file}@r{]}
27460 Print the entire architecture configuration. The optional argument
27461 @var{file} names the file where the output goes.
27463 @kindex maint print c-tdesc
27464 @item maint print c-tdesc
27465 Print the current target description (@pxref{Target Descriptions}) as
27466 a C source file. The created source file can be used in @value{GDBN}
27467 when an XML parser is not available to parse the description.
27469 @kindex maint print dummy-frames
27470 @item maint print dummy-frames
27471 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
27474 (@value{GDBP}) @kbd{b add}
27476 (@value{GDBP}) @kbd{print add(2,3)}
27477 Breakpoint 2, add (a=2, b=3) at @dots{}
27479 The program being debugged stopped while in a function called from GDB.
27481 (@value{GDBP}) @kbd{maint print dummy-frames}
27482 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6
27483 top=0x0200bdd4 id=@{stack=0x200bddc,code=0x101405c@}
27484 call_lo=0x01014000 call_hi=0x01014001
27488 Takes an optional file parameter.
27490 @kindex maint print registers
27491 @kindex maint print raw-registers
27492 @kindex maint print cooked-registers
27493 @kindex maint print register-groups
27494 @item maint print registers @r{[}@var{file}@r{]}
27495 @itemx maint print raw-registers @r{[}@var{file}@r{]}
27496 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
27497 @itemx maint print register-groups @r{[}@var{file}@r{]}
27498 Print @value{GDBN}'s internal register data structures.
27500 The command @code{maint print raw-registers} includes the contents of
27501 the raw register cache; the command @code{maint print cooked-registers}
27502 includes the (cooked) value of all registers; and the command
27503 @code{maint print register-groups} includes the groups that each
27504 register is a member of. @xref{Registers,, Registers, gdbint,
27505 @value{GDBN} Internals}.
27507 These commands take an optional parameter, a file name to which to
27508 write the information.
27510 @kindex maint print reggroups
27511 @item maint print reggroups @r{[}@var{file}@r{]}
27512 Print @value{GDBN}'s internal register group data structures. The
27513 optional argument @var{file} tells to what file to write the
27516 The register groups info looks like this:
27519 (@value{GDBP}) @kbd{maint print reggroups}
27532 This command forces @value{GDBN} to flush its internal register cache.
27534 @kindex maint print objfiles
27535 @cindex info for known object files
27536 @item maint print objfiles
27537 Print a dump of all known object files. For each object file, this
27538 command prints its name, address in memory, and all of its psymtabs
27541 @kindex maint print statistics
27542 @cindex bcache statistics
27543 @item maint print statistics
27544 This command prints, for each object file in the program, various data
27545 about that object file followed by the byte cache (@dfn{bcache})
27546 statistics for the object file. The objfile data includes the number
27547 of minimal, partial, full, and stabs symbols, the number of types
27548 defined by the objfile, the number of as yet unexpanded psym tables,
27549 the number of line tables and string tables, and the amount of memory
27550 used by the various tables. The bcache statistics include the counts,
27551 sizes, and counts of duplicates of all and unique objects, max,
27552 average, and median entry size, total memory used and its overhead and
27553 savings, and various measures of the hash table size and chain
27556 @kindex maint print target-stack
27557 @cindex target stack description
27558 @item maint print target-stack
27559 A @dfn{target} is an interface between the debugger and a particular
27560 kind of file or process. Targets can be stacked in @dfn{strata},
27561 so that more than one target can potentially respond to a request.
27562 In particular, memory accesses will walk down the stack of targets
27563 until they find a target that is interested in handling that particular
27566 This command prints a short description of each layer that was pushed on
27567 the @dfn{target stack}, starting from the top layer down to the bottom one.
27569 @kindex maint print type
27570 @cindex type chain of a data type
27571 @item maint print type @var{expr}
27572 Print the type chain for a type specified by @var{expr}. The argument
27573 can be either a type name or a symbol. If it is a symbol, the type of
27574 that symbol is described. The type chain produced by this command is
27575 a recursive definition of the data type as stored in @value{GDBN}'s
27576 data structures, including its flags and contained types.
27578 @kindex maint set dwarf2 max-cache-age
27579 @kindex maint show dwarf2 max-cache-age
27580 @item maint set dwarf2 max-cache-age
27581 @itemx maint show dwarf2 max-cache-age
27582 Control the DWARF 2 compilation unit cache.
27584 @cindex DWARF 2 compilation units cache
27585 In object files with inter-compilation-unit references, such as those
27586 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF 2
27587 reader needs to frequently refer to previously read compilation units.
27588 This setting controls how long a compilation unit will remain in the
27589 cache if it is not referenced. A higher limit means that cached
27590 compilation units will be stored in memory longer, and more total
27591 memory will be used. Setting it to zero disables caching, which will
27592 slow down @value{GDBN} startup, but reduce memory consumption.
27594 @kindex maint set profile
27595 @kindex maint show profile
27596 @cindex profiling GDB
27597 @item maint set profile
27598 @itemx maint show profile
27599 Control profiling of @value{GDBN}.
27601 Profiling will be disabled until you use the @samp{maint set profile}
27602 command to enable it. When you enable profiling, the system will begin
27603 collecting timing and execution count data; when you disable profiling or
27604 exit @value{GDBN}, the results will be written to a log file. Remember that
27605 if you use profiling, @value{GDBN} will overwrite the profiling log file
27606 (often called @file{gmon.out}). If you have a record of important profiling
27607 data in a @file{gmon.out} file, be sure to move it to a safe location.
27609 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
27610 compiled with the @samp{-pg} compiler option.
27612 @kindex maint set show-debug-regs
27613 @kindex maint show show-debug-regs
27614 @cindex hardware debug registers
27615 @item maint set show-debug-regs
27616 @itemx maint show show-debug-regs
27617 Control whether to show variables that mirror the hardware debug
27618 registers. Use @code{ON} to enable, @code{OFF} to disable. If
27619 enabled, the debug registers values are shown when @value{GDBN} inserts or
27620 removes a hardware breakpoint or watchpoint, and when the inferior
27621 triggers a hardware-assisted breakpoint or watchpoint.
27623 @kindex maint space
27624 @cindex memory used by commands
27626 Control whether to display memory usage for each command. If set to a
27627 nonzero value, @value{GDBN} will display how much memory each command
27628 took, following the command's own output. This can also be requested
27629 by invoking @value{GDBN} with the @option{--statistics} command-line
27630 switch (@pxref{Mode Options}).
27633 @cindex time of command execution
27635 Control whether to display the execution time for each command. If
27636 set to a nonzero value, @value{GDBN} will display how much time it
27637 took to execute each command, following the command's own output.
27638 The time is not printed for the commands that run the target, since
27639 there's no mechanism currently to compute how much time was spend
27640 by @value{GDBN} and how much time was spend by the program been debugged.
27641 it's not possibly currently
27642 This can also be requested by invoking @value{GDBN} with the
27643 @option{--statistics} command-line switch (@pxref{Mode Options}).
27645 @kindex maint translate-address
27646 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
27647 Find the symbol stored at the location specified by the address
27648 @var{addr} and an optional section name @var{section}. If found,
27649 @value{GDBN} prints the name of the closest symbol and an offset from
27650 the symbol's location to the specified address. This is similar to
27651 the @code{info address} command (@pxref{Symbols}), except that this
27652 command also allows to find symbols in other sections.
27654 If section was not specified, the section in which the symbol was found
27655 is also printed. For dynamically linked executables, the name of
27656 executable or shared library containing the symbol is printed as well.
27660 The following command is useful for non-interactive invocations of
27661 @value{GDBN}, such as in the test suite.
27664 @item set watchdog @var{nsec}
27665 @kindex set watchdog
27666 @cindex watchdog timer
27667 @cindex timeout for commands
27668 Set the maximum number of seconds @value{GDBN} will wait for the
27669 target operation to finish. If this time expires, @value{GDBN}
27670 reports and error and the command is aborted.
27672 @item show watchdog
27673 Show the current setting of the target wait timeout.
27676 @node Remote Protocol
27677 @appendix @value{GDBN} Remote Serial Protocol
27682 * Stop Reply Packets::
27683 * General Query Packets::
27684 * Register Packet Format::
27685 * Tracepoint Packets::
27686 * Host I/O Packets::
27688 * Notification Packets::
27689 * Remote Non-Stop::
27690 * Packet Acknowledgment::
27692 * File-I/O Remote Protocol Extension::
27693 * Library List Format::
27694 * Memory Map Format::
27700 There may be occasions when you need to know something about the
27701 protocol---for example, if there is only one serial port to your target
27702 machine, you might want your program to do something special if it
27703 recognizes a packet meant for @value{GDBN}.
27705 In the examples below, @samp{->} and @samp{<-} are used to indicate
27706 transmitted and received data, respectively.
27708 @cindex protocol, @value{GDBN} remote serial
27709 @cindex serial protocol, @value{GDBN} remote
27710 @cindex remote serial protocol
27711 All @value{GDBN} commands and responses (other than acknowledgments
27712 and notifications, see @ref{Notification Packets}) are sent as a
27713 @var{packet}. A @var{packet} is introduced with the character
27714 @samp{$}, the actual @var{packet-data}, and the terminating character
27715 @samp{#} followed by a two-digit @var{checksum}:
27718 @code{$}@var{packet-data}@code{#}@var{checksum}
27722 @cindex checksum, for @value{GDBN} remote
27724 The two-digit @var{checksum} is computed as the modulo 256 sum of all
27725 characters between the leading @samp{$} and the trailing @samp{#} (an
27726 eight bit unsigned checksum).
27728 Implementors should note that prior to @value{GDBN} 5.0 the protocol
27729 specification also included an optional two-digit @var{sequence-id}:
27732 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
27735 @cindex sequence-id, for @value{GDBN} remote
27737 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
27738 has never output @var{sequence-id}s. Stubs that handle packets added
27739 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
27741 When either the host or the target machine receives a packet, the first
27742 response expected is an acknowledgment: either @samp{+} (to indicate
27743 the package was received correctly) or @samp{-} (to request
27747 -> @code{$}@var{packet-data}@code{#}@var{checksum}
27752 The @samp{+}/@samp{-} acknowledgments can be disabled
27753 once a connection is established.
27754 @xref{Packet Acknowledgment}, for details.
27756 The host (@value{GDBN}) sends @var{command}s, and the target (the
27757 debugging stub incorporated in your program) sends a @var{response}. In
27758 the case of step and continue @var{command}s, the response is only sent
27759 when the operation has completed, and the target has again stopped all
27760 threads in all attached processes. This is the default all-stop mode
27761 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
27762 execution mode; see @ref{Remote Non-Stop}, for details.
27764 @var{packet-data} consists of a sequence of characters with the
27765 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
27768 @cindex remote protocol, field separator
27769 Fields within the packet should be separated using @samp{,} @samp{;} or
27770 @samp{:}. Except where otherwise noted all numbers are represented in
27771 @sc{hex} with leading zeros suppressed.
27773 Implementors should note that prior to @value{GDBN} 5.0, the character
27774 @samp{:} could not appear as the third character in a packet (as it
27775 would potentially conflict with the @var{sequence-id}).
27777 @cindex remote protocol, binary data
27778 @anchor{Binary Data}
27779 Binary data in most packets is encoded either as two hexadecimal
27780 digits per byte of binary data. This allowed the traditional remote
27781 protocol to work over connections which were only seven-bit clean.
27782 Some packets designed more recently assume an eight-bit clean
27783 connection, and use a more efficient encoding to send and receive
27786 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
27787 as an escape character. Any escaped byte is transmitted as the escape
27788 character followed by the original character XORed with @code{0x20}.
27789 For example, the byte @code{0x7d} would be transmitted as the two
27790 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
27791 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
27792 @samp{@}}) must always be escaped. Responses sent by the stub
27793 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
27794 is not interpreted as the start of a run-length encoded sequence
27797 Response @var{data} can be run-length encoded to save space.
27798 Run-length encoding replaces runs of identical characters with one
27799 instance of the repeated character, followed by a @samp{*} and a
27800 repeat count. The repeat count is itself sent encoded, to avoid
27801 binary characters in @var{data}: a value of @var{n} is sent as
27802 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
27803 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
27804 code 32) for a repeat count of 3. (This is because run-length
27805 encoding starts to win for counts 3 or more.) Thus, for example,
27806 @samp{0* } is a run-length encoding of ``0000'': the space character
27807 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
27810 The printable characters @samp{#} and @samp{$} or with a numeric value
27811 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
27812 seven repeats (@samp{$}) can be expanded using a repeat count of only
27813 five (@samp{"}). For example, @samp{00000000} can be encoded as
27816 The error response returned for some packets includes a two character
27817 error number. That number is not well defined.
27819 @cindex empty response, for unsupported packets
27820 For any @var{command} not supported by the stub, an empty response
27821 (@samp{$#00}) should be returned. That way it is possible to extend the
27822 protocol. A newer @value{GDBN} can tell if a packet is supported based
27825 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
27826 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
27832 The following table provides a complete list of all currently defined
27833 @var{command}s and their corresponding response @var{data}.
27834 @xref{File-I/O Remote Protocol Extension}, for details about the File
27835 I/O extension of the remote protocol.
27837 Each packet's description has a template showing the packet's overall
27838 syntax, followed by an explanation of the packet's meaning. We
27839 include spaces in some of the templates for clarity; these are not
27840 part of the packet's syntax. No @value{GDBN} packet uses spaces to
27841 separate its components. For example, a template like @samp{foo
27842 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
27843 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
27844 @var{baz}. @value{GDBN} does not transmit a space character between the
27845 @samp{foo} and the @var{bar}, or between the @var{bar} and the
27848 @cindex @var{thread-id}, in remote protocol
27849 @anchor{thread-id syntax}
27850 Several packets and replies include a @var{thread-id} field to identify
27851 a thread. Normally these are positive numbers with a target-specific
27852 interpretation, formatted as big-endian hex strings. A @var{thread-id}
27853 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
27856 In addition, the remote protocol supports a multiprocess feature in
27857 which the @var{thread-id} syntax is extended to optionally include both
27858 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
27859 The @var{pid} (process) and @var{tid} (thread) components each have the
27860 format described above: a positive number with target-specific
27861 interpretation formatted as a big-endian hex string, literal @samp{-1}
27862 to indicate all processes or threads (respectively), or @samp{0} to
27863 indicate an arbitrary process or thread. Specifying just a process, as
27864 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
27865 error to specify all processes but a specific thread, such as
27866 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
27867 for those packets and replies explicitly documented to include a process
27868 ID, rather than a @var{thread-id}.
27870 The multiprocess @var{thread-id} syntax extensions are only used if both
27871 @value{GDBN} and the stub report support for the @samp{multiprocess}
27872 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
27875 Note that all packet forms beginning with an upper- or lower-case
27876 letter, other than those described here, are reserved for future use.
27878 Here are the packet descriptions.
27883 @cindex @samp{!} packet
27884 @anchor{extended mode}
27885 Enable extended mode. In extended mode, the remote server is made
27886 persistent. The @samp{R} packet is used to restart the program being
27892 The remote target both supports and has enabled extended mode.
27896 @cindex @samp{?} packet
27897 Indicate the reason the target halted. The reply is the same as for
27898 step and continue. This packet has a special interpretation when the
27899 target is in non-stop mode; see @ref{Remote Non-Stop}.
27902 @xref{Stop Reply Packets}, for the reply specifications.
27904 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
27905 @cindex @samp{A} packet
27906 Initialized @code{argv[]} array passed into program. @var{arglen}
27907 specifies the number of bytes in the hex encoded byte stream
27908 @var{arg}. See @code{gdbserver} for more details.
27913 The arguments were set.
27919 @cindex @samp{b} packet
27920 (Don't use this packet; its behavior is not well-defined.)
27921 Change the serial line speed to @var{baud}.
27923 JTC: @emph{When does the transport layer state change? When it's
27924 received, or after the ACK is transmitted. In either case, there are
27925 problems if the command or the acknowledgment packet is dropped.}
27927 Stan: @emph{If people really wanted to add something like this, and get
27928 it working for the first time, they ought to modify ser-unix.c to send
27929 some kind of out-of-band message to a specially-setup stub and have the
27930 switch happen "in between" packets, so that from remote protocol's point
27931 of view, nothing actually happened.}
27933 @item B @var{addr},@var{mode}
27934 @cindex @samp{B} packet
27935 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
27936 breakpoint at @var{addr}.
27938 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
27939 (@pxref{insert breakpoint or watchpoint packet}).
27941 @cindex @samp{bc} packet
27944 Backward continue. Execute the target system in reverse. No parameter.
27945 @xref{Reverse Execution}, for more information.
27948 @xref{Stop Reply Packets}, for the reply specifications.
27950 @cindex @samp{bs} packet
27953 Backward single step. Execute one instruction in reverse. No parameter.
27954 @xref{Reverse Execution}, for more information.
27957 @xref{Stop Reply Packets}, for the reply specifications.
27959 @item c @r{[}@var{addr}@r{]}
27960 @cindex @samp{c} packet
27961 Continue. @var{addr} is address to resume. If @var{addr} is omitted,
27962 resume at current address.
27965 @xref{Stop Reply Packets}, for the reply specifications.
27967 @item C @var{sig}@r{[};@var{addr}@r{]}
27968 @cindex @samp{C} packet
27969 Continue with signal @var{sig} (hex signal number). If
27970 @samp{;@var{addr}} is omitted, resume at same address.
27973 @xref{Stop Reply Packets}, for the reply specifications.
27976 @cindex @samp{d} packet
27979 Don't use this packet; instead, define a general set packet
27980 (@pxref{General Query Packets}).
27984 @cindex @samp{D} packet
27985 The first form of the packet is used to detach @value{GDBN} from the
27986 remote system. It is sent to the remote target
27987 before @value{GDBN} disconnects via the @code{detach} command.
27989 The second form, including a process ID, is used when multiprocess
27990 protocol extensions are enabled (@pxref{multiprocess extensions}), to
27991 detach only a specific process. The @var{pid} is specified as a
27992 big-endian hex string.
28002 @item F @var{RC},@var{EE},@var{CF};@var{XX}
28003 @cindex @samp{F} packet
28004 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
28005 This is part of the File-I/O protocol extension. @xref{File-I/O
28006 Remote Protocol Extension}, for the specification.
28009 @anchor{read registers packet}
28010 @cindex @samp{g} packet
28011 Read general registers.
28015 @item @var{XX@dots{}}
28016 Each byte of register data is described by two hex digits. The bytes
28017 with the register are transmitted in target byte order. The size of
28018 each register and their position within the @samp{g} packet are
28019 determined by the @value{GDBN} internal gdbarch functions
28020 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}. The
28021 specification of several standard @samp{g} packets is specified below.
28026 @item G @var{XX@dots{}}
28027 @cindex @samp{G} packet
28028 Write general registers. @xref{read registers packet}, for a
28029 description of the @var{XX@dots{}} data.
28039 @item H @var{c} @var{thread-id}
28040 @cindex @samp{H} packet
28041 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
28042 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
28043 should be @samp{c} for step and continue operations, @samp{g} for other
28044 operations. The thread designator @var{thread-id} has the format and
28045 interpretation described in @ref{thread-id syntax}.
28056 @c 'H': How restrictive (or permissive) is the thread model. If a
28057 @c thread is selected and stopped, are other threads allowed
28058 @c to continue to execute? As I mentioned above, I think the
28059 @c semantics of each command when a thread is selected must be
28060 @c described. For example:
28062 @c 'g': If the stub supports threads and a specific thread is
28063 @c selected, returns the register block from that thread;
28064 @c otherwise returns current registers.
28066 @c 'G' If the stub supports threads and a specific thread is
28067 @c selected, sets the registers of the register block of
28068 @c that thread; otherwise sets current registers.
28070 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
28071 @anchor{cycle step packet}
28072 @cindex @samp{i} packet
28073 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
28074 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
28075 step starting at that address.
28078 @cindex @samp{I} packet
28079 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
28083 @cindex @samp{k} packet
28086 FIXME: @emph{There is no description of how to operate when a specific
28087 thread context has been selected (i.e.@: does 'k' kill only that
28090 @item m @var{addr},@var{length}
28091 @cindex @samp{m} packet
28092 Read @var{length} bytes of memory starting at address @var{addr}.
28093 Note that @var{addr} may not be aligned to any particular boundary.
28095 The stub need not use any particular size or alignment when gathering
28096 data from memory for the response; even if @var{addr} is word-aligned
28097 and @var{length} is a multiple of the word size, the stub is free to
28098 use byte accesses, or not. For this reason, this packet may not be
28099 suitable for accessing memory-mapped I/O devices.
28100 @cindex alignment of remote memory accesses
28101 @cindex size of remote memory accesses
28102 @cindex memory, alignment and size of remote accesses
28106 @item @var{XX@dots{}}
28107 Memory contents; each byte is transmitted as a two-digit hexadecimal
28108 number. The reply may contain fewer bytes than requested if the
28109 server was able to read only part of the region of memory.
28114 @item M @var{addr},@var{length}:@var{XX@dots{}}
28115 @cindex @samp{M} packet
28116 Write @var{length} bytes of memory starting at address @var{addr}.
28117 @var{XX@dots{}} is the data; each byte is transmitted as a two-digit
28118 hexadecimal number.
28125 for an error (this includes the case where only part of the data was
28130 @cindex @samp{p} packet
28131 Read the value of register @var{n}; @var{n} is in hex.
28132 @xref{read registers packet}, for a description of how the returned
28133 register value is encoded.
28137 @item @var{XX@dots{}}
28138 the register's value
28142 Indicating an unrecognized @var{query}.
28145 @item P @var{n@dots{}}=@var{r@dots{}}
28146 @anchor{write register packet}
28147 @cindex @samp{P} packet
28148 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
28149 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
28150 digits for each byte in the register (target byte order).
28160 @item q @var{name} @var{params}@dots{}
28161 @itemx Q @var{name} @var{params}@dots{}
28162 @cindex @samp{q} packet
28163 @cindex @samp{Q} packet
28164 General query (@samp{q}) and set (@samp{Q}). These packets are
28165 described fully in @ref{General Query Packets}.
28168 @cindex @samp{r} packet
28169 Reset the entire system.
28171 Don't use this packet; use the @samp{R} packet instead.
28174 @cindex @samp{R} packet
28175 Restart the program being debugged. @var{XX}, while needed, is ignored.
28176 This packet is only available in extended mode (@pxref{extended mode}).
28178 The @samp{R} packet has no reply.
28180 @item s @r{[}@var{addr}@r{]}
28181 @cindex @samp{s} packet
28182 Single step. @var{addr} is the address at which to resume. If
28183 @var{addr} is omitted, resume at same address.
28186 @xref{Stop Reply Packets}, for the reply specifications.
28188 @item S @var{sig}@r{[};@var{addr}@r{]}
28189 @anchor{step with signal packet}
28190 @cindex @samp{S} packet
28191 Step with signal. This is analogous to the @samp{C} packet, but
28192 requests a single-step, rather than a normal resumption of execution.
28195 @xref{Stop Reply Packets}, for the reply specifications.
28197 @item t @var{addr}:@var{PP},@var{MM}
28198 @cindex @samp{t} packet
28199 Search backwards starting at address @var{addr} for a match with pattern
28200 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
28201 @var{addr} must be at least 3 digits.
28203 @item T @var{thread-id}
28204 @cindex @samp{T} packet
28205 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
28210 thread is still alive
28216 Packets starting with @samp{v} are identified by a multi-letter name,
28217 up to the first @samp{;} or @samp{?} (or the end of the packet).
28219 @item vAttach;@var{pid}
28220 @cindex @samp{vAttach} packet
28221 Attach to a new process with the specified process ID @var{pid}.
28222 The process ID is a
28223 hexadecimal integer identifying the process. In all-stop mode, all
28224 threads in the attached process are stopped; in non-stop mode, it may be
28225 attached without being stopped if that is supported by the target.
28227 @c In non-stop mode, on a successful vAttach, the stub should set the
28228 @c current thread to a thread of the newly-attached process. After
28229 @c attaching, GDB queries for the attached process's thread ID with qC.
28230 @c Also note that, from a user perspective, whether or not the
28231 @c target is stopped on attach in non-stop mode depends on whether you
28232 @c use the foreground or background version of the attach command, not
28233 @c on what vAttach does; GDB does the right thing with respect to either
28234 @c stopping or restarting threads.
28236 This packet is only available in extended mode (@pxref{extended mode}).
28242 @item @r{Any stop packet}
28243 for success in all-stop mode (@pxref{Stop Reply Packets})
28245 for success in non-stop mode (@pxref{Remote Non-Stop})
28248 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
28249 @cindex @samp{vCont} packet
28250 Resume the inferior, specifying different actions for each thread.
28251 If an action is specified with no @var{thread-id}, then it is applied to any
28252 threads that don't have a specific action specified; if no default action is
28253 specified then other threads should remain stopped in all-stop mode and
28254 in their current state in non-stop mode.
28255 Specifying multiple
28256 default actions is an error; specifying no actions is also an error.
28257 Thread IDs are specified using the syntax described in @ref{thread-id syntax}.
28259 Currently supported actions are:
28265 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
28269 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
28274 The optional argument @var{addr} normally associated with the
28275 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
28276 not supported in @samp{vCont}.
28278 The @samp{t} action is only relevant in non-stop mode
28279 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
28280 A stop reply should be generated for any affected thread not already stopped.
28281 When a thread is stopped by means of a @samp{t} action,
28282 the corresponding stop reply should indicate that the thread has stopped with
28283 signal @samp{0}, regardless of whether the target uses some other signal
28284 as an implementation detail.
28287 @xref{Stop Reply Packets}, for the reply specifications.
28290 @cindex @samp{vCont?} packet
28291 Request a list of actions supported by the @samp{vCont} packet.
28295 @item vCont@r{[};@var{action}@dots{}@r{]}
28296 The @samp{vCont} packet is supported. Each @var{action} is a supported
28297 command in the @samp{vCont} packet.
28299 The @samp{vCont} packet is not supported.
28302 @item vFile:@var{operation}:@var{parameter}@dots{}
28303 @cindex @samp{vFile} packet
28304 Perform a file operation on the target system. For details,
28305 see @ref{Host I/O Packets}.
28307 @item vFlashErase:@var{addr},@var{length}
28308 @cindex @samp{vFlashErase} packet
28309 Direct the stub to erase @var{length} bytes of flash starting at
28310 @var{addr}. The region may enclose any number of flash blocks, but
28311 its start and end must fall on block boundaries, as indicated by the
28312 flash block size appearing in the memory map (@pxref{Memory Map
28313 Format}). @value{GDBN} groups flash memory programming operations
28314 together, and sends a @samp{vFlashDone} request after each group; the
28315 stub is allowed to delay erase operation until the @samp{vFlashDone}
28316 packet is received.
28318 The stub must support @samp{vCont} if it reports support for
28319 multiprocess extensions (@pxref{multiprocess extensions}). Note that in
28320 this case @samp{vCont} actions can be specified to apply to all threads
28321 in a process by using the @samp{p@var{pid}.-1} form of the
28332 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
28333 @cindex @samp{vFlashWrite} packet
28334 Direct the stub to write data to flash address @var{addr}. The data
28335 is passed in binary form using the same encoding as for the @samp{X}
28336 packet (@pxref{Binary Data}). The memory ranges specified by
28337 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
28338 not overlap, and must appear in order of increasing addresses
28339 (although @samp{vFlashErase} packets for higher addresses may already
28340 have been received; the ordering is guaranteed only between
28341 @samp{vFlashWrite} packets). If a packet writes to an address that was
28342 neither erased by a preceding @samp{vFlashErase} packet nor by some other
28343 target-specific method, the results are unpredictable.
28351 for vFlashWrite addressing non-flash memory
28357 @cindex @samp{vFlashDone} packet
28358 Indicate to the stub that flash programming operation is finished.
28359 The stub is permitted to delay or batch the effects of a group of
28360 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
28361 @samp{vFlashDone} packet is received. The contents of the affected
28362 regions of flash memory are unpredictable until the @samp{vFlashDone}
28363 request is completed.
28365 @item vKill;@var{pid}
28366 @cindex @samp{vKill} packet
28367 Kill the process with the specified process ID. @var{pid} is a
28368 hexadecimal integer identifying the process. This packet is used in
28369 preference to @samp{k} when multiprocess protocol extensions are
28370 supported; see @ref{multiprocess extensions}.
28380 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
28381 @cindex @samp{vRun} packet
28382 Run the program @var{filename}, passing it each @var{argument} on its
28383 command line. The file and arguments are hex-encoded strings. If
28384 @var{filename} is an empty string, the stub may use a default program
28385 (e.g.@: the last program run). The program is created in the stopped
28388 @c FIXME: What about non-stop mode?
28390 This packet is only available in extended mode (@pxref{extended mode}).
28396 @item @r{Any stop packet}
28397 for success (@pxref{Stop Reply Packets})
28401 @anchor{vStopped packet}
28402 @cindex @samp{vStopped} packet
28404 In non-stop mode (@pxref{Remote Non-Stop}), acknowledge a previous stop
28405 reply and prompt for the stub to report another one.
28409 @item @r{Any stop packet}
28410 if there is another unreported stop event (@pxref{Stop Reply Packets})
28412 if there are no unreported stop events
28415 @item X @var{addr},@var{length}:@var{XX@dots{}}
28417 @cindex @samp{X} packet
28418 Write data to memory, where the data is transmitted in binary.
28419 @var{addr} is address, @var{length} is number of bytes,
28420 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
28430 @item z @var{type},@var{addr},@var{length}
28431 @itemx Z @var{type},@var{addr},@var{length}
28432 @anchor{insert breakpoint or watchpoint packet}
28433 @cindex @samp{z} packet
28434 @cindex @samp{Z} packets
28435 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
28436 watchpoint starting at address @var{address} and covering the next
28437 @var{length} bytes.
28439 Each breakpoint and watchpoint packet @var{type} is documented
28442 @emph{Implementation notes: A remote target shall return an empty string
28443 for an unrecognized breakpoint or watchpoint packet @var{type}. A
28444 remote target shall support either both or neither of a given
28445 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
28446 avoid potential problems with duplicate packets, the operations should
28447 be implemented in an idempotent way.}
28449 @item z0,@var{addr},@var{length}
28450 @itemx Z0,@var{addr},@var{length}
28451 @cindex @samp{z0} packet
28452 @cindex @samp{Z0} packet
28453 Insert (@samp{Z0}) or remove (@samp{z0}) a memory breakpoint at address
28454 @var{addr} of size @var{length}.
28456 A memory breakpoint is implemented by replacing the instruction at
28457 @var{addr} with a software breakpoint or trap instruction. The
28458 @var{length} is used by targets that indicates the size of the
28459 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
28460 @sc{mips} can insert either a 2 or 4 byte breakpoint).
28462 @emph{Implementation note: It is possible for a target to copy or move
28463 code that contains memory breakpoints (e.g., when implementing
28464 overlays). The behavior of this packet, in the presence of such a
28465 target, is not defined.}
28477 @item z1,@var{addr},@var{length}
28478 @itemx Z1,@var{addr},@var{length}
28479 @cindex @samp{z1} packet
28480 @cindex @samp{Z1} packet
28481 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
28482 address @var{addr} of size @var{length}.
28484 A hardware breakpoint is implemented using a mechanism that is not
28485 dependant on being able to modify the target's memory.
28487 @emph{Implementation note: A hardware breakpoint is not affected by code
28500 @item z2,@var{addr},@var{length}
28501 @itemx Z2,@var{addr},@var{length}
28502 @cindex @samp{z2} packet
28503 @cindex @samp{Z2} packet
28504 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint.
28516 @item z3,@var{addr},@var{length}
28517 @itemx Z3,@var{addr},@var{length}
28518 @cindex @samp{z3} packet
28519 @cindex @samp{Z3} packet
28520 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint.
28532 @item z4,@var{addr},@var{length}
28533 @itemx Z4,@var{addr},@var{length}
28534 @cindex @samp{z4} packet
28535 @cindex @samp{Z4} packet
28536 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint.
28550 @node Stop Reply Packets
28551 @section Stop Reply Packets
28552 @cindex stop reply packets
28554 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
28555 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
28556 receive any of the below as a reply. Except for @samp{?}
28557 and @samp{vStopped}, that reply is only returned
28558 when the target halts. In the below the exact meaning of @dfn{signal
28559 number} is defined by the header @file{include/gdb/signals.h} in the
28560 @value{GDBN} source code.
28562 As in the description of request packets, we include spaces in the
28563 reply templates for clarity; these are not part of the reply packet's
28564 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
28570 The program received signal number @var{AA} (a two-digit hexadecimal
28571 number). This is equivalent to a @samp{T} response with no
28572 @var{n}:@var{r} pairs.
28574 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
28575 @cindex @samp{T} packet reply
28576 The program received signal number @var{AA} (a two-digit hexadecimal
28577 number). This is equivalent to an @samp{S} response, except that the
28578 @samp{@var{n}:@var{r}} pairs can carry values of important registers
28579 and other information directly in the stop reply packet, reducing
28580 round-trip latency. Single-step and breakpoint traps are reported
28581 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
28585 If @var{n} is a hexadecimal number, it is a register number, and the
28586 corresponding @var{r} gives that register's value. @var{r} is a
28587 series of bytes in target byte order, with each byte given by a
28588 two-digit hex number.
28591 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
28592 the stopped thread, as specified in @ref{thread-id syntax}.
28595 If @var{n} is a recognized @dfn{stop reason}, it describes a more
28596 specific event that stopped the target. The currently defined stop
28597 reasons are listed below. @var{aa} should be @samp{05}, the trap
28598 signal. At most one stop reason should be present.
28601 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
28602 and go on to the next; this allows us to extend the protocol in the
28606 The currently defined stop reasons are:
28612 The packet indicates a watchpoint hit, and @var{r} is the data address, in
28615 @cindex shared library events, remote reply
28617 The packet indicates that the loaded libraries have changed.
28618 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
28619 list of loaded libraries. @var{r} is ignored.
28621 @cindex replay log events, remote reply
28623 The packet indicates that the target cannot continue replaying
28624 logged execution events, because it has reached the end (or the
28625 beginning when executing backward) of the log. The value of @var{r}
28626 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
28627 for more information.
28633 @itemx W @var{AA} ; process:@var{pid}
28634 The process exited, and @var{AA} is the exit status. This is only
28635 applicable to certain targets.
28637 The second form of the response, including the process ID of the exited
28638 process, can be used only when @value{GDBN} has reported support for
28639 multiprocess protocol extensions; see @ref{multiprocess extensions}.
28640 The @var{pid} is formatted as a big-endian hex string.
28643 @itemx X @var{AA} ; process:@var{pid}
28644 The process terminated with signal @var{AA}.
28646 The second form of the response, including the process ID of the
28647 terminated process, can be used only when @value{GDBN} has reported
28648 support for multiprocess protocol extensions; see @ref{multiprocess
28649 extensions}. The @var{pid} is formatted as a big-endian hex string.
28651 @item O @var{XX}@dots{}
28652 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
28653 written as the program's console output. This can happen at any time
28654 while the program is running and the debugger should continue to wait
28655 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
28657 @item F @var{call-id},@var{parameter}@dots{}
28658 @var{call-id} is the identifier which says which host system call should
28659 be called. This is just the name of the function. Translation into the
28660 correct system call is only applicable as it's defined in @value{GDBN}.
28661 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
28664 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
28665 this very system call.
28667 The target replies with this packet when it expects @value{GDBN} to
28668 call a host system call on behalf of the target. @value{GDBN} replies
28669 with an appropriate @samp{F} packet and keeps up waiting for the next
28670 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
28671 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
28672 Protocol Extension}, for more details.
28676 @node General Query Packets
28677 @section General Query Packets
28678 @cindex remote query requests
28680 Packets starting with @samp{q} are @dfn{general query packets};
28681 packets starting with @samp{Q} are @dfn{general set packets}. General
28682 query and set packets are a semi-unified form for retrieving and
28683 sending information to and from the stub.
28685 The initial letter of a query or set packet is followed by a name
28686 indicating what sort of thing the packet applies to. For example,
28687 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
28688 definitions with the stub. These packet names follow some
28693 The name must not contain commas, colons or semicolons.
28695 Most @value{GDBN} query and set packets have a leading upper case
28698 The names of custom vendor packets should use a company prefix, in
28699 lower case, followed by a period. For example, packets designed at
28700 the Acme Corporation might begin with @samp{qacme.foo} (for querying
28701 foos) or @samp{Qacme.bar} (for setting bars).
28704 The name of a query or set packet should be separated from any
28705 parameters by a @samp{:}; the parameters themselves should be
28706 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
28707 full packet name, and check for a separator or the end of the packet,
28708 in case two packet names share a common prefix. New packets should not begin
28709 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
28710 packets predate these conventions, and have arguments without any terminator
28711 for the packet name; we suspect they are in widespread use in places that
28712 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
28713 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
28716 Like the descriptions of the other packets, each description here
28717 has a template showing the packet's overall syntax, followed by an
28718 explanation of the packet's meaning. We include spaces in some of the
28719 templates for clarity; these are not part of the packet's syntax. No
28720 @value{GDBN} packet uses spaces to separate its components.
28722 Here are the currently defined query and set packets:
28727 @cindex current thread, remote request
28728 @cindex @samp{qC} packet
28729 Return the current thread ID.
28733 @item QC @var{thread-id}
28734 Where @var{thread-id} is a thread ID as documented in
28735 @ref{thread-id syntax}.
28736 @item @r{(anything else)}
28737 Any other reply implies the old thread ID.
28740 @item qCRC:@var{addr},@var{length}
28741 @cindex CRC of memory block, remote request
28742 @cindex @samp{qCRC} packet
28743 Compute the CRC checksum of a block of memory using CRC-32 defined in
28744 IEEE 802.3. The CRC is computed byte at a time, taking the most
28745 significant bit of each byte first. The initial pattern code
28746 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
28748 @emph{Note:} This is the same CRC used in validating separate debug
28749 files (@pxref{Separate Debug Files, , Debugging Information in Separate
28750 Files}). However the algorithm is slightly different. When validating
28751 separate debug files, the CRC is computed taking the @emph{least}
28752 significant bit of each byte first, and the final result is inverted to
28753 detect trailing zeros.
28758 An error (such as memory fault)
28759 @item C @var{crc32}
28760 The specified memory region's checksum is @var{crc32}.
28764 @itemx qsThreadInfo
28765 @cindex list active threads, remote request
28766 @cindex @samp{qfThreadInfo} packet
28767 @cindex @samp{qsThreadInfo} packet
28768 Obtain a list of all active thread IDs from the target (OS). Since there
28769 may be too many active threads to fit into one reply packet, this query
28770 works iteratively: it may require more than one query/reply sequence to
28771 obtain the entire list of threads. The first query of the sequence will
28772 be the @samp{qfThreadInfo} query; subsequent queries in the
28773 sequence will be the @samp{qsThreadInfo} query.
28775 NOTE: This packet replaces the @samp{qL} query (see below).
28779 @item m @var{thread-id}
28781 @item m @var{thread-id},@var{thread-id}@dots{}
28782 a comma-separated list of thread IDs
28784 (lower case letter @samp{L}) denotes end of list.
28787 In response to each query, the target will reply with a list of one or
28788 more thread IDs, separated by commas.
28789 @value{GDBN} will respond to each reply with a request for more thread
28790 ids (using the @samp{qs} form of the query), until the target responds
28791 with @samp{l} (lower-case el, for @dfn{last}).
28792 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
28795 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
28796 @cindex get thread-local storage address, remote request
28797 @cindex @samp{qGetTLSAddr} packet
28798 Fetch the address associated with thread local storage specified
28799 by @var{thread-id}, @var{offset}, and @var{lm}.
28801 @var{thread-id} is the thread ID associated with the
28802 thread for which to fetch the TLS address. @xref{thread-id syntax}.
28804 @var{offset} is the (big endian, hex encoded) offset associated with the
28805 thread local variable. (This offset is obtained from the debug
28806 information associated with the variable.)
28808 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
28809 the load module associated with the thread local storage. For example,
28810 a @sc{gnu}/Linux system will pass the link map address of the shared
28811 object associated with the thread local storage under consideration.
28812 Other operating environments may choose to represent the load module
28813 differently, so the precise meaning of this parameter will vary.
28817 @item @var{XX}@dots{}
28818 Hex encoded (big endian) bytes representing the address of the thread
28819 local storage requested.
28822 An error occurred. @var{nn} are hex digits.
28825 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
28828 @item qL @var{startflag} @var{threadcount} @var{nextthread}
28829 Obtain thread information from RTOS. Where: @var{startflag} (one hex
28830 digit) is one to indicate the first query and zero to indicate a
28831 subsequent query; @var{threadcount} (two hex digits) is the maximum
28832 number of threads the response packet can contain; and @var{nextthread}
28833 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
28834 returned in the response as @var{argthread}.
28836 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
28840 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
28841 Where: @var{count} (two hex digits) is the number of threads being
28842 returned; @var{done} (one hex digit) is zero to indicate more threads
28843 and one indicates no further threads; @var{argthreadid} (eight hex
28844 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
28845 is a sequence of thread IDs from the target. @var{threadid} (eight hex
28846 digits). See @code{remote.c:parse_threadlist_response()}.
28850 @cindex section offsets, remote request
28851 @cindex @samp{qOffsets} packet
28852 Get section offsets that the target used when relocating the downloaded
28857 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
28858 Relocate the @code{Text} section by @var{xxx} from its original address.
28859 Relocate the @code{Data} section by @var{yyy} from its original address.
28860 If the object file format provides segment information (e.g.@: @sc{elf}
28861 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
28862 segments by the supplied offsets.
28864 @emph{Note: while a @code{Bss} offset may be included in the response,
28865 @value{GDBN} ignores this and instead applies the @code{Data} offset
28866 to the @code{Bss} section.}
28868 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
28869 Relocate the first segment of the object file, which conventionally
28870 contains program code, to a starting address of @var{xxx}. If
28871 @samp{DataSeg} is specified, relocate the second segment, which
28872 conventionally contains modifiable data, to a starting address of
28873 @var{yyy}. @value{GDBN} will report an error if the object file
28874 does not contain segment information, or does not contain at least
28875 as many segments as mentioned in the reply. Extra segments are
28876 kept at fixed offsets relative to the last relocated segment.
28879 @item qP @var{mode} @var{thread-id}
28880 @cindex thread information, remote request
28881 @cindex @samp{qP} packet
28882 Returns information on @var{thread-id}. Where: @var{mode} is a hex
28883 encoded 32 bit mode; @var{thread-id} is a thread ID
28884 (@pxref{thread-id syntax}).
28886 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
28889 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
28893 @cindex non-stop mode, remote request
28894 @cindex @samp{QNonStop} packet
28896 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
28897 @xref{Remote Non-Stop}, for more information.
28902 The request succeeded.
28905 An error occurred. @var{nn} are hex digits.
28908 An empty reply indicates that @samp{QNonStop} is not supported by
28912 This packet is not probed by default; the remote stub must request it,
28913 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28914 Use of this packet is controlled by the @code{set non-stop} command;
28915 @pxref{Non-Stop Mode}.
28917 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
28918 @cindex pass signals to inferior, remote request
28919 @cindex @samp{QPassSignals} packet
28920 @anchor{QPassSignals}
28921 Each listed @var{signal} should be passed directly to the inferior process.
28922 Signals are numbered identically to continue packets and stop replies
28923 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
28924 strictly greater than the previous item. These signals do not need to stop
28925 the inferior, or be reported to @value{GDBN}. All other signals should be
28926 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
28927 combine; any earlier @samp{QPassSignals} list is completely replaced by the
28928 new list. This packet improves performance when using @samp{handle
28929 @var{signal} nostop noprint pass}.
28934 The request succeeded.
28937 An error occurred. @var{nn} are hex digits.
28940 An empty reply indicates that @samp{QPassSignals} is not supported by
28944 Use of this packet is controlled by the @code{set remote pass-signals}
28945 command (@pxref{Remote Configuration, set remote pass-signals}).
28946 This packet is not probed by default; the remote stub must request it,
28947 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
28949 @item qRcmd,@var{command}
28950 @cindex execute remote command, remote request
28951 @cindex @samp{qRcmd} packet
28952 @var{command} (hex encoded) is passed to the local interpreter for
28953 execution. Invalid commands should be reported using the output
28954 string. Before the final result packet, the target may also respond
28955 with a number of intermediate @samp{O@var{output}} console output
28956 packets. @emph{Implementors should note that providing access to a
28957 stubs's interpreter may have security implications}.
28962 A command response with no output.
28964 A command response with the hex encoded output string @var{OUTPUT}.
28966 Indicate a badly formed request.
28968 An empty reply indicates that @samp{qRcmd} is not recognized.
28971 (Note that the @code{qRcmd} packet's name is separated from the
28972 command by a @samp{,}, not a @samp{:}, contrary to the naming
28973 conventions above. Please don't use this packet as a model for new
28976 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
28977 @cindex searching memory, in remote debugging
28978 @cindex @samp{qSearch:memory} packet
28979 @anchor{qSearch memory}
28980 Search @var{length} bytes at @var{address} for @var{search-pattern}.
28981 @var{address} and @var{length} are encoded in hex.
28982 @var{search-pattern} is a sequence of bytes, hex encoded.
28987 The pattern was not found.
28989 The pattern was found at @var{address}.
28991 A badly formed request or an error was encountered while searching memory.
28993 An empty reply indicates that @samp{qSearch:memory} is not recognized.
28996 @item QStartNoAckMode
28997 @cindex @samp{QStartNoAckMode} packet
28998 @anchor{QStartNoAckMode}
28999 Request that the remote stub disable the normal @samp{+}/@samp{-}
29000 protocol acknowledgments (@pxref{Packet Acknowledgment}).
29005 The stub has switched to no-acknowledgment mode.
29006 @value{GDBN} acknowledges this reponse,
29007 but neither the stub nor @value{GDBN} shall send or expect further
29008 @samp{+}/@samp{-} acknowledgments in the current connection.
29010 An empty reply indicates that the stub does not support no-acknowledgment mode.
29013 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
29014 @cindex supported packets, remote query
29015 @cindex features of the remote protocol
29016 @cindex @samp{qSupported} packet
29017 @anchor{qSupported}
29018 Tell the remote stub about features supported by @value{GDBN}, and
29019 query the stub for features it supports. This packet allows
29020 @value{GDBN} and the remote stub to take advantage of each others'
29021 features. @samp{qSupported} also consolidates multiple feature probes
29022 at startup, to improve @value{GDBN} performance---a single larger
29023 packet performs better than multiple smaller probe packets on
29024 high-latency links. Some features may enable behavior which must not
29025 be on by default, e.g.@: because it would confuse older clients or
29026 stubs. Other features may describe packets which could be
29027 automatically probed for, but are not. These features must be
29028 reported before @value{GDBN} will use them. This ``default
29029 unsupported'' behavior is not appropriate for all packets, but it
29030 helps to keep the initial connection time under control with new
29031 versions of @value{GDBN} which support increasing numbers of packets.
29035 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
29036 The stub supports or does not support each returned @var{stubfeature},
29037 depending on the form of each @var{stubfeature} (see below for the
29040 An empty reply indicates that @samp{qSupported} is not recognized,
29041 or that no features needed to be reported to @value{GDBN}.
29044 The allowed forms for each feature (either a @var{gdbfeature} in the
29045 @samp{qSupported} packet, or a @var{stubfeature} in the response)
29049 @item @var{name}=@var{value}
29050 The remote protocol feature @var{name} is supported, and associated
29051 with the specified @var{value}. The format of @var{value} depends
29052 on the feature, but it must not include a semicolon.
29054 The remote protocol feature @var{name} is supported, and does not
29055 need an associated value.
29057 The remote protocol feature @var{name} is not supported.
29059 The remote protocol feature @var{name} may be supported, and
29060 @value{GDBN} should auto-detect support in some other way when it is
29061 needed. This form will not be used for @var{gdbfeature} notifications,
29062 but may be used for @var{stubfeature} responses.
29065 Whenever the stub receives a @samp{qSupported} request, the
29066 supplied set of @value{GDBN} features should override any previous
29067 request. This allows @value{GDBN} to put the stub in a known
29068 state, even if the stub had previously been communicating with
29069 a different version of @value{GDBN}.
29071 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
29076 This feature indicates whether @value{GDBN} supports multiprocess
29077 extensions to the remote protocol. @value{GDBN} does not use such
29078 extensions unless the stub also reports that it supports them by
29079 including @samp{multiprocess+} in its @samp{qSupported} reply.
29080 @xref{multiprocess extensions}, for details.
29083 Stubs should ignore any unknown values for
29084 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
29085 packet supports receiving packets of unlimited length (earlier
29086 versions of @value{GDBN} may reject overly long responses). Additional values
29087 for @var{gdbfeature} may be defined in the future to let the stub take
29088 advantage of new features in @value{GDBN}, e.g.@: incompatible
29089 improvements in the remote protocol---the @samp{multiprocess} feature is
29090 an example of such a feature. The stub's reply should be independent
29091 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
29092 describes all the features it supports, and then the stub replies with
29093 all the features it supports.
29095 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
29096 responses, as long as each response uses one of the standard forms.
29098 Some features are flags. A stub which supports a flag feature
29099 should respond with a @samp{+} form response. Other features
29100 require values, and the stub should respond with an @samp{=}
29103 Each feature has a default value, which @value{GDBN} will use if
29104 @samp{qSupported} is not available or if the feature is not mentioned
29105 in the @samp{qSupported} response. The default values are fixed; a
29106 stub is free to omit any feature responses that match the defaults.
29108 Not all features can be probed, but for those which can, the probing
29109 mechanism is useful: in some cases, a stub's internal
29110 architecture may not allow the protocol layer to know some information
29111 about the underlying target in advance. This is especially common in
29112 stubs which may be configured for multiple targets.
29114 These are the currently defined stub features and their properties:
29116 @multitable @columnfractions 0.35 0.2 0.12 0.2
29117 @c NOTE: The first row should be @headitem, but we do not yet require
29118 @c a new enough version of Texinfo (4.7) to use @headitem.
29120 @tab Value Required
29124 @item @samp{PacketSize}
29129 @item @samp{qXfer:auxv:read}
29134 @item @samp{qXfer:features:read}
29139 @item @samp{qXfer:libraries:read}
29144 @item @samp{qXfer:memory-map:read}
29149 @item @samp{qXfer:spu:read}
29154 @item @samp{qXfer:spu:write}
29159 @item @samp{qXfer:siginfo:read}
29164 @item @samp{qXfer:siginfo:write}
29169 @item @samp{QNonStop}
29174 @item @samp{QPassSignals}
29179 @item @samp{QStartNoAckMode}
29184 @item @samp{multiprocess}
29189 @item @samp{ConditionalTracepoints}
29194 @item @samp{ReverseContinue}
29199 @item @samp{ReverseStep}
29206 These are the currently defined stub features, in more detail:
29209 @cindex packet size, remote protocol
29210 @item PacketSize=@var{bytes}
29211 The remote stub can accept packets up to at least @var{bytes} in
29212 length. @value{GDBN} will send packets up to this size for bulk
29213 transfers, and will never send larger packets. This is a limit on the
29214 data characters in the packet, including the frame and checksum.
29215 There is no trailing NUL byte in a remote protocol packet; if the stub
29216 stores packets in a NUL-terminated format, it should allow an extra
29217 byte in its buffer for the NUL. If this stub feature is not supported,
29218 @value{GDBN} guesses based on the size of the @samp{g} packet response.
29220 @item qXfer:auxv:read
29221 The remote stub understands the @samp{qXfer:auxv:read} packet
29222 (@pxref{qXfer auxiliary vector read}).
29224 @item qXfer:features:read
29225 The remote stub understands the @samp{qXfer:features:read} packet
29226 (@pxref{qXfer target description read}).
29228 @item qXfer:libraries:read
29229 The remote stub understands the @samp{qXfer:libraries:read} packet
29230 (@pxref{qXfer library list read}).
29232 @item qXfer:memory-map:read
29233 The remote stub understands the @samp{qXfer:memory-map:read} packet
29234 (@pxref{qXfer memory map read}).
29236 @item qXfer:spu:read
29237 The remote stub understands the @samp{qXfer:spu:read} packet
29238 (@pxref{qXfer spu read}).
29240 @item qXfer:spu:write
29241 The remote stub understands the @samp{qXfer:spu:write} packet
29242 (@pxref{qXfer spu write}).
29244 @item qXfer:siginfo:read
29245 The remote stub understands the @samp{qXfer:siginfo:read} packet
29246 (@pxref{qXfer siginfo read}).
29248 @item qXfer:siginfo:write
29249 The remote stub understands the @samp{qXfer:siginfo:write} packet
29250 (@pxref{qXfer siginfo write}).
29253 The remote stub understands the @samp{QNonStop} packet
29254 (@pxref{QNonStop}).
29257 The remote stub understands the @samp{QPassSignals} packet
29258 (@pxref{QPassSignals}).
29260 @item QStartNoAckMode
29261 The remote stub understands the @samp{QStartNoAckMode} packet and
29262 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
29265 @anchor{multiprocess extensions}
29266 @cindex multiprocess extensions, in remote protocol
29267 The remote stub understands the multiprocess extensions to the remote
29268 protocol syntax. The multiprocess extensions affect the syntax of
29269 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
29270 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
29271 replies. Note that reporting this feature indicates support for the
29272 syntactic extensions only, not that the stub necessarily supports
29273 debugging of more than one process at a time. The stub must not use
29274 multiprocess extensions in packet replies unless @value{GDBN} has also
29275 indicated it supports them in its @samp{qSupported} request.
29277 @item qXfer:osdata:read
29278 The remote stub understands the @samp{qXfer:osdata:read} packet
29279 ((@pxref{qXfer osdata read}).
29281 @item ConditionalTracepoints
29282 The remote stub accepts and implements conditional expressions defined
29283 for tracepoints (@pxref{Tracepoint Conditions}).
29285 @item ReverseContinue
29286 The remote stub accepts and implements the reverse continue packet
29290 The remote stub accepts and implements the reverse step packet
29296 @cindex symbol lookup, remote request
29297 @cindex @samp{qSymbol} packet
29298 Notify the target that @value{GDBN} is prepared to serve symbol lookup
29299 requests. Accept requests from the target for the values of symbols.
29304 The target does not need to look up any (more) symbols.
29305 @item qSymbol:@var{sym_name}
29306 The target requests the value of symbol @var{sym_name} (hex encoded).
29307 @value{GDBN} may provide the value by using the
29308 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
29312 @item qSymbol:@var{sym_value}:@var{sym_name}
29313 Set the value of @var{sym_name} to @var{sym_value}.
29315 @var{sym_name} (hex encoded) is the name of a symbol whose value the
29316 target has previously requested.
29318 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
29319 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
29325 The target does not need to look up any (more) symbols.
29326 @item qSymbol:@var{sym_name}
29327 The target requests the value of a new symbol @var{sym_name} (hex
29328 encoded). @value{GDBN} will continue to supply the values of symbols
29329 (if available), until the target ceases to request them.
29334 @xref{Tracepoint Packets}.
29336 @item qThreadExtraInfo,@var{thread-id}
29337 @cindex thread attributes info, remote request
29338 @cindex @samp{qThreadExtraInfo} packet
29339 Obtain a printable string description of a thread's attributes from
29340 the target OS. @var{thread-id} is a thread ID;
29341 see @ref{thread-id syntax}. This
29342 string may contain anything that the target OS thinks is interesting
29343 for @value{GDBN} to tell the user about the thread. The string is
29344 displayed in @value{GDBN}'s @code{info threads} display. Some
29345 examples of possible thread extra info strings are @samp{Runnable}, or
29346 @samp{Blocked on Mutex}.
29350 @item @var{XX}@dots{}
29351 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
29352 comprising the printable string containing the extra information about
29353 the thread's attributes.
29356 (Note that the @code{qThreadExtraInfo} packet's name is separated from
29357 the command by a @samp{,}, not a @samp{:}, contrary to the naming
29358 conventions above. Please don't use this packet as a model for new
29366 @xref{Tracepoint Packets}.
29368 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
29369 @cindex read special object, remote request
29370 @cindex @samp{qXfer} packet
29371 @anchor{qXfer read}
29372 Read uninterpreted bytes from the target's special data area
29373 identified by the keyword @var{object}. Request @var{length} bytes
29374 starting at @var{offset} bytes into the data. The content and
29375 encoding of @var{annex} is specific to @var{object}; it can supply
29376 additional details about what data to access.
29378 Here are the specific requests of this form defined so far. All
29379 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
29380 formats, listed below.
29383 @item qXfer:auxv:read::@var{offset},@var{length}
29384 @anchor{qXfer auxiliary vector read}
29385 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
29386 auxiliary vector}. Note @var{annex} must be empty.
29388 This packet is not probed by default; the remote stub must request it,
29389 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29391 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
29392 @anchor{qXfer target description read}
29393 Access the @dfn{target description}. @xref{Target Descriptions}. The
29394 annex specifies which XML document to access. The main description is
29395 always loaded from the @samp{target.xml} annex.
29397 This packet is not probed by default; the remote stub must request it,
29398 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29400 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
29401 @anchor{qXfer library list read}
29402 Access the target's list of loaded libraries. @xref{Library List Format}.
29403 The annex part of the generic @samp{qXfer} packet must be empty
29404 (@pxref{qXfer read}).
29406 Targets which maintain a list of libraries in the program's memory do
29407 not need to implement this packet; it is designed for platforms where
29408 the operating system manages the list of loaded libraries.
29410 This packet is not probed by default; the remote stub must request it,
29411 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29413 @item qXfer:memory-map:read::@var{offset},@var{length}
29414 @anchor{qXfer memory map read}
29415 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
29416 annex part of the generic @samp{qXfer} packet must be empty
29417 (@pxref{qXfer read}).
29419 This packet is not probed by default; the remote stub must request it,
29420 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29422 @item qXfer:siginfo:read::@var{offset},@var{length}
29423 @anchor{qXfer siginfo read}
29424 Read contents of the extra signal information on the target
29425 system. The annex part of the generic @samp{qXfer} packet must be
29426 empty (@pxref{qXfer read}).
29428 This packet is not probed by default; the remote stub must request it,
29429 by supplying an appropriate @samp{qSupported} response
29430 (@pxref{qSupported}).
29432 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
29433 @anchor{qXfer spu read}
29434 Read contents of an @code{spufs} file on the target system. The
29435 annex specifies which file to read; it must be of the form
29436 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
29437 in the target process, and @var{name} identifes the @code{spufs} file
29438 in that context to be accessed.
29440 This packet is not probed by default; the remote stub must request it,
29441 by supplying an appropriate @samp{qSupported} response
29442 (@pxref{qSupported}).
29444 @item qXfer:osdata:read::@var{offset},@var{length}
29445 @anchor{qXfer osdata read}
29446 Access the target's @dfn{operating system information}.
29447 @xref{Operating System Information}.
29454 Data @var{data} (@pxref{Binary Data}) has been read from the
29455 target. There may be more data at a higher address (although
29456 it is permitted to return @samp{m} even for the last valid
29457 block of data, as long as at least one byte of data was read).
29458 @var{data} may have fewer bytes than the @var{length} in the
29462 Data @var{data} (@pxref{Binary Data}) has been read from the target.
29463 There is no more data to be read. @var{data} may have fewer bytes
29464 than the @var{length} in the request.
29467 The @var{offset} in the request is at the end of the data.
29468 There is no more data to be read.
29471 The request was malformed, or @var{annex} was invalid.
29474 The offset was invalid, or there was an error encountered reading the data.
29475 @var{nn} is a hex-encoded @code{errno} value.
29478 An empty reply indicates the @var{object} string was not recognized by
29479 the stub, or that the object does not support reading.
29482 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
29483 @cindex write data into object, remote request
29484 @anchor{qXfer write}
29485 Write uninterpreted bytes into the target's special data area
29486 identified by the keyword @var{object}, starting at @var{offset} bytes
29487 into the data. @var{data}@dots{} is the binary-encoded data
29488 (@pxref{Binary Data}) to be written. The content and encoding of @var{annex}
29489 is specific to @var{object}; it can supply additional details about what data
29492 Here are the specific requests of this form defined so far. All
29493 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
29494 formats, listed below.
29497 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
29498 @anchor{qXfer siginfo write}
29499 Write @var{data} to the extra signal information on the target system.
29500 The annex part of the generic @samp{qXfer} packet must be
29501 empty (@pxref{qXfer write}).
29503 This packet is not probed by default; the remote stub must request it,
29504 by supplying an appropriate @samp{qSupported} response
29505 (@pxref{qSupported}).
29507 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
29508 @anchor{qXfer spu write}
29509 Write @var{data} to an @code{spufs} file on the target system. The
29510 annex specifies which file to write; it must be of the form
29511 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
29512 in the target process, and @var{name} identifes the @code{spufs} file
29513 in that context to be accessed.
29515 This packet is not probed by default; the remote stub must request it,
29516 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
29522 @var{nn} (hex encoded) is the number of bytes written.
29523 This may be fewer bytes than supplied in the request.
29526 The request was malformed, or @var{annex} was invalid.
29529 The offset was invalid, or there was an error encountered writing the data.
29530 @var{nn} is a hex-encoded @code{errno} value.
29533 An empty reply indicates the @var{object} string was not
29534 recognized by the stub, or that the object does not support writing.
29537 @item qXfer:@var{object}:@var{operation}:@dots{}
29538 Requests of this form may be added in the future. When a stub does
29539 not recognize the @var{object} keyword, or its support for
29540 @var{object} does not recognize the @var{operation} keyword, the stub
29541 must respond with an empty packet.
29543 @item qAttached:@var{pid}
29544 @cindex query attached, remote request
29545 @cindex @samp{qAttached} packet
29546 Return an indication of whether the remote server attached to an
29547 existing process or created a new process. When the multiprocess
29548 protocol extensions are supported (@pxref{multiprocess extensions}),
29549 @var{pid} is an integer in hexadecimal format identifying the target
29550 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
29551 the query packet will be simplified as @samp{qAttached}.
29553 This query is used, for example, to know whether the remote process
29554 should be detached or killed when a @value{GDBN} session is ended with
29555 the @code{quit} command.
29560 The remote server attached to an existing process.
29562 The remote server created a new process.
29564 A badly formed request or an error was encountered.
29569 @node Register Packet Format
29570 @section Register Packet Format
29572 The following @code{g}/@code{G} packets have previously been defined.
29573 In the below, some thirty-two bit registers are transferred as
29574 sixty-four bits. Those registers should be zero/sign extended (which?)
29575 to fill the space allocated. Register bytes are transferred in target
29576 byte order. The two nibbles within a register byte are transferred
29577 most-significant - least-significant.
29583 All registers are transferred as thirty-two bit quantities in the order:
29584 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
29585 registers; fsr; fir; fp.
29589 All registers are transferred as sixty-four bit quantities (including
29590 thirty-two bit registers such as @code{sr}). The ordering is the same
29595 @node Tracepoint Packets
29596 @section Tracepoint Packets
29597 @cindex tracepoint packets
29598 @cindex packets, tracepoint
29600 Here we describe the packets @value{GDBN} uses to implement
29601 tracepoints (@pxref{Tracepoints}).
29605 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:X@var{len},@var{bytes}]@r{[}-@r{]}
29606 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
29607 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
29608 the tracepoint is disabled. @var{step} is the tracepoint's step
29609 count, and @var{pass} is its pass count. If an @samp{X} is present,
29610 it introduces a tracepoint condition, which consists of a hexadecimal
29611 length, followed by a comma and hex-encoded bytes, in a manner similar
29612 to action encodings as described below. If the trailing @samp{-} is
29613 present, further @samp{QTDP} packets will follow to specify this
29614 tracepoint's actions.
29619 The packet was understood and carried out.
29621 The packet was not recognized.
29624 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
29625 Define actions to be taken when a tracepoint is hit. @var{n} and
29626 @var{addr} must be the same as in the initial @samp{QTDP} packet for
29627 this tracepoint. This packet may only be sent immediately after
29628 another @samp{QTDP} packet that ended with a @samp{-}. If the
29629 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
29630 specifying more actions for this tracepoint.
29632 In the series of action packets for a given tracepoint, at most one
29633 can have an @samp{S} before its first @var{action}. If such a packet
29634 is sent, it and the following packets define ``while-stepping''
29635 actions. Any prior packets define ordinary actions --- that is, those
29636 taken when the tracepoint is first hit. If no action packet has an
29637 @samp{S}, then all the packets in the series specify ordinary
29638 tracepoint actions.
29640 The @samp{@var{action}@dots{}} portion of the packet is a series of
29641 actions, concatenated without separators. Each action has one of the
29647 Collect the registers whose bits are set in @var{mask}. @var{mask} is
29648 a hexadecimal number whose @var{i}'th bit is set if register number
29649 @var{i} should be collected. (The least significant bit is numbered
29650 zero.) Note that @var{mask} may be any number of digits long; it may
29651 not fit in a 32-bit word.
29653 @item M @var{basereg},@var{offset},@var{len}
29654 Collect @var{len} bytes of memory starting at the address in register
29655 number @var{basereg}, plus @var{offset}. If @var{basereg} is
29656 @samp{-1}, then the range has a fixed address: @var{offset} is the
29657 address of the lowest byte to collect. The @var{basereg},
29658 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
29659 values (the @samp{-1} value for @var{basereg} is a special case).
29661 @item X @var{len},@var{expr}
29662 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
29663 it directs. @var{expr} is an agent expression, as described in
29664 @ref{Agent Expressions}. Each byte of the expression is encoded as a
29665 two-digit hex number in the packet; @var{len} is the number of bytes
29666 in the expression (and thus one-half the number of hex digits in the
29671 Any number of actions may be packed together in a single @samp{QTDP}
29672 packet, as long as the packet does not exceed the maximum packet
29673 length (400 bytes, for many stubs). There may be only one @samp{R}
29674 action per tracepoint, and it must precede any @samp{M} or @samp{X}
29675 actions. Any registers referred to by @samp{M} and @samp{X} actions
29676 must be collected by a preceding @samp{R} action. (The
29677 ``while-stepping'' actions are treated as if they were attached to a
29678 separate tracepoint, as far as these restrictions are concerned.)
29683 The packet was understood and carried out.
29685 The packet was not recognized.
29688 @item QTFrame:@var{n}
29689 Select the @var{n}'th tracepoint frame from the buffer, and use the
29690 register and memory contents recorded there to answer subsequent
29691 request packets from @value{GDBN}.
29693 A successful reply from the stub indicates that the stub has found the
29694 requested frame. The response is a series of parts, concatenated
29695 without separators, describing the frame we selected. Each part has
29696 one of the following forms:
29700 The selected frame is number @var{n} in the trace frame buffer;
29701 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
29702 was no frame matching the criteria in the request packet.
29705 The selected trace frame records a hit of tracepoint number @var{t};
29706 @var{t} is a hexadecimal number.
29710 @item QTFrame:pc:@var{addr}
29711 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29712 currently selected frame whose PC is @var{addr};
29713 @var{addr} is a hexadecimal number.
29715 @item QTFrame:tdp:@var{t}
29716 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29717 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
29718 is a hexadecimal number.
29720 @item QTFrame:range:@var{start}:@var{end}
29721 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
29722 currently selected frame whose PC is between @var{start} (inclusive)
29723 and @var{end} (exclusive); @var{start} and @var{end} are hexadecimal
29726 @item QTFrame:outside:@var{start}:@var{end}
29727 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
29728 frame @emph{outside} the given range of addresses.
29731 Begin the tracepoint experiment. Begin collecting data from tracepoint
29732 hits in the trace frame buffer.
29735 End the tracepoint experiment. Stop collecting trace frames.
29738 Clear the table of tracepoints, and empty the trace frame buffer.
29740 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
29741 Establish the given ranges of memory as ``transparent''. The stub
29742 will answer requests for these ranges from memory's current contents,
29743 if they were not collected as part of the tracepoint hit.
29745 @value{GDBN} uses this to mark read-only regions of memory, like those
29746 containing program code. Since these areas never change, they should
29747 still have the same contents they did when the tracepoint was hit, so
29748 there's no reason for the stub to refuse to provide their contents.
29751 Ask the stub if there is a trace experiment running right now.
29756 There is no trace experiment running.
29758 There is a trace experiment running.
29764 @node Host I/O Packets
29765 @section Host I/O Packets
29766 @cindex Host I/O, remote protocol
29767 @cindex file transfer, remote protocol
29769 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
29770 operations on the far side of a remote link. For example, Host I/O is
29771 used to upload and download files to a remote target with its own
29772 filesystem. Host I/O uses the same constant values and data structure
29773 layout as the target-initiated File-I/O protocol. However, the
29774 Host I/O packets are structured differently. The target-initiated
29775 protocol relies on target memory to store parameters and buffers.
29776 Host I/O requests are initiated by @value{GDBN}, and the
29777 target's memory is not involved. @xref{File-I/O Remote Protocol
29778 Extension}, for more details on the target-initiated protocol.
29780 The Host I/O request packets all encode a single operation along with
29781 its arguments. They have this format:
29785 @item vFile:@var{operation}: @var{parameter}@dots{}
29786 @var{operation} is the name of the particular request; the target
29787 should compare the entire packet name up to the second colon when checking
29788 for a supported operation. The format of @var{parameter} depends on
29789 the operation. Numbers are always passed in hexadecimal. Negative
29790 numbers have an explicit minus sign (i.e.@: two's complement is not
29791 used). Strings (e.g.@: filenames) are encoded as a series of
29792 hexadecimal bytes. The last argument to a system call may be a
29793 buffer of escaped binary data (@pxref{Binary Data}).
29797 The valid responses to Host I/O packets are:
29801 @item F @var{result} [, @var{errno}] [; @var{attachment}]
29802 @var{result} is the integer value returned by this operation, usually
29803 non-negative for success and -1 for errors. If an error has occured,
29804 @var{errno} will be included in the result. @var{errno} will have a
29805 value defined by the File-I/O protocol (@pxref{Errno Values}). For
29806 operations which return data, @var{attachment} supplies the data as a
29807 binary buffer. Binary buffers in response packets are escaped in the
29808 normal way (@pxref{Binary Data}). See the individual packet
29809 documentation for the interpretation of @var{result} and
29813 An empty response indicates that this operation is not recognized.
29817 These are the supported Host I/O operations:
29820 @item vFile:open: @var{pathname}, @var{flags}, @var{mode}
29821 Open a file at @var{pathname} and return a file descriptor for it, or
29822 return -1 if an error occurs. @var{pathname} is a string,
29823 @var{flags} is an integer indicating a mask of open flags
29824 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
29825 of mode bits to use if the file is created (@pxref{mode_t Values}).
29826 @xref{open}, for details of the open flags and mode values.
29828 @item vFile:close: @var{fd}
29829 Close the open file corresponding to @var{fd} and return 0, or
29830 -1 if an error occurs.
29832 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
29833 Read data from the open file corresponding to @var{fd}. Up to
29834 @var{count} bytes will be read from the file, starting at @var{offset}
29835 relative to the start of the file. The target may read fewer bytes;
29836 common reasons include packet size limits and an end-of-file
29837 condition. The number of bytes read is returned. Zero should only be
29838 returned for a successful read at the end of the file, or if
29839 @var{count} was zero.
29841 The data read should be returned as a binary attachment on success.
29842 If zero bytes were read, the response should include an empty binary
29843 attachment (i.e.@: a trailing semicolon). The return value is the
29844 number of target bytes read; the binary attachment may be longer if
29845 some characters were escaped.
29847 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
29848 Write @var{data} (a binary buffer) to the open file corresponding
29849 to @var{fd}. Start the write at @var{offset} from the start of the
29850 file. Unlike many @code{write} system calls, there is no
29851 separate @var{count} argument; the length of @var{data} in the
29852 packet is used. @samp{vFile:write} returns the number of bytes written,
29853 which may be shorter than the length of @var{data}, or -1 if an
29856 @item vFile:unlink: @var{pathname}
29857 Delete the file at @var{pathname} on the target. Return 0,
29858 or -1 if an error occurs. @var{pathname} is a string.
29863 @section Interrupts
29864 @cindex interrupts (remote protocol)
29866 When a program on the remote target is running, @value{GDBN} may
29867 attempt to interrupt it by sending a @samp{Ctrl-C} or a @code{BREAK},
29868 control of which is specified via @value{GDBN}'s @samp{remotebreak}
29869 setting (@pxref{set remotebreak}).
29871 The precise meaning of @code{BREAK} is defined by the transport
29872 mechanism and may, in fact, be undefined. @value{GDBN} does not
29873 currently define a @code{BREAK} mechanism for any of the network
29874 interfaces except for TCP, in which case @value{GDBN} sends the
29875 @code{telnet} BREAK sequence.
29877 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
29878 transport mechanisms. It is represented by sending the single byte
29879 @code{0x03} without any of the usual packet overhead described in
29880 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
29881 transmitted as part of a packet, it is considered to be packet data
29882 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
29883 (@pxref{X packet}), used for binary downloads, may include an unescaped
29884 @code{0x03} as part of its packet.
29886 Stubs are not required to recognize these interrupt mechanisms and the
29887 precise meaning associated with receipt of the interrupt is
29888 implementation defined. If the target supports debugging of multiple
29889 threads and/or processes, it should attempt to interrupt all
29890 currently-executing threads and processes.
29891 If the stub is successful at interrupting the
29892 running program, it should send one of the stop
29893 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
29894 of successfully stopping the program in all-stop mode, and a stop reply
29895 for each stopped thread in non-stop mode.
29896 Interrupts received while the
29897 program is stopped are discarded.
29899 @node Notification Packets
29900 @section Notification Packets
29901 @cindex notification packets
29902 @cindex packets, notification
29904 The @value{GDBN} remote serial protocol includes @dfn{notifications},
29905 packets that require no acknowledgment. Both the GDB and the stub
29906 may send notifications (although the only notifications defined at
29907 present are sent by the stub). Notifications carry information
29908 without incurring the round-trip latency of an acknowledgment, and so
29909 are useful for low-impact communications where occasional packet loss
29912 A notification packet has the form @samp{% @var{data} #
29913 @var{checksum}}, where @var{data} is the content of the notification,
29914 and @var{checksum} is a checksum of @var{data}, computed and formatted
29915 as for ordinary @value{GDBN} packets. A notification's @var{data}
29916 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
29917 receiving a notification, the recipient sends no @samp{+} or @samp{-}
29918 to acknowledge the notification's receipt or to report its corruption.
29920 Every notification's @var{data} begins with a name, which contains no
29921 colon characters, followed by a colon character.
29923 Recipients should silently ignore corrupted notifications and
29924 notifications they do not understand. Recipients should restart
29925 timeout periods on receipt of a well-formed notification, whether or
29926 not they understand it.
29928 Senders should only send the notifications described here when this
29929 protocol description specifies that they are permitted. In the
29930 future, we may extend the protocol to permit existing notifications in
29931 new contexts; this rule helps older senders avoid confusing newer
29934 (Older versions of @value{GDBN} ignore bytes received until they see
29935 the @samp{$} byte that begins an ordinary packet, so new stubs may
29936 transmit notifications without fear of confusing older clients. There
29937 are no notifications defined for @value{GDBN} to send at the moment, but we
29938 assume that most older stubs would ignore them, as well.)
29940 The following notification packets from the stub to @value{GDBN} are
29944 @item Stop: @var{reply}
29945 Report an asynchronous stop event in non-stop mode.
29946 The @var{reply} has the form of a stop reply, as
29947 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
29948 for information on how these notifications are acknowledged by
29952 @node Remote Non-Stop
29953 @section Remote Protocol Support for Non-Stop Mode
29955 @value{GDBN}'s remote protocol supports non-stop debugging of
29956 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
29957 supports non-stop mode, it should report that to @value{GDBN} by including
29958 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
29960 @value{GDBN} typically sends a @samp{QNonStop} packet only when
29961 establishing a new connection with the stub. Entering non-stop mode
29962 does not alter the state of any currently-running threads, but targets
29963 must stop all threads in any already-attached processes when entering
29964 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
29965 probe the target state after a mode change.
29967 In non-stop mode, when an attached process encounters an event that
29968 would otherwise be reported with a stop reply, it uses the
29969 asynchronous notification mechanism (@pxref{Notification Packets}) to
29970 inform @value{GDBN}. In contrast to all-stop mode, where all threads
29971 in all processes are stopped when a stop reply is sent, in non-stop
29972 mode only the thread reporting the stop event is stopped. That is,
29973 when reporting a @samp{S} or @samp{T} response to indicate completion
29974 of a step operation, hitting a breakpoint, or a fault, only the
29975 affected thread is stopped; any other still-running threads continue
29976 to run. When reporting a @samp{W} or @samp{X} response, all running
29977 threads belonging to other attached processes continue to run.
29979 Only one stop reply notification at a time may be pending; if
29980 additional stop events occur before @value{GDBN} has acknowledged the
29981 previous notification, they must be queued by the stub for later
29982 synchronous transmission in response to @samp{vStopped} packets from
29983 @value{GDBN}. Because the notification mechanism is unreliable,
29984 the stub is permitted to resend a stop reply notification
29985 if it believes @value{GDBN} may not have received it. @value{GDBN}
29986 ignores additional stop reply notifications received before it has
29987 finished processing a previous notification and the stub has completed
29988 sending any queued stop events.
29990 Otherwise, @value{GDBN} must be prepared to receive a stop reply
29991 notification at any time. Specifically, they may appear when
29992 @value{GDBN} is not otherwise reading input from the stub, or when
29993 @value{GDBN} is expecting to read a normal synchronous response or a
29994 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
29995 Notification packets are distinct from any other communication from
29996 the stub so there is no ambiguity.
29998 After receiving a stop reply notification, @value{GDBN} shall
29999 acknowledge it by sending a @samp{vStopped} packet (@pxref{vStopped packet})
30000 as a regular, synchronous request to the stub. Such acknowledgment
30001 is not required to happen immediately, as @value{GDBN} is permitted to
30002 send other, unrelated packets to the stub first, which the stub should
30005 Upon receiving a @samp{vStopped} packet, if the stub has other queued
30006 stop events to report to @value{GDBN}, it shall respond by sending a
30007 normal stop reply response. @value{GDBN} shall then send another
30008 @samp{vStopped} packet to solicit further responses; again, it is
30009 permitted to send other, unrelated packets as well which the stub
30010 should process normally.
30012 If the stub receives a @samp{vStopped} packet and there are no
30013 additional stop events to report, the stub shall return an @samp{OK}
30014 response. At this point, if further stop events occur, the stub shall
30015 send a new stop reply notification, @value{GDBN} shall accept the
30016 notification, and the process shall be repeated.
30018 In non-stop mode, the target shall respond to the @samp{?} packet as
30019 follows. First, any incomplete stop reply notification/@samp{vStopped}
30020 sequence in progress is abandoned. The target must begin a new
30021 sequence reporting stop events for all stopped threads, whether or not
30022 it has previously reported those events to @value{GDBN}. The first
30023 stop reply is sent as a synchronous reply to the @samp{?} packet, and
30024 subsequent stop replies are sent as responses to @samp{vStopped} packets
30025 using the mechanism described above. The target must not send
30026 asynchronous stop reply notifications until the sequence is complete.
30027 If all threads are running when the target receives the @samp{?} packet,
30028 or if the target is not attached to any process, it shall respond
30031 @node Packet Acknowledgment
30032 @section Packet Acknowledgment
30034 @cindex acknowledgment, for @value{GDBN} remote
30035 @cindex packet acknowledgment, for @value{GDBN} remote
30036 By default, when either the host or the target machine receives a packet,
30037 the first response expected is an acknowledgment: either @samp{+} (to indicate
30038 the package was received correctly) or @samp{-} (to request retransmission).
30039 This mechanism allows the @value{GDBN} remote protocol to operate over
30040 unreliable transport mechanisms, such as a serial line.
30042 In cases where the transport mechanism is itself reliable (such as a pipe or
30043 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
30044 It may be desirable to disable them in that case to reduce communication
30045 overhead, or for other reasons. This can be accomplished by means of the
30046 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
30048 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
30049 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
30050 and response format still includes the normal checksum, as described in
30051 @ref{Overview}, but the checksum may be ignored by the receiver.
30053 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
30054 no-acknowledgment mode, it should report that to @value{GDBN}
30055 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
30056 @pxref{qSupported}.
30057 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
30058 disabled via the @code{set remote noack-packet off} command
30059 (@pxref{Remote Configuration}),
30060 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
30061 Only then may the stub actually turn off packet acknowledgments.
30062 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
30063 response, which can be safely ignored by the stub.
30065 Note that @code{set remote noack-packet} command only affects negotiation
30066 between @value{GDBN} and the stub when subsequent connections are made;
30067 it does not affect the protocol acknowledgment state for any current
30069 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
30070 new connection is established,
30071 there is also no protocol request to re-enable the acknowledgments
30072 for the current connection, once disabled.
30077 Example sequence of a target being re-started. Notice how the restart
30078 does not get any direct output:
30083 @emph{target restarts}
30086 <- @code{T001:1234123412341234}
30090 Example sequence of a target being stepped by a single instruction:
30093 -> @code{G1445@dots{}}
30098 <- @code{T001:1234123412341234}
30102 <- @code{1455@dots{}}
30106 @node File-I/O Remote Protocol Extension
30107 @section File-I/O Remote Protocol Extension
30108 @cindex File-I/O remote protocol extension
30111 * File-I/O Overview::
30112 * Protocol Basics::
30113 * The F Request Packet::
30114 * The F Reply Packet::
30115 * The Ctrl-C Message::
30117 * List of Supported Calls::
30118 * Protocol-specific Representation of Datatypes::
30120 * File-I/O Examples::
30123 @node File-I/O Overview
30124 @subsection File-I/O Overview
30125 @cindex file-i/o overview
30127 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
30128 target to use the host's file system and console I/O to perform various
30129 system calls. System calls on the target system are translated into a
30130 remote protocol packet to the host system, which then performs the needed
30131 actions and returns a response packet to the target system.
30132 This simulates file system operations even on targets that lack file systems.
30134 The protocol is defined to be independent of both the host and target systems.
30135 It uses its own internal representation of datatypes and values. Both
30136 @value{GDBN} and the target's @value{GDBN} stub are responsible for
30137 translating the system-dependent value representations into the internal
30138 protocol representations when data is transmitted.
30140 The communication is synchronous. A system call is possible only when
30141 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
30142 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
30143 the target is stopped to allow deterministic access to the target's
30144 memory. Therefore File-I/O is not interruptible by target signals. On
30145 the other hand, it is possible to interrupt File-I/O by a user interrupt
30146 (@samp{Ctrl-C}) within @value{GDBN}.
30148 The target's request to perform a host system call does not finish
30149 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
30150 after finishing the system call, the target returns to continuing the
30151 previous activity (continue, step). No additional continue or step
30152 request from @value{GDBN} is required.
30155 (@value{GDBP}) continue
30156 <- target requests 'system call X'
30157 target is stopped, @value{GDBN} executes system call
30158 -> @value{GDBN} returns result
30159 ... target continues, @value{GDBN} returns to wait for the target
30160 <- target hits breakpoint and sends a Txx packet
30163 The protocol only supports I/O on the console and to regular files on
30164 the host file system. Character or block special devices, pipes,
30165 named pipes, sockets or any other communication method on the host
30166 system are not supported by this protocol.
30168 File I/O is not supported in non-stop mode.
30170 @node Protocol Basics
30171 @subsection Protocol Basics
30172 @cindex protocol basics, file-i/o
30174 The File-I/O protocol uses the @code{F} packet as the request as well
30175 as reply packet. Since a File-I/O system call can only occur when
30176 @value{GDBN} is waiting for a response from the continuing or stepping target,
30177 the File-I/O request is a reply that @value{GDBN} has to expect as a result
30178 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
30179 This @code{F} packet contains all information needed to allow @value{GDBN}
30180 to call the appropriate host system call:
30184 A unique identifier for the requested system call.
30187 All parameters to the system call. Pointers are given as addresses
30188 in the target memory address space. Pointers to strings are given as
30189 pointer/length pair. Numerical values are given as they are.
30190 Numerical control flags are given in a protocol-specific representation.
30194 At this point, @value{GDBN} has to perform the following actions.
30198 If the parameters include pointer values to data needed as input to a
30199 system call, @value{GDBN} requests this data from the target with a
30200 standard @code{m} packet request. This additional communication has to be
30201 expected by the target implementation and is handled as any other @code{m}
30205 @value{GDBN} translates all value from protocol representation to host
30206 representation as needed. Datatypes are coerced into the host types.
30209 @value{GDBN} calls the system call.
30212 It then coerces datatypes back to protocol representation.
30215 If the system call is expected to return data in buffer space specified
30216 by pointer parameters to the call, the data is transmitted to the
30217 target using a @code{M} or @code{X} packet. This packet has to be expected
30218 by the target implementation and is handled as any other @code{M} or @code{X}
30223 Eventually @value{GDBN} replies with another @code{F} packet which contains all
30224 necessary information for the target to continue. This at least contains
30231 @code{errno}, if has been changed by the system call.
30238 After having done the needed type and value coercion, the target continues
30239 the latest continue or step action.
30241 @node The F Request Packet
30242 @subsection The @code{F} Request Packet
30243 @cindex file-i/o request packet
30244 @cindex @code{F} request packet
30246 The @code{F} request packet has the following format:
30249 @item F@var{call-id},@var{parameter@dots{}}
30251 @var{call-id} is the identifier to indicate the host system call to be called.
30252 This is just the name of the function.
30254 @var{parameter@dots{}} are the parameters to the system call.
30255 Parameters are hexadecimal integer values, either the actual values in case
30256 of scalar datatypes, pointers to target buffer space in case of compound
30257 datatypes and unspecified memory areas, or pointer/length pairs in case
30258 of string parameters. These are appended to the @var{call-id} as a
30259 comma-delimited list. All values are transmitted in ASCII
30260 string representation, pointer/length pairs separated by a slash.
30266 @node The F Reply Packet
30267 @subsection The @code{F} Reply Packet
30268 @cindex file-i/o reply packet
30269 @cindex @code{F} reply packet
30271 The @code{F} reply packet has the following format:
30275 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
30277 @var{retcode} is the return code of the system call as hexadecimal value.
30279 @var{errno} is the @code{errno} set by the call, in protocol-specific
30281 This parameter can be omitted if the call was successful.
30283 @var{Ctrl-C flag} is only sent if the user requested a break. In this
30284 case, @var{errno} must be sent as well, even if the call was successful.
30285 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
30292 or, if the call was interrupted before the host call has been performed:
30299 assuming 4 is the protocol-specific representation of @code{EINTR}.
30304 @node The Ctrl-C Message
30305 @subsection The @samp{Ctrl-C} Message
30306 @cindex ctrl-c message, in file-i/o protocol
30308 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
30309 reply packet (@pxref{The F Reply Packet}),
30310 the target should behave as if it had
30311 gotten a break message. The meaning for the target is ``system call
30312 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
30313 (as with a break message) and return to @value{GDBN} with a @code{T02}
30316 It's important for the target to know in which
30317 state the system call was interrupted. There are two possible cases:
30321 The system call hasn't been performed on the host yet.
30324 The system call on the host has been finished.
30328 These two states can be distinguished by the target by the value of the
30329 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
30330 call hasn't been performed. This is equivalent to the @code{EINTR} handling
30331 on POSIX systems. In any other case, the target may presume that the
30332 system call has been finished --- successfully or not --- and should behave
30333 as if the break message arrived right after the system call.
30335 @value{GDBN} must behave reliably. If the system call has not been called
30336 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
30337 @code{errno} in the packet. If the system call on the host has been finished
30338 before the user requests a break, the full action must be finished by
30339 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
30340 The @code{F} packet may only be sent when either nothing has happened
30341 or the full action has been completed.
30344 @subsection Console I/O
30345 @cindex console i/o as part of file-i/o
30347 By default and if not explicitly closed by the target system, the file
30348 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
30349 on the @value{GDBN} console is handled as any other file output operation
30350 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
30351 by @value{GDBN} so that after the target read request from file descriptor
30352 0 all following typing is buffered until either one of the following
30357 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
30359 system call is treated as finished.
30362 The user presses @key{RET}. This is treated as end of input with a trailing
30366 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
30367 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
30371 If the user has typed more characters than fit in the buffer given to
30372 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
30373 either another @code{read(0, @dots{})} is requested by the target, or debugging
30374 is stopped at the user's request.
30377 @node List of Supported Calls
30378 @subsection List of Supported Calls
30379 @cindex list of supported file-i/o calls
30396 @unnumberedsubsubsec open
30397 @cindex open, file-i/o system call
30402 int open(const char *pathname, int flags);
30403 int open(const char *pathname, int flags, mode_t mode);
30407 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
30410 @var{flags} is the bitwise @code{OR} of the following values:
30414 If the file does not exist it will be created. The host
30415 rules apply as far as file ownership and time stamps
30419 When used with @code{O_CREAT}, if the file already exists it is
30420 an error and open() fails.
30423 If the file already exists and the open mode allows
30424 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
30425 truncated to zero length.
30428 The file is opened in append mode.
30431 The file is opened for reading only.
30434 The file is opened for writing only.
30437 The file is opened for reading and writing.
30441 Other bits are silently ignored.
30445 @var{mode} is the bitwise @code{OR} of the following values:
30449 User has read permission.
30452 User has write permission.
30455 Group has read permission.
30458 Group has write permission.
30461 Others have read permission.
30464 Others have write permission.
30468 Other bits are silently ignored.
30471 @item Return value:
30472 @code{open} returns the new file descriptor or -1 if an error
30479 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
30482 @var{pathname} refers to a directory.
30485 The requested access is not allowed.
30488 @var{pathname} was too long.
30491 A directory component in @var{pathname} does not exist.
30494 @var{pathname} refers to a device, pipe, named pipe or socket.
30497 @var{pathname} refers to a file on a read-only filesystem and
30498 write access was requested.
30501 @var{pathname} is an invalid pointer value.
30504 No space on device to create the file.
30507 The process already has the maximum number of files open.
30510 The limit on the total number of files open on the system
30514 The call was interrupted by the user.
30520 @unnumberedsubsubsec close
30521 @cindex close, file-i/o system call
30530 @samp{Fclose,@var{fd}}
30532 @item Return value:
30533 @code{close} returns zero on success, or -1 if an error occurred.
30539 @var{fd} isn't a valid open file descriptor.
30542 The call was interrupted by the user.
30548 @unnumberedsubsubsec read
30549 @cindex read, file-i/o system call
30554 int read(int fd, void *buf, unsigned int count);
30558 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
30560 @item Return value:
30561 On success, the number of bytes read is returned.
30562 Zero indicates end of file. If count is zero, read
30563 returns zero as well. On error, -1 is returned.
30569 @var{fd} is not a valid file descriptor or is not open for
30573 @var{bufptr} is an invalid pointer value.
30576 The call was interrupted by the user.
30582 @unnumberedsubsubsec write
30583 @cindex write, file-i/o system call
30588 int write(int fd, const void *buf, unsigned int count);
30592 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
30594 @item Return value:
30595 On success, the number of bytes written are returned.
30596 Zero indicates nothing was written. On error, -1
30603 @var{fd} is not a valid file descriptor or is not open for
30607 @var{bufptr} is an invalid pointer value.
30610 An attempt was made to write a file that exceeds the
30611 host-specific maximum file size allowed.
30614 No space on device to write the data.
30617 The call was interrupted by the user.
30623 @unnumberedsubsubsec lseek
30624 @cindex lseek, file-i/o system call
30629 long lseek (int fd, long offset, int flag);
30633 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
30635 @var{flag} is one of:
30639 The offset is set to @var{offset} bytes.
30642 The offset is set to its current location plus @var{offset}
30646 The offset is set to the size of the file plus @var{offset}
30650 @item Return value:
30651 On success, the resulting unsigned offset in bytes from
30652 the beginning of the file is returned. Otherwise, a
30653 value of -1 is returned.
30659 @var{fd} is not a valid open file descriptor.
30662 @var{fd} is associated with the @value{GDBN} console.
30665 @var{flag} is not a proper value.
30668 The call was interrupted by the user.
30674 @unnumberedsubsubsec rename
30675 @cindex rename, file-i/o system call
30680 int rename(const char *oldpath, const char *newpath);
30684 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
30686 @item Return value:
30687 On success, zero is returned. On error, -1 is returned.
30693 @var{newpath} is an existing directory, but @var{oldpath} is not a
30697 @var{newpath} is a non-empty directory.
30700 @var{oldpath} or @var{newpath} is a directory that is in use by some
30704 An attempt was made to make a directory a subdirectory
30708 A component used as a directory in @var{oldpath} or new
30709 path is not a directory. Or @var{oldpath} is a directory
30710 and @var{newpath} exists but is not a directory.
30713 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
30716 No access to the file or the path of the file.
30720 @var{oldpath} or @var{newpath} was too long.
30723 A directory component in @var{oldpath} or @var{newpath} does not exist.
30726 The file is on a read-only filesystem.
30729 The device containing the file has no room for the new
30733 The call was interrupted by the user.
30739 @unnumberedsubsubsec unlink
30740 @cindex unlink, file-i/o system call
30745 int unlink(const char *pathname);
30749 @samp{Funlink,@var{pathnameptr}/@var{len}}
30751 @item Return value:
30752 On success, zero is returned. On error, -1 is returned.
30758 No access to the file or the path of the file.
30761 The system does not allow unlinking of directories.
30764 The file @var{pathname} cannot be unlinked because it's
30765 being used by another process.
30768 @var{pathnameptr} is an invalid pointer value.
30771 @var{pathname} was too long.
30774 A directory component in @var{pathname} does not exist.
30777 A component of the path is not a directory.
30780 The file is on a read-only filesystem.
30783 The call was interrupted by the user.
30789 @unnumberedsubsubsec stat/fstat
30790 @cindex fstat, file-i/o system call
30791 @cindex stat, file-i/o system call
30796 int stat(const char *pathname, struct stat *buf);
30797 int fstat(int fd, struct stat *buf);
30801 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
30802 @samp{Ffstat,@var{fd},@var{bufptr}}
30804 @item Return value:
30805 On success, zero is returned. On error, -1 is returned.
30811 @var{fd} is not a valid open file.
30814 A directory component in @var{pathname} does not exist or the
30815 path is an empty string.
30818 A component of the path is not a directory.
30821 @var{pathnameptr} is an invalid pointer value.
30824 No access to the file or the path of the file.
30827 @var{pathname} was too long.
30830 The call was interrupted by the user.
30836 @unnumberedsubsubsec gettimeofday
30837 @cindex gettimeofday, file-i/o system call
30842 int gettimeofday(struct timeval *tv, void *tz);
30846 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
30848 @item Return value:
30849 On success, 0 is returned, -1 otherwise.
30855 @var{tz} is a non-NULL pointer.
30858 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
30864 @unnumberedsubsubsec isatty
30865 @cindex isatty, file-i/o system call
30870 int isatty(int fd);
30874 @samp{Fisatty,@var{fd}}
30876 @item Return value:
30877 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
30883 The call was interrupted by the user.
30888 Note that the @code{isatty} call is treated as a special case: it returns
30889 1 to the target if the file descriptor is attached
30890 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
30891 would require implementing @code{ioctl} and would be more complex than
30896 @unnumberedsubsubsec system
30897 @cindex system, file-i/o system call
30902 int system(const char *command);
30906 @samp{Fsystem,@var{commandptr}/@var{len}}
30908 @item Return value:
30909 If @var{len} is zero, the return value indicates whether a shell is
30910 available. A zero return value indicates a shell is not available.
30911 For non-zero @var{len}, the value returned is -1 on error and the
30912 return status of the command otherwise. Only the exit status of the
30913 command is returned, which is extracted from the host's @code{system}
30914 return value by calling @code{WEXITSTATUS(retval)}. In case
30915 @file{/bin/sh} could not be executed, 127 is returned.
30921 The call was interrupted by the user.
30926 @value{GDBN} takes over the full task of calling the necessary host calls
30927 to perform the @code{system} call. The return value of @code{system} on
30928 the host is simplified before it's returned
30929 to the target. Any termination signal information from the child process
30930 is discarded, and the return value consists
30931 entirely of the exit status of the called command.
30933 Due to security concerns, the @code{system} call is by default refused
30934 by @value{GDBN}. The user has to allow this call explicitly with the
30935 @code{set remote system-call-allowed 1} command.
30938 @item set remote system-call-allowed
30939 @kindex set remote system-call-allowed
30940 Control whether to allow the @code{system} calls in the File I/O
30941 protocol for the remote target. The default is zero (disabled).
30943 @item show remote system-call-allowed
30944 @kindex show remote system-call-allowed
30945 Show whether the @code{system} calls are allowed in the File I/O
30949 @node Protocol-specific Representation of Datatypes
30950 @subsection Protocol-specific Representation of Datatypes
30951 @cindex protocol-specific representation of datatypes, in file-i/o protocol
30954 * Integral Datatypes::
30956 * Memory Transfer::
30961 @node Integral Datatypes
30962 @unnumberedsubsubsec Integral Datatypes
30963 @cindex integral datatypes, in file-i/o protocol
30965 The integral datatypes used in the system calls are @code{int},
30966 @code{unsigned int}, @code{long}, @code{unsigned long},
30967 @code{mode_t}, and @code{time_t}.
30969 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
30970 implemented as 32 bit values in this protocol.
30972 @code{long} and @code{unsigned long} are implemented as 64 bit types.
30974 @xref{Limits}, for corresponding MIN and MAX values (similar to those
30975 in @file{limits.h}) to allow range checking on host and target.
30977 @code{time_t} datatypes are defined as seconds since the Epoch.
30979 All integral datatypes transferred as part of a memory read or write of a
30980 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
30983 @node Pointer Values
30984 @unnumberedsubsubsec Pointer Values
30985 @cindex pointer values, in file-i/o protocol
30987 Pointers to target data are transmitted as they are. An exception
30988 is made for pointers to buffers for which the length isn't
30989 transmitted as part of the function call, namely strings. Strings
30990 are transmitted as a pointer/length pair, both as hex values, e.g.@:
30997 which is a pointer to data of length 18 bytes at position 0x1aaf.
30998 The length is defined as the full string length in bytes, including
30999 the trailing null byte. For example, the string @code{"hello world"}
31000 at address 0x123456 is transmitted as
31006 @node Memory Transfer
31007 @unnumberedsubsubsec Memory Transfer
31008 @cindex memory transfer, in file-i/o protocol
31010 Structured data which is transferred using a memory read or write (for
31011 example, a @code{struct stat}) is expected to be in a protocol-specific format
31012 with all scalar multibyte datatypes being big endian. Translation to
31013 this representation needs to be done both by the target before the @code{F}
31014 packet is sent, and by @value{GDBN} before
31015 it transfers memory to the target. Transferred pointers to structured
31016 data should point to the already-coerced data at any time.
31020 @unnumberedsubsubsec struct stat
31021 @cindex struct stat, in file-i/o protocol
31023 The buffer of type @code{struct stat} used by the target and @value{GDBN}
31024 is defined as follows:
31028 unsigned int st_dev; /* device */
31029 unsigned int st_ino; /* inode */
31030 mode_t st_mode; /* protection */
31031 unsigned int st_nlink; /* number of hard links */
31032 unsigned int st_uid; /* user ID of owner */
31033 unsigned int st_gid; /* group ID of owner */
31034 unsigned int st_rdev; /* device type (if inode device) */
31035 unsigned long st_size; /* total size, in bytes */
31036 unsigned long st_blksize; /* blocksize for filesystem I/O */
31037 unsigned long st_blocks; /* number of blocks allocated */
31038 time_t st_atime; /* time of last access */
31039 time_t st_mtime; /* time of last modification */
31040 time_t st_ctime; /* time of last change */
31044 The integral datatypes conform to the definitions given in the
31045 appropriate section (see @ref{Integral Datatypes}, for details) so this
31046 structure is of size 64 bytes.
31048 The values of several fields have a restricted meaning and/or
31054 A value of 0 represents a file, 1 the console.
31057 No valid meaning for the target. Transmitted unchanged.
31060 Valid mode bits are described in @ref{Constants}. Any other
31061 bits have currently no meaning for the target.
31066 No valid meaning for the target. Transmitted unchanged.
31071 These values have a host and file system dependent
31072 accuracy. Especially on Windows hosts, the file system may not
31073 support exact timing values.
31076 The target gets a @code{struct stat} of the above representation and is
31077 responsible for coercing it to the target representation before
31080 Note that due to size differences between the host, target, and protocol
31081 representations of @code{struct stat} members, these members could eventually
31082 get truncated on the target.
31084 @node struct timeval
31085 @unnumberedsubsubsec struct timeval
31086 @cindex struct timeval, in file-i/o protocol
31088 The buffer of type @code{struct timeval} used by the File-I/O protocol
31089 is defined as follows:
31093 time_t tv_sec; /* second */
31094 long tv_usec; /* microsecond */
31098 The integral datatypes conform to the definitions given in the
31099 appropriate section (see @ref{Integral Datatypes}, for details) so this
31100 structure is of size 8 bytes.
31103 @subsection Constants
31104 @cindex constants, in file-i/o protocol
31106 The following values are used for the constants inside of the
31107 protocol. @value{GDBN} and target are responsible for translating these
31108 values before and after the call as needed.
31119 @unnumberedsubsubsec Open Flags
31120 @cindex open flags, in file-i/o protocol
31122 All values are given in hexadecimal representation.
31134 @node mode_t Values
31135 @unnumberedsubsubsec mode_t Values
31136 @cindex mode_t values, in file-i/o protocol
31138 All values are given in octal representation.
31155 @unnumberedsubsubsec Errno Values
31156 @cindex errno values, in file-i/o protocol
31158 All values are given in decimal representation.
31183 @code{EUNKNOWN} is used as a fallback error value if a host system returns
31184 any error value not in the list of supported error numbers.
31187 @unnumberedsubsubsec Lseek Flags
31188 @cindex lseek flags, in file-i/o protocol
31197 @unnumberedsubsubsec Limits
31198 @cindex limits, in file-i/o protocol
31200 All values are given in decimal representation.
31203 INT_MIN -2147483648
31205 UINT_MAX 4294967295
31206 LONG_MIN -9223372036854775808
31207 LONG_MAX 9223372036854775807
31208 ULONG_MAX 18446744073709551615
31211 @node File-I/O Examples
31212 @subsection File-I/O Examples
31213 @cindex file-i/o examples
31215 Example sequence of a write call, file descriptor 3, buffer is at target
31216 address 0x1234, 6 bytes should be written:
31219 <- @code{Fwrite,3,1234,6}
31220 @emph{request memory read from target}
31223 @emph{return "6 bytes written"}
31227 Example sequence of a read call, file descriptor 3, buffer is at target
31228 address 0x1234, 6 bytes should be read:
31231 <- @code{Fread,3,1234,6}
31232 @emph{request memory write to target}
31233 -> @code{X1234,6:XXXXXX}
31234 @emph{return "6 bytes read"}
31238 Example sequence of a read call, call fails on the host due to invalid
31239 file descriptor (@code{EBADF}):
31242 <- @code{Fread,3,1234,6}
31246 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
31250 <- @code{Fread,3,1234,6}
31255 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
31259 <- @code{Fread,3,1234,6}
31260 -> @code{X1234,6:XXXXXX}
31264 @node Library List Format
31265 @section Library List Format
31266 @cindex library list format, remote protocol
31268 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
31269 same process as your application to manage libraries. In this case,
31270 @value{GDBN} can use the loader's symbol table and normal memory
31271 operations to maintain a list of shared libraries. On other
31272 platforms, the operating system manages loaded libraries.
31273 @value{GDBN} can not retrieve the list of currently loaded libraries
31274 through memory operations, so it uses the @samp{qXfer:libraries:read}
31275 packet (@pxref{qXfer library list read}) instead. The remote stub
31276 queries the target's operating system and reports which libraries
31279 The @samp{qXfer:libraries:read} packet returns an XML document which
31280 lists loaded libraries and their offsets. Each library has an
31281 associated name and one or more segment or section base addresses,
31282 which report where the library was loaded in memory.
31284 For the common case of libraries that are fully linked binaries, the
31285 library should have a list of segments. If the target supports
31286 dynamic linking of a relocatable object file, its library XML element
31287 should instead include a list of allocated sections. The segment or
31288 section bases are start addresses, not relocation offsets; they do not
31289 depend on the library's link-time base addresses.
31291 @value{GDBN} must be linked with the Expat library to support XML
31292 library lists. @xref{Expat}.
31294 A simple memory map, with one loaded library relocated by a single
31295 offset, looks like this:
31299 <library name="/lib/libc.so.6">
31300 <segment address="0x10000000"/>
31305 Another simple memory map, with one loaded library with three
31306 allocated sections (.text, .data, .bss), looks like this:
31310 <library name="sharedlib.o">
31311 <section address="0x10000000"/>
31312 <section address="0x20000000"/>
31313 <section address="0x30000000"/>
31318 The format of a library list is described by this DTD:
31321 <!-- library-list: Root element with versioning -->
31322 <!ELEMENT library-list (library)*>
31323 <!ATTLIST library-list version CDATA #FIXED "1.0">
31324 <!ELEMENT library (segment*, section*)>
31325 <!ATTLIST library name CDATA #REQUIRED>
31326 <!ELEMENT segment EMPTY>
31327 <!ATTLIST segment address CDATA #REQUIRED>
31328 <!ELEMENT section EMPTY>
31329 <!ATTLIST section address CDATA #REQUIRED>
31332 In addition, segments and section descriptors cannot be mixed within a
31333 single library element, and you must supply at least one segment or
31334 section for each library.
31336 @node Memory Map Format
31337 @section Memory Map Format
31338 @cindex memory map format
31340 To be able to write into flash memory, @value{GDBN} needs to obtain a
31341 memory map from the target. This section describes the format of the
31344 The memory map is obtained using the @samp{qXfer:memory-map:read}
31345 (@pxref{qXfer memory map read}) packet and is an XML document that
31346 lists memory regions.
31348 @value{GDBN} must be linked with the Expat library to support XML
31349 memory maps. @xref{Expat}.
31351 The top-level structure of the document is shown below:
31354 <?xml version="1.0"?>
31355 <!DOCTYPE memory-map
31356 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
31357 "http://sourceware.org/gdb/gdb-memory-map.dtd">
31363 Each region can be either:
31368 A region of RAM starting at @var{addr} and extending for @var{length}
31372 <memory type="ram" start="@var{addr}" length="@var{length}"/>
31377 A region of read-only memory:
31380 <memory type="rom" start="@var{addr}" length="@var{length}"/>
31385 A region of flash memory, with erasure blocks @var{blocksize}
31389 <memory type="flash" start="@var{addr}" length="@var{length}">
31390 <property name="blocksize">@var{blocksize}</property>
31396 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
31397 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
31398 packets to write to addresses in such ranges.
31400 The formal DTD for memory map format is given below:
31403 <!-- ................................................... -->
31404 <!-- Memory Map XML DTD ................................ -->
31405 <!-- File: memory-map.dtd .............................. -->
31406 <!-- .................................... .............. -->
31407 <!-- memory-map.dtd -->
31408 <!-- memory-map: Root element with versioning -->
31409 <!ELEMENT memory-map (memory | property)>
31410 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
31411 <!ELEMENT memory (property)>
31412 <!-- memory: Specifies a memory region,
31413 and its type, or device. -->
31414 <!ATTLIST memory type CDATA #REQUIRED
31415 start CDATA #REQUIRED
31416 length CDATA #REQUIRED
31417 device CDATA #IMPLIED>
31418 <!-- property: Generic attribute tag -->
31419 <!ELEMENT property (#PCDATA | property)*>
31420 <!ATTLIST property name CDATA #REQUIRED>
31423 @include agentexpr.texi
31425 @node Target Descriptions
31426 @appendix Target Descriptions
31427 @cindex target descriptions
31429 @strong{Warning:} target descriptions are still under active development,
31430 and the contents and format may change between @value{GDBN} releases.
31431 The format is expected to stabilize in the future.
31433 One of the challenges of using @value{GDBN} to debug embedded systems
31434 is that there are so many minor variants of each processor
31435 architecture in use. It is common practice for vendors to start with
31436 a standard processor core --- ARM, PowerPC, or MIPS, for example ---
31437 and then make changes to adapt it to a particular market niche. Some
31438 architectures have hundreds of variants, available from dozens of
31439 vendors. This leads to a number of problems:
31443 With so many different customized processors, it is difficult for
31444 the @value{GDBN} maintainers to keep up with the changes.
31446 Since individual variants may have short lifetimes or limited
31447 audiences, it may not be worthwhile to carry information about every
31448 variant in the @value{GDBN} source tree.
31450 When @value{GDBN} does support the architecture of the embedded system
31451 at hand, the task of finding the correct architecture name to give the
31452 @command{set architecture} command can be error-prone.
31455 To address these problems, the @value{GDBN} remote protocol allows a
31456 target system to not only identify itself to @value{GDBN}, but to
31457 actually describe its own features. This lets @value{GDBN} support
31458 processor variants it has never seen before --- to the extent that the
31459 descriptions are accurate, and that @value{GDBN} understands them.
31461 @value{GDBN} must be linked with the Expat library to support XML
31462 target descriptions. @xref{Expat}.
31465 * Retrieving Descriptions:: How descriptions are fetched from a target.
31466 * Target Description Format:: The contents of a target description.
31467 * Predefined Target Types:: Standard types available for target
31469 * Standard Target Features:: Features @value{GDBN} knows about.
31472 @node Retrieving Descriptions
31473 @section Retrieving Descriptions
31475 Target descriptions can be read from the target automatically, or
31476 specified by the user manually. The default behavior is to read the
31477 description from the target. @value{GDBN} retrieves it via the remote
31478 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
31479 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
31480 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
31481 XML document, of the form described in @ref{Target Description
31484 Alternatively, you can specify a file to read for the target description.
31485 If a file is set, the target will not be queried. The commands to
31486 specify a file are:
31489 @cindex set tdesc filename
31490 @item set tdesc filename @var{path}
31491 Read the target description from @var{path}.
31493 @cindex unset tdesc filename
31494 @item unset tdesc filename
31495 Do not read the XML target description from a file. @value{GDBN}
31496 will use the description supplied by the current target.
31498 @cindex show tdesc filename
31499 @item show tdesc filename
31500 Show the filename to read for a target description, if any.
31504 @node Target Description Format
31505 @section Target Description Format
31506 @cindex target descriptions, XML format
31508 A target description annex is an @uref{http://www.w3.org/XML/, XML}
31509 document which complies with the Document Type Definition provided in
31510 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
31511 means you can use generally available tools like @command{xmllint} to
31512 check that your feature descriptions are well-formed and valid.
31513 However, to help people unfamiliar with XML write descriptions for
31514 their targets, we also describe the grammar here.
31516 Target descriptions can identify the architecture of the remote target
31517 and (for some architectures) provide information about custom register
31518 sets. They can also identify the OS ABI of the remote target.
31519 @value{GDBN} can use this information to autoconfigure for your
31520 target, or to warn you if you connect to an unsupported target.
31522 Here is a simple target description:
31525 <target version="1.0">
31526 <architecture>i386:x86-64</architecture>
31531 This minimal description only says that the target uses
31532 the x86-64 architecture.
31534 A target description has the following overall form, with [ ] marking
31535 optional elements and @dots{} marking repeatable elements. The elements
31536 are explained further below.
31539 <?xml version="1.0"?>
31540 <!DOCTYPE target SYSTEM "gdb-target.dtd">
31541 <target version="1.0">
31542 @r{[}@var{architecture}@r{]}
31543 @r{[}@var{osabi}@r{]}
31544 @r{[}@var{compatible}@r{]}
31545 @r{[}@var{feature}@dots{}@r{]}
31550 The description is generally insensitive to whitespace and line
31551 breaks, under the usual common-sense rules. The XML version
31552 declaration and document type declaration can generally be omitted
31553 (@value{GDBN} does not require them), but specifying them may be
31554 useful for XML validation tools. The @samp{version} attribute for
31555 @samp{<target>} may also be omitted, but we recommend
31556 including it; if future versions of @value{GDBN} use an incompatible
31557 revision of @file{gdb-target.dtd}, they will detect and report
31558 the version mismatch.
31560 @subsection Inclusion
31561 @cindex target descriptions, inclusion
31564 @cindex <xi:include>
31567 It can sometimes be valuable to split a target description up into
31568 several different annexes, either for organizational purposes, or to
31569 share files between different possible target descriptions. You can
31570 divide a description into multiple files by replacing any element of
31571 the target description with an inclusion directive of the form:
31574 <xi:include href="@var{document}"/>
31578 When @value{GDBN} encounters an element of this form, it will retrieve
31579 the named XML @var{document}, and replace the inclusion directive with
31580 the contents of that document. If the current description was read
31581 using @samp{qXfer}, then so will be the included document;
31582 @var{document} will be interpreted as the name of an annex. If the
31583 current description was read from a file, @value{GDBN} will look for
31584 @var{document} as a file in the same directory where it found the
31585 original description.
31587 @subsection Architecture
31588 @cindex <architecture>
31590 An @samp{<architecture>} element has this form:
31593 <architecture>@var{arch}</architecture>
31596 @var{arch} is one of the architectures from the set accepted by
31597 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31600 @cindex @code{<osabi>}
31602 This optional field was introduced in @value{GDBN} version 7.0.
31603 Previous versions of @value{GDBN} ignore it.
31605 An @samp{<osabi>} element has this form:
31608 <osabi>@var{abi-name}</osabi>
31611 @var{abi-name} is an OS ABI name from the same selection accepted by
31612 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
31614 @subsection Compatible Architecture
31615 @cindex @code{<compatible>}
31617 This optional field was introduced in @value{GDBN} version 7.0.
31618 Previous versions of @value{GDBN} ignore it.
31620 A @samp{<compatible>} element has this form:
31623 <compatible>@var{arch}</compatible>
31626 @var{arch} is one of the architectures from the set accepted by
31627 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
31629 A @samp{<compatible>} element is used to specify that the target
31630 is able to run binaries in some other than the main target architecture
31631 given by the @samp{<architecture>} element. For example, on the
31632 Cell Broadband Engine, the main architecture is @code{powerpc:common}
31633 or @code{powerpc:common64}, but the system is able to run binaries
31634 in the @code{spu} architecture as well. The way to describe this
31635 capability with @samp{<compatible>} is as follows:
31638 <architecture>powerpc:common</architecture>
31639 <compatible>spu</compatible>
31642 @subsection Features
31645 Each @samp{<feature>} describes some logical portion of the target
31646 system. Features are currently used to describe available CPU
31647 registers and the types of their contents. A @samp{<feature>} element
31651 <feature name="@var{name}">
31652 @r{[}@var{type}@dots{}@r{]}
31658 Each feature's name should be unique within the description. The name
31659 of a feature does not matter unless @value{GDBN} has some special
31660 knowledge of the contents of that feature; if it does, the feature
31661 should have its standard name. @xref{Standard Target Features}.
31665 Any register's value is a collection of bits which @value{GDBN} must
31666 interpret. The default interpretation is a two's complement integer,
31667 but other types can be requested by name in the register description.
31668 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
31669 Target Types}), and the description can define additional composite types.
31671 Each type element must have an @samp{id} attribute, which gives
31672 a unique (within the containing @samp{<feature>}) name to the type.
31673 Types must be defined before they are used.
31676 Some targets offer vector registers, which can be treated as arrays
31677 of scalar elements. These types are written as @samp{<vector>} elements,
31678 specifying the array element type, @var{type}, and the number of elements,
31682 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
31686 If a register's value is usefully viewed in multiple ways, define it
31687 with a union type containing the useful representations. The
31688 @samp{<union>} element contains one or more @samp{<field>} elements,
31689 each of which has a @var{name} and a @var{type}:
31692 <union id="@var{id}">
31693 <field name="@var{name}" type="@var{type}"/>
31698 @subsection Registers
31701 Each register is represented as an element with this form:
31704 <reg name="@var{name}"
31705 bitsize="@var{size}"
31706 @r{[}regnum="@var{num}"@r{]}
31707 @r{[}save-restore="@var{save-restore}"@r{]}
31708 @r{[}type="@var{type}"@r{]}
31709 @r{[}group="@var{group}"@r{]}/>
31713 The components are as follows:
31718 The register's name; it must be unique within the target description.
31721 The register's size, in bits.
31724 The register's number. If omitted, a register's number is one greater
31725 than that of the previous register (either in the current feature or in
31726 a preceeding feature); the first register in the target description
31727 defaults to zero. This register number is used to read or write
31728 the register; e.g.@: it is used in the remote @code{p} and @code{P}
31729 packets, and registers appear in the @code{g} and @code{G} packets
31730 in order of increasing register number.
31733 Whether the register should be preserved across inferior function
31734 calls; this must be either @code{yes} or @code{no}. The default is
31735 @code{yes}, which is appropriate for most registers except for
31736 some system control registers; this is not related to the target's
31740 The type of the register. @var{type} may be a predefined type, a type
31741 defined in the current feature, or one of the special types @code{int}
31742 and @code{float}. @code{int} is an integer type of the correct size
31743 for @var{bitsize}, and @code{float} is a floating point type (in the
31744 architecture's normal floating point format) of the correct size for
31745 @var{bitsize}. The default is @code{int}.
31748 The register group to which this register belongs. @var{group} must
31749 be either @code{general}, @code{float}, or @code{vector}. If no
31750 @var{group} is specified, @value{GDBN} will not display the register
31751 in @code{info registers}.
31755 @node Predefined Target Types
31756 @section Predefined Target Types
31757 @cindex target descriptions, predefined types
31759 Type definitions in the self-description can build up composite types
31760 from basic building blocks, but can not define fundamental types. Instead,
31761 standard identifiers are provided by @value{GDBN} for the fundamental
31762 types. The currently supported types are:
31771 Signed integer types holding the specified number of bits.
31778 Unsigned integer types holding the specified number of bits.
31782 Pointers to unspecified code and data. The program counter and
31783 any dedicated return address register may be marked as code
31784 pointers; printing a code pointer converts it into a symbolic
31785 address. The stack pointer and any dedicated address registers
31786 may be marked as data pointers.
31789 Single precision IEEE floating point.
31792 Double precision IEEE floating point.
31795 The 12-byte extended precision format used by ARM FPA registers.
31799 @node Standard Target Features
31800 @section Standard Target Features
31801 @cindex target descriptions, standard features
31803 A target description must contain either no registers or all the
31804 target's registers. If the description contains no registers, then
31805 @value{GDBN} will assume a default register layout, selected based on
31806 the architecture. If the description contains any registers, the
31807 default layout will not be used; the standard registers must be
31808 described in the target description, in such a way that @value{GDBN}
31809 can recognize them.
31811 This is accomplished by giving specific names to feature elements
31812 which contain standard registers. @value{GDBN} will look for features
31813 with those names and verify that they contain the expected registers;
31814 if any known feature is missing required registers, or if any required
31815 feature is missing, @value{GDBN} will reject the target
31816 description. You can add additional registers to any of the
31817 standard features --- @value{GDBN} will display them just as if
31818 they were added to an unrecognized feature.
31820 This section lists the known features and their expected contents.
31821 Sample XML documents for these features are included in the
31822 @value{GDBN} source tree, in the directory @file{gdb/features}.
31824 Names recognized by @value{GDBN} should include the name of the
31825 company or organization which selected the name, and the overall
31826 architecture to which the feature applies; so e.g.@: the feature
31827 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
31829 The names of registers are not case sensitive for the purpose
31830 of recognizing standard features, but @value{GDBN} will only display
31831 registers using the capitalization used in the description.
31837 * PowerPC Features::
31842 @subsection ARM Features
31843 @cindex target descriptions, ARM features
31845 The @samp{org.gnu.gdb.arm.core} feature is required for ARM targets.
31846 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
31847 @samp{lr}, @samp{pc}, and @samp{cpsr}.
31849 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
31850 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
31852 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
31853 it should contain at least registers @samp{wR0} through @samp{wR15} and
31854 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
31855 @samp{wCSSF}, and @samp{wCASF} registers are optional.
31857 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
31858 should contain at least registers @samp{d0} through @samp{d15}. If
31859 they are present, @samp{d16} through @samp{d31} should also be included.
31860 @value{GDBN} will synthesize the single-precision registers from
31861 halves of the double-precision registers.
31863 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
31864 need to contain registers; it instructs @value{GDBN} to display the
31865 VFP double-precision registers as vectors and to synthesize the
31866 quad-precision registers from pairs of double-precision registers.
31867 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
31868 be present and include 32 double-precision registers.
31870 @node MIPS Features
31871 @subsection MIPS Features
31872 @cindex target descriptions, MIPS features
31874 The @samp{org.gnu.gdb.mips.cpu} feature is required for MIPS targets.
31875 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
31876 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
31879 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
31880 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
31881 registers. They may be 32-bit or 64-bit depending on the target.
31883 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
31884 it may be optional in a future version of @value{GDBN}. It should
31885 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
31886 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
31888 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
31889 contain a single register, @samp{restart}, which is used by the
31890 Linux kernel to control restartable syscalls.
31892 @node M68K Features
31893 @subsection M68K Features
31894 @cindex target descriptions, M68K features
31897 @item @samp{org.gnu.gdb.m68k.core}
31898 @itemx @samp{org.gnu.gdb.coldfire.core}
31899 @itemx @samp{org.gnu.gdb.fido.core}
31900 One of those features must be always present.
31901 The feature that is present determines which flavor of m68k is
31902 used. The feature that is present should contain registers
31903 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
31904 @samp{sp}, @samp{ps} and @samp{pc}.
31906 @item @samp{org.gnu.gdb.coldfire.fp}
31907 This feature is optional. If present, it should contain registers
31908 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
31912 @node PowerPC Features
31913 @subsection PowerPC Features
31914 @cindex target descriptions, PowerPC features
31916 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
31917 targets. It should contain registers @samp{r0} through @samp{r31},
31918 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
31919 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
31921 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
31922 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
31924 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
31925 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
31928 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
31929 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
31930 will combine these registers with the floating point registers
31931 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
31932 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
31933 through @samp{vs63}, the set of vector registers for POWER7.
31935 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
31936 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
31937 @samp{spefscr}. SPE targets should provide 32-bit registers in
31938 @samp{org.gnu.gdb.power.core} and provide the upper halves in
31939 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
31940 these to present registers @samp{ev0} through @samp{ev31} to the
31943 @node Operating System Information
31944 @appendix Operating System Information
31945 @cindex operating system information
31951 Users of @value{GDBN} often wish to obtain information about the state of
31952 the operating system running on the target---for example the list of
31953 processes, or the list of open files. This section describes the
31954 mechanism that makes it possible. This mechanism is similar to the
31955 target features mechanism (@pxref{Target Descriptions}), but focuses
31956 on a different aspect of target.
31958 Operating system information is retrived from the target via the
31959 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
31960 read}). The object name in the request should be @samp{osdata}, and
31961 the @var{annex} identifies the data to be fetched.
31964 @appendixsection Process list
31965 @cindex operating system information, process list
31967 When requesting the process list, the @var{annex} field in the
31968 @samp{qXfer} request should be @samp{processes}. The returned data is
31969 an XML document. The formal syntax of this document is defined in
31970 @file{gdb/features/osdata.dtd}.
31972 An example document is:
31975 <?xml version="1.0"?>
31976 <!DOCTYPE target SYSTEM "osdata.dtd">
31977 <osdata type="processes">
31979 <column name="pid">1</column>
31980 <column name="user">root</column>
31981 <column name="command">/sbin/init</column>
31986 Each item should include a column whose name is @samp{pid}. The value
31987 of that column should identify the process on the target. The
31988 @samp{user} and @samp{command} columns are optional, and will be
31989 displayed by @value{GDBN}. Target may provide additional columns,
31990 which @value{GDBN} currently ignores.
32004 % I think something like @colophon should be in texinfo. In the
32006 \long\def\colophon{\hbox to0pt{}\vfill
32007 \centerline{The body of this manual is set in}
32008 \centerline{\fontname\tenrm,}
32009 \centerline{with headings in {\bf\fontname\tenbf}}
32010 \centerline{and examples in {\tt\fontname\tentt}.}
32011 \centerline{{\it\fontname\tenit\/},}
32012 \centerline{{\bf\fontname\tenbf}, and}
32013 \centerline{{\sl\fontname\tensl\/}}
32014 \centerline{are used for emphasis.}\vfill}
32016 % Blame: doc@cygnus.com, 1991.