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
130 * Languages:: Using @value{GDBN} with different languages
132 * Symbols:: Examining the symbol table
133 * Altering:: Altering execution
134 * GDB Files:: @value{GDBN} files
135 * Targets:: Specifying a debugging target
136 * Configurations:: Configuration-specific information
137 * Controlling GDB:: Controlling @value{GDBN}
138 * Sequences:: Canned sequences of commands
139 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
140 * Annotations:: @value{GDBN}'s annotation interface.
141 * GDB/MI:: @value{GDBN}'s Machine Interface.
143 * GDB Bugs:: Reporting bugs in @value{GDBN}
144 * Formatting Documentation:: How to format and print @value{GDBN} documentation
146 * Command Line Editing:: Command Line Editing
147 * Using History Interactively:: Using History Interactively
148 * Installing GDB:: Installing GDB
154 @c the replication sucks, but this avoids a texinfo 3.12 lameness
159 @top Debugging with @value{GDBN}
161 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
163 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
166 Copyright (C) 1988-2000 Free Software Foundation, Inc.
169 * Summary:: Summary of @value{GDBN}
170 * Sample Session:: A sample @value{GDBN} session
172 * Invocation:: Getting in and out of @value{GDBN}
173 * Commands:: @value{GDBN} commands
174 * Running:: Running programs under @value{GDBN}
175 * Stopping:: Stopping and continuing
176 * Stack:: Examining the stack
177 * Source:: Examining source files
178 * Data:: Examining data
180 * Languages:: Using @value{GDBN} with different languages
182 * Symbols:: Examining the symbol table
183 * Altering:: Altering execution
184 * GDB Files:: @value{GDBN} files
185 * Targets:: Specifying a debugging target
186 * Configurations:: Configuration-specific information
187 * Controlling GDB:: Controlling @value{GDBN}
188 * Sequences:: Canned sequences of commands
189 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
190 * Annotations:: @value{GDBN}'s annotation interface.
192 * GDB Bugs:: Reporting bugs in @value{GDBN}
193 * Formatting Documentation:: How to format and print @value{GDBN} documentation
195 * Command Line Editing:: Command Line Editing
196 * Using History Interactively:: Using History Interactively
197 * Installing GDB:: Installing GDB
203 @c TeX can handle the contents at the start but makeinfo 3.12 can not
209 @unnumbered Summary of @value{GDBN}
211 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
212 going on ``inside'' another program while it executes---or what another
213 program was doing at the moment it crashed.
215 @value{GDBN} can do four main kinds of things (plus other things in support of
216 these) to help you catch bugs in the act:
220 Start your program, specifying anything that might affect its behavior.
223 Make your program stop on specified conditions.
226 Examine what has happened, when your program has stopped.
229 Change things in your program, so you can experiment with correcting the
230 effects of one bug and go on to learn about another.
233 You can use @value{GDBN} to debug programs written in C and C++.
234 For more information, see @ref{Support,,Supported languages}.
235 For more information, see @ref{C,,C and C++}.
239 Support for Modula-2 and Chill is partial. For information on Modula-2,
240 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
243 Debugging Pascal programs which use sets, subranges, file variables, or
244 nested functions does not currently work. @value{GDBN} does not support
245 entering expressions, printing values, or similar features using Pascal
249 @value{GDBN} can be used to debug programs written in Fortran, although
250 it may be necessary to refer to some variables with a trailing
254 * Free Software:: Freely redistributable software
255 * Contributors:: Contributors to GDB
259 @unnumberedsec Free software
261 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
262 General Public License
263 (GPL). The GPL gives you the freedom to copy or adapt a licensed
264 program---but every person getting a copy also gets with it the
265 freedom to modify that copy (which means that they must get access to
266 the source code), and the freedom to distribute further copies.
267 Typical software companies use copyrights to limit your freedoms; the
268 Free Software Foundation uses the GPL to preserve these freedoms.
270 Fundamentally, the General Public License is a license which says that
271 you have these freedoms and that you cannot take these freedoms away
275 @unnumberedsec Contributors to @value{GDBN}
277 Richard Stallman was the original author of @value{GDBN}, and of many
278 other @sc{gnu} programs. Many others have contributed to its
279 development. This section attempts to credit major contributors. One
280 of the virtues of free software is that everyone is free to contribute
281 to it; with regret, we cannot actually acknowledge everyone here. The
282 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
283 blow-by-blow account.
285 Changes much prior to version 2.0 are lost in the mists of time.
288 @emph{Plea:} Additions to this section are particularly welcome. If you
289 or your friends (or enemies, to be evenhanded) have been unfairly
290 omitted from this list, we would like to add your names!
293 So that they may not regard their many labors as thankless, we
294 particularly thank those who shepherded @value{GDBN} through major
296 Andrew Cagney (release 5.0);
297 Jim Blandy (release 4.18);
298 Jason Molenda (release 4.17);
299 Stan Shebs (release 4.14);
300 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
301 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
302 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
303 Jim Kingdon (releases 3.5, 3.4, and 3.3);
304 and Randy Smith (releases 3.2, 3.1, and 3.0).
306 Richard Stallman, assisted at various times by Peter TerMaat, Chris
307 Hanson, and Richard Mlynarik, handled releases through 2.8.
309 Michael Tiemann is the author of most of the @sc{gnu} C++ support in
310 @value{GDBN}, with significant additional contributions from Per
311 Bothner. James Clark wrote the @sc{gnu} C++ demangler. Early work on
312 C++ was by Peter TerMaat (who also did much general update work leading
315 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
316 object-file formats; BFD was a joint project of David V.
317 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
319 David Johnson wrote the original COFF support; Pace Willison did
320 the original support for encapsulated COFF.
322 Brent Benson of Harris Computer Systems contributed DWARF2 support.
324 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
325 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
327 Jean-Daniel Fekete contributed Sun 386i support.
328 Chris Hanson improved the HP9000 support.
329 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
330 David Johnson contributed Encore Umax support.
331 Jyrki Kuoppala contributed Altos 3068 support.
332 Jeff Law contributed HP PA and SOM support.
333 Keith Packard contributed NS32K support.
334 Doug Rabson contributed Acorn Risc Machine support.
335 Bob Rusk contributed Harris Nighthawk CX-UX support.
336 Chris Smith contributed Convex support (and Fortran debugging).
337 Jonathan Stone contributed Pyramid support.
338 Michael Tiemann contributed SPARC support.
339 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
340 Pace Willison contributed Intel 386 support.
341 Jay Vosburgh contributed Symmetry support.
343 Andreas Schwab contributed M68K Linux support.
345 Rich Schaefer and Peter Schauer helped with support of SunOS shared
348 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
349 about several machine instruction sets.
351 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
352 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
353 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
354 and RDI targets, respectively.
356 Brian Fox is the author of the readline libraries providing
357 command-line editing and command history.
359 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
360 Modula-2 support, and contributed the Languages chapter of this manual.
362 Fred Fish wrote most of the support for Unix System Vr4.
363 He also enhanced the command-completion support to cover C++ overloaded
366 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
369 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
371 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
373 Toshiba sponsored the support for the TX39 Mips processor.
375 Matsushita sponsored the support for the MN10200 and MN10300 processors.
377 Fujitsu sponsored the support for SPARClite and FR30 processors.
379 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
382 Michael Snyder added support for tracepoints.
384 Stu Grossman wrote gdbserver.
386 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
387 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
389 The following people at the Hewlett-Packard Company contributed
390 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
391 (narrow mode), HP's implementation of kernel threads, HP's aC++
392 compiler, and the terminal user interface: Ben Krepp, Richard Title,
393 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
394 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
395 information in this manual.
397 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
398 development since 1991. Cygnus engineers who have worked on @value{GDBN}
399 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
400 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
401 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
402 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
403 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
404 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
405 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
406 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
407 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
408 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
409 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
410 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
411 Zuhn have made contributions both large and small.
415 @chapter A Sample @value{GDBN} Session
417 You can use this manual at your leisure to read all about @value{GDBN}.
418 However, a handful of commands are enough to get started using the
419 debugger. This chapter illustrates those commands.
422 In this sample session, we emphasize user input like this: @b{input},
423 to make it easier to pick out from the surrounding output.
426 @c FIXME: this example may not be appropriate for some configs, where
427 @c FIXME...primary interest is in remote use.
429 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
430 processor) exhibits the following bug: sometimes, when we change its
431 quote strings from the default, the commands used to capture one macro
432 definition within another stop working. In the following short @code{m4}
433 session, we define a macro @code{foo} which expands to @code{0000}; we
434 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
435 same thing. However, when we change the open quote string to
436 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
437 procedure fails to define a new synonym @code{baz}:
446 @b{define(bar,defn(`foo'))}
450 @b{changequote(<QUOTE>,<UNQUOTE>)}
452 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
455 m4: End of input: 0: fatal error: EOF in string
459 Let us use @value{GDBN} to try to see what is going on.
462 $ @b{@value{GDBP} m4}
463 @c FIXME: this falsifies the exact text played out, to permit smallbook
464 @c FIXME... format to come out better.
465 @value{GDBN} is free software and you are welcome to distribute copies
466 of it under certain conditions; type "show copying" to see
468 There is absolutely no warranty for @value{GDBN}; type "show warranty"
471 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
476 @value{GDBN} reads only enough symbol data to know where to find the
477 rest when needed; as a result, the first prompt comes up very quickly.
478 We now tell @value{GDBN} to use a narrower display width than usual, so
479 that examples fit in this manual.
482 (@value{GDBP}) @b{set width 70}
486 We need to see how the @code{m4} built-in @code{changequote} works.
487 Having looked at the source, we know the relevant subroutine is
488 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
489 @code{break} command.
492 (@value{GDBP}) @b{break m4_changequote}
493 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
497 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
498 control; as long as control does not reach the @code{m4_changequote}
499 subroutine, the program runs as usual:
502 (@value{GDBP}) @b{run}
503 Starting program: /work/Editorial/gdb/gnu/m4/m4
511 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
512 suspends execution of @code{m4}, displaying information about the
513 context where it stops.
516 @b{changequote(<QUOTE>,<UNQUOTE>)}
518 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
520 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
524 Now we use the command @code{n} (@code{next}) to advance execution to
525 the next line of the current function.
529 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
534 @code{set_quotes} looks like a promising subroutine. We can go into it
535 by using the command @code{s} (@code{step}) instead of @code{next}.
536 @code{step} goes to the next line to be executed in @emph{any}
537 subroutine, so it steps into @code{set_quotes}.
541 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
543 530 if (lquote != def_lquote)
547 The display that shows the subroutine where @code{m4} is now
548 suspended (and its arguments) is called a stack frame display. It
549 shows a summary of the stack. We can use the @code{backtrace}
550 command (which can also be spelled @code{bt}), to see where we are
551 in the stack as a whole: the @code{backtrace} command displays a
552 stack frame for each active subroutine.
555 (@value{GDBP}) @b{bt}
556 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
558 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
560 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
561 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
563 #4 0x79dc in expand_input () at macro.c:40
564 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
568 We step through a few more lines to see what happens. The first two
569 times, we can use @samp{s}; the next two times we use @code{n} to avoid
570 falling into the @code{xstrdup} subroutine.
574 0x3b5c 532 if (rquote != def_rquote)
576 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
577 def_lquote : xstrdup(lq);
579 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
582 538 len_lquote = strlen(rquote);
586 The last line displayed looks a little odd; we can examine the variables
587 @code{lquote} and @code{rquote} to see if they are in fact the new left
588 and right quotes we specified. We use the command @code{p}
589 (@code{print}) to see their values.
592 (@value{GDBP}) @b{p lquote}
593 $1 = 0x35d40 "<QUOTE>"
594 (@value{GDBP}) @b{p rquote}
595 $2 = 0x35d50 "<UNQUOTE>"
599 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
600 To look at some context, we can display ten lines of source
601 surrounding the current line with the @code{l} (@code{list}) command.
607 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
609 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
612 538 len_lquote = strlen(rquote);
613 539 len_rquote = strlen(lquote);
620 Let us step past the two lines that set @code{len_lquote} and
621 @code{len_rquote}, and then examine the values of those variables.
625 539 len_rquote = strlen(lquote);
628 (@value{GDBP}) @b{p len_lquote}
630 (@value{GDBP}) @b{p len_rquote}
635 That certainly looks wrong, assuming @code{len_lquote} and
636 @code{len_rquote} are meant to be the lengths of @code{lquote} and
637 @code{rquote} respectively. We can set them to better values using
638 the @code{p} command, since it can print the value of
639 any expression---and that expression can include subroutine calls and
643 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
645 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
650 Is that enough to fix the problem of using the new quotes with the
651 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
652 executing with the @code{c} (@code{continue}) command, and then try the
653 example that caused trouble initially:
659 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
666 Success! The new quotes now work just as well as the default ones. The
667 problem seems to have been just the two typos defining the wrong
668 lengths. We allow @code{m4} exit by giving it an EOF as input:
672 Program exited normally.
676 The message @samp{Program exited normally.} is from @value{GDBN}; it
677 indicates @code{m4} has finished executing. We can end our @value{GDBN}
678 session with the @value{GDBN} @code{quit} command.
681 (@value{GDBP}) @b{quit}
685 @chapter Getting In and Out of @value{GDBN}
687 This chapter discusses how to start @value{GDBN}, and how to get out of it.
691 type @samp{@value{GDBP}} to start @value{GDBN}.
693 type @kbd{quit} or @kbd{C-d} to exit.
697 * Invoking GDB:: How to start @value{GDBN}
698 * Quitting GDB:: How to quit @value{GDBN}
699 * Shell Commands:: How to use shell commands inside @value{GDBN}
703 @section Invoking @value{GDBN}
705 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
706 @value{GDBN} reads commands from the terminal until you tell it to exit.
708 You can also run @code{@value{GDBP}} with a variety of arguments and options,
709 to specify more of your debugging environment at the outset.
711 The command-line options described here are designed
712 to cover a variety of situations; in some environments, some of these
713 options may effectively be unavailable.
715 The most usual way to start @value{GDBN} is with one argument,
716 specifying an executable program:
719 @value{GDBP} @var{program}
723 You can also start with both an executable program and a core file
727 @value{GDBP} @var{program} @var{core}
730 You can, instead, specify a process ID as a second argument, if you want
731 to debug a running process:
734 @value{GDBP} @var{program} 1234
738 would attach @value{GDBN} to process @code{1234} (unless you also have a file
739 named @file{1234}; @value{GDBN} does check for a core file first).
741 Taking advantage of the second command-line argument requires a fairly
742 complete operating system; when you use @value{GDBN} as a remote
743 debugger attached to a bare board, there may not be any notion of
744 ``process'', and there is often no way to get a core dump. @value{GDBN}
745 will warn you if it is unable to attach or to read core dumps.
747 You can run @code{@value{GDBP}} without printing the front material, which describes
748 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
755 You can further control how @value{GDBN} starts up by using command-line
756 options. @value{GDBN} itself can remind you of the options available.
766 to display all available options and briefly describe their use
767 (@samp{@value{GDBP} -h} is a shorter equivalent).
769 All options and command line arguments you give are processed
770 in sequential order. The order makes a difference when the
771 @samp{-x} option is used.
775 * File Options:: Choosing files
776 * Mode Options:: Choosing modes
780 @subsection Choosing files
782 When @value{GDBN} starts, it reads any arguments other than options as
783 specifying an executable file and core file (or process ID). This is
784 the same as if the arguments were specified by the @samp{-se} and
785 @samp{-c} options respectively. (@value{GDBN} reads the first argument
786 that does not have an associated option flag as equivalent to the
787 @samp{-se} option followed by that argument; and the second argument
788 that does not have an associated option flag, if any, as equivalent to
789 the @samp{-c} option followed by that argument.)
791 If @value{GDBN} has not been configured to included core file support,
792 such as for most embedded targets, then it will complain about a second
793 argument and ignore it.
795 Many options have both long and short forms; both are shown in the
796 following list. @value{GDBN} also recognizes the long forms if you truncate
797 them, so long as enough of the option is present to be unambiguous.
798 (If you prefer, you can flag option arguments with @samp{--} rather
799 than @samp{-}, though we illustrate the more usual convention.)
801 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
802 @c way, both those who look for -foo and --foo in the index, will find
806 @item -symbols @var{file}
808 @cindex @code{--symbols}
810 Read symbol table from file @var{file}.
812 @item -exec @var{file}
814 @cindex @code{--exec}
816 Use file @var{file} as the executable file to execute when appropriate,
817 and for examining pure data in conjunction with a core dump.
821 Read symbol table from file @var{file} and use it as the executable
824 @item -core @var{file}
826 @cindex @code{--core}
828 Use file @var{file} as a core dump to examine.
830 @item -c @var{number}
831 Connect to process ID @var{number}, as with the @code{attach} command
832 (unless there is a file in core-dump format named @var{number}, in which
833 case @samp{-c} specifies that file as a core dump to read).
835 @item -command @var{file}
837 @cindex @code{--command}
839 Execute @value{GDBN} commands from file @var{file}. @xref{Command
840 Files,, Command files}.
842 @item -directory @var{directory}
843 @itemx -d @var{directory}
844 @cindex @code{--directory}
846 Add @var{directory} to the path to search for source files.
850 @cindex @code{--mapped}
852 @emph{Warning: this option depends on operating system facilities that are not
853 supported on all systems.}@*
854 If memory-mapped files are available on your system through the @code{mmap}
855 system call, you can use this option
856 to have @value{GDBN} write the symbols from your
857 program into a reusable file in the current directory. If the program you are debugging is
858 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
859 Future @value{GDBN} debugging sessions notice the presence of this file,
860 and can quickly map in symbol information from it, rather than reading
861 the symbol table from the executable program.
863 The @file{.syms} file is specific to the host machine where @value{GDBN}
864 is run. It holds an exact image of the internal @value{GDBN} symbol
865 table. It cannot be shared across multiple host platforms.
869 @cindex @code{--readnow}
871 Read each symbol file's entire symbol table immediately, rather than
872 the default, which is to read it incrementally as it is needed.
873 This makes startup slower, but makes future operations faster.
877 You typically combine the @code{-mapped} and @code{-readnow} options in
878 order to build a @file{.syms} file that contains complete symbol
879 information. (@xref{Files,,Commands to specify files}, for information
880 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
881 but build a @file{.syms} file for future use is:
884 gdb -batch -nx -mapped -readnow programname
888 @subsection Choosing modes
890 You can run @value{GDBN} in various alternative modes---for example, in
891 batch mode or quiet mode.
898 Do not execute commands found in any initialization files (normally
899 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
900 @value{GDBN} executes the commands in these files after all the command
901 options and arguments have been processed. @xref{Command Files,,Command
907 @cindex @code{--quiet}
908 @cindex @code{--silent}
910 ``Quiet''. Do not print the introductory and copyright messages. These
911 messages are also suppressed in batch mode.
914 @cindex @code{--batch}
915 Run in batch mode. Exit with status @code{0} after processing all the
916 command files specified with @samp{-x} (and all commands from
917 initialization files, if not inhibited with @samp{-n}). Exit with
918 nonzero status if an error occurs in executing the @value{GDBN} commands
919 in the command files.
921 Batch mode may be useful for running @value{GDBN} as a filter, for
922 example to download and run a program on another computer; in order to
923 make this more useful, the message
926 Program exited normally.
930 (which is ordinarily issued whenever a program running under
931 @value{GDBN} control terminates) is not issued when running in batch
936 @cindex @code{--nowindows}
938 ``No windows''. If @value{GDBN} comes with a graphical user interface
939 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
940 interface. If no GUI is available, this option has no effect.
944 @cindex @code{--windows}
946 If @value{GDBN} includes a GUI, then this option requires it to be
949 @item -cd @var{directory}
951 Run @value{GDBN} using @var{directory} as its working directory,
952 instead of the current directory.
956 @cindex @code{--fullname}
958 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
959 subprocess. It tells @value{GDBN} to output the full file name and line
960 number in a standard, recognizable fashion each time a stack frame is
961 displayed (which includes each time your program stops). This
962 recognizable format looks like two @samp{\032} characters, followed by
963 the file name, line number and character position separated by colons,
964 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
965 @samp{\032} characters as a signal to display the source code for the
969 @cindex @code{--epoch}
970 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
971 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
972 routines so as to allow Epoch to display values of expressions in a
975 @item -annotate @var{level}
976 @cindex @code{--annotate}
977 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
978 effect is identical to using @samp{set annotate @var{level}}
979 (@pxref{Annotations}).
980 Annotation level controls how much information does @value{GDBN} print
981 together with its prompt, values of expressions, source lines, and other
982 types of output. Level 0 is the normal, level 1 is for use when
983 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
984 maximum annotation suitable for programs that control @value{GDBN}.
987 @cindex @code{--async}
988 Use the asynchronous event loop for the command-line interface.
989 @value{GDBN} processes all events, such as user keyboard input, via a
990 special event loop. This allows @value{GDBN} to accept and process user
991 commands in parallel with the debugged process being
992 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
993 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
994 suspended when the debuggee runs.}, so you don't need to wait for
995 control to return to @value{GDBN} before you type the next command.
996 (@emph{Note:} as of version 5.0, the target side of the asynchronous
997 operation is not yet in place, so @samp{-async} does not work fully
999 @c FIXME: when the target side of the event loop is done, the above NOTE
1000 @c should be removed.
1002 When the standard input is connected to a terminal device, @value{GDBN}
1003 uses the asynchronous event loop by default, unless disabled by the
1004 @samp{-noasync} option.
1007 @cindex @code{--noasync}
1008 Disable the asynchronous event loop for the command-line interface.
1010 @item -baud @var{bps}
1012 @cindex @code{--baud}
1014 Set the line speed (baud rate or bits per second) of any serial
1015 interface used by @value{GDBN} for remote debugging.
1017 @item -tty @var{device}
1018 @itemx -t @var{device}
1019 @cindex @code{--tty}
1021 Run using @var{device} for your program's standard input and output.
1022 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1024 @c resolve the situation of these eventually
1026 @c @cindex @code{--tui}
1027 @c Use a Terminal User Interface. For information, use your Web browser to
1028 @c read the file @file{TUI.html}, which is usually installed in the
1029 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1030 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1031 @c @value{GDBN} under @sc{gnu} Emacs}).
1034 @c @cindex @code{--xdb}
1035 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1036 @c For information, see the file @file{xdb_trans.html}, which is usually
1037 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1040 @item -interpreter @var{interp}
1041 @cindex @code{--interpreter}
1042 Use the interpreter @var{interp} for interface with the controlling
1043 program or device. This option is meant to be set by programs which
1044 communicate with @value{GDBN} using it as a back end. For example,
1045 @samp{--interpreter=mi} causes @value{GDBN} to use the @dfn{gdbmi
1046 interface} (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}).
1049 @cindex @code{--write}
1050 Open the executable and core files for both reading and writing. This
1051 is equivalent to the @samp{set write on} command inside @value{GDBN}
1055 @cindex @code{--statistics}
1056 This option causes @value{GDBN} to print statistics about time and
1057 memory usage after it completes each command and returns to the prompt.
1060 @cindex @code{--version}
1061 This option causes @value{GDBN} to print its version number and
1062 no-warranty blurb, and exit.
1067 @section Quitting @value{GDBN}
1068 @cindex exiting @value{GDBN}
1069 @cindex leaving @value{GDBN}
1072 @kindex quit @r{[}@var{expression}@r{]}
1073 @kindex q @r{(@code{quit})}
1074 @item quit @r{[}@var{expression}@r{]}
1076 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1077 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1078 do not supply @var{expression}, @value{GDBN} will terminate normally;
1079 otherwise it will terminate using the result of @var{expression} as the
1084 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1085 terminates the action of any @value{GDBN} command that is in progress and
1086 returns to @value{GDBN} command level. It is safe to type the interrupt
1087 character at any time because @value{GDBN} does not allow it to take effect
1088 until a time when it is safe.
1090 If you have been using @value{GDBN} to control an attached process or
1091 device, you can release it with the @code{detach} command
1092 (@pxref{Attach, ,Debugging an already-running process}).
1094 @node Shell Commands
1095 @section Shell commands
1097 If you need to execute occasional shell commands during your
1098 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1099 just use the @code{shell} command.
1103 @cindex shell escape
1104 @item shell @var{command string}
1105 Invoke a standard shell to execute @var{command string}.
1106 If it exists, the environment variable @code{SHELL} determines which
1107 shell to run. Otherwise @value{GDBN} uses the default shell
1108 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1111 The utility @code{make} is often needed in development environments.
1112 You do not have to use the @code{shell} command for this purpose in
1117 @cindex calling make
1118 @item make @var{make-args}
1119 Execute the @code{make} program with the specified
1120 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1124 @chapter @value{GDBN} Commands
1126 You can abbreviate a @value{GDBN} command to the first few letters of the command
1127 name, if that abbreviation is unambiguous; and you can repeat certain
1128 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1129 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1130 show you the alternatives available, if there is more than one possibility).
1133 * Command Syntax:: How to give commands to @value{GDBN}
1134 * Completion:: Command completion
1135 * Help:: How to ask @value{GDBN} for help
1138 @node Command Syntax
1139 @section Command syntax
1141 A @value{GDBN} command is a single line of input. There is no limit on
1142 how long it can be. It starts with a command name, which is followed by
1143 arguments whose meaning depends on the command name. For example, the
1144 command @code{step} accepts an argument which is the number of times to
1145 step, as in @samp{step 5}. You can also use the @code{step} command
1146 with no arguments. Some commands do not allow any arguments.
1148 @cindex abbreviation
1149 @value{GDBN} command names may always be truncated if that abbreviation is
1150 unambiguous. Other possible command abbreviations are listed in the
1151 documentation for individual commands. In some cases, even ambiguous
1152 abbreviations are allowed; for example, @code{s} is specially defined as
1153 equivalent to @code{step} even though there are other commands whose
1154 names start with @code{s}. You can test abbreviations by using them as
1155 arguments to the @code{help} command.
1157 @cindex repeating commands
1158 @kindex RET @r{(repeat last command)}
1159 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1160 repeat the previous command. Certain commands (for example, @code{run})
1161 will not repeat this way; these are commands whose unintentional
1162 repetition might cause trouble and which you are unlikely to want to
1165 The @code{list} and @code{x} commands, when you repeat them with
1166 @key{RET}, construct new arguments rather than repeating
1167 exactly as typed. This permits easy scanning of source or memory.
1169 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1170 output, in a way similar to the common utility @code{more}
1171 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1172 @key{RET} too many in this situation, @value{GDBN} disables command
1173 repetition after any command that generates this sort of display.
1175 @kindex # @r{(a comment)}
1177 Any text from a @kbd{#} to the end of the line is a comment; it does
1178 nothing. This is useful mainly in command files (@pxref{Command
1179 Files,,Command files}).
1182 @section Command completion
1185 @cindex word completion
1186 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1187 only one possibility; it can also show you what the valid possibilities
1188 are for the next word in a command, at any time. This works for @value{GDBN}
1189 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1191 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1192 of a word. If there is only one possibility, @value{GDBN} fills in the
1193 word, and waits for you to finish the command (or press @key{RET} to
1194 enter it). For example, if you type
1196 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1197 @c complete accuracy in these examples; space introduced for clarity.
1198 @c If texinfo enhancements make it unnecessary, it would be nice to
1199 @c replace " @key" by "@key" in the following...
1201 (@value{GDBP}) info bre @key{TAB}
1205 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1206 the only @code{info} subcommand beginning with @samp{bre}:
1209 (@value{GDBP}) info breakpoints
1213 You can either press @key{RET} at this point, to run the @code{info
1214 breakpoints} command, or backspace and enter something else, if
1215 @samp{breakpoints} does not look like the command you expected. (If you
1216 were sure you wanted @code{info breakpoints} in the first place, you
1217 might as well just type @key{RET} immediately after @samp{info bre},
1218 to exploit command abbreviations rather than command completion).
1220 If there is more than one possibility for the next word when you press
1221 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1222 characters and try again, or just press @key{TAB} a second time;
1223 @value{GDBN} displays all the possible completions for that word. For
1224 example, you might want to set a breakpoint on a subroutine whose name
1225 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1226 just sounds the bell. Typing @key{TAB} again displays all the
1227 function names in your program that begin with those characters, for
1231 (@value{GDBP}) b make_ @key{TAB}
1232 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1233 make_a_section_from_file make_environ
1234 make_abs_section make_function_type
1235 make_blockvector make_pointer_type
1236 make_cleanup make_reference_type
1237 make_command make_symbol_completion_list
1238 (@value{GDBP}) b make_
1242 After displaying the available possibilities, @value{GDBN} copies your
1243 partial input (@samp{b make_} in the example) so you can finish the
1246 If you just want to see the list of alternatives in the first place, you
1247 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1248 means @kbd{@key{META} ?}. You can type this either by holding down a
1249 key designated as the @key{META} shift on your keyboard (if there is
1250 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1252 @cindex quotes in commands
1253 @cindex completion of quoted strings
1254 Sometimes the string you need, while logically a ``word'', may contain
1255 parentheses or other characters that @value{GDBN} normally excludes from
1256 its notion of a word. To permit word completion to work in this
1257 situation, you may enclose words in @code{'} (single quote marks) in
1258 @value{GDBN} commands.
1260 The most likely situation where you might need this is in typing the
1261 name of a C++ function. This is because C++ allows function overloading
1262 (multiple definitions of the same function, distinguished by argument
1263 type). For example, when you want to set a breakpoint you may need to
1264 distinguish whether you mean the version of @code{name} that takes an
1265 @code{int} parameter, @code{name(int)}, or the version that takes a
1266 @code{float} parameter, @code{name(float)}. To use the word-completion
1267 facilities in this situation, type a single quote @code{'} at the
1268 beginning of the function name. This alerts @value{GDBN} that it may need to
1269 consider more information than usual when you press @key{TAB} or
1270 @kbd{M-?} to request word completion:
1273 (@value{GDBP}) b 'bubble( @kbd{M-?}
1274 bubble(double,double) bubble(int,int)
1275 (@value{GDBP}) b 'bubble(
1278 In some cases, @value{GDBN} can tell that completing a name requires using
1279 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1280 completing as much as it can) if you do not type the quote in the first
1284 (@value{GDBP}) b bub @key{TAB}
1285 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1286 (@value{GDBP}) b 'bubble(
1290 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1291 you have not yet started typing the argument list when you ask for
1292 completion on an overloaded symbol.
1294 For more information about overloaded functions, see @ref{C plus plus
1295 expressions, ,C++ expressions}. You can use the command @code{set
1296 overload-resolution off} to disable overload resolution;
1297 see @ref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1301 @section Getting help
1302 @cindex online documentation
1305 You can always ask @value{GDBN} itself for information on its commands,
1306 using the command @code{help}.
1309 @kindex h @r{(@code{help})}
1312 You can use @code{help} (abbreviated @code{h}) with no arguments to
1313 display a short list of named classes of commands:
1317 List of classes of commands:
1319 aliases -- Aliases of other commands
1320 breakpoints -- Making program stop at certain points
1321 data -- Examining data
1322 files -- Specifying and examining files
1323 internals -- Maintenance commands
1324 obscure -- Obscure features
1325 running -- Running the program
1326 stack -- Examining the stack
1327 status -- Status inquiries
1328 support -- Support facilities
1329 tracepoints -- Tracing of program execution without@*
1330 stopping the program
1331 user-defined -- User-defined commands
1333 Type "help" followed by a class name for a list of
1334 commands in that class.
1335 Type "help" followed by command name for full
1337 Command name abbreviations are allowed if unambiguous.
1340 @c the above line break eliminates huge line overfull...
1342 @item help @var{class}
1343 Using one of the general help classes as an argument, you can get a
1344 list of the individual commands in that class. For example, here is the
1345 help display for the class @code{status}:
1348 (@value{GDBP}) help status
1353 @c Line break in "show" line falsifies real output, but needed
1354 @c to fit in smallbook page size.
1355 info -- Generic command for showing things
1356 about the program being debugged
1357 show -- Generic command for showing things
1360 Type "help" followed by command name for full
1362 Command name abbreviations are allowed if unambiguous.
1366 @item help @var{command}
1367 With a command name as @code{help} argument, @value{GDBN} displays a
1368 short paragraph on how to use that command.
1371 @item apropos @var{args}
1372 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1373 commands, and their documentation, for the regular expression specified in
1374 @var{args}. It prints out all matches found. For example:
1380 @noindent results in:
1384 set symbol-reloading -- Set dynamic symbol table reloading
1385 multiple times in one run
1386 show symbol-reloading -- Show dynamic symbol table reloading
1387 multiple times in one run
1392 @item complete @var{args}
1393 The @code{complete @var{args}} command lists all the possible completions
1394 for the beginning of a command. Use @var{args} to specify the beginning of the
1395 command you want completed. For example:
1401 @noindent results in:
1412 @noindent This is intended for use by @sc{gnu} Emacs.
1415 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1416 and @code{show} to inquire about the state of your program, or the state
1417 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1418 manual introduces each of them in the appropriate context. The listings
1419 under @code{info} and under @code{show} in the Index point to
1420 all the sub-commands. @xref{Index}.
1425 @kindex i @r{(@code{info})}
1427 This command (abbreviated @code{i}) is for describing the state of your
1428 program. For example, you can list the arguments given to your program
1429 with @code{info args}, list the registers currently in use with @code{info
1430 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1431 You can get a complete list of the @code{info} sub-commands with
1432 @w{@code{help info}}.
1436 You can assign the result of an expression to an environment variable with
1437 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1438 @code{set prompt $}.
1442 In contrast to @code{info}, @code{show} is for describing the state of
1443 @value{GDBN} itself.
1444 You can change most of the things you can @code{show}, by using the
1445 related command @code{set}; for example, you can control what number
1446 system is used for displays with @code{set radix}, or simply inquire
1447 which is currently in use with @code{show radix}.
1450 To display all the settable parameters and their current
1451 values, you can use @code{show} with no arguments; you may also use
1452 @code{info set}. Both commands produce the same display.
1453 @c FIXME: "info set" violates the rule that "info" is for state of
1454 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1455 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1459 Here are three miscellaneous @code{show} subcommands, all of which are
1460 exceptional in lacking corresponding @code{set} commands:
1463 @kindex show version
1464 @cindex version number
1466 Show what version of @value{GDBN} is running. You should include this
1467 information in @value{GDBN} bug-reports. If multiple versions of
1468 @value{GDBN} are in use at your site, you may need to determine which
1469 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1470 commands are introduced, and old ones may wither away. Also, many
1471 system vendors ship variant versions of @value{GDBN}, and there are
1472 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1473 The version number is the same as the one announced when you start
1476 @kindex show copying
1478 Display information about permission for copying @value{GDBN}.
1480 @kindex show warranty
1482 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1483 if your version of @value{GDBN} comes with one.
1488 @chapter Running Programs Under @value{GDBN}
1490 When you run a program under @value{GDBN}, you must first generate
1491 debugging information when you compile it.
1493 You may start @value{GDBN} with its arguments, if any, in an environment
1494 of your choice. If you are doing native debugging, you may redirect
1495 your program's input and output, debug an already running process, or
1496 kill a child process.
1499 * Compilation:: Compiling for debugging
1500 * Starting:: Starting your program
1501 * Arguments:: Your program's arguments
1502 * Environment:: Your program's environment
1504 * Working Directory:: Your program's working directory
1505 * Input/Output:: Your program's input and output
1506 * Attach:: Debugging an already-running process
1507 * Kill Process:: Killing the child process
1509 * Threads:: Debugging programs with multiple threads
1510 * Processes:: Debugging programs with multiple processes
1514 @section Compiling for debugging
1516 In order to debug a program effectively, you need to generate
1517 debugging information when you compile it. This debugging information
1518 is stored in the object file; it describes the data type of each
1519 variable or function and the correspondence between source line numbers
1520 and addresses in the executable code.
1522 To request debugging information, specify the @samp{-g} option when you run
1525 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1526 options together. Using those compilers, you cannot generate optimized
1527 executables containing debugging information.
1529 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1530 without @samp{-O}, making it possible to debug optimized code. We
1531 recommend that you @emph{always} use @samp{-g} whenever you compile a
1532 program. You may think your program is correct, but there is no sense
1533 in pushing your luck.
1535 @cindex optimized code, debugging
1536 @cindex debugging optimized code
1537 When you debug a program compiled with @samp{-g -O}, remember that the
1538 optimizer is rearranging your code; the debugger shows you what is
1539 really there. Do not be too surprised when the execution path does not
1540 exactly match your source file! An extreme example: if you define a
1541 variable, but never use it, @value{GDBN} never sees that
1542 variable---because the compiler optimizes it out of existence.
1544 Some things do not work as well with @samp{-g -O} as with just
1545 @samp{-g}, particularly on machines with instruction scheduling. If in
1546 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1547 please report it to us as a bug (including a test case!).
1549 Older versions of the @sc{gnu} C compiler permitted a variant option
1550 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1551 format; if your @sc{gnu} C compiler has this option, do not use it.
1555 @section Starting your program
1561 @kindex r @r{(@code{run})}
1564 Use the @code{run} command to start your program under @value{GDBN}.
1565 You must first specify the program name (except on VxWorks) with an
1566 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1567 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1568 (@pxref{Files, ,Commands to specify files}).
1572 If you are running your program in an execution environment that
1573 supports processes, @code{run} creates an inferior process and makes
1574 that process run your program. (In environments without processes,
1575 @code{run} jumps to the start of your program.)
1577 The execution of a program is affected by certain information it
1578 receives from its superior. @value{GDBN} provides ways to specify this
1579 information, which you must do @emph{before} starting your program. (You
1580 can change it after starting your program, but such changes only affect
1581 your program the next time you start it.) This information may be
1582 divided into four categories:
1585 @item The @emph{arguments.}
1586 Specify the arguments to give your program as the arguments of the
1587 @code{run} command. If a shell is available on your target, the shell
1588 is used to pass the arguments, so that you may use normal conventions
1589 (such as wildcard expansion or variable substitution) in describing
1591 In Unix systems, you can control which shell is used with the
1592 @code{SHELL} environment variable.
1593 @xref{Arguments, ,Your program's arguments}.
1595 @item The @emph{environment.}
1596 Your program normally inherits its environment from @value{GDBN}, but you can
1597 use the @value{GDBN} commands @code{set environment} and @code{unset
1598 environment} to change parts of the environment that affect
1599 your program. @xref{Environment, ,Your program's environment}.
1601 @item The @emph{working directory.}
1602 Your program inherits its working directory from @value{GDBN}. You can set
1603 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1604 @xref{Working Directory, ,Your program's working directory}.
1606 @item The @emph{standard input and output.}
1607 Your program normally uses the same device for standard input and
1608 standard output as @value{GDBN} is using. You can redirect input and output
1609 in the @code{run} command line, or you can use the @code{tty} command to
1610 set a different device for your program.
1611 @xref{Input/Output, ,Your program's input and output}.
1614 @emph{Warning:} While input and output redirection work, you cannot use
1615 pipes to pass the output of the program you are debugging to another
1616 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1620 When you issue the @code{run} command, your program begins to execute
1621 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1622 of how to arrange for your program to stop. Once your program has
1623 stopped, you may call functions in your program, using the @code{print}
1624 or @code{call} commands. @xref{Data, ,Examining Data}.
1626 If the modification time of your symbol file has changed since the last
1627 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1628 table, and reads it again. When it does this, @value{GDBN} tries to retain
1629 your current breakpoints.
1632 @section Your program's arguments
1634 @cindex arguments (to your program)
1635 The arguments to your program can be specified by the arguments of the
1637 They are passed to a shell, which expands wildcard characters and
1638 performs redirection of I/O, and thence to your program. Your
1639 @code{SHELL} environment variable (if it exists) specifies what shell
1640 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1641 the default shell (@file{/bin/sh} on Unix).
1643 On non-Unix systems, the program is usually invoked directly by
1644 @value{GDBN}, which emulates I/O redirection via the appropriate system
1645 calls, and the wildcard characters are expanded by the startup code of
1646 the program, not by the shell.
1648 @code{run} with no arguments uses the same arguments used by the previous
1649 @code{run}, or those set by the @code{set args} command.
1654 Specify the arguments to be used the next time your program is run. If
1655 @code{set args} has no arguments, @code{run} executes your program
1656 with no arguments. Once you have run your program with arguments,
1657 using @code{set args} before the next @code{run} is the only way to run
1658 it again without arguments.
1662 Show the arguments to give your program when it is started.
1666 @section Your program's environment
1668 @cindex environment (of your program)
1669 The @dfn{environment} consists of a set of environment variables and
1670 their values. Environment variables conventionally record such things as
1671 your user name, your home directory, your terminal type, and your search
1672 path for programs to run. Usually you set up environment variables with
1673 the shell and they are inherited by all the other programs you run. When
1674 debugging, it can be useful to try running your program with a modified
1675 environment without having to start @value{GDBN} over again.
1679 @item path @var{directory}
1680 Add @var{directory} to the front of the @code{PATH} environment variable
1681 (the search path for executables) that will be passed to your program.
1682 The value of @code{PATH} used by @value{GDBN} does not change.
1683 You may specify several directory names, separated by whitespace or by a
1684 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1685 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1686 is moved to the front, so it is searched sooner.
1688 You can use the string @samp{$cwd} to refer to whatever is the current
1689 working directory at the time @value{GDBN} searches the path. If you
1690 use @samp{.} instead, it refers to the directory where you executed the
1691 @code{path} command. @value{GDBN} replaces @samp{.} in the
1692 @var{directory} argument (with the current path) before adding
1693 @var{directory} to the search path.
1694 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1695 @c document that, since repeating it would be a no-op.
1699 Display the list of search paths for executables (the @code{PATH}
1700 environment variable).
1702 @kindex show environment
1703 @item show environment @r{[}@var{varname}@r{]}
1704 Print the value of environment variable @var{varname} to be given to
1705 your program when it starts. If you do not supply @var{varname},
1706 print the names and values of all environment variables to be given to
1707 your program. You can abbreviate @code{environment} as @code{env}.
1709 @kindex set environment
1710 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1711 Set environment variable @var{varname} to @var{value}. The value
1712 changes for your program only, not for @value{GDBN} itself. @var{value} may
1713 be any string; the values of environment variables are just strings, and
1714 any interpretation is supplied by your program itself. The @var{value}
1715 parameter is optional; if it is eliminated, the variable is set to a
1717 @c "any string" here does not include leading, trailing
1718 @c blanks. Gnu asks: does anyone care?
1720 For example, this command:
1727 tells the debugged program, when subsequently run, that its user is named
1728 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1729 are not actually required.)
1731 @kindex unset environment
1732 @item unset environment @var{varname}
1733 Remove variable @var{varname} from the environment to be passed to your
1734 program. This is different from @samp{set env @var{varname} =};
1735 @code{unset environment} removes the variable from the environment,
1736 rather than assigning it an empty value.
1739 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1741 by your @code{SHELL} environment variable if it exists (or
1742 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1743 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1744 @file{.bashrc} for BASH---any variables you set in that file affect
1745 your program. You may wish to move setting of environment variables to
1746 files that are only run when you sign on, such as @file{.login} or
1749 @node Working Directory
1750 @section Your program's working directory
1752 @cindex working directory (of your program)
1753 Each time you start your program with @code{run}, it inherits its
1754 working directory from the current working directory of @value{GDBN}.
1755 The @value{GDBN} working directory is initially whatever it inherited
1756 from its parent process (typically the shell), but you can specify a new
1757 working directory in @value{GDBN} with the @code{cd} command.
1759 The @value{GDBN} working directory also serves as a default for the commands
1760 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1765 @item cd @var{directory}
1766 Set the @value{GDBN} working directory to @var{directory}.
1770 Print the @value{GDBN} working directory.
1774 @section Your program's input and output
1779 By default, the program you run under @value{GDBN} does input and output to
1780 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1781 to its own terminal modes to interact with you, but it records the terminal
1782 modes your program was using and switches back to them when you continue
1783 running your program.
1786 @kindex info terminal
1788 Displays information recorded by @value{GDBN} about the terminal modes your
1792 You can redirect your program's input and/or output using shell
1793 redirection with the @code{run} command. For example,
1800 starts your program, diverting its output to the file @file{outfile}.
1803 @cindex controlling terminal
1804 Another way to specify where your program should do input and output is
1805 with the @code{tty} command. This command accepts a file name as
1806 argument, and causes this file to be the default for future @code{run}
1807 commands. It also resets the controlling terminal for the child
1808 process, for future @code{run} commands. For example,
1815 directs that processes started with subsequent @code{run} commands
1816 default to do input and output on the terminal @file{/dev/ttyb} and have
1817 that as their controlling terminal.
1819 An explicit redirection in @code{run} overrides the @code{tty} command's
1820 effect on the input/output device, but not its effect on the controlling
1823 When you use the @code{tty} command or redirect input in the @code{run}
1824 command, only the input @emph{for your program} is affected. The input
1825 for @value{GDBN} still comes from your terminal.
1828 @section Debugging an already-running process
1833 @item attach @var{process-id}
1834 This command attaches to a running process---one that was started
1835 outside @value{GDBN}. (@code{info files} shows your active
1836 targets.) The command takes as argument a process ID. The usual way to
1837 find out the process-id of a Unix process is with the @code{ps} utility,
1838 or with the @samp{jobs -l} shell command.
1840 @code{attach} does not repeat if you press @key{RET} a second time after
1841 executing the command.
1844 To use @code{attach}, your program must be running in an environment
1845 which supports processes; for example, @code{attach} does not work for
1846 programs on bare-board targets that lack an operating system. You must
1847 also have permission to send the process a signal.
1849 When you use @code{attach}, the debugger finds the program running in
1850 the process first by looking in the current working directory, then (if
1851 the program is not found) by using the source file search path
1852 (@pxref{Source Path, ,Specifying source directories}). You can also use
1853 the @code{file} command to load the program. @xref{Files, ,Commands to
1856 The first thing @value{GDBN} does after arranging to debug the specified
1857 process is to stop it. You can examine and modify an attached process
1858 with all the @value{GDBN} commands that are ordinarily available when
1859 you start processes with @code{run}. You can insert breakpoints; you
1860 can step and continue; you can modify storage. If you would rather the
1861 process continue running, you may use the @code{continue} command after
1862 attaching @value{GDBN} to the process.
1867 When you have finished debugging the attached process, you can use the
1868 @code{detach} command to release it from @value{GDBN} control. Detaching
1869 the process continues its execution. After the @code{detach} command,
1870 that process and @value{GDBN} become completely independent once more, and you
1871 are ready to @code{attach} another process or start one with @code{run}.
1872 @code{detach} does not repeat if you press @key{RET} again after
1873 executing the command.
1876 If you exit @value{GDBN} or use the @code{run} command while you have an
1877 attached process, you kill that process. By default, @value{GDBN} asks
1878 for confirmation if you try to do either of these things; you can
1879 control whether or not you need to confirm by using the @code{set
1880 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1884 @section Killing the child process
1889 Kill the child process in which your program is running under @value{GDBN}.
1892 This command is useful if you wish to debug a core dump instead of a
1893 running process. @value{GDBN} ignores any core dump file while your program
1896 On some operating systems, a program cannot be executed outside @value{GDBN}
1897 while you have breakpoints set on it inside @value{GDBN}. You can use the
1898 @code{kill} command in this situation to permit running your program
1899 outside the debugger.
1901 The @code{kill} command is also useful if you wish to recompile and
1902 relink your program, since on many systems it is impossible to modify an
1903 executable file while it is running in a process. In this case, when you
1904 next type @code{run}, @value{GDBN} notices that the file has changed, and
1905 reads the symbol table again (while trying to preserve your current
1906 breakpoint settings).
1909 @section Debugging programs with multiple threads
1911 @cindex threads of execution
1912 @cindex multiple threads
1913 @cindex switching threads
1914 In some operating systems, such as HP-UX and Solaris, a single program
1915 may have more than one @dfn{thread} of execution. The precise semantics
1916 of threads differ from one operating system to another, but in general
1917 the threads of a single program are akin to multiple processes---except
1918 that they share one address space (that is, they can all examine and
1919 modify the same variables). On the other hand, each thread has its own
1920 registers and execution stack, and perhaps private memory.
1922 @value{GDBN} provides these facilities for debugging multi-thread
1926 @item automatic notification of new threads
1927 @item @samp{thread @var{threadno}}, a command to switch among threads
1928 @item @samp{info threads}, a command to inquire about existing threads
1929 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1930 a command to apply a command to a list of threads
1931 @item thread-specific breakpoints
1935 @emph{Warning:} These facilities are not yet available on every
1936 @value{GDBN} configuration where the operating system supports threads.
1937 If your @value{GDBN} does not support threads, these commands have no
1938 effect. For example, a system without thread support shows no output
1939 from @samp{info threads}, and always rejects the @code{thread} command,
1943 (@value{GDBP}) info threads
1944 (@value{GDBP}) thread 1
1945 Thread ID 1 not known. Use the "info threads" command to
1946 see the IDs of currently known threads.
1948 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1949 @c doesn't support threads"?
1952 @cindex focus of debugging
1953 @cindex current thread
1954 The @value{GDBN} thread debugging facility allows you to observe all
1955 threads while your program runs---but whenever @value{GDBN} takes
1956 control, one thread in particular is always the focus of debugging.
1957 This thread is called the @dfn{current thread}. Debugging commands show
1958 program information from the perspective of the current thread.
1960 @cindex @code{New} @var{systag} message
1961 @cindex thread identifier (system)
1962 @c FIXME-implementors!! It would be more helpful if the [New...] message
1963 @c included GDB's numeric thread handle, so you could just go to that
1964 @c thread without first checking `info threads'.
1965 Whenever @value{GDBN} detects a new thread in your program, it displays
1966 the target system's identification for the thread with a message in the
1967 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1968 whose form varies depending on the particular system. For example, on
1969 LynxOS, you might see
1972 [New process 35 thread 27]
1976 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1977 the @var{systag} is simply something like @samp{process 368}, with no
1980 @c FIXME!! (1) Does the [New...] message appear even for the very first
1981 @c thread of a program, or does it only appear for the
1982 @c second---i.e., when it becomes obvious we have a multithread
1984 @c (2) *Is* there necessarily a first thread always? Or do some
1985 @c multithread systems permit starting a program with multiple
1986 @c threads ab initio?
1988 @cindex thread number
1989 @cindex thread identifier (GDB)
1990 For debugging purposes, @value{GDBN} associates its own thread
1991 number---always a single integer---with each thread in your program.
1994 @kindex info threads
1996 Display a summary of all threads currently in your
1997 program. @value{GDBN} displays for each thread (in this order):
2000 @item the thread number assigned by @value{GDBN}
2002 @item the target system's thread identifier (@var{systag})
2004 @item the current stack frame summary for that thread
2008 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2009 indicates the current thread.
2013 @c end table here to get a little more width for example
2016 (@value{GDBP}) info threads
2017 3 process 35 thread 27 0x34e5 in sigpause ()
2018 2 process 35 thread 23 0x34e5 in sigpause ()
2019 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2025 @cindex thread number
2026 @cindex thread identifier (GDB)
2027 For debugging purposes, @value{GDBN} associates its own thread
2028 number---a small integer assigned in thread-creation order---with each
2029 thread in your program.
2031 @cindex @code{New} @var{systag} message, on HP-UX
2032 @cindex thread identifier (system), on HP-UX
2033 @c FIXME-implementors!! It would be more helpful if the [New...] message
2034 @c included GDB's numeric thread handle, so you could just go to that
2035 @c thread without first checking `info threads'.
2036 Whenever @value{GDBN} detects a new thread in your program, it displays
2037 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2038 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2039 whose form varies depending on the particular system. For example, on
2043 [New thread 2 (system thread 26594)]
2047 when @value{GDBN} notices a new thread.
2050 @kindex info threads
2052 Display a summary of all threads currently in your
2053 program. @value{GDBN} displays for each thread (in this order):
2056 @item the thread number assigned by @value{GDBN}
2058 @item the target system's thread identifier (@var{systag})
2060 @item the current stack frame summary for that thread
2064 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2065 indicates the current thread.
2069 @c end table here to get a little more width for example
2072 (@value{GDBP}) info threads
2073 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2075 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2076 from /usr/lib/libc.2
2077 1 system thread 27905 0x7b003498 in _brk () \@*
2078 from /usr/lib/libc.2
2082 @kindex thread @var{threadno}
2083 @item thread @var{threadno}
2084 Make thread number @var{threadno} the current thread. The command
2085 argument @var{threadno} is the internal @value{GDBN} thread number, as
2086 shown in the first field of the @samp{info threads} display.
2087 @value{GDBN} responds by displaying the system identifier of the thread
2088 you selected, and its current stack frame summary:
2091 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2092 (@value{GDBP}) thread 2
2093 [Switching to process 35 thread 23]
2094 0x34e5 in sigpause ()
2098 As with the @samp{[New @dots{}]} message, the form of the text after
2099 @samp{Switching to} depends on your system's conventions for identifying
2102 @kindex thread apply
2103 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2104 The @code{thread apply} command allows you to apply a command to one or
2105 more threads. Specify the numbers of the threads that you want affected
2106 with the command argument @var{threadno}. @var{threadno} is the internal
2107 @value{GDBN} thread number, as shown in the first field of the @samp{info
2108 threads} display. To apply a command to all threads, use
2109 @code{thread apply all} @var{args}.
2112 @cindex automatic thread selection
2113 @cindex switching threads automatically
2114 @cindex threads, automatic switching
2115 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2116 signal, it automatically selects the thread where that breakpoint or
2117 signal happened. @value{GDBN} alerts you to the context switch with a
2118 message of the form @samp{[Switching to @var{systag}]} to identify the
2121 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2122 more information about how @value{GDBN} behaves when you stop and start
2123 programs with multiple threads.
2125 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2126 watchpoints in programs with multiple threads.
2129 @section Debugging programs with multiple processes
2131 @cindex fork, debugging programs which call
2132 @cindex multiple processes
2133 @cindex processes, multiple
2134 On most systems, @value{GDBN} has no special support for debugging
2135 programs which create additional processes using the @code{fork}
2136 function. When a program forks, @value{GDBN} will continue to debug the
2137 parent process and the child process will run unimpeded. If you have
2138 set a breakpoint in any code which the child then executes, the child
2139 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2140 will cause it to terminate.
2142 However, if you want to debug the child process there is a workaround
2143 which isn't too painful. Put a call to @code{sleep} in the code which
2144 the child process executes after the fork. It may be useful to sleep
2145 only if a certain environment variable is set, or a certain file exists,
2146 so that the delay need not occur when you don't want to run @value{GDBN}
2147 on the child. While the child is sleeping, use the @code{ps} program to
2148 get its process ID. Then tell @value{GDBN} (a new invocation of
2149 @value{GDBN} if you are also debugging the parent process) to attach to
2150 the child process (@pxref{Attach}). From that point on you can debug
2151 the child process just like any other process which you attached to.
2153 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2154 debugging programs that create additional processes using the
2155 @code{fork} or @code{vfork} function.
2157 By default, when a program forks, @value{GDBN} will continue to debug
2158 the parent process and the child process will run unimpeded.
2160 If you want to follow the child process instead of the parent process,
2161 use the command @w{@code{set follow-fork-mode}}.
2164 @kindex set follow-fork-mode
2165 @item set follow-fork-mode @var{mode}
2166 Set the debugger response to a program call of @code{fork} or
2167 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2168 process. The @var{mode} can be:
2172 The original process is debugged after a fork. The child process runs
2173 unimpeded. This is the default.
2176 The new process is debugged after a fork. The parent process runs
2180 The debugger will ask for one of the above choices.
2183 @item show follow-fork-mode
2184 Display the current debugger response to a @code{fork} or @code{vfork} call.
2187 If you ask to debug a child process and a @code{vfork} is followed by an
2188 @code{exec}, @value{GDBN} executes the new target up to the first
2189 breakpoint in the new target. If you have a breakpoint set on
2190 @code{main} in your original program, the breakpoint will also be set on
2191 the child process's @code{main}.
2193 When a child process is spawned by @code{vfork}, you cannot debug the
2194 child or parent until an @code{exec} call completes.
2196 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2197 call executes, the new target restarts. To restart the parent process,
2198 use the @code{file} command with the parent executable name as its
2201 You can use the @code{catch} command to make @value{GDBN} stop whenever
2202 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2203 Catchpoints, ,Setting catchpoints}.
2206 @chapter Stopping and Continuing
2208 The principal purposes of using a debugger are so that you can stop your
2209 program before it terminates; or so that, if your program runs into
2210 trouble, you can investigate and find out why.
2212 Inside @value{GDBN}, your program may stop for any of several reasons,
2213 such as a signal, a breakpoint, or reaching a new line after a
2214 @value{GDBN} command such as @code{step}. You may then examine and
2215 change variables, set new breakpoints or remove old ones, and then
2216 continue execution. Usually, the messages shown by @value{GDBN} provide
2217 ample explanation of the status of your program---but you can also
2218 explicitly request this information at any time.
2221 @kindex info program
2223 Display information about the status of your program: whether it is
2224 running or not, what process it is, and why it stopped.
2228 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2229 * Continuing and Stepping:: Resuming execution
2231 * Thread Stops:: Stopping and starting multi-thread programs
2235 @section Breakpoints, watchpoints, and catchpoints
2238 A @dfn{breakpoint} makes your program stop whenever a certain point in
2239 the program is reached. For each breakpoint, you can add conditions to
2240 control in finer detail whether your program stops. You can set
2241 breakpoints with the @code{break} command and its variants (@pxref{Set
2242 Breaks, ,Setting breakpoints}), to specify the place where your program
2243 should stop by line number, function name or exact address in the
2246 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2247 breakpoints in shared libraries before the executable is run. There is
2248 a minor limitation on HP-UX systems: you must wait until the executable
2249 is run in order to set breakpoints in shared library routines that are
2250 not called directly by the program (for example, routines that are
2251 arguments in a @code{pthread_create} call).
2254 @cindex memory tracing
2255 @cindex breakpoint on memory address
2256 @cindex breakpoint on variable modification
2257 A @dfn{watchpoint} is a special breakpoint that stops your program
2258 when the value of an expression changes. You must use a different
2259 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2260 watchpoints}), but aside from that, you can manage a watchpoint like
2261 any other breakpoint: you enable, disable, and delete both breakpoints
2262 and watchpoints using the same commands.
2264 You can arrange to have values from your program displayed automatically
2265 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2269 @cindex breakpoint on events
2270 A @dfn{catchpoint} is another special breakpoint that stops your program
2271 when a certain kind of event occurs, such as the throwing of a C++
2272 exception or the loading of a library. As with watchpoints, you use a
2273 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2274 catchpoints}), but aside from that, you can manage a catchpoint like any
2275 other breakpoint. (To stop when your program receives a signal, use the
2276 @code{handle} command; see @ref{Signals, ,Signals}.)
2278 @cindex breakpoint numbers
2279 @cindex numbers for breakpoints
2280 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2281 catchpoint when you create it; these numbers are successive integers
2282 starting with one. In many of the commands for controlling various
2283 features of breakpoints you use the breakpoint number to say which
2284 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2285 @dfn{disabled}; if disabled, it has no effect on your program until you
2288 @cindex breakpoint ranges
2289 @cindex ranges of breakpoints
2290 Some @value{GDBN} commands accept a range of breakpoints on which to
2291 operate. A breakpoint range is either a single breakpoint number, like
2292 @samp{5}, or two such numbers, in increasing order, separated by a
2293 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2294 all breakpoint in that range are operated on.
2297 * Set Breaks:: Setting breakpoints
2298 * Set Watchpoints:: Setting watchpoints
2299 * Set Catchpoints:: Setting catchpoints
2300 * Delete Breaks:: Deleting breakpoints
2301 * Disabling:: Disabling breakpoints
2302 * Conditions:: Break conditions
2303 * Break Commands:: Breakpoint command lists
2304 * Breakpoint Menus:: Breakpoint menus
2305 * Error in Breakpoints:: ``Cannot insert breakpoints''
2309 @subsection Setting breakpoints
2311 @c FIXME LMB what does GDB do if no code on line of breakpt?
2312 @c consider in particular declaration with/without initialization.
2314 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2317 @kindex b @r{(@code{break})}
2318 @vindex $bpnum@r{, convenience variable}
2319 @cindex latest breakpoint
2320 Breakpoints are set with the @code{break} command (abbreviated
2321 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2322 number of the breakpoint you've set most recently; see @ref{Convenience
2323 Vars,, Convenience variables}, for a discussion of what you can do with
2324 convenience variables.
2326 You have several ways to say where the breakpoint should go.
2329 @item break @var{function}
2330 Set a breakpoint at entry to function @var{function}.
2331 When using source languages that permit overloading of symbols, such as
2332 C++, @var{function} may refer to more than one possible place to break.
2333 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2335 @item break +@var{offset}
2336 @itemx break -@var{offset}
2337 Set a breakpoint some number of lines forward or back from the position
2338 at which execution stopped in the currently selected @dfn{stack frame}.
2339 (@xref{Frames, ,Frames}, for a description of stack frames.)
2341 @item break @var{linenum}
2342 Set a breakpoint at line @var{linenum} in the current source file.
2343 The current source file is the last file whose source text was printed.
2344 The breakpoint will stop your program just before it executes any of the
2347 @item break @var{filename}:@var{linenum}
2348 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2350 @item break @var{filename}:@var{function}
2351 Set a breakpoint at entry to function @var{function} found in file
2352 @var{filename}. Specifying a file name as well as a function name is
2353 superfluous except when multiple files contain similarly named
2356 @item break *@var{address}
2357 Set a breakpoint at address @var{address}. You can use this to set
2358 breakpoints in parts of your program which do not have debugging
2359 information or source files.
2362 When called without any arguments, @code{break} sets a breakpoint at
2363 the next instruction to be executed in the selected stack frame
2364 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2365 innermost, this makes your program stop as soon as control
2366 returns to that frame. This is similar to the effect of a
2367 @code{finish} command in the frame inside the selected frame---except
2368 that @code{finish} does not leave an active breakpoint. If you use
2369 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2370 the next time it reaches the current location; this may be useful
2373 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2374 least one instruction has been executed. If it did not do this, you
2375 would be unable to proceed past a breakpoint without first disabling the
2376 breakpoint. This rule applies whether or not the breakpoint already
2377 existed when your program stopped.
2379 @item break @dots{} if @var{cond}
2380 Set a breakpoint with condition @var{cond}; evaluate the expression
2381 @var{cond} each time the breakpoint is reached, and stop only if the
2382 value is nonzero---that is, if @var{cond} evaluates as true.
2383 @samp{@dots{}} stands for one of the possible arguments described
2384 above (or no argument) specifying where to break. @xref{Conditions,
2385 ,Break conditions}, for more information on breakpoint conditions.
2388 @item tbreak @var{args}
2389 Set a breakpoint enabled only for one stop. @var{args} are the
2390 same as for the @code{break} command, and the breakpoint is set in the same
2391 way, but the breakpoint is automatically deleted after the first time your
2392 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2395 @item hbreak @var{args}
2396 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2397 @code{break} command and the breakpoint is set in the same way, but the
2398 breakpoint requires hardware support and some target hardware may not
2399 have this support. The main purpose of this is EPROM/ROM code
2400 debugging, so you can set a breakpoint at an instruction without
2401 changing the instruction. This can be used with the new trap-generation
2402 provided by SPARClite DSU and some x86-based targets. These targets
2403 will generate traps when a program accesses some data or instruction
2404 address that is assigned to the debug registers. However the hardware
2405 breakpoint registers can take a limited number of breakpoints. For
2406 example, on the DSU, only two data breakpoints can be set at a time, and
2407 @value{GDBN} will reject this command if more than two are used. Delete
2408 or disable unused hardware breakpoints before setting new ones
2409 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2412 @item thbreak @var{args}
2413 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2414 are the same as for the @code{hbreak} command and the breakpoint is set in
2415 the same way. However, like the @code{tbreak} command,
2416 the breakpoint is automatically deleted after the
2417 first time your program stops there. Also, like the @code{hbreak}
2418 command, the breakpoint requires hardware support and some target hardware
2419 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2420 See also @ref{Conditions, ,Break conditions}.
2423 @cindex regular expression
2424 @item rbreak @var{regex}
2425 Set breakpoints on all functions matching the regular expression
2426 @var{regex}. This command sets an unconditional breakpoint on all
2427 matches, printing a list of all breakpoints it set. Once these
2428 breakpoints are set, they are treated just like the breakpoints set with
2429 the @code{break} command. You can delete them, disable them, or make
2430 them conditional the same way as any other breakpoint.
2432 The syntax of the regular expression is the standard one used with tools
2433 like @file{grep}. Note that this is different from the syntax used by
2434 shells, so for instance @code{foo*} matches all functions that include
2435 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2436 @code{.*} leading and trailing the regular expression you supply, so to
2437 match only functions that begin with @code{foo}, use @code{^foo}.
2439 When debugging C++ programs, @code{rbreak} is useful for setting
2440 breakpoints on overloaded functions that are not members of any special
2443 @kindex info breakpoints
2444 @cindex @code{$_} and @code{info breakpoints}
2445 @item info breakpoints @r{[}@var{n}@r{]}
2446 @itemx info break @r{[}@var{n}@r{]}
2447 @itemx info watchpoints @r{[}@var{n}@r{]}
2448 Print a table of all breakpoints, watchpoints, and catchpoints set and
2449 not deleted, with the following columns for each breakpoint:
2452 @item Breakpoint Numbers
2454 Breakpoint, watchpoint, or catchpoint.
2456 Whether the breakpoint is marked to be disabled or deleted when hit.
2457 @item Enabled or Disabled
2458 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2459 that are not enabled.
2461 Where the breakpoint is in your program, as a memory address.
2463 Where the breakpoint is in the source for your program, as a file and
2468 If a breakpoint is conditional, @code{info break} shows the condition on
2469 the line following the affected breakpoint; breakpoint commands, if any,
2470 are listed after that.
2473 @code{info break} with a breakpoint
2474 number @var{n} as argument lists only that breakpoint. The
2475 convenience variable @code{$_} and the default examining-address for
2476 the @code{x} command are set to the address of the last breakpoint
2477 listed (@pxref{Memory, ,Examining memory}).
2480 @code{info break} displays a count of the number of times the breakpoint
2481 has been hit. This is especially useful in conjunction with the
2482 @code{ignore} command. You can ignore a large number of breakpoint
2483 hits, look at the breakpoint info to see how many times the breakpoint
2484 was hit, and then run again, ignoring one less than that number. This
2485 will get you quickly to the last hit of that breakpoint.
2488 @value{GDBN} allows you to set any number of breakpoints at the same place in
2489 your program. There is nothing silly or meaningless about this. When
2490 the breakpoints are conditional, this is even useful
2491 (@pxref{Conditions, ,Break conditions}).
2493 @cindex negative breakpoint numbers
2494 @cindex internal @value{GDBN} breakpoints
2495 @value{GDBN} itself sometimes sets breakpoints in your program for special
2496 purposes, such as proper handling of @code{longjmp} (in C programs).
2497 These internal breakpoints are assigned negative numbers, starting with
2498 @code{-1}; @samp{info breakpoints} does not display them.
2500 You can see these breakpoints with the @value{GDBN} maintenance command
2501 @samp{maint info breakpoints}.
2504 @kindex maint info breakpoints
2505 @item maint info breakpoints
2506 Using the same format as @samp{info breakpoints}, display both the
2507 breakpoints you've set explicitly, and those @value{GDBN} is using for
2508 internal purposes. Internal breakpoints are shown with negative
2509 breakpoint numbers. The type column identifies what kind of breakpoint
2514 Normal, explicitly set breakpoint.
2517 Normal, explicitly set watchpoint.
2520 Internal breakpoint, used to handle correctly stepping through
2521 @code{longjmp} calls.
2523 @item longjmp resume
2524 Internal breakpoint at the target of a @code{longjmp}.
2527 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2530 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2533 Shared library events.
2540 @node Set Watchpoints
2541 @subsection Setting watchpoints
2543 @cindex setting watchpoints
2544 @cindex software watchpoints
2545 @cindex hardware watchpoints
2546 You can use a watchpoint to stop execution whenever the value of an
2547 expression changes, without having to predict a particular place where
2550 Depending on your system, watchpoints may be implemented in software or
2551 hardware. @value{GDBN} does software watchpointing by single-stepping your
2552 program and testing the variable's value each time, which is hundreds of
2553 times slower than normal execution. (But this may still be worth it, to
2554 catch errors where you have no clue what part of your program is the
2557 On some systems, such as HP-UX, Linux and some other x86-based targets,
2558 @value{GDBN} includes support for
2559 hardware watchpoints, which do not slow down the running of your
2564 @item watch @var{expr}
2565 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2566 is written into by the program and its value changes.
2569 @item rwatch @var{expr}
2570 Set a watchpoint that will break when watch @var{expr} is read by the program.
2573 @item awatch @var{expr}
2574 Set a watchpoint that will break when @var{expr} is either read or written into
2577 @kindex info watchpoints
2578 @item info watchpoints
2579 This command prints a list of watchpoints, breakpoints, and catchpoints;
2580 it is the same as @code{info break}.
2583 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2584 watchpoints execute very quickly, and the debugger reports a change in
2585 value at the exact instruction where the change occurs. If @value{GDBN}
2586 cannot set a hardware watchpoint, it sets a software watchpoint, which
2587 executes more slowly and reports the change in value at the next
2588 statement, not the instruction, after the change occurs.
2590 When you issue the @code{watch} command, @value{GDBN} reports
2593 Hardware watchpoint @var{num}: @var{expr}
2597 if it was able to set a hardware watchpoint.
2599 Currently, the @code{awatch} and @code{rwatch} commands can only set
2600 hardware watchpoints, because accesses to data that don't change the
2601 value of the watched expression cannot be detected without examining
2602 every instruction as it is being executed, and @value{GDBN} does not do
2603 that currently. If @value{GDBN} finds that it is unable to set a
2604 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2605 will print a message like this:
2608 Expression cannot be implemented with read/access watchpoint.
2611 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2612 data type of the watched expression is wider than what a hardware
2613 watchpoint on the target machine can handle. For example, some systems
2614 can only watch regions that are up to 4 bytes wide; on such systems you
2615 cannot set hardware watchpoints for an expression that yields a
2616 double-precision floating-point number (which is typically 8 bytes
2617 wide). As a work-around, it might be possible to break the large region
2618 into a series of smaller ones and watch them with separate watchpoints.
2620 If you set too many hardware watchpoints, @value{GDBN} might be unable
2621 to insert all of them when you resume the execution of your program.
2622 Since the precise number of active watchpoints is unknown until such
2623 time as the program is about to be resumed, @value{GDBN} might not be
2624 able to warn you about this when you set the watchpoints, and the
2625 warning will be printed only when the program is resumed:
2628 Hardware watchpoint @var{num}: Could not insert watchpoint
2632 If this happens, delete or disable some of the watchpoints.
2634 The SPARClite DSU will generate traps when a program accesses some data
2635 or instruction address that is assigned to the debug registers. For the
2636 data addresses, DSU facilitates the @code{watch} command. However the
2637 hardware breakpoint registers can only take two data watchpoints, and
2638 both watchpoints must be the same kind. For example, you can set two
2639 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2640 @strong{or} two with @code{awatch} commands, but you cannot set one
2641 watchpoint with one command and the other with a different command.
2642 @value{GDBN} will reject the command if you try to mix watchpoints.
2643 Delete or disable unused watchpoint commands before setting new ones.
2645 If you call a function interactively using @code{print} or @code{call},
2646 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2647 kind of breakpoint or the call completes.
2649 @value{GDBN} automatically deletes watchpoints that watch local
2650 (automatic) variables, or expressions that involve such variables, when
2651 they go out of scope, that is, when the execution leaves the block in
2652 which these variables were defined. In particular, when the program
2653 being debugged terminates, @emph{all} local variables go out of scope,
2654 and so only watchpoints that watch global variables remain set. If you
2655 rerun the program, you will need to set all such watchpoints again. One
2656 way of doing that would be to set a code breakpoint at the entry to the
2657 @code{main} function and when it breaks, set all the watchpoints.
2660 @cindex watchpoints and threads
2661 @cindex threads and watchpoints
2662 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2663 usefulness. With the current watchpoint implementation, @value{GDBN}
2664 can only watch the value of an expression @emph{in a single thread}. If
2665 you are confident that the expression can only change due to the current
2666 thread's activity (and if you are also confident that no other thread
2667 can become current), then you can use watchpoints as usual. However,
2668 @value{GDBN} may not notice when a non-current thread's activity changes
2671 @c FIXME: this is almost identical to the previous paragraph.
2672 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2673 have only limited usefulness. If @value{GDBN} creates a software
2674 watchpoint, it can only watch the value of an expression @emph{in a
2675 single thread}. If you are confident that the expression can only
2676 change due to the current thread's activity (and if you are also
2677 confident that no other thread can become current), then you can use
2678 software watchpoints as usual. However, @value{GDBN} may not notice
2679 when a non-current thread's activity changes the expression. (Hardware
2680 watchpoints, in contrast, watch an expression in all threads.)
2683 @node Set Catchpoints
2684 @subsection Setting catchpoints
2685 @cindex catchpoints, setting
2686 @cindex exception handlers
2687 @cindex event handling
2689 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2690 kinds of program events, such as C++ exceptions or the loading of a
2691 shared library. Use the @code{catch} command to set a catchpoint.
2695 @item catch @var{event}
2696 Stop when @var{event} occurs. @var{event} can be any of the following:
2700 The throwing of a C++ exception.
2704 The catching of a C++ exception.
2708 A call to @code{exec}. This is currently only available for HP-UX.
2712 A call to @code{fork}. This is currently only available for HP-UX.
2716 A call to @code{vfork}. This is currently only available for HP-UX.
2719 @itemx load @var{libname}
2721 The dynamic loading of any shared library, or the loading of the library
2722 @var{libname}. This is currently only available for HP-UX.
2725 @itemx unload @var{libname}
2726 @kindex catch unload
2727 The unloading of any dynamically loaded shared library, or the unloading
2728 of the library @var{libname}. This is currently only available for HP-UX.
2731 @item tcatch @var{event}
2732 Set a catchpoint that is enabled only for one stop. The catchpoint is
2733 automatically deleted after the first time the event is caught.
2737 Use the @code{info break} command to list the current catchpoints.
2739 There are currently some limitations to C++ exception handling
2740 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2744 If you call a function interactively, @value{GDBN} normally returns
2745 control to you when the function has finished executing. If the call
2746 raises an exception, however, the call may bypass the mechanism that
2747 returns control to you and cause your program either to abort or to
2748 simply continue running until it hits a breakpoint, catches a signal
2749 that @value{GDBN} is listening for, or exits. This is the case even if
2750 you set a catchpoint for the exception; catchpoints on exceptions are
2751 disabled within interactive calls.
2754 You cannot raise an exception interactively.
2757 You cannot install an exception handler interactively.
2760 @cindex raise exceptions
2761 Sometimes @code{catch} is not the best way to debug exception handling:
2762 if you need to know exactly where an exception is raised, it is better to
2763 stop @emph{before} the exception handler is called, since that way you
2764 can see the stack before any unwinding takes place. If you set a
2765 breakpoint in an exception handler instead, it may not be easy to find
2766 out where the exception was raised.
2768 To stop just before an exception handler is called, you need some
2769 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2770 raised by calling a library function named @code{__raise_exception}
2771 which has the following ANSI C interface:
2774 /* @var{addr} is where the exception identifier is stored.
2775 @var{id} is the exception identifier. */
2776 void __raise_exception (void **addr, void *id);
2780 To make the debugger catch all exceptions before any stack
2781 unwinding takes place, set a breakpoint on @code{__raise_exception}
2782 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2784 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2785 that depends on the value of @var{id}, you can stop your program when
2786 a specific exception is raised. You can use multiple conditional
2787 breakpoints to stop your program when any of a number of exceptions are
2792 @subsection Deleting breakpoints
2794 @cindex clearing breakpoints, watchpoints, catchpoints
2795 @cindex deleting breakpoints, watchpoints, catchpoints
2796 It is often necessary to eliminate a breakpoint, watchpoint, or
2797 catchpoint once it has done its job and you no longer want your program
2798 to stop there. This is called @dfn{deleting} the breakpoint. A
2799 breakpoint that has been deleted no longer exists; it is forgotten.
2801 With the @code{clear} command you can delete breakpoints according to
2802 where they are in your program. With the @code{delete} command you can
2803 delete individual breakpoints, watchpoints, or catchpoints by specifying
2804 their breakpoint numbers.
2806 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2807 automatically ignores breakpoints on the first instruction to be executed
2808 when you continue execution without changing the execution address.
2813 Delete any breakpoints at the next instruction to be executed in the
2814 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2815 the innermost frame is selected, this is a good way to delete a
2816 breakpoint where your program just stopped.
2818 @item clear @var{function}
2819 @itemx clear @var{filename}:@var{function}
2820 Delete any breakpoints set at entry to the function @var{function}.
2822 @item clear @var{linenum}
2823 @itemx clear @var{filename}:@var{linenum}
2824 Delete any breakpoints set at or within the code of the specified line.
2826 @cindex delete breakpoints
2828 @kindex d @r{(@code{delete})}
2829 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2830 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2831 ranges specified as arguments. If no argument is specified, delete all
2832 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2833 confirm off}). You can abbreviate this command as @code{d}.
2837 @subsection Disabling breakpoints
2839 @kindex disable breakpoints
2840 @kindex enable breakpoints
2841 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2842 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2843 it had been deleted, but remembers the information on the breakpoint so
2844 that you can @dfn{enable} it again later.
2846 You disable and enable breakpoints, watchpoints, and catchpoints with
2847 the @code{enable} and @code{disable} commands, optionally specifying one
2848 or more breakpoint numbers as arguments. Use @code{info break} or
2849 @code{info watch} to print a list of breakpoints, watchpoints, and
2850 catchpoints if you do not know which numbers to use.
2852 A breakpoint, watchpoint, or catchpoint can have any of four different
2853 states of enablement:
2857 Enabled. The breakpoint stops your program. A breakpoint set
2858 with the @code{break} command starts out in this state.
2860 Disabled. The breakpoint has no effect on your program.
2862 Enabled once. The breakpoint stops your program, but then becomes
2865 Enabled for deletion. The breakpoint stops your program, but
2866 immediately after it does so it is deleted permanently. A breakpoint
2867 set with the @code{tbreak} command starts out in this state.
2870 You can use the following commands to enable or disable breakpoints,
2871 watchpoints, and catchpoints:
2874 @kindex disable breakpoints
2876 @kindex dis @r{(@code{disable})}
2877 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2878 Disable the specified breakpoints---or all breakpoints, if none are
2879 listed. A disabled breakpoint has no effect but is not forgotten. All
2880 options such as ignore-counts, conditions and commands are remembered in
2881 case the breakpoint is enabled again later. You may abbreviate
2882 @code{disable} as @code{dis}.
2884 @kindex enable breakpoints
2886 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2887 Enable the specified breakpoints (or all defined breakpoints). They
2888 become effective once again in stopping your program.
2890 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2891 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2892 of these breakpoints immediately after stopping your program.
2894 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2895 Enable the specified breakpoints to work once, then die. @value{GDBN}
2896 deletes any of these breakpoints as soon as your program stops there.
2899 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2900 @c confusing: tbreak is also initially enabled.
2901 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2902 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2903 subsequently, they become disabled or enabled only when you use one of
2904 the commands above. (The command @code{until} can set and delete a
2905 breakpoint of its own, but it does not change the state of your other
2906 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2910 @subsection Break conditions
2911 @cindex conditional breakpoints
2912 @cindex breakpoint conditions
2914 @c FIXME what is scope of break condition expr? Context where wanted?
2915 @c in particular for a watchpoint?
2916 The simplest sort of breakpoint breaks every time your program reaches a
2917 specified place. You can also specify a @dfn{condition} for a
2918 breakpoint. A condition is just a Boolean expression in your
2919 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2920 a condition evaluates the expression each time your program reaches it,
2921 and your program stops only if the condition is @emph{true}.
2923 This is the converse of using assertions for program validation; in that
2924 situation, you want to stop when the assertion is violated---that is,
2925 when the condition is false. In C, if you want to test an assertion expressed
2926 by the condition @var{assert}, you should set the condition
2927 @samp{! @var{assert}} on the appropriate breakpoint.
2929 Conditions are also accepted for watchpoints; you may not need them,
2930 since a watchpoint is inspecting the value of an expression anyhow---but
2931 it might be simpler, say, to just set a watchpoint on a variable name,
2932 and specify a condition that tests whether the new value is an interesting
2935 Break conditions can have side effects, and may even call functions in
2936 your program. This can be useful, for example, to activate functions
2937 that log program progress, or to use your own print functions to
2938 format special data structures. The effects are completely predictable
2939 unless there is another enabled breakpoint at the same address. (In
2940 that case, @value{GDBN} might see the other breakpoint first and stop your
2941 program without checking the condition of this one.) Note that
2942 breakpoint commands are usually more convenient and flexible than break
2944 purpose of performing side effects when a breakpoint is reached
2945 (@pxref{Break Commands, ,Breakpoint command lists}).
2947 Break conditions can be specified when a breakpoint is set, by using
2948 @samp{if} in the arguments to the @code{break} command. @xref{Set
2949 Breaks, ,Setting breakpoints}. They can also be changed at any time
2950 with the @code{condition} command.
2952 You can also use the @code{if} keyword with the @code{watch} command.
2953 The @code{catch} command does not recognize the @code{if} keyword;
2954 @code{condition} is the only way to impose a further condition on a
2959 @item condition @var{bnum} @var{expression}
2960 Specify @var{expression} as the break condition for breakpoint,
2961 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2962 breakpoint @var{bnum} stops your program only if the value of
2963 @var{expression} is true (nonzero, in C). When you use
2964 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2965 syntactic correctness, and to determine whether symbols in it have
2966 referents in the context of your breakpoint. If @var{expression} uses
2967 symbols not referenced in the context of the breakpoint, @value{GDBN}
2968 prints an error message:
2971 No symbol "foo" in current context.
2976 not actually evaluate @var{expression} at the time the @code{condition}
2977 command (or a command that sets a breakpoint with a condition, like
2978 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2980 @item condition @var{bnum}
2981 Remove the condition from breakpoint number @var{bnum}. It becomes
2982 an ordinary unconditional breakpoint.
2985 @cindex ignore count (of breakpoint)
2986 A special case of a breakpoint condition is to stop only when the
2987 breakpoint has been reached a certain number of times. This is so
2988 useful that there is a special way to do it, using the @dfn{ignore
2989 count} of the breakpoint. Every breakpoint has an ignore count, which
2990 is an integer. Most of the time, the ignore count is zero, and
2991 therefore has no effect. But if your program reaches a breakpoint whose
2992 ignore count is positive, then instead of stopping, it just decrements
2993 the ignore count by one and continues. As a result, if the ignore count
2994 value is @var{n}, the breakpoint does not stop the next @var{n} times
2995 your program reaches it.
2999 @item ignore @var{bnum} @var{count}
3000 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3001 The next @var{count} times the breakpoint is reached, your program's
3002 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3005 To make the breakpoint stop the next time it is reached, specify
3008 When you use @code{continue} to resume execution of your program from a
3009 breakpoint, you can specify an ignore count directly as an argument to
3010 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3011 Stepping,,Continuing and stepping}.
3013 If a breakpoint has a positive ignore count and a condition, the
3014 condition is not checked. Once the ignore count reaches zero,
3015 @value{GDBN} resumes checking the condition.
3017 You could achieve the effect of the ignore count with a condition such
3018 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3019 is decremented each time. @xref{Convenience Vars, ,Convenience
3023 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3026 @node Break Commands
3027 @subsection Breakpoint command lists
3029 @cindex breakpoint commands
3030 You can give any breakpoint (or watchpoint or catchpoint) a series of
3031 commands to execute when your program stops due to that breakpoint. For
3032 example, you might want to print the values of certain expressions, or
3033 enable other breakpoints.
3038 @item commands @r{[}@var{bnum}@r{]}
3039 @itemx @dots{} @var{command-list} @dots{}
3041 Specify a list of commands for breakpoint number @var{bnum}. The commands
3042 themselves appear on the following lines. Type a line containing just
3043 @code{end} to terminate the commands.
3045 To remove all commands from a breakpoint, type @code{commands} and
3046 follow it immediately with @code{end}; that is, give no commands.
3048 With no @var{bnum} argument, @code{commands} refers to the last
3049 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3050 recently encountered).
3053 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3054 disabled within a @var{command-list}.
3056 You can use breakpoint commands to start your program up again. Simply
3057 use the @code{continue} command, or @code{step}, or any other command
3058 that resumes execution.
3060 Any other commands in the command list, after a command that resumes
3061 execution, are ignored. This is because any time you resume execution
3062 (even with a simple @code{next} or @code{step}), you may encounter
3063 another breakpoint---which could have its own command list, leading to
3064 ambiguities about which list to execute.
3067 If the first command you specify in a command list is @code{silent}, the
3068 usual message about stopping at a breakpoint is not printed. This may
3069 be desirable for breakpoints that are to print a specific message and
3070 then continue. If none of the remaining commands print anything, you
3071 see no sign that the breakpoint was reached. @code{silent} is
3072 meaningful only at the beginning of a breakpoint command list.
3074 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3075 print precisely controlled output, and are often useful in silent
3076 breakpoints. @xref{Output, ,Commands for controlled output}.
3078 For example, here is how you could use breakpoint commands to print the
3079 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3085 printf "x is %d\n",x
3090 One application for breakpoint commands is to compensate for one bug so
3091 you can test for another. Put a breakpoint just after the erroneous line
3092 of code, give it a condition to detect the case in which something
3093 erroneous has been done, and give it commands to assign correct values
3094 to any variables that need them. End with the @code{continue} command
3095 so that your program does not stop, and start with the @code{silent}
3096 command so that no output is produced. Here is an example:
3107 @node Breakpoint Menus
3108 @subsection Breakpoint menus
3110 @cindex symbol overloading
3112 Some programming languages (notably C++) permit a single function name
3113 to be defined several times, for application in different contexts.
3114 This is called @dfn{overloading}. When a function name is overloaded,
3115 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3116 a breakpoint. If you realize this is a problem, you can use
3117 something like @samp{break @var{function}(@var{types})} to specify which
3118 particular version of the function you want. Otherwise, @value{GDBN} offers
3119 you a menu of numbered choices for different possible breakpoints, and
3120 waits for your selection with the prompt @samp{>}. The first two
3121 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3122 sets a breakpoint at each definition of @var{function}, and typing
3123 @kbd{0} aborts the @code{break} command without setting any new
3126 For example, the following session excerpt shows an attempt to set a
3127 breakpoint at the overloaded symbol @code{String::after}.
3128 We choose three particular definitions of that function name:
3130 @c FIXME! This is likely to change to show arg type lists, at least
3133 (@value{GDBP}) b String::after
3136 [2] file:String.cc; line number:867
3137 [3] file:String.cc; line number:860
3138 [4] file:String.cc; line number:875
3139 [5] file:String.cc; line number:853
3140 [6] file:String.cc; line number:846
3141 [7] file:String.cc; line number:735
3143 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3144 Breakpoint 2 at 0xb344: file String.cc, line 875.
3145 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3146 Multiple breakpoints were set.
3147 Use the "delete" command to delete unwanted
3153 @c @ifclear BARETARGET
3154 @node Error in Breakpoints
3155 @subsection ``Cannot insert breakpoints''
3157 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3159 Under some operating systems, breakpoints cannot be used in a program if
3160 any other process is running that program. In this situation,
3161 attempting to run or continue a program with a breakpoint causes
3162 @value{GDBN} to print an error message:
3165 Cannot insert breakpoints.
3166 The same program may be running in another process.
3169 When this happens, you have three ways to proceed:
3173 Remove or disable the breakpoints, then continue.
3176 Suspend @value{GDBN}, and copy the file containing your program to a new
3177 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3178 that @value{GDBN} should run your program under that name.
3179 Then start your program again.
3182 Relink your program so that the text segment is nonsharable, using the
3183 linker option @samp{-N}. The operating system limitation may not apply
3184 to nonsharable executables.
3188 A similar message can be printed if you request too many active
3189 hardware-assisted breakpoints and watchpoints:
3191 @c FIXME: the precise wording of this message may change; the relevant
3192 @c source change is not committed yet (Sep 3, 1999).
3194 Stopped; cannot insert breakpoints.
3195 You may have requested too many hardware breakpoints and watchpoints.
3199 This message is printed when you attempt to resume the program, since
3200 only then @value{GDBN} knows exactly how many hardware breakpoints and
3201 watchpoints it needs to insert.
3203 When this message is printed, you need to disable or remove some of the
3204 hardware-assisted breakpoints and watchpoints, and then continue.
3207 @node Continuing and Stepping
3208 @section Continuing and stepping
3212 @cindex resuming execution
3213 @dfn{Continuing} means resuming program execution until your program
3214 completes normally. In contrast, @dfn{stepping} means executing just
3215 one more ``step'' of your program, where ``step'' may mean either one
3216 line of source code, or one machine instruction (depending on what
3217 particular command you use). Either when continuing or when stepping,
3218 your program may stop even sooner, due to a breakpoint or a signal. (If
3219 it stops due to a signal, you may want to use @code{handle}, or use
3220 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3224 @kindex c @r{(@code{continue})}
3225 @kindex fg @r{(resume foreground execution)}
3226 @item continue @r{[}@var{ignore-count}@r{]}
3227 @itemx c @r{[}@var{ignore-count}@r{]}
3228 @itemx fg @r{[}@var{ignore-count}@r{]}
3229 Resume program execution, at the address where your program last stopped;
3230 any breakpoints set at that address are bypassed. The optional argument
3231 @var{ignore-count} allows you to specify a further number of times to
3232 ignore a breakpoint at this location; its effect is like that of
3233 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3235 The argument @var{ignore-count} is meaningful only when your program
3236 stopped due to a breakpoint. At other times, the argument to
3237 @code{continue} is ignored.
3239 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3240 debugged program is deemed to be the foreground program) are provided
3241 purely for convenience, and have exactly the same behavior as
3245 To resume execution at a different place, you can use @code{return}
3246 (@pxref{Returning, ,Returning from a function}) to go back to the
3247 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3248 different address}) to go to an arbitrary location in your program.
3250 A typical technique for using stepping is to set a breakpoint
3251 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3252 beginning of the function or the section of your program where a problem
3253 is believed to lie, run your program until it stops at that breakpoint,
3254 and then step through the suspect area, examining the variables that are
3255 interesting, until you see the problem happen.
3259 @kindex s @r{(@code{step})}
3261 Continue running your program until control reaches a different source
3262 line, then stop it and return control to @value{GDBN}. This command is
3263 abbreviated @code{s}.
3266 @c "without debugging information" is imprecise; actually "without line
3267 @c numbers in the debugging information". (gcc -g1 has debugging info but
3268 @c not line numbers). But it seems complex to try to make that
3269 @c distinction here.
3270 @emph{Warning:} If you use the @code{step} command while control is
3271 within a function that was compiled without debugging information,
3272 execution proceeds until control reaches a function that does have
3273 debugging information. Likewise, it will not step into a function which
3274 is compiled without debugging information. To step through functions
3275 without debugging information, use the @code{stepi} command, described
3279 The @code{step} command only stops at the first instruction of a source
3280 line. This prevents the multiple stops that could otherwise occur in
3281 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3282 to stop if a function that has debugging information is called within
3283 the line. In other words, @code{step} @emph{steps inside} any functions
3284 called within the line.
3286 Also, the @code{step} command only enters a function if there is line
3287 number information for the function. Otherwise it acts like the
3288 @code{next} command. This avoids problems when using @code{cc -gl}
3289 on MIPS machines. Previously, @code{step} entered subroutines if there
3290 was any debugging information about the routine.
3292 @item step @var{count}
3293 Continue running as in @code{step}, but do so @var{count} times. If a
3294 breakpoint is reached, or a signal not related to stepping occurs before
3295 @var{count} steps, stepping stops right away.
3298 @kindex n @r{(@code{next})}
3299 @item next @r{[}@var{count}@r{]}
3300 Continue to the next source line in the current (innermost) stack frame.
3301 This is similar to @code{step}, but function calls that appear within
3302 the line of code are executed without stopping. Execution stops when
3303 control reaches a different line of code at the original stack level
3304 that was executing when you gave the @code{next} command. This command
3305 is abbreviated @code{n}.
3307 An argument @var{count} is a repeat count, as for @code{step}.
3310 @c FIX ME!! Do we delete this, or is there a way it fits in with
3311 @c the following paragraph? --- Vctoria
3313 @c @code{next} within a function that lacks debugging information acts like
3314 @c @code{step}, but any function calls appearing within the code of the
3315 @c function are executed without stopping.
3317 The @code{next} command only stops at the first instruction of a
3318 source line. This prevents multiple stops that could otherwise occur in
3319 @code{switch} statements, @code{for} loops, etc.
3321 @kindex set step-mode
3323 @cindex functions without line info, and stepping
3324 @cindex stepping into functions with no line info
3325 @itemx set step-mode on
3326 The @code{set step-mode on} command causes the @code{step} command to
3327 stop at the first instruction of a function which contains no debug line
3328 information rather than stepping over it.
3330 This is useful in cases where you may be interested in inspecting the
3331 machine instructions of a function which has no symbolic info and do not
3332 want @value{GDBN} to automatically skip over this function.
3334 @item set step-mode off
3335 Causes the @code{step} command to step over any functions which contains no
3336 debug information. This is the default.
3340 Continue running until just after function in the selected stack frame
3341 returns. Print the returned value (if any).
3343 Contrast this with the @code{return} command (@pxref{Returning,
3344 ,Returning from a function}).
3347 @kindex u @r{(@code{until})}
3350 Continue running until a source line past the current line, in the
3351 current stack frame, is reached. This command is used to avoid single
3352 stepping through a loop more than once. It is like the @code{next}
3353 command, except that when @code{until} encounters a jump, it
3354 automatically continues execution until the program counter is greater
3355 than the address of the jump.
3357 This means that when you reach the end of a loop after single stepping
3358 though it, @code{until} makes your program continue execution until it
3359 exits the loop. In contrast, a @code{next} command at the end of a loop
3360 simply steps back to the beginning of the loop, which forces you to step
3361 through the next iteration.
3363 @code{until} always stops your program if it attempts to exit the current
3366 @code{until} may produce somewhat counterintuitive results if the order
3367 of machine code does not match the order of the source lines. For
3368 example, in the following excerpt from a debugging session, the @code{f}
3369 (@code{frame}) command shows that execution is stopped at line
3370 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3374 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3376 (@value{GDBP}) until
3377 195 for ( ; argc > 0; NEXTARG) @{
3380 This happened because, for execution efficiency, the compiler had
3381 generated code for the loop closure test at the end, rather than the
3382 start, of the loop---even though the test in a C @code{for}-loop is
3383 written before the body of the loop. The @code{until} command appeared
3384 to step back to the beginning of the loop when it advanced to this
3385 expression; however, it has not really gone to an earlier
3386 statement---not in terms of the actual machine code.
3388 @code{until} with no argument works by means of single
3389 instruction stepping, and hence is slower than @code{until} with an
3392 @item until @var{location}
3393 @itemx u @var{location}
3394 Continue running your program until either the specified location is
3395 reached, or the current stack frame returns. @var{location} is any of
3396 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3397 ,Setting breakpoints}). This form of the command uses breakpoints,
3398 and hence is quicker than @code{until} without an argument.
3401 @kindex si @r{(@code{stepi})}
3403 @itemx stepi @var{arg}
3405 Execute one machine instruction, then stop and return to the debugger.
3407 It is often useful to do @samp{display/i $pc} when stepping by machine
3408 instructions. This makes @value{GDBN} automatically display the next
3409 instruction to be executed, each time your program stops. @xref{Auto
3410 Display,, Automatic display}.
3412 An argument is a repeat count, as in @code{step}.
3416 @kindex ni @r{(@code{nexti})}
3418 @itemx nexti @var{arg}
3420 Execute one machine instruction, but if it is a function call,
3421 proceed until the function returns.
3423 An argument is a repeat count, as in @code{next}.
3430 A signal is an asynchronous event that can happen in a program. The
3431 operating system defines the possible kinds of signals, and gives each
3432 kind a name and a number. For example, in Unix @code{SIGINT} is the
3433 signal a program gets when you type an interrupt character (often @kbd{C-c});
3434 @code{SIGSEGV} is the signal a program gets from referencing a place in
3435 memory far away from all the areas in use; @code{SIGALRM} occurs when
3436 the alarm clock timer goes off (which happens only if your program has
3437 requested an alarm).
3439 @cindex fatal signals
3440 Some signals, including @code{SIGALRM}, are a normal part of the
3441 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3442 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3443 program has not specified in advance some other way to handle the signal.
3444 @code{SIGINT} does not indicate an error in your program, but it is normally
3445 fatal so it can carry out the purpose of the interrupt: to kill the program.
3447 @value{GDBN} has the ability to detect any occurrence of a signal in your
3448 program. You can tell @value{GDBN} in advance what to do for each kind of
3451 @cindex handling signals
3452 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3453 (so as not to interfere with their role in the functioning of your program)
3454 but to stop your program immediately whenever an error signal happens.
3455 You can change these settings with the @code{handle} command.
3458 @kindex info signals
3461 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3462 handle each one. You can use this to see the signal numbers of all
3463 the defined types of signals.
3465 @code{info handle} is an alias for @code{info signals}.
3468 @item handle @var{signal} @var{keywords}@dots{}
3469 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3470 can be the number of a signal or its name (with or without the
3471 @samp{SIG} at the beginning); a list of signal numberss of the form
3472 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3473 known signals. The @var{keywords} say what change to make.
3477 The keywords allowed by the @code{handle} command can be abbreviated.
3478 Their full names are:
3482 @value{GDBN} should not stop your program when this signal happens. It may
3483 still print a message telling you that the signal has come in.
3486 @value{GDBN} should stop your program when this signal happens. This implies
3487 the @code{print} keyword as well.
3490 @value{GDBN} should print a message when this signal happens.
3493 @value{GDBN} should not mention the occurrence of the signal at all. This
3494 implies the @code{nostop} keyword as well.
3498 @value{GDBN} should allow your program to see this signal; your program
3499 can handle the signal, or else it may terminate if the signal is fatal
3500 and not handled. @code{pass} and @code{noignore} are synonyms.
3504 @value{GDBN} should not allow your program to see this signal.
3505 @code{nopass} and @code{ignore} are synonyms.
3509 When a signal stops your program, the signal is not visible to the
3511 continue. Your program sees the signal then, if @code{pass} is in
3512 effect for the signal in question @emph{at that time}. In other words,
3513 after @value{GDBN} reports a signal, you can use the @code{handle}
3514 command with @code{pass} or @code{nopass} to control whether your
3515 program sees that signal when you continue.
3517 You can also use the @code{signal} command to prevent your program from
3518 seeing a signal, or cause it to see a signal it normally would not see,
3519 or to give it any signal at any time. For example, if your program stopped
3520 due to some sort of memory reference error, you might store correct
3521 values into the erroneous variables and continue, hoping to see more
3522 execution; but your program would probably terminate immediately as
3523 a result of the fatal signal once it saw the signal. To prevent this,
3524 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3528 @section Stopping and starting multi-thread programs
3530 When your program has multiple threads (@pxref{Threads,, Debugging
3531 programs with multiple threads}), you can choose whether to set
3532 breakpoints on all threads, or on a particular thread.
3535 @cindex breakpoints and threads
3536 @cindex thread breakpoints
3537 @kindex break @dots{} thread @var{threadno}
3538 @item break @var{linespec} thread @var{threadno}
3539 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3540 @var{linespec} specifies source lines; there are several ways of
3541 writing them, but the effect is always to specify some source line.
3543 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3544 to specify that you only want @value{GDBN} to stop the program when a
3545 particular thread reaches this breakpoint. @var{threadno} is one of the
3546 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3547 column of the @samp{info threads} display.
3549 If you do not specify @samp{thread @var{threadno}} when you set a
3550 breakpoint, the breakpoint applies to @emph{all} threads of your
3553 You can use the @code{thread} qualifier on conditional breakpoints as
3554 well; in this case, place @samp{thread @var{threadno}} before the
3555 breakpoint condition, like this:
3558 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3563 @cindex stopped threads
3564 @cindex threads, stopped
3565 Whenever your program stops under @value{GDBN} for any reason,
3566 @emph{all} threads of execution stop, not just the current thread. This
3567 allows you to examine the overall state of the program, including
3568 switching between threads, without worrying that things may change
3571 @cindex continuing threads
3572 @cindex threads, continuing
3573 Conversely, whenever you restart the program, @emph{all} threads start
3574 executing. @emph{This is true even when single-stepping} with commands
3575 like @code{step} or @code{next}.
3577 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3578 Since thread scheduling is up to your debugging target's operating
3579 system (not controlled by @value{GDBN}), other threads may
3580 execute more than one statement while the current thread completes a
3581 single step. Moreover, in general other threads stop in the middle of a
3582 statement, rather than at a clean statement boundary, when the program
3585 You might even find your program stopped in another thread after
3586 continuing or even single-stepping. This happens whenever some other
3587 thread runs into a breakpoint, a signal, or an exception before the
3588 first thread completes whatever you requested.
3590 On some OSes, you can lock the OS scheduler and thus allow only a single
3594 @item set scheduler-locking @var{mode}
3595 Set the scheduler locking mode. If it is @code{off}, then there is no
3596 locking and any thread may run at any time. If @code{on}, then only the
3597 current thread may run when the inferior is resumed. The @code{step}
3598 mode optimizes for single-stepping. It stops other threads from
3599 ``seizing the prompt'' by preempting the current thread while you are
3600 stepping. Other threads will only rarely (or never) get a chance to run
3601 when you step. They are more likely to run when you @samp{next} over a
3602 function call, and they are completely free to run when you use commands
3603 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3604 thread hits a breakpoint during its timeslice, they will never steal the
3605 @value{GDBN} prompt away from the thread that you are debugging.
3607 @item show scheduler-locking
3608 Display the current scheduler locking mode.
3613 @chapter Examining the Stack
3615 When your program has stopped, the first thing you need to know is where it
3616 stopped and how it got there.
3619 Each time your program performs a function call, information about the call
3621 That information includes the location of the call in your program,
3622 the arguments of the call,
3623 and the local variables of the function being called.
3624 The information is saved in a block of data called a @dfn{stack frame}.
3625 The stack frames are allocated in a region of memory called the @dfn{call
3628 When your program stops, the @value{GDBN} commands for examining the
3629 stack allow you to see all of this information.
3631 @cindex selected frame
3632 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3633 @value{GDBN} commands refer implicitly to the selected frame. In
3634 particular, whenever you ask @value{GDBN} for the value of a variable in
3635 your program, the value is found in the selected frame. There are
3636 special @value{GDBN} commands to select whichever frame you are
3637 interested in. @xref{Selection, ,Selecting a frame}.
3639 When your program stops, @value{GDBN} automatically selects the
3640 currently executing frame and describes it briefly, similar to the
3641 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3644 * Frames:: Stack frames
3645 * Backtrace:: Backtraces
3646 * Selection:: Selecting a frame
3647 * Frame Info:: Information on a frame
3652 @section Stack frames
3654 @cindex frame, definition
3656 The call stack is divided up into contiguous pieces called @dfn{stack
3657 frames}, or @dfn{frames} for short; each frame is the data associated
3658 with one call to one function. The frame contains the arguments given
3659 to the function, the function's local variables, and the address at
3660 which the function is executing.
3662 @cindex initial frame
3663 @cindex outermost frame
3664 @cindex innermost frame
3665 When your program is started, the stack has only one frame, that of the
3666 function @code{main}. This is called the @dfn{initial} frame or the
3667 @dfn{outermost} frame. Each time a function is called, a new frame is
3668 made. Each time a function returns, the frame for that function invocation
3669 is eliminated. If a function is recursive, there can be many frames for
3670 the same function. The frame for the function in which execution is
3671 actually occurring is called the @dfn{innermost} frame. This is the most
3672 recently created of all the stack frames that still exist.
3674 @cindex frame pointer
3675 Inside your program, stack frames are identified by their addresses. A
3676 stack frame consists of many bytes, each of which has its own address; each
3677 kind of computer has a convention for choosing one byte whose
3678 address serves as the address of the frame. Usually this address is kept
3679 in a register called the @dfn{frame pointer register} while execution is
3680 going on in that frame.
3682 @cindex frame number
3683 @value{GDBN} assigns numbers to all existing stack frames, starting with
3684 zero for the innermost frame, one for the frame that called it,
3685 and so on upward. These numbers do not really exist in your program;
3686 they are assigned by @value{GDBN} to give you a way of designating stack
3687 frames in @value{GDBN} commands.
3689 @c The -fomit-frame-pointer below perennially causes hbox overflow
3690 @c underflow problems.
3691 @cindex frameless execution
3692 Some compilers provide a way to compile functions so that they operate
3693 without stack frames. (For example, the @value{GCC} option
3695 @samp{-fomit-frame-pointer}
3697 generates functions without a frame.)
3698 This is occasionally done with heavily used library functions to save
3699 the frame setup time. @value{GDBN} has limited facilities for dealing
3700 with these function invocations. If the innermost function invocation
3701 has no stack frame, @value{GDBN} nevertheless regards it as though
3702 it had a separate frame, which is numbered zero as usual, allowing
3703 correct tracing of the function call chain. However, @value{GDBN} has
3704 no provision for frameless functions elsewhere in the stack.
3707 @kindex frame@r{, command}
3708 @cindex current stack frame
3709 @item frame @var{args}
3710 The @code{frame} command allows you to move from one stack frame to another,
3711 and to print the stack frame you select. @var{args} may be either the
3712 address of the frame or the stack frame number. Without an argument,
3713 @code{frame} prints the current stack frame.
3715 @kindex select-frame
3716 @cindex selecting frame silently
3718 The @code{select-frame} command allows you to move from one stack frame
3719 to another without printing the frame. This is the silent version of
3728 @cindex stack traces
3729 A backtrace is a summary of how your program got where it is. It shows one
3730 line per frame, for many frames, starting with the currently executing
3731 frame (frame zero), followed by its caller (frame one), and on up the
3736 @kindex bt @r{(@code{backtrace})}
3739 Print a backtrace of the entire stack: one line per frame for all
3740 frames in the stack.
3742 You can stop the backtrace at any time by typing the system interrupt
3743 character, normally @kbd{C-c}.
3745 @item backtrace @var{n}
3747 Similar, but print only the innermost @var{n} frames.
3749 @item backtrace -@var{n}
3751 Similar, but print only the outermost @var{n} frames.
3756 @kindex info s @r{(@code{info stack})}
3757 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3758 are additional aliases for @code{backtrace}.
3760 Each line in the backtrace shows the frame number and the function name.
3761 The program counter value is also shown---unless you use @code{set
3762 print address off}. The backtrace also shows the source file name and
3763 line number, as well as the arguments to the function. The program
3764 counter value is omitted if it is at the beginning of the code for that
3767 Here is an example of a backtrace. It was made with the command
3768 @samp{bt 3}, so it shows the innermost three frames.
3772 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3774 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3775 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3777 (More stack frames follow...)
3782 The display for frame zero does not begin with a program counter
3783 value, indicating that your program has stopped at the beginning of the
3784 code for line @code{993} of @code{builtin.c}.
3787 @section Selecting a frame
3789 Most commands for examining the stack and other data in your program work on
3790 whichever stack frame is selected at the moment. Here are the commands for
3791 selecting a stack frame; all of them finish by printing a brief description
3792 of the stack frame just selected.
3795 @kindex frame@r{, selecting}
3796 @kindex f @r{(@code{frame})}
3799 Select frame number @var{n}. Recall that frame zero is the innermost
3800 (currently executing) frame, frame one is the frame that called the
3801 innermost one, and so on. The highest-numbered frame is the one for
3804 @item frame @var{addr}
3806 Select the frame at address @var{addr}. This is useful mainly if the
3807 chaining of stack frames has been damaged by a bug, making it
3808 impossible for @value{GDBN} to assign numbers properly to all frames. In
3809 addition, this can be useful when your program has multiple stacks and
3810 switches between them.
3812 On the SPARC architecture, @code{frame} needs two addresses to
3813 select an arbitrary frame: a frame pointer and a stack pointer.
3815 On the MIPS and Alpha architecture, it needs two addresses: a stack
3816 pointer and a program counter.
3818 On the 29k architecture, it needs three addresses: a register stack
3819 pointer, a program counter, and a memory stack pointer.
3820 @c note to future updaters: this is conditioned on a flag
3821 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3822 @c as of 27 Jan 1994.
3826 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3827 advances toward the outermost frame, to higher frame numbers, to frames
3828 that have existed longer. @var{n} defaults to one.
3831 @kindex do @r{(@code{down})}
3833 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3834 advances toward the innermost frame, to lower frame numbers, to frames
3835 that were created more recently. @var{n} defaults to one. You may
3836 abbreviate @code{down} as @code{do}.
3839 All of these commands end by printing two lines of output describing the
3840 frame. The first line shows the frame number, the function name, the
3841 arguments, and the source file and line number of execution in that
3842 frame. The second line shows the text of that source line.
3850 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3852 10 read_input_file (argv[i]);
3856 After such a printout, the @code{list} command with no arguments
3857 prints ten lines centered on the point of execution in the frame.
3858 @xref{List, ,Printing source lines}.
3861 @kindex down-silently
3863 @item up-silently @var{n}
3864 @itemx down-silently @var{n}
3865 These two commands are variants of @code{up} and @code{down},
3866 respectively; they differ in that they do their work silently, without
3867 causing display of the new frame. They are intended primarily for use
3868 in @value{GDBN} command scripts, where the output might be unnecessary and
3873 @section Information about a frame
3875 There are several other commands to print information about the selected
3881 When used without any argument, this command does not change which
3882 frame is selected, but prints a brief description of the currently
3883 selected stack frame. It can be abbreviated @code{f}. With an
3884 argument, this command is used to select a stack frame.
3885 @xref{Selection, ,Selecting a frame}.
3888 @kindex info f @r{(@code{info frame})}
3891 This command prints a verbose description of the selected stack frame,
3896 the address of the frame
3898 the address of the next frame down (called by this frame)
3900 the address of the next frame up (caller of this frame)
3902 the language in which the source code corresponding to this frame is written
3904 the address of the frame's arguments
3906 the address of the frame's local variables
3908 the program counter saved in it (the address of execution in the caller frame)
3910 which registers were saved in the frame
3913 @noindent The verbose description is useful when
3914 something has gone wrong that has made the stack format fail to fit
3915 the usual conventions.
3917 @item info frame @var{addr}
3918 @itemx info f @var{addr}
3919 Print a verbose description of the frame at address @var{addr}, without
3920 selecting that frame. The selected frame remains unchanged by this
3921 command. This requires the same kind of address (more than one for some
3922 architectures) that you specify in the @code{frame} command.
3923 @xref{Selection, ,Selecting a frame}.
3927 Print the arguments of the selected frame, each on a separate line.
3931 Print the local variables of the selected frame, each on a separate
3932 line. These are all variables (declared either static or automatic)
3933 accessible at the point of execution of the selected frame.
3936 @cindex catch exceptions, list active handlers
3937 @cindex exception handlers, how to list
3939 Print a list of all the exception handlers that are active in the
3940 current stack frame at the current point of execution. To see other
3941 exception handlers, visit the associated frame (using the @code{up},
3942 @code{down}, or @code{frame} commands); then type @code{info catch}.
3943 @xref{Set Catchpoints, , Setting catchpoints}.
3949 @chapter Examining Source Files
3951 @value{GDBN} can print parts of your program's source, since the debugging
3952 information recorded in the program tells @value{GDBN} what source files were
3953 used to build it. When your program stops, @value{GDBN} spontaneously prints
3954 the line where it stopped. Likewise, when you select a stack frame
3955 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3956 execution in that frame has stopped. You can print other portions of
3957 source files by explicit command.
3959 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3960 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3961 @value{GDBN} under @sc{gnu} Emacs}.
3964 * List:: Printing source lines
3965 * Search:: Searching source files
3966 * Source Path:: Specifying source directories
3967 * Machine Code:: Source and machine code
3971 @section Printing source lines
3974 @kindex l @r{(@code{list})}
3975 To print lines from a source file, use the @code{list} command
3976 (abbreviated @code{l}). By default, ten lines are printed.
3977 There are several ways to specify what part of the file you want to print.
3979 Here are the forms of the @code{list} command most commonly used:
3982 @item list @var{linenum}
3983 Print lines centered around line number @var{linenum} in the
3984 current source file.
3986 @item list @var{function}
3987 Print lines centered around the beginning of function
3991 Print more lines. If the last lines printed were printed with a
3992 @code{list} command, this prints lines following the last lines
3993 printed; however, if the last line printed was a solitary line printed
3994 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3995 Stack}), this prints lines centered around that line.
3998 Print lines just before the lines last printed.
4001 By default, @value{GDBN} prints ten source lines with any of these forms of
4002 the @code{list} command. You can change this using @code{set listsize}:
4005 @kindex set listsize
4006 @item set listsize @var{count}
4007 Make the @code{list} command display @var{count} source lines (unless
4008 the @code{list} argument explicitly specifies some other number).
4010 @kindex show listsize
4012 Display the number of lines that @code{list} prints.
4015 Repeating a @code{list} command with @key{RET} discards the argument,
4016 so it is equivalent to typing just @code{list}. This is more useful
4017 than listing the same lines again. An exception is made for an
4018 argument of @samp{-}; that argument is preserved in repetition so that
4019 each repetition moves up in the source file.
4022 In general, the @code{list} command expects you to supply zero, one or two
4023 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4024 of writing them, but the effect is always to specify some source line.
4025 Here is a complete description of the possible arguments for @code{list}:
4028 @item list @var{linespec}
4029 Print lines centered around the line specified by @var{linespec}.
4031 @item list @var{first},@var{last}
4032 Print lines from @var{first} to @var{last}. Both arguments are
4035 @item list ,@var{last}
4036 Print lines ending with @var{last}.
4038 @item list @var{first},
4039 Print lines starting with @var{first}.
4042 Print lines just after the lines last printed.
4045 Print lines just before the lines last printed.
4048 As described in the preceding table.
4051 Here are the ways of specifying a single source line---all the
4056 Specifies line @var{number} of the current source file.
4057 When a @code{list} command has two linespecs, this refers to
4058 the same source file as the first linespec.
4061 Specifies the line @var{offset} lines after the last line printed.
4062 When used as the second linespec in a @code{list} command that has
4063 two, this specifies the line @var{offset} lines down from the
4067 Specifies the line @var{offset} lines before the last line printed.
4069 @item @var{filename}:@var{number}
4070 Specifies line @var{number} in the source file @var{filename}.
4072 @item @var{function}
4073 Specifies the line that begins the body of the function @var{function}.
4074 For example: in C, this is the line with the open brace.
4076 @item @var{filename}:@var{function}
4077 Specifies the line of the open-brace that begins the body of the
4078 function @var{function} in the file @var{filename}. You only need the
4079 file name with a function name to avoid ambiguity when there are
4080 identically named functions in different source files.
4082 @item *@var{address}
4083 Specifies the line containing the program address @var{address}.
4084 @var{address} may be any expression.
4088 @section Searching source files
4090 @kindex reverse-search
4092 There are two commands for searching through the current source file for a
4097 @kindex forward-search
4098 @item forward-search @var{regexp}
4099 @itemx search @var{regexp}
4100 The command @samp{forward-search @var{regexp}} checks each line,
4101 starting with the one following the last line listed, for a match for
4102 @var{regexp}. It lists the line that is found. You can use the
4103 synonym @samp{search @var{regexp}} or abbreviate the command name as
4106 @item reverse-search @var{regexp}
4107 The command @samp{reverse-search @var{regexp}} checks each line, starting
4108 with the one before the last line listed and going backward, for a match
4109 for @var{regexp}. It lists the line that is found. You can abbreviate
4110 this command as @code{rev}.
4114 @section Specifying source directories
4117 @cindex directories for source files
4118 Executable programs sometimes do not record the directories of the source
4119 files from which they were compiled, just the names. Even when they do,
4120 the directories could be moved between the compilation and your debugging
4121 session. @value{GDBN} has a list of directories to search for source files;
4122 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4123 it tries all the directories in the list, in the order they are present
4124 in the list, until it finds a file with the desired name. Note that
4125 the executable search path is @emph{not} used for this purpose. Neither is
4126 the current working directory, unless it happens to be in the source
4129 If @value{GDBN} cannot find a source file in the source path, and the
4130 object program records a directory, @value{GDBN} tries that directory
4131 too. If the source path is empty, and there is no record of the
4132 compilation directory, @value{GDBN} looks in the current directory as a
4135 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4136 any information it has cached about where source files are found and where
4137 each line is in the file.
4141 When you start @value{GDBN}, its source path includes only @samp{cdir}
4142 and @samp{cwd}, in that order.
4143 To add other directories, use the @code{directory} command.
4146 @item directory @var{dirname} @dots{}
4147 @item dir @var{dirname} @dots{}
4148 Add directory @var{dirname} to the front of the source path. Several
4149 directory names may be given to this command, separated by @samp{:}
4150 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4151 part of absolute file names) or
4152 whitespace. You may specify a directory that is already in the source
4153 path; this moves it forward, so @value{GDBN} searches it sooner.
4157 @vindex $cdir@r{, convenience variable}
4158 @vindex $cwdr@r{, convenience variable}
4159 @cindex compilation directory
4160 @cindex current directory
4161 @cindex working directory
4162 @cindex directory, current
4163 @cindex directory, compilation
4164 You can use the string @samp{$cdir} to refer to the compilation
4165 directory (if one is recorded), and @samp{$cwd} to refer to the current
4166 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4167 tracks the current working directory as it changes during your @value{GDBN}
4168 session, while the latter is immediately expanded to the current
4169 directory at the time you add an entry to the source path.
4172 Reset the source path to empty again. This requires confirmation.
4174 @c RET-repeat for @code{directory} is explicitly disabled, but since
4175 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4177 @item show directories
4178 @kindex show directories
4179 Print the source path: show which directories it contains.
4182 If your source path is cluttered with directories that are no longer of
4183 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4184 versions of source. You can correct the situation as follows:
4188 Use @code{directory} with no argument to reset the source path to empty.
4191 Use @code{directory} with suitable arguments to reinstall the
4192 directories you want in the source path. You can add all the
4193 directories in one command.
4197 @section Source and machine code
4199 You can use the command @code{info line} to map source lines to program
4200 addresses (and vice versa), and the command @code{disassemble} to display
4201 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4202 mode, the @code{info line} command causes the arrow to point to the
4203 line specified. Also, @code{info line} prints addresses in symbolic form as
4208 @item info line @var{linespec}
4209 Print the starting and ending addresses of the compiled code for
4210 source line @var{linespec}. You can specify source lines in any of
4211 the ways understood by the @code{list} command (@pxref{List, ,Printing
4215 For example, we can use @code{info line} to discover the location of
4216 the object code for the first line of function
4217 @code{m4_changequote}:
4219 @c FIXME: I think this example should also show the addresses in
4220 @c symbolic form, as they usually would be displayed.
4222 (@value{GDBP}) info line m4_changequote
4223 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4227 We can also inquire (using @code{*@var{addr}} as the form for
4228 @var{linespec}) what source line covers a particular address:
4230 (@value{GDBP}) info line *0x63ff
4231 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4234 @cindex @code{$_} and @code{info line}
4235 @kindex x@r{(examine), and} info line
4236 After @code{info line}, the default address for the @code{x} command
4237 is changed to the starting address of the line, so that @samp{x/i} is
4238 sufficient to begin examining the machine code (@pxref{Memory,
4239 ,Examining memory}). Also, this address is saved as the value of the
4240 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4245 @cindex assembly instructions
4246 @cindex instructions, assembly
4247 @cindex machine instructions
4248 @cindex listing machine instructions
4250 This specialized command dumps a range of memory as machine
4251 instructions. The default memory range is the function surrounding the
4252 program counter of the selected frame. A single argument to this
4253 command is a program counter value; @value{GDBN} dumps the function
4254 surrounding this value. Two arguments specify a range of addresses
4255 (first inclusive, second exclusive) to dump.
4258 The following example shows the disassembly of a range of addresses of
4259 HP PA-RISC 2.0 code:
4262 (@value{GDBP}) disas 0x32c4 0x32e4
4263 Dump of assembler code from 0x32c4 to 0x32e4:
4264 0x32c4 <main+204>: addil 0,dp
4265 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4266 0x32cc <main+212>: ldil 0x3000,r31
4267 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4268 0x32d4 <main+220>: ldo 0(r31),rp
4269 0x32d8 <main+224>: addil -0x800,dp
4270 0x32dc <main+228>: ldo 0x588(r1),r26
4271 0x32e0 <main+232>: ldil 0x3000,r31
4272 End of assembler dump.
4275 Some architectures have more than one commonly-used set of instruction
4276 mnemonics or other syntax.
4279 @kindex set disassembly-flavor
4280 @cindex assembly instructions
4281 @cindex instructions, assembly
4282 @cindex machine instructions
4283 @cindex listing machine instructions
4284 @cindex Intel disassembly flavor
4285 @cindex AT&T disassembly flavor
4286 @item set disassembly-flavor @var{instruction-set}
4287 Select the instruction set to use when disassembling the
4288 program via the @code{disassemble} or @code{x/i} commands.
4290 Currently this command is only defined for the Intel x86 family. You
4291 can set @var{instruction-set} to either @code{intel} or @code{att}.
4292 The default is @code{att}, the AT&T flavor used by default by Unix
4293 assemblers for x86-based targets.
4298 @chapter Examining Data
4300 @cindex printing data
4301 @cindex examining data
4304 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4305 @c document because it is nonstandard... Under Epoch it displays in a
4306 @c different window or something like that.
4307 The usual way to examine data in your program is with the @code{print}
4308 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4309 evaluates and prints the value of an expression of the language your
4310 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4311 Different Languages}).
4314 @item print @var{expr}
4315 @itemx print /@var{f} @var{expr}
4316 @var{expr} is an expression (in the source language). By default the
4317 value of @var{expr} is printed in a format appropriate to its data type;
4318 you can choose a different format by specifying @samp{/@var{f}}, where
4319 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4323 @itemx print /@var{f}
4324 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4325 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4326 conveniently inspect the same value in an alternative format.
4329 A more low-level way of examining data is with the @code{x} command.
4330 It examines data in memory at a specified address and prints it in a
4331 specified format. @xref{Memory, ,Examining memory}.
4333 If you are interested in information about types, or about how the
4334 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4335 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4339 * Expressions:: Expressions
4340 * Variables:: Program variables
4341 * Arrays:: Artificial arrays
4342 * Output Formats:: Output formats
4343 * Memory:: Examining memory
4344 * Auto Display:: Automatic display
4345 * Print Settings:: Print settings
4346 * Value History:: Value history
4347 * Convenience Vars:: Convenience variables
4348 * Registers:: Registers
4349 * Floating Point Hardware:: Floating point hardware
4350 * Memory Region Attributes:: Memory region attributes
4354 @section Expressions
4357 @code{print} and many other @value{GDBN} commands accept an expression and
4358 compute its value. Any kind of constant, variable or operator defined
4359 by the programming language you are using is valid in an expression in
4360 @value{GDBN}. This includes conditional expressions, function calls, casts
4361 and string constants. It unfortunately does not include symbols defined
4362 by preprocessor @code{#define} commands.
4364 @value{GDBN} supports array constants in expressions input by
4365 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4366 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4367 memory that is @code{malloc}ed in the target program.
4369 Because C is so widespread, most of the expressions shown in examples in
4370 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4371 Languages}, for information on how to use expressions in other
4374 In this section, we discuss operators that you can use in @value{GDBN}
4375 expressions regardless of your programming language.
4377 Casts are supported in all languages, not just in C, because it is so
4378 useful to cast a number into a pointer in order to examine a structure
4379 at that address in memory.
4380 @c FIXME: casts supported---Mod2 true?
4382 @value{GDBN} supports these operators, in addition to those common
4383 to programming languages:
4387 @samp{@@} is a binary operator for treating parts of memory as arrays.
4388 @xref{Arrays, ,Artificial arrays}, for more information.
4391 @samp{::} allows you to specify a variable in terms of the file or
4392 function where it is defined. @xref{Variables, ,Program variables}.
4394 @cindex @{@var{type}@}
4395 @cindex type casting memory
4396 @cindex memory, viewing as typed object
4397 @cindex casts, to view memory
4398 @item @{@var{type}@} @var{addr}
4399 Refers to an object of type @var{type} stored at address @var{addr} in
4400 memory. @var{addr} may be any expression whose value is an integer or
4401 pointer (but parentheses are required around binary operators, just as in
4402 a cast). This construct is allowed regardless of what kind of data is
4403 normally supposed to reside at @var{addr}.
4407 @section Program variables
4409 The most common kind of expression to use is the name of a variable
4412 Variables in expressions are understood in the selected stack frame
4413 (@pxref{Selection, ,Selecting a frame}); they must be either:
4417 global (or file-static)
4424 visible according to the scope rules of the
4425 programming language from the point of execution in that frame
4428 @noindent This means that in the function
4443 you can examine and use the variable @code{a} whenever your program is
4444 executing within the function @code{foo}, but you can only use or
4445 examine the variable @code{b} while your program is executing inside
4446 the block where @code{b} is declared.
4448 @cindex variable name conflict
4449 There is an exception: you can refer to a variable or function whose
4450 scope is a single source file even if the current execution point is not
4451 in this file. But it is possible to have more than one such variable or
4452 function with the same name (in different source files). If that
4453 happens, referring to that name has unpredictable effects. If you wish,
4454 you can specify a static variable in a particular function or file,
4455 using the colon-colon notation:
4457 @cindex colon-colon, context for variables/functions
4459 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4460 @cindex @code{::}, context for variables/functions
4463 @var{file}::@var{variable}
4464 @var{function}::@var{variable}
4468 Here @var{file} or @var{function} is the name of the context for the
4469 static @var{variable}. In the case of file names, you can use quotes to
4470 make sure @value{GDBN} parses the file name as a single word---for example,
4471 to print a global value of @code{x} defined in @file{f2.c}:
4474 (@value{GDBP}) p 'f2.c'::x
4477 @cindex C++ scope resolution
4478 This use of @samp{::} is very rarely in conflict with the very similar
4479 use of the same notation in C++. @value{GDBN} also supports use of the C++
4480 scope resolution operator in @value{GDBN} expressions.
4481 @c FIXME: Um, so what happens in one of those rare cases where it's in
4484 @cindex wrong values
4485 @cindex variable values, wrong
4487 @emph{Warning:} Occasionally, a local variable may appear to have the
4488 wrong value at certain points in a function---just after entry to a new
4489 scope, and just before exit.
4491 You may see this problem when you are stepping by machine instructions.
4492 This is because, on most machines, it takes more than one instruction to
4493 set up a stack frame (including local variable definitions); if you are
4494 stepping by machine instructions, variables may appear to have the wrong
4495 values until the stack frame is completely built. On exit, it usually
4496 also takes more than one machine instruction to destroy a stack frame;
4497 after you begin stepping through that group of instructions, local
4498 variable definitions may be gone.
4500 This may also happen when the compiler does significant optimizations.
4501 To be sure of always seeing accurate values, turn off all optimization
4504 @cindex ``No symbol "foo" in current context''
4505 Another possible effect of compiler optimizations is to optimize
4506 unused variables out of existence, or assign variables to registers (as
4507 opposed to memory addresses). Depending on the support for such cases
4508 offered by the debug info format used by the compiler, @value{GDBN}
4509 might not be able to display values for such local variables. If that
4510 happens, @value{GDBN} will print a message like this:
4513 No symbol "foo" in current context.
4516 To solve such problems, either recompile without optimizations, or use a
4517 different debug info format, if the compiler supports several such
4518 formats. For example, @value{NGCC}, the @sc{gnu} C/C++ compiler usually
4519 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4520 in a format that is superior to formats such as COFF. You may be able
4521 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4522 debug info. See @ref{Debugging Options,,Options for Debugging Your
4523 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4528 @section Artificial arrays
4530 @cindex artificial array
4531 @kindex @@@r{, referencing memory as an array}
4532 It is often useful to print out several successive objects of the
4533 same type in memory; a section of an array, or an array of
4534 dynamically determined size for which only a pointer exists in the
4537 You can do this by referring to a contiguous span of memory as an
4538 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4539 operand of @samp{@@} should be the first element of the desired array
4540 and be an individual object. The right operand should be the desired length
4541 of the array. The result is an array value whose elements are all of
4542 the type of the left argument. The first element is actually the left
4543 argument; the second element comes from bytes of memory immediately
4544 following those that hold the first element, and so on. Here is an
4545 example. If a program says
4548 int *array = (int *) malloc (len * sizeof (int));
4552 you can print the contents of @code{array} with
4558 The left operand of @samp{@@} must reside in memory. Array values made
4559 with @samp{@@} in this way behave just like other arrays in terms of
4560 subscripting, and are coerced to pointers when used in expressions.
4561 Artificial arrays most often appear in expressions via the value history
4562 (@pxref{Value History, ,Value history}), after printing one out.
4564 Another way to create an artificial array is to use a cast.
4565 This re-interprets a value as if it were an array.
4566 The value need not be in memory:
4568 (@value{GDBP}) p/x (short[2])0x12345678
4569 $1 = @{0x1234, 0x5678@}
4572 As a convenience, if you leave the array length out (as in
4573 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4574 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4576 (@value{GDBP}) p/x (short[])0x12345678
4577 $2 = @{0x1234, 0x5678@}
4580 Sometimes the artificial array mechanism is not quite enough; in
4581 moderately complex data structures, the elements of interest may not
4582 actually be adjacent---for example, if you are interested in the values
4583 of pointers in an array. One useful work-around in this situation is
4584 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4585 variables}) as a counter in an expression that prints the first
4586 interesting value, and then repeat that expression via @key{RET}. For
4587 instance, suppose you have an array @code{dtab} of pointers to
4588 structures, and you are interested in the values of a field @code{fv}
4589 in each structure. Here is an example of what you might type:
4599 @node Output Formats
4600 @section Output formats
4602 @cindex formatted output
4603 @cindex output formats
4604 By default, @value{GDBN} prints a value according to its data type. Sometimes
4605 this is not what you want. For example, you might want to print a number
4606 in hex, or a pointer in decimal. Or you might want to view data in memory
4607 at a certain address as a character string or as an instruction. To do
4608 these things, specify an @dfn{output format} when you print a value.
4610 The simplest use of output formats is to say how to print a value
4611 already computed. This is done by starting the arguments of the
4612 @code{print} command with a slash and a format letter. The format
4613 letters supported are:
4617 Regard the bits of the value as an integer, and print the integer in
4621 Print as integer in signed decimal.
4624 Print as integer in unsigned decimal.
4627 Print as integer in octal.
4630 Print as integer in binary. The letter @samp{t} stands for ``two''.
4631 @footnote{@samp{b} cannot be used because these format letters are also
4632 used with the @code{x} command, where @samp{b} stands for ``byte'';
4633 see @ref{Memory,,Examining memory}.}
4636 @cindex unknown address, locating
4637 @cindex locate address
4638 Print as an address, both absolute in hexadecimal and as an offset from
4639 the nearest preceding symbol. You can use this format used to discover
4640 where (in what function) an unknown address is located:
4643 (@value{GDBP}) p/a 0x54320
4644 $3 = 0x54320 <_initialize_vx+396>
4648 The command @code{info symbol 0x54320} yields similar results.
4649 @xref{Symbols, info symbol}.
4652 Regard as an integer and print it as a character constant.
4655 Regard the bits of the value as a floating point number and print
4656 using typical floating point syntax.
4659 For example, to print the program counter in hex (@pxref{Registers}), type
4666 Note that no space is required before the slash; this is because command
4667 names in @value{GDBN} cannot contain a slash.
4669 To reprint the last value in the value history with a different format,
4670 you can use the @code{print} command with just a format and no
4671 expression. For example, @samp{p/x} reprints the last value in hex.
4674 @section Examining memory
4676 You can use the command @code{x} (for ``examine'') to examine memory in
4677 any of several formats, independently of your program's data types.
4679 @cindex examining memory
4681 @kindex x @r{(examine memory)}
4682 @item x/@var{nfu} @var{addr}
4685 Use the @code{x} command to examine memory.
4688 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4689 much memory to display and how to format it; @var{addr} is an
4690 expression giving the address where you want to start displaying memory.
4691 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4692 Several commands set convenient defaults for @var{addr}.
4695 @item @var{n}, the repeat count
4696 The repeat count is a decimal integer; the default is 1. It specifies
4697 how much memory (counting by units @var{u}) to display.
4698 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4701 @item @var{f}, the display format
4702 The display format is one of the formats used by @code{print},
4703 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4704 The default is @samp{x} (hexadecimal) initially.
4705 The default changes each time you use either @code{x} or @code{print}.
4707 @item @var{u}, the unit size
4708 The unit size is any of
4714 Halfwords (two bytes).
4716 Words (four bytes). This is the initial default.
4718 Giant words (eight bytes).
4721 Each time you specify a unit size with @code{x}, that size becomes the
4722 default unit the next time you use @code{x}. (For the @samp{s} and
4723 @samp{i} formats, the unit size is ignored and is normally not written.)
4725 @item @var{addr}, starting display address
4726 @var{addr} is the address where you want @value{GDBN} to begin displaying
4727 memory. The expression need not have a pointer value (though it may);
4728 it is always interpreted as an integer address of a byte of memory.
4729 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4730 @var{addr} is usually just after the last address examined---but several
4731 other commands also set the default address: @code{info breakpoints} (to
4732 the address of the last breakpoint listed), @code{info line} (to the
4733 starting address of a line), and @code{print} (if you use it to display
4734 a value from memory).
4737 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4738 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4739 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4740 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4741 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4743 Since the letters indicating unit sizes are all distinct from the
4744 letters specifying output formats, you do not have to remember whether
4745 unit size or format comes first; either order works. The output
4746 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4747 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4749 Even though the unit size @var{u} is ignored for the formats @samp{s}
4750 and @samp{i}, you might still want to use a count @var{n}; for example,
4751 @samp{3i} specifies that you want to see three machine instructions,
4752 including any operands. The command @code{disassemble} gives an
4753 alternative way of inspecting machine instructions; see @ref{Machine
4754 Code,,Source and machine code}.
4756 All the defaults for the arguments to @code{x} are designed to make it
4757 easy to continue scanning memory with minimal specifications each time
4758 you use @code{x}. For example, after you have inspected three machine
4759 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4760 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4761 the repeat count @var{n} is used again; the other arguments default as
4762 for successive uses of @code{x}.
4764 @cindex @code{$_}, @code{$__}, and value history
4765 The addresses and contents printed by the @code{x} command are not saved
4766 in the value history because there is often too much of them and they
4767 would get in the way. Instead, @value{GDBN} makes these values available for
4768 subsequent use in expressions as values of the convenience variables
4769 @code{$_} and @code{$__}. After an @code{x} command, the last address
4770 examined is available for use in expressions in the convenience variable
4771 @code{$_}. The contents of that address, as examined, are available in
4772 the convenience variable @code{$__}.
4774 If the @code{x} command has a repeat count, the address and contents saved
4775 are from the last memory unit printed; this is not the same as the last
4776 address printed if several units were printed on the last line of output.
4779 @section Automatic display
4780 @cindex automatic display
4781 @cindex display of expressions
4783 If you find that you want to print the value of an expression frequently
4784 (to see how it changes), you might want to add it to the @dfn{automatic
4785 display list} so that @value{GDBN} prints its value each time your program stops.
4786 Each expression added to the list is given a number to identify it;
4787 to remove an expression from the list, you specify that number.
4788 The automatic display looks like this:
4792 3: bar[5] = (struct hack *) 0x3804
4796 This display shows item numbers, expressions and their current values. As with
4797 displays you request manually using @code{x} or @code{print}, you can
4798 specify the output format you prefer; in fact, @code{display} decides
4799 whether to use @code{print} or @code{x} depending on how elaborate your
4800 format specification is---it uses @code{x} if you specify a unit size,
4801 or one of the two formats (@samp{i} and @samp{s}) that are only
4802 supported by @code{x}; otherwise it uses @code{print}.
4806 @item display @var{expr}
4807 Add the expression @var{expr} to the list of expressions to display
4808 each time your program stops. @xref{Expressions, ,Expressions}.
4810 @code{display} does not repeat if you press @key{RET} again after using it.
4812 @item display/@var{fmt} @var{expr}
4813 For @var{fmt} specifying only a display format and not a size or
4814 count, add the expression @var{expr} to the auto-display list but
4815 arrange to display it each time in the specified format @var{fmt}.
4816 @xref{Output Formats,,Output formats}.
4818 @item display/@var{fmt} @var{addr}
4819 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4820 number of units, add the expression @var{addr} as a memory address to
4821 be examined each time your program stops. Examining means in effect
4822 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4825 For example, @samp{display/i $pc} can be helpful, to see the machine
4826 instruction about to be executed each time execution stops (@samp{$pc}
4827 is a common name for the program counter; @pxref{Registers, ,Registers}).
4830 @kindex delete display
4832 @item undisplay @var{dnums}@dots{}
4833 @itemx delete display @var{dnums}@dots{}
4834 Remove item numbers @var{dnums} from the list of expressions to display.
4836 @code{undisplay} does not repeat if you press @key{RET} after using it.
4837 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4839 @kindex disable display
4840 @item disable display @var{dnums}@dots{}
4841 Disable the display of item numbers @var{dnums}. A disabled display
4842 item is not printed automatically, but is not forgotten. It may be
4843 enabled again later.
4845 @kindex enable display
4846 @item enable display @var{dnums}@dots{}
4847 Enable display of item numbers @var{dnums}. It becomes effective once
4848 again in auto display of its expression, until you specify otherwise.
4851 Display the current values of the expressions on the list, just as is
4852 done when your program stops.
4854 @kindex info display
4856 Print the list of expressions previously set up to display
4857 automatically, each one with its item number, but without showing the
4858 values. This includes disabled expressions, which are marked as such.
4859 It also includes expressions which would not be displayed right now
4860 because they refer to automatic variables not currently available.
4863 If a display expression refers to local variables, then it does not make
4864 sense outside the lexical context for which it was set up. Such an
4865 expression is disabled when execution enters a context where one of its
4866 variables is not defined. For example, if you give the command
4867 @code{display last_char} while inside a function with an argument
4868 @code{last_char}, @value{GDBN} displays this argument while your program
4869 continues to stop inside that function. When it stops elsewhere---where
4870 there is no variable @code{last_char}---the display is disabled
4871 automatically. The next time your program stops where @code{last_char}
4872 is meaningful, you can enable the display expression once again.
4874 @node Print Settings
4875 @section Print settings
4877 @cindex format options
4878 @cindex print settings
4879 @value{GDBN} provides the following ways to control how arrays, structures,
4880 and symbols are printed.
4883 These settings are useful for debugging programs in any language:
4886 @kindex set print address
4887 @item set print address
4888 @itemx set print address on
4889 @value{GDBN} prints memory addresses showing the location of stack
4890 traces, structure values, pointer values, breakpoints, and so forth,
4891 even when it also displays the contents of those addresses. The default
4892 is @code{on}. For example, this is what a stack frame display looks like with
4893 @code{set print address on}:
4898 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4900 530 if (lquote != def_lquote)
4904 @item set print address off
4905 Do not print addresses when displaying their contents. For example,
4906 this is the same stack frame displayed with @code{set print address off}:
4910 (@value{GDBP}) set print addr off
4912 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4913 530 if (lquote != def_lquote)
4917 You can use @samp{set print address off} to eliminate all machine
4918 dependent displays from the @value{GDBN} interface. For example, with
4919 @code{print address off}, you should get the same text for backtraces on
4920 all machines---whether or not they involve pointer arguments.
4922 @kindex show print address
4923 @item show print address
4924 Show whether or not addresses are to be printed.
4927 When @value{GDBN} prints a symbolic address, it normally prints the
4928 closest earlier symbol plus an offset. If that symbol does not uniquely
4929 identify the address (for example, it is a name whose scope is a single
4930 source file), you may need to clarify. One way to do this is with
4931 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4932 you can set @value{GDBN} to print the source file and line number when
4933 it prints a symbolic address:
4936 @kindex set print symbol-filename
4937 @item set print symbol-filename on
4938 Tell @value{GDBN} to print the source file name and line number of a
4939 symbol in the symbolic form of an address.
4941 @item set print symbol-filename off
4942 Do not print source file name and line number of a symbol. This is the
4945 @kindex show print symbol-filename
4946 @item show print symbol-filename
4947 Show whether or not @value{GDBN} will print the source file name and
4948 line number of a symbol in the symbolic form of an address.
4951 Another situation where it is helpful to show symbol filenames and line
4952 numbers is when disassembling code; @value{GDBN} shows you the line
4953 number and source file that corresponds to each instruction.
4955 Also, you may wish to see the symbolic form only if the address being
4956 printed is reasonably close to the closest earlier symbol:
4959 @kindex set print max-symbolic-offset
4960 @item set print max-symbolic-offset @var{max-offset}
4961 Tell @value{GDBN} to only display the symbolic form of an address if the
4962 offset between the closest earlier symbol and the address is less than
4963 @var{max-offset}. The default is 0, which tells @value{GDBN}
4964 to always print the symbolic form of an address if any symbol precedes it.
4966 @kindex show print max-symbolic-offset
4967 @item show print max-symbolic-offset
4968 Ask how large the maximum offset is that @value{GDBN} prints in a
4972 @cindex wild pointer, interpreting
4973 @cindex pointer, finding referent
4974 If you have a pointer and you are not sure where it points, try
4975 @samp{set print symbol-filename on}. Then you can determine the name
4976 and source file location of the variable where it points, using
4977 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4978 For example, here @value{GDBN} shows that a variable @code{ptt} points
4979 at another variable @code{t}, defined in @file{hi2.c}:
4982 (@value{GDBP}) set print symbol-filename on
4983 (@value{GDBP}) p/a ptt
4984 $4 = 0xe008 <t in hi2.c>
4988 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4989 does not show the symbol name and filename of the referent, even with
4990 the appropriate @code{set print} options turned on.
4993 Other settings control how different kinds of objects are printed:
4996 @kindex set print array
4997 @item set print array
4998 @itemx set print array on
4999 Pretty print arrays. This format is more convenient to read,
5000 but uses more space. The default is off.
5002 @item set print array off
5003 Return to compressed format for arrays.
5005 @kindex show print array
5006 @item show print array
5007 Show whether compressed or pretty format is selected for displaying
5010 @kindex set print elements
5011 @item set print elements @var{number-of-elements}
5012 Set a limit on how many elements of an array @value{GDBN} will print.
5013 If @value{GDBN} is printing a large array, it stops printing after it has
5014 printed the number of elements set by the @code{set print elements} command.
5015 This limit also applies to the display of strings.
5016 When @value{GDBN} starts, this limit is set to 200.
5017 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5019 @kindex show print elements
5020 @item show print elements
5021 Display the number of elements of a large array that @value{GDBN} will print.
5022 If the number is 0, then the printing is unlimited.
5024 @kindex set print null-stop
5025 @item set print null-stop
5026 Cause @value{GDBN} to stop printing the characters of an array when the first
5027 @sc{null} is encountered. This is useful when large arrays actually
5028 contain only short strings.
5031 @kindex set print pretty
5032 @item set print pretty on
5033 Cause @value{GDBN} to print structures in an indented format with one member
5034 per line, like this:
5049 @item set print pretty off
5050 Cause @value{GDBN} to print structures in a compact format, like this:
5054 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5055 meat = 0x54 "Pork"@}
5060 This is the default format.
5062 @kindex show print pretty
5063 @item show print pretty
5064 Show which format @value{GDBN} is using to print structures.
5066 @kindex set print sevenbit-strings
5067 @item set print sevenbit-strings on
5068 Print using only seven-bit characters; if this option is set,
5069 @value{GDBN} displays any eight-bit characters (in strings or
5070 character values) using the notation @code{\}@var{nnn}. This setting is
5071 best if you are working in English (@sc{ascii}) and you use the
5072 high-order bit of characters as a marker or ``meta'' bit.
5074 @item set print sevenbit-strings off
5075 Print full eight-bit characters. This allows the use of more
5076 international character sets, and is the default.
5078 @kindex show print sevenbit-strings
5079 @item show print sevenbit-strings
5080 Show whether or not @value{GDBN} is printing only seven-bit characters.
5082 @kindex set print union
5083 @item set print union on
5084 Tell @value{GDBN} to print unions which are contained in structures. This
5085 is the default setting.
5087 @item set print union off
5088 Tell @value{GDBN} not to print unions which are contained in structures.
5090 @kindex show print union
5091 @item show print union
5092 Ask @value{GDBN} whether or not it will print unions which are contained in
5095 For example, given the declarations
5098 typedef enum @{Tree, Bug@} Species;
5099 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5100 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5111 struct thing foo = @{Tree, @{Acorn@}@};
5115 with @code{set print union on} in effect @samp{p foo} would print
5118 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5122 and with @code{set print union off} in effect it would print
5125 $1 = @{it = Tree, form = @{...@}@}
5131 These settings are of interest when debugging C++ programs:
5135 @kindex set print demangle
5136 @item set print demangle
5137 @itemx set print demangle on
5138 Print C++ names in their source form rather than in the encoded
5139 (``mangled'') form passed to the assembler and linker for type-safe
5140 linkage. The default is on.
5142 @kindex show print demangle
5143 @item show print demangle
5144 Show whether C++ names are printed in mangled or demangled form.
5146 @kindex set print asm-demangle
5147 @item set print asm-demangle
5148 @itemx set print asm-demangle on
5149 Print C++ names in their source form rather than their mangled form, even
5150 in assembler code printouts such as instruction disassemblies.
5153 @kindex show print asm-demangle
5154 @item show print asm-demangle
5155 Show whether C++ names in assembly listings are printed in mangled
5158 @kindex set demangle-style
5159 @cindex C++ symbol decoding style
5160 @cindex symbol decoding style, C++
5161 @item set demangle-style @var{style}
5162 Choose among several encoding schemes used by different compilers to
5163 represent C++ names. The choices for @var{style} are currently:
5167 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5170 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5171 This is the default.
5174 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5177 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5180 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5181 @strong{Warning:} this setting alone is not sufficient to allow
5182 debugging @code{cfront}-generated executables. @value{GDBN} would
5183 require further enhancement to permit that.
5186 If you omit @var{style}, you will see a list of possible formats.
5188 @kindex show demangle-style
5189 @item show demangle-style
5190 Display the encoding style currently in use for decoding C++ symbols.
5192 @kindex set print object
5193 @item set print object
5194 @itemx set print object on
5195 When displaying a pointer to an object, identify the @emph{actual}
5196 (derived) type of the object rather than the @emph{declared} type, using
5197 the virtual function table.
5199 @item set print object off
5200 Display only the declared type of objects, without reference to the
5201 virtual function table. This is the default setting.
5203 @kindex show print object
5204 @item show print object
5205 Show whether actual, or declared, object types are displayed.
5207 @kindex set print static-members
5208 @item set print static-members
5209 @itemx set print static-members on
5210 Print static members when displaying a C++ object. The default is on.
5212 @item set print static-members off
5213 Do not print static members when displaying a C++ object.
5215 @kindex show print static-members
5216 @item show print static-members
5217 Show whether C++ static members are printed, or not.
5219 @c These don't work with HP ANSI C++ yet.
5220 @kindex set print vtbl
5221 @item set print vtbl
5222 @itemx set print vtbl on
5223 Pretty print C++ virtual function tables. The default is off.
5224 (The @code{vtbl} commands do not work on programs compiled with the HP
5225 ANSI C++ compiler (@code{aCC}).)
5227 @item set print vtbl off
5228 Do not pretty print C++ virtual function tables.
5230 @kindex show print vtbl
5231 @item show print vtbl
5232 Show whether C++ virtual function tables are pretty printed, or not.
5236 @section Value history
5238 @cindex value history
5239 Values printed by the @code{print} command are saved in the @value{GDBN}
5240 @dfn{value history}. This allows you to refer to them in other expressions.
5241 Values are kept until the symbol table is re-read or discarded
5242 (for example with the @code{file} or @code{symbol-file} commands).
5243 When the symbol table changes, the value history is discarded,
5244 since the values may contain pointers back to the types defined in the
5249 @cindex history number
5250 The values printed are given @dfn{history numbers} by which you can
5251 refer to them. These are successive integers starting with one.
5252 @code{print} shows you the history number assigned to a value by
5253 printing @samp{$@var{num} = } before the value; here @var{num} is the
5256 To refer to any previous value, use @samp{$} followed by the value's
5257 history number. The way @code{print} labels its output is designed to
5258 remind you of this. Just @code{$} refers to the most recent value in
5259 the history, and @code{$$} refers to the value before that.
5260 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5261 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5262 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5264 For example, suppose you have just printed a pointer to a structure and
5265 want to see the contents of the structure. It suffices to type
5271 If you have a chain of structures where the component @code{next} points
5272 to the next one, you can print the contents of the next one with this:
5279 You can print successive links in the chain by repeating this
5280 command---which you can do by just typing @key{RET}.
5282 Note that the history records values, not expressions. If the value of
5283 @code{x} is 4 and you type these commands:
5291 then the value recorded in the value history by the @code{print} command
5292 remains 4 even though the value of @code{x} has changed.
5297 Print the last ten values in the value history, with their item numbers.
5298 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5299 values} does not change the history.
5301 @item show values @var{n}
5302 Print ten history values centered on history item number @var{n}.
5305 Print ten history values just after the values last printed. If no more
5306 values are available, @code{show values +} produces no display.
5309 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5310 same effect as @samp{show values +}.
5312 @node Convenience Vars
5313 @section Convenience variables
5315 @cindex convenience variables
5316 @value{GDBN} provides @dfn{convenience variables} that you can use within
5317 @value{GDBN} to hold on to a value and refer to it later. These variables
5318 exist entirely within @value{GDBN}; they are not part of your program, and
5319 setting a convenience variable has no direct effect on further execution
5320 of your program. That is why you can use them freely.
5322 Convenience variables are prefixed with @samp{$}. Any name preceded by
5323 @samp{$} can be used for a convenience variable, unless it is one of
5324 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5325 (Value history references, in contrast, are @emph{numbers} preceded
5326 by @samp{$}. @xref{Value History, ,Value history}.)
5328 You can save a value in a convenience variable with an assignment
5329 expression, just as you would set a variable in your program.
5333 set $foo = *object_ptr
5337 would save in @code{$foo} the value contained in the object pointed to by
5340 Using a convenience variable for the first time creates it, but its
5341 value is @code{void} until you assign a new value. You can alter the
5342 value with another assignment at any time.
5344 Convenience variables have no fixed types. You can assign a convenience
5345 variable any type of value, including structures and arrays, even if
5346 that variable already has a value of a different type. The convenience
5347 variable, when used as an expression, has the type of its current value.
5350 @kindex show convenience
5351 @item show convenience
5352 Print a list of convenience variables used so far, and their values.
5353 Abbreviated @code{show conv}.
5356 One of the ways to use a convenience variable is as a counter to be
5357 incremented or a pointer to be advanced. For example, to print
5358 a field from successive elements of an array of structures:
5362 print bar[$i++]->contents
5366 Repeat that command by typing @key{RET}.
5368 Some convenience variables are created automatically by @value{GDBN} and given
5369 values likely to be useful.
5372 @vindex $_@r{, convenience variable}
5374 The variable @code{$_} is automatically set by the @code{x} command to
5375 the last address examined (@pxref{Memory, ,Examining memory}). Other
5376 commands which provide a default address for @code{x} to examine also
5377 set @code{$_} to that address; these commands include @code{info line}
5378 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5379 except when set by the @code{x} command, in which case it is a pointer
5380 to the type of @code{$__}.
5382 @vindex $__@r{, convenience variable}
5384 The variable @code{$__} is automatically set by the @code{x} command
5385 to the value found in the last address examined. Its type is chosen
5386 to match the format in which the data was printed.
5389 @vindex $_exitcode@r{, convenience variable}
5390 The variable @code{$_exitcode} is automatically set to the exit code when
5391 the program being debugged terminates.
5394 On HP-UX systems, if you refer to a function or variable name that
5395 begins with a dollar sign, @value{GDBN} searches for a user or system
5396 name first, before it searches for a convenience variable.
5402 You can refer to machine register contents, in expressions, as variables
5403 with names starting with @samp{$}. The names of registers are different
5404 for each machine; use @code{info registers} to see the names used on
5408 @kindex info registers
5409 @item info registers
5410 Print the names and values of all registers except floating-point
5411 registers (in the selected stack frame).
5413 @kindex info all-registers
5414 @cindex floating point registers
5415 @item info all-registers
5416 Print the names and values of all registers, including floating-point
5419 @item info registers @var{regname} @dots{}
5420 Print the @dfn{relativized} value of each specified register @var{regname}.
5421 As discussed in detail below, register values are normally relative to
5422 the selected stack frame. @var{regname} may be any register name valid on
5423 the machine you are using, with or without the initial @samp{$}.
5426 @value{GDBN} has four ``standard'' register names that are available (in
5427 expressions) on most machines---whenever they do not conflict with an
5428 architecture's canonical mnemonics for registers. The register names
5429 @code{$pc} and @code{$sp} are used for the program counter register and
5430 the stack pointer. @code{$fp} is used for a register that contains a
5431 pointer to the current stack frame, and @code{$ps} is used for a
5432 register that contains the processor status. For example,
5433 you could print the program counter in hex with
5440 or print the instruction to be executed next with
5447 or add four to the stack pointer@footnote{This is a way of removing
5448 one word from the stack, on machines where stacks grow downward in
5449 memory (most machines, nowadays). This assumes that the innermost
5450 stack frame is selected; setting @code{$sp} is not allowed when other
5451 stack frames are selected. To pop entire frames off the stack,
5452 regardless of machine architecture, use @code{return};
5453 see @ref{Returning, ,Returning from a function}.} with
5459 Whenever possible, these four standard register names are available on
5460 your machine even though the machine has different canonical mnemonics,
5461 so long as there is no conflict. The @code{info registers} command
5462 shows the canonical names. For example, on the SPARC, @code{info
5463 registers} displays the processor status register as @code{$psr} but you
5464 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5465 is an alias for the @sc{eflags} register.
5467 @value{GDBN} always considers the contents of an ordinary register as an
5468 integer when the register is examined in this way. Some machines have
5469 special registers which can hold nothing but floating point; these
5470 registers are considered to have floating point values. There is no way
5471 to refer to the contents of an ordinary register as floating point value
5472 (although you can @emph{print} it as a floating point value with
5473 @samp{print/f $@var{regname}}).
5475 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5476 means that the data format in which the register contents are saved by
5477 the operating system is not the same one that your program normally
5478 sees. For example, the registers of the 68881 floating point
5479 coprocessor are always saved in ``extended'' (raw) format, but all C
5480 programs expect to work with ``double'' (virtual) format. In such
5481 cases, @value{GDBN} normally works with the virtual format only (the format
5482 that makes sense for your program), but the @code{info registers} command
5483 prints the data in both formats.
5485 Normally, register values are relative to the selected stack frame
5486 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5487 value that the register would contain if all stack frames farther in
5488 were exited and their saved registers restored. In order to see the
5489 true contents of hardware registers, you must select the innermost
5490 frame (with @samp{frame 0}).
5492 However, @value{GDBN} must deduce where registers are saved, from the machine
5493 code generated by your compiler. If some registers are not saved, or if
5494 @value{GDBN} is unable to locate the saved registers, the selected stack
5495 frame makes no difference.
5497 @node Floating Point Hardware
5498 @section Floating point hardware
5499 @cindex floating point
5501 Depending on the configuration, @value{GDBN} may be able to give
5502 you more information about the status of the floating point hardware.
5507 Display hardware-dependent information about the floating
5508 point unit. The exact contents and layout vary depending on the
5509 floating point chip. Currently, @samp{info float} is supported on
5510 the ARM and x86 machines.
5513 @node Memory Region Attributes
5514 @section Memory Region Attributes
5515 @cindex memory region attributes
5517 @dfn{Memory region attributes} allow you to describe special handling
5518 required by regions of your target's memory. @value{GDBN} uses attributes
5519 to determine whether to allow certain types of memory accesses; whether to
5520 use specific width accesses; and whether to cache target memory.
5522 Defined memory regions can be individually enabled and disabled. When a
5523 memory region is disabled, @value{GDBN} uses the default attributes when
5524 accessing memory in that region. Similarly, if no memory regions have
5525 been defined, @value{GDBN} uses the default attributes when accessing
5528 When a memory region is defined, it is given a number to identify it;
5529 to enable, disable, or remove a memory region, you specify that number.
5533 @item mem @var{address1} @var{address1} @var{attributes}@dots{}
5534 Define memory region bounded by @var{address1} and @var{address2}
5535 with attributes @var{attributes}@dots{}.
5538 @item delete mem @var{nums}@dots{}
5539 Remove memory region numbers @var{nums}.
5542 @item disable mem @var{nums}@dots{}
5543 Disable memory region numbers @var{nums}.
5544 A disabled memory region is not forgotten.
5545 It may be enabled again later.
5548 @item enable mem @var{nums}@dots{}
5549 Enable memory region numbers @var{nums}.
5553 Print a table of all defined memory regions, with the following columns
5557 @item Memory Region Number
5558 @item Enabled or Disabled.
5559 Enabled memory regions are marked with @samp{y}.
5560 Disabled memory regions are marked with @samp{n}.
5563 The address defining the inclusive lower bound of the memory region.
5566 The address defining the exclusive upper bound of the memory region.
5569 The list of attributes set for this memory region.
5574 @subsection Attributes
5576 @subsubsection Memory Access Mode
5577 The access mode attributes set whether @value{GDBN} may make read or
5578 write accesses to a memory region.
5580 While these attributes prevent @value{GDBN} from performing invalid
5581 memory accesses, they do nothing to prevent the target system, I/O DMA,
5582 etc. from accessing memory.
5586 Memory is read only.
5588 Memory is write only.
5590 Memory is read/write (default).
5593 @subsubsection Memory Access Size
5594 The acccess size attributes tells @value{GDBN} to use specific sized
5595 accesses in the memory region. Often memory mapped device registers
5596 require specific sized accesses. If no access size attribute is
5597 specified, @value{GDBN} may use accesses of any size.
5601 Use 8 bit memory accesses.
5603 Use 16 bit memory accesses.
5605 Use 32 bit memory accesses.
5607 Use 64 bit memory accesses.
5610 @c @subsubsection Hardware/Software Breakpoints
5611 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5612 @c will use hardware or software breakpoints for the internal breakpoints
5613 @c used by the step, next, finish, until, etc. commands.
5617 @c Always use hardware breakpoints
5618 @c @item swbreak (default)
5621 @subsubsection Data Cache
5622 The data cache attributes set whether @value{GDBN} will cache target
5623 memory. While this generally improves performance by reducing debug
5624 protocol overhead, it can lead to incorrect results because @value{GDBN}
5625 does not know about volatile variables or memory mapped device
5630 Enable @value{GDBN} to cache target memory.
5631 @item nocache (default)
5632 Disable @value{GDBN} from caching target memory.
5635 @c @subsubsection Memory Write Verification
5636 @c The memory write verification attributes set whether @value{GDBN}
5637 @c will re-reads data after each write to verify the write was successful.
5641 @c @item noverify (default)
5645 @chapter Using @value{GDBN} with Different Languages
5648 Although programming languages generally have common aspects, they are
5649 rarely expressed in the same manner. For instance, in ANSI C,
5650 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5651 Modula-2, it is accomplished by @code{p^}. Values can also be
5652 represented (and displayed) differently. Hex numbers in C appear as
5653 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5655 @cindex working language
5656 Language-specific information is built into @value{GDBN} for some languages,
5657 allowing you to express operations like the above in your program's
5658 native language, and allowing @value{GDBN} to output values in a manner
5659 consistent with the syntax of your program's native language. The
5660 language you use to build expressions is called the @dfn{working
5664 * Setting:: Switching between source languages
5665 * Show:: Displaying the language
5666 * Checks:: Type and range checks
5667 * Support:: Supported languages
5671 @section Switching between source languages
5673 There are two ways to control the working language---either have @value{GDBN}
5674 set it automatically, or select it manually yourself. You can use the
5675 @code{set language} command for either purpose. On startup, @value{GDBN}
5676 defaults to setting the language automatically. The working language is
5677 used to determine how expressions you type are interpreted, how values
5680 In addition to the working language, every source file that
5681 @value{GDBN} knows about has its own working language. For some object
5682 file formats, the compiler might indicate which language a particular
5683 source file is in. However, most of the time @value{GDBN} infers the
5684 language from the name of the file. The language of a source file
5685 controls whether C++ names are demangled---this way @code{backtrace} can
5686 show each frame appropriately for its own language. There is no way to
5687 set the language of a source file from within @value{GDBN}, but you can
5688 set the language associated with a filename extension. @xref{Show, ,
5689 Displaying the language}.
5691 This is most commonly a problem when you use a program, such
5692 as @code{cfront} or @code{f2c}, that generates C but is written in
5693 another language. In that case, make the
5694 program use @code{#line} directives in its C output; that way
5695 @value{GDBN} will know the correct language of the source code of the original
5696 program, and will display that source code, not the generated C code.
5699 * Filenames:: Filename extensions and languages.
5700 * Manually:: Setting the working language manually
5701 * Automatically:: Having @value{GDBN} infer the source language
5705 @subsection List of filename extensions and languages
5707 If a source file name ends in one of the following extensions, then
5708 @value{GDBN} infers that its language is the one indicated.
5733 Modula-2 source file
5737 Assembler source file. This actually behaves almost like C, but
5738 @value{GDBN} does not skip over function prologues when stepping.
5741 In addition, you may set the language associated with a filename
5742 extension. @xref{Show, , Displaying the language}.
5745 @subsection Setting the working language
5747 If you allow @value{GDBN} to set the language automatically,
5748 expressions are interpreted the same way in your debugging session and
5751 @kindex set language
5752 If you wish, you may set the language manually. To do this, issue the
5753 command @samp{set language @var{lang}}, where @var{lang} is the name of
5755 @code{c} or @code{modula-2}.
5756 For a list of the supported languages, type @samp{set language}.
5758 Setting the language manually prevents @value{GDBN} from updating the working
5759 language automatically. This can lead to confusion if you try
5760 to debug a program when the working language is not the same as the
5761 source language, when an expression is acceptable to both
5762 languages---but means different things. For instance, if the current
5763 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5771 might not have the effect you intended. In C, this means to add
5772 @code{b} and @code{c} and place the result in @code{a}. The result
5773 printed would be the value of @code{a}. In Modula-2, this means to compare
5774 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5777 @subsection Having @value{GDBN} infer the source language
5779 To have @value{GDBN} set the working language automatically, use
5780 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5781 then infers the working language. That is, when your program stops in a
5782 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5783 working language to the language recorded for the function in that
5784 frame. If the language for a frame is unknown (that is, if the function
5785 or block corresponding to the frame was defined in a source file that
5786 does not have a recognized extension), the current working language is
5787 not changed, and @value{GDBN} issues a warning.
5789 This may not seem necessary for most programs, which are written
5790 entirely in one source language. However, program modules and libraries
5791 written in one source language can be used by a main program written in
5792 a different source language. Using @samp{set language auto} in this
5793 case frees you from having to set the working language manually.
5796 @section Displaying the language
5798 The following commands help you find out which language is the
5799 working language, and also what language source files were written in.
5801 @kindex show language
5802 @kindex info frame@r{, show the source language}
5803 @kindex info source@r{, show the source language}
5806 Display the current working language. This is the
5807 language you can use with commands such as @code{print} to
5808 build and compute expressions that may involve variables in your program.
5811 Display the source language for this frame. This language becomes the
5812 working language if you use an identifier from this frame.
5813 @xref{Frame Info, ,Information about a frame}, to identify the other
5814 information listed here.
5817 Display the source language of this source file.
5818 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5819 information listed here.
5822 In unusual circumstances, you may have source files with extensions
5823 not in the standard list. You can then set the extension associated
5824 with a language explicitly:
5826 @kindex set extension-language
5827 @kindex info extensions
5829 @item set extension-language @var{.ext} @var{language}
5830 Set source files with extension @var{.ext} to be assumed to be in
5831 the source language @var{language}.
5833 @item info extensions
5834 List all the filename extensions and the associated languages.
5838 @section Type and range checking
5841 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5842 checking are included, but they do not yet have any effect. This
5843 section documents the intended facilities.
5845 @c FIXME remove warning when type/range code added
5847 Some languages are designed to guard you against making seemingly common
5848 errors through a series of compile- and run-time checks. These include
5849 checking the type of arguments to functions and operators, and making
5850 sure mathematical overflows are caught at run time. Checks such as
5851 these help to ensure a program's correctness once it has been compiled
5852 by eliminating type mismatches, and providing active checks for range
5853 errors when your program is running.
5855 @value{GDBN} can check for conditions like the above if you wish.
5856 Although @value{GDBN} does not check the statements in your program, it
5857 can check expressions entered directly into @value{GDBN} for evaluation via
5858 the @code{print} command, for example. As with the working language,
5859 @value{GDBN} can also decide whether or not to check automatically based on
5860 your program's source language. @xref{Support, ,Supported languages},
5861 for the default settings of supported languages.
5864 * Type Checking:: An overview of type checking
5865 * Range Checking:: An overview of range checking
5868 @cindex type checking
5869 @cindex checks, type
5871 @subsection An overview of type checking
5873 Some languages, such as Modula-2, are strongly typed, meaning that the
5874 arguments to operators and functions have to be of the correct type,
5875 otherwise an error occurs. These checks prevent type mismatch
5876 errors from ever causing any run-time problems. For example,
5884 The second example fails because the @code{CARDINAL} 1 is not
5885 type-compatible with the @code{REAL} 2.3.
5887 For the expressions you use in @value{GDBN} commands, you can tell the
5888 @value{GDBN} type checker to skip checking;
5889 to treat any mismatches as errors and abandon the expression;
5890 or to only issue warnings when type mismatches occur,
5891 but evaluate the expression anyway. When you choose the last of
5892 these, @value{GDBN} evaluates expressions like the second example above, but
5893 also issues a warning.
5895 Even if you turn type checking off, there may be other reasons
5896 related to type that prevent @value{GDBN} from evaluating an expression.
5897 For instance, @value{GDBN} does not know how to add an @code{int} and
5898 a @code{struct foo}. These particular type errors have nothing to do
5899 with the language in use, and usually arise from expressions, such as
5900 the one described above, which make little sense to evaluate anyway.
5902 Each language defines to what degree it is strict about type. For
5903 instance, both Modula-2 and C require the arguments to arithmetical
5904 operators to be numbers. In C, enumerated types and pointers can be
5905 represented as numbers, so that they are valid arguments to mathematical
5906 operators. @xref{Support, ,Supported languages}, for further
5907 details on specific languages.
5909 @value{GDBN} provides some additional commands for controlling the type checker:
5911 @kindex set check@r{, type}
5912 @kindex set check type
5913 @kindex show check type
5915 @item set check type auto
5916 Set type checking on or off based on the current working language.
5917 @xref{Support, ,Supported languages}, for the default settings for
5920 @item set check type on
5921 @itemx set check type off
5922 Set type checking on or off, overriding the default setting for the
5923 current working language. Issue a warning if the setting does not
5924 match the language default. If any type mismatches occur in
5925 evaluating an expression while type checking is on, @value{GDBN} prints a
5926 message and aborts evaluation of the expression.
5928 @item set check type warn
5929 Cause the type checker to issue warnings, but to always attempt to
5930 evaluate the expression. Evaluating the expression may still
5931 be impossible for other reasons. For example, @value{GDBN} cannot add
5932 numbers and structures.
5935 Show the current setting of the type checker, and whether or not @value{GDBN}
5936 is setting it automatically.
5939 @cindex range checking
5940 @cindex checks, range
5941 @node Range Checking
5942 @subsection An overview of range checking
5944 In some languages (such as Modula-2), it is an error to exceed the
5945 bounds of a type; this is enforced with run-time checks. Such range
5946 checking is meant to ensure program correctness by making sure
5947 computations do not overflow, or indices on an array element access do
5948 not exceed the bounds of the array.
5950 For expressions you use in @value{GDBN} commands, you can tell
5951 @value{GDBN} to treat range errors in one of three ways: ignore them,
5952 always treat them as errors and abandon the expression, or issue
5953 warnings but evaluate the expression anyway.
5955 A range error can result from numerical overflow, from exceeding an
5956 array index bound, or when you type a constant that is not a member
5957 of any type. Some languages, however, do not treat overflows as an
5958 error. In many implementations of C, mathematical overflow causes the
5959 result to ``wrap around'' to lower values---for example, if @var{m} is
5960 the largest integer value, and @var{s} is the smallest, then
5963 @var{m} + 1 @result{} @var{s}
5966 This, too, is specific to individual languages, and in some cases
5967 specific to individual compilers or machines. @xref{Support, ,
5968 Supported languages}, for further details on specific languages.
5970 @value{GDBN} provides some additional commands for controlling the range checker:
5972 @kindex set check@r{, range}
5973 @kindex set check range
5974 @kindex show check range
5976 @item set check range auto
5977 Set range checking on or off based on the current working language.
5978 @xref{Support, ,Supported languages}, for the default settings for
5981 @item set check range on
5982 @itemx set check range off
5983 Set range checking on or off, overriding the default setting for the
5984 current working language. A warning is issued if the setting does not
5985 match the language default. If a range error occurs and range checking is on,
5986 then a message is printed and evaluation of the expression is aborted.
5988 @item set check range warn
5989 Output messages when the @value{GDBN} range checker detects a range error,
5990 but attempt to evaluate the expression anyway. Evaluating the
5991 expression may still be impossible for other reasons, such as accessing
5992 memory that the process does not own (a typical example from many Unix
5996 Show the current setting of the range checker, and whether or not it is
5997 being set automatically by @value{GDBN}.
6001 @section Supported languages
6003 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
6004 @c This is false ...
6005 Some @value{GDBN} features may be used in expressions regardless of the
6006 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
6007 and the @samp{@{type@}addr} construct (@pxref{Expressions,
6008 ,Expressions}) can be used with the constructs of any supported
6011 The following sections detail to what degree each source language is
6012 supported by @value{GDBN}. These sections are not meant to be language
6013 tutorials or references, but serve only as a reference guide to what the
6014 @value{GDBN} expression parser accepts, and what input and output
6015 formats should look like for different languages. There are many good
6016 books written on each of these languages; please look to these for a
6017 language reference or tutorial.
6021 * Modula-2:: Modula-2
6026 @subsection C and C++
6029 @cindex expressions in C or C++
6031 Since C and C++ are so closely related, many features of @value{GDBN} apply
6032 to both languages. Whenever this is the case, we discuss those languages
6036 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
6037 @cindex @sc{gnu} C++
6038 The C++ debugging facilities are jointly implemented by the C++
6039 compiler and @value{GDBN}. Therefore, to debug your C++ code
6040 effectively, you must compile your C++ programs with a supported
6041 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
6042 compiler (@code{aCC}).
6044 For best results when using @sc{gnu} C++, use the stabs debugging
6045 format. You can select that format explicitly with the @code{g++}
6046 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
6047 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
6048 CC, gcc.info, Using @sc{gnu} CC}, for more information.
6051 * C Operators:: C and C++ operators
6052 * C Constants:: C and C++ constants
6053 * C plus plus expressions:: C++ expressions
6054 * C Defaults:: Default settings for C and C++
6055 * C Checks:: C and C++ type and range checks
6056 * Debugging C:: @value{GDBN} and C
6057 * Debugging C plus plus:: @value{GDBN} features for C++
6061 @subsubsection C and C++ operators
6063 @cindex C and C++ operators
6065 Operators must be defined on values of specific types. For instance,
6066 @code{+} is defined on numbers, but not on structures. Operators are
6067 often defined on groups of types.
6069 For the purposes of C and C++, the following definitions hold:
6074 @emph{Integral types} include @code{int} with any of its storage-class
6075 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6078 @emph{Floating-point types} include @code{float}, @code{double}, and
6079 @code{long double} (if supported by the target platform).
6082 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
6085 @emph{Scalar types} include all of the above.
6090 The following operators are supported. They are listed here
6091 in order of increasing precedence:
6095 The comma or sequencing operator. Expressions in a comma-separated list
6096 are evaluated from left to right, with the result of the entire
6097 expression being the last expression evaluated.
6100 Assignment. The value of an assignment expression is the value
6101 assigned. Defined on scalar types.
6104 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6105 and translated to @w{@code{@var{a} = @var{a op b}}}.
6106 @w{@code{@var{op}=}} and @code{=} have the same precedence.
6107 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6108 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6111 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6112 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6116 Logical @sc{or}. Defined on integral types.
6119 Logical @sc{and}. Defined on integral types.
6122 Bitwise @sc{or}. Defined on integral types.
6125 Bitwise exclusive-@sc{or}. Defined on integral types.
6128 Bitwise @sc{and}. Defined on integral types.
6131 Equality and inequality. Defined on scalar types. The value of these
6132 expressions is 0 for false and non-zero for true.
6134 @item <@r{, }>@r{, }<=@r{, }>=
6135 Less than, greater than, less than or equal, greater than or equal.
6136 Defined on scalar types. The value of these expressions is 0 for false
6137 and non-zero for true.
6140 left shift, and right shift. Defined on integral types.
6143 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6146 Addition and subtraction. Defined on integral types, floating-point types and
6149 @item *@r{, }/@r{, }%
6150 Multiplication, division, and modulus. Multiplication and division are
6151 defined on integral and floating-point types. Modulus is defined on
6155 Increment and decrement. When appearing before a variable, the
6156 operation is performed before the variable is used in an expression;
6157 when appearing after it, the variable's value is used before the
6158 operation takes place.
6161 Pointer dereferencing. Defined on pointer types. Same precedence as
6165 Address operator. Defined on variables. Same precedence as @code{++}.
6167 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6168 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6169 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6170 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6174 Negative. Defined on integral and floating-point types. Same
6175 precedence as @code{++}.
6178 Logical negation. Defined on integral types. Same precedence as
6182 Bitwise complement operator. Defined on integral types. Same precedence as
6187 Structure member, and pointer-to-structure member. For convenience,
6188 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6189 pointer based on the stored type information.
6190 Defined on @code{struct} and @code{union} data.
6193 Dereferences of pointers to members.
6196 Array indexing. @code{@var{a}[@var{i}]} is defined as
6197 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6200 Function parameter list. Same precedence as @code{->}.
6203 C++ scope resolution operator. Defined on @code{struct}, @code{union},
6204 and @code{class} types.
6207 Doubled colons also represent the @value{GDBN} scope operator
6208 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6212 If an operator is redefined in the user code, @value{GDBN} usually
6213 attempts to invoke the redefined version instead of using the operator's
6221 @subsubsection C and C++ constants
6223 @cindex C and C++ constants
6225 @value{GDBN} allows you to express the constants of C and C++ in the
6230 Integer constants are a sequence of digits. Octal constants are
6231 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6232 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6233 @samp{l}, specifying that the constant should be treated as a
6237 Floating point constants are a sequence of digits, followed by a decimal
6238 point, followed by a sequence of digits, and optionally followed by an
6239 exponent. An exponent is of the form:
6240 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6241 sequence of digits. The @samp{+} is optional for positive exponents.
6242 A floating-point constant may also end with a letter @samp{f} or
6243 @samp{F}, specifying that the constant should be treated as being of
6244 the @code{float} (as opposed to the default @code{double}) type; or with
6245 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6249 Enumerated constants consist of enumerated identifiers, or their
6250 integral equivalents.
6253 Character constants are a single character surrounded by single quotes
6254 (@code{'}), or a number---the ordinal value of the corresponding character
6255 (usually its @sc{ascii} value). Within quotes, the single character may
6256 be represented by a letter or by @dfn{escape sequences}, which are of
6257 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6258 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6259 @samp{@var{x}} is a predefined special character---for example,
6260 @samp{\n} for newline.
6263 String constants are a sequence of character constants surrounded by
6264 double quotes (@code{"}). Any valid character constant (as described
6265 above) may appear. Double quotes within the string must be preceded by
6266 a backslash, so for instance @samp{"a\"b'c"} is a string of five
6270 Pointer constants are an integral value. You can also write pointers
6271 to constants using the C operator @samp{&}.
6274 Array constants are comma-separated lists surrounded by braces @samp{@{}
6275 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6276 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6277 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6281 * C plus plus expressions::
6288 @node C plus plus expressions
6289 @subsubsection C++ expressions
6291 @cindex expressions in C++
6292 @value{GDBN} expression handling can interpret most C++ expressions.
6294 @cindex C++ support, not in @sc{coff}
6295 @cindex @sc{coff} versus C++
6296 @cindex C++ and object formats
6297 @cindex object formats and C++
6298 @cindex a.out and C++
6299 @cindex @sc{ecoff} and C++
6300 @cindex @sc{xcoff} and C++
6301 @cindex @sc{elf}/stabs and C++
6302 @cindex @sc{elf}/@sc{dwarf} and C++
6303 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6304 @c periodically whether this has happened...
6306 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6307 proper compiler. Typically, C++ debugging depends on the use of
6308 additional debugging information in the symbol table, and thus requires
6309 special support. In particular, if your compiler generates a.out, MIPS
6310 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6311 symbol table, these facilities are all available. (With @sc{gnu} CC,
6312 you can use the @samp{-gstabs} option to request stabs debugging
6313 extensions explicitly.) Where the object code format is standard
6314 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6315 support in @value{GDBN} does @emph{not} work.
6320 @cindex member functions
6322 Member function calls are allowed; you can use expressions like
6325 count = aml->GetOriginal(x, y)
6328 @vindex this@r{, inside C@t{++} member functions}
6329 @cindex namespace in C++
6331 While a member function is active (in the selected stack frame), your
6332 expressions have the same namespace available as the member function;
6333 that is, @value{GDBN} allows implicit references to the class instance
6334 pointer @code{this} following the same rules as C++.
6336 @cindex call overloaded functions
6337 @cindex overloaded functions, calling
6338 @cindex type conversions in C++
6340 You can call overloaded functions; @value{GDBN} resolves the function
6341 call to the right definition, with some restrictions. @value{GDBN} does not
6342 perform overload resolution involving user-defined type conversions,
6343 calls to constructors, or instantiations of templates that do not exist
6344 in the program. It also cannot handle ellipsis argument lists or
6347 It does perform integral conversions and promotions, floating-point
6348 promotions, arithmetic conversions, pointer conversions, conversions of
6349 class objects to base classes, and standard conversions such as those of
6350 functions or arrays to pointers; it requires an exact match on the
6351 number of function arguments.
6353 Overload resolution is always performed, unless you have specified
6354 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6355 ,@value{GDBN} features for C++}.
6357 You must specify @code{set overload-resolution off} in order to use an
6358 explicit function signature to call an overloaded function, as in
6360 p 'foo(char,int)'('x', 13)
6363 The @value{GDBN} command-completion facility can simplify this;
6364 see @ref{Completion, ,Command completion}.
6366 @cindex reference declarations
6368 @value{GDBN} understands variables declared as C++ references; you can use
6369 them in expressions just as you do in C++ source---they are automatically
6372 In the parameter list shown when @value{GDBN} displays a frame, the values of
6373 reference variables are not displayed (unlike other variables); this
6374 avoids clutter, since references are often used for large structures.
6375 The @emph{address} of a reference variable is always shown, unless
6376 you have specified @samp{set print address off}.
6379 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6380 expressions can use it just as expressions in your program do. Since
6381 one scope may be defined in another, you can use @code{::} repeatedly if
6382 necessary, for example in an expression like
6383 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6384 resolving name scope by reference to source files, in both C and C++
6385 debugging (@pxref{Variables, ,Program variables}).
6388 In addition, when used with HP's C++ compiler, @value{GDBN} supports
6389 calling virtual functions correctly, printing out virtual bases of
6390 objects, calling functions in a base subobject, casting objects, and
6391 invoking user-defined operators.
6394 @subsubsection C and C++ defaults
6396 @cindex C and C++ defaults
6398 If you allow @value{GDBN} to set type and range checking automatically, they
6399 both default to @code{off} whenever the working language changes to
6400 C or C++. This happens regardless of whether you or @value{GDBN}
6401 selects the working language.
6403 If you allow @value{GDBN} to set the language automatically, it
6404 recognizes source files whose names end with @file{.c}, @file{.C}, or
6405 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6406 these files, it sets the working language to C or C++.
6407 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6408 for further details.
6410 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6411 @c unimplemented. If (b) changes, it might make sense to let this node
6412 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6415 @subsubsection C and C++ type and range checks
6417 @cindex C and C++ checks
6419 By default, when @value{GDBN} parses C or C++ expressions, type checking
6420 is not used. However, if you turn type checking on, @value{GDBN}
6421 considers two variables type equivalent if:
6425 The two variables are structured and have the same structure, union, or
6429 The two variables have the same type name, or types that have been
6430 declared equivalent through @code{typedef}.
6433 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6436 The two @code{struct}, @code{union}, or @code{enum} variables are
6437 declared in the same declaration. (Note: this may not be true for all C
6442 Range checking, if turned on, is done on mathematical operations. Array
6443 indices are not checked, since they are often used to index a pointer
6444 that is not itself an array.
6447 @subsubsection @value{GDBN} and C
6449 The @code{set print union} and @code{show print union} commands apply to
6450 the @code{union} type. When set to @samp{on}, any @code{union} that is
6451 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6452 appears as @samp{@{...@}}.
6454 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6455 with pointers and a memory allocation function. @xref{Expressions,
6459 * Debugging C plus plus::
6462 @node Debugging C plus plus
6463 @subsubsection @value{GDBN} features for C++
6465 @cindex commands for C++
6467 Some @value{GDBN} commands are particularly useful with C++, and some are
6468 designed specifically for use with C++. Here is a summary:
6471 @cindex break in overloaded functions
6472 @item @r{breakpoint menus}
6473 When you want a breakpoint in a function whose name is overloaded,
6474 @value{GDBN} breakpoint menus help you specify which function definition
6475 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6477 @cindex overloading in C++
6478 @item rbreak @var{regex}
6479 Setting breakpoints using regular expressions is helpful for setting
6480 breakpoints on overloaded functions that are not members of any special
6482 @xref{Set Breaks, ,Setting breakpoints}.
6484 @cindex C++ exception handling
6487 Debug C++ exception handling using these commands. @xref{Set
6488 Catchpoints, , Setting catchpoints}.
6491 @item ptype @var{typename}
6492 Print inheritance relationships as well as other information for type
6494 @xref{Symbols, ,Examining the Symbol Table}.
6496 @cindex C++ symbol display
6497 @item set print demangle
6498 @itemx show print demangle
6499 @itemx set print asm-demangle
6500 @itemx show print asm-demangle
6501 Control whether C++ symbols display in their source form, both when
6502 displaying code as C++ source and when displaying disassemblies.
6503 @xref{Print Settings, ,Print settings}.
6505 @item set print object
6506 @itemx show print object
6507 Choose whether to print derived (actual) or declared types of objects.
6508 @xref{Print Settings, ,Print settings}.
6510 @item set print vtbl
6511 @itemx show print vtbl
6512 Control the format for printing virtual function tables.
6513 @xref{Print Settings, ,Print settings}.
6514 (The @code{vtbl} commands do not work on programs compiled with the HP
6515 ANSI C++ compiler (@code{aCC}).)
6517 @kindex set overload-resolution
6518 @cindex overloaded functions, overload resolution
6519 @item set overload-resolution on
6520 Enable overload resolution for C++ expression evaluation. The default
6521 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6522 and searches for a function whose signature matches the argument types,
6523 using the standard C++ conversion rules (see @ref{C plus plus expressions, ,C++
6524 expressions}, for details). If it cannot find a match, it emits a
6527 @item set overload-resolution off
6528 Disable overload resolution for C++ expression evaluation. For
6529 overloaded functions that are not class member functions, @value{GDBN}
6530 chooses the first function of the specified name that it finds in the
6531 symbol table, whether or not its arguments are of the correct type. For
6532 overloaded functions that are class member functions, @value{GDBN}
6533 searches for a function whose signature @emph{exactly} matches the
6536 @item @r{Overloaded symbol names}
6537 You can specify a particular definition of an overloaded symbol, using
6538 the same notation that is used to declare such symbols in C++: type
6539 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6540 also use the @value{GDBN} command-line word completion facilities to list the
6541 available choices, or to finish the type list for you.
6542 @xref{Completion,, Command completion}, for details on how to do this.
6546 @subsection Modula-2
6548 @cindex Modula-2, @value{GDBN} support
6550 The extensions made to @value{GDBN} to support Modula-2 only support
6551 output from the @sc{gnu} Modula-2 compiler (which is currently being
6552 developed). Other Modula-2 compilers are not currently supported, and
6553 attempting to debug executables produced by them is most likely
6554 to give an error as @value{GDBN} reads in the executable's symbol
6557 @cindex expressions in Modula-2
6559 * M2 Operators:: Built-in operators
6560 * Built-In Func/Proc:: Built-in functions and procedures
6561 * M2 Constants:: Modula-2 constants
6562 * M2 Defaults:: Default settings for Modula-2
6563 * Deviations:: Deviations from standard Modula-2
6564 * M2 Checks:: Modula-2 type and range checks
6565 * M2 Scope:: The scope operators @code{::} and @code{.}
6566 * GDB/M2:: @value{GDBN} and Modula-2
6570 @subsubsection Operators
6571 @cindex Modula-2 operators
6573 Operators must be defined on values of specific types. For instance,
6574 @code{+} is defined on numbers, but not on structures. Operators are
6575 often defined on groups of types. For the purposes of Modula-2, the
6576 following definitions hold:
6581 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6585 @emph{Character types} consist of @code{CHAR} and its subranges.
6588 @emph{Floating-point types} consist of @code{REAL}.
6591 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6595 @emph{Scalar types} consist of all of the above.
6598 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6601 @emph{Boolean types} consist of @code{BOOLEAN}.
6605 The following operators are supported, and appear in order of
6606 increasing precedence:
6610 Function argument or array index separator.
6613 Assignment. The value of @var{var} @code{:=} @var{value} is
6617 Less than, greater than on integral, floating-point, or enumerated
6621 Less than or equal to, greater than or equal to
6622 on integral, floating-point and enumerated types, or set inclusion on
6623 set types. Same precedence as @code{<}.
6625 @item =@r{, }<>@r{, }#
6626 Equality and two ways of expressing inequality, valid on scalar types.
6627 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6628 available for inequality, since @code{#} conflicts with the script
6632 Set membership. Defined on set types and the types of their members.
6633 Same precedence as @code{<}.
6636 Boolean disjunction. Defined on boolean types.
6639 Boolean conjunction. Defined on boolean types.
6642 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6645 Addition and subtraction on integral and floating-point types, or union
6646 and difference on set types.
6649 Multiplication on integral and floating-point types, or set intersection
6653 Division on floating-point types, or symmetric set difference on set
6654 types. Same precedence as @code{*}.
6657 Integer division and remainder. Defined on integral types. Same
6658 precedence as @code{*}.
6661 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6664 Pointer dereferencing. Defined on pointer types.
6667 Boolean negation. Defined on boolean types. Same precedence as
6671 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6672 precedence as @code{^}.
6675 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6678 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6682 @value{GDBN} and Modula-2 scope operators.
6686 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6687 treats the use of the operator @code{IN}, or the use of operators
6688 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6689 @code{<=}, and @code{>=} on sets as an error.
6692 @cindex Modula-2 built-ins
6693 @node Built-In Func/Proc
6694 @subsubsection Built-in functions and procedures
6696 Modula-2 also makes available several built-in procedures and functions.
6697 In describing these, the following metavariables are used:
6702 represents an @code{ARRAY} variable.
6705 represents a @code{CHAR} constant or variable.
6708 represents a variable or constant of integral type.
6711 represents an identifier that belongs to a set. Generally used in the
6712 same function with the metavariable @var{s}. The type of @var{s} should
6713 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6716 represents a variable or constant of integral or floating-point type.
6719 represents a variable or constant of floating-point type.
6725 represents a variable.
6728 represents a variable or constant of one of many types. See the
6729 explanation of the function for details.
6732 All Modula-2 built-in procedures also return a result, described below.
6736 Returns the absolute value of @var{n}.
6739 If @var{c} is a lower case letter, it returns its upper case
6740 equivalent, otherwise it returns its argument.
6743 Returns the character whose ordinal value is @var{i}.
6746 Decrements the value in the variable @var{v} by one. Returns the new value.
6748 @item DEC(@var{v},@var{i})
6749 Decrements the value in the variable @var{v} by @var{i}. Returns the
6752 @item EXCL(@var{m},@var{s})
6753 Removes the element @var{m} from the set @var{s}. Returns the new
6756 @item FLOAT(@var{i})
6757 Returns the floating point equivalent of the integer @var{i}.
6760 Returns the index of the last member of @var{a}.
6763 Increments the value in the variable @var{v} by one. Returns the new value.
6765 @item INC(@var{v},@var{i})
6766 Increments the value in the variable @var{v} by @var{i}. Returns the
6769 @item INCL(@var{m},@var{s})
6770 Adds the element @var{m} to the set @var{s} if it is not already
6771 there. Returns the new set.
6774 Returns the maximum value of the type @var{t}.
6777 Returns the minimum value of the type @var{t}.
6780 Returns boolean TRUE if @var{i} is an odd number.
6783 Returns the ordinal value of its argument. For example, the ordinal
6784 value of a character is its @sc{ascii} value (on machines supporting the
6785 @sc{ascii} character set). @var{x} must be of an ordered type, which include
6786 integral, character and enumerated types.
6789 Returns the size of its argument. @var{x} can be a variable or a type.
6791 @item TRUNC(@var{r})
6792 Returns the integral part of @var{r}.
6794 @item VAL(@var{t},@var{i})
6795 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6799 @emph{Warning:} Sets and their operations are not yet supported, so
6800 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6804 @cindex Modula-2 constants
6806 @subsubsection Constants
6808 @value{GDBN} allows you to express the constants of Modula-2 in the following
6814 Integer constants are simply a sequence of digits. When used in an
6815 expression, a constant is interpreted to be type-compatible with the
6816 rest of the expression. Hexadecimal integers are specified by a
6817 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6820 Floating point constants appear as a sequence of digits, followed by a
6821 decimal point and another sequence of digits. An optional exponent can
6822 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6823 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6824 digits of the floating point constant must be valid decimal (base 10)
6828 Character constants consist of a single character enclosed by a pair of
6829 like quotes, either single (@code{'}) or double (@code{"}). They may
6830 also be expressed by their ordinal value (their @sc{ascii} value, usually)
6831 followed by a @samp{C}.
6834 String constants consist of a sequence of characters enclosed by a
6835 pair of like quotes, either single (@code{'}) or double (@code{"}).
6836 Escape sequences in the style of C are also allowed. @xref{C
6837 Constants, ,C and C++ constants}, for a brief explanation of escape
6841 Enumerated constants consist of an enumerated identifier.
6844 Boolean constants consist of the identifiers @code{TRUE} and
6848 Pointer constants consist of integral values only.
6851 Set constants are not yet supported.
6855 @subsubsection Modula-2 defaults
6856 @cindex Modula-2 defaults
6858 If type and range checking are set automatically by @value{GDBN}, they
6859 both default to @code{on} whenever the working language changes to
6860 Modula-2. This happens regardless of whether you or @value{GDBN}
6861 selected the working language.
6863 If you allow @value{GDBN} to set the language automatically, then entering
6864 code compiled from a file whose name ends with @file{.mod} sets the
6865 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6866 the language automatically}, for further details.
6869 @subsubsection Deviations from standard Modula-2
6870 @cindex Modula-2, deviations from
6872 A few changes have been made to make Modula-2 programs easier to debug.
6873 This is done primarily via loosening its type strictness:
6877 Unlike in standard Modula-2, pointer constants can be formed by
6878 integers. This allows you to modify pointer variables during
6879 debugging. (In standard Modula-2, the actual address contained in a
6880 pointer variable is hidden from you; it can only be modified
6881 through direct assignment to another pointer variable or expression that
6882 returned a pointer.)
6885 C escape sequences can be used in strings and characters to represent
6886 non-printable characters. @value{GDBN} prints out strings with these
6887 escape sequences embedded. Single non-printable characters are
6888 printed using the @samp{CHR(@var{nnn})} format.
6891 The assignment operator (@code{:=}) returns the value of its right-hand
6895 All built-in procedures both modify @emph{and} return their argument.
6899 @subsubsection Modula-2 type and range checks
6900 @cindex Modula-2 checks
6903 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6906 @c FIXME remove warning when type/range checks added
6908 @value{GDBN} considers two Modula-2 variables type equivalent if:
6912 They are of types that have been declared equivalent via a @code{TYPE
6913 @var{t1} = @var{t2}} statement
6916 They have been declared on the same line. (Note: This is true of the
6917 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6920 As long as type checking is enabled, any attempt to combine variables
6921 whose types are not equivalent is an error.
6923 Range checking is done on all mathematical operations, assignment, array
6924 index bounds, and all built-in functions and procedures.
6927 @subsubsection The scope operators @code{::} and @code{.}
6929 @cindex @code{.}, Modula-2 scope operator
6930 @cindex colon, doubled as scope operator
6932 @vindex colon-colon@r{, in Modula-2}
6933 @c Info cannot handle :: but TeX can.
6936 @vindex ::@r{, in Modula-2}
6939 There are a few subtle differences between the Modula-2 scope operator
6940 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6945 @var{module} . @var{id}
6946 @var{scope} :: @var{id}
6950 where @var{scope} is the name of a module or a procedure,
6951 @var{module} the name of a module, and @var{id} is any declared
6952 identifier within your program, except another module.
6954 Using the @code{::} operator makes @value{GDBN} search the scope
6955 specified by @var{scope} for the identifier @var{id}. If it is not
6956 found in the specified scope, then @value{GDBN} searches all scopes
6957 enclosing the one specified by @var{scope}.
6959 Using the @code{.} operator makes @value{GDBN} search the current scope for
6960 the identifier specified by @var{id} that was imported from the
6961 definition module specified by @var{module}. With this operator, it is
6962 an error if the identifier @var{id} was not imported from definition
6963 module @var{module}, or if @var{id} is not an identifier in
6967 @subsubsection @value{GDBN} and Modula-2
6969 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6970 Five subcommands of @code{set print} and @code{show print} apply
6971 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6972 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6973 apply to C++, and the last to the C @code{union} type, which has no direct
6974 analogue in Modula-2.
6976 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6977 with any language, is not useful with Modula-2. Its
6978 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6979 created in Modula-2 as they can in C or C++. However, because an
6980 address can be specified by an integral constant, the construct
6981 @samp{@{@var{type}@}@var{adrexp}} is still useful.
6983 @cindex @code{#} in Modula-2
6984 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6985 interpreted as the beginning of a comment. Use @code{<>} instead.
6990 The extensions made to @value{GDBN} to support Chill only support output
6991 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
6992 supported, and attempting to debug executables produced by them is most
6993 likely to give an error as @value{GDBN} reads in the executable's symbol
6996 @c This used to say "... following Chill related topics ...", but since
6997 @c menus are not shown in the printed manual, it would look awkward.
6998 This section covers the Chill related topics and the features
6999 of @value{GDBN} which support these topics.
7002 * How modes are displayed:: How modes are displayed
7003 * Locations:: Locations and their accesses
7004 * Values and their Operations:: Values and their Operations
7005 * Chill type and range checks::
7009 @node How modes are displayed
7010 @subsubsection How modes are displayed
7012 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
7013 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
7014 slightly from the standard specification of the Chill language. The
7017 @c FIXME: this @table's contents effectively disable @code by using @r
7018 @c on every @item. So why does it need @code?
7020 @item @r{@emph{Discrete modes:}}
7023 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
7026 @emph{Boolean Mode} which is predefined by @code{BOOL},
7028 @emph{Character Mode} which is predefined by @code{CHAR},
7030 @emph{Set Mode} which is displayed by the keyword @code{SET}.
7032 (@value{GDBP}) ptype x
7033 type = SET (karli = 10, susi = 20, fritzi = 100)
7035 If the type is an unnumbered set the set element values are omitted.
7037 @emph{Range Mode} which is displayed by
7039 @code{type = <basemode>(<lower bound> : <upper bound>)}
7041 where @code{<lower bound>, <upper bound>} can be of any discrete literal
7042 expression (e.g. set element names).
7045 @item @r{@emph{Powerset Mode:}}
7046 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7047 the member mode of the powerset. The member mode can be any discrete mode.
7049 (@value{GDBP}) ptype x
7050 type = POWERSET SET (egon, hugo, otto)
7053 @item @r{@emph{Reference Modes:}}
7056 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
7057 followed by the mode name to which the reference is bound.
7059 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7062 @item @r{@emph{Procedure mode}}
7063 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7064 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7065 list>} is a list of the parameter modes. @code{<return mode>} indicates
7066 the mode of the result of the procedure if any. The exceptionlist lists
7067 all possible exceptions which can be raised by the procedure.
7070 @item @r{@emph{Instance mode}}
7071 The instance mode is represented by a structure, which has a static
7072 type, and is therefore not really of interest.
7075 @item @r{@emph{Synchronization Modes:}}
7078 @emph{Event Mode} which is displayed by
7080 @code{EVENT (<event length>)}
7082 where @code{(<event length>)} is optional.
7084 @emph{Buffer Mode} which is displayed by
7086 @code{BUFFER (<buffer length>)<buffer element mode>}
7088 where @code{(<buffer length>)} is optional.
7091 @item @r{@emph{Timing Modes:}}
7094 @emph{Duration Mode} which is predefined by @code{DURATION}
7096 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7099 @item @r{@emph{Real Modes:}}
7100 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7102 @item @r{@emph{String Modes:}}
7105 @emph{Character String Mode} which is displayed by
7107 @code{CHARS(<string length>)}
7109 followed by the keyword @code{VARYING} if the String Mode is a varying
7112 @emph{Bit String Mode} which is displayed by
7119 @item @r{@emph{Array Mode:}}
7120 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7121 followed by the element mode (which may in turn be an array mode).
7123 (@value{GDBP}) ptype x
7126 SET (karli = 10, susi = 20, fritzi = 100)
7129 @item @r{@emph{Structure Mode}}
7130 The Structure mode is displayed by the keyword @code{STRUCT(<field
7131 list>)}. The @code{<field list>} consists of names and modes of fields
7132 of the structure. Variant structures have the keyword @code{CASE <field>
7133 OF <variant fields> ESAC} in their field list. Since the current version
7134 of the GNU Chill compiler doesn't implement tag processing (no runtime
7135 checks of variant fields, and therefore no debugging info), the output
7136 always displays all variant fields.
7138 (@value{GDBP}) ptype str
7153 @subsubsection Locations and their accesses
7155 A location in Chill is an object which can contain values.
7157 A value of a location is generally accessed by the (declared) name of
7158 the location. The output conforms to the specification of values in
7159 Chill programs. How values are specified
7160 is the topic of the next section, @ref{Values and their Operations}.
7162 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7163 display or change the result of a currently-active procedure:
7170 This does the same as the Chill action @code{RESULT EXPR} (which
7171 is not available in @value{GDBN}).
7173 Values of reference mode locations are printed by @code{PTR(<hex
7174 value>)} in case of a free reference mode, and by @code{(REF <reference
7175 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7176 represents the address where the reference points to. To access the
7177 value of the location referenced by the pointer, use the dereference
7180 Values of procedure mode locations are displayed by
7183 (<argument modes> ) <return mode> @} <address> <name of procedure
7186 @code{<argument modes>} is a list of modes according to the parameter
7187 specification of the procedure and @code{<address>} shows the address of
7191 Locations of instance modes are displayed just like a structure with two
7192 fields specifying the @emph{process type} and the @emph{copy number} of
7193 the investigated instance location@footnote{This comes from the current
7194 implementation of instances. They are implemented as a structure (no
7195 na). The output should be something like @code{[<name of the process>;
7196 <instance number>]}.}. The field names are @code{__proc_type} and
7199 Locations of synchronization modes are displayed like a structure with
7200 the field name @code{__event_data} in case of a event mode location, and
7201 like a structure with the field @code{__buffer_data} in case of a buffer
7202 mode location (refer to previous paragraph).
7204 Structure Mode locations are printed by @code{[.<field name>: <value>,
7205 ...]}. The @code{<field name>} corresponds to the structure mode
7206 definition and the layout of @code{<value>} varies depending of the mode
7207 of the field. If the investigated structure mode location is of variant
7208 structure mode, the variant parts of the structure are enclosed in curled
7209 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
7210 on the same memory location and represent the current values of the
7211 memory location in their specific modes. Since no tag processing is done
7212 all variants are displayed. A variant field is printed by
7213 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7216 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7217 [.cs: []], (susi) = [.ds: susi]}]
7221 Substructures of string mode-, array mode- or structure mode-values
7222 (e.g. array slices, fields of structure locations) are accessed using
7223 certain operations which are described in the next section, @ref{Values
7224 and their Operations}.
7226 A location value may be interpreted as having a different mode using the
7227 location conversion. This mode conversion is written as @code{<mode
7228 name>(<location>)}. The user has to consider that the sizes of the modes
7229 have to be equal otherwise an error occurs. Furthermore, no range
7230 checking of the location against the destination mode is performed, and
7231 therefore the result can be quite confusing.
7234 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7237 @node Values and their Operations
7238 @subsubsection Values and their Operations
7240 Values are used to alter locations, to investigate complex structures in
7241 more detail or to filter relevant information out of a large amount of
7242 data. There are several (mode dependent) operations defined which enable
7243 such investigations. These operations are not only applicable to
7244 constant values but also to locations, which can become quite useful
7245 when debugging complex structures. During parsing the command line
7246 (e.g. evaluating an expression) @value{GDBN} treats location names as
7247 the values behind these locations.
7249 This section describes how values have to be specified and which
7250 operations are legal to be used with such values.
7253 @item Literal Values
7254 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
7255 For detailed specification refer to the @sc{gnu} Chill implementation Manual
7257 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
7258 @c be converted to a @ref.
7263 @emph{Integer Literals} are specified in the same manner as in Chill
7264 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7266 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7268 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7271 @emph{Set Literals} are defined by a name which was specified in a set
7272 mode. The value delivered by a Set Literal is the set value. This is
7273 comparable to an enumeration in C/C++ language.
7275 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7276 emptiness literal delivers either the empty reference value, the empty
7277 procedure value or the empty instance value.
7280 @emph{Character String Literals} are defined by a sequence of characters
7281 enclosed in single- or double quotes. If a single- or double quote has
7282 to be part of the string literal it has to be stuffed (specified twice).
7284 @emph{Bitstring Literals} are specified in the same manner as in Chill
7285 programs (refer z200/88 chpt 5.2.4.8).
7287 @emph{Floating point literals} are specified in the same manner as in
7288 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7293 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7294 name>} can be omitted if the mode of the tuple is unambiguous. This
7295 unambiguity is derived from the context of a evaluated expression.
7296 @code{<tuple>} can be one of the following:
7299 @item @emph{Powerset Tuple}
7300 @item @emph{Array Tuple}
7301 @item @emph{Structure Tuple}
7302 Powerset tuples, array tuples and structure tuples are specified in the
7303 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7306 @item String Element Value
7307 A string element value is specified by
7309 @code{<string value>(<index>)}
7311 where @code{<index>} is a integer expression. It delivers a character
7312 value which is equivalent to the character indexed by @code{<index>} in
7315 @item String Slice Value
7316 A string slice value is specified by @code{<string value>(<slice
7317 spec>)}, where @code{<slice spec>} can be either a range of integer
7318 expressions or specified by @code{<start expr> up <size>}.
7319 @code{<size>} denotes the number of elements which the slice contains.
7320 The delivered value is a string value, which is part of the specified
7323 @item Array Element Values
7324 An array element value is specified by @code{<array value>(<expr>)} and
7325 delivers a array element value of the mode of the specified array.
7327 @item Array Slice Values
7328 An array slice is specified by @code{<array value>(<slice spec>)}, where
7329 @code{<slice spec>} can be either a range specified by expressions or by
7330 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7331 arrayelements the slice contains. The delivered value is an array value
7332 which is part of the specified array.
7334 @item Structure Field Values
7335 A structure field value is derived by @code{<structure value>.<field
7336 name>}, where @code{<field name>} indicates the name of a field specified
7337 in the mode definition of the structure. The mode of the delivered value
7338 corresponds to this mode definition in the structure definition.
7340 @item Procedure Call Value
7341 The procedure call value is derived from the return value of the
7342 procedure@footnote{If a procedure call is used for instance in an
7343 expression, then this procedure is called with all its side
7344 effects. This can lead to confusing results if used carelessly.}.
7346 Values of duration mode locations are represented by @code{ULONG} literals.
7348 Values of time mode locations appear as
7350 @code{TIME(<secs>:<nsecs>)}
7355 This is not implemented yet:
7356 @item Built-in Value
7358 The following built in functions are provided:
7370 @item @code{UPPER()}
7371 @item @code{LOWER()}
7372 @item @code{LENGTH()}
7376 @item @code{ARCSIN()}
7377 @item @code{ARCCOS()}
7378 @item @code{ARCTAN()}
7385 For a detailed description refer to the GNU Chill implementation manual
7389 @item Zero-adic Operator Value
7390 The zero-adic operator value is derived from the instance value for the
7391 current active process.
7393 @item Expression Values
7394 The value delivered by an expression is the result of the evaluation of
7395 the specified expression. If there are error conditions (mode
7396 incompatibility, etc.) the evaluation of expressions is aborted with a
7397 corresponding error message. Expressions may be parenthesised which
7398 causes the evaluation of this expression before any other expression
7399 which uses the result of the parenthesised expression. The following
7400 operators are supported by @value{GDBN}:
7403 @item @code{OR, ORIF, XOR}
7404 @itemx @code{AND, ANDIF}
7406 Logical operators defined over operands of boolean mode.
7409 Equality and inequality operators defined over all modes.
7413 Relational operators defined over predefined modes.
7416 @itemx @code{*, /, MOD, REM}
7417 Arithmetic operators defined over predefined modes.
7420 Change sign operator.
7423 String concatenation operator.
7426 String repetition operator.
7429 Referenced location operator which can be used either to take the
7430 address of a location (@code{->loc}), or to dereference a reference
7431 location (@code{loc->}).
7433 @item @code{OR, XOR}
7436 Powerset and bitstring operators.
7440 Powerset inclusion operators.
7443 Membership operator.
7447 @node Chill type and range checks
7448 @subsubsection Chill type and range checks
7450 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7451 of the two modes are equal. This rule applies recursively to more
7452 complex datatypes which means that complex modes are treated
7453 equivalent if all element modes (which also can be complex modes like
7454 structures, arrays, etc.) have the same size.
7456 Range checking is done on all mathematical operations, assignment, array
7457 index bounds and all built in procedures.
7459 Strong type checks are forced using the @value{GDBN} command @code{set
7460 check strong}. This enforces strong type and range checks on all
7461 operations where Chill constructs are used (expressions, built in
7462 functions, etc.) in respect to the semantics as defined in the z.200
7463 language specification.
7465 All checks can be disabled by the @value{GDBN} command @code{set check
7469 @c Deviations from the Chill Standard Z200/88
7470 see last paragraph ?
7473 @node Chill defaults
7474 @subsubsection Chill defaults
7476 If type and range checking are set automatically by @value{GDBN}, they
7477 both default to @code{on} whenever the working language changes to
7478 Chill. This happens regardless of whether you or @value{GDBN}
7479 selected the working language.
7481 If you allow @value{GDBN} to set the language automatically, then entering
7482 code compiled from a file whose name ends with @file{.ch} sets the
7483 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7484 the language automatically}, for further details.
7487 @chapter Examining the Symbol Table
7489 The commands described in this chapter allow you to inquire about the
7490 symbols (names of variables, functions and types) defined in your
7491 program. This information is inherent in the text of your program and
7492 does not change as your program executes. @value{GDBN} finds it in your
7493 program's symbol table, in the file indicated when you started @value{GDBN}
7494 (@pxref{File Options, ,Choosing files}), or by one of the
7495 file-management commands (@pxref{Files, ,Commands to specify files}).
7497 @cindex symbol names
7498 @cindex names of symbols
7499 @cindex quoting names
7500 Occasionally, you may need to refer to symbols that contain unusual
7501 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7502 most frequent case is in referring to static variables in other
7503 source files (@pxref{Variables,,Program variables}). File names
7504 are recorded in object files as debugging symbols, but @value{GDBN} would
7505 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7506 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7507 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7514 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7517 @kindex info address
7518 @item info address @var{symbol}
7519 Describe where the data for @var{symbol} is stored. For a register
7520 variable, this says which register it is kept in. For a non-register
7521 local variable, this prints the stack-frame offset at which the variable
7524 Note the contrast with @samp{print &@var{symbol}}, which does not work
7525 at all for a register variable, and for a stack local variable prints
7526 the exact address of the current instantiation of the variable.
7529 @item info symbol @var{addr}
7530 Print the name of a symbol which is stored at the address @var{addr}.
7531 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
7532 nearest symbol and an offset from it:
7535 (@value{GDBP}) info symbol 0x54320
7536 _initialize_vx + 396 in section .text
7540 This is the opposite of the @code{info address} command. You can use
7541 it to find out the name of a variable or a function given its address.
7544 @item whatis @var{expr}
7545 Print the data type of expression @var{expr}. @var{expr} is not
7546 actually evaluated, and any side-effecting operations (such as
7547 assignments or function calls) inside it do not take place.
7548 @xref{Expressions, ,Expressions}.
7551 Print the data type of @code{$}, the last value in the value history.
7554 @item ptype @var{typename}
7555 Print a description of data type @var{typename}. @var{typename} may be
7556 the name of a type, or for C code it may have the form @samp{class
7557 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7558 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7560 @item ptype @var{expr}
7562 Print a description of the type of expression @var{expr}. @code{ptype}
7563 differs from @code{whatis} by printing a detailed description, instead
7564 of just the name of the type.
7566 For example, for this variable declaration:
7569 struct complex @{double real; double imag;@} v;
7573 the two commands give this output:
7577 (@value{GDBP}) whatis v
7578 type = struct complex
7579 (@value{GDBP}) ptype v
7580 type = struct complex @{
7588 As with @code{whatis}, using @code{ptype} without an argument refers to
7589 the type of @code{$}, the last value in the value history.
7592 @item info types @var{regexp}
7594 Print a brief description of all types whose names match @var{regexp}
7595 (or all types in your program, if you supply no argument). Each
7596 complete typename is matched as though it were a complete line; thus,
7597 @samp{i type value} gives information on all types in your program whose
7598 names include the string @code{value}, but @samp{i type ^value$} gives
7599 information only on types whose complete name is @code{value}.
7601 This command differs from @code{ptype} in two ways: first, like
7602 @code{whatis}, it does not print a detailed description; second, it
7603 lists all source files where a type is defined.
7607 Show the name of the current source file---that is, the source file for
7608 the function containing the current point of execution---and the language
7611 @kindex info sources
7613 Print the names of all source files in your program for which there is
7614 debugging information, organized into two lists: files whose symbols
7615 have already been read, and files whose symbols will be read when needed.
7617 @kindex info functions
7618 @item info functions
7619 Print the names and data types of all defined functions.
7621 @item info functions @var{regexp}
7622 Print the names and data types of all defined functions
7623 whose names contain a match for regular expression @var{regexp}.
7624 Thus, @samp{info fun step} finds all functions whose names
7625 include @code{step}; @samp{info fun ^step} finds those whose names
7626 start with @code{step}.
7628 @kindex info variables
7629 @item info variables
7630 Print the names and data types of all variables that are declared
7631 outside of functions (i.e., excluding local variables).
7633 @item info variables @var{regexp}
7634 Print the names and data types of all variables (except for local
7635 variables) whose names contain a match for regular expression
7639 This was never implemented.
7640 @kindex info methods
7642 @itemx info methods @var{regexp}
7643 The @code{info methods} command permits the user to examine all defined
7644 methods within C++ program, or (with the @var{regexp} argument) a
7645 specific set of methods found in the various C++ classes. Many
7646 C++ classes provide a large number of methods. Thus, the output
7647 from the @code{ptype} command can be overwhelming and hard to use. The
7648 @code{info-methods} command filters the methods, printing only those
7649 which match the regular-expression @var{regexp}.
7652 @cindex reloading symbols
7653 Some systems allow individual object files that make up your program to
7654 be replaced without stopping and restarting your program. For example,
7655 in VxWorks you can simply recompile a defective object file and keep on
7656 running. If you are running on one of these systems, you can allow
7657 @value{GDBN} to reload the symbols for automatically relinked modules:
7660 @kindex set symbol-reloading
7661 @item set symbol-reloading on
7662 Replace symbol definitions for the corresponding source file when an
7663 object file with a particular name is seen again.
7665 @item set symbol-reloading off
7666 Do not replace symbol definitions when encountering object files of the
7667 same name more than once. This is the default state; if you are not
7668 running on a system that permits automatic relinking of modules, you
7669 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
7670 may discard symbols when linking large programs, that may contain
7671 several modules (from different directories or libraries) with the same
7674 @kindex show symbol-reloading
7675 @item show symbol-reloading
7676 Show the current @code{on} or @code{off} setting.
7679 @kindex set opaque-type-resolution
7680 @item set opaque-type-resolution on
7681 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7682 declared as a pointer to a @code{struct}, @code{class}, or
7683 @code{union}---for example, @code{struct MyType *}---that is used in one
7684 source file although the full declaration of @code{struct MyType} is in
7685 another source file. The default is on.
7687 A change in the setting of this subcommand will not take effect until
7688 the next time symbols for a file are loaded.
7690 @item set opaque-type-resolution off
7691 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7692 is printed as follows:
7694 @{<no data fields>@}
7697 @kindex show opaque-type-resolution
7698 @item show opaque-type-resolution
7699 Show whether opaque types are resolved or not.
7701 @kindex maint print symbols
7703 @kindex maint print psymbols
7704 @cindex partial symbol dump
7705 @item maint print symbols @var{filename}
7706 @itemx maint print psymbols @var{filename}
7707 @itemx maint print msymbols @var{filename}
7708 Write a dump of debugging symbol data into the file @var{filename}.
7709 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7710 symbols with debugging data are included. If you use @samp{maint print
7711 symbols}, @value{GDBN} includes all the symbols for which it has already
7712 collected full details: that is, @var{filename} reflects symbols for
7713 only those files whose symbols @value{GDBN} has read. You can use the
7714 command @code{info sources} to find out which files these are. If you
7715 use @samp{maint print psymbols} instead, the dump shows information about
7716 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7717 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7718 @samp{maint print msymbols} dumps just the minimal symbol information
7719 required for each object file from which @value{GDBN} has read some symbols.
7720 @xref{Files, ,Commands to specify files}, for a discussion of how
7721 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7725 @chapter Altering Execution
7727 Once you think you have found an error in your program, you might want to
7728 find out for certain whether correcting the apparent error would lead to
7729 correct results in the rest of the run. You can find the answer by
7730 experiment, using the @value{GDBN} features for altering execution of the
7733 For example, you can store new values into variables or memory
7734 locations, give your program a signal, restart it at a different
7735 address, or even return prematurely from a function.
7738 * Assignment:: Assignment to variables
7739 * Jumping:: Continuing at a different address
7740 * Signaling:: Giving your program a signal
7741 * Returning:: Returning from a function
7742 * Calling:: Calling your program's functions
7743 * Patching:: Patching your program
7747 @section Assignment to variables
7750 @cindex setting variables
7751 To alter the value of a variable, evaluate an assignment expression.
7752 @xref{Expressions, ,Expressions}. For example,
7759 stores the value 4 into the variable @code{x}, and then prints the
7760 value of the assignment expression (which is 4).
7761 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7762 information on operators in supported languages.
7764 @kindex set variable
7765 @cindex variables, setting
7766 If you are not interested in seeing the value of the assignment, use the
7767 @code{set} command instead of the @code{print} command. @code{set} is
7768 really the same as @code{print} except that the expression's value is
7769 not printed and is not put in the value history (@pxref{Value History,
7770 ,Value history}). The expression is evaluated only for its effects.
7772 If the beginning of the argument string of the @code{set} command
7773 appears identical to a @code{set} subcommand, use the @code{set
7774 variable} command instead of just @code{set}. This command is identical
7775 to @code{set} except for its lack of subcommands. For example, if your
7776 program has a variable @code{width}, you get an error if you try to set
7777 a new value with just @samp{set width=13}, because @value{GDBN} has the
7778 command @code{set width}:
7781 (@value{GDBP}) whatis width
7783 (@value{GDBP}) p width
7785 (@value{GDBP}) set width=47
7786 Invalid syntax in expression.
7790 The invalid expression, of course, is @samp{=47}. In
7791 order to actually set the program's variable @code{width}, use
7794 (@value{GDBP}) set var width=47
7797 Because the @code{set} command has many subcommands that can conflict
7798 with the names of program variables, it is a good idea to use the
7799 @code{set variable} command instead of just @code{set}. For example, if
7800 your program has a variable @code{g}, you run into problems if you try
7801 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7802 the command @code{set gnutarget}, abbreviated @code{set g}:
7806 (@value{GDBP}) whatis g
7810 (@value{GDBP}) set g=4
7814 The program being debugged has been started already.
7815 Start it from the beginning? (y or n) y
7816 Starting program: /home/smith/cc_progs/a.out
7817 "/home/smith/cc_progs/a.out": can't open to read symbols:
7819 (@value{GDBP}) show g
7820 The current BFD target is "=4".
7825 The program variable @code{g} did not change, and you silently set the
7826 @code{gnutarget} to an invalid value. In order to set the variable
7830 (@value{GDBP}) set var g=4
7833 @value{GDBN} allows more implicit conversions in assignments than C; you can
7834 freely store an integer value into a pointer variable or vice versa,
7835 and you can convert any structure to any other structure that is the
7836 same length or shorter.
7837 @comment FIXME: how do structs align/pad in these conversions?
7838 @comment /doc@cygnus.com 18dec1990
7840 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7841 construct to generate a value of specified type at a specified address
7842 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7843 to memory location @code{0x83040} as an integer (which implies a certain size
7844 and representation in memory), and
7847 set @{int@}0x83040 = 4
7851 stores the value 4 into that memory location.
7854 @section Continuing at a different address
7856 Ordinarily, when you continue your program, you do so at the place where
7857 it stopped, with the @code{continue} command. You can instead continue at
7858 an address of your own choosing, with the following commands:
7862 @item jump @var{linespec}
7863 Resume execution at line @var{linespec}. Execution stops again
7864 immediately if there is a breakpoint there. @xref{List, ,Printing
7865 source lines}, for a description of the different forms of
7866 @var{linespec}. It is common practice to use the @code{tbreak} command
7867 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7870 The @code{jump} command does not change the current stack frame, or
7871 the stack pointer, or the contents of any memory location or any
7872 register other than the program counter. If line @var{linespec} is in
7873 a different function from the one currently executing, the results may
7874 be bizarre if the two functions expect different patterns of arguments or
7875 of local variables. For this reason, the @code{jump} command requests
7876 confirmation if the specified line is not in the function currently
7877 executing. However, even bizarre results are predictable if you are
7878 well acquainted with the machine-language code of your program.
7880 @item jump *@var{address}
7881 Resume execution at the instruction at address @var{address}.
7884 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7885 On many systems, you can get much the same effect as the @code{jump}
7886 command by storing a new value into the register @code{$pc}. The
7887 difference is that this does not start your program running; it only
7888 changes the address of where it @emph{will} run when you continue. For
7896 makes the next @code{continue} command or stepping command execute at
7897 address @code{0x485}, rather than at the address where your program stopped.
7898 @xref{Continuing and Stepping, ,Continuing and stepping}.
7900 The most common occasion to use the @code{jump} command is to back
7901 up---perhaps with more breakpoints set---over a portion of a program
7902 that has already executed, in order to examine its execution in more
7907 @section Giving your program a signal
7911 @item signal @var{signal}
7912 Resume execution where your program stopped, but immediately give it the
7913 signal @var{signal}. @var{signal} can be the name or the number of a
7914 signal. For example, on many systems @code{signal 2} and @code{signal
7915 SIGINT} are both ways of sending an interrupt signal.
7917 Alternatively, if @var{signal} is zero, continue execution without
7918 giving a signal. This is useful when your program stopped on account of
7919 a signal and would ordinary see the signal when resumed with the
7920 @code{continue} command; @samp{signal 0} causes it to resume without a
7923 @code{signal} does not repeat when you press @key{RET} a second time
7924 after executing the command.
7928 Invoking the @code{signal} command is not the same as invoking the
7929 @code{kill} utility from the shell. Sending a signal with @code{kill}
7930 causes @value{GDBN} to decide what to do with the signal depending on
7931 the signal handling tables (@pxref{Signals}). The @code{signal} command
7932 passes the signal directly to your program.
7936 @section Returning from a function
7939 @cindex returning from a function
7942 @itemx return @var{expression}
7943 You can cancel execution of a function call with the @code{return}
7944 command. If you give an
7945 @var{expression} argument, its value is used as the function's return
7949 When you use @code{return}, @value{GDBN} discards the selected stack frame
7950 (and all frames within it). You can think of this as making the
7951 discarded frame return prematurely. If you wish to specify a value to
7952 be returned, give that value as the argument to @code{return}.
7954 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7955 frame}), and any other frames inside of it, leaving its caller as the
7956 innermost remaining frame. That frame becomes selected. The
7957 specified value is stored in the registers used for returning values
7960 The @code{return} command does not resume execution; it leaves the
7961 program stopped in the state that would exist if the function had just
7962 returned. In contrast, the @code{finish} command (@pxref{Continuing
7963 and Stepping, ,Continuing and stepping}) resumes execution until the
7964 selected stack frame returns naturally.
7967 @section Calling program functions
7969 @cindex calling functions
7972 @item call @var{expr}
7973 Evaluate the expression @var{expr} without displaying @code{void}
7977 You can use this variant of the @code{print} command if you want to
7978 execute a function from your program, but without cluttering the output
7979 with @code{void} returned values. If the result is not void, it
7980 is printed and saved in the value history.
7982 For the A29K, a user-controlled variable @code{call_scratch_address},
7983 specifies the location of a scratch area to be used when @value{GDBN}
7984 calls a function in the target. This is necessary because the usual
7985 method of putting the scratch area on the stack does not work in systems
7986 that have separate instruction and data spaces.
7989 @section Patching programs
7991 @cindex patching binaries
7992 @cindex writing into executables
7993 @cindex writing into corefiles
7995 By default, @value{GDBN} opens the file containing your program's
7996 executable code (or the corefile) read-only. This prevents accidental
7997 alterations to machine code; but it also prevents you from intentionally
7998 patching your program's binary.
8000 If you'd like to be able to patch the binary, you can specify that
8001 explicitly with the @code{set write} command. For example, you might
8002 want to turn on internal debugging flags, or even to make emergency
8008 @itemx set write off
8009 If you specify @samp{set write on}, @value{GDBN} opens executable and
8010 core files for both reading and writing; if you specify @samp{set write
8011 off} (the default), @value{GDBN} opens them read-only.
8013 If you have already loaded a file, you must load it again (using the
8014 @code{exec-file} or @code{core-file} command) after changing @code{set
8015 write}, for your new setting to take effect.
8019 Display whether executable files and core files are opened for writing
8024 @chapter @value{GDBN} Files
8026 @value{GDBN} needs to know the file name of the program to be debugged,
8027 both in order to read its symbol table and in order to start your
8028 program. To debug a core dump of a previous run, you must also tell
8029 @value{GDBN} the name of the core dump file.
8032 * Files:: Commands to specify files
8033 * Symbol Errors:: Errors reading symbol files
8037 @section Commands to specify files
8039 @cindex symbol table
8040 @cindex core dump file
8042 You may want to specify executable and core dump file names. The usual
8043 way to do this is at start-up time, using the arguments to
8044 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
8045 Out of @value{GDBN}}).
8047 Occasionally it is necessary to change to a different file during a
8048 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
8049 a file you want to use. In these situations the @value{GDBN} commands
8050 to specify new files are useful.
8053 @cindex executable file
8055 @item file @var{filename}
8056 Use @var{filename} as the program to be debugged. It is read for its
8057 symbols and for the contents of pure memory. It is also the program
8058 executed when you use the @code{run} command. If you do not specify a
8059 directory and the file is not found in the @value{GDBN} working directory,
8060 @value{GDBN} uses the environment variable @code{PATH} as a list of
8061 directories to search, just as the shell does when looking for a program
8062 to run. You can change the value of this variable, for both @value{GDBN}
8063 and your program, using the @code{path} command.
8065 On systems with memory-mapped files, an auxiliary file named
8066 @file{@var{filename}.syms} may hold symbol table information for
8067 @var{filename}. If so, @value{GDBN} maps in the symbol table from
8068 @file{@var{filename}.syms}, starting up more quickly. See the
8069 descriptions of the file options @samp{-mapped} and @samp{-readnow}
8070 (available on the command line, and with the commands @code{file},
8071 @code{symbol-file}, or @code{add-symbol-file}, described below),
8072 for more information.
8075 @code{file} with no argument makes @value{GDBN} discard any information it
8076 has on both executable file and the symbol table.
8079 @item exec-file @r{[} @var{filename} @r{]}
8080 Specify that the program to be run (but not the symbol table) is found
8081 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
8082 if necessary to locate your program. Omitting @var{filename} means to
8083 discard information on the executable file.
8086 @item symbol-file @r{[} @var{filename} @r{]}
8087 Read symbol table information from file @var{filename}. @code{PATH} is
8088 searched when necessary. Use the @code{file} command to get both symbol
8089 table and program to run from the same file.
8091 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8092 program's symbol table.
8094 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8095 of its convenience variables, the value history, and all breakpoints and
8096 auto-display expressions. This is because they may contain pointers to
8097 the internal data recording symbols and data types, which are part of
8098 the old symbol table data being discarded inside @value{GDBN}.
8100 @code{symbol-file} does not repeat if you press @key{RET} again after
8103 When @value{GDBN} is configured for a particular environment, it
8104 understands debugging information in whatever format is the standard
8105 generated for that environment; you may use either a @sc{gnu} compiler, or
8106 other compilers that adhere to the local conventions.
8107 Best results are usually obtained from @sc{gnu} compilers; for example,
8108 using @code{@value{GCC}} you can generate debugging information for
8111 For most kinds of object files, with the exception of old SVR3 systems
8112 using COFF, the @code{symbol-file} command does not normally read the
8113 symbol table in full right away. Instead, it scans the symbol table
8114 quickly to find which source files and which symbols are present. The
8115 details are read later, one source file at a time, as they are needed.
8117 The purpose of this two-stage reading strategy is to make @value{GDBN}
8118 start up faster. For the most part, it is invisible except for
8119 occasional pauses while the symbol table details for a particular source
8120 file are being read. (The @code{set verbose} command can turn these
8121 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8122 warnings and messages}.)
8124 We have not implemented the two-stage strategy for COFF yet. When the
8125 symbol table is stored in COFF format, @code{symbol-file} reads the
8126 symbol table data in full right away. Note that ``stabs-in-COFF''
8127 still does the two-stage strategy, since the debug info is actually
8131 @cindex reading symbols immediately
8132 @cindex symbols, reading immediately
8134 @cindex memory-mapped symbol file
8135 @cindex saving symbol table
8136 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8137 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8138 You can override the @value{GDBN} two-stage strategy for reading symbol
8139 tables by using the @samp{-readnow} option with any of the commands that
8140 load symbol table information, if you want to be sure @value{GDBN} has the
8141 entire symbol table available.
8143 If memory-mapped files are available on your system through the
8144 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8145 cause @value{GDBN} to write the symbols for your program into a reusable
8146 file. Future @value{GDBN} debugging sessions map in symbol information
8147 from this auxiliary symbol file (if the program has not changed), rather
8148 than spending time reading the symbol table from the executable
8149 program. Using the @samp{-mapped} option has the same effect as
8150 starting @value{GDBN} with the @samp{-mapped} command-line option.
8152 You can use both options together, to make sure the auxiliary symbol
8153 file has all the symbol information for your program.
8155 The auxiliary symbol file for a program called @var{myprog} is called
8156 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8157 than the corresponding executable), @value{GDBN} always attempts to use
8158 it when you debug @var{myprog}; no special options or commands are
8161 The @file{.syms} file is specific to the host machine where you run
8162 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8163 symbol table. It cannot be shared across multiple host platforms.
8165 @c FIXME: for now no mention of directories, since this seems to be in
8166 @c flux. 13mar1992 status is that in theory GDB would look either in
8167 @c current dir or in same dir as myprog; but issues like competing
8168 @c GDB's, or clutter in system dirs, mean that in practice right now
8169 @c only current dir is used. FFish says maybe a special GDB hierarchy
8170 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8175 @item core-file @r{[} @var{filename} @r{]}
8176 Specify the whereabouts of a core dump file to be used as the ``contents
8177 of memory''. Traditionally, core files contain only some parts of the
8178 address space of the process that generated them; @value{GDBN} can access the
8179 executable file itself for other parts.
8181 @code{core-file} with no argument specifies that no core file is
8184 Note that the core file is ignored when your program is actually running
8185 under @value{GDBN}. So, if you have been running your program and you
8186 wish to debug a core file instead, you must kill the subprocess in which
8187 the program is running. To do this, use the @code{kill} command
8188 (@pxref{Kill Process, ,Killing the child process}).
8190 @kindex add-symbol-file
8191 @cindex dynamic linking
8192 @item add-symbol-file @var{filename} @var{address}
8193 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8194 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address}
8195 The @code{add-symbol-file} command reads additional symbol table
8196 information from the file @var{filename}. You would use this command
8197 when @var{filename} has been dynamically loaded (by some other means)
8198 into the program that is running. @var{address} should be the memory
8199 address at which the file has been loaded; @value{GDBN} cannot figure
8200 this out for itself. You can additionally specify an arbitrary number
8201 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
8202 section name and base address for that section. You can specify any
8203 @var{address} as an expression.
8205 The symbol table of the file @var{filename} is added to the symbol table
8206 originally read with the @code{symbol-file} command. You can use the
8207 @code{add-symbol-file} command any number of times; the new symbol data
8208 thus read keeps adding to the old. To discard all old symbol data
8209 instead, use the @code{symbol-file} command without any arguments.
8211 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8213 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8214 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8215 table information for @var{filename}.
8217 @kindex add-shared-symbol-file
8218 @item add-shared-symbol-file
8219 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8220 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8221 shared libraries, however if @value{GDBN} does not find yours, you can run
8222 @code{add-shared-symbol-file}. It takes no arguments.
8226 The @code{section} command changes the base address of section SECTION of
8227 the exec file to ADDR. This can be used if the exec file does not contain
8228 section addresses, (such as in the a.out format), or when the addresses
8229 specified in the file itself are wrong. Each section must be changed
8230 separately. The @code{info files} command, described below, lists all
8231 the sections and their addresses.
8237 @code{info files} and @code{info target} are synonymous; both print the
8238 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8239 including the names of the executable and core dump files currently in
8240 use by @value{GDBN}, and the files from which symbols were loaded. The
8241 command @code{help target} lists all possible targets rather than
8246 All file-specifying commands allow both absolute and relative file names
8247 as arguments. @value{GDBN} always converts the file name to an absolute file
8248 name and remembers it that way.
8250 @cindex shared libraries
8251 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8254 @value{GDBN} automatically loads symbol definitions from shared libraries
8255 when you use the @code{run} command, or when you examine a core file.
8256 (Before you issue the @code{run} command, @value{GDBN} does not understand
8257 references to a function in a shared library, however---unless you are
8258 debugging a core file).
8260 On HP-UX, if the program loads a library explicitly, @value{GDBN}
8261 automatically loads the symbols at the time of the @code{shl_load} call.
8263 @c FIXME: some @value{GDBN} release may permit some refs to undef
8264 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8265 @c FIXME...lib; check this from time to time when updating manual
8268 @kindex info sharedlibrary
8271 @itemx info sharedlibrary
8272 Print the names of the shared libraries which are currently loaded.
8274 @kindex sharedlibrary
8276 @item sharedlibrary @var{regex}
8277 @itemx share @var{regex}
8278 Load shared object library symbols for files matching a
8279 Unix regular expression.
8280 As with files loaded automatically, it only loads shared libraries
8281 required by your program for a core file or after typing @code{run}. If
8282 @var{regex} is omitted all shared libraries required by your program are
8286 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8287 and automatically reads in symbols from the newly loaded library, up to
8288 a threshold that is initially set but that you can modify if you wish.
8290 Beyond that threshold, symbols from shared libraries must be explicitly
8291 loaded. To load these symbols, use the command @code{sharedlibrary
8292 @var{filename}}. The base address of the shared library is determined
8293 automatically by @value{GDBN} and need not be specified.
8295 To display or set the threshold, use the commands:
8298 @kindex set auto-solib-add
8299 @item set auto-solib-add @var{threshold}
8300 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8301 nonzero, symbols from all shared object libraries will be loaded
8302 automatically when the inferior begins execution or when the dynamic
8303 linker informs @value{GDBN} that a new library has been loaded, until
8304 the symbol table of the program and libraries exceeds this threshold.
8305 Otherwise, symbols must be loaded manually, using the
8306 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8308 @kindex show auto-solib-add
8309 @item show auto-solib-add
8310 Display the current autoloading size threshold, in megabytes.
8314 @section Errors reading symbol files
8316 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8317 such as symbol types it does not recognize, or known bugs in compiler
8318 output. By default, @value{GDBN} does not notify you of such problems, since
8319 they are relatively common and primarily of interest to people
8320 debugging compilers. If you are interested in seeing information
8321 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8322 only one message about each such type of problem, no matter how many
8323 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8324 to see how many times the problems occur, with the @code{set
8325 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8328 The messages currently printed, and their meanings, include:
8331 @item inner block not inside outer block in @var{symbol}
8333 The symbol information shows where symbol scopes begin and end
8334 (such as at the start of a function or a block of statements). This
8335 error indicates that an inner scope block is not fully contained
8336 in its outer scope blocks.
8338 @value{GDBN} circumvents the problem by treating the inner block as if it had
8339 the same scope as the outer block. In the error message, @var{symbol}
8340 may be shown as ``@code{(don't know)}'' if the outer block is not a
8343 @item block at @var{address} out of order
8345 The symbol information for symbol scope blocks should occur in
8346 order of increasing addresses. This error indicates that it does not
8349 @value{GDBN} does not circumvent this problem, and has trouble
8350 locating symbols in the source file whose symbols it is reading. (You
8351 can often determine what source file is affected by specifying
8352 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8355 @item bad block start address patched
8357 The symbol information for a symbol scope block has a start address
8358 smaller than the address of the preceding source line. This is known
8359 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8361 @value{GDBN} circumvents the problem by treating the symbol scope block as
8362 starting on the previous source line.
8364 @item bad string table offset in symbol @var{n}
8367 Symbol number @var{n} contains a pointer into the string table which is
8368 larger than the size of the string table.
8370 @value{GDBN} circumvents the problem by considering the symbol to have the
8371 name @code{foo}, which may cause other problems if many symbols end up
8374 @item unknown symbol type @code{0x@var{nn}}
8376 The symbol information contains new data types that @value{GDBN} does
8377 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8378 uncomprehended information, in hexadecimal.
8380 @value{GDBN} circumvents the error by ignoring this symbol information.
8381 This usually allows you to debug your program, though certain symbols
8382 are not accessible. If you encounter such a problem and feel like
8383 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8384 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8385 and examine @code{*bufp} to see the symbol.
8387 @item stub type has NULL name
8389 @value{GDBN} could not find the full definition for a struct or class.
8391 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8392 The symbol information for a C++ member function is missing some
8393 information that recent versions of the compiler should have output for
8396 @item info mismatch between compiler and debugger
8398 @value{GDBN} could not parse a type specification output by the compiler.
8403 @chapter Specifying a Debugging Target
8405 @cindex debugging target
8408 A @dfn{target} is the execution environment occupied by your program.
8410 Often, @value{GDBN} runs in the same host environment as your program;
8411 in that case, the debugging target is specified as a side effect when
8412 you use the @code{file} or @code{core} commands. When you need more
8413 flexibility---for example, running @value{GDBN} on a physically separate
8414 host, or controlling a standalone system over a serial port or a
8415 realtime system over a TCP/IP connection---you can use the @code{target}
8416 command to specify one of the target types configured for @value{GDBN}
8417 (@pxref{Target Commands, ,Commands for managing targets}).
8420 * Active Targets:: Active targets
8421 * Target Commands:: Commands for managing targets
8422 * Byte Order:: Choosing target byte order
8423 * Remote:: Remote debugging
8424 * KOD:: Kernel Object Display
8428 @node Active Targets
8429 @section Active targets
8431 @cindex stacking targets
8432 @cindex active targets
8433 @cindex multiple targets
8435 There are three classes of targets: processes, core files, and
8436 executable files. @value{GDBN} can work concurrently on up to three
8437 active targets, one in each class. This allows you to (for example)
8438 start a process and inspect its activity without abandoning your work on
8441 For example, if you execute @samp{gdb a.out}, then the executable file
8442 @code{a.out} is the only active target. If you designate a core file as
8443 well---presumably from a prior run that crashed and coredumped---then
8444 @value{GDBN} has two active targets and uses them in tandem, looking
8445 first in the corefile target, then in the executable file, to satisfy
8446 requests for memory addresses. (Typically, these two classes of target
8447 are complementary, since core files contain only a program's
8448 read-write memory---variables and so on---plus machine status, while
8449 executable files contain only the program text and initialized data.)
8451 When you type @code{run}, your executable file becomes an active process
8452 target as well. When a process target is active, all @value{GDBN}
8453 commands requesting memory addresses refer to that target; addresses in
8454 an active core file or executable file target are obscured while the
8455 process target is active.
8457 Use the @code{core-file} and @code{exec-file} commands to select a new
8458 core file or executable target (@pxref{Files, ,Commands to specify
8459 files}). To specify as a target a process that is already running, use
8460 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8463 @node Target Commands
8464 @section Commands for managing targets
8467 @item target @var{type} @var{parameters}
8468 Connects the @value{GDBN} host environment to a target machine or
8469 process. A target is typically a protocol for talking to debugging
8470 facilities. You use the argument @var{type} to specify the type or
8471 protocol of the target machine.
8473 Further @var{parameters} are interpreted by the target protocol, but
8474 typically include things like device names or host names to connect
8475 with, process numbers, and baud rates.
8477 The @code{target} command does not repeat if you press @key{RET} again
8478 after executing the command.
8482 Displays the names of all targets available. To display targets
8483 currently selected, use either @code{info target} or @code{info files}
8484 (@pxref{Files, ,Commands to specify files}).
8486 @item help target @var{name}
8487 Describe a particular target, including any parameters necessary to
8490 @kindex set gnutarget
8491 @item set gnutarget @var{args}
8492 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8493 knows whether it is reading an @dfn{executable},
8494 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8495 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8496 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8499 @emph{Warning:} To specify a file format with @code{set gnutarget},
8500 you must know the actual BFD name.
8504 @xref{Files, , Commands to specify files}.
8506 @kindex show gnutarget
8507 @item show gnutarget
8508 Use the @code{show gnutarget} command to display what file format
8509 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8510 @value{GDBN} will determine the file format for each file automatically,
8511 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8514 Here are some common targets (available, or not, depending on the GDB
8519 @item target exec @var{program}
8520 An executable file. @samp{target exec @var{program}} is the same as
8521 @samp{exec-file @var{program}}.
8524 @item target core @var{filename}
8525 A core dump file. @samp{target core @var{filename}} is the same as
8526 @samp{core-file @var{filename}}.
8528 @kindex target remote
8529 @item target remote @var{dev}
8530 Remote serial target in GDB-specific protocol. The argument @var{dev}
8531 specifies what serial device to use for the connection (e.g.
8532 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8533 supports the @code{load} command. This is only useful if you have
8534 some other way of getting the stub to the target system, and you can put
8535 it somewhere in memory where it won't get clobbered by the download.
8539 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
8547 works; however, you cannot assume that a specific memory map, device
8548 drivers, or even basic I/O is available, although some simulators do
8549 provide these. For info about any processor-specific simulator details,
8550 see the appropriate section in @ref{Embedded Processors, ,Embedded
8555 Some configurations may include these targets as well:
8560 @item target nrom @var{dev}
8561 NetROM ROM emulator. This target only supports downloading.
8565 Different targets are available on different configurations of @value{GDBN};
8566 your configuration may have more or fewer targets.
8568 Many remote targets require you to download the executable's code
8569 once you've successfully established a connection.
8573 @kindex load @var{filename}
8574 @item load @var{filename}
8575 Depending on what remote debugging facilities are configured into
8576 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8577 is meant to make @var{filename} (an executable) available for debugging
8578 on the remote system---by downloading, or dynamic linking, for example.
8579 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8580 the @code{add-symbol-file} command.
8582 If your @value{GDBN} does not have a @code{load} command, attempting to
8583 execute it gets the error message ``@code{You can't do that when your
8584 target is @dots{}}''
8586 The file is loaded at whatever address is specified in the executable.
8587 For some object file formats, you can specify the load address when you
8588 link the program; for other formats, like a.out, the object file format
8589 specifies a fixed address.
8590 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8592 @code{load} does not repeat if you press @key{RET} again after using it.
8596 @section Choosing target byte order
8598 @cindex choosing target byte order
8599 @cindex target byte order
8601 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8602 offer the ability to run either big-endian or little-endian byte
8603 orders. Usually the executable or symbol will include a bit to
8604 designate the endian-ness, and you will not need to worry about
8605 which to use. However, you may still find it useful to adjust
8606 @value{GDBN}'s idea of processor endian-ness manually.
8609 @kindex set endian big
8610 @item set endian big
8611 Instruct @value{GDBN} to assume the target is big-endian.
8613 @kindex set endian little
8614 @item set endian little
8615 Instruct @value{GDBN} to assume the target is little-endian.
8617 @kindex set endian auto
8618 @item set endian auto
8619 Instruct @value{GDBN} to use the byte order associated with the
8623 Display @value{GDBN}'s current idea of the target byte order.
8627 Note that these commands merely adjust interpretation of symbolic
8628 data on the host, and that they have absolutely no effect on the
8632 @section Remote debugging
8633 @cindex remote debugging
8635 If you are trying to debug a program running on a machine that cannot run
8636 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8637 For example, you might use remote debugging on an operating system kernel,
8638 or on a small system which does not have a general purpose operating system
8639 powerful enough to run a full-featured debugger.
8641 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8642 to make this work with particular debugging targets. In addition,
8643 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8644 but not specific to any particular target system) which you can use if you
8645 write the remote stubs---the code that runs on the remote system to
8646 communicate with @value{GDBN}.
8648 Other remote targets may be available in your
8649 configuration of @value{GDBN}; use @code{help target} to list them.
8652 * Remote Serial:: @value{GDBN} remote serial protocol
8656 @subsection The @value{GDBN} remote serial protocol
8658 @cindex remote serial debugging, overview
8659 To debug a program running on another machine (the debugging
8660 @dfn{target} machine), you must first arrange for all the usual
8661 prerequisites for the program to run by itself. For example, for a C
8666 A startup routine to set up the C runtime environment; these usually
8667 have a name like @file{crt0}. The startup routine may be supplied by
8668 your hardware supplier, or you may have to write your own.
8671 A C subroutine library to support your program's
8672 subroutine calls, notably managing input and output.
8675 A way of getting your program to the other machine---for example, a
8676 download program. These are often supplied by the hardware
8677 manufacturer, but you may have to write your own from hardware
8681 The next step is to arrange for your program to use a serial port to
8682 communicate with the machine where @value{GDBN} is running (the @dfn{host}
8683 machine). In general terms, the scheme looks like this:
8687 @value{GDBN} already understands how to use this protocol; when everything
8688 else is set up, you can simply use the @samp{target remote} command
8689 (@pxref{Targets,,Specifying a Debugging Target}).
8691 @item On the target,
8692 you must link with your program a few special-purpose subroutines that
8693 implement the @value{GDBN} remote serial protocol. The file containing these
8694 subroutines is called a @dfn{debugging stub}.
8696 On certain remote targets, you can use an auxiliary program
8697 @code{gdbserver} instead of linking a stub into your program.
8698 @xref{Server,,Using the @code{gdbserver} program}, for details.
8701 The debugging stub is specific to the architecture of the remote
8702 machine; for example, use @file{sparc-stub.c} to debug programs on
8705 @cindex remote serial stub list
8706 These working remote stubs are distributed with @value{GDBN}:
8711 @cindex @file{i386-stub.c}
8714 For Intel 386 and compatible architectures.
8717 @cindex @file{m68k-stub.c}
8718 @cindex Motorola 680x0
8720 For Motorola 680x0 architectures.
8723 @cindex @file{sh-stub.c}
8726 For Hitachi SH architectures.
8729 @cindex @file{sparc-stub.c}
8731 For @sc{sparc} architectures.
8734 @cindex @file{sparcl-stub.c}
8737 For Fujitsu @sc{sparclite} architectures.
8741 The @file{README} file in the @value{GDBN} distribution may list other
8742 recently added stubs.
8745 * Stub Contents:: What the stub can do for you
8746 * Bootstrapping:: What you must do for the stub
8747 * Debug Session:: Putting it all together
8748 * Protocol:: Definition of the communication protocol
8749 * Server:: Using the `gdbserver' program
8750 * NetWare:: Using the `gdbserve.nlm' program
8754 @subsubsection What the stub can do for you
8756 @cindex remote serial stub
8757 The debugging stub for your architecture supplies these three
8761 @item set_debug_traps
8762 @kindex set_debug_traps
8763 @cindex remote serial stub, initialization
8764 This routine arranges for @code{handle_exception} to run when your
8765 program stops. You must call this subroutine explicitly near the
8766 beginning of your program.
8768 @item handle_exception
8769 @kindex handle_exception
8770 @cindex remote serial stub, main routine
8771 This is the central workhorse, but your program never calls it
8772 explicitly---the setup code arranges for @code{handle_exception} to
8773 run when a trap is triggered.
8775 @code{handle_exception} takes control when your program stops during
8776 execution (for example, on a breakpoint), and mediates communications
8777 with @value{GDBN} on the host machine. This is where the communications
8778 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
8779 representative on the target machine. It begins by sending summary
8780 information on the state of your program, then continues to execute,
8781 retrieving and transmitting any information @value{GDBN} needs, until you
8782 execute a @value{GDBN} command that makes your program resume; at that point,
8783 @code{handle_exception} returns control to your own code on the target
8787 @cindex @code{breakpoint} subroutine, remote
8788 Use this auxiliary subroutine to make your program contain a
8789 breakpoint. Depending on the particular situation, this may be the only
8790 way for @value{GDBN} to get control. For instance, if your target
8791 machine has some sort of interrupt button, you won't need to call this;
8792 pressing the interrupt button transfers control to
8793 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
8794 simply receiving characters on the serial port may also trigger a trap;
8795 again, in that situation, you don't need to call @code{breakpoint} from
8796 your own program---simply running @samp{target remote} from the host
8797 @value{GDBN} session gets control.
8799 Call @code{breakpoint} if none of these is true, or if you simply want
8800 to make certain your program stops at a predetermined point for the
8801 start of your debugging session.
8805 @subsubsection What you must do for the stub
8807 @cindex remote stub, support routines
8808 The debugging stubs that come with @value{GDBN} are set up for a particular
8809 chip architecture, but they have no information about the rest of your
8810 debugging target machine.
8812 First of all you need to tell the stub how to communicate with the
8816 @item int getDebugChar()
8817 @kindex getDebugChar
8818 Write this subroutine to read a single character from the serial port.
8819 It may be identical to @code{getchar} for your target system; a
8820 different name is used to allow you to distinguish the two if you wish.
8822 @item void putDebugChar(int)
8823 @kindex putDebugChar
8824 Write this subroutine to write a single character to the serial port.
8825 It may be identical to @code{putchar} for your target system; a
8826 different name is used to allow you to distinguish the two if you wish.
8829 @cindex control C, and remote debugging
8830 @cindex interrupting remote targets
8831 If you want @value{GDBN} to be able to stop your program while it is
8832 running, you need to use an interrupt-driven serial driver, and arrange
8833 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
8834 character). That is the character which @value{GDBN} uses to tell the
8835 remote system to stop.
8837 Getting the debugging target to return the proper status to @value{GDBN}
8838 probably requires changes to the standard stub; one quick and dirty way
8839 is to just execute a breakpoint instruction (the ``dirty'' part is that
8840 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
8842 Other routines you need to supply are:
8845 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
8846 @kindex exceptionHandler
8847 Write this function to install @var{exception_address} in the exception
8848 handling tables. You need to do this because the stub does not have any
8849 way of knowing what the exception handling tables on your target system
8850 are like (for example, the processor's table might be in @sc{rom},
8851 containing entries which point to a table in @sc{ram}).
8852 @var{exception_number} is the exception number which should be changed;
8853 its meaning is architecture-dependent (for example, different numbers
8854 might represent divide by zero, misaligned access, etc). When this
8855 exception occurs, control should be transferred directly to
8856 @var{exception_address}, and the processor state (stack, registers,
8857 and so on) should be just as it is when a processor exception occurs. So if
8858 you want to use a jump instruction to reach @var{exception_address}, it
8859 should be a simple jump, not a jump to subroutine.
8861 For the 386, @var{exception_address} should be installed as an interrupt
8862 gate so that interrupts are masked while the handler runs. The gate
8863 should be at privilege level 0 (the most privileged level). The
8864 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
8865 help from @code{exceptionHandler}.
8867 @item void flush_i_cache()
8868 @kindex flush_i_cache
8869 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
8870 instruction cache, if any, on your target machine. If there is no
8871 instruction cache, this subroutine may be a no-op.
8873 On target machines that have instruction caches, @value{GDBN} requires this
8874 function to make certain that the state of your program is stable.
8878 You must also make sure this library routine is available:
8881 @item void *memset(void *, int, int)
8883 This is the standard library function @code{memset} that sets an area of
8884 memory to a known value. If you have one of the free versions of
8885 @code{libc.a}, @code{memset} can be found there; otherwise, you must
8886 either obtain it from your hardware manufacturer, or write your own.
8889 If you do not use the GNU C compiler, you may need other standard
8890 library subroutines as well; this varies from one stub to another,
8891 but in general the stubs are likely to use any of the common library
8892 subroutines which @code{@value{GCC}} generates as inline code.
8896 @subsubsection Putting it all together
8898 @cindex remote serial debugging summary
8899 In summary, when your program is ready to debug, you must follow these
8904 Make sure you have defined the supporting low-level routines
8905 (@pxref{Bootstrapping,,What you must do for the stub}):
8907 @code{getDebugChar}, @code{putDebugChar},
8908 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
8912 Insert these lines near the top of your program:
8920 For the 680x0 stub only, you need to provide a variable called
8921 @code{exceptionHook}. Normally you just use:
8924 void (*exceptionHook)() = 0;
8928 but if before calling @code{set_debug_traps}, you set it to point to a
8929 function in your program, that function is called when
8930 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
8931 error). The function indicated by @code{exceptionHook} is called with
8932 one parameter: an @code{int} which is the exception number.
8935 Compile and link together: your program, the @value{GDBN} debugging stub for
8936 your target architecture, and the supporting subroutines.
8939 Make sure you have a serial connection between your target machine and
8940 the @value{GDBN} host, and identify the serial port on the host.
8943 @c The "remote" target now provides a `load' command, so we should
8944 @c document that. FIXME.
8945 Download your program to your target machine (or get it there by
8946 whatever means the manufacturer provides), and start it.
8949 To start remote debugging, run @value{GDBN} on the host machine, and specify
8950 as an executable file the program that is running in the remote machine.
8951 This tells @value{GDBN} how to find your program's symbols and the contents
8955 @cindex serial line, @code{target remote}
8956 Establish communication using the @code{target remote} command.
8957 Its argument specifies how to communicate with the target
8958 machine---either via a devicename attached to a direct serial line, or a
8959 TCP port (usually to a terminal server which in turn has a serial line
8960 to the target). For example, to use a serial line connected to the
8961 device named @file{/dev/ttyb}:
8964 target remote /dev/ttyb
8967 @cindex TCP port, @code{target remote}
8968 To use a TCP connection, use an argument of the form
8969 @code{@var{host}:port}. For example, to connect to port 2828 on a
8970 terminal server named @code{manyfarms}:
8973 target remote manyfarms:2828
8977 Now you can use all the usual commands to examine and change data and to
8978 step and continue the remote program.
8980 To resume the remote program and stop debugging it, use the @code{detach}
8983 @cindex interrupting remote programs
8984 @cindex remote programs, interrupting
8985 Whenever @value{GDBN} is waiting for the remote program, if you type the
8986 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
8987 program. This may or may not succeed, depending in part on the hardware
8988 and the serial drivers the remote system uses. If you type the
8989 interrupt character once again, @value{GDBN} displays this prompt:
8992 Interrupted while waiting for the program.
8993 Give up (and stop debugging it)? (y or n)
8996 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
8997 (If you decide you want to try again later, you can use @samp{target
8998 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
8999 goes back to waiting.
9002 @subsubsection Communication protocol
9004 @cindex debugging stub, example
9005 @cindex remote stub, example
9006 @cindex stub example, remote debugging
9007 The stub files provided with @value{GDBN} implement the target side of the
9008 communication protocol, and the @value{GDBN} side is implemented in the
9009 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
9010 these subroutines to communicate, and ignore the details. (If you're
9011 implementing your own stub file, you can still ignore the details: start
9012 with one of the existing stub files. @file{sparc-stub.c} is the best
9013 organized, and therefore the easiest to read.)
9015 However, there may be occasions when you need to know something about
9016 the protocol---for example, if there is only one serial port to your
9017 target machine, you might want your program to do something special if
9018 it recognizes a packet meant for @value{GDBN}.
9020 In the examples below, @samp{<-} and @samp{->} are used to indicate
9021 transmitted and received data respectfully.
9023 @cindex protocol, @value{GDBN} remote serial
9024 @cindex serial protocol, @value{GDBN} remote
9025 @cindex remote serial protocol
9026 All @value{GDBN} commands and responses (other than acknowledgments) are
9027 sent as a @var{packet}. A @var{packet} is introduced with the character
9028 @samp{$}, the actual @var{packet-data}, and the terminating character
9029 @samp{#} followed by a two-digit @var{checksum}:
9032 @code{$}@var{packet-data}@code{#}@var{checksum}
9036 @cindex checksum, for @value{GDBN} remote
9038 The two-digit @var{checksum} is computed as the modulo 256 sum of all
9039 characters between the leading @samp{$} and the trailing @samp{#} (an
9040 eight bit unsigned checksum).
9042 Implementors should note that prior to @value{GDBN} 5.0 the protocol
9043 specification also included an optional two-digit @var{sequence-id}:
9046 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
9049 @cindex sequence-id, for @value{GDBN} remote
9051 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
9052 has never output @var{sequence-id}s. Stubs that handle packets added
9053 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
9055 @cindex acknowledgment, for @value{GDBN} remote
9056 When either the host or the target machine receives a packet, the first
9057 response expected is an acknowledgment: either @samp{+} (to indicate
9058 the package was received correctly) or @samp{-} (to request
9062 <- @code{$}@var{packet-data}@code{#}@var{checksum}
9067 The host (@value{GDBN}) sends @var{command}s, and the target (the
9068 debugging stub incorporated in your program) sends a @var{response}. In
9069 the case of step and continue @var{command}s, the response is only sent
9070 when the operation has completed (the target has again stopped).
9072 @var{packet-data} consists of a sequence of characters with the
9073 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
9076 Fields within the packet should be separated using @samp{,} @samp{;} or
9077 @samp{:}. Except where otherwise noted all numbers are represented in
9078 HEX with leading zeros suppressed.
9080 Implementors should note that prior to @value{GDBN} 5.0, the character
9081 @samp{:} could not appear as the third character in a packet (as it
9082 would potentially conflict with the @var{sequence-id}).
9084 Response @var{data} can be run-length encoded to save space. A @samp{*}
9085 means that the next character is an @sc{ascii} encoding giving a repeat count
9086 which stands for that many repetitions of the character preceding the
9087 @samp{*}. The encoding is @code{n+29}, yielding a printable character
9088 where @code{n >=3} (which is where rle starts to win). The printable
9089 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
9090 value greater than 126 should not be used.
9092 Some remote systems have used a different run-length encoding mechanism
9093 loosely refered to as the cisco encoding. Following the @samp{*}
9094 character are two hex digits that indicate the size of the packet.
9101 means the same as "0000".
9103 The error response returned for some packets includes a two character
9104 error number. That number is not well defined.
9106 For any @var{command} not supported by the stub, an empty response
9107 (@samp{$#00}) should be returned. That way it is possible to extend the
9108 protocol. A newer @value{GDBN} can tell if a packet is supported based
9111 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
9112 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
9115 Below is a complete list of all currently defined @var{command}s and
9116 their corresponding response @var{data}:
9118 @multitable @columnfractions .30 .30 .40
9126 Use the extended remote protocol. Sticky---only needs to be set once.
9127 The extended remote protocol supports the @samp{R} packet.
9131 Stubs that support the extended remote protocol return @samp{} which,
9132 unfortunately, is identical to the response returned by stubs that do not
9133 support protocol extensions.
9138 Indicate the reason the target halted. The reply is the same as for step
9147 @tab Reserved for future use
9149 @item set program arguments @strong{(reserved)}
9150 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
9155 Initialized @samp{argv[]} array passed into program. @var{arglen}
9156 specifies the number of bytes in the hex encoded byte stream @var{arg}.
9157 See @file{gdbserver} for more details.
9159 @tab reply @code{OK}
9161 @tab reply @code{E}@var{NN}
9163 @item set baud @strong{(deprecated)}
9164 @tab @code{b}@var{baud}
9166 Change the serial line speed to @var{baud}. JTC: @emph{When does the
9167 transport layer state change? When it's received, or after the ACK is
9168 transmitted. In either case, there are problems if the command or the
9169 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
9170 to add something like this, and get it working for the first time, they
9171 ought to modify ser-unix.c to send some kind of out-of-band message to a
9172 specially-setup stub and have the switch happen "in between" packets, so
9173 that from remote protocol's point of view, nothing actually
9176 @item set breakpoint @strong{(deprecated)}
9177 @tab @code{B}@var{addr},@var{mode}
9179 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
9180 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
9184 @tab @code{c}@var{addr}
9186 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9192 @item continue with signal
9193 @tab @code{C}@var{sig}@code{;}@var{addr}
9195 Continue with signal @var{sig} (hex signal number). If
9196 @code{;}@var{addr} is omitted, resume at same address.
9201 @item toggle debug @strong{(deprecated)}
9209 Detach @value{GDBN} from the remote system. Sent to the remote target before
9210 @value{GDBN} disconnects.
9212 @tab reply @emph{no response}
9214 @value{GDBN} does not check for any response after sending this packet.
9218 @tab Reserved for future use
9222 @tab Reserved for future use
9226 @tab Reserved for future use
9230 @tab Reserved for future use
9232 @item read registers
9234 @tab Read general registers.
9236 @tab reply @var{XX...}
9238 Each byte of register data is described by two hex digits. The bytes
9239 with the register are transmitted in target byte order. The size of
9240 each register and their position within the @samp{g} @var{packet} are
9241 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
9242 @var{REGISTER_NAME} macros. The specification of several standard
9243 @code{g} packets is specified below.
9245 @tab @code{E}@var{NN}
9249 @tab @code{G}@var{XX...}
9251 See @samp{g} for a description of the @var{XX...} data.
9253 @tab reply @code{OK}
9256 @tab reply @code{E}@var{NN}
9261 @tab Reserved for future use
9264 @tab @code{H}@var{c}@var{t...}
9266 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
9267 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
9268 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
9269 thread used in other operations. If zero, pick a thread, any thread.
9271 @tab reply @code{OK}
9274 @tab reply @code{E}@var{NN}
9278 @c 'H': How restrictive (or permissive) is the thread model. If a
9279 @c thread is selected and stopped, are other threads allowed
9280 @c to continue to execute? As I mentioned above, I think the
9281 @c semantics of each command when a thread is selected must be
9282 @c described. For example:
9284 @c 'g': If the stub supports threads and a specific thread is
9285 @c selected, returns the register block from that thread;
9286 @c otherwise returns current registers.
9288 @c 'G' If the stub supports threads and a specific thread is
9289 @c selected, sets the registers of the register block of
9290 @c that thread; otherwise sets current registers.
9292 @item cycle step @strong{(draft)}
9293 @tab @code{i}@var{addr}@code{,}@var{nnn}
9295 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9296 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9297 step starting at that address.
9299 @item signal then cycle step @strong{(reserved)}
9302 See @samp{i} and @samp{S} for likely syntax and semantics.
9306 @tab Reserved for future use
9310 @tab Reserved for future use
9315 FIXME: @emph{There is no description of how operate when a specific
9316 thread context has been selected (ie. does 'k' kill only that thread?)}.
9320 @tab Reserved for future use
9324 @tab Reserved for future use
9327 @tab @code{m}@var{addr}@code{,}@var{length}
9329 Read @var{length} bytes of memory starting at address @var{addr}.
9330 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9331 using word alligned accesses. FIXME: @emph{A word aligned memory
9332 transfer mechanism is needed.}
9334 @tab reply @var{XX...}
9336 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9337 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9338 sized memory transfers are assumed using word alligned accesses. FIXME:
9339 @emph{A word aligned memory transfer mechanism is needed.}
9341 @tab reply @code{E}@var{NN}
9342 @tab @var{NN} is errno
9345 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9347 Write @var{length} bytes of memory starting at address @var{addr}.
9348 @var{XX...} is the data.
9350 @tab reply @code{OK}
9353 @tab reply @code{E}@var{NN}
9355 for an error (this includes the case where only part of the data was
9360 @tab Reserved for future use
9364 @tab Reserved for future use
9368 @tab Reserved for future use
9372 @tab Reserved for future use
9374 @item read reg @strong{(reserved)}
9375 @tab @code{p}@var{n...}
9379 @tab return @var{r....}
9380 @tab The hex encoded value of the register in target byte order.
9383 @tab @code{P}@var{n...}@code{=}@var{r...}
9385 Write register @var{n...} with value @var{r...}, which contains two hex
9386 digits for each byte in the register (target byte order).
9388 @tab reply @code{OK}
9391 @tab reply @code{E}@var{NN}
9395 @tab @code{q}@var{query}
9397 Request info about @var{query}. In general @value{GDBN} queries
9398 have a leading upper case letter. Custom vendor queries should use a
9399 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
9400 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
9401 must ensure that they match the full @var{query} name.
9403 @tab reply @code{XX...}
9404 @tab Hex encoded data from query. The reply can not be empty.
9406 @tab reply @code{E}@var{NN}
9410 @tab Indicating an unrecognized @var{query}.
9413 @tab @code{Q}@var{var}@code{=}@var{val}
9415 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
9418 @item reset @strong{(deprecated)}
9421 Reset the entire system.
9423 @item remote restart
9424 @tab @code{R}@var{XX}
9426 Restart the remote server. @var{XX} while needed has no clear
9427 definition. FIXME: @emph{An example interaction explaining how this
9428 packet is used in extended-remote mode is needed}.
9431 @tab @code{s}@var{addr}
9433 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9439 @item step with signal
9440 @tab @code{S}@var{sig}@code{;}@var{addr}
9442 Like @samp{C} but step not continue.
9448 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
9450 Search backwards starting at address @var{addr} for a match with pattern
9451 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
9452 bytes. @var{addr} must be at least 3 digits.
9455 @tab @code{T}@var{XX}
9456 @tab Find out if the thread XX is alive.
9458 @tab reply @code{OK}
9459 @tab thread is still alive
9461 @tab reply @code{E}@var{NN}
9466 @tab Reserved for future use
9470 @tab Reserved for future use
9474 @tab Reserved for future use
9478 @tab Reserved for future use
9482 @tab Reserved for future use
9486 @tab Reserved for future use
9490 @tab Reserved for future use
9492 @item write mem (binary)
9493 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
9495 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
9496 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
9497 escaped using @code{0x7d}.
9499 @tab reply @code{OK}
9502 @tab reply @code{E}@var{NN}
9507 @tab Reserved for future use
9511 @tab Reserved for future use
9513 @item remove break or watchpoint @strong{(draft)}
9514 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9518 @item insert break or watchpoint @strong{(draft)}
9519 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9521 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
9522 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
9523 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
9524 bytes. For a software breakpoint, @var{length} specifies the size of
9525 the instruction to be patched. For hardware breakpoints and watchpoints
9526 @var{length} specifies the memory region to be monitored. To avoid
9527 potential problems with duplicate packets, the operations should be
9528 implemented in an idempotent way.
9530 @tab reply @code{E}@var{NN}
9533 @tab reply @code{OK}
9537 @tab If not supported.
9541 @tab Reserved for future use
9545 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
9546 receive any of the below as a reply. In the case of the @samp{C},
9547 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
9548 when the target halts. In the below the exact meaning of @samp{signal
9549 number} is poorly defined. In general one of the UNIX signal numbering
9550 conventions is used.
9552 @multitable @columnfractions .4 .6
9554 @item @code{S}@var{AA}
9555 @tab @var{AA} is the signal number
9557 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
9559 @var{AA} = two hex digit signal number; @var{n...} = register number
9560 (hex), @var{r...} = target byte ordered register contents, size defined
9561 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
9562 thread process ID, this is a hex integer; @var{n...} = other string not
9563 starting with valid hex digit. @value{GDBN} should ignore this
9564 @var{n...}, @var{r...} pair and go on to the next. This way we can
9565 extend the protocol.
9567 @item @code{W}@var{AA}
9569 The process exited, and @var{AA} is the exit status. This is only
9570 applicable for certains sorts of targets.
9572 @item @code{X}@var{AA}
9574 The process terminated with signal @var{AA}.
9576 @item @code{N}@var{AA}@code{;}@var{t...}@code{;}@var{d...}@code{;}@var{b...} @strong{(obsolete)}
9578 @var{AA} = signal number; @var{t...} = address of symbol "_start";
9579 @var{d...} = base of data section; @var{b...} = base of bss section.
9580 @emph{Note: only used by Cisco Systems targets. The difference between
9581 this reply and the "qOffsets" query is that the 'N' packet may arrive
9582 spontaneously whereas the 'qOffsets' is a query initiated by the host
9585 @item @code{O}@var{XX...}
9587 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
9588 while the program is running and the debugger should continue to wait
9593 The following set and query packets have already been defined.
9595 @multitable @columnfractions .2 .2 .6
9597 @item current thread
9598 @tab @code{q}@code{C}
9599 @tab Return the current thread id.
9601 @tab reply @code{QC}@var{pid}
9603 Where @var{pid} is a HEX encoded 16 bit process id.
9606 @tab Any other reply implies the old pid.
9608 @item all thread ids
9609 @tab @code{q}@code{fThreadInfo}
9611 @tab @code{q}@code{sThreadInfo}
9613 Obtain a list of active thread ids from the target (OS). Since there
9614 may be too many active threads to fit into one reply packet, this query
9615 works iteratively: it may require more than one query/reply sequence to
9616 obtain the entire list of threads. The first query of the sequence will
9617 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
9618 sequence will be the @code{qs}@code{ThreadInfo} query.
9621 @tab NOTE: replaces the @code{qL} query (see below).
9623 @tab reply @code{m}@var{<id>}
9624 @tab A single thread id
9626 @tab reply @code{m}@var{<id>},@var{<id>...}
9627 @tab a comma-separated list of thread ids
9630 @tab (lower case 'el') denotes end of list.
9634 In response to each query, the target will reply with a list of one
9635 or more thread ids, in big-endian hex, separated by commas. GDB will
9636 respond to each reply with a request for more thread ids (using the
9637 @code{qs} form of the query), until the target responds with @code{l}
9638 (lower-case el, for @code{'last'}).
9640 @item extra thread info
9641 @tab @code{q}@code{ThreadExtraInfo}@code{,}@var{id}
9646 Where @var{<id>} is a thread-id in big-endian hex.
9647 Obtain a printable string description of a thread's attributes from
9648 the target OS. This string may contain anything that the target OS
9649 thinks is interesting for @value{GDBN} to tell the user about the thread.
9650 The string is displayed in @value{GDBN}'s @samp{info threads} display.
9651 Some examples of possible thread extra info strings are "Runnable", or
9654 @tab reply @var{XX...}
9656 Where @var{XX...} is a hex encoding of @sc{ascii} data, comprising the
9657 printable string containing the extra information about the thread's
9660 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
9661 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
9666 Obtain thread information from RTOS. Where: @var{startflag} (one hex
9667 digit) is one to indicate the first query and zero to indicate a
9668 subsequent query; @var{threadcount} (two hex digits) is the maximum
9669 number of threads the response packet can contain; and @var{nextthread}
9670 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
9671 returned in the response as @var{argthread}.
9674 @tab NOTE: this query is replaced by the @code{q}@code{fThreadInfo}
9677 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
9682 Where: @var{count} (two hex digits) is the number of threads being
9683 returned; @var{done} (one hex digit) is zero to indicate more threads
9684 and one indicates no further threads; @var{argthreadid} (eight hex
9685 digits) is @var{nextthread} from the request packet; @var{thread...} is
9686 a sequence of thread IDs from the target. @var{threadid} (eight hex
9687 digits). See @code{remote.c:parse_threadlist_response()}.
9689 @item compute CRC of memory block
9690 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
9693 @tab reply @code{E}@var{NN}
9694 @tab An error (such as memory fault)
9696 @tab reply @code{C}@var{CRC32}
9697 @tab A 32 bit cyclic redundancy check of the specified memory region.
9699 @item query sect offs
9700 @tab @code{q}@code{Offsets}
9702 Get section offsets that the target used when re-locating the downloaded
9703 image. @emph{Note: while a @code{Bss} offset is included in the
9704 response, @value{GDBN} ignores this and instead applies the @code{Data}
9705 offset to the @code{Bss} section.}
9707 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
9709 @item thread info request
9710 @tab @code{q}@code{P}@var{mode}@var{threadid}
9715 Returns information on @var{threadid}. Where: @var{mode} is a hex
9716 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
9720 See @code{remote.c:remote_unpack_thread_info_response()}.
9722 @item remote command
9723 @tab @code{q}@code{Rcmd,}@var{COMMAND}
9728 @var{COMMAND} (hex encoded) is passed to the local interpreter for
9729 execution. Invalid commands should be reported using the output string.
9730 Before the final result packet, the target may also respond with a
9731 number of intermediate @code{O}@var{OUTPUT} console output
9732 packets. @emph{Implementors should note that providing access to a
9733 stubs's interpreter may have security implications}.
9735 @tab reply @code{OK}
9737 A command response with no output.
9739 @tab reply @var{OUTPUT}
9741 A command response with the hex encoded output string @var{OUTPUT}.
9743 @tab reply @code{E}@var{NN}
9745 Indicate a badly formed request.
9750 When @samp{q}@samp{Rcmd} is not recognized.
9754 The following @samp{g}/@samp{G} packets have previously been defined.
9755 In the below, some thirty-two bit registers are transferred as sixty-four
9756 bits. Those registers should be zero/sign extended (which?) to fill the
9757 space allocated. Register bytes are transfered in target byte order.
9758 The two nibbles within a register byte are transfered most-significant -
9761 @multitable @columnfractions .5 .5
9765 All registers are transfered as thirty-two bit quantities in the order:
9766 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
9767 registers; fsr; fir; fp.
9771 All registers are transfered as sixty-four bit quantities (including
9772 thirty-two bit registers such as @code{sr}). The ordering is the same
9777 Example sequence of a target being re-started. Notice how the restart
9778 does not get any direct output:
9783 @emph{target restarts}
9786 -> @code{T001:1234123412341234}
9790 Example sequence of a target being stepped by a single instruction:
9798 -> @code{T001:1234123412341234}
9807 @subsubsection Using the @code{gdbserver} program
9810 @cindex remote connection without stubs
9811 @code{gdbserver} is a control program for Unix-like systems, which
9812 allows you to connect your program with a remote @value{GDBN} via
9813 @code{target remote}---but without linking in the usual debugging stub.
9815 @code{gdbserver} is not a complete replacement for the debugging stubs,
9816 because it requires essentially the same operating-system facilities
9817 that @value{GDBN} itself does. In fact, a system that can run
9818 @code{gdbserver} to connect to a remote @value{GDBN} could also run
9819 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
9820 because it is a much smaller program than @value{GDBN} itself. It is
9821 also easier to port than all of @value{GDBN}, so you may be able to get
9822 started more quickly on a new system by using @code{gdbserver}.
9823 Finally, if you develop code for real-time systems, you may find that
9824 the tradeoffs involved in real-time operation make it more convenient to
9825 do as much development work as possible on another system, for example
9826 by cross-compiling. You can use @code{gdbserver} to make a similar
9827 choice for debugging.
9829 @value{GDBN} and @code{gdbserver} communicate via either a serial line
9830 or a TCP connection, using the standard @value{GDBN} remote serial
9834 @item On the target machine,
9835 you need to have a copy of the program you want to debug.
9836 @code{gdbserver} does not need your program's symbol table, so you can
9837 strip the program if necessary to save space. @value{GDBN} on the host
9838 system does all the symbol handling.
9840 To use the server, you must tell it how to communicate with @value{GDBN};
9841 the name of your program; and the arguments for your program. The
9845 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
9848 @var{comm} is either a device name (to use a serial line) or a TCP
9849 hostname and portnumber. For example, to debug Emacs with the argument
9850 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
9854 target> gdbserver /dev/com1 emacs foo.txt
9857 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
9860 To use a TCP connection instead of a serial line:
9863 target> gdbserver host:2345 emacs foo.txt
9866 The only difference from the previous example is the first argument,
9867 specifying that you are communicating with the host @value{GDBN} via
9868 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
9869 expect a TCP connection from machine @samp{host} to local TCP port 2345.
9870 (Currently, the @samp{host} part is ignored.) You can choose any number
9871 you want for the port number as long as it does not conflict with any
9872 TCP ports already in use on the target system (for example, @code{23} is
9873 reserved for @code{telnet}).@footnote{If you choose a port number that
9874 conflicts with another service, @code{gdbserver} prints an error message
9875 and exits.} You must use the same port number with the host @value{GDBN}
9876 @code{target remote} command.
9878 @item On the @value{GDBN} host machine,
9879 you need an unstripped copy of your program, since @value{GDBN} needs
9880 symbols and debugging information. Start up @value{GDBN} as usual,
9881 using the name of the local copy of your program as the first argument.
9882 (You may also need the @w{@samp{--baud}} option if the serial line is
9883 running at anything other than 9600@dmn{bps}.) After that, use @code{target
9884 remote} to establish communications with @code{gdbserver}. Its argument
9885 is either a device name (usually a serial device, like
9886 @file{/dev/ttyb}), or a TCP port descriptor in the form
9887 @code{@var{host}:@var{PORT}}. For example:
9890 (@value{GDBP}) target remote /dev/ttyb
9894 communicates with the server via serial line @file{/dev/ttyb}, and
9897 (@value{GDBP}) target remote the-target:2345
9901 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
9902 For TCP connections, you must start up @code{gdbserver} prior to using
9903 the @code{target remote} command. Otherwise you may get an error whose
9904 text depends on the host system, but which usually looks something like
9905 @samp{Connection refused}.
9909 @subsubsection Using the @code{gdbserve.nlm} program
9911 @kindex gdbserve.nlm
9912 @code{gdbserve.nlm} is a control program for NetWare systems, which
9913 allows you to connect your program with a remote @value{GDBN} via
9914 @code{target remote}.
9916 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
9917 using the standard @value{GDBN} remote serial protocol.
9920 @item On the target machine,
9921 you need to have a copy of the program you want to debug.
9922 @code{gdbserve.nlm} does not need your program's symbol table, so you
9923 can strip the program if necessary to save space. @value{GDBN} on the
9924 host system does all the symbol handling.
9926 To use the server, you must tell it how to communicate with
9927 @value{GDBN}; the name of your program; and the arguments for your
9928 program. The syntax is:
9931 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
9932 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
9935 @var{board} and @var{port} specify the serial line; @var{baud} specifies
9936 the baud rate used by the connection. @var{port} and @var{node} default
9937 to 0, @var{baud} defaults to 9600@dmn{bps}.
9939 For example, to debug Emacs with the argument @samp{foo.txt}and
9940 communicate with @value{GDBN} over serial port number 2 or board 1
9941 using a 19200@dmn{bps} connection:
9944 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
9947 @item On the @value{GDBN} host machine,
9948 you need an unstripped copy of your program, since @value{GDBN} needs
9949 symbols and debugging information. Start up @value{GDBN} as usual,
9950 using the name of the local copy of your program as the first argument.
9951 (You may also need the @w{@samp{--baud}} option if the serial line is
9952 running at anything other than 9600@dmn{bps}. After that, use @code{target
9953 remote} to establish communications with @code{gdbserve.nlm}. Its
9954 argument is a device name (usually a serial device, like
9955 @file{/dev/ttyb}). For example:
9958 (@value{GDBP}) target remote /dev/ttyb
9962 communications with the server via serial line @file{/dev/ttyb}.
9966 @section Kernel Object Display
9968 @cindex kernel object display
9969 @cindex kernel object
9972 Some targets support kernel object display. Using this facility,
9973 @value{GDBN} communicates specially with the underlying operating system
9974 and can display information about operating system-level objects such as
9975 mutexes and other synchronization objects. Exactly which objects can be
9976 displayed is determined on a per-OS basis.
9978 Use the @code{set os} command to set the operating system. This tells
9979 @value{GDBN} which kernel object display module to initialize:
9982 (@value{GDBP}) set os cisco
9985 If @code{set os} succeeds, @value{GDBN} will display some information
9986 about the operating system, and will create a new @code{info} command
9987 which can be used to query the target. The @code{info} command is named
9988 after the operating system:
9991 (@value{GDBP}) info cisco
9992 List of Cisco Kernel Objects
9994 any Any and all objects
9997 Further subcommands can be used to query about particular objects known
10000 There is currently no way to determine whether a given operating system
10001 is supported other than to try it.
10004 @node Configurations
10005 @chapter Configuration-Specific Information
10007 While nearly all @value{GDBN} commands are available for all native and
10008 cross versions of the debugger, there are some exceptions. This chapter
10009 describes things that are only available in certain configurations.
10011 There are three major categories of configurations: native
10012 configurations, where the host and target are the same, embedded
10013 operating system configurations, which are usually the same for several
10014 different processor architectures, and bare embedded processors, which
10015 are quite different from each other.
10020 * Embedded Processors::
10027 This section describes details specific to particular native
10032 * SVR4 Process Information:: SVR4 process information
10038 On HP-UX systems, if you refer to a function or variable name that
10039 begins with a dollar sign, @value{GDBN} searches for a user or system
10040 name first, before it searches for a convenience variable.
10042 @node SVR4 Process Information
10043 @subsection SVR4 process information
10046 @cindex process image
10048 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10049 used to examine the image of a running process using file-system
10050 subroutines. If @value{GDBN} is configured for an operating system with
10051 this facility, the command @code{info proc} is available to report on
10052 several kinds of information about the process running your program.
10053 @code{info proc} works only on SVR4 systems that include the
10054 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10055 and Unixware, but not HP-UX or Linux, for example.
10060 Summarize available information about the process.
10062 @kindex info proc mappings
10063 @item info proc mappings
10064 Report on the address ranges accessible in the program, with information
10065 on whether your program may read, write, or execute each range.
10067 @kindex info proc times
10068 @item info proc times
10069 Starting time, user CPU time, and system CPU time for your program and
10072 @kindex info proc id
10074 Report on the process IDs related to your program: its own process ID,
10075 the ID of its parent, the process group ID, and the session ID.
10077 @kindex info proc status
10078 @item info proc status
10079 General information on the state of the process. If the process is
10080 stopped, this report includes the reason for stopping, and any signal
10083 @item info proc all
10084 Show all the above information about the process.
10088 @section Embedded Operating Systems
10090 This section describes configurations involving the debugging of
10091 embedded operating systems that are available for several different
10095 * VxWorks:: Using @value{GDBN} with VxWorks
10098 @value{GDBN} includes the ability to debug programs running on
10099 various real-time operating systems.
10102 @subsection Using @value{GDBN} with VxWorks
10108 @kindex target vxworks
10109 @item target vxworks @var{machinename}
10110 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
10111 is the target system's machine name or IP address.
10115 On VxWorks, @code{load} links @var{filename} dynamically on the
10116 current target system as well as adding its symbols in @value{GDBN}.
10118 @value{GDBN} enables developers to spawn and debug tasks running on networked
10119 VxWorks targets from a Unix host. Already-running tasks spawned from
10120 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
10121 both the Unix host and on the VxWorks target. The program
10122 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
10123 installed with the name @code{vxgdb}, to distinguish it from a
10124 @value{GDBN} for debugging programs on the host itself.)
10127 @item VxWorks-timeout @var{args}
10128 @kindex vxworks-timeout
10129 All VxWorks-based targets now support the option @code{vxworks-timeout}.
10130 This option is set by the user, and @var{args} represents the number of
10131 seconds @value{GDBN} waits for responses to rpc's. You might use this if
10132 your VxWorks target is a slow software simulator or is on the far side
10133 of a thin network line.
10136 The following information on connecting to VxWorks was current when
10137 this manual was produced; newer releases of VxWorks may use revised
10140 @kindex INCLUDE_RDB
10141 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
10142 to include the remote debugging interface routines in the VxWorks
10143 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
10144 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
10145 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
10146 source debugging task @code{tRdbTask} when VxWorks is booted. For more
10147 information on configuring and remaking VxWorks, see the manufacturer's
10149 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
10151 Once you have included @file{rdb.a} in your VxWorks system image and set
10152 your Unix execution search path to find @value{GDBN}, you are ready to
10153 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
10154 @code{vxgdb}, depending on your installation).
10156 @value{GDBN} comes up showing the prompt:
10163 * VxWorks Connection:: Connecting to VxWorks
10164 * VxWorks Download:: VxWorks download
10165 * VxWorks Attach:: Running tasks
10168 @node VxWorks Connection
10169 @subsubsection Connecting to VxWorks
10171 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
10172 network. To connect to a target whose host name is ``@code{tt}'', type:
10175 (vxgdb) target vxworks tt
10179 @value{GDBN} displays messages like these:
10182 Attaching remote machine across net...
10187 @value{GDBN} then attempts to read the symbol tables of any object modules
10188 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
10189 these files by searching the directories listed in the command search
10190 path (@pxref{Environment, ,Your program's environment}); if it fails
10191 to find an object file, it displays a message such as:
10194 prog.o: No such file or directory.
10197 When this happens, add the appropriate directory to the search path with
10198 the @value{GDBN} command @code{path}, and execute the @code{target}
10201 @node VxWorks Download
10202 @subsubsection VxWorks download
10204 @cindex download to VxWorks
10205 If you have connected to the VxWorks target and you want to debug an
10206 object that has not yet been loaded, you can use the @value{GDBN}
10207 @code{load} command to download a file from Unix to VxWorks
10208 incrementally. The object file given as an argument to the @code{load}
10209 command is actually opened twice: first by the VxWorks target in order
10210 to download the code, then by @value{GDBN} in order to read the symbol
10211 table. This can lead to problems if the current working directories on
10212 the two systems differ. If both systems have NFS mounted the same
10213 filesystems, you can avoid these problems by using absolute paths.
10214 Otherwise, it is simplest to set the working directory on both systems
10215 to the directory in which the object file resides, and then to reference
10216 the file by its name, without any path. For instance, a program
10217 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
10218 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
10219 program, type this on VxWorks:
10222 -> cd "@var{vxpath}/vw/demo/rdb"
10226 Then, in @value{GDBN}, type:
10229 (vxgdb) cd @var{hostpath}/vw/demo/rdb
10230 (vxgdb) load prog.o
10233 @value{GDBN} displays a response similar to this:
10236 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
10239 You can also use the @code{load} command to reload an object module
10240 after editing and recompiling the corresponding source file. Note that
10241 this makes @value{GDBN} delete all currently-defined breakpoints,
10242 auto-displays, and convenience variables, and to clear the value
10243 history. (This is necessary in order to preserve the integrity of
10244 debugger's data structures that reference the target system's symbol
10247 @node VxWorks Attach
10248 @subsubsection Running tasks
10250 @cindex running VxWorks tasks
10251 You can also attach to an existing task using the @code{attach} command as
10255 (vxgdb) attach @var{task}
10259 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
10260 or suspended when you attach to it. Running tasks are suspended at
10261 the time of attachment.
10263 @node Embedded Processors
10264 @section Embedded Processors
10266 This section goes into details specific to particular embedded
10270 * A29K Embedded:: AMD A29K Embedded
10272 * H8/300:: Hitachi H8/300
10273 * H8/500:: Hitachi H8/500
10274 * i960:: Intel i960
10275 * M32R/D:: Mitsubishi M32R/D
10276 * M68K:: Motorola M68K
10277 * M88K:: Motorola M88K
10278 * MIPS Embedded:: MIPS Embedded
10279 * PA:: HP PA Embedded
10282 * Sparclet:: Tsqware Sparclet
10283 * Sparclite:: Fujitsu Sparclite
10284 * ST2000:: Tandem ST2000
10285 * Z8000:: Zilog Z8000
10288 @node A29K Embedded
10289 @subsection AMD A29K Embedded
10294 * Comms (EB29K):: Communications setup
10295 * gdb-EB29K:: EB29K cross-debugging
10296 * Remote Log:: Remote log
10301 @kindex target adapt
10302 @item target adapt @var{dev}
10303 Adapt monitor for A29K.
10305 @kindex target amd-eb
10306 @item target amd-eb @var{dev} @var{speed} @var{PROG}
10308 Remote PC-resident AMD EB29K board, attached over serial lines.
10309 @var{dev} is the serial device, as for @code{target remote};
10310 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
10311 name of the program to be debugged, as it appears to DOS on the PC.
10312 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
10317 @subsubsection A29K UDI
10320 @cindex AMD29K via UDI
10322 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
10323 protocol for debugging the a29k processor family. To use this
10324 configuration with AMD targets running the MiniMON monitor, you need the
10325 program @code{MONTIP}, available from AMD at no charge. You can also
10326 use @value{GDBN} with the UDI-conformant a29k simulator program
10327 @code{ISSTIP}, also available from AMD.
10330 @item target udi @var{keyword}
10332 Select the UDI interface to a remote a29k board or simulator, where
10333 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
10334 This file contains keyword entries which specify parameters used to
10335 connect to a29k targets. If the @file{udi_soc} file is not in your
10336 working directory, you must set the environment variable @samp{UDICONF}
10341 @subsubsection EBMON protocol for AMD29K
10343 @cindex EB29K board
10344 @cindex running 29K programs
10346 AMD distributes a 29K development board meant to fit in a PC, together
10347 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10348 term, this development system is called the ``EB29K''. To use
10349 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10350 must first connect a serial cable between the PC (which hosts the EB29K
10351 board) and a serial port on the Unix system. In the following, we
10352 assume you've hooked the cable between the PC's @file{COM1} port and
10353 @file{/dev/ttya} on the Unix system.
10355 @node Comms (EB29K)
10356 @subsubsection Communications setup
10358 The next step is to set up the PC's port, by doing something like this
10362 C:\> MODE com1:9600,n,8,1,none
10366 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
10367 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
10368 you must match the communications parameters when establishing the Unix
10369 end of the connection as well.
10370 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
10371 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
10373 @c It's optional, but it's unwise to omit it: who knows what is the
10374 @c default value set when the DOS machines boots? "No retry" means that
10375 @c the DOS serial device driver won't retry the operation if it fails;
10376 @c I understand that this is needed because the GDB serial protocol
10377 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
10379 To give control of the PC to the Unix side of the serial line, type
10380 the following at the DOS console:
10387 (Later, if you wish to return control to the DOS console, you can use
10388 the command @code{CTTY con}---but you must send it over the device that
10389 had control, in our example over the @file{COM1} serial line.)
10391 From the Unix host, use a communications program such as @code{tip} or
10392 @code{cu} to communicate with the PC; for example,
10395 cu -s 9600 -l /dev/ttya
10399 The @code{cu} options shown specify, respectively, the linespeed and the
10400 serial port to use. If you use @code{tip} instead, your command line
10401 may look something like the following:
10404 tip -9600 /dev/ttya
10408 Your system may require a different name where we show
10409 @file{/dev/ttya} as the argument to @code{tip}. The communications
10410 parameters, including which port to use, are associated with the
10411 @code{tip} argument in the ``remote'' descriptions file---normally the
10412 system table @file{/etc/remote}.
10413 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
10414 @c the DOS side's comms setup? cu can support -o (odd
10415 @c parity), -e (even parity)---apparently no settings for no parity or
10416 @c for character size. Taken from stty maybe...? John points out tip
10417 @c can set these as internal variables, eg ~s parity=none; man stty
10418 @c suggests that it *might* work to stty these options with stdin or
10419 @c stdout redirected... ---doc@cygnus.com, 25feb91
10421 @c There's nothing to be done for the "none" part of the DOS MODE
10422 @c command. The rest of the parameters should be matched by the
10423 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
10426 Using the @code{tip} or @code{cu} connection, change the DOS working
10427 directory to the directory containing a copy of your 29K program, then
10428 start the PC program @code{EBMON} (an EB29K control program supplied
10429 with your board by AMD). You should see an initial display from
10430 @code{EBMON} similar to the one that follows, ending with the
10431 @code{EBMON} prompt @samp{#}---
10436 G:\> CD \usr\joe\work29k
10438 G:\USR\JOE\WORK29K> EBMON
10439 Am29000 PC Coprocessor Board Monitor, version 3.0-18
10440 Copyright 1990 Advanced Micro Devices, Inc.
10441 Written by Gibbons and Associates, Inc.
10443 Enter '?' or 'H' for help
10445 PC Coprocessor Type = EB29K
10447 Memory Base = 0xd0000
10449 Data Memory Size = 2048KB
10450 Available I-RAM Range = 0x8000 to 0x1fffff
10451 Available D-RAM Range = 0x80002000 to 0x801fffff
10454 Register Stack Size = 0x800
10455 Memory Stack Size = 0x1800
10458 Am29027 Available = No
10459 Byte Write Available = Yes
10464 Then exit the @code{cu} or @code{tip} program (done in the example by
10465 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
10466 running, ready for @value{GDBN} to take over.
10468 For this example, we've assumed what is probably the most convenient
10469 way to make sure the same 29K program is on both the PC and the Unix
10470 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
10471 PC as a file system on the Unix host. If you do not have PC/NFS or
10472 something similar connecting the two systems, you must arrange some
10473 other way---perhaps floppy-disk transfer---of getting the 29K program
10474 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
10478 @subsubsection EB29K cross-debugging
10480 Finally, @code{cd} to the directory containing an image of your 29K
10481 program on the Unix system, and start @value{GDBN}---specifying as argument the
10482 name of your 29K program:
10485 cd /usr/joe/work29k
10490 Now you can use the @code{target} command:
10493 target amd-eb /dev/ttya 9600 MYFOO
10494 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
10495 @c emphasize that this is the name as seen by DOS (since I think DOS is
10496 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
10500 In this example, we've assumed your program is in a file called
10501 @file{myfoo}. Note that the filename given as the last argument to
10502 @code{target amd-eb} should be the name of the program as it appears to DOS.
10503 In our example this is simply @code{MYFOO}, but in general it can include
10504 a DOS path, and depending on your transfer mechanism may not resemble
10505 the name on the Unix side.
10507 At this point, you can set any breakpoints you wish; when you are ready
10508 to see your program run on the 29K board, use the @value{GDBN} command
10511 To stop debugging the remote program, use the @value{GDBN} @code{detach}
10514 To return control of the PC to its console, use @code{tip} or @code{cu}
10515 once again, after your @value{GDBN} session has concluded, to attach to
10516 @code{EBMON}. You can then type the command @code{q} to shut down
10517 @code{EBMON}, returning control to the DOS command-line interpreter.
10518 Type @kbd{CTTY con} to return command input to the main DOS console,
10519 and type @kbd{~.} to leave @code{tip} or @code{cu}.
10522 @subsubsection Remote log
10523 @cindex @file{eb.log}, a log file for EB29K
10524 @cindex log file for EB29K
10526 The @code{target amd-eb} command creates a file @file{eb.log} in the
10527 current working directory, to help debug problems with the connection.
10528 @file{eb.log} records all the output from @code{EBMON}, including echoes
10529 of the commands sent to it. Running @samp{tail -f} on this file in
10530 another window often helps to understand trouble with @code{EBMON}, or
10531 unexpected events on the PC side of the connection.
10539 @item target rdi @var{dev}
10540 ARM Angel monitor, via RDI library interface to ADP protocol. You may
10541 use this target to communicate with both boards running the Angel
10542 monitor, or with the EmbeddedICE JTAG debug device.
10545 @item target rdp @var{dev}
10551 @subsection Hitachi H8/300
10555 @kindex target hms@r{, with H8/300}
10556 @item target hms @var{dev}
10557 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
10558 Use special commands @code{device} and @code{speed} to control the serial
10559 line and the communications speed used.
10561 @kindex target e7000@r{, with H8/300}
10562 @item target e7000 @var{dev}
10563 E7000 emulator for Hitachi H8 and SH.
10565 @kindex target sh3@r{, with H8/300}
10566 @kindex target sh3e@r{, with H8/300}
10567 @item target sh3 @var{dev}
10568 @itemx target sh3e @var{dev}
10569 Hitachi SH-3 and SH-3E target systems.
10573 @cindex download to H8/300 or H8/500
10574 @cindex H8/300 or H8/500 download
10575 @cindex download to Hitachi SH
10576 @cindex Hitachi SH download
10577 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
10578 board, the @code{load} command downloads your program to the Hitachi
10579 board and also opens it as the current executable target for
10580 @value{GDBN} on your host (like the @code{file} command).
10582 @value{GDBN} needs to know these things to talk to your
10583 Hitachi SH, H8/300, or H8/500:
10587 that you want to use @samp{target hms}, the remote debugging interface
10588 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
10589 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
10590 the default when @value{GDBN} is configured specifically for the Hitachi SH,
10591 H8/300, or H8/500.)
10594 what serial device connects your host to your Hitachi board (the first
10595 serial device available on your host is the default).
10598 what speed to use over the serial device.
10602 * Hitachi Boards:: Connecting to Hitachi boards.
10603 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
10604 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
10607 @node Hitachi Boards
10608 @subsubsection Connecting to Hitachi boards
10610 @c only for Unix hosts
10612 @cindex serial device, Hitachi micros
10613 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
10614 need to explicitly set the serial device. The default @var{port} is the
10615 first available port on your host. This is only necessary on Unix
10616 hosts, where it is typically something like @file{/dev/ttya}.
10619 @cindex serial line speed, Hitachi micros
10620 @code{@value{GDBN}} has another special command to set the communications
10621 speed: @samp{speed @var{bps}}. This command also is only used from Unix
10622 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
10623 the DOS @code{mode} command (for instance,
10624 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
10626 The @samp{device} and @samp{speed} commands are available only when you
10627 use a Unix host to debug your Hitachi microprocessor programs. If you
10629 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
10630 called @code{asynctsr} to communicate with the development board
10631 through a PC serial port. You must also use the DOS @code{mode} command
10632 to set up the serial port on the DOS side.
10634 The following sample session illustrates the steps needed to start a
10635 program under @value{GDBN} control on an H8/300. The example uses a
10636 sample H8/300 program called @file{t.x}. The procedure is the same for
10637 the Hitachi SH and the H8/500.
10639 First hook up your development board. In this example, we use a
10640 board attached to serial port @code{COM2}; if you use a different serial
10641 port, substitute its name in the argument of the @code{mode} command.
10642 When you call @code{asynctsr}, the auxiliary comms program used by the
10643 debugger, you give it just the numeric part of the serial port's name;
10644 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
10648 C:\H8300\TEST> asynctsr 2
10649 C:\H8300\TEST> mode com2:9600,n,8,1,p
10651 Resident portion of MODE loaded
10653 COM2: 9600, n, 8, 1, p
10658 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
10659 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
10660 disable it, or even boot without it, to use @code{asynctsr} to control
10661 your development board.
10664 @kindex target hms@r{, and serial protocol}
10665 Now that serial communications are set up, and the development board is
10666 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
10667 the name of your program as the argument. @code{@value{GDBN}} prompts
10668 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
10669 commands to begin your debugging session: @samp{target hms} to specify
10670 cross-debugging to the Hitachi board, and the @code{load} command to
10671 download your program to the board. @code{load} displays the names of
10672 the program's sections, and a @samp{*} for each 2K of data downloaded.
10673 (If you want to refresh @value{GDBN} data on symbols or on the
10674 executable file without downloading, use the @value{GDBN} commands
10675 @code{file} or @code{symbol-file}. These commands, and @code{load}
10676 itself, are described in @ref{Files,,Commands to specify files}.)
10679 (eg-C:\H8300\TEST) @value{GDBP} t.x
10680 @value{GDBN} is free software and you are welcome to distribute copies
10681 of it under certain conditions; type "show copying" to see
10683 There is absolutely no warranty for @value{GDBN}; type "show warranty"
10685 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
10686 (@value{GDBP}) target hms
10687 Connected to remote H8/300 HMS system.
10688 (@value{GDBP}) load t.x
10689 .text : 0x8000 .. 0xabde ***********
10690 .data : 0xabde .. 0xad30 *
10691 .stack : 0xf000 .. 0xf014 *
10694 At this point, you're ready to run or debug your program. From here on,
10695 you can use all the usual @value{GDBN} commands. The @code{break} command
10696 sets breakpoints; the @code{run} command starts your program;
10697 @code{print} or @code{x} display data; the @code{continue} command
10698 resumes execution after stopping at a breakpoint. You can use the
10699 @code{help} command at any time to find out more about @value{GDBN} commands.
10701 Remember, however, that @emph{operating system} facilities aren't
10702 available on your development board; for example, if your program hangs,
10703 you can't send an interrupt---but you can press the @sc{reset} switch!
10705 Use the @sc{reset} button on the development board
10708 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
10709 no way to pass an interrupt signal to the development board); and
10712 to return to the @value{GDBN} command prompt after your program finishes
10713 normally. The communications protocol provides no other way for @value{GDBN}
10714 to detect program completion.
10717 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
10718 development board as a ``normal exit'' of your program.
10721 @subsubsection Using the E7000 in-circuit emulator
10723 @kindex target e7000@r{, with Hitachi ICE}
10724 You can use the E7000 in-circuit emulator to develop code for either the
10725 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
10726 e7000} command to connect @value{GDBN} to your E7000:
10729 @item target e7000 @var{port} @var{speed}
10730 Use this form if your E7000 is connected to a serial port. The
10731 @var{port} argument identifies what serial port to use (for example,
10732 @samp{com2}). The third argument is the line speed in bits per second
10733 (for example, @samp{9600}).
10735 @item target e7000 @var{hostname}
10736 If your E7000 is installed as a host on a TCP/IP network, you can just
10737 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
10740 @node Hitachi Special
10741 @subsubsection Special @value{GDBN} commands for Hitachi micros
10743 Some @value{GDBN} commands are available only for the H8/300:
10747 @kindex set machine
10748 @kindex show machine
10749 @item set machine h8300
10750 @itemx set machine h8300h
10751 Condition @value{GDBN} for one of the two variants of the H8/300
10752 architecture with @samp{set machine}. You can use @samp{show machine}
10753 to check which variant is currently in effect.
10762 @kindex set memory @var{mod}
10763 @cindex memory models, H8/500
10764 @item set memory @var{mod}
10766 Specify which H8/500 memory model (@var{mod}) you are using with
10767 @samp{set memory}; check which memory model is in effect with @samp{show
10768 memory}. The accepted values for @var{mod} are @code{small},
10769 @code{big}, @code{medium}, and @code{compact}.
10774 @subsection Intel i960
10778 @kindex target mon960
10779 @item target mon960 @var{dev}
10780 MON960 monitor for Intel i960.
10782 @kindex target nindy
10783 @item target nindy @var{devicename}
10784 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10785 the name of the serial device to use for the connection, e.g.
10792 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
10793 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
10794 tell @value{GDBN} how to connect to the 960 in several ways:
10798 Through command line options specifying serial port, version of the
10799 Nindy protocol, and communications speed;
10802 By responding to a prompt on startup;
10805 By using the @code{target} command at any point during your @value{GDBN}
10806 session. @xref{Target Commands, ,Commands for managing targets}.
10810 @cindex download to Nindy-960
10811 With the Nindy interface to an Intel 960 board, @code{load}
10812 downloads @var{filename} to the 960 as well as adding its symbols in
10816 * Nindy Startup:: Startup with Nindy
10817 * Nindy Options:: Options for Nindy
10818 * Nindy Reset:: Nindy reset command
10821 @node Nindy Startup
10822 @subsubsection Startup with Nindy
10824 If you simply start @code{@value{GDBP}} without using any command-line
10825 options, you are prompted for what serial port to use, @emph{before} you
10826 reach the ordinary @value{GDBN} prompt:
10829 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
10833 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
10834 identifies the serial port you want to use. You can, if you choose,
10835 simply start up with no Nindy connection by responding to the prompt
10836 with an empty line. If you do this and later wish to attach to Nindy,
10837 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
10839 @node Nindy Options
10840 @subsubsection Options for Nindy
10842 These are the startup options for beginning your @value{GDBN} session with a
10843 Nindy-960 board attached:
10846 @item -r @var{port}
10847 Specify the serial port name of a serial interface to be used to connect
10848 to the target system. This option is only available when @value{GDBN} is
10849 configured for the Intel 960 target architecture. You may specify
10850 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
10851 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
10852 suffix for a specific @code{tty} (e.g. @samp{-r a}).
10855 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
10856 the ``old'' Nindy monitor protocol to connect to the target system.
10857 This option is only available when @value{GDBN} is configured for the Intel 960
10858 target architecture.
10861 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
10862 connect to a target system that expects the newer protocol, the connection
10863 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
10864 attempts to reconnect at several different line speeds. You can abort
10865 this process with an interrupt.
10869 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
10870 system, in an attempt to reset it, before connecting to a Nindy target.
10873 @emph{Warning:} Many target systems do not have the hardware that this
10874 requires; it only works with a few boards.
10878 The standard @samp{-b} option controls the line speed used on the serial
10883 @subsubsection Nindy reset command
10888 For a Nindy target, this command sends a ``break'' to the remote target
10889 system; this is only useful if the target has been equipped with a
10890 circuit to perform a hard reset (or some other interesting action) when
10891 a break is detected.
10896 @subsection Mitsubishi M32R/D
10900 @kindex target m32r
10901 @item target m32r @var{dev}
10902 Mitsubishi M32R/D ROM monitor.
10909 The Motorola m68k configuration includes ColdFire support, and
10910 target command for the following ROM monitors.
10914 @kindex target abug
10915 @item target abug @var{dev}
10916 ABug ROM monitor for M68K.
10918 @kindex target cpu32bug
10919 @item target cpu32bug @var{dev}
10920 CPU32BUG monitor, running on a CPU32 (M68K) board.
10922 @kindex target dbug
10923 @item target dbug @var{dev}
10924 dBUG ROM monitor for Motorola ColdFire.
10927 @item target est @var{dev}
10928 EST-300 ICE monitor, running on a CPU32 (M68K) board.
10930 @kindex target rom68k
10931 @item target rom68k @var{dev}
10932 ROM 68K monitor, running on an M68K IDP board.
10936 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
10937 instead have only a single special target command:
10941 @kindex target es1800
10942 @item target es1800 @var{dev}
10943 ES-1800 emulator for M68K.
10951 @kindex target rombug
10952 @item target rombug @var{dev}
10953 ROMBUG ROM monitor for OS/9000.
10963 @item target bug @var{dev}
10964 BUG monitor, running on a MVME187 (m88k) board.
10968 @node MIPS Embedded
10969 @subsection MIPS Embedded
10971 @cindex MIPS boards
10972 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
10973 MIPS board attached to a serial line. This is available when
10974 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
10977 Use these @value{GDBN} commands to specify the connection to your target board:
10980 @item target mips @var{port}
10981 @kindex target mips @var{port}
10982 To run a program on the board, start up @code{@value{GDBP}} with the
10983 name of your program as the argument. To connect to the board, use the
10984 command @samp{target mips @var{port}}, where @var{port} is the name of
10985 the serial port connected to the board. If the program has not already
10986 been downloaded to the board, you may use the @code{load} command to
10987 download it. You can then use all the usual @value{GDBN} commands.
10989 For example, this sequence connects to the target board through a serial
10990 port, and loads and runs a program called @var{prog} through the
10994 host$ @value{GDBP} @var{prog}
10995 @value{GDBN} is free software and @dots{}
10996 (@value{GDBP}) target mips /dev/ttyb
10997 (@value{GDBP}) load @var{prog}
11001 @item target mips @var{hostname}:@var{portnumber}
11002 On some @value{GDBN} host configurations, you can specify a TCP
11003 connection (for instance, to a serial line managed by a terminal
11004 concentrator) instead of a serial port, using the syntax
11005 @samp{@var{hostname}:@var{portnumber}}.
11007 @item target pmon @var{port}
11008 @kindex target pmon @var{port}
11011 @item target ddb @var{port}
11012 @kindex target ddb @var{port}
11013 NEC's DDB variant of PMON for Vr4300.
11015 @item target lsi @var{port}
11016 @kindex target lsi @var{port}
11017 LSI variant of PMON.
11019 @kindex target r3900
11020 @item target r3900 @var{dev}
11021 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11023 @kindex target array
11024 @item target array @var{dev}
11025 Array Tech LSI33K RAID controller board.
11031 @value{GDBN} also supports these special commands for MIPS targets:
11034 @item set processor @var{args}
11035 @itemx show processor
11036 @kindex set processor @var{args}
11037 @kindex show processor
11038 Use the @code{set processor} command to set the type of MIPS
11039 processor when you want to access processor-type-specific registers.
11040 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11041 to use the CPU registers appropriate for the 3041 chip.
11042 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11043 is using. Use the @code{info reg} command to see what registers
11044 @value{GDBN} is using.
11046 @item set mipsfpu double
11047 @itemx set mipsfpu single
11048 @itemx set mipsfpu none
11049 @itemx show mipsfpu
11050 @kindex set mipsfpu
11051 @kindex show mipsfpu
11052 @cindex MIPS remote floating point
11053 @cindex floating point, MIPS remote
11054 If your target board does not support the MIPS floating point
11055 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11056 need this, you may wish to put the command in your @value{GDBN} init
11057 file). This tells @value{GDBN} how to find the return value of
11058 functions which return floating point values. It also allows
11059 @value{GDBN} to avoid saving the floating point registers when calling
11060 functions on the board. If you are using a floating point coprocessor
11061 with only single precision floating point support, as on the @sc{r4650}
11062 processor, use the command @samp{set mipsfpu single}. The default
11063 double precision floating point coprocessor may be selected using
11064 @samp{set mipsfpu double}.
11066 In previous versions the only choices were double precision or no
11067 floating point, so @samp{set mipsfpu on} will select double precision
11068 and @samp{set mipsfpu off} will select no floating point.
11070 As usual, you can inquire about the @code{mipsfpu} variable with
11071 @samp{show mipsfpu}.
11073 @item set remotedebug @var{n}
11074 @itemx show remotedebug
11075 @kindex set remotedebug@r{, MIPS protocol}
11076 @kindex show remotedebug@r{, MIPS protocol}
11077 @cindex @code{remotedebug}, MIPS protocol
11078 @cindex MIPS @code{remotedebug} protocol
11079 @c FIXME! For this to be useful, you must know something about the MIPS
11080 @c FIXME...protocol. Where is it described?
11081 You can see some debugging information about communications with the board
11082 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11083 @samp{set remotedebug 1}, every packet is displayed. If you set it
11084 to @code{2}, every character is displayed. You can check the current value
11085 at any time with the command @samp{show remotedebug}.
11087 @item set timeout @var{seconds}
11088 @itemx set retransmit-timeout @var{seconds}
11089 @itemx show timeout
11090 @itemx show retransmit-timeout
11091 @cindex @code{timeout}, MIPS protocol
11092 @cindex @code{retransmit-timeout}, MIPS protocol
11093 @kindex set timeout
11094 @kindex show timeout
11095 @kindex set retransmit-timeout
11096 @kindex show retransmit-timeout
11097 You can control the timeout used while waiting for a packet, in the MIPS
11098 remote protocol, with the @code{set timeout @var{seconds}} command. The
11099 default is 5 seconds. Similarly, you can control the timeout used while
11100 waiting for an acknowledgement of a packet with the @code{set
11101 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11102 You can inspect both values with @code{show timeout} and @code{show
11103 retransmit-timeout}. (These commands are @emph{only} available when
11104 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11106 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11107 is waiting for your program to stop. In that case, @value{GDBN} waits
11108 forever because it has no way of knowing how long the program is going
11109 to run before stopping.
11113 @subsection PowerPC
11117 @kindex target dink32
11118 @item target dink32 @var{dev}
11119 DINK32 ROM monitor.
11121 @kindex target ppcbug
11122 @item target ppcbug @var{dev}
11123 @kindex target ppcbug1
11124 @item target ppcbug1 @var{dev}
11125 PPCBUG ROM monitor for PowerPC.
11128 @item target sds @var{dev}
11129 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11134 @subsection HP PA Embedded
11138 @kindex target op50n
11139 @item target op50n @var{dev}
11140 OP50N monitor, running on an OKI HPPA board.
11142 @kindex target w89k
11143 @item target w89k @var{dev}
11144 W89K monitor, running on a Winbond HPPA board.
11149 @subsection Hitachi SH
11153 @kindex target hms@r{, with Hitachi SH}
11154 @item target hms @var{dev}
11155 A Hitachi SH board attached via serial line to your host. Use special
11156 commands @code{device} and @code{speed} to control the serial line and
11157 the communications speed used.
11159 @kindex target e7000@r{, with Hitachi SH}
11160 @item target e7000 @var{dev}
11161 E7000 emulator for Hitachi SH.
11163 @kindex target sh3@r{, with SH}
11164 @kindex target sh3e@r{, with SH}
11165 @item target sh3 @var{dev}
11166 @item target sh3e @var{dev}
11167 Hitachi SH-3 and SH-3E target systems.
11172 @subsection Tsqware Sparclet
11176 @value{GDBN} enables developers to debug tasks running on
11177 Sparclet targets from a Unix host.
11178 @value{GDBN} uses code that runs on
11179 both the Unix host and on the Sparclet target. The program
11180 @code{@value{GDBP}} is installed and executed on the Unix host.
11183 @item remotetimeout @var{args}
11184 @kindex remotetimeout
11185 @value{GDBN} supports the option @code{remotetimeout}.
11186 This option is set by the user, and @var{args} represents the number of
11187 seconds @value{GDBN} waits for responses.
11190 @cindex compiling, on Sparclet
11191 When compiling for debugging, include the options @samp{-g} to get debug
11192 information and @samp{-Ttext} to relocate the program to where you wish to
11193 load it on the target. You may also want to add the options @samp{-n} or
11194 @samp{-N} in order to reduce the size of the sections. Example:
11197 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11200 You can use @code{objdump} to verify that the addresses are what you intended:
11203 sparclet-aout-objdump --headers --syms prog
11206 @cindex running, on Sparclet
11208 your Unix execution search path to find @value{GDBN}, you are ready to
11209 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
11210 (or @code{sparclet-aout-gdb}, depending on your installation).
11212 @value{GDBN} comes up showing the prompt:
11219 * Sparclet File:: Setting the file to debug
11220 * Sparclet Connection:: Connecting to Sparclet
11221 * Sparclet Download:: Sparclet download
11222 * Sparclet Execution:: Running and debugging
11225 @node Sparclet File
11226 @subsubsection Setting file to debug
11228 The @value{GDBN} command @code{file} lets you choose with program to debug.
11231 (gdbslet) file prog
11235 @value{GDBN} then attempts to read the symbol table of @file{prog}.
11236 @value{GDBN} locates
11237 the file by searching the directories listed in the command search
11239 If the file was compiled with debug information (option "-g"), source
11240 files will be searched as well.
11241 @value{GDBN} locates
11242 the source files by searching the directories listed in the directory search
11243 path (@pxref{Environment, ,Your program's environment}).
11245 to find a file, it displays a message such as:
11248 prog: No such file or directory.
11251 When this happens, add the appropriate directories to the search paths with
11252 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
11253 @code{target} command again.
11255 @node Sparclet Connection
11256 @subsubsection Connecting to Sparclet
11258 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
11259 To connect to a target on serial port ``@code{ttya}'', type:
11262 (gdbslet) target sparclet /dev/ttya
11263 Remote target sparclet connected to /dev/ttya
11264 main () at ../prog.c:3
11268 @value{GDBN} displays messages like these:
11274 @node Sparclet Download
11275 @subsubsection Sparclet download
11277 @cindex download to Sparclet
11278 Once connected to the Sparclet target,
11279 you can use the @value{GDBN}
11280 @code{load} command to download the file from the host to the target.
11281 The file name and load offset should be given as arguments to the @code{load}
11283 Since the file format is aout, the program must be loaded to the starting
11284 address. You can use @code{objdump} to find out what this value is. The load
11285 offset is an offset which is added to the VMA (virtual memory address)
11286 of each of the file's sections.
11287 For instance, if the program
11288 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
11289 and bss at 0x12010170, in @value{GDBN}, type:
11292 (gdbslet) load prog 0x12010000
11293 Loading section .text, size 0xdb0 vma 0x12010000
11296 If the code is loaded at a different address then what the program was linked
11297 to, you may need to use the @code{section} and @code{add-symbol-file} commands
11298 to tell @value{GDBN} where to map the symbol table.
11300 @node Sparclet Execution
11301 @subsubsection Running and debugging
11303 @cindex running and debugging Sparclet programs
11304 You can now begin debugging the task using @value{GDBN}'s execution control
11305 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
11306 manual for the list of commands.
11310 Breakpoint 1 at 0x12010000: file prog.c, line 3.
11312 Starting program: prog
11313 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
11314 3 char *symarg = 0;
11316 4 char *execarg = "hello!";
11321 @subsection Fujitsu Sparclite
11325 @kindex target sparclite
11326 @item target sparclite @var{dev}
11327 Fujitsu sparclite boards, used only for the purpose of loading.
11328 You must use an additional command to debug the program.
11329 For example: target remote @var{dev} using @value{GDBN} standard
11335 @subsection Tandem ST2000
11337 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11340 To connect your ST2000 to the host system, see the manufacturer's
11341 manual. Once the ST2000 is physically attached, you can run:
11344 target st2000 @var{dev} @var{speed}
11348 to establish it as your debugging environment. @var{dev} is normally
11349 the name of a serial device, such as @file{/dev/ttya}, connected to the
11350 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11351 connection (for example, to a serial line attached via a terminal
11352 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11354 The @code{load} and @code{attach} commands are @emph{not} defined for
11355 this target; you must load your program into the ST2000 as you normally
11356 would for standalone operation. @value{GDBN} reads debugging information
11357 (such as symbols) from a separate, debugging version of the program
11358 available on your host computer.
11359 @c FIXME!! This is terribly vague; what little content is here is
11360 @c basically hearsay.
11362 @cindex ST2000 auxiliary commands
11363 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11367 @item st2000 @var{command}
11368 @kindex st2000 @var{cmd}
11369 @cindex STDBUG commands (ST2000)
11370 @cindex commands to STDBUG (ST2000)
11371 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11372 manual for available commands.
11375 @cindex connect (to STDBUG)
11376 Connect the controlling terminal to the STDBUG command monitor. When
11377 you are done interacting with STDBUG, typing either of two character
11378 sequences gets you back to the @value{GDBN} command prompt:
11379 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11380 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11384 @subsection Zilog Z8000
11387 @cindex simulator, Z8000
11388 @cindex Zilog Z8000 simulator
11390 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11393 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11394 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11395 segmented variant). The simulator recognizes which architecture is
11396 appropriate by inspecting the object code.
11399 @item target sim @var{args}
11401 @kindex target sim@r{, with Z8000}
11402 Debug programs on a simulated CPU. If the simulator supports setup
11403 options, specify them via @var{args}.
11407 After specifying this target, you can debug programs for the simulated
11408 CPU in the same style as programs for your host computer; use the
11409 @code{file} command to load a new program image, the @code{run} command
11410 to run your program, and so on.
11412 As well as making available all the usual machine registers
11413 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11414 additional items of information as specially named registers:
11419 Counts clock-ticks in the simulator.
11422 Counts instructions run in the simulator.
11425 Execution time in 60ths of a second.
11429 You can refer to these values in @value{GDBN} expressions with the usual
11430 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11431 conditional breakpoint that suspends only after at least 5000
11432 simulated clock ticks.
11434 @node Architectures
11435 @section Architectures
11437 This section describes characteristics of architectures that affect
11438 all uses of @value{GDBN} with the architecture, both native and cross.
11451 @kindex set rstack_high_address
11452 @cindex AMD 29K register stack
11453 @cindex register stack, AMD29K
11454 @item set rstack_high_address @var{address}
11455 On AMD 29000 family processors, registers are saved in a separate
11456 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11457 extent of this stack. Normally, @value{GDBN} just assumes that the
11458 stack is ``large enough''. This may result in @value{GDBN} referencing
11459 memory locations that do not exist. If necessary, you can get around
11460 this problem by specifying the ending address of the register stack with
11461 the @code{set rstack_high_address} command. The argument should be an
11462 address, which you probably want to precede with @samp{0x} to specify in
11465 @kindex show rstack_high_address
11466 @item show rstack_high_address
11467 Display the current limit of the register stack, on AMD 29000 family
11475 See the following section.
11480 @cindex stack on Alpha
11481 @cindex stack on MIPS
11482 @cindex Alpha stack
11484 Alpha- and MIPS-based computers use an unusual stack frame, which
11485 sometimes requires @value{GDBN} to search backward in the object code to
11486 find the beginning of a function.
11488 @cindex response time, MIPS debugging
11489 To improve response time (especially for embedded applications, where
11490 @value{GDBN} may be restricted to a slow serial line for this search)
11491 you may want to limit the size of this search, using one of these
11495 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
11496 @item set heuristic-fence-post @var{limit}
11497 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
11498 search for the beginning of a function. A value of @var{0} (the
11499 default) means there is no limit. However, except for @var{0}, the
11500 larger the limit the more bytes @code{heuristic-fence-post} must search
11501 and therefore the longer it takes to run.
11503 @item show heuristic-fence-post
11504 Display the current limit.
11508 These commands are available @emph{only} when @value{GDBN} is configured
11509 for debugging programs on Alpha or MIPS processors.
11512 @node Controlling GDB
11513 @chapter Controlling @value{GDBN}
11515 You can alter the way @value{GDBN} interacts with you by using the
11516 @code{set} command. For commands controlling how @value{GDBN} displays
11517 data, see @ref{Print Settings, ,Print settings}. Other settings are
11522 * Editing:: Command editing
11523 * History:: Command history
11524 * Screen Size:: Screen size
11525 * Numbers:: Numbers
11526 * Messages/Warnings:: Optional warnings and messages
11527 * Debugging Output:: Optional messages about internal happenings
11535 @value{GDBN} indicates its readiness to read a command by printing a string
11536 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
11537 can change the prompt string with the @code{set prompt} command. For
11538 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
11539 the prompt in one of the @value{GDBN} sessions so that you can always tell
11540 which one you are talking to.
11542 @emph{Note:} @code{set prompt} does not add a space for you after the
11543 prompt you set. This allows you to set a prompt which ends in a space
11544 or a prompt that does not.
11548 @item set prompt @var{newprompt}
11549 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
11551 @kindex show prompt
11553 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
11557 @section Command editing
11559 @cindex command line editing
11561 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
11562 @sc{gnu} library provides consistent behavior for programs which provide a
11563 command line interface to the user. Advantages are @sc{gnu} Emacs-style
11564 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
11565 substitution, and a storage and recall of command history across
11566 debugging sessions.
11568 You may control the behavior of command line editing in @value{GDBN} with the
11569 command @code{set}.
11572 @kindex set editing
11575 @itemx set editing on
11576 Enable command line editing (enabled by default).
11578 @item set editing off
11579 Disable command line editing.
11581 @kindex show editing
11583 Show whether command line editing is enabled.
11587 @section Command history
11589 @value{GDBN} can keep track of the commands you type during your
11590 debugging sessions, so that you can be certain of precisely what
11591 happened. Use these commands to manage the @value{GDBN} command
11595 @cindex history substitution
11596 @cindex history file
11597 @kindex set history filename
11598 @kindex GDBHISTFILE
11599 @item set history filename @var{fname}
11600 Set the name of the @value{GDBN} command history file to @var{fname}.
11601 This is the file where @value{GDBN} reads an initial command history
11602 list, and where it writes the command history from this session when it
11603 exits. You can access this list through history expansion or through
11604 the history command editing characters listed below. This file defaults
11605 to the value of the environment variable @code{GDBHISTFILE}, or to
11606 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
11609 @cindex history save
11610 @kindex set history save
11611 @item set history save
11612 @itemx set history save on
11613 Record command history in a file, whose name may be specified with the
11614 @code{set history filename} command. By default, this option is disabled.
11616 @item set history save off
11617 Stop recording command history in a file.
11619 @cindex history size
11620 @kindex set history size
11621 @item set history size @var{size}
11622 Set the number of commands which @value{GDBN} keeps in its history list.
11623 This defaults to the value of the environment variable
11624 @code{HISTSIZE}, or to 256 if this variable is not set.
11627 @cindex history expansion
11628 History expansion assigns special meaning to the character @kbd{!}.
11629 @ifset have-readline-appendices
11630 @xref{Event Designators}.
11633 Since @kbd{!} is also the logical not operator in C, history expansion
11634 is off by default. If you decide to enable history expansion with the
11635 @code{set history expansion on} command, you may sometimes need to
11636 follow @kbd{!} (when it is used as logical not, in an expression) with
11637 a space or a tab to prevent it from being expanded. The readline
11638 history facilities do not attempt substitution on the strings
11639 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
11641 The commands to control history expansion are:
11644 @kindex set history expansion
11645 @item set history expansion on
11646 @itemx set history expansion
11647 Enable history expansion. History expansion is off by default.
11649 @item set history expansion off
11650 Disable history expansion.
11652 The readline code comes with more complete documentation of
11653 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
11654 or @code{vi} may wish to read it.
11655 @ifset have-readline-appendices
11656 @xref{Command Line Editing}.
11660 @kindex show history
11662 @itemx show history filename
11663 @itemx show history save
11664 @itemx show history size
11665 @itemx show history expansion
11666 These commands display the state of the @value{GDBN} history parameters.
11667 @code{show history} by itself displays all four states.
11673 @item show commands
11674 Display the last ten commands in the command history.
11676 @item show commands @var{n}
11677 Print ten commands centered on command number @var{n}.
11679 @item show commands +
11680 Print ten commands just after the commands last printed.
11684 @section Screen size
11685 @cindex size of screen
11686 @cindex pauses in output
11688 Certain commands to @value{GDBN} may produce large amounts of
11689 information output to the screen. To help you read all of it,
11690 @value{GDBN} pauses and asks you for input at the end of each page of
11691 output. Type @key{RET} when you want to continue the output, or @kbd{q}
11692 to discard the remaining output. Also, the screen width setting
11693 determines when to wrap lines of output. Depending on what is being
11694 printed, @value{GDBN} tries to break the line at a readable place,
11695 rather than simply letting it overflow onto the following line.
11697 Normally @value{GDBN} knows the size of the screen from the terminal
11698 driver software. For example, on Unix @value{GDBN} uses the termcap data base
11699 together with the value of the @code{TERM} environment variable and the
11700 @code{stty rows} and @code{stty cols} settings. If this is not correct,
11701 you can override it with the @code{set height} and @code{set
11708 @kindex show height
11709 @item set height @var{lpp}
11711 @itemx set width @var{cpl}
11713 These @code{set} commands specify a screen height of @var{lpp} lines and
11714 a screen width of @var{cpl} characters. The associated @code{show}
11715 commands display the current settings.
11717 If you specify a height of zero lines, @value{GDBN} does not pause during
11718 output no matter how long the output is. This is useful if output is to a
11719 file or to an editor buffer.
11721 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
11722 from wrapping its output.
11727 @cindex number representation
11728 @cindex entering numbers
11730 You can always enter numbers in octal, decimal, or hexadecimal in
11731 @value{GDBN} by the usual conventions: octal numbers begin with
11732 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
11733 begin with @samp{0x}. Numbers that begin with none of these are, by
11734 default, entered in base 10; likewise, the default display for
11735 numbers---when no particular format is specified---is base 10. You can
11736 change the default base for both input and output with the @code{set
11740 @kindex set input-radix
11741 @item set input-radix @var{base}
11742 Set the default base for numeric input. Supported choices
11743 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11744 specified either unambiguously or using the current default radix; for
11754 sets the base to decimal. On the other hand, @samp{set radix 10}
11755 leaves the radix unchanged no matter what it was.
11757 @kindex set output-radix
11758 @item set output-radix @var{base}
11759 Set the default base for numeric display. Supported choices
11760 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11761 specified either unambiguously or using the current default radix.
11763 @kindex show input-radix
11764 @item show input-radix
11765 Display the current default base for numeric input.
11767 @kindex show output-radix
11768 @item show output-radix
11769 Display the current default base for numeric display.
11772 @node Messages/Warnings
11773 @section Optional warnings and messages
11775 By default, @value{GDBN} is silent about its inner workings. If you are
11776 running on a slow machine, you may want to use the @code{set verbose}
11777 command. This makes @value{GDBN} tell you when it does a lengthy
11778 internal operation, so you will not think it has crashed.
11780 Currently, the messages controlled by @code{set verbose} are those
11781 which announce that the symbol table for a source file is being read;
11782 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
11785 @kindex set verbose
11786 @item set verbose on
11787 Enables @value{GDBN} output of certain informational messages.
11789 @item set verbose off
11790 Disables @value{GDBN} output of certain informational messages.
11792 @kindex show verbose
11794 Displays whether @code{set verbose} is on or off.
11797 By default, if @value{GDBN} encounters bugs in the symbol table of an
11798 object file, it is silent; but if you are debugging a compiler, you may
11799 find this information useful (@pxref{Symbol Errors, ,Errors reading
11804 @kindex set complaints
11805 @item set complaints @var{limit}
11806 Permits @value{GDBN} to output @var{limit} complaints about each type of
11807 unusual symbols before becoming silent about the problem. Set
11808 @var{limit} to zero to suppress all complaints; set it to a large number
11809 to prevent complaints from being suppressed.
11811 @kindex show complaints
11812 @item show complaints
11813 Displays how many symbol complaints @value{GDBN} is permitted to produce.
11817 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
11818 lot of stupid questions to confirm certain commands. For example, if
11819 you try to run a program which is already running:
11823 The program being debugged has been started already.
11824 Start it from the beginning? (y or n)
11827 If you are willing to unflinchingly face the consequences of your own
11828 commands, you can disable this ``feature'':
11832 @kindex set confirm
11834 @cindex confirmation
11835 @cindex stupid questions
11836 @item set confirm off
11837 Disables confirmation requests.
11839 @item set confirm on
11840 Enables confirmation requests (the default).
11842 @kindex show confirm
11844 Displays state of confirmation requests.
11848 @node Debugging Output
11849 @section Optional messages about internal happenings
11851 @kindex set debug arch
11852 @item set debug arch
11853 Turns on or off display of gdbarch debugging info. The default is off
11854 @kindex show debug arch
11855 @item show debug arch
11856 Displays the current state of displaying gdbarch debugging info.
11857 @kindex set debug event
11858 @item set debug event
11859 Turns on or off display of @value{GDBN} event debugging info. The
11861 @kindex show debug event
11862 @item show debug event
11863 Displays the current state of displaying @value{GDBN} event debugging
11865 @kindex set debug expression
11866 @item set debug expression
11867 Turns on or off display of @value{GDBN} expression debugging info. The
11869 @kindex show debug expression
11870 @item show debug expression
11871 Displays the current state of displaying @value{GDBN} expression
11873 @kindex set debug overload
11874 @item set debug overload
11875 Turns on or off display of @value{GDBN} C++ overload debugging
11876 info. This includes info such as ranking of functions, etc. The default
11878 @kindex show debug overload
11879 @item show debug overload
11880 Displays the current state of displaying @value{GDBN} C++ overload
11882 @kindex set debug remote
11883 @cindex packets, reporting on stdout
11884 @cindex serial connections, debugging
11885 @item set debug remote
11886 Turns on or off display of reports on all packets sent back and forth across
11887 the serial line to the remote machine. The info is printed on the
11888 @value{GDBN} standard output stream. The default is off.
11889 @kindex show debug remote
11890 @item show debug remote
11891 Displays the state of display of remote packets.
11892 @kindex set debug serial
11893 @item set debug serial
11894 Turns on or off display of @value{GDBN} serial debugging info. The
11896 @kindex show debug serial
11897 @item show debug serial
11898 Displays the current state of displaying @value{GDBN} serial debugging
11900 @kindex set debug target
11901 @item set debug target
11902 Turns on or off display of @value{GDBN} target debugging info. This info
11903 includes what is going on at the target level of GDB, as it happens. The
11905 @kindex show debug target
11906 @item show debug target
11907 Displays the current state of displaying @value{GDBN} target debugging
11909 @kindex set debug varobj
11910 @item set debug varobj
11911 Turns on or off display of @value{GDBN} variable object debugging
11912 info. The default is off.
11913 @kindex show debug varobj
11914 @item show debug varobj
11915 Displays the current state of displaying @value{GDBN} variable object
11920 @chapter Canned Sequences of Commands
11922 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
11923 command lists}), @value{GDBN} provides two ways to store sequences of
11924 commands for execution as a unit: user-defined commands and command
11928 * Define:: User-defined commands
11929 * Hooks:: User-defined command hooks
11930 * Command Files:: Command files
11931 * Output:: Commands for controlled output
11935 @section User-defined commands
11937 @cindex user-defined command
11938 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
11939 which you assign a new name as a command. This is done with the
11940 @code{define} command. User commands may accept up to 10 arguments
11941 separated by whitespace. Arguments are accessed within the user command
11942 via @var{$arg0@dots{}$arg9}. A trivial example:
11946 print $arg0 + $arg1 + $arg2
11950 To execute the command use:
11957 This defines the command @code{adder}, which prints the sum of
11958 its three arguments. Note the arguments are text substitutions, so they may
11959 reference variables, use complex expressions, or even perform inferior
11965 @item define @var{commandname}
11966 Define a command named @var{commandname}. If there is already a command
11967 by that name, you are asked to confirm that you want to redefine it.
11969 The definition of the command is made up of other @value{GDBN} command lines,
11970 which are given following the @code{define} command. The end of these
11971 commands is marked by a line containing @code{end}.
11976 Takes a single argument, which is an expression to evaluate.
11977 It is followed by a series of commands that are executed
11978 only if the expression is true (nonzero).
11979 There can then optionally be a line @code{else}, followed
11980 by a series of commands that are only executed if the expression
11981 was false. The end of the list is marked by a line containing @code{end}.
11985 The syntax is similar to @code{if}: the command takes a single argument,
11986 which is an expression to evaluate, and must be followed by the commands to
11987 execute, one per line, terminated by an @code{end}.
11988 The commands are executed repeatedly as long as the expression
11992 @item document @var{commandname}
11993 Document the user-defined command @var{commandname}, so that it can be
11994 accessed by @code{help}. The command @var{commandname} must already be
11995 defined. This command reads lines of documentation just as @code{define}
11996 reads the lines of the command definition, ending with @code{end}.
11997 After the @code{document} command is finished, @code{help} on command
11998 @var{commandname} displays the documentation you have written.
12000 You may use the @code{document} command again to change the
12001 documentation of a command. Redefining the command with @code{define}
12002 does not change the documentation.
12004 @kindex help user-defined
12005 @item help user-defined
12006 List all user-defined commands, with the first line of the documentation
12011 @itemx show user @var{commandname}
12012 Display the @value{GDBN} commands used to define @var{commandname} (but
12013 not its documentation). If no @var{commandname} is given, display the
12014 definitions for all user-defined commands.
12018 When user-defined commands are executed, the
12019 commands of the definition are not printed. An error in any command
12020 stops execution of the user-defined command.
12022 If used interactively, commands that would ask for confirmation proceed
12023 without asking when used inside a user-defined command. Many @value{GDBN}
12024 commands that normally print messages to say what they are doing omit the
12025 messages when used in a user-defined command.
12028 @section User-defined command hooks
12029 @cindex command hooks
12030 @cindex hooks, for commands
12031 @cindex hooks, pre-command
12035 You may define @dfn{hooks}, which are a special kind of user-defined
12036 command. Whenever you run the command @samp{foo}, if the user-defined
12037 command @samp{hook-foo} exists, it is executed (with no arguments)
12038 before that command.
12040 @cindex hooks, post-command
12043 A hook may also be defined which is run after the command you executed.
12044 Whenever you run the command @samp{foo}, if the user-defined command
12045 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12046 that command. Post-execution hooks may exist simultaneously with
12047 pre-execution hooks, for the same command.
12049 It is valid for a hook to call the command which it hooks. If this
12050 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12052 @c It would be nice if hookpost could be passed a parameter indicating
12053 @c if the command it hooks executed properly or not. FIXME!
12055 @kindex stop@r{, a pseudo-command}
12056 In addition, a pseudo-command, @samp{stop} exists. Defining
12057 (@samp{hook-stop}) makes the associated commands execute every time
12058 execution stops in your program: before breakpoint commands are run,
12059 displays are printed, or the stack frame is printed.
12061 For example, to ignore @code{SIGALRM} signals while
12062 single-stepping, but treat them normally during normal execution,
12067 handle SIGALRM nopass
12071 handle SIGALRM pass
12074 define hook-continue
12075 handle SIGLARM pass
12079 As a further example, to hook at the begining and end of the @code{echo}
12080 command, and to add extra text to the beginning and end of the message,
12088 define hookpost-echo
12092 (@value{GDBP}) echo Hello World
12093 <<<---Hello World--->>>
12098 You can define a hook for any single-word command in @value{GDBN}, but
12099 not for command aliases; you should define a hook for the basic command
12100 name, e.g. @code{backtrace} rather than @code{bt}.
12101 @c FIXME! So how does Joe User discover whether a command is an alias
12103 If an error occurs during the execution of your hook, execution of
12104 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12105 (before the command that you actually typed had a chance to run).
12107 If you try to define a hook which does not match any known command, you
12108 get a warning from the @code{define} command.
12110 @node Command Files
12111 @section Command files
12113 @cindex command files
12114 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12115 commands. Comments (lines starting with @kbd{#}) may also be included.
12116 An empty line in a command file does nothing; it does not mean to repeat
12117 the last command, as it would from the terminal.
12120 @cindex @file{.gdbinit}
12121 @cindex @file{gdb.ini}
12122 When you start @value{GDBN}, it automatically executes commands from its
12123 @dfn{init files}. These are files named @file{.gdbinit} on Unix and
12124 @file{gdb.ini} on DOS/Windows. During startup, @value{GDBN} does the
12129 Reads the init file (if any) in your home directory@footnote{On
12130 DOS/Windows systems, the home directory is the one pointed to by the
12131 @code{HOME} environment variable.}.
12134 Processes command line options and operands.
12137 Reads the init file (if any) in the current working directory.
12140 Reads command files specified by the @samp{-x} option.
12143 The init file in your home directory can set options (such as @samp{set
12144 complaints}) that affect subsequent processing of command line options
12145 and operands. Init files are not executed if you use the @samp{-nx}
12146 option (@pxref{Mode Options, ,Choosing modes}).
12148 @cindex init file name
12149 On some configurations of @value{GDBN}, the init file is known by a
12150 different name (these are typically environments where a specialized
12151 form of @value{GDBN} may need to coexist with other forms, hence a
12152 different name for the specialized version's init file). These are the
12153 environments with special init file names:
12155 @cindex @file{.vxgdbinit}
12158 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
12160 @cindex @file{.os68gdbinit}
12162 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
12164 @cindex @file{.esgdbinit}
12166 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
12169 You can also request the execution of a command file with the
12170 @code{source} command:
12174 @item source @var{filename}
12175 Execute the command file @var{filename}.
12178 The lines in a command file are executed sequentially. They are not
12179 printed as they are executed. An error in any command terminates execution
12180 of the command file.
12182 Commands that would ask for confirmation if used interactively proceed
12183 without asking when used in a command file. Many @value{GDBN} commands that
12184 normally print messages to say what they are doing omit the messages
12185 when called from command files.
12188 @section Commands for controlled output
12190 During the execution of a command file or a user-defined command, normal
12191 @value{GDBN} output is suppressed; the only output that appears is what is
12192 explicitly printed by the commands in the definition. This section
12193 describes three commands useful for generating exactly the output you
12198 @item echo @var{text}
12199 @c I do not consider backslash-space a standard C escape sequence
12200 @c because it is not in ANSI.
12201 Print @var{text}. Nonprinting characters can be included in
12202 @var{text} using C escape sequences, such as @samp{\n} to print a
12203 newline. @strong{No newline is printed unless you specify one.}
12204 In addition to the standard C escape sequences, a backslash followed
12205 by a space stands for a space. This is useful for displaying a
12206 string with spaces at the beginning or the end, since leading and
12207 trailing spaces are otherwise trimmed from all arguments.
12208 To print @samp{@w{ }and foo =@w{ }}, use the command
12209 @samp{echo \@w{ }and foo = \@w{ }}.
12211 A backslash at the end of @var{text} can be used, as in C, to continue
12212 the command onto subsequent lines. For example,
12215 echo This is some text\n\
12216 which is continued\n\
12217 onto several lines.\n
12220 produces the same output as
12223 echo This is some text\n
12224 echo which is continued\n
12225 echo onto several lines.\n
12229 @item output @var{expression}
12230 Print the value of @var{expression} and nothing but that value: no
12231 newlines, no @samp{$@var{nn} = }. The value is not entered in the
12232 value history either. @xref{Expressions, ,Expressions}, for more information
12235 @item output/@var{fmt} @var{expression}
12236 Print the value of @var{expression} in format @var{fmt}. You can use
12237 the same formats as for @code{print}. @xref{Output Formats,,Output
12238 formats}, for more information.
12241 @item printf @var{string}, @var{expressions}@dots{}
12242 Print the values of the @var{expressions} under the control of
12243 @var{string}. The @var{expressions} are separated by commas and may be
12244 either numbers or pointers. Their values are printed as specified by
12245 @var{string}, exactly as if your program were to execute the C
12247 @c FIXME: the above implies that at least all ANSI C formats are
12248 @c supported, but it isn't true: %E and %G don't work (or so it seems).
12249 @c Either this is a bug, or the manual should document what formats are
12253 printf (@var{string}, @var{expressions}@dots{});
12256 For example, you can print two values in hex like this:
12259 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
12262 The only backslash-escape sequences that you can use in the format
12263 string are the simple ones that consist of backslash followed by a
12268 @chapter Using @value{GDBN} under @sc{gnu} Emacs
12271 @cindex @sc{gnu} Emacs
12272 A special interface allows you to use @sc{gnu} Emacs to view (and
12273 edit) the source files for the program you are debugging with
12276 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
12277 executable file you want to debug as an argument. This command starts
12278 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
12279 created Emacs buffer.
12280 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
12282 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
12287 All ``terminal'' input and output goes through the Emacs buffer.
12290 This applies both to @value{GDBN} commands and their output, and to the input
12291 and output done by the program you are debugging.
12293 This is useful because it means that you can copy the text of previous
12294 commands and input them again; you can even use parts of the output
12297 All the facilities of Emacs' Shell mode are available for interacting
12298 with your program. In particular, you can send signals the usual
12299 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
12304 @value{GDBN} displays source code through Emacs.
12307 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
12308 source file for that frame and puts an arrow (@samp{=>}) at the
12309 left margin of the current line. Emacs uses a separate buffer for
12310 source display, and splits the screen to show both your @value{GDBN} session
12313 Explicit @value{GDBN} @code{list} or search commands still produce output as
12314 usual, but you probably have no reason to use them from Emacs.
12317 @emph{Warning:} If the directory where your program resides is not your
12318 current directory, it can be easy to confuse Emacs about the location of
12319 the source files, in which case the auxiliary display buffer does not
12320 appear to show your source. @value{GDBN} can find programs by searching your
12321 environment's @code{PATH} variable, so the @value{GDBN} input and output
12322 session proceeds normally; but Emacs does not get enough information
12323 back from @value{GDBN} to locate the source files in this situation. To
12324 avoid this problem, either start @value{GDBN} mode from the directory where
12325 your program resides, or specify an absolute file name when prompted for the
12326 @kbd{M-x gdb} argument.
12328 A similar confusion can result if you use the @value{GDBN} @code{file} command to
12329 switch to debugging a program in some other location, from an existing
12330 @value{GDBN} buffer in Emacs.
12333 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
12334 you need to call @value{GDBN} by a different name (for example, if you keep
12335 several configurations around, with different names) you can set the
12336 Emacs variable @code{gdb-command-name}; for example,
12339 (setq gdb-command-name "mygdb")
12343 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
12344 in your @file{.emacs} file) makes Emacs call the program named
12345 ``@code{mygdb}'' instead.
12347 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
12348 addition to the standard Shell mode commands:
12352 Describe the features of Emacs' @value{GDBN} Mode.
12355 Execute to another source line, like the @value{GDBN} @code{step} command; also
12356 update the display window to show the current file and location.
12359 Execute to next source line in this function, skipping all function
12360 calls, like the @value{GDBN} @code{next} command. Then update the display window
12361 to show the current file and location.
12364 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
12365 display window accordingly.
12367 @item M-x gdb-nexti
12368 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
12369 display window accordingly.
12372 Execute until exit from the selected stack frame, like the @value{GDBN}
12373 @code{finish} command.
12376 Continue execution of your program, like the @value{GDBN} @code{continue}
12379 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
12382 Go up the number of frames indicated by the numeric argument
12383 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
12384 like the @value{GDBN} @code{up} command.
12386 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
12389 Go down the number of frames indicated by the numeric argument, like the
12390 @value{GDBN} @code{down} command.
12392 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
12395 Read the number where the cursor is positioned, and insert it at the end
12396 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
12397 around an address that was displayed earlier, type @kbd{disassemble};
12398 then move the cursor to the address display, and pick up the
12399 argument for @code{disassemble} by typing @kbd{C-x &}.
12401 You can customize this further by defining elements of the list
12402 @code{gdb-print-command}; once it is defined, you can format or
12403 otherwise process numbers picked up by @kbd{C-x &} before they are
12404 inserted. A numeric argument to @kbd{C-x &} indicates that you
12405 wish special formatting, and also acts as an index to pick an element of the
12406 list. If the list element is a string, the number to be inserted is
12407 formatted using the Emacs function @code{format}; otherwise the number
12408 is passed as an argument to the corresponding list element.
12411 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
12412 tells @value{GDBN} to set a breakpoint on the source line point is on.
12414 If you accidentally delete the source-display buffer, an easy way to get
12415 it back is to type the command @code{f} in the @value{GDBN} buffer, to
12416 request a frame display; when you run under Emacs, this recreates
12417 the source buffer if necessary to show you the context of the current
12420 The source files displayed in Emacs are in ordinary Emacs buffers
12421 which are visiting the source files in the usual way. You can edit
12422 the files with these buffers if you wish; but keep in mind that @value{GDBN}
12423 communicates with Emacs in terms of line numbers. If you add or
12424 delete lines from the text, the line numbers that @value{GDBN} knows cease
12425 to correspond properly with the code.
12427 @c The following dropped because Epoch is nonstandard. Reactivate
12428 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
12430 @kindex Emacs Epoch environment
12434 Version 18 of @sc{gnu} Emacs has a built-in window system
12435 called the @code{epoch}
12436 environment. Users of this environment can use a new command,
12437 @code{inspect} which performs identically to @code{print} except that
12438 each value is printed in its own window.
12441 @include annotate.texi
12442 @include gdbmi.texinfo
12445 @chapter Reporting Bugs in @value{GDBN}
12446 @cindex bugs in @value{GDBN}
12447 @cindex reporting bugs in @value{GDBN}
12449 Your bug reports play an essential role in making @value{GDBN} reliable.
12451 Reporting a bug may help you by bringing a solution to your problem, or it
12452 may not. But in any case the principal function of a bug report is to help
12453 the entire community by making the next version of @value{GDBN} work better. Bug
12454 reports are your contribution to the maintenance of @value{GDBN}.
12456 In order for a bug report to serve its purpose, you must include the
12457 information that enables us to fix the bug.
12460 * Bug Criteria:: Have you found a bug?
12461 * Bug Reporting:: How to report bugs
12465 @section Have you found a bug?
12466 @cindex bug criteria
12468 If you are not sure whether you have found a bug, here are some guidelines:
12471 @cindex fatal signal
12472 @cindex debugger crash
12473 @cindex crash of debugger
12475 If the debugger gets a fatal signal, for any input whatever, that is a
12476 @value{GDBN} bug. Reliable debuggers never crash.
12478 @cindex error on valid input
12480 If @value{GDBN} produces an error message for valid input, that is a
12481 bug. (Note that if you're cross debugging, the problem may also be
12482 somewhere in the connection to the target.)
12484 @cindex invalid input
12486 If @value{GDBN} does not produce an error message for invalid input,
12487 that is a bug. However, you should note that your idea of
12488 ``invalid input'' might be our idea of ``an extension'' or ``support
12489 for traditional practice''.
12492 If you are an experienced user of debugging tools, your suggestions
12493 for improvement of @value{GDBN} are welcome in any case.
12496 @node Bug Reporting
12497 @section How to report bugs
12498 @cindex bug reports
12499 @cindex @value{GDBN} bugs, reporting
12501 A number of companies and individuals offer support for @sc{gnu} products.
12502 If you obtained @value{GDBN} from a support organization, we recommend you
12503 contact that organization first.
12505 You can find contact information for many support companies and
12506 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
12508 @c should add a web page ref...
12510 In any event, we also recommend that you send bug reports for
12511 @value{GDBN} to this addresses:
12517 @strong{Do not send bug reports to @samp{info-gdb}, or to
12518 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
12519 not want to receive bug reports. Those that do have arranged to receive
12522 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
12523 serves as a repeater. The mailing list and the newsgroup carry exactly
12524 the same messages. Often people think of posting bug reports to the
12525 newsgroup instead of mailing them. This appears to work, but it has one
12526 problem which can be crucial: a newsgroup posting often lacks a mail
12527 path back to the sender. Thus, if we need to ask for more information,
12528 we may be unable to reach you. For this reason, it is better to send
12529 bug reports to the mailing list.
12531 As a last resort, send bug reports on paper to:
12534 @sc{gnu} Debugger Bugs
12535 Free Software Foundation Inc.
12536 59 Temple Place - Suite 330
12537 Boston, MA 02111-1307
12541 The fundamental principle of reporting bugs usefully is this:
12542 @strong{report all the facts}. If you are not sure whether to state a
12543 fact or leave it out, state it!
12545 Often people omit facts because they think they know what causes the
12546 problem and assume that some details do not matter. Thus, you might
12547 assume that the name of the variable you use in an example does not matter.
12548 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
12549 stray memory reference which happens to fetch from the location where that
12550 name is stored in memory; perhaps, if the name were different, the contents
12551 of that location would fool the debugger into doing the right thing despite
12552 the bug. Play it safe and give a specific, complete example. That is the
12553 easiest thing for you to do, and the most helpful.
12555 Keep in mind that the purpose of a bug report is to enable us to fix the
12556 bug. It may be that the bug has been reported previously, but neither
12557 you nor we can know that unless your bug report is complete and
12560 Sometimes people give a few sketchy facts and ask, ``Does this ring a
12561 bell?'' Those bug reports are useless, and we urge everyone to
12562 @emph{refuse to respond to them} except to chide the sender to report
12565 To enable us to fix the bug, you should include all these things:
12569 The version of @value{GDBN}. @value{GDBN} announces it if you start
12570 with no arguments; you can also print it at any time using @code{show
12573 Without this, we will not know whether there is any point in looking for
12574 the bug in the current version of @value{GDBN}.
12577 The type of machine you are using, and the operating system name and
12581 What compiler (and its version) was used to compile @value{GDBN}---e.g.
12582 ``@value{GCC}--2.8.1''.
12585 What compiler (and its version) was used to compile the program you are
12586 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
12587 C Compiler''. For GCC, you can say @code{gcc --version} to get this
12588 information; for other compilers, see the documentation for those
12592 The command arguments you gave the compiler to compile your example and
12593 observe the bug. For example, did you use @samp{-O}? To guarantee
12594 you will not omit something important, list them all. A copy of the
12595 Makefile (or the output from make) is sufficient.
12597 If we were to try to guess the arguments, we would probably guess wrong
12598 and then we might not encounter the bug.
12601 A complete input script, and all necessary source files, that will
12605 A description of what behavior you observe that you believe is
12606 incorrect. For example, ``It gets a fatal signal.''
12608 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
12609 will certainly notice it. But if the bug is incorrect output, we might
12610 not notice unless it is glaringly wrong. You might as well not give us
12611 a chance to make a mistake.
12613 Even if the problem you experience is a fatal signal, you should still
12614 say so explicitly. Suppose something strange is going on, such as, your
12615 copy of @value{GDBN} is out of synch, or you have encountered a bug in
12616 the C library on your system. (This has happened!) Your copy might
12617 crash and ours would not. If you told us to expect a crash, then when
12618 ours fails to crash, we would know that the bug was not happening for
12619 us. If you had not told us to expect a crash, then we would not be able
12620 to draw any conclusion from our observations.
12623 If you wish to suggest changes to the @value{GDBN} source, send us context
12624 diffs. If you even discuss something in the @value{GDBN} source, refer to
12625 it by context, not by line number.
12627 The line numbers in our development sources will not match those in your
12628 sources. Your line numbers would convey no useful information to us.
12632 Here are some things that are not necessary:
12636 A description of the envelope of the bug.
12638 Often people who encounter a bug spend a lot of time investigating
12639 which changes to the input file will make the bug go away and which
12640 changes will not affect it.
12642 This is often time consuming and not very useful, because the way we
12643 will find the bug is by running a single example under the debugger
12644 with breakpoints, not by pure deduction from a series of examples.
12645 We recommend that you save your time for something else.
12647 Of course, if you can find a simpler example to report @emph{instead}
12648 of the original one, that is a convenience for us. Errors in the
12649 output will be easier to spot, running under the debugger will take
12650 less time, and so on.
12652 However, simplification is not vital; if you do not want to do this,
12653 report the bug anyway and send us the entire test case you used.
12656 A patch for the bug.
12658 A patch for the bug does help us if it is a good one. But do not omit
12659 the necessary information, such as the test case, on the assumption that
12660 a patch is all we need. We might see problems with your patch and decide
12661 to fix the problem another way, or we might not understand it at all.
12663 Sometimes with a program as complicated as @value{GDBN} it is very hard to
12664 construct an example that will make the program follow a certain path
12665 through the code. If you do not send us the example, we will not be able
12666 to construct one, so we will not be able to verify that the bug is fixed.
12668 And if we cannot understand what bug you are trying to fix, or why your
12669 patch should be an improvement, we will not install it. A test case will
12670 help us to understand.
12673 A guess about what the bug is or what it depends on.
12675 Such guesses are usually wrong. Even we cannot guess right about such
12676 things without first using the debugger to find the facts.
12679 @c The readline documentation is distributed with the readline code
12680 @c and consists of the two following files:
12682 @c inc-hist.texinfo
12683 @c Use -I with makeinfo to point to the appropriate directory,
12684 @c environment var TEXINPUTS with TeX.
12685 @include rluser.texinfo
12686 @include inc-hist.texinfo
12689 @node Formatting Documentation
12690 @appendix Formatting Documentation
12692 @cindex @value{GDBN} reference card
12693 @cindex reference card
12694 The @value{GDBN} 4 release includes an already-formatted reference card, ready
12695 for printing with PostScript or Ghostscript, in the @file{gdb}
12696 subdirectory of the main source directory@footnote{In
12697 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
12698 release.}. If you can use PostScript or Ghostscript with your printer,
12699 you can print the reference card immediately with @file{refcard.ps}.
12701 The release also includes the source for the reference card. You
12702 can format it, using @TeX{}, by typing:
12708 The @value{GDBN} reference card is designed to print in @dfn{landscape}
12709 mode on US ``letter'' size paper;
12710 that is, on a sheet 11 inches wide by 8.5 inches
12711 high. You will need to specify this form of printing as an option to
12712 your @sc{dvi} output program.
12714 @cindex documentation
12716 All the documentation for @value{GDBN} comes as part of the machine-readable
12717 distribution. The documentation is written in Texinfo format, which is
12718 a documentation system that uses a single source file to produce both
12719 on-line information and a printed manual. You can use one of the Info
12720 formatting commands to create the on-line version of the documentation
12721 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
12723 @value{GDBN} includes an already formatted copy of the on-line Info
12724 version of this manual in the @file{gdb} subdirectory. The main Info
12725 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
12726 subordinate files matching @samp{gdb.info*} in the same directory. If
12727 necessary, you can print out these files, or read them with any editor;
12728 but they are easier to read using the @code{info} subsystem in @sc{gnu}
12729 Emacs or the standalone @code{info} program, available as part of the
12730 @sc{gnu} Texinfo distribution.
12732 If you want to format these Info files yourself, you need one of the
12733 Info formatting programs, such as @code{texinfo-format-buffer} or
12736 If you have @code{makeinfo} installed, and are in the top level
12737 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
12738 version @value{GDBVN}), you can make the Info file by typing:
12745 If you want to typeset and print copies of this manual, you need @TeX{},
12746 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
12747 Texinfo definitions file.
12749 @TeX{} is a typesetting program; it does not print files directly, but
12750 produces output files called @sc{dvi} files. To print a typeset
12751 document, you need a program to print @sc{dvi} files. If your system
12752 has @TeX{} installed, chances are it has such a program. The precise
12753 command to use depends on your system; @kbd{lpr -d} is common; another
12754 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
12755 require a file name without any extension or a @samp{.dvi} extension.
12757 @TeX{} also requires a macro definitions file called
12758 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
12759 written in Texinfo format. On its own, @TeX{} cannot either read or
12760 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
12761 and is located in the @file{gdb-@var{version-number}/texinfo}
12764 If you have @TeX{} and a @sc{dvi} printer program installed, you can
12765 typeset and print this manual. First switch to the the @file{gdb}
12766 subdirectory of the main source directory (for example, to
12767 @file{gdb-@value{GDBVN}/gdb}) and type:
12773 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
12775 @node Installing GDB
12776 @appendix Installing @value{GDBN}
12777 @cindex configuring @value{GDBN}
12778 @cindex installation
12780 @value{GDBN} comes with a @code{configure} script that automates the process
12781 of preparing @value{GDBN} for installation; you can then use @code{make} to
12782 build the @code{gdb} program.
12784 @c irrelevant in info file; it's as current as the code it lives with.
12785 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
12786 look at the @file{README} file in the sources; we may have improved the
12787 installation procedures since publishing this manual.}
12790 The @value{GDBN} distribution includes all the source code you need for
12791 @value{GDBN} in a single directory, whose name is usually composed by
12792 appending the version number to @samp{gdb}.
12794 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
12795 @file{gdb-@value{GDBVN}} directory. That directory contains:
12798 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
12799 script for configuring @value{GDBN} and all its supporting libraries
12801 @item gdb-@value{GDBVN}/gdb
12802 the source specific to @value{GDBN} itself
12804 @item gdb-@value{GDBVN}/bfd
12805 source for the Binary File Descriptor library
12807 @item gdb-@value{GDBVN}/include
12808 @sc{gnu} include files
12810 @item gdb-@value{GDBVN}/libiberty
12811 source for the @samp{-liberty} free software library
12813 @item gdb-@value{GDBVN}/opcodes
12814 source for the library of opcode tables and disassemblers
12816 @item gdb-@value{GDBVN}/readline
12817 source for the @sc{gnu} command-line interface
12819 @item gdb-@value{GDBVN}/glob
12820 source for the @sc{gnu} filename pattern-matching subroutine
12822 @item gdb-@value{GDBVN}/mmalloc
12823 source for the @sc{gnu} memory-mapped malloc package
12826 The simplest way to configure and build @value{GDBN} is to run @code{configure}
12827 from the @file{gdb-@var{version-number}} source directory, which in
12828 this example is the @file{gdb-@value{GDBVN}} directory.
12830 First switch to the @file{gdb-@var{version-number}} source directory
12831 if you are not already in it; then run @code{configure}. Pass the
12832 identifier for the platform on which @value{GDBN} will run as an
12838 cd gdb-@value{GDBVN}
12839 ./configure @var{host}
12844 where @var{host} is an identifier such as @samp{sun4} or
12845 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
12846 (You can often leave off @var{host}; @code{configure} tries to guess the
12847 correct value by examining your system.)
12849 Running @samp{configure @var{host}} and then running @code{make} builds the
12850 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
12851 libraries, then @code{gdb} itself. The configured source files, and the
12852 binaries, are left in the corresponding source directories.
12855 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
12856 system does not recognize this automatically when you run a different
12857 shell, you may need to run @code{sh} on it explicitly:
12860 sh configure @var{host}
12863 If you run @code{configure} from a directory that contains source
12864 directories for multiple libraries or programs, such as the
12865 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
12866 creates configuration files for every directory level underneath (unless
12867 you tell it not to, with the @samp{--norecursion} option).
12869 You can run the @code{configure} script from any of the
12870 subordinate directories in the @value{GDBN} distribution if you only want to
12871 configure that subdirectory, but be sure to specify a path to it.
12873 For example, with version @value{GDBVN}, type the following to configure only
12874 the @code{bfd} subdirectory:
12878 cd gdb-@value{GDBVN}/bfd
12879 ../configure @var{host}
12883 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
12884 However, you should make sure that the shell on your path (named by
12885 the @samp{SHELL} environment variable) is publicly readable. Remember
12886 that @value{GDBN} uses the shell to start your program---some systems refuse to
12887 let @value{GDBN} debug child processes whose programs are not readable.
12890 * Separate Objdir:: Compiling @value{GDBN} in another directory
12891 * Config Names:: Specifying names for hosts and targets
12892 * Configure Options:: Summary of options for configure
12895 @node Separate Objdir
12896 @section Compiling @value{GDBN} in another directory
12898 If you want to run @value{GDBN} versions for several host or target machines,
12899 you need a different @code{gdb} compiled for each combination of
12900 host and target. @code{configure} is designed to make this easy by
12901 allowing you to generate each configuration in a separate subdirectory,
12902 rather than in the source directory. If your @code{make} program
12903 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
12904 @code{make} in each of these directories builds the @code{gdb}
12905 program specified there.
12907 To build @code{gdb} in a separate directory, run @code{configure}
12908 with the @samp{--srcdir} option to specify where to find the source.
12909 (You also need to specify a path to find @code{configure}
12910 itself from your working directory. If the path to @code{configure}
12911 would be the same as the argument to @samp{--srcdir}, you can leave out
12912 the @samp{--srcdir} option; it is assumed.)
12914 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
12915 separate directory for a Sun 4 like this:
12919 cd gdb-@value{GDBVN}
12922 ../gdb-@value{GDBVN}/configure sun4
12927 When @code{configure} builds a configuration using a remote source
12928 directory, it creates a tree for the binaries with the same structure
12929 (and using the same names) as the tree under the source directory. In
12930 the example, you'd find the Sun 4 library @file{libiberty.a} in the
12931 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
12932 @file{gdb-sun4/gdb}.
12934 One popular reason to build several @value{GDBN} configurations in separate
12935 directories is to configure @value{GDBN} for cross-compiling (where
12936 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
12937 programs that run on another machine---the @dfn{target}).
12938 You specify a cross-debugging target by
12939 giving the @samp{--target=@var{target}} option to @code{configure}.
12941 When you run @code{make} to build a program or library, you must run
12942 it in a configured directory---whatever directory you were in when you
12943 called @code{configure} (or one of its subdirectories).
12945 The @code{Makefile} that @code{configure} generates in each source
12946 directory also runs recursively. If you type @code{make} in a source
12947 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
12948 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
12949 will build all the required libraries, and then build GDB.
12951 When you have multiple hosts or targets configured in separate
12952 directories, you can run @code{make} on them in parallel (for example,
12953 if they are NFS-mounted on each of the hosts); they will not interfere
12957 @section Specifying names for hosts and targets
12959 The specifications used for hosts and targets in the @code{configure}
12960 script are based on a three-part naming scheme, but some short predefined
12961 aliases are also supported. The full naming scheme encodes three pieces
12962 of information in the following pattern:
12965 @var{architecture}-@var{vendor}-@var{os}
12968 For example, you can use the alias @code{sun4} as a @var{host} argument,
12969 or as the value for @var{target} in a @code{--target=@var{target}}
12970 option. The equivalent full name is @samp{sparc-sun-sunos4}.
12972 The @code{configure} script accompanying @value{GDBN} does not provide
12973 any query facility to list all supported host and target names or
12974 aliases. @code{configure} calls the Bourne shell script
12975 @code{config.sub} to map abbreviations to full names; you can read the
12976 script, if you wish, or you can use it to test your guesses on
12977 abbreviations---for example:
12980 % sh config.sub i386-linux
12982 % sh config.sub alpha-linux
12983 alpha-unknown-linux-gnu
12984 % sh config.sub hp9k700
12986 % sh config.sub sun4
12987 sparc-sun-sunos4.1.1
12988 % sh config.sub sun3
12989 m68k-sun-sunos4.1.1
12990 % sh config.sub i986v
12991 Invalid configuration `i986v': machine `i986v' not recognized
12995 @code{config.sub} is also distributed in the @value{GDBN} source
12996 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
12998 @node Configure Options
12999 @section @code{configure} options
13001 Here is a summary of the @code{configure} options and arguments that
13002 are most often useful for building @value{GDBN}. @code{configure} also has
13003 several other options not listed here. @inforef{What Configure
13004 Does,,configure.info}, for a full explanation of @code{configure}.
13007 configure @r{[}--help@r{]}
13008 @r{[}--prefix=@var{dir}@r{]}
13009 @r{[}--exec-prefix=@var{dir}@r{]}
13010 @r{[}--srcdir=@var{dirname}@r{]}
13011 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
13012 @r{[}--target=@var{target}@r{]}
13017 You may introduce options with a single @samp{-} rather than
13018 @samp{--} if you prefer; but you may abbreviate option names if you use
13023 Display a quick summary of how to invoke @code{configure}.
13025 @item --prefix=@var{dir}
13026 Configure the source to install programs and files under directory
13029 @item --exec-prefix=@var{dir}
13030 Configure the source to install programs under directory
13033 @c avoid splitting the warning from the explanation:
13035 @item --srcdir=@var{dirname}
13036 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
13037 @code{make} that implements the @code{VPATH} feature.}@*
13038 Use this option to make configurations in directories separate from the
13039 @value{GDBN} source directories. Among other things, you can use this to
13040 build (or maintain) several configurations simultaneously, in separate
13041 directories. @code{configure} writes configuration specific files in
13042 the current directory, but arranges for them to use the source in the
13043 directory @var{dirname}. @code{configure} creates directories under
13044 the working directory in parallel to the source directories below
13047 @item --norecursion
13048 Configure only the directory level where @code{configure} is executed; do not
13049 propagate configuration to subdirectories.
13051 @item --target=@var{target}
13052 Configure @value{GDBN} for cross-debugging programs running on the specified
13053 @var{target}. Without this option, @value{GDBN} is configured to debug
13054 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
13056 There is no convenient way to generate a list of all available targets.
13058 @item @var{host} @dots{}
13059 Configure @value{GDBN} to run on the specified @var{host}.
13061 There is no convenient way to generate a list of all available hosts.
13064 There are many other options available as well, but they are generally
13065 needed for special purposes only.
13073 % I think something like @colophon should be in texinfo. In the
13075 \long\def\colophon{\hbox to0pt{}\vfill
13076 \centerline{The body of this manual is set in}
13077 \centerline{\fontname\tenrm,}
13078 \centerline{with headings in {\bf\fontname\tenbf}}
13079 \centerline{and examples in {\tt\fontname\tentt}.}
13080 \centerline{{\it\fontname\tenit\/},}
13081 \centerline{{\bf\fontname\tenbf}, and}
13082 \centerline{{\sl\fontname\tensl\/}}
13083 \centerline{are used for emphasis.}\vfill}
13085 % Blame: doc@cygnus.com, 1991.
13088 @c TeX can handle the contents at the start but makeinfo 3.12 can not