libbpf: BTF validation can use layout for unknown kinds

BTF parsing can use layout to navigate unknown kinds, so
btf_validate_type() should take layout information into
account to avoid failure when an unrecognized kind is met.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260326145444.2076244-6-alan.maguire@oracle.com

src/btf.c

@@ -746,8 +746,12 @@ static int btf_validate_type(const struct btf *btf, const struct btf_type *t, __
 		break;
 	}
 	default:
-		pr_warn("btf: type [%u]: unrecognized kind %u\n", id, kind);
-		return -EINVAL;
+		/* Kind may be represented in kind layout information. */
+		if (btf_type_size_unknown(btf, t) < 0) {
+			pr_warn("btf: type [%u]: unrecognized kind %u\n", id, kind);
+			return -EINVAL;
+		}
+		break;
 	}
 	return 0;
 }