u-boot启动之Makefile结构分析_makefile中-u -s -t-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_41354745/article/details/84029143

本文深入探讨了U-Boot启动过程中Makefile的结构和作用。配置命令生成了config.mk和开发板相关的头文件，如smdk2410.h。在编译过程中，Makefile指定了start.S作为首个编译文件，并确定了链接地址0x33f80000，此地址在boards/smdk2410/config.mk中定义。整个流程揭示了U-Boot构建系统的内在逻辑。

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先进行配置命令：

make	smdk2410_config

在Makefile文件中：

smdk2410_config	:	unconfig
	@$(MKCONFIG) $(@:_config=) arm arm920t smdk2410 NULL s3c24x0

因此mkconfig文件中会传入如下参数：

#Parameters:  	Target  	Architecture 	 CPU     	 Board        [VENDOR]    	 [SOC]
mkconfig	smdk2410	arm		arm920t		smdk2410	NULL		s3c24x0
$0		$1		 $2      	 $3		$4          	 $5          	 $6

配置命令过后，mkconfig创建了一些链接文件，在include目录下新建了一个config.mk文件，其内容是：

ARCH   = arm
CPU    = arm920t
BOARD  = smdk2410
SOC    = s3c24x0

在include/configs目录下新建了一个开发板相关的头文件smdk2410.h，内容是：

/* Automatically generated - do not edit */
#include <configs/smdk2410.h>"

编译命令：

	make

分析顶层Makefile：

# load ARCH, BOARD, and CPU configuration
include $(OBJTREE)/include/config.mk
export	ARCH CPU BOARD VENDOR SOC
...
ifeq ($(ARCH),arm)		/* ARCH = arm */
CROSS_COMPILE = arm-linux-
endif
...
OBJS  = cpu/$(CPU)/start.o	/* CPU = arm920t */
...
LIBS  = lib_generic/libgeneric.a
LIBS += board/$(BOARDDIR)/lib$(BOARD).a		/* BOARD = smdk2410 */
LIBS += cpu/$(CPU)/lib$(CPU).a				/* CPU = arm920t */
...
ALL = $(obj)u-boot.srec $(obj)u-boot.bin $(obj)System.map $(U_BOOT_NAND)
all:		$(ALL)
...
$(obj)u-boot.bin:	$(obj)u-boot	/* 该u-boot为elf格式，u-boot.bin是二进制格式 */
		$(OBJCOPY) ${OBJCFLAGS} -O binary $< $@
...
$(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

执行make命令，得到：

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/.*\(__u_boot_cmd_.*\)/-u\1/p'|sort|uniq`;\
                
  cd /work/system/u-boot-1.1.6 && 
  arm-linux-ld -Bstatic -T /work/system/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 \
                        -Map u-boot.map -o u-boot

由Makefile得知:
a.第一个文件：cpu/arm920t/start.S;
b.链接地址：board/smdk2410/u-boot.lds与0x33f80000
0x33f80000是在boards/smdk2410/config.mk文件中定义的

TEXT_BASE = 0x33F80000	/* 若要改变u-boot放的位置，可以改这个地址 */

而该LDFLAGS在顶层目录的config.mk中定义：

config.mk:189:LDFLAGS += -Bstatic -T $(LDSCRIPT) -Ttext $(TEXT_BASE) $(PLATFORM_LDFLAGS)