uboot的源文件众多,学习庞然大物首先找到脊椎--顶层的makfile,逐一破解。但是,uboot的makefile同样是一个庞然大物,所以也要找到它的主线。倘若过分专注部分细节,很难做到把握全局,实际上也不可能很好理解细节。
介于此,笔者已经写了一篇uboot makefile整体解析,可以先从主体上把握makefile。然后,再读这篇makefile强大功能实现的细节,才能做到循序渐进。
说明:uboot顶层makefile的注释机会全部源码都搬上来了,而注释都是黑体加粗以与源码有强烈的区别。
VERSION = 1 //主版本号
PATCHLEVEL = 1 //次级版本号
SUBLEVEL = 6
EXTRAVERSION = //版本号扩展
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION) //这个Uboot的版本为1.1.6
VERSION_FILE = $(obj)include/version_autogenerated.h
//生成uboot的版本信息
HOSTARCH := $(shell uname -m | \
sed -e s/i.86/i386/ \
-e s/sun4u/sparc64/ \
-e s/arm.*/arm/ \
-e s/sa110/arm/ \
-e s/powerpc/ppc/ \
-e s/macppc/ppc/)
//获取主机架构,笔者电脑是酷睿双核,#uname –m输出结构是i686,执行替换命令sed -e s/i.86/i386/后,就变成了i386,
//并且将这个值保存在HOSTARCH变量中。
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
sed -e 's/\(cygwin\).*/cygwin/')
//获取主机操作系统,执行#uname -s可以查看自己的操作系统类型,笔者使用的操作系统是Linux。tr '[:upper:]' '[:lower:]'
//具有大写转小写的功能,所以最终HOSTOS的值为linux。
export HOSTARCH HOSTOS
//将两个变量导出,可以供嵌套的makefile调用
# Deal with colliding definitions from tcsh etc.
VENDOR=
#########################################################################
# U-boot build supports producing a object files to the separate external
# directory. Two use cases are supported:
# 1) Add O= to the make command line
# 'make O=/tmp/build all'
# 2) Set environement variable BUILD_DIR to point to the desired location
# 'export BUILD_DIR=/tmp/build'
# 'make'
# The second approach can also be used with a MAKEALL script
# 'export BUILD_DIR=/tmp/build'
# './MAKEALL'
# Command line 'O=' setting overrides BUILD_DIR environent variable.
# When none of the above methods is used the local build is performed and
# the object files are placed in the source directory.
//上边的注释讲的是uboot支持编译时,将目标文件生成在其他的目录中,这样可以保持源文件的干净,另外从目标
//文件的生成目录中查看生成的文件时一目了然。如果想要这样做,提供了两种方法。第一种方法是执行命令
//#make O=/tmp/build all;第二种方法,可以先在命令行模式定义环境变量export BUILD_DIR=/tmp/build',
//然后再执行make就行了。通常懒惰的编译方式就是让生成的目标文件和源文件混在一起,那么BUILD_DIR就会没定义。
ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif
//这是第一种方法的实现过程,$(origin O)是输出变量O的定义来源,假设在命令行模式输//入#make O=/tmp/build all
//来编译,那么O的定义来源是命令行,函数的输出是command line。
ifneq ($(BUILD_DIR),)
//倘若BUILD_DIR定义过了,也就是不希望目标文件与源文件混在一起,那么直到“endif # //ifneq ($(BUILD_DIR),)”
//的内容都有效;倘若没有定义BUILD_DIR,那么这部分代码将不起作用。
saved-output := $(BUILD_DIR)
// 将BUILD_DIR保存在saved-output变量中
# Attempt to create a output directory.
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})
//-d是判断BUILD_DIR是否存在,倘若不存在就就创建。mkdir的-p参数代表若路径中的
//某些目录不存在,也一并创建
# Verify if it was successful.
//核查BUILD_DIR是否已经创建
BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
//试图进入$(BUILD_DIR),倘若能进入,则将它的路径赋给BUILD_DIR,注意这时的BUILD_DIR已经是一个真实存在
//目录的代言人,而之前的只是希望创建的目录。需要说明的是倘若BUILD_DIR还没有创建,那么cd $(BUILD_DIR)将执
//行错误,返回值是空,虽然这时发生错误,但是编译会忽略这个错误还能继续进行。
$(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
// 如果没有创建成功,就执行error函数,输出信息output directory "$(saved-output)" does not exist),然后编译终止
endif # ifneq ($(BUILD_DIR),)
OBJTREE := $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
//如果BUILD_DIR不为空,目标目录就等于BUILD_DIR;倘若没定义,就取为当前目录
SRCTREE := $(CURDIR)//源文件目录等于当前文件夹
TOPDIR := $(SRCTREE)//顶层目录等于源文件目录
LNDIR := $(OBJTREE) //连接目录等于BUILD_DIR
export TOPDIR SRCTREE OBJTREE//将这三个变量导出
MKCONFIG := $(SRCTREE)/mkconfig//指定mkconfig的位置
export MKCONFIG //将MKCONFIG变量导出
ifneq ($(OBJTREE),$(SRCTREE)) //如果目标目录和源文件目录不相等
REMOTE_BUILD := 1 //就定义REMOTE_BUILD变量并取值为1
export REMOTE_BUILD //然后再将变量导出
endif
# $(obj) and (src) are defined in config.mk but here in main Makefile
# we also need them before config.mk is included which is the case for
# some targets like unconfig, clean, clobber, distclean, etc.
//obj和src的定义也出现在了顶层目录的config.mk中,但是config.mk中的定义由于受下边//红色加粗判断语句的影响,只有
//在“make *_config”执行后($(OBJTREE)/include/config.mk就会存在),再执行的make程序才能将config.mk包含进顶
//层makefile中。而在没有先执行“make *_config”或者$(OBJTREE)/include/config.mk不存在的情况下,如果想执行unconfig
//, clean, clobber, distclean,而这些命令用到了变量obj、src,所以这里提前包含进去。
//但是我也有疑惑,为什么不能将顶层目录的config.mk包含在全局中,设计者为什么要把它放在条件执行里边。
ifneq ($(OBJTREE),$(SRCTREE))
obj := $(OBJTREE)/
src := $(SRCTREE)/
else
obj :=
src :=
endif
export obj src
//定义变量obj和src,并将这两个变量导出,obj是编译目标文件的前缀,从而实现生成的目标文件在于源文件相区别的目录中
#########################################################################
ifeq ($(OBJTREE)/include/config.mk,$(wildcard $(OBJTREE)/include/config.mk))
//这个ifeq横跨的范围非常广,用红色加粗字体表明。只有$(OBJTREE)/include/config.mk存在(也就是说已经
//执行了make *.config)的情况下,这部分包含的内容才有效
# load ARCH, BOARD, and CPU configuration
include $(OBJTREE)/include/config.mk //将make *_config生成的config.mk文件包含进来
export ARCH CPU BOARD VENDOR SOC //导出5个变量以供其他子目录的makefile调用
ifndef CROSS_COMPILE
ifeq ($(HOSTARCH),ppc)
CROSS_COMPILE =
else
ifeq ($(ARCH),ppc)
CROSS_COMPILE = powerpc-linux-
endif
ifeq ($(ARCH),arm)
CROSS_COMPILE = arm-linux- //根据变量ARCH可以使这行满足条件,确定了交叉编译使//用arm-linux-
endif
ifeq ($(ARCH),i386)
ifeq ($(HOSTARCH),i386)
CROSS_COMPILE =
else
CROSS_COMPILE = i386-linux-
endif
endif
ifeq ($(ARCH),mips)
CROSS_COMPILE = mips_4KC-
endif
ifeq ($(ARCH),nios)
CROSS_COMPILE = nios-elf-
endif
ifeq ($(ARCH),nios2)
CROSS_COMPILE = nios2-elf-
endif
ifeq ($(ARCH),m68k)
CROSS_COMPILE = m68k-elf-
endif
ifeq ($(ARCH),microblaze)
CROSS_COMPILE = mb-
endif
ifeq ($(ARCH),blackfin)
CROSS_COMPILE = bfin-elf-
endif
ifeq ($(ARCH),avr32)
CROSS_COMPILE = avr32-
endif
endif
endif
export CROSS_COMPILE //导出交叉编译变量
# load other configuration
include $(TOPDIR)/config.mk //将顶层的config.mk也包含进来
#########################################################################
# U-Boot objects....order is important (i.e. start must be first)
OBJS = cpu/$(CPU)/start.o
ifeq ($(CPU),i386)
OBJS += cpu/$(CPU)/start16.o
OBJS += cpu/$(CPU)/reset.o
endif
ifeq ($(CPU),ppc4xx)
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc83xx)
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc85xx)
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc86xx)
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),bf533)
OBJS += cpu/$(CPU)/start1.o cpu/$(CPU)/interrupt.o cpu/$(CPU)/cache.o
OBJS += cpu/$(CPU)/cplbhdlr.o cpu/$(CPU)/cplbmgr.o cpu/$(CPU)/flush.o
endif
//确定目标文件构成
OBJS := $(addprefix $(obj),$(OBJS))
//给待生成的目标文件带上路径
LIBS = lib_generic/libgeneric.a
LIBS += board/$(BOARDDIR)/lib$(BOARD).a
LIBS += cpu/$(CPU)/lib$(CPU).a
ifdef SOC
LIBS += cpu/$(CPU)/$(SOC)/lib$(SOC).a
endif
LIBS += lib_$(ARCH)/lib$(ARCH).a
LIBS += fs/cramfs/libcramfs.a fs/fat/libfat.a fs/fdos/libfdos.a fs/jffs2/libjffs2.a \
fs/reiserfs/libreiserfs.a fs/ext2/libext2fs.a
LIBS += net/libnet.a
LIBS += disk/libdisk.a
LIBS += rtc/librtc.a
LIBS += dtt/libdtt.a
LIBS += drivers/libdrivers.a
LIBS += drivers/nand/libnand.a
LIBS += drivers/nand_legacy/libnand_legacy.a
LIBS += drivers/sk98lin/libsk98lin.a
LIBS += post/libpost.a post/cpu/libcpu.a
LIBS += common/libcommon.a
LIBS += $(BOARDLIBS)
//确定库文件构成
LIBS := $(addprefix $(obj),$(LIBS))
//给待生成的库文件带上路径
.PHONY : $(LIBS)
//将带生成的库文件作为伪目标来处理
# Add GCC lib
PLATFORM_LIBS += -L $(shell dirname `$(CC) $(CFLAGS) -print-libgcc-file-name`) -lgcc
//添加系统标准库
# The "tools" are needed early, so put this first
# Don't include stuff already done in $(LIBS)
SUBDIRS = tools \
examples \
post \
post/cpu
.PHONY : $(SUBDIRS)
//定义make执行要首先处理的目录
ifeq ($(CONFIG_NAND_U_BOOT),y)
NAND_SPL = nand_spl
U_BOOT_NAND = $(obj)u-boot-nand.bin
endif
//假若定义了CONFIG_NAND_U_BOOT,那么将总目标all中添加$(obj)u-boot-nand.bin,否则不添加
__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS))
//OBJS、LIBS除去$(obj)部分的路径
#########################################################################
ALL = $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND)
//总目标的构成,也可以人为添加其他的目标
all: $(ALL)
//定义总目标all
$(obj)u-boot.hex: $(obj)u-boot
$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@
//生成16进制的可执行程序
$(obj)u-boot.srec: $(obj)u-boot
$(OBJCOPY) ${OBJCFLAGS} -O srec $< $@
$(obj)u-boot.bin: $(obj)u-boot
$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@
//生成2进制的可执行程序
$(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 $< > $@
//生成反汇编文件u-boot.dis
$(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) $$UNDEF_SYM $(__OBJS) \
--start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \
-Map u-boot.map -o u-boot
//生成elf格式的u-boot文件
$(OBJS):
$(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))
//中间目标文件生成
$(LIBS):
$(MAKE) -C $(dir $(subst $(obj),,$@))
//中间库文件生成
$(SUBDIRS):
$(MAKE) -C $@ all
//SUBDIRS目录处理
$(NAND_SPL): version
$(MAKE) -C nand_spl/board/$(BOARDDIR) all
$(U_BOOT_NAND): $(NAND_SPL) $(obj)u-boot.bin
cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin
version:
@echo -n "#define U_BOOT_VERSION \"U-Boot " > $(VERSION_FILE); \
echo -n "$(U_BOOT_VERSION)" >> $(VERSION_FILE); \
echo -n $(shell $(CONFIG_SHELL) $(TOPDIR)/tools/setlocalversion \
$(TOPDIR)) >> $(VERSION_FILE); \
echo "\"" >> $(VERSION_FILE)
//版本头文件生成
gdbtools:
$(MAKE) -C tools/gdb all || exit 1
updater:
$(MAKE) -C tools/updater all || exit 1
env:
$(MAKE) -C tools/env all || exit 1
depend dep:
for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; done
//执行make depend或者make dep都能触发命令
tags 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
//生成map文件
#########################################################################
else
all $(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 1
endif
//倘若没有include $(OBJTREE)/include/config.mk 文件,将打印出错误信息“System not configured
//- see README”,并且make程序也结束
.PHONY : CHANGELOG
CHANGELOG:
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 $(obj)board/*/*/config.tmp
//删除配置文件,即与make *_config过程相反
//剩下的*_config,属于相似内容,只举一个常见的smdk2410_config,以作说明
smdk2410_config : unconfig
@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 NULL s3c24x0
//执行make smdk2410_config,就会调用顶层目录中的mkconfig(shell脚本),同时给这个脚本传入参数
//arm arm920t smdk2410 NULL s3c24x0。mkconfig脚本根据这些传入的参数生成与开发板相适应的一系列配置文件。
#########################################################################
//不要忘记makfile的最后边,还有一部分很重要的内容
clean: //clean删除
find $(OBJTREE) -type f \
\( -name 'core' -o -name '*.bak' -o -name '*~' \
-o -name '*.o' -o -name '*.a' \) -print \
| xargs rm -f
rm -f $(obj)examples/hello_world $(obj)examples/timer \
$(obj)examples/eepro100_eeprom $(obj)examples/sched \
$(obj)examples/mem_to_mem_idma2intr $(obj)examples/82559_eeprom \
$(obj)examples/smc91111_eeprom $(obj)examples/interrupt \
$(obj)examples/test_burst
rm -f $(obj)tools/img2srec $(obj)tools/mkimage $(obj)tools/envcrc \
$(obj)tools/gen_eth_addr
rm -f $(obj)tools/mpc86x_clk $(obj)tools/ncb
rm -f $(obj)tools/easylogo/easylogo $(obj)tools/bmp_logo
rm -f $(obj)tools/gdb/astest $(obj)tools/gdb/gdbcont $(obj)tools/gdb/gdbsend
rm -f $(obj)tools/env/fw_printenv $(obj)tools/env/fw_setenv
rm -f $(obj)board/cray/L1/bootscript.c $(obj)board/cray/L1/bootscript.image
rm -f $(obj)board/netstar/eeprom $(obj)board/netstar/crcek $(obj)board/netstar/crcit
rm -f $(obj)board/netstar/*.srec $(obj)board/netstar/*.bin
rm -f $(obj)board/trab/trab_fkt $(obj)board/voiceblue/eeprom
rm -f $(obj)board/integratorap/u-boot.lds $(obj)board/integratorcp/u-boot.lds
rm -f $(obj)include/bmp_logo.h
rm -f $(obj)nand_spl/u-boot-spl $(obj)nand_spl/u-boot-spl.map
clobber: clean //除了调用clean删除,还要再执行额外的删除命令
find $(OBJTREE) -type f \( -name .depend \
-o -name '*.srec' -o -name '*.bin' -o -name u-boot.img \) \
-print0 \
| xargs -0 rm -f
rm -f $(OBJS) $(obj)*.bak $(obj)ctags $(obj)etags $(obj)TAGS $(obj)include/version_autogenerated.h
rm -fr $(obj)*.*~
rm -f $(obj)u-boot $(obj)u-boot.map $(obj)u-boot.hex $(ALL)
rm -f $(obj)tools/crc32.c $(obj)tools/environment.c $(obj)tools/env/crc32.c
rm -f $(obj)tools/inca-swap-bytes $(obj)cpu/mpc824x/bedbug_603e.c
rm -f $(obj)include/asm/proc $(obj)include/asm/arch $(obj)include/asm
[ ! -d $(OBJTREE)/nand_spl ] || find $(obj)nand_spl -lname "*" -print | xargs rm -f
ifeq ($(OBJTREE),$(SRCTREE))
mrproper \
distclean: clobber unconfig //倘若目标目录与源目录相同,distclean调用clobber unconfig来删除
else
mrproper \
distclean: clobber unconfig //倘若目标目录与源目录不相同,distclean调用clobber unconfig来删除
rm -rf $(OBJTREE)/* //而且,还要删除OBJTREE目录下的所有内容
endif
backup: //打包备份
F=`basename $(TOPDIR)` ; cd .. ; \ //跳到当前目录的外边,然后打包整个文件夹
gtar --force-local -zcvf `date "+$ $F-%Y-%m-%d-%T.tar.gz"` $ $F //打包,名字中插入日期
#########################################################################
//最后,插入编译过程中重要的打印信息(要深入理解u-boot的makefile工作原理,必须做实际的实验,实际的make一下,
//看看你正想了解的地方发生了什么)
start.o
libsmdk2410.a
libarm920t.a
all目标的实现
参考博客:U-Boot Makefile分析