int
umain()
{
    asm volatile
    (
            ".global sys_yield\n\t"
            ".bss\n\t"
            ".comm a, 1\n\t"
            ".comm sys_yield, 4\n\t"

            ".text\n\t"
            // ".set global_alias, cprintf"
            :
            :
            :
    );
    return 0;
}