File System:
Unix is heavily based on the filesystem concept; almost everything in Unix can be treated as a file. The kernel builds a structured file system on top of unstructured hardware, and the resulting file abstraction is heavily used throughout the whole system.
1.Arm编译器arm-linux-4.1.1，放在/usr/local下面了
2.添加编译器路径到PATH变量
export $PATH=/usr/local/arm-linux-4.1.1/bin:$PATH
可以在.bashrc文件里加，那么就不用每次都写了
3. . build/envsetup.sh 设置环境
4.chooscompo 选择配置，不同的平台我想会不一样吧。
5，make ARCH=arm CROSS_COMPILE=arm-linux- showcommands
showcommands是为了打印编译命令出来