STACK_OFFSET
tf->tf_out[6] = (vaddr_t)newsp - STACK_OFFSET;
tf->tf_out[6] = stack - STACK_OFFSET;
return (void *)((uintptr_t)tf->tf_out[6] + STACK_OFFSET);
tf->tf_out[6] = (vaddr_t)newsp - STACK_OFFSET;
npcb->pcb_sp = (long)rp - STACK_OFFSET;