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261 lines
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<html lang="en">
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<head>
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<title>Stop Reply Packets - Debugging with GDB</title>
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<meta name="description" content="Debugging with GDB">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Remote-Protocol.html#Remote-Protocol" title="Remote Protocol">
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<link rel="prev" href="Packets.html#Packets" title="Packets">
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<link rel="next" href="General-Query-Packets.html#General-Query-Packets" title="General Query Packets">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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(a) The FSF's Back-Cover Text is: ``You are free to copy and modify
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</head>
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<body>
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<div class="node">
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<a name="Stop-Reply-Packets"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="General-Query-Packets.html#General-Query-Packets">General Query Packets</a>,
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Previous: <a rel="previous" accesskey="p" href="Packets.html#Packets">Packets</a>,
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Up: <a rel="up" accesskey="u" href="Remote-Protocol.html#Remote-Protocol">Remote Protocol</a>
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<hr>
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</div>
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<h3 class="section">E.3 Stop Reply Packets</h3>
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<p><a name="index-stop-reply-packets-3481"></a>
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The ‘<samp><span class="samp">C</span></samp>’, ‘<samp><span class="samp">c</span></samp>’, ‘<samp><span class="samp">S</span></samp>’, ‘<samp><span class="samp">s</span></samp>’, ‘<samp><span class="samp">vCont</span></samp>’,
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‘<samp><span class="samp">vAttach</span></samp>’, ‘<samp><span class="samp">vRun</span></samp>’, ‘<samp><span class="samp">vStopped</span></samp>’, and ‘<samp><span class="samp">?</span></samp>’ packets can
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receive any of the below as a reply. Except for ‘<samp><span class="samp">?</span></samp>’
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and ‘<samp><span class="samp">vStopped</span></samp>’, that reply is only returned
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when the target halts. In the below the exact meaning of <dfn>signal
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number</dfn> is defined by the header <samp><span class="file">include/gdb/signals.h</span></samp> in the
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<span class="sc">gdb</span> source code.
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<p>In non-stop mode, the server will simply reply ‘<samp><span class="samp">OK</span></samp>’ to commands
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such as ‘<samp><span class="samp">vCont</span></samp>’; any stop will be the subject of a future
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notification. See <a href="Remote-Non_002dStop.html#Remote-Non_002dStop">Remote Non-Stop</a>.
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<p>As in the description of request packets, we include spaces in the
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reply templates for clarity; these are not part of the reply packet's
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syntax. No <span class="sc">gdb</span> stop reply packet uses spaces to separate its
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components.
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<dl>
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<dt>‘<samp><span class="samp">S </span><var>AA</var></samp>’<dd>The program received signal number <var>AA</var> (a two-digit hexadecimal
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number). This is equivalent to a ‘<samp><span class="samp">T</span></samp>’ response with no
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<var>n</var>:<var>r</var> pairs.
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<br><dt>‘<samp><span class="samp">T </span><var>AA</var> <var>n1</var><span class="samp">:</span><var>r1</var><span class="samp">;</span><var>n2</var><span class="samp">:</span><var>r2</var><span class="samp">;...</span></samp>’<dd><a name="index-g_t_0040samp_007bT_007d-packet-reply-3482"></a>The program received signal number <var>AA</var> (a two-digit hexadecimal
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number). This is equivalent to an ‘<samp><span class="samp">S</span></samp>’ response, except that the
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‘<samp><var>n</var><span class="samp">:</span><var>r</var></samp>’ pairs can carry values of important registers
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and other information directly in the stop reply packet, reducing
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round-trip latency. Single-step and breakpoint traps are reported
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this way. Each ‘<samp><var>n</var><span class="samp">:</span><var>r</var></samp>’ pair is interpreted as follows:
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<ul>
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<li>If <var>n</var> is a hexadecimal number, it is a register number, and the
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corresponding <var>r</var> gives that register's value. The data <var>r</var> is a
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series of bytes in target byte order, with each byte given by a
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two-digit hex number.
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<li>If <var>n</var> is ‘<samp><span class="samp">thread</span></samp>’, then <var>r</var> is the <var>thread-id</var> of
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the stopped thread, as specified in <a href="thread_002did-syntax.html#thread_002did-syntax">thread-id syntax</a>.
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<li>If <var>n</var> is ‘<samp><span class="samp">core</span></samp>’, then <var>r</var> is the hexadecimal number of
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the core on which the stop event was detected.
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<li>If <var>n</var> is a recognized <dfn>stop reason</dfn>, it describes a more
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specific event that stopped the target. The currently defined stop
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reasons are listed below. The <var>aa</var> should be ‘<samp><span class="samp">05</span></samp>’, the trap
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signal. At most one stop reason should be present.
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<li>Otherwise, <span class="sc">gdb</span> should ignore this ‘<samp><var>n</var><span class="samp">:</span><var>r</var></samp>’ pair
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and go on to the next; this allows us to extend the protocol in the
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future.
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</ul>
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<p>The currently defined stop reasons are:
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<dl>
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<dt>‘<samp><span class="samp">watch</span></samp>’<dt>‘<samp><span class="samp">rwatch</span></samp>’<dt>‘<samp><span class="samp">awatch</span></samp>’<dd>The packet indicates a watchpoint hit, and <var>r</var> is the data address, in
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hex.
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<br><dt>‘<samp><span class="samp">syscall_entry</span></samp>’<dt>‘<samp><span class="samp">syscall_return</span></samp>’<dd>The packet indicates a syscall entry or return, and <var>r</var> is the
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syscall number, in hex.
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<p><a name="index-shared-library-events_002c-remote-reply-3483"></a><br><dt>‘<samp><span class="samp">library</span></samp>’<dd>The packet indicates that the loaded libraries have changed.
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<span class="sc">gdb</span> should use ‘<samp><span class="samp">qXfer:libraries:read</span></samp>’ to fetch a new
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list of loaded libraries. The <var>r</var> part is ignored.
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<p><a name="index-replay-log-events_002c-remote-reply-3484"></a><br><dt>‘<samp><span class="samp">replaylog</span></samp>’<dd>The packet indicates that the target cannot continue replaying
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logged execution events, because it has reached the end (or the
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beginning when executing backward) of the log. The value of <var>r</var>
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will be either ‘<samp><span class="samp">begin</span></samp>’ or ‘<samp><span class="samp">end</span></samp>’. See <a href="Reverse-Execution.html#Reverse-Execution">Reverse Execution</a>,
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for more information.
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<br><dt>‘<samp><span class="samp">swbreak</span></samp>’<dd><a name="swbreak-stop-reason"></a>The packet indicates a software breakpoint instruction was executed,
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irrespective of whether it was <span class="sc">gdb</span> that planted the
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breakpoint or the breakpoint is hardcoded in the program. The <var>r</var>
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part must be left empty.
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<p>On some architectures, such as x86, at the architecture level, when a
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breakpoint instruction executes the program counter points at the
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breakpoint address plus an offset. On such targets, the stub is
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responsible for adjusting the PC to point back at the breakpoint
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address.
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<p>This packet should not be sent by default; older <span class="sc">gdb</span> versions
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did not support it. <span class="sc">gdb</span> requests it, by supplying an
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appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The
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remote stub must also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature
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indicating support.
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<p>This packet is required for correct non-stop mode operation.
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<br><dt>‘<samp><span class="samp">hwbreak</span></samp>’<dd>The packet indicates the target stopped for a hardware breakpoint.
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The <var>r</var> part must be left empty.
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<p>The same remarks about ‘<samp><span class="samp">qSupported</span></samp>’ and non-stop mode above
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apply.
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<p><a name="index-fork-events_002c-remote-reply-3485"></a><br><dt>‘<samp><span class="samp">fork</span></samp>’<dd>The packet indicates that <code>fork</code> was called, and <var>r</var>
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is the thread ID of the new child process. Refer to
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<a href="thread_002did-syntax.html#thread_002did-syntax">thread-id syntax</a> for the format of the <var>thread-id</var>
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field. This packet is only applicable to targets that support
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fork events.
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<p>This packet should not be sent by default; older <span class="sc">gdb</span> versions
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did not support it. <span class="sc">gdb</span> requests it, by supplying an
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appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The
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remote stub must also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature
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indicating support.
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<p><a name="index-vfork-events_002c-remote-reply-3486"></a><br><dt>‘<samp><span class="samp">vfork</span></samp>’<dd>The packet indicates that <code>vfork</code> was called, and <var>r</var>
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is the thread ID of the new child process. Refer to
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<a href="thread_002did-syntax.html#thread_002did-syntax">thread-id syntax</a> for the format of the <var>thread-id</var>
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field. This packet is only applicable to targets that support
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vfork events.
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<p>This packet should not be sent by default; older <span class="sc">gdb</span> versions
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did not support it. <span class="sc">gdb</span> requests it, by supplying an
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appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The
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remote stub must also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature
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indicating support.
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<p><a name="index-vforkdone-events_002c-remote-reply-3487"></a><br><dt>‘<samp><span class="samp">vforkdone</span></samp>’<dd>The packet indicates that a child process created by a vfork
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has either called <code>exec</code> or terminated, so that the
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address spaces of the parent and child process are no longer
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shared. The <var>r</var> part is ignored. This packet is only
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applicable to targets that support vforkdone events.
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<p>This packet should not be sent by default; older <span class="sc">gdb</span> versions
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did not support it. <span class="sc">gdb</span> requests it, by supplying an
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appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The
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remote stub must also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature
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indicating support.
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<p><a name="index-exec-events_002c-remote-reply-3488"></a><br><dt>‘<samp><span class="samp">exec</span></samp>’<dd>The packet indicates that <code>execve</code> was called, and <var>r</var>
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is the absolute pathname of the file that was executed, in hex.
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This packet is only applicable to targets that support exec events.
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<p>This packet should not be sent by default; older <span class="sc">gdb</span> versions
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did not support it. <span class="sc">gdb</span> requests it, by supplying an
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appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The
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remote stub must also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature
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indicating support.
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<p><a name="index-thread-create-event_002c-remote-reply-3489"></a><a name="thread-create-event"></a><br><dt>‘<samp><span class="samp">create</span></samp>’<dd>The packet indicates that the thread was just created. The new thread
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is stopped until <span class="sc">gdb</span> sets it running with a resumption packet
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(see <a href="vCont-packet.html#vCont-packet">vCont packet</a>). This packet should not be sent by default;
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<span class="sc">gdb</span> requests it with the <a href="QThreadEvents.html#QThreadEvents">QThreadEvents</a> packet. See
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also the ‘<samp><span class="samp">w</span></samp>’ (see <a href="thread-exit-event.html#thread-exit-event">thread exit event</a>) remote reply below. The
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<var>r</var> part is ignored.
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</dl>
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<br><dt>‘<samp><span class="samp">W </span><var>AA</var></samp>’<dt>‘<samp><span class="samp">W </span><var>AA</var><span class="samp"> ; process:</span><var>pid</var></samp>’<dd>The process exited, and <var>AA</var> is the exit status. This is only
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applicable to certain targets.
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<p>The second form of the response, including the process ID of the
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exited process, can be used only when <span class="sc">gdb</span> has reported
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support for multiprocess protocol extensions; see <a href="multiprocess-extensions.html#multiprocess-extensions">multiprocess extensions</a>. Both <var>AA</var> and <var>pid</var> are formatted as big-endian
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hex strings.
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<br><dt>‘<samp><span class="samp">X </span><var>AA</var></samp>’<dt>‘<samp><span class="samp">X </span><var>AA</var><span class="samp"> ; process:</span><var>pid</var></samp>’<dd>The process terminated with signal <var>AA</var>.
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<p>The second form of the response, including the process ID of the
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terminated process, can be used only when <span class="sc">gdb</span> has reported
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support for multiprocess protocol extensions; see <a href="multiprocess-extensions.html#multiprocess-extensions">multiprocess extensions</a>. Both <var>AA</var> and <var>pid</var> are formatted as big-endian
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hex strings.
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<p><a name="thread-exit-event"></a><a name="index-thread-exit-event_002c-remote-reply-3490"></a><br><dt>‘<samp><span class="samp">w </span><var>AA</var><span class="samp"> ; </span><var>tid</var></samp>’<dd>
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The thread exited, and <var>AA</var> is the exit status. This response
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should not be sent by default; <span class="sc">gdb</span> requests it with the
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<a href="QThreadEvents.html#QThreadEvents">QThreadEvents</a> packet. See also <a href="thread-create-event.html#thread-create-event">thread create event</a> above.
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<var>AA</var> is formatted as a big-endian hex string.
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<br><dt>‘<samp><span class="samp">N</span></samp>’<dd>There are no resumed threads left in the target. In other words, even
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though the process is alive, the last resumed thread has exited. For
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example, say the target process has two threads: thread 1 and thread
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2. The client leaves thread 1 stopped, and resumes thread 2, which
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subsequently exits. At this point, even though the process is still
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alive, and thus no ‘<samp><span class="samp">W</span></samp>’ stop reply is sent, no thread is actually
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executing either. The ‘<samp><span class="samp">N</span></samp>’ stop reply thus informs the client
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that it can stop waiting for stop replies. This packet should not be
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sent by default; older <span class="sc">gdb</span> versions did not support it.
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<span class="sc">gdb</span> requests it, by supplying an appropriate
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‘<samp><span class="samp">qSupported</span></samp>’ feature (see <a href="qSupported.html#qSupported">qSupported</a>). The remote stub must
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also supply the appropriate ‘<samp><span class="samp">qSupported</span></samp>’ feature indicating
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support.
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<br><dt>‘<samp><span class="samp">O </span><var>XX</var><span class="samp">...</span></samp>’<dd>‘<samp><var>XX</var><span class="samp">...</span></samp>’ is hex encoding of <span class="sc">ascii</span> data, to be
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written as the program's console output. This can happen at any time
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while the program is running and the debugger should continue to wait
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for ‘<samp><span class="samp">W</span></samp>’, ‘<samp><span class="samp">T</span></samp>’, etc. This reply is not permitted in non-stop mode.
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<br><dt>‘<samp><span class="samp">F </span><var>call-id</var><span class="samp">,</span><var>parameter</var><span class="samp">...</span></samp>’<dd><var>call-id</var> is the identifier which says which host system call should
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be called. This is just the name of the function. Translation into the
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correct system call is only applicable as it's defined in <span class="sc">gdb</span>.
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See <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension">File-I/O Remote Protocol Extension</a>, for a list of implemented
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system calls.
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<p>‘<samp><var>parameter</var><span class="samp">...</span></samp>’ is a list of parameters as defined for
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this very system call.
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<p>The target replies with this packet when it expects <span class="sc">gdb</span> to
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call a host system call on behalf of the target. <span class="sc">gdb</span> replies
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with an appropriate ‘<samp><span class="samp">F</span></samp>’ packet and keeps up waiting for the next
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reply packet from the target. The latest ‘<samp><span class="samp">C</span></samp>’, ‘<samp><span class="samp">c</span></samp>’, ‘<samp><span class="samp">S</span></samp>’
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or ‘<samp><span class="samp">s</span></samp>’ action is expected to be continued. See <a href="File_002dI_002fO-Remote-Protocol-Extension.html#File_002dI_002fO-Remote-Protocol-Extension">File-I/O Remote Protocol Extension</a>, for more details.
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</dl>
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</body></html>
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