samples/bpf: simplify spintest with kprobe.multi

With the introduction of kprobe.multi, it is now possible to attach
multiple kprobes to a single BPF program without the need for multiple
definitions. Additionally, this method supports wildcard-based
matching, allowing for further simplification of BPF programs. In here,
an asterisk (*) wildcard is used to map to all symbols relevant to
spin_{lock|unlock}.

Furthermore, since kprobe.multi handles symbol matching, this commit
eliminates the need for the previous logic of reading the ksym table to
verify the existence of symbols.
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Link: https://lore.kernel.org/r/20230818090119.477441-10-danieltimlee@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

samples/bpf/spintest.bpf.c

@@ -47,20 +47,9 @@ int foo(struct pt_regs *ctx) \
 }
 
 /* add kprobes to all possible *spin* functions */
-SEC("kprobe/spin_unlock")PROG(p1)
-SEC("kprobe/spin_lock")PROG(p2)
-SEC("kprobe/mutex_spin_on_owner")PROG(p3)
-SEC("kprobe/rwsem_spin_on_owner")PROG(p4)
-SEC("kprobe/spin_unlock_irqrestore")PROG(p5)
-SEC("kprobe/_raw_spin_unlock_irqrestore")PROG(p6)
-SEC("kprobe/_raw_spin_unlock_bh")PROG(p7)
-SEC("kprobe/_raw_spin_unlock")PROG(p8)
-SEC("kprobe/_raw_spin_lock_irqsave")PROG(p9)
-SEC("kprobe/_raw_spin_trylock_bh")PROG(p10)
-SEC("kprobe/_raw_spin_lock_irq")PROG(p11)
-SEC("kprobe/_raw_spin_trylock")PROG(p12)
-SEC("kprobe/_raw_spin_lock")PROG(p13)
-SEC("kprobe/_raw_spin_lock_bh")PROG(p14)
+SEC("kprobe.multi/spin_*lock*")PROG(spin_lock)
+SEC("kprobe.multi/*_spin_on_owner")PROG(spin_on_owner)
+SEC("kprobe.multi/_raw_spin_*lock*")PROG(raw_spin_lock)
 
 /* and to inner bpf helpers */
 SEC("kprobe/htab_map_update_elem")PROG(p15)

samples/bpf/spintest_user.c

@@ -9,13 +9,12 @@
 
 int main(int ac, char **argv)
 {
-	char filename[256], symbol[256];
 	struct bpf_object *obj = NULL;
 	struct bpf_link *links[20];
 	long key, next_key, value;
 	struct bpf_program *prog;
 	int map_fd, i, j = 0;
-	const char *section;
+	char filename[256];
 	struct ksym *sym;
 
 	if (load_kallsyms()) {
@@ -44,20 +43,13 @@ int main(int ac, char **argv)
 	}
 
 	bpf_object__for_each_program(prog, obj) {
-		section = bpf_program__section_name(prog);
-		if (sscanf(section, "kprobe/%s", symbol) != 1)
-			continue;
-
-		/* Attach prog only when symbol exists */
-		if (ksym_get_addr(symbol)) {
-			links[j] = bpf_program__attach(prog);
-			if (libbpf_get_error(links[j])) {
-				fprintf(stderr, "bpf_program__attach failed\n");
-				links[j] = NULL;
-				goto cleanup;
-			}
-			j++;
+		links[j] = bpf_program__attach(prog);
+		if (libbpf_get_error(links[j])) {
+			fprintf(stderr, "bpf_program__attach failed\n");
+			links[j] = NULL;
+			goto cleanup;
 		}
+		j++;
 	}
 
 	for (i = 0; i < 5; i++) {