Linux移植之make uImage编译过程分析

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

    zImage Image xipImage bootpImage uImage: vmlinux
        $(Q)$(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

    vmlinux: $(vmlinux-lds) $(vmlinux-init) $(vmlinux-main) $(kallsyms.o) FORCE
    ifdef CONFIG_HEADERS_CHECK
        $(Q)$(MAKE) -f $(srctree)/Makefile headers_check
    endif
        $(call if_changed_rule,vmlinux__)
        $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
        $(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

    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)

    $(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：

    head-y        := arch/arm/kernel/head$(MMUEXT).o arch/arm/kernel/init_task.o

init-y被定义在顶层Makefile中：

 init-y        := init/
 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

 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

    ifdef CONFIG_KALLSYMS_EXTRA_PASS
    last_kallsyms :=
    else
    last_kallsyms :=
    endif

    kallsyms.o := .tmp_kallsyms$(last_kallsyms).o

顶层的Makefile会包含配置好的.config文件

    KCONFIG_CONFIG    ?= .config

经查看CONFIG_KALLSYMS_EXTRA_PASS在.config没有设置，所以last_kallsyms := 3

 # 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

    .tmp_kallsyms1.o .tmp_kallsyms2.o .tmp_kallsyms3.o: %.o: %.S scripts FORCE
        $(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：

 PHONY += scripts
    scripts: scripts_basic include/config/auto.conf
    $(Q)$(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：

        $(call if_changed_rule,vmlinux__)
        $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost $@
        $(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

    if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ),                 \
        @set -e;                                                             \
        $(rule_$()))

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

    define rule_vmlinux__
        :
        $(if $(CONFIG_KALLSYMS),,+$(call cmd,vmlinux_version))

        $(call cmd,vmlinux__)
        $(Q)echo 'cmd_$@ := $(cmd_vmlinux__)' > $(@D)/.$(@F).cmd

        $(Q)$(if $($(quiet)cmd_sysmap),                                      \
          echo '  $($(quiet)cmd_sysmap)  System.map' &&)                     \
            $(cmd_sysmap) $@ System.map;                                         \
        if [ $$? -ne  ]; then                                               \
            rm -f $@;                                                    \
            /bin/false;                                                  \
        fi;
        $(verify_kallsyms)
        endef

将上述内容实际打印出来得到，在编译内核时需要输入make V=1才能显示完整的内核编译信息。

set -e; if [ ! -r .version ]; then rm -f .version; echo  >.version; else mv .version .old_version; expr $(cat .old_version) +  >.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.-glibc-2.3./lib/gcc/arm-linux/3.4./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- -mno-thumb-interwork -D__LINUX_ARM_ARCH__= -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- -mno-thumb-interwork -D__LINUX_ARM_ARCH__= -march=armv4t -mtune=arm9tdmi -msoft-float -gdwarf2   -nostdinc -isystem /work/tools/gcc-3.4.-glibc-2.3./lib/gcc/arm-linux/3.4./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- -mno-thumb-interwork -D__LINUX_ARM_ARCH__= -march=armv4t -mtune=arm9tdmi -msoft-float -gdwarf2   -nostdinc -isystem /work/tools/gcc-3.4.-glibc-2.3./lib/gcc/arm-linux/3.4./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  ]; 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。

    zImage Image xipImage bootpImage uImage: vmlinux
        $(Q)$(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 - < 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.-glibc-2.3./lib/gcc/arm-linux/3.4./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。