Matheus Tavares Bernardino <quic_mathb...@quicinc.com> writes:
> Hi, Nick.
>
>> Nicholas Piggin <npig...@gmail.com> wrote:
>>
>> On Tue Jul 11, 2023 at 9:03 PM AEST, Matheus Tavares Bernardino wrote:
>> > > Nicholas Piggin <npig...@gmail.com> wrote:
>> > >
>> > > diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
>> > > index 6911b73c07..ce8b42eb15 100644
>> > > --- a/gdbstub/gdbstub.c
>> > > +++ b/gdbstub/gdbstub.c
>> > > @@ -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
>> >
>> > Makes sense to me, but shouldn't we send the stop-reply packet only for
>> > Ctrl+C/0x03?
>>
>> Good question.
>>
>> I think if we get a character here that's not a 3, we're already in
>> trouble, and we eat it so even worse. Since we only send a stop packet
>> back when the vm stops, then if we don't send one now we might never
>> send it. At least if we send one then the client might have some chance
>> to get back to a sane state.
>
> I just noticed now (as I was integrating the latest upstream patches
> with our downstream qemu-system-hexagon) that this causes the
> gdbstub-untimely-packet tcg test to fail.
>
> My first thought was that, if 0x3 is the only valid case where we will
> read a char when the cpu is running, perhaps not issuing the stop-reply
> isn't that bad as GDB would ignore it anyways. E.g. from a `set debug
> remote 1` output:
>
> Sending packet: $qSupported:multiprocess+;swbreak+;hwbreak+;qRelocInsn+;
> fork-events+;vfork-events+;exec-events+;vContSupported+;
> QThreadEvents+;no-resumed+;
> xmlRegisters=i386#6a...
> Packet instead of Ack, ignoring it
>
> So, perhaps, we could do:
>
> diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
> index f123b40ce7..8af066301a 100644
> --- a/gdbstub/gdbstub.c
> +++ b/gdbstub/gdbstub.c
> @@ -2055,8 +2055,9 @@ void gdb_read_byte(uint8_t ch)
> */
> if (ch != 0x03) {
> warn_report("gdbstub: client sent packet while target
> running\n");
This warning seems to be triggering either way, investigating now.
> + } else {
> + gdbserver_state.allow_stop_reply = true;
> }
> - gdbserver_state.allow_stop_reply = true;
> vm_stop(RUN_STATE_PAUSED);
> } else
> #endif
> -- >8 --
>
> Alternatively, since GDB ignores the packet anyways, should we just let
> this be and refactor/remove the test?
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
