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<h4 class="subsection">D.14.5 The &lsquo;<samp><span class="samp">Ctrl-C</span></samp>&rsquo; Message</h4>

<p><a name="index-ctrl_002dc-message_002c-in-file_002di_002fo-protocol-2501"></a>
If the &lsquo;<samp><span class="samp">Ctrl-C</span></samp>&rsquo; 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 &ldquo;system call
interrupted by <code>SIGINT</code>&rdquo;.  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 &mdash; successfully or not &mdash; 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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