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| <title>Debugging with GDB: Signaling</title> |
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| <a name="Giving-your-Program-a-Signal"></a> |
| <h3 class="section">17.3 Giving your Program a Signal</h3> |
| <a name="index-deliver-a-signal-to-a-program"></a> |
| |
| <dl compact="compact"> |
| <dd><a name="index-signal"></a> |
| </dd> |
| <dt><code>signal <var>signal</var></code></dt> |
| <dd><p>Resume execution where your program is stopped, but immediately give it the |
| signal <var>signal</var>. The <var>signal</var> can be the name or the number of a |
| signal. For example, on many systems <code>signal 2</code> and <code>signal |
| SIGINT</code> are both ways of sending an interrupt signal. |
| </p> |
| <p>Alternatively, if <var>signal</var> is zero, continue execution without |
| giving a signal. This is useful when your program stopped on account of |
| a signal and would ordinarily see the signal when resumed with the |
| <code>continue</code> command; ‘<samp>signal 0</samp>’ causes it to resume without a |
| signal. |
| </p> |
| <p><em>Note:</em> When resuming a multi-threaded program, <var>signal</var> is |
| delivered to the currently selected thread, not the thread that last |
| reported a stop. This includes the situation where a thread was |
| stopped due to a signal. So if you want to continue execution |
| suppressing the signal that stopped a thread, you should select that |
| same thread before issuing the ‘<samp>signal 0</samp>’ command. If you issue |
| the ‘<samp>signal 0</samp>’ command with another thread as the selected one, |
| <small>GDB</small> detects that and asks for confirmation. |
| </p> |
| <p>Invoking the <code>signal</code> command is not the same as invoking the |
| <code>kill</code> utility from the shell. Sending a signal with <code>kill</code> |
| causes <small>GDB</small> to decide what to do with the signal depending on |
| the signal handling tables (see <a href="Signals.html#Signals">Signals</a>). The <code>signal</code> command |
| passes the signal directly to your program. |
| </p> |
| <p><code>signal</code> does not repeat when you press <tt class="key">RET</tt> a second time |
| after executing the command. |
| </p> |
| <a name="index-queue_002dsignal"></a> |
| </dd> |
| <dt><code>queue-signal <var>signal</var></code></dt> |
| <dd><p>Queue <var>signal</var> to be delivered immediately to the current thread |
| when execution of the thread resumes. The <var>signal</var> can be the name or |
| the number of a signal. For example, on many systems <code>signal 2</code> and |
| <code>signal SIGINT</code> are both ways of sending an interrupt signal. |
| The handling of the signal must be set to pass the signal to the program, |
| otherwise <small>GDB</small> will report an error. |
| You can control the handling of signals from <small>GDB</small> with the |
| <code>handle</code> command (see <a href="Signals.html#Signals">Signals</a>). |
| </p> |
| <p>Alternatively, if <var>signal</var> is zero, any currently queued signal |
| for the current thread is discarded and when execution resumes no signal |
| will be delivered. This is useful when your program stopped on account |
| of a signal and would ordinarily see the signal when resumed with the |
| <code>continue</code> command. |
| </p> |
| <p>This command differs from the <code>signal</code> command in that the signal |
| is just queued, execution is not resumed. And <code>queue-signal</code> cannot |
| be used to pass a signal whose handling state has been set to <code>nopass</code> |
| (see <a href="Signals.html#Signals">Signals</a>). |
| </p></dd> |
| </dl> |
| |
| <p>See <a href="Signals.html#stepping-into-signal-handlers">stepping into signal handlers</a>, for information on how stepping |
| commands behave when the thread has a signal queued. |
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