fix(bpf): get_on_cpu_cycles not returning delta

Current code assigns val to c.counter, which is always
0 since it's not used by bpf_perf_event_read_value -
we're using bpf_perf_event_read in this function since the
former produces a strange verifier error.

Fixes: #1402

Signed-off-by: Dave Tucker <[email protected]>

bpfassets/libbpf/src/kepler.bpf.c

@@ -135,7 +135,7 @@ static inline u64 get_on_cpu_cycles(u32 *cpu_id)
 	if (error < 0) {
 		return delta;
 	}
-	val = c.counter;
+	val = error;
 	prev_val = bpf_map_lookup_elem(&cpu_cycles, cpu_id);
 	delta = calc_delta(prev_val, &val);
 	bpf_map_update_elem(&cpu_cycles, cpu_id, &val, BPF_ANY);