uboot的makefile文件分析

VERSION = 1
PATCHLEVEL = 3
SUBLEVEL = 4
EXTRAVERSION =
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)   打印uboot版本号
VERSION_FILE = $(obj)include/version_autogenerated.h     编译才能在include目录下生成version_autogenerated.h 里面是一个宏，
定义的是U_BOOT_VERSION “U_boot 1.3.4”

export    HOSTARCH HOSTOS  两个自定义的环境变量，
HOSTARCH 主人使用的编译这个uboot的电脑的CPU版本号和CPU架构（ARCH架构英语单词简写）
HOSTARCH := $(shell uname -m | \    直接终端输入uname -m得到版本号          “|”是管道，替换命令
    sed -e s/i.86/i386/ \           将符合i.86的版本号信息用i386代替，是intel的CPU就是用i386代替，
        -e s/sun4u/sparc64/ \         都是CPU的厂商。不同CPU就是不同厂商代替型号
        -e s/arm.*/arm/ \
        -e s/sa110/arm/ \
        -e s/powerpc/ppc/ \
        -e s/ppc64/ppc/ \
        -e s/macppc/ppc/)

HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \       uname -s 得到的是Linux  采用'[:upper:]' '[:lower:]'
        sed -e 's/\(cygwin\).*/cygwin/')                         将大写改为小写，执行得到linux

ifeq (,$(findstring s,$(MAKEFLAGS)))      静默编译，：静默编译就是不想在终端打印信息，直接让其在后台编译，就叫静默编译
XECHO = echo
else
XECHO = :                                 $(findstring s,$(MAKEFLAGS))等于空，就不打印，否侧执行XECHO = echo打印出信息
endif

静默编译的使用方法：就是编译时make -s，-s会作为MAKEFLAGS传给Makefile，在这段代码作用下XECHO变量就会被变成空
（默认时ＸＥＣＨＯ是等于echo），于是就实现了静默编译

两种便宜方法：
一是原地编译，就是在．ｃ文件下生成．ｏ文件，二是制定文件夹编译，就是将生成的．ｏ文件都放在一个文件夹中。
默认的是原地编译，第二种方法有两种方式使用：
第一种：ｍａｋｅ　Ｏ＝输出目录
第二种：ｅｘｐｏｒｔ　ＢＵＩｌＤ—ＤＩＲ＝输出目录　然后再ｍａｋｅ
如果两种方式都有，使用ｍａｋｅ　Ｏ＝输出目录优先
#########################################################################
#
# 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.
#

ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif

ifneq ($(BUILD_DIR),)
saved-output := $(BUILD_DIR)

# Attempt to create a output 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),)
//OBJTREE :是编译出的.o的文件存放的目录的根目录，在默认编译下，ＯＢＪＴＲＥＥ等于当前目录；在Ｏ＝ｘｘ编译下，ＯＢＪＴＲＥＥ
//就等于等于我们设置的那个输出目录
//SRCTREE：源码目录，其实就是源代码的根目录，也就是当前目录。总结：在默认编译下OBJTREE与SRCTREE相等，在O=xx这种编译下
//OBJTREE与SRCTREE不相等，Makefile中定义的这两个变量。其实是为了记录编译后的.o文件去往哪里放。
//就是为了实现O=xx这种编译方式。
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

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

# Make sure CDPATH settings don't interfere
unexport CDPATH

#########################################################################
//配置设置 三个重要变量CROSS_COMPILE，MKCONFIG，ARCH
/*#在config.mk的（94到107行）定义的这些就是用来生成交叉编译工具链的，属于后缀，CROSS_COMPILE使用条件编译生成前缀
# 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
*/

ifeq ($(ARCH),powerpc)
ARCH = ppc
endif

ifeq ($(obj)include/config.mk,$(wildcard $(obj)include/config.mk))

# load ARCH, BOARD, and CPU configuration
include $(obj)include/config.mk
export    ARCH CPU BOARD VENDOR SOC

ifndef CROSS_COMPILE
ifeq ($(HOSTARCH),$(ARCH))
CROSS_COMPILE =
else
ifeq ($(ARCH),ppc)
CROSS_COMPILE = ppc_8xx-
endif
ifeq ($(ARCH),arm)
#CROSS_COMPILE = arm-linux-
#CROSS_COMPILE = /usr/local/arm/4.4.1-eabi-cortex-a8/usr/bin/arm-linux-
#CROSS_COMPILE = /usr/local/arm/4.2.2-eabi/usr/bin/arm-linux-
CROSS_COMPILE = /usr/local/arm/arm-2009q3/bin/arm-none-linux-gnueabi-            //前缀定义
endif
ifeq ($(ARCH),i386)
CROSS_COMPILE = i386-linux-
endif
ifeq ($(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 ($(ARCH),blackfin)
CROSS_COMPILE = bfin-uclinux-
endif
ifeq ($(ARCH),avr32)
CROSS_COMPILE = avr32-linux-
endif
ifeq ($(ARCH),sh)
CROSS_COMPILE = sh4-linux-
endif
ifeq ($(ARCH),sparc)
CROSS_COMPILE = sparc-elf-
endif    # sparc
endif    # HOSTARCH,ARCH
endif    # CROSS_COMPILE

export    CROSS_COMPILE

# load other configuration
include $(TOPDIR)/config.mk    //主makefile 添加了这个，过度到config.mk分析

#########################################################################
# U-Boot objects....order is important (i.e. start must be first)
//主makefile的核心部分
//OBJS所有uboot编译文件的集合

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 ($(CPU),mpc85xx)
OBJS += cpu/$(CPU)/resetvec.o
endif

OBJS := $(addprefix $(obj),$(OBJS))

LIBS  = lib_generic/libgeneric.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
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/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/nand_legacy/libnand_legacy.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/sk98lin/libsk98lin.a
LIBS += drivers/pci/libpci.a
LIBS += drivers/pcmcia/libpcmcia.a
LIBS += drivers/spi/libspi.a
ifeq ($(CPU),mpc83xx)
LIBS += drivers/qe/qe.a
endif
ifeq ($(CPU),mpc85xx)
LIBS += drivers/qe/qe.a
endif
LIBS += drivers/rtc/librtc.a
LIBS += drivers/serial/libserial.a
LIBS += drivers/usb/libusb.a
LIBS += drivers/video/libvideo.a
LIBS += common/libcommon.a
LIBS += libfdt/libfdt.a
LIBS += api/libapi.a
LIBS += post/libpost.a

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

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

# Add GCC lib
PLATFORM_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 \
      api_examples

.PHONY : $(SUBDIRS)

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_bl1
U_BOOT_ONENAND = $(obj)u-boot-onenand.bin
endif

__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS)) $(subst $(obj),,$(LIBBOARD))

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

ALL += $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND) $(U_BOOT_ONENAND) $(obj)u-boot.dis
ifeq ($(ARCH),blackfin)
ALL += $(obj)u-boot.ldr
endif

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 $< $@

$(obj)u-boot.ldr:    $(obj)u-boot
        $(LDR) -T $(CONFIG_BFIN_CPU) -f -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.sha1:    $(obj)u-boot.bin
        $(obj)tools/ubsha1 $(obj)u-boot.bin

$(obj)u-boot.dis:    $(obj)u-boot
        $(OBJDUMP) -d $< > $@

$(obj)u-boot:        depend $(SUBDIRS) $(OBJS) $(LIBBOARD) $(LIBS) $(LDSCRIPT)
        UNDEF_SYM=`$(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

$(OBJS):    depend $(obj)include/autoconf.mk
        $(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))

$(LIBS):    depend $(obj)include/autoconf.mk
        $(MAKE) -C $(dir $(subst $(obj),,$@))

$(LIBBOARD):    depend $(LIBS) $(obj)include/autoconf.mk
        $(MAKE) -C $(dir $(subst $(obj),,$@))

$(SUBDIRS):    depend $(obj)include/autoconf.mk
        $(MAKE) -C $@ all

$(LDSCRIPT):    depend $(obj)include/autoconf.mk
        $(MAKE) -C $(dir $@) $(notdir $@)

$(NAND_SPL):    $(VERSION_FILE)    $(obj)include/autoconf.mk
        $(MAKE) -C nand_spl/board/$(BOARDDIR) all

$(U_BOOT_NAND):    $(NAND_SPL) $(obj)u-boot.bin $(obj)include/autoconf.mk
        cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin