linux-kernel - [PATCH bpf-next v8 0/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

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Message-ID: <20250807023430.4566-1-phoenix500526@163.com>
Date: Thu,  7 Aug 2025 02:34:26 +0000
From: Jiawei Zhao <phoenix500526@....com>
To: ast@...nel.org
Cc: daniel@...earbox.net,
	andrii@...nel.org,
	yonghong.song@...ux.dev,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v8 0/2] 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 and PC-relative addressing mode for global variable,
e.g. "1@-96(%rbp,%rax,8)" and "-1@...1(%rip)".

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:
- Add a bpf-next tag to the patch series.
- update the commit message of the second commit

Jiawei Zhao (2):
  libbpf: fix USDT SIB argument handling causing unrecognized register
    error
  selftests/bpf: Add an usdt_o2 test case in selftests to cover SIB
    handling logic

 tools/lib/bpf/usdt.bpf.h                      | 33 ++++++++-
 tools/lib/bpf/usdt.c                          | 43 +++++++++--
 tools/testing/selftests/bpf/Makefile          |  8 +++
 .../selftests/bpf/prog_tests/usdt_o2.c        | 71 +++++++++++++++++++
 .../selftests/bpf/progs/test_usdt_o2.c        | 37 ++++++++++
 5 files changed, 185 insertions(+), 7 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o2.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o2.c

-- 
2.43.0