u-boot顶层Makefile分析

1.u-boot制作命令

make forlinx_nand_ram256_config；

make all;

2.顶层mkconfig分析，参考 U-BOOT顶层目录mkconfig分析

mkconfig脚本执行后会生成以下3个文件,这些文件中提供的变量会在Makefile中其它地方使用。

MKCONFIG    := $(SRCTREE)/mkconfig

forlinx_nand_ram256_config :  unconfig
    @$(MKCONFIG) smdk6410 arm s3c64xx smdk6410 samsung s3c6410 NAND ram256

unconfig:
    @rm -f $(obj)include/config.h $(obj)include/config.mk \
        $(obj)board/*/config.tmp $(obj)board/*/*/config.tmp

./include/config.mk

./board/samsung/smdk6410/config.mk

./include/config.h

3.顶层config.mk分析，参考 u-boot顶层目录config.mk分析

这个文件设置的变量会在Makefile其它地方使用。

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

4.变量打印，修改Makefile查看变量的具体内容。

display1:
    @echo "PLATFORM_RELFLAGS : $(PLATFORM_RELFLAGS)"
    @echo "PLATFORM_CPPFLAGS : $(PLATFORM_CPPFLAGS)"
    @echo "CPPFLAGS : $(CPPFLAGS)"
    @echo "CFLAGS : $(CFLAGS)"
    @echo "AFLAGS : $(AFLAGS)"
    @echo "LDFLAGS : $(LDFLAGS)"
    @echo "CPP: $(CPP)"
    @echo "MAKE: $(MAKE)"
    @echo "CROSS_COMPILE: $(CROSS_COMPILE)"
    @echo "BOARDDIR : $(BOARDDIR)"
    @echo "HOSTCC : $(HOSTCC)"
    @echo "HOSTCFLAGS : $(HOSTCFLAGS)"
    @echo "ALL : $(ALL)"
    @echo "SUBDIRS : $(SUBDIRS)"
    @echo "OBJS : $(OBJS)"
    @echo "__OBJS : $(__OBJS)"
    @echo "LIBS : $(LIBS)"
    @echo "__LIBS : $(__LIBS)"
    @echo "LDSCRIPT: $(LDSCRIPT)"

执行make display1即可查看到各个变量的具体值如下：

 PLATFORM_RELFLAGS :  -fno-strict-aliasing  -fno-common -ffixed-r8 -msoft-float
 PLATFORM_CPPFLAGS :  -DCONFIG_ARM -D__ARM__ -march=armv5t
 CPPFLAGS : -g  -Os   -fno-strict-aliasing  -fno-common -ffixed-r8 -msoft-float  -D__KERNEL__ -DTEXT_BASE=0xCFE00000  -I/home/yjg/arm6410/qudong/-uboot/uboot_ok6410/include -fno-builtin -ffreestanding -nostdinc -isystem /usr/local/arm/4.3./bin/../lib/gcc/arm-none-linux-gnueabi/4.3./include -pipe  -DCONFIG_ARM -D__ARM__ -march=armv5t
 CFLAGS : -g  -Os   -fno-strict-aliasing  -fno-common -ffixed-r8 -msoft-float  -D__KERNEL__ -DTEXT_BASE=0xCFE00000  -I/home/yjg/arm6410/qudong/-uboot/uboot_ok6410/include -fno-builtin -ffreestanding -nostdinc -isystem /usr/local/arm/4.3./bin/../lib/gcc/arm-none-linux-gnueabi/4.3./include -pipe  -DCONFIG_ARM -D__ARM__ -march=armv5t -Wall -Wstrict-prototypes
 AFLAGS :  -D__ASSEMBLY__ -g  -Os   -fno-strict-aliasing  -fno-common -ffixed-r8 -msoft-float  -D__KERNEL__ -DTEXT_BASE=0xCFE00000  -I/home/yjg/arm6410/qudong/-uboot/uboot_ok6410/include -fno-builtin -ffreestanding -nostdinc -isystem /usr/local/arm/4.3./bin/../lib/gcc/arm-none-linux-gnueabi/4.3./include -pipe  -DCONFIG_ARM -D__ARM__ -march=armv5t
 LDFLAGS : -Bstatic -T /home/yjg/arm6410/qudong/-uboot/uboot_ok6410/board/samsung/smdk6410/u-boot.lds -Ttext 0xCFE00000
 CPP: /usr/local/arm/4.3./bin/arm-linux-gcc -E
 MAKE: make
 CROSS_COMPILE: /usr/local/arm/4.3./bin/arm-linux-
 BOARDDIR : samsung/smdk6410
 HOSTCC : gcc
 HOSTCFLAGS : -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer
 ALL : u-boot.srec u-boot.bin System.map
 SUBDIRS : tools examples post post/cpu
 OBJS : cpu/s3c64xx/start.o
 __OBJS : cpu/s3c64xx/start.o
 LIBS : lib_generic/libgeneric.a board/samsung/smdk6410/libsmdk6410.a cpu/s3c64xx/libs3c64xx.a cpu/s3c64xx/s3c6410/libs3c6410.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/onenand/libonenand.a drivers/sk98lin/libsk98lin.a post/libpost.a post/cpu/libcpu.a common/libcommon.a
 __LIBS : lib_generic/libgeneric.a board/samsung/smdk6410/libsmdk6410.a cpu/s3c64xx/libs3c64xx.a cpu/s3c64xx/s3c6410/libs3c6410.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/onenand/libonenand.a drivers/sk98lin/libsk98lin.a post/libpost.a post/cpu/libcpu.a common/libcommon.a
 LDSCRIPT: /home/yjg/arm6410/qudong/-uboot/uboot_ok6410/board/samsung/smdk6410/u-boot.lds

make display1

从上面可以看出make的最终目标为ALL : u-boot.srec u-boot.bin System.map

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

u-boot.srec u-boot.bin都依赖于u-boot

$(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)System.map:    $(obj)u-boot
        @$(NM) $< | \
        grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \
        sort > $(obj)System.map

5. make u-boot分析，参考 详细分析make uboot 最后的编译链接的具体执行过程

$(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

上述目标的生成可分解为4个步骤：

5.0 生成版本信息文件：

生成include/version_autogenerated.h文件，内容如下：

#define U_BOOT_VERSION "U-Boot 1.1.6"

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)

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

5.1 确定UNDEF_SYM变量值

打印出UNDEF_SYM变量值如下，其中的-u__u_boot_cmd_xxx用作arm-linux-ld命令的参数,意思就是，在ld的时候不定义这些符号，即不定义__u_boot_cmd_xxx，等等这些符号，我的理解是因为开始需要从某个库中载入其他的符号，而这个时候还没有载入到那个包含此符号定义的库，所以暂时先加入这个-u说明，先不定义这些符号，等到所有的库都加载完了再去找这些符号的定义，此时已经加载完所有的库了，也就能找到这些符号的定义了。

-u__u_boot_cmd_base
-u__u_boot_cmd_bdinfo
-u__u_boot_cmd_bootelf
-u__u_boot_cmd_bootm
-u__u_boot_cmd_bootp
-u__u_boot_cmd_bootvx
-u__u_boot_cmd_branch
-u__u_boot_cmd_cmp
-u__u_boot_cmd_cp
-u__u_boot_cmd_crc32
-u__u_boot_cmd_date
-u__u_boot_cmd_dcache
-u__u_boot_cmd_dnw
-u__u_boot_cmd_echo
-u__u_boot_cmd_end
-u__u_boot_cmd_erase
-u__u_boot_cmd_exit
-u__u_boot_cmd_fatinfo
-u__u_boot_cmd_fatload
-u__u_boot_cmd_fatls
-u__u_boot_cmd_flinfo
-u__u_boot_cmd_go
-u__u_boot_cmd_help
-u__u_boot_cmd_icache
-u__u_boot_cmd_imls
-u__u_boot_cmd_itest
-u__u_boot_cmd_loadb
-u__u_boot_cmd_loads
-u__u_boot_cmd_loady
-u__u_boot_cmd_loop
-u__u_boot_cmd_md
-u__u_boot_cmd_mm
-u__u_boot_cmd_movi
-u__u_boot_cmd_mtest
-u__u_boot_cmd_mw
-u__u_boot_cmd_nand
-u__u_boot_cmd_nboot
-u__u_boot_cmd_nfs
-u__u_boot_cmd_nm
-u__u_boot_cmd_ping
-u__u_boot_cmd_printenv
-u__u_boot_cmd_protect
-u__u_boot_cmd_question_mark
-u__u_boot_cmd_rarpboot
-u__u_boot_cmd_reset
-u__u_boot_cmd_saveenv
-u__u_boot_cmd_setenv
-u__u_boot_cmd_sleep
-u__u_boot_cmd_start
-u__u_boot_cmd_test
-u__u_boot_cmd_tftpboot
-u__u_boot_cmd_usb
-u__u_boot_cmd_version

UNDEF_SYM:

5.2 切换到u-boot顶层目录

5.3 arm-linux-ld链接生成最终elf类型的u-boot。

这里要注意连接器脚本文件u-boot.lds

LDFLAGS : -Bstatic -T /home/yjg/arm6410/qudong/-uboot/uboot_ok6410/board/samsung/smdk6410/u-boot.lds -Ttext 0xCFE00000

从其中可以发现cpu/s3c64xx/start.S是u-boot执行的第一个文件，后面就从这个函数入手分析u-boot的启动流程。

 OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 /*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/
 OUTPUT_ARCH(arm)
 ENTRY(_start)
 SECTIONS
 {
     . = 0x00000000;

     . = ALIGN();
     .text      :
     {
       cpu/s3c64xx/start.o    (.text)
       cpu/s3c64xx/s3c6410/cpu_init.o    (.text)
       cpu/s3c64xx/onenand_cp.o    (.text)
       cpu/s3c64xx/nand_cp.o    (.text)
       cpu/s3c64xx/movi.o (.text)
       *(.text)
       lib_arm/div0.o
     }

     . = ALIGN();
     .rodata : { *(.rodata) }

     . = ALIGN();
     .data : { *(.data) }

     . = ALIGN();
     .got : { *(.got) }

     __u_boot_cmd_start = .;
     .u_boot_cmd : { *(.u_boot_cmd) }
     __u_boot_cmd_end = .;

     . = ALIGN();
     .mmudata : { *(.mmudata) }

     . = ALIGN();
     __bss_start = .;
     .bss : { *(.bss) }
     _end = .;
 }