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| <h4 class="node-heading">gdb man</h4> |
| <a name="gdb-man-1"></a> |
| <h3 class="heading">gdb man</h3> |
| |
| |
| <p>gdb [<samp>-help</samp>] [<samp>-nh</samp>] [<samp>-nx</samp>] [<samp>-q</samp>] |
| [<samp>-batch</samp>] [<samp>-cd=</samp><var>dir</var>] [<samp>-f</samp>] |
| [<samp>-b</samp> <!-- /@w --><var>bps</var>] |
| [<samp>-tty=</samp><var>dev</var>] [<samp>-s</samp> <var>symfile</var>] |
| [<samp>-e</samp> <!-- /@w --><var>prog</var>] [<samp>-se</samp> <!-- /@w --><var>prog</var>] |
| [<samp>-c</samp> <!-- /@w --><var>core</var>] [<samp>-p</samp> <!-- /@w --><var>procID</var>] |
| [<samp>-x</samp> <!-- /@w --><var>cmds</var>] [<samp>-d</samp> <!-- /@w --><var>dir</var>] |
| [<var>prog</var>|<var>prog</var> <var>procID</var>|<var>prog</var> <var>core</var>] |
| </p> |
| <p>The purpose of a debugger such as <small>GDB</small> 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. |
| </p> |
| <p><small>GDB</small> can do four main kinds of things (plus other things in support of |
| these) to help you catch bugs in the act: |
| </p> |
| <ul> |
| <li> Start your program, specifying anything that might affect its behavior. |
| |
| </li><li> Make your program stop on specified conditions. |
| |
| </li><li> Examine what has happened, when your program has stopped. |
| |
| </li><li> Change things in your program, so you can experiment with correcting the |
| effects of one bug and go on to learn about another. |
| </li></ul> |
| |
| <p>You can use <small>GDB</small> to debug programs written in C, C<tt>++</tt>, Fortran and |
| Modula-2. |
| </p> |
| <p><small>GDB</small> is invoked with the shell command <code>gdb</code>. Once started, it reads |
| commands from the terminal until you tell it to exit with the <small>GDB</small> |
| command <code>quit</code>. You can get online help from <small>GDB</small> itself |
| by using the command <code>help</code>. |
| </p> |
| <p>You can run <code>gdb</code> with no arguments or options; but the most |
| usual way to start <small>GDB</small> is with one argument or two, specifying an |
| executable program as the argument: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">gdb program |
| </pre></div> |
| |
| <p>You can also start with both an executable program and a core file specified: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">gdb program core |
| </pre></div> |
| |
| <p>You can, instead, specify a process ID as a second argument, if you want |
| to debug a running process: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">gdb program 1234 |
| gdb -p 1234 |
| </pre></div> |
| |
| <p>would attach <small>GDB</small> to process <code>1234</code> (unless you also have a file |
| named <samp>1234</samp>; <small>GDB</small> does check for a core file first). |
| With option <samp>-p</samp> you can omit the <var>program</var> filename. |
| </p> |
| <p>Here are some of the most frequently needed <small>GDB</small> commands: |
| </p> |
| <dl compact="compact"> |
| <dt><code>break [<var>file</var>:]<var>functiop</var></code></dt> |
| <dd><p>Set a breakpoint at <var>function</var> (in <var>file</var>). |
| </p> |
| </dd> |
| <dt><code>run [<var>arglist</var>]</code></dt> |
| <dd><p>Start your program (with <var>arglist</var>, if specified). |
| </p> |
| </dd> |
| <dt><code>bt</code></dt> |
| <dd><p>Backtrace: display the program stack. |
| </p> |
| </dd> |
| <dt><code>print <var>expr</var></code></dt> |
| <dd><p>Display the value of an expression. |
| </p> |
| </dd> |
| <dt><code>c</code></dt> |
| <dd><p>Continue running your program (after stopping, e.g. at a breakpoint). |
| </p> |
| </dd> |
| <dt><code>next</code></dt> |
| <dd><p>Execute next program line (after stopping); step <em>over</em> any |
| function calls in the line. |
| </p> |
| </dd> |
| <dt><code>edit [<var>file</var>:]<var>function</var></code></dt> |
| <dd><p>look at the program line where it is presently stopped. |
| </p> |
| </dd> |
| <dt><code>list [<var>file</var>:]<var>function</var></code></dt> |
| <dd><p>type the text of the program in the vicinity of where it is presently stopped. |
| </p> |
| </dd> |
| <dt><code>step</code></dt> |
| <dd><p>Execute next program line (after stopping); step <em>into</em> any |
| function calls in the line. |
| </p> |
| </dd> |
| <dt><code>help [<var>name</var>]</code></dt> |
| <dd><p>Show information about <small>GDB</small> command <var>name</var>, or general information |
| about using <small>GDB</small>. |
| </p> |
| </dd> |
| <dt><code>quit</code></dt> |
| <dd><p>Exit from <small>GDB</small>. |
| </p></dd> |
| </dl> |
| |
| |
| <p>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 <samp>-se</samp> option, and the second, |
| if any, is equivalent to a <samp>-c</samp> 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 <samp>+</samp> rather than <samp>-</samp>, though we illustrate the |
| more usual convention.) |
| </p> |
| <p>All the options and command line arguments you give are processed |
| in sequential order. The order makes a difference when the <samp>-x</samp> |
| option is used. |
| </p> |
| <dl compact="compact"> |
| <dt><code>-help</code></dt> |
| <dt><code>-h</code></dt> |
| <dd><p>List all options, with brief explanations. |
| </p> |
| </dd> |
| <dt><code>-symbols=<var>file</var></code></dt> |
| <dt><code>-s <var>file</var></code></dt> |
| <dd><p>Read symbol table from file <var>file</var>. |
| </p> |
| </dd> |
| <dt><code>-write</code></dt> |
| <dd><p>Enable writing into executable and core files. |
| </p> |
| </dd> |
| <dt><code>-exec=<var>file</var></code></dt> |
| <dt><code>-e <var>file</var></code></dt> |
| <dd><p>Use file <var>file</var> as the executable file to execute when |
| appropriate, and for examining pure data in conjunction with a core |
| dump. |
| </p> |
| </dd> |
| <dt><code>-se=<var>file</var></code></dt> |
| <dd><p>Read symbol table from file <var>file</var> and use it as the executable |
| file. |
| </p> |
| </dd> |
| <dt><code>-core=<var>file</var></code></dt> |
| <dt><code>-c <var>file</var></code></dt> |
| <dd><p>Use file <var>file</var> as a core dump to examine. |
| </p> |
| </dd> |
| <dt><code>-command=<var>file</var></code></dt> |
| <dt><code>-x <var>file</var></code></dt> |
| <dd><p>Execute <small>GDB</small> commands from file <var>file</var>. |
| </p> |
| </dd> |
| <dt><code>-ex <var>command</var></code></dt> |
| <dd><p>Execute given <small>GDB</small> <var>command</var>. |
| </p> |
| </dd> |
| <dt><code>-directory=<var>directory</var></code></dt> |
| <dt><code>-d <var>directory</var></code></dt> |
| <dd><p>Add <var>directory</var> to the path to search for source files. |
| </p> |
| </dd> |
| <dt><code>-nh</code></dt> |
| <dd><p>Do not execute commands from <samp>~/.gdbinit</samp>. |
| </p> |
| </dd> |
| <dt><code>-nx</code></dt> |
| <dt><code>-n</code></dt> |
| <dd><p>Do not execute commands from any <samp>.gdbinit</samp> initialization files. |
| </p> |
| </dd> |
| <dt><code>-quiet</code></dt> |
| <dt><code>-q</code></dt> |
| <dd><p>“Quiet”. Do not print the introductory and copyright messages. These |
| messages are also suppressed in batch mode. |
| </p> |
| </dd> |
| <dt><code>-batch</code></dt> |
| <dd><p>Run in batch mode. Exit with status <code>0</code> after processing all the command |
| files specified with <samp>-x</samp> (and <samp>.gdbinit</samp>, if not inhibited). |
| Exit with nonzero status if an error occurs in executing the <small>GDB</small> |
| commands in the command files. |
| </p> |
| <p>Batch mode may be useful for running <small>GDB</small> as a filter, for example to |
| download and run a program on another computer; in order to make this |
| more useful, the message |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">Program exited normally. |
| </pre></div> |
| |
| <p>(which is ordinarily issued whenever a program running under <small>GDB</small> control |
| terminates) is not issued when running in batch mode. |
| </p> |
| </dd> |
| <dt><code>-cd=<var>directory</var></code></dt> |
| <dd><p>Run <small>GDB</small> using <var>directory</var> as its working directory, |
| instead of the current directory. |
| </p> |
| </dd> |
| <dt><code>-fullname</code></dt> |
| <dt><code>-f</code></dt> |
| <dd><p>Emacs sets this option when it runs <small>GDB</small> as a subprocess. It tells |
| <small>GDB</small> 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 ‘<samp>\032</samp>’ characters, followed by the file name, line number |
| and character position separated by colons, and a newline. The |
| Emacs-to-<small>GDB</small> interface program uses the two ‘<samp>\032</samp>’ |
| characters as a signal to display the source code for the frame. |
| </p> |
| </dd> |
| <dt><code>-b <var>bps</var></code></dt> |
| <dd><p>Set the line speed (baud rate or bits per second) of any serial |
| interface used by <small>GDB</small> for remote debugging. |
| </p> |
| </dd> |
| <dt><code>-tty=<var>device</var></code></dt> |
| <dd><p>Run using <var>device</var> for your program’s standard input and output. |
| </p></dd> |
| </dl> |
| |
| |
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