perf test sigtrap: Generalize the BTF routine to reuse it in this test

Move the part that loads the BTF info to a "btf__available()" that will
lazy load the BTF info so that if we need it for some other test, which
we will in the following cset, we can reuse it.

At some point this will move from this specific 'perf test' entry to be
used in other parts of perf, do it when needed.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20231129154718.326330-2-acme@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/sigtrap.c

@@ -57,36 +57,51 @@ static struct perf_event_attr make_event_attr(void)
 #ifdef HAVE_BPF_SKEL
 #include <bpf/btf.h>
 
-static bool attr_has_sigtrap(void)
+static struct btf *btf;
+
+static bool btf__available(void)
 {
-	bool ret = false;
-	struct btf *btf;
-	const struct btf_type *t;
+	if (btf == NULL)
+		btf = btf__load_vmlinux_btf();
+
+	return btf != NULL;
+}
+
+static void btf__exit(void)
+{
+	btf__free(btf);
+	btf = NULL;
+}
+
+static const struct btf_member *__btf_type__find_member_by_name(int type_id, const char *member_name)
+{
+	const struct btf_type *t = btf__type_by_id(btf, type_id);
 	const struct btf_member *m;
-	const char *name;
-	int i, id;
+	int i;
+
+	for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
+		const char *current_member_name = btf__name_by_offset(btf, m->name_off);
+		if (!strcmp(current_member_name, member_name))
+			return m;
+	}
+
+	return NULL;
+}
+
+static bool attr_has_sigtrap(void)
+{
+	int id;
 
-	btf = btf__load_vmlinux_btf();
-	if (btf == NULL) {
+	if (!btf__available()) {
 		/* should be an old kernel */
 		return false;
 	}
 
 	id = btf__find_by_name_kind(btf, "perf_event_attr", BTF_KIND_STRUCT);
 	if (id < 0)
-		goto out;
+		return false;
 
-	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);
-	return ret;
+	return __btf_type__find_member_by_name(id, "sigtrap") != NULL;
 }
 #else  /* !HAVE_BPF_SKEL */
 static bool attr_has_sigtrap(void)
@@ -109,6 +124,10 @@ static bool attr_has_sigtrap(void)
 
 	return ret;
 }
+
+static void btf__exit(void)
+{
+}
 #endif  /* HAVE_BPF_SKEL */
 
 static void
@@ -221,6 +240,7 @@ static int test__sigtrap(struct test_suite *test __maybe_unused, int subtest __m
 	sigaction(SIGTRAP, &oldact, NULL);
 out:
 	pthread_barrier_destroy(&barrier);
+	btf__exit();
 	return ret;
 }