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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: 758370052f ("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>
This commit is contained in:
Nicholas Piggin 2023-07-11 18:59:03 +10:00 committed by Peter Maydell
parent fe6bda58e0
commit 108e8180c6
1 changed files with 11 additions and 2 deletions
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13
gdbstub/gdbstub.c
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@ -2051,8 +2051,17 @@ void gdb_read_byte(uint8_t ch)
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