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<title>Debugging with GDB: The Ctrl-C Message</title>

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<a name="The-Ctrl_002dC-Message"></a>
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Next: <a href="Console-I_002fO.html#Console-I_002fO" accesskey="n" rel="next">Console I/O</a>, Previous: <a href="The-F-Reply-Packet.html#The-F-Reply-Packet" accesskey="p" rel="prev">The F Reply Packet</a>, Up: <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension" accesskey="u" rel="up">File-I/O Remote Protocol Extension</a> &nbsp; [<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="The-Ctrl_002dC-Message-1"></a>
<h4 class="subsection">E.13.5 The &lsquo;<samp>Ctrl-C</samp>&rsquo; Message</h4>
<a name="index-ctrl_002dc-message_002c-in-file_002di_002fo-protocol"></a>

<p>If the &lsquo;<samp>Ctrl-C</samp>&rsquo; flag is set in the <small>GDB</small>
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 <small>GDB</small> with a <code>T02</code>
packet.
</p>
<p>It&rsquo;s important for the target to know in which
state the system call was interrupted.  There are two possible cases:
</p>
<ul>
<li> The system call hasn&rsquo;t been performed on the host yet.

</li><li> The system call on the host has been finished.

</li></ul>

<p>These two states can be distinguished by the target by the value of the
returned <code>errno</code>.  If it&rsquo;s the protocol representation of <code>EINTR</code>, the system
call hasn&rsquo;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>
<p><small>GDB</small> must behave reliably.  If the system call has not been called
yet, <small>GDB</small> 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
<small>GDB</small>.  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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