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[37]_uboot中顶层Makefile、config.mk、u-boot.lds之间的三角恋关系之简单分析

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这里只贴出Makefile、config.mk、u-boot.lds中关键的部分，不会全部列出，因为uboot中的Makefile、config.mk、u-boot.lds实在是太长了，仅仅是uboot的顶层Makefile就接近3200行…. 

在编译uboot之前，需要对uboot做的配置(make x210_sd_config),到底这一步做了什么呢？下面是我在Makefile中搜索目标后找到的相关的语句：
2589 x210_sd_config :        unconfig
2590         @$(MKCONFIG) $(@:_config=) arm s5pc11x x210 samsung s5pc110
2591         @echo "TEXT_BASE = 0xc3e00000" > $(obj)board/samsung/x210/config.mk
执行命令传入6个参数，分别是x210_sd、arm s5pc11x x210 samsung s5pc110，其中$# = 6 、$1=arm、$2=s5pc11x、$3=x210、$4=samsung、$5=s5pc110这几个参数会被写入include/comfig.mk配置脚本中。
还有"TEXT_BASE = 0xc3e00000"这个地址被创建并追加到board/samsung/x210/config.mk这个配置文件中....
这里是uboot的24~42行，主要是定义了uboot版本、主机架构主机系统等信息，可以描述信息。
VERSION = 2017
PATCHLEVEL = 7
SUBLEVEL = 10
EXTRAVERSION = acer
U_BOOT_VERSION = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL).$(EXTRAVERSION) ## u-boot版本：2017.7.10.acer
VERSION_FILE = $(obj)include/version_autogenerated.h  ## uboot/include/version_autogenerated.h
HOSTARCH := $(shell uname -m | \   #在linux命令行执行 uname -m 命令可查看主机架构
	sed -e s/i.86/i386/ \
	    -e s/sun4u/sparc64/ \
	    -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:]' | \ #在linux命令行下执行 uname -s 命令可查看主机系统
	    sed -e 's/\(cygwin\).*/cygwin/')

export	HOSTARCH HOSTOS  #导出环境变量：主机架构、主机系统


这里是uboot主Makefile的131~~184行，主要是加载主机架构、板级、cpu相关的信息，并指定交叉编译工具链...

# load ARCH, BOARD, and CPU configuration

include $(obj)include/config.mk


## 引入uboot配置阶段生成的配置文件include/config.mk，指明ARCH、CPU、BOARD、VENDOR、SOC

export


ARCH CPU BOARD VENDOR SOC


#导出来config.mk文件中这几个环境变量

ifndef CROSS_COMPILE

ifeq ($(HOSTARCH),$(ARCH))

CROSS_COMPILE =

else

ifeq ($(ARCH),ppc)

CROSS_COMPILE = ppc_8xx-

endif

ifeq ($(ARCH),arm) # arm 架构前面已经导出来了，就是HOSTARCH

#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-linux-2009q3/bin/arm-none-linux-gnueabi-

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   #加载顶层目录下的config.mk

这里是源码目录下config.mk,主要是如何构成一个完整的工具链，以及和前面inlcude/config.mk内核做比较并从刑定义一下目录结构...
#########################################################################
#
# Option checker (courtesy linux kernel) to ensure
# only supported compiler options are used
#
cc-option = $(shell if $(CC) $(CFLAGS) $(1) -S -o /dev/null -xc /dev/null \
		> /dev/null 2>&1; then echo "$(1)"; else echo "$(2)"; fi ;)

#
# 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

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

# Load generated board configuration   			#加载生成的板级信息2018.06.15 ，该板级信息存在include/config.mk中
sinclude $(OBJTREE)/include/autoconf.mk

ifdef	ARCH									# ARCH   = arm
sinclude $(TOPDIR)/$(ARCH)_config.mk			# include architecture dependend rules
endif
ifdef	CPU										# CPU    = s5pc11x
sinclude $(TOPDIR)/cpu/$(CPU)/config.mk			# include  CPU	specific rules
endif
ifdef	SOC										#
sinclude $(TOPDIR)/cpu/$(CPU)/$(SOC)/config.mk	# include  SoC	specific rules
endif
ifdef	VENDOR									# VENDOR = samsung
BOARDDIR = $(VENDOR)/$(BOARD)														### BOARDDIR = samsung/x210
else
BOARDDIR = $(BOARD)								# 
endif
ifdef	BOARD									# BOARD  = x210
sinclude $(TOPDIR)/board/$(BOARDDIR)/config.mk	# include board specific rules     	### board/samsung/x210/
endif
注意事项：在Makefile 或 配置脚本 中定义变量并赋值，需注意“=” 和 “:=” 这两种定义方法的区别
这里是config.mk的147行，引入链接u-boot.lds脚本:（144~148行）
ifeq ($(CONFIG_NAND_U_BOOT),y)
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot-nand.lds
else
LDSCRIPT := $(TOPDIR)/board/$(BOARDDIR)/u-boot.lds   #u-boot.lds的引入
endif

这是u-boot.lds链接脚本的相关内容：(24~67行)
OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
/*OUTPUT_FORMAT("elf32-arm", "elf32-arm", "elf32-arm")*/
OUTPUT_ARCH(arm)
ENTRY(_start)        # uboot启动的入口就是从这里开始的 (这里是个关键)
SECTIONS
{
	. = 0x00000000;                                 # 链接地址

	. = ALIGN(4);                                   # 4字节对齐
	.text      :                                    # 代码段
	{
	  cpu/s5pc11x/start.o	(.text)
	  cpu/s5pc11x/s5pc110/cpu_init.o	(.text)
	  board/samsung/x210/lowlevel_init.o	(.text)
          cpu/s5pc11x/onenand_cp.o      (.text)                 
          cpu/s5pc11x/nand_cp.o (.text)                     
          cpu/s5pc11x/movi.o (.text) 
          common/secure_boot.o (.text) 
	  common/ace_sha1.o (.text)
	  cpu/s5pc11x/pmic.o (.text)
	  *(.text)
	}

	. = ALIGN(4);                                # 4字节对齐
	.rodata : { *(.rodata) }                     # 只读数据段

	. = ALIGN(4);
	.data : { *(.data) }                         # 数据段

	. = ALIGN(4);
	.got : { *(.got) }                            #自定义段

	__u_boot_cmd_start = .;
	.u_boot_cmd : { *(.u_boot_cmd) }               #自定义段
	__u_boot_cmd_end = .;

	. = ALIGN(4);
	.mmudata : { *(.mmudata) }

	. = ALIGN(4);
	__bss_start = .;
	.bss : { *(.bss) }                            #bss段
	_end = .;
}

后续……..


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