Re: [RFC PATCH v2 0/2] Enable PC diversion via the plugin API

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

Florian Hofhammer <florian.hofhammer@epfl.ch> writes:

> Hi,
>
> Sorry for necrobumping this thread. I just wanted to follow up on this
> and ask if there is still interest in this plugin API extension or if it
> is going to be dropped in favor of the Lorelei patches (which would also
> fulfill my original use case).

These are the system call filter patches?

I guess that depends on if being able to change PC is only for skipping
syscalls?

>
> Thanks for your time,
> Florian
>
> On 06/10/2025 15:21, Florian Hofhammer wrote:
>> Hi,
>> 
>> As originally discussed in the thread at
>> https://lists.nongnu.org/archive/html/qemu-devel/2025-08/msg00656.html
>> and later proposed in a patch at
>> https://lists.nongnu.org/archive/html/qemu-devel/2025-09/msg02218.html,
>> I am sending an updated version of my patch based on the previous
>> feedback.
>> 
>> Notable changes to v1:
>> - Added a setjmp() in the syscall handling path to allow redirecting
>>   the PC via cpu_loop_exit() also in syscall callbacks. The previous
>>   version would only work in instruction execution / memory access
>>   callback contexts, as the setjmp() corresponding to the longjmp() in
>>   cpu_loop_exit() was only live in those contexts.
>> - Added a flag to make sure the new API function is only called in
>>   contexts where it makes sense, i.e., during execution of guest code.
>> - Added a test that checks the new functionality by skipping a
>>   non-existent sentinel syscall.
>> 
>> I made it an RFC patch this time as I am not entirely sure if my
>> setting/handling of the new flag makes sense the way it is. I briefly
>> looked into making the QEMU_PLUGIN_CB_* flags actual flags via a
>> bitfield instead of enum values, but that would have required touching
>> a lot of code all over the place, so I'm not sure this is the way to go.
>> 
>> Happy to get feedback and your thoughts on the patches!
>> 
>> Thanks,
>> Florian
>> 
>> 
>> Florian Hofhammer (2):
>>   plugins: Add PC diversion API function
>>   tests/tcg: add test for qemu_plugin_set_pc API
>> 
>>  include/qemu/qemu-plugin.h                    | 15 +++++++
>>  linux-user/aarch64/cpu_loop.c                 |  2 +-
>>  linux-user/alpha/cpu_loop.c                   |  2 +-
>>  linux-user/arm/cpu_loop.c                     |  2 +-
>>  linux-user/hexagon/cpu_loop.c                 |  2 +-
>>  linux-user/hppa/cpu_loop.c                    |  4 ++
>>  linux-user/i386/cpu_loop.c                    |  8 ++--
>>  linux-user/include/special-errno.h            |  8 ++++
>>  linux-user/loongarch64/cpu_loop.c             |  5 ++-
>>  linux-user/m68k/cpu_loop.c                    |  2 +-
>>  linux-user/microblaze/cpu_loop.c              |  2 +-
>>  linux-user/mips/cpu_loop.c                    |  5 ++-
>>  linux-user/openrisc/cpu_loop.c                |  2 +-
>>  linux-user/ppc/cpu_loop.c                     |  6 ++-
>>  linux-user/riscv/cpu_loop.c                   |  2 +-
>>  linux-user/s390x/cpu_loop.c                   |  2 +-
>>  linux-user/sh4/cpu_loop.c                     |  2 +-
>>  linux-user/sparc/cpu_loop.c                   |  4 +-
>>  linux-user/syscall.c                          |  8 ++++
>>  linux-user/xtensa/cpu_loop.c                  |  3 ++
>>  plugins/api.c                                 | 17 +++++++-
>>  plugins/core.c                                | 25 ++++++-----
>>  tests/tcg/multiarch/Makefile.target           | 42 +++++++++++++++++++
>>  .../tcg/multiarch/test-plugin-skip-syscalls.c | 26 ++++++++++++
>>  tests/tcg/plugins/syscall.c                   |  6 +++
>>  25 files changed, 170 insertions(+), 32 deletions(-)
>>  create mode 100644 tests/tcg/multiarch/test-plugin-skip-syscalls.c
>> 

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro