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| <title>Debugging with GDB: Stop Reply Packets</title> |
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| <a name="Stop-Reply-Packets"></a> |
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| 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> |
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| <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>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> |
| <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 memory 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> |
| </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>. |
| The <var>pid</var> is formatted as a big-endian hex string. |
| </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>. The <var>pid</var> is formatted as a big-endian hex string. |
| </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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