u-boot编译过程分析
文章目录
- U-boot Makefile国建过程
- 主机构建环境配置过程
- 定义主机系统架构
- 定义主机操作系统类型
- 定义SHELL脚本的解释器
- 设定编译输出目录
- 目标机相关配置过程
- mkconfig脚本
- 传递给mkconfig脚本参数
- 检查参数合法性
- 创建到目录板相关目录的链接
- 构建`include/config.mk`文件
- 构建`include/config.h`文件
- make命令执行过程
- 顶层目录`config,mk`分析
- 包含与开发板相关的配置文件
- `u-boot.lds`文件
U-boot Makefile国建过程
主机构建环境配置过程
定义主机系统架构
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/ppc64/ppc/ \-e s/macppc/ppc/)
$(shell xxx)
是shell后面的语句,按照shell脚本进行执行
sed -e s/in/out/
是将输入的in
替换成out
运行示例:
andrew@andrew-Thurley:~/work/test$ uname -m
x86_64
# .为单个字符的通配符
andrew@andrew-Thurley:~/work/test$ uname -m |sed -e s/x86.64/x86/
x86
定义主机操作系统类型
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \sed -e 's/\(cygwin\).*/cygwin/')
tr '[:upper:]' '[:lower:]'
的作用是将标准输入中的所有大写字母转换为小写字母
执行示例
andrew@andrew-Thurley:~/work/test$ uname -s | tr '[:upper:]' '[:lower:]' | sed -e 's/\(cygwin\).*/cygwin/'
linux
定义SHELL脚本的解释器
uboot
顶层的Makefile
通过如下代码定义了shell
脚本的解释器SHELL
。"$BASH"的作用实质上是生成字符串"BASH"的作用实质上是生成字符串"BASH"的作用实质上是生成字符串"BASH" ,前一个$
的作用是说明第二个$
是普通字符。
# Set shell to bash if possible, otherwise fall back to sh
SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \else if [ -x /bin/bash ]; then echo /bin/bash; \else echo sh; fi; fi)
上述脚本的作用为,若当前Makefile
的shell
中定义了$BASH
环境变量,且文件$BASH
是可执行文件,则SHELL
的值为”$BASH“
,若/bin/bash
是可执行文件,则SHELL
的值为"/bin/bash"
。若以上两者都不成立,将sh
赋值给SHELL
变量。
设定编译输出目录
ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif
$(origin O)
表示,(origin O)
函数的输出,$(origin variable)
的输出是结果是一个字符串,由变量variable
定义的方式决定,若variable
是作为make
的参数时,$(origin variable)
输出commond line
字符串。
以上方式实现的效果为 make O=/tmp/buildall
, 因为,O作为make的参数,所以$(origin variable)
输出commond line
, BUILD_DIR
为/tmp/buildall
。
接下来的配置如下:
ifneq ($(BUILD_DIR),) #如果目录存在,就将目录赋值给saved-output
saved-output := $(BUILD_DIR)# Attempt to create a output directory.
# 目录存在接着执行,目录不存在创建目录
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})# Verify if it was successful.
# 确保目录存在
BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
# 对目录进行检测
$(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
endif # ifneq ($(BUILD_DIR),)
CURDIR表示的是当前目录
OBJTREE 若是没有定义BUILD_DIR,则输出目录就是CURDIR,也就是执行make的地方,这就是执行make没有指定目录的时候生成的u-boot会在顶层目录上。
$(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
如果第BUILD_DIR存在就BUILD_DIR,入股不存在就使用CURDIR
OBJTREE := $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
SRCTREE := $(CURDIR)
TOPDIR := $(SRCTREE)
LNDIR := $(OBJTREE)
export TOPDIR SRCTREE OBJTREEMKCONFIG := $(SRCTREE)/mkconfig
export MKCONFIGifneq ($(OBJTREE),$(SRCTREE))
REMOTE_BUILD := 1
export REMOTE_BUILD
endif
在没有包含config.mk之前先将obj,src变量定义好,并临时放到环境中
export obj src
# $(obj) and (src) are defined in config.mk but here in main Makefile
# we also need them before config.mk is included which is the case for
# some targets like unconfig, clean, clobber, distclean, etc.
ifneq ($(OBJTREE),$(SRCTREE))
obj := $(OBJTREE)/
src := $(SRCTREE)/
else
obj :=
src :=
endif
export obj src
目标机相关配置过程
顶层Makefile
存在与具体开发板的相关配置,其中@
的作用就执行该命令时不显示obj
是编译输出的目录,因此unconfig
的作用就是清楚上次执行make *_config
命令生成的配置文件。
$(@:_config=)
将传进来的所有参数的_config
替换为空,其中@
是指规则的目标,使用的语法为@(text:patternA=patternB)
这样的语法,将text
中所有以patternA
结尾的文本替换为patternB
,因此$(@:_config=)
的作用是将smdk2410_config
后面的_config
去掉,得到smdk2410
最终的效果相当于:
@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 samsung s3c24x0
==>
./mkconfig smdk2410 arm arm920t smdk2410 samsung s3c24x0
这种使用方法在mkconfig
中有给出
# Parameters: Target Architecture CPU Board [VENDOR] [SOC]
unconfig:@rm -f $(obj)include/config.h $(obj)include/config.mk \$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp \$(obj)include/autoconf.mk $(obj)include/autoconf.mk.depsmdk2410_config : unconfig@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 samsung s3c24x0
mkconfig脚本
传递给mkconfig脚本参数
传递给mkconfig
脚本的含义如下:
- smdk2410, Target(目标板的型号)
- arm, Architecture(目标板的CPU架构)
- arm920t, CPU(CPU使用的具体CPU型号)
- smdk2410,开发板名称
- samsung,VENDOR生产厂家名称
- s3c24x0,SOC(片上系统)
其中环境变量$#
表示传递给脚本的的参数的个数,
shift
的作用是原来的参数$1
将丢失,并将后面的参数向前进行平移,
APPEND=no # Default: Create new config file
BOARD_NAME="" # Name to print in make output
TARGETS=""while [ $# -gt 0 ] ; docase "$1" in--) shift ; break ;;-a) shift ; APPEND=yes ;;-n) shift ; BOARD_NAME="${1%%_config}" ; shift ;;-t) shift ; TARGETS="`echo $1 | sed 's:_: :g'` ${TARGETS}" ; shift ;;*) break ;;esac
done[ "${BOARD_NAME}" ] || BOARD_NAME="$1"
上述代码执行结束之后 BOARD_NAME = smdk2410
,因为顶层Makefile构造的mkconfig执行语句为
:./mkconfig smdk2410 arm arm920t smdk2410 samsung s3c24x0
检查参数合法性
下面的代码用于检查参数的合法性,参数的个数少于4个和多于6个都将认为是不合法的
[ $# -lt 4 ] && exit 1
[ $# -gt 6 ] && exit 1if [ "${ARCH}" -a "${ARCH}" != "$2" ]; thenecho "Failed: \$ARCH=${ARCH}, should be '$2' for ${BOARD_NAME}" 1>&2exit 1
fi
创建到目录板相关目录的链接
若编译输出到外部目录,则下面代码游戏哦啊。
"$SRCTREE" != "$OBJTREE"
条件成立的时候,就是外部定义了输出外部目录的时候
#
# Create link to architecture specific headers
#
if [ "$SRCTREE" != "$OBJTREE" ] ; thenmkdir -p ${OBJTREE}/includemkdir -p ${OBJTREE}/include2cd ${OBJTREE}/include2rm -f asmln -s ${SRCTREE}/include/asm-$2 asmLNPREFIX="../../include2/asm/"cd ../includerm -rf asm-$2rm -f asmmkdir asm-$2ln -s asm-$2 asm
若将目标文件设定为输出到源文件所在目录,就在顶层目录中的include目录下建立到asm-arm
目录的符号连接,代码如下,其中的ln -s asm-$2 asm
即 ln -s asm-arm asm
elsecd ./includerm -f asmln -s asm-$2 asm
fi
紧接着该脚本通过下面的代码建立符号链接include/asm-arm/arch
,若&6
(SOC)为空,则其链接到include/asm-arm/arch-arm920t
目录,否则使其链接到include/asm-arm/arch-s3cx0
目录,事实上include/asm-arm/arch-arm920t
并不存在,因此第六个参数必须填写。,否则会编译失效。
rm -f asm-$2/archif [ -z "$6" -o "$6" = "NULL" ] ; thenln -s ${LNPREFIX}arch-$3 asm-$2/arch
elseln -s ${LNPREFIX}arch-$6 asm-$2/arch
fi
开发板是arm
架构 proc链接到proc-armv
下。
if [ "$2" = "arm" ] ; thenrm -f asm-$2/procln -s ${LNPREFIX}proc-armv asm-$2/proc
fi
构建include/config.mk
文件
#
# Create include file for Make
#
echo "ARCH = $2" > config.mk
echo "CPU = $3" >> config.mk
echo "BOARD = $4" >> config.mk[ "$5" ] && [ "$5" != "NULL" ] && echo "VENDOR = $5" >> config.mk[ "$6" ] && [ "$6" != "NULL" ] && echo "SOC = $6" >> config.mk
上面代码实现的内容
ARCH = arm
CPU = arm920t
BOARD = smdk2410
VENDOR = samsung
SOC = s3c24x0
构建include/config.h
文件
#
# Create board specific header file
#
if [ "$APPEND" = "yes" ] # Append to existing config file
thenecho >> config.h #加个回车键
else> config.h # Create new config file
fi
echo "/* Automatically generated - do not edit */" >>config.hfor i in ${TARGETS} ; doecho "#define CONFIG_MK_${i} 1" >>config.h ;
doneecho "#include <configs/$1.h>" >>config.h
echo "#include <asm/config.h>" >>config.hexit 0
make命令执行过程
在搞清楚主机的构建环境和目标机相关配置之后,下面来分析执行make
命令并最终生成u-boot
镜像的过程。
正常的执行make smdk2410_config
时会进入到ifeq
的目录。
若主机和开发板的环境一样,则使用主机编译器,交叉编译工具定义为空
# set default to nothing for native builds
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?=
endif
紧接着包含顶层目录下的config.mk
# load other configuration
include $(TOPDIR)/config.mk
# The "tools" are needed early, so put this first
# Don't include stuff already done in $(LIBS)
SUBDIRS = tools \examples/standalone \examples/api.PHONY : $(SUBDIRS)ifeq ($(obj)include/config.mk,$(wildcard $(obj)include/config.mk))# Include autoconf.mk before config.mk so that the config options are available
# to all top level build files. We need the dummy all: target to prevent the
# dependency target in autoconf.mk.dep from being the default.
all:
sinclude $(obj)include/autoconf.mk.dep
sinclude $(obj)include/autoconf.mk# load ARCH, BOARD, and CPU configuration
include $(obj)include/config.mk
export ARCH CPU BOARD VENDOR SOC# set default to nothing for native builds
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?=
endif# load other configuration
include $(TOPDIR)/config.mk#########################################################################
# U-Boot objects....order is important (i.e. start must be first)OBJS = cpu/$(CPU)/start.o
ifeq ($(CPU),i386)
OBJS += cpu/$(CPU)/start16.o
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),ppc4xx)
OBJS += cpu/$(CPU)/resetvec.o
endif
ifeq ($(CPU),mpc85xx)
OBJS += cpu/$(CPU)/resetvec.o
endifOBJS := $(addprefix $(obj),$(OBJS))LIBS = lib_generic/libgeneric.a
LIBS += lib_generic/lzma/liblzma.a
LIBS += lib_generic/lzo/liblzo.a
LIBS += $(shell if [ -f board/$(VENDOR)/common/Makefile ]; then echo \"board/$(VENDOR)/common/lib$(VENDOR).a"; fi)
LIBS += cpu/$(CPU)/lib$(CPU).a
ifdef SOC
LIBS += cpu/$(CPU)/$(SOC)/lib$(SOC).a
endif
ifeq ($(CPU),ixp)
LIBS += cpu/ixp/npe/libnpe.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 fs/yaffs2/libyaffs2.a \fs/ubifs/libubifs.a
LIBS += net/libnet.a
LIBS += disk/libdisk.a
LIBS += drivers/bios_emulator/libatibiosemu.a
LIBS += drivers/block/libblock.a
LIBS += drivers/dma/libdma.a
LIBS += drivers/fpga/libfpga.a
LIBS += drivers/gpio/libgpio.a
LIBS += drivers/hwmon/libhwmon.a
LIBS += drivers/i2c/libi2c.a
LIBS += drivers/input/libinput.a
LIBS += drivers/misc/libmisc.a
LIBS += drivers/mmc/libmmc.a
LIBS += drivers/mtd/libmtd.a
LIBS += drivers/mtd/nand/libnand.a
LIBS += drivers/mtd/onenand/libonenand.a
LIBS += drivers/mtd/ubi/libubi.a
LIBS += drivers/mtd/spi/libspi_flash.a
LIBS += drivers/net/libnet.a
LIBS += drivers/net/phy/libphy.a
LIBS += drivers/net/sk98lin/libsk98lin.a
LIBS += drivers/pci/libpci.a
LIBS += drivers/pcmcia/libpcmcia.a
LIBS += drivers/power/libpower.a
LIBS += drivers/spi/libspi.a
ifeq ($(CPU),mpc83xx)
LIBS += drivers/qe/qe.a
endif
ifeq ($(CPU),mpc85xx)
LIBS += drivers/qe/qe.a
LIBS += cpu/mpc8xxx/ddr/libddr.a
LIBS += cpu/mpc8xxx/lib8xxx.a
TAG_SUBDIRS += cpu/mpc8xxx
endif
ifeq ($(CPU),mpc86xx)
LIBS += cpu/mpc8xxx/ddr/libddr.a
LIBS += cpu/mpc8xxx/lib8xxx.a
TAG_SUBDIRS += cpu/mpc8xxx
endif
LIBS += drivers/rtc/librtc.a
LIBS += drivers/serial/libserial.a
LIBS += drivers/twserial/libtws.a
LIBS += drivers/usb/gadget/libusb_gadget.a
LIBS += drivers/usb/host/libusb_host.a
LIBS += drivers/usb/musb/libusb_musb.a
LIBS += drivers/video/libvideo.a
LIBS += drivers/watchdog/libwatchdog.a
LIBS += common/libcommon.a
LIBS += libfdt/libfdt.a
LIBS += api/libapi.a
LIBS += post/libpost.aLIBS := $(addprefix $(obj),$(LIBS))
.PHONY : $(LIBS) $(TIMESTAMP_FILE) $(VERSION_FILE)LIBBOARD = board/$(BOARDDIR)/lib$(BOARD).a
LIBBOARD := $(addprefix $(obj),$(LIBBOARD))# Add GCC lib
ifdef USE_PRIVATE_LIBGCC
ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
PLATFORM_LIBGCC = -L $(OBJTREE)/lib_$(ARCH) -lgcc
else
PLATFORM_LIBGCC = -L $(USE_PRIVATE_LIBGCC) -lgcc
endif
else
PLATFORM_LIBGCC = -L $(shell dirname `$(CC) $(CFLAGS) -print-libgcc-file-name`) -lgcc
endif
PLATFORM_LIBS += $(PLATFORM_LIBGCC)
export PLATFORM_LIBS# Special flags for CPP when processing the linker script.
# Pass the version down so we can handle backwards compatibility
# on the fly.
LDPPFLAGS += \-include $(TOPDIR)/include/u-boot/u-boot.lds.h \$(shell $(LD) --version | \sed -ne 's/GNU ld version \([0-9][0-9]*\)\.\([0-9][0-9]*\).*/-DLD_MAJOR=\1 -DLD_MINOR=\2/p')ifeq ($(CONFIG_NAND_U_BOOT),y)
NAND_SPL = nand_spl
U_BOOT_NAND = $(obj)u-boot-nand.bin
endififeq ($(CONFIG_ONENAND_U_BOOT),y)
ONENAND_IPL = onenand_ipl
U_BOOT_ONENAND = $(obj)u-boot-onenand.bin
ONENAND_BIN ?= $(obj)onenand_ipl/onenand-ipl-2k.bin
endif__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS)) $(subst $(obj),,$(LIBBOARD))#########################################################################
########################################################################## Always append ALL so that arch config.mk's can add custom ones
ALL += $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND) $(U_BOOT_ONENAND)all: $(ALL)$(obj)u-boot.hex: $(obj)u-boot$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@$(obj)u-boot.srec: $(obj)u-boot$(OBJCOPY) -O srec $< $@$(obj)u-boot.bin: $(obj)u-boot$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@$(obj)u-boot.ldr: $(obj)u-boot$(obj)tools/envcrc --binary > $(obj)env-ldr.o$(LDR) -T $(CONFIG_BFIN_CPU) -c $@ $< $(LDR_FLAGS)$(obj)u-boot.ldr.hex: $(obj)u-boot.ldr$(OBJCOPY) ${OBJCFLAGS} -O ihex $< $@ -I binary$(obj)u-boot.ldr.srec: $(obj)u-boot.ldr$(OBJCOPY) ${OBJCFLAGS} -O srec $< $@ -I binary$(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.kwb: $(obj)u-boot.bin$(obj)tools/mkimage -n $(KWD_CONFIG) -T kwbimage \-a $(TEXT_BASE) -e $(TEXT_BASE) -d $< $@$(obj)u-boot.sha1: $(obj)u-boot.bin$(obj)tools/ubsha1 $(obj)u-boot.bin$(obj)u-boot.dis: $(obj)u-boot$(OBJDUMP) -d $< > $@GEN_UBOOT = \UNDEF_SYM=`$(OBJDUMP) -x $(LIBBOARD) $(LIBS) | \sed -n -e 's/.*\($(SYM_PREFIX)__u_boot_cmd_.*\)/-u\1/p'|sort|uniq`;\cd $(LNDIR) && $(LD) $(LDFLAGS) $$UNDEF_SYM $(__OBJS) \--start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \-Map u-boot.map -o u-boot
$(obj)u-boot: depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds$(GEN_UBOOT)
ifeq ($(CONFIG_KALLSYMS),y)smap=`$(call SYSTEM_MAP,u-boot) | \awk '$$2 ~ /[tTwW]/ {printf $$1 $$3 "\\\\000"}'` ; \$(CC) $(CFLAGS) -DSYSTEM_MAP="\"$${smap}\"" \-c common/system_map.c -o $(obj)common/system_map.o$(GEN_UBOOT) $(obj)common/system_map.o
endif$(OBJS): depend$(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))$(LIBS): depend $(SUBDIRS)$(MAKE) -C $(dir $(subst $(obj),,$@))$(LIBBOARD): depend $(LIBS)$(MAKE) -C $(dir $(subst $(obj),,$@))$(SUBDIRS): depend$(MAKE) -C $@ all$(LDSCRIPT): depend$(MAKE) -C $(dir $@) $(notdir $@)$(obj)u-boot.lds: $(LDSCRIPT)$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -ansi -D__ASSEMBLY__ -P - <$^ >$@$(NAND_SPL): $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk$(MAKE) -C nand_spl/board/$(BOARDDIR) all$(U_BOOT_NAND): $(NAND_SPL) $(obj)u-boot.bincat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin$(ONENAND_IPL): $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk$(MAKE) -C onenand_ipl/board/$(BOARDDIR) all$(U_BOOT_ONENAND): $(ONENAND_IPL) $(obj)u-boot.bincat $(ONENAND_BIN) $(obj)u-boot.bin > $(obj)u-boot-onenand.bin$(VERSION_FILE):@( printf '#define U_BOOT_VERSION "U-Boot %s%s"\n' "$(U_BOOT_VERSION)" \'$(shell $(TOPDIR)/tools/setlocalversion $(TOPDIR))' ) > $@.tmp@cmp -s $@ $@.tmp && rm -f $@.tmp || mv -f $@.tmp $@$(TIMESTAMP_FILE):@date +'#define U_BOOT_DATE "%b %d %C%y"' > $@@date +'#define U_BOOT_TIME "%T"' >> $@gdbtools:$(MAKE) -C tools/gdb all || exit 1updater:$(MAKE) -C tools/updater all || exit 1env:$(MAKE) -C tools/env all MTD_VERSION=${MTD_VERSION} || exit 1depend dep: $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mkfor dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; doneTAG_SUBDIRS += include
TAG_SUBDIRS += lib_generic board/$(BOARDDIR)
TAG_SUBDIRS += cpu/$(CPU)
TAG_SUBDIRS += lib_$(ARCH)
TAG_SUBDIRS += fs/cramfs
TAG_SUBDIRS += fs/fat
TAG_SUBDIRS += fs/fdos
TAG_SUBDIRS += fs/jffs2
TAG_SUBDIRS += fs/yaffs2
TAG_SUBDIRS += net
TAG_SUBDIRS += disk
TAG_SUBDIRS += common
TAG_SUBDIRS += drivers/bios_emulator
TAG_SUBDIRS += drivers/block
TAG_SUBDIRS += drivers/gpio
TAG_SUBDIRS += drivers/hwmon
TAG_SUBDIRS += drivers/i2c
TAG_SUBDIRS += drivers/input
TAG_SUBDIRS += drivers/misc
TAG_SUBDIRS += drivers/mmc
TAG_SUBDIRS += drivers/mtd
TAG_SUBDIRS += drivers/mtd/nand
TAG_SUBDIRS += drivers/mtd/onenand
TAG_SUBDIRS += drivers/mtd/spi
TAG_SUBDIRS += drivers/net
TAG_SUBDIRS += drivers/net/sk98lin
TAG_SUBDIRS += drivers/pci
TAG_SUBDIRS += drivers/pcmcia
TAG_SUBDIRS += drivers/qe
TAG_SUBDIRS += drivers/rtc
TAG_SUBDIRS += drivers/serial
TAG_SUBDIRS += drivers/spi
TAG_SUBDIRS += drivers/usb
TAG_SUBDIRS += drivers/videotags ctags:ctags -w -o $(obj)ctags `find $(SUBDIRS) $(TAG_SUBDIRS) \-name '*.[ch]' -print`etags:etags -a -o $(obj)etags `find $(SUBDIRS) $(TAG_SUBDIRS) \-name '*.[ch]' -print`
cscope:find $(SUBDIRS) $(TAG_SUBDIRS) -name '*.[ch]' -print \> cscope.filescscope -b -q -kSYSTEM_MAP = \$(NM) $1 | \grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \LC_ALL=C sort
$(obj)System.map: $(obj)u-boot@$(call SYSTEM_MAP,$<) > $(obj)System.map#
# Auto-generate the autoconf.mk file (which is included by all makefiles)
#
# This target actually generates 2 files; autoconf.mk and autoconf.mk.dep.
# the dep file is only include in this top level makefile to determine when
# to regenerate the autoconf.mk file.
$(obj)include/autoconf.mk.dep: $(obj)include/config.h include/common.h@$(XECHO) Generating $@ ; \set -e ; \: Generate the dependancies ; \$(CC) -x c -DDO_DEPS_ONLY -M $(HOSTCFLAGS) $(CPPFLAGS) \-MQ $(obj)include/autoconf.mk include/common.h > $@$(obj)include/autoconf.mk: $(obj)include/config.h@$(XECHO) Generating $@ ; \set -e ; \: Extract the config macros ; \$(CPP) $(CFLAGS) -DDO_DEPS_ONLY -dM include/common.h | \sed -n -f tools/scripts/define2mk.sed > $@.tmp && \mv $@.tmp $@#########################################################################
else # !config.mk
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) $(TIMESTAMP_FILE) $(VERSION_FILE) gdbtools updater env depend \
dep tags ctags etags cscope $(obj)System.map:@echo "System not configured - see README" >&2@ exit 1
endif # config.mk
顶层目录config,mk
分析
设置编译选项
# clean the slate ...
PLATFORM_RELFLAGS =
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =
检查编译器是否支持某些选项的函数定义
#########################################################################
#
# Option checker (courtesy linux kernel) to ensure
# only supported compiler options are used
#
cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)
函数使用
可以向这样调用cc-option函数
GFLAGS += $(call cc-option, option1, option2)
CFLAGS += $(call cc-option,-fno-stack-protector)
执行交叉编译工具
#
# Include the make variables (CC, etc...)
#
AS = $(CROSS_COMPILE)as
LD = $(CROSS_COMPILE)ld
CC = $(CROSS_COMPILE)gcc
CPP = $(CC) -E
AR = $(CROSS_COMPILE)ar
NM = $(CROSS_COMPILE)nm
LDR = $(CROSS_COMPILE)ldr
STRIP = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
RANLIB = $(CROSS_COMPILE)RANLIB
对于arm开发板,上面代码中的CROSS_COMPILE在lib_arm/config.mk中定义
CROSS_COMPILE ?= arm-linux-
包含与开发板相关的配置文件
在下面的代码中,$(ARCH)
的值为"arm",因此将lib_arm/config.mk
包含进来
# Load generated board configuration
sinclude $(OBJTREE)/include/autoconf.mkifdef ARCH
sinclude $(TOPDIR)/lib_$(ARCH)/config.mk # include architecture dependend rules
endif
depend的作用是,生成depend依赖,执行该命令将一次进入$(SUBDIRS)
表示的子目录中,并执行,make _depend
命令,生成各个子目录中的.depend文件,在.depend文件中列出每个目标文件的依赖文件
$(obj)u-boot: depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT) $(obj)u-boot.lds$(GEN_UBOOT)
u-boot.lds
文件
# 指定输出的可执行文件是32位的ARM指令,小端模式的ELF格式
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
# 指定输出可执行平台为ARM
OUTPUT_ARCH(arm)# 指定程序的入口为_start
ENTRY(_start)
SECTIONS
{# 指定目标代码的起始地址从0x00开始,"."代表当前位置. = 0x00000000;# 标示4字节对齐. = ALIGN(4);.text :{# 表明 start.o是代码段的第一个.o文件cpu/arm920t/start.o (.text)# 代码段的其余部分*(.text)}. = ALIGN(4);.rodata : { *(SORT_BY_ALIGNMENT(SORT_BY_NAME(.rodata*))) }. = ALIGN(4);# 数据段.data : { *(.data) }. = ALIGN(4);.got : { *(.got) }. = .;__u_boot_cmd_start = .;.u_boot_cmd : { *(.u_boot_cmd) }__u_boot_cmd_end = .;. = ALIGN(4);# __bss_start 标号指向bss段的开始位置__bss_start = .;# 这里是bss段 存放程序中位初始化变量的一块内存.bss (NOLOAD) : { *(.bss) . = ALIGN(4); }_end = .;
}
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