selftests/bpf: Test bpf_map__set_autocreate() and related log fixup logic

Add a subtest that excercises bpf_map__set_autocreate() API and
validates that libbpf properly fixes up BPF verifier log with correct
map information.
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220428041523.4089853-5-andrii@kernel.org

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

@@ -85,7 +85,6 @@ static void bad_core_relo_subprog(void)
 	if (!ASSERT_ERR(err, "load_fail"))
 		goto cleanup;
 
-	/* there should be no prog loading log because we specified per-prog log buf */
 	ASSERT_HAS_SUBSTR(log_buf,
 			  ": <invalid CO-RE relocation>\n"
 			  "failed to resolve CO-RE relocation <byte_off> ",
@@ -101,6 +100,40 @@ static void bad_core_relo_subprog(void)
 	test_log_fixup__destroy(skel);
 }
 
+static void missing_map(void)
+{
+	char log_buf[8 * 1024];
+	struct test_log_fixup* skel;
+	int err;
+
+	skel = test_log_fixup__open();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	bpf_map__set_autocreate(skel->maps.missing_map, false);
+
+	bpf_program__set_autoload(skel->progs.use_missing_map, true);
+	bpf_program__set_log_buf(skel->progs.use_missing_map, log_buf, sizeof(log_buf));
+
+	err = test_log_fixup__load(skel);
+	if (!ASSERT_ERR(err, "load_fail"))
+		goto cleanup;
+
+	ASSERT_TRUE(bpf_map__autocreate(skel->maps.existing_map), "existing_map_autocreate");
+	ASSERT_FALSE(bpf_map__autocreate(skel->maps.missing_map), "missing_map_autocreate");
+
+	ASSERT_HAS_SUBSTR(log_buf,
+			  "8: <invalid BPF map reference>\n"
+			  "BPF map 'missing_map' is referenced but wasn't created\n",
+			  "log_buf");
+
+	if (env.verbosity > VERBOSE_NONE)
+		printf("LOG:   \n=================\n%s=================\n", log_buf);
+
+cleanup:
+	test_log_fixup__destroy(skel);
+}
+
 void test_log_fixup(void)
 {
 	if (test__start_subtest("bad_core_relo_trunc_none"))
@@ -111,4 +144,6 @@ void test_log_fixup(void)
 		bad_core_relo(250, TRUNC_FULL  /* truncate also libbpf's message patch */);
 	if (test__start_subtest("bad_core_relo_subprog"))
 		bad_core_relo_subprog();
+	if (test__start_subtest("missing_map"))
+		missing_map();
 }

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

@@ -35,4 +35,30 @@ int bad_relo_subprog(const void *ctx)
 	return bad_subprog() + bpf_core_field_size(t->pid);
 }
 
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} existing_map SEC(".maps");
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, int);
+} missing_map SEC(".maps");
+
+SEC("?raw_tp/sys_enter")
+int use_missing_map(const void *ctx)
+{
+	int zero = 0, *value;
+
+	value = bpf_map_lookup_elem(&existing_map, &zero);
+
+	value = bpf_map_lookup_elem(&missing_map, &zero);
+
+	return value != NULL;
+}
+
 char _license[] SEC("license") = "GPL";