bpf: Add type_id pointer as argument to __btf_resolve_size

Adding type_id pointer as argument to __btf_resolve_size
to return also BTF ID of the resolved type. It will be
used in following changes.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200825192124.710397-6-jolsa@kernel.org

kernel/bpf/btf.c

@@ -1082,6 +1082,7 @@ static const struct resolve_vertex *env_stack_peak(struct btf_verifier_env *env)
  * *elem_id: id of u32
  * *total_nelems: (x * y).  Hence, individual elem size is
  *                (*type_size / *total_nelems)
+ * *type_id: id of type if it's changed within the function, 0 if not
  *
  * type: is not an array (e.g. const struct X)
  * return type: type "struct X"
@@ -1089,15 +1090,16 @@ static const struct resolve_vertex *env_stack_peak(struct btf_verifier_env *env)
  * *elem_type: same as return type ("struct X")
  * *elem_id: 0
  * *total_nelems: 1
+ * *type_id: id of type if it's changed within the function, 0 if not
  */
 static const struct btf_type *
 __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		   u32 *type_size, const struct btf_type **elem_type,
-		   u32 *elem_id, u32 *total_nelems)
+		   u32 *elem_id, u32 *total_nelems, u32 *type_id)
 {
 	const struct btf_type *array_type = NULL;
 	const struct btf_array *array = NULL;
-	u32 i, size, nelems = 1;
+	u32 i, size, nelems = 1, id = 0;
 
 	for (i = 0; i < MAX_RESOLVE_DEPTH; i++) {
 		switch (BTF_INFO_KIND(type->info)) {
@@ -1118,6 +1120,7 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		case BTF_KIND_VOLATILE:
 		case BTF_KIND_CONST:
 		case BTF_KIND_RESTRICT:
+			id = type->type;
 			type = btf_type_by_id(btf, type->type);
 			break;
 
@@ -1150,6 +1153,8 @@ __btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		*elem_type = type;
 	if (elem_id)
 		*elem_id = array ? array->type : 0;
+	if (type_id && id)
+		*type_id = id;
 
 	return array_type ? : type;
 }
@@ -1158,7 +1163,7 @@ const struct btf_type *
 btf_resolve_size(const struct btf *btf, const struct btf_type *type,
 		 u32 *type_size)
 {
-	return __btf_resolve_size(btf, type, type_size, NULL, NULL);
+	return __btf_resolve_size(btf, type, type_size, NULL, NULL, NULL, NULL);
 }
 
 /* The input param "type_id" must point to a needs_resolve type */
@@ -3988,7 +3993,7 @@ int btf_struct_access(struct bpf_verifier_log *log,
 		mname = __btf_name_by_offset(btf_vmlinux, member->name_off);
 
 		mtype = __btf_resolve_size(btf_vmlinux, mtype, &msize,
-					   &elem_type, NULL, &total_nelems);
+					   &elem_type, NULL, &total_nelems, NULL);
 		if (IS_ERR(mtype)) {
 			bpf_log(log, "field %s doesn't have size\n", mname);
 			return -EFAULT;