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Info file gdb.info, produced by Makeinfo, -*- Text -*- from input file gdb-all.texinfo. This file documents the GNU debugger GDB. Copyright (C) 1988, 1989, 1990, 1991 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 section entitled "GNU General Public License" is included exactly as in the original, and provided 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, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English. File: gdb.info, Node: Top, Next: Summary, Prev: (dir), Up: (dir) This file describes version 4.0 of GDB, the GNU symbolic debugger. * Menu: * Summary:: Summary of GDB * New Features:: New Features in GDB version 4.0 * Sample Session:: A Sample GDB Session * Invocation:: Getting In and Out of GDB * Commands:: * Running:: Running Programs Under GDB * Stopping:: Stopping and Continuing * Stack:: Examining the Stack * Source:: Examining Source Files * Data:: Examining Data * Symbols:: Examining the Symbol Table * Altering:: Altering Execution * 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 * Renamed Commands:: * Installing GDB:: Installing GDB * Copying:: GNU GENERAL PUBLIC LICENSE * Index:: Index -- The Detailed Node Listing -- Summary of GDB * Free Software:: Free Software * Contributors:: Contributors to GDB Getting In and Out of GDB * Starting GDB:: Starting GDB * Leaving GDB:: Leaving GDB * Shell Commands:: Shell Commands Starting GDB * File Options:: Choosing Files * Mode Options:: Choosing Modes GDB Commands * Command Syntax:: Command Syntax * Help:: Getting 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 Stopping and Continuing * Breakpoints:: Breakpoints, Watchpoints, and Exceptions * Continuing and Stepping:: Resuming Execution * Signals:: Signals Breakpoints, Watchpoints, and Exceptions * Set Breaks:: Setting Breakpoints * Set Watchpoints:: Setting Watchpoints * Exception Handling:: Breakpoints and Exceptions * Delete Breaks:: Deleting Breakpoints * Disabling:: Disabling Breakpoints * Conditions:: Break Conditions * Break Commands:: Breakpoint Command Lists * Breakpoint Menus:: Breakpoint Menus * Error in Breakpoints:: Examining the Stack * Frames:: Stack Frames * Backtrace:: Backtraces * Selection:: Selecting a Frame * Frame Info:: Information on a Frame 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 Altering Execution * Assignment:: Assignment to Variables * Jumping:: Continuing at a Different Address * Signaling:: Giving the Program a Signal * Returning:: Returning from a Function * Calling:: Calling your Program's Functions GDB's 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 * Remote:: Remote Debugging Remote Debugging * i960-Nindy Remote:: * EB29K Remote:: * VxWorks Remote:: GDB with a Remote i960 (Nindy) * Nindy Startup:: Startup with Nindy * Nindy Options:: Options for Nindy * Nindy reset:: Nindy Reset Command GDB with a Remote EB29K * Comms (EB29K):: Communications Setup * gdb-EB29K:: EB29K cross-debugging * Remote Log:: Remote Log GDB and VxWorks * VxWorks connection:: Connecting to VxWorks * VxWorks download:: VxWorks Download * VxWorks attach:: Running Tasks 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 * 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 File: gdb.info, Node: Summary, Next: New Features, 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. GDB can be used to debug programs written in C and C++. Pascal support is being implemented, and Fortran support will be added when a GNU Fortran compiler is ready. * Menu: * Free Software:: Free 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 can't take these freedoms away from anyone else. For full details, *note Copying::.. 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; let's be evenhanded) have been unfairly omitted from this list, we would like to add your names! So that they may not regard their long labor as thankless, we particularly thank those who shepherded GDB through major releases: John Gilmore (release 4.0); Jim Kingdon (releases 3.9, 3.5, 3.4, 3.3); and Randy Smith (releases 3.2, 3.1, 3.0). As major maintainer of GDB for some period, each contributed significantly to the structure, stability, and capabilities of the entire debugger. Richard Stallman, assisted at various times by Pete 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 4.0 uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of V. Gumby 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. 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. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine 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. Rich Schaefer 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 and Wind River Systems contributed remote debugging modules for their products. Brian Fox is the author of the readline libraries providing command-line editing and command history. File: gdb.info, Node: New Features, Next: Sample Session, Prev: Summary, Up: Top New Features since GDB version 3.5 ********************************** *Targets* Using the new command `target', you can select at runtime whether you are debugging local files, local processes, standalone systems over a serial port, realtime systems over a TCP/IP connection, etc. Internally, GDB now uses a function vector to mediate access to different targets; if you need to add your own support for a remote protocol, this makes it much easier. *Watchpoints* GDB now sports watchpoints as well as breakpoints. You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place in your program where this may happen. *Object Code Formats* GDB uses a new scheme called the Binary File Descriptor (BFD) Library to permit it to switch dynamically, without reconfiguration or recompilation, between different object-file formats. Formats currently supported are COFF, a.out, and the Intel 960 b.out; files may be read as .o's, archive libraries, or core dumps. BFD is available as a subroutine library so that other programs may take advantage of it, and the other GNU binary utilities are being converted to use it. *Configuration* Compile-time configuration (to select a particular architecture and operating system) is much easier. The script `configure' now allows you to configure GDB as either a native debugger or a cross-debugger. *Interaction* The user interface to GDB's control variables has been simplified and consolidated in two commands, `set' and `show'. Output lines are now broken at readable places, rather than overflowing onto the next line. You can suppress output of machine-level addresses, displaying only source language information. *Source Language* GDB now has limited support for C++ exception handling: GDB can break when an exception is raised, before the stack is peeled back to the exception handler's context. *Command Rationalization* Many GDB commands have been renamed to make them easier to remember and use. In particular, the subcommands of `info' and `show'/`set' are grouped to make the former refer to the state of your program, and the latter refer to the state of GDB itself. *Note Renamed Commands::, for details on what commands were renamed. *Ports* GDB has been ported to the following new architectures: AT&T 3b1, Acorn RISC machine, HP300 running HPUX, big- and little-endian MIPS machines, Motorola 88k, Sun 386i, and Sun 3 running SunOS 4. In addition, the following are supported as targets only: AMD 29k, Intel 960, and Wind River's VxWorks. *Shared Libraries* GDB 4.0 supports SunOS shared libraries. *Work in Progress* Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture support. File: gdb.info, Node: Sample Session, Next: Invocation, Prev: New Features, 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 these 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's definition in another stop working. In the following short `m4' session, we define a macro `foo' which expands to `0000'; we then use the `m4' builtin `defn' to define `bar' as the same thing. However, when we change the open quote string to `<QUOTE>' and the close quote string to `<UNQUOTE>', 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(<QUOTE>,<UNQUOTE>) define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz C-d m4: End of input: 0: fatal error: EOF in string Let's use GDB to try to see what's going on. $ gdb m4 Reading symbol data from m4...done. (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 then tell GDB to use a narrower display width than usual, so that examples will fit in this manual. (gdb) set width 70 Let's see how the `m4' builtin `changequote' works. Having looked at the source, we know the relevant subroutine is `m4_changequote', so we set a breakpoint there with GDB's `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(<QUOTE>,<UNQUOTE>) 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 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 530 if (lquote != def_lquote) The summary display showing the subroutine where `m4' is now suspended (and its arguments) is called a stack frame display. We can use the `backtrace' command (which can also be spelled `bt'), to see where we are in the stack: it displays a stack frame for each active subroutine. (gdb) bt #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") 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 Let's 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; let's examine the variables `lquote' and `rquote' to see if they are in fact the new left and right quotes we specified. We can use the command `p' (`print') to see their values. (gdb) p lquote $1 = 0x35d40 "<QUOTE>" (gdb) p rquote $2 = 0x35d50 "<UNQUOTE>" `lquote' and `rquote' are indeed the new left and right quotes. Let's 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's 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. Let's try setting them to better values. We can use the `p' command for this, since it'll 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 Let's see if that fixes 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(<QUOTE>foo<UNQUOTE>)) 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'll let `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 ************************* * Menu: * Starting GDB:: Starting GDB * Leaving GDB:: Leaving GDB * Shell Commands:: Shell Commands File: gdb.info, Node: Starting GDB, Next: Leaving GDB, Prev: Invocation, Up: Invocation Starting GDB ============ GDB is invoked with the shell command `gdb'. Once started, it reads commands from the terminal until you tell it to exit. You can run `gdb' with no arguments or options; but the most usual way to start GDB is with one argument or two, specifying an executable program as the argument: gdb program You can also start with both an executable program and a core file specified: gdb program core You can further control how GDB starts up by using command-line options. GDB itself can remind you of the options available: gdb -help will 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, Prev: Starting GDB, Up: Starting GDB Choosing Files -------------- As shown above, any arguments other than options specify an executable file and core file; that is, the first argument encountered with no associated option flag is equivalent to a `-se' option, and the second, if any, is equivalent to a `-c' option. Many options have both long and short forms; both are shown here. The long forms are also recognized 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. `-command=FILE' `-x FILE' Execute GDB commands from file FILE. *Note Command Files::. `-directory=DIRECTORY' `-d DIRECTORY' Add DIRECTORY to the path to search for source files. File: gdb.info, Node: Mode Options, Prev: File Options, Up: Starting GDB Choosing Modes -------------- `-nx' `-n' Do not execute commands from any `.gdbinit' initialization files. Normally, the commands in these files are executed after all the command options and arguments have been processed. *Note Command Files::. `-quiet' `-q' "Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode, or if an executable file name is specified on the GDB command line. `-batch' Run in batch mode. Exit with status `0' after processing all the command files specified with `-x' (and `.gdbinit', if not inhibited). 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' 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 the 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: Leaving GDB, Next: Shell Commands, Prev: Starting GDB, Up: Invocation Leaving GDB =========== `quit' To exit GDB, use the `quit' command (abbreviated `q'), or type an end-of-file character (usually `C-d'). An interrupt (often `C-c') will not exit from GDB, but rather will terminate the action of any GDB command that is in progress and return 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've been using GDB to control an attached process or device, you can release it with the `detach' command; *note Attach::.. File: gdb.info, Node: Shell Commands, Prev: Leaving GDB, Up: Invocation Shell Commands ============== If you need to execute occasional shell commands during your debugging session, there's no need to leave or suspend GDB; you can just use the `shell' command. `shell COMMAND STRING' Directs GDB to invoke an inferior shell to execute COMMAND STRING. If it exists, the environment variable `SHELL' is used for the name of the shell to run. Otherwise GDB uses `/bin/sh'. The utility `make' is often needed in development environments. You don't have to use the `shell' command for this purpose in GDB: `make MAKE-ARGS' Causes GDB to execute an inferior `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 ************ * Menu: * Command Syntax:: Command Syntax * Help:: Getting Help File: gdb.info, Node: Command Syntax, Next: Help, 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 RET) means to repeat the previous command. Certain commands (for example, `run') will not repeat this way; these are commands for which unintentional repetition might cause trouble and which you are unlikely to want to repeat. The `list' and `x' commands, when you repeat them with RET, construct new arguments rather than repeating exactly as typed. This permits easy scanning of source or memory. A line of input starting with `#' is a comment; it does nothing. This is useful mainly in command files (*Note Command Files::). File: gdb.info, Node: Help, Prev: Command Syntax, 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 will display a short paragraph on how to use that command. 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. `info' This command (abbreviated `i') is for describing the state of your program; for example, it can list the arguments given to your program (`info args'), the registers currently in use (`info registers'), or the breakpoints you've set (`info breakpoints'). You can get a complete list of the `info' sub-commands with `help info'. `show' In contrast, `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 make sure what version of GDB you're running; as GDB evolves, new commands are introduced, and old ones may wither away. The version number is also announced when you start GDB with no arguments. `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 ************************** * 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 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. 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 the program is correct, but there's no sense in pushing your luck. 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 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. File: gdb.info, Node: Starting, Next: Arguments, Prev: Compilation, Up: Running Starting your Program ===================== `run' `r' Use the `run' command to start your program under GDB. You must first specify the program name (except on VxWorks) with an argument to GDB (*note Invocation::.), or using the `file' or `exec-file' command (*note Files::.). On targets that support processes, `run' creates an inferior process and makes that process run your program. On other targets, `run' jumps to the start of the program. The execution of a program is affected by certain information it receives from its superior. GDB provides ways to specify this information, which you must do before starting the program. (You can change it after starting the program, but such changes will only affect the program the next time you start it.) This information may be divided into four categories: The arguments. You specify the arguments to give your program as the arguments of the `run' command. If a shell is available on your target, the shell is used to pass the arguments, so that you may use normal conventions (such as wildcard expansion or variable substitution) in describing the arguments. In Unix systems, you can control which shell is used with the `SHELL' environment variable. *Note Arguments::. The environment. Your program normally inherits its environment from GDB, but you can use the GDB commands `set environment' and `unset environment' to change parts of the environment that will be given to the program. *Note Environment::. The working directory. Your program inherits its working directory from GDB. You can set GDB's working directory with the `cd' command in GDB. *Note Working Directory::. The standard input and output. Your program normally uses the same device for standard input and standard output as GDB is using. You can redirect input and output in the `run' command line, or you can use the `tty' command to set a different device for your program. *Note Input/Output::. *Warning:* While input and output redirection work, you can't use pipes to pass the output of the program you're debugging to another program; if you attempt this, GDB is likely to wind up debugging the wrong program. When you issue the `run' command, your program begins to execute immediately. *Note Stopping::, for discussion of how to arrange for your program to stop. Once your program has been started by the `run' command (and then stopped), you may evaluate expressions that involve calls to functions in the inferior, using the `print' or `call' commands. *Note Data::. If the modification time of your symbol file has changed since the last time GDB read its symbols, GDB will discard its symbol table and re-read it. In this process, it tries to retain your current breakpoints. File: gdb.info, Node: Arguments, Next: Environment, Prev: Starting, Up: Running Your Program's Arguments ======================== The arguments to your program can be specified by the arguments of the `run' command. They are passed to a shell, which expands wildcard characters and performs redirection of I/O, and thence to the program. GDB uses the shell indicated by your environment variable `SHELL' if it exists; otherwise, GDB uses `/bin/sh'. `run' with no arguments uses the same arguments used by the previous `run', or those set by the `set args' command. `set args' Specify the arguments to be used the next time your program is run. If `set args' has no arguments, `run' will execute your program with no arguments. Once you have run your program with arguments, using `set args' before the next `run' is the only way to run it again without arguments. `show args' Show the arguments to give your program when it is started. File: gdb.info, Node: Environment, Next: Working Directory, Prev: Arguments, Up: Running Your Program's Environment ========================== The "environment" consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running the program with a modified environment without having to start GDB over again. `path DIRECTORY' Add DIRECTORY to the front of the `PATH' environment variable (the search path for executables), for both GDB and your program. You may specify several directory names, separated by `:' or whitespace. If DIRECTORY is already in the path, it is moved to the front, so it will be searched sooner. You can use the string `$cwd' to refer to whatever is the current working directory at the time GDB searches the path. If you use `.' instead, it refers to the directory where you executed the `path' command. GDB fills in the current path where needed in the DIRECTORY argument, before adding it to the search path. `show paths' Display the list of search paths for executables (the `PATH' environment variable). `show environment [VARNAME]' Print the value of environment variable VARNAME to be given to your program when it starts. If you don't supply VARNAME, print the names and values of all environment variables to be given to your program. You can abbreviate `environment' as `env'. `set environment VARNAME [=] VALUE' Sets environment variable VARNAME to VALUE. The value changes for your program only, not for GDB itself. VALUE may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The VALUE parameter is optional; if it is eliminated, the variable is set to a null value. For example, this command: set env USER = foo tells a Unix program, when subsequently run, that its user is named `foo'. (The spaces around `=' are used for clarity here; they are not actually required.) `unset environment VARNAME' Remove variable VARNAME from the environment to be passed to your program. This is different from `set env VARNAME ='; `unset environment' removes the variable from the environment, rather than assigning it an empty value. File: gdb.info, Node: Working Directory, Next: Input/Output, Prev: Environment, Up: Running Your Program's Working Directory ================================ Each time you start your program with `run', it inherits its working directory from the current working directory of GDB. GDB's working directory is initially whatever it inherited from its parent process (typically the shell), but you can specify a new working directory in GDB with the `cd' command. The GDB working directory also serves as a default for the commands that specify files for GDB to operate on. *Note Files::. `cd DIRECTORY' Set GDB's working directory to DIRECTORY. `pwd' Print GDB's working directory. File: gdb.info, Node: Input/Output, Next: Attach, Prev: Working Directory, Up: Running Your Program's Input and Output =============================== By default, the program you run under GDB does input and output to the same terminal that GDB uses. GDB switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program. `info terminal' Displays GDB's recorded information about the terminal modes your program is using. You can redirect the program's input and/or output using shell redirection with the `run' command. For example, run > outfile starts the program, diverting its output to the file `outfile'. Another way to specify where the program should do input and output is with the `tty' command. This command accepts a file name as argument, and causes this file to be the default for future `run' commands. It also resets the controlling terminal for the child process, for future `run' commands. For example, tty /dev/ttyb directs that processes started with subsequent `run' commands default to do input and output on the terminal `/dev/ttyb' and have that as their controlling terminal. An explicit redirection in `run' overrides the `tty' command's effect on the input/output device, but not its effect on the controlling terminal. When you use the `tty' command or redirect input in the `run' command, only the input *for your program* is affected. The input for GDB still comes from your terminal. File: gdb.info, Node: Attach, Next: Kill Process, Prev: Input/Output, Up: Running Debugging an Already-Running Process ==================================== `attach PROCESS-ID' This command attaches to a running process--one that was started outside GDB. (`info files' will show your active targets.) The command takes as argument a process ID. The usual way to find out the process-id of a Unix process is with the `ps' utility, or with the `jobs -l' shell command. `attach' will not repeat if you press RET a second time after executing the command. To use `attach', you must be debugging in an environment which supports processes. You must also have permission to send the process a signal, and it must have the same effective user ID as the GDB process. When using `attach', you should first use the `file' command to specify the program running in the process and load its symbol table. *Note Files::. The first thing GDB does after arranging to debug the specified process is to stop it. You can examine and modify an attached process with all the GDB commands that are ordinarily available when you start processes with `run'. You can insert breakpoints; you can step and continue; you can modify storage. If you would rather the process continue running, you may use the `continue' command after attaching GDB to the process. `detach' When you have finished debugging the attached process, you can use the `detach' command to release it from GDB's control. Detaching the process continues its execution. After the `detach' command, that process and GDB become completely independent once more, and you are ready to `attach' another process or start one with `run'. `detach' will not repeat if you press RET again after executing the command. If you exit GDB or use the `run' command while you have an attached process, you kill that process. By default, you will be asked for confirmation if you try to do either of these things; you can control whether or not you need to confirm by using the `set confirm' command (*note Messages/Warnings::.). File: gdb.info, Node: Kill Process, Prev: Attach, Up: Running Killing the Child Process ========================= `kill' Kill the child process in which your program is running under GDB. This command is useful if you wish to debug a core dump instead of a running process. GDB ignores any core dump file while your program is running. On some operating systems, a program can't be executed outside GDB while you have breakpoints set on it inside GDB. You can use the `kill' command in this situation to permit running the program outside the debugger. The `kill' command is also useful if you wish to recompile and relink the program, since on many systems it is impossible to modify an executable file while it is running in a process. In this case, when you next type `run', GDB will notice that the file has changed, and will re-read the symbol table (while trying to preserve your current breakpoint settings). File: gdb.info, Node: Stopping, Next: Stack, Prev: Running, Up: Top Stopping and Continuing *********************** The principal purpose of using a debugger is so that you can stop your program before it terminates; or so that, if the program runs into trouble, you can investigate and find out why. Inside GDB, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a GDB command such as `step'. You may then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by GDB provide ample explanation of the status of your program--but you can also explicitly request this information at any time. `info program' Display information about the status of your program: whether it is running or not, what process it is, and why it stopped. * Menu: * Breakpoints:: Breakpoints, Watchpoints, and Exceptions * Continuing and Stepping:: Resuming Execution * Signals:: Signals File: gdb.info, Node: Breakpoints, Next: Continuing and Stepping, Prev: Stopping, Up: Stopping Breakpoints, Watchpoints, and Exceptions ======================================== A "breakpoint" makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add various conditions to control in finer detail whether the program will stop. You can set breakpoints with the `break' command and its variants (*note Set Breaks::.), to specify the place where the program should stop by line number, function name or exact address in the program. In languages with exception handling (such as GNU C++), you can also set breakpoints where an exception is raised (*note Exception Handling::.). A "watchpoint" is a special breakpoint that stops your program when the value of an expression changes. You must use a different command to set watchpoints (*note Set Watchpoints::.), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands. Each breakpoint or watchpoint is assigned a number when it is created; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be "enabled" or "disabled"; if disabled, it has no effect on the program until you enable it again. * Menu: * Set Breaks:: Setting Breakpoints * Set Watchpoints:: Setting Watchpoints * Exception Handling:: Breakpoints and Exceptions * Delete Breaks:: Deleting Breakpoints * Disabling:: Disabling Breakpoints * Conditions:: Break Conditions * Break Commands:: Breakpoint Command Lists * Breakpoint Menus:: Breakpoint Menus * Error in Breakpoints::