libbpf: bpf__find_by_name[_kind] should use btf__get_nr_types()

When operating on split BTF, btf__find_by_name[_kind] will not
iterate over all types since they use btf->nr_types to show
the number of types to iterate over. For split BTF this is
the number of types _on top of base BTF_, so it will
underestimate the number of types to iterate over, especially
for vmlinux + module BTF, where the latter is much smaller.

Use btf__get_nr_types() instead.

Fixes: ba451366 ("libbpf: Implement basic split BTF support")
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1605437195-2175-1-git-send-email-alan.maguire@oracle.com

tools/lib/bpf/btf.c

@@ -674,12 +674,12 @@ int btf__resolve_type(const struct btf *btf, __u32 type_id)
 
 __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
 {
-	__u32 i;
+	__u32 i, nr_types = btf__get_nr_types(btf);
 
 	if (!strcmp(type_name, "void"))
 		return 0;
 
-	for (i = 1; i <= btf->nr_types; i++) {
+	for (i = 1; i <= nr_types; i++) {
 		const struct btf_type *t = btf__type_by_id(btf, i);
 		const char *name = btf__name_by_offset(btf, t->name_off);
 
@@ -693,12 +693,12 @@ __s32 btf__find_by_name(const struct btf *btf, const char *type_name)
 __s32 btf__find_by_name_kind(const struct btf *btf, const char *type_name,
 			     __u32 kind)
 {
-	__u32 i;
+	__u32 i, nr_types = btf__get_nr_types(btf);
 
 	if (kind == BTF_KIND_UNKN || !strcmp(type_name, "void"))
 		return 0;
 
-	for (i = 1; i <= btf->nr_types; i++) {
+	for (i = 1; i <= nr_types; i++) {
 		const struct btf_type *t = btf__type_by_id(btf, i);
 		const char *name;