selftests/bpf: Add extra link to uprobe_multi tests

Attaching extra program to same functions system wide for api
and link tests.

This way we can test the pid filter works properly when there's
extra system wide consumer on the same uprobe that will trigger
the original uprobe handler.

We expect to have the same counts as before.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230809083440.3209381-29-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: olsajiri

tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c

@@ -184,6 +184,12 @@ __test_attach_api(const char *binary, const char *pattern, struct bpf_uprobe_mul
 	if (!ASSERT_OK_PTR(skel->links.uretprobe_sleep, "bpf_program__attach_uprobe_multi"))
 		goto cleanup;
 
+	opts->retprobe = false;
+	skel->links.uprobe_extra = bpf_program__attach_uprobe_multi(skel->progs.uprobe_extra, -1,
+								    binary, pattern, opts);
+	if (!ASSERT_OK_PTR(skel->links.uprobe_extra, "bpf_program__attach_uprobe_multi"))
+		goto cleanup;
+
 	uprobe_multi_test_run(skel, child);
 
 cleanup:
@@ -240,6 +246,7 @@ static void __test_link_api(struct child *child)
 		"uprobe_multi_func_2",
 		"uprobe_multi_func_3",
 	};
+	int link_extra_fd = -1;
 	int err;
 
 	err = elf_resolve_syms_offsets(path, 3, syms, (unsigned long **) &offsets);
@@ -279,6 +286,13 @@ static void __test_link_api(struct child *child)
 	if (!ASSERT_GE(link4_fd, 0, "link4_fd"))
 		goto cleanup;
 
+	opts.kprobe_multi.flags = 0;
+	opts.uprobe_multi.pid = 0;
+	prog_fd = bpf_program__fd(skel->progs.uprobe_extra);
+	link_extra_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_UPROBE_MULTI, &opts);
+	if (!ASSERT_GE(link_extra_fd, 0, "link_extra_fd"))
+		goto cleanup;
+
 	uprobe_multi_test_run(skel, child);
 
 cleanup:
@@ -290,6 +304,8 @@ static void __test_link_api(struct child *child)
 		close(link3_fd);
 	if (link4_fd >= 0)
 		close(link4_fd);
+	if (link_extra_fd >= 0)
+		close(link_extra_fd);
 
 	uprobe_multi__destroy(skel);
 	free(offsets);

tools/testing/selftests/bpf/progs/uprobe_multi.c

@@ -93,3 +93,9 @@ int uretprobe_sleep(struct pt_regs *ctx)
 	uprobe_multi_check(ctx, true, true);
 	return 0;
 }
+
+SEC("uprobe.multi//proc/self/exe:uprobe_multi_func_*")
+int uprobe_extra(struct pt_regs *ctx)
+{
+	return 0;
+}