uImage生成过程
当编译linux的时候，运行make uImage，如果一切正常，最后会生成uImage。
如下具体讲解uImage生成过程：
1. 生成uImag的工具mkimage由arch/arm/boot/Makefile中的MKIMAGE定义.
Linux commit: e33936451 已经将此代码移到：<scripts/Makefile.lib>.
MKIMAGE := $(srctree)/scripts/mkuboot.sh
mkuboot.sh的作用是去找到是否存在"mkimage"，此工具是用来生成最后的uImage。
mkuboot.sh 首先检查toolchain是否拥有mkimage (使用-z来判空)，如果没有，再检查系统中是否拥有mkimage；如果没有则报错。
注：其中使用type命令来查找。
type: Display information about command type (type [-afptP] name [name ...])
==> # type mkimage
==> mkimage is /usr/bin/mkimage
然后调用：mkimage $@
2. 从makefile.boot中传入生成uImage的相关参数（e.g: arm/arm/mach-at91/Makefile.boot）
ifneq ($(MACHINE),) include $(srctree)/$(MACHINE)/Makefile.boot endif
3. 通过mkimage来生成uImage，其过程是加上0x40 bytes 的kernel头 on zImage.
Linux commit: e33936451 已经进行如下实现：
# SRCARCH just happens to match slightly more than ARCH (on sparc), so reduces
# the number of overrides in arch makefiles
UIMAGE_ARCH ?= $(SRCARCH)
UIMAGE_COMPRESSION ?= $(if $(2),$(2),none)
UIMAGE_OPTS-y ?=
UIMAGE_TYPE ?= kernel
UIMAGE_LOADADDR ?= arch_must_set_this
UIMAGE_ENTRYADDR ?= $(UIMAGE_LOADADDR)
UIMAGE_NAME ?= 'Linux-$(KERNELRELEASE)'
UIMAGE_IN ?= $<
UIMAGE_OUT ?= $@
quiet_cmd_uimage = UIMAGE $(UIMAGE_OUT)
cmd_uimage = $(CONFIG_SHELL) $(MKIMAGE) -A $(UIMAGE_ARCH) -O linux \
-C $(UIMAGE_COMPRESSION) $(UIMAGE_OPTS-y) \
-T $(UIMAGE_TYPE) \
-a $(UIMAGE_LOADADDR) -e $(UIMAGE_ENTRYADDR) \
-n $(UIMAGE_NAME) -d $(UIMAGE_IN) $(UIMAGE_OUT)
quiet_cmd_uimage = UIMAGE $@ cmd_uimage = $(CONFIG_SHELL) $(MKIMAGE) -A arm -O linux -T kernel / -C none -a $(LOADADDR) -e $(STARTADDR) / -n 'Linux-$(KERNELRELEASE)' -d $< $@
mkimage的参数如下：
Usage: mkimage -l image -l ==> list image header information mkimage [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image -A ==> set architecture to 'arch' -O ==> set operating system to 'os' -T ==> set image type to 'type' -C ==> set compression type 'comp' -a ==> set load address to 'addr' (hex) -e ==> set entry point to 'ep' (hex) -n ==> set image name to 'name' -d ==> use image data from 'datafile' -x ==> set XIP (execute in place)
Load address 由下面代码获得
ifeq ($(CONFIG_ZBOOT_ROM),y) $(obj)/uImage: LOADADDR=$(CONFIG_ZBOOT_ROM_TEXT) else $(obj)/uImage: LOADADDR=$(ZRELADDR) endif
start address 由下面代码获得
$(obj)/uImage: STARTADDR=$(LOADADDR)
由zImage 生成uImage:
注：zImage的生成过程：http://blog.csdn.net/voice_shen/article/details/17713441
$(obj)/uImage: $(obj)/zImage FORCE $(call if_changed,uimage) @echo ' Image $@ is ready'
也可以自行用mkimage来生成uImage，
mkimage -A arm -O linux -T kernel -C none -a
e.g : mkimage -A arm -O linux -T kernel -C none -a 0x70008000 -e 0x70008000 -n linux-2.6.30 -d zImage uImage
其中：0x8000这32K 空间是：Note that the kernel uses 16K of RAM below the image to store page tables. The recommended placement is 32KiB into RAM. （来自Documentation/arm/booting文件）