| Message ID | 20230623035304.279833-1-npiggin@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | gdbstub: Permit reverse step/break to provide stop response | expand |
> Nicholas Piggin <npiggin@gmail.com> wrote: > > The final part of the reverse step and break handling is to bring > the machine back to a debug stop state. gdb expects a response. > > A gdb 'rsi' command hangs forever because the gdbstub filters out > the response (also observable with reverse_debugging.py avocado > tests). > > Fix by setting allow_stop_reply for the gdb backward packets. Ah, it's interesting that [1] doesn't include 'bc' and 'bs' in the list of cmds that may respond with a stop-reply packet: "The 'C', 'c', 'S', 's', 'vCont', 'vAttach', 'vRun', 'vStopped', and '?' packets can receive any of the below as a reply." But their definitions at [2] do say the following: 'bc' (and 'bc') [...] Reply: See Stop Reply Packets, for the reply specifications. So I guess the list from [1] is not exhaustive. Anyway, thanks for the fix! Acked-by: Matheus Tavares Bernardino <quic_mathbern@quicinc.com> [1]: https://sourceware.org/gdb/onlinedocs/gdb/Stop-Reply-Packets.html#Stop-Reply-Packets [2]: https://sourceware.org/gdb/onlinedocs/gdb/Packets.html#Packets
Nicholas Piggin <npiggin@gmail.com> writes: > The final part of the reverse step and break handling is to bring > the machine back to a debug stop state. gdb expects a response. > > A gdb 'rsi' command hangs forever because the gdbstub filters out > the response (also observable with reverse_debugging.py avocado > tests). > > Fix by setting allow_stop_reply for the gdb backward packets. > > Fixes: 758370052fb ("gdbstub: only send stop-reply packets when allowed to") > Cc: qemu-stable@nongnu.org > Cc: Matheus Tavares Bernardino <quic_mathbern@quicinc.com> > Cc: Alex Bennée <alex.bennee@linaro.org> > Cc: Taylor Simpson <tsimpson@quicinc.com> > Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Queued to gdbstub/next, thanks.
On Fri, 23 Jun 2023 at 13:19, Matheus Tavares Bernardino <quic_mathbern@quicinc.com> wrote: > > > Nicholas Piggin <npiggin@gmail.com> wrote: > > > > The final part of the reverse step and break handling is to bring > > the machine back to a debug stop state. gdb expects a response. > > > > A gdb 'rsi' command hangs forever because the gdbstub filters out > > the response (also observable with reverse_debugging.py avocado > > tests). > > > > Fix by setting allow_stop_reply for the gdb backward packets. > > Ah, it's interesting that [1] doesn't include 'bc' and 'bs' in the list > of cmds that may respond with a stop-reply packet: > > "The 'C', 'c', 'S', 's', 'vCont', 'vAttach', 'vRun', 'vStopped', and > '?' packets can receive any of the below as a reply." > > But their definitions at [2] do say the following: > > 'bc' (and 'bc') > [...] > Reply: See Stop Reply Packets, for the reply specifications. > > So I guess the list from [1] is not exhaustive. Anyway, thanks for the > fix! That looks like it's probably a gdb docs bug (forgetting to update that list when the bc/bs packets were added); we should probably report that to upstream gdb. thanks -- PMM
Peter Maydell <peter.maydell@linaro.org> wrote: > > On Fri, 23 Jun 2023 at 13:19, Matheus Tavares Bernardino <quic_mathbern@quicinc.com> wrote: > > > > Ah, it's interesting that [1] doesn't include 'bc' and 'bs' in the list > > of cmds that may respond with a stop-reply packet: > > > > "The 'C', 'c', 'S', 's', 'vCont', 'vAttach', 'vRun', 'vStopped', and > > '?' packets can receive any of the below as a reply." > > > > But their definitions at [2] do say the following: > > > > 'bc' (and 'bc') > > [...] > > Reply: See Stop Reply Packets, for the reply specifications. > > > > So I guess the list from [1] is not exhaustive. Anyway, thanks for the > > fix! > > That looks like it's probably a gdb docs bug (forgetting to > update that list when the bc/bs packets were added); we > should probably report that to upstream gdb. Good idea, done: https://sourceware.org/pipermail/gdb/2023-June/050804.html
diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c index be18568d0a..9496d7b175 100644 --- a/gdbstub/gdbstub.c +++ b/gdbstub/gdbstub.c @@ -1814,6 +1814,7 @@ static int gdb_handle_packet(const char *line_buf) .handler = handle_backward, .cmd = "b", .cmd_startswith = 1, + .allow_stop_reply = true, .schema = "o0" }; cmd_parser = &backward_cmd_desc;
The final part of the reverse step and break handling is to bring the machine back to a debug stop state. gdb expects a response. A gdb 'rsi' command hangs forever because the gdbstub filters out the response (also observable with reverse_debugging.py avocado tests). Fix by setting allow_stop_reply for the gdb backward packets. Fixes: 758370052fb ("gdbstub: only send stop-reply packets when allowed to") Cc: qemu-stable@nongnu.org Cc: Matheus Tavares Bernardino <quic_mathbern@quicinc.com> Cc: Alex Bennée <alex.bennee@linaro.org> Cc: Taylor Simpson <tsimpson@quicinc.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- gdbstub/gdbstub.c | 1 + 1 file changed, 1 insertion(+)