selftests/bpf: Add a BTF verification test for kflagged type_tag

Add a BTF verification test case for a type_tag with a kflag set.
Type tags with a kflag are now valid.

Add BTF_DECL_ATTR_ENC and BTF_TYPE_ATTR_ENC test helper macros,
corresponding to *_TAG_ENC.

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

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

···
 	.raw_types = {
 		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),	/* [1] */
 		BTF_VAR_ENC(NAME_TBD, 1, 0),			/* [2] */
-		BTF_TYPE_ENC(NAME_TBD, BTF_INFO_ENC(BTF_KIND_DECL_TAG, 1, 0), 2), (-1),
+		BTF_DECL_ATTR_ENC(NAME_TBD, 2, -1),
 		BTF_END_RAW,
 	},
 	BTF_STR_SEC("\0local\0tag1"),
···
 	.max_entries = 1,
 	.btf_load_err = true,
 	.err_str = "Type tags don't precede modifiers",
+},
+{
+	.descr = "type_tag test #7, tag with kflag",
+	.raw_types = {
+		BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),	/* [1] */
+		BTF_TYPE_ATTR_ENC(NAME_TBD, 1),			/* [2] */
+		BTF_PTR_ENC(2),					/* [3] */
+		BTF_END_RAW,
+	},
+	BTF_STR_SEC("\0tag"),
+	.map_type = BPF_MAP_TYPE_ARRAY,
+	.map_name = "tag_type_check_btf",
+	.key_size = sizeof(int),
+	.value_size = 4,
+	.key_type_id = 1,
+	.value_type_id = 1,
+	.max_entries = 1,
 },
 {
 	.descr = "enum64 test #1, unsigned, size 8",

tools/testing/selftests/bpf/test_btf.h

···
 #define BTF_TYPE_FLOAT_ENC(name, sz) \
 	BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_FLOAT, 0, 0), sz)
 
+#define BTF_DECL_ATTR_ENC(value, type, component_idx)	\
+	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_DECL_TAG, 1, 0), type), (component_idx)
+
 #define BTF_DECL_TAG_ENC(value, type, component_idx)	\
 	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_DECL_TAG, 0, 0), type), (component_idx)
+
+#define BTF_TYPE_ATTR_ENC(value, type)	\
+	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_TYPE_TAG, 1, 0), type)
 
 #define BTF_TYPE_TAG_ENC(value, type)	\
 	BTF_TYPE_ENC(value, BTF_INFO_ENC(BTF_KIND_TYPE_TAG, 0, 0), type)