PTR24_ALIGN
PTR24_ALIGN, NULL, NULL, NULL, NULL, NULL, 0);
PTR24_ALIGN, NULL, NULL, NULL, NULL, static_arena, 0);
if (stksize <= sizeof (kthread_t) + PTR24_ALIGN)
stksize -= SA(sizeof (kthread_t) + PTR24_ALIGN - 1);
stksize &= -PTR24_ALIGN; /* make thread aligned */
ASSERT(((uintptr_t)t & (PTR24_ALIGN - 1)) == 0);