linux-kernel - Re:Re: [PATCH bpf-next v8 2/2] selftests/bpf: Add an usdt_o2 test case in selftests to cover SIB handling logic

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Message-ID: <10b5dedd.4d59.198a755e12e.Coremail.phoenix500526@163.com>
Date: Thu, 14 Aug 2025 14:48:00 +0800 (CST)
From: 赵佳炜 <phoenix500526@....com>
To: "Andrii Nakryiko" <andrii.nakryiko@...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 v8 2/2] selftests/bpf: Add an usdt_o2 test
 case in selftests to cover SIB handling logic






>Have you considered using GCC's __attribute__((optimize("O2")))
>attribute. It seems like Clang doesn't have support for something like
>that, but we'll still have this covered in BPF CI for GCC-built
>selftests. Then I'd just add this as another subtest to existing usdt
>tests.
>
>Can you please try that?

Done


>Is semaphore essential to this test?


It's no essential. I've already removed it in the new patch. 



At 2025-08-14 08:04:35, "Andrii Nakryiko" <andrii.nakryiko@...il.com> wrote:
>On Wed, Aug 6, 2025 at 7:35 PM Jiawei Zhao <phoenix500526@....com> 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)".
>>
>> In this patch:
>> - add usdt_o2 test case to cover SIB addressing usdt argument spec
>>   handling logic
>>
>> Signed-off-by: Jiawei Zhao <phoenix500526@....com>
>> ---
>>  tools/testing/selftests/bpf/Makefile          |  8 +++
>>  .../selftests/bpf/prog_tests/usdt_o2.c        | 71 +++++++++++++++++++
>>  .../selftests/bpf/progs/test_usdt_o2.c        | 37 ++++++++++
>>  3 files changed, 116 insertions(+)
>>  create mode 100644 tools/testing/selftests/bpf/prog_tests/usdt_o2.c
>>  create mode 100644 tools/testing/selftests/bpf/progs/test_usdt_o2.c
>>
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index 910d8d6402ef..68cf6a9cf05f 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -759,6 +759,14 @@ TRUNNER_BPF_BUILD_RULE := $$(error no BPF objects should be built)
>>  TRUNNER_BPF_CFLAGS :=
>>  $(eval $(call DEFINE_TEST_RUNNER,test_maps))
>>
>> +# Use -O2 optimization to generate SIB addressing usdt argument spec
>> +# Only apply on x86 architecture where SIB addressing is relevant
>> +ifeq ($(ARCH), x86)
>> +$(OUTPUT)/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
>> +$(OUTPUT)/cpuv4/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
>> +$(OUTPUT)/no_alu32/usdt_o2.test.o: CFLAGS:=$(subst O0,O2,$(CFLAGS))
>> +endif
>> +
>
>Have you considered using GCC's __attribute__((optimize("O2")))
>attribute. It seems like Clang doesn't have support for something like
>that, but we'll still have this covered in BPF CI for GCC-built
>selftests. Then I'd just add this as another subtest to existing usdt
>tests.
>
>Can you please try that?
>
>>  # Define test_verifier test runner.
>>  # It is much simpler than test_maps/test_progs and sufficiently different from
>>  # them (e.g., test.h is using completely pattern), that it's worth just
>> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt_o2.c b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c
>> new file mode 100644
>> index 000000000000..f04b756b3640
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/prog_tests/usdt_o2.c
>> @@ -0,0 +1,71 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2025 Jiawei Zhao <phoenix500526@....com>. */
>> +#include <test_progs.h>
>> +
>> +#define _SDT_HAS_SEMAPHORES 1
>> +#include "../sdt.h"
>> +#include "test_usdt_o2.skel.h"
>> +
>> +int lets_test_this(int);
>> +
>> +#define test_value 0xFEDCBA9876543210ULL
>> +#define SEC(name) __attribute__((section(name), used))
>> +
>> +
>> +static volatile __u64 array[1] = {test_value};
>> +unsigned short test_usdt1_semaphore SEC(".probes");
>> +
>
>Is semaphore essential to this test?
>
>> +static __always_inline void trigger_func(void)
>> +{
>> +       /* Base address + offset + (index * scale) */
>> +       if (test_usdt1_semaphore) {
>> +               for (volatile int i = 0; i <= 0; i++)
>> +                       STAP_PROBE1(test, usdt1, array[i]);
>> +       }
>> +}
>> +
>
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