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<title>Debugging with GDB: In-process Agent</title>
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<a name="In_002dprocess-Agent"></a>
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<div class="header">
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<p>
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Next: <a href="GDB-Bugs.html#GDB-Bugs" accesskey="n" rel="next">GDB Bugs</a>, Previous: <a href="JIT-Interface.html#JIT-Interface" accesskey="p" rel="previous">JIT Interface</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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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<hr>
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<a name="In_002dprocess-Agent-1"></a>
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<h2 class="chapter">30 In-process Agent</h2>
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<a name="index-debugging-agent"></a>
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<p>The traditional debugging model is conceptually low-speed, but works fine,
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because most bugs can be reproduced in debugging-mode execution. However,
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as multi-core or many-core processors are becoming mainstream, and
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multi-threaded programs become more and more popular, there should be more
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and more bugs that only manifest themselves at normal-mode execution, for
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example, thread races, because debugger’s interference with the program’s
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timing may conceal the bugs. On the other hand, in some applications,
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it is not feasible for the debugger to interrupt the program’s execution
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long enough for the developer to learn anything helpful about its behavior.
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If the program’s correctness depends on its real-time behavior, delays
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introduced by a debugger might cause the program to fail, even when the
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code itself is correct. It is useful to be able to observe the program’s
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behavior without interrupting it.
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</p>
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<p>Therefore, traditional debugging model is too intrusive to reproduce
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some bugs. In order to reduce the interference with the program, we can
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reduce the number of operations performed by debugger. The
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<em>In-process Agent</em>, a shared library, is running within the same
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process with inferior, and is able to perform some debugging operations
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itself. As a result, debugger is only involved when necessary, and
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performance of debugging can be improved accordingly. Note that
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interference with program can be reduced but can’t be removed completely,
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because the in-process agent will still stop or slow down the program.
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</p>
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<p>The in-process agent can interpret and execute Agent Expressions
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(see <a href="Agent-Expressions.html#Agent-Expressions">Agent Expressions</a>) during performing debugging operations. The
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agent expressions can be used for different purposes, such as collecting
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data in tracepoints, and condition evaluation in breakpoints.
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</p>
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<a name="Control-Agent"></a><p>You can control whether the in-process agent is used as an aid for
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debugging with the following commands:
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</p>
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<dl compact="compact">
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<dd><a name="index-set-agent-on"></a>
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</dd>
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<dt><code>set agent on</code></dt>
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<dd><p>Causes the in-process agent to perform some operations on behalf of the
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debugger. Just which operations requested by the user will be done
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by the in-process agent depends on the its capabilities. For example,
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if you request to evaluate breakpoint conditions in the in-process agent,
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and the in-process agent has such capability as well, then breakpoint
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conditions will be evaluated in the in-process agent.
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</p>
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<a name="index-set-agent-off"></a>
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</dd>
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<dt><code>set agent off</code></dt>
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<dd><p>Disables execution of debugging operations by the in-process agent. All
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of the operations will be performed by <small>GDB</small>.
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</p>
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<a name="index-show-agent"></a>
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</dd>
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<dt><code>show agent</code></dt>
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<dd><p>Display the current setting of execution of debugging operations by
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the in-process agent.
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</p></dd>
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</dl>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="In_002dprocess-Agent-Protocol.html#In_002dprocess-Agent-Protocol" accesskey="1">In-process Agent Protocol</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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Next: <a href="GDB-Bugs.html#GDB-Bugs" accesskey="n" rel="next">GDB Bugs</a>, Previous: <a href="JIT-Interface.html#JIT-Interface" accesskey="p" rel="previous">JIT Interface</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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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