Merge branch 'libbpf-fix-usdt-sib-argument-handling-causing-unrecognized-register...

Jiawei Zhao says:

====================
libbpf: fix USDT SIB argument handling causing unrecognized register error

When using GCC on x86-64 to compile an usdt prog with -O1 or higher
optimization, the compiler will generate SIB addressing mode for global
array, e.g. "1@-96(%rbp,%rax,8)".

The current USDT implementation in libbpf cannot parse these two formats,
causing `bpf_program__attach_usdt()` to fail with -ENOENT
(unrecognized register).

This patch series adds support for SIB addressing mode in USDT probes.
The main changes include:
- add correct handling logic for SIB-addressed arguments in
  `parse_usdt_arg`.
- add an usdt_o2 test case to cover SIB addressing mode.

Testing shows that the SIB probe correctly generates 8@(%rcx,%rax,8)
argument spec and passes all validation checks.

The modification history of this patch series:
Change since v1:
- refactor the code to make it more readable
- modify the commit message to explain why and how

Change since v2:
- fix the `scale` uninitialized error

Change since v3:
- force -O2 optimization for usdt.test.o to generate SIB addressing usdt
  and pass all test cases.

Change since v4:
- split the patch into two parts, one for the fix and the other for the
  test

Change since v5:
- Only enable optimization for x86 architecture to generate SIB addressing
  usdt argument spec.

Change since v6:
- Add an usdt_o2 test case to cover SIB addressing mode.
- Reinstate the usdt.c test case.

Change since v7:
- Refactor modifications to __bpf_usdt_arg_spec to avoid increasing its size,
  achieving better compatibility
- Fix some minor code style issues
- Refactor the usdt_o2 test case, removing semaphore and adding GCC attribute
  to force -O2 optimization

Change since v8:
- Refactor the usdt_o2 test case, using assembly to force SIB addressing mode.

Change since v9:
- Only enable the usdt_o2 test case on x86_64 and i386 architectures since the
  SIB addressing mode is only supported on x86_64 and i386.

Change since v10:
- Replace `__attribute__((optimize("O2")))` with `#pragma GCC optimize("O1")`
  to fix the issue where the optimized compilation condition works improperly.
- Renamed test case usdt_o2 and relevant files name to usdt_o1 in that O1
  level optimization is enough to generate SIB addressing usdt argument spec.

Change since v11:
- Replace `STAP_PROBE1` with `STAP_PROBE_ASM`
- Use bit fields instead of bit shifting operations
- Merge the usdt_o1 test case into the usdt test case

Change since v12:
- This patch is same with the v12 but with a new version number.

Change since v13(resolve some review comments):
- https://lore.kernel.org/bpf/CAEf4BzZWd2zUC=U6uGJFF3EMZ7zWGLweQAG3CJWTeHy-5yFEPw@mail.gmail.com/
- https://lore.kernel.org/bpf/CAEf4Bzbs3hV_Q47+d93tTX13WkrpkpOb4=U04mZCjHyZg4aVdw@mail.gmail.com/

Change since v14:
- fix a typo in __bpf_usdt_arg_spec

Change since v15(resolve some review comments):
- https://lore.kernel.org/bpf/CAEf4BzaxuYijEfQMDFZ+CQdjxLuDZiesUXNA-SiopS+5+VxRaA@mail.gmail.com/
- https://lore.kernel.org/bpf/CAEf4BzaHi5kpuJ6OVvDU62LT5g0qHbWYMfb_FBQ3iuvvUF9fag@mail.gmail.com/
- https://lore.kernel.org/bpf/d438bf3a-a9c9-4d34-b814-63f2e9bb3a85@linux.dev/
====================

Link: https://patch.msgid.link/20250827053128.1301287-1-phoenix500526@163.com
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>