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