oversize_header_alloc
big = oversize_header_alloc((uintptr_t)ret, size);
static oversize_t *oversize_header_alloc(uintptr_t, size_t);
np = oversize_header_alloc((uintptr_t)off,
tail = oversize_header_alloc(taddr, frag_size);
big = oversize_header_alloc(ret_addr -
tail = oversize_header_alloc(taddr, tsize);
big = oversize_header_alloc(ret_addr -
big = oversize_header_alloc(ret_addr -
tail = oversize_header_alloc(taddr, tail_sz);