This is Info file ./gdb.info, produced by Makeinfo version 1.68 from the input file gdb.texinfo. START-INFO-DIR-ENTRY * Gdb: (gdb). The GNU debugger. END-INFO-DIR-ENTRY This file documents the GNU debugger GDB. This is the Seventh Edition, February 1999, of `Debugging with GDB: the GNU Source-Level Debugger' for GDB Version 4.18. Copyright (C) 1988-1999 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions.  File: gdb.info, Node: Top, Next: Summary, Prev: (dir), Up: (dir) Debugging with GDB ****************** This file describes GDB, the GNU symbolic debugger. This is the Seventh Edition, February 1999, for GDB Version 4.18. Copyright (C) 1988-1999 Free Software Foundation, Inc. * Menu: * Summary:: Summary of GDB * Sample Session:: A sample GDB session * Invocation:: Getting in and out of GDB * Commands:: GDB commands * Running:: Running programs under GDB * Stopping:: Stopping and continuing * Stack:: Examining the stack * Source:: Examining source files * Data:: Examining data * Languages:: Using GDB with different languages * Symbols:: Examining the symbol table * Altering:: Altering execution * GDB Files:: GDB files * Targets:: Specifying a debugging target * Controlling GDB:: Controlling GDB * Sequences:: Canned sequences of commands * Emacs:: Using GDB under GNU Emacs * GDB Bugs:: Reporting bugs in GDB * Formatting Documentation:: How to format and print GDB documentation * Command Line Editing:: Command Line Editing * Using History Interactively:: Using History Interactively * Installing GDB:: Installing GDB * Index:: Index -- The Detailed Node Listing -- Summary of GDB * Free Software:: Freely redistributable software * Contributors:: Contributors to GDB Getting In and Out of GDB * Invoking GDB:: How to start GDB * Quitting GDB:: How to quit GDB * Shell Commands:: How to use shell commands inside GDB Invoking GDB * File Options:: Choosing files * Mode Options:: Choosing modes GDB Commands * Command Syntax:: How to give commands to GDB * Completion:: Command completion * Help:: How to ask GDB for help Running Programs Under GDB * Compilation:: Compiling for debugging * Starting:: Starting your program * Arguments:: Your program's arguments * Environment:: Your program's environment * Working Directory:: Your program's working directory * Input/Output:: Your program's input and output * Attach:: Debugging an already-running process * Kill Process:: Killing the child process * Process Information:: Additional process information * Threads:: Debugging programs with multiple threads * Processes:: Debugging programs with multiple processes Stopping and Continuing * Breakpoints:: Breakpoints, watchpoints, and catchpoints * Continuing and Stepping:: Resuming execution * Signals:: Signals * Thread Stops:: Stopping and starting multi-thread programs Breakpoints and watchpoints * Set Breaks:: Setting breakpoints * Set Watchpoints:: Setting watchpoints * Set Catchpoints:: Setting catchpoints * Delete Breaks:: Deleting breakpoints * Disabling:: Disabling breakpoints * Conditions:: Break conditions * Break Commands:: Breakpoint command lists * Breakpoint Menus:: Breakpoint menus Examining the Stack * Frames:: Stack frames * Backtrace:: Backtraces * Selection:: Selecting a frame * Frame Info:: Information on a frame * Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack Examining Source Files * List:: Printing source lines * Search:: Searching source files * Source Path:: Specifying source directories * Machine Code:: Source and machine code Examining Data * Expressions:: Expressions * Variables:: Program variables * Arrays:: Artificial arrays * Output Formats:: Output formats * Memory:: Examining memory * Auto Display:: Automatic display * Print Settings:: Print settings * Value History:: Value history * Convenience Vars:: Convenience variables * Registers:: Registers * Floating Point Hardware:: Floating point hardware Using GDB with Different Languages * Setting:: Switching between source languages * Show:: Displaying the language * Checks:: Type and range checks * Support:: Supported languages Switching between source languages * Filenames:: Filename extensions and languages. * Manually:: Setting the working language manually * Automatically:: Having GDB infer the source language Type and range checking * Type Checking:: An overview of type checking * Range Checking:: An overview of range checking Supported languages * C:: C and C++ C Language Support * C Operators:: C operators C Language Support * C Operators:: C and C++ operators * C Constants:: C and C++ constants * Cplus expressions:: C++ expressions * C Defaults:: Default settings for C and C++ * C Checks:: C and C++ type and range checks * Debugging C:: GDB and C * Debugging C plus plus:: GDB features for C++ Modula-2 * M2 Operators:: Built-in operators * Built-In Func/Proc:: Built-in functions and procedures * M2 Constants:: Modula-2 constants * M2 Defaults:: Default settings for Modula-2 * Deviations:: Deviations from standard Modula-2 * M2 Checks:: Modula-2 type and range checks * M2 Scope:: The scope operators `::' and `.' * GDB/M2:: GDB and Modula-2 Altering Execution * Assignment:: Assignment to variables * Jumping:: Continuing at a different address * Signaling:: Giving your program a signal * Returning:: Returning from a function * Calling:: Calling your program's functions * Patching:: Patching your program GDB Files * Files:: Commands to specify files * Symbol Errors:: Errors reading symbol files Specifying a Debugging Target * Active Targets:: Active targets * Target Commands:: Commands for managing targets * Byte Order:: Choosing target byte order * Remote:: Remote debugging Remote debugging * Remote Serial:: GDB remote serial protocol * i960-Nindy Remote:: GDB with a remote i960 (Nindy) * UDI29K Remote:: The UDI protocol for AMD29K * EB29K Remote:: The EBMON protocol for AMD29K * VxWorks Remote:: GDB and VxWorks * ST2000 Remote:: GDB with a Tandem ST2000 * Hitachi Remote:: GDB and Hitachi Microprocessors * MIPS Remote:: GDB and MIPS boards * Simulator:: Simulated CPU target Controlling GDB * Prompt:: Prompt * Editing:: Command editing * History:: Command history * Screen Size:: Screen size * Numbers:: Numbers * Messages/Warnings:: Optional warnings and messages Canned Sequences of Commands * Define:: User-defined commands * Hooks:: User-defined command hooks * Command Files:: Command files * Output:: Commands for controlled output Reporting Bugs in GDB * Bug Criteria:: Have you found a bug? * Bug Reporting:: How to report bugs Installing GDB * Separate Objdir:: Compiling GDB in another directory * Config Names:: Specifying names for hosts and targets * Configure Options:: Summary of options for configure  File: gdb.info, Node: Summary, Next: Sample Session, Prev: Top, Up: Top Summary of GDB ************** The purpose of a debugger such as GDB is to allow you to see what is going on "inside" another program while it executes--or what another program was doing at the moment it crashed. GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act: * Start your program, specifying anything that might affect its behavior. * Make your program stop on specified conditions. * Examine what has happened, when your program has stopped. * Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another. You can use GDB to debug programs written in C or C++. For more information, see *Note C and C++: C. Support for Modula-2 and Chill is partial. For information on Modula-2, see *Note Modula-2: Modula-2. There is no further documentation on Chill yet. Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. GDB does not support entering expressions, printing values, or similar features using Pascal syntax. GDB can be used to debug programs written in Fortran, although it does not yet support entering expressions, printing values, or similar features using Fortran syntax. It may be necessary to refer to some variables with a trailing underscore. * Menu: * Free Software:: Freely redistributable software * Contributors:: Contributors to GDB  File: gdb.info, Node: Free Software, Next: Contributors, Prev: Summary, Up: Summary Free software ============= GDB is "free software", protected by the GNU General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program--but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms. Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.  File: gdb.info, Node: Contributors, Prev: Free Software, Up: Summary Contributors to GDB =================== Richard Stallman was the original author of GDB, and of many other GNU programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file `ChangeLog' in the GDB distribution approximates a blow-by-blow account. Changes much prior to version 2.0 are lost in the mists of time. *Plea:* Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names! So that they may not regard their many labors as thankless, we particularly thank those who shepherded GDB through major releases: Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0). Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8. Michael Tiemann is the author of most of the GNU C++ support in GDB, with significant additional contributions from Per Bothner. James Clark wrote the GNU C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0). GDB 4 uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore. David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF. Brent Benson of Harris Computer Systems contributed DWARF 2 support. Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support. Andreas Schwab contributed M68K Linux support. Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries. Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about several machine instruction sets. Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively. Brian Fox is the author of the readline libraries providing command-line editing and command history. Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual. Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C++ overloaded symbols. Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and Super-H processors. NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors. Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors. Toshiba sponsored the support for the TX39 Mips processor. Matsushita sponsored the support for the MN10200 and MN10300 processors. Fujitsu sponsored the support for SPARClite and FR30 processors Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints. Michael Snyder added support for tracepoints. Stu Grossman wrote gdbserver. Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout GDB. The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC++ compiler, and the terminal user interface: Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific information in this manual. Cygnus Solutions has sponsored GDB maintenance and much of its development since 1991. Cygnus engineers who have worked on GDB fulltime include Mark Alexander, Jim Blandy, Per Bothner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small.  File: gdb.info, Node: Sample Session, Next: Invocation, Prev: Summary, Up: Top A Sample GDB Session ******************** You can use this manual at your leisure to read all about GDB. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands. One of the preliminary versions of GNU `m4' (a generic macro processor) exhibits the following bug: sometimes, when we change its quote strings from the default, the commands used to capture one macro definition within another stop working. In the following short `m4' session, we define a macro `foo' which expands to `0000'; we then use the `m4' built-in `defn' to define `bar' as the same thing. However, when we change the open quote string to `' and the close quote string to `', the same procedure fails to define a new synonym `baz': $ cd gnu/m4 $ ./m4 define(foo,0000) foo 0000 define(bar,defn(`foo')) bar 0000 changequote(,) define(baz,defn(foo)) baz C-d m4: End of input: 0: fatal error: EOF in string Let us use GDB to try to see what is going on. $ gdb m4 GDB is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for GDB; type "show warranty" for details. GDB 4.18, Copyright 1999 Free Software Foundation, Inc... (gdb) GDB reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell GDB to use a narrower display width than usual, so that examples fit in this manual. (gdb) set width 70 We need to see how the `m4' built-in `changequote' works. Having looked at the source, we know the relevant subroutine is `m4_changequote', so we set a breakpoint there with the GDB `break' command. (gdb) break m4_changequote Breakpoint 1 at 0x62f4: file builtin.c, line 879. Using the `run' command, we start `m4' running under GDB control; as long as control does not reach the `m4_changequote' subroutine, the program runs as usual: (gdb) run Starting program: /work/Editorial/gdb/gnu/m4/m4 define(foo,0000) foo 0000 To trigger the breakpoint, we call `changequote'. GDB suspends execution of `m4', displaying information about the context where it stops. changequote(,) Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3)) Now we use the command `n' (`next') to advance execution to the next line of the current function. (gdb) n 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ : nil, `set_quotes' looks like a promising subroutine. We can go into it by using the command `s' (`step') instead of `next'. `step' goes to the next line to be executed in *any* subroutine, so it steps into `set_quotes'. (gdb) s set_quotes (lq=0x34c78 "", rq=0x34c88 "") at input.c:530 530 if (lquote != def_lquote) The display that shows the subroutine where `m4' is now suspended (and its arguments) is called a stack frame display. It shows a summary of the stack. We can use the `backtrace' command (which can also be spelled `bt'), to see where we are in the stack as a whole: the `backtrace' command displays a stack frame for each active subroutine. (gdb) bt #0 set_quotes (lq=0x34c78 "", rq=0x34c88 "") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 We step through a few more lines to see what happens. The first two times, we can use `s'; the next two times we use `n' to avoid falling into the `xstrdup' subroutine. (gdb) s 0x3b5c 532 if (rquote != def_rquote) (gdb) s 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ def_lquote : xstrdup(lq); (gdb) n 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup(rq); (gdb) n 538 len_lquote = strlen(rquote); The last line displayed looks a little odd; we can examine the variables `lquote' and `rquote' to see if they are in fact the new left and right quotes we specified. We use the command `p' (`print') to see their values. (gdb) p lquote $1 = 0x35d40 "" (gdb) p rquote $2 = 0x35d50 "" `lquote' and `rquote' are indeed the new left and right quotes. To look at some context, we can display ten lines of source surrounding the current line with the `l' (`list') command. (gdb) l 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ : xstrdup (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 } 541 542 void Let us step past the two lines that set `len_lquote' and `len_rquote', and then examine the values of those variables. (gdb) n 539 len_rquote = strlen(lquote); (gdb) n 540 } (gdb) p len_lquote $3 = 9 (gdb) p len_rquote $4 = 7 That certainly looks wrong, assuming `len_lquote' and `len_rquote' are meant to be the lengths of `lquote' and `rquote' respectively. We can set them to better values using the `p' command, since it can print the value of any expression--and that expression can include subroutine calls and assignments. (gdb) p len_lquote=strlen(lquote) $5 = 7 (gdb) p len_rquote=strlen(rquote) $6 = 9 Is that enough to fix the problem of using the new quotes with the `m4' built-in `defn'? We can allow `m4' to continue executing with the `c' (`continue') command, and then try the example that caused trouble initially: (gdb) c Continuing. define(baz,defn(foo)) baz 0000 Success! The new quotes now work just as well as the default ones. The problem seems to have been just the two typos defining the wrong lengths. We allow `m4' exit by giving it an EOF as input: C-d Program exited normally. The message `Program exited normally.' is from GDB; it indicates `m4' has finished executing. We can end our GDB session with the GDB `quit' command. (gdb) quit  File: gdb.info, Node: Invocation, Next: Commands, Prev: Sample Session, Up: Top Getting In and Out of GDB ************************* This chapter discusses how to start GDB, and how to get out of it. The essentials are: * type `gdb' to start GDB. * type `quit' or `C-d' to exit. * Menu: * Invoking GDB:: How to start GDB * Quitting GDB:: How to quit GDB * Shell Commands:: How to use shell commands inside GDB  File: gdb.info, Node: Invoking GDB, Next: Quitting GDB, Prev: Invocation, Up: Invocation Invoking GDB ============ Invoke GDB by running the program `gdb'. Once started, GDB reads commands from the terminal until you tell it to exit. You can also run `gdb' with a variety of arguments and options, to specify more of your debugging environment at the outset. The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable. The most usual way to start GDB is with one argument, specifying an executable program: gdb PROGRAM You can also start with both an executable program and a core file specified: gdb PROGRAM CORE You can, instead, specify a process ID as a second argument, if you want to debug a running process: gdb PROGRAM 1234 would attach GDB to process `1234' (unless you also have a file named `1234'; GDB does check for a core file first). Taking advantage of the second command-line argument requires a fairly complete operating system; when you use GDB as a remote debugger attached to a bare board, there may not be any notion of "process", and there is often no way to get a core dump. You can run `gdb' without printing the front material, which describes GDB's non-warranty, by specifying `-silent': gdb -silent You can further control how GDB starts up by using command-line options. GDB itself can remind you of the options available. Type gdb -help to display all available options and briefly describe their use (`gdb -h' is a shorter equivalent). All options and command line arguments you give are processed in sequential order. The order makes a difference when the `-x' option is used. * Menu: * File Options:: Choosing files * Mode Options:: Choosing modes  File: gdb.info, Node: File Options, Next: Mode Options, Up: Invoking GDB Choosing files -------------- When GDB starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the `-se' and `-c' options respectively. (GDB reads the first argument that does not have an associated option flag as equivalent to the `-se' option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the `-c' option followed by that argument.) Many options have both long and short forms; both are shown in the following list. GDB also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with `--' rather than `-', though we illustrate the more usual convention.) `-symbols FILE' `-s FILE' Read symbol table from file FILE. `-exec FILE' `-e FILE' Use file FILE as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. `-se FILE' Read symbol table from file FILE and use it as the executable file. `-core FILE' `-c FILE' Use file FILE as a core dump to examine. `-c NUMBER' Connect to process ID NUMBER, as with the `attach' command (unless there is a file in core-dump format named NUMBER, in which case `-c' specifies that file as a core dump to read). `-command FILE' `-x FILE' Execute GDB commands from file FILE. *Note Command files: Command Files. `-directory DIRECTORY' `-d DIRECTORY' Add DIRECTORY to the path to search for source files. `-m' `-mapped' *Warning: this option depends on operating system facilities that are not supported on all systems.* If memory-mapped files are available on your system through the `mmap' system call, you can use this option to have GDB write the symbols from your program into a reusable file in the current directory. If the program you are debugging is called `/tmp/fred', the mapped symbol file is `./fred.syms'. Future GDB debugging sessions notice the presence of this file, and can quickly map in symbol information from it, rather than reading the symbol table from the executable program. The `.syms' file is specific to the host machine where GDB is run. It holds an exact image of the internal GDB symbol table. It cannot be shared across multiple host platforms. `-r' `-readnow' Read each symbol file's entire symbol table immediately, rather than the default, which is to read it incrementally as it is needed. This makes startup slower, but makes future operations faster. The `-mapped' and `-readnow' options are typically combined in order to build a `.syms' file that contains complete symbol information. (*Note Commands to specify files: Files, for information on `.syms' files.) A simple GDB invocation to do nothing but build a `.syms' file for future use is: gdb -batch -nx -mapped -readnow programname  File: gdb.info, Node: Mode Options, Prev: File Options, Up: Invoking GDB Choosing modes -------------- You can run GDB in various alternative modes--for example, in batch mode or quiet mode. `-nx' `-n' Do not execute commands from any initialization files (normally called `.gdbinit', or `gdb.ini' on PCs). Normally, the commands in these files are executed after all the command options and arguments have been processed. *Note Command files: Command Files. `-quiet' `-q' "Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode. `-batch' Run in batch mode. Exit with status `0' after processing all the command files specified with `-x' (and all commands from initialization files, if not inhibited with `-n'). Exit with nonzero status if an error occurs in executing the GDB commands in the command files. Batch mode may be useful for running GDB as a filter, for example to download and run a program on another computer; in order to make this more useful, the message Program exited normally. (which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode. `-cd DIRECTORY' Run GDB using DIRECTORY as its working directory, instead of the current directory. `-fullname' `-f' GNU Emacs sets this option when it runs GDB as a subprocess. It tells GDB to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time your program stops). This recognizable format looks like two `\032' characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two `\032' characters as a signal to display the source code for the frame. `-b BPS' Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging. `-tty DEVICE' Run using DEVICE for your program's standard input and output.  File: gdb.info, Node: Quitting GDB, Next: Shell Commands, Prev: Invoking GDB, Up: Invocation Quitting GDB ============ `quit' To exit GDB, use the `quit' command (abbreviated `q'), or type an end-of-file character (usually `C-d'). If you do not supply EXPRESSION, GDB will terminate normally; otherwise it will terminate using the result of EXPRESSION as the error code. An interrupt (often `C-c') does not exit from GDB, but rather terminates the action of any GDB command that is in progress and returns to GDB command level. It is safe to type the interrupt character at any time because GDB does not allow it to take effect until a time when it is safe. If you have been using GDB to control an attached process or device, you can release it with the `detach' command (*note Debugging an already-running process: Attach.).  File: gdb.info, Node: Shell Commands, Prev: Quitting GDB, Up: Invocation Shell commands ============== If you need to execute occasional shell commands during your debugging session, there is no need to leave or suspend GDB; you can just use the `shell' command. `shell COMMAND STRING' Invoke a standard shell to execute COMMAND STRING. If it exists, the environment variable `SHELL' determines which shell to run. Otherwise GDB uses `/bin/sh'. The utility `make' is often needed in development environments. You do not have to use the `shell' command for this purpose in GDB: `make MAKE-ARGS' Execute the `make' program with the specified arguments. This is equivalent to `shell make MAKE-ARGS'.  File: gdb.info, Node: Commands, Next: Running, Prev: Invocation, Up: Top GDB Commands ************ You can abbreviate a GDB command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain GDB commands by typing just . You can also use the key to get GDB to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility). * Menu: * Command Syntax:: How to give commands to GDB * Completion:: Command completion * Help:: How to ask GDB for help  File: gdb.info, Node: Command Syntax, Next: Completion, Prev: Commands, Up: Commands Command syntax ============== A GDB command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command `step' accepts an argument which is the number of times to step, as in `step 5'. You can also use the `step' command with no arguments. Some command names do not allow any arguments. GDB command names may always be truncated if that abbreviation is unambiguous. Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, `s' is specially defined as equivalent to `step' even though there are other commands whose names start with `s'. You can test abbreviations by using them as arguments to the `help' command. A blank line as input to GDB (typing just ) means to repeat the previous command. Certain commands (for example, `run') will not repeat this way; these are commands whose unintentional repetition might cause trouble and which you are unlikely to want to repeat. The `list' and `x' commands, when you repeat them with , construct new arguments rather than repeating exactly as typed. This permits easy scanning of source or memory. GDB can also use in another way: to partition lengthy output, in a way similar to the common utility `more' (*note Screen size: Screen Size.). Since it is easy to press one too many in this situation, GDB disables command repetition after any command that generates this sort of display. Any text from a `#' to the end of the line is a comment; it does nothing. This is useful mainly in command files (*note Command files: Command Files.).  File: gdb.info, Node: Completion, Next: Help, Prev: Command Syntax, Up: Commands Command completion ================== GDB can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for GDB commands, GDB subcommands, and the names of symbols in your program. Press the key whenever you want GDB to fill out the rest of a word. If there is only one possibility, GDB fills in the word, and waits for you to finish the command (or press to enter it). For example, if you type (gdb) info bre GDB fills in the rest of the word `breakpoints', since that is the only `info' subcommand beginning with `bre': (gdb) info breakpoints You can either press at this point, to run the `info breakpoints' command, or backspace and enter something else, if `breakpoints' does not look like the command you expected. (If you were sure you wanted `info breakpoints' in the first place, you might as well just type immediately after `info bre', to exploit command abbreviations rather than command completion). If there is more than one possibility for the next word when you press , GDB sounds a bell. You can either supply more characters and try again, or just press a second time; GDB displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with `make_', but when you type `b make_' GDB just sounds the bell. Typing again displays all the function names in your program that begin with those characters, for example: (gdb) b make_ GDB sounds bell; press again, to see: make_a_section_from_file make_environ make_abs_section make_function_type make_blockvector make_pointer_type make_cleanup make_reference_type make_command make_symbol_completion_list (gdb) b make_ After displaying the available possibilities, GDB copies your partial input (`b make_' in the example) so you can finish the command. If you just want to see the list of alternatives in the first place, you can press `M-?' rather than pressing twice. `M-?' means ` ?'. You can type this either by holding down a key designated as the shift on your keyboard (if there is one) while typing `?', or as followed by `?'. Sometimes the string you need, while logically a "word", may contain parentheses or other characters that GDB normally excludes from its notion of a word. To permit word completion to work in this situation, you may enclose words in `'' (single quote marks) in GDB commands. The most likely situation where you might need this is in typing the name of a C++ function. This is because C++ allows function overloading (multiple definitions of the same function, distinguished by argument type). For example, when you want to set a breakpoint you may need to distinguish whether you mean the version of `name' that takes an `int' parameter, `name(int)', or the version that takes a `float' parameter, `name(float)'. To use the word-completion facilities in this situation, type a single quote `'' at the beginning of the function name. This alerts GDB that it may need to consider more information than usual when you press or `M-?' to request word completion: (gdb) b 'bubble( bubble(double,double) bubble(int,int) (gdb) b 'bubble( In some cases, GDB can tell that completing a name requires using quotes. When this happens, GDB inserts the quote for you (while completing as much as it can) if you do not type the quote in the first place: (gdb) b bub GDB alters your input line to the following, and rings a bell: (gdb) b 'bubble( In general, GDB can tell that a quote is needed (and inserts it) if you have not yet started typing the argument list when you ask for completion on an overloaded symbol. For more information about overloaded functions, *note C++ expressions: Cplus expressions.. You can use the command `set overload-resolution off' to disable overload resolution; *note GDB features for C++: Debugging C plus plus..  File: gdb.info, Node: Help, Prev: Completion, Up: Commands Getting help ============ You can always ask GDB itself for information on its commands, using the command `help'. `help' `h' You can use `help' (abbreviated `h') with no arguments to display a short list of named classes of commands: (gdb) help List of classes of commands: running -- Running the program stack -- Examining the stack data -- Examining data breakpoints -- Making program stop at certain points files -- Specifying and examining files status -- Status inquiries support -- Support facilities user-defined -- User-defined commands aliases -- Aliases of other commands obscure -- Obscure features Type "help" followed by a class name for a list of commands in that class. Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb) `help CLASS' Using one of the general help classes as an argument, you can get a list of the individual commands in that class. For example, here is the help display for the class `status': (gdb) help status Status inquiries. List of commands: show -- Generic command for showing things set with "set" info -- Generic command for printing status Type "help" followed by command name for full documentation. Command name abbreviations are allowed if unambiguous. (gdb) `help COMMAND' With a command name as `help' argument, GDB displays a short paragraph on how to use that command. `complete ARGS' The `complete ARGS' command lists all the possible completions for the beginning of a command. Use ARGS to specify the beginning of the command you want completed. For example: complete i results in: info inspect ignore This is intended for use by GNU Emacs. In addition to `help', you can use the GDB commands `info' and `show' to inquire about the state of your program, or the state of GDB itself. Each command supports many topics of inquiry; this manual introduces each of them in the appropriate context. The listings under `info' and under `show' in the Index point to all the sub-commands. *Note Index::. `info' This command (abbreviated `i') is for describing the state of your program. For example, you can list the arguments given to your program with `info args', list the registers currently in use with `info registers', or list the breakpoints you have set with `info breakpoints'. You can get a complete list of the `info' sub-commands with `help info'. `set' You can assign the result of an expression to an environment variable with `set'. For example, you can set the GDB prompt to a $-sign with `set prompt $'. `show' In contrast to `info', `show' is for describing the state of GDB itself. You can change most of the things you can `show', by using the related command `set'; for example, you can control what number system is used for displays with `set radix', or simply inquire which is currently in use with `show radix'. To display all the settable parameters and their current values, you can use `show' with no arguments; you may also use `info set'. Both commands produce the same display. Here are three miscellaneous `show' subcommands, all of which are exceptional in lacking corresponding `set' commands: `show version' Show what version of GDB is running. You should include this information in GDB bug-reports. If multiple versions of GDB are in use at your site, you may occasionally want to determine which version of GDB you are running; as GDB evolves, new commands are introduced, and old ones may wither away. The version number is also announced when you start GDB. `show copying' Display information about permission for copying GDB. `show warranty' Display the GNU "NO WARRANTY" statement.  File: gdb.info, Node: Running, Next: Stopping, Prev: Commands, Up: Top Running Programs Under GDB ************************** When you run a program under GDB, you must first generate debugging information when you compile it. You may start GDB with its arguments, if any, in an environment of your choice. You may redirect your program's input and output, debug an already running process, or kill a child process. * Menu: * Compilation:: Compiling for debugging * Starting:: Starting your program * Arguments:: Your program's arguments * Environment:: Your program's environment * Working Directory:: Your program's working directory * Input/Output:: Your program's input and output * Attach:: Debugging an already-running process * Kill Process:: Killing the child process * Process Information:: Additional process information * Threads:: Debugging programs with multiple threads * Processes:: Debugging programs with multiple processes  File: gdb.info, Node: Compilation, Next: Starting, Prev: Running, Up: Running Compiling for debugging ======================= In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code. To request debugging information, specify the `-g' option when you run the compiler. Many C compilers are unable to handle the `-g' and `-O' options together. Using those compilers, you cannot generate optimized executables containing debugging information. GCC, the GNU C compiler, supports `-g' with or without `-O', making it possible to debug optimized code. We recommend that you *always* use `-g' whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck. When you debug a program compiled with `-g -O', remember that the optimizer is rearranging your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, GDB never sees that variable--because the compiler optimizes it out of existence. Some things do not work as well with `-g -O' as with just `-g', particularly on machines with instruction scheduling. If in doubt, recompile with `-g' alone, and if this fixes the problem, please report it to us as a bug (including a test case!). Older versions of the GNU C compiler permitted a variant option `-gg' for debugging information. GDB no longer supports this format; if your GNU C compiler has this option, do not use it.