Re: [PATCH v2] perf test: Skip sigtrap test on old kernels

[Jiri Olsa <olsajiri@gmail.com>]

On Tue, Sep 06, 2022 at 10:04:07PM -0700, Namhyung Kim wrote:
> If it runs on an old kernel, perf_event_open would fail because of the
> new fields sigtrap and sig_data.  Just skipping the test could miss an
> actual bug in the kernel.
> 
> Let's check BTF if it has the perf_event_attr.sigtrap field.
> 
> Cc: Marco Elver <elver@google.com>
> Cc: Song Liu <songliubraving@fb.com>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/tests/sigtrap.c | 46 +++++++++++++++++++++++++++++++++++++-
>  1 file changed, 45 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/sigtrap.c b/tools/perf/tests/sigtrap.c
> index e32ece90e164..32f08ce0f2b0 100644
> --- a/tools/perf/tests/sigtrap.c
> +++ b/tools/perf/tests/sigtrap.c
> @@ -16,6 +16,8 @@
>  #include <sys/syscall.h>
>  #include <unistd.h>
>  
> +#include <bpf/btf.h>
> +
>  #include "cloexec.h"
>  #include "debug.h"
>  #include "event.h"
> @@ -54,6 +56,42 @@ static struct perf_event_attr make_event_attr(void)
>  	return attr;
>  }
>  
> +static bool attr_has_sigtrap(void)
> +{
> +	bool ret = false;
> +
> +#ifdef HAVE_BPF_SKEL
> +
> +	struct btf *btf;
> +	const struct btf_type *t;
> +	const struct btf_member *m;
> +	const char *name;
> +	int i, id;
> +
> +	/* just assume it doesn't have the field */
> +	btf = btf__load_vmlinux_btf();
> +	if (btf == NULL)
> +		return false;
> +
> +	id = btf__find_by_name_kind(btf, "perf_event_attr", BTF_KIND_STRUCT);
> +	if (id < 0)
> +		goto out;
> +
> +	t = btf__type_by_id(btf, id);
> +	for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
> +		name = btf__name_by_offset(btf, m->name_off);
> +		if (!strcmp(name, "sigtrap")) {
> +			ret = true;
> +			break;
> +		}
> +	}
> +out:
> +	btf__free(btf);
> +#endif

would it be easier to call perf_event_open for simple event with
sigtrap set (and perhaps remove_on_exec) ? perf_copy_attr checks
on reserved fields

jirka


> +
> +	return ret;
> +}
> +
>  static void
>  sigtrap_handler(int signum __maybe_unused, siginfo_t *info, void *ucontext __maybe_unused)
>  {
> @@ -139,7 +177,13 @@ static int test__sigtrap(struct test_suite *test __maybe_unused, int subtest __m
>  
>  	fd = sys_perf_event_open(&attr, 0, -1, -1, perf_event_open_cloexec_flag());
>  	if (fd < 0) {
> -		pr_debug("FAILED sys_perf_event_open(): %s\n", str_error_r(errno, sbuf, sizeof(sbuf)));
> +		if (attr_has_sigtrap()) {
> +			pr_debug("FAILED sys_perf_event_open(): %s\n",
> +				 str_error_r(errno, sbuf, sizeof(sbuf)));
> +		} else {
> +			pr_debug("perf_event_attr doesn't have sigtrap\n");
> +			ret = TEST_SKIP;
> +		}
>  		goto out_restore_sigaction;
>  	}
>  
> -- 
> 2.37.2.789.g6183377224-goog
>