int
do_semop(arglast)
int *arglast;
{
#ifdef HAS_SEM
    register STR **st = stack->ary_array;
    register int sp = arglast[0];
    STR *opstr;
    char *opbuf;
    int id, opsize;

    id = (int)str_gnum(st[++sp]);
    opstr = st[++sp];
    opbuf = str_get(opstr);
    opsize = opstr->str_cur;
    if (opsize < sizeof(struct sembuf)
	|| (opsize % sizeof(struct sembuf)) != 0) {
	errno = EINVAL;
	return -1;
    }
    errno = 0;
    return semop(id, (struct sembuf *)opbuf, opsize/sizeof(struct sembuf));
#else
    fatal("semop not implemented");
#endif
}