libbpf-tools: Allow softirqs to run on old kernels

This is part of efforts towards #4231. Fallback to raw tracepoints
if tp_btf is not available.

Signed-off-by: Hengqi Chen <chenhengqi@outlook.com>

Author: chenhengqi

libbpf-tools/softirqs.bpf.c

@@ -20,31 +20,26 @@ struct {
 __u64 counts[NR_SOFTIRQS] = {};
 struct hist hists[NR_SOFTIRQS] = {};
 
-SEC("tp_btf/softirq_entry")
-int BPF_PROG(softirq_entry, unsigned int vec_nr)
+static int handle_entry(unsigned int vec_nr)
 {
 	u64 ts = bpf_ktime_get_ns();
 	u32 key = 0;
 
-	bpf_map_update_elem(&start, &key, &ts, 0);
+	bpf_map_update_elem(&start, &key, &ts, BPF_ANY);
 	return 0;
 }
 
-SEC("tp_btf/softirq_exit")
-int BPF_PROG(softirq_exit, unsigned int vec_nr)
+static int handle_exit(unsigned int vec_nr)
 {
+	u64 delta, *tsp;
 	u32 key = 0;
-	s64 delta;
-	u64 *tsp;
 
 	if (vec_nr >= NR_SOFTIRQS)
 		return 0;
 	tsp = bpf_map_lookup_elem(&start, &key);
-	if (!tsp || !*tsp)
+	if (!tsp)
 		return 0;
 	delta = bpf_ktime_get_ns() - *tsp;
-	if (delta < 0)
-		return 0;
 	if (!targ_ns)
 		delta /= 1000U;
 
@@ -64,4 +59,28 @@ int BPF_PROG(softirq_exit, unsigned int vec_nr)
 	return 0;
 }
 
+SEC("tp_btf/softirq_entry")
+int BPF_PROG(softirq_entry_btf, unsigned int vec_nr)
+{
+	return handle_entry(vec_nr);
+}
+
+SEC("tp_btf/softirq_exit")
+int BPF_PROG(softirq_exit_btf, unsigned int vec_nr)
+{
+	return handle_exit(vec_nr);
+}
+
+SEC("raw_tp/softirq_entry")
+int BPF_PROG(softirq_entry, unsigned int vec_nr)
+{
+	return handle_entry(vec_nr);
+}
+
+SEC("raw_tp/softirq_exit")
+int BPF_PROG(softirq_exit, unsigned int vec_nr)
+{
+	return handle_exit(vec_nr);
+}
+
 char LICENSE[] SEC("license") = "GPL";

libbpf-tools/softirqs.c

@@ -204,6 +204,14 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
+	if (probe_tp_btf("softirq_entry")) {
+		bpf_program__set_autoload(obj->progs.softirq_entry, false);
+		bpf_program__set_autoload(obj->progs.softirq_exit, false);
+	} else {
+		bpf_program__set_autoload(obj->progs.softirq_entry_btf, false);
+		bpf_program__set_autoload(obj->progs.softirq_exit_btf, false);
+	}
+
 	/* initialize global data (filtering options) */
 	obj->rodata->targ_dist = env.distributed;
 	obj->rodata->targ_ns = env.nanoseconds;