Re: [for-5.0 PATCH 00/11] Support for reverse debugging with GDB

["Alex Bennée" <alex.bennee@linaro.org>]

(looping the list back in)

Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:

>> From: Alex Bennée [mailto:alex.bennee@linaro.org]
>> Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:
>> 
>> >> From: Markus Armbruster [mailto:armbru@redhat.com]
>> >> Kevin Wolf <kwolf@redhat.com> writes:
>> >>
>> >> > Am 09.01.2020 um 07:13 hat Pavel Dovgalyuk geschrieben:
>> >> >> Ping.
>> >> >
>> >> > I think you have my Acked-by for the block-related patches in this
>> >> > series now. If I missed something, please let me know.
>> >>
>> >> Pavel, whom are you nudging to do what?
>> >
>> > I'm not sure.
>> > My prior patches for record/replay were pulled by Paolo.
>> > But reverse debugging is more like a modification of things,
>> > and not a completely new subsystem.
>> > Everything but gdbstub was already acked by the maintainers.
>> 
>> I'm having a look at the series now. What would help is if we can have
>> some sort of test case to ensure expected behaviour is protected. We
>> have a basic smoke test for record/replay and my gdbstub series:
>> 
>>   https://github.com/stsquad/qemu/tree/gdbstub/sve-registers-v5
>> 
>> introduces some infrastructure for testing thing via gdbstub. The main
>> thing needed now is some sort of gdb capability test to ensure the gdb
>> we are using supports whatever extensions it needs to work.
>
> The smoke test may be rather easy:
> 1. Execute qemu record with qcow2 image and rrsnapshot
> 2. Start qemu replay with -S
> 3. Connect gdb to qemu
> 4. stepi
> 5. break $pc
> 6. Save pc to X
> 7. stepi 10
> 8. Save pc to Y
> 9. stepi
> 10. reverse-stepi
> 11. pc should be Y
> 12. reverse-continue
> 13. pc should be X
>
> Is it possible with your infrastructure?

I think so - even if the reverse step instructions are not in the python
API the script can always do:

 gdb.parse_and_eval("command")

The main thing is ensuring probing the gdb for a version/feature first
so we can safely exit and skip the test if the host gdb isn't capable.
For the SVE testing I've had to use my own compiled version of GDB which
is a little ugly:

 ~/lsrc/qemu.git/tests/guest-debug/run-test.py \
   --qemu ./aarch64-linux-user/qemu-aarch64 \
   --qargs "-cpu max" \
   --bin ./tests/tcg/aarch64-linux-user/sve-ioctls \
   --test ~/lsrc/qemu.git/tests/tcg/aarch64/gdbstub/test-sve-ioctl.py \
   --gdb ~/src/tools/binutils-gdb.git/builds/all/install/bin/gdb

We should probably wrap that up into the tests/tcg configure.sh code so
the GDB used can persist with the build. Maybe via:

  ./configure --with-gdb=~/src/tools/binutils-gdb.git/builds/all/install/bin/gdb

-- 
Alex Bennée