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| <h4 class="subsection">20.5.1 What the Stub Can Do for You</h4> |
| |
| <p><a name="index-remote-serial-stub-1424"></a>The debugging stub for your architecture supplies these three |
| subroutines: |
| |
| <dl> |
| <dt><code>set_debug_traps</code><dd><a name="index-set_005fdebug_005ftraps-1425"></a><a name="index-remote-serial-stub_002c-initialization-1426"></a>This routine arranges for <code>handle_exception</code> to run when your |
| program stops. You must call this subroutine explicitly in your |
| program's startup code. |
| |
| <br><dt><code>handle_exception</code><dd><a name="index-handle_005fexception-1427"></a><a name="index-remote-serial-stub_002c-main-routine-1428"></a>This is the central workhorse, but your program never calls it |
| explicitly—the setup code arranges for <code>handle_exception</code> to |
| run when a trap is triggered. |
| |
| <p><code>handle_exception</code> takes control when your program stops during |
| execution (for example, on a breakpoint), and mediates communications |
| with <span class="sc">gdb</span> on the host machine. This is where the communications |
| protocol is implemented; <code>handle_exception</code> acts as the <span class="sc">gdb</span> |
| representative on the target machine. It begins by sending summary |
| information on the state of your program, then continues to execute, |
| retrieving and transmitting any information <span class="sc">gdb</span> needs, until you |
| execute a <span class="sc">gdb</span> command that makes your program resume; at that point, |
| <code>handle_exception</code> returns control to your own code on the target |
| machine. |
| |
| <br><dt><code>breakpoint</code><dd><a name="index-g_t_0040code_007bbreakpoint_007d-subroutine_002c-remote-1429"></a>Use this auxiliary subroutine to make your program contain a |
| breakpoint. Depending on the particular situation, this may be the only |
| way for <span class="sc">gdb</span> to get control. For instance, if your target |
| machine has some sort of interrupt button, you won't need to call this; |
| pressing the interrupt button transfers control to |
| <code>handle_exception</code>—in effect, to <span class="sc">gdb</span>. On some machines, |
| simply receiving characters on the serial port may also trigger a trap; |
| again, in that situation, you don't need to call <code>breakpoint</code> from |
| your own program—simply running ‘<samp><span class="samp">target remote</span></samp>’ from the host |
| <span class="sc">gdb</span> session gets control. |
| |
| <p>Call <code>breakpoint</code> if none of these is true, or if you simply want |
| to make certain your program stops at a predetermined point for the |
| start of your debugging session. |
| </dl> |
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