pcb_savefpusmall
union savefpu pcb_savefpusmall __aligned(64);
__CTASSERT(offsetof(struct pcb, pcb_savefpusmall) == 128);
PAGE_SIZE - offsetof(struct pcb, pcb_savefpusmall);
pcb->pcb_savefpu = &pcb->pcb_savefpusmall;
pcb->pcb_savefpu != &pcb->pcb_savefpusmall) {