> For the complete documentation index, see [llms.txt](https://nankai.gitbook.io/ucore-os-on-risc-v64/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nankai.gitbook.io/ucore-os-on-risc-v64/lab0.5/zhen-zheng-de-ru-kou-dian.md).

# 真正的入口点

我们在`kern/init/init.c`编写函数`kern_init`, 作为“真正的”内核入口点。为了让我们能看到一些效果，我们希望它能在命令行进行格式化输出。

如果我们在linux下运行一个C程序，需要格式化输出，那么大一学生都知道我们应该`#include<stdio.h>`。于是我们在`kern/init/init.c`也这么写一句。且慢！linux下，当我们调用C语言标准库的函数时，实际上依赖于`glibc`提供的运行时环境，也就是一定程度上依赖于操作系统提供的支持。可是我们并没有把`glibc`移植到ucore里！

怎么办呢？只能自己动手，丰衣足食。QEMU里的OpenSBI固件提供了输入一个字符和输出一个字符的接口，我们一会把这个接口一层层封装起来，提供`stdio.h`里的格式化输出函数`cprintf()`来使用。这里格式化输出函数的名字不使用原先的`printf()`，强调这是我们在ucore里重新实现的函数。

接下来就去看看，我们是怎么从OpenSBI的接口一层层封装到格式化输入输出函数的。


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