perf record: Handle argument change in sched_switch

Recently sched_switch tracepoint added a new argument for prev_state,
but it's hard to handle the change in a BPF program.  Instead, we can
check the function prototype in BTF before loading the program.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20220518224725.742882-5-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index b5e2d038da50..874856c55101 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -89,6 +89,33 @@ static void off_cpu_finish(void *arg __maybe_unused)
 	off_cpu_bpf__destroy(skel);
 }
 
+/* v5.18 kernel added prev_state arg, so it needs to check the signature */
+static void check_sched_switch_args(void)
+{
+	const struct btf *btf = bpf_object__btf(skel->obj);
+	const struct btf_type *t1, *t2, *t3;
+	u32 type_id;
+
+	type_id = btf__find_by_name_kind(btf, "bpf_trace_sched_switch",
+					 BTF_KIND_TYPEDEF);
+	if ((s32)type_id < 0)
+		return;
+
+	t1 = btf__type_by_id(btf, type_id);
+	if (t1 == NULL)
+		return;
+
+	t2 = btf__type_by_id(btf, t1->type);
+	if (t2 == NULL || !btf_is_ptr(t2))
+		return;
+
+	t3 = btf__type_by_id(btf, t2->type);
+	if (t3 && btf_is_func_proto(t3) && btf_vlen(t3) == 4) {
+		/* new format: pass prev_state as 4th arg */
+		skel->rodata->has_prev_state = true;
+	}
+}
+
 int off_cpu_prepare(struct evlist *evlist, struct target *target)
 {
 	int err, fd, i;
@@ -117,6 +144,7 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target)
 	}
 
 	set_max_rlimit();
+	check_sched_switch_args();
 
 	err = off_cpu_bpf__load(skel);
 	if (err) {