rem: user_sigaction(int sig, const struct sigaction *act, struct sigaction *oact)
add: user_sigaction(int sig, const struct sigaction *userAction, struct sigaction *userOldAction)
context: user_sigaction(int sig, const struct sigaction *act, struct sigaction *oact){	struct sigaction kact;	struct sigaction koact;	int rc;		if ((!act) || (!oact))		return EINVAL;		rc = user_memcpy(&kact, act, sizeof(struct sigaction));	if (rc < 0)		return rc;	rc = user_memcpy(&koact, oact, sizeof(struct sigaction));	if (rc < 0)		return rc;	rc = sys_sigaction(sig, &kact, &koact);	if (rc < 0)		return rc;	rc = user_memcpy(oact, &koact, sizeof(struct sigaction));	return rc;}