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| <h4 class="subsection">E.13.5 The ‘<samp><span class="samp">Ctrl-C</span></samp>’ Message</h4> |
| |
| <p><a name="index-ctrl_002dc-message_002c-in-file_002di_002fo-protocol-3601"></a> |
| If the ‘<samp><span class="samp">Ctrl-C</span></samp>’ flag is set in the <span class="sc">gdb</span> |
| reply packet (see <a href="The-F-Reply-Packet.html#The-F-Reply-Packet">The F Reply Packet</a>), |
| the target should behave as if it had |
| gotten a break message. The meaning for the target is “system call |
| interrupted by <code>SIGINT</code>”. Consequentially, the target should actually stop |
| (as with a break message) and return to <span class="sc">gdb</span> with a <code>T02</code> |
| packet. |
| |
| <p>It's important for the target to know in which |
| state the system call was interrupted. There are two possible cases: |
| |
| <ul> |
| <li>The system call hasn't been performed on the host yet. |
| |
| <li>The system call on the host has been finished. |
| |
| </ul> |
| |
| <p>These two states can be distinguished by the target by the value of the |
| returned <code>errno</code>. If it's the protocol representation of <code>EINTR</code>, the system |
| call hasn't been performed. This is equivalent to the <code>EINTR</code> handling |
| on POSIX systems. In any other case, the target may presume that the |
| system call has been finished — successfully or not — and should behave |
| as if the break message arrived right after the system call. |
| |
| <p><span class="sc">gdb</span> must behave reliably. If the system call has not been called |
| yet, <span class="sc">gdb</span> may send the <code>F</code> reply immediately, setting <code>EINTR</code> as |
| <code>errno</code> in the packet. If the system call on the host has been finished |
| before the user requests a break, the full action must be finished by |
| <span class="sc">gdb</span>. This requires sending <code>M</code> or <code>X</code> packets as necessary. |
| The <code>F</code> packet may only be sent when either nothing has happened |
| or the full action has been completed. |
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