FRAMELEN
#define trapframe(p) ((struct trapframe *)((void *)(p)->p_addr + USPACE - FRAMELEN + 8))
limit = (struct callframe *)(p->p_addr + USPACE - FRAMELEN);
uspace = (register_t)proc0paddr + USPACE - FRAMELEN;
kstack = (register_t)p2->p_addr + USPACE - FRAMELEN -