linux-kernel - Re:Re: [PATCH bpf-next v12 0/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

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Message-ID: <7078a326.98e2.198d25bb89b.Coremail.phoenix500526@163.com>
Date: Fri, 22 Aug 2025 23:18:03 +0800 (CST)
From: 赵佳炜 <phoenix500526@....com>
To: "Jiri Olsa" <olsajiri@...il.com>
Cc: ast@...nel.org, 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: Re:Re: [PATCH bpf-next v12 0/2] libbpf: fix USDT SIB argument
 handling causing unrecognized register error










Ok, done.







At 2025-08-22 21:17:55, "Jiri Olsa" <olsajiri@...il.com> wrote:
>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@...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:
>> - 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
>> 
>>