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- <a name="Remote-Non_002dStop"></a>
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- <p>
- Next: <a href="Packet-Acknowledgment.html#Packet-Acknowledgment" accesskey="n" rel="next">Packet Acknowledgment</a>, Previous: <a href="Notification-Packets.html#Notification-Packets" accesskey="p" rel="prev">Notification 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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- <a name="Remote-Protocol-Support-for-Non_002dStop-Mode"></a>
- <h3 class="section">E.10 Remote Protocol Support for Non-Stop Mode</h3>
-
- <p><small>GDB</small>’s remote protocol supports non-stop debugging of
- multi-threaded programs, as described in <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>. If the stub
- supports non-stop mode, it should report that to <small>GDB</small> by including
- ‘<samp>QNonStop+</samp>’ in its ‘<samp>qSupported</samp>’ response (see <a href="General-Query-Packets.html#qSupported">qSupported</a>).
- </p>
- <p><small>GDB</small> typically sends a ‘<samp>QNonStop</samp>’ packet only when
- establishing a new connection with the stub. Entering non-stop mode
- does not alter the state of any currently-running threads, but targets
- must stop all threads in any already-attached processes when entering
- all-stop mode. <small>GDB</small> uses the ‘<samp>?</samp>’ packet as necessary to
- probe the target state after a mode change.
- </p>
- <p>In non-stop mode, when an attached process encounters an event that
- would otherwise be reported with a stop reply, it uses the
- asynchronous notification mechanism (see <a href="Notification-Packets.html#Notification-Packets">Notification Packets</a>) to
- inform <small>GDB</small>. In contrast to all-stop mode, where all threads
- in all processes are stopped when a stop reply is sent, in non-stop
- mode only the thread reporting the stop event is stopped. That is,
- when reporting a ‘<samp>S</samp>’ or ‘<samp>T</samp>’ response to indicate completion
- of a step operation, hitting a breakpoint, or a fault, only the
- affected thread is stopped; any other still-running threads continue
- to run. When reporting a ‘<samp>W</samp>’ or ‘<samp>X</samp>’ response, all running
- threads belonging to other attached processes continue to run.
- </p>
- <p>In non-stop mode, the target shall respond to the ‘<samp>?</samp>’ packet as
- follows. First, any incomplete stop reply notification/‘<samp>vStopped</samp>’
- sequence in progress is abandoned. The target must begin a new
- sequence reporting stop events for all stopped threads, whether or not
- it has previously reported those events to <small>GDB</small>. The first
- stop reply is sent as a synchronous reply to the ‘<samp>?</samp>’ packet, and
- subsequent stop replies are sent as responses to ‘<samp>vStopped</samp>’ packets
- using the mechanism described above. The target must not send
- asynchronous stop reply notifications until the sequence is complete.
- If all threads are running when the target receives the ‘<samp>?</samp>’ packet,
- or if the target is not attached to any process, it shall respond
- ‘<samp>OK</samp>’.
- </p>
- <p>If the stub supports non-stop mode, it should also support the
- ‘<samp>swbreak</samp>’ stop reason if software breakpoints are supported, and
- the ‘<samp>hwbreak</samp>’ stop reason if hardware breakpoints are supported
- (see <a href="Stop-Reply-Packets.html#swbreak-stop-reason">swbreak stop reason</a>). This is because given the asynchronous
- nature of non-stop mode, between the time a thread hits a breakpoint
- and the time the event is finally processed by <small>GDB</small>, the
- breakpoint may have already been removed from the target. Due to
- this, <small>GDB</small> needs to be able to tell whether a trap stop was
- caused by a delayed breakpoint event, which should be ignored, as
- opposed to a random trap signal, which should be reported to the user.
- Note the ‘<samp>swbreak</samp>’ feature implies that the target is responsible
- for adjusting the PC when a software breakpoint triggers, if
- necessary, such as on the x86 architecture.
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- Next: <a href="Packet-Acknowledgment.html#Packet-Acknowledgment" accesskey="n" rel="next">Packet Acknowledgment</a>, Previous: <a href="Notification-Packets.html#Notification-Packets" accesskey="p" rel="prev">Notification 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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