410 lines
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410 lines
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Man-Pages.html#Man-Pages" rel="up" title="Man Pages">
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<a name="gdb-man"></a>
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<div class="header">
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<p>
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Next: <a href="gdbserver-man.html#gdbserver-man" accesskey="n" rel="next">gdbserver man</a>, Up: <a href="Man-Pages.html#Man-Pages" accesskey="u" rel="up">Man Pages</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="node-heading">gdb man</h4>
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<a name="gdb-man-1"></a>
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<h3 class="heading">gdb man</h3>
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<p>gdb [OPTIONS] [<var>prog</var>|<var>prog</var> <var>procID</var>|<var>prog</var> <var>core</var>]
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</p>
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<p>The purpose of a debugger such as <small>GDB</small> is to allow you to see what is
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going on “inside” another program while it executes – or what another
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program was doing at the moment it crashed.
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</p>
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<p><small>GDB</small> can do four main kinds of things (plus other things in support of
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these) to help you catch bugs in the act:
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</p>
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<ul>
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<li> Start your program, specifying anything that might affect its behavior.
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</li><li> Make your program stop on specified conditions.
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</li><li> Examine what has happened, when your program has stopped.
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</li><li> Change things in your program, so you can experiment with correcting the
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effects of one bug and go on to learn about another.
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</li></ul>
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<p>You can use <small>GDB</small> to debug programs written in C, C<tt>++</tt>, Fortran and
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Modula-2.
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</p>
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<p><small>GDB</small> is invoked with the shell command <code>gdb</code>. Once started, it reads
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commands from the terminal until you tell it to exit with the <small>GDB</small>
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command <code>quit</code> or <code>exit</code>. You can get online help from <small>GDB</small> itself
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by using the command <code>help</code>.
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</p>
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<p>You can run <code>gdb</code> with no arguments or options; but the most
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usual way to start <small>GDB</small> is with one argument or two, specifying an
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executable program as the argument:
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</p>
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<div class="smallexample">
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<pre class="smallexample">gdb program
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</pre></div>
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<p>You can also start with both an executable program and a core file specified:
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</p>
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<div class="smallexample">
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<pre class="smallexample">gdb program core
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</pre></div>
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<p>You can, instead, specify a process ID as a second argument or use option
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<code>-p</code>, if you want to debug a running process:
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</p>
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<div class="smallexample">
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<pre class="smallexample">gdb program 1234
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gdb -p 1234
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</pre></div>
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<p>would attach <small>GDB</small> to process <code>1234</code>. With option <samp>-p</samp> you
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can omit the <var>program</var> filename.
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</p>
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<p>Here are some of the most frequently needed <small>GDB</small> commands:
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</p>
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<dl compact="compact">
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<dt><code>break [<var>file</var>:][<var>function</var>|<var>line</var>]</code></dt>
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<dd><p>Set a breakpoint at <var>function</var> or <var>line</var> (in <var>file</var>).
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</p>
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</dd>
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<dt><code>run [<var>arglist</var>]</code></dt>
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<dd><p>Start your program (with <var>arglist</var>, if specified).
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</p>
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</dd>
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<dt><code>bt</code></dt>
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<dd><p>Backtrace: display the program stack.
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</p>
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</dd>
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<dt><code>print <var>expr</var></code></dt>
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<dd><p>Display the value of an expression.
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</p>
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</dd>
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<dt><code>c</code></dt>
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<dd><p>Continue running your program (after stopping, e.g. at a breakpoint).
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</p>
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</dd>
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<dt><code>next</code></dt>
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<dd><p>Execute next program line (after stopping); step <em>over</em> any
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function calls in the line.
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</p>
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</dd>
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<dt><code>edit [<var>file</var>:]<var>function</var></code></dt>
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<dd><p>look at the program line where it is presently stopped.
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</p>
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</dd>
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<dt><code>list [<var>file</var>:]<var>function</var></code></dt>
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<dd><p>type the text of the program in the vicinity of where it is presently stopped.
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</p>
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</dd>
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<dt><code>step</code></dt>
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<dd><p>Execute next program line (after stopping); step <em>into</em> any
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function calls in the line.
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</p>
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</dd>
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<dt><code>help [<var>name</var>]</code></dt>
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<dd><p>Show information about <small>GDB</small> command <var>name</var>, or general information
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about using <small>GDB</small>.
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</p>
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</dd>
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<dt><code>quit</code></dt>
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<dt><code>exit</code></dt>
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<dd><p>Exit from <small>GDB</small>.
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</p></dd>
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</dl>
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<p>Any arguments other than options specify an executable
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file and core file (or process ID); that is, the first argument
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encountered with no
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associated option flag is equivalent to a <samp>--se</samp> option, and the second,
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if any, is equivalent to a <samp>-c</samp> option if it’s the name of a file.
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Many options have
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both long and abbreviated forms; both are shown here. The long forms are also
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recognized if you truncate them, so long as enough of the option is
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present to be unambiguous.
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</p>
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<p>The abbreviated forms are shown here with ‘<samp>-</samp>’ and long forms are shown
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with ‘<samp>--</samp>’ to reflect how they are shown in <samp>--help</samp>. However,
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<small>GDB</small> recognizes all of the following conventions for most options:
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</p>
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<dl compact="compact">
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<dt><code>--option=<var>value</var></code></dt>
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<dt><code>--option <var>value</var></code></dt>
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<dt><code>-option=<var>value</var></code></dt>
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<dt><code>-option <var>value</var></code></dt>
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<dt><code>--o=<var>value</var></code></dt>
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<dt><code>--o <var>value</var></code></dt>
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<dt><code>-o=<var>value</var></code></dt>
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<dt><code>-o <var>value</var></code></dt>
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</dl>
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<p>All the options and command line arguments you give are processed
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in sequential order. The order makes a difference when the <samp>-x</samp>
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option is used.
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</p>
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<dl compact="compact">
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<dt><code>--help</code></dt>
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<dt><code>-h</code></dt>
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<dd><p>List all options, with brief explanations.
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</p>
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</dd>
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<dt><code>--symbols=<var>file</var></code></dt>
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<dt><code>-s <var>file</var></code></dt>
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<dd><p>Read symbol table from <var>file</var>.
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</p>
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</dd>
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<dt><code>--write</code></dt>
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<dd><p>Enable writing into executable and core files.
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</p>
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</dd>
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<dt><code>--exec=<var>file</var></code></dt>
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<dt><code>-e <var>file</var></code></dt>
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<dd><p>Use <var>file</var> as the executable file to execute when
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appropriate, and for examining pure data in conjunction with a core
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dump.
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</p>
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</dd>
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<dt><code>--se=<var>file</var></code></dt>
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<dd><p>Read symbol table from <var>file</var> and use it as the executable
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file.
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</p>
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</dd>
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<dt><code>--core=<var>file</var></code></dt>
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<dt><code>-c <var>file</var></code></dt>
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<dd><p>Use <var>file</var> as a core dump to examine.
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</p>
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</dd>
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<dt><code>--command=<var>file</var></code></dt>
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<dt><code>-x <var>file</var></code></dt>
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<dd><p>Execute <small>GDB</small> commands from <var>file</var>.
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</p>
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</dd>
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<dt><code>--eval-command=<var>command</var></code></dt>
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<dt><code>-ex <var>command</var></code></dt>
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<dd><p>Execute given <small>GDB</small> <var>command</var>.
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</p>
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</dd>
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<dt><code>--init-eval-command=<var>command</var></code></dt>
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<dt><code>-iex</code></dt>
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<dd><p>Execute <small>GDB</small> <var>command</var> before loading the inferior.
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</p>
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</dd>
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<dt><code>--directory=<var>directory</var></code></dt>
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<dt><code>-d <var>directory</var></code></dt>
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<dd><p>Add <var>directory</var> to the path to search for source files.
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</p>
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</dd>
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<dt><code>--nh</code></dt>
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<dd><p>Do not execute commands from <samp>~/.config/gdb/gdbinit</samp>,
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<samp>~/.gdbinit</samp>, <samp>~/.config/gdb/gdbearlyinit</samp>, or
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<samp>~/.gdbearlyinit</samp>
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</p>
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</dd>
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<dt><code>--nx</code></dt>
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<dt><code>-n</code></dt>
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<dd><p>Do not execute commands from any <samp>.gdbinit</samp> or
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<samp>.gdbearlyinit</samp> initialization files.
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</p>
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</dd>
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<dt><code>--quiet</code></dt>
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<dt><code>--silent</code></dt>
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<dt><code>-q</code></dt>
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<dd><p>“Quiet”. Do not print the introductory and copyright messages. These
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messages are also suppressed in batch mode.
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</p>
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</dd>
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<dt><code>--batch</code></dt>
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<dd><p>Run in batch mode. Exit with status <code>0</code> after processing all the command
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files specified with <samp>-x</samp> (and <samp>.gdbinit</samp>, if not inhibited).
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Exit with nonzero status if an error occurs in executing the <small>GDB</small>
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commands in the command files.
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</p>
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<p>Batch mode may be useful for running <small>GDB</small> as a filter, for example to
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download and run a program on another computer; in order to make this
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more useful, the message
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</p>
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<div class="smallexample">
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<pre class="smallexample">Program exited normally.
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</pre></div>
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<p>(which is ordinarily issued whenever a program running under <small>GDB</small> control
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terminates) is not issued when running in batch mode.
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</p>
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</dd>
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<dt><code>--batch-silent</code></dt>
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<dd><p>Run in batch mode, just like <samp>--batch</samp>, but totally silent. All <small>GDB</small>
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output is supressed (stderr is unaffected). This is much quieter than
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<samp>--silent</samp> and would be useless for an interactive session.
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</p>
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<p>This is particularly useful when using targets that give ‘<samp>Loading section</samp>’
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messages, for example.
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</p>
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<p>Note that targets that give their output via <small>GDB</small>, as opposed to writing
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directly to <code>stdout</code>, will also be made silent.
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</p>
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</dd>
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<dt><code>--args <var>prog</var> [<var>arglist</var>]</code></dt>
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<dd><p>Change interpretation of command line so that arguments following this
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option are passed as arguments to the inferior. As an example, take
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the following command:
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</p>
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<div class="smallexample">
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<pre class="smallexample">gdb ./a.out -q
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</pre></div>
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<p>It would start <small>GDB</small> with <samp>-q</samp>, not printing the introductory message. On
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the other hand, using:
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</p>
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<div class="smallexample">
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<pre class="smallexample">gdb --args ./a.out -q
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</pre></div>
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<p>starts <small>GDB</small> with the introductory message, and passes the option to the inferior.
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</p>
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</dd>
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<dt><code>--pid=<var>pid</var></code></dt>
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<dd><p>Attach <small>GDB</small> to an already running program, with the PID <var>pid</var>.
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</p>
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</dd>
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<dt><code>--tui</code></dt>
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<dd><p>Open the terminal user interface.
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</p>
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</dd>
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<dt><code>--readnow</code></dt>
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<dd><p>Read all symbols from the given symfile on the first access.
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</p>
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</dd>
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<dt><code>--readnever</code></dt>
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<dd><p>Do not read symbol files.
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</p>
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</dd>
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<dt><code>--dbx</code></dt>
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<dd><p>Run in DBX compatibility mode.
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</p>
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</dd>
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<dt><code>--return-child-result</code></dt>
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<dd><p><small>GDB</small>’s exit code will be the same as the child’s exit code.
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</p>
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</dd>
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<dt><code>--configuration</code></dt>
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<dd><p>Print details about GDB configuration and then exit.
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</p>
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</dd>
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<dt><code>--version</code></dt>
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<dd><p>Print version information and then exit.
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</p>
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</dd>
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<dt><code>--cd=<var>directory</var></code></dt>
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<dd><p>Run <small>GDB</small> using <var>directory</var> as its working directory,
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instead of the current directory.
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</p>
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</dd>
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<dt><code>--data-directory=<var>directory</var></code></dt>
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<dt><code>-D</code></dt>
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<dd><p>Run <small>GDB</small> using <var>directory</var> as its data directory. The data
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directory is where <small>GDB</small> searches for its auxiliary files.
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</p>
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</dd>
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<dt><code>--fullname</code></dt>
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<dt><code>-f</code></dt>
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<dd><p>Emacs sets this option when it runs <small>GDB</small> as a subprocess. It tells
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<small>GDB</small> to output the full file name and line number in a standard,
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recognizable fashion each time a stack frame is displayed (which
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includes each time the program stops). This recognizable format looks
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like two ‘<samp>\032</samp>’ characters, followed by the file name, line number
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and character position separated by colons, and a newline. The
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Emacs-to-<small>GDB</small> interface program uses the two ‘<samp>\032</samp>’
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characters as a signal to display the source code for the frame.
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</p>
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</dd>
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<dt><code>-b <var>baudrate</var></code></dt>
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<dd><p>Set the line speed (baud rate or bits per second) of any serial
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interface used by <small>GDB</small> for remote debugging.
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</p>
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</dd>
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<dt><code>-l <var>timeout</var></code></dt>
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<dd><p>Set timeout, in seconds, for remote debugging.
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</p>
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</dd>
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<dt><code>--tty=<var>device</var></code></dt>
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<dd><p>Run using <var>device</var> for your program’s standard input and output.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="gdbserver-man.html#gdbserver-man" accesskey="n" rel="next">gdbserver man</a>, Up: <a href="Man-Pages.html#Man-Pages" accesskey="u" rel="up">Man Pages</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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