libbpf: Make BTF finalization strict

With valid ELF and valid BTF, there is no reason (apart from bugs) why BTF
finalization should fail. So make it strict and return error if it fails. This
makes CO-RE relocation more reliable, as they are not going to be just
silently skipped, if BTF finalization failed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200708015318.3827358-2-andriin@fb.com

tools/lib/bpf/libbpf.c

@@ -2473,19 +2473,11 @@ static int bpf_object__finalize_btf(struct bpf_object *obj)
 		return 0;
 
 	err = btf__finalize_data(obj, obj->btf);
-	if (!err)
-		return 0;
-
-	pr_warn("Error finalizing %s: %d.\n", BTF_ELF_SEC, err);
-	btf__free(obj->btf);
-	obj->btf = NULL;
-	btf_ext__free(obj->btf_ext);
-	obj->btf_ext = NULL;
-
-	if (libbpf_needs_btf(obj)) {
-		pr_warn("BTF is required, but is missing or corrupted.\n");
-		return -ENOENT;
+	if (err) {
+		pr_warn("Error finalizing %s: %d.\n", BTF_ELF_SEC, err);
+		return err;
 	}
+
 	return 0;
 }