Re: [PATCH v6 0/3] riscv/ptrace: add new regset to access original a0 register

[Charlie Jenkins <charlie@rivosinc.com>]

On Wed, Jan 15, 2025 at 07:13:26PM +0800, Celeste Liu wrote:
> The orig_a0 is missing in struct user_regs_struct of riscv, and there is
> no way to add it without breaking UAPI. (See Link tag below)
> 
> Like NT_ARM_SYSTEM_CALL do, we add a new regset name NT_RISCV_ORIG_A0 to
> access original a0 register from userspace via ptrace API.
> 
> Link: https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/
> 
> Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
> ---
> Changes in v6:
> - Fix obsolute comment.
> - Copy include/linux/stddef.h to tools/include to use offsetofend in
>   selftests.
> - Link to v5: https://lore.kernel.org/r/20250115-riscv-new-regset-v5-0-d0e6ec031a23@coelacanthus.name
> 
> Changes in v5:
> - Fix wrong usage in selftests.
> - Link to v4: https://lore.kernel.org/r/20241226-riscv-new-regset-v4-0-4496a29d0436@coelacanthus.name
> 
> Changes in v4:
> - Fix a copy paste error in selftest. (Forget to commit...)
> - Link to v3: https://lore.kernel.org/r/20241226-riscv-new-regset-v3-0-f5b96465826b@coelacanthus.name
> 
> Changes in v3:
> - Use return 0 directly for readability.
> - Fix test for modify a0.
> - Add Fixes: tag
> - Remove useless Cc: stable.
> - Selftest will check both a0 and orig_a0, but depends on the
>   correctness of PTRACE_GET_SYSCALL_INFO.
> - Link to v2: https://lore.kernel.org/r/20241203-riscv-new-regset-v2-0-d37da8c0cba6@coelacanthus.name
> 
> Changes in v2:
> - Fix integer width.
> - Add selftest.
> - Link to v1: https://lore.kernel.org/r/20241201-riscv-new-regset-v1-1-c83c58abcc7b@coelacanthus.name
> 
> ---
> Celeste Liu (3):
>       riscv/ptrace: add new regset to access original a0 register
>       tools: copy include/linux/stddef.h to tools/include
>       riscv: selftests: Add a ptrace test to verify a0 and orig_a0 access
> 
>  arch/riscv/kernel/ptrace.c                   |  32 +++++
>  include/uapi/linux/elf.h                     |   1 +
>  tools/include/linux/stddef.h                 |  85 ++++++++++++
>  tools/include/uapi/linux/stddef.h            |   6 +-
>  tools/testing/selftests/riscv/abi/.gitignore |   1 +
>  tools/testing/selftests/riscv/abi/Makefile   |   6 +-
>  tools/testing/selftests/riscv/abi/ptrace.c   | 193 +++++++++++++++++++++++++++
>  7 files changed, 319 insertions(+), 5 deletions(-)
> ---
> base-commit: 0e287d31b62bb53ad81d5e59778384a40f8b6f56
> change-id: 20241201-riscv-new-regset-d529b952ad0d
> 
> Best regards,
> -- 
> Celeste Liu <uwu@coelacanthus.name>
> 

There is also this series that looks like it will solve this problem by
providing an architecture agnostic way of changing syscall args with
PTRACE_SET_SYSCALL_INFO [1].

- Charlie

[1] https://lore.kernel.org/lkml/20250113170925.GA392@altlinux.org/