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gdb - The GNU Debugger



        gdb - The GNU Debugger


        gdb    [-help] [-nx] [-q] [-batch] [-cd=dir] [-f] [-b bps] [-tty=dev]
               [-s symfile] [-e prog] [-se prog] [-c core] [-x cmds] [-d dir]


        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
           ·   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 cor‐
               recting the effects of one bug and go on to learn about another.
        You  can  use  GDB  to  debug programs written in C, C++, and Modula-2.
        Fortran support will be added when a GNU Fortran compiler is ready.
        GDB is invoked with the shell command gdb.  Once started, it reads com‐
        mands  from the terminal until you tell it to exit with the GDB command
        quit.  You can get online help from gdb itself  by  using  the  command
        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
        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).
        Here are some of the most frequently needed GDB commands:
        break [file:]function
                Set a breakpoint at function (in file).
        run [arglist]
               Start your program (with arglist, if specified).
        bt     Backtrace: display the program stack.
        print expr
                Display the value of an expression.
        c      Continue running your program (after stopping, e.g. at a  break‐
        next   Execute  next program line (after stopping); step over any func‐
               tion calls in the line.
        step   Execute next program line (after stopping); step into any  func‐
               tion calls in the line.
        help [name]
               Show  information about GDB command name, or general information
               about using GDB.
        quit   Exit from GDB.
        For full details on GDB, see Using GDB: A Guide to the GNU Source-Level
        Debugger, by Richard M. Stallman and Roland H. Pesch.  The same text is
        available online as the gdb entry in the info program.


        Any arguments other than options specify an executable  file  and  core
        file  (or  process ID); 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 if it’s the name of a file.
        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.)
        All the options and command line arguments you give  are  processed  in
        sequential order.  The order makes a difference when the ‘-x’ option is
        -h     List all options, with brief explanations.
        -s file
                Read symbol table from file file.
        -e file
                Use file file as the executable file to execute when  appropri‐
               ate,  and  for  examining  pure  data in conjunction with a core
                Read symbol table from file file and use it as  the  executable
        -c file
                Use file file as a core dump to examine.
        -x file
                Execute GDB commands from file file.
        -d directory
                Add directory to the path to search for source files.
        -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.
        -q     ‘‘Quiet’’.   Do  not  print  the introductory and copyright mes‐
               sages.  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 ‘.gdbinit’, if not inhib‐
               ited).  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 exam‐
               ple 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.
                Run GDB using directory as its working  directory,  instead  of
               the current directory.
        -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 dis‐
               played (which includes each time the program stops).  This  rec‐
               ognizable  format  looks  like two ‘ 32’ 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 ‘ 32’ 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.
                Run using device for your program’s standard input and  output.
        ‘gdb’  entry in info; Using GDB: A Guide to the GNU Source-Level Debug‐
        ger, Richard M. Stallman and Roland H. Pesch, July 1991.


        Copyright (c) 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 that the
        entire resulting derived work is distributed under the terms of a  per‐
        mission notice identical to this one.
        Permission  is granted to copy and distribute translations of this man‐
        ual into another language, under the above conditions for modified ver‐
        sions,  except  that this permission notice may be included in transla‐
        tions approved by the Free Software Foundation instead of in the origi‐
        nal English.


Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.