嵌入式 rootfs uImage 制作分析

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    #mkdir build
    #cd build
    #mkdir rootfs
    #mkdir scripts
    #mkdir user
    #ls
    build linux rootfs scripts user Makefile
    
下文中的环境变量
-----------------------------------------------------------------------------------------------
CROSS_COMPILE=arm-linux-gnueabihf-
-----------------------------------------------------------------------------------------------

一、下载最新busybox   放到user/下
    #cd user/busybox
     1、#make menuconfig
             Busybox Setting--->|
                                        |General Configuration---><*>Don't use /usr
                                        |
                                        |Build Options--->|<*>Bulid Busbox as a static binary()
                                        |                        |
                                        |                        |(arm-linux-gnueabihf-)Cross Compiler prefix     解释：配置交叉编译工具
                                        |                        
                                        |Installation Options--->(../../rootfs)Bustbox installation prefix 解释：配置安装目录
           
            
             Init Utilities--->|
                                  |[ ]Support running init from within an initrd(not initramfs)  解释：去掉生成 linuxrc
    2、#make

    3、#make install
        在../../rootfs 下产生/bin,/sbin

二、配置rootfs
    #cd rootfs/
    
    1、#ln -fs bin/busybox init (配置init 进程)
        
    2、#mkdir -p dev etc etc/init.d home lib proc sys tmp user
    
    3、使用busybox 中的 mdev(在sbin/下) 来自动创建设备节点，所以只需要先创建如下两个设备文件
        #cd dev/
        #mknod -m 660 console c 5 1
        #mknod -m 660 null c 1 3

        将busybox/examples/mdev.conf 拷贝到 etc/下
    4、inittab
        将busybox/examples/inittab 拷贝到 etc/下

# Boot-time system configuration/initialization script.
# This is run first except when booting in single-user mode.
#
::sysinit:/etc/init.d/rcS
# Start an "askfirst" shell on the console (whatever that may be)
::askfirst:-/bin/sh
# Stuff to do when restarting the init process
::restart:/sbin/init

# Stuff to do before rebooting
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::shutdown:/sbin/swapoff -a

    5、创建etc/init.d/rcS
        内容：

#!/bin/sh

#add setting here for auto start program
PATH=/sbin:/bin:/usr/sbin:/usr/bin
runlevel=S
prevlevel=N
umask 022
export PATH runlevel prevlevel

#See docs/mdev.txt
#mount all fs in fstab,proc and sysfs are must for mdev
mount -a

#create device nodes
echo /sbin/mdev > /proc/sys/kernel/hotplug

#seed  all device nodes
mdev -s

#create pts directory for remote login such as SSH and telnet
mkdir -p /dev/pts
mount -t devpts devpts /dev/pts



if [ -f /etc/hostname ]; then
/bin/hostname -F /etc/hostname
fi

if [ -e /sys/class/net/eth0 ]; then
ifconfig eth0 192.168.1.15
fi

echo "rcS done!"

    6、创建etc/fstab   (由rcS中 mount -a 调用)      
        内容：

#
# /etc/fstab: static file system information.
#
#
#
# file system   mount       type    options           dump    pass

#for mdev
proc /proc       proc    defaults          0       0
sysfs /sys        sysfs   defaults          0       0

#make sure /dev /tmp /var are tmpfs(tmpfs use ram as media) thus can be r/w
tmpfs /tmp        tmpfs   defaults          0       0
tmpfs /dev        tmpfs   defaults          0       0
tmpfs /var        tmpfs   defaults          0       0

#usbfs /proc/bus/usb  usbfs   defaults          0       0

三、将roofs编译进内核
   
    #cd linux
    1、make menuconfig
            General setup--->|
                                        |[*]Initial RAM filesystem and RAM disk (initramfs / initrd) support
                                        |(../rootfs)Initramfs source file(s)
                                        |
                                        |
                                        |[*]support initial ramdisks compressed using gzip
                                        |
                                        |Build-in initramfs compression mode (Gzip)
    2、编译并安装内核模块到rootfs/
        make -C linux O=build ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} -j4 INSTALL_MOD_PATH=output modules
        make -C linux O=build ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} -j4 INSTALL_MOD_PATH=output modules_install
    3、生成uImage
        make -C linux O=build ARCH=arm CROSS_COMPILE=${CROSS_COMPILE} -j4 INSTALL_MOD_PATH=output uImage
        cd build/ && ${CROSS_COMPILE}objcopy -R .note.gnu.build-id -S -O binary vmlinux bImage