从零开始uboot—分析uboot1.1.6(4)

操作系统：ubuntu10.04 


前言：
    要完成自己的uboot，首先要熟悉广泛使用的Uboot的架构，实现。
    而看linux的大项目的源码，切入点基本都是从makefile开始。

1，makefile详解：
    如果对makefile有疑惑的请看：*makefile 博文链接  

(C) Copyright 2000-2006
# Wolfgang Denk, DENX Software Engineering, [e-mail].
#
# See file CREDITS for list of people who contributed to this
# project.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundatio; either version 2 of
# the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA 02111-1307 USA
#

VERSION = 1
PATCHLEVEL = 1
SUBLEVEL = 6
EXTRAVERSION =
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
VERSION_FILE = $(obj)include/version_autogenerated.h

#########################################################################
#@定义主机系统架构@:
# “sed –e”表示后面跟的是一串命令脚本，而表达式“s/abc/def/”表示要从标准输入中，
# 查找到内容为“abc”的，然后替换成“def”。其中“abc”表达式用可以使用“.”作为通配符。
# 命令“uname –m”将输出主机CPU的体系架构类型。作者的电脑使用Intel Core2系列的CPU，
# 因此“uname –m”输出“i686”。 “i686”可以匹配命令“sed -e s/i.86/i386/”中的“i.86”，
# 因此在作者的机器上执行Makefile，HOSTARCH 将被设置成“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/powerpc/ppc/ \
     -e s/macppc/ppc/)

#########################################################################
#@定义主机操作系统类型@:
# “uname –s”输出主机内核名字，作者使用Linux发行版Ubuntu11.10，因此“uname –s”结果是“Linux”。
# “tr '[:upper:]' '[:lower:]'”作用是将标准输入中的所有大写字母转换为响应的小写字母。
# 因此执行结果是将HOSTOS 设置为“linux”。
#########################################################################
HOSTOS := $(shell uname -s | tr '[:upper:]' '[:lower:]' | \
     sed -e 's/\(cygwin\).*/cygwin/')

        #导出变量HOSTARCH HOSTOS SHELL，使别的文件可以使用这些变量
export HOSTARCH HOSTOS

# Deal with colliding definitions from tcsh etc.
VENDOR=

#########################################################################
#
# 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.
#

#########################################################################
#@设定编译输出目录@:
# 函数$( origin, variable) 输出的结果是一个字符串，输出结果由变量variable定义的方式决定，
# 若variable在命令行中定义过，则origin函数返回值为"command line"。
# 假若在命令行中执行了“export BUILD_DIR=/tmp/build”的命令，则“$(origin O)”值为“command line”，
# 而BUILD_DIR被设置为“/tmp/build”。
#
# 假若在命令行中执行了“make xx_config”的命令，则“$(origin O)”输出值不为为“command line”，
# 故BUILD_DIR没有被操作。
#########################################################################
ifdef O
ifeq ("$(origin O)", "command line")
BUILD_DIR := $(O)
endif
endif

#判断 BUILD_DIR 变量是否不为空，当前 BUILD_DIR 为 空，条件为假。
ifneq ($(BUILD_DIR),)
saved-output := $(BUILD_DIR)

#若${BUILD_DIR}表示的目录没有被创建，则创建该目录。
# Attempt to create a output directory.
$(shell [ -d ${BUILD_DIR} ] || mkdir -p ${BUILD_DIR})

#若$(BUILD_DIR)为创建失败或不存在，则将其赋值为当前目录路径（源代码目录）。
#并检查$(BUILD_DIR)目录是否存在。
#Pwd命令用以获取当前路径
# 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变量指示Make当前的工作目录，由于当前Make在U-Boot顶层目录执行Makefile，
#因此CURDIR此时就是U-Boot顶层目录。
#执行完上面的代码后， SRCTREE，src变量就是U-Boot代码顶层目录，而OBJTREE，obj变量就是输出目录，
#若没有定义BUILD_DIR环境变量，则SRCTREE，src变量与OBJTREE，obj变量都是U-Boot源代码目录。
#而MKCONFIG则表示U-Boot根目录下的mkconfig脚本。
#if函数计算OBJTREE的值，如果BUILD_DIR不为空，if函数的值就是BUILD_DIR，否则是CURDIR.
#CURDIR是个环境变量。代表当前文件的目录,即uboot根目录，设为 : ./。
# CURDIR = ./
# OBJTREE = ./
# SPLTREE = ./spl
# SRCTREE = ./
# TOPDIR = ./
# LNDIR = ./
#导出变量TOPDIR SRCTREE OBJTREE SPLTREE，使别的文件可以使用这些变量
#########################################################################
OBJTREE := $(if $(BUILD_DIR),$(BUILD_DIR),$(CURDIR))
SRCTREE := $(CURDIR)
TOPDIR := $(SRCTREE)
LNDIR := $(OBJTREE)
export TOPDIR SRCTREE OBJTREE

# MKCONFIG = ./mkconfig
#导出变量MKCONFIG
MKCONFIG := $(SRCTREE)/mkconfig
export MKCONFIG

#########################################################################
#判断变量OBJTREE 与 SRCTREE 是否不相等，OBJTREE为./，SRCTREE为./，条件为假。
#########################################################################
ifneq ($(OBJTREE),$(SRCTREE))
REMOTE_BUILD := 1
export REMOTE_BUILD
endif

#########################################################################
#判断变量OBJTREE 与 SRCTREE 是否不相等，OBJTREE为./，SRCTREE为./，条件为假。
#则 obj 为 空
# src 为 空
#导出变量 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

#########################################################################
#########################################################################
#使用“$(wildcard *.c) ”来获取工作目录下的所有的.c 文件列表
#在当前例子中，则是为了找到 ./include/config.mk
#判断是否找到 ./include/config.mk
#########################################################################
ifeq ($(OBJTREE)/include/config.mk,$(wildcard $(OBJTREE)/include/config.mk))

#########################################################################
#包含 ./include/config.mk
# ARCH = arm
# CPU = arm920t
# BOARD = 100ask24x0
# VENDOR =
# SOC = s3c24x0
#########################################################################
# load ARCH, BOARD, and CPU configuration
include $(OBJTREE)/include/config.mk
export ARCH CPU BOARD VENDOR SOC

#########################################################################
#若主机架构与开发板结构相同，就使用主机的编译器，而不是交叉编译器
#当前 HOSTARCH 为 i386
#当前 ARCH 为 arm
#条件为假，则 CROSS_COMPILE 为交叉编译器,即 CROSS_COMPILE = arm-linux-
#########################################################################
ifndef CROSS_COMPILE
ifeq ($(HOSTARCH),ppc)
CROSS_COMPILE =
else
    ifeq ($(ARCH),ppc)
    CROSS_COMPILE = powerpc-linux-
    endif

    ifeq ($(ARCH),arm)
    CROSS_COMPILE = arm-linux-
    endif

    ifeq ($(ARCH),i386)
        ifeq ($(HOSTARCH),i386)
        CROSS_COMPILE =
        else
        CROSS_COMPILE = i386-linux-
        endif
    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-elf-
    endif

    ifeq ($(ARCH),avr32)
    CROSS_COMPILE = avr32-
    endif
endif
#($(HOSTARCH),ppc)
endif
#ifndef CROSS_COMPILE

export CROSS_COMPILE

#包含 ./config.mk 文件,其主要是一些变量和函数的定义,编译链接的参数设置以及依赖规则.
# load other configuration
include $(TOPDIR)/config.mk

#########################################################################
# U-Boot objects....order is important (i.e. start must be first)

#OBJS = cpu/arm920t/start.o
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 ($(CPU),mpc83xx)
OBJS += cpu/$(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

#########################################################################
#加前缀，如
#$(addprefix src/,foo bar)
#结果：src/foo src/bar
#当前 obj :=
#OBJS := cpu/arm920t/start.o
#########################################################################
OBJS := $(addprefix $(obj),$(OBJS))

LIBS = lib_generic/libgeneric.a
LIBS += board/$(BOARDDIR)/lib$(BOARD).a
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
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)
#确保可以对LIBS进行操作

# 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)

#########################################################################
#如果CONFIG_NAND_U_BOOT变量是否等于 y，当前没有定义CONFIG_NAND_U_BOOT变量，条件为假。
#则不执行条件中的代码
#########################################################################
ifeq ($(CONFIG_NAND_U_BOOT),y)
NAND_SPL = nand_spl
U_BOOT_NAND = $(obj)u-boot-nand.bin
endif


#如果对 makefile中subst 函数有疑问的请看：http://blog.chinaunix.net/uid-28458801-id-4080763.html
#__OBJS := cpu/arm920t/start.o
#__LIBS := lib_generic/libgeneric.a board/100ask24x0/lib100ask24x0.a
#         cpu/arm920t/libarm920t.a cpu/arm920t/s3c24x0/libs3c24x0.a lib_arm/libarm.a
#         fs/cramfs/libcramfs.a fs/fat/libfat.a fs/fdos/libfdos.a fs/jffs2/libjffs2.a fs/reiserfs/libreiserfs.a fs/ext2/libext2fs.a
#         net/libnet.a disk/libdisk.a rtc/librtc.a dtt/libdtt.a
#         drivers/libdrivers.a drivers/nand/libnand.a drivers/nand_legacy/libnand_legacy.a drivers/usb/libusb.a drivers/sk98lin/libsk98lin.a
#         common/libcommon.a
__OBJS := $(subst $(obj),,$(OBJS))
__LIBS := $(subst $(obj),,$(LIBS))

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

ALL = $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND)

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.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

未完，待续。。。