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

[Celeste Liu <uwu@coelacanthus.name>]

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>