uboot学习——基于S3C2440的u-boot-1.1.6分析（一）

编译u-bbot-1.1.6分为两步——1.配置；2.编译。关于配置可参考u-boot分析mkconfig。

（1）从Makefile开始，分析Makfile开始的部分可以得出几个重要的目录设定。

（2）包含include/config.mk，把配置时的几个参数包含到Makfile，并制定交叉编译前缀。

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

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

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

export    CROSS_COMPIL

（3）包含顶层目录下的config.mk，这个文件里面主要定义了交叉编译器及选项和编译规则。

# load other configuration
include $(TOPDIR)/config.mk
#比如 一下为config.mk部分内容
...
# clean the slate ...
PLATFORM_RELFLAGS =   #在arm920t文件夹下的config.mk文件夹下有追加，后边有包含这个文件
PLATFORM_CPPFLAGS =
PLATFORM_LDFLAGS =
...
#
# 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
STRIP    = $(CROSS_COMPILE)strip
OBJCOPY = $(CROSS_COMPILE)objcopy
OBJDUMP = $(CROSS_COMPILE)objdump
RANLIB    = $(CROSS_COMPILE)RANLIB
...
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds
...
LDFLAGS += -Bstatic -T $(LDSCRIPT) -Ttext $(TEXT_BASE) $(PLATFORM_LDFLAGS) 
...

（4）包含u-boot所必须的目标文件

OBJS  = cpu/$(CPU)/start.o# 顺序很重要，start.o必须放第一位 
OBJS := $(addprefix $(obj),$(OBJS))

（5）包含所需的库文件

LIBS  = lib_generic/libgeneric.a              
LIBS += board/$(BOARDDIR)/lib$(BOARD).a    # board/100ask24x0/lib100ask24x0.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/usb/libusb.a
LIBS += drivers/sk98lin/libsk98lin.a
LIBS += common/libcommon.a
LIBS += $(BOARDLIBS)

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

根据上面的include/config.mk文件定义的ARCH、CPU、BOARD、SOC这些变量。硬件平台依赖的目录文件可以根据这些定义来确定。

（8）最终生成的各种镜像文件：

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_.*)/-u1/p'|sort|uniq`;
        cd $(LNDIR) && $(LD) $(LDFLAGS) $$UNDEF_SYM $(__OBJS) 
            --start-group $(__LIBS) --end-group $(PLATFORM_LIBS) 
            -Map u-boot.map -o u-boot

通过make后，逆向工程看出

UNDEF_SYM=`arm-linux-objdump -x 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 |sed  -n -e 's/.*(__u_boot_cmd_.*)/-u1/p'|sort|uniq`; //换行
        cd /home/work/u-boot-1.1.6 && arm-linux-ld -Bstatic -T /home/work/u-boot-1.1.6/board/100ask24x0/u-boot.lds -Ttext 0x33F80000  $UNDEF_SYM cpu/arm920t/start.o 
            --start-group 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 
                          --end-group -L /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/armv4t -lgcc -lc -L/usr/local/arm/4.3.2/arm-none-linux-gnueabi/libc/armv4t/usr/lib 
            -Map u-boot.map -o u-boot

分析u-boot.lds