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  18. <title>Stop Reply Packets (Debugging with GDB)</title>

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  28. <link href="Remote-Protocol.html#Remote-Protocol" rel="up" title="Remote Protocol">

  29. <link href="General-Query-Packets.html#General-Query-Packets" rel="next" title="General Query Packets">

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  61. 

  62. <body lang="en">

  63. <a name="Stop-Reply-Packets"></a>

  64. <div class="header">

  65. <p>

  66. 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> &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>

  67. </div>

  68. <hr>

  69. <a name="Stop-Reply-Packets-1"></a>

  70. <h3 class="section">E.3 Stop Reply Packets</h3>

  71. <a name="index-stop-reply-packets"></a>

  72. 

  73. <p>The &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo;, &lsquo;<samp>s</samp>&rsquo;, &lsquo;<samp>vCont</samp>&rsquo;,

  74. &lsquo;<samp>vAttach</samp>&rsquo;, &lsquo;<samp>vRun</samp>&rsquo;, &lsquo;<samp>vStopped</samp>&rsquo;, and &lsquo;<samp>?</samp>&rsquo; packets can

  75. receive any of the below as a reply.  Except for &lsquo;<samp>?</samp>&rsquo;

  76. and &lsquo;<samp>vStopped</samp>&rsquo;, that reply is only returned

  77. when the target halts.  In the below the exact meaning of <em>signal

  78. number</em> is defined by the header <samp>include/gdb/signals.h</samp> in the

  79. <small>GDB</small> source code.

  80. </p>

  81. <p>In non-stop mode, the server will simply reply &lsquo;<samp>OK</samp>&rsquo; to commands

  82. such as &lsquo;<samp>vCont</samp>&rsquo;; any stop will be the subject of a future

  83. notification.  See <a href="Remote-Non_002dStop.html#Remote-Non_002dStop">Remote Non-Stop</a>.

  84. </p>

  85. <p>As in the description of request packets, we include spaces in the

  86. reply templates for clarity; these are not part of the reply packet&rsquo;s

  87. syntax.  No <small>GDB</small> stop reply packet uses spaces to separate its

  88. components.

  89. </p>

  90. <dl compact="compact">

  91. <dt>&lsquo;<samp>S <var>AA</var></samp>&rsquo;</dt>

  92. <dd><p>The program received signal number <var>AA</var> (a two-digit hexadecimal

  93. number).  This is equivalent to a &lsquo;<samp>T</samp>&rsquo; response with no

  94. <var>n</var>:<var>r</var> pairs.

  95. </p>

  96. </dd>

  97. <dt>&lsquo;<samp>T <var>AA</var> <var>n1</var>:<var>r1</var>;<var>n2</var>:<var>r2</var>;&hellip;</samp>&rsquo;</dt>

  98. <dd><a name="index-T-packet-reply"></a>

  99. <p>The program received signal number <var>AA</var> (a two-digit hexadecimal

  100. number).  This is equivalent to an &lsquo;<samp>S</samp>&rsquo; response, except that the

  101. &lsquo;<samp><var>n</var>:<var>r</var></samp>&rsquo; pairs can carry values of important registers

  102. and other information directly in the stop reply packet, reducing

  103. round-trip latency.  Single-step and breakpoint traps are reported

  104. this way.  Each &lsquo;<samp><var>n</var>:<var>r</var></samp>&rsquo; pair is interpreted as follows:

  105. </p>

  106. <ul>

  107. <li> If <var>n</var> is a hexadecimal number, it is a register number, and the

  108. corresponding <var>r</var> gives that register&rsquo;s value.  The data <var>r</var> is a

  109. series of bytes in target byte order, with each byte given by a

  110. two-digit hex number.

  111. 

  112. </li><li> If <var>n</var> is &lsquo;<samp>thread</samp>&rsquo;, then <var>r</var> is the <var>thread-id</var> of

  113. the stopped thread, as specified in <a href="Packets.html#thread_002did-syntax">thread-id syntax</a>.

  114. 

  115. </li><li> If <var>n</var> is &lsquo;<samp>core</samp>&rsquo;, then <var>r</var> is the hexadecimal number of

  116. the core on which the stop event was detected.

  117. 

  118. </li><li> If <var>n</var> is a recognized <em>stop reason</em>, it describes a more

  119. specific event that stopped the target.  The currently defined stop

  120. reasons are listed below.  The <var>aa</var> should be &lsquo;<samp>05</samp>&rsquo;, the trap

  121. signal.  At most one stop reason should be present.

  122. 

  123. </li><li> Otherwise, <small>GDB</small> should ignore this &lsquo;<samp><var>n</var>:<var>r</var></samp>&rsquo; pair

  124. and go on to the next; this allows us to extend the protocol in the

  125. future.

  126. </li></ul>

  127. 

  128. <p>The currently defined stop reasons are:

  129. </p>

  130. <dl compact="compact">

  131. <dt>&lsquo;<samp>watch</samp>&rsquo;</dt>

  132. <dt>&lsquo;<samp>rwatch</samp>&rsquo;</dt>

  133. <dt>&lsquo;<samp>awatch</samp>&rsquo;</dt>

  134. <dd><p>The packet indicates a watchpoint hit, and <var>r</var> is the data address, in

  135. hex.

  136. </p>

  137. </dd>

  138. <dt>&lsquo;<samp>syscall_entry</samp>&rsquo;</dt>

  139. <dt>&lsquo;<samp>syscall_return</samp>&rsquo;</dt>

  140. <dd><p>The packet indicates a syscall entry or return, and <var>r</var> is the

  141. syscall number, in hex.

  142. </p>

  143. <a name="index-shared-library-events_002c-remote-reply"></a>

  144. </dd>

  145. <dt>&lsquo;<samp>library</samp>&rsquo;</dt>

  146. <dd><p>The packet indicates that the loaded libraries have changed.

  147. <small>GDB</small> should use &lsquo;<samp>qXfer:libraries:read</samp>&rsquo; to fetch a new

  148. list of loaded libraries.  The <var>r</var> part is ignored.

  149. </p>

  150. <a name="index-replay-log-events_002c-remote-reply"></a>

  151. </dd>

  152. <dt>&lsquo;<samp>replaylog</samp>&rsquo;</dt>

  153. <dd><p>The packet indicates that the target cannot continue replaying 

  154. logged execution events, because it has reached the end (or the

  155. beginning when executing backward) of the log.  The value of <var>r</var>

  156. will be either &lsquo;<samp>begin</samp>&rsquo; or &lsquo;<samp>end</samp>&rsquo;.  See <a href="Reverse-Execution.html#Reverse-Execution">Reverse Execution</a>, 

  157. for more information.

  158. </p>

  159. </dd>

  160. <dt>&lsquo;<samp>swbreak</samp>&rsquo;</dt>

  161. <dd><a name="swbreak-stop-reason"></a><p>The packet indicates a software breakpoint instruction was executed,

  162. irrespective of whether it was <small>GDB</small> that planted the

  163. breakpoint or the breakpoint is hardcoded in the program.  The <var>r</var>

  164. part must be left empty.

  165. </p>

  166. <p>On some architectures, such as x86, at the architecture level, when a

  167. breakpoint instruction executes the program counter points at the

  168. breakpoint address plus an offset.  On such targets, the stub is

  169. responsible for adjusting the PC to point back at the breakpoint

  170. address.

  171. </p>

  172. <p>This packet should not be sent by default; older <small>GDB</small> versions

  173. did not support it.  <small>GDB</small> requests it, by supplying an

  174. appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The

  175. remote stub must also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature

  176. indicating support.

  177. </p>

  178. <p>This packet is required for correct non-stop mode operation.

  179. </p>

  180. </dd>

  181. <dt>&lsquo;<samp>hwbreak</samp>&rsquo;</dt>

  182. <dd><p>The packet indicates the target stopped for a hardware breakpoint.

  183. The <var>r</var> part must be left empty.

  184. </p>

  185. <p>The same remarks about &lsquo;<samp>qSupported</samp>&rsquo; and non-stop mode above

  186. apply.

  187. </p>

  188. <a name="index-fork-events_002c-remote-reply"></a>

  189. </dd>

  190. <dt>&lsquo;<samp>fork</samp>&rsquo;</dt>

  191. <dd><p>The packet indicates that <code>fork</code> was called, and <var>r</var>

  192. is the thread ID of the new child process.  Refer to

  193. <a href="Packets.html#thread_002did-syntax">thread-id syntax</a> for the format of the <var>thread-id</var>

  194. field.  This packet is only applicable to targets that support

  195. fork events.

  196. </p>

  197. <p>This packet should not be sent by default; older <small>GDB</small> versions

  198. did not support it.  <small>GDB</small> requests it, by supplying an

  199. appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The

  200. remote stub must also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature

  201. indicating support.

  202. </p>

  203. <a name="index-vfork-events_002c-remote-reply"></a>

  204. </dd>

  205. <dt>&lsquo;<samp>vfork</samp>&rsquo;</dt>

  206. <dd><p>The packet indicates that <code>vfork</code> was called, and <var>r</var>

  207. is the thread ID of the new child process. Refer to

  208. <a href="Packets.html#thread_002did-syntax">thread-id syntax</a> for the format of the <var>thread-id</var>

  209. field.  This packet is only applicable to targets that support

  210. vfork events.

  211. </p>

  212. <p>This packet should not be sent by default; older <small>GDB</small> versions

  213. did not support it.  <small>GDB</small> requests it, by supplying an

  214. appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The

  215. remote stub must also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature

  216. indicating support.

  217. </p>

  218. <a name="index-vforkdone-events_002c-remote-reply"></a>

  219. </dd>

  220. <dt>&lsquo;<samp>vforkdone</samp>&rsquo;</dt>

  221. <dd><p>The packet indicates that a child process created by a vfork

  222. has either called <code>exec</code> or terminated, so that the

  223. address spaces of the parent and child process are no longer

  224. shared. The <var>r</var> part is ignored.  This packet is only

  225. applicable to targets that support vforkdone events.

  226. </p>

  227. <p>This packet should not be sent by default; older <small>GDB</small> versions

  228. did not support it.  <small>GDB</small> requests it, by supplying an

  229. appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The

  230. remote stub must also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature

  231. indicating support.

  232. </p>

  233. <a name="index-exec-events_002c-remote-reply"></a>

  234. </dd>

  235. <dt>&lsquo;<samp>exec</samp>&rsquo;</dt>

  236. <dd><p>The packet indicates that <code>execve</code> was called, and <var>r</var>

  237. is the absolute pathname of the file that was executed, in hex.

  238. This packet is only applicable to targets that support exec events.

  239. </p>

  240. <p>This packet should not be sent by default; older <small>GDB</small> versions

  241. did not support it.  <small>GDB</small> requests it, by supplying an

  242. appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The

  243. remote stub must also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature

  244. indicating support.

  245. </p>

  246. <a name="index-thread-create-event_002c-remote-reply"></a>

  247. <a name="thread-create-event"></a></dd>

  248. <dt>&lsquo;<samp>create</samp>&rsquo;</dt>

  249. <dd><p>The packet indicates that the thread was just created.  The new thread

  250. is stopped until <small>GDB</small> sets it running with a resumption packet

  251. (see <a href="Packets.html#vCont-packet">vCont packet</a>).  This packet should not be sent by default;

  252. <small>GDB</small> requests it with the <a href="General-Query-Packets.html#QThreadEvents">QThreadEvents</a> packet.  See

  253. also the &lsquo;<samp>w</samp>&rsquo; (see <a href="#thread-exit-event">thread exit event</a>) remote reply below.  The

  254. <var>r</var> part is ignored.

  255. </p>

  256. </dd>

  257. </dl>

  258. 

  259. </dd>

  260. <dt>&lsquo;<samp>W <var>AA</var></samp>&rsquo;</dt>

  261. <dt>&lsquo;<samp>W <var>AA</var> ; process:<var>pid</var></samp>&rsquo;</dt>

  262. <dd><p>The process exited, and <var>AA</var> is the exit status.  This is only

  263. applicable to certain targets.

  264. </p>

  265. <p>The second form of the response, including the process ID of the

  266. exited process, can be used only when <small>GDB</small> has reported

  267. 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

  268. hex strings.

  269. </p>

  270. </dd>

  271. <dt>&lsquo;<samp>X <var>AA</var></samp>&rsquo;</dt>

  272. <dt>&lsquo;<samp>X <var>AA</var> ; process:<var>pid</var></samp>&rsquo;</dt>

  273. <dd><p>The process terminated with signal <var>AA</var>.

  274. </p>

  275. <p>The second form of the response, including the process ID of the

  276. terminated process, can be used only when <small>GDB</small> has reported

  277. 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

  278. hex strings.

  279. </p>

  280. <a name="thread-exit-event"></a><a name="index-thread-exit-event_002c-remote-reply"></a>

  281. </dd>

  282. <dt>&lsquo;<samp>w <var>AA</var> ; <var>tid</var></samp>&rsquo;</dt>

  283. <dd>

  284. <p>The thread exited, and <var>AA</var> is the exit status.  This response

  285. should not be sent by default; <small>GDB</small> requests it with the

  286. <a href="General-Query-Packets.html#QThreadEvents">QThreadEvents</a> packet.  See also <a href="#thread-create-event">thread create event</a> above.

  287. <var>AA</var> is formatted as a big-endian hex string.

  288. </p>

  289. </dd>

  290. <dt>&lsquo;<samp>N</samp>&rsquo;</dt>

  291. <dd><p>There are no resumed threads left in the target.  In other words, even

  292. though the process is alive, the last resumed thread has exited.  For

  293. example, say the target process has two threads: thread 1 and thread

  294. 2.  The client leaves thread 1 stopped, and resumes thread 2, which

  295. subsequently exits.  At this point, even though the process is still

  296. alive, and thus no &lsquo;<samp>W</samp>&rsquo; stop reply is sent, no thread is actually

  297. executing either.  The &lsquo;<samp>N</samp>&rsquo; stop reply thus informs the client

  298. that it can stop waiting for stop replies.  This packet should not be

  299. sent by default; older <small>GDB</small> versions did not support it.

  300. <small>GDB</small> requests it, by supplying an appropriate

  301. &lsquo;<samp>qSupported</samp>&rsquo; feature (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).  The remote stub must

  302. also supply the appropriate &lsquo;<samp>qSupported</samp>&rsquo; feature indicating

  303. support.

  304. </p>

  305. </dd>

  306. <dt>&lsquo;<samp>O <var>XX</var>&hellip;</samp>&rsquo;</dt>

  307. <dd><p>&lsquo;<samp><var>XX</var>&hellip;</samp>&rsquo; is hex encoding of <small>ASCII</small> data, to be

  308. written as the program&rsquo;s console output.  This can happen at any time

  309. while the program is running and the debugger should continue to wait

  310. for &lsquo;<samp>W</samp>&rsquo;, &lsquo;<samp>T</samp>&rsquo;, etc.  This reply is not permitted in non-stop mode.

  311. </p>

  312. </dd>

  313. <dt>&lsquo;<samp>F <var>call-id</var>,<var>parameter</var>&hellip;</samp>&rsquo;</dt>

  314. <dd><p><var>call-id</var> is the identifier which says which host system call should

  315. be called.  This is just the name of the function.  Translation into the

  316. correct system call is only applicable as it&rsquo;s defined in <small>GDB</small>.

  317. 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

  318. system calls.

  319. </p>

  320. <p>&lsquo;<samp><var>parameter</var>&hellip;</samp>&rsquo; is a list of parameters as defined for

  321. this very system call.

  322. </p>

  323. <p>The target replies with this packet when it expects <small>GDB</small> to

  324. call a host system call on behalf of the target.  <small>GDB</small> replies

  325. with an appropriate &lsquo;<samp>F</samp>&rsquo; packet and keeps up waiting for the next

  326. reply packet from the target.  The latest &lsquo;<samp>C</samp>&rsquo;, &lsquo;<samp>c</samp>&rsquo;, &lsquo;<samp>S</samp>&rsquo;

  327. or &lsquo;<samp>s</samp>&rsquo; 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.

  328. </p>

  329. </dd>

  330. </dl>

  331. 

  332. <hr>

  333. <div class="header">

  334. <p>

  335. 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> &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>

  336. </div>

  337. 

  338. 

  339. 

  340. </body>

  341. </html>