selftests/bpf: Tests for enum fwd resolved as full enum64

A set of test cases to verify enum fwd resolution logic:
- verify that enum fwd can be resolved as full enum64;
- verify that enum64 fwd can be resolved as full enum;
- verify that enum size is considered when enums are compared for
  equivalence.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20221101235413.1824260-2-eddyz87@gmail.com

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

@@ -7133,7 +7133,7 @@ static struct btf_dedup_test dedup_tests[] = {
 				BTF_ENUM_ENC(NAME_NTH(4), 456),
 			/* [4] fwd enum 'e2' after full enum */
 			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 0), 4),
-			/* [5] incompatible fwd enum with different size */
+			/* [5] fwd enum with different size, size does not matter for fwd */
 			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 0), 1),
 			/* [6] incompatible full enum with different value */
 			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
@@ -7150,9 +7150,7 @@ static struct btf_dedup_test dedup_tests[] = {
 			/* [2] full enum 'e2' */
 			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
 				BTF_ENUM_ENC(NAME_NTH(4), 456),
-			/* [3] incompatible fwd enum with different size */
-			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 0), 1),
-			/* [4] incompatible full enum with different value */
+			/* [3] incompatible full enum with different value */
 			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
 				BTF_ENUM_ENC(NAME_NTH(2), 321),
 			BTF_END_RAW,
@@ -7611,7 +7609,87 @@ static struct btf_dedup_test dedup_tests[] = {
 		BTF_STR_SEC("\0e1\0e1_val"),
 	},
 },
-
+{
+	.descr = "dedup: enum of different size: no dedup",
+	.input = {
+		.raw_types = {
+			/* [1] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			/* [2] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 2),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val"),
+	},
+	.expect = {
+		.raw_types = {
+			/* [1] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			/* [2] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 2),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val"),
+	},
+},
+{
+	.descr = "dedup: enum fwd to enum64",
+	.input = {
+		.raw_types = {
+			/* [1] enum64 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM64, 0, 1), 8),
+				BTF_ENUM64_ENC(NAME_NTH(2), 1, 0),
+			/* [2] enum 'e1' fwd */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 0), 4),
+			/* [3] typedef enum 'e1' td */
+			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0), 2),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val\0td"),
+	},
+	.expect = {
+		.raw_types = {
+			/* [1] enum64 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM64, 0, 1), 8),
+				BTF_ENUM64_ENC(NAME_NTH(2), 1, 0),
+			/* [2] typedef enum 'e1' td */
+			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0), 1),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val\0td"),
+	},
+},
+{
+	.descr = "dedup: enum64 fwd to enum",
+	.input = {
+		.raw_types = {
+			/* [1] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			/* [2] enum64 'e1' fwd */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM64, 0, 0), 8),
+			/* [3] typedef enum 'e1' td */
+			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0), 2),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val\0td"),
+	},
+	.expect = {
+		.raw_types = {
+			/* [1] enum 'e1' */
+			BTF_TYPE_ENC(NAME_NTH(1), BTF_INFO_ENC(BTF_KIND_ENUM, 0, 1), 4),
+				BTF_ENUM_ENC(NAME_NTH(2), 1),
+			/* [2] typedef enum 'e1' td */
+			BTF_TYPE_ENC(NAME_NTH(3), BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0), 1),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0e1\0e1_val\0td"),
+	},
+},
 };
 
 static int btf_type_size(const struct btf_type *t)