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<title>Debugging with GDB: Stub Contents</title>
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<p>
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Next: <a href="Bootstrapping.html#Bootstrapping" accesskey="n" rel="next">Bootstrapping</a>, Up: <a href="Remote-Stub.html#Remote-Stub" accesskey="u" rel="up">Remote Stub</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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<a name="What-the-Stub-Can-Do-for-You"></a>
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<h4 class="subsection">20.5.1 What the Stub Can Do for You</h4>
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<a name="index-remote-serial-stub"></a>
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<p>The debugging stub for your architecture supplies these three
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subroutines:
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</p>
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<dl compact="compact">
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<dt><code>set_debug_traps</code></dt>
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<dd><a name="index-set_005fdebug_005ftraps"></a>
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<a name="index-remote-serial-stub_002c-initialization"></a>
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<p>This routine arranges for <code>handle_exception</code> to run when your
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program stops. You must call this subroutine explicitly in your
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program’s startup code.
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</p>
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</dd>
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<dt><code>handle_exception</code></dt>
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<dd><a name="index-handle_005fexception"></a>
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<a name="index-remote-serial-stub_002c-main-routine"></a>
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<p>This is the central workhorse, but your program never calls it
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explicitly—the setup code arranges for <code>handle_exception</code> to
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run when a trap is triggered.
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</p>
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<p><code>handle_exception</code> takes control when your program stops during
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execution (for example, on a breakpoint), and mediates communications
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with <small>GDB</small> on the host machine. This is where the communications
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protocol is implemented; <code>handle_exception</code> acts as the <small>GDB</small>
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representative on the target machine. It begins by sending summary
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information on the state of your program, then continues to execute,
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retrieving and transmitting any information <small>GDB</small> needs, until you
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execute a <small>GDB</small> command that makes your program resume; at that point,
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<code>handle_exception</code> returns control to your own code on the target
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machine.
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</p>
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</dd>
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<dt><code>breakpoint</code></dt>
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<dd><a name="index-breakpoint-subroutine_002c-remote"></a>
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<p>Use this auxiliary subroutine to make your program contain a
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breakpoint. Depending on the particular situation, this may be the only
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way for <small>GDB</small> to get control. For instance, if your target
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machine has some sort of interrupt button, you won’t need to call this;
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pressing the interrupt button transfers control to
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<code>handle_exception</code>—in effect, to <small>GDB</small>. On some machines,
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simply receiving characters on the serial port may also trigger a trap;
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again, in that situation, you don’t need to call <code>breakpoint</code> from
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your own program—simply running ‘<samp>target remote</samp>’ from the host
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<small>GDB</small> session gets control.
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</p>
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<p>Call <code>breakpoint</code> if none of these is true, or if you simply want
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to make certain your program stops at a predetermined point for the
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start of your debugging session.
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</p></dd>
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</dl>
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Next: <a href="Bootstrapping.html#Bootstrapping" accesskey="n" rel="next">Bootstrapping</a>, Up: <a href="Remote-Stub.html#Remote-Stub" accesskey="u" rel="up">Remote Stub</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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