bpf: Change return value of verifier function add_subprog()

Currently, verifier function add_subprog() returns 0 for success
and negative value for failure. Change the return value
to be the subprog number for success. This functionality will be
used in the next patch to save a call to find_subprog().

Signed-off-by: Yonghong Song <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Acked-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: yonghong-song

kernel/bpf/verifier.c

@@ -1530,15 +1530,15 @@ static int add_subprog(struct bpf_verifier_env *env, int off)
 	}
 	ret = find_subprog(env, off);
 	if (ret >= 0)
-		return 0;
+		return ret;
 	if (env->subprog_cnt >= BPF_MAX_SUBPROGS) {
 		verbose(env, "too many subprograms\n");
 		return -E2BIG;
 	}
 	env->subprog_info[env->subprog_cnt++].start = off;
 	sort(env->subprog_info, env->subprog_cnt,
 	     sizeof(env->subprog_info[0]), cmp_subprogs, NULL);
-	return 0;
+	return env->subprog_cnt - 1;
 }
 
 static int check_subprogs(struct bpf_verifier_env *env)