https://blog.wongcw.com/2018/12/01/linux-%e5%9f%ba%e9%87%91%e6%9c%83%e8%88%87risc-v-%e5%9f%ba%e9%87%91%e6%9c%83%e5%90%88%e4%bd%9c%e6%8e%a8%e5%bb%a3%e9%96%8b%e6%ba%90%e8%8a%af%e7%89%87/