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。"$ B A S H " 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 OBJTREE
MKCONFIG := $(SRCTREE)/mkconfig
export MKCONFIG
ifneq ($(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 $(obj)include/autoconf.mk.dep
smdk2410_config : unconfig
@$(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 ] ; do
case "$1" in
--) shift ; break ;;
-a) shift ; APPEND=yes ;;
-n) shift ; BOARD_NAME="${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
[ $# -gt 6 ] && exit 1
if [ "${ARCH}" -a "${ARCH}" != "$2" ]; then
echo "Failed: \$ARCH=${ARCH}, should be '$2' for ${BOARD_NAME}" 1>&2
exit 1
fi
创建到目录板相关目录的链接
若编译输出到外部目录，则下面代码游戏哦啊。
"$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" ] ; 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 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
else
cd ./include
rm -f asm
ln -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/arch
if [ -z "$6" -o "$6" = "NULL" ] ; then
ln -s ${LNPREFIX}arch-$3 asm-$2/arch
else
ln -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" ] ; then
rm -f asm-$2/proc
ln -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
then
echo >> config.h #加个回车键
else
> config.h # Create new config file
fi
echo "/* Automatically generated - do not edit */" >>config.h
for i in ${TARGETS} ; do
echo "#define CONFIG_MK_${i} 1" >>config.h ;
done
echo "#include $1 .h>" >>config.h
echo "#include " >>config.h
exit 0
make命令执行过程
在搞清楚主机的构建环境和目标机相关配置之后，下面来分析执行make命令并最终生成u-boot镜像的过程。
正常的执行make smdk2410_config时会进入到ifeq的目录。
若主机和开发板的环境一样，则使用主机编译器，交叉编译工具定义为空
# set default to nothing for native builds
ifeq ($(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
endif
OBJS := $(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.a
LIBS := $(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 = $(obj)u-boot-nand.bin
endif
ifeq ($(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="\"$${smap}\"" \
-c common/system_map.c -o $(obj)common/system_map.o
$(GEN_UBOOT) $(obj)common/system_map.o
endif
$(OBJS): depend
$(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))
$(LIBS): depend $(SUBDIRS)
$(MAKE) -C $(dir $(subst $(obj),,$@))
$(LIBBOARD): depend $(LIBS)
$(MAKE) -C $(dir $(subst $(obj),,$@))
$(SUBDIRS): depend
$(MAKE) -C $@ all
$(LDSCRIPT): depend
$(MAKE) -C $(dir $@) $(notdir $@)
$(obj)u-boot.lds: $(LDSCRIPT)
$(CPP) $(CPPFLAGS) $(LDPPFLAGS) -ansi -D__ASSEMBLY__ -P - <$^ >$@
$(NAND_SPL): $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
$(MAKE) -C nand_spl/board/$(BOARDDIR) all
$(U_BOOT_NAND): $(NAND_SPL) $(obj)u-boot.bin
cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin
$(ONENAND_IPL): $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
$(MAKE) -C onenand_ipl/board/$(BOARDDIR) all
$(U_BOOT_ONENAND): $(ONENAND_IPL) $(obj)u-boot.bin
cat $(ONENAND_BIN) $(obj)u-boot.bin > $(obj)u-boot-onenand.bin
$(VERSION_FILE):
@( printf '#define U_BOOT_VERSION "U-Boot %s%s"\n' "$(U_BOOT_VERSION)" \
'$(shell $(TOPDIR)/tools/setlocalversion $(TOPDIR))' ) > [email protected]
@cmp -s $@ [email protected] && rm -f [email protected] || mv -f [email protected] $@
$(TIMESTAMP_FILE):
@date +'#define U_BOOT_DATE "%b %d %C%y"' > $@
@date +'#define U_BOOT_TIME "%T"' >> $@
gdbtools:
$(MAKE) -C tools/gdb all || exit 1
updater:
$(MAKE) -C tools/updater all || exit 1
env:
$(MAKE) -C tools/env all MTD_VERSION=${MTD_VERSION} || exit 1
depend dep: $(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; done
TAG_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/video
tags 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.files
cscope -b -q -k
SYSTEM_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.mk
ifdef 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 = .;
}