On Wed, Aug 6, 2025 at 7:35 PM Jiawei Zhao <phoenix500...@163.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@4+t1(%rip)".
>
> In this patch:
> - add usdt_o2 test case to cover SIB addressing usdt argument spec
> handling logic
>
> Signed-off-by: Jiawei Zhao <phoenix500...@163.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 <phoenix500...@163.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]);
> + }
> +}
> +
[...]
