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Message-ID: <CAEf4BzYVhVabvXRNGycSzA57HbF7ECZeYCQ1chq7HxXTi6gogQ@mail.gmail.com>
Date: Wed, 11 Feb 2026 13:45:24 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>
Subject: Re: [PATCHv3 bpf-next 4/5] selftests/bpf: Add test for checking
correct nop of optimized usdt
On Wed, Feb 11, 2026 at 12:49 AM Jiri Olsa <jolsa@...nel.org> wrote:
>
> Adding test that attaches bpf program on usdt probe in 2 scenarios;
>
> - attach program on top of usdt_1, which is single nop instruction,
> so the probe stays on nop instruction and is not optimized.
>
> - attach program on top of usdt_2 which is probe defined on top
> of nop,nop5 combo, so the probe is placed on top of nop5 and
> is optimized.
>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
> tools/testing/selftests/bpf/.gitignore | 2 +
> tools/testing/selftests/bpf/Makefile | 3 +-
> tools/testing/selftests/bpf/prog_tests/usdt.c | 85 +++++++++++++++++++
> tools/testing/selftests/bpf/progs/test_usdt.c | 9 ++
> tools/testing/selftests/bpf/usdt_1.c | 18 ++++
> tools/testing/selftests/bpf/usdt_2.c | 16 ++++
> 6 files changed, 132 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/bpf/usdt_1.c
> create mode 100644 tools/testing/selftests/bpf/usdt_2.c
>
> diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
> index a3ea98211ea6..bfdc5518ecc8 100644
> --- a/tools/testing/selftests/bpf/.gitignore
> +++ b/tools/testing/selftests/bpf/.gitignore
> @@ -47,3 +47,5 @@ verification_cert.h
> *.BTF
> *.BTF_ids
> *.BTF.base
> +usdt_1
> +usdt_2
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index c6bf4dfb1495..306949162a5b 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -749,7 +749,8 @@ TRUNNER_EXTRA_SOURCES := test_progs.c \
> $(VERIFY_SIG_HDR) \
> flow_dissector_load.h \
> ip_check_defrag_frags.h \
> - bpftool_helpers.c
> + bpftool_helpers.c \
> + usdt_1.c usdt_2.c
> TRUNNER_LIB_SOURCES := find_bit.c
> TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read \
> $(OUTPUT)/liburandom_read.so \
> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
> index f4be5269fa90..6daed3dfa75b 100644
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
> @@ -247,6 +247,89 @@ static void subtest_basic_usdt(bool optimized)
> #undef TRIGGER
> }
>
> +#ifdef __x86_64__
> +extern void usdt_1(void);
> +extern void usdt_2(void);
> +
> +/* nop, nop5 */
> +static unsigned char nop1_nop5_combo[6] = { 0x90, 0x0f, 0x1f, 0x44, 0x00, 0x00 };
> +static unsigned char nop1[6] = { 0x90 };
> +
> +static void *find_instr(void *fn, unsigned char *instr, size_t cnt)
> +{
> + int i;
> +
> + for (i = 0; i < 10; i++) {
> + if (!memcmp(instr, fn + i, cnt))
> + return fn + i;
> + }
> + return NULL;
> +}
> +
> +static void subtest_optimized_attach(void)
> +{
> + struct test_usdt *skel;
> + __u8 *addr_1, *addr_2;
> +
> + /* usdt_1 USDT probe has single nop instruction */
> + addr_1 = find_instr(usdt_1, nop1_nop5_combo, 6);
> + if (!ASSERT_NULL(addr_1, "usdt_1_find_nop1_nop5_combo"))
> + return;
> +
> + addr_1 = find_instr(usdt_1, nop1, 1);
> + if (!ASSERT_OK_PTR(addr_1, "usdt_1_find_nop1"))
> + return;
> +
> + /* usdt_1 USDT probe has nop,nop5 instructions combo */
> + addr_2 = find_instr(usdt_2, nop1_nop5_combo, 6);
> + if (!ASSERT_OK_PTR(addr_2, "usdt_2_find_nop1_nop5_combo"))
> + return;
> +
> + skel = test_usdt__open_and_load();
> + if (!ASSERT_OK_PTR(skel, "test_usdt__open_and_load"))
> + return;
> +
> + /*
> + * Attach program on top of usdt_1 which is single nop probe,
> + * so the probe won't get optimized.
> + */
> + skel->links.usdt_executed = bpf_program__attach_usdt(skel->progs.usdt_executed,
> + 0 /*self*/, "/proc/self/exe",
> + "optimized_attach", "usdt_1", NULL);
> + if (!ASSERT_OK_PTR(skel->links.usdt_executed, "bpf_program__attach_usdt"))
> + goto cleanup;
> +
> + usdt_1();
> + usdt_1();
> +
> + /* nop is on addr_1 address */
> + ASSERT_EQ(*addr_1, 0xcc, "int3");
> + ASSERT_EQ(skel->bss->executed, 2, "executed");
> +
> + bpf_link__destroy(skel->links.usdt_executed);
> +
> + /*
> + * Attach program on top of usdt_2 which is probe defined on top
> + * of nop1,nop5 combo, so the probe gets optimized on top of nop5.
> + */
> + skel->links.usdt_executed = bpf_program__attach_usdt(skel->progs.usdt_executed,
> + 0 /*self*/, "/proc/self/exe",
> + "optimized_attach", "usdt_2", NULL);
> + if (!ASSERT_OK_PTR(skel->links.usdt_executed, "bpf_program__attach_usdt"))
> + goto cleanup;
> +
> + usdt_2();
> + usdt_2();
> +
> + /* nop5 is on addr_2 + 1 address */
> + ASSERT_EQ(*(addr_2 + 1), 0xe8, "call");
> + ASSERT_EQ(skel->bss->executed, 4, "executed");
> +
> +cleanup:
> + test_usdt__destroy(skel);
> +}
> +#endif
> +
> unsigned short test_usdt_100_semaphore SEC(".probes");
> unsigned short test_usdt_300_semaphore SEC(".probes");
> unsigned short test_usdt_400_semaphore SEC(".probes");
> @@ -516,6 +599,8 @@ void test_usdt(void)
> #ifdef __x86_64__
> if (test__start_subtest("basic_optimized"))
> subtest_basic_usdt(true);
> + if (test__start_subtest("optimized_attach"))
> + subtest_optimized_attach();
> #endif
> if (test__start_subtest("multispec"))
> subtest_multispec_usdt();
> diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
> index a78c87537b07..6911868cdf67 100644
> --- a/tools/testing/selftests/bpf/progs/test_usdt.c
> +++ b/tools/testing/selftests/bpf/progs/test_usdt.c
> @@ -138,4 +138,13 @@ int usdt_sib(struct pt_regs *ctx)
> return 0;
> }
>
> +int executed;
> +
> +SEC("usdt")
> +int usdt_executed(struct pt_regs *ctx)
> +{
> + executed++;
did you try capturing pt_reg's ip value and validating it?
> + return 0;
> +}
> +
> char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/usdt_1.c b/tools/testing/selftests/bpf/usdt_1.c
> new file mode 100644
> index 000000000000..4f06e8bcf58b
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/usdt_1.c
> @@ -0,0 +1,18 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#if defined(__x86_64__)
> +
> +/*
> + * Include usdt.h with defined USDT_NOP macro to use single
> + * nop instruction.
> + */
> +#define USDT_NOP .byte 0x90
> +#include "usdt.h"
> +
> +__attribute__((aligned(16)))
> +void usdt_1(void)
> +{
> + USDT(optimized_attach, usdt_1);
> +}
> +
> +#endif
> diff --git a/tools/testing/selftests/bpf/usdt_2.c b/tools/testing/selftests/bpf/usdt_2.c
> new file mode 100644
> index 000000000000..789883aaca4c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/usdt_2.c
> @@ -0,0 +1,16 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#if defined(__x86_64__)
> +
> +/*
> + * Include usdt.h with default nop,nop5 instructions combo.
> + */
> +#include "usdt.h"
> +
> +__attribute__((aligned(16)))
> +void usdt_2(void)
> +{
> + USDT(optimized_attach, usdt_2);
> +}
> +
> +#endif
> --
> 2.53.0
>
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