libbpf: Assume unsigned values for BTF_KIND_ENUM

Currently, BTF_KIND_ENUM type doesn't record whether enum values should be
interpreted as signed or unsigned. In Linux, most enums are unsigned, though,
so interpreting them as unsigned matches real world better.

Change btf_dump test case to test maximum 32-bit value, instead of negative
value.
Signed-off-by: NAndrii Nakryiko <andriin@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200303003233.3496043-3-andriin@fb.com

tools/lib/bpf/btf_dump.c

@@ -916,13 +916,13 @@ static void btf_dump_emit_enum_def(struct btf_dump *d, __u32 id,
 			/* enumerators share namespace with typedef idents */
 			dup_cnt = btf_dump_name_dups(d, d->ident_names, name);
 			if (dup_cnt > 1) {
-				btf_dump_printf(d, "\n%s%s___%zu = %d,",
+				btf_dump_printf(d, "\n%s%s___%zu = %u,",
 						pfx(lvl + 1), name, dup_cnt,
-						(__s32)v->val);
+						(__u32)v->val);
 			} else {
-				btf_dump_printf(d, "\n%s%s = %d,",
+				btf_dump_printf(d, "\n%s%s = %u,",
 						pfx(lvl + 1), name,
-						(__s32)v->val);
+						(__u32)v->val);
 			}
 		}
 		btf_dump_printf(d, "\n%s}", pfx(lvl));

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

@@ -13,7 +13,7 @@ enum e1 {
 
 enum e2 {
 	C = 100,
-	D = -100,
+	D = 4294967295,
 	E = 0,
 };