selftests/bpf: Test libbpf API function btf__add_tag()

Add btf_write tests with btf__add_tag() function.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210914223036.247560-1-yhs@fb.com

tools/testing/selftests/bpf/btf_helpers.c

@@ -24,11 +24,12 @@ static const char * const btf_kind_str_mapping[] = {
 	[BTF_KIND_VAR]		= "VAR",
 	[BTF_KIND_DATASEC]	= "DATASEC",
 	[BTF_KIND_FLOAT]	= "FLOAT",
+	[BTF_KIND_TAG]		= "TAG",
 };
 
 static const char *btf_kind_str(__u16 kind)
 {
-	if (kind > BTF_KIND_DATASEC)
+	if (kind > BTF_KIND_TAG)
 		return "UNKNOWN";
 	return btf_kind_str_mapping[kind];
 }
@@ -177,6 +178,10 @@ int fprintf_btf_type_raw(FILE *out, const struct btf *btf, __u32 id)
 	case BTF_KIND_FLOAT:
 		fprintf(out, " size=%u", t->size);
 		break;
+	case BTF_KIND_TAG:
+		fprintf(out, " type_id=%u component_idx=%d",
+			t->type, btf_tag(t)->component_idx);
+		break;
 	default:
 		break;
 	}

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

@@ -281,5 +281,26 @@ void test_btf_write() {
 		     "[17] DATASEC 'datasec1' size=12 vlen=1\n"
 		     "\ttype_id=1 offset=4 size=8", "raw_dump");
 
+	/* TAG */
+	id = btf__add_tag(btf, "tag1", 16, -1);
+	ASSERT_EQ(id, 18, "tag_id");
+	t = btf__type_by_id(btf, 18);
+	ASSERT_STREQ(btf__str_by_offset(btf, t->name_off), "tag1", "tag_value");
+	ASSERT_EQ(btf_kind(t), BTF_KIND_TAG, "tag_kind");
+	ASSERT_EQ(t->type, 16, "tag_type");
+	ASSERT_EQ(btf_tag(t)->component_idx, -1, "tag_component_idx");
+	ASSERT_STREQ(btf_type_raw_dump(btf, 18),
+		     "[18] TAG 'tag1' type_id=16 component_idx=-1", "raw_dump");
+
+	id = btf__add_tag(btf, "tag2", 14, 1);
+	ASSERT_EQ(id, 19, "tag_id");
+	t = btf__type_by_id(btf, 19);
+	ASSERT_STREQ(btf__str_by_offset(btf, t->name_off), "tag2", "tag_value");
+	ASSERT_EQ(btf_kind(t), BTF_KIND_TAG, "tag_kind");
+	ASSERT_EQ(t->type, 14, "tag_type");
+	ASSERT_EQ(btf_tag(t)->component_idx, 1, "tag_component_idx");
+	ASSERT_STREQ(btf_type_raw_dump(btf, 19),
+		     "[19] TAG 'tag2' type_id=14 component_idx=1", "raw_dump");
+
 	btf__free(btf);
 }