alignof
len = roundup(len, alignof(struct stat));
assert(off % alignof(struct direct) == 0);
assert(off % alignof(struct direct) == 0);
assert(off % alignof(struct direct) == 0);
len = roundup2(len, alignof(__max_align_t));
} __aligned(alignof(__max_align_t));
#define _Alignof(x) alignof(x)
align = alignof(uint64_t);
char filebuf[MAXBLOCKSIZE] __aligned(alignof(uint64_t));