VERSION = 1//主版本號
PATCHLEVEL = 1//次版本號
SUBLEVEL = 6//修正版本號
EXTRAVERSION =//版本號擴展
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)//這個Uboot的版本爲1.1.6
VERSION_FILE = $(obj)include/version_autogenerated.h
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/)
首先執行uname -m得到I686,通過管道傳送給sed命令,然後sed命令將執行sed -e s/i.86/i386/,將I686替換成i386,最後的結果是HOSTARCH=i386.
I686 表示Ubuntu， sed命令是替換命令
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
sed -e 's/\(cygwin\).*/cygwin/')
首先執行uname -s 查看開發平臺的系統,結果爲Linux,然後通過管道傳送給tr命令,tr命令利用字符類[:lower:]和[:upper:]將Linux字符串轉化爲linux,然後再利用sed命令.最後的結果是HOSTOS=linux
export HOSTARCH HOSTOS
這些變量傳遞給下一層的Makefile
Uboot支持將目標文件生成在外部的文件夾中，有兩種命令可以實現。
1，加入O=命令
2，設定環境變量BUILD_DIR
如果以上兩種方式都沒有定義，那麼它將會被存放在源碼目錄下
ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif
上面的意思是如果定義了O命令，並且O=指定的目錄和command line指定的目錄一樣
BUILD_DIR就爲O=定義的目錄
origin函數不像其它的函數，他並不操作變量的值，只是告訴你這個變量從哪裏來
ifneq ($(BUILD_DIR),)
saved-output := $(BUILD_DIR)
再判斷BUILD_DIR是否爲0，若不爲0，則save-output即保存BUILD_DIR指定的輸出目錄
# Attempt to create a output directory.
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})
build_dir是不是一個目錄 ，如果沒有就創建， [ ] 就是個條件判斷語句
BUILD_DIR := $(shell cd $(BUILD_DIR) && /bin/pwd)
先打開這個目錄，再調用Pwd顯示當前路徑，在將這個路徑值賦給BUILD_DIR
$(if $(BUILD_DIR),,$(error output directory "$(saved-output)" does not exist))
endif # ifneq ($(BUILD_DIR),)
如果BUILD_DIR還不存在的話，則輸出saved-output中的目錄does not exist
OBJTREE := $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
SRCTREE := $(CURDIR)
TOPDIR := $(SRCTREE)
LNDIR := $(OBJTREE)
export TOPDIR SRCTREE OBJTREE
OPDIR SRCTREE OBJTREE這三個目錄會給下層的makefile調用，需要在這裏指定並export
OBJTREE和LNDIR爲存放生成文件的目錄，TOPDIR與SRCTREE爲源碼所在目錄
MKCONFIG := $(SRCTREE)/mkconfig
export MKCONFIG
定義變量MKCONFIG：這個變量指向一個腳本，即頂層源碼目錄的mkconfig。
ifneq ($(OBJTREE),$(SRCTREE))
REMOTE_BUILD := 1
export REMOTE_BUILD
endif
如果輸出目錄與源碼目錄不等，則設定REMOTE_BUILD項，並導出
ifneq ($(OBJTREE),$(SRCTREE))
obj := $(OBJTREE)/
src := $(SRCTREE)/
else
obj :=
src :=
endif
export obj src
如果輸出目錄OBJTREE與SRCTREE即當前的Uboot目錄不等的話，對obj和src進行賦值，否則則obj,src爲空。
obj src會在主目錄中的config.mk定義，但在主makefile包含config.mk之前也需要，譬如unconfig, clean, clobber, distclean
ifeq ($(OBJTREE)/include/config.mk,$(wildcard $(OBJTREE)/include/config.mk))
在分析這個及以下命令之前，我們需要了解在在編譯U－BOOT之前，先要執行# make smdk6410_config
smdk6410_config是Makefile的一個目標，定義如下：
smdk6410_config : unconfig
@$(MKCONFIG) $(@:_config=) arm s3c64xx smdk6410 samsung s3c6410
unconfig:
@rm -f $(obj)include/config.h $(obj)include/config.mk \
$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp
首先執行unconfig，obj src爲上面所定義的，這個命令清理上一次執行make *_config時生成的頭文件和makefile的包含文件。主要是include/config.h 和include/config.mk文件。
然後再執行@$(MKCONFIG) $(@:_config=) arm s3c64xx smdk6410 samsung s3c6410
MKCONFIG 是頂層目錄下的mkcofig腳本文件，後面五個是傳入的參數。頂層目錄下的mkcofig稍後分析
主要生成生成Makefile包含文件include/config.mk，用五個傳入的參數定義五個變量
ARCH = arm
CPU = s3c64xx
BOARD = smdk6410
VENDOR = samsung
SOC = s3c6410
生成include/config.h頭文件，只有一行：
#include "config/smdk6410.h"
# load ARCH, BOARD, and CPU configuration
include $(OBJTREE)/include/config.mk
export ARCH CPU BOARD VENDOR SOC
包含include/config.mk，導出ARCH CPU BOARD VENDOR SOC這五個變量
ifndef CROSS_COMPILE
ifeq ($(ARCH),arm)//ARCH = arm
CROSS_COMPILE = arm-linux-
endif
endif
CROSS_COMPILE = /usr/local/arm/4.2.2-eabi/usr/bin/arm-linux-
export CROSS_COMPILE
指定交叉編譯器前綴，我只寫出了與ARM相關的交叉編譯前綴
/usr/local/arm/4.2.2-eabi/usr/bin/這個目錄是安裝交叉編譯器的目錄
# load other configuration
include $(TOPDIR)/config.mk
包含頂層目錄下的config.mk，這個文件裏面主要定義了交叉編譯器及選項和編譯規則
稍後分析頂層目錄的config.mk
下面就是Uboot需要的目標文件和庫文件，$(CPU)已經指定了CPU = s3c64xx
與之相關的VENDOR = samsung
# 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 ($(CPU),mpc85xx)
OBJS += cpu/$(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
OBJS := $(addprefix $(obj),$(OBJS))
addprefix爲增加前綴函數
庫文件，由各個目錄下的makefile生成，鏈接時需要這些文件
這些文件涉及到的目錄有lib_generic,board,cpu,lib_arm,fs,net,disk,rtc,dtt,drivers,post,common
將與平臺相關的進行下面替換
$(ARCH) = arm
$(CPU) = s3c64xx
$(BOARD) = smdk6410
$(VENDOR) = samsung
$(SOC) = s3c6410
LIBS = lib_generic/libgeneric.a
LIBS += board/$(BOARDDIR)/lib$(BOARD).a
BOARDDIR好像爲VENDOR = samsung
LIBS += cpu/$(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
# add to support onenand. by scsuh
LIBS += drivers/onenand/libonenand.a
ifeq ($(CPU),mpc83xx)
LIBS += drivers/qe/qe.a
endif
LIBS += drivers/sk98lin/libsk98lin.a
LIBS += post/libpost.a post/cpu/libcpu.a
LIBS += common/libcommon.a
LIBS += $(BOARDLIBS)
LIBS := $(addprefix $(obj),$(LIBS))
.PHONY : $(LIBS)
加入GCC的庫,CC和CFLAGS都是make的隱含變量，CC表示C編譯器，cflags表示執行CC時的命令行參數
# 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 \
post \
post/cpu
.PHONY : $(SUBDIRS)
.PHONY是什麼僞目標，不是很懂
ifeq ($(CONFIG_NAND_U_BOOT),y)
NAND_SPL = nand_spl
U_BOOT_NAND = $(obj)u-boot-nand.bin
endif
__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS))
$(subst text, to, from)字符串替換函數,將$(obj)中的$(OBJS)置空
下面最終生成各種鏡像文件
ALL = $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND)
最後要生成的文件，U_BOOT_NAND在前面定義了，爲u-boot-nand.bin
all依賴於$(ALL) 最終生成鏡像文件,注意各種依賴關係
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 $< $@
$(OBJDUMP) -d $< > $<.dis
$(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 $< > $@
$(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) $$UNDEF_SYM $(__OBJS) \
--start-group $(__LIBS) --end-group $(PLATFORM_LIBS) \
-Map u-boot.map -o u-boot
$(OBJS):
$(MAKE) -C cpu/$(CPU) $(if $(REMOTE_BUILD),$@,$(notdir $@))
$(LIBS):
$(MAKE) -C $(dir $(subst $(obj),,$@))
$(SUBDIRS):
$(MAKE) -C $@ all
$(NAND_SPL): version
$(MAKE) -C nand_spl/board/$(BOARDDIR) all
$(U_BOOT_NAND): $(NAND_SPL) $(obj)u-boot.bin
cat $(obj)nand_spl/u-boot-spl-16k.bin $(obj)u-boot.bin > $(obj)u-boot-nand.bin
version:
@echo -n "#define U_BOOT_VERSION \"U-Boot " > $(VERSION_FILE); \
echo -n "$(U_BOOT_VERSION)" >> $(VERSION_FILE); \
echo -n $(shell $(CONFIG_SHELL) $(TOPDIR)/tools/setlocalversion \
$(TOPDIR)) >> $(VERSION_FILE); \
echo "\"" >> $(VERSION_FILE)
gdbtools:
$(MAKE) -C tools/gdb all || exit 1
updater:
$(MAKE) -C tools/updater all || exit 1
env:
$(MAKE) -C tools/env all || exit 1
depend dep:
for dir in $(SUBDIRS) ; do $(MAKE) -C $$dir _depend ; done
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
下面接着分析
unconfig:
@rm -f $(obj)include/config.h $(obj)include/config.mk \
$(obj)board/*/config.tmp $(obj)board/*/*/config.tmp
這句話已經分析過了，就是在mkconfig是先執行的操作，即刪除上一次makeXXX時存在的頭文件和包含文件
接下來很長一段是與平臺和開發板相關的xxx_config定義,譬如在執行make smdk6410_config時
會找到如下定義：
smdk6410_config : unconfig
@$(MKCONFIG) $(@:_config=) arm s3c64xx smdk6410 samsung s3c6410
最後是clean命令的定義
clean:
find $(OBJTREE) -type f \
\( -name 'core' -o -name '*.bak' -o -name '*~' \
-o -name '*~' -o -name '.depend*' \
-o -name '*.o' -o -name '*.a' \) -print \
| xargs rm -f
rm -f u-boot*
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
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
else
mrproper \
distclean: clobber unconfig
rm -rf $(OBJTREE)/*
endif
backup:
F=`basename $(TOPDIR)` ; cd .. ; \
gtar --force-local -zcvf `date "+$$F-%Y-%m-%d-%T.tar.gz"` $$F
哈哈，終於結束了，下次再講講Uboot究竟是如何生成鏡像文件的，任務好重啊，哈哈