u-boot的Makefile分析

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2024-10-22 15:16:39 212人阅读

由顶层Makefile文件，梳理U-Boot的编译流程。

小技巧：

在大型Makefile中，很多时候需要确定某个变量的值，一个小方法就是：

$(shell echo "VARIABLE0_VAL = $(VARIABLE0_VAL)" > v_file.txt )
$(shell echo "VARIABLE1_VAL = $(VARIABLE1_VAL)" >> v_file.txt )

1、首先，确定make过程中需要的变量(Makefile的注视符改为/* */)。

VERSION = 2010
PATCHLEVEL = 06
SUBLEVEL =
EXTRAVERSION =
ifneq "$(SUBLEVEL)" ""
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
else
/* U_BOOT_VERSION = 2010.06 */
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL)$(EXTRAVERSION)
endif

/* obj变量为空 */
TIMESTAMP_FILE = $(obj)include/timestamp_autogenerated.h
VERSION_FILE = $(obj)include/version_autogenerated.h

/* HOSTARCH：获取主机的硬件架构
 * "sed -e"表示后面跟的是命令脚本，"s/xxx/yyy/"表示从打印信息中查找"xxx"然后替换为"yyy"，"."为通配符。
 * uname -m获取主机架构信息的命令
 * 执行流程：
 * uname -m结果为"i686"，符合"s/i.86/i386/"命令脚本，"i686"被替换为"i386"
 * 最终结果：HOSTARCH = i386
 */
HOSTARCH := $(shell uname -m | 	sed -e s/i.86/i386/ 	    -e s/sun4u/sparc64/ 	    -e s/arm.*/arm/ 	    -e s/sa110/arm/ 	    -e s/ppc64/powerpc/ 	    -e s/ppc/powerpc/ 	    -e s/macppc/powerpc/)

/* -s, print the kernel name
 * [:upper:], all upper case letters
 * [:lower:], all lower case letters
 * 执行流程：
 * uname -s得到内核名"Linux"，tr把字串的大写转换成小写
 * 最终结果：HOSTOS = linux
 */
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | 	    sed -e 's/\(cygwin\).*/cygwin/')

/* Set shell to bash if possible, otherwise fall back to sh
 * 最终结果：SHELL = /bin/bash
 */
SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; 	else if [ -x /bin/bash ]; then echo /bin/bash; 	else echo sh; fi; fi)

/* HOSTARCH HOSTOS SHELL 是编译u-boot的主机的信息 */
export	HOSTARCH HOSTOS SHELL

/* Deal with colliding definitions from tcsh etc. */
VENDOR=

/*  Allow for silent builds */
ifeq (,$(findstring s,$(MAKEFLAGS)))
XECHO = echo
else
XECHO = :
endif

/* U-boot支持在其他目录编译处理目标文件，这样可以保持源代码洁净
 * 指定目录的方式有2种：
 * 1) 执行make命令时附加"-O dir"项 --'make O=/tmp/build all'
 * 2) 设置环境变量BUILD_DIR --'export BUILD_DIR=/tmp/build'; 'make'
 */
ifdef O
/* origin函数的作用是告知某个变量来自与那里，它并不改变变量。
 * origin函数有如下几种情况
 * 1) 若从未定义过变量O，$(origin O)返回'undefined'
 * 2) 若变量O为环境变量，$(origin O)返回'environment'
 * 3) 若变量O为默认定义，$(origin O)返回'default'
 * 4) 若变量O定义在Makefile中，$(origin O)返回'file'
 * 5) 若变量O来自命令行，$(origin O)返回'command line'
 * 6) 若变量O被重新定义过，$(origin O)返回'override'
 * 7) 若变量O是自动变量，如"$@""$<"等，$(origin O)返回'automatic'
 */
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif

/* 若BUILD_DIR不为空，赋值给变量saved-output */
ifneq ($(BUILD_DIR),)
saved-output := $(BUILD_DIR)

/* Attempt to create a output directory.
 * -d FILE：FILE exists and is a directory
 */
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})

/* Verify if it was successful. */
BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
$(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
endif # ifneq ($(BUILD_DIR),)

/* CURDIR 	= .
 * OBJTREE 	= .
 * SRCTREE 	= .
 * TOPDIR 	= .
 * LNDIR  	= .
 */
OBJTREE		:= $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
SRCTREE		:= $(CURDIR)
TOPDIR		:= $(SRCTREE)
LNDIR		:= $(OBJTREE)
export	TOPDIR SRCTREE OBJTREE

/* MKCONFIG = ./mkconfig
 * mkconfig的分析见上篇：《u-boot的Makefile分析之mkconfig》
 * http://blog.csdn.net/u013686019/article/details/42295291
 */
MKCONFIG	:= $(SRCTREE)/mkconfig
export MKCONFIG

ifneq ($(OBJTREE),$(SRCTREE))
REMOTE_BUILD	:= 1
export REMOTE_BUILD
endif

/* $(obj) and (src) are defined in config.mk but here in main Makefile
 * we also need them before config.mk is included which is the case for
 * some targets like unconfig, clean, clobber, distclean, etc.
 */
ifneq ($(OBJTREE),$(SRCTREE))
obj := $(OBJTREE)/
src := $(SRCTREE)/
else
obj :=
src :=
endif
export obj src

/* Make sure CDPATH settings don't interfere */
unexport CDPATH

#########################################################################

/* The "tools" are needed early, so put this first
 * Don't include stuff already done in $(LIBS)
 */
SUBDIRS	= tools 	  examples/standalone 	  examples/api
/* .PHONY用来标明一个伪目标
 * 何为"伪目标"？就是我们定义了一个目标，但这个目标不依赖具体的文件
 * "伪目标"有何作用？假设Makefile所在的目录有一个文件，其名字和Makefile中的一个目标相同；由于该文件没有依赖任何文件，所以它一直是最新的，根据make的编译规则，与文件同名的目标将不会被执行
 */
.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

include $(obj)include/config.mk
/* arm  arm920t smdk2410 samsung s3c24x0  */
export	ARCH CPU BOARD VENDOR SOC

/* 该ifeq不会被执行，CROSS_COMPILE ?= arm-linux-在文件arch/arm/config.mk中赋值 */
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE ?=
endif
$(shell echo "HOSTARCH     = $(HOSTARCH)" > v_file.txt )
$(shell echo "ARCH         = $(ARCH)" >> v_file.txt )
$(shell echo "CROSS_COMPILE= $(CROSS_COMPILE)" >> v_file.txt )
/* load other configuration */
include $(TOPDIR)/config.mk

2、其次，根据指定的CPU，最先编译start.S文件。

/* U-Boot objects....order is important (i.e. start must be first) /* 
OBJS  = $(CPUDIR)/start.o

3、针对不同的CPU、开发板，调用它们各自目录下的Makefile生成相应的库。

/* addprefix,加前缀函数
 * 功能：把前缀加到中的每个单词后面
 * 示例：$(addprefix src/,foo bar)返回值是“src/foo src/bar”
 */
OBJS := $(addprefix $(obj),$(OBJS))

LIBS  = lib/libgeneric.a
LIBS += lib/lzma/liblzma.a
LIBS += lib/lzo/liblzo.a
LIBS += $(shell if [ -f board/$(VENDOR)/common/Makefile ]; then echo 	"board/$(VENDOR)/common/lib$(VENDOR).a"; fi)
LIBS += $(CPUDIR)/lib$(CPU).a
ifdef SOC
LIBS += $(CPUDIR)/$(SOC)/lib$(SOC).a
endif

LIBS += arch/$(ARCH)/lib/lib$(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/pci/libpci.a
LIBS += drivers/pcmcia/libpcmcia.a
LIBS += drivers/power/libpower.a
LIBS += drivers/spi/libspi.a
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/usb/phy/libusb_phy.a
LIBS += drivers/video/libvideo.a
LIBS += drivers/watchdog/libwatchdog.a
LIBS += common/libcommon.a
LIBS += lib/libfdt/libfdt.a
LIBS += api/libapi.a
LIBS += post/libpost.a

LIBS := $(addprefix $(obj),$(LIBS))
.PHONY : $(LIBS) $(TIMESTAMP_FILE) $(VERSION_FILE)

/* BOARDDIR = samsung/smdk2410 */
LIBBOARD = board/$(BOARDDIR)/lib$(BOARD).a
LIBBOARD := $(addprefix $(obj),$(LIBBOARD))

$(OBJS):	depend
		$(MAKE) -C $(CPUDIR) $(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))' ) > $@.tmp
		@cmp -s $@ $@.tmp && rm -f $@.tmp || mv -f $@.tmp $@

$(TIMESTAMP_FILE):
		@LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"' > $@
		@LC_ALL=C 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

# Explicitly make _depend in subdirs containing multiple targets to prevent
# parallel sub-makes creating .depend files simultaneously.
depend dep:	$(TIMESTAMP_FILE) $(VERSION_FILE) $(obj)include/autoconf.mk
		for dir in $(SUBDIRS) $(CPUDIR) $(dir $(LDSCRIPT)) ; do 			$(MAKE) -C $$dir _depend ; done

TAG_SUBDIRS = $(SUBDIRS)
TAG_SUBDIRS += $(dir $(__LIBS))
TAG_SUBDIRS += include

tags ctags:
		ctags -w -o $(obj)ctags `find $(TAG_SUBDIRS) 						-name '*.[chS]' -print`

etags:
		etags -a -o $(obj)etags `find $(TAG_SUBDIRS) 						-name '*.[chS]' -print`
cscope:
		find $(TAG_SUBDIRS) -name '*.[chS]' -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 $(filter-out tools,$(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

tools:
	$(MAKE) -C tools
tools-all:
	$(MAKE) -C tools HOST_TOOLS_ALL=y
endif	# config.mk

.PHONY : CHANGELOG
CHANGELOG:
	git log --no-merges U-Boot-1_1_5.. | 	unexpand -a | sed -e 's/\s\s*$$//' > $@

include/license.h: tools/bin2header COPYING
	 cat COPYING | gzip -9 -c | ./tools/bin2header license_gzip > include/license.h
#########################################################################

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

%: %_config
	$(MAKE)

#########################################################################
smdk2410_config	:	unconfig
	@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 samsung s3c24x0

4、将以上生成的.o、.a文件按board/$(BOARDDIR)/config.mk、u-boot.lds确定的地址、脚本进行链接。

5、并根据需要转换成其他格式的可执行文件，如二进制格式、S_Record格式等：

/* Add GCC lib */
ifdef USE_PRIVATE_LIBGCC
	ifeq ("$(USE_PRIVATE_LIBGCC)", "yes")
		PLATFORM_LIBGCC = -L $(OBJTREE)/arch/$(ARCH)/lib -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

/* subst函数：
 * $(subst from, to, text)，在文本"text"中用"to"代替每一处的"from"
 */
__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)

/* 在顶层的config.mk
 * 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
 */
/* 根据生成的u-boot转换成其他格式的可执行文件 */
$(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
		$(CREATE_LDR_ENV)
		$(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
		$(obj)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.imx:       $(obj)u-boot.bin
		$(obj)tools/mkimage -n $(IMX_CONFIG) -T imximage 		-e $(TEXT_BASE) -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

u-boot的Makefile分析

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u-boot的Makefile分析

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