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