Re: [PATCH bpf-next v2 1/3] selftests/bpf: Refactor the failed assertion to another subtest

[Jiri Olsa <olsajiri@gmail.com>]

On Sun, Jun 15, 2025 at 11:53:51AM -0700, Yonghong Song wrote:

SNIP

> 
> There are total 301 locations for usdt_300. For gcc11 built binary, there are
> 300 spec's. But for clang20 built binary, there are 3 spec's. The libbpf default
> BPF_USDT_MAX_SPEC_CNT is 256. So for gcc11, the above bpf_program__attach_usdt() will
> fail, but the function will succeed for clang20.
> 
> Note that we cannot just change BPF_USDT_MAX_SPEC_CNT from 256 to 2 (through overwriting
> BPF_USDT_MAX_SPEC_CNT before usdt.bpf.h) since it will cause other test failures.
> We cannot just set BPF_USDT_MAX_SPEC_CNT to 2 for test_usdt_multispec.c since we
> have below in the Makefile:
>   test_usdt.skel.h-deps := test_usdt.bpf.o test_usdt_multispec.bpf.o
> and the linker will enforce that BPF_USDT_MAX_SPEC_CNT values for both progs must
> be the same.
> 
> The refactoring does not change existing test result. But the future change will
> allow to set BPF_USDT_MAX_SPEC_CNT to be 2 for arm64/clang20 case, which will have
> the same attachment failure as in gcc11.
> 
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
>  tools/testing/selftests/bpf/prog_tests/usdt.c | 35 +++++++++++++------
>  1 file changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
> index 495d66414b57..dc29ef94312a 100644
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
> @@ -270,18 +270,8 @@ static void subtest_multispec_usdt(void)
>  	 */
>  	trigger_300_usdts();

should above line (plus the comment) ...

>  
> -	/* we'll reuse usdt_100 BPF program for usdt_300 test */
>  	bpf_link__destroy(skel->links.usdt_100);
> -	skel->links.usdt_100 = bpf_program__attach_usdt(skel->progs.usdt_100, -1, "/proc/self/exe",
> -							"test", "usdt_300", NULL);
> -	err = -errno;
> -	if (!ASSERT_ERR_PTR(skel->links.usdt_100, "usdt_300_bad_attach"))
> -		goto cleanup;
> -	ASSERT_EQ(err, -E2BIG, "usdt_300_attach_err");
>  
> -	/* let's check that there are no "dangling" BPF programs attached due
> -	 * to partial success of the above test:usdt_300 attachment
> -	 */

... and the code below (up to usdt_301_sum assert)
go to the new subtest_multispec_fail_usdt test as well?

jirka

>  	bss->usdt_100_called = 0;
>  	bss->usdt_100_sum = 0;
>  
> @@ -312,6 +302,29 @@ static void subtest_multispec_usdt(void)
>  	test_usdt__destroy(skel);
>  }
>  
> +static void subtest_multispec_fail_usdt(void)
> +{
> +	LIBBPF_OPTS(bpf_usdt_opts, opts);
> +	struct test_usdt *skel;
> +	int err;
> +
> +	skel = test_usdt__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "skel_open"))
> +		return;
> +
> +	skel->bss->my_pid = getpid();
> +
> +	skel->links.usdt_100 = bpf_program__attach_usdt(skel->progs.usdt_100, -1, "/proc/self/exe",
> +							"test", "usdt_300", NULL);
> +	err = -errno;
> +	if (!ASSERT_ERR_PTR(skel->links.usdt_100, "usdt_300_bad_attach"))
> +		goto cleanup;
> +	ASSERT_EQ(err, -E2BIG, "usdt_300_attach_err");
> +
> +cleanup:
> +	test_usdt__destroy(skel);
> +}
> +
>  static FILE *urand_spawn(int *pid)
>  {
>  	FILE *f;
> @@ -422,6 +435,8 @@ void test_usdt(void)
>  		subtest_basic_usdt();
>  	if (test__start_subtest("multispec"))
>  		subtest_multispec_usdt();
> +	if (test__start_subtest("multispec_fail"))
> +		subtest_multispec_fail_usdt();
>  	if (test__start_subtest("urand_auto_attach"))
>  		subtest_urandom_usdt(true /* auto_attach */);
>  	if (test__start_subtest("urand_pid_attach"))
> -- 
> 2.47.1
> 
>