编译出uboot可以运行的linux内核代码的命令是make uImage，下面详细介绍下生成linux-2.6.22.6/arch/arm/boot/uImage的过程：
1、vmlinux、Image、uImage、zImage的区别
2、vmlinux生成过程简介
3、uImage生成过程简介
1、vmlinux、Image、uImage、zImage的区别，在执行make uImage之后会在%生成如下几个文件Image、uImage、zImage。
vmlinux是可引导的、压缩的内核。“vm”代表“Virtual Memory”。Linux 支持虚拟内存，不像老的操作系统比如DOS有640KB内存的限制。Linux能够使用硬盘空间作为虚拟内存，因此得名“vm”。它是elf格式的文件， 编译内核首先生成的是vmlinux，其它的文件都是基于此生成的。
Image是vmlinux经过OBJCOPY后生成的纯二进制映像文件
zImage是Image经过压缩后形成的一种映像压缩文件
uImage是在zImage基础上在前面64字节加上内核信息后的映像压缩文件，供uboot使用。可以从文件大小看到1848724-1848660=64字节
2、vmlinux生成过程简介，make uImage之后最先生成的是vmlinux，因为uImage依赖于vmlinux，在linux-2.6.22.6/arch/arm/Makefile下面有uImage这个目标，可以看到它依赖于vmlinux，所以先要分析vmlinux的生成过程
227 zImage Image xipImage bootpImage uImage: vmlinux 228 $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@
在linux-2.6.22.6/Makefile顶层Makefile下，定义了vmlinux这个目标
745 vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) $(kallsyms.o) FORCE 746 ifdef CONFIG_HEADERS_CHECK 747 $(Q)$(MAKE) -f $(srctree)/Makefile headers_check 748 endif 749 $(call if_changed_rule,vmlinux__) 750 $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@ 751 $(Q)rm -f .old_version
先逐个分析她的依赖vmlinux-lds、vmlinux-init、vmlinux-main、kallsyms.o、FORCE
1）、vmlinux-lds，它是一个链接脚本在链接的时候使用，它跟体系结构相关
611 vmlinux-lds := arch/$(ARCH)/kernel/vmlinux.lds
arch/$(ARCH)/kernel/vmlinux.lds一开始是不存在的，它依赖于$(vmlinux-dirs)
755 $(sort $(vmlinux-init) $(vmlinux-main)) $(vmlinux-lds): $(vmlinux-dirs) ;
vmlinux-dirs这个变量是产生子目录下built-in.o文件的根源，这个在Linux移植之子目录下的built-in.o生成过程分析会介绍。
2）、vmlinux-init := $(head-y) $(init-y)，其中head-y被定义在linux-2.6.22.6/arch/arm/Makefile中：
94 head-y := arch/arm/kernel/head$(MMUEXT).o arch/arm/kernel/init_task.o
init-y被定义在顶层Makefile中：
434 init-y := init/ 573 init-y := $(patsubst %/, %/built-in.o, $(init-y))
patsubst是Makefile的函数，意思是找到符合%/格式的，然后以%/built-in.o替换，所以最终init-y = init/built-in.o
所以vmlinux-init = arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o
3）、vmlinux-main被定义在顶层的Makefile中
609 vmlinux-main := $(core-y) $(libs-y) $(drivers-y) $(net-y)
类似与vmlinux-init的分析，最终vmlinux-main = usr/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o lib/lib.a lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o
4）、kallsyms.o被定义在顶层的Makefile中
679 ifdef CONFIG_KALLSYMS_EXTRA_PASS 680 last_kallsyms := 3 681 else 682 last_kallsyms := 2 683 endif 684 685 kallsyms.o := .tmp_kallsyms$(last_kallsyms).o
顶层的Makefile会包含配置好的.config文件
192 KCONFIG_CONFIG ?= .config
经查看CONFIG_KALLSYMS_EXTRA_PASS在.config没有设置，所以last_kallsyms := 3
62 # CONFIG_KALLSYMS_EXTRA_PASS is not set
最终kallsyms.o = .tmp_kallsyms2.o
接着寻找.tmp_kallsyms2.o，同样在顶层Makefile中
713 .tmp_kallsyms1.o .tmp_kallsyms2.o .tmp_kallsyms3.o: %.o: %.S scripts FORCE 714 $(call if_changed_dep,as_o_S)
$(call if_changed_dep,as_o_S)当这条规则被使用时它将检查哪些文件需要更新，或命令行被改变。同时它会重新检测依赖关系的改变并将生成新的依赖文件。所以这里是检查.o、.S、scripts文件是否被更新过。
scripts的定义如下：
429 PHONY += scripts 430 scripts: scripts_basic include/config/auto.conf 431 $(Q)$(MAKE) $(build)=$(@)
总结一下kallsyms.o依赖的作用就是检测以下所有生产vmlinux相关的文件是否更新过。
5）、FORCE在Linux移植之配置过程分析已经介绍过，每次执行的时候都认为这个变量是最新的
6）、因为CONFIG_HEADERS_CHECK在.config中没有找到，所以执行的规则为：
749 $(call if_changed_rule,vmlinux__) 750 $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@ 751 $(Q)rm -f .old_version
$(call if_changed_rule,vmlinux__)检查规则是否被改变。它的意思是调用if_changed_rule函数，函数参数为$(1)=vmlinux__。具体分析参考https://blog.csdn.net/zxygww/article/details/50249531。它被定义在linux-2.6.22.6\scripts\Kbuild.include中
183 if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \ 184 @set -e; \ 185 $(rule_$(1)))
这段话的意思是if_changed 函数在当发现规则的依赖有更新，或者是对应目标的命令行参数发生改变时($(if strip $(any-prereq) $(arg-check)) 语句结果不为空)，执行后面的语句。set -e 表示如果命令执行有错那么命令停止执行并退出。接着执行 $(cmd_$(1) 里的命令rule_vmlinux__：它在顶层Makefile定义为一个shell脚本调用
634 define rule_vmlinux__ 635 : 636 $(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version)) 637 638 $(call cmd,vmlinux__) 639 $(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd 640 641 $(Q)$(if $($(quiet)cmd_sysmap), \ 642 echo ' $($(quiet)cmd_sysmap) System.map' &&) \ 643 $(cmd_sysmap) $@ System.map; \ 644 if [ $$? -ne 0 ]; then \ 645 rm -f $@; \ 646 /bin/false; \ 647 fi; 648 $(verify_kallsyms) 649 endef
将上述内容实际打印出来得到
set -e; if [ ! -r .version ]; then rm -f .version; echo 1 >.version; else mv .version .old_version; expr 0$(cat .old_version) + 1 >.version; fi; make -f scripts/Makefile.build obj=init CHK include/linux/compile.h /bin/bash /work/system/linux-2.6.22.6/scripts/mkcompile_h include/linux/compile.h \ "arm" "" "" "arm-linux-gcc -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Os -marm -fno-omit-frame-pointer -mapcs -mno-sched-prolog -mapcs-32 -mno-thumb-interwork -D__LINUX_ARM_ARCH__=4 -march=armv4t -mtune=arm9tdmi -malignment-traps -msoft-float -Uarm -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -Wdeclaration-after-statement " UPD include/linux/compile.h arm-linux-gcc -Wp,-MD,init/.version.o.d -nostdinc -isystem /work/tools/gcc-3.4.5-glibc-2.3.6/lib/gcc/arm-linux/3.4.5/include -D__KERNEL__ -Iinclude -include include/linux/autoconf.h -mlittle-endian -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Os -marm -fno-omit-frame-pointer -mapcs -mno-sched-prolog -mapcs-32 -mno-thumb-interwork -D__LINUX_ARM_ARCH__=4 -march=armv4t -mtune=arm9tdmi -malignment-traps -msoft-float -Uarm -fno-omit-frame-pointer -fno-optimize-sibling-calls -g -Wdeclaration-after-statement -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(version)" -D"KBUILD_MODNAME=KBUILD_STR(version)" -c -o init/version.o init/version.c arm-linux-ld -EL -r -o init/built-in.o init/main.o init/version.o init/mounts.o init/initramfs.o init/calibrate.o arm-linux-ld -EL -p --no-undefined -X -o .tmp_vmlinux1 -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group echo 'cmd_.tmp_vmlinux1 := arm-linux-ld -EL -p --no-undefined -X -o .tmp_vmlinux1 -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group ' > ./..tmp_vmlinux1.cmd arm-linux-nm -n .tmp_vmlinux1 | scripts/kallsyms > .tmp_kallsyms1.S arm-linux-gcc -Wp,-MD,./..tmp_kallsyms1.o.d -D__ASSEMBLY__ -mapcs-32 -mno-thumb-interwork -D__LINUX_ARM_ARCH__=4 -march=armv4t -mtune=arm9tdmi -msoft-float -gdwarf2 -nostdinc -isystem /work/tools/gcc-3.4.5-glibc-2.3.6/lib/gcc/arm-linux/3.4.5/include -D__KERNEL__ -Iinclude -include include/linux/autoconf.h -mlittle-endian -c -o .tmp_kallsyms1.o .tmp_kallsyms1.S arm-linux-ld -EL -p --no-undefined -X -o .tmp_vmlinux2 -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group .tmp_kallsyms1.o arm-linux-nm -n .tmp_vmlinux2 | scripts/kallsyms > .tmp_kallsyms2.S arm-linux-gcc -Wp,-MD,./..tmp_kallsyms2.o.d -D__ASSEMBLY__ -mapcs-32 -mno-thumb-interwork -D__LINUX_ARM_ARCH__=4 -march=armv4t -mtune=arm9tdmi -msoft-float -gdwarf2 -nostdinc -isystem /work/tools/gcc-3.4.5-glibc-2.3.6/lib/gcc/arm-linux/3.4.5/include -D__KERNEL__ -Iinclude -include include/linux/autoconf.h -mlittle-endian -c -o .tmp_kallsyms2.o .tmp_kallsyms2.S arm-linux-ld -EL -p --no-undefined -X -o vmlinux -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group .tmp_kallsyms2.o echo 'cmd_vmlinux := arm-linux-ld -EL -p --no-undefined -X -o vmlinux -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group .tmp_kallsyms2.o' > ./.vmlinux.cmd echo ' /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap System.map' && /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap vmlinux System.map; if [ $? -ne 0 ]; then rm -f vmlinux; /bin/false; fi; /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap System.map echo ' /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap .tmp_System.map' && /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap .tmp_vmlinux2 .tmp_System.map /bin/bash /work/system/linux-2.6.22.6/scripts/mksysmap .tmp_System.map cmp -s System.map .tmp_System.map || (echo Inconsistent kallsyms data; echo Try setting CONFIG_KALLSYMS_EXTRA_PASS; rm .tmp_kallsyms* ; /bin/false )
我们的目标是最后生成vmlinux，取出目标vmlinux部分信息
arm-linux-ld -EL -p --no-undefined -X -o vmlinux -T arch/arm/kernel/vmlinux.lds arch/arm/kernel/head.o arch/arm/kernel/init_task.o init/built-in.o --start-group usr/built-in.o arch/arm/kernel/built-in.o arch/arm/mm/built-in.o arch/arm/common/built-in.o arch/arm/mach-s3c2410/built-in.o arch/arm/mach-s3c2400/built-in.o arch/arm/mach-s3c2412/built-in.o arch/arm/mach-s3c2440/built-in.o arch/arm/mach-s3c2442/built-in.o arch/arm/mach-s3c2443/built-in.o arch/arm/nwfpe/built-in.o arch/arm/plat-s3c24xx/built-in.o kernel/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o arch/arm/lib/lib.a lib/lib.a arch/arm/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o net/built-in.o --end-group .tmp_kallsyms2.o
经过链接最终得到了vmlinux ，可以看到链接脚本为arch/arm/kernel/vmlinux.lds，第一个文件为arch/arm/kernel/head.s
3、uImage生成过程简介，接着分析生成uImage的过程，这个文件是uboot最终用到的内核文件
在linux-2.6.22.6/arch/arm/Makefile中有如下定义，依赖vmlinux经过第二步已经生成了，接着分析规则。
227 zImage Image xipImage bootpImage uImage: vmlinux 228 $(Q)$(MAKE) $(build)=$(boot) MACHINE=$(MACHINE) $(boot)/$@
将规则展开后得到：
make -f scripts/Makefile.build obj=arch/arm/boot MACHINE=arch/arm/mach-s3c2410/ arch/arm/boot/uImage
直接将这个规则执行后的结果打印出来分析，首先由vmlinux生成二进制文件Image
arm-linux-objcopy -O binary -R .note -R .comment -S vmlinux arch/arm/boot/Image
接着将Image压缩成piggy.gz
gzip -f -9 < arch/arm/boot/compressed/../Image > arch/arm/boot/compressed/piggy.gz
接着将解压缩代码与压缩后的linux代码链接在一起生成arch/arm/boot/compressed/vmlinux，这样的话从开始地址0x30008000处的程序为解压程序的head.S汇编码，在head.S中会调用arch/arm/boot/compressed/misc.c中的解压代码完成解压，将arch/arm/boot/compressed/piggy.c解压出来放在物理地址为0x30008000处。具体解压过程不必关心。
arm-linux-ld -EL --defsym zreladdr=0x30008000 --defsym params_phys=0x30000100 -p --no-undefined -X /work/tools/gcc-3.4.5-glibc-2.3.6/lib/gcc/arm-linux/3.4.5/libgcc.a -T arch/arm/boot/compressed/vmlinux.lds arch/arm/boot/compressed/head.o arch/arm/boot/compressed/piggy.o arch/arm/boot/compressed/misc.o -o arch/arm/boot/compressed/vmlinux
接着将arch/arm/boot/compressed/vmlinux文件生成二进制文件arch/arm/boot/zImage。
arm-linux-objcopy -O binary -R .note -R .comment -S arch/arm/boot/compressed/vmlinux arch/arm/boot/zImage
最后在0x30008000地址之前加上64字节的内核信息生成uImage
/bin/bash /work/system/linux-2.6.22.6/scripts/mkuboot.sh -A arm -O linux -T kernel -C none -a 0x30008000 -e 0x30008000 -n 'Linux-2.6.22.6' -d arch/arm/boot/zImage arch/arm/boot/uImage
以上就是uImage生成过程的反推。最后可以在linux-2.6.22.6/arch/arm/boot目录下找到uImage文件。并且会在inux-2.6.22.6\include目录下生产一个config文件夹，里面的linux-2.6.22.6\include\config\auto.conf文件是在make uImage一开始就读取.config文件然后产生的，这个文件供Makefile调用；另外会产生inux-2.6.22.6\include\linux\autoconf.h这个头文件供内核源码使用；还有一个include\asm-arm\Mach-types.h产生被内核源码调用。