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編譯器arm-linux-4.1.1，放在/usr/local下面了
2.添加編譯器路徑到PATH變量
export $PATH=/usr/local/arm-linux-4.1.1/bin:$PATH
可以在.bashrc文件里加，那么就不用每次都寫了
3. . build/envsetup.sh 設置環境
4.chooscompo 選擇配置，不同的平臺我想會不一樣吧。
5，make ARCH=arm CROSS_COMPILE=arm-linux- showcommands
showcommands是為了打印編譯命令出來