1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
36 @c THIS MANUAL REQUIRES TEXINFO 3.12 OR LATER.
38 @c This is a dir.info fragment to support semi-automated addition of
39 @c manuals to an info tree.
40 @dircategory Programming & development tools.
42 * Gdb: (gdb). The @sc{gnu} debugger.
46 This file documents the @sc{gnu} debugger @value{GDBN}.
49 This is the @value{EDITION} Edition, @value{DATE},
50 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
51 for @value{GDBN} Version @value{GDBVN}.
53 Copyright (C) 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
54 Free Software Foundation, Inc.
56 Permission is granted to copy, distribute and/or modify this document
57 under the terms of the GNU Free Documentation License, Version 1.1 or
58 any later version published by the Free Software Foundation; with the
59 Invariant Sections being ``A Sample GDB Session'' and ``Free
60 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
61 with the Back-Cover Texts as in (a) below.
63 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
64 this GNU Manual, like GNU software. Copies published by the Free
65 Software Foundation raise funds for GNU development.''
69 @title Debugging with @value{GDBN}
70 @subtitle The @sc{gnu} Source-Level Debugger
72 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
73 @subtitle @value{DATE}
74 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
78 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
79 \hfill {\it Debugging with @value{GDBN}}\par
80 \hfill \TeX{}info \texinfoversion\par
84 @vskip 0pt plus 1filll
85 Copyright @copyright{} 1988,1989,1990,1991,1992,1993,1994,1995,1996,1998,1999,2000,2001
86 Free Software Foundation, Inc.
88 Published by the Free Software Foundation @*
89 59 Temple Place - Suite 330, @*
90 Boston, MA 02111-1307 USA @*
93 Permission is granted to copy, distribute and/or modify this document
94 under the terms of the GNU Free Documentation License, Version 1.1 or
95 any later version published by the Free Software Foundation; with the
96 Invariant Sections being ``A Sample GDB Session'' and ``Free
97 Software'', with the Front-Cover texts being ``A GNU Manual,'' and
98 with the Back-Cover Texts as in (a) below.
100 (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify
101 this GNU Manual, like GNU software. Copies published by the Free
102 Software Foundation raise funds for GNU development.''
107 @node Top, Summary, (dir), (dir)
109 @top Debugging with @value{GDBN}
111 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
113 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
116 Copyright (C) 1988-2001 Free Software Foundation, Inc.
119 * Summary:: Summary of @value{GDBN}
120 * Sample Session:: A sample @value{GDBN} session
122 * Invocation:: Getting in and out of @value{GDBN}
123 * Commands:: @value{GDBN} commands
124 * Running:: Running programs under @value{GDBN}
125 * Stopping:: Stopping and continuing
126 * Stack:: Examining the stack
127 * Source:: Examining source files
128 * Data:: Examining data
129 * Tracepoints:: Debugging remote targets non-intrusively
131 * Languages:: Using @value{GDBN} with different languages
133 * Symbols:: Examining the symbol table
134 * Altering:: Altering execution
135 * GDB Files:: @value{GDBN} files
136 * Targets:: Specifying a debugging target
137 * Configurations:: Configuration-specific information
138 * Controlling GDB:: Controlling @value{GDBN}
139 * Sequences:: Canned sequences of commands
140 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
141 * Annotations:: @value{GDBN}'s annotation interface.
142 * GDB/MI:: @value{GDBN}'s Machine Interface.
144 * GDB Bugs:: Reporting bugs in @value{GDBN}
145 * Formatting Documentation:: How to format and print @value{GDBN} documentation
147 * Command Line Editing:: Command Line Editing
148 * Using History Interactively:: Using History Interactively
149 * Installing GDB:: Installing GDB
155 @c the replication sucks, but this avoids a texinfo 3.12 lameness
160 @top Debugging with @value{GDBN}
162 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
164 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
167 Copyright (C) 1988-2000 Free Software Foundation, Inc.
170 * Summary:: Summary of @value{GDBN}
171 * Sample Session:: A sample @value{GDBN} session
173 * Invocation:: Getting in and out of @value{GDBN}
174 * Commands:: @value{GDBN} commands
175 * Running:: Running programs under @value{GDBN}
176 * Stopping:: Stopping and continuing
177 * Stack:: Examining the stack
178 * Source:: Examining source files
179 * Data:: Examining data
181 * Languages:: Using @value{GDBN} with different languages
183 * Symbols:: Examining the symbol table
184 * Altering:: Altering execution
185 * GDB Files:: @value{GDBN} files
186 * Targets:: Specifying a debugging target
187 * Configurations:: Configuration-specific information
188 * Controlling GDB:: Controlling @value{GDBN}
189 * Sequences:: Canned sequences of commands
190 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
191 * Annotations:: @value{GDBN}'s annotation interface.
193 * GDB Bugs:: Reporting bugs in @value{GDBN}
194 * Formatting Documentation:: How to format and print @value{GDBN} documentation
196 * Command Line Editing:: Command Line Editing
197 * Using History Interactively:: Using History Interactively
198 * Installing GDB:: Installing GDB
204 @c TeX can handle the contents at the start but makeinfo 3.12 can not
210 @unnumbered Summary of @value{GDBN}
212 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
213 going on ``inside'' another program while it executes---or what another
214 program was doing at the moment it crashed.
216 @value{GDBN} can do four main kinds of things (plus other things in support of
217 these) to help you catch bugs in the act:
221 Start your program, specifying anything that might affect its behavior.
224 Make your program stop on specified conditions.
227 Examine what has happened, when your program has stopped.
230 Change things in your program, so you can experiment with correcting the
231 effects of one bug and go on to learn about another.
234 You can use @value{GDBN} to debug programs written in C and C++.
235 For more information, see @ref{Support,,Supported languages}.
236 For more information, see @ref{C,,C and C++}.
240 Support for Modula-2 and Chill is partial. For information on Modula-2,
241 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
244 Debugging Pascal programs which use sets, subranges, file variables, or
245 nested functions does not currently work. @value{GDBN} does not support
246 entering expressions, printing values, or similar features using Pascal
250 @value{GDBN} can be used to debug programs written in Fortran, although
251 it may be necessary to refer to some variables with a trailing
255 * Free Software:: Freely redistributable software
256 * Contributors:: Contributors to GDB
260 @unnumberedsec Free software
262 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
263 General Public License
264 (GPL). The GPL gives you the freedom to copy or adapt a licensed
265 program---but every person getting a copy also gets with it the
266 freedom to modify that copy (which means that they must get access to
267 the source code), and the freedom to distribute further copies.
268 Typical software companies use copyrights to limit your freedoms; the
269 Free Software Foundation uses the GPL to preserve these freedoms.
271 Fundamentally, the General Public License is a license which says that
272 you have these freedoms and that you cannot take these freedoms away
276 @unnumberedsec Contributors to @value{GDBN}
278 Richard Stallman was the original author of @value{GDBN}, and of many
279 other @sc{gnu} programs. Many others have contributed to its
280 development. This section attempts to credit major contributors. One
281 of the virtues of free software is that everyone is free to contribute
282 to it; with regret, we cannot actually acknowledge everyone here. The
283 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
284 blow-by-blow account.
286 Changes much prior to version 2.0 are lost in the mists of time.
289 @emph{Plea:} Additions to this section are particularly welcome. If you
290 or your friends (or enemies, to be evenhanded) have been unfairly
291 omitted from this list, we would like to add your names!
294 So that they may not regard their many labors as thankless, we
295 particularly thank those who shepherded @value{GDBN} through major
297 Andrew Cagney (releases 5.0 and 5.1);
298 Jim Blandy (release 4.18);
299 Jason Molenda (release 4.17);
300 Stan Shebs (release 4.14);
301 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
302 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
303 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
304 Jim Kingdon (releases 3.5, 3.4, and 3.3);
305 and Randy Smith (releases 3.2, 3.1, and 3.0).
307 Richard Stallman, assisted at various times by Peter TerMaat, Chris
308 Hanson, and Richard Mlynarik, handled releases through 2.8.
310 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
311 in @value{GDBN}, with significant additional contributions from Per
312 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
313 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
314 much general update work leading to release 3.0).
316 @value{GDBN} uses the BFD subroutine library to examine multiple
317 object-file formats; BFD was a joint project of David V.
318 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
320 David Johnson wrote the original COFF support; Pace Willison did
321 the original support for encapsulated COFF.
323 Brent Benson of Harris Computer Systems contributed DWARF2 support.
325 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
326 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
328 Jean-Daniel Fekete contributed Sun 386i support.
329 Chris Hanson improved the HP9000 support.
330 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
331 David Johnson contributed Encore Umax support.
332 Jyrki Kuoppala contributed Altos 3068 support.
333 Jeff Law contributed HP PA and SOM support.
334 Keith Packard contributed NS32K support.
335 Doug Rabson contributed Acorn Risc Machine support.
336 Bob Rusk contributed Harris Nighthawk CX-UX support.
337 Chris Smith contributed Convex support (and Fortran debugging).
338 Jonathan Stone contributed Pyramid support.
339 Michael Tiemann contributed SPARC support.
340 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
341 Pace Willison contributed Intel 386 support.
342 Jay Vosburgh contributed Symmetry support.
344 Andreas Schwab contributed M68K Linux support.
346 Rich Schaefer and Peter Schauer helped with support of SunOS shared
349 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
350 about several machine instruction sets.
352 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
353 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
354 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
355 and RDI targets, respectively.
357 Brian Fox is the author of the readline libraries providing
358 command-line editing and command history.
360 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
361 Modula-2 support, and contributed the Languages chapter of this manual.
363 Fred Fish wrote most of the support for Unix System Vr4.
364 He also enhanced the command-completion support to cover C@t{++} overloaded
367 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
370 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
372 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
374 Toshiba sponsored the support for the TX39 Mips processor.
376 Matsushita sponsored the support for the MN10200 and MN10300 processors.
378 Fujitsu sponsored the support for SPARClite and FR30 processors.
380 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
383 Michael Snyder added support for tracepoints.
385 Stu Grossman wrote gdbserver.
387 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
388 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
390 The following people at the Hewlett-Packard Company contributed
391 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
392 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
393 compiler, and the terminal user interface: Ben Krepp, Richard Title,
394 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
395 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
396 information in this manual.
398 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
399 Robert Hoehne made significant contributions to the DJGPP port.
401 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
402 development since 1991. Cygnus engineers who have worked on @value{GDBN}
403 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
404 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
405 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
406 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
407 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
408 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
409 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
410 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
411 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
412 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
413 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
414 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
415 Zuhn have made contributions both large and small.
419 @chapter A Sample @value{GDBN} Session
421 You can use this manual at your leisure to read all about @value{GDBN}.
422 However, a handful of commands are enough to get started using the
423 debugger. This chapter illustrates those commands.
426 In this sample session, we emphasize user input like this: @b{input},
427 to make it easier to pick out from the surrounding output.
430 @c FIXME: this example may not be appropriate for some configs, where
431 @c FIXME...primary interest is in remote use.
433 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
434 processor) exhibits the following bug: sometimes, when we change its
435 quote strings from the default, the commands used to capture one macro
436 definition within another stop working. In the following short @code{m4}
437 session, we define a macro @code{foo} which expands to @code{0000}; we
438 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
439 same thing. However, when we change the open quote string to
440 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
441 procedure fails to define a new synonym @code{baz}:
450 @b{define(bar,defn(`foo'))}
454 @b{changequote(<QUOTE>,<UNQUOTE>)}
456 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
459 m4: End of input: 0: fatal error: EOF in string
463 Let us use @value{GDBN} to try to see what is going on.
466 $ @b{@value{GDBP} m4}
467 @c FIXME: this falsifies the exact text played out, to permit smallbook
468 @c FIXME... format to come out better.
469 @value{GDBN} is free software and you are welcome to distribute copies
470 of it under certain conditions; type "show copying" to see
472 There is absolutely no warranty for @value{GDBN}; type "show warranty"
475 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
480 @value{GDBN} reads only enough symbol data to know where to find the
481 rest when needed; as a result, the first prompt comes up very quickly.
482 We now tell @value{GDBN} to use a narrower display width than usual, so
483 that examples fit in this manual.
486 (@value{GDBP}) @b{set width 70}
490 We need to see how the @code{m4} built-in @code{changequote} works.
491 Having looked at the source, we know the relevant subroutine is
492 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
493 @code{break} command.
496 (@value{GDBP}) @b{break m4_changequote}
497 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
501 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
502 control; as long as control does not reach the @code{m4_changequote}
503 subroutine, the program runs as usual:
506 (@value{GDBP}) @b{run}
507 Starting program: /work/Editorial/gdb/gnu/m4/m4
515 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
516 suspends execution of @code{m4}, displaying information about the
517 context where it stops.
520 @b{changequote(<QUOTE>,<UNQUOTE>)}
522 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
524 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
528 Now we use the command @code{n} (@code{next}) to advance execution to
529 the next line of the current function.
533 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
538 @code{set_quotes} looks like a promising subroutine. We can go into it
539 by using the command @code{s} (@code{step}) instead of @code{next}.
540 @code{step} goes to the next line to be executed in @emph{any}
541 subroutine, so it steps into @code{set_quotes}.
545 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
547 530 if (lquote != def_lquote)
551 The display that shows the subroutine where @code{m4} is now
552 suspended (and its arguments) is called a stack frame display. It
553 shows a summary of the stack. We can use the @code{backtrace}
554 command (which can also be spelled @code{bt}), to see where we are
555 in the stack as a whole: the @code{backtrace} command displays a
556 stack frame for each active subroutine.
559 (@value{GDBP}) @b{bt}
560 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
562 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
564 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
565 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
567 #4 0x79dc in expand_input () at macro.c:40
568 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
572 We step through a few more lines to see what happens. The first two
573 times, we can use @samp{s}; the next two times we use @code{n} to avoid
574 falling into the @code{xstrdup} subroutine.
578 0x3b5c 532 if (rquote != def_rquote)
580 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
581 def_lquote : xstrdup(lq);
583 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
586 538 len_lquote = strlen(rquote);
590 The last line displayed looks a little odd; we can examine the variables
591 @code{lquote} and @code{rquote} to see if they are in fact the new left
592 and right quotes we specified. We use the command @code{p}
593 (@code{print}) to see their values.
596 (@value{GDBP}) @b{p lquote}
597 $1 = 0x35d40 "<QUOTE>"
598 (@value{GDBP}) @b{p rquote}
599 $2 = 0x35d50 "<UNQUOTE>"
603 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
604 To look at some context, we can display ten lines of source
605 surrounding the current line with the @code{l} (@code{list}) command.
611 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
613 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
616 538 len_lquote = strlen(rquote);
617 539 len_rquote = strlen(lquote);
624 Let us step past the two lines that set @code{len_lquote} and
625 @code{len_rquote}, and then examine the values of those variables.
629 539 len_rquote = strlen(lquote);
632 (@value{GDBP}) @b{p len_lquote}
634 (@value{GDBP}) @b{p len_rquote}
639 That certainly looks wrong, assuming @code{len_lquote} and
640 @code{len_rquote} are meant to be the lengths of @code{lquote} and
641 @code{rquote} respectively. We can set them to better values using
642 the @code{p} command, since it can print the value of
643 any expression---and that expression can include subroutine calls and
647 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
649 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
654 Is that enough to fix the problem of using the new quotes with the
655 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
656 executing with the @code{c} (@code{continue}) command, and then try the
657 example that caused trouble initially:
663 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
670 Success! The new quotes now work just as well as the default ones. The
671 problem seems to have been just the two typos defining the wrong
672 lengths. We allow @code{m4} exit by giving it an EOF as input:
676 Program exited normally.
680 The message @samp{Program exited normally.} is from @value{GDBN}; it
681 indicates @code{m4} has finished executing. We can end our @value{GDBN}
682 session with the @value{GDBN} @code{quit} command.
685 (@value{GDBP}) @b{quit}
689 @chapter Getting In and Out of @value{GDBN}
691 This chapter discusses how to start @value{GDBN}, and how to get out of it.
695 type @samp{@value{GDBP}} to start @value{GDBN}.
697 type @kbd{quit} or @kbd{C-d} to exit.
701 * Invoking GDB:: How to start @value{GDBN}
702 * Quitting GDB:: How to quit @value{GDBN}
703 * Shell Commands:: How to use shell commands inside @value{GDBN}
707 @section Invoking @value{GDBN}
709 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
710 @value{GDBN} reads commands from the terminal until you tell it to exit.
712 You can also run @code{@value{GDBP}} with a variety of arguments and options,
713 to specify more of your debugging environment at the outset.
715 The command-line options described here are designed
716 to cover a variety of situations; in some environments, some of these
717 options may effectively be unavailable.
719 The most usual way to start @value{GDBN} is with one argument,
720 specifying an executable program:
723 @value{GDBP} @var{program}
727 You can also start with both an executable program and a core file
731 @value{GDBP} @var{program} @var{core}
734 You can, instead, specify a process ID as a second argument, if you want
735 to debug a running process:
738 @value{GDBP} @var{program} 1234
742 would attach @value{GDBN} to process @code{1234} (unless you also have a file
743 named @file{1234}; @value{GDBN} does check for a core file first).
745 Taking advantage of the second command-line argument requires a fairly
746 complete operating system; when you use @value{GDBN} as a remote
747 debugger attached to a bare board, there may not be any notion of
748 ``process'', and there is often no way to get a core dump. @value{GDBN}
749 will warn you if it is unable to attach or to read core dumps.
751 You can run @code{@value{GDBP}} without printing the front material, which describes
752 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
759 You can further control how @value{GDBN} starts up by using command-line
760 options. @value{GDBN} itself can remind you of the options available.
770 to display all available options and briefly describe their use
771 (@samp{@value{GDBP} -h} is a shorter equivalent).
773 All options and command line arguments you give are processed
774 in sequential order. The order makes a difference when the
775 @samp{-x} option is used.
779 * File Options:: Choosing files
780 * Mode Options:: Choosing modes
784 @subsection Choosing files
786 When @value{GDBN} starts, it reads any arguments other than options as
787 specifying an executable file and core file (or process ID). This is
788 the same as if the arguments were specified by the @samp{-se} and
789 @samp{-c} options respectively. (@value{GDBN} reads the first argument
790 that does not have an associated option flag as equivalent to the
791 @samp{-se} option followed by that argument; and the second argument
792 that does not have an associated option flag, if any, as equivalent to
793 the @samp{-c} option followed by that argument.)
795 If @value{GDBN} has not been configured to included core file support,
796 such as for most embedded targets, then it will complain about a second
797 argument and ignore it.
799 Many options have both long and short forms; both are shown in the
800 following list. @value{GDBN} also recognizes the long forms if you truncate
801 them, so long as enough of the option is present to be unambiguous.
802 (If you prefer, you can flag option arguments with @samp{--} rather
803 than @samp{-}, though we illustrate the more usual convention.)
805 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
806 @c way, both those who look for -foo and --foo in the index, will find
810 @item -symbols @var{file}
812 @cindex @code{--symbols}
814 Read symbol table from file @var{file}.
816 @item -exec @var{file}
818 @cindex @code{--exec}
820 Use file @var{file} as the executable file to execute when appropriate,
821 and for examining pure data in conjunction with a core dump.
825 Read symbol table from file @var{file} and use it as the executable
828 @item -core @var{file}
830 @cindex @code{--core}
832 Use file @var{file} as a core dump to examine.
834 @item -c @var{number}
835 Connect to process ID @var{number}, as with the @code{attach} command
836 (unless there is a file in core-dump format named @var{number}, in which
837 case @samp{-c} specifies that file as a core dump to read).
839 @item -command @var{file}
841 @cindex @code{--command}
843 Execute @value{GDBN} commands from file @var{file}. @xref{Command
844 Files,, Command files}.
846 @item -directory @var{directory}
847 @itemx -d @var{directory}
848 @cindex @code{--directory}
850 Add @var{directory} to the path to search for source files.
854 @cindex @code{--mapped}
856 @emph{Warning: this option depends on operating system facilities that are not
857 supported on all systems.}@*
858 If memory-mapped files are available on your system through the @code{mmap}
859 system call, you can use this option
860 to have @value{GDBN} write the symbols from your
861 program into a reusable file in the current directory. If the program you are debugging is
862 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
863 Future @value{GDBN} debugging sessions notice the presence of this file,
864 and can quickly map in symbol information from it, rather than reading
865 the symbol table from the executable program.
867 The @file{.syms} file is specific to the host machine where @value{GDBN}
868 is run. It holds an exact image of the internal @value{GDBN} symbol
869 table. It cannot be shared across multiple host platforms.
873 @cindex @code{--readnow}
875 Read each symbol file's entire symbol table immediately, rather than
876 the default, which is to read it incrementally as it is needed.
877 This makes startup slower, but makes future operations faster.
881 You typically combine the @code{-mapped} and @code{-readnow} options in
882 order to build a @file{.syms} file that contains complete symbol
883 information. (@xref{Files,,Commands to specify files}, for information
884 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
885 but build a @file{.syms} file for future use is:
888 gdb -batch -nx -mapped -readnow programname
892 @subsection Choosing modes
894 You can run @value{GDBN} in various alternative modes---for example, in
895 batch mode or quiet mode.
902 Do not execute commands found in any initialization files (normally
903 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
904 @value{GDBN} executes the commands in these files after all the command
905 options and arguments have been processed. @xref{Command Files,,Command
911 @cindex @code{--quiet}
912 @cindex @code{--silent}
914 ``Quiet''. Do not print the introductory and copyright messages. These
915 messages are also suppressed in batch mode.
918 @cindex @code{--batch}
919 Run in batch mode. Exit with status @code{0} after processing all the
920 command files specified with @samp{-x} (and all commands from
921 initialization files, if not inhibited with @samp{-n}). Exit with
922 nonzero status if an error occurs in executing the @value{GDBN} commands
923 in the command files.
925 Batch mode may be useful for running @value{GDBN} as a filter, for
926 example to download and run a program on another computer; in order to
927 make this more useful, the message
930 Program exited normally.
934 (which is ordinarily issued whenever a program running under
935 @value{GDBN} control terminates) is not issued when running in batch
940 @cindex @code{--nowindows}
942 ``No windows''. If @value{GDBN} comes with a graphical user interface
943 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
944 interface. If no GUI is available, this option has no effect.
948 @cindex @code{--windows}
950 If @value{GDBN} includes a GUI, then this option requires it to be
953 @item -cd @var{directory}
955 Run @value{GDBN} using @var{directory} as its working directory,
956 instead of the current directory.
960 @cindex @code{--fullname}
962 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
963 subprocess. It tells @value{GDBN} to output the full file name and line
964 number in a standard, recognizable fashion each time a stack frame is
965 displayed (which includes each time your program stops). This
966 recognizable format looks like two @samp{\032} characters, followed by
967 the file name, line number and character position separated by colons,
968 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
969 @samp{\032} characters as a signal to display the source code for the
973 @cindex @code{--epoch}
974 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
975 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
976 routines so as to allow Epoch to display values of expressions in a
979 @item -annotate @var{level}
980 @cindex @code{--annotate}
981 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
982 effect is identical to using @samp{set annotate @var{level}}
983 (@pxref{Annotations}).
984 Annotation level controls how much information does @value{GDBN} print
985 together with its prompt, values of expressions, source lines, and other
986 types of output. Level 0 is the normal, level 1 is for use when
987 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
988 maximum annotation suitable for programs that control @value{GDBN}.
991 @cindex @code{--async}
992 Use the asynchronous event loop for the command-line interface.
993 @value{GDBN} processes all events, such as user keyboard input, via a
994 special event loop. This allows @value{GDBN} to accept and process user
995 commands in parallel with the debugged process being
996 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
997 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
998 suspended when the debuggee runs.}, so you don't need to wait for
999 control to return to @value{GDBN} before you type the next command.
1000 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1001 operation is not yet in place, so @samp{-async} does not work fully
1003 @c FIXME: when the target side of the event loop is done, the above NOTE
1004 @c should be removed.
1006 When the standard input is connected to a terminal device, @value{GDBN}
1007 uses the asynchronous event loop by default, unless disabled by the
1008 @samp{-noasync} option.
1011 @cindex @code{--noasync}
1012 Disable the asynchronous event loop for the command-line interface.
1014 @item -baud @var{bps}
1016 @cindex @code{--baud}
1018 Set the line speed (baud rate or bits per second) of any serial
1019 interface used by @value{GDBN} for remote debugging.
1021 @item -tty @var{device}
1022 @itemx -t @var{device}
1023 @cindex @code{--tty}
1025 Run using @var{device} for your program's standard input and output.
1026 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1028 @c resolve the situation of these eventually
1030 @c @cindex @code{--tui}
1031 @c Use a Terminal User Interface. For information, use your Web browser to
1032 @c read the file @file{TUI.html}, which is usually installed in the
1033 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1034 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1035 @c @value{GDBN} under @sc{gnu} Emacs}).
1038 @c @cindex @code{--xdb}
1039 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1040 @c For information, see the file @file{xdb_trans.html}, which is usually
1041 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1044 @item -interpreter @var{interp}
1045 @cindex @code{--interpreter}
1046 Use the interpreter @var{interp} for interface with the controlling
1047 program or device. This option is meant to be set by programs which
1048 communicate with @value{GDBN} using it as a back end. For example,
1049 @samp{--interpreter=mi} causes @value{GDBN} to use the @dfn{gdbmi
1050 interface} (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}).
1053 @cindex @code{--write}
1054 Open the executable and core files for both reading and writing. This
1055 is equivalent to the @samp{set write on} command inside @value{GDBN}
1059 @cindex @code{--statistics}
1060 This option causes @value{GDBN} to print statistics about time and
1061 memory usage after it completes each command and returns to the prompt.
1064 @cindex @code{--version}
1065 This option causes @value{GDBN} to print its version number and
1066 no-warranty blurb, and exit.
1071 @section Quitting @value{GDBN}
1072 @cindex exiting @value{GDBN}
1073 @cindex leaving @value{GDBN}
1076 @kindex quit @r{[}@var{expression}@r{]}
1077 @kindex q @r{(@code{quit})}
1078 @item quit @r{[}@var{expression}@r{]}
1080 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1081 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1082 do not supply @var{expression}, @value{GDBN} will terminate normally;
1083 otherwise it will terminate using the result of @var{expression} as the
1088 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1089 terminates the action of any @value{GDBN} command that is in progress and
1090 returns to @value{GDBN} command level. It is safe to type the interrupt
1091 character at any time because @value{GDBN} does not allow it to take effect
1092 until a time when it is safe.
1094 If you have been using @value{GDBN} to control an attached process or
1095 device, you can release it with the @code{detach} command
1096 (@pxref{Attach, ,Debugging an already-running process}).
1098 @node Shell Commands
1099 @section Shell commands
1101 If you need to execute occasional shell commands during your
1102 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1103 just use the @code{shell} command.
1107 @cindex shell escape
1108 @item shell @var{command string}
1109 Invoke a standard shell to execute @var{command string}.
1110 If it exists, the environment variable @code{SHELL} determines which
1111 shell to run. Otherwise @value{GDBN} uses the default shell
1112 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1115 The utility @code{make} is often needed in development environments.
1116 You do not have to use the @code{shell} command for this purpose in
1121 @cindex calling make
1122 @item make @var{make-args}
1123 Execute the @code{make} program with the specified
1124 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1128 @chapter @value{GDBN} Commands
1130 You can abbreviate a @value{GDBN} command to the first few letters of the command
1131 name, if that abbreviation is unambiguous; and you can repeat certain
1132 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1133 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1134 show you the alternatives available, if there is more than one possibility).
1137 * Command Syntax:: How to give commands to @value{GDBN}
1138 * Completion:: Command completion
1139 * Help:: How to ask @value{GDBN} for help
1142 @node Command Syntax
1143 @section Command syntax
1145 A @value{GDBN} command is a single line of input. There is no limit on
1146 how long it can be. It starts with a command name, which is followed by
1147 arguments whose meaning depends on the command name. For example, the
1148 command @code{step} accepts an argument which is the number of times to
1149 step, as in @samp{step 5}. You can also use the @code{step} command
1150 with no arguments. Some commands do not allow any arguments.
1152 @cindex abbreviation
1153 @value{GDBN} command names may always be truncated if that abbreviation is
1154 unambiguous. Other possible command abbreviations are listed in the
1155 documentation for individual commands. In some cases, even ambiguous
1156 abbreviations are allowed; for example, @code{s} is specially defined as
1157 equivalent to @code{step} even though there are other commands whose
1158 names start with @code{s}. You can test abbreviations by using them as
1159 arguments to the @code{help} command.
1161 @cindex repeating commands
1162 @kindex RET @r{(repeat last command)}
1163 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1164 repeat the previous command. Certain commands (for example, @code{run})
1165 will not repeat this way; these are commands whose unintentional
1166 repetition might cause trouble and which you are unlikely to want to
1169 The @code{list} and @code{x} commands, when you repeat them with
1170 @key{RET}, construct new arguments rather than repeating
1171 exactly as typed. This permits easy scanning of source or memory.
1173 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1174 output, in a way similar to the common utility @code{more}
1175 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1176 @key{RET} too many in this situation, @value{GDBN} disables command
1177 repetition after any command that generates this sort of display.
1179 @kindex # @r{(a comment)}
1181 Any text from a @kbd{#} to the end of the line is a comment; it does
1182 nothing. This is useful mainly in command files (@pxref{Command
1183 Files,,Command files}).
1186 @section Command completion
1189 @cindex word completion
1190 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1191 only one possibility; it can also show you what the valid possibilities
1192 are for the next word in a command, at any time. This works for @value{GDBN}
1193 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1195 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1196 of a word. If there is only one possibility, @value{GDBN} fills in the
1197 word, and waits for you to finish the command (or press @key{RET} to
1198 enter it). For example, if you type
1200 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1201 @c complete accuracy in these examples; space introduced for clarity.
1202 @c If texinfo enhancements make it unnecessary, it would be nice to
1203 @c replace " @key" by "@key" in the following...
1205 (@value{GDBP}) info bre @key{TAB}
1209 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1210 the only @code{info} subcommand beginning with @samp{bre}:
1213 (@value{GDBP}) info breakpoints
1217 You can either press @key{RET} at this point, to run the @code{info
1218 breakpoints} command, or backspace and enter something else, if
1219 @samp{breakpoints} does not look like the command you expected. (If you
1220 were sure you wanted @code{info breakpoints} in the first place, you
1221 might as well just type @key{RET} immediately after @samp{info bre},
1222 to exploit command abbreviations rather than command completion).
1224 If there is more than one possibility for the next word when you press
1225 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1226 characters and try again, or just press @key{TAB} a second time;
1227 @value{GDBN} displays all the possible completions for that word. For
1228 example, you might want to set a breakpoint on a subroutine whose name
1229 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1230 just sounds the bell. Typing @key{TAB} again displays all the
1231 function names in your program that begin with those characters, for
1235 (@value{GDBP}) b make_ @key{TAB}
1236 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1237 make_a_section_from_file make_environ
1238 make_abs_section make_function_type
1239 make_blockvector make_pointer_type
1240 make_cleanup make_reference_type
1241 make_command make_symbol_completion_list
1242 (@value{GDBP}) b make_
1246 After displaying the available possibilities, @value{GDBN} copies your
1247 partial input (@samp{b make_} in the example) so you can finish the
1250 If you just want to see the list of alternatives in the first place, you
1251 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1252 means @kbd{@key{META} ?}. You can type this either by holding down a
1253 key designated as the @key{META} shift on your keyboard (if there is
1254 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1256 @cindex quotes in commands
1257 @cindex completion of quoted strings
1258 Sometimes the string you need, while logically a ``word'', may contain
1259 parentheses or other characters that @value{GDBN} normally excludes from
1260 its notion of a word. To permit word completion to work in this
1261 situation, you may enclose words in @code{'} (single quote marks) in
1262 @value{GDBN} commands.
1264 The most likely situation where you might need this is in typing the
1265 name of a C@t{++} function. This is because C@t{++} allows function
1266 overloading (multiple definitions of the same function, distinguished
1267 by argument type). For example, when you want to set a breakpoint you
1268 may need to distinguish whether you mean the version of @code{name}
1269 that takes an @code{int} parameter, @code{name(int)}, or the version
1270 that takes a @code{float} parameter, @code{name(float)}. To use the
1271 word-completion facilities in this situation, type a single quote
1272 @code{'} at the beginning of the function name. This alerts
1273 @value{GDBN} that it may need to consider more information than usual
1274 when you press @key{TAB} or @kbd{M-?} to request word completion:
1277 (@value{GDBP}) b 'bubble( @kbd{M-?}
1278 bubble(double,double) bubble(int,int)
1279 (@value{GDBP}) b 'bubble(
1282 In some cases, @value{GDBN} can tell that completing a name requires using
1283 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1284 completing as much as it can) if you do not type the quote in the first
1288 (@value{GDBP}) b bub @key{TAB}
1289 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1290 (@value{GDBP}) b 'bubble(
1294 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1295 you have not yet started typing the argument list when you ask for
1296 completion on an overloaded symbol.
1298 For more information about overloaded functions, see @ref{C plus plus
1299 expressions, ,C@t{++} expressions}. You can use the command @code{set
1300 overload-resolution off} to disable overload resolution;
1301 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1305 @section Getting help
1306 @cindex online documentation
1309 You can always ask @value{GDBN} itself for information on its commands,
1310 using the command @code{help}.
1313 @kindex h @r{(@code{help})}
1316 You can use @code{help} (abbreviated @code{h}) with no arguments to
1317 display a short list of named classes of commands:
1321 List of classes of commands:
1323 aliases -- Aliases of other commands
1324 breakpoints -- Making program stop at certain points
1325 data -- Examining data
1326 files -- Specifying and examining files
1327 internals -- Maintenance commands
1328 obscure -- Obscure features
1329 running -- Running the program
1330 stack -- Examining the stack
1331 status -- Status inquiries
1332 support -- Support facilities
1333 tracepoints -- Tracing of program execution without@*
1334 stopping the program
1335 user-defined -- User-defined commands
1337 Type "help" followed by a class name for a list of
1338 commands in that class.
1339 Type "help" followed by command name for full
1341 Command name abbreviations are allowed if unambiguous.
1344 @c the above line break eliminates huge line overfull...
1346 @item help @var{class}
1347 Using one of the general help classes as an argument, you can get a
1348 list of the individual commands in that class. For example, here is the
1349 help display for the class @code{status}:
1352 (@value{GDBP}) help status
1357 @c Line break in "show" line falsifies real output, but needed
1358 @c to fit in smallbook page size.
1359 info -- Generic command for showing things
1360 about the program being debugged
1361 show -- Generic command for showing things
1364 Type "help" followed by command name for full
1366 Command name abbreviations are allowed if unambiguous.
1370 @item help @var{command}
1371 With a command name as @code{help} argument, @value{GDBN} displays a
1372 short paragraph on how to use that command.
1375 @item apropos @var{args}
1376 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1377 commands, and their documentation, for the regular expression specified in
1378 @var{args}. It prints out all matches found. For example:
1389 set symbol-reloading -- Set dynamic symbol table reloading
1390 multiple times in one run
1391 show symbol-reloading -- Show dynamic symbol table reloading
1392 multiple times in one run
1397 @item complete @var{args}
1398 The @code{complete @var{args}} command lists all the possible completions
1399 for the beginning of a command. Use @var{args} to specify the beginning of the
1400 command you want completed. For example:
1406 @noindent results in:
1417 @noindent This is intended for use by @sc{gnu} Emacs.
1420 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1421 and @code{show} to inquire about the state of your program, or the state
1422 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1423 manual introduces each of them in the appropriate context. The listings
1424 under @code{info} and under @code{show} in the Index point to
1425 all the sub-commands. @xref{Index}.
1430 @kindex i @r{(@code{info})}
1432 This command (abbreviated @code{i}) is for describing the state of your
1433 program. For example, you can list the arguments given to your program
1434 with @code{info args}, list the registers currently in use with @code{info
1435 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1436 You can get a complete list of the @code{info} sub-commands with
1437 @w{@code{help info}}.
1441 You can assign the result of an expression to an environment variable with
1442 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1443 @code{set prompt $}.
1447 In contrast to @code{info}, @code{show} is for describing the state of
1448 @value{GDBN} itself.
1449 You can change most of the things you can @code{show}, by using the
1450 related command @code{set}; for example, you can control what number
1451 system is used for displays with @code{set radix}, or simply inquire
1452 which is currently in use with @code{show radix}.
1455 To display all the settable parameters and their current
1456 values, you can use @code{show} with no arguments; you may also use
1457 @code{info set}. Both commands produce the same display.
1458 @c FIXME: "info set" violates the rule that "info" is for state of
1459 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1460 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1464 Here are three miscellaneous @code{show} subcommands, all of which are
1465 exceptional in lacking corresponding @code{set} commands:
1468 @kindex show version
1469 @cindex version number
1471 Show what version of @value{GDBN} is running. You should include this
1472 information in @value{GDBN} bug-reports. If multiple versions of
1473 @value{GDBN} are in use at your site, you may need to determine which
1474 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1475 commands are introduced, and old ones may wither away. Also, many
1476 system vendors ship variant versions of @value{GDBN}, and there are
1477 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1478 The version number is the same as the one announced when you start
1481 @kindex show copying
1483 Display information about permission for copying @value{GDBN}.
1485 @kindex show warranty
1487 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1488 if your version of @value{GDBN} comes with one.
1493 @chapter Running Programs Under @value{GDBN}
1495 When you run a program under @value{GDBN}, you must first generate
1496 debugging information when you compile it.
1498 You may start @value{GDBN} with its arguments, if any, in an environment
1499 of your choice. If you are doing native debugging, you may redirect
1500 your program's input and output, debug an already running process, or
1501 kill a child process.
1504 * Compilation:: Compiling for debugging
1505 * Starting:: Starting your program
1506 * Arguments:: Your program's arguments
1507 * Environment:: Your program's environment
1509 * Working Directory:: Your program's working directory
1510 * Input/Output:: Your program's input and output
1511 * Attach:: Debugging an already-running process
1512 * Kill Process:: Killing the child process
1514 * Threads:: Debugging programs with multiple threads
1515 * Processes:: Debugging programs with multiple processes
1519 @section Compiling for debugging
1521 In order to debug a program effectively, you need to generate
1522 debugging information when you compile it. This debugging information
1523 is stored in the object file; it describes the data type of each
1524 variable or function and the correspondence between source line numbers
1525 and addresses in the executable code.
1527 To request debugging information, specify the @samp{-g} option when you run
1530 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1531 options together. Using those compilers, you cannot generate optimized
1532 executables containing debugging information.
1534 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1535 without @samp{-O}, making it possible to debug optimized code. We
1536 recommend that you @emph{always} use @samp{-g} whenever you compile a
1537 program. You may think your program is correct, but there is no sense
1538 in pushing your luck.
1540 @cindex optimized code, debugging
1541 @cindex debugging optimized code
1542 When you debug a program compiled with @samp{-g -O}, remember that the
1543 optimizer is rearranging your code; the debugger shows you what is
1544 really there. Do not be too surprised when the execution path does not
1545 exactly match your source file! An extreme example: if you define a
1546 variable, but never use it, @value{GDBN} never sees that
1547 variable---because the compiler optimizes it out of existence.
1549 Some things do not work as well with @samp{-g -O} as with just
1550 @samp{-g}, particularly on machines with instruction scheduling. If in
1551 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1552 please report it to us as a bug (including a test case!).
1554 Older versions of the @sc{gnu} C compiler permitted a variant option
1555 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1556 format; if your @sc{gnu} C compiler has this option, do not use it.
1560 @section Starting your program
1566 @kindex r @r{(@code{run})}
1569 Use the @code{run} command to start your program under @value{GDBN}.
1570 You must first specify the program name (except on VxWorks) with an
1571 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1572 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1573 (@pxref{Files, ,Commands to specify files}).
1577 If you are running your program in an execution environment that
1578 supports processes, @code{run} creates an inferior process and makes
1579 that process run your program. (In environments without processes,
1580 @code{run} jumps to the start of your program.)
1582 The execution of a program is affected by certain information it
1583 receives from its superior. @value{GDBN} provides ways to specify this
1584 information, which you must do @emph{before} starting your program. (You
1585 can change it after starting your program, but such changes only affect
1586 your program the next time you start it.) This information may be
1587 divided into four categories:
1590 @item The @emph{arguments.}
1591 Specify the arguments to give your program as the arguments of the
1592 @code{run} command. If a shell is available on your target, the shell
1593 is used to pass the arguments, so that you may use normal conventions
1594 (such as wildcard expansion or variable substitution) in describing
1596 In Unix systems, you can control which shell is used with the
1597 @code{SHELL} environment variable.
1598 @xref{Arguments, ,Your program's arguments}.
1600 @item The @emph{environment.}
1601 Your program normally inherits its environment from @value{GDBN}, but you can
1602 use the @value{GDBN} commands @code{set environment} and @code{unset
1603 environment} to change parts of the environment that affect
1604 your program. @xref{Environment, ,Your program's environment}.
1606 @item The @emph{working directory.}
1607 Your program inherits its working directory from @value{GDBN}. You can set
1608 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1609 @xref{Working Directory, ,Your program's working directory}.
1611 @item The @emph{standard input and output.}
1612 Your program normally uses the same device for standard input and
1613 standard output as @value{GDBN} is using. You can redirect input and output
1614 in the @code{run} command line, or you can use the @code{tty} command to
1615 set a different device for your program.
1616 @xref{Input/Output, ,Your program's input and output}.
1619 @emph{Warning:} While input and output redirection work, you cannot use
1620 pipes to pass the output of the program you are debugging to another
1621 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1625 When you issue the @code{run} command, your program begins to execute
1626 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1627 of how to arrange for your program to stop. Once your program has
1628 stopped, you may call functions in your program, using the @code{print}
1629 or @code{call} commands. @xref{Data, ,Examining Data}.
1631 If the modification time of your symbol file has changed since the last
1632 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1633 table, and reads it again. When it does this, @value{GDBN} tries to retain
1634 your current breakpoints.
1637 @section Your program's arguments
1639 @cindex arguments (to your program)
1640 The arguments to your program can be specified by the arguments of the
1642 They are passed to a shell, which expands wildcard characters and
1643 performs redirection of I/O, and thence to your program. Your
1644 @code{SHELL} environment variable (if it exists) specifies what shell
1645 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1646 the default shell (@file{/bin/sh} on Unix).
1648 On non-Unix systems, the program is usually invoked directly by
1649 @value{GDBN}, which emulates I/O redirection via the appropriate system
1650 calls, and the wildcard characters are expanded by the startup code of
1651 the program, not by the shell.
1653 @code{run} with no arguments uses the same arguments used by the previous
1654 @code{run}, or those set by the @code{set args} command.
1659 Specify the arguments to be used the next time your program is run. If
1660 @code{set args} has no arguments, @code{run} executes your program
1661 with no arguments. Once you have run your program with arguments,
1662 using @code{set args} before the next @code{run} is the only way to run
1663 it again without arguments.
1667 Show the arguments to give your program when it is started.
1671 @section Your program's environment
1673 @cindex environment (of your program)
1674 The @dfn{environment} consists of a set of environment variables and
1675 their values. Environment variables conventionally record such things as
1676 your user name, your home directory, your terminal type, and your search
1677 path for programs to run. Usually you set up environment variables with
1678 the shell and they are inherited by all the other programs you run. When
1679 debugging, it can be useful to try running your program with a modified
1680 environment without having to start @value{GDBN} over again.
1684 @item path @var{directory}
1685 Add @var{directory} to the front of the @code{PATH} environment variable
1686 (the search path for executables) that will be passed to your program.
1687 The value of @code{PATH} used by @value{GDBN} does not change.
1688 You may specify several directory names, separated by whitespace or by a
1689 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1690 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1691 is moved to the front, so it is searched sooner.
1693 You can use the string @samp{$cwd} to refer to whatever is the current
1694 working directory at the time @value{GDBN} searches the path. If you
1695 use @samp{.} instead, it refers to the directory where you executed the
1696 @code{path} command. @value{GDBN} replaces @samp{.} in the
1697 @var{directory} argument (with the current path) before adding
1698 @var{directory} to the search path.
1699 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1700 @c document that, since repeating it would be a no-op.
1704 Display the list of search paths for executables (the @code{PATH}
1705 environment variable).
1707 @kindex show environment
1708 @item show environment @r{[}@var{varname}@r{]}
1709 Print the value of environment variable @var{varname} to be given to
1710 your program when it starts. If you do not supply @var{varname},
1711 print the names and values of all environment variables to be given to
1712 your program. You can abbreviate @code{environment} as @code{env}.
1714 @kindex set environment
1715 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1716 Set environment variable @var{varname} to @var{value}. The value
1717 changes for your program only, not for @value{GDBN} itself. @var{value} may
1718 be any string; the values of environment variables are just strings, and
1719 any interpretation is supplied by your program itself. The @var{value}
1720 parameter is optional; if it is eliminated, the variable is set to a
1722 @c "any string" here does not include leading, trailing
1723 @c blanks. Gnu asks: does anyone care?
1725 For example, this command:
1732 tells the debugged program, when subsequently run, that its user is named
1733 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1734 are not actually required.)
1736 @kindex unset environment
1737 @item unset environment @var{varname}
1738 Remove variable @var{varname} from the environment to be passed to your
1739 program. This is different from @samp{set env @var{varname} =};
1740 @code{unset environment} removes the variable from the environment,
1741 rather than assigning it an empty value.
1744 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1746 by your @code{SHELL} environment variable if it exists (or
1747 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1748 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1749 @file{.bashrc} for BASH---any variables you set in that file affect
1750 your program. You may wish to move setting of environment variables to
1751 files that are only run when you sign on, such as @file{.login} or
1754 @node Working Directory
1755 @section Your program's working directory
1757 @cindex working directory (of your program)
1758 Each time you start your program with @code{run}, it inherits its
1759 working directory from the current working directory of @value{GDBN}.
1760 The @value{GDBN} working directory is initially whatever it inherited
1761 from its parent process (typically the shell), but you can specify a new
1762 working directory in @value{GDBN} with the @code{cd} command.
1764 The @value{GDBN} working directory also serves as a default for the commands
1765 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1770 @item cd @var{directory}
1771 Set the @value{GDBN} working directory to @var{directory}.
1775 Print the @value{GDBN} working directory.
1779 @section Your program's input and output
1784 By default, the program you run under @value{GDBN} does input and output to
1785 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1786 to its own terminal modes to interact with you, but it records the terminal
1787 modes your program was using and switches back to them when you continue
1788 running your program.
1791 @kindex info terminal
1793 Displays information recorded by @value{GDBN} about the terminal modes your
1797 You can redirect your program's input and/or output using shell
1798 redirection with the @code{run} command. For example,
1805 starts your program, diverting its output to the file @file{outfile}.
1808 @cindex controlling terminal
1809 Another way to specify where your program should do input and output is
1810 with the @code{tty} command. This command accepts a file name as
1811 argument, and causes this file to be the default for future @code{run}
1812 commands. It also resets the controlling terminal for the child
1813 process, for future @code{run} commands. For example,
1820 directs that processes started with subsequent @code{run} commands
1821 default to do input and output on the terminal @file{/dev/ttyb} and have
1822 that as their controlling terminal.
1824 An explicit redirection in @code{run} overrides the @code{tty} command's
1825 effect on the input/output device, but not its effect on the controlling
1828 When you use the @code{tty} command or redirect input in the @code{run}
1829 command, only the input @emph{for your program} is affected. The input
1830 for @value{GDBN} still comes from your terminal.
1833 @section Debugging an already-running process
1838 @item attach @var{process-id}
1839 This command attaches to a running process---one that was started
1840 outside @value{GDBN}. (@code{info files} shows your active
1841 targets.) The command takes as argument a process ID. The usual way to
1842 find out the process-id of a Unix process is with the @code{ps} utility,
1843 or with the @samp{jobs -l} shell command.
1845 @code{attach} does not repeat if you press @key{RET} a second time after
1846 executing the command.
1849 To use @code{attach}, your program must be running in an environment
1850 which supports processes; for example, @code{attach} does not work for
1851 programs on bare-board targets that lack an operating system. You must
1852 also have permission to send the process a signal.
1854 When you use @code{attach}, the debugger finds the program running in
1855 the process first by looking in the current working directory, then (if
1856 the program is not found) by using the source file search path
1857 (@pxref{Source Path, ,Specifying source directories}). You can also use
1858 the @code{file} command to load the program. @xref{Files, ,Commands to
1861 The first thing @value{GDBN} does after arranging to debug the specified
1862 process is to stop it. You can examine and modify an attached process
1863 with all the @value{GDBN} commands that are ordinarily available when
1864 you start processes with @code{run}. You can insert breakpoints; you
1865 can step and continue; you can modify storage. If you would rather the
1866 process continue running, you may use the @code{continue} command after
1867 attaching @value{GDBN} to the process.
1872 When you have finished debugging the attached process, you can use the
1873 @code{detach} command to release it from @value{GDBN} control. Detaching
1874 the process continues its execution. After the @code{detach} command,
1875 that process and @value{GDBN} become completely independent once more, and you
1876 are ready to @code{attach} another process or start one with @code{run}.
1877 @code{detach} does not repeat if you press @key{RET} again after
1878 executing the command.
1881 If you exit @value{GDBN} or use the @code{run} command while you have an
1882 attached process, you kill that process. By default, @value{GDBN} asks
1883 for confirmation if you try to do either of these things; you can
1884 control whether or not you need to confirm by using the @code{set
1885 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1889 @section Killing the child process
1894 Kill the child process in which your program is running under @value{GDBN}.
1897 This command is useful if you wish to debug a core dump instead of a
1898 running process. @value{GDBN} ignores any core dump file while your program
1901 On some operating systems, a program cannot be executed outside @value{GDBN}
1902 while you have breakpoints set on it inside @value{GDBN}. You can use the
1903 @code{kill} command in this situation to permit running your program
1904 outside the debugger.
1906 The @code{kill} command is also useful if you wish to recompile and
1907 relink your program, since on many systems it is impossible to modify an
1908 executable file while it is running in a process. In this case, when you
1909 next type @code{run}, @value{GDBN} notices that the file has changed, and
1910 reads the symbol table again (while trying to preserve your current
1911 breakpoint settings).
1914 @section Debugging programs with multiple threads
1916 @cindex threads of execution
1917 @cindex multiple threads
1918 @cindex switching threads
1919 In some operating systems, such as HP-UX and Solaris, a single program
1920 may have more than one @dfn{thread} of execution. The precise semantics
1921 of threads differ from one operating system to another, but in general
1922 the threads of a single program are akin to multiple processes---except
1923 that they share one address space (that is, they can all examine and
1924 modify the same variables). On the other hand, each thread has its own
1925 registers and execution stack, and perhaps private memory.
1927 @value{GDBN} provides these facilities for debugging multi-thread
1931 @item automatic notification of new threads
1932 @item @samp{thread @var{threadno}}, a command to switch among threads
1933 @item @samp{info threads}, a command to inquire about existing threads
1934 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1935 a command to apply a command to a list of threads
1936 @item thread-specific breakpoints
1940 @emph{Warning:} These facilities are not yet available on every
1941 @value{GDBN} configuration where the operating system supports threads.
1942 If your @value{GDBN} does not support threads, these commands have no
1943 effect. For example, a system without thread support shows no output
1944 from @samp{info threads}, and always rejects the @code{thread} command,
1948 (@value{GDBP}) info threads
1949 (@value{GDBP}) thread 1
1950 Thread ID 1 not known. Use the "info threads" command to
1951 see the IDs of currently known threads.
1953 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1954 @c doesn't support threads"?
1957 @cindex focus of debugging
1958 @cindex current thread
1959 The @value{GDBN} thread debugging facility allows you to observe all
1960 threads while your program runs---but whenever @value{GDBN} takes
1961 control, one thread in particular is always the focus of debugging.
1962 This thread is called the @dfn{current thread}. Debugging commands show
1963 program information from the perspective of the current thread.
1965 @cindex @code{New} @var{systag} message
1966 @cindex thread identifier (system)
1967 @c FIXME-implementors!! It would be more helpful if the [New...] message
1968 @c included GDB's numeric thread handle, so you could just go to that
1969 @c thread without first checking `info threads'.
1970 Whenever @value{GDBN} detects a new thread in your program, it displays
1971 the target system's identification for the thread with a message in the
1972 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1973 whose form varies depending on the particular system. For example, on
1974 LynxOS, you might see
1977 [New process 35 thread 27]
1981 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1982 the @var{systag} is simply something like @samp{process 368}, with no
1985 @c FIXME!! (1) Does the [New...] message appear even for the very first
1986 @c thread of a program, or does it only appear for the
1987 @c second---i.e., when it becomes obvious we have a multithread
1989 @c (2) *Is* there necessarily a first thread always? Or do some
1990 @c multithread systems permit starting a program with multiple
1991 @c threads ab initio?
1993 @cindex thread number
1994 @cindex thread identifier (GDB)
1995 For debugging purposes, @value{GDBN} associates its own thread
1996 number---always a single integer---with each thread in your program.
1999 @kindex info threads
2001 Display a summary of all threads currently in your
2002 program. @value{GDBN} displays for each thread (in this order):
2005 @item the thread number assigned by @value{GDBN}
2007 @item the target system's thread identifier (@var{systag})
2009 @item the current stack frame summary for that thread
2013 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2014 indicates the current thread.
2018 @c end table here to get a little more width for example
2021 (@value{GDBP}) info threads
2022 3 process 35 thread 27 0x34e5 in sigpause ()
2023 2 process 35 thread 23 0x34e5 in sigpause ()
2024 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2030 @cindex thread number
2031 @cindex thread identifier (GDB)
2032 For debugging purposes, @value{GDBN} associates its own thread
2033 number---a small integer assigned in thread-creation order---with each
2034 thread in your program.
2036 @cindex @code{New} @var{systag} message, on HP-UX
2037 @cindex thread identifier (system), on HP-UX
2038 @c FIXME-implementors!! It would be more helpful if the [New...] message
2039 @c included GDB's numeric thread handle, so you could just go to that
2040 @c thread without first checking `info threads'.
2041 Whenever @value{GDBN} detects a new thread in your program, it displays
2042 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2043 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2044 whose form varies depending on the particular system. For example, on
2048 [New thread 2 (system thread 26594)]
2052 when @value{GDBN} notices a new thread.
2055 @kindex info threads
2057 Display a summary of all threads currently in your
2058 program. @value{GDBN} displays for each thread (in this order):
2061 @item the thread number assigned by @value{GDBN}
2063 @item the target system's thread identifier (@var{systag})
2065 @item the current stack frame summary for that thread
2069 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2070 indicates the current thread.
2074 @c end table here to get a little more width for example
2077 (@value{GDBP}) info threads
2078 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2080 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2081 from /usr/lib/libc.2
2082 1 system thread 27905 0x7b003498 in _brk () \@*
2083 from /usr/lib/libc.2
2087 @kindex thread @var{threadno}
2088 @item thread @var{threadno}
2089 Make thread number @var{threadno} the current thread. The command
2090 argument @var{threadno} is the internal @value{GDBN} thread number, as
2091 shown in the first field of the @samp{info threads} display.
2092 @value{GDBN} responds by displaying the system identifier of the thread
2093 you selected, and its current stack frame summary:
2096 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2097 (@value{GDBP}) thread 2
2098 [Switching to process 35 thread 23]
2099 0x34e5 in sigpause ()
2103 As with the @samp{[New @dots{}]} message, the form of the text after
2104 @samp{Switching to} depends on your system's conventions for identifying
2107 @kindex thread apply
2108 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2109 The @code{thread apply} command allows you to apply a command to one or
2110 more threads. Specify the numbers of the threads that you want affected
2111 with the command argument @var{threadno}. @var{threadno} is the internal
2112 @value{GDBN} thread number, as shown in the first field of the @samp{info
2113 threads} display. To apply a command to all threads, use
2114 @code{thread apply all} @var{args}.
2117 @cindex automatic thread selection
2118 @cindex switching threads automatically
2119 @cindex threads, automatic switching
2120 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2121 signal, it automatically selects the thread where that breakpoint or
2122 signal happened. @value{GDBN} alerts you to the context switch with a
2123 message of the form @samp{[Switching to @var{systag}]} to identify the
2126 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2127 more information about how @value{GDBN} behaves when you stop and start
2128 programs with multiple threads.
2130 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2131 watchpoints in programs with multiple threads.
2134 @section Debugging programs with multiple processes
2136 @cindex fork, debugging programs which call
2137 @cindex multiple processes
2138 @cindex processes, multiple
2139 On most systems, @value{GDBN} has no special support for debugging
2140 programs which create additional processes using the @code{fork}
2141 function. When a program forks, @value{GDBN} will continue to debug the
2142 parent process and the child process will run unimpeded. If you have
2143 set a breakpoint in any code which the child then executes, the child
2144 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2145 will cause it to terminate.
2147 However, if you want to debug the child process there is a workaround
2148 which isn't too painful. Put a call to @code{sleep} in the code which
2149 the child process executes after the fork. It may be useful to sleep
2150 only if a certain environment variable is set, or a certain file exists,
2151 so that the delay need not occur when you don't want to run @value{GDBN}
2152 on the child. While the child is sleeping, use the @code{ps} program to
2153 get its process ID. Then tell @value{GDBN} (a new invocation of
2154 @value{GDBN} if you are also debugging the parent process) to attach to
2155 the child process (@pxref{Attach}). From that point on you can debug
2156 the child process just like any other process which you attached to.
2158 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2159 debugging programs that create additional processes using the
2160 @code{fork} or @code{vfork} function.
2162 By default, when a program forks, @value{GDBN} will continue to debug
2163 the parent process and the child process will run unimpeded.
2165 If you want to follow the child process instead of the parent process,
2166 use the command @w{@code{set follow-fork-mode}}.
2169 @kindex set follow-fork-mode
2170 @item set follow-fork-mode @var{mode}
2171 Set the debugger response to a program call of @code{fork} or
2172 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2173 process. The @var{mode} can be:
2177 The original process is debugged after a fork. The child process runs
2178 unimpeded. This is the default.
2181 The new process is debugged after a fork. The parent process runs
2185 The debugger will ask for one of the above choices.
2188 @item show follow-fork-mode
2189 Display the current debugger response to a @code{fork} or @code{vfork} call.
2192 If you ask to debug a child process and a @code{vfork} is followed by an
2193 @code{exec}, @value{GDBN} executes the new target up to the first
2194 breakpoint in the new target. If you have a breakpoint set on
2195 @code{main} in your original program, the breakpoint will also be set on
2196 the child process's @code{main}.
2198 When a child process is spawned by @code{vfork}, you cannot debug the
2199 child or parent until an @code{exec} call completes.
2201 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2202 call executes, the new target restarts. To restart the parent process,
2203 use the @code{file} command with the parent executable name as its
2206 You can use the @code{catch} command to make @value{GDBN} stop whenever
2207 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2208 Catchpoints, ,Setting catchpoints}.
2211 @chapter Stopping and Continuing
2213 The principal purposes of using a debugger are so that you can stop your
2214 program before it terminates; or so that, if your program runs into
2215 trouble, you can investigate and find out why.
2217 Inside @value{GDBN}, your program may stop for any of several reasons,
2218 such as a signal, a breakpoint, or reaching a new line after a
2219 @value{GDBN} command such as @code{step}. You may then examine and
2220 change variables, set new breakpoints or remove old ones, and then
2221 continue execution. Usually, the messages shown by @value{GDBN} provide
2222 ample explanation of the status of your program---but you can also
2223 explicitly request this information at any time.
2226 @kindex info program
2228 Display information about the status of your program: whether it is
2229 running or not, what process it is, and why it stopped.
2233 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2234 * Continuing and Stepping:: Resuming execution
2236 * Thread Stops:: Stopping and starting multi-thread programs
2240 @section Breakpoints, watchpoints, and catchpoints
2243 A @dfn{breakpoint} makes your program stop whenever a certain point in
2244 the program is reached. For each breakpoint, you can add conditions to
2245 control in finer detail whether your program stops. You can set
2246 breakpoints with the @code{break} command and its variants (@pxref{Set
2247 Breaks, ,Setting breakpoints}), to specify the place where your program
2248 should stop by line number, function name or exact address in the
2251 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2252 breakpoints in shared libraries before the executable is run. There is
2253 a minor limitation on HP-UX systems: you must wait until the executable
2254 is run in order to set breakpoints in shared library routines that are
2255 not called directly by the program (for example, routines that are
2256 arguments in a @code{pthread_create} call).
2259 @cindex memory tracing
2260 @cindex breakpoint on memory address
2261 @cindex breakpoint on variable modification
2262 A @dfn{watchpoint} is a special breakpoint that stops your program
2263 when the value of an expression changes. You must use a different
2264 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2265 watchpoints}), but aside from that, you can manage a watchpoint like
2266 any other breakpoint: you enable, disable, and delete both breakpoints
2267 and watchpoints using the same commands.
2269 You can arrange to have values from your program displayed automatically
2270 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2274 @cindex breakpoint on events
2275 A @dfn{catchpoint} is another special breakpoint that stops your program
2276 when a certain kind of event occurs, such as the throwing of a C@t{++}
2277 exception or the loading of a library. As with watchpoints, you use a
2278 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2279 catchpoints}), but aside from that, you can manage a catchpoint like any
2280 other breakpoint. (To stop when your program receives a signal, use the
2281 @code{handle} command; see @ref{Signals, ,Signals}.)
2283 @cindex breakpoint numbers
2284 @cindex numbers for breakpoints
2285 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2286 catchpoint when you create it; these numbers are successive integers
2287 starting with one. In many of the commands for controlling various
2288 features of breakpoints you use the breakpoint number to say which
2289 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2290 @dfn{disabled}; if disabled, it has no effect on your program until you
2293 @cindex breakpoint ranges
2294 @cindex ranges of breakpoints
2295 Some @value{GDBN} commands accept a range of breakpoints on which to
2296 operate. A breakpoint range is either a single breakpoint number, like
2297 @samp{5}, or two such numbers, in increasing order, separated by a
2298 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2299 all breakpoint in that range are operated on.
2302 * Set Breaks:: Setting breakpoints
2303 * Set Watchpoints:: Setting watchpoints
2304 * Set Catchpoints:: Setting catchpoints
2305 * Delete Breaks:: Deleting breakpoints
2306 * Disabling:: Disabling breakpoints
2307 * Conditions:: Break conditions
2308 * Break Commands:: Breakpoint command lists
2309 * Breakpoint Menus:: Breakpoint menus
2310 * Error in Breakpoints:: ``Cannot insert breakpoints''
2314 @subsection Setting breakpoints
2316 @c FIXME LMB what does GDB do if no code on line of breakpt?
2317 @c consider in particular declaration with/without initialization.
2319 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2322 @kindex b @r{(@code{break})}
2323 @vindex $bpnum@r{, convenience variable}
2324 @cindex latest breakpoint
2325 Breakpoints are set with the @code{break} command (abbreviated
2326 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2327 number of the breakpoint you've set most recently; see @ref{Convenience
2328 Vars,, Convenience variables}, for a discussion of what you can do with
2329 convenience variables.
2331 You have several ways to say where the breakpoint should go.
2334 @item break @var{function}
2335 Set a breakpoint at entry to function @var{function}.
2336 When using source languages that permit overloading of symbols, such as
2337 C@t{++}, @var{function} may refer to more than one possible place to break.
2338 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2340 @item break +@var{offset}
2341 @itemx break -@var{offset}
2342 Set a breakpoint some number of lines forward or back from the position
2343 at which execution stopped in the currently selected @dfn{stack frame}.
2344 (@xref{Frames, ,Frames}, for a description of stack frames.)
2346 @item break @var{linenum}
2347 Set a breakpoint at line @var{linenum} in the current source file.
2348 The current source file is the last file whose source text was printed.
2349 The breakpoint will stop your program just before it executes any of the
2352 @item break @var{filename}:@var{linenum}
2353 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2355 @item break @var{filename}:@var{function}
2356 Set a breakpoint at entry to function @var{function} found in file
2357 @var{filename}. Specifying a file name as well as a function name is
2358 superfluous except when multiple files contain similarly named
2361 @item break *@var{address}
2362 Set a breakpoint at address @var{address}. You can use this to set
2363 breakpoints in parts of your program which do not have debugging
2364 information or source files.
2367 When called without any arguments, @code{break} sets a breakpoint at
2368 the next instruction to be executed in the selected stack frame
2369 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2370 innermost, this makes your program stop as soon as control
2371 returns to that frame. This is similar to the effect of a
2372 @code{finish} command in the frame inside the selected frame---except
2373 that @code{finish} does not leave an active breakpoint. If you use
2374 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2375 the next time it reaches the current location; this may be useful
2378 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2379 least one instruction has been executed. If it did not do this, you
2380 would be unable to proceed past a breakpoint without first disabling the
2381 breakpoint. This rule applies whether or not the breakpoint already
2382 existed when your program stopped.
2384 @item break @dots{} if @var{cond}
2385 Set a breakpoint with condition @var{cond}; evaluate the expression
2386 @var{cond} each time the breakpoint is reached, and stop only if the
2387 value is nonzero---that is, if @var{cond} evaluates as true.
2388 @samp{@dots{}} stands for one of the possible arguments described
2389 above (or no argument) specifying where to break. @xref{Conditions,
2390 ,Break conditions}, for more information on breakpoint conditions.
2393 @item tbreak @var{args}
2394 Set a breakpoint enabled only for one stop. @var{args} are the
2395 same as for the @code{break} command, and the breakpoint is set in the same
2396 way, but the breakpoint is automatically deleted after the first time your
2397 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2400 @item hbreak @var{args}
2401 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2402 @code{break} command and the breakpoint is set in the same way, but the
2403 breakpoint requires hardware support and some target hardware may not
2404 have this support. The main purpose of this is EPROM/ROM code
2405 debugging, so you can set a breakpoint at an instruction without
2406 changing the instruction. This can be used with the new trap-generation
2407 provided by SPARClite DSU and some x86-based targets. These targets
2408 will generate traps when a program accesses some data or instruction
2409 address that is assigned to the debug registers. However the hardware
2410 breakpoint registers can take a limited number of breakpoints. For
2411 example, on the DSU, only two data breakpoints can be set at a time, and
2412 @value{GDBN} will reject this command if more than two are used. Delete
2413 or disable unused hardware breakpoints before setting new ones
2414 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2417 @item thbreak @var{args}
2418 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2419 are the same as for the @code{hbreak} command and the breakpoint is set in
2420 the same way. However, like the @code{tbreak} command,
2421 the breakpoint is automatically deleted after the
2422 first time your program stops there. Also, like the @code{hbreak}
2423 command, the breakpoint requires hardware support and some target hardware
2424 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2425 See also @ref{Conditions, ,Break conditions}.
2428 @cindex regular expression
2429 @item rbreak @var{regex}
2430 Set breakpoints on all functions matching the regular expression
2431 @var{regex}. This command sets an unconditional breakpoint on all
2432 matches, printing a list of all breakpoints it set. Once these
2433 breakpoints are set, they are treated just like the breakpoints set with
2434 the @code{break} command. You can delete them, disable them, or make
2435 them conditional the same way as any other breakpoint.
2437 The syntax of the regular expression is the standard one used with tools
2438 like @file{grep}. Note that this is different from the syntax used by
2439 shells, so for instance @code{foo*} matches all functions that include
2440 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2441 @code{.*} leading and trailing the regular expression you supply, so to
2442 match only functions that begin with @code{foo}, use @code{^foo}.
2444 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2445 breakpoints on overloaded functions that are not members of any special
2448 @kindex info breakpoints
2449 @cindex @code{$_} and @code{info breakpoints}
2450 @item info breakpoints @r{[}@var{n}@r{]}
2451 @itemx info break @r{[}@var{n}@r{]}
2452 @itemx info watchpoints @r{[}@var{n}@r{]}
2453 Print a table of all breakpoints, watchpoints, and catchpoints set and
2454 not deleted, with the following columns for each breakpoint:
2457 @item Breakpoint Numbers
2459 Breakpoint, watchpoint, or catchpoint.
2461 Whether the breakpoint is marked to be disabled or deleted when hit.
2462 @item Enabled or Disabled
2463 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2464 that are not enabled.
2466 Where the breakpoint is in your program, as a memory address.
2468 Where the breakpoint is in the source for your program, as a file and
2473 If a breakpoint is conditional, @code{info break} shows the condition on
2474 the line following the affected breakpoint; breakpoint commands, if any,
2475 are listed after that.
2478 @code{info break} with a breakpoint
2479 number @var{n} as argument lists only that breakpoint. The
2480 convenience variable @code{$_} and the default examining-address for
2481 the @code{x} command are set to the address of the last breakpoint
2482 listed (@pxref{Memory, ,Examining memory}).
2485 @code{info break} displays a count of the number of times the breakpoint
2486 has been hit. This is especially useful in conjunction with the
2487 @code{ignore} command. You can ignore a large number of breakpoint
2488 hits, look at the breakpoint info to see how many times the breakpoint
2489 was hit, and then run again, ignoring one less than that number. This
2490 will get you quickly to the last hit of that breakpoint.
2493 @value{GDBN} allows you to set any number of breakpoints at the same place in
2494 your program. There is nothing silly or meaningless about this. When
2495 the breakpoints are conditional, this is even useful
2496 (@pxref{Conditions, ,Break conditions}).
2498 @cindex negative breakpoint numbers
2499 @cindex internal @value{GDBN} breakpoints
2500 @value{GDBN} itself sometimes sets breakpoints in your program for special
2501 purposes, such as proper handling of @code{longjmp} (in C programs).
2502 These internal breakpoints are assigned negative numbers, starting with
2503 @code{-1}; @samp{info breakpoints} does not display them.
2505 You can see these breakpoints with the @value{GDBN} maintenance command
2506 @samp{maint info breakpoints}.
2509 @kindex maint info breakpoints
2510 @item maint info breakpoints
2511 Using the same format as @samp{info breakpoints}, display both the
2512 breakpoints you've set explicitly, and those @value{GDBN} is using for
2513 internal purposes. Internal breakpoints are shown with negative
2514 breakpoint numbers. The type column identifies what kind of breakpoint
2519 Normal, explicitly set breakpoint.
2522 Normal, explicitly set watchpoint.
2525 Internal breakpoint, used to handle correctly stepping through
2526 @code{longjmp} calls.
2528 @item longjmp resume
2529 Internal breakpoint at the target of a @code{longjmp}.
2532 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2535 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2538 Shared library events.
2545 @node Set Watchpoints
2546 @subsection Setting watchpoints
2548 @cindex setting watchpoints
2549 @cindex software watchpoints
2550 @cindex hardware watchpoints
2551 You can use a watchpoint to stop execution whenever the value of an
2552 expression changes, without having to predict a particular place where
2555 Depending on your system, watchpoints may be implemented in software or
2556 hardware. @value{GDBN} does software watchpointing by single-stepping your
2557 program and testing the variable's value each time, which is hundreds of
2558 times slower than normal execution. (But this may still be worth it, to
2559 catch errors where you have no clue what part of your program is the
2562 On some systems, such as HP-UX, Linux and some other x86-based targets,
2563 @value{GDBN} includes support for
2564 hardware watchpoints, which do not slow down the running of your
2569 @item watch @var{expr}
2570 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2571 is written into by the program and its value changes.
2574 @item rwatch @var{expr}
2575 Set a watchpoint that will break when watch @var{expr} is read by the program.
2578 @item awatch @var{expr}
2579 Set a watchpoint that will break when @var{expr} is either read or written into
2582 @kindex info watchpoints
2583 @item info watchpoints
2584 This command prints a list of watchpoints, breakpoints, and catchpoints;
2585 it is the same as @code{info break}.
2588 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2589 watchpoints execute very quickly, and the debugger reports a change in
2590 value at the exact instruction where the change occurs. If @value{GDBN}
2591 cannot set a hardware watchpoint, it sets a software watchpoint, which
2592 executes more slowly and reports the change in value at the next
2593 statement, not the instruction, after the change occurs.
2595 When you issue the @code{watch} command, @value{GDBN} reports
2598 Hardware watchpoint @var{num}: @var{expr}
2602 if it was able to set a hardware watchpoint.
2604 Currently, the @code{awatch} and @code{rwatch} commands can only set
2605 hardware watchpoints, because accesses to data that don't change the
2606 value of the watched expression cannot be detected without examining
2607 every instruction as it is being executed, and @value{GDBN} does not do
2608 that currently. If @value{GDBN} finds that it is unable to set a
2609 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2610 will print a message like this:
2613 Expression cannot be implemented with read/access watchpoint.
2616 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2617 data type of the watched expression is wider than what a hardware
2618 watchpoint on the target machine can handle. For example, some systems
2619 can only watch regions that are up to 4 bytes wide; on such systems you
2620 cannot set hardware watchpoints for an expression that yields a
2621 double-precision floating-point number (which is typically 8 bytes
2622 wide). As a work-around, it might be possible to break the large region
2623 into a series of smaller ones and watch them with separate watchpoints.
2625 If you set too many hardware watchpoints, @value{GDBN} might be unable
2626 to insert all of them when you resume the execution of your program.
2627 Since the precise number of active watchpoints is unknown until such
2628 time as the program is about to be resumed, @value{GDBN} might not be
2629 able to warn you about this when you set the watchpoints, and the
2630 warning will be printed only when the program is resumed:
2633 Hardware watchpoint @var{num}: Could not insert watchpoint
2637 If this happens, delete or disable some of the watchpoints.
2639 The SPARClite DSU will generate traps when a program accesses some data
2640 or instruction address that is assigned to the debug registers. For the
2641 data addresses, DSU facilitates the @code{watch} command. However the
2642 hardware breakpoint registers can only take two data watchpoints, and
2643 both watchpoints must be the same kind. For example, you can set two
2644 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2645 @strong{or} two with @code{awatch} commands, but you cannot set one
2646 watchpoint with one command and the other with a different command.
2647 @value{GDBN} will reject the command if you try to mix watchpoints.
2648 Delete or disable unused watchpoint commands before setting new ones.
2650 If you call a function interactively using @code{print} or @code{call},
2651 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2652 kind of breakpoint or the call completes.
2654 @value{GDBN} automatically deletes watchpoints that watch local
2655 (automatic) variables, or expressions that involve such variables, when
2656 they go out of scope, that is, when the execution leaves the block in
2657 which these variables were defined. In particular, when the program
2658 being debugged terminates, @emph{all} local variables go out of scope,
2659 and so only watchpoints that watch global variables remain set. If you
2660 rerun the program, you will need to set all such watchpoints again. One
2661 way of doing that would be to set a code breakpoint at the entry to the
2662 @code{main} function and when it breaks, set all the watchpoints.
2665 @cindex watchpoints and threads
2666 @cindex threads and watchpoints
2667 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2668 usefulness. With the current watchpoint implementation, @value{GDBN}
2669 can only watch the value of an expression @emph{in a single thread}. If
2670 you are confident that the expression can only change due to the current
2671 thread's activity (and if you are also confident that no other thread
2672 can become current), then you can use watchpoints as usual. However,
2673 @value{GDBN} may not notice when a non-current thread's activity changes
2676 @c FIXME: this is almost identical to the previous paragraph.
2677 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2678 have only limited usefulness. If @value{GDBN} creates a software
2679 watchpoint, it can only watch the value of an expression @emph{in a
2680 single thread}. If you are confident that the expression can only
2681 change due to the current thread's activity (and if you are also
2682 confident that no other thread can become current), then you can use
2683 software watchpoints as usual. However, @value{GDBN} may not notice
2684 when a non-current thread's activity changes the expression. (Hardware
2685 watchpoints, in contrast, watch an expression in all threads.)
2688 @node Set Catchpoints
2689 @subsection Setting catchpoints
2690 @cindex catchpoints, setting
2691 @cindex exception handlers
2692 @cindex event handling
2694 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2695 kinds of program events, such as C@t{++} exceptions or the loading of a
2696 shared library. Use the @code{catch} command to set a catchpoint.
2700 @item catch @var{event}
2701 Stop when @var{event} occurs. @var{event} can be any of the following:
2705 The throwing of a C@t{++} exception.
2709 The catching of a C@t{++} exception.
2713 A call to @code{exec}. This is currently only available for HP-UX.
2717 A call to @code{fork}. This is currently only available for HP-UX.
2721 A call to @code{vfork}. This is currently only available for HP-UX.
2724 @itemx load @var{libname}
2726 The dynamic loading of any shared library, or the loading of the library
2727 @var{libname}. This is currently only available for HP-UX.
2730 @itemx unload @var{libname}
2731 @kindex catch unload
2732 The unloading of any dynamically loaded shared library, or the unloading
2733 of the library @var{libname}. This is currently only available for HP-UX.
2736 @item tcatch @var{event}
2737 Set a catchpoint that is enabled only for one stop. The catchpoint is
2738 automatically deleted after the first time the event is caught.
2742 Use the @code{info break} command to list the current catchpoints.
2744 There are currently some limitations to C@t{++} exception handling
2745 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2749 If you call a function interactively, @value{GDBN} normally returns
2750 control to you when the function has finished executing. If the call
2751 raises an exception, however, the call may bypass the mechanism that
2752 returns control to you and cause your program either to abort or to
2753 simply continue running until it hits a breakpoint, catches a signal
2754 that @value{GDBN} is listening for, or exits. This is the case even if
2755 you set a catchpoint for the exception; catchpoints on exceptions are
2756 disabled within interactive calls.
2759 You cannot raise an exception interactively.
2762 You cannot install an exception handler interactively.
2765 @cindex raise exceptions
2766 Sometimes @code{catch} is not the best way to debug exception handling:
2767 if you need to know exactly where an exception is raised, it is better to
2768 stop @emph{before} the exception handler is called, since that way you
2769 can see the stack before any unwinding takes place. If you set a
2770 breakpoint in an exception handler instead, it may not be easy to find
2771 out where the exception was raised.
2773 To stop just before an exception handler is called, you need some
2774 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2775 raised by calling a library function named @code{__raise_exception}
2776 which has the following ANSI C interface:
2779 /* @var{addr} is where the exception identifier is stored.
2780 @var{id} is the exception identifier. */
2781 void __raise_exception (void **addr, void *id);
2785 To make the debugger catch all exceptions before any stack
2786 unwinding takes place, set a breakpoint on @code{__raise_exception}
2787 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2789 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2790 that depends on the value of @var{id}, you can stop your program when
2791 a specific exception is raised. You can use multiple conditional
2792 breakpoints to stop your program when any of a number of exceptions are
2797 @subsection Deleting breakpoints
2799 @cindex clearing breakpoints, watchpoints, catchpoints
2800 @cindex deleting breakpoints, watchpoints, catchpoints
2801 It is often necessary to eliminate a breakpoint, watchpoint, or
2802 catchpoint once it has done its job and you no longer want your program
2803 to stop there. This is called @dfn{deleting} the breakpoint. A
2804 breakpoint that has been deleted no longer exists; it is forgotten.
2806 With the @code{clear} command you can delete breakpoints according to
2807 where they are in your program. With the @code{delete} command you can
2808 delete individual breakpoints, watchpoints, or catchpoints by specifying
2809 their breakpoint numbers.
2811 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2812 automatically ignores breakpoints on the first instruction to be executed
2813 when you continue execution without changing the execution address.
2818 Delete any breakpoints at the next instruction to be executed in the
2819 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2820 the innermost frame is selected, this is a good way to delete a
2821 breakpoint where your program just stopped.
2823 @item clear @var{function}
2824 @itemx clear @var{filename}:@var{function}
2825 Delete any breakpoints set at entry to the function @var{function}.
2827 @item clear @var{linenum}
2828 @itemx clear @var{filename}:@var{linenum}
2829 Delete any breakpoints set at or within the code of the specified line.
2831 @cindex delete breakpoints
2833 @kindex d @r{(@code{delete})}
2834 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2835 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2836 ranges specified as arguments. If no argument is specified, delete all
2837 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2838 confirm off}). You can abbreviate this command as @code{d}.
2842 @subsection Disabling breakpoints
2844 @kindex disable breakpoints
2845 @kindex enable breakpoints
2846 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2847 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2848 it had been deleted, but remembers the information on the breakpoint so
2849 that you can @dfn{enable} it again later.
2851 You disable and enable breakpoints, watchpoints, and catchpoints with
2852 the @code{enable} and @code{disable} commands, optionally specifying one
2853 or more breakpoint numbers as arguments. Use @code{info break} or
2854 @code{info watch} to print a list of breakpoints, watchpoints, and
2855 catchpoints if you do not know which numbers to use.
2857 A breakpoint, watchpoint, or catchpoint can have any of four different
2858 states of enablement:
2862 Enabled. The breakpoint stops your program. A breakpoint set
2863 with the @code{break} command starts out in this state.
2865 Disabled. The breakpoint has no effect on your program.
2867 Enabled once. The breakpoint stops your program, but then becomes
2870 Enabled for deletion. The breakpoint stops your program, but
2871 immediately after it does so it is deleted permanently. A breakpoint
2872 set with the @code{tbreak} command starts out in this state.
2875 You can use the following commands to enable or disable breakpoints,
2876 watchpoints, and catchpoints:
2879 @kindex disable breakpoints
2881 @kindex dis @r{(@code{disable})}
2882 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2883 Disable the specified breakpoints---or all breakpoints, if none are
2884 listed. A disabled breakpoint has no effect but is not forgotten. All
2885 options such as ignore-counts, conditions and commands are remembered in
2886 case the breakpoint is enabled again later. You may abbreviate
2887 @code{disable} as @code{dis}.
2889 @kindex enable breakpoints
2891 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2892 Enable the specified breakpoints (or all defined breakpoints). They
2893 become effective once again in stopping your program.
2895 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2896 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2897 of these breakpoints immediately after stopping your program.
2899 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2900 Enable the specified breakpoints to work once, then die. @value{GDBN}
2901 deletes any of these breakpoints as soon as your program stops there.
2904 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2905 @c confusing: tbreak is also initially enabled.
2906 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2907 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2908 subsequently, they become disabled or enabled only when you use one of
2909 the commands above. (The command @code{until} can set and delete a
2910 breakpoint of its own, but it does not change the state of your other
2911 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2915 @subsection Break conditions
2916 @cindex conditional breakpoints
2917 @cindex breakpoint conditions
2919 @c FIXME what is scope of break condition expr? Context where wanted?
2920 @c in particular for a watchpoint?
2921 The simplest sort of breakpoint breaks every time your program reaches a
2922 specified place. You can also specify a @dfn{condition} for a
2923 breakpoint. A condition is just a Boolean expression in your
2924 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2925 a condition evaluates the expression each time your program reaches it,
2926 and your program stops only if the condition is @emph{true}.
2928 This is the converse of using assertions for program validation; in that
2929 situation, you want to stop when the assertion is violated---that is,
2930 when the condition is false. In C, if you want to test an assertion expressed
2931 by the condition @var{assert}, you should set the condition
2932 @samp{! @var{assert}} on the appropriate breakpoint.
2934 Conditions are also accepted for watchpoints; you may not need them,
2935 since a watchpoint is inspecting the value of an expression anyhow---but
2936 it might be simpler, say, to just set a watchpoint on a variable name,
2937 and specify a condition that tests whether the new value is an interesting
2940 Break conditions can have side effects, and may even call functions in
2941 your program. This can be useful, for example, to activate functions
2942 that log program progress, or to use your own print functions to
2943 format special data structures. The effects are completely predictable
2944 unless there is another enabled breakpoint at the same address. (In
2945 that case, @value{GDBN} might see the other breakpoint first and stop your
2946 program without checking the condition of this one.) Note that
2947 breakpoint commands are usually more convenient and flexible than break
2949 purpose of performing side effects when a breakpoint is reached
2950 (@pxref{Break Commands, ,Breakpoint command lists}).
2952 Break conditions can be specified when a breakpoint is set, by using
2953 @samp{if} in the arguments to the @code{break} command. @xref{Set
2954 Breaks, ,Setting breakpoints}. They can also be changed at any time
2955 with the @code{condition} command.
2957 You can also use the @code{if} keyword with the @code{watch} command.
2958 The @code{catch} command does not recognize the @code{if} keyword;
2959 @code{condition} is the only way to impose a further condition on a
2964 @item condition @var{bnum} @var{expression}
2965 Specify @var{expression} as the break condition for breakpoint,
2966 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2967 breakpoint @var{bnum} stops your program only if the value of
2968 @var{expression} is true (nonzero, in C). When you use
2969 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2970 syntactic correctness, and to determine whether symbols in it have
2971 referents in the context of your breakpoint. If @var{expression} uses
2972 symbols not referenced in the context of the breakpoint, @value{GDBN}
2973 prints an error message:
2976 No symbol "foo" in current context.
2981 not actually evaluate @var{expression} at the time the @code{condition}
2982 command (or a command that sets a breakpoint with a condition, like
2983 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2985 @item condition @var{bnum}
2986 Remove the condition from breakpoint number @var{bnum}. It becomes
2987 an ordinary unconditional breakpoint.
2990 @cindex ignore count (of breakpoint)
2991 A special case of a breakpoint condition is to stop only when the
2992 breakpoint has been reached a certain number of times. This is so
2993 useful that there is a special way to do it, using the @dfn{ignore
2994 count} of the breakpoint. Every breakpoint has an ignore count, which
2995 is an integer. Most of the time, the ignore count is zero, and
2996 therefore has no effect. But if your program reaches a breakpoint whose
2997 ignore count is positive, then instead of stopping, it just decrements
2998 the ignore count by one and continues. As a result, if the ignore count
2999 value is @var{n}, the breakpoint does not stop the next @var{n} times
3000 your program reaches it.
3004 @item ignore @var{bnum} @var{count}
3005 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3006 The next @var{count} times the breakpoint is reached, your program's
3007 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3010 To make the breakpoint stop the next time it is reached, specify
3013 When you use @code{continue} to resume execution of your program from a
3014 breakpoint, you can specify an ignore count directly as an argument to
3015 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3016 Stepping,,Continuing and stepping}.
3018 If a breakpoint has a positive ignore count and a condition, the
3019 condition is not checked. Once the ignore count reaches zero,
3020 @value{GDBN} resumes checking the condition.
3022 You could achieve the effect of the ignore count with a condition such
3023 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3024 is decremented each time. @xref{Convenience Vars, ,Convenience
3028 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3031 @node Break Commands
3032 @subsection Breakpoint command lists
3034 @cindex breakpoint commands
3035 You can give any breakpoint (or watchpoint or catchpoint) a series of
3036 commands to execute when your program stops due to that breakpoint. For
3037 example, you might want to print the values of certain expressions, or
3038 enable other breakpoints.
3043 @item commands @r{[}@var{bnum}@r{]}
3044 @itemx @dots{} @var{command-list} @dots{}
3046 Specify a list of commands for breakpoint number @var{bnum}. The commands
3047 themselves appear on the following lines. Type a line containing just
3048 @code{end} to terminate the commands.
3050 To remove all commands from a breakpoint, type @code{commands} and
3051 follow it immediately with @code{end}; that is, give no commands.
3053 With no @var{bnum} argument, @code{commands} refers to the last
3054 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3055 recently encountered).
3058 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3059 disabled within a @var{command-list}.
3061 You can use breakpoint commands to start your program up again. Simply
3062 use the @code{continue} command, or @code{step}, or any other command
3063 that resumes execution.
3065 Any other commands in the command list, after a command that resumes
3066 execution, are ignored. This is because any time you resume execution
3067 (even with a simple @code{next} or @code{step}), you may encounter
3068 another breakpoint---which could have its own command list, leading to
3069 ambiguities about which list to execute.
3072 If the first command you specify in a command list is @code{silent}, the
3073 usual message about stopping at a breakpoint is not printed. This may
3074 be desirable for breakpoints that are to print a specific message and
3075 then continue. If none of the remaining commands print anything, you
3076 see no sign that the breakpoint was reached. @code{silent} is
3077 meaningful only at the beginning of a breakpoint command list.
3079 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3080 print precisely controlled output, and are often useful in silent
3081 breakpoints. @xref{Output, ,Commands for controlled output}.
3083 For example, here is how you could use breakpoint commands to print the
3084 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3090 printf "x is %d\n",x
3095 One application for breakpoint commands is to compensate for one bug so
3096 you can test for another. Put a breakpoint just after the erroneous line
3097 of code, give it a condition to detect the case in which something
3098 erroneous has been done, and give it commands to assign correct values
3099 to any variables that need them. End with the @code{continue} command
3100 so that your program does not stop, and start with the @code{silent}
3101 command so that no output is produced. Here is an example:
3112 @node Breakpoint Menus
3113 @subsection Breakpoint menus
3115 @cindex symbol overloading
3117 Some programming languages (notably C@t{++}) permit a single function name
3118 to be defined several times, for application in different contexts.
3119 This is called @dfn{overloading}. When a function name is overloaded,
3120 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3121 a breakpoint. If you realize this is a problem, you can use
3122 something like @samp{break @var{function}(@var{types})} to specify which
3123 particular version of the function you want. Otherwise, @value{GDBN} offers
3124 you a menu of numbered choices for different possible breakpoints, and
3125 waits for your selection with the prompt @samp{>}. The first two
3126 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3127 sets a breakpoint at each definition of @var{function}, and typing
3128 @kbd{0} aborts the @code{break} command without setting any new
3131 For example, the following session excerpt shows an attempt to set a
3132 breakpoint at the overloaded symbol @code{String::after}.
3133 We choose three particular definitions of that function name:
3135 @c FIXME! This is likely to change to show arg type lists, at least
3138 (@value{GDBP}) b String::after
3141 [2] file:String.cc; line number:867
3142 [3] file:String.cc; line number:860
3143 [4] file:String.cc; line number:875
3144 [5] file:String.cc; line number:853
3145 [6] file:String.cc; line number:846
3146 [7] file:String.cc; line number:735
3148 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3149 Breakpoint 2 at 0xb344: file String.cc, line 875.
3150 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3151 Multiple breakpoints were set.
3152 Use the "delete" command to delete unwanted
3158 @c @ifclear BARETARGET
3159 @node Error in Breakpoints
3160 @subsection ``Cannot insert breakpoints''
3162 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3164 Under some operating systems, breakpoints cannot be used in a program if
3165 any other process is running that program. In this situation,
3166 attempting to run or continue a program with a breakpoint causes
3167 @value{GDBN} to print an error message:
3170 Cannot insert breakpoints.
3171 The same program may be running in another process.
3174 When this happens, you have three ways to proceed:
3178 Remove or disable the breakpoints, then continue.
3181 Suspend @value{GDBN}, and copy the file containing your program to a new
3182 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3183 that @value{GDBN} should run your program under that name.
3184 Then start your program again.
3187 Relink your program so that the text segment is nonsharable, using the
3188 linker option @samp{-N}. The operating system limitation may not apply
3189 to nonsharable executables.
3193 A similar message can be printed if you request too many active
3194 hardware-assisted breakpoints and watchpoints:
3196 @c FIXME: the precise wording of this message may change; the relevant
3197 @c source change is not committed yet (Sep 3, 1999).
3199 Stopped; cannot insert breakpoints.
3200 You may have requested too many hardware breakpoints and watchpoints.
3204 This message is printed when you attempt to resume the program, since
3205 only then @value{GDBN} knows exactly how many hardware breakpoints and
3206 watchpoints it needs to insert.
3208 When this message is printed, you need to disable or remove some of the
3209 hardware-assisted breakpoints and watchpoints, and then continue.
3212 @node Continuing and Stepping
3213 @section Continuing and stepping
3217 @cindex resuming execution
3218 @dfn{Continuing} means resuming program execution until your program
3219 completes normally. In contrast, @dfn{stepping} means executing just
3220 one more ``step'' of your program, where ``step'' may mean either one
3221 line of source code, or one machine instruction (depending on what
3222 particular command you use). Either when continuing or when stepping,
3223 your program may stop even sooner, due to a breakpoint or a signal. (If
3224 it stops due to a signal, you may want to use @code{handle}, or use
3225 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3229 @kindex c @r{(@code{continue})}
3230 @kindex fg @r{(resume foreground execution)}
3231 @item continue @r{[}@var{ignore-count}@r{]}
3232 @itemx c @r{[}@var{ignore-count}@r{]}
3233 @itemx fg @r{[}@var{ignore-count}@r{]}
3234 Resume program execution, at the address where your program last stopped;
3235 any breakpoints set at that address are bypassed. The optional argument
3236 @var{ignore-count} allows you to specify a further number of times to
3237 ignore a breakpoint at this location; its effect is like that of
3238 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3240 The argument @var{ignore-count} is meaningful only when your program
3241 stopped due to a breakpoint. At other times, the argument to
3242 @code{continue} is ignored.
3244 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3245 debugged program is deemed to be the foreground program) are provided
3246 purely for convenience, and have exactly the same behavior as
3250 To resume execution at a different place, you can use @code{return}
3251 (@pxref{Returning, ,Returning from a function}) to go back to the
3252 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3253 different address}) to go to an arbitrary location in your program.
3255 A typical technique for using stepping is to set a breakpoint
3256 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3257 beginning of the function or the section of your program where a problem
3258 is believed to lie, run your program until it stops at that breakpoint,
3259 and then step through the suspect area, examining the variables that are
3260 interesting, until you see the problem happen.
3264 @kindex s @r{(@code{step})}
3266 Continue running your program until control reaches a different source
3267 line, then stop it and return control to @value{GDBN}. This command is
3268 abbreviated @code{s}.
3271 @c "without debugging information" is imprecise; actually "without line
3272 @c numbers in the debugging information". (gcc -g1 has debugging info but
3273 @c not line numbers). But it seems complex to try to make that
3274 @c distinction here.
3275 @emph{Warning:} If you use the @code{step} command while control is
3276 within a function that was compiled without debugging information,
3277 execution proceeds until control reaches a function that does have
3278 debugging information. Likewise, it will not step into a function which
3279 is compiled without debugging information. To step through functions
3280 without debugging information, use the @code{stepi} command, described
3284 The @code{step} command only stops at the first instruction of a source
3285 line. This prevents the multiple stops that could otherwise occur in
3286 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3287 to stop if a function that has debugging information is called within
3288 the line. In other words, @code{step} @emph{steps inside} any functions
3289 called within the line.
3291 Also, the @code{step} command only enters a function if there is line
3292 number information for the function. Otherwise it acts like the
3293 @code{next} command. This avoids problems when using @code{cc -gl}
3294 on MIPS machines. Previously, @code{step} entered subroutines if there
3295 was any debugging information about the routine.
3297 @item step @var{count}
3298 Continue running as in @code{step}, but do so @var{count} times. If a
3299 breakpoint is reached, or a signal not related to stepping occurs before
3300 @var{count} steps, stepping stops right away.
3303 @kindex n @r{(@code{next})}
3304 @item next @r{[}@var{count}@r{]}
3305 Continue to the next source line in the current (innermost) stack frame.
3306 This is similar to @code{step}, but function calls that appear within
3307 the line of code are executed without stopping. Execution stops when
3308 control reaches a different line of code at the original stack level
3309 that was executing when you gave the @code{next} command. This command
3310 is abbreviated @code{n}.
3312 An argument @var{count} is a repeat count, as for @code{step}.
3315 @c FIX ME!! Do we delete this, or is there a way it fits in with
3316 @c the following paragraph? --- Vctoria
3318 @c @code{next} within a function that lacks debugging information acts like
3319 @c @code{step}, but any function calls appearing within the code of the
3320 @c function are executed without stopping.
3322 The @code{next} command only stops at the first instruction of a
3323 source line. This prevents multiple stops that could otherwise occur in
3324 @code{switch} statements, @code{for} loops, etc.
3326 @kindex set step-mode
3328 @cindex functions without line info, and stepping
3329 @cindex stepping into functions with no line info
3330 @itemx set step-mode on
3331 The @code{set step-mode on} command causes the @code{step} command to
3332 stop at the first instruction of a function which contains no debug line
3333 information rather than stepping over it.
3335 This is useful in cases where you may be interested in inspecting the
3336 machine instructions of a function which has no symbolic info and do not
3337 want @value{GDBN} to automatically skip over this function.
3339 @item set step-mode off
3340 Causes the @code{step} command to step over any functions which contains no
3341 debug information. This is the default.
3345 Continue running until just after function in the selected stack frame
3346 returns. Print the returned value (if any).
3348 Contrast this with the @code{return} command (@pxref{Returning,
3349 ,Returning from a function}).
3352 @kindex u @r{(@code{until})}
3355 Continue running until a source line past the current line, in the
3356 current stack frame, is reached. This command is used to avoid single
3357 stepping through a loop more than once. It is like the @code{next}
3358 command, except that when @code{until} encounters a jump, it
3359 automatically continues execution until the program counter is greater
3360 than the address of the jump.
3362 This means that when you reach the end of a loop after single stepping
3363 though it, @code{until} makes your program continue execution until it
3364 exits the loop. In contrast, a @code{next} command at the end of a loop
3365 simply steps back to the beginning of the loop, which forces you to step
3366 through the next iteration.
3368 @code{until} always stops your program if it attempts to exit the current
3371 @code{until} may produce somewhat counterintuitive results if the order
3372 of machine code does not match the order of the source lines. For
3373 example, in the following excerpt from a debugging session, the @code{f}
3374 (@code{frame}) command shows that execution is stopped at line
3375 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3379 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3381 (@value{GDBP}) until
3382 195 for ( ; argc > 0; NEXTARG) @{
3385 This happened because, for execution efficiency, the compiler had
3386 generated code for the loop closure test at the end, rather than the
3387 start, of the loop---even though the test in a C @code{for}-loop is
3388 written before the body of the loop. The @code{until} command appeared
3389 to step back to the beginning of the loop when it advanced to this
3390 expression; however, it has not really gone to an earlier
3391 statement---not in terms of the actual machine code.
3393 @code{until} with no argument works by means of single
3394 instruction stepping, and hence is slower than @code{until} with an
3397 @item until @var{location}
3398 @itemx u @var{location}
3399 Continue running your program until either the specified location is
3400 reached, or the current stack frame returns. @var{location} is any of
3401 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3402 ,Setting breakpoints}). This form of the command uses breakpoints,
3403 and hence is quicker than @code{until} without an argument.
3406 @kindex si @r{(@code{stepi})}
3408 @itemx stepi @var{arg}
3410 Execute one machine instruction, then stop and return to the debugger.
3412 It is often useful to do @samp{display/i $pc} when stepping by machine
3413 instructions. This makes @value{GDBN} automatically display the next
3414 instruction to be executed, each time your program stops. @xref{Auto
3415 Display,, Automatic display}.
3417 An argument is a repeat count, as in @code{step}.
3421 @kindex ni @r{(@code{nexti})}
3423 @itemx nexti @var{arg}
3425 Execute one machine instruction, but if it is a function call,
3426 proceed until the function returns.
3428 An argument is a repeat count, as in @code{next}.
3435 A signal is an asynchronous event that can happen in a program. The
3436 operating system defines the possible kinds of signals, and gives each
3437 kind a name and a number. For example, in Unix @code{SIGINT} is the
3438 signal a program gets when you type an interrupt character (often @kbd{C-c});
3439 @code{SIGSEGV} is the signal a program gets from referencing a place in
3440 memory far away from all the areas in use; @code{SIGALRM} occurs when
3441 the alarm clock timer goes off (which happens only if your program has
3442 requested an alarm).
3444 @cindex fatal signals
3445 Some signals, including @code{SIGALRM}, are a normal part of the
3446 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3447 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3448 program has not specified in advance some other way to handle the signal.
3449 @code{SIGINT} does not indicate an error in your program, but it is normally
3450 fatal so it can carry out the purpose of the interrupt: to kill the program.
3452 @value{GDBN} has the ability to detect any occurrence of a signal in your
3453 program. You can tell @value{GDBN} in advance what to do for each kind of
3456 @cindex handling signals
3457 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3458 (so as not to interfere with their role in the functioning of your program)
3459 but to stop your program immediately whenever an error signal happens.
3460 You can change these settings with the @code{handle} command.
3463 @kindex info signals
3466 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3467 handle each one. You can use this to see the signal numbers of all
3468 the defined types of signals.
3470 @code{info handle} is an alias for @code{info signals}.
3473 @item handle @var{signal} @var{keywords}@dots{}
3474 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3475 can be the number of a signal or its name (with or without the
3476 @samp{SIG} at the beginning); a list of signal numberss of the form
3477 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3478 known signals. The @var{keywords} say what change to make.
3482 The keywords allowed by the @code{handle} command can be abbreviated.
3483 Their full names are:
3487 @value{GDBN} should not stop your program when this signal happens. It may
3488 still print a message telling you that the signal has come in.
3491 @value{GDBN} should stop your program when this signal happens. This implies
3492 the @code{print} keyword as well.
3495 @value{GDBN} should print a message when this signal happens.
3498 @value{GDBN} should not mention the occurrence of the signal at all. This
3499 implies the @code{nostop} keyword as well.
3503 @value{GDBN} should allow your program to see this signal; your program
3504 can handle the signal, or else it may terminate if the signal is fatal
3505 and not handled. @code{pass} and @code{noignore} are synonyms.
3509 @value{GDBN} should not allow your program to see this signal.
3510 @code{nopass} and @code{ignore} are synonyms.
3514 When a signal stops your program, the signal is not visible to the
3516 continue. Your program sees the signal then, if @code{pass} is in
3517 effect for the signal in question @emph{at that time}. In other words,
3518 after @value{GDBN} reports a signal, you can use the @code{handle}
3519 command with @code{pass} or @code{nopass} to control whether your
3520 program sees that signal when you continue.
3522 You can also use the @code{signal} command to prevent your program from
3523 seeing a signal, or cause it to see a signal it normally would not see,
3524 or to give it any signal at any time. For example, if your program stopped
3525 due to some sort of memory reference error, you might store correct
3526 values into the erroneous variables and continue, hoping to see more
3527 execution; but your program would probably terminate immediately as
3528 a result of the fatal signal once it saw the signal. To prevent this,
3529 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3533 @section Stopping and starting multi-thread programs
3535 When your program has multiple threads (@pxref{Threads,, Debugging
3536 programs with multiple threads}), you can choose whether to set
3537 breakpoints on all threads, or on a particular thread.
3540 @cindex breakpoints and threads
3541 @cindex thread breakpoints
3542 @kindex break @dots{} thread @var{threadno}
3543 @item break @var{linespec} thread @var{threadno}
3544 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3545 @var{linespec} specifies source lines; there are several ways of
3546 writing them, but the effect is always to specify some source line.
3548 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3549 to specify that you only want @value{GDBN} to stop the program when a
3550 particular thread reaches this breakpoint. @var{threadno} is one of the
3551 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3552 column of the @samp{info threads} display.
3554 If you do not specify @samp{thread @var{threadno}} when you set a
3555 breakpoint, the breakpoint applies to @emph{all} threads of your
3558 You can use the @code{thread} qualifier on conditional breakpoints as
3559 well; in this case, place @samp{thread @var{threadno}} before the
3560 breakpoint condition, like this:
3563 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3568 @cindex stopped threads
3569 @cindex threads, stopped
3570 Whenever your program stops under @value{GDBN} for any reason,
3571 @emph{all} threads of execution stop, not just the current thread. This
3572 allows you to examine the overall state of the program, including
3573 switching between threads, without worrying that things may change
3576 @cindex continuing threads
3577 @cindex threads, continuing
3578 Conversely, whenever you restart the program, @emph{all} threads start
3579 executing. @emph{This is true even when single-stepping} with commands
3580 like @code{step} or @code{next}.
3582 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3583 Since thread scheduling is up to your debugging target's operating
3584 system (not controlled by @value{GDBN}), other threads may
3585 execute more than one statement while the current thread completes a
3586 single step. Moreover, in general other threads stop in the middle of a
3587 statement, rather than at a clean statement boundary, when the program
3590 You might even find your program stopped in another thread after
3591 continuing or even single-stepping. This happens whenever some other
3592 thread runs into a breakpoint, a signal, or an exception before the
3593 first thread completes whatever you requested.
3595 On some OSes, you can lock the OS scheduler and thus allow only a single
3599 @item set scheduler-locking @var{mode}
3600 Set the scheduler locking mode. If it is @code{off}, then there is no
3601 locking and any thread may run at any time. If @code{on}, then only the
3602 current thread may run when the inferior is resumed. The @code{step}
3603 mode optimizes for single-stepping. It stops other threads from
3604 ``seizing the prompt'' by preempting the current thread while you are
3605 stepping. Other threads will only rarely (or never) get a chance to run
3606 when you step. They are more likely to run when you @samp{next} over a
3607 function call, and they are completely free to run when you use commands
3608 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3609 thread hits a breakpoint during its timeslice, they will never steal the
3610 @value{GDBN} prompt away from the thread that you are debugging.
3612 @item show scheduler-locking
3613 Display the current scheduler locking mode.
3618 @chapter Examining the Stack
3620 When your program has stopped, the first thing you need to know is where it
3621 stopped and how it got there.
3624 Each time your program performs a function call, information about the call
3626 That information includes the location of the call in your program,
3627 the arguments of the call,
3628 and the local variables of the function being called.
3629 The information is saved in a block of data called a @dfn{stack frame}.
3630 The stack frames are allocated in a region of memory called the @dfn{call
3633 When your program stops, the @value{GDBN} commands for examining the
3634 stack allow you to see all of this information.
3636 @cindex selected frame
3637 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3638 @value{GDBN} commands refer implicitly to the selected frame. In
3639 particular, whenever you ask @value{GDBN} for the value of a variable in
3640 your program, the value is found in the selected frame. There are
3641 special @value{GDBN} commands to select whichever frame you are
3642 interested in. @xref{Selection, ,Selecting a frame}.
3644 When your program stops, @value{GDBN} automatically selects the
3645 currently executing frame and describes it briefly, similar to the
3646 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3649 * Frames:: Stack frames
3650 * Backtrace:: Backtraces
3651 * Selection:: Selecting a frame
3652 * Frame Info:: Information on a frame
3657 @section Stack frames
3659 @cindex frame, definition
3661 The call stack is divided up into contiguous pieces called @dfn{stack
3662 frames}, or @dfn{frames} for short; each frame is the data associated
3663 with one call to one function. The frame contains the arguments given
3664 to the function, the function's local variables, and the address at
3665 which the function is executing.
3667 @cindex initial frame
3668 @cindex outermost frame
3669 @cindex innermost frame
3670 When your program is started, the stack has only one frame, that of the
3671 function @code{main}. This is called the @dfn{initial} frame or the
3672 @dfn{outermost} frame. Each time a function is called, a new frame is
3673 made. Each time a function returns, the frame for that function invocation
3674 is eliminated. If a function is recursive, there can be many frames for
3675 the same function. The frame for the function in which execution is
3676 actually occurring is called the @dfn{innermost} frame. This is the most
3677 recently created of all the stack frames that still exist.
3679 @cindex frame pointer
3680 Inside your program, stack frames are identified by their addresses. A
3681 stack frame consists of many bytes, each of which has its own address; each
3682 kind of computer has a convention for choosing one byte whose
3683 address serves as the address of the frame. Usually this address is kept
3684 in a register called the @dfn{frame pointer register} while execution is
3685 going on in that frame.
3687 @cindex frame number
3688 @value{GDBN} assigns numbers to all existing stack frames, starting with
3689 zero for the innermost frame, one for the frame that called it,
3690 and so on upward. These numbers do not really exist in your program;
3691 they are assigned by @value{GDBN} to give you a way of designating stack
3692 frames in @value{GDBN} commands.
3694 @c The -fomit-frame-pointer below perennially causes hbox overflow
3695 @c underflow problems.
3696 @cindex frameless execution
3697 Some compilers provide a way to compile functions so that they operate
3698 without stack frames. (For example, the @value{GCC} option
3700 @samp{-fomit-frame-pointer}
3702 generates functions without a frame.)
3703 This is occasionally done with heavily used library functions to save
3704 the frame setup time. @value{GDBN} has limited facilities for dealing
3705 with these function invocations. If the innermost function invocation
3706 has no stack frame, @value{GDBN} nevertheless regards it as though
3707 it had a separate frame, which is numbered zero as usual, allowing
3708 correct tracing of the function call chain. However, @value{GDBN} has
3709 no provision for frameless functions elsewhere in the stack.
3712 @kindex frame@r{, command}
3713 @cindex current stack frame
3714 @item frame @var{args}
3715 The @code{frame} command allows you to move from one stack frame to another,
3716 and to print the stack frame you select. @var{args} may be either the
3717 address of the frame or the stack frame number. Without an argument,
3718 @code{frame} prints the current stack frame.
3720 @kindex select-frame
3721 @cindex selecting frame silently
3723 The @code{select-frame} command allows you to move from one stack frame
3724 to another without printing the frame. This is the silent version of
3733 @cindex stack traces
3734 A backtrace is a summary of how your program got where it is. It shows one
3735 line per frame, for many frames, starting with the currently executing
3736 frame (frame zero), followed by its caller (frame one), and on up the
3741 @kindex bt @r{(@code{backtrace})}
3744 Print a backtrace of the entire stack: one line per frame for all
3745 frames in the stack.
3747 You can stop the backtrace at any time by typing the system interrupt
3748 character, normally @kbd{C-c}.
3750 @item backtrace @var{n}
3752 Similar, but print only the innermost @var{n} frames.
3754 @item backtrace -@var{n}
3756 Similar, but print only the outermost @var{n} frames.
3761 @kindex info s @r{(@code{info stack})}
3762 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3763 are additional aliases for @code{backtrace}.
3765 Each line in the backtrace shows the frame number and the function name.
3766 The program counter value is also shown---unless you use @code{set
3767 print address off}. The backtrace also shows the source file name and
3768 line number, as well as the arguments to the function. The program
3769 counter value is omitted if it is at the beginning of the code for that
3772 Here is an example of a backtrace. It was made with the command
3773 @samp{bt 3}, so it shows the innermost three frames.
3777 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3779 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3780 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3782 (More stack frames follow...)
3787 The display for frame zero does not begin with a program counter
3788 value, indicating that your program has stopped at the beginning of the
3789 code for line @code{993} of @code{builtin.c}.
3792 @section Selecting a frame
3794 Most commands for examining the stack and other data in your program work on
3795 whichever stack frame is selected at the moment. Here are the commands for
3796 selecting a stack frame; all of them finish by printing a brief description
3797 of the stack frame just selected.
3800 @kindex frame@r{, selecting}
3801 @kindex f @r{(@code{frame})}
3804 Select frame number @var{n}. Recall that frame zero is the innermost
3805 (currently executing) frame, frame one is the frame that called the
3806 innermost one, and so on. The highest-numbered frame is the one for
3809 @item frame @var{addr}
3811 Select the frame at address @var{addr}. This is useful mainly if the
3812 chaining of stack frames has been damaged by a bug, making it
3813 impossible for @value{GDBN} to assign numbers properly to all frames. In
3814 addition, this can be useful when your program has multiple stacks and
3815 switches between them.
3817 On the SPARC architecture, @code{frame} needs two addresses to
3818 select an arbitrary frame: a frame pointer and a stack pointer.
3820 On the MIPS and Alpha architecture, it needs two addresses: a stack
3821 pointer and a program counter.
3823 On the 29k architecture, it needs three addresses: a register stack
3824 pointer, a program counter, and a memory stack pointer.
3825 @c note to future updaters: this is conditioned on a flag
3826 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3827 @c as of 27 Jan 1994.
3831 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3832 advances toward the outermost frame, to higher frame numbers, to frames
3833 that have existed longer. @var{n} defaults to one.
3836 @kindex do @r{(@code{down})}
3838 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3839 advances toward the innermost frame, to lower frame numbers, to frames
3840 that were created more recently. @var{n} defaults to one. You may
3841 abbreviate @code{down} as @code{do}.
3844 All of these commands end by printing two lines of output describing the
3845 frame. The first line shows the frame number, the function name, the
3846 arguments, and the source file and line number of execution in that
3847 frame. The second line shows the text of that source line.
3855 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3857 10 read_input_file (argv[i]);
3861 After such a printout, the @code{list} command with no arguments
3862 prints ten lines centered on the point of execution in the frame.
3863 @xref{List, ,Printing source lines}.
3866 @kindex down-silently
3868 @item up-silently @var{n}
3869 @itemx down-silently @var{n}
3870 These two commands are variants of @code{up} and @code{down},
3871 respectively; they differ in that they do their work silently, without
3872 causing display of the new frame. They are intended primarily for use
3873 in @value{GDBN} command scripts, where the output might be unnecessary and
3878 @section Information about a frame
3880 There are several other commands to print information about the selected
3886 When used without any argument, this command does not change which
3887 frame is selected, but prints a brief description of the currently
3888 selected stack frame. It can be abbreviated @code{f}. With an
3889 argument, this command is used to select a stack frame.
3890 @xref{Selection, ,Selecting a frame}.
3893 @kindex info f @r{(@code{info frame})}
3896 This command prints a verbose description of the selected stack frame,
3901 the address of the frame
3903 the address of the next frame down (called by this frame)
3905 the address of the next frame up (caller of this frame)
3907 the language in which the source code corresponding to this frame is written
3909 the address of the frame's arguments
3911 the address of the frame's local variables
3913 the program counter saved in it (the address of execution in the caller frame)
3915 which registers were saved in the frame
3918 @noindent The verbose description is useful when
3919 something has gone wrong that has made the stack format fail to fit
3920 the usual conventions.
3922 @item info frame @var{addr}
3923 @itemx info f @var{addr}
3924 Print a verbose description of the frame at address @var{addr}, without
3925 selecting that frame. The selected frame remains unchanged by this
3926 command. This requires the same kind of address (more than one for some
3927 architectures) that you specify in the @code{frame} command.
3928 @xref{Selection, ,Selecting a frame}.
3932 Print the arguments of the selected frame, each on a separate line.
3936 Print the local variables of the selected frame, each on a separate
3937 line. These are all variables (declared either static or automatic)
3938 accessible at the point of execution of the selected frame.
3941 @cindex catch exceptions, list active handlers
3942 @cindex exception handlers, how to list
3944 Print a list of all the exception handlers that are active in the
3945 current stack frame at the current point of execution. To see other
3946 exception handlers, visit the associated frame (using the @code{up},
3947 @code{down}, or @code{frame} commands); then type @code{info catch}.
3948 @xref{Set Catchpoints, , Setting catchpoints}.
3954 @chapter Examining Source Files
3956 @value{GDBN} can print parts of your program's source, since the debugging
3957 information recorded in the program tells @value{GDBN} what source files were
3958 used to build it. When your program stops, @value{GDBN} spontaneously prints
3959 the line where it stopped. Likewise, when you select a stack frame
3960 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3961 execution in that frame has stopped. You can print other portions of
3962 source files by explicit command.
3964 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3965 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3966 @value{GDBN} under @sc{gnu} Emacs}.
3969 * List:: Printing source lines
3970 * Search:: Searching source files
3971 * Source Path:: Specifying source directories
3972 * Machine Code:: Source and machine code
3976 @section Printing source lines
3979 @kindex l @r{(@code{list})}
3980 To print lines from a source file, use the @code{list} command
3981 (abbreviated @code{l}). By default, ten lines are printed.
3982 There are several ways to specify what part of the file you want to print.
3984 Here are the forms of the @code{list} command most commonly used:
3987 @item list @var{linenum}
3988 Print lines centered around line number @var{linenum} in the
3989 current source file.
3991 @item list @var{function}
3992 Print lines centered around the beginning of function
3996 Print more lines. If the last lines printed were printed with a
3997 @code{list} command, this prints lines following the last lines
3998 printed; however, if the last line printed was a solitary line printed
3999 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4000 Stack}), this prints lines centered around that line.
4003 Print lines just before the lines last printed.
4006 By default, @value{GDBN} prints ten source lines with any of these forms of
4007 the @code{list} command. You can change this using @code{set listsize}:
4010 @kindex set listsize
4011 @item set listsize @var{count}
4012 Make the @code{list} command display @var{count} source lines (unless
4013 the @code{list} argument explicitly specifies some other number).
4015 @kindex show listsize
4017 Display the number of lines that @code{list} prints.
4020 Repeating a @code{list} command with @key{RET} discards the argument,
4021 so it is equivalent to typing just @code{list}. This is more useful
4022 than listing the same lines again. An exception is made for an
4023 argument of @samp{-}; that argument is preserved in repetition so that
4024 each repetition moves up in the source file.
4027 In general, the @code{list} command expects you to supply zero, one or two
4028 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4029 of writing them, but the effect is always to specify some source line.
4030 Here is a complete description of the possible arguments for @code{list}:
4033 @item list @var{linespec}
4034 Print lines centered around the line specified by @var{linespec}.
4036 @item list @var{first},@var{last}
4037 Print lines from @var{first} to @var{last}. Both arguments are
4040 @item list ,@var{last}
4041 Print lines ending with @var{last}.
4043 @item list @var{first},
4044 Print lines starting with @var{first}.
4047 Print lines just after the lines last printed.
4050 Print lines just before the lines last printed.
4053 As described in the preceding table.
4056 Here are the ways of specifying a single source line---all the
4061 Specifies line @var{number} of the current source file.
4062 When a @code{list} command has two linespecs, this refers to
4063 the same source file as the first linespec.
4066 Specifies the line @var{offset} lines after the last line printed.
4067 When used as the second linespec in a @code{list} command that has
4068 two, this specifies the line @var{offset} lines down from the
4072 Specifies the line @var{offset} lines before the last line printed.
4074 @item @var{filename}:@var{number}
4075 Specifies line @var{number} in the source file @var{filename}.
4077 @item @var{function}
4078 Specifies the line that begins the body of the function @var{function}.
4079 For example: in C, this is the line with the open brace.
4081 @item @var{filename}:@var{function}
4082 Specifies the line of the open-brace that begins the body of the
4083 function @var{function} in the file @var{filename}. You only need the
4084 file name with a function name to avoid ambiguity when there are
4085 identically named functions in different source files.
4087 @item *@var{address}
4088 Specifies the line containing the program address @var{address}.
4089 @var{address} may be any expression.
4093 @section Searching source files
4095 @kindex reverse-search
4097 There are two commands for searching through the current source file for a
4102 @kindex forward-search
4103 @item forward-search @var{regexp}
4104 @itemx search @var{regexp}
4105 The command @samp{forward-search @var{regexp}} checks each line,
4106 starting with the one following the last line listed, for a match for
4107 @var{regexp}. It lists the line that is found. You can use the
4108 synonym @samp{search @var{regexp}} or abbreviate the command name as
4111 @item reverse-search @var{regexp}
4112 The command @samp{reverse-search @var{regexp}} checks each line, starting
4113 with the one before the last line listed and going backward, for a match
4114 for @var{regexp}. It lists the line that is found. You can abbreviate
4115 this command as @code{rev}.
4119 @section Specifying source directories
4122 @cindex directories for source files
4123 Executable programs sometimes do not record the directories of the source
4124 files from which they were compiled, just the names. Even when they do,
4125 the directories could be moved between the compilation and your debugging
4126 session. @value{GDBN} has a list of directories to search for source files;
4127 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4128 it tries all the directories in the list, in the order they are present
4129 in the list, until it finds a file with the desired name. Note that
4130 the executable search path is @emph{not} used for this purpose. Neither is
4131 the current working directory, unless it happens to be in the source
4134 If @value{GDBN} cannot find a source file in the source path, and the
4135 object program records a directory, @value{GDBN} tries that directory
4136 too. If the source path is empty, and there is no record of the
4137 compilation directory, @value{GDBN} looks in the current directory as a
4140 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4141 any information it has cached about where source files are found and where
4142 each line is in the file.
4146 When you start @value{GDBN}, its source path includes only @samp{cdir}
4147 and @samp{cwd}, in that order.
4148 To add other directories, use the @code{directory} command.
4151 @item directory @var{dirname} @dots{}
4152 @item dir @var{dirname} @dots{}
4153 Add directory @var{dirname} to the front of the source path. Several
4154 directory names may be given to this command, separated by @samp{:}
4155 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4156 part of absolute file names) or
4157 whitespace. You may specify a directory that is already in the source
4158 path; this moves it forward, so @value{GDBN} searches it sooner.
4162 @vindex $cdir@r{, convenience variable}
4163 @vindex $cwdr@r{, convenience variable}
4164 @cindex compilation directory
4165 @cindex current directory
4166 @cindex working directory
4167 @cindex directory, current
4168 @cindex directory, compilation
4169 You can use the string @samp{$cdir} to refer to the compilation
4170 directory (if one is recorded), and @samp{$cwd} to refer to the current
4171 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4172 tracks the current working directory as it changes during your @value{GDBN}
4173 session, while the latter is immediately expanded to the current
4174 directory at the time you add an entry to the source path.
4177 Reset the source path to empty again. This requires confirmation.
4179 @c RET-repeat for @code{directory} is explicitly disabled, but since
4180 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4182 @item show directories
4183 @kindex show directories
4184 Print the source path: show which directories it contains.
4187 If your source path is cluttered with directories that are no longer of
4188 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4189 versions of source. You can correct the situation as follows:
4193 Use @code{directory} with no argument to reset the source path to empty.
4196 Use @code{directory} with suitable arguments to reinstall the
4197 directories you want in the source path. You can add all the
4198 directories in one command.
4202 @section Source and machine code
4204 You can use the command @code{info line} to map source lines to program
4205 addresses (and vice versa), and the command @code{disassemble} to display
4206 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4207 mode, the @code{info line} command causes the arrow to point to the
4208 line specified. Also, @code{info line} prints addresses in symbolic form as
4213 @item info line @var{linespec}
4214 Print the starting and ending addresses of the compiled code for
4215 source line @var{linespec}. You can specify source lines in any of
4216 the ways understood by the @code{list} command (@pxref{List, ,Printing
4220 For example, we can use @code{info line} to discover the location of
4221 the object code for the first line of function
4222 @code{m4_changequote}:
4224 @c FIXME: I think this example should also show the addresses in
4225 @c symbolic form, as they usually would be displayed.
4227 (@value{GDBP}) info line m4_changequote
4228 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4232 We can also inquire (using @code{*@var{addr}} as the form for
4233 @var{linespec}) what source line covers a particular address:
4235 (@value{GDBP}) info line *0x63ff
4236 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4239 @cindex @code{$_} and @code{info line}
4240 @kindex x@r{(examine), and} info line
4241 After @code{info line}, the default address for the @code{x} command
4242 is changed to the starting address of the line, so that @samp{x/i} is
4243 sufficient to begin examining the machine code (@pxref{Memory,
4244 ,Examining memory}). Also, this address is saved as the value of the
4245 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4250 @cindex assembly instructions
4251 @cindex instructions, assembly
4252 @cindex machine instructions
4253 @cindex listing machine instructions
4255 This specialized command dumps a range of memory as machine
4256 instructions. The default memory range is the function surrounding the
4257 program counter of the selected frame. A single argument to this
4258 command is a program counter value; @value{GDBN} dumps the function
4259 surrounding this value. Two arguments specify a range of addresses
4260 (first inclusive, second exclusive) to dump.
4263 The following example shows the disassembly of a range of addresses of
4264 HP PA-RISC 2.0 code:
4267 (@value{GDBP}) disas 0x32c4 0x32e4
4268 Dump of assembler code from 0x32c4 to 0x32e4:
4269 0x32c4 <main+204>: addil 0,dp
4270 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4271 0x32cc <main+212>: ldil 0x3000,r31
4272 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4273 0x32d4 <main+220>: ldo 0(r31),rp
4274 0x32d8 <main+224>: addil -0x800,dp
4275 0x32dc <main+228>: ldo 0x588(r1),r26
4276 0x32e0 <main+232>: ldil 0x3000,r31
4277 End of assembler dump.
4280 Some architectures have more than one commonly-used set of instruction
4281 mnemonics or other syntax.
4284 @kindex set disassembly-flavor
4285 @cindex assembly instructions
4286 @cindex instructions, assembly
4287 @cindex machine instructions
4288 @cindex listing machine instructions
4289 @cindex Intel disassembly flavor
4290 @cindex AT&T disassembly flavor
4291 @item set disassembly-flavor @var{instruction-set}
4292 Select the instruction set to use when disassembling the
4293 program via the @code{disassemble} or @code{x/i} commands.
4295 Currently this command is only defined for the Intel x86 family. You
4296 can set @var{instruction-set} to either @code{intel} or @code{att}.
4297 The default is @code{att}, the AT&T flavor used by default by Unix
4298 assemblers for x86-based targets.
4303 @chapter Examining Data
4305 @cindex printing data
4306 @cindex examining data
4309 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4310 @c document because it is nonstandard... Under Epoch it displays in a
4311 @c different window or something like that.
4312 The usual way to examine data in your program is with the @code{print}
4313 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4314 evaluates and prints the value of an expression of the language your
4315 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4316 Different Languages}).
4319 @item print @var{expr}
4320 @itemx print /@var{f} @var{expr}
4321 @var{expr} is an expression (in the source language). By default the
4322 value of @var{expr} is printed in a format appropriate to its data type;
4323 you can choose a different format by specifying @samp{/@var{f}}, where
4324 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4328 @itemx print /@var{f}
4329 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4330 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4331 conveniently inspect the same value in an alternative format.
4334 A more low-level way of examining data is with the @code{x} command.
4335 It examines data in memory at a specified address and prints it in a
4336 specified format. @xref{Memory, ,Examining memory}.
4338 If you are interested in information about types, or about how the
4339 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4340 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4344 * Expressions:: Expressions
4345 * Variables:: Program variables
4346 * Arrays:: Artificial arrays
4347 * Output Formats:: Output formats
4348 * Memory:: Examining memory
4349 * Auto Display:: Automatic display
4350 * Print Settings:: Print settings
4351 * Value History:: Value history
4352 * Convenience Vars:: Convenience variables
4353 * Registers:: Registers
4354 * Floating Point Hardware:: Floating point hardware
4355 * Memory Region Attributes:: Memory region attributes
4359 @section Expressions
4362 @code{print} and many other @value{GDBN} commands accept an expression and
4363 compute its value. Any kind of constant, variable or operator defined
4364 by the programming language you are using is valid in an expression in
4365 @value{GDBN}. This includes conditional expressions, function calls, casts
4366 and string constants. It unfortunately does not include symbols defined
4367 by preprocessor @code{#define} commands.
4369 @value{GDBN} supports array constants in expressions input by
4370 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4371 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4372 memory that is @code{malloc}ed in the target program.
4374 Because C is so widespread, most of the expressions shown in examples in
4375 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4376 Languages}, for information on how to use expressions in other
4379 In this section, we discuss operators that you can use in @value{GDBN}
4380 expressions regardless of your programming language.
4382 Casts are supported in all languages, not just in C, because it is so
4383 useful to cast a number into a pointer in order to examine a structure
4384 at that address in memory.
4385 @c FIXME: casts supported---Mod2 true?
4387 @value{GDBN} supports these operators, in addition to those common
4388 to programming languages:
4392 @samp{@@} is a binary operator for treating parts of memory as arrays.
4393 @xref{Arrays, ,Artificial arrays}, for more information.
4396 @samp{::} allows you to specify a variable in terms of the file or
4397 function where it is defined. @xref{Variables, ,Program variables}.
4399 @cindex @{@var{type}@}
4400 @cindex type casting memory
4401 @cindex memory, viewing as typed object
4402 @cindex casts, to view memory
4403 @item @{@var{type}@} @var{addr}
4404 Refers to an object of type @var{type} stored at address @var{addr} in
4405 memory. @var{addr} may be any expression whose value is an integer or
4406 pointer (but parentheses are required around binary operators, just as in
4407 a cast). This construct is allowed regardless of what kind of data is
4408 normally supposed to reside at @var{addr}.
4412 @section Program variables
4414 The most common kind of expression to use is the name of a variable
4417 Variables in expressions are understood in the selected stack frame
4418 (@pxref{Selection, ,Selecting a frame}); they must be either:
4422 global (or file-static)
4429 visible according to the scope rules of the
4430 programming language from the point of execution in that frame
4433 @noindent This means that in the function
4448 you can examine and use the variable @code{a} whenever your program is
4449 executing within the function @code{foo}, but you can only use or
4450 examine the variable @code{b} while your program is executing inside
4451 the block where @code{b} is declared.
4453 @cindex variable name conflict
4454 There is an exception: you can refer to a variable or function whose
4455 scope is a single source file even if the current execution point is not
4456 in this file. But it is possible to have more than one such variable or
4457 function with the same name (in different source files). If that
4458 happens, referring to that name has unpredictable effects. If you wish,
4459 you can specify a static variable in a particular function or file,
4460 using the colon-colon notation:
4462 @cindex colon-colon, context for variables/functions
4464 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4465 @cindex @code{::}, context for variables/functions
4468 @var{file}::@var{variable}
4469 @var{function}::@var{variable}
4473 Here @var{file} or @var{function} is the name of the context for the
4474 static @var{variable}. In the case of file names, you can use quotes to
4475 make sure @value{GDBN} parses the file name as a single word---for example,
4476 to print a global value of @code{x} defined in @file{f2.c}:
4479 (@value{GDBP}) p 'f2.c'::x
4482 @cindex C@t{++} scope resolution
4483 This use of @samp{::} is very rarely in conflict with the very similar
4484 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4485 scope resolution operator in @value{GDBN} expressions.
4486 @c FIXME: Um, so what happens in one of those rare cases where it's in
4489 @cindex wrong values
4490 @cindex variable values, wrong
4492 @emph{Warning:} Occasionally, a local variable may appear to have the
4493 wrong value at certain points in a function---just after entry to a new
4494 scope, and just before exit.
4496 You may see this problem when you are stepping by machine instructions.
4497 This is because, on most machines, it takes more than one instruction to
4498 set up a stack frame (including local variable definitions); if you are
4499 stepping by machine instructions, variables may appear to have the wrong
4500 values until the stack frame is completely built. On exit, it usually
4501 also takes more than one machine instruction to destroy a stack frame;
4502 after you begin stepping through that group of instructions, local
4503 variable definitions may be gone.
4505 This may also happen when the compiler does significant optimizations.
4506 To be sure of always seeing accurate values, turn off all optimization
4509 @cindex ``No symbol "foo" in current context''
4510 Another possible effect of compiler optimizations is to optimize
4511 unused variables out of existence, or assign variables to registers (as
4512 opposed to memory addresses). Depending on the support for such cases
4513 offered by the debug info format used by the compiler, @value{GDBN}
4514 might not be able to display values for such local variables. If that
4515 happens, @value{GDBN} will print a message like this:
4518 No symbol "foo" in current context.
4521 To solve such problems, either recompile without optimizations, or use a
4522 different debug info format, if the compiler supports several such
4523 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4524 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4525 in a format that is superior to formats such as COFF. You may be able
4526 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4527 debug info. See @ref{Debugging Options,,Options for Debugging Your
4528 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4533 @section Artificial arrays
4535 @cindex artificial array
4536 @kindex @@@r{, referencing memory as an array}
4537 It is often useful to print out several successive objects of the
4538 same type in memory; a section of an array, or an array of
4539 dynamically determined size for which only a pointer exists in the
4542 You can do this by referring to a contiguous span of memory as an
4543 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4544 operand of @samp{@@} should be the first element of the desired array
4545 and be an individual object. The right operand should be the desired length
4546 of the array. The result is an array value whose elements are all of
4547 the type of the left argument. The first element is actually the left
4548 argument; the second element comes from bytes of memory immediately
4549 following those that hold the first element, and so on. Here is an
4550 example. If a program says
4553 int *array = (int *) malloc (len * sizeof (int));
4557 you can print the contents of @code{array} with
4563 The left operand of @samp{@@} must reside in memory. Array values made
4564 with @samp{@@} in this way behave just like other arrays in terms of
4565 subscripting, and are coerced to pointers when used in expressions.
4566 Artificial arrays most often appear in expressions via the value history
4567 (@pxref{Value History, ,Value history}), after printing one out.
4569 Another way to create an artificial array is to use a cast.
4570 This re-interprets a value as if it were an array.
4571 The value need not be in memory:
4573 (@value{GDBP}) p/x (short[2])0x12345678
4574 $1 = @{0x1234, 0x5678@}
4577 As a convenience, if you leave the array length out (as in
4578 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4579 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4581 (@value{GDBP}) p/x (short[])0x12345678
4582 $2 = @{0x1234, 0x5678@}
4585 Sometimes the artificial array mechanism is not quite enough; in
4586 moderately complex data structures, the elements of interest may not
4587 actually be adjacent---for example, if you are interested in the values
4588 of pointers in an array. One useful work-around in this situation is
4589 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4590 variables}) as a counter in an expression that prints the first
4591 interesting value, and then repeat that expression via @key{RET}. For
4592 instance, suppose you have an array @code{dtab} of pointers to
4593 structures, and you are interested in the values of a field @code{fv}
4594 in each structure. Here is an example of what you might type:
4604 @node Output Formats
4605 @section Output formats
4607 @cindex formatted output
4608 @cindex output formats
4609 By default, @value{GDBN} prints a value according to its data type. Sometimes
4610 this is not what you want. For example, you might want to print a number
4611 in hex, or a pointer in decimal. Or you might want to view data in memory
4612 at a certain address as a character string or as an instruction. To do
4613 these things, specify an @dfn{output format} when you print a value.
4615 The simplest use of output formats is to say how to print a value
4616 already computed. This is done by starting the arguments of the
4617 @code{print} command with a slash and a format letter. The format
4618 letters supported are:
4622 Regard the bits of the value as an integer, and print the integer in
4626 Print as integer in signed decimal.
4629 Print as integer in unsigned decimal.
4632 Print as integer in octal.
4635 Print as integer in binary. The letter @samp{t} stands for ``two''.
4636 @footnote{@samp{b} cannot be used because these format letters are also
4637 used with the @code{x} command, where @samp{b} stands for ``byte'';
4638 see @ref{Memory,,Examining memory}.}
4641 @cindex unknown address, locating
4642 @cindex locate address
4643 Print as an address, both absolute in hexadecimal and as an offset from
4644 the nearest preceding symbol. You can use this format used to discover
4645 where (in what function) an unknown address is located:
4648 (@value{GDBP}) p/a 0x54320
4649 $3 = 0x54320 <_initialize_vx+396>
4653 The command @code{info symbol 0x54320} yields similar results.
4654 @xref{Symbols, info symbol}.
4657 Regard as an integer and print it as a character constant.
4660 Regard the bits of the value as a floating point number and print
4661 using typical floating point syntax.
4664 For example, to print the program counter in hex (@pxref{Registers}), type
4671 Note that no space is required before the slash; this is because command
4672 names in @value{GDBN} cannot contain a slash.
4674 To reprint the last value in the value history with a different format,
4675 you can use the @code{print} command with just a format and no
4676 expression. For example, @samp{p/x} reprints the last value in hex.
4679 @section Examining memory
4681 You can use the command @code{x} (for ``examine'') to examine memory in
4682 any of several formats, independently of your program's data types.
4684 @cindex examining memory
4686 @kindex x @r{(examine memory)}
4687 @item x/@var{nfu} @var{addr}
4690 Use the @code{x} command to examine memory.
4693 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4694 much memory to display and how to format it; @var{addr} is an
4695 expression giving the address where you want to start displaying memory.
4696 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4697 Several commands set convenient defaults for @var{addr}.
4700 @item @var{n}, the repeat count
4701 The repeat count is a decimal integer; the default is 1. It specifies
4702 how much memory (counting by units @var{u}) to display.
4703 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4706 @item @var{f}, the display format
4707 The display format is one of the formats used by @code{print},
4708 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4709 The default is @samp{x} (hexadecimal) initially.
4710 The default changes each time you use either @code{x} or @code{print}.
4712 @item @var{u}, the unit size
4713 The unit size is any of
4719 Halfwords (two bytes).
4721 Words (four bytes). This is the initial default.
4723 Giant words (eight bytes).
4726 Each time you specify a unit size with @code{x}, that size becomes the
4727 default unit the next time you use @code{x}. (For the @samp{s} and
4728 @samp{i} formats, the unit size is ignored and is normally not written.)
4730 @item @var{addr}, starting display address
4731 @var{addr} is the address where you want @value{GDBN} to begin displaying
4732 memory. The expression need not have a pointer value (though it may);
4733 it is always interpreted as an integer address of a byte of memory.
4734 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4735 @var{addr} is usually just after the last address examined---but several
4736 other commands also set the default address: @code{info breakpoints} (to
4737 the address of the last breakpoint listed), @code{info line} (to the
4738 starting address of a line), and @code{print} (if you use it to display
4739 a value from memory).
4742 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4743 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4744 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4745 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4746 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4748 Since the letters indicating unit sizes are all distinct from the
4749 letters specifying output formats, you do not have to remember whether
4750 unit size or format comes first; either order works. The output
4751 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4752 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4754 Even though the unit size @var{u} is ignored for the formats @samp{s}
4755 and @samp{i}, you might still want to use a count @var{n}; for example,
4756 @samp{3i} specifies that you want to see three machine instructions,
4757 including any operands. The command @code{disassemble} gives an
4758 alternative way of inspecting machine instructions; see @ref{Machine
4759 Code,,Source and machine code}.
4761 All the defaults for the arguments to @code{x} are designed to make it
4762 easy to continue scanning memory with minimal specifications each time
4763 you use @code{x}. For example, after you have inspected three machine
4764 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4765 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4766 the repeat count @var{n} is used again; the other arguments default as
4767 for successive uses of @code{x}.
4769 @cindex @code{$_}, @code{$__}, and value history
4770 The addresses and contents printed by the @code{x} command are not saved
4771 in the value history because there is often too much of them and they
4772 would get in the way. Instead, @value{GDBN} makes these values available for
4773 subsequent use in expressions as values of the convenience variables
4774 @code{$_} and @code{$__}. After an @code{x} command, the last address
4775 examined is available for use in expressions in the convenience variable
4776 @code{$_}. The contents of that address, as examined, are available in
4777 the convenience variable @code{$__}.
4779 If the @code{x} command has a repeat count, the address and contents saved
4780 are from the last memory unit printed; this is not the same as the last
4781 address printed if several units were printed on the last line of output.
4784 @section Automatic display
4785 @cindex automatic display
4786 @cindex display of expressions
4788 If you find that you want to print the value of an expression frequently
4789 (to see how it changes), you might want to add it to the @dfn{automatic
4790 display list} so that @value{GDBN} prints its value each time your program stops.
4791 Each expression added to the list is given a number to identify it;
4792 to remove an expression from the list, you specify that number.
4793 The automatic display looks like this:
4797 3: bar[5] = (struct hack *) 0x3804
4801 This display shows item numbers, expressions and their current values. As with
4802 displays you request manually using @code{x} or @code{print}, you can
4803 specify the output format you prefer; in fact, @code{display} decides
4804 whether to use @code{print} or @code{x} depending on how elaborate your
4805 format specification is---it uses @code{x} if you specify a unit size,
4806 or one of the two formats (@samp{i} and @samp{s}) that are only
4807 supported by @code{x}; otherwise it uses @code{print}.
4811 @item display @var{expr}
4812 Add the expression @var{expr} to the list of expressions to display
4813 each time your program stops. @xref{Expressions, ,Expressions}.
4815 @code{display} does not repeat if you press @key{RET} again after using it.
4817 @item display/@var{fmt} @var{expr}
4818 For @var{fmt} specifying only a display format and not a size or
4819 count, add the expression @var{expr} to the auto-display list but
4820 arrange to display it each time in the specified format @var{fmt}.
4821 @xref{Output Formats,,Output formats}.
4823 @item display/@var{fmt} @var{addr}
4824 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4825 number of units, add the expression @var{addr} as a memory address to
4826 be examined each time your program stops. Examining means in effect
4827 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4830 For example, @samp{display/i $pc} can be helpful, to see the machine
4831 instruction about to be executed each time execution stops (@samp{$pc}
4832 is a common name for the program counter; @pxref{Registers, ,Registers}).
4835 @kindex delete display
4837 @item undisplay @var{dnums}@dots{}
4838 @itemx delete display @var{dnums}@dots{}
4839 Remove item numbers @var{dnums} from the list of expressions to display.
4841 @code{undisplay} does not repeat if you press @key{RET} after using it.
4842 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4844 @kindex disable display
4845 @item disable display @var{dnums}@dots{}
4846 Disable the display of item numbers @var{dnums}. A disabled display
4847 item is not printed automatically, but is not forgotten. It may be
4848 enabled again later.
4850 @kindex enable display
4851 @item enable display @var{dnums}@dots{}
4852 Enable display of item numbers @var{dnums}. It becomes effective once
4853 again in auto display of its expression, until you specify otherwise.
4856 Display the current values of the expressions on the list, just as is
4857 done when your program stops.
4859 @kindex info display
4861 Print the list of expressions previously set up to display
4862 automatically, each one with its item number, but without showing the
4863 values. This includes disabled expressions, which are marked as such.
4864 It also includes expressions which would not be displayed right now
4865 because they refer to automatic variables not currently available.
4868 If a display expression refers to local variables, then it does not make
4869 sense outside the lexical context for which it was set up. Such an
4870 expression is disabled when execution enters a context where one of its
4871 variables is not defined. For example, if you give the command
4872 @code{display last_char} while inside a function with an argument
4873 @code{last_char}, @value{GDBN} displays this argument while your program
4874 continues to stop inside that function. When it stops elsewhere---where
4875 there is no variable @code{last_char}---the display is disabled
4876 automatically. The next time your program stops where @code{last_char}
4877 is meaningful, you can enable the display expression once again.
4879 @node Print Settings
4880 @section Print settings
4882 @cindex format options
4883 @cindex print settings
4884 @value{GDBN} provides the following ways to control how arrays, structures,
4885 and symbols are printed.
4888 These settings are useful for debugging programs in any language:
4891 @kindex set print address
4892 @item set print address
4893 @itemx set print address on
4894 @value{GDBN} prints memory addresses showing the location of stack
4895 traces, structure values, pointer values, breakpoints, and so forth,
4896 even when it also displays the contents of those addresses. The default
4897 is @code{on}. For example, this is what a stack frame display looks like with
4898 @code{set print address on}:
4903 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4905 530 if (lquote != def_lquote)
4909 @item set print address off
4910 Do not print addresses when displaying their contents. For example,
4911 this is the same stack frame displayed with @code{set print address off}:
4915 (@value{GDBP}) set print addr off
4917 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4918 530 if (lquote != def_lquote)
4922 You can use @samp{set print address off} to eliminate all machine
4923 dependent displays from the @value{GDBN} interface. For example, with
4924 @code{print address off}, you should get the same text for backtraces on
4925 all machines---whether or not they involve pointer arguments.
4927 @kindex show print address
4928 @item show print address
4929 Show whether or not addresses are to be printed.
4932 When @value{GDBN} prints a symbolic address, it normally prints the
4933 closest earlier symbol plus an offset. If that symbol does not uniquely
4934 identify the address (for example, it is a name whose scope is a single
4935 source file), you may need to clarify. One way to do this is with
4936 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4937 you can set @value{GDBN} to print the source file and line number when
4938 it prints a symbolic address:
4941 @kindex set print symbol-filename
4942 @item set print symbol-filename on
4943 Tell @value{GDBN} to print the source file name and line number of a
4944 symbol in the symbolic form of an address.
4946 @item set print symbol-filename off
4947 Do not print source file name and line number of a symbol. This is the
4950 @kindex show print symbol-filename
4951 @item show print symbol-filename
4952 Show whether or not @value{GDBN} will print the source file name and
4953 line number of a symbol in the symbolic form of an address.
4956 Another situation where it is helpful to show symbol filenames and line
4957 numbers is when disassembling code; @value{GDBN} shows you the line
4958 number and source file that corresponds to each instruction.
4960 Also, you may wish to see the symbolic form only if the address being
4961 printed is reasonably close to the closest earlier symbol:
4964 @kindex set print max-symbolic-offset
4965 @item set print max-symbolic-offset @var{max-offset}
4966 Tell @value{GDBN} to only display the symbolic form of an address if the
4967 offset between the closest earlier symbol and the address is less than
4968 @var{max-offset}. The default is 0, which tells @value{GDBN}
4969 to always print the symbolic form of an address if any symbol precedes it.
4971 @kindex show print max-symbolic-offset
4972 @item show print max-symbolic-offset
4973 Ask how large the maximum offset is that @value{GDBN} prints in a
4977 @cindex wild pointer, interpreting
4978 @cindex pointer, finding referent
4979 If you have a pointer and you are not sure where it points, try
4980 @samp{set print symbol-filename on}. Then you can determine the name
4981 and source file location of the variable where it points, using
4982 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4983 For example, here @value{GDBN} shows that a variable @code{ptt} points
4984 at another variable @code{t}, defined in @file{hi2.c}:
4987 (@value{GDBP}) set print symbol-filename on
4988 (@value{GDBP}) p/a ptt
4989 $4 = 0xe008 <t in hi2.c>
4993 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4994 does not show the symbol name and filename of the referent, even with
4995 the appropriate @code{set print} options turned on.
4998 Other settings control how different kinds of objects are printed:
5001 @kindex set print array
5002 @item set print array
5003 @itemx set print array on
5004 Pretty print arrays. This format is more convenient to read,
5005 but uses more space. The default is off.
5007 @item set print array off
5008 Return to compressed format for arrays.
5010 @kindex show print array
5011 @item show print array
5012 Show whether compressed or pretty format is selected for displaying
5015 @kindex set print elements
5016 @item set print elements @var{number-of-elements}
5017 Set a limit on how many elements of an array @value{GDBN} will print.
5018 If @value{GDBN} is printing a large array, it stops printing after it has
5019 printed the number of elements set by the @code{set print elements} command.
5020 This limit also applies to the display of strings.
5021 When @value{GDBN} starts, this limit is set to 200.
5022 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5024 @kindex show print elements
5025 @item show print elements
5026 Display the number of elements of a large array that @value{GDBN} will print.
5027 If the number is 0, then the printing is unlimited.
5029 @kindex set print null-stop
5030 @item set print null-stop
5031 Cause @value{GDBN} to stop printing the characters of an array when the first
5032 @sc{null} is encountered. This is useful when large arrays actually
5033 contain only short strings.
5036 @kindex set print pretty
5037 @item set print pretty on
5038 Cause @value{GDBN} to print structures in an indented format with one member
5039 per line, like this:
5054 @item set print pretty off
5055 Cause @value{GDBN} to print structures in a compact format, like this:
5059 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5060 meat = 0x54 "Pork"@}
5065 This is the default format.
5067 @kindex show print pretty
5068 @item show print pretty
5069 Show which format @value{GDBN} is using to print structures.
5071 @kindex set print sevenbit-strings
5072 @item set print sevenbit-strings on
5073 Print using only seven-bit characters; if this option is set,
5074 @value{GDBN} displays any eight-bit characters (in strings or
5075 character values) using the notation @code{\}@var{nnn}. This setting is
5076 best if you are working in English (@sc{ascii}) and you use the
5077 high-order bit of characters as a marker or ``meta'' bit.
5079 @item set print sevenbit-strings off
5080 Print full eight-bit characters. This allows the use of more
5081 international character sets, and is the default.
5083 @kindex show print sevenbit-strings
5084 @item show print sevenbit-strings
5085 Show whether or not @value{GDBN} is printing only seven-bit characters.
5087 @kindex set print union
5088 @item set print union on
5089 Tell @value{GDBN} to print unions which are contained in structures. This
5090 is the default setting.
5092 @item set print union off
5093 Tell @value{GDBN} not to print unions which are contained in structures.
5095 @kindex show print union
5096 @item show print union
5097 Ask @value{GDBN} whether or not it will print unions which are contained in
5100 For example, given the declarations
5103 typedef enum @{Tree, Bug@} Species;
5104 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5105 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5116 struct thing foo = @{Tree, @{Acorn@}@};
5120 with @code{set print union on} in effect @samp{p foo} would print
5123 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5127 and with @code{set print union off} in effect it would print
5130 $1 = @{it = Tree, form = @{...@}@}
5136 These settings are of interest when debugging C@t{++} programs:
5140 @kindex set print demangle
5141 @item set print demangle
5142 @itemx set print demangle on
5143 Print C@t{++} names in their source form rather than in the encoded
5144 (``mangled'') form passed to the assembler and linker for type-safe
5145 linkage. The default is on.
5147 @kindex show print demangle
5148 @item show print demangle
5149 Show whether C@t{++} names are printed in mangled or demangled form.
5151 @kindex set print asm-demangle
5152 @item set print asm-demangle
5153 @itemx set print asm-demangle on
5154 Print C@t{++} names in their source form rather than their mangled form, even
5155 in assembler code printouts such as instruction disassemblies.
5158 @kindex show print asm-demangle
5159 @item show print asm-demangle
5160 Show whether C@t{++} names in assembly listings are printed in mangled
5163 @kindex set demangle-style
5164 @cindex C@t{++} symbol decoding style
5165 @cindex symbol decoding style, C@t{++}
5166 @item set demangle-style @var{style}
5167 Choose among several encoding schemes used by different compilers to
5168 represent C@t{++} names. The choices for @var{style} are currently:
5172 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5175 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5176 This is the default.
5179 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5182 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5185 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5186 @strong{Warning:} this setting alone is not sufficient to allow
5187 debugging @code{cfront}-generated executables. @value{GDBN} would
5188 require further enhancement to permit that.
5191 If you omit @var{style}, you will see a list of possible formats.
5193 @kindex show demangle-style
5194 @item show demangle-style
5195 Display the encoding style currently in use for decoding C@t{++} symbols.
5197 @kindex set print object
5198 @item set print object
5199 @itemx set print object on
5200 When displaying a pointer to an object, identify the @emph{actual}
5201 (derived) type of the object rather than the @emph{declared} type, using
5202 the virtual function table.
5204 @item set print object off
5205 Display only the declared type of objects, without reference to the
5206 virtual function table. This is the default setting.
5208 @kindex show print object
5209 @item show print object
5210 Show whether actual, or declared, object types are displayed.
5212 @kindex set print static-members
5213 @item set print static-members
5214 @itemx set print static-members on
5215 Print static members when displaying a C@t{++} object. The default is on.
5217 @item set print static-members off
5218 Do not print static members when displaying a C@t{++} object.
5220 @kindex show print static-members
5221 @item show print static-members
5222 Show whether C@t{++} static members are printed, or not.
5224 @c These don't work with HP ANSI C++ yet.
5225 @kindex set print vtbl
5226 @item set print vtbl
5227 @itemx set print vtbl on
5228 Pretty print C@t{++} virtual function tables. The default is off.
5229 (The @code{vtbl} commands do not work on programs compiled with the HP
5230 ANSI C@t{++} compiler (@code{aCC}).)
5232 @item set print vtbl off
5233 Do not pretty print C@t{++} virtual function tables.
5235 @kindex show print vtbl
5236 @item show print vtbl
5237 Show whether C@t{++} virtual function tables are pretty printed, or not.
5241 @section Value history
5243 @cindex value history
5244 Values printed by the @code{print} command are saved in the @value{GDBN}
5245 @dfn{value history}. This allows you to refer to them in other expressions.
5246 Values are kept until the symbol table is re-read or discarded
5247 (for example with the @code{file} or @code{symbol-file} commands).
5248 When the symbol table changes, the value history is discarded,
5249 since the values may contain pointers back to the types defined in the
5254 @cindex history number
5255 The values printed are given @dfn{history numbers} by which you can
5256 refer to them. These are successive integers starting with one.
5257 @code{print} shows you the history number assigned to a value by
5258 printing @samp{$@var{num} = } before the value; here @var{num} is the
5261 To refer to any previous value, use @samp{$} followed by the value's
5262 history number. The way @code{print} labels its output is designed to
5263 remind you of this. Just @code{$} refers to the most recent value in
5264 the history, and @code{$$} refers to the value before that.
5265 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5266 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5267 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5269 For example, suppose you have just printed a pointer to a structure and
5270 want to see the contents of the structure. It suffices to type
5276 If you have a chain of structures where the component @code{next} points
5277 to the next one, you can print the contents of the next one with this:
5284 You can print successive links in the chain by repeating this
5285 command---which you can do by just typing @key{RET}.
5287 Note that the history records values, not expressions. If the value of
5288 @code{x} is 4 and you type these commands:
5296 then the value recorded in the value history by the @code{print} command
5297 remains 4 even though the value of @code{x} has changed.
5302 Print the last ten values in the value history, with their item numbers.
5303 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5304 values} does not change the history.
5306 @item show values @var{n}
5307 Print ten history values centered on history item number @var{n}.
5310 Print ten history values just after the values last printed. If no more
5311 values are available, @code{show values +} produces no display.
5314 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5315 same effect as @samp{show values +}.
5317 @node Convenience Vars
5318 @section Convenience variables
5320 @cindex convenience variables
5321 @value{GDBN} provides @dfn{convenience variables} that you can use within
5322 @value{GDBN} to hold on to a value and refer to it later. These variables
5323 exist entirely within @value{GDBN}; they are not part of your program, and
5324 setting a convenience variable has no direct effect on further execution
5325 of your program. That is why you can use them freely.
5327 Convenience variables are prefixed with @samp{$}. Any name preceded by
5328 @samp{$} can be used for a convenience variable, unless it is one of
5329 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5330 (Value history references, in contrast, are @emph{numbers} preceded
5331 by @samp{$}. @xref{Value History, ,Value history}.)
5333 You can save a value in a convenience variable with an assignment
5334 expression, just as you would set a variable in your program.
5338 set $foo = *object_ptr
5342 would save in @code{$foo} the value contained in the object pointed to by
5345 Using a convenience variable for the first time creates it, but its
5346 value is @code{void} until you assign a new value. You can alter the
5347 value with another assignment at any time.
5349 Convenience variables have no fixed types. You can assign a convenience
5350 variable any type of value, including structures and arrays, even if
5351 that variable already has a value of a different type. The convenience
5352 variable, when used as an expression, has the type of its current value.
5355 @kindex show convenience
5356 @item show convenience
5357 Print a list of convenience variables used so far, and their values.
5358 Abbreviated @code{show conv}.
5361 One of the ways to use a convenience variable is as a counter to be
5362 incremented or a pointer to be advanced. For example, to print
5363 a field from successive elements of an array of structures:
5367 print bar[$i++]->contents
5371 Repeat that command by typing @key{RET}.
5373 Some convenience variables are created automatically by @value{GDBN} and given
5374 values likely to be useful.
5377 @vindex $_@r{, convenience variable}
5379 The variable @code{$_} is automatically set by the @code{x} command to
5380 the last address examined (@pxref{Memory, ,Examining memory}). Other
5381 commands which provide a default address for @code{x} to examine also
5382 set @code{$_} to that address; these commands include @code{info line}
5383 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5384 except when set by the @code{x} command, in which case it is a pointer
5385 to the type of @code{$__}.
5387 @vindex $__@r{, convenience variable}
5389 The variable @code{$__} is automatically set by the @code{x} command
5390 to the value found in the last address examined. Its type is chosen
5391 to match the format in which the data was printed.
5394 @vindex $_exitcode@r{, convenience variable}
5395 The variable @code{$_exitcode} is automatically set to the exit code when
5396 the program being debugged terminates.
5399 On HP-UX systems, if you refer to a function or variable name that
5400 begins with a dollar sign, @value{GDBN} searches for a user or system
5401 name first, before it searches for a convenience variable.
5407 You can refer to machine register contents, in expressions, as variables
5408 with names starting with @samp{$}. The names of registers are different
5409 for each machine; use @code{info registers} to see the names used on
5413 @kindex info registers
5414 @item info registers
5415 Print the names and values of all registers except floating-point
5416 registers (in the selected stack frame).
5418 @kindex info all-registers
5419 @cindex floating point registers
5420 @item info all-registers
5421 Print the names and values of all registers, including floating-point
5424 @item info registers @var{regname} @dots{}
5425 Print the @dfn{relativized} value of each specified register @var{regname}.
5426 As discussed in detail below, register values are normally relative to
5427 the selected stack frame. @var{regname} may be any register name valid on
5428 the machine you are using, with or without the initial @samp{$}.
5431 @value{GDBN} has four ``standard'' register names that are available (in
5432 expressions) on most machines---whenever they do not conflict with an
5433 architecture's canonical mnemonics for registers. The register names
5434 @code{$pc} and @code{$sp} are used for the program counter register and
5435 the stack pointer. @code{$fp} is used for a register that contains a
5436 pointer to the current stack frame, and @code{$ps} is used for a
5437 register that contains the processor status. For example,
5438 you could print the program counter in hex with
5445 or print the instruction to be executed next with
5452 or add four to the stack pointer@footnote{This is a way of removing
5453 one word from the stack, on machines where stacks grow downward in
5454 memory (most machines, nowadays). This assumes that the innermost
5455 stack frame is selected; setting @code{$sp} is not allowed when other
5456 stack frames are selected. To pop entire frames off the stack,
5457 regardless of machine architecture, use @code{return};
5458 see @ref{Returning, ,Returning from a function}.} with
5464 Whenever possible, these four standard register names are available on
5465 your machine even though the machine has different canonical mnemonics,
5466 so long as there is no conflict. The @code{info registers} command
5467 shows the canonical names. For example, on the SPARC, @code{info
5468 registers} displays the processor status register as @code{$psr} but you
5469 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5470 is an alias for the @sc{eflags} register.
5472 @value{GDBN} always considers the contents of an ordinary register as an
5473 integer when the register is examined in this way. Some machines have
5474 special registers which can hold nothing but floating point; these
5475 registers are considered to have floating point values. There is no way
5476 to refer to the contents of an ordinary register as floating point value
5477 (although you can @emph{print} it as a floating point value with
5478 @samp{print/f $@var{regname}}).
5480 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5481 means that the data format in which the register contents are saved by
5482 the operating system is not the same one that your program normally
5483 sees. For example, the registers of the 68881 floating point
5484 coprocessor are always saved in ``extended'' (raw) format, but all C
5485 programs expect to work with ``double'' (virtual) format. In such
5486 cases, @value{GDBN} normally works with the virtual format only (the format
5487 that makes sense for your program), but the @code{info registers} command
5488 prints the data in both formats.
5490 Normally, register values are relative to the selected stack frame
5491 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5492 value that the register would contain if all stack frames farther in
5493 were exited and their saved registers restored. In order to see the
5494 true contents of hardware registers, you must select the innermost
5495 frame (with @samp{frame 0}).
5497 However, @value{GDBN} must deduce where registers are saved, from the machine
5498 code generated by your compiler. If some registers are not saved, or if
5499 @value{GDBN} is unable to locate the saved registers, the selected stack
5500 frame makes no difference.
5502 @node Floating Point Hardware
5503 @section Floating point hardware
5504 @cindex floating point
5506 Depending on the configuration, @value{GDBN} may be able to give
5507 you more information about the status of the floating point hardware.
5512 Display hardware-dependent information about the floating
5513 point unit. The exact contents and layout vary depending on the
5514 floating point chip. Currently, @samp{info float} is supported on
5515 the ARM and x86 machines.
5518 @node Memory Region Attributes
5519 @section Memory Region Attributes
5520 @cindex memory region attributes
5522 @dfn{Memory region attributes} allow you to describe special handling
5523 required by regions of your target's memory. @value{GDBN} uses attributes
5524 to determine whether to allow certain types of memory accesses; whether to
5525 use specific width accesses; and whether to cache target memory.
5527 Defined memory regions can be individually enabled and disabled. When a
5528 memory region is disabled, @value{GDBN} uses the default attributes when
5529 accessing memory in that region. Similarly, if no memory regions have
5530 been defined, @value{GDBN} uses the default attributes when accessing
5533 When a memory region is defined, it is given a number to identify it;
5534 to enable, disable, or remove a memory region, you specify that number.
5538 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5539 Define memory region bounded by @var{address1} and @var{address2}
5540 with attributes @var{attributes}@dots{}.
5543 @item delete mem @var{nums}@dots{}
5544 Remove memory region numbers @var{nums}.
5547 @item disable mem @var{nums}@dots{}
5548 Disable memory region numbers @var{nums}.
5549 A disabled memory region is not forgotten.
5550 It may be enabled again later.
5553 @item enable mem @var{nums}@dots{}
5554 Enable memory region numbers @var{nums}.
5558 Print a table of all defined memory regions, with the following columns
5562 @item Memory Region Number
5563 @item Enabled or Disabled.
5564 Enabled memory regions are marked with @samp{y}.
5565 Disabled memory regions are marked with @samp{n}.
5568 The address defining the inclusive lower bound of the memory region.
5571 The address defining the exclusive upper bound of the memory region.
5574 The list of attributes set for this memory region.
5579 @subsection Attributes
5581 @subsubsection Memory Access Mode
5582 The access mode attributes set whether @value{GDBN} may make read or
5583 write accesses to a memory region.
5585 While these attributes prevent @value{GDBN} from performing invalid
5586 memory accesses, they do nothing to prevent the target system, I/O DMA,
5587 etc. from accessing memory.
5591 Memory is read only.
5593 Memory is write only.
5595 Memory is read/write (default).
5598 @subsubsection Memory Access Size
5599 The acccess size attributes tells @value{GDBN} to use specific sized
5600 accesses in the memory region. Often memory mapped device registers
5601 require specific sized accesses. If no access size attribute is
5602 specified, @value{GDBN} may use accesses of any size.
5606 Use 8 bit memory accesses.
5608 Use 16 bit memory accesses.
5610 Use 32 bit memory accesses.
5612 Use 64 bit memory accesses.
5615 @c @subsubsection Hardware/Software Breakpoints
5616 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5617 @c will use hardware or software breakpoints for the internal breakpoints
5618 @c used by the step, next, finish, until, etc. commands.
5622 @c Always use hardware breakpoints
5623 @c @item swbreak (default)
5626 @subsubsection Data Cache
5627 The data cache attributes set whether @value{GDBN} will cache target
5628 memory. While this generally improves performance by reducing debug
5629 protocol overhead, it can lead to incorrect results because @value{GDBN}
5630 does not know about volatile variables or memory mapped device
5635 Enable @value{GDBN} to cache target memory.
5636 @item nocache (default)
5637 Disable @value{GDBN} from caching target memory.
5640 @c @subsubsection Memory Write Verification
5641 @c The memory write verification attributes set whether @value{GDBN}
5642 @c will re-reads data after each write to verify the write was successful.
5646 @c @item noverify (default)
5650 @chapter Tracepoints
5651 @c This chapter is based on the documentation written by Michael
5652 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
5655 In some applications, it is not feasible for the debugger to interrupt
5656 the program's execution long enough for the developer to learn
5657 anything helpful about its behavior. If the program's correctness
5658 depends on its real-time behavior, delays introduced by a debugger
5659 might cause the program to change its behavior drastically, or perhaps
5660 fail, even when the code itself is correct. It is useful to be able
5661 to observe the program's behavior without interrupting it.
5663 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
5664 specify locations in the program, called @dfn{tracepoints}, and
5665 arbitrary expressions to evaluate when those tracepoints are reached.
5666 Later, using the @code{tfind} command, you can examine the values
5667 those expressions had when the program hit the tracepoints. The
5668 expressions may also denote objects in memory---structures or arrays,
5669 for example---whose values @value{GDBN} should record; while visiting
5670 a particular tracepoint, you may inspect those objects as if they were
5671 in memory at that moment. However, because @value{GDBN} records these
5672 values without interacting with you, it can do so quickly and
5673 unobtrusively, hopefully not disturbing the program's behavior.
5675 The tracepoint facility is currently available only for remote
5676 targets. @xref{Targets}.
5678 This chapter describes the tracepoint commands and features.
5682 * Analyze Collected Data::
5683 * Tracepoint Variables::
5686 @node Set Tracepoints
5687 @section Commands to Set Tracepoints
5689 Before running such a @dfn{trace experiment}, an arbitrary number of
5690 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
5691 tracepoint has a number assigned to it by @value{GDBN}. Like with
5692 breakpoints, tracepoint numbers are successive integers starting from
5693 one. Many of the commands associated with tracepoints take the
5694 tracepoint number as their argument, to identify which tracepoint to
5697 For each tracepoint, you can specify, in advance, some arbitrary set
5698 of data that you want the target to collect in the trace buffer when
5699 it hits that tracepoint. The collected data can include registers,
5700 local variables, or global data. Later, you can use @value{GDBN}
5701 commands to examine the values these data had at the time the
5704 This section describes commands to set tracepoints and associated
5705 conditions and actions.
5708 * Create and Delete Tracepoints::
5709 * Enable and Disable Tracepoints::
5710 * Tracepoint Passcounts::
5711 * Tracepoint Actions::
5712 * Listing Tracepoints::
5713 * Starting and Stopping Trace Experiment::
5716 @node Create and Delete Tracepoints
5717 @subsection Create and Delete Tracepoints
5720 @cindex set tracepoint
5723 The @code{trace} command is very similar to the @code{break} command.
5724 Its argument can be a source line, a function name, or an address in
5725 the target program. @xref{Set Breaks}. The @code{trace} command
5726 defines a tracepoint, which is a point in the target program where the
5727 debugger will briefly stop, collect some data, and then allow the
5728 program to continue. Setting a tracepoint or changing its commands
5729 doesn't take effect until the next @code{tstart} command; thus, you
5730 cannot change the tracepoint attributes once a trace experiment is
5733 Here are some examples of using the @code{trace} command:
5736 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
5738 (@value{GDBP}) @b{trace +2} // 2 lines forward
5740 (@value{GDBP}) @b{trace my_function} // first source line of function
5742 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
5744 (@value{GDBP}) @b{trace *0x2117c4} // an address
5748 You can abbreviate @code{trace} as @code{tr}.
5751 @cindex last tracepoint number
5752 @cindex recent tracepoint number
5753 @cindex tracepoint number
5754 The convenience variable @code{$tpnum} records the tracepoint number
5755 of the most recently set tracepoint.
5757 @kindex delete tracepoint
5758 @cindex tracepoint deletion
5759 @item delete tracepoint @r{[}@var{num}@r{]}
5760 Permanently delete one or more tracepoints. With no argument, the
5761 default is to delete all tracepoints.
5766 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
5768 (@value{GDBP}) @b{delete trace} // remove all tracepoints
5772 You can abbreviate this command as @code{del tr}.
5775 @node Enable and Disable Tracepoints
5776 @subsection Enable and Disable Tracepoints
5779 @kindex disable tracepoint
5780 @item disable tracepoint @r{[}@var{num}@r{]}
5781 Disable tracepoint @var{num}, or all tracepoints if no argument
5782 @var{num} is given. A disabled tracepoint will have no effect during
5783 the next trace experiment, but it is not forgotten. You can re-enable
5784 a disabled tracepoint using the @code{enable tracepoint} command.
5786 @kindex enable tracepoint
5787 @item enable tracepoint @r{[}@var{num}@r{]}
5788 Enable tracepoint @var{num}, or all tracepoints. The enabled
5789 tracepoints will become effective the next time a trace experiment is
5793 @node Tracepoint Passcounts
5794 @subsection Tracepoint Passcounts
5798 @cindex tracepoint pass count
5799 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
5800 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
5801 automatically stop a trace experiment. If a tracepoint's passcount is
5802 @var{n}, then the trace experiment will be automatically stopped on
5803 the @var{n}'th time that tracepoint is hit. If the tracepoint number
5804 @var{num} is not specified, the @code{passcount} command sets the
5805 passcount of the most recently defined tracepoint. If no passcount is
5806 given, the trace experiment will run until stopped explicitly by the
5812 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of tracepoint 2
5814 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
5815 // most recently defined tracepoint.
5816 (@value{GDBP}) @b{trace foo}
5817 (@value{GDBP}) @b{pass 3}
5818 (@value{GDBP}) @b{trace bar}
5819 (@value{GDBP}) @b{pass 2}
5820 (@value{GDBP}) @b{trace baz}
5821 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
5822 // executed 3 times OR when bar has
5823 // been executed 2 times
5824 // OR when baz has been executed 1 time.
5828 @node Tracepoint Actions
5829 @subsection Tracepoint Action Lists
5833 @cindex tracepoint actions
5834 @item actions @r{[}@var{num}@r{]}
5835 This command will prompt for a list of actions to be taken when the
5836 tracepoint is hit. If the tracepoint number @var{num} is not
5837 specified, this command sets the actions for the one that was most
5838 recently defined (so that you can define a tracepoint and then say
5839 @code{actions} without bothering about its number). You specify the
5840 actions themselves on the following lines, one action at a time, and
5841 terminate the actions list with a line containing just @code{end}. So
5842 far, the only defined actions are @code{collect} and
5843 @code{while-stepping}.
5845 @cindex remove actions from a tracepoint
5846 To remove all actions from a tracepoint, type @samp{actions @var{num}}
5847 and follow it immediately with @samp{end}.
5850 (@value{GDBP}) @b{collect @var{data}} // collect some data
5852 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times and collect data
5854 (@value{GDBP}) @b{end} // signals the end of actions.
5857 In the following example, the action list begins with @code{collect}
5858 commands indicating the things to be collected when the tracepoint is
5859 hit. Then, in order to single-step and collect additional data
5860 following the tracepoint, a @code{while-stepping} command is used,
5861 followed by the list of things to be collected while stepping. The
5862 @code{while-stepping} command is terminated by its own separate
5863 @code{end} command. Lastly, the action list is terminated by an
5867 (@value{GDBP}) @b{trace foo}
5868 (@value{GDBP}) @b{actions}
5869 Enter actions for tracepoint 1, one per line:
5878 @kindex collect @r{(tracepoints)}
5879 @item collect @var{expr1}, @var{expr2}, @dots{}
5880 Collect values of the given expressions when the tracepoint is hit.
5881 This command accepts a comma-separated list of any valid expressions.
5882 In addition to global, static, or local variables, the following
5883 special arguments are supported:
5887 collect all registers
5890 collect all function arguments
5893 collect all local variables.
5896 You can give several consecutive @code{collect} commands, each one
5897 with a single argument, or one @code{collect} command with several
5898 arguments separated by commas: the effect is the same.
5900 @kindex while-stepping @r{(tracepoints)}
5901 @item while-stepping @var{n}
5902 Perform @var{n} single-step traces after the tracepoint, collecting
5903 new data at each step. The @code{while-stepping} command is
5904 followed by the list of what to collect while stepping (followed by
5905 its own @code{end} command):
5909 > collect $regs, myglobal
5915 You may abbreviate @code{while-stepping} as @code{ws} or
5919 @node Listing Tracepoints
5920 @subsection Listing Tracepoints
5923 @kindex info tracepoints
5924 @cindex information about tracepoints
5925 @item info tracepoints @r{[}@var{num}@r{]}
5926 Display information the tracepoint @var{num}. If you don't specify a
5927 tracepoint number displays information about all the tracepoints
5928 defined so far. For each tracepoint, the following information is
5935 whether it is enabled or disabled
5939 its passcount as given by the @code{passcount @var{n}} command
5941 its step count as given by the @code{while-stepping @var{n}} command
5943 where in the source files is the tracepoint set
5945 its action list as given by the @code{actions} command
5949 (@value{GDBP}) @b{info trace}
5950 Num Enb Address PassC StepC What
5951 1 y 0x002117c4 0 0 <gdb_asm>
5952 2 y 0x0020dc64 0 0 in gdb_test at gdb_test.c:375
5953 3 y 0x0020b1f4 0 0 in collect_data at ../foo.c:1741
5958 This command can be abbreviated @code{info tp}.
5961 @node Starting and Stopping Trace Experiment
5962 @subsection Starting and Stopping Trace Experiment
5966 @cindex start a new trace experiment
5967 @cindex collected data discarded
5969 This command takes no arguments. It starts the trace experiment, and
5970 begins collecting data. This has the side effect of discarding all
5971 the data collected in the trace buffer during the previous trace
5975 @cindex stop a running trace experiment
5977 This command takes no arguments. It ends the trace experiment, and
5978 stops collecting data.
5980 @strong{Note:} a trace experiment and data collection may stop
5981 automatically if any tracepoint's passcount is reached
5982 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
5985 @cindex status of trace data collection
5986 @cindex trace experiment, status of
5988 This command displays the status of the current trace data
5992 Here is an example of the commands we described so far:
5995 (@value{GDBP}) @b{trace gdb_c_test}
5996 (@value{GDBP}) @b{actions}
5997 Enter actions for tracepoint #1, one per line.
5998 > collect $regs,$locals,$args
6003 (@value{GDBP}) @b{tstart}
6004 [time passes @dots{}]
6005 (@value{GDBP}) @b{tstop}
6009 @node Analyze Collected Data
6010 @section Using the collected data
6012 After the tracepoint experiment ends, you use @value{GDBN} commands
6013 for examining the trace data. The basic idea is that each tracepoint
6014 collects a trace @dfn{snapshot} every time it is hit and another
6015 snapshot every time it single-steps. All these snapshots are
6016 consecutively numbered from zero and go into a buffer, and you can
6017 examine them later. The way you examine them is to @dfn{focus} on a
6018 specific trace snapshot. When the remote stub is focused on a trace
6019 snapshot, it will respond to all @value{GDBN} requests for memory and
6020 registers by reading from the buffer which belongs to that snapshot,
6021 rather than from @emph{real} memory or registers of the program being
6022 debugged. This means that @strong{all} @value{GDBN} commands
6023 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6024 behave as if we were currently debugging the program state as it was
6025 when the tracepoint occurred. Any requests for data that are not in
6026 the buffer will fail.
6029 * tfind:: How to select a trace snapshot
6030 * tdump:: How to display all data for a snapshot
6031 * save-tracepoints:: How to save tracepoints for a future run
6035 @subsection @code{tfind @var{n}}
6038 @cindex select trace snapshot
6039 @cindex find trace snapshot
6040 The basic command for selecting a trace snapshot from the buffer is
6041 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6042 counting from zero. If no argument @var{n} is given, the next
6043 snapshot is selected.
6045 Here are the various forms of using the @code{tfind} command.
6049 Find the first snapshot in the buffer. This is a synonym for
6050 @code{tfind 0} (since 0 is the number of the first snapshot).
6053 Stop debugging trace snapshots, resume @emph{live} debugging.
6056 Same as @samp{tfind none}.
6059 No argument means find the next trace snapshot.
6062 Find the previous trace snapshot before the current one. This permits
6063 retracing earlier steps.
6065 @item tfind tracepoint @var{num}
6066 Find the next snapshot associated with tracepoint @var{num}. Search
6067 proceeds forward from the last examined trace snapshot. If no
6068 argument @var{num} is given, it means find the next snapshot collected
6069 for the same tracepoint as the current snapshot.
6071 @item tfind pc @var{addr}
6072 Find the next snapshot associated with the value @var{addr} of the
6073 program counter. Search proceeds forward from the last examined trace
6074 snapshot. If no argument @var{addr} is given, it means find the next
6075 snapshot with the same value of PC as the current snapshot.
6077 @item tfind outside @var{addr1}, @var{addr2}
6078 Find the next snapshot whose PC is outside the given range of
6081 @item tfind range @var{addr1}, @var{addr2}
6082 Find the next snapshot whose PC is between @var{addr1} and
6083 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6085 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6086 Find the next snapshot associated with the source line @var{n}. If
6087 the optional argument @var{file} is given, refer to line @var{n} in
6088 that source file. Search proceeds forward from the last examined
6089 trace snapshot. If no argument @var{n} is given, it means find the
6090 next line other than the one currently being examined; thus saying
6091 @code{tfind line} repeatedly can appear to have the same effect as
6092 stepping from line to line in a @emph{live} debugging session.
6095 The default arguments for the @code{tfind} commands are specifically
6096 designed to make it easy to scan through the trace buffer. For
6097 instance, @code{tfind} with no argument selects the next trace
6098 snapshot, and @code{tfind -} with no argument selects the previous
6099 trace snapshot. So, by giving one @code{tfind} command, and then
6100 simply hitting @key{RET} repeatedly you can examine all the trace
6101 snapshots in order. Or, by saying @code{tfind -} and then hitting
6102 @key{RET} repeatedly you can examine the snapshots in reverse order.
6103 The @code{tfind line} command with no argument selects the snapshot
6104 for the next source line executed. The @code{tfind pc} command with
6105 no argument selects the next snapshot with the same program counter
6106 (PC) as the current frame. The @code{tfind tracepoint} command with
6107 no argument selects the next trace snapshot collected by the same
6108 tracepoint as the current one.
6110 In addition to letting you scan through the trace buffer manually,
6111 these commands make it easy to construct @value{GDBN} scripts that
6112 scan through the trace buffer and print out whatever collected data
6113 you are interested in. Thus, if we want to examine the PC, FP, and SP
6114 registers from each trace frame in the buffer, we can say this:
6117 (@value{GDBP}) @b{tfind start}
6118 (@value{GDBP}) @b{while ($trace_frame != -1)}
6119 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6120 $trace_frame, $pc, $sp, $fp
6124 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6125 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6126 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6127 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6128 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6129 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6130 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6131 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6132 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6133 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6134 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6137 Or, if we want to examine the variable @code{X} at each source line in
6141 (@value{GDBP}) @b{tfind start}
6142 (@value{GDBP}) @b{while ($trace_frame != -1)}
6143 > printf "Frame %d, X == %d\n", $trace_frame, X
6153 @subsection @code{tdump}
6155 @cindex dump all data collected at tracepoint
6156 @cindex tracepoint data, display
6158 This command takes no arguments. It prints all the data collected at
6159 the current trace snapshot.
6162 (@value{GDBP}) @b{trace 444}
6163 (@value{GDBP}) @b{actions}
6164 Enter actions for tracepoint #2, one per line:
6165 > collect $regs, $locals, $args, gdb_long_test
6168 (@value{GDBP}) @b{tstart}
6170 (@value{GDBP}) @b{tfind line 444}
6171 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6173 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6175 (@value{GDBP}) @b{tdump}
6176 Data collected at tracepoint 2, trace frame 1:
6177 d0 0xc4aa0085 -995491707
6181 d4 0x71aea3d 119204413
6186 a1 0x3000668 50333288
6189 a4 0x3000698 50333336
6191 fp 0x30bf3c 0x30bf3c
6192 sp 0x30bf34 0x30bf34
6194 pc 0x20b2c8 0x20b2c8
6198 p = 0x20e5b4 "gdb-test"
6205 gdb_long_test = 17 '\021'
6210 @node save-tracepoints
6211 @subsection @code{save-tracepoints @var{filename}}
6212 @kindex save-tracepoints
6213 @cindex save tracepoints for future sessions
6215 This command saves all current tracepoint definitions together with
6216 their actions and passcounts, into a file @file{@var{filename}}
6217 suitable for use in a later debugging session. To read the saved
6218 tracepoint definitions, use the @code{source} command (@pxref{Command
6221 @node Tracepoint Variables
6222 @section Convenience Variables for Tracepoints
6223 @cindex tracepoint variables
6224 @cindex convenience variables for tracepoints
6227 @vindex $trace_frame
6228 @item (int) $trace_frame
6229 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6230 snapshot is selected.
6233 @item (int) $tracepoint
6234 The tracepoint for the current trace snapshot.
6237 @item (int) $trace_line
6238 The line number for the current trace snapshot.
6241 @item (char []) $trace_file
6242 The source file for the current trace snapshot.
6245 @item (char []) $trace_func
6246 The name of the function containing @code{$tracepoint}.
6249 Note: @code{$trace_file} is not suitable for use in @code{printf},
6250 use @code{output} instead.
6252 Here's a simple example of using these convenience variables for
6253 stepping through all the trace snapshots and printing some of their
6257 (@value{GDBP}) @b{tfind start}
6259 (@value{GDBP}) @b{while $trace_frame != -1}
6260 > output $trace_file
6261 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
6267 @chapter Using @value{GDBN} with Different Languages
6270 Although programming languages generally have common aspects, they are
6271 rarely expressed in the same manner. For instance, in ANSI C,
6272 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
6273 Modula-2, it is accomplished by @code{p^}. Values can also be
6274 represented (and displayed) differently. Hex numbers in C appear as
6275 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
6277 @cindex working language
6278 Language-specific information is built into @value{GDBN} for some languages,
6279 allowing you to express operations like the above in your program's
6280 native language, and allowing @value{GDBN} to output values in a manner
6281 consistent with the syntax of your program's native language. The
6282 language you use to build expressions is called the @dfn{working
6286 * Setting:: Switching between source languages
6287 * Show:: Displaying the language
6288 * Checks:: Type and range checks
6289 * Support:: Supported languages
6293 @section Switching between source languages
6295 There are two ways to control the working language---either have @value{GDBN}
6296 set it automatically, or select it manually yourself. You can use the
6297 @code{set language} command for either purpose. On startup, @value{GDBN}
6298 defaults to setting the language automatically. The working language is
6299 used to determine how expressions you type are interpreted, how values
6302 In addition to the working language, every source file that
6303 @value{GDBN} knows about has its own working language. For some object
6304 file formats, the compiler might indicate which language a particular
6305 source file is in. However, most of the time @value{GDBN} infers the
6306 language from the name of the file. The language of a source file
6307 controls whether C@t{++} names are demangled---this way @code{backtrace} can
6308 show each frame appropriately for its own language. There is no way to
6309 set the language of a source file from within @value{GDBN}, but you can
6310 set the language associated with a filename extension. @xref{Show, ,
6311 Displaying the language}.
6313 This is most commonly a problem when you use a program, such
6314 as @code{cfront} or @code{f2c}, that generates C but is written in
6315 another language. In that case, make the
6316 program use @code{#line} directives in its C output; that way
6317 @value{GDBN} will know the correct language of the source code of the original
6318 program, and will display that source code, not the generated C code.
6321 * Filenames:: Filename extensions and languages.
6322 * Manually:: Setting the working language manually
6323 * Automatically:: Having @value{GDBN} infer the source language
6327 @subsection List of filename extensions and languages
6329 If a source file name ends in one of the following extensions, then
6330 @value{GDBN} infers that its language is the one indicated.
6355 Modula-2 source file
6359 Assembler source file. This actually behaves almost like C, but
6360 @value{GDBN} does not skip over function prologues when stepping.
6363 In addition, you may set the language associated with a filename
6364 extension. @xref{Show, , Displaying the language}.
6367 @subsection Setting the working language
6369 If you allow @value{GDBN} to set the language automatically,
6370 expressions are interpreted the same way in your debugging session and
6373 @kindex set language
6374 If you wish, you may set the language manually. To do this, issue the
6375 command @samp{set language @var{lang}}, where @var{lang} is the name of
6377 @code{c} or @code{modula-2}.
6378 For a list of the supported languages, type @samp{set language}.
6380 Setting the language manually prevents @value{GDBN} from updating the working
6381 language automatically. This can lead to confusion if you try
6382 to debug a program when the working language is not the same as the
6383 source language, when an expression is acceptable to both
6384 languages---but means different things. For instance, if the current
6385 source file were written in C, and @value{GDBN} was parsing Modula-2, a
6393 might not have the effect you intended. In C, this means to add
6394 @code{b} and @code{c} and place the result in @code{a}. The result
6395 printed would be the value of @code{a}. In Modula-2, this means to compare
6396 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
6399 @subsection Having @value{GDBN} infer the source language
6401 To have @value{GDBN} set the working language automatically, use
6402 @samp{set language local} or @samp{set language auto}. @value{GDBN}
6403 then infers the working language. That is, when your program stops in a
6404 frame (usually by encountering a breakpoint), @value{GDBN} sets the
6405 working language to the language recorded for the function in that
6406 frame. If the language for a frame is unknown (that is, if the function
6407 or block corresponding to the frame was defined in a source file that
6408 does not have a recognized extension), the current working language is
6409 not changed, and @value{GDBN} issues a warning.
6411 This may not seem necessary for most programs, which are written
6412 entirely in one source language. However, program modules and libraries
6413 written in one source language can be used by a main program written in
6414 a different source language. Using @samp{set language auto} in this
6415 case frees you from having to set the working language manually.
6418 @section Displaying the language
6420 The following commands help you find out which language is the
6421 working language, and also what language source files were written in.
6423 @kindex show language
6424 @kindex info frame@r{, show the source language}
6425 @kindex info source@r{, show the source language}
6428 Display the current working language. This is the
6429 language you can use with commands such as @code{print} to
6430 build and compute expressions that may involve variables in your program.
6433 Display the source language for this frame. This language becomes the
6434 working language if you use an identifier from this frame.
6435 @xref{Frame Info, ,Information about a frame}, to identify the other
6436 information listed here.
6439 Display the source language of this source file.
6440 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
6441 information listed here.
6444 In unusual circumstances, you may have source files with extensions
6445 not in the standard list. You can then set the extension associated
6446 with a language explicitly:
6448 @kindex set extension-language
6449 @kindex info extensions
6451 @item set extension-language @var{.ext} @var{language}
6452 Set source files with extension @var{.ext} to be assumed to be in
6453 the source language @var{language}.
6455 @item info extensions
6456 List all the filename extensions and the associated languages.
6460 @section Type and range checking
6463 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
6464 checking are included, but they do not yet have any effect. This
6465 section documents the intended facilities.
6467 @c FIXME remove warning when type/range code added
6469 Some languages are designed to guard you against making seemingly common
6470 errors through a series of compile- and run-time checks. These include
6471 checking the type of arguments to functions and operators, and making
6472 sure mathematical overflows are caught at run time. Checks such as
6473 these help to ensure a program's correctness once it has been compiled
6474 by eliminating type mismatches, and providing active checks for range
6475 errors when your program is running.
6477 @value{GDBN} can check for conditions like the above if you wish.
6478 Although @value{GDBN} does not check the statements in your program, it
6479 can check expressions entered directly into @value{GDBN} for evaluation via
6480 the @code{print} command, for example. As with the working language,
6481 @value{GDBN} can also decide whether or not to check automatically based on
6482 your program's source language. @xref{Support, ,Supported languages},
6483 for the default settings of supported languages.
6486 * Type Checking:: An overview of type checking
6487 * Range Checking:: An overview of range checking
6490 @cindex type checking
6491 @cindex checks, type
6493 @subsection An overview of type checking
6495 Some languages, such as Modula-2, are strongly typed, meaning that the
6496 arguments to operators and functions have to be of the correct type,
6497 otherwise an error occurs. These checks prevent type mismatch
6498 errors from ever causing any run-time problems. For example,
6506 The second example fails because the @code{CARDINAL} 1 is not
6507 type-compatible with the @code{REAL} 2.3.
6509 For the expressions you use in @value{GDBN} commands, you can tell the
6510 @value{GDBN} type checker to skip checking;
6511 to treat any mismatches as errors and abandon the expression;
6512 or to only issue warnings when type mismatches occur,
6513 but evaluate the expression anyway. When you choose the last of
6514 these, @value{GDBN} evaluates expressions like the second example above, but
6515 also issues a warning.
6517 Even if you turn type checking off, there may be other reasons
6518 related to type that prevent @value{GDBN} from evaluating an expression.
6519 For instance, @value{GDBN} does not know how to add an @code{int} and
6520 a @code{struct foo}. These particular type errors have nothing to do
6521 with the language in use, and usually arise from expressions, such as
6522 the one described above, which make little sense to evaluate anyway.
6524 Each language defines to what degree it is strict about type. For
6525 instance, both Modula-2 and C require the arguments to arithmetical
6526 operators to be numbers. In C, enumerated types and pointers can be
6527 represented as numbers, so that they are valid arguments to mathematical
6528 operators. @xref{Support, ,Supported languages}, for further
6529 details on specific languages.
6531 @value{GDBN} provides some additional commands for controlling the type checker:
6533 @kindex set check@r{, type}
6534 @kindex set check type
6535 @kindex show check type
6537 @item set check type auto
6538 Set type checking on or off based on the current working language.
6539 @xref{Support, ,Supported languages}, for the default settings for
6542 @item set check type on
6543 @itemx set check type off
6544 Set type checking on or off, overriding the default setting for the
6545 current working language. Issue a warning if the setting does not
6546 match the language default. If any type mismatches occur in
6547 evaluating an expression while type checking is on, @value{GDBN} prints a
6548 message and aborts evaluation of the expression.
6550 @item set check type warn
6551 Cause the type checker to issue warnings, but to always attempt to
6552 evaluate the expression. Evaluating the expression may still
6553 be impossible for other reasons. For example, @value{GDBN} cannot add
6554 numbers and structures.
6557 Show the current setting of the type checker, and whether or not @value{GDBN}
6558 is setting it automatically.
6561 @cindex range checking
6562 @cindex checks, range
6563 @node Range Checking
6564 @subsection An overview of range checking
6566 In some languages (such as Modula-2), it is an error to exceed the
6567 bounds of a type; this is enforced with run-time checks. Such range
6568 checking is meant to ensure program correctness by making sure
6569 computations do not overflow, or indices on an array element access do
6570 not exceed the bounds of the array.
6572 For expressions you use in @value{GDBN} commands, you can tell
6573 @value{GDBN} to treat range errors in one of three ways: ignore them,
6574 always treat them as errors and abandon the expression, or issue
6575 warnings but evaluate the expression anyway.
6577 A range error can result from numerical overflow, from exceeding an
6578 array index bound, or when you type a constant that is not a member
6579 of any type. Some languages, however, do not treat overflows as an
6580 error. In many implementations of C, mathematical overflow causes the
6581 result to ``wrap around'' to lower values---for example, if @var{m} is
6582 the largest integer value, and @var{s} is the smallest, then
6585 @var{m} + 1 @result{} @var{s}
6588 This, too, is specific to individual languages, and in some cases
6589 specific to individual compilers or machines. @xref{Support, ,
6590 Supported languages}, for further details on specific languages.
6592 @value{GDBN} provides some additional commands for controlling the range checker:
6594 @kindex set check@r{, range}
6595 @kindex set check range
6596 @kindex show check range
6598 @item set check range auto
6599 Set range checking on or off based on the current working language.
6600 @xref{Support, ,Supported languages}, for the default settings for
6603 @item set check range on
6604 @itemx set check range off
6605 Set range checking on or off, overriding the default setting for the
6606 current working language. A warning is issued if the setting does not
6607 match the language default. If a range error occurs and range checking is on,
6608 then a message is printed and evaluation of the expression is aborted.
6610 @item set check range warn
6611 Output messages when the @value{GDBN} range checker detects a range error,
6612 but attempt to evaluate the expression anyway. Evaluating the
6613 expression may still be impossible for other reasons, such as accessing
6614 memory that the process does not own (a typical example from many Unix
6618 Show the current setting of the range checker, and whether or not it is
6619 being set automatically by @value{GDBN}.
6623 @section Supported languages
6625 @value{GDBN} supports C, C@t{++}, Fortran, Java, Chill, assembly, and Modula-2.
6626 @c This is false ...
6627 Some @value{GDBN} features may be used in expressions regardless of the
6628 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6629 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6630 ,Expressions}) can be used with the constructs of any supported
6633 The following sections detail to what degree each source language is
6634 supported by @value{GDBN}. These sections are not meant to be language
6635 tutorials or references, but serve only as a reference guide to what the
6636 @value{GDBN} expression parser accepts, and what input and output
6637 formats should look like for different languages. There are many good
6638 books written on each of these languages; please look to these for a
6639 language reference or tutorial.
6643 * Modula-2:: Modula-2
6648 @subsection C and C@t{++}
6650 @cindex C and C@t{++}
6651 @cindex expressions in C or C@t{++}
6653 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
6654 to both languages. Whenever this is the case, we discuss those languages
6658 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6659 @cindex @sc{gnu} C@t{++}
6660 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
6661 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
6662 effectively, you must compile your C@t{++} programs with a supported
6663 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
6664 compiler (@code{aCC}).
6666 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
6667 format. You can select that format explicitly with the @code{g++}
6668 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6669 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6670 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6673 * C Operators:: C and C@t{++} operators
6674 * C Constants:: C and C@t{++} constants
6675 * C plus plus expressions:: C@t{++} expressions
6676 * C Defaults:: Default settings for C and C@t{++}
6677 * C Checks:: C and C@t{++} type and range checks
6678 * Debugging C:: @value{GDBN} and C
6679 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
6683 @subsubsection C and C@t{++} operators
6685 @cindex C and C@t{++} operators
6687 Operators must be defined on values of specific types. For instance,
6688 @code{+} is defined on numbers, but not on structures. Operators are
6689 often defined on groups of types.
6691 For the purposes of C and C@t{++}, the following definitions hold:
6696 @emph{Integral types} include @code{int} with any of its storage-class
6697 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
6700 @emph{Floating-point types} include @code{float}, @code{double}, and
6701 @code{long double} (if supported by the target platform).
6704 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6707 @emph{Scalar types} include all of the above.
6712 The following operators are supported. They are listed here
6713 in order of increasing precedence:
6717 The comma or sequencing operator. Expressions in a comma-separated list
6718 are evaluated from left to right, with the result of the entire
6719 expression being the last expression evaluated.
6722 Assignment. The value of an assignment expression is the value
6723 assigned. Defined on scalar types.
6726 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6727 and translated to @w{@code{@var{a} = @var{a op b}}}.
6728 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6729 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6730 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6733 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6734 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6738 Logical @sc{or}. Defined on integral types.
6741 Logical @sc{and}. Defined on integral types.
6744 Bitwise @sc{or}. Defined on integral types.
6747 Bitwise exclusive-@sc{or}. Defined on integral types.
6750 Bitwise @sc{and}. Defined on integral types.
6753 Equality and inequality. Defined on scalar types. The value of these
6754 expressions is 0 for false and non-zero for true.
6756 @item <@r{, }>@r{, }<=@r{, }>=
6757 Less than, greater than, less than or equal, greater than or equal.
6758 Defined on scalar types. The value of these expressions is 0 for false
6759 and non-zero for true.
6762 left shift, and right shift. Defined on integral types.
6765 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6768 Addition and subtraction. Defined on integral types, floating-point types and
6771 @item *@r{, }/@r{, }%
6772 Multiplication, division, and modulus. Multiplication and division are
6773 defined on integral and floating-point types. Modulus is defined on
6777 Increment and decrement. When appearing before a variable, the
6778 operation is performed before the variable is used in an expression;
6779 when appearing after it, the variable's value is used before the
6780 operation takes place.
6783 Pointer dereferencing. Defined on pointer types. Same precedence as
6787 Address operator. Defined on variables. Same precedence as @code{++}.
6789 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
6790 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
6791 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6792 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
6796 Negative. Defined on integral and floating-point types. Same
6797 precedence as @code{++}.
6800 Logical negation. Defined on integral types. Same precedence as
6804 Bitwise complement operator. Defined on integral types. Same precedence as
6809 Structure member, and pointer-to-structure member. For convenience,
6810 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6811 pointer based on the stored type information.
6812 Defined on @code{struct} and @code{union} data.
6815 Dereferences of pointers to members.
6818 Array indexing. @code{@var{a}[@var{i}]} is defined as
6819 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6822 Function parameter list. Same precedence as @code{->}.
6825 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
6826 and @code{class} types.
6829 Doubled colons also represent the @value{GDBN} scope operator
6830 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6834 If an operator is redefined in the user code, @value{GDBN} usually
6835 attempts to invoke the redefined version instead of using the operator's
6843 @subsubsection C and C@t{++} constants
6845 @cindex C and C@t{++} constants
6847 @value{GDBN} allows you to express the constants of C and C@t{++} in the
6852 Integer constants are a sequence of digits. Octal constants are
6853 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6854 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6855 @samp{l}, specifying that the constant should be treated as a
6859 Floating point constants are a sequence of digits, followed by a decimal
6860 point, followed by a sequence of digits, and optionally followed by an
6861 exponent. An exponent is of the form:
6862 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6863 sequence of digits. The @samp{+} is optional for positive exponents.
6864 A floating-point constant may also end with a letter @samp{f} or
6865 @samp{F}, specifying that the constant should be treated as being of
6866 the @code{float} (as opposed to the default @code{double}) type; or with
6867 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6871 Enumerated constants consist of enumerated identifiers, or their
6872 integral equivalents.
6875 Character constants are a single character surrounded by single quotes
6876 (@code{'}), or a number---the ordinal value of the corresponding character
6877 (usually its @sc{ascii} value). Within quotes, the single character may
6878 be represented by a letter or by @dfn{escape sequences}, which are of
6879 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6880 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6881 @samp{@var{x}} is a predefined special character---for example,
6882 @samp{\n} for newline.
6885 String constants are a sequence of character constants surrounded by
6886 double quotes (@code{"}). Any valid character constant (as described
6887 above) may appear. Double quotes within the string must be preceded by
6888 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6892 Pointer constants are an integral value. You can also write pointers
6893 to constants using the C operator @samp{&}.
6896 Array constants are comma-separated lists surrounded by braces @samp{@{}
6897 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6898 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6899 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6903 * C plus plus expressions::
6910 @node C plus plus expressions
6911 @subsubsection C@t{++} expressions
6913 @cindex expressions in C@t{++}
6914 @value{GDBN} expression handling can interpret most C@t{++} expressions.
6916 @cindex C@t{++} support, not in @sc{coff}
6917 @cindex @sc{coff} versus C@t{++}
6918 @cindex C@t{++} and object formats
6919 @cindex object formats and C@t{++}
6920 @cindex a.out and C@t{++}
6921 @cindex @sc{ecoff} and C@t{++}
6922 @cindex @sc{xcoff} and C@t{++}
6923 @cindex @sc{elf}/stabs and C@t{++}
6924 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
6925 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6926 @c periodically whether this has happened...
6928 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
6929 proper compiler. Typically, C@t{++} debugging depends on the use of
6930 additional debugging information in the symbol table, and thus requires
6931 special support. In particular, if your compiler generates a.out, MIPS
6932 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6933 symbol table, these facilities are all available. (With @sc{gnu} CC,
6934 you can use the @samp{-gstabs} option to request stabs debugging
6935 extensions explicitly.) Where the object code format is standard
6936 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
6937 support in @value{GDBN} does @emph{not} work.
6942 @cindex member functions
6944 Member function calls are allowed; you can use expressions like
6947 count = aml->GetOriginal(x, y)
6950 @vindex this@r{, inside C@t{++} member functions}
6951 @cindex namespace in C@t{++}
6953 While a member function is active (in the selected stack frame), your
6954 expressions have the same namespace available as the member function;
6955 that is, @value{GDBN} allows implicit references to the class instance
6956 pointer @code{this} following the same rules as C@t{++}.
6958 @cindex call overloaded functions
6959 @cindex overloaded functions, calling
6960 @cindex type conversions in C@t{++}
6962 You can call overloaded functions; @value{GDBN} resolves the function
6963 call to the right definition, with some restrictions. @value{GDBN} does not
6964 perform overload resolution involving user-defined type conversions,
6965 calls to constructors, or instantiations of templates that do not exist
6966 in the program. It also cannot handle ellipsis argument lists or
6969 It does perform integral conversions and promotions, floating-point
6970 promotions, arithmetic conversions, pointer conversions, conversions of
6971 class objects to base classes, and standard conversions such as those of
6972 functions or arrays to pointers; it requires an exact match on the
6973 number of function arguments.
6975 Overload resolution is always performed, unless you have specified
6976 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6977 ,@value{GDBN} features for C@t{++}}.
6979 You must specify @code{set overload-resolution off} in order to use an
6980 explicit function signature to call an overloaded function, as in
6982 p 'foo(char,int)'('x', 13)
6985 The @value{GDBN} command-completion facility can simplify this;
6986 see @ref{Completion, ,Command completion}.
6988 @cindex reference declarations
6990 @value{GDBN} understands variables declared as C@t{++} references; you can use
6991 them in expressions just as you do in C@t{++} source---they are automatically
6994 In the parameter list shown when @value{GDBN} displays a frame, the values of
6995 reference variables are not displayed (unlike other variables); this
6996 avoids clutter, since references are often used for large structures.
6997 The @emph{address} of a reference variable is always shown, unless
6998 you have specified @samp{set print address off}.
7001 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
7002 expressions can use it just as expressions in your program do. Since
7003 one scope may be defined in another, you can use @code{::} repeatedly if
7004 necessary, for example in an expression like
7005 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
7006 resolving name scope by reference to source files, in both C and C@t{++}
7007 debugging (@pxref{Variables, ,Program variables}).
7010 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
7011 calling virtual functions correctly, printing out virtual bases of
7012 objects, calling functions in a base subobject, casting objects, and
7013 invoking user-defined operators.
7016 @subsubsection C and C@t{++} defaults
7018 @cindex C and C@t{++} defaults
7020 If you allow @value{GDBN} to set type and range checking automatically, they
7021 both default to @code{off} whenever the working language changes to
7022 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
7023 selects the working language.
7025 If you allow @value{GDBN} to set the language automatically, it
7026 recognizes source files whose names end with @file{.c}, @file{.C}, or
7027 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
7028 these files, it sets the working language to C or C@t{++}.
7029 @xref{Automatically, ,Having @value{GDBN} infer the source language},
7030 for further details.
7032 @c Type checking is (a) primarily motivated by Modula-2, and (b)
7033 @c unimplemented. If (b) changes, it might make sense to let this node
7034 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
7037 @subsubsection C and C@t{++} type and range checks
7039 @cindex C and C@t{++} checks
7041 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
7042 is not used. However, if you turn type checking on, @value{GDBN}
7043 considers two variables type equivalent if:
7047 The two variables are structured and have the same structure, union, or
7051 The two variables have the same type name, or types that have been
7052 declared equivalent through @code{typedef}.
7055 @c leaving this out because neither J Gilmore nor R Pesch understand it.
7058 The two @code{struct}, @code{union}, or @code{enum} variables are
7059 declared in the same declaration. (Note: this may not be true for all C
7064 Range checking, if turned on, is done on mathematical operations. Array
7065 indices are not checked, since they are often used to index a pointer
7066 that is not itself an array.
7069 @subsubsection @value{GDBN} and C
7071 The @code{set print union} and @code{show print union} commands apply to
7072 the @code{union} type. When set to @samp{on}, any @code{union} that is
7073 inside a @code{struct} or @code{class} is also printed. Otherwise, it
7074 appears as @samp{@{...@}}.
7076 The @code{@@} operator aids in the debugging of dynamic arrays, formed
7077 with pointers and a memory allocation function. @xref{Expressions,
7081 * Debugging C plus plus::
7084 @node Debugging C plus plus
7085 @subsubsection @value{GDBN} features for C@t{++}
7087 @cindex commands for C@t{++}
7089 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
7090 designed specifically for use with C@t{++}. Here is a summary:
7093 @cindex break in overloaded functions
7094 @item @r{breakpoint menus}
7095 When you want a breakpoint in a function whose name is overloaded,
7096 @value{GDBN} breakpoint menus help you specify which function definition
7097 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
7099 @cindex overloading in C@t{++}
7100 @item rbreak @var{regex}
7101 Setting breakpoints using regular expressions is helpful for setting
7102 breakpoints on overloaded functions that are not members of any special
7104 @xref{Set Breaks, ,Setting breakpoints}.
7106 @cindex C@t{++} exception handling
7109 Debug C@t{++} exception handling using these commands. @xref{Set
7110 Catchpoints, , Setting catchpoints}.
7113 @item ptype @var{typename}
7114 Print inheritance relationships as well as other information for type
7116 @xref{Symbols, ,Examining the Symbol Table}.
7118 @cindex C@t{++} symbol display
7119 @item set print demangle
7120 @itemx show print demangle
7121 @itemx set print asm-demangle
7122 @itemx show print asm-demangle
7123 Control whether C@t{++} symbols display in their source form, both when
7124 displaying code as C@t{++} source and when displaying disassemblies.
7125 @xref{Print Settings, ,Print settings}.
7127 @item set print object
7128 @itemx show print object
7129 Choose whether to print derived (actual) or declared types of objects.
7130 @xref{Print Settings, ,Print settings}.
7132 @item set print vtbl
7133 @itemx show print vtbl
7134 Control the format for printing virtual function tables.
7135 @xref{Print Settings, ,Print settings}.
7136 (The @code{vtbl} commands do not work on programs compiled with the HP
7137 ANSI C@t{++} compiler (@code{aCC}).)
7139 @kindex set overload-resolution
7140 @cindex overloaded functions, overload resolution
7141 @item set overload-resolution on
7142 Enable overload resolution for C@t{++} expression evaluation. The default
7143 is on. For overloaded functions, @value{GDBN} evaluates the arguments
7144 and searches for a function whose signature matches the argument types,
7145 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
7146 expressions}, for details). If it cannot find a match, it emits a
7149 @item set overload-resolution off
7150 Disable overload resolution for C@t{++} expression evaluation. For
7151 overloaded functions that are not class member functions, @value{GDBN}
7152 chooses the first function of the specified name that it finds in the
7153 symbol table, whether or not its arguments are of the correct type. For
7154 overloaded functions that are class member functions, @value{GDBN}
7155 searches for a function whose signature @emph{exactly} matches the
7158 @item @r{Overloaded symbol names}
7159 You can specify a particular definition of an overloaded symbol, using
7160 the same notation that is used to declare such symbols in C@t{++}: type
7161 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
7162 also use the @value{GDBN} command-line word completion facilities to list the
7163 available choices, or to finish the type list for you.
7164 @xref{Completion,, Command completion}, for details on how to do this.
7168 @subsection Modula-2
7170 @cindex Modula-2, @value{GDBN} support
7172 The extensions made to @value{GDBN} to support Modula-2 only support
7173 output from the @sc{gnu} Modula-2 compiler (which is currently being
7174 developed). Other Modula-2 compilers are not currently supported, and
7175 attempting to debug executables produced by them is most likely
7176 to give an error as @value{GDBN} reads in the executable's symbol
7179 @cindex expressions in Modula-2
7181 * M2 Operators:: Built-in operators
7182 * Built-In Func/Proc:: Built-in functions and procedures
7183 * M2 Constants:: Modula-2 constants
7184 * M2 Defaults:: Default settings for Modula-2
7185 * Deviations:: Deviations from standard Modula-2
7186 * M2 Checks:: Modula-2 type and range checks
7187 * M2 Scope:: The scope operators @code{::} and @code{.}
7188 * GDB/M2:: @value{GDBN} and Modula-2
7192 @subsubsection Operators
7193 @cindex Modula-2 operators
7195 Operators must be defined on values of specific types. For instance,
7196 @code{+} is defined on numbers, but not on structures. Operators are
7197 often defined on groups of types. For the purposes of Modula-2, the
7198 following definitions hold:
7203 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
7207 @emph{Character types} consist of @code{CHAR} and its subranges.
7210 @emph{Floating-point types} consist of @code{REAL}.
7213 @emph{Pointer types} consist of anything declared as @code{POINTER TO
7217 @emph{Scalar types} consist of all of the above.
7220 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
7223 @emph{Boolean types} consist of @code{BOOLEAN}.
7227 The following operators are supported, and appear in order of
7228 increasing precedence:
7232 Function argument or array index separator.
7235 Assignment. The value of @var{var} @code{:=} @var{value} is
7239 Less than, greater than on integral, floating-point, or enumerated
7243 Less than or equal to, greater than or equal to
7244 on integral, floating-point and enumerated types, or set inclusion on
7245 set types. Same precedence as @code{<}.
7247 @item =@r{, }<>@r{, }#
7248 Equality and two ways of expressing inequality, valid on scalar types.
7249 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
7250 available for inequality, since @code{#} conflicts with the script
7254 Set membership. Defined on set types and the types of their members.
7255 Same precedence as @code{<}.
7258 Boolean disjunction. Defined on boolean types.
7261 Boolean conjunction. Defined on boolean types.
7264 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7267 Addition and subtraction on integral and floating-point types, or union
7268 and difference on set types.
7271 Multiplication on integral and floating-point types, or set intersection
7275 Division on floating-point types, or symmetric set difference on set
7276 types. Same precedence as @code{*}.
7279 Integer division and remainder. Defined on integral types. Same
7280 precedence as @code{*}.
7283 Negative. Defined on @code{INTEGER} and @code{REAL} data.
7286 Pointer dereferencing. Defined on pointer types.
7289 Boolean negation. Defined on boolean types. Same precedence as
7293 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
7294 precedence as @code{^}.
7297 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
7300 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
7304 @value{GDBN} and Modula-2 scope operators.
7308 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
7309 treats the use of the operator @code{IN}, or the use of operators
7310 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
7311 @code{<=}, and @code{>=} on sets as an error.
7314 @cindex Modula-2 built-ins
7315 @node Built-In Func/Proc
7316 @subsubsection Built-in functions and procedures
7318 Modula-2 also makes available several built-in procedures and functions.
7319 In describing these, the following metavariables are used:
7324 represents an @code{ARRAY} variable.
7327 represents a @code{CHAR} constant or variable.
7330 represents a variable or constant of integral type.
7333 represents an identifier that belongs to a set. Generally used in the
7334 same function with the metavariable @var{s}. The type of @var{s} should
7335 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
7338 represents a variable or constant of integral or floating-point type.
7341 represents a variable or constant of floating-point type.
7347 represents a variable.
7350 represents a variable or constant of one of many types. See the
7351 explanation of the function for details.
7354 All Modula-2 built-in procedures also return a result, described below.
7358 Returns the absolute value of @var{n}.
7361 If @var{c} is a lower case letter, it returns its upper case
7362 equivalent, otherwise it returns its argument.
7365 Returns the character whose ordinal value is @var{i}.
7368 Decrements the value in the variable @var{v} by one. Returns the new value.
7370 @item DEC(@var{v},@var{i})
7371 Decrements the value in the variable @var{v} by @var{i}. Returns the
7374 @item EXCL(@var{m},@var{s})
7375 Removes the element @var{m} from the set @var{s}. Returns the new
7378 @item FLOAT(@var{i})
7379 Returns the floating point equivalent of the integer @var{i}.
7382 Returns the index of the last member of @var{a}.
7385 Increments the value in the variable @var{v} by one. Returns the new value.
7387 @item INC(@var{v},@var{i})
7388 Increments the value in the variable @var{v} by @var{i}. Returns the
7391 @item INCL(@var{m},@var{s})
7392 Adds the element @var{m} to the set @var{s} if it is not already
7393 there. Returns the new set.
7396 Returns the maximum value of the type @var{t}.
7399 Returns the minimum value of the type @var{t}.
7402 Returns boolean TRUE if @var{i} is an odd number.
7405 Returns the ordinal value of its argument. For example, the ordinal
7406 value of a character is its @sc{ascii} value (on machines supporting the
7407 @sc{ascii} character set). @var{x} must be of an ordered type, which include
7408 integral, character and enumerated types.
7411 Returns the size of its argument. @var{x} can be a variable or a type.
7413 @item TRUNC(@var{r})
7414 Returns the integral part of @var{r}.
7416 @item VAL(@var{t},@var{i})
7417 Returns the member of the type @var{t} whose ordinal value is @var{i}.
7421 @emph{Warning:} Sets and their operations are not yet supported, so
7422 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
7426 @cindex Modula-2 constants
7428 @subsubsection Constants
7430 @value{GDBN} allows you to express the constants of Modula-2 in the following
7436 Integer constants are simply a sequence of digits. When used in an
7437 expression, a constant is interpreted to be type-compatible with the
7438 rest of the expression. Hexadecimal integers are specified by a
7439 trailing @samp{H}, and octal integers by a trailing @samp{B}.
7442 Floating point constants appear as a sequence of digits, followed by a
7443 decimal point and another sequence of digits. An optional exponent can
7444 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
7445 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
7446 digits of the floating point constant must be valid decimal (base 10)
7450 Character constants consist of a single character enclosed by a pair of
7451 like quotes, either single (@code{'}) or double (@code{"}). They may
7452 also be expressed by their ordinal value (their @sc{ascii} value, usually)
7453 followed by a @samp{C}.
7456 String constants consist of a sequence of characters enclosed by a
7457 pair of like quotes, either single (@code{'}) or double (@code{"}).
7458 Escape sequences in the style of C are also allowed. @xref{C
7459 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
7463 Enumerated constants consist of an enumerated identifier.
7466 Boolean constants consist of the identifiers @code{TRUE} and
7470 Pointer constants consist of integral values only.
7473 Set constants are not yet supported.
7477 @subsubsection Modula-2 defaults
7478 @cindex Modula-2 defaults
7480 If type and range checking are set automatically by @value{GDBN}, they
7481 both default to @code{on} whenever the working language changes to
7482 Modula-2. This happens regardless of whether you or @value{GDBN}
7483 selected the working language.
7485 If you allow @value{GDBN} to set the language automatically, then entering
7486 code compiled from a file whose name ends with @file{.mod} sets the
7487 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
7488 the language automatically}, for further details.
7491 @subsubsection Deviations from standard Modula-2
7492 @cindex Modula-2, deviations from
7494 A few changes have been made to make Modula-2 programs easier to debug.
7495 This is done primarily via loosening its type strictness:
7499 Unlike in standard Modula-2, pointer constants can be formed by
7500 integers. This allows you to modify pointer variables during
7501 debugging. (In standard Modula-2, the actual address contained in a
7502 pointer variable is hidden from you; it can only be modified
7503 through direct assignment to another pointer variable or expression that
7504 returned a pointer.)
7507 C escape sequences can be used in strings and characters to represent
7508 non-printable characters. @value{GDBN} prints out strings with these
7509 escape sequences embedded. Single non-printable characters are
7510 printed using the @samp{CHR(@var{nnn})} format.
7513 The assignment operator (@code{:=}) returns the value of its right-hand
7517 All built-in procedures both modify @emph{and} return their argument.
7521 @subsubsection Modula-2 type and range checks
7522 @cindex Modula-2 checks
7525 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
7528 @c FIXME remove warning when type/range checks added
7530 @value{GDBN} considers two Modula-2 variables type equivalent if:
7534 They are of types that have been declared equivalent via a @code{TYPE
7535 @var{t1} = @var{t2}} statement
7538 They have been declared on the same line. (Note: This is true of the
7539 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
7542 As long as type checking is enabled, any attempt to combine variables
7543 whose types are not equivalent is an error.
7545 Range checking is done on all mathematical operations, assignment, array
7546 index bounds, and all built-in functions and procedures.
7549 @subsubsection The scope operators @code{::} and @code{.}
7551 @cindex @code{.}, Modula-2 scope operator
7552 @cindex colon, doubled as scope operator
7554 @vindex colon-colon@r{, in Modula-2}
7555 @c Info cannot handle :: but TeX can.
7558 @vindex ::@r{, in Modula-2}
7561 There are a few subtle differences between the Modula-2 scope operator
7562 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
7567 @var{module} . @var{id}
7568 @var{scope} :: @var{id}
7572 where @var{scope} is the name of a module or a procedure,
7573 @var{module} the name of a module, and @var{id} is any declared
7574 identifier within your program, except another module.
7576 Using the @code{::} operator makes @value{GDBN} search the scope
7577 specified by @var{scope} for the identifier @var{id}. If it is not
7578 found in the specified scope, then @value{GDBN} searches all scopes
7579 enclosing the one specified by @var{scope}.
7581 Using the @code{.} operator makes @value{GDBN} search the current scope for
7582 the identifier specified by @var{id} that was imported from the
7583 definition module specified by @var{module}. With this operator, it is
7584 an error if the identifier @var{id} was not imported from definition
7585 module @var{module}, or if @var{id} is not an identifier in
7589 @subsubsection @value{GDBN} and Modula-2
7591 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
7592 Five subcommands of @code{set print} and @code{show print} apply
7593 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
7594 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
7595 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
7596 analogue in Modula-2.
7598 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
7599 with any language, is not useful with Modula-2. Its
7600 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
7601 created in Modula-2 as they can in C or C@t{++}. However, because an
7602 address can be specified by an integral constant, the construct
7603 @samp{@{@var{type}@}@var{adrexp}} is still useful.
7605 @cindex @code{#} in Modula-2
7606 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
7607 interpreted as the beginning of a comment. Use @code{<>} instead.
7612 The extensions made to @value{GDBN} to support Chill only support output
7613 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
7614 supported, and attempting to debug executables produced by them is most
7615 likely to give an error as @value{GDBN} reads in the executable's symbol
7618 @c This used to say "... following Chill related topics ...", but since
7619 @c menus are not shown in the printed manual, it would look awkward.
7620 This section covers the Chill related topics and the features
7621 of @value{GDBN} which support these topics.
7624 * How modes are displayed:: How modes are displayed
7625 * Locations:: Locations and their accesses
7626 * Values and their Operations:: Values and their Operations
7627 * Chill type and range checks::
7631 @node How modes are displayed
7632 @subsubsection How modes are displayed
7634 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7635 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7636 slightly from the standard specification of the Chill language. The
7639 @c FIXME: this @table's contents effectively disable @code by using @r
7640 @c on every @item. So why does it need @code?
7642 @item @r{@emph{Discrete modes:}}
7645 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7648 @emph{Boolean Mode} which is predefined by @code{BOOL},
7650 @emph{Character Mode} which is predefined by @code{CHAR},
7652 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7654 (@value{GDBP}) ptype x
7655 type = SET (karli = 10, susi = 20, fritzi = 100)
7657 If the type is an unnumbered set the set element values are omitted.
7659 @emph{Range Mode} which is displayed by
7661 @code{type = <basemode>(<lower bound> : <upper bound>)}
7663 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7664 expression (e.g. set element names).
7667 @item @r{@emph{Powerset Mode:}}
7668 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7669 the member mode of the powerset. The member mode can be any discrete mode.
7671 (@value{GDBP}) ptype x
7672 type = POWERSET SET (egon, hugo, otto)
7675 @item @r{@emph{Reference Modes:}}
7678 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7679 followed by the mode name to which the reference is bound.
7681 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7684 @item @r{@emph{Procedure mode}}
7685 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7686 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7687 list>} is a list of the parameter modes. @code{<return mode>} indicates
7688 the mode of the result of the procedure if any. The exceptionlist lists
7689 all possible exceptions which can be raised by the procedure.
7692 @item @r{@emph{Instance mode}}
7693 The instance mode is represented by a structure, which has a static
7694 type, and is therefore not really of interest.
7697 @item @r{@emph{Synchronization Modes:}}
7700 @emph{Event Mode} which is displayed by
7702 @code{EVENT (<event length>)}
7704 where @code{(<event length>)} is optional.
7706 @emph{Buffer Mode} which is displayed by
7708 @code{BUFFER (<buffer length>)<buffer element mode>}
7710 where @code{(<buffer length>)} is optional.
7713 @item @r{@emph{Timing Modes:}}
7716 @emph{Duration Mode} which is predefined by @code{DURATION}
7718 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7721 @item @r{@emph{Real Modes:}}
7722 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7724 @item @r{@emph{String Modes:}}
7727 @emph{Character String Mode} which is displayed by
7729 @code{CHARS(<string length>)}
7731 followed by the keyword @code{VARYING} if the String Mode is a varying
7734 @emph{Bit String Mode} which is displayed by
7741 @item @r{@emph{Array Mode:}}
7742 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7743 followed by the element mode (which may in turn be an array mode).
7745 (@value{GDBP}) ptype x
7748 SET (karli = 10, susi = 20, fritzi = 100)
7751 @item @r{@emph{Structure Mode}}
7752 The Structure mode is displayed by the keyword @code{STRUCT(<field
7753 list>)}. The @code{<field list>} consists of names and modes of fields
7754 of the structure. Variant structures have the keyword @code{CASE <field>
7755 OF <variant fields> ESAC} in their field list. Since the current version
7756 of the GNU Chill compiler doesn't implement tag processing (no runtime
7757 checks of variant fields, and therefore no debugging info), the output
7758 always displays all variant fields.
7760 (@value{GDBP}) ptype str
7775 @subsubsection Locations and their accesses
7777 A location in Chill is an object which can contain values.
7779 A value of a location is generally accessed by the (declared) name of
7780 the location. The output conforms to the specification of values in
7781 Chill programs. How values are specified
7782 is the topic of the next section, @ref{Values and their Operations}.
7784 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7785 display or change the result of a currently-active procedure:
7792 This does the same as the Chill action @code{RESULT EXPR} (which
7793 is not available in @value{GDBN}).
7795 Values of reference mode locations are printed by @code{PTR(<hex
7796 value>)} in case of a free reference mode, and by @code{(REF <reference
7797 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7798 represents the address where the reference points to. To access the
7799 value of the location referenced by the pointer, use the dereference
7802 Values of procedure mode locations are displayed by
7805 (<argument modes> ) <return mode> @} <address> <name of procedure
7808 @code{<argument modes>} is a list of modes according to the parameter
7809 specification of the procedure and @code{<address>} shows the address of
7813 Locations of instance modes are displayed just like a structure with two
7814 fields specifying the @emph{process type} and the @emph{copy number} of
7815 the investigated instance location@footnote{This comes from the current
7816 implementation of instances. They are implemented as a structure (no
7817 na). The output should be something like @code{[<name of the process>;
7818 <instance number>]}.}. The field names are @code{__proc_type} and
7821 Locations of synchronization modes are displayed like a structure with
7822 the field name @code{__event_data} in case of a event mode location, and
7823 like a structure with the field @code{__buffer_data} in case of a buffer
7824 mode location (refer to previous paragraph).
7826 Structure Mode locations are printed by @code{[.<field name>: <value>,
7827 ...]}. The @code{<field name>} corresponds to the structure mode
7828 definition and the layout of @code{<value>} varies depending of the mode
7829 of the field. If the investigated structure mode location is of variant
7830 structure mode, the variant parts of the structure are enclosed in curled
7831 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7832 on the same memory location and represent the current values of the
7833 memory location in their specific modes. Since no tag processing is done
7834 all variants are displayed. A variant field is printed by
7835 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7838 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7839 [.cs: []], (susi) = [.ds: susi]}]
7843 Substructures of string mode-, array mode- or structure mode-values
7844 (e.g. array slices, fields of structure locations) are accessed using
7845 certain operations which are described in the next section, @ref{Values
7846 and their Operations}.
7848 A location value may be interpreted as having a different mode using the
7849 location conversion. This mode conversion is written as @code{<mode
7850 name>(<location>)}. The user has to consider that the sizes of the modes
7851 have to be equal otherwise an error occurs. Furthermore, no range
7852 checking of the location against the destination mode is performed, and
7853 therefore the result can be quite confusing.
7856 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7859 @node Values and their Operations
7860 @subsubsection Values and their Operations
7862 Values are used to alter locations, to investigate complex structures in
7863 more detail or to filter relevant information out of a large amount of
7864 data. There are several (mode dependent) operations defined which enable
7865 such investigations. These operations are not only applicable to
7866 constant values but also to locations, which can become quite useful
7867 when debugging complex structures. During parsing the command line
7868 (e.g. evaluating an expression) @value{GDBN} treats location names as
7869 the values behind these locations.
7871 This section describes how values have to be specified and which
7872 operations are legal to be used with such values.
7875 @item Literal Values
7876 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7877 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7879 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7880 @c be converted to a @ref.
7885 @emph{Integer Literals} are specified in the same manner as in Chill
7886 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7888 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7890 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7893 @emph{Set Literals} are defined by a name which was specified in a set
7894 mode. The value delivered by a Set Literal is the set value. This is
7895 comparable to an enumeration in C/C@t{++} language.
7897 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7898 emptiness literal delivers either the empty reference value, the empty
7899 procedure value or the empty instance value.
7902 @emph{Character String Literals} are defined by a sequence of characters
7903 enclosed in single- or double quotes. If a single- or double quote has
7904 to be part of the string literal it has to be stuffed (specified twice).
7906 @emph{Bitstring Literals} are specified in the same manner as in Chill
7907 programs (refer z200/88 chpt 5.2.4.8).
7909 @emph{Floating point literals} are specified in the same manner as in
7910 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7915 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7916 name>} can be omitted if the mode of the tuple is unambiguous. This
7917 unambiguity is derived from the context of a evaluated expression.
7918 @code{<tuple>} can be one of the following:
7921 @item @emph{Powerset Tuple}
7922 @item @emph{Array Tuple}
7923 @item @emph{Structure Tuple}
7924 Powerset tuples, array tuples and structure tuples are specified in the
7925 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7928 @item String Element Value
7929 A string element value is specified by
7931 @code{<string value>(<index>)}
7933 where @code{<index>} is a integer expression. It delivers a character
7934 value which is equivalent to the character indexed by @code{<index>} in
7937 @item String Slice Value
7938 A string slice value is specified by @code{<string value>(<slice
7939 spec>)}, where @code{<slice spec>} can be either a range of integer
7940 expressions or specified by @code{<start expr> up <size>}.
7941 @code{<size>} denotes the number of elements which the slice contains.
7942 The delivered value is a string value, which is part of the specified
7945 @item Array Element Values
7946 An array element value is specified by @code{<array value>(<expr>)} and
7947 delivers a array element value of the mode of the specified array.
7949 @item Array Slice Values
7950 An array slice is specified by @code{<array value>(<slice spec>)}, where
7951 @code{<slice spec>} can be either a range specified by expressions or by
7952 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7953 arrayelements the slice contains. The delivered value is an array value
7954 which is part of the specified array.
7956 @item Structure Field Values
7957 A structure field value is derived by @code{<structure value>.<field
7958 name>}, where @code{<field name>} indicates the name of a field specified
7959 in the mode definition of the structure. The mode of the delivered value
7960 corresponds to this mode definition in the structure definition.
7962 @item Procedure Call Value
7963 The procedure call value is derived from the return value of the
7964 procedure@footnote{If a procedure call is used for instance in an
7965 expression, then this procedure is called with all its side
7966 effects. This can lead to confusing results if used carelessly.}.
7968 Values of duration mode locations are represented by @code{ULONG} literals.
7970 Values of time mode locations appear as
7972 @code{TIME(<secs>:<nsecs>)}
7977 This is not implemented yet:
7978 @item Built-in Value
7980 The following built in functions are provided:
7992 @item @code{UPPER()}
7993 @item @code{LOWER()}
7994 @item @code{LENGTH()}
7998 @item @code{ARCSIN()}
7999 @item @code{ARCCOS()}
8000 @item @code{ARCTAN()}
8007 For a detailed description refer to the GNU Chill implementation manual
8011 @item Zero-adic Operator Value
8012 The zero-adic operator value is derived from the instance value for the
8013 current active process.
8015 @item Expression Values
8016 The value delivered by an expression is the result of the evaluation of
8017 the specified expression. If there are error conditions (mode
8018 incompatibility, etc.) the evaluation of expressions is aborted with a
8019 corresponding error message. Expressions may be parenthesised which
8020 causes the evaluation of this expression before any other expression
8021 which uses the result of the parenthesised expression. The following
8022 operators are supported by @value{GDBN}:
8025 @item @code{OR, ORIF, XOR}
8026 @itemx @code{AND, ANDIF}
8028 Logical operators defined over operands of boolean mode.
8031 Equality and inequality operators defined over all modes.
8035 Relational operators defined over predefined modes.
8038 @itemx @code{*, /, MOD, REM}
8039 Arithmetic operators defined over predefined modes.
8042 Change sign operator.
8045 String concatenation operator.
8048 String repetition operator.
8051 Referenced location operator which can be used either to take the
8052 address of a location (@code{->loc}), or to dereference a reference
8053 location (@code{loc->}).
8055 @item @code{OR, XOR}
8058 Powerset and bitstring operators.
8062 Powerset inclusion operators.
8065 Membership operator.
8069 @node Chill type and range checks
8070 @subsubsection Chill type and range checks
8072 @value{GDBN} considers two Chill variables mode equivalent if the sizes
8073 of the two modes are equal. This rule applies recursively to more
8074 complex datatypes which means that complex modes are treated
8075 equivalent if all element modes (which also can be complex modes like
8076 structures, arrays, etc.) have the same size.
8078 Range checking is done on all mathematical operations, assignment, array
8079 index bounds and all built in procedures.
8081 Strong type checks are forced using the @value{GDBN} command @code{set
8082 check strong}. This enforces strong type and range checks on all
8083 operations where Chill constructs are used (expressions, built in
8084 functions, etc.) in respect to the semantics as defined in the z.200
8085 language specification.
8087 All checks can be disabled by the @value{GDBN} command @code{set check
8091 @c Deviations from the Chill Standard Z200/88
8092 see last paragraph ?
8095 @node Chill defaults
8096 @subsubsection Chill defaults
8098 If type and range checking are set automatically by @value{GDBN}, they
8099 both default to @code{on} whenever the working language changes to
8100 Chill. This happens regardless of whether you or @value{GDBN}
8101 selected the working language.
8103 If you allow @value{GDBN} to set the language automatically, then entering
8104 code compiled from a file whose name ends with @file{.ch} sets the
8105 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
8106 the language automatically}, for further details.
8109 @chapter Examining the Symbol Table
8111 The commands described in this chapter allow you to inquire about the
8112 symbols (names of variables, functions and types) defined in your
8113 program. This information is inherent in the text of your program and
8114 does not change as your program executes. @value{GDBN} finds it in your
8115 program's symbol table, in the file indicated when you started @value{GDBN}
8116 (@pxref{File Options, ,Choosing files}), or by one of the
8117 file-management commands (@pxref{Files, ,Commands to specify files}).
8119 @cindex symbol names
8120 @cindex names of symbols
8121 @cindex quoting names
8122 Occasionally, you may need to refer to symbols that contain unusual
8123 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8124 most frequent case is in referring to static variables in other
8125 source files (@pxref{Variables,,Program variables}). File names
8126 are recorded in object files as debugging symbols, but @value{GDBN} would
8127 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8128 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8129 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8136 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8139 @kindex info address
8140 @cindex address of a symbol
8141 @item info address @var{symbol}
8142 Describe where the data for @var{symbol} is stored. For a register
8143 variable, this says which register it is kept in. For a non-register
8144 local variable, this prints the stack-frame offset at which the variable
8147 Note the contrast with @samp{print &@var{symbol}}, which does not work
8148 at all for a register variable, and for a stack local variable prints
8149 the exact address of the current instantiation of the variable.
8152 @cindex symbol from address
8153 @item info symbol @var{addr}
8154 Print the name of a symbol which is stored at the address @var{addr}.
8155 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8156 nearest symbol and an offset from it:
8159 (@value{GDBP}) info symbol 0x54320
8160 _initialize_vx + 396 in section .text
8164 This is the opposite of the @code{info address} command. You can use
8165 it to find out the name of a variable or a function given its address.
8168 @item whatis @var{expr}
8169 Print the data type of expression @var{expr}. @var{expr} is not
8170 actually evaluated, and any side-effecting operations (such as
8171 assignments or function calls) inside it do not take place.
8172 @xref{Expressions, ,Expressions}.
8175 Print the data type of @code{$}, the last value in the value history.
8178 @item ptype @var{typename}
8179 Print a description of data type @var{typename}. @var{typename} may be
8180 the name of a type, or for C code it may have the form @samp{class
8181 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8182 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8184 @item ptype @var{expr}
8186 Print a description of the type of expression @var{expr}. @code{ptype}
8187 differs from @code{whatis} by printing a detailed description, instead
8188 of just the name of the type.
8190 For example, for this variable declaration:
8193 struct complex @{double real; double imag;@} v;
8197 the two commands give this output:
8201 (@value{GDBP}) whatis v
8202 type = struct complex
8203 (@value{GDBP}) ptype v
8204 type = struct complex @{
8212 As with @code{whatis}, using @code{ptype} without an argument refers to
8213 the type of @code{$}, the last value in the value history.
8216 @item info types @var{regexp}
8218 Print a brief description of all types whose names match @var{regexp}
8219 (or all types in your program, if you supply no argument). Each
8220 complete typename is matched as though it were a complete line; thus,
8221 @samp{i type value} gives information on all types in your program whose
8222 names include the string @code{value}, but @samp{i type ^value$} gives
8223 information only on types whose complete name is @code{value}.
8225 This command differs from @code{ptype} in two ways: first, like
8226 @code{whatis}, it does not print a detailed description; second, it
8227 lists all source files where a type is defined.
8230 @cindex local variables
8231 @item info scope @var{addr}
8232 List all the variables local to a particular scope. This command
8233 accepts a location---a function name, a source line, or an address
8234 preceded by a @samp{*}, and prints all the variables local to the
8235 scope defined by that location. For example:
8238 (@value{GDBP}) @b{info scope command_line_handler}
8239 Scope for command_line_handler:
8240 Symbol rl is an argument at stack/frame offset 8, length 4.
8241 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8242 Symbol linelength is in static storage at address 0x150a1c, length 4.
8243 Symbol p is a local variable in register $esi, length 4.
8244 Symbol p1 is a local variable in register $ebx, length 4.
8245 Symbol nline is a local variable in register $edx, length 4.
8246 Symbol repeat is a local variable at frame offset -8, length 4.
8251 Show the name of the current source file---that is, the source file for
8252 the function containing the current point of execution---and the language
8255 @kindex info sources
8257 Print the names of all source files in your program for which there is
8258 debugging information, organized into two lists: files whose symbols
8259 have already been read, and files whose symbols will be read when needed.
8261 @kindex info functions
8262 @item info functions
8263 Print the names and data types of all defined functions.
8265 @item info functions @var{regexp}
8266 Print the names and data types of all defined functions
8267 whose names contain a match for regular expression @var{regexp}.
8268 Thus, @samp{info fun step} finds all functions whose names
8269 include @code{step}; @samp{info fun ^step} finds those whose names
8270 start with @code{step}.
8272 @kindex info variables
8273 @item info variables
8274 Print the names and data types of all variables that are declared
8275 outside of functions (i.e., excluding local variables).
8277 @item info variables @var{regexp}
8278 Print the names and data types of all variables (except for local
8279 variables) whose names contain a match for regular expression
8283 This was never implemented.
8284 @kindex info methods
8286 @itemx info methods @var{regexp}
8287 The @code{info methods} command permits the user to examine all defined
8288 methods within C@t{++} program, or (with the @var{regexp} argument) a
8289 specific set of methods found in the various C@t{++} classes. Many
8290 C@t{++} classes provide a large number of methods. Thus, the output
8291 from the @code{ptype} command can be overwhelming and hard to use. The
8292 @code{info-methods} command filters the methods, printing only those
8293 which match the regular-expression @var{regexp}.
8296 @cindex reloading symbols
8297 Some systems allow individual object files that make up your program to
8298 be replaced without stopping and restarting your program. For example,
8299 in VxWorks you can simply recompile a defective object file and keep on
8300 running. If you are running on one of these systems, you can allow
8301 @value{GDBN} to reload the symbols for automatically relinked modules:
8304 @kindex set symbol-reloading
8305 @item set symbol-reloading on
8306 Replace symbol definitions for the corresponding source file when an
8307 object file with a particular name is seen again.
8309 @item set symbol-reloading off
8310 Do not replace symbol definitions when encountering object files of the
8311 same name more than once. This is the default state; if you are not
8312 running on a system that permits automatic relinking of modules, you
8313 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8314 may discard symbols when linking large programs, that may contain
8315 several modules (from different directories or libraries) with the same
8318 @kindex show symbol-reloading
8319 @item show symbol-reloading
8320 Show the current @code{on} or @code{off} setting.
8323 @kindex set opaque-type-resolution
8324 @item set opaque-type-resolution on
8325 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8326 declared as a pointer to a @code{struct}, @code{class}, or
8327 @code{union}---for example, @code{struct MyType *}---that is used in one
8328 source file although the full declaration of @code{struct MyType} is in
8329 another source file. The default is on.
8331 A change in the setting of this subcommand will not take effect until
8332 the next time symbols for a file are loaded.
8334 @item set opaque-type-resolution off
8335 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8336 is printed as follows:
8338 @{<no data fields>@}
8341 @kindex show opaque-type-resolution
8342 @item show opaque-type-resolution
8343 Show whether opaque types are resolved or not.
8345 @kindex maint print symbols
8347 @kindex maint print psymbols
8348 @cindex partial symbol dump
8349 @item maint print symbols @var{filename}
8350 @itemx maint print psymbols @var{filename}
8351 @itemx maint print msymbols @var{filename}
8352 Write a dump of debugging symbol data into the file @var{filename}.
8353 These commands are used to debug the @value{GDBN} symbol-reading code. Only
8354 symbols with debugging data are included. If you use @samp{maint print
8355 symbols}, @value{GDBN} includes all the symbols for which it has already
8356 collected full details: that is, @var{filename} reflects symbols for
8357 only those files whose symbols @value{GDBN} has read. You can use the
8358 command @code{info sources} to find out which files these are. If you
8359 use @samp{maint print psymbols} instead, the dump shows information about
8360 symbols that @value{GDBN} only knows partially---that is, symbols defined in
8361 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
8362 @samp{maint print msymbols} dumps just the minimal symbol information
8363 required for each object file from which @value{GDBN} has read some symbols.
8364 @xref{Files, ,Commands to specify files}, for a discussion of how
8365 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
8369 @chapter Altering Execution
8371 Once you think you have found an error in your program, you might want to
8372 find out for certain whether correcting the apparent error would lead to
8373 correct results in the rest of the run. You can find the answer by
8374 experiment, using the @value{GDBN} features for altering execution of the
8377 For example, you can store new values into variables or memory
8378 locations, give your program a signal, restart it at a different
8379 address, or even return prematurely from a function.
8382 * Assignment:: Assignment to variables
8383 * Jumping:: Continuing at a different address
8384 * Signaling:: Giving your program a signal
8385 * Returning:: Returning from a function
8386 * Calling:: Calling your program's functions
8387 * Patching:: Patching your program
8391 @section Assignment to variables
8394 @cindex setting variables
8395 To alter the value of a variable, evaluate an assignment expression.
8396 @xref{Expressions, ,Expressions}. For example,
8403 stores the value 4 into the variable @code{x}, and then prints the
8404 value of the assignment expression (which is 4).
8405 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
8406 information on operators in supported languages.
8408 @kindex set variable
8409 @cindex variables, setting
8410 If you are not interested in seeing the value of the assignment, use the
8411 @code{set} command instead of the @code{print} command. @code{set} is
8412 really the same as @code{print} except that the expression's value is
8413 not printed and is not put in the value history (@pxref{Value History,
8414 ,Value history}). The expression is evaluated only for its effects.
8416 If the beginning of the argument string of the @code{set} command
8417 appears identical to a @code{set} subcommand, use the @code{set
8418 variable} command instead of just @code{set}. This command is identical
8419 to @code{set} except for its lack of subcommands. For example, if your
8420 program has a variable @code{width}, you get an error if you try to set
8421 a new value with just @samp{set width=13}, because @value{GDBN} has the
8422 command @code{set width}:
8425 (@value{GDBP}) whatis width
8427 (@value{GDBP}) p width
8429 (@value{GDBP}) set width=47
8430 Invalid syntax in expression.
8434 The invalid expression, of course, is @samp{=47}. In
8435 order to actually set the program's variable @code{width}, use
8438 (@value{GDBP}) set var width=47
8441 Because the @code{set} command has many subcommands that can conflict
8442 with the names of program variables, it is a good idea to use the
8443 @code{set variable} command instead of just @code{set}. For example, if
8444 your program has a variable @code{g}, you run into problems if you try
8445 to set a new value with just @samp{set g=4}, because @value{GDBN} has
8446 the command @code{set gnutarget}, abbreviated @code{set g}:
8450 (@value{GDBP}) whatis g
8454 (@value{GDBP}) set g=4
8458 The program being debugged has been started already.
8459 Start it from the beginning? (y or n) y
8460 Starting program: /home/smith/cc_progs/a.out
8461 "/home/smith/cc_progs/a.out": can't open to read symbols:
8463 (@value{GDBP}) show g
8464 The current BFD target is "=4".
8469 The program variable @code{g} did not change, and you silently set the
8470 @code{gnutarget} to an invalid value. In order to set the variable
8474 (@value{GDBP}) set var g=4
8477 @value{GDBN} allows more implicit conversions in assignments than C; you can
8478 freely store an integer value into a pointer variable or vice versa,
8479 and you can convert any structure to any other structure that is the
8480 same length or shorter.
8481 @comment FIXME: how do structs align/pad in these conversions?
8482 @comment /doc@cygnus.com 18dec1990
8484 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
8485 construct to generate a value of specified type at a specified address
8486 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
8487 to memory location @code{0x83040} as an integer (which implies a certain size
8488 and representation in memory), and
8491 set @{int@}0x83040 = 4
8495 stores the value 4 into that memory location.
8498 @section Continuing at a different address
8500 Ordinarily, when you continue your program, you do so at the place where
8501 it stopped, with the @code{continue} command. You can instead continue at
8502 an address of your own choosing, with the following commands:
8506 @item jump @var{linespec}
8507 Resume execution at line @var{linespec}. Execution stops again
8508 immediately if there is a breakpoint there. @xref{List, ,Printing
8509 source lines}, for a description of the different forms of
8510 @var{linespec}. It is common practice to use the @code{tbreak} command
8511 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
8514 The @code{jump} command does not change the current stack frame, or
8515 the stack pointer, or the contents of any memory location or any
8516 register other than the program counter. If line @var{linespec} is in
8517 a different function from the one currently executing, the results may
8518 be bizarre if the two functions expect different patterns of arguments or
8519 of local variables. For this reason, the @code{jump} command requests
8520 confirmation if the specified line is not in the function currently
8521 executing. However, even bizarre results are predictable if you are
8522 well acquainted with the machine-language code of your program.
8524 @item jump *@var{address}
8525 Resume execution at the instruction at address @var{address}.
8528 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
8529 On many systems, you can get much the same effect as the @code{jump}
8530 command by storing a new value into the register @code{$pc}. The
8531 difference is that this does not start your program running; it only
8532 changes the address of where it @emph{will} run when you continue. For
8540 makes the next @code{continue} command or stepping command execute at
8541 address @code{0x485}, rather than at the address where your program stopped.
8542 @xref{Continuing and Stepping, ,Continuing and stepping}.
8544 The most common occasion to use the @code{jump} command is to back
8545 up---perhaps with more breakpoints set---over a portion of a program
8546 that has already executed, in order to examine its execution in more
8551 @section Giving your program a signal
8555 @item signal @var{signal}
8556 Resume execution where your program stopped, but immediately give it the
8557 signal @var{signal}. @var{signal} can be the name or the number of a
8558 signal. For example, on many systems @code{signal 2} and @code{signal
8559 SIGINT} are both ways of sending an interrupt signal.
8561 Alternatively, if @var{signal} is zero, continue execution without
8562 giving a signal. This is useful when your program stopped on account of
8563 a signal and would ordinary see the signal when resumed with the
8564 @code{continue} command; @samp{signal 0} causes it to resume without a
8567 @code{signal} does not repeat when you press @key{RET} a second time
8568 after executing the command.
8572 Invoking the @code{signal} command is not the same as invoking the
8573 @code{kill} utility from the shell. Sending a signal with @code{kill}
8574 causes @value{GDBN} to decide what to do with the signal depending on
8575 the signal handling tables (@pxref{Signals}). The @code{signal} command
8576 passes the signal directly to your program.
8580 @section Returning from a function
8583 @cindex returning from a function
8586 @itemx return @var{expression}
8587 You can cancel execution of a function call with the @code{return}
8588 command. If you give an
8589 @var{expression} argument, its value is used as the function's return
8593 When you use @code{return}, @value{GDBN} discards the selected stack frame
8594 (and all frames within it). You can think of this as making the
8595 discarded frame return prematurely. If you wish to specify a value to
8596 be returned, give that value as the argument to @code{return}.
8598 This pops the selected stack frame (@pxref{Selection, ,Selecting a
8599 frame}), and any other frames inside of it, leaving its caller as the
8600 innermost remaining frame. That frame becomes selected. The
8601 specified value is stored in the registers used for returning values
8604 The @code{return} command does not resume execution; it leaves the
8605 program stopped in the state that would exist if the function had just
8606 returned. In contrast, the @code{finish} command (@pxref{Continuing
8607 and Stepping, ,Continuing and stepping}) resumes execution until the
8608 selected stack frame returns naturally.
8611 @section Calling program functions
8613 @cindex calling functions
8616 @item call @var{expr}
8617 Evaluate the expression @var{expr} without displaying @code{void}
8621 You can use this variant of the @code{print} command if you want to
8622 execute a function from your program, but without cluttering the output
8623 with @code{void} returned values. If the result is not void, it
8624 is printed and saved in the value history.
8626 For the A29K, a user-controlled variable @code{call_scratch_address},
8627 specifies the location of a scratch area to be used when @value{GDBN}
8628 calls a function in the target. This is necessary because the usual
8629 method of putting the scratch area on the stack does not work in systems
8630 that have separate instruction and data spaces.
8633 @section Patching programs
8635 @cindex patching binaries
8636 @cindex writing into executables
8637 @cindex writing into corefiles
8639 By default, @value{GDBN} opens the file containing your program's
8640 executable code (or the corefile) read-only. This prevents accidental
8641 alterations to machine code; but it also prevents you from intentionally
8642 patching your program's binary.
8644 If you'd like to be able to patch the binary, you can specify that
8645 explicitly with the @code{set write} command. For example, you might
8646 want to turn on internal debugging flags, or even to make emergency
8652 @itemx set write off
8653 If you specify @samp{set write on}, @value{GDBN} opens executable and
8654 core files for both reading and writing; if you specify @samp{set write
8655 off} (the default), @value{GDBN} opens them read-only.
8657 If you have already loaded a file, you must load it again (using the
8658 @code{exec-file} or @code{core-file} command) after changing @code{set
8659 write}, for your new setting to take effect.
8663 Display whether executable files and core files are opened for writing
8668 @chapter @value{GDBN} Files
8670 @value{GDBN} needs to know the file name of the program to be debugged,
8671 both in order to read its symbol table and in order to start your
8672 program. To debug a core dump of a previous run, you must also tell
8673 @value{GDBN} the name of the core dump file.
8676 * Files:: Commands to specify files
8677 * Symbol Errors:: Errors reading symbol files
8681 @section Commands to specify files
8683 @cindex symbol table
8684 @cindex core dump file
8686 You may want to specify executable and core dump file names. The usual
8687 way to do this is at start-up time, using the arguments to
8688 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8689 Out of @value{GDBN}}).
8691 Occasionally it is necessary to change to a different file during a
8692 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8693 a file you want to use. In these situations the @value{GDBN} commands
8694 to specify new files are useful.
8697 @cindex executable file
8699 @item file @var{filename}
8700 Use @var{filename} as the program to be debugged. It is read for its
8701 symbols and for the contents of pure memory. It is also the program
8702 executed when you use the @code{run} command. If you do not specify a
8703 directory and the file is not found in the @value{GDBN} working directory,
8704 @value{GDBN} uses the environment variable @code{PATH} as a list of
8705 directories to search, just as the shell does when looking for a program
8706 to run. You can change the value of this variable, for both @value{GDBN}
8707 and your program, using the @code{path} command.
8709 On systems with memory-mapped files, an auxiliary file named
8710 @file{@var{filename}.syms} may hold symbol table information for
8711 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8712 @file{@var{filename}.syms}, starting up more quickly. See the
8713 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8714 (available on the command line, and with the commands @code{file},
8715 @code{symbol-file}, or @code{add-symbol-file}, described below),
8716 for more information.
8719 @code{file} with no argument makes @value{GDBN} discard any information it
8720 has on both executable file and the symbol table.
8723 @item exec-file @r{[} @var{filename} @r{]}
8724 Specify that the program to be run (but not the symbol table) is found
8725 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8726 if necessary to locate your program. Omitting @var{filename} means to
8727 discard information on the executable file.
8730 @item symbol-file @r{[} @var{filename} @r{]}
8731 Read symbol table information from file @var{filename}. @code{PATH} is
8732 searched when necessary. Use the @code{file} command to get both symbol
8733 table and program to run from the same file.
8735 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8736 program's symbol table.
8738 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8739 of its convenience variables, the value history, and all breakpoints and
8740 auto-display expressions. This is because they may contain pointers to
8741 the internal data recording symbols and data types, which are part of
8742 the old symbol table data being discarded inside @value{GDBN}.
8744 @code{symbol-file} does not repeat if you press @key{RET} again after
8747 When @value{GDBN} is configured for a particular environment, it
8748 understands debugging information in whatever format is the standard
8749 generated for that environment; you may use either a @sc{gnu} compiler, or
8750 other compilers that adhere to the local conventions.
8751 Best results are usually obtained from @sc{gnu} compilers; for example,
8752 using @code{@value{GCC}} you can generate debugging information for
8755 For most kinds of object files, with the exception of old SVR3 systems
8756 using COFF, the @code{symbol-file} command does not normally read the
8757 symbol table in full right away. Instead, it scans the symbol table
8758 quickly to find which source files and which symbols are present. The
8759 details are read later, one source file at a time, as they are needed.
8761 The purpose of this two-stage reading strategy is to make @value{GDBN}
8762 start up faster. For the most part, it is invisible except for
8763 occasional pauses while the symbol table details for a particular source
8764 file are being read. (The @code{set verbose} command can turn these
8765 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8766 warnings and messages}.)
8768 We have not implemented the two-stage strategy for COFF yet. When the
8769 symbol table is stored in COFF format, @code{symbol-file} reads the
8770 symbol table data in full right away. Note that ``stabs-in-COFF''
8771 still does the two-stage strategy, since the debug info is actually
8775 @cindex reading symbols immediately
8776 @cindex symbols, reading immediately
8778 @cindex memory-mapped symbol file
8779 @cindex saving symbol table
8780 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8781 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8782 You can override the @value{GDBN} two-stage strategy for reading symbol
8783 tables by using the @samp{-readnow} option with any of the commands that
8784 load symbol table information, if you want to be sure @value{GDBN} has the
8785 entire symbol table available.
8787 If memory-mapped files are available on your system through the
8788 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8789 cause @value{GDBN} to write the symbols for your program into a reusable
8790 file. Future @value{GDBN} debugging sessions map in symbol information
8791 from this auxiliary symbol file (if the program has not changed), rather
8792 than spending time reading the symbol table from the executable
8793 program. Using the @samp{-mapped} option has the same effect as
8794 starting @value{GDBN} with the @samp{-mapped} command-line option.
8796 You can use both options together, to make sure the auxiliary symbol
8797 file has all the symbol information for your program.
8799 The auxiliary symbol file for a program called @var{myprog} is called
8800 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8801 than the corresponding executable), @value{GDBN} always attempts to use
8802 it when you debug @var{myprog}; no special options or commands are
8805 The @file{.syms} file is specific to the host machine where you run
8806 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8807 symbol table. It cannot be shared across multiple host platforms.
8809 @c FIXME: for now no mention of directories, since this seems to be in
8810 @c flux. 13mar1992 status is that in theory GDB would look either in
8811 @c current dir or in same dir as myprog; but issues like competing
8812 @c GDB's, or clutter in system dirs, mean that in practice right now
8813 @c only current dir is used. FFish says maybe a special GDB hierarchy
8814 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8819 @item core-file @r{[} @var{filename} @r{]}
8820 Specify the whereabouts of a core dump file to be used as the ``contents
8821 of memory''. Traditionally, core files contain only some parts of the
8822 address space of the process that generated them; @value{GDBN} can access the
8823 executable file itself for other parts.
8825 @code{core-file} with no argument specifies that no core file is
8828 Note that the core file is ignored when your program is actually running
8829 under @value{GDBN}. So, if you have been running your program and you
8830 wish to debug a core file instead, you must kill the subprocess in which
8831 the program is running. To do this, use the @code{kill} command
8832 (@pxref{Kill Process, ,Killing the child process}).
8834 @kindex add-symbol-file
8835 @cindex dynamic linking
8836 @item add-symbol-file @var{filename} @var{address}
8837 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8838 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address}
8839 The @code{add-symbol-file} command reads additional symbol table
8840 information from the file @var{filename}. You would use this command
8841 when @var{filename} has been dynamically loaded (by some other means)
8842 into the program that is running. @var{address} should be the memory
8843 address at which the file has been loaded; @value{GDBN} cannot figure
8844 this out for itself. You can additionally specify an arbitrary number
8845 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8846 section name and base address for that section. You can specify any
8847 @var{address} as an expression.
8849 The symbol table of the file @var{filename} is added to the symbol table
8850 originally read with the @code{symbol-file} command. You can use the
8851 @code{add-symbol-file} command any number of times; the new symbol data
8852 thus read keeps adding to the old. To discard all old symbol data
8853 instead, use the @code{symbol-file} command without any arguments.
8855 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8857 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8858 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8859 table information for @var{filename}.
8861 @kindex add-shared-symbol-file
8862 @item add-shared-symbol-file
8863 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8864 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8865 shared libraries, however if @value{GDBN} does not find yours, you can run
8866 @code{add-shared-symbol-file}. It takes no arguments.
8870 The @code{section} command changes the base address of section SECTION of
8871 the exec file to ADDR. This can be used if the exec file does not contain
8872 section addresses, (such as in the a.out format), or when the addresses
8873 specified in the file itself are wrong. Each section must be changed
8874 separately. The @code{info files} command, described below, lists all
8875 the sections and their addresses.
8881 @code{info files} and @code{info target} are synonymous; both print the
8882 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8883 including the names of the executable and core dump files currently in
8884 use by @value{GDBN}, and the files from which symbols were loaded. The
8885 command @code{help target} lists all possible targets rather than
8890 All file-specifying commands allow both absolute and relative file names
8891 as arguments. @value{GDBN} always converts the file name to an absolute file
8892 name and remembers it that way.
8894 @cindex shared libraries
8895 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8898 @value{GDBN} automatically loads symbol definitions from shared libraries
8899 when you use the @code{run} command, or when you examine a core file.
8900 (Before you issue the @code{run} command, @value{GDBN} does not understand
8901 references to a function in a shared library, however---unless you are
8902 debugging a core file).
8904 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8905 automatically loads the symbols at the time of the @code{shl_load} call.
8907 @c FIXME: some @value{GDBN} release may permit some refs to undef
8908 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8909 @c FIXME...lib; check this from time to time when updating manual
8912 @kindex info sharedlibrary
8915 @itemx info sharedlibrary
8916 Print the names of the shared libraries which are currently loaded.
8918 @kindex sharedlibrary
8920 @item sharedlibrary @var{regex}
8921 @itemx share @var{regex}
8922 Load shared object library symbols for files matching a
8923 Unix regular expression.
8924 As with files loaded automatically, it only loads shared libraries
8925 required by your program for a core file or after typing @code{run}. If
8926 @var{regex} is omitted all shared libraries required by your program are
8930 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8931 and automatically reads in symbols from the newly loaded library, up to
8932 a threshold that is initially set but that you can modify if you wish.
8934 Beyond that threshold, symbols from shared libraries must be explicitly
8935 loaded. To load these symbols, use the command @code{sharedlibrary
8936 @var{filename}}. The base address of the shared library is determined
8937 automatically by @value{GDBN} and need not be specified.
8939 To display or set the threshold, use the commands:
8942 @kindex set auto-solib-add
8943 @item set auto-solib-add @var{threshold}
8944 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8945 nonzero, symbols from all shared object libraries will be loaded
8946 automatically when the inferior begins execution or when the dynamic
8947 linker informs @value{GDBN} that a new library has been loaded, until
8948 the symbol table of the program and libraries exceeds this threshold.
8949 Otherwise, symbols must be loaded manually, using the
8950 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8952 @kindex show auto-solib-add
8953 @item show auto-solib-add
8954 Display the current autoloading size threshold, in megabytes.
8958 @section Errors reading symbol files
8960 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8961 such as symbol types it does not recognize, or known bugs in compiler
8962 output. By default, @value{GDBN} does not notify you of such problems, since
8963 they are relatively common and primarily of interest to people
8964 debugging compilers. If you are interested in seeing information
8965 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8966 only one message about each such type of problem, no matter how many
8967 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8968 to see how many times the problems occur, with the @code{set
8969 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8972 The messages currently printed, and their meanings, include:
8975 @item inner block not inside outer block in @var{symbol}
8977 The symbol information shows where symbol scopes begin and end
8978 (such as at the start of a function or a block of statements). This
8979 error indicates that an inner scope block is not fully contained
8980 in its outer scope blocks.
8982 @value{GDBN} circumvents the problem by treating the inner block as if it had
8983 the same scope as the outer block. In the error message, @var{symbol}
8984 may be shown as ``@code{(don't know)}'' if the outer block is not a
8987 @item block at @var{address} out of order
8989 The symbol information for symbol scope blocks should occur in
8990 order of increasing addresses. This error indicates that it does not
8993 @value{GDBN} does not circumvent this problem, and has trouble
8994 locating symbols in the source file whose symbols it is reading. (You
8995 can often determine what source file is affected by specifying
8996 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8999 @item bad block start address patched
9001 The symbol information for a symbol scope block has a start address
9002 smaller than the address of the preceding source line. This is known
9003 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9005 @value{GDBN} circumvents the problem by treating the symbol scope block as
9006 starting on the previous source line.
9008 @item bad string table offset in symbol @var{n}
9011 Symbol number @var{n} contains a pointer into the string table which is
9012 larger than the size of the string table.
9014 @value{GDBN} circumvents the problem by considering the symbol to have the
9015 name @code{foo}, which may cause other problems if many symbols end up
9018 @item unknown symbol type @code{0x@var{nn}}
9020 The symbol information contains new data types that @value{GDBN} does
9021 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9022 uncomprehended information, in hexadecimal.
9024 @value{GDBN} circumvents the error by ignoring this symbol information.
9025 This usually allows you to debug your program, though certain symbols
9026 are not accessible. If you encounter such a problem and feel like
9027 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9028 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9029 and examine @code{*bufp} to see the symbol.
9031 @item stub type has NULL name
9033 @value{GDBN} could not find the full definition for a struct or class.
9035 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9036 The symbol information for a C@t{++} member function is missing some
9037 information that recent versions of the compiler should have output for
9040 @item info mismatch between compiler and debugger
9042 @value{GDBN} could not parse a type specification output by the compiler.
9047 @chapter Specifying a Debugging Target
9049 @cindex debugging target
9052 A @dfn{target} is the execution environment occupied by your program.
9054 Often, @value{GDBN} runs in the same host environment as your program;
9055 in that case, the debugging target is specified as a side effect when
9056 you use the @code{file} or @code{core} commands. When you need more
9057 flexibility---for example, running @value{GDBN} on a physically separate
9058 host, or controlling a standalone system over a serial port or a
9059 realtime system over a TCP/IP connection---you can use the @code{target}
9060 command to specify one of the target types configured for @value{GDBN}
9061 (@pxref{Target Commands, ,Commands for managing targets}).
9064 * Active Targets:: Active targets
9065 * Target Commands:: Commands for managing targets
9066 * Byte Order:: Choosing target byte order
9067 * Remote:: Remote debugging
9068 * KOD:: Kernel Object Display
9072 @node Active Targets
9073 @section Active targets
9075 @cindex stacking targets
9076 @cindex active targets
9077 @cindex multiple targets
9079 There are three classes of targets: processes, core files, and
9080 executable files. @value{GDBN} can work concurrently on up to three
9081 active targets, one in each class. This allows you to (for example)
9082 start a process and inspect its activity without abandoning your work on
9085 For example, if you execute @samp{gdb a.out}, then the executable file
9086 @code{a.out} is the only active target. If you designate a core file as
9087 well---presumably from a prior run that crashed and coredumped---then
9088 @value{GDBN} has two active targets and uses them in tandem, looking
9089 first in the corefile target, then in the executable file, to satisfy
9090 requests for memory addresses. (Typically, these two classes of target
9091 are complementary, since core files contain only a program's
9092 read-write memory---variables and so on---plus machine status, while
9093 executable files contain only the program text and initialized data.)
9095 When you type @code{run}, your executable file becomes an active process
9096 target as well. When a process target is active, all @value{GDBN}
9097 commands requesting memory addresses refer to that target; addresses in
9098 an active core file or executable file target are obscured while the
9099 process target is active.
9101 Use the @code{core-file} and @code{exec-file} commands to select a new
9102 core file or executable target (@pxref{Files, ,Commands to specify
9103 files}). To specify as a target a process that is already running, use
9104 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9107 @node Target Commands
9108 @section Commands for managing targets
9111 @item target @var{type} @var{parameters}
9112 Connects the @value{GDBN} host environment to a target machine or
9113 process. A target is typically a protocol for talking to debugging
9114 facilities. You use the argument @var{type} to specify the type or
9115 protocol of the target machine.
9117 Further @var{parameters} are interpreted by the target protocol, but
9118 typically include things like device names or host names to connect
9119 with, process numbers, and baud rates.
9121 The @code{target} command does not repeat if you press @key{RET} again
9122 after executing the command.
9126 Displays the names of all targets available. To display targets
9127 currently selected, use either @code{info target} or @code{info files}
9128 (@pxref{Files, ,Commands to specify files}).
9130 @item help target @var{name}
9131 Describe a particular target, including any parameters necessary to
9134 @kindex set gnutarget
9135 @item set gnutarget @var{args}
9136 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9137 knows whether it is reading an @dfn{executable},
9138 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9139 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9140 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9143 @emph{Warning:} To specify a file format with @code{set gnutarget},
9144 you must know the actual BFD name.
9148 @xref{Files, , Commands to specify files}.
9150 @kindex show gnutarget
9151 @item show gnutarget
9152 Use the @code{show gnutarget} command to display what file format
9153 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9154 @value{GDBN} will determine the file format for each file automatically,
9155 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9158 Here are some common targets (available, or not, depending on the GDB
9163 @item target exec @var{program}
9164 An executable file. @samp{target exec @var{program}} is the same as
9165 @samp{exec-file @var{program}}.
9168 @item target core @var{filename}
9169 A core dump file. @samp{target core @var{filename}} is the same as
9170 @samp{core-file @var{filename}}.
9172 @kindex target remote
9173 @item target remote @var{dev}
9174 Remote serial target in GDB-specific protocol. The argument @var{dev}
9175 specifies what serial device to use for the connection (e.g.
9176 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9177 supports the @code{load} command. This is only useful if you have
9178 some other way of getting the stub to the target system, and you can put
9179 it somewhere in memory where it won't get clobbered by the download.
9183 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9191 works; however, you cannot assume that a specific memory map, device
9192 drivers, or even basic I/O is available, although some simulators do
9193 provide these. For info about any processor-specific simulator details,
9194 see the appropriate section in @ref{Embedded Processors, ,Embedded
9199 Some configurations may include these targets as well:
9204 @item target nrom @var{dev}
9205 NetROM ROM emulator. This target only supports downloading.
9209 Different targets are available on different configurations of @value{GDBN};
9210 your configuration may have more or fewer targets.
9212 Many remote targets require you to download the executable's code
9213 once you've successfully established a connection.
9217 @kindex load @var{filename}
9218 @item load @var{filename}
9219 Depending on what remote debugging facilities are configured into
9220 @value{GDBN}, the @code{load} command may be available. Where it exists, it
9221 is meant to make @var{filename} (an executable) available for debugging
9222 on the remote system---by downloading, or dynamic linking, for example.
9223 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
9224 the @code{add-symbol-file} command.
9226 If your @value{GDBN} does not have a @code{load} command, attempting to
9227 execute it gets the error message ``@code{You can't do that when your
9228 target is @dots{}}''
9230 The file is loaded at whatever address is specified in the executable.
9231 For some object file formats, you can specify the load address when you
9232 link the program; for other formats, like a.out, the object file format
9233 specifies a fixed address.
9234 @c FIXME! This would be a good place for an xref to the GNU linker doc.
9236 @code{load} does not repeat if you press @key{RET} again after using it.
9240 @section Choosing target byte order
9242 @cindex choosing target byte order
9243 @cindex target byte order
9245 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
9246 offer the ability to run either big-endian or little-endian byte
9247 orders. Usually the executable or symbol will include a bit to
9248 designate the endian-ness, and you will not need to worry about
9249 which to use. However, you may still find it useful to adjust
9250 @value{GDBN}'s idea of processor endian-ness manually.
9253 @kindex set endian big
9254 @item set endian big
9255 Instruct @value{GDBN} to assume the target is big-endian.
9257 @kindex set endian little
9258 @item set endian little
9259 Instruct @value{GDBN} to assume the target is little-endian.
9261 @kindex set endian auto
9262 @item set endian auto
9263 Instruct @value{GDBN} to use the byte order associated with the
9267 Display @value{GDBN}'s current idea of the target byte order.
9271 Note that these commands merely adjust interpretation of symbolic
9272 data on the host, and that they have absolutely no effect on the
9276 @section Remote debugging
9277 @cindex remote debugging
9279 If you are trying to debug a program running on a machine that cannot run
9280 @value{GDBN} in the usual way, it is often useful to use remote debugging.
9281 For example, you might use remote debugging on an operating system kernel,
9282 or on a small system which does not have a general purpose operating system
9283 powerful enough to run a full-featured debugger.
9285 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
9286 to make this work with particular debugging targets. In addition,
9287 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
9288 but not specific to any particular target system) which you can use if you
9289 write the remote stubs---the code that runs on the remote system to
9290 communicate with @value{GDBN}.
9292 Other remote targets may be available in your
9293 configuration of @value{GDBN}; use @code{help target} to list them.
9296 * Remote Serial:: @value{GDBN} remote serial protocol
9300 @subsection The @value{GDBN} remote serial protocol
9302 @cindex remote serial debugging, overview
9303 To debug a program running on another machine (the debugging
9304 @dfn{target} machine), you must first arrange for all the usual
9305 prerequisites for the program to run by itself. For example, for a C
9310 A startup routine to set up the C runtime environment; these usually
9311 have a name like @file{crt0}. The startup routine may be supplied by
9312 your hardware supplier, or you may have to write your own.
9315 A C subroutine library to support your program's
9316 subroutine calls, notably managing input and output.
9319 A way of getting your program to the other machine---for example, a
9320 download program. These are often supplied by the hardware
9321 manufacturer, but you may have to write your own from hardware
9325 The next step is to arrange for your program to use a serial port to
9326 communicate with the machine where @value{GDBN} is running (the @dfn{host}
9327 machine). In general terms, the scheme looks like this:
9331 @value{GDBN} already understands how to use this protocol; when everything
9332 else is set up, you can simply use the @samp{target remote} command
9333 (@pxref{Targets,,Specifying a Debugging Target}).
9335 @item On the target,
9336 you must link with your program a few special-purpose subroutines that
9337 implement the @value{GDBN} remote serial protocol. The file containing these
9338 subroutines is called a @dfn{debugging stub}.
9340 On certain remote targets, you can use an auxiliary program
9341 @code{gdbserver} instead of linking a stub into your program.
9342 @xref{Server,,Using the @code{gdbserver} program}, for details.
9345 The debugging stub is specific to the architecture of the remote
9346 machine; for example, use @file{sparc-stub.c} to debug programs on
9349 @cindex remote serial stub list
9350 These working remote stubs are distributed with @value{GDBN}:
9355 @cindex @file{i386-stub.c}
9358 For Intel 386 and compatible architectures.
9361 @cindex @file{m68k-stub.c}
9362 @cindex Motorola 680x0
9364 For Motorola 680x0 architectures.
9367 @cindex @file{sh-stub.c}
9370 For Hitachi SH architectures.
9373 @cindex @file{sparc-stub.c}
9375 For @sc{sparc} architectures.
9378 @cindex @file{sparcl-stub.c}
9381 For Fujitsu @sc{sparclite} architectures.
9385 The @file{README} file in the @value{GDBN} distribution may list other
9386 recently added stubs.
9389 * Stub Contents:: What the stub can do for you
9390 * Bootstrapping:: What you must do for the stub
9391 * Debug Session:: Putting it all together
9392 * Protocol:: Definition of the communication protocol
9393 * Server:: Using the `gdbserver' program
9394 * NetWare:: Using the `gdbserve.nlm' program
9398 @subsubsection What the stub can do for you
9400 @cindex remote serial stub
9401 The debugging stub for your architecture supplies these three
9405 @item set_debug_traps
9406 @kindex set_debug_traps
9407 @cindex remote serial stub, initialization
9408 This routine arranges for @code{handle_exception} to run when your
9409 program stops. You must call this subroutine explicitly near the
9410 beginning of your program.
9412 @item handle_exception
9413 @kindex handle_exception
9414 @cindex remote serial stub, main routine
9415 This is the central workhorse, but your program never calls it
9416 explicitly---the setup code arranges for @code{handle_exception} to
9417 run when a trap is triggered.
9419 @code{handle_exception} takes control when your program stops during
9420 execution (for example, on a breakpoint), and mediates communications
9421 with @value{GDBN} on the host machine. This is where the communications
9422 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
9423 representative on the target machine. It begins by sending summary
9424 information on the state of your program, then continues to execute,
9425 retrieving and transmitting any information @value{GDBN} needs, until you
9426 execute a @value{GDBN} command that makes your program resume; at that point,
9427 @code{handle_exception} returns control to your own code on the target
9431 @cindex @code{breakpoint} subroutine, remote
9432 Use this auxiliary subroutine to make your program contain a
9433 breakpoint. Depending on the particular situation, this may be the only
9434 way for @value{GDBN} to get control. For instance, if your target
9435 machine has some sort of interrupt button, you won't need to call this;
9436 pressing the interrupt button transfers control to
9437 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
9438 simply receiving characters on the serial port may also trigger a trap;
9439 again, in that situation, you don't need to call @code{breakpoint} from
9440 your own program---simply running @samp{target remote} from the host
9441 @value{GDBN} session gets control.
9443 Call @code{breakpoint} if none of these is true, or if you simply want
9444 to make certain your program stops at a predetermined point for the
9445 start of your debugging session.
9449 @subsubsection What you must do for the stub
9451 @cindex remote stub, support routines
9452 The debugging stubs that come with @value{GDBN} are set up for a particular
9453 chip architecture, but they have no information about the rest of your
9454 debugging target machine.
9456 First of all you need to tell the stub how to communicate with the
9460 @item int getDebugChar()
9461 @kindex getDebugChar
9462 Write this subroutine to read a single character from the serial port.
9463 It may be identical to @code{getchar} for your target system; a
9464 different name is used to allow you to distinguish the two if you wish.
9466 @item void putDebugChar(int)
9467 @kindex putDebugChar
9468 Write this subroutine to write a single character to the serial port.
9469 It may be identical to @code{putchar} for your target system; a
9470 different name is used to allow you to distinguish the two if you wish.
9473 @cindex control C, and remote debugging
9474 @cindex interrupting remote targets
9475 If you want @value{GDBN} to be able to stop your program while it is
9476 running, you need to use an interrupt-driven serial driver, and arrange
9477 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
9478 character). That is the character which @value{GDBN} uses to tell the
9479 remote system to stop.
9481 Getting the debugging target to return the proper status to @value{GDBN}
9482 probably requires changes to the standard stub; one quick and dirty way
9483 is to just execute a breakpoint instruction (the ``dirty'' part is that
9484 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
9486 Other routines you need to supply are:
9489 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
9490 @kindex exceptionHandler
9491 Write this function to install @var{exception_address} in the exception
9492 handling tables. You need to do this because the stub does not have any
9493 way of knowing what the exception handling tables on your target system
9494 are like (for example, the processor's table might be in @sc{rom},
9495 containing entries which point to a table in @sc{ram}).
9496 @var{exception_number} is the exception number which should be changed;
9497 its meaning is architecture-dependent (for example, different numbers
9498 might represent divide by zero, misaligned access, etc). When this
9499 exception occurs, control should be transferred directly to
9500 @var{exception_address}, and the processor state (stack, registers,
9501 and so on) should be just as it is when a processor exception occurs. So if
9502 you want to use a jump instruction to reach @var{exception_address}, it
9503 should be a simple jump, not a jump to subroutine.
9505 For the 386, @var{exception_address} should be installed as an interrupt
9506 gate so that interrupts are masked while the handler runs. The gate
9507 should be at privilege level 0 (the most privileged level). The
9508 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
9509 help from @code{exceptionHandler}.
9511 @item void flush_i_cache()
9512 @kindex flush_i_cache
9513 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
9514 instruction cache, if any, on your target machine. If there is no
9515 instruction cache, this subroutine may be a no-op.
9517 On target machines that have instruction caches, @value{GDBN} requires this
9518 function to make certain that the state of your program is stable.
9522 You must also make sure this library routine is available:
9525 @item void *memset(void *, int, int)
9527 This is the standard library function @code{memset} that sets an area of
9528 memory to a known value. If you have one of the free versions of
9529 @code{libc.a}, @code{memset} can be found there; otherwise, you must
9530 either obtain it from your hardware manufacturer, or write your own.
9533 If you do not use the GNU C compiler, you may need other standard
9534 library subroutines as well; this varies from one stub to another,
9535 but in general the stubs are likely to use any of the common library
9536 subroutines which @code{@value{GCC}} generates as inline code.
9540 @subsubsection Putting it all together
9542 @cindex remote serial debugging summary
9543 In summary, when your program is ready to debug, you must follow these
9548 Make sure you have defined the supporting low-level routines
9549 (@pxref{Bootstrapping,,What you must do for the stub}):
9551 @code{getDebugChar}, @code{putDebugChar},
9552 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
9556 Insert these lines near the top of your program:
9564 For the 680x0 stub only, you need to provide a variable called
9565 @code{exceptionHook}. Normally you just use:
9568 void (*exceptionHook)() = 0;
9572 but if before calling @code{set_debug_traps}, you set it to point to a
9573 function in your program, that function is called when
9574 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
9575 error). The function indicated by @code{exceptionHook} is called with
9576 one parameter: an @code{int} which is the exception number.
9579 Compile and link together: your program, the @value{GDBN} debugging stub for
9580 your target architecture, and the supporting subroutines.
9583 Make sure you have a serial connection between your target machine and
9584 the @value{GDBN} host, and identify the serial port on the host.
9587 @c The "remote" target now provides a `load' command, so we should
9588 @c document that. FIXME.
9589 Download your program to your target machine (or get it there by
9590 whatever means the manufacturer provides), and start it.
9593 To start remote debugging, run @value{GDBN} on the host machine, and specify
9594 as an executable file the program that is running in the remote machine.
9595 This tells @value{GDBN} how to find your program's symbols and the contents
9599 @cindex serial line, @code{target remote}
9600 Establish communication using the @code{target remote} command.
9601 Its argument specifies how to communicate with the target
9602 machine---either via a devicename attached to a direct serial line, or a
9603 TCP port (usually to a terminal server which in turn has a serial line
9604 to the target). For example, to use a serial line connected to the
9605 device named @file{/dev/ttyb}:
9608 target remote /dev/ttyb
9611 @cindex TCP port, @code{target remote}
9612 To use a TCP connection, use an argument of the form
9613 @code{@var{host}:port}. For example, to connect to port 2828 on a
9614 terminal server named @code{manyfarms}:
9617 target remote manyfarms:2828
9621 Now you can use all the usual commands to examine and change data and to
9622 step and continue the remote program.
9624 To resume the remote program and stop debugging it, use the @code{detach}
9627 @cindex interrupting remote programs
9628 @cindex remote programs, interrupting
9629 Whenever @value{GDBN} is waiting for the remote program, if you type the
9630 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
9631 program. This may or may not succeed, depending in part on the hardware
9632 and the serial drivers the remote system uses. If you type the
9633 interrupt character once again, @value{GDBN} displays this prompt:
9636 Interrupted while waiting for the program.
9637 Give up (and stop debugging it)? (y or n)
9640 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
9641 (If you decide you want to try again later, you can use @samp{target
9642 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
9643 goes back to waiting.
9646 @subsubsection Communication protocol
9648 @cindex debugging stub, example
9649 @cindex remote stub, example
9650 @cindex stub example, remote debugging
9651 The stub files provided with @value{GDBN} implement the target side of the
9652 communication protocol, and the @value{GDBN} side is implemented in the
9653 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
9654 these subroutines to communicate, and ignore the details. (If you're
9655 implementing your own stub file, you can still ignore the details: start
9656 with one of the existing stub files. @file{sparc-stub.c} is the best
9657 organized, and therefore the easiest to read.)
9659 However, there may be occasions when you need to know something about
9660 the protocol---for example, if there is only one serial port to your
9661 target machine, you might want your program to do something special if
9662 it recognizes a packet meant for @value{GDBN}.
9664 In the examples below, @samp{<-} and @samp{->} are used to indicate
9665 transmitted and received data respectfully.
9667 @cindex protocol, @value{GDBN} remote serial
9668 @cindex serial protocol, @value{GDBN} remote
9669 @cindex remote serial protocol
9670 All @value{GDBN} commands and responses (other than acknowledgments) are
9671 sent as a @var{packet}. A @var{packet} is introduced with the character
9672 @samp{$}, the actual @var{packet-data}, and the terminating character
9673 @samp{#} followed by a two-digit @var{checksum}:
9676 @code{$}@var{packet-data}@code{#}@var{checksum}
9680 @cindex checksum, for @value{GDBN} remote
9682 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9683 characters between the leading @samp{$} and the trailing @samp{#} (an
9684 eight bit unsigned checksum).
9686 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9687 specification also included an optional two-digit @var{sequence-id}:
9690 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9693 @cindex sequence-id, for @value{GDBN} remote
9695 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9696 has never output @var{sequence-id}s. Stubs that handle packets added
9697 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9699 @cindex acknowledgment, for @value{GDBN} remote
9700 When either the host or the target machine receives a packet, the first
9701 response expected is an acknowledgment: either @samp{+} (to indicate
9702 the package was received correctly) or @samp{-} (to request
9706 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9711 The host (@value{GDBN}) sends @var{command}s, and the target (the
9712 debugging stub incorporated in your program) sends a @var{response}. In
9713 the case of step and continue @var{command}s, the response is only sent
9714 when the operation has completed (the target has again stopped).
9716 @var{packet-data} consists of a sequence of characters with the
9717 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9720 Fields within the packet should be separated using @samp{,} @samp{;} or
9721 @samp{:}. Except where otherwise noted all numbers are represented in
9722 HEX with leading zeros suppressed.
9724 Implementors should note that prior to @value{GDBN} 5.0, the character
9725 @samp{:} could not appear as the third character in a packet (as it
9726 would potentially conflict with the @var{sequence-id}).
9728 Response @var{data} can be run-length encoded to save space. A @samp{*}
9729 means that the next character is an @sc{ascii} encoding giving a repeat count
9730 which stands for that many repetitions of the character preceding the
9731 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9732 where @code{n >=3} (which is where rle starts to win). The printable
9733 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9734 value greater than 126 should not be used.
9736 Some remote systems have used a different run-length encoding mechanism
9737 loosely refered to as the cisco encoding. Following the @samp{*}
9738 character are two hex digits that indicate the size of the packet.
9745 means the same as "0000".
9747 The error response returned for some packets includes a two character
9748 error number. That number is not well defined.
9750 For any @var{command} not supported by the stub, an empty response
9751 (@samp{$#00}) should be returned. That way it is possible to extend the
9752 protocol. A newer @value{GDBN} can tell if a packet is supported based
9755 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9756 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9759 Below is a complete list of all currently defined @var{command}s and
9760 their corresponding response @var{data}:
9762 @multitable @columnfractions .30 .30 .40
9770 Use the extended remote protocol. Sticky---only needs to be set once.
9771 The extended remote protocol supports the @samp{R} packet.
9775 Stubs that support the extended remote protocol return @samp{} which,
9776 unfortunately, is identical to the response returned by stubs that do not
9777 support protocol extensions.
9782 Indicate the reason the target halted. The reply is the same as for step
9791 @tab Reserved for future use
9793 @item set program arguments @strong{(reserved)}
9794 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9799 Initialized @samp{argv[]} array passed into program. @var{arglen}
9800 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9801 See @file{gdbserver} for more details.
9803 @tab reply @code{OK}
9805 @tab reply @code{E}@var{NN}
9807 @item set baud @strong{(deprecated)}
9808 @tab @code{b}@var{baud}
9810 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9811 transport layer state change? When it's received, or after the ACK is
9812 transmitted. In either case, there are problems if the command or the
9813 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9814 to add something like this, and get it working for the first time, they
9815 ought to modify ser-unix.c to send some kind of out-of-band message to a
9816 specially-setup stub and have the switch happen "in between" packets, so
9817 that from remote protocol's point of view, nothing actually
9820 @item set breakpoint @strong{(deprecated)}
9821 @tab @code{B}@var{addr},@var{mode}
9823 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9824 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9828 @tab @code{c}@var{addr}
9830 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9836 @item continue with signal
9837 @tab @code{C}@var{sig}@code{;}@var{addr}
9839 Continue with signal @var{sig} (hex signal number). If
9840 @code{;}@var{addr} is omitted, resume at same address.
9845 @item toggle debug @strong{(deprecated)}
9853 Detach @value{GDBN} from the remote system. Sent to the remote target before
9854 @value{GDBN} disconnects.
9856 @tab reply @emph{no response}
9858 @value{GDBN} does not check for any response after sending this packet.
9862 @tab Reserved for future use
9866 @tab Reserved for future use
9870 @tab Reserved for future use
9874 @tab Reserved for future use
9876 @item read registers
9878 @tab Read general registers.
9880 @tab reply @var{XX...}
9882 Each byte of register data is described by two hex digits. The bytes
9883 with the register are transmitted in target byte order. The size of
9884 each register and their position within the @samp{g} @var{packet} are
9885 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9886 @var{REGISTER_NAME} macros. The specification of several standard
9887 @code{g} packets is specified below.
9889 @tab @code{E}@var{NN}
9893 @tab @code{G}@var{XX...}
9895 See @samp{g} for a description of the @var{XX...} data.
9897 @tab reply @code{OK}
9900 @tab reply @code{E}@var{NN}
9905 @tab Reserved for future use
9908 @tab @code{H}@var{c}@var{t...}
9910 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9911 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9912 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9913 thread used in other operations. If zero, pick a thread, any thread.
9915 @tab reply @code{OK}
9918 @tab reply @code{E}@var{NN}
9922 @c 'H': How restrictive (or permissive) is the thread model. If a
9923 @c thread is selected and stopped, are other threads allowed
9924 @c to continue to execute? As I mentioned above, I think the
9925 @c semantics of each command when a thread is selected must be
9926 @c described. For example:
9928 @c 'g': If the stub supports threads and a specific thread is
9929 @c selected, returns the register block from that thread;
9930 @c otherwise returns current registers.
9932 @c 'G' If the stub supports threads and a specific thread is
9933 @c selected, sets the registers of the register block of
9934 @c that thread; otherwise sets current registers.
9936 @item cycle step @strong{(draft)}
9937 @tab @code{i}@var{addr}@code{,}@var{nnn}
9939 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9940 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9941 step starting at that address.
9943 @item signal then cycle step @strong{(reserved)}
9946 See @samp{i} and @samp{S} for likely syntax and semantics.
9950 @tab Reserved for future use
9954 @tab Reserved for future use
9959 FIXME: @emph{There is no description of how operate when a specific
9960 thread context has been selected (ie. does 'k' kill only that thread?)}.
9964 @tab Reserved for future use
9968 @tab Reserved for future use
9971 @tab @code{m}@var{addr}@code{,}@var{length}
9973 Read @var{length} bytes of memory starting at address @var{addr}.
9974 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9975 using word alligned accesses. FIXME: @emph{A word aligned memory
9976 transfer mechanism is needed.}
9978 @tab reply @var{XX...}
9980 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9981 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9982 sized memory transfers are assumed using word alligned accesses. FIXME:
9983 @emph{A word aligned memory transfer mechanism is needed.}
9985 @tab reply @code{E}@var{NN}
9986 @tab @var{NN} is errno
9989 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9991 Write @var{length} bytes of memory starting at address @var{addr}.
9992 @var{XX...} is the data.
9994 @tab reply @code{OK}
9997 @tab reply @code{E}@var{NN}
9999 for an error (this includes the case where only part of the data was
10004 @tab Reserved for future use
10008 @tab Reserved for future use
10012 @tab Reserved for future use
10016 @tab Reserved for future use
10018 @item read reg @strong{(reserved)}
10019 @tab @code{p}@var{n...}
10021 See write register.
10023 @tab return @var{r....}
10024 @tab The hex encoded value of the register in target byte order.
10027 @tab @code{P}@var{n...}@code{=}@var{r...}
10029 Write register @var{n...} with value @var{r...}, which contains two hex
10030 digits for each byte in the register (target byte order).
10032 @tab reply @code{OK}
10035 @tab reply @code{E}@var{NN}
10038 @item general query
10039 @tab @code{q}@var{query}
10041 Request info about @var{query}. In general @value{GDBN} queries
10042 have a leading upper case letter. Custom vendor queries should use a
10043 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
10044 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
10045 must ensure that they match the full @var{query} name.
10047 @tab reply @code{XX...}
10048 @tab Hex encoded data from query. The reply can not be empty.
10050 @tab reply @code{E}@var{NN}
10054 @tab Indicating an unrecognized @var{query}.
10057 @tab @code{Q}@var{var}@code{=}@var{val}
10059 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
10060 naming conventions.
10062 @item reset @strong{(deprecated)}
10065 Reset the entire system.
10067 @item remote restart
10068 @tab @code{R}@var{XX}
10070 Restart the remote server. @var{XX} while needed has no clear
10071 definition. FIXME: @emph{An example interaction explaining how this
10072 packet is used in extended-remote mode is needed}.
10075 @tab @code{s}@var{addr}
10077 @var{addr} is address to resume. If @var{addr} is omitted, resume at
10083 @item step with signal
10084 @tab @code{S}@var{sig}@code{;}@var{addr}
10086 Like @samp{C} but step not continue.
10092 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
10094 Search backwards starting at address @var{addr} for a match with pattern
10095 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
10096 bytes. @var{addr} must be at least 3 digits.
10099 @tab @code{T}@var{XX}
10100 @tab Find out if the thread XX is alive.
10102 @tab reply @code{OK}
10103 @tab thread is still alive
10105 @tab reply @code{E}@var{NN}
10106 @tab thread is dead
10110 @tab Reserved for future use
10114 @tab Reserved for future use
10118 @tab Reserved for future use
10122 @tab Reserved for future use
10126 @tab Reserved for future use
10130 @tab Reserved for future use
10134 @tab Reserved for future use
10136 @item write mem (binary)
10137 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
10139 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
10140 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
10141 escaped using @code{0x7d}.
10143 @tab reply @code{OK}
10146 @tab reply @code{E}@var{NN}
10151 @tab Reserved for future use
10155 @tab Reserved for future use
10157 @item remove break or watchpoint @strong{(draft)}
10158 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10162 @item insert break or watchpoint @strong{(draft)}
10163 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
10165 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
10166 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
10167 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
10168 bytes. For a software breakpoint, @var{length} specifies the size of
10169 the instruction to be patched. For hardware breakpoints and watchpoints
10170 @var{length} specifies the memory region to be monitored. To avoid
10171 potential problems with duplicate packets, the operations should be
10172 implemented in an idempotent way.
10174 @tab reply @code{E}@var{NN}
10177 @tab reply @code{OK}
10181 @tab If not supported.
10185 @tab Reserved for future use
10189 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
10190 receive any of the below as a reply. In the case of the @samp{C},
10191 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
10192 when the target halts. In the below the exact meaning of @samp{signal
10193 number} is poorly defined. In general one of the UNIX signal numbering
10194 conventions is used.
10196 @multitable @columnfractions .4 .6
10198 @item @code{S}@var{AA}
10199 @tab @var{AA} is the signal number
10201 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
10203 @var{AA} = two hex digit signal number; @var{n...} = register number
10204 (hex), @var{r...} = target byte ordered register contents, size defined
10205 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
10206 thread process ID, this is a hex integer; @var{n...} = other string not
10207 starting with valid hex digit. @value{GDBN} should ignore this
10208 @var{n...}, @var{r...} pair and go on to the next. This way we can
10209 extend the protocol.
10211 @item @code{W}@var{AA}
10213 The process exited, and @var{AA} is the exit status. This is only
10214 applicable for certains sorts of targets.
10216 @item @code{X}@var{AA}
10218 The process terminated with signal @var{AA}.
10220 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
10222 @var{AA} = signal number; @var{t...} = address of symbol "_start";
10223 @var{d...} = base of data section; @var{b...} = base of bss section.
10224 @emph{Note: only used by Cisco Systems targets. The difference between
10225 this reply and the "qOffsets" query is that the 'N' packet may arrive
10226 spontaneously whereas the 'qOffsets' is a query initiated by the host
10229 @item @code{O}@var{XX...}
10231 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
10232 while the program is running and the debugger should continue to wait
10237 The following set and query packets have already been defined.
10239 @multitable @columnfractions .2 .2 .6
10241 @item current thread
10242 @tab @code{q}@code{C}
10243 @tab Return the current thread id.
10245 @tab reply @code{QC}@var{pid}
10247 Where @var{pid} is a HEX encoded 16 bit process id.
10250 @tab Any other reply implies the old pid.
10252 @item all thread ids
10253 @tab @code{q}@code{fThreadInfo}
10255 @tab @code{q}@code{sThreadInfo}
10257 Obtain a list of active thread ids from the target (OS). Since there
10258 may be too many active threads to fit into one reply packet, this query
10259 works iteratively: it may require more than one query/reply sequence to
10260 obtain the entire list of threads. The first query of the sequence will
10261 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
10262 sequence will be the @code{qs}@code{ThreadInfo} query.
10265 @tab NOTE: replaces the @code{qL} query (see below).
10267 @tab reply @code{m}@var{<id>}
10268 @tab A single thread id
10270 @tab reply @code{m}@var{<id>},@var{<id>...}
10271 @tab a comma-separated list of thread ids
10273 @tab reply @code{l}
10274 @tab (lower case 'el') denotes end of list.
10278 In response to each query, the target will reply with a list of one
10279 or more thread ids, in big-endian hex, separated by commas. GDB will
10280 respond to each reply with a request for more thread ids (using the
10281 @code{qs} form of the query), until the target responds with @code{l}
10282 (lower-case el, for @code{'last'}).
10284 @item extra thread info
10285 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
10290 Where @var{<id>} is a thread-id in big-endian hex.
10291 Obtain a printable string description of a thread's attributes from
10292 the target OS. This string may contain anything that the target OS
10293 thinks is interesting for @value{GDBN} to tell the user about the thread.
10294 The string is displayed in @value{GDBN}'s @samp{info threads} display.
10295 Some examples of possible thread extra info strings are "Runnable", or
10296 "Blocked on Mutex".
10298 @tab reply @var{XX...}
10300 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
10301 printable string containing the extra information about the thread's
10304 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
10305 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
10310 Obtain thread information from RTOS. Where: @var{startflag} (one hex
10311 digit) is one to indicate the first query and zero to indicate a
10312 subsequent query; @var{threadcount} (two hex digits) is the maximum
10313 number of threads the response packet can contain; and @var{nextthread}
10314 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
10315 returned in the response as @var{argthread}.
10318 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
10321 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
10326 Where: @var{count} (two hex digits) is the number of threads being
10327 returned; @var{done} (one hex digit) is zero to indicate more threads
10328 and one indicates no further threads; @var{argthreadid} (eight hex
10329 digits) is @var{nextthread} from the request packet; @var{thread...} is
10330 a sequence of thread IDs from the target. @var{threadid} (eight hex
10331 digits). See @code{remote.c:parse_threadlist_response()}.
10333 @item compute CRC of memory block
10334 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
10337 @tab reply @code{E}@var{NN}
10338 @tab An error (such as memory fault)
10340 @tab reply @code{C}@var{CRC32}
10341 @tab A 32 bit cyclic redundancy check of the specified memory region.
10343 @item query sect offs
10344 @tab @code{q}@code{Offsets}
10346 Get section offsets that the target used when re-locating the downloaded
10347 image. @emph{Note: while a @code{Bss} offset is included in the
10348 response, @value{GDBN} ignores this and instead applies the @code{Data}
10349 offset to the @code{Bss} section.}
10351 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
10353 @item thread info request
10354 @tab @code{q}@code{P}@var{mode}@var{threadid}
10359 Returns information on @var{threadid}. Where: @var{mode} is a hex
10360 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
10364 See @code{remote.c:remote_unpack_thread_info_response()}.
10366 @item remote command
10367 @tab @code{q}@code{Rcmd,}@var{COMMAND}
10372 @var{COMMAND} (hex encoded) is passed to the local interpreter for
10373 execution. Invalid commands should be reported using the output string.
10374 Before the final result packet, the target may also respond with a
10375 number of intermediate @code{O}@var{OUTPUT} console output
10376 packets. @emph{Implementors should note that providing access to a
10377 stubs's interpreter may have security implications}.
10379 @tab reply @code{OK}
10381 A command response with no output.
10383 @tab reply @var{OUTPUT}
10385 A command response with the hex encoded output string @var{OUTPUT}.
10387 @tab reply @code{E}@var{NN}
10389 Indicate a badly formed request.
10394 When @samp{q}@samp{Rcmd} is not recognized.
10398 The following @samp{g}/@samp{G} packets have previously been defined.
10399 In the below, some thirty-two bit registers are transferred as sixty-four
10400 bits. Those registers should be zero/sign extended (which?) to fill the
10401 space allocated. Register bytes are transfered in target byte order.
10402 The two nibbles within a register byte are transfered most-significant -
10405 @multitable @columnfractions .5 .5
10409 All registers are transfered as thirty-two bit quantities in the order:
10410 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
10411 registers; fsr; fir; fp.
10415 All registers are transfered as sixty-four bit quantities (including
10416 thirty-two bit registers such as @code{sr}). The ordering is the same
10421 Example sequence of a target being re-started. Notice how the restart
10422 does not get any direct output:
10427 @emph{target restarts}
10430 -> @code{T001:1234123412341234}
10434 Example sequence of a target being stepped by a single instruction:
10442 -> @code{T001:1234123412341234}
10451 @subsubsection Using the @code{gdbserver} program
10454 @cindex remote connection without stubs
10455 @code{gdbserver} is a control program for Unix-like systems, which
10456 allows you to connect your program with a remote @value{GDBN} via
10457 @code{target remote}---but without linking in the usual debugging stub.
10459 @code{gdbserver} is not a complete replacement for the debugging stubs,
10460 because it requires essentially the same operating-system facilities
10461 that @value{GDBN} itself does. In fact, a system that can run
10462 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10463 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10464 because it is a much smaller program than @value{GDBN} itself. It is
10465 also easier to port than all of @value{GDBN}, so you may be able to get
10466 started more quickly on a new system by using @code{gdbserver}.
10467 Finally, if you develop code for real-time systems, you may find that
10468 the tradeoffs involved in real-time operation make it more convenient to
10469 do as much development work as possible on another system, for example
10470 by cross-compiling. You can use @code{gdbserver} to make a similar
10471 choice for debugging.
10473 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10474 or a TCP connection, using the standard @value{GDBN} remote serial
10478 @item On the target machine,
10479 you need to have a copy of the program you want to debug.
10480 @code{gdbserver} does not need your program's symbol table, so you can
10481 strip the program if necessary to save space. @value{GDBN} on the host
10482 system does all the symbol handling.
10484 To use the server, you must tell it how to communicate with @value{GDBN};
10485 the name of your program; and the arguments for your program. The
10489 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10492 @var{comm} is either a device name (to use a serial line) or a TCP
10493 hostname and portnumber. For example, to debug Emacs with the argument
10494 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10498 target> gdbserver /dev/com1 emacs foo.txt
10501 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10504 To use a TCP connection instead of a serial line:
10507 target> gdbserver host:2345 emacs foo.txt
10510 The only difference from the previous example is the first argument,
10511 specifying that you are communicating with the host @value{GDBN} via
10512 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10513 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10514 (Currently, the @samp{host} part is ignored.) You can choose any number
10515 you want for the port number as long as it does not conflict with any
10516 TCP ports already in use on the target system (for example, @code{23} is
10517 reserved for @code{telnet}).@footnote{If you choose a port number that
10518 conflicts with another service, @code{gdbserver} prints an error message
10519 and exits.} You must use the same port number with the host @value{GDBN}
10520 @code{target remote} command.
10522 @item On the @value{GDBN} host machine,
10523 you need an unstripped copy of your program, since @value{GDBN} needs
10524 symbols and debugging information. Start up @value{GDBN} as usual,
10525 using the name of the local copy of your program as the first argument.
10526 (You may also need the @w{@samp{--baud}} option if the serial line is
10527 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10528 remote} to establish communications with @code{gdbserver}. Its argument
10529 is either a device name (usually a serial device, like
10530 @file{/dev/ttyb}), or a TCP port descriptor in the form
10531 @code{@var{host}:@var{PORT}}. For example:
10534 (@value{GDBP}) target remote /dev/ttyb
10538 communicates with the server via serial line @file{/dev/ttyb}, and
10541 (@value{GDBP}) target remote the-target:2345
10545 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10546 For TCP connections, you must start up @code{gdbserver} prior to using
10547 the @code{target remote} command. Otherwise you may get an error whose
10548 text depends on the host system, but which usually looks something like
10549 @samp{Connection refused}.
10553 @subsubsection Using the @code{gdbserve.nlm} program
10555 @kindex gdbserve.nlm
10556 @code{gdbserve.nlm} is a control program for NetWare systems, which
10557 allows you to connect your program with a remote @value{GDBN} via
10558 @code{target remote}.
10560 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10561 using the standard @value{GDBN} remote serial protocol.
10564 @item On the target machine,
10565 you need to have a copy of the program you want to debug.
10566 @code{gdbserve.nlm} does not need your program's symbol table, so you
10567 can strip the program if necessary to save space. @value{GDBN} on the
10568 host system does all the symbol handling.
10570 To use the server, you must tell it how to communicate with
10571 @value{GDBN}; the name of your program; and the arguments for your
10572 program. The syntax is:
10575 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10576 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10579 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10580 the baud rate used by the connection. @var{port} and @var{node} default
10581 to 0, @var{baud} defaults to 9600@dmn{bps}.
10583 For example, to debug Emacs with the argument @samp{foo.txt}and
10584 communicate with @value{GDBN} over serial port number 2 or board 1
10585 using a 19200@dmn{bps} connection:
10588 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10591 @item On the @value{GDBN} host machine,
10592 you need an unstripped copy of your program, since @value{GDBN} needs
10593 symbols and debugging information. Start up @value{GDBN} as usual,
10594 using the name of the local copy of your program as the first argument.
10595 (You may also need the @w{@samp{--baud}} option if the serial line is
10596 running at anything other than 9600@dmn{bps}. After that, use @code{target
10597 remote} to establish communications with @code{gdbserve.nlm}. Its
10598 argument is a device name (usually a serial device, like
10599 @file{/dev/ttyb}). For example:
10602 (@value{GDBP}) target remote /dev/ttyb
10606 communications with the server via serial line @file{/dev/ttyb}.
10610 @section Kernel Object Display
10612 @cindex kernel object display
10613 @cindex kernel object
10616 Some targets support kernel object display. Using this facility,
10617 @value{GDBN} communicates specially with the underlying operating system
10618 and can display information about operating system-level objects such as
10619 mutexes and other synchronization objects. Exactly which objects can be
10620 displayed is determined on a per-OS basis.
10622 Use the @code{set os} command to set the operating system. This tells
10623 @value{GDBN} which kernel object display module to initialize:
10626 (@value{GDBP}) set os cisco
10629 If @code{set os} succeeds, @value{GDBN} will display some information
10630 about the operating system, and will create a new @code{info} command
10631 which can be used to query the target. The @code{info} command is named
10632 after the operating system:
10635 (@value{GDBP}) info cisco
10636 List of Cisco Kernel Objects
10638 any Any and all objects
10641 Further subcommands can be used to query about particular objects known
10644 There is currently no way to determine whether a given operating system
10645 is supported other than to try it.
10648 @node Configurations
10649 @chapter Configuration-Specific Information
10651 While nearly all @value{GDBN} commands are available for all native and
10652 cross versions of the debugger, there are some exceptions. This chapter
10653 describes things that are only available in certain configurations.
10655 There are three major categories of configurations: native
10656 configurations, where the host and target are the same, embedded
10657 operating system configurations, which are usually the same for several
10658 different processor architectures, and bare embedded processors, which
10659 are quite different from each other.
10664 * Embedded Processors::
10671 This section describes details specific to particular native
10676 * SVR4 Process Information:: SVR4 process information
10682 On HP-UX systems, if you refer to a function or variable name that
10683 begins with a dollar sign, @value{GDBN} searches for a user or system
10684 name first, before it searches for a convenience variable.
10686 @node SVR4 Process Information
10687 @subsection SVR4 process information
10690 @cindex process image
10692 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10693 used to examine the image of a running process using file-system
10694 subroutines. If @value{GDBN} is configured for an operating system with
10695 this facility, the command @code{info proc} is available to report on
10696 several kinds of information about the process running your program.
10697 @code{info proc} works only on SVR4 systems that include the
10698 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10699 and Unixware, but not HP-UX or Linux, for example.
10704 Summarize available information about the process.
10706 @kindex info proc mappings
10707 @item info proc mappings
10708 Report on the address ranges accessible in the program, with information
10709 on whether your program may read, write, or execute each range.
10711 @kindex info proc times
10712 @item info proc times
10713 Starting time, user CPU time, and system CPU time for your program and
10716 @kindex info proc id
10718 Report on the process IDs related to your program: its own process ID,
10719 the ID of its parent, the process group ID, and the session ID.
10721 @kindex info proc status
10722 @item info proc status
10723 General information on the state of the process. If the process is
10724 stopped, this report includes the reason for stopping, and any signal
10727 @item info proc all
10728 Show all the above information about the process.
10732 @section Embedded Operating Systems
10734 This section describes configurations involving the debugging of
10735 embedded operating systems that are available for several different
10739 * VxWorks:: Using @value{GDBN} with VxWorks
10742 @value{GDBN} includes the ability to debug programs running on
10743 various real-time operating systems.
10746 @subsection Using @value{GDBN} with VxWorks
10752 @kindex target vxworks
10753 @item target vxworks @var{machinename}
10754 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10755 is the target system's machine name or IP address.
10759 On VxWorks, @code{load} links @var{filename} dynamically on the
10760 current target system as well as adding its symbols in @value{GDBN}.
10762 @value{GDBN} enables developers to spawn and debug tasks running on networked
10763 VxWorks targets from a Unix host. Already-running tasks spawned from
10764 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10765 both the Unix host and on the VxWorks target. The program
10766 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10767 installed with the name @code{vxgdb}, to distinguish it from a
10768 @value{GDBN} for debugging programs on the host itself.)
10771 @item VxWorks-timeout @var{args}
10772 @kindex vxworks-timeout
10773 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10774 This option is set by the user, and @var{args} represents the number of
10775 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10776 your VxWorks target is a slow software simulator or is on the far side
10777 of a thin network line.
10780 The following information on connecting to VxWorks was current when
10781 this manual was produced; newer releases of VxWorks may use revised
10784 @kindex INCLUDE_RDB
10785 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10786 to include the remote debugging interface routines in the VxWorks
10787 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10788 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10789 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10790 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10791 information on configuring and remaking VxWorks, see the manufacturer's
10793 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
10795 Once you have included @file{rdb.a} in your VxWorks system image and set
10796 your Unix execution search path to find @value{GDBN}, you are ready to
10797 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
10798 @code{vxgdb}, depending on your installation).
10800 @value{GDBN} comes up showing the prompt:
10807 * VxWorks Connection:: Connecting to VxWorks
10808 * VxWorks Download:: VxWorks download
10809 * VxWorks Attach:: Running tasks
10812 @node VxWorks Connection
10813 @subsubsection Connecting to VxWorks
10815 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
10816 network. To connect to a target whose host name is ``@code{tt}'', type:
10819 (vxgdb) target vxworks tt
10823 @value{GDBN} displays messages like these:
10826 Attaching remote machine across net...
10831 @value{GDBN} then attempts to read the symbol tables of any object modules
10832 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
10833 these files by searching the directories listed in the command search
10834 path (@pxref{Environment, ,Your program's environment}); if it fails
10835 to find an object file, it displays a message such as:
10838 prog.o: No such file or directory.
10841 When this happens, add the appropriate directory to the search path with
10842 the @value{GDBN} command @code{path}, and execute the @code{target}
10845 @node VxWorks Download
10846 @subsubsection VxWorks download
10848 @cindex download to VxWorks
10849 If you have connected to the VxWorks target and you want to debug an
10850 object that has not yet been loaded, you can use the @value{GDBN}
10851 @code{load} command to download a file from Unix to VxWorks
10852 incrementally. The object file given as an argument to the @code{load}
10853 command is actually opened twice: first by the VxWorks target in order
10854 to download the code, then by @value{GDBN} in order to read the symbol
10855 table. This can lead to problems if the current working directories on
10856 the two systems differ. If both systems have NFS mounted the same
10857 filesystems, you can avoid these problems by using absolute paths.
10858 Otherwise, it is simplest to set the working directory on both systems
10859 to the directory in which the object file resides, and then to reference
10860 the file by its name, without any path. For instance, a program
10861 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
10862 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
10863 program, type this on VxWorks:
10866 -> cd "@var{vxpath}/vw/demo/rdb"
10870 Then, in @value{GDBN}, type:
10873 (vxgdb) cd @var{hostpath}/vw/demo/rdb
10874 (vxgdb) load prog.o
10877 @value{GDBN} displays a response similar to this:
10880 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
10883 You can also use the @code{load} command to reload an object module
10884 after editing and recompiling the corresponding source file. Note that
10885 this makes @value{GDBN} delete all currently-defined breakpoints,
10886 auto-displays, and convenience variables, and to clear the value
10887 history. (This is necessary in order to preserve the integrity of
10888 debugger's data structures that reference the target system's symbol
10891 @node VxWorks Attach
10892 @subsubsection Running tasks
10894 @cindex running VxWorks tasks
10895 You can also attach to an existing task using the @code{attach} command as
10899 (vxgdb) attach @var{task}
10903 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
10904 or suspended when you attach to it. Running tasks are suspended at
10905 the time of attachment.
10907 @node Embedded Processors
10908 @section Embedded Processors
10910 This section goes into details specific to particular embedded
10914 * A29K Embedded:: AMD A29K Embedded
10916 * H8/300:: Hitachi H8/300
10917 * H8/500:: Hitachi H8/500
10918 * i960:: Intel i960
10919 * M32R/D:: Mitsubishi M32R/D
10920 * M68K:: Motorola M68K
10921 * M88K:: Motorola M88K
10922 * MIPS Embedded:: MIPS Embedded
10923 * PA:: HP PA Embedded
10926 * Sparclet:: Tsqware Sparclet
10927 * Sparclite:: Fujitsu Sparclite
10928 * ST2000:: Tandem ST2000
10929 * Z8000:: Zilog Z8000
10932 @node A29K Embedded
10933 @subsection AMD A29K Embedded
10938 * Comms (EB29K):: Communications setup
10939 * gdb-EB29K:: EB29K cross-debugging
10940 * Remote Log:: Remote log
10945 @kindex target adapt
10946 @item target adapt @var{dev}
10947 Adapt monitor for A29K.
10949 @kindex target amd-eb
10950 @item target amd-eb @var{dev} @var{speed} @var{PROG}
10952 Remote PC-resident AMD EB29K board, attached over serial lines.
10953 @var{dev} is the serial device, as for @code{target remote};
10954 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
10955 name of the program to be debugged, as it appears to DOS on the PC.
10956 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
10961 @subsubsection A29K UDI
10964 @cindex AMD29K via UDI
10966 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
10967 protocol for debugging the a29k processor family. To use this
10968 configuration with AMD targets running the MiniMON monitor, you need the
10969 program @code{MONTIP}, available from AMD at no charge. You can also
10970 use @value{GDBN} with the UDI-conformant a29k simulator program
10971 @code{ISSTIP}, also available from AMD.
10974 @item target udi @var{keyword}
10976 Select the UDI interface to a remote a29k board or simulator, where
10977 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
10978 This file contains keyword entries which specify parameters used to
10979 connect to a29k targets. If the @file{udi_soc} file is not in your
10980 working directory, you must set the environment variable @samp{UDICONF}
10985 @subsubsection EBMON protocol for AMD29K
10987 @cindex EB29K board
10988 @cindex running 29K programs
10990 AMD distributes a 29K development board meant to fit in a PC, together
10991 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10992 term, this development system is called the ``EB29K''. To use
10993 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10994 must first connect a serial cable between the PC (which hosts the EB29K
10995 board) and a serial port on the Unix system. In the following, we
10996 assume you've hooked the cable between the PC's @file{COM1} port and
10997 @file{/dev/ttya} on the Unix system.
10999 @node Comms (EB29K)
11000 @subsubsection Communications setup
11002 The next step is to set up the PC's port, by doing something like this
11006 C:\> MODE com1:9600,n,8,1,none
11010 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
11011 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
11012 you must match the communications parameters when establishing the Unix
11013 end of the connection as well.
11014 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
11015 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
11017 @c It's optional, but it's unwise to omit it: who knows what is the
11018 @c default value set when the DOS machines boots? "No retry" means that
11019 @c the DOS serial device driver won't retry the operation if it fails;
11020 @c I understand that this is needed because the GDB serial protocol
11021 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
11023 To give control of the PC to the Unix side of the serial line, type
11024 the following at the DOS console:
11031 (Later, if you wish to return control to the DOS console, you can use
11032 the command @code{CTTY con}---but you must send it over the device that
11033 had control, in our example over the @file{COM1} serial line.)
11035 From the Unix host, use a communications program such as @code{tip} or
11036 @code{cu} to communicate with the PC; for example,
11039 cu -s 9600 -l /dev/ttya
11043 The @code{cu} options shown specify, respectively, the linespeed and the
11044 serial port to use. If you use @code{tip} instead, your command line
11045 may look something like the following:
11048 tip -9600 /dev/ttya
11052 Your system may require a different name where we show
11053 @file{/dev/ttya} as the argument to @code{tip}. The communications
11054 parameters, including which port to use, are associated with the
11055 @code{tip} argument in the ``remote'' descriptions file---normally the
11056 system table @file{/etc/remote}.
11057 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
11058 @c the DOS side's comms setup? cu can support -o (odd
11059 @c parity), -e (even parity)---apparently no settings for no parity or
11060 @c for character size. Taken from stty maybe...? John points out tip
11061 @c can set these as internal variables, eg ~s parity=none; man stty
11062 @c suggests that it *might* work to stty these options with stdin or
11063 @c stdout redirected... ---doc@cygnus.com, 25feb91
11065 @c There's nothing to be done for the "none" part of the DOS MODE
11066 @c command. The rest of the parameters should be matched by the
11067 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
11070 Using the @code{tip} or @code{cu} connection, change the DOS working
11071 directory to the directory containing a copy of your 29K program, then
11072 start the PC program @code{EBMON} (an EB29K control program supplied
11073 with your board by AMD). You should see an initial display from
11074 @code{EBMON} similar to the one that follows, ending with the
11075 @code{EBMON} prompt @samp{#}---
11080 G:\> CD \usr\joe\work29k
11082 G:\USR\JOE\WORK29K> EBMON
11083 Am29000 PC Coprocessor Board Monitor, version 3.0-18
11084 Copyright 1990 Advanced Micro Devices, Inc.
11085 Written by Gibbons and Associates, Inc.
11087 Enter '?' or 'H' for help
11089 PC Coprocessor Type = EB29K
11091 Memory Base = 0xd0000
11093 Data Memory Size = 2048KB
11094 Available I-RAM Range = 0x8000 to 0x1fffff
11095 Available D-RAM Range = 0x80002000 to 0x801fffff
11098 Register Stack Size = 0x800
11099 Memory Stack Size = 0x1800
11102 Am29027 Available = No
11103 Byte Write Available = Yes
11108 Then exit the @code{cu} or @code{tip} program (done in the example by
11109 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
11110 running, ready for @value{GDBN} to take over.
11112 For this example, we've assumed what is probably the most convenient
11113 way to make sure the same 29K program is on both the PC and the Unix
11114 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
11115 PC as a file system on the Unix host. If you do not have PC/NFS or
11116 something similar connecting the two systems, you must arrange some
11117 other way---perhaps floppy-disk transfer---of getting the 29K program
11118 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
11122 @subsubsection EB29K cross-debugging
11124 Finally, @code{cd} to the directory containing an image of your 29K
11125 program on the Unix system, and start @value{GDBN}---specifying as argument the
11126 name of your 29K program:
11129 cd /usr/joe/work29k
11134 Now you can use the @code{target} command:
11137 target amd-eb /dev/ttya 9600 MYFOO
11138 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
11139 @c emphasize that this is the name as seen by DOS (since I think DOS is
11140 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
11144 In this example, we've assumed your program is in a file called
11145 @file{myfoo}. Note that the filename given as the last argument to
11146 @code{target amd-eb} should be the name of the program as it appears to DOS.
11147 In our example this is simply @code{MYFOO}, but in general it can include
11148 a DOS path, and depending on your transfer mechanism may not resemble
11149 the name on the Unix side.
11151 At this point, you can set any breakpoints you wish; when you are ready
11152 to see your program run on the 29K board, use the @value{GDBN} command
11155 To stop debugging the remote program, use the @value{GDBN} @code{detach}
11158 To return control of the PC to its console, use @code{tip} or @code{cu}
11159 once again, after your @value{GDBN} session has concluded, to attach to
11160 @code{EBMON}. You can then type the command @code{q} to shut down
11161 @code{EBMON}, returning control to the DOS command-line interpreter.
11162 Type @kbd{CTTY con} to return command input to the main DOS console,
11163 and type @kbd{~.} to leave @code{tip} or @code{cu}.
11166 @subsubsection Remote log
11167 @cindex @file{eb.log}, a log file for EB29K
11168 @cindex log file for EB29K
11170 The @code{target amd-eb} command creates a file @file{eb.log} in the
11171 current working directory, to help debug problems with the connection.
11172 @file{eb.log} records all the output from @code{EBMON}, including echoes
11173 of the commands sent to it. Running @samp{tail -f} on this file in
11174 another window often helps to understand trouble with @code{EBMON}, or
11175 unexpected events on the PC side of the connection.
11183 @item target rdi @var{dev}
11184 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11185 use this target to communicate with both boards running the Angel
11186 monitor, or with the EmbeddedICE JTAG debug device.
11189 @item target rdp @var{dev}
11195 @subsection Hitachi H8/300
11199 @kindex target hms@r{, with H8/300}
11200 @item target hms @var{dev}
11201 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11202 Use special commands @code{device} and @code{speed} to control the serial
11203 line and the communications speed used.
11205 @kindex target e7000@r{, with H8/300}
11206 @item target e7000 @var{dev}
11207 E7000 emulator for Hitachi H8 and SH.
11209 @kindex target sh3@r{, with H8/300}
11210 @kindex target sh3e@r{, with H8/300}
11211 @item target sh3 @var{dev}
11212 @itemx target sh3e @var{dev}
11213 Hitachi SH-3 and SH-3E target systems.
11217 @cindex download to H8/300 or H8/500
11218 @cindex H8/300 or H8/500 download
11219 @cindex download to Hitachi SH
11220 @cindex Hitachi SH download
11221 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11222 board, the @code{load} command downloads your program to the Hitachi
11223 board and also opens it as the current executable target for
11224 @value{GDBN} on your host (like the @code{file} command).
11226 @value{GDBN} needs to know these things to talk to your
11227 Hitachi SH, H8/300, or H8/500:
11231 that you want to use @samp{target hms}, the remote debugging interface
11232 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11233 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11234 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11235 H8/300, or H8/500.)
11238 what serial device connects your host to your Hitachi board (the first
11239 serial device available on your host is the default).
11242 what speed to use over the serial device.
11246 * Hitachi Boards:: Connecting to Hitachi boards.
11247 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11248 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11251 @node Hitachi Boards
11252 @subsubsection Connecting to Hitachi boards
11254 @c only for Unix hosts
11256 @cindex serial device, Hitachi micros
11257 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11258 need to explicitly set the serial device. The default @var{port} is the
11259 first available port on your host. This is only necessary on Unix
11260 hosts, where it is typically something like @file{/dev/ttya}.
11263 @cindex serial line speed, Hitachi micros
11264 @code{@value{GDBN}} has another special command to set the communications
11265 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11266 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11267 the DOS @code{mode} command (for instance,
11268 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11270 The @samp{device} and @samp{speed} commands are available only when you
11271 use a Unix host to debug your Hitachi microprocessor programs. If you
11273 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11274 called @code{asynctsr} to communicate with the development board
11275 through a PC serial port. You must also use the DOS @code{mode} command
11276 to set up the serial port on the DOS side.
11278 The following sample session illustrates the steps needed to start a
11279 program under @value{GDBN} control on an H8/300. The example uses a
11280 sample H8/300 program called @file{t.x}. The procedure is the same for
11281 the Hitachi SH and the H8/500.
11283 First hook up your development board. In this example, we use a
11284 board attached to serial port @code{COM2}; if you use a different serial
11285 port, substitute its name in the argument of the @code{mode} command.
11286 When you call @code{asynctsr}, the auxiliary comms program used by the
11287 debugger, you give it just the numeric part of the serial port's name;
11288 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11292 C:\H8300\TEST> asynctsr 2
11293 C:\H8300\TEST> mode com2:9600,n,8,1,p
11295 Resident portion of MODE loaded
11297 COM2: 9600, n, 8, 1, p
11302 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11303 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11304 disable it, or even boot without it, to use @code{asynctsr} to control
11305 your development board.
11308 @kindex target hms@r{, and serial protocol}
11309 Now that serial communications are set up, and the development board is
11310 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11311 the name of your program as the argument. @code{@value{GDBN}} prompts
11312 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11313 commands to begin your debugging session: @samp{target hms} to specify
11314 cross-debugging to the Hitachi board, and the @code{load} command to
11315 download your program to the board. @code{load} displays the names of
11316 the program's sections, and a @samp{*} for each 2K of data downloaded.
11317 (If you want to refresh @value{GDBN} data on symbols or on the
11318 executable file without downloading, use the @value{GDBN} commands
11319 @code{file} or @code{symbol-file}. These commands, and @code{load}
11320 itself, are described in @ref{Files,,Commands to specify files}.)
11323 (eg-C:\H8300\TEST) @value{GDBP} t.x
11324 @value{GDBN} is free software and you are welcome to distribute copies
11325 of it under certain conditions; type "show copying" to see
11327 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11329 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11330 (@value{GDBP}) target hms
11331 Connected to remote H8/300 HMS system.
11332 (@value{GDBP}) load t.x
11333 .text : 0x8000 .. 0xabde ***********
11334 .data : 0xabde .. 0xad30 *
11335 .stack : 0xf000 .. 0xf014 *
11338 At this point, you're ready to run or debug your program. From here on,
11339 you can use all the usual @value{GDBN} commands. The @code{break} command
11340 sets breakpoints; the @code{run} command starts your program;
11341 @code{print} or @code{x} display data; the @code{continue} command
11342 resumes execution after stopping at a breakpoint. You can use the
11343 @code{help} command at any time to find out more about @value{GDBN} commands.
11345 Remember, however, that @emph{operating system} facilities aren't
11346 available on your development board; for example, if your program hangs,
11347 you can't send an interrupt---but you can press the @sc{reset} switch!
11349 Use the @sc{reset} button on the development board
11352 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11353 no way to pass an interrupt signal to the development board); and
11356 to return to the @value{GDBN} command prompt after your program finishes
11357 normally. The communications protocol provides no other way for @value{GDBN}
11358 to detect program completion.
11361 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11362 development board as a ``normal exit'' of your program.
11365 @subsubsection Using the E7000 in-circuit emulator
11367 @kindex target e7000@r{, with Hitachi ICE}
11368 You can use the E7000 in-circuit emulator to develop code for either the
11369 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11370 e7000} command to connect @value{GDBN} to your E7000:
11373 @item target e7000 @var{port} @var{speed}
11374 Use this form if your E7000 is connected to a serial port. The
11375 @var{port} argument identifies what serial port to use (for example,
11376 @samp{com2}). The third argument is the line speed in bits per second
11377 (for example, @samp{9600}).
11379 @item target e7000 @var{hostname}
11380 If your E7000 is installed as a host on a TCP/IP network, you can just
11381 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11384 @node Hitachi Special
11385 @subsubsection Special @value{GDBN} commands for Hitachi micros
11387 Some @value{GDBN} commands are available only for the H8/300:
11391 @kindex set machine
11392 @kindex show machine
11393 @item set machine h8300
11394 @itemx set machine h8300h
11395 Condition @value{GDBN} for one of the two variants of the H8/300
11396 architecture with @samp{set machine}. You can use @samp{show machine}
11397 to check which variant is currently in effect.
11406 @kindex set memory @var{mod}
11407 @cindex memory models, H8/500
11408 @item set memory @var{mod}
11410 Specify which H8/500 memory model (@var{mod}) you are using with
11411 @samp{set memory}; check which memory model is in effect with @samp{show
11412 memory}. The accepted values for @var{mod} are @code{small},
11413 @code{big}, @code{medium}, and @code{compact}.
11418 @subsection Intel i960
11422 @kindex target mon960
11423 @item target mon960 @var{dev}
11424 MON960 monitor for Intel i960.
11426 @kindex target nindy
11427 @item target nindy @var{devicename}
11428 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11429 the name of the serial device to use for the connection, e.g.
11436 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11437 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11438 tell @value{GDBN} how to connect to the 960 in several ways:
11442 Through command line options specifying serial port, version of the
11443 Nindy protocol, and communications speed;
11446 By responding to a prompt on startup;
11449 By using the @code{target} command at any point during your @value{GDBN}
11450 session. @xref{Target Commands, ,Commands for managing targets}.
11454 @cindex download to Nindy-960
11455 With the Nindy interface to an Intel 960 board, @code{load}
11456 downloads @var{filename} to the 960 as well as adding its symbols in
11460 * Nindy Startup:: Startup with Nindy
11461 * Nindy Options:: Options for Nindy
11462 * Nindy Reset:: Nindy reset command
11465 @node Nindy Startup
11466 @subsubsection Startup with Nindy
11468 If you simply start @code{@value{GDBP}} without using any command-line
11469 options, you are prompted for what serial port to use, @emph{before} you
11470 reach the ordinary @value{GDBN} prompt:
11473 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11477 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11478 identifies the serial port you want to use. You can, if you choose,
11479 simply start up with no Nindy connection by responding to the prompt
11480 with an empty line. If you do this and later wish to attach to Nindy,
11481 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11483 @node Nindy Options
11484 @subsubsection Options for Nindy
11486 These are the startup options for beginning your @value{GDBN} session with a
11487 Nindy-960 board attached:
11490 @item -r @var{port}
11491 Specify the serial port name of a serial interface to be used to connect
11492 to the target system. This option is only available when @value{GDBN} is
11493 configured for the Intel 960 target architecture. You may specify
11494 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11495 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11496 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11499 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11500 the ``old'' Nindy monitor protocol to connect to the target system.
11501 This option is only available when @value{GDBN} is configured for the Intel 960
11502 target architecture.
11505 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11506 connect to a target system that expects the newer protocol, the connection
11507 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11508 attempts to reconnect at several different line speeds. You can abort
11509 this process with an interrupt.
11513 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11514 system, in an attempt to reset it, before connecting to a Nindy target.
11517 @emph{Warning:} Many target systems do not have the hardware that this
11518 requires; it only works with a few boards.
11522 The standard @samp{-b} option controls the line speed used on the serial
11527 @subsubsection Nindy reset command
11532 For a Nindy target, this command sends a ``break'' to the remote target
11533 system; this is only useful if the target has been equipped with a
11534 circuit to perform a hard reset (or some other interesting action) when
11535 a break is detected.
11540 @subsection Mitsubishi M32R/D
11544 @kindex target m32r
11545 @item target m32r @var{dev}
11546 Mitsubishi M32R/D ROM monitor.
11553 The Motorola m68k configuration includes ColdFire support, and
11554 target command for the following ROM monitors.
11558 @kindex target abug
11559 @item target abug @var{dev}
11560 ABug ROM monitor for M68K.
11562 @kindex target cpu32bug
11563 @item target cpu32bug @var{dev}
11564 CPU32BUG monitor, running on a CPU32 (M68K) board.
11566 @kindex target dbug
11567 @item target dbug @var{dev}
11568 dBUG ROM monitor for Motorola ColdFire.
11571 @item target est @var{dev}
11572 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11574 @kindex target rom68k
11575 @item target rom68k @var{dev}
11576 ROM 68K monitor, running on an M68K IDP board.
11580 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11581 instead have only a single special target command:
11585 @kindex target es1800
11586 @item target es1800 @var{dev}
11587 ES-1800 emulator for M68K.
11595 @kindex target rombug
11596 @item target rombug @var{dev}
11597 ROMBUG ROM monitor for OS/9000.
11607 @item target bug @var{dev}
11608 BUG monitor, running on a MVME187 (m88k) board.
11612 @node MIPS Embedded
11613 @subsection MIPS Embedded
11615 @cindex MIPS boards
11616 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11617 MIPS board attached to a serial line. This is available when
11618 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11621 Use these @value{GDBN} commands to specify the connection to your target board:
11624 @item target mips @var{port}
11625 @kindex target mips @var{port}
11626 To run a program on the board, start up @code{@value{GDBP}} with the
11627 name of your program as the argument. To connect to the board, use the
11628 command @samp{target mips @var{port}}, where @var{port} is the name of
11629 the serial port connected to the board. If the program has not already
11630 been downloaded to the board, you may use the @code{load} command to
11631 download it. You can then use all the usual @value{GDBN} commands.
11633 For example, this sequence connects to the target board through a serial
11634 port, and loads and runs a program called @var{prog} through the
11638 host$ @value{GDBP} @var{prog}
11639 @value{GDBN} is free software and @dots{}
11640 (@value{GDBP}) target mips /dev/ttyb
11641 (@value{GDBP}) load @var{prog}
11645 @item target mips @var{hostname}:@var{portnumber}
11646 On some @value{GDBN} host configurations, you can specify a TCP
11647 connection (for instance, to a serial line managed by a terminal
11648 concentrator) instead of a serial port, using the syntax
11649 @samp{@var{hostname}:@var{portnumber}}.
11651 @item target pmon @var{port}
11652 @kindex target pmon @var{port}
11655 @item target ddb @var{port}
11656 @kindex target ddb @var{port}
11657 NEC's DDB variant of PMON for Vr4300.
11659 @item target lsi @var{port}
11660 @kindex target lsi @var{port}
11661 LSI variant of PMON.
11663 @kindex target r3900
11664 @item target r3900 @var{dev}
11665 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11667 @kindex target array
11668 @item target array @var{dev}
11669 Array Tech LSI33K RAID controller board.
11675 @value{GDBN} also supports these special commands for MIPS targets:
11678 @item set processor @var{args}
11679 @itemx show processor
11680 @kindex set processor @var{args}
11681 @kindex show processor
11682 Use the @code{set processor} command to set the type of MIPS
11683 processor when you want to access processor-type-specific registers.
11684 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11685 to use the CPU registers appropriate for the 3041 chip.
11686 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11687 is using. Use the @code{info reg} command to see what registers
11688 @value{GDBN} is using.
11690 @item set mipsfpu double
11691 @itemx set mipsfpu single
11692 @itemx set mipsfpu none
11693 @itemx show mipsfpu
11694 @kindex set mipsfpu
11695 @kindex show mipsfpu
11696 @cindex MIPS remote floating point
11697 @cindex floating point, MIPS remote
11698 If your target board does not support the MIPS floating point
11699 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11700 need this, you may wish to put the command in your @value{GDBN} init
11701 file). This tells @value{GDBN} how to find the return value of
11702 functions which return floating point values. It also allows
11703 @value{GDBN} to avoid saving the floating point registers when calling
11704 functions on the board. If you are using a floating point coprocessor
11705 with only single precision floating point support, as on the @sc{r4650}
11706 processor, use the command @samp{set mipsfpu single}. The default
11707 double precision floating point coprocessor may be selected using
11708 @samp{set mipsfpu double}.
11710 In previous versions the only choices were double precision or no
11711 floating point, so @samp{set mipsfpu on} will select double precision
11712 and @samp{set mipsfpu off} will select no floating point.
11714 As usual, you can inquire about the @code{mipsfpu} variable with
11715 @samp{show mipsfpu}.
11717 @item set remotedebug @var{n}
11718 @itemx show remotedebug
11719 @kindex set remotedebug@r{, MIPS protocol}
11720 @kindex show remotedebug@r{, MIPS protocol}
11721 @cindex @code{remotedebug}, MIPS protocol
11722 @cindex MIPS @code{remotedebug} protocol
11723 @c FIXME! For this to be useful, you must know something about the MIPS
11724 @c FIXME...protocol. Where is it described?
11725 You can see some debugging information about communications with the board
11726 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11727 @samp{set remotedebug 1}, every packet is displayed. If you set it
11728 to @code{2}, every character is displayed. You can check the current value
11729 at any time with the command @samp{show remotedebug}.
11731 @item set timeout @var{seconds}
11732 @itemx set retransmit-timeout @var{seconds}
11733 @itemx show timeout
11734 @itemx show retransmit-timeout
11735 @cindex @code{timeout}, MIPS protocol
11736 @cindex @code{retransmit-timeout}, MIPS protocol
11737 @kindex set timeout
11738 @kindex show timeout
11739 @kindex set retransmit-timeout
11740 @kindex show retransmit-timeout
11741 You can control the timeout used while waiting for a packet, in the MIPS
11742 remote protocol, with the @code{set timeout @var{seconds}} command. The
11743 default is 5 seconds. Similarly, you can control the timeout used while
11744 waiting for an acknowledgement of a packet with the @code{set
11745 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11746 You can inspect both values with @code{show timeout} and @code{show
11747 retransmit-timeout}. (These commands are @emph{only} available when
11748 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11750 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11751 is waiting for your program to stop. In that case, @value{GDBN} waits
11752 forever because it has no way of knowing how long the program is going
11753 to run before stopping.
11757 @subsection PowerPC
11761 @kindex target dink32
11762 @item target dink32 @var{dev}
11763 DINK32 ROM monitor.
11765 @kindex target ppcbug
11766 @item target ppcbug @var{dev}
11767 @kindex target ppcbug1
11768 @item target ppcbug1 @var{dev}
11769 PPCBUG ROM monitor for PowerPC.
11772 @item target sds @var{dev}
11773 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11778 @subsection HP PA Embedded
11782 @kindex target op50n
11783 @item target op50n @var{dev}
11784 OP50N monitor, running on an OKI HPPA board.
11786 @kindex target w89k
11787 @item target w89k @var{dev}
11788 W89K monitor, running on a Winbond HPPA board.
11793 @subsection Hitachi SH
11797 @kindex target hms@r{, with Hitachi SH}
11798 @item target hms @var{dev}
11799 A Hitachi SH board attached via serial line to your host. Use special
11800 commands @code{device} and @code{speed} to control the serial line and
11801 the communications speed used.
11803 @kindex target e7000@r{, with Hitachi SH}
11804 @item target e7000 @var{dev}
11805 E7000 emulator for Hitachi SH.
11807 @kindex target sh3@r{, with SH}
11808 @kindex target sh3e@r{, with SH}
11809 @item target sh3 @var{dev}
11810 @item target sh3e @var{dev}
11811 Hitachi SH-3 and SH-3E target systems.
11816 @subsection Tsqware Sparclet
11820 @value{GDBN} enables developers to debug tasks running on
11821 Sparclet targets from a Unix host.
11822 @value{GDBN} uses code that runs on
11823 both the Unix host and on the Sparclet target. The program
11824 @code{@value{GDBP}} is installed and executed on the Unix host.
11827 @item remotetimeout @var{args}
11828 @kindex remotetimeout
11829 @value{GDBN} supports the option @code{remotetimeout}.
11830 This option is set by the user, and @var{args} represents the number of
11831 seconds @value{GDBN} waits for responses.
11834 @cindex compiling, on Sparclet
11835 When compiling for debugging, include the options @samp{-g} to get debug
11836 information and @samp{-Ttext} to relocate the program to where you wish to
11837 load it on the target. You may also want to add the options @samp{-n} or
11838 @samp{-N} in order to reduce the size of the sections. Example:
11841 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11844 You can use @code{objdump} to verify that the addresses are what you intended:
11847 sparclet-aout-objdump --headers --syms prog
11850 @cindex running, on Sparclet
11852 your Unix execution search path to find @value{GDBN}, you are ready to
11853 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11854 (or @code{sparclet-aout-gdb}, depending on your installation).
11856 @value{GDBN} comes up showing the prompt:
11863 * Sparclet File:: Setting the file to debug
11864 * Sparclet Connection:: Connecting to Sparclet
11865 * Sparclet Download:: Sparclet download
11866 * Sparclet Execution:: Running and debugging
11869 @node Sparclet File
11870 @subsubsection Setting file to debug
11872 The @value{GDBN} command @code{file} lets you choose with program to debug.
11875 (gdbslet) file prog
11879 @value{GDBN} then attempts to read the symbol table of @file{prog}.
11880 @value{GDBN} locates
11881 the file by searching the directories listed in the command search
11883 If the file was compiled with debug information (option "-g"), source
11884 files will be searched as well.
11885 @value{GDBN} locates
11886 the source files by searching the directories listed in the directory search
11887 path (@pxref{Environment, ,Your program's environment}).
11889 to find a file, it displays a message such as:
11892 prog: No such file or directory.
11895 When this happens, add the appropriate directories to the search paths with
11896 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
11897 @code{target} command again.
11899 @node Sparclet Connection
11900 @subsubsection Connecting to Sparclet
11902 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
11903 To connect to a target on serial port ``@code{ttya}'', type:
11906 (gdbslet) target sparclet /dev/ttya
11907 Remote target sparclet connected to /dev/ttya
11908 main () at ../prog.c:3
11912 @value{GDBN} displays messages like these:
11918 @node Sparclet Download
11919 @subsubsection Sparclet download
11921 @cindex download to Sparclet
11922 Once connected to the Sparclet target,
11923 you can use the @value{GDBN}
11924 @code{load} command to download the file from the host to the target.
11925 The file name and load offset should be given as arguments to the @code{load}
11927 Since the file format is aout, the program must be loaded to the starting
11928 address. You can use @code{objdump} to find out what this value is. The load
11929 offset is an offset which is added to the VMA (virtual memory address)
11930 of each of the file's sections.
11931 For instance, if the program
11932 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11933 and bss at 0x12010170, in @value{GDBN}, type:
11936 (gdbslet) load prog 0x12010000
11937 Loading section .text, size 0xdb0 vma 0x12010000
11940 If the code is loaded at a different address then what the program was linked
11941 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11942 to tell @value{GDBN} where to map the symbol table.
11944 @node Sparclet Execution
11945 @subsubsection Running and debugging
11947 @cindex running and debugging Sparclet programs
11948 You can now begin debugging the task using @value{GDBN}'s execution control
11949 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11950 manual for the list of commands.
11954 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11956 Starting program: prog
11957 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11958 3 char *symarg = 0;
11960 4 char *execarg = "hello!";
11965 @subsection Fujitsu Sparclite
11969 @kindex target sparclite
11970 @item target sparclite @var{dev}
11971 Fujitsu sparclite boards, used only for the purpose of loading.
11972 You must use an additional command to debug the program.
11973 For example: target remote @var{dev} using @value{GDBN} standard
11979 @subsection Tandem ST2000
11981 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11984 To connect your ST2000 to the host system, see the manufacturer's
11985 manual. Once the ST2000 is physically attached, you can run:
11988 target st2000 @var{dev} @var{speed}
11992 to establish it as your debugging environment. @var{dev} is normally
11993 the name of a serial device, such as @file{/dev/ttya}, connected to the
11994 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11995 connection (for example, to a serial line attached via a terminal
11996 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11998 The @code{load} and @code{attach} commands are @emph{not} defined for
11999 this target; you must load your program into the ST2000 as you normally
12000 would for standalone operation. @value{GDBN} reads debugging information
12001 (such as symbols) from a separate, debugging version of the program
12002 available on your host computer.
12003 @c FIXME!! This is terribly vague; what little content is here is
12004 @c basically hearsay.
12006 @cindex ST2000 auxiliary commands
12007 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12011 @item st2000 @var{command}
12012 @kindex st2000 @var{cmd}
12013 @cindex STDBUG commands (ST2000)
12014 @cindex commands to STDBUG (ST2000)
12015 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12016 manual for available commands.
12019 @cindex connect (to STDBUG)
12020 Connect the controlling terminal to the STDBUG command monitor. When
12021 you are done interacting with STDBUG, typing either of two character
12022 sequences gets you back to the @value{GDBN} command prompt:
12023 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12024 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12028 @subsection Zilog Z8000
12031 @cindex simulator, Z8000
12032 @cindex Zilog Z8000 simulator
12034 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12037 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12038 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12039 segmented variant). The simulator recognizes which architecture is
12040 appropriate by inspecting the object code.
12043 @item target sim @var{args}
12045 @kindex target sim@r{, with Z8000}
12046 Debug programs on a simulated CPU. If the simulator supports setup
12047 options, specify them via @var{args}.
12051 After specifying this target, you can debug programs for the simulated
12052 CPU in the same style as programs for your host computer; use the
12053 @code{file} command to load a new program image, the @code{run} command
12054 to run your program, and so on.
12056 As well as making available all the usual machine registers
12057 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12058 additional items of information as specially named registers:
12063 Counts clock-ticks in the simulator.
12066 Counts instructions run in the simulator.
12069 Execution time in 60ths of a second.
12073 You can refer to these values in @value{GDBN} expressions with the usual
12074 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12075 conditional breakpoint that suspends only after at least 5000
12076 simulated clock ticks.
12078 @node Architectures
12079 @section Architectures
12081 This section describes characteristics of architectures that affect
12082 all uses of @value{GDBN} with the architecture, both native and cross.
12095 @kindex set rstack_high_address
12096 @cindex AMD 29K register stack
12097 @cindex register stack, AMD29K
12098 @item set rstack_high_address @var{address}
12099 On AMD 29000 family processors, registers are saved in a separate
12100 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12101 extent of this stack. Normally, @value{GDBN} just assumes that the
12102 stack is ``large enough''. This may result in @value{GDBN} referencing
12103 memory locations that do not exist. If necessary, you can get around
12104 this problem by specifying the ending address of the register stack with
12105 the @code{set rstack_high_address} command. The argument should be an
12106 address, which you probably want to precede with @samp{0x} to specify in
12109 @kindex show rstack_high_address
12110 @item show rstack_high_address
12111 Display the current limit of the register stack, on AMD 29000 family
12119 See the following section.
12124 @cindex stack on Alpha
12125 @cindex stack on MIPS
12126 @cindex Alpha stack
12128 Alpha- and MIPS-based computers use an unusual stack frame, which
12129 sometimes requires @value{GDBN} to search backward in the object code to
12130 find the beginning of a function.
12132 @cindex response time, MIPS debugging
12133 To improve response time (especially for embedded applications, where
12134 @value{GDBN} may be restricted to a slow serial line for this search)
12135 you may want to limit the size of this search, using one of these
12139 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12140 @item set heuristic-fence-post @var{limit}
12141 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12142 search for the beginning of a function. A value of @var{0} (the
12143 default) means there is no limit. However, except for @var{0}, the
12144 larger the limit the more bytes @code{heuristic-fence-post} must search
12145 and therefore the longer it takes to run.
12147 @item show heuristic-fence-post
12148 Display the current limit.
12152 These commands are available @emph{only} when @value{GDBN} is configured
12153 for debugging programs on Alpha or MIPS processors.
12156 @node Controlling GDB
12157 @chapter Controlling @value{GDBN}
12159 You can alter the way @value{GDBN} interacts with you by using the
12160 @code{set} command. For commands controlling how @value{GDBN} displays
12161 data, see @ref{Print Settings, ,Print settings}. Other settings are
12166 * Editing:: Command editing
12167 * History:: Command history
12168 * Screen Size:: Screen size
12169 * Numbers:: Numbers
12170 * Messages/Warnings:: Optional warnings and messages
12171 * Debugging Output:: Optional messages about internal happenings
12179 @value{GDBN} indicates its readiness to read a command by printing a string
12180 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12181 can change the prompt string with the @code{set prompt} command. For
12182 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12183 the prompt in one of the @value{GDBN} sessions so that you can always tell
12184 which one you are talking to.
12186 @emph{Note:} @code{set prompt} does not add a space for you after the
12187 prompt you set. This allows you to set a prompt which ends in a space
12188 or a prompt that does not.
12192 @item set prompt @var{newprompt}
12193 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12195 @kindex show prompt
12197 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12201 @section Command editing
12203 @cindex command line editing
12205 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12206 @sc{gnu} library provides consistent behavior for programs which provide a
12207 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12208 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12209 substitution, and a storage and recall of command history across
12210 debugging sessions.
12212 You may control the behavior of command line editing in @value{GDBN} with the
12213 command @code{set}.
12216 @kindex set editing
12219 @itemx set editing on
12220 Enable command line editing (enabled by default).
12222 @item set editing off
12223 Disable command line editing.
12225 @kindex show editing
12227 Show whether command line editing is enabled.
12231 @section Command history
12233 @value{GDBN} can keep track of the commands you type during your
12234 debugging sessions, so that you can be certain of precisely what
12235 happened. Use these commands to manage the @value{GDBN} command
12239 @cindex history substitution
12240 @cindex history file
12241 @kindex set history filename
12242 @kindex GDBHISTFILE
12243 @item set history filename @var{fname}
12244 Set the name of the @value{GDBN} command history file to @var{fname}.
12245 This is the file where @value{GDBN} reads an initial command history
12246 list, and where it writes the command history from this session when it
12247 exits. You can access this list through history expansion or through
12248 the history command editing characters listed below. This file defaults
12249 to the value of the environment variable @code{GDBHISTFILE}, or to
12250 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12253 @cindex history save
12254 @kindex set history save
12255 @item set history save
12256 @itemx set history save on
12257 Record command history in a file, whose name may be specified with the
12258 @code{set history filename} command. By default, this option is disabled.
12260 @item set history save off
12261 Stop recording command history in a file.
12263 @cindex history size
12264 @kindex set history size
12265 @item set history size @var{size}
12266 Set the number of commands which @value{GDBN} keeps in its history list.
12267 This defaults to the value of the environment variable
12268 @code{HISTSIZE}, or to 256 if this variable is not set.
12271 @cindex history expansion
12272 History expansion assigns special meaning to the character @kbd{!}.
12273 @ifset have-readline-appendices
12274 @xref{Event Designators}.
12277 Since @kbd{!} is also the logical not operator in C, history expansion
12278 is off by default. If you decide to enable history expansion with the
12279 @code{set history expansion on} command, you may sometimes need to
12280 follow @kbd{!} (when it is used as logical not, in an expression) with
12281 a space or a tab to prevent it from being expanded. The readline
12282 history facilities do not attempt substitution on the strings
12283 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12285 The commands to control history expansion are:
12288 @kindex set history expansion
12289 @item set history expansion on
12290 @itemx set history expansion
12291 Enable history expansion. History expansion is off by default.
12293 @item set history expansion off
12294 Disable history expansion.
12296 The readline code comes with more complete documentation of
12297 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12298 or @code{vi} may wish to read it.
12299 @ifset have-readline-appendices
12300 @xref{Command Line Editing}.
12304 @kindex show history
12306 @itemx show history filename
12307 @itemx show history save
12308 @itemx show history size
12309 @itemx show history expansion
12310 These commands display the state of the @value{GDBN} history parameters.
12311 @code{show history} by itself displays all four states.
12317 @item show commands
12318 Display the last ten commands in the command history.
12320 @item show commands @var{n}
12321 Print ten commands centered on command number @var{n}.
12323 @item show commands +
12324 Print ten commands just after the commands last printed.
12328 @section Screen size
12329 @cindex size of screen
12330 @cindex pauses in output
12332 Certain commands to @value{GDBN} may produce large amounts of
12333 information output to the screen. To help you read all of it,
12334 @value{GDBN} pauses and asks you for input at the end of each page of
12335 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12336 to discard the remaining output. Also, the screen width setting
12337 determines when to wrap lines of output. Depending on what is being
12338 printed, @value{GDBN} tries to break the line at a readable place,
12339 rather than simply letting it overflow onto the following line.
12341 Normally @value{GDBN} knows the size of the screen from the terminal
12342 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12343 together with the value of the @code{TERM} environment variable and the
12344 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12345 you can override it with the @code{set height} and @code{set
12352 @kindex show height
12353 @item set height @var{lpp}
12355 @itemx set width @var{cpl}
12357 These @code{set} commands specify a screen height of @var{lpp} lines and
12358 a screen width of @var{cpl} characters. The associated @code{show}
12359 commands display the current settings.
12361 If you specify a height of zero lines, @value{GDBN} does not pause during
12362 output no matter how long the output is. This is useful if output is to a
12363 file or to an editor buffer.
12365 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12366 from wrapping its output.
12371 @cindex number representation
12372 @cindex entering numbers
12374 You can always enter numbers in octal, decimal, or hexadecimal in
12375 @value{GDBN} by the usual conventions: octal numbers begin with
12376 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12377 begin with @samp{0x}. Numbers that begin with none of these are, by
12378 default, entered in base 10; likewise, the default display for
12379 numbers---when no particular format is specified---is base 10. You can
12380 change the default base for both input and output with the @code{set
12384 @kindex set input-radix
12385 @item set input-radix @var{base}
12386 Set the default base for numeric input. Supported choices
12387 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12388 specified either unambiguously or using the current default radix; for
12398 sets the base to decimal. On the other hand, @samp{set radix 10}
12399 leaves the radix unchanged no matter what it was.
12401 @kindex set output-radix
12402 @item set output-radix @var{base}
12403 Set the default base for numeric display. Supported choices
12404 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12405 specified either unambiguously or using the current default radix.
12407 @kindex show input-radix
12408 @item show input-radix
12409 Display the current default base for numeric input.
12411 @kindex show output-radix
12412 @item show output-radix
12413 Display the current default base for numeric display.
12416 @node Messages/Warnings
12417 @section Optional warnings and messages
12419 By default, @value{GDBN} is silent about its inner workings. If you are
12420 running on a slow machine, you may want to use the @code{set verbose}
12421 command. This makes @value{GDBN} tell you when it does a lengthy
12422 internal operation, so you will not think it has crashed.
12424 Currently, the messages controlled by @code{set verbose} are those
12425 which announce that the symbol table for a source file is being read;
12426 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12429 @kindex set verbose
12430 @item set verbose on
12431 Enables @value{GDBN} output of certain informational messages.
12433 @item set verbose off
12434 Disables @value{GDBN} output of certain informational messages.
12436 @kindex show verbose
12438 Displays whether @code{set verbose} is on or off.
12441 By default, if @value{GDBN} encounters bugs in the symbol table of an
12442 object file, it is silent; but if you are debugging a compiler, you may
12443 find this information useful (@pxref{Symbol Errors, ,Errors reading
12448 @kindex set complaints
12449 @item set complaints @var{limit}
12450 Permits @value{GDBN} to output @var{limit} complaints about each type of
12451 unusual symbols before becoming silent about the problem. Set
12452 @var{limit} to zero to suppress all complaints; set it to a large number
12453 to prevent complaints from being suppressed.
12455 @kindex show complaints
12456 @item show complaints
12457 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12461 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12462 lot of stupid questions to confirm certain commands. For example, if
12463 you try to run a program which is already running:
12467 The program being debugged has been started already.
12468 Start it from the beginning? (y or n)
12471 If you are willing to unflinchingly face the consequences of your own
12472 commands, you can disable this ``feature'':
12476 @kindex set confirm
12478 @cindex confirmation
12479 @cindex stupid questions
12480 @item set confirm off
12481 Disables confirmation requests.
12483 @item set confirm on
12484 Enables confirmation requests (the default).
12486 @kindex show confirm
12488 Displays state of confirmation requests.
12492 @node Debugging Output
12493 @section Optional messages about internal happenings
12495 @kindex set debug arch
12496 @item set debug arch
12497 Turns on or off display of gdbarch debugging info. The default is off
12498 @kindex show debug arch
12499 @item show debug arch
12500 Displays the current state of displaying gdbarch debugging info.
12501 @kindex set debug event
12502 @item set debug event
12503 Turns on or off display of @value{GDBN} event debugging info. The
12505 @kindex show debug event
12506 @item show debug event
12507 Displays the current state of displaying @value{GDBN} event debugging
12509 @kindex set debug expression
12510 @item set debug expression
12511 Turns on or off display of @value{GDBN} expression debugging info. The
12513 @kindex show debug expression
12514 @item show debug expression
12515 Displays the current state of displaying @value{GDBN} expression
12517 @kindex set debug overload
12518 @item set debug overload
12519 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12520 info. This includes info such as ranking of functions, etc. The default
12522 @kindex show debug overload
12523 @item show debug overload
12524 Displays the current state of displaying @value{GDBN} C@t{++} overload
12526 @kindex set debug remote
12527 @cindex packets, reporting on stdout
12528 @cindex serial connections, debugging
12529 @item set debug remote
12530 Turns on or off display of reports on all packets sent back and forth across
12531 the serial line to the remote machine. The info is printed on the
12532 @value{GDBN} standard output stream. The default is off.
12533 @kindex show debug remote
12534 @item show debug remote
12535 Displays the state of display of remote packets.
12536 @kindex set debug serial
12537 @item set debug serial
12538 Turns on or off display of @value{GDBN} serial debugging info. The
12540 @kindex show debug serial
12541 @item show debug serial
12542 Displays the current state of displaying @value{GDBN} serial debugging
12544 @kindex set debug target
12545 @item set debug target
12546 Turns on or off display of @value{GDBN} target debugging info. This info
12547 includes what is going on at the target level of GDB, as it happens. The
12549 @kindex show debug target
12550 @item show debug target
12551 Displays the current state of displaying @value{GDBN} target debugging
12553 @kindex set debug varobj
12554 @item set debug varobj
12555 Turns on or off display of @value{GDBN} variable object debugging
12556 info. The default is off.
12557 @kindex show debug varobj
12558 @item show debug varobj
12559 Displays the current state of displaying @value{GDBN} variable object
12564 @chapter Canned Sequences of Commands
12566 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12567 command lists}), @value{GDBN} provides two ways to store sequences of
12568 commands for execution as a unit: user-defined commands and command
12572 * Define:: User-defined commands
12573 * Hooks:: User-defined command hooks
12574 * Command Files:: Command files
12575 * Output:: Commands for controlled output
12579 @section User-defined commands
12581 @cindex user-defined command
12582 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12583 which you assign a new name as a command. This is done with the
12584 @code{define} command. User commands may accept up to 10 arguments
12585 separated by whitespace. Arguments are accessed within the user command
12586 via @var{$arg0@dots{}$arg9}. A trivial example:
12590 print $arg0 + $arg1 + $arg2
12594 To execute the command use:
12601 This defines the command @code{adder}, which prints the sum of
12602 its three arguments. Note the arguments are text substitutions, so they may
12603 reference variables, use complex expressions, or even perform inferior
12609 @item define @var{commandname}
12610 Define a command named @var{commandname}. If there is already a command
12611 by that name, you are asked to confirm that you want to redefine it.
12613 The definition of the command is made up of other @value{GDBN} command lines,
12614 which are given following the @code{define} command. The end of these
12615 commands is marked by a line containing @code{end}.
12620 Takes a single argument, which is an expression to evaluate.
12621 It is followed by a series of commands that are executed
12622 only if the expression is true (nonzero).
12623 There can then optionally be a line @code{else}, followed
12624 by a series of commands that are only executed if the expression
12625 was false. The end of the list is marked by a line containing @code{end}.
12629 The syntax is similar to @code{if}: the command takes a single argument,
12630 which is an expression to evaluate, and must be followed by the commands to
12631 execute, one per line, terminated by an @code{end}.
12632 The commands are executed repeatedly as long as the expression
12636 @item document @var{commandname}
12637 Document the user-defined command @var{commandname}, so that it can be
12638 accessed by @code{help}. The command @var{commandname} must already be
12639 defined. This command reads lines of documentation just as @code{define}
12640 reads the lines of the command definition, ending with @code{end}.
12641 After the @code{document} command is finished, @code{help} on command
12642 @var{commandname} displays the documentation you have written.
12644 You may use the @code{document} command again to change the
12645 documentation of a command. Redefining the command with @code{define}
12646 does not change the documentation.
12648 @kindex help user-defined
12649 @item help user-defined
12650 List all user-defined commands, with the first line of the documentation
12655 @itemx show user @var{commandname}
12656 Display the @value{GDBN} commands used to define @var{commandname} (but
12657 not its documentation). If no @var{commandname} is given, display the
12658 definitions for all user-defined commands.
12662 When user-defined commands are executed, the
12663 commands of the definition are not printed. An error in any command
12664 stops execution of the user-defined command.
12666 If used interactively, commands that would ask for confirmation proceed
12667 without asking when used inside a user-defined command. Many @value{GDBN}
12668 commands that normally print messages to say what they are doing omit the
12669 messages when used in a user-defined command.
12672 @section User-defined command hooks
12673 @cindex command hooks
12674 @cindex hooks, for commands
12675 @cindex hooks, pre-command
12679 You may define @dfn{hooks}, which are a special kind of user-defined
12680 command. Whenever you run the command @samp{foo}, if the user-defined
12681 command @samp{hook-foo} exists, it is executed (with no arguments)
12682 before that command.
12684 @cindex hooks, post-command
12687 A hook may also be defined which is run after the command you executed.
12688 Whenever you run the command @samp{foo}, if the user-defined command
12689 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12690 that command. Post-execution hooks may exist simultaneously with
12691 pre-execution hooks, for the same command.
12693 It is valid for a hook to call the command which it hooks. If this
12694 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12696 @c It would be nice if hookpost could be passed a parameter indicating
12697 @c if the command it hooks executed properly or not. FIXME!
12699 @kindex stop@r{, a pseudo-command}
12700 In addition, a pseudo-command, @samp{stop} exists. Defining
12701 (@samp{hook-stop}) makes the associated commands execute every time
12702 execution stops in your program: before breakpoint commands are run,
12703 displays are printed, or the stack frame is printed.
12705 For example, to ignore @code{SIGALRM} signals while
12706 single-stepping, but treat them normally during normal execution,
12711 handle SIGALRM nopass
12715 handle SIGALRM pass
12718 define hook-continue
12719 handle SIGLARM pass
12723 As a further example, to hook at the begining and end of the @code{echo}
12724 command, and to add extra text to the beginning and end of the message,
12732 define hookpost-echo
12736 (@value{GDBP}) echo Hello World
12737 <<<---Hello World--->>>
12742 You can define a hook for any single-word command in @value{GDBN}, but
12743 not for command aliases; you should define a hook for the basic command
12744 name, e.g. @code{backtrace} rather than @code{bt}.
12745 @c FIXME! So how does Joe User discover whether a command is an alias
12747 If an error occurs during the execution of your hook, execution of
12748 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12749 (before the command that you actually typed had a chance to run).
12751 If you try to define a hook which does not match any known command, you
12752 get a warning from the @code{define} command.
12754 @node Command Files
12755 @section Command files
12757 @cindex command files
12758 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12759 commands. Comments (lines starting with @kbd{#}) may also be included.
12760 An empty line in a command file does nothing; it does not mean to repeat
12761 the last command, as it would from the terminal.
12764 @cindex @file{.gdbinit}
12765 @cindex @file{gdb.ini}
12766 When you start @value{GDBN}, it automatically executes commands from its
12767 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
12768 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
12773 Reads the init file (if any) in your home directory@footnote{On
12774 DOS/Windows systems, the home directory is the one pointed to by the
12775 @code{HOME} environment variable.}.
12778 Processes command line options and operands.
12781 Reads the init file (if any) in the current working directory.
12784 Reads command files specified by the @samp{-x} option.
12787 The init file in your home directory can set options (such as @samp{set
12788 complaints}) that affect subsequent processing of command line options
12789 and operands. Init files are not executed if you use the @samp{-nx}
12790 option (@pxref{Mode Options, ,Choosing modes}).
12792 @cindex init file name
12793 On some configurations of @value{GDBN}, the init file is known by a
12794 different name (these are typically environments where a specialized
12795 form of @value{GDBN} may need to coexist with other forms, hence a
12796 different name for the specialized version's init file). These are the
12797 environments with special init file names:
12799 @cindex @file{.vxgdbinit}
12802 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12804 @cindex @file{.os68gdbinit}
12806 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12808 @cindex @file{.esgdbinit}
12810 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12813 You can also request the execution of a command file with the
12814 @code{source} command:
12818 @item source @var{filename}
12819 Execute the command file @var{filename}.
12822 The lines in a command file are executed sequentially. They are not
12823 printed as they are executed. An error in any command terminates execution
12824 of the command file.
12826 Commands that would ask for confirmation if used interactively proceed
12827 without asking when used in a command file. Many @value{GDBN} commands that
12828 normally print messages to say what they are doing omit the messages
12829 when called from command files.
12832 @section Commands for controlled output
12834 During the execution of a command file or a user-defined command, normal
12835 @value{GDBN} output is suppressed; the only output that appears is what is
12836 explicitly printed by the commands in the definition. This section
12837 describes three commands useful for generating exactly the output you
12842 @item echo @var{text}
12843 @c I do not consider backslash-space a standard C escape sequence
12844 @c because it is not in ANSI.
12845 Print @var{text}. Nonprinting characters can be included in
12846 @var{text} using C escape sequences, such as @samp{\n} to print a
12847 newline. @strong{No newline is printed unless you specify one.}
12848 In addition to the standard C escape sequences, a backslash followed
12849 by a space stands for a space. This is useful for displaying a
12850 string with spaces at the beginning or the end, since leading and
12851 trailing spaces are otherwise trimmed from all arguments.
12852 To print @samp{@w{ }and foo =@w{ }}, use the command
12853 @samp{echo \@w{ }and foo = \@w{ }}.
12855 A backslash at the end of @var{text} can be used, as in C, to continue
12856 the command onto subsequent lines. For example,
12859 echo This is some text\n\
12860 which is continued\n\
12861 onto several lines.\n
12864 produces the same output as
12867 echo This is some text\n
12868 echo which is continued\n
12869 echo onto several lines.\n
12873 @item output @var{expression}
12874 Print the value of @var{expression} and nothing but that value: no
12875 newlines, no @samp{$@var{nn} = }. The value is not entered in the
12876 value history either. @xref{Expressions, ,Expressions}, for more information
12879 @item output/@var{fmt} @var{expression}
12880 Print the value of @var{expression} in format @var{fmt}. You can use
12881 the same formats as for @code{print}. @xref{Output Formats,,Output
12882 formats}, for more information.
12885 @item printf @var{string}, @var{expressions}@dots{}
12886 Print the values of the @var{expressions} under the control of
12887 @var{string}. The @var{expressions} are separated by commas and may be
12888 either numbers or pointers. Their values are printed as specified by
12889 @var{string}, exactly as if your program were to execute the C
12891 @c FIXME: the above implies that at least all ANSI C formats are
12892 @c supported, but it isn't true: %E and %G don't work (or so it seems).
12893 @c Either this is a bug, or the manual should document what formats are
12897 printf (@var{string}, @var{expressions}@dots{});
12900 For example, you can print two values in hex like this:
12903 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
12906 The only backslash-escape sequences that you can use in the format
12907 string are the simple ones that consist of backslash followed by a
12912 @chapter Using @value{GDBN} under @sc{gnu} Emacs
12915 @cindex @sc{gnu} Emacs
12916 A special interface allows you to use @sc{gnu} Emacs to view (and
12917 edit) the source files for the program you are debugging with
12920 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
12921 executable file you want to debug as an argument. This command starts
12922 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
12923 created Emacs buffer.
12924 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
12926 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
12931 All ``terminal'' input and output goes through the Emacs buffer.
12934 This applies both to @value{GDBN} commands and their output, and to the input
12935 and output done by the program you are debugging.
12937 This is useful because it means that you can copy the text of previous
12938 commands and input them again; you can even use parts of the output
12941 All the facilities of Emacs' Shell mode are available for interacting
12942 with your program. In particular, you can send signals the usual
12943 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
12948 @value{GDBN} displays source code through Emacs.
12951 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
12952 source file for that frame and puts an arrow (@samp{=>}) at the
12953 left margin of the current line. Emacs uses a separate buffer for
12954 source display, and splits the screen to show both your @value{GDBN} session
12957 Explicit @value{GDBN} @code{list} or search commands still produce output as
12958 usual, but you probably have no reason to use them from Emacs.
12961 @emph{Warning:} If the directory where your program resides is not your
12962 current directory, it can be easy to confuse Emacs about the location of
12963 the source files, in which case the auxiliary display buffer does not
12964 appear to show your source. @value{GDBN} can find programs by searching your
12965 environment's @code{PATH} variable, so the @value{GDBN} input and output
12966 session proceeds normally; but Emacs does not get enough information
12967 back from @value{GDBN} to locate the source files in this situation. To
12968 avoid this problem, either start @value{GDBN} mode from the directory where
12969 your program resides, or specify an absolute file name when prompted for the
12970 @kbd{M-x gdb} argument.
12972 A similar confusion can result if you use the @value{GDBN} @code{file} command to
12973 switch to debugging a program in some other location, from an existing
12974 @value{GDBN} buffer in Emacs.
12977 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
12978 you need to call @value{GDBN} by a different name (for example, if you keep
12979 several configurations around, with different names) you can set the
12980 Emacs variable @code{gdb-command-name}; for example,
12983 (setq gdb-command-name "mygdb")
12987 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
12988 in your @file{.emacs} file) makes Emacs call the program named
12989 ``@code{mygdb}'' instead.
12991 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
12992 addition to the standard Shell mode commands:
12996 Describe the features of Emacs' @value{GDBN} Mode.
12999 Execute to another source line, like the @value{GDBN} @code{step} command; also
13000 update the display window to show the current file and location.
13003 Execute to next source line in this function, skipping all function
13004 calls, like the @value{GDBN} @code{next} command. Then update the display window
13005 to show the current file and location.
13008 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13009 display window accordingly.
13011 @item M-x gdb-nexti
13012 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13013 display window accordingly.
13016 Execute until exit from the selected stack frame, like the @value{GDBN}
13017 @code{finish} command.
13020 Continue execution of your program, like the @value{GDBN} @code{continue}
13023 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13026 Go up the number of frames indicated by the numeric argument
13027 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13028 like the @value{GDBN} @code{up} command.
13030 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13033 Go down the number of frames indicated by the numeric argument, like the
13034 @value{GDBN} @code{down} command.
13036 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13039 Read the number where the cursor is positioned, and insert it at the end
13040 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13041 around an address that was displayed earlier, type @kbd{disassemble};
13042 then move the cursor to the address display, and pick up the
13043 argument for @code{disassemble} by typing @kbd{C-x &}.
13045 You can customize this further by defining elements of the list
13046 @code{gdb-print-command}; once it is defined, you can format or
13047 otherwise process numbers picked up by @kbd{C-x &} before they are
13048 inserted. A numeric argument to @kbd{C-x &} indicates that you
13049 wish special formatting, and also acts as an index to pick an element of the
13050 list. If the list element is a string, the number to be inserted is
13051 formatted using the Emacs function @code{format}; otherwise the number
13052 is passed as an argument to the corresponding list element.
13055 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13056 tells @value{GDBN} to set a breakpoint on the source line point is on.
13058 If you accidentally delete the source-display buffer, an easy way to get
13059 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13060 request a frame display; when you run under Emacs, this recreates
13061 the source buffer if necessary to show you the context of the current
13064 The source files displayed in Emacs are in ordinary Emacs buffers
13065 which are visiting the source files in the usual way. You can edit
13066 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13067 communicates with Emacs in terms of line numbers. If you add or
13068 delete lines from the text, the line numbers that @value{GDBN} knows cease
13069 to correspond properly with the code.
13071 @c The following dropped because Epoch is nonstandard. Reactivate
13072 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13074 @kindex Emacs Epoch environment
13078 Version 18 of @sc{gnu} Emacs has a built-in window system
13079 called the @code{epoch}
13080 environment. Users of this environment can use a new command,
13081 @code{inspect} which performs identically to @code{print} except that
13082 each value is printed in its own window.
13085 @include annotate.texi
13086 @include gdbmi.texinfo
13089 @chapter Reporting Bugs in @value{GDBN}
13090 @cindex bugs in @value{GDBN}
13091 @cindex reporting bugs in @value{GDBN}
13093 Your bug reports play an essential role in making @value{GDBN} reliable.
13095 Reporting a bug may help you by bringing a solution to your problem, or it
13096 may not. But in any case the principal function of a bug report is to help
13097 the entire community by making the next version of @value{GDBN} work better. Bug
13098 reports are your contribution to the maintenance of @value{GDBN}.
13100 In order for a bug report to serve its purpose, you must include the
13101 information that enables us to fix the bug.
13104 * Bug Criteria:: Have you found a bug?
13105 * Bug Reporting:: How to report bugs
13109 @section Have you found a bug?
13110 @cindex bug criteria
13112 If you are not sure whether you have found a bug, here are some guidelines:
13115 @cindex fatal signal
13116 @cindex debugger crash
13117 @cindex crash of debugger
13119 If the debugger gets a fatal signal, for any input whatever, that is a
13120 @value{GDBN} bug. Reliable debuggers never crash.
13122 @cindex error on valid input
13124 If @value{GDBN} produces an error message for valid input, that is a
13125 bug. (Note that if you're cross debugging, the problem may also be
13126 somewhere in the connection to the target.)
13128 @cindex invalid input
13130 If @value{GDBN} does not produce an error message for invalid input,
13131 that is a bug. However, you should note that your idea of
13132 ``invalid input'' might be our idea of ``an extension'' or ``support
13133 for traditional practice''.
13136 If you are an experienced user of debugging tools, your suggestions
13137 for improvement of @value{GDBN} are welcome in any case.
13140 @node Bug Reporting
13141 @section How to report bugs
13142 @cindex bug reports
13143 @cindex @value{GDBN} bugs, reporting
13145 A number of companies and individuals offer support for @sc{gnu} products.
13146 If you obtained @value{GDBN} from a support organization, we recommend you
13147 contact that organization first.
13149 You can find contact information for many support companies and
13150 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13152 @c should add a web page ref...
13154 In any event, we also recommend that you send bug reports for
13155 @value{GDBN} to this addresses:
13161 @strong{Do not send bug reports to @samp{info-gdb}, or to
13162 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13163 not want to receive bug reports. Those that do have arranged to receive
13166 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13167 serves as a repeater. The mailing list and the newsgroup carry exactly
13168 the same messages. Often people think of posting bug reports to the
13169 newsgroup instead of mailing them. This appears to work, but it has one
13170 problem which can be crucial: a newsgroup posting often lacks a mail
13171 path back to the sender. Thus, if we need to ask for more information,
13172 we may be unable to reach you. For this reason, it is better to send
13173 bug reports to the mailing list.
13175 As a last resort, send bug reports on paper to:
13178 @sc{gnu} Debugger Bugs
13179 Free Software Foundation Inc.
13180 59 Temple Place - Suite 330
13181 Boston, MA 02111-1307
13185 The fundamental principle of reporting bugs usefully is this:
13186 @strong{report all the facts}. If you are not sure whether to state a
13187 fact or leave it out, state it!
13189 Often people omit facts because they think they know what causes the
13190 problem and assume that some details do not matter. Thus, you might
13191 assume that the name of the variable you use in an example does not matter.
13192 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13193 stray memory reference which happens to fetch from the location where that
13194 name is stored in memory; perhaps, if the name were different, the contents
13195 of that location would fool the debugger into doing the right thing despite
13196 the bug. Play it safe and give a specific, complete example. That is the
13197 easiest thing for you to do, and the most helpful.
13199 Keep in mind that the purpose of a bug report is to enable us to fix the
13200 bug. It may be that the bug has been reported previously, but neither
13201 you nor we can know that unless your bug report is complete and
13204 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13205 bell?'' Those bug reports are useless, and we urge everyone to
13206 @emph{refuse to respond to them} except to chide the sender to report
13209 To enable us to fix the bug, you should include all these things:
13213 The version of @value{GDBN}. @value{GDBN} announces it if you start
13214 with no arguments; you can also print it at any time using @code{show
13217 Without this, we will not know whether there is any point in looking for
13218 the bug in the current version of @value{GDBN}.
13221 The type of machine you are using, and the operating system name and
13225 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13226 ``@value{GCC}--2.8.1''.
13229 What compiler (and its version) was used to compile the program you are
13230 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13231 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13232 information; for other compilers, see the documentation for those
13236 The command arguments you gave the compiler to compile your example and
13237 observe the bug. For example, did you use @samp{-O}? To guarantee
13238 you will not omit something important, list them all. A copy of the
13239 Makefile (or the output from make) is sufficient.
13241 If we were to try to guess the arguments, we would probably guess wrong
13242 and then we might not encounter the bug.
13245 A complete input script, and all necessary source files, that will
13249 A description of what behavior you observe that you believe is
13250 incorrect. For example, ``It gets a fatal signal.''
13252 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13253 will certainly notice it. But if the bug is incorrect output, we might
13254 not notice unless it is glaringly wrong. You might as well not give us
13255 a chance to make a mistake.
13257 Even if the problem you experience is a fatal signal, you should still
13258 say so explicitly. Suppose something strange is going on, such as, your
13259 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13260 the C library on your system. (This has happened!) Your copy might
13261 crash and ours would not. If you told us to expect a crash, then when
13262 ours fails to crash, we would know that the bug was not happening for
13263 us. If you had not told us to expect a crash, then we would not be able
13264 to draw any conclusion from our observations.
13267 If you wish to suggest changes to the @value{GDBN} source, send us context
13268 diffs. If you even discuss something in the @value{GDBN} source, refer to
13269 it by context, not by line number.
13271 The line numbers in our development sources will not match those in your
13272 sources. Your line numbers would convey no useful information to us.
13276 Here are some things that are not necessary:
13280 A description of the envelope of the bug.
13282 Often people who encounter a bug spend a lot of time investigating
13283 which changes to the input file will make the bug go away and which
13284 changes will not affect it.
13286 This is often time consuming and not very useful, because the way we
13287 will find the bug is by running a single example under the debugger
13288 with breakpoints, not by pure deduction from a series of examples.
13289 We recommend that you save your time for something else.
13291 Of course, if you can find a simpler example to report @emph{instead}
13292 of the original one, that is a convenience for us. Errors in the
13293 output will be easier to spot, running under the debugger will take
13294 less time, and so on.
13296 However, simplification is not vital; if you do not want to do this,
13297 report the bug anyway and send us the entire test case you used.
13300 A patch for the bug.
13302 A patch for the bug does help us if it is a good one. But do not omit
13303 the necessary information, such as the test case, on the assumption that
13304 a patch is all we need. We might see problems with your patch and decide
13305 to fix the problem another way, or we might not understand it at all.
13307 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13308 construct an example that will make the program follow a certain path
13309 through the code. If you do not send us the example, we will not be able
13310 to construct one, so we will not be able to verify that the bug is fixed.
13312 And if we cannot understand what bug you are trying to fix, or why your
13313 patch should be an improvement, we will not install it. A test case will
13314 help us to understand.
13317 A guess about what the bug is or what it depends on.
13319 Such guesses are usually wrong. Even we cannot guess right about such
13320 things without first using the debugger to find the facts.
13323 @c The readline documentation is distributed with the readline code
13324 @c and consists of the two following files:
13326 @c inc-hist.texinfo
13327 @c Use -I with makeinfo to point to the appropriate directory,
13328 @c environment var TEXINPUTS with TeX.
13329 @include rluser.texinfo
13330 @include inc-hist.texinfo
13333 @node Formatting Documentation
13334 @appendix Formatting Documentation
13336 @cindex @value{GDBN} reference card
13337 @cindex reference card
13338 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13339 for printing with PostScript or Ghostscript, in the @file{gdb}
13340 subdirectory of the main source directory@footnote{In
13341 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13342 release.}. If you can use PostScript or Ghostscript with your printer,
13343 you can print the reference card immediately with @file{refcard.ps}.
13345 The release also includes the source for the reference card. You
13346 can format it, using @TeX{}, by typing:
13352 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13353 mode on US ``letter'' size paper;
13354 that is, on a sheet 11 inches wide by 8.5 inches
13355 high. You will need to specify this form of printing as an option to
13356 your @sc{dvi} output program.
13358 @cindex documentation
13360 All the documentation for @value{GDBN} comes as part of the machine-readable
13361 distribution. The documentation is written in Texinfo format, which is
13362 a documentation system that uses a single source file to produce both
13363 on-line information and a printed manual. You can use one of the Info
13364 formatting commands to create the on-line version of the documentation
13365 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
13367 @value{GDBN} includes an already formatted copy of the on-line Info
13368 version of this manual in the @file{gdb} subdirectory. The main Info
13369 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
13370 subordinate files matching @samp{gdb.info*} in the same directory. If
13371 necessary, you can print out these files, or read them with any editor;
13372 but they are easier to read using the @code{info} subsystem in @sc{gnu}
13373 Emacs or the standalone @code{info} program, available as part of the
13374 @sc{gnu} Texinfo distribution.
13376 If you want to format these Info files yourself, you need one of the
13377 Info formatting programs, such as @code{texinfo-format-buffer} or
13380 If you have @code{makeinfo} installed, and are in the top level
13381 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
13382 version @value{GDBVN}), you can make the Info file by typing:
13389 If you want to typeset and print copies of this manual, you need @TeX{},
13390 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
13391 Texinfo definitions file.
13393 @TeX{} is a typesetting program; it does not print files directly, but
13394 produces output files called @sc{dvi} files. To print a typeset
13395 document, you need a program to print @sc{dvi} files. If your system
13396 has @TeX{} installed, chances are it has such a program. The precise
13397 command to use depends on your system; @kbd{lpr -d} is common; another
13398 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
13399 require a file name without any extension or a @samp{.dvi} extension.
13401 @TeX{} also requires a macro definitions file called
13402 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
13403 written in Texinfo format. On its own, @TeX{} cannot either read or
13404 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
13405 and is located in the @file{gdb-@var{version-number}/texinfo}
13408 If you have @TeX{} and a @sc{dvi} printer program installed, you can
13409 typeset and print this manual. First switch to the the @file{gdb}
13410 subdirectory of the main source directory (for example, to
13411 @file{gdb-@value{GDBVN}/gdb}) and type:
13417 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
13419 @node Installing GDB
13420 @appendix Installing @value{GDBN}
13421 @cindex configuring @value{GDBN}
13422 @cindex installation
13424 @value{GDBN} comes with a @code{configure} script that automates the process
13425 of preparing @value{GDBN} for installation; you can then use @code{make} to
13426 build the @code{gdb} program.
13428 @c irrelevant in info file; it's as current as the code it lives with.
13429 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
13430 look at the @file{README} file in the sources; we may have improved the
13431 installation procedures since publishing this manual.}
13434 The @value{GDBN} distribution includes all the source code you need for
13435 @value{GDBN} in a single directory, whose name is usually composed by
13436 appending the version number to @samp{gdb}.
13438 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
13439 @file{gdb-@value{GDBVN}} directory. That directory contains:
13442 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
13443 script for configuring @value{GDBN} and all its supporting libraries
13445 @item gdb-@value{GDBVN}/gdb
13446 the source specific to @value{GDBN} itself
13448 @item gdb-@value{GDBVN}/bfd
13449 source for the Binary File Descriptor library
13451 @item gdb-@value{GDBVN}/include
13452 @sc{gnu} include files
13454 @item gdb-@value{GDBVN}/libiberty
13455 source for the @samp{-liberty} free software library
13457 @item gdb-@value{GDBVN}/opcodes
13458 source for the library of opcode tables and disassemblers
13460 @item gdb-@value{GDBVN}/readline
13461 source for the @sc{gnu} command-line interface
13463 @item gdb-@value{GDBVN}/glob
13464 source for the @sc{gnu} filename pattern-matching subroutine
13466 @item gdb-@value{GDBVN}/mmalloc
13467 source for the @sc{gnu} memory-mapped malloc package
13470 The simplest way to configure and build @value{GDBN} is to run @code{configure}
13471 from the @file{gdb-@var{version-number}} source directory, which in
13472 this example is the @file{gdb-@value{GDBVN}} directory.
13474 First switch to the @file{gdb-@var{version-number}} source directory
13475 if you are not already in it; then run @code{configure}. Pass the
13476 identifier for the platform on which @value{GDBN} will run as an
13482 cd gdb-@value{GDBVN}
13483 ./configure @var{host}
13488 where @var{host} is an identifier such as @samp{sun4} or
13489 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
13490 (You can often leave off @var{host}; @code{configure} tries to guess the
13491 correct value by examining your system.)
13493 Running @samp{configure @var{host}} and then running @code{make} builds the
13494 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
13495 libraries, then @code{gdb} itself. The configured source files, and the
13496 binaries, are left in the corresponding source directories.
13499 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
13500 system does not recognize this automatically when you run a different
13501 shell, you may need to run @code{sh} on it explicitly:
13504 sh configure @var{host}
13507 If you run @code{configure} from a directory that contains source
13508 directories for multiple libraries or programs, such as the
13509 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
13510 creates configuration files for every directory level underneath (unless
13511 you tell it not to, with the @samp{--norecursion} option).
13513 You can run the @code{configure} script from any of the
13514 subordinate directories in the @value{GDBN} distribution if you only want to
13515 configure that subdirectory, but be sure to specify a path to it.
13517 For example, with version @value{GDBVN}, type the following to configure only
13518 the @code{bfd} subdirectory:
13522 cd gdb-@value{GDBVN}/bfd
13523 ../configure @var{host}
13527 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
13528 However, you should make sure that the shell on your path (named by
13529 the @samp{SHELL} environment variable) is publicly readable. Remember
13530 that @value{GDBN} uses the shell to start your program---some systems refuse to
13531 let @value{GDBN} debug child processes whose programs are not readable.
13534 * Separate Objdir:: Compiling @value{GDBN} in another directory
13535 * Config Names:: Specifying names for hosts and targets
13536 * Configure Options:: Summary of options for configure
13539 @node Separate Objdir
13540 @section Compiling @value{GDBN} in another directory
13542 If you want to run @value{GDBN} versions for several host or target machines,
13543 you need a different @code{gdb} compiled for each combination of
13544 host and target. @code{configure} is designed to make this easy by
13545 allowing you to generate each configuration in a separate subdirectory,
13546 rather than in the source directory. If your @code{make} program
13547 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
13548 @code{make} in each of these directories builds the @code{gdb}
13549 program specified there.
13551 To build @code{gdb} in a separate directory, run @code{configure}
13552 with the @samp{--srcdir} option to specify where to find the source.
13553 (You also need to specify a path to find @code{configure}
13554 itself from your working directory. If the path to @code{configure}
13555 would be the same as the argument to @samp{--srcdir}, you can leave out
13556 the @samp{--srcdir} option; it is assumed.)
13558 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
13559 separate directory for a Sun 4 like this:
13563 cd gdb-@value{GDBVN}
13566 ../gdb-@value{GDBVN}/configure sun4
13571 When @code{configure} builds a configuration using a remote source
13572 directory, it creates a tree for the binaries with the same structure
13573 (and using the same names) as the tree under the source directory. In
13574 the example, you'd find the Sun 4 library @file{libiberty.a} in the
13575 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
13576 @file{gdb-sun4/gdb}.
13578 One popular reason to build several @value{GDBN} configurations in separate
13579 directories is to configure @value{GDBN} for cross-compiling (where
13580 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
13581 programs that run on another machine---the @dfn{target}).
13582 You specify a cross-debugging target by
13583 giving the @samp{--target=@var{target}} option to @code{configure}.
13585 When you run @code{make} to build a program or library, you must run
13586 it in a configured directory---whatever directory you were in when you
13587 called @code{configure} (or one of its subdirectories).
13589 The @code{Makefile} that @code{configure} generates in each source
13590 directory also runs recursively. If you type @code{make} in a source
13591 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
13592 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
13593 will build all the required libraries, and then build GDB.
13595 When you have multiple hosts or targets configured in separate
13596 directories, you can run @code{make} on them in parallel (for example,
13597 if they are NFS-mounted on each of the hosts); they will not interfere
13601 @section Specifying names for hosts and targets
13603 The specifications used for hosts and targets in the @code{configure}
13604 script are based on a three-part naming scheme, but some short predefined
13605 aliases are also supported. The full naming scheme encodes three pieces
13606 of information in the following pattern:
13609 @var{architecture}-@var{vendor}-@var{os}
13612 For example, you can use the alias @code{sun4} as a @var{host} argument,
13613 or as the value for @var{target} in a @code{--target=@var{target}}
13614 option. The equivalent full name is @samp{sparc-sun-sunos4}.
13616 The @code{configure} script accompanying @value{GDBN} does not provide
13617 any query facility to list all supported host and target names or
13618 aliases. @code{configure} calls the Bourne shell script
13619 @code{config.sub} to map abbreviations to full names; you can read the
13620 script, if you wish, or you can use it to test your guesses on
13621 abbreviations---for example:
13624 % sh config.sub i386-linux
13626 % sh config.sub alpha-linux
13627 alpha-unknown-linux-gnu
13628 % sh config.sub hp9k700
13630 % sh config.sub sun4
13631 sparc-sun-sunos4.1.1
13632 % sh config.sub sun3
13633 m68k-sun-sunos4.1.1
13634 % sh config.sub i986v
13635 Invalid configuration `i986v': machine `i986v' not recognized
13639 @code{config.sub} is also distributed in the @value{GDBN} source
13640 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
13642 @node Configure Options
13643 @section @code{configure} options
13645 Here is a summary of the @code{configure} options and arguments that
13646 are most often useful for building @value{GDBN}. @code{configure} also has
13647 several other options not listed here. @inforef{What Configure
13648 Does,,configure.info}, for a full explanation of @code{configure}.
13651 configure @r{[}--help@r{]}
13652 @r{[}--prefix=@var{dir}@r{]}
13653 @r{[}--exec-prefix=@var{dir}@r{]}
13654 @r{[}--srcdir=@var{dirname}@r{]}
13655 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
13656 @r{[}--target=@var{target}@r{]}
13661 You may introduce options with a single @samp{-} rather than
13662 @samp{--} if you prefer; but you may abbreviate option names if you use
13667 Display a quick summary of how to invoke @code{configure}.
13669 @item --prefix=@var{dir}
13670 Configure the source to install programs and files under directory
13673 @item --exec-prefix=@var{dir}
13674 Configure the source to install programs under directory
13677 @c avoid splitting the warning from the explanation:
13679 @item --srcdir=@var{dirname}
13680 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13681 @code{make} that implements the @code{VPATH} feature.}@*
13682 Use this option to make configurations in directories separate from the
13683 @value{GDBN} source directories. Among other things, you can use this to
13684 build (or maintain) several configurations simultaneously, in separate
13685 directories. @code{configure} writes configuration specific files in
13686 the current directory, but arranges for them to use the source in the
13687 directory @var{dirname}. @code{configure} creates directories under
13688 the working directory in parallel to the source directories below
13691 @item --norecursion
13692 Configure only the directory level where @code{configure} is executed; do not
13693 propagate configuration to subdirectories.
13695 @item --target=@var{target}
13696 Configure @value{GDBN} for cross-debugging programs running on the specified
13697 @var{target}. Without this option, @value{GDBN} is configured to debug
13698 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13700 There is no convenient way to generate a list of all available targets.
13702 @item @var{host} @dots{}
13703 Configure @value{GDBN} to run on the specified @var{host}.
13705 There is no convenient way to generate a list of all available hosts.
13708 There are many other options available as well, but they are generally
13709 needed for special purposes only.
13717 % I think something like @colophon should be in texinfo. In the
13719 \long\def\colophon{\hbox to0pt{}\vfill
13720 \centerline{The body of this manual is set in}
13721 \centerline{\fontname\tenrm,}
13722 \centerline{with headings in {\bf\fontname\tenbf}}
13723 \centerline{and examples in {\tt\fontname\tentt}.}
13724 \centerline{{\it\fontname\tenit\/},}
13725 \centerline{{\bf\fontname\tenbf}, and}
13726 \centerline{{\sl\fontname\tensl\/}}
13727 \centerline{are used for emphasis.}\vfill}
13729 % Blame: doc@cygnus.com, 1991.
13732 @c TeX can handle the contents at the start but makeinfo 3.12 can not