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| <h2 class="chapter">13 Tracepoints</h2> |
| |
| <!-- This chapter is based on the documentation written by Michael --> |
| <!-- Snyder, David Taylor, Jim Blandy, and Elena Zannoni. --> |
| <p><a name="index-tracepoints-680"></a>In some applications, it is not feasible for the debugger to interrupt |
| the program's execution long enough for the developer to learn |
| anything helpful about its behavior. If the program's correctness |
| depends on its real-time behavior, delays introduced by a debugger |
| might cause the program to change its behavior drastically, or perhaps |
| fail, even when the code itself is correct. It is useful to be able |
| to observe the program's behavior without interrupting it. |
| |
| <p>Using <span class="sc">gdb</span>'s <code>trace</code> and <code>collect</code> commands, you can |
| specify locations in the program, called <dfn>tracepoints</dfn>, and |
| arbitrary expressions to evaluate when those tracepoints are reached. |
| Later, using the <code>tfind</code> command, you can examine the values |
| those expressions had when the program hit the tracepoints. The |
| expressions may also denote objects in memory—structures or arrays, |
| for example—whose values <span class="sc">gdb</span> should record; while visiting |
| a particular tracepoint, you may inspect those objects as if they were |
| in memory at that moment. However, because <span class="sc">gdb</span> records these |
| values without interacting with you, it can do so quickly and |
| unobtrusively, hopefully not disturbing the program's behavior. |
| |
| <p>The tracepoint facility is currently available only for remote |
| targets. See <a href="Targets.html#Targets">Targets</a>. In addition, your remote target must know |
| how to collect trace data. This functionality is implemented in the |
| remote stub; however, none of the stubs distributed with <span class="sc">gdb</span> |
| support tracepoints as of this writing. The format of the remote |
| packets used to implement tracepoints are described in <a href="Tracepoint-Packets.html#Tracepoint-Packets">Tracepoint Packets</a>. |
| |
| <p>It is also possible to get trace data from a file, in a manner reminiscent |
| of corefiles; you specify the filename, and use <code>tfind</code> to search |
| through the file. See <a href="Trace-Files.html#Trace-Files">Trace Files</a>, for more details. |
| |
| <p>This chapter describes the tracepoint commands and features. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Set-Tracepoints.html#Set-Tracepoints">Set Tracepoints</a> |
| <li><a accesskey="2" href="Analyze-Collected-Data.html#Analyze-Collected-Data">Analyze Collected Data</a> |
| <li><a accesskey="3" href="Tracepoint-Variables.html#Tracepoint-Variables">Tracepoint Variables</a> |
| <li><a accesskey="4" href="Trace-Files.html#Trace-Files">Trace Files</a> |
| </ul> |
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