selftests/bpf: Add non-standardly sized enum tests for btf_dump

Add few custom enum definitions testing mode(byte) and mode(word)
attributes.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221212211505.558851-4-andrii@kernel.org

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

@@ -25,6 +25,39 @@ typedef enum {
 	H = 2,
 } e3_t;
 
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *enum e_byte {
+ *	EBYTE_1 = 0,
+ *	EBYTE_2 = 1,
+ *} __attribute__((mode(byte)));
+ *
+ */
+/* ----- END-EXPECTED-OUTPUT ----- */
+enum e_byte {
+	EBYTE_1,
+	EBYTE_2,
+} __attribute__((mode(byte)));
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+/*
+ *enum e_word {
+ *	EWORD_1 = 0LL,
+ *	EWORD_2 = 1LL,
+ *} __attribute__((mode(word)));
+ *
+ */
+/* ----- END-EXPECTED-OUTPUT ----- */
+enum e_word {
+	EWORD_1,
+	EWORD_2,
+} __attribute__((mode(word))); /* force to use 8-byte backing for this enum */
+
+/* ----- START-EXPECTED-OUTPUT ----- */
+enum e_big {
+	EBIG_1 = 1000000000000ULL,
+};
+
 typedef int int_t;
 
 typedef volatile const int * volatile const crazy_ptr_t;
@@ -224,6 +257,9 @@ struct root_struct {
 	enum e2 _2;
 	e2_t _2_1;
 	e3_t _2_2;
+	enum e_byte _100;
+	enum e_word _101;
+	enum e_big _102;
 	struct struct_w_typedefs _3;
 	anon_struct_t _7;
 	struct struct_fwd *_8;