selftests/bpf: Add a btf_dump test for type_tags

Factor out common routines handling custom BTF from
test_btf_dump_incremental. Then use them in the
test_btf_dump_type_tags.

test_btf_dump_type_tags verifies that a type tag is dumped correctly
with respect to its kflag.

Signed-off-by: Ihor Solodrai <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Eduard Zingerman <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

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

···
 	return err;
 }
 
-static char *dump_buf;
-static size_t dump_buf_sz;
-static FILE *dump_buf_file;
+struct test_ctx {
+	struct btf *btf;
+	struct btf_dump *d;
+	char *dump_buf;
+	size_t dump_buf_sz;
+	FILE *dump_buf_file;
+};
+
+static void test_ctx__free(struct test_ctx *t)
+{
+	fclose(t->dump_buf_file);
+	free(t->dump_buf);
+	btf_dump__free(t->d);
+	btf__free(t->btf);
+}
+
+static int test_ctx__init(struct test_ctx *t)
+{
+	t->dump_buf_file = open_memstream(&t->dump_buf, &t->dump_buf_sz);
+	if (!ASSERT_OK_PTR(t->dump_buf_file, "dump_memstream"))
+		return -1;
+	t->btf = btf__new_empty();
+	if (!ASSERT_OK_PTR(t->btf, "new_empty"))
+		goto err_out;
+	t->d = btf_dump__new(t->btf, btf_dump_printf, t->dump_buf_file, NULL);
+	if (!ASSERT_OK(libbpf_get_error(t->d), "btf_dump__new"))
+		goto err_out;
+
+	return 0;
+
+err_out:
+	test_ctx__free(t);
+	return -1;
+}
+
+static void test_ctx__dump_and_compare(struct test_ctx *t,
+				       const char *expected_output,
+				       const char *message)
+{
+	int i, err;
+
+	for (i = 1; i < btf__type_cnt(t->btf); i++) {
+		err = btf_dump__dump_type(t->d, i);
+		ASSERT_OK(err, "dump_type_ok");
+	}
+
+	fflush(t->dump_buf_file);
+	t->dump_buf[t->dump_buf_sz] = 0; /* some libc implementations don't do this */
+
+	ASSERT_STREQ(t->dump_buf, expected_output, message);
+}
 
 static void test_btf_dump_incremental(void)
 {
-	struct btf *btf = NULL;
-	struct btf_dump *d = NULL;
-	int id, err, i;
+	struct test_ctx t = {};
+	struct btf *btf;
+	int id, err;
 
-	dump_buf_file = open_memstream(&dump_buf, &dump_buf_sz);
-	if (!ASSERT_OK_PTR(dump_buf_file, "dump_memstream"))
+	if (test_ctx__init(&t))
 		return;
-	btf = btf__new_empty();
-	if (!ASSERT_OK_PTR(btf, "new_empty"))
-		goto err_out;
-	d = btf_dump__new(btf, btf_dump_printf, dump_buf_file, NULL);
-	if (!ASSERT_OK(libbpf_get_error(d), "btf_dump__new"))
-		goto err_out;
+
+	btf = t.btf;
 
 	/* First, generate BTF corresponding to the following C code:
 	 *
···
 	err = btf__add_field(btf, "x", 4, 0, 0);
 	ASSERT_OK(err, "field_ok");
 
-	for (i = 1; i < btf__type_cnt(btf); i++) {
-		err = btf_dump__dump_type(d, i);
-		ASSERT_OK(err, "dump_type_ok");
-	}
-
-	fflush(dump_buf_file);
-	dump_buf[dump_buf_sz] = 0; /* some libc implementations don't do this */
-
-	ASSERT_STREQ(dump_buf,
+	test_ctx__dump_and_compare(&t,
 "enum x;\n"
 "\n"
 "enum x {\n"
···
 	 * enum values don't conflict;
 	 *
 	 */
-	fseek(dump_buf_file, 0, SEEK_SET);
+	fseek(t.dump_buf_file, 0, SEEK_SET);
 
 	id = btf__add_struct(btf, "s", 4);
 	ASSERT_EQ(id, 7, "struct_id");
···
 	err = btf__add_field(btf, "s", 6, 64, 0);
 	ASSERT_OK(err, "field_ok");
 
-	for (i = 1; i < btf__type_cnt(btf); i++) {
-		err = btf_dump__dump_type(d, i);
-		ASSERT_OK(err, "dump_type_ok");
-	}
-
-	fflush(dump_buf_file);
-	dump_buf[dump_buf_sz] = 0; /* some libc implementations don't do this */
-	ASSERT_STREQ(dump_buf,
+	test_ctx__dump_and_compare(&t,
 "struct s___2 {\n"
 "	enum x x;\n"
 "	enum {\n"
···
 "	struct s s;\n"
 "};\n\n" , "c_dump1");
 
-err_out:
-	fclose(dump_buf_file);
-	free(dump_buf);
-	btf_dump__free(d);
-	btf__free(btf);
+	test_ctx__free(&t);
+}
+
+static void test_btf_dump_type_tags(void)
+{
+	struct test_ctx t = {};
+	struct btf *btf;
+	int id, err;
+
+	if (test_ctx__init(&t))
+		return;
+
+	btf = t.btf;
+
+	/* Generate BTF corresponding to the following C code:
+	 *
+	 * struct s {
+	 *   void __attribute__((btf_type_tag(\"void_tag\"))) *p1;
+	 *   void __attribute__((void_attr)) *p2;
+	 * };
+	 *
+	 */
+
+	id = btf__add_type_tag(btf, "void_tag", 0);
+	ASSERT_EQ(id, 1, "type_tag_id");
+	id = btf__add_ptr(btf, id);
+	ASSERT_EQ(id, 2, "void_ptr_id1");
+
+	id = btf__add_type_attr(btf, "void_attr", 0);
+	ASSERT_EQ(id, 3, "type_attr_id");
+	id = btf__add_ptr(btf, id);
+	ASSERT_EQ(id, 4, "void_ptr_id2");
+
+	id = btf__add_struct(btf, "s", 8);
+	ASSERT_EQ(id, 5, "struct_id");
+	err = btf__add_field(btf, "p1", 2, 0, 0);
+	ASSERT_OK(err, "field_ok1");
+	err = btf__add_field(btf, "p2", 4, 0, 0);
+	ASSERT_OK(err, "field_ok2");
+
+	test_ctx__dump_and_compare(&t,
+"struct s {\n"
+"	void __attribute__((btf_type_tag(\"void_tag\"))) *p1;\n"
+"	void __attribute__((void_attr)) *p2;\n"
+"};\n\n", "dump_and_compare");
+
+	test_ctx__free(&t);
 }
 
 #define STRSIZE				4096
···
 	}
 	if (test__start_subtest("btf_dump: incremental"))
 		test_btf_dump_incremental();
+
+	if (test__start_subtest("btf_dump: type_tags"))
+		test_btf_dump_type_tags();
 
 	btf = libbpf_find_kernel_btf();
 	if (!ASSERT_OK_PTR(btf, "no kernel BTF found"))