本文以2410开发板为例；
1. uboot编译命令
我们一般通过两条命令来编译uboot；
# make smdk2410_config
# make
执行第一条命令后，生成了两个文件：include下config.h config.mk；这两个文件是如何生成的呢？在Makefile中找到对应的smdk2410_config标号处。
unconfig是这个目标的依赖关系，这也是一个标号。它的作用是删除上次运行此命令生成的文件。
$(MKCONFIG) 是顶层目录下 mkconfig 脚本。
$(@:_config=) 的值是 smdk2410，这个写法就是把目标中的_config替换掉。
其实也可以这样写：
效果是一样。红色的字都是作为参数传递给mkconfig 这个shell脚本。
2. mkconfig脚本，
#!/bin/sh -e# Script to create header files and links to configure# U-Boot for a specific board.## Parameters: Target Architecture CPU Board [VENDOR] [SOC] 这6个就是对传递进来的参数说明## (C) 2002-2006 DENX Software Engineering, Wolfgang Denk <wd@denx.de>#APPEND=no # Default: Create new config fileBOARD_NAME="" # Name to print in make outputwhile [ $# -gt 0 ] ; do case "$1" in --) shift ; break ;; -a) shift ; APPEND=yes ;; -n) shift ; BOARD_NAME="${1%%_config}" ; shift ;; *) break ;; esacdone[ "${BOARD_NAME}" ] || BOARD_NAME="$1"[ $# -lt 4 ] && exit 1 参数小于4个就退出[ $# -gt 6 ] && exit 1 参数大于6个就退出echo "Configuring for ${BOARD_NAME} board..."## Create link to architecture specific headers 这段代码主要是将和arm架构有关的头文件做个链接，将asm连接到asm-arm#if [ "$SRCTREE" != "$OBJTREE" ] ; then mkdir -p ${OBJTREE}/include mkdir -p ${OBJTREE}/include2 cd ${OBJTREE}/include2 rm -f asm ln -s ${SRCTREE}/include/asm-$2 asm LNPREFIX="../../include2/asm/" cd ../include rm -rf asm-$2 rm -f asm mkdir asm-$2 ln -s asm-$2 asmelse cd ./include rm -f asm ln -s asm-$2 asmfirm -f asm-$2/archif [ -z "$6" -o "$6" = "NULL" ] ; then ln -s ${LNPREFIX}arch-$3 asm-$2/archelse ln -s ${LNPREFIX}arch-$6 asm-$2/archfiif [ "$2" = "arm" ] ; then rm -f asm-$2/proc ln -s ${LNPREFIX}proc-armv asm-$2/procfi## Create include file for Make 这段就是创建include/config.mk#echo "ARCH = $2" > config.mkecho "CPU = $3" >> config.mkecho "BOARD = $4" >> config.mk[ "$5" ] && [ "$5" != "NULL" ] && echo "VENDOR = $5" >> config.mk[ "$6" ] && [ "$6" != "NULL" ] && echo "SOC = $6" >> config.mk生成的文件是这样的：
## Create board specific header file 说明下开发板配置文件在哪，好让后面真正编译的时候可以找到这个配置文件#if [ "$APPEND" = "yes" ] # Append to existing config filethen echo >> config.helse > config.h # Create new config filefiecho "/* Automatically generated - do not edit */" >>config.hecho "#include <configs/$1.h>" >>config.h生成的文件如下：
exit 0至此第一条命令已经讲解完了。
3. make命令过程详解。
#########################################################################ifeq ($(OBJTREE)/include/config.mk,$(wildcard $(OBJTREE)/include/config.mk))# load ARCH, BOARD, and CPU configurationinclude $(OBJTREE)/include/config.mkexport ARCH CPU BOARD VENDOR SOC 将参数导入环境变量中选择交叉编译器ifndef CROSS_COMPILEifeq ($(HOSTARCH),ppc)CROSS_COMPILE =elseifeq ($(ARCH),ppc)CROSS_COMPILE = powerpc-linux-endififeq ($(ARCH),arm)CROSS_COMPILE = arm-linux-endififeq ($(ARCH),i386)ifeq ($(HOSTARCH),i386)CROSS_COMPILE =elseCROSS_COMPILE = i386-linux-endifendififeq ($(ARCH),mips)CROSS_COMPILE = mips_4KC-endififeq ($(ARCH),nios)CROSS_COMPILE = nios-elf-endififeq ($(ARCH),nios2)CROSS_COMPILE = nios2-elf-endififeq ($(ARCH),m68k)CROSS_COMPILE = m68k-elf-endififeq ($(ARCH),microblaze)CROSS_COMPILE = mb-endififeq ($(ARCH),blackfin)CROSS_COMPILE = bfin-elf-endififeq ($(ARCH),avr32)CROSS_COMPILE = avr32-endifendifendifCROSS_COMPILE = arm-linux-export CROSS_COMPILE# load other configurationinclude $(TOPDIR)/config.mk 这个文件主要实现交叉编译所需的基本配置########################################################################## U-Boot objects....order is important (i.e. start must be first)目标文件OBJS = cpu/$(CPU)/start.o 程序的入口就在start.s文件中ifeq ($(CPU),i386)OBJS += cpu/$(CPU)/start16.oOBJS += cpu/$(CPU)/reset.oendififeq ($(CPU),ppc4xx)OBJS += cpu/$(CPU)/resetvec.oendififeq ($(CPU),mpc85xx)OBJS += cpu/$(CPU)/resetvec.oendififeq ($(CPU),mpc86xx)OBJS += cpu/$(CPU)/resetvec.oendififeq ($(CPU),bf533)OBJS += cpu/$(CPU)/start1.o cpu/$(CPU)/interrupt.o cpu/$(CPU)/cache.oOBJS += cpu/$(CPU)/cplbhdlr.o cpu/$(CPU)/cplbmgr.o cpu/$(CPU)/flush.oendifOBJS := $(addprefix $(obj),$(OBJS))目标文件依赖库LIBS = lib_generic/libgeneric.aLIBS += board/$(BOARDDIR)/lib$(BOARD).aLIBS += cpu/$(CPU)/lib$(CPU).aifdef SOCLIBS += cpu/$(CPU)/$(SOC)/lib$(SOC).aendifLIBS += lib_$(ARCH)/lib$(ARCH).aLIBS += fs/cramfs/libcramfs.a fs/fat/libfat.a fs/fdos/libfdos.a fs/jffs2/libjffs2.a / fs/reiserfs/libreiserfs.a fs/ext2/libext2fs.aLIBS += net/libnet.aLIBS += disk/libdisk.aLIBS += rtc/librtc.aLIBS += dtt/libdtt.aLIBS += drivers/libdrivers.aLIBS += drivers/nand/libnand.aLIBS += drivers/nand_legacy/libnand_legacy.a# add to support onenand. by scsuhLIBS += drivers/onenand/libonenand.aifeq ($(CPU),mpc83xx)LIBS += drivers/qe/qe.aendifLIBS += drivers/sk98lin/libsk98lin.aLIBS += post/libpost.a post/cpu/libcpu.aLIBS += common/libcommon.aLIBS += $(BOARDLIBS)LIBS := $(addprefix $(obj),$(LIBS)).PHONY : $(LIBS)# Add GCC libPLATFORM_LIBS += -L $(shell dirname `$(CC) $(CFLAGS) -print-libgcc-file-name`) -lgcc# The "tools" are needed early, so put this first# Don't include stuff already done in $(LIBS)SUBDIRS = tools / examples / post / post/cpu.PHONY : $(SUBDIRS)ifeq ($(CONFIG_NAND_U_BOOT),y)NAND_SPL = nand_splU_BOOT_NAND = $(obj)u-boot-nand.binendif__OBJS := $(subst $(obj),,$(OBJS))__LIBS := $(subst $(obj),,$(LIBS))##################################################################################################################################################这个就是我们最终生成的目标文件ALL = $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND)all: $(ALL)$(obj)u-boot.hex: $(obj)u-boot $(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@$(obj)u-boot.srec: $(obj)u-boot $(OBJCOPY) ${OBJCFLAGS} -O srec $< $@$(obj)u-boot.bin: $(obj)u-boot $(OBJCOPY) ${OBJCFLAGS} -O binary $< $@ $(OBJDUMP) -d $< > $<.dis$(obj)u-boot.img: $(obj)u-boot.bin ./tools/mkimage -A $(ARCH) -T firmware -C none / -a $(TEXT_BASE) -e 0 / -n $(shell sed -n -e 's/.*U_BOOT_VERSION//p' $(VERSION_FILE) | / sed -e 's/"[ ]*$$/ for $(BOARD) board"/') / -d $< $@$(obj)u-boot.dis: $(obj)u-boot $(OBJDUMP) -d $< > $@
将生成的目标文件都连接起来$(obj)u-boot: depend version $(SUBDIRS) $(OBJS) $(LIBS) $(LDSCRIPT) UNDEF_SYM=`$(OBJDUMP) -x $(LIBS) |sed -n -e 's/.*/(__u_boot_cmd_.*/)/-u/1/p'|sort|uniq`;/ cd $(LNDIR) && $(LD) $(LDFLAGS) $$UNDEF_SYM $(__OBJS) / --start-group $(__LIBS) --end-group $(PLATFORM_LIBS) / -Map u-boot.map -o u-boot$(OBJS): $(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))$(LIBS): 分别对各个目录下的库文件进行编译 $(MAKE) -C $(dir $(subst $(obj),,$@))$(SUBDIRS): $(MAKE) -C $@ all$(NAND_SPL): version $(MAKE) -C nand_spl/board/$(BOARDDIR) all$(U_BOOT_NAND): $(NAND_SPL) $(obj)u-boot.bin cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.binversion: @echo -n "#define U_BOOT_VERSION /"U-Boot " > $(VERSION_FILE); / echo -n "$(U_BOOT_VERSION)" >> $(VERSION_FILE); / echo -n $(shell $(CONFIG_SHELL) $(TOPDIR)/tools/setlocalversion / $(TOPDIR)) >> $(VERSION_FILE); / echo "/"" >> $(VERSION_FILE)gdbtools: $(MAKE) -C tools/gdb all || exit 1updater: $(MAKE) -C tools/updater all || exit 1env: $(MAKE) -C tools/env all || exit 1depend dep: for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; donetags ctags: ctags -w -o $(OBJTREE)/ctags `find $(SUBDIRS) include / lib_generic board/$(BOARDDIR) cpu/$(CPU) lib_$(ARCH) / fs/cramfs fs/fat fs/fdos fs/jffs2 / net disk rtc dtt drivers drivers/sk98lin common / /( -name CVS -prune /) -o /( -name '*.[ch]' -print /)`etags: etags -a -o $(OBJTREE)/etags `find $(SUBDIRS) include / lib_generic board/$(BOARDDIR) cpu/$(CPU) lib_$(ARCH) / fs/cramfs fs/fat fs/fdos fs/jffs2 / net disk rtc dtt drivers drivers/sk98lin common / /( -name CVS -prune /) -o /( -name '*.[ch]' -print /)`$(obj)System.map: $(obj)u-boot @$(NM) $< | / grep -v '/(compiled/)/|/(/.o$$/)/|/( [aUw] /)/|/(/./.ng$$/)/|/(LASH[RL]DI/)' | / sort > $(obj)System.map#########################################################################elseall $(obj)u-boot.hex $(obj)u-boot.srec $(obj)u-boot.bin /$(obj)u-boot.img $(obj)u-boot.dis $(obj)u-boot /$(SUBDIRS) version gdbtools updater env depend /dep tags ctags etags $(obj)System.map: @echo "System not configured - see README" >&2 @ exit 1endif.PHONY : CHANGELOGCHANGELOG: git log --no-merges U-Boot-1_1_5.. | / unexpand -a | sed -e 's//s/s*$$//' > $@#########################################################################unconfig: @rm -f $(obj)include/config.h $(obj)include/config.mk / $(obj)board/*/config.tmp $(obj)board/*/*/config.tmp
至此对Uboot的分析结束了，可能讲述的不是太详细，但我想大家对整个编译流程应该挺清晰了。
希望大家可以给点建议，让这篇文章更好。
