On Thu, Aug 21, 2025 at 03:27:10PM +0000, Jiawei Zhao wrote:
> 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@4+t1(%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:
> - 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
hi,
I can see patchset v12 twice with different stats.. this one's the latter,
but you might want to resend with new version
jirka
>
> Jiawei Zhao (2):
> libbpf: fix USDT SIB argument handling causing unrecognized register
> error
> selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover
> SIB handling logic
>
> tools/lib/bpf/usdt.bpf.h | 47 ++++++++++++++-
> tools/lib/bpf/usdt.c | 58 +++++++++++++++++--
> tools/testing/selftests/bpf/prog_tests/usdt.c | 44 +++++++++++++-
> tools/testing/selftests/bpf/progs/test_usdt.c | 30 ++++++++++
> 4 files changed, 170 insertions(+), 9 deletions(-)
>
> --
> 2.43.0
>
>
