def _pack_64b_int_arg(arg):
    """Helper function to pack a 64-bit integer argument."""
    return ((arg >> 56) & 0xff), ((arg >> 48) & 0xff), ((arg >> 40) & 0xff), ((arg >> 32) & 0xff), \
           ((arg >> 24) & 0xff), ((arg >> 16) & 0xff), ((arg >> 8) & 0xff), (arg & 0xff)