gdbstub: Fix client Ctrl-C handling
The gdb remote protocol has a special interrupt character (0x03) that is
transmitted outside the regular packet processing, and represents a
Ctrl-C pressed in the client. Despite not being a regular packet, it
does expect a regular stop response if the stub successfully stops the
running program.
See: https://sourceware.org/gdb/onlinedocs/gdb/Interrupts.html
Inhibiting the stop reply packet can lead to gdb client hang. So permit
a stop response when receiving a character from gdb that stops the vm.
Additionally, add a warning if that was not a 0x03 character, because
the gdb session is likely to end up getting confused if this happens.
Cc: qemu-stable@nongnu.org
Fixes: 758370052fb ("gdbstub: only send stop-reply packets when allowed to")
Reported-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Message-id: 20230711085903.304496-1-npiggin@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
index 6911b73..ce8b42e 100644
--- a/gdbstub/gdbstub.c
+++ b/gdbstub/gdbstub.c
@@ -2051,8 +2051,17 @@
return;
}
if (runstate_is_running()) {
- /* when the CPU is running, we cannot do anything except stop
- it when receiving a char */
+ /*
+ * When the CPU is running, we cannot do anything except stop
+ * it when receiving a char. This is expected on a Ctrl-C in the
+ * gdb client. Because we are in all-stop mode, gdb sends a
+ * 0x03 byte which is not a usual packet, so we handle it specially
+ * here, but it does expect a stop reply.
+ */
+ if (ch != 0x03) {
+ warn_report("gdbstub: client sent packet while target running\n");
+ }
+ gdbserver_state.allow_stop_reply = true;
vm_stop(RUN_STATE_PAUSED);
} else
#endif
