嵌入式Linux之uboot源码make编译逆向分析
一、make编译逆向分析之prepare
在上一篇文章中分析Makefile文件依赖关系时采用自顶向下的方法，从顶层目标开始到最原始的依赖结束。
此处我们采用自下而上的方式，从最原始的依赖开始，一步一步的执行命令生成目标。
完整的prepare的目标依赖：
依次从最右边的依赖说起；
1.1 .config(配置阶段)
.config在执行make smdk2410_defconfig配置时生成，文件scripts/kconfig/Makefile中定义了所有匹配%_defconfig的目标：
%_defconfig: $(obj)/conf
$(Q)$< $(silent) --defconfig=arch/$(SRCARCH)/configs/$@ $(Kconfig)
展开为：
smdk2410_defconfig: scripts/kconfig/conf
$(Q)scripts/kconfig/conf --defconfig=arch/../configs/smdk2410_defconfig Kconfig
在配置阶段，scripts/kconfig/conf搜集所有默认的Kconfig配置，然后用指定的smdk2410_defconfig配置进行更新并输出到根目录的.config文件中：
1.2 include/config/auto.conf的规则
在编译阶段，scripts/kconfig/conf读取配置阶段生成的.config，并检查最新配置生成以下4个文件：
- include/generated/autoconf.h；
- include/config/auto.conf.cmd；
- include/config/tristate.conf；
- include/config/auto.conf；
在生成include/config/auto.conf的规则中：
# If .config is newer than include/config/auto.conf, someone tinkered # with it and forgot to run make oldconfig. # if auto.conf.cmd is missing then we are probably in a cleaned tree so # we execute the config step to be sure to catch updated Kconfig files include/config/%.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig @# If the following part fails, include/config/auto.conf should be @# deleted so "make silentoldconfig" will be re-run on the next build. $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.autoconf || \ { rm -f include/config/auto.conf; false; } @# include/config.h has been updated after "make silentoldconfig". @# We need to touch include/config/auto.conf so it gets newer @# than include/config.h. @# Otherwise, 'make silentoldconfig' would be invoked twice. $(Q)touch include/config/auto.conf
(1) 首先执行\$(MAKE) -f \$(srctree)/Makefile silentoldconfig外，即调用make -f ./Makefile silentoldconfig的最终结果是执行scripts/kconfig/Makefile中的规则：
silentoldconfig: $(obj)/conf $(Q)mkdir -p include/config include/generated $< $(silent) --$@ $(Kconfig)
这个规则展开为：
silentoldconfig: scripts/kconfig/conf mkdir -p include/config include/generated scripts/kconfig/conf --silentoldconfig Kconfig
(2) 然后执行\$(MAKE) -f \$(srctree)/scripts/Makefile.autoconf，在scripts/Makefile.autoconf的文件头部定义有：
# This helper makefile is used for creating # - symbolic links (arch/$ARCH/include/asm/arch # - include/autoconf.mk, {spl,tpl}/include/autoconf.mk # - include/config.h # # When our migration to Kconfig is done # (= When we move all CONFIGs from header files to Kconfig) # this makefile can be deleted. # # SPDX-License-Identifier: GPL-2.0 # __all: include/autoconf.mk include/autoconf.mk.dep ifeq ($(shell grep -q '^CONFIG_SPL=y' include/config/auto.conf 2>/dev/null && echo y),y) __all: spl/include/autoconf.mk endif ifeq ($(shell grep -q '^CONFIG_TPL=y' include/config/auto.conf 2>/dev/null && echo y),y) __all: tpl/include/autoconf.mk endif
此处没有设置CONFIG_SPL=y或CONFIG_TPL=y，所以整个makefile的__all的依赖有：
- include/autoconf.mk
- include/autoconf.mk.dep
然而include/autoconf.mk还要进一步依赖于config.h。
1.2.1 include/config.h的规则
所有的autoconf.mk都依赖于include/config.h：
include/autoconf.mk include/autoconf.mk.dep \
spl/include/autoconf.mk tpl/include/autoconf.mk: include/config.h
实际上include/config.h由宏filechk_config_h生成：
# include/config.h # Prior to Kconfig, it was generated by mkconfig. Now it is created here. define filechk_config_h (echo "/* Automatically generated - do not edit */"; \ for i in $$(echo $(CONFIG_SYS_EXTRA_OPTIONS) | sed 's/,/ /g'); do \ echo \#define CONFIG_$$i \ | sed '/=/ {s/=/ /;q; } ; { s/$$/ 1/; }'; \ done; \ echo \#define CONFIG_BOARDDIR board/$(if $(VENDOR),$(VENDOR)/)$(BOARD);\ echo \#include \<config_defaults.h\>; \ echo \#include \<config_uncmd_spl.h\>; \ echo \#include \<configs/$(CONFIG_SYS_CONFIG_NAME).h\>; \ echo \#include \<asm/config.h\>; \ echo \#include \<config_fallbacks.h\>;) endef include/config.h: scripts/Makefile.autoconf create_symlink FORCE $(call filechk,config_h)
最终生成的include/config.h也比较简单，不妨看看：
/* Automatically generated - do not edit */ #define CONFIG_BOARDDIR board/samsung/smdk2410 #include <config_defaults.h> #include <config_uncmd_spl.h> #include <configs/smdk2410.h> #include <asm/config.h> #include <config_fallbacks.h>
生成config.h之前，还要应用create_symlink生成相应的符号链接。
1.2.2 create_symlink的规则
# symbolic links # If arch/$(ARCH)/mach-$(SOC)/include/mach exists, # make a symbolic link to that directory. # Otherwise, create a symbolic link to arch/$(ARCH)/include/asm/arch-$(SOC). PHONY += create_symlink create_symlink: ifdef CONFIG_CREATE_ARCH_SYMLINK ifneq ($(KBUILD_SRC),) $(Q)mkdir -p include/asm $(Q)if [ -d $(KBUILD_SRC)/arch/$(ARCH)/mach-$(SOC)/include/mach ]; then \ dest=arch/$(ARCH)/mach-$(SOC)/include/mach; \ else \ dest=arch/$(ARCH)/include/asm/arch-$(if $(SOC),$(SOC),$(CPU)); \ fi; \ ln -fsn $(KBUILD_SRC)/$$dest include/asm/arch else $(Q)if [ -d arch/$(ARCH)/mach-$(SOC)/include/mach ]; then \ dest=../../mach-$(SOC)/include/mach; \ else \ dest=arch-$(if $(SOC),$(SOC),$(CPU)); \ fi; \ ln -fsn $$dest arch/$(ARCH)/include/asm/arch endif endif
注释已经很好解释了create_symlink的行为：
- 如果arch/\$(ARCH)/mach-\$(SOC)/include/mach存在，则生成符号链接：
arch/$(ARCH)/include/asm/arch --> arch/$(ARCH)/mach-$(SOC)
- 否则生成符号链接：
arch/$(ARCH)/include/asm/arch -->arch/$(ARCH)/include/asm/arch-$(SOC)
对基于arm v9架构的s3c24x0芯片，arch/arm/mach-s3c2440文件夹不存在，所以生成链接：
arch/arm/include/asm/arch --> arch/arm/include/asm/arch-s3c24x0
简单说来，create_symlink就是将芯片arch/arm/include/asm/arch-s3c24x0链接到跟芯片名字无关的arch/arm/include/asm下。
1.2.3 include/autoconf.mk的规则
# We are migrating from board headers to Kconfig little by little. # In the interim, we use both of # - include/config/auto.conf (generated by Kconfig) # - include/autoconf.mk (used in the U-Boot conventional configuration) # The following rule creates autoconf.mk # include/config/auto.conf is grepped in order to avoid duplication of the # same CONFIG macros quiet_cmd_autoconf = GEN $@ cmd_autoconf = \ $(CPP) $(c_flags) $2 -DDO_DEPS_ONLY -dM $(srctree)/include/common.h > $@.tmp && { \ sed -n -f $(srctree)/tools/scripts/define2mk.sed $@.tmp | \ while read line; do \ if [ -n "${KCONFIG_IGNORE_DUPLICATES}" ] || \ ! grep -q "$${line%=*}=" include/config/auto.conf; then \ echo "$$line"; \ fi \ done > $@; \ rm $@.tmp; \ } || { \ rm $@.tmp; false; \ } include/autoconf.mk: FORCE $(call cmd,autoconf)
从cmd_autoconf来看，这里会根据include/common.h的依赖，然后调用tools/scripts/define2mk.sed，并合并之前生成的include/config/auto.conf生成最终的autoconf.mk。
1.2.4 include/autoconf.mk.dep的规则
quiet_cmd_autoconf_dep = GEN $@ cmd_autoconf_dep = $(CC) -x c -DDO_DEPS_ONLY -M -MP $(c_flags) \ -MQ include/config/auto.conf $(srctree)/include/common.h > $@ || { \ rm $@; false; \ } include/autoconf.mk.dep: FORCE $(call cmd,autoconf_dep)
这个规则比较简单，由于autoconf.mk由common.h和auto.conf而来，因此直接处理这两个文件的依赖并合并到autoconf.mk.dep中。
1.3 include/config/uboot.release
define filechk_uboot.release echo "$(UBOOTVERSION)$$($(CONFIG_SHELL) $(srctree)/scripts/setlocalversion $(srctree))" endef # Store (new) UBOOTRELEASE string in include/config/uboot.release include/config/uboot.release: include/config/auto.conf FORCE $(call filechk,uboot.release)
命令$(call filechk,uboot.release)展开后就是调用宏filechk_uboot.release，最终将字符串2016.09写入include/config/uboot.release中。
1.4 timestamp.h和version.h的规则
ersion_h := include/generated/version_autogenerated.h timestamp_h := include/generated/timestamp_autogenerated.h ... # Generate some files # --------------------------------------------------------------------------- define filechk_version.h (echo \#define PLAIN_VERSION \"$(UBOOTRELEASE)\"; \ echo \#define U_BOOT_VERSION \"U-Boot \" PLAIN_VERSION; \ echo \#define CC_VERSION_STRING \"$$(LC_ALL=C $(CC) --version | head -n 1)\"; \ echo \#define LD_VERSION_STRING \"$$(LC_ALL=C $(LD) --version | head -n 1)\"; ) endef # The SOURCE_DATE_EPOCH mechanism requires a date that behaves like GNU date. # The BSD date on the other hand behaves different and would produce errors # with the misused '-d' switch. Respect that and search a working date with # well known pre- and suffixes for the GNU variant of date. define filechk_timestamp.h (if test -n "$${SOURCE_DATE_EPOCH}"; then \ SOURCE_DATE="@$${SOURCE_DATE_EPOCH}"; \ DATE=""; \ for date in gdate date.gnu date; do \ $${date} -u -d "$${SOURCE_DATE}" >/dev/null 2>&1 && DATE="$${date}"; \ done; \ if test -n "$${DATE}"; then \ LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DATE "%b %d %C%y"'; \ LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TIME "%T"'; \ LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_TZ "%z"'; \ LC_ALL=C $${DATE} -u -d "$${SOURCE_DATE}" +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \ else \ return 42; \ fi; \ else \ LC_ALL=C date +'#define U_BOOT_DATE "%b %d %C%y"'; \ LC_ALL=C date +'#define U_BOOT_TIME "%T"'; \ LC_ALL=C date +'#define U_BOOT_TZ "%z"'; \ LC_ALL=C date +'#define U_BOOT_DMI_DATE "%m/%d/%Y"'; \ fi) endef $(version_h): include/config/uboot.release FORCE $(call filechk,version.h) $(timestamp_h): $(srctree)/Makefile FORCE $(call filechk,timestamp.h)
1.4.1 include/generated/version_autogenerated.h
根据include/config/uboot.release文件，规则调用filechk_version.h宏生成版本相关字符串文件include/generated/version_autogenerated.h，如下：
#define PLAIN_VERSION "2016.05" #define U_BOOT_VERSION "U-Boot " PLAIN_VERSION #define CC_VERSION_STRING "arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2008q3-72) 4.3.2" #define LD_VERSION_STRING "GNU ld (Sourcery G++ Lite 2008q3-72) 2.18.50.20080215
1.4.2 include/generated/timestamp_autogenerated.h
调用宏filechk_timestamp.h生成编译的时间戳文件，如下：
#define U_BOOT_DATE "Jun 07 2021" #define U_BOOT_TIME "01:58:59" #define U_BOOT_TZ "+0800" #define U_BOOT_DMI_DATE "06/07/2021"
1.5 outputmakfile的规则
PHONY += outputmakefile # outputmakefile generates a Makefile in the output directory, if using a # separate output directory. This allows convenient use of make in the # output directory. outputmakefile: ifneq ($(KBUILD_SRC),) $(Q)ln -fsn $(srctree) source $(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \ $(srctree) $(objtree) $(VERSION) $(PATCHLEVEL) endif
- 如果编译没有设置O，即输出和代码都在同一个目录下，则outputmakefile的规则什么都不做；
- 如果编译指定了输出目录O，则调用scripts/mkmakefile在O选项指定的目录下生成一个简单的makefile
1.6 scripts_basic的规则
# Basic helpers built in scripts/ PHONY += scripts_basic scripts_basic: $(Q)$(MAKE) $(build)=scripts/basic $(Q)rm -f .tmp_quiet_recordmcount
scripts_basic的执行结果就是编译生成scripts/basic/fixdep工具，该工具是u-boot编译系统中最常用的工具，用于在编译过程中修正每一个生成文件的依赖关系。
1.7 parepare0的规则
prepare0: archprepare FORCE
$(Q)$(MAKE) $(build)=.
展开后为：
prepare0: archprepare FORCE
make -f ./scripts/Makefile.build obj=.
编译时，命令make -f ./scripts/Makefile.build obj=.不会生成任何目标。
1.8 prepare系列目标总结
prepare阶段主要做了以下工作：
- scripts_basic规则生成fixdep工具，用于对整个系统生成目标文件相应依赖文件的更新；
- 配置阶段，scripts/kconfig/conf根据传入的指定配置文件在根目录下生成.config文件；
- 编译阶段，scripts/kconfig/conf读取配置阶段生成的.config，并检查最新配置生成以下文件：
- include/generated/autoconf.h
- include/config/auto.conf.cmd
- include/config/tristate.conf
- include/config/auto.conf
- 调用宏filechk_config_h生成include/config.h文件；
- 调用命令cmd_autoconf_dep生成autoconf.mk和autoconf.mk.cmd文件；
- 调用宏filechk_uboot.release生成include/config/uboot.release文件；
- 调用宏filechk_version.h生成include/generated/version_autogenerated.h文件；
- 调用宏filechk_timestamp.h生成include/generated/timestamp_autogenerated.h文件；
- 调用宏create_symlink就是将芯片arch/\$(ARCH)/include/asm/arch-\$(SOC)链接到跟芯片名字无关的arch/\$(ARCH)/include/asm下。
二、make编译逆向分析之u-boot
完整的u-boot的目标依赖：
从图上可见，除了prepare依赖外，u-boot还依赖于文件\$(head-y)，\$(libs-y)和$(LDSCRIPT)，即依赖于：
- 启动文件arch/arm/cpu/$(CPU)/start.o ；
- 各个目录下的build-in.o ；
- 链接脚本文件arch/arm/cpu/u-boot.lds；
2.1 启动文件start.o
$(head-y)在arch/arm/Makefile中被直接指定：
head-y := arch/arm/cpu/$(CPU)/start.o
在顶层makefile中被指定给变量u-boot-init：
u-boot-init := $(head-y)
2.2 各目录下的build-in.o
$(libs-y)在顶层的makefile中被指定为各个子目录下的build-in.o的集合：
libs-y += lib/
...
libs-y += fs/
libs-y += net/
libs-y += disk/
libs-y += drivers/
...
libs-y += $(if $(BOARDDIR),board/$(BOARDDIR)/)
libs-y := $(sort $(libs-y))
...
libs-y := $(patsubst %/, %/built-in.o, $(libs-y))
...
u-boot-main := $(libs-y)
以上脚本中，先将\$(libs-y)设置为各子目录的集合，最后调用patsubst函数将\$(libs-y)设置为这些目录下的built-in.o文件的集合，最后赋值给变量u-boot-main作为链接的主体文件。
各目录下的built-in.o是如何生成的呢？
以drivers/mmc/built-in.o为例，先查看生成的依赖文件drivers/mmc/.built-in.o.cmd：
cmd_drivers/mmc/built-in.o := rm -f drivers/mmc/built-in.o; arm-linux-ar rcs drivers/mmc/built-in.o
生成built-in.o的规则在scripts/Makefile.build中定义：
# # Rule to compile a set of .o files into one .o file # ifdef builtin-target quiet_cmd_link_o_target = LD $@ # If the list of objects to link is empty, just create an empty built-in.o cmd_link_o_target = $(if $(strip $(obj-y)),\ $(LD) $(ld_flags) -r -o $@ $(filter $(obj-y), $^) \ $(cmd_secanalysis),\ rm -f $@; $(AR) rcs$(KBUILD_ARFLAGS) $@) $(builtin-target): $(obj-y) FORCE $(call if_changed,link_o_target) targets += $(builtin-target) endif # builtin-target
2.3 链接脚本u-boot.lds
链接脚本的规则如下：
quiet_cmd_cpp_lds = LDS $@ cmd_cpp_lds = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) \ -D__ASSEMBLY__ -x assembler-with-cpp -P -o $@ $< u-boot.lds: $(LDSCRIPT) prepare FORCE $(call if_changed_dep,cpp_lds)
2.4 生成u-boot规则
顶层Makefile中定义了生成u-boot文件的规则：
# Rule to link u-boot # May be overridden by arch/$(ARCH)/config.mk quiet_cmd_u-boot__ ?= LD $@ cmd_u-boot__ ?= $(LD) $(LDFLAGS) $(LDFLAGS_u-boot) -o $@ \ -T u-boot.lds $(u-boot-init) \ --start-group $(u-boot-main) --end-group \ $(PLATFORM_LIBS) -Map u-boot.map ... u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE $(call if_changed,u-boot__) ...
u-boot文件的生成很简单，调用ld命令，将\$(u-boot-init)和\$(u-boot-main)指定的一系列文件通过脚本u-boot.lds连接起来。
生成了u-boot文件后，后续就是针对u-boot文件的各种处理了。
三、make编译逆向分析之 顶层目标依赖
顶层目标依赖：
显然，在生成了u-boot的基础上，进一步生成所需要的各种目标文件：
3.1 u-boot.srec
# Normally we fill empty space with 0xff quiet_cmd_objcopy = OBJCOPY $@ cmd_objcopy = $(OBJCOPY) --gap-fill=0xff $(OBJCOPYFLAGS) \ $(OBJCOPYFLAGS_$(@F)) $< $@ ... OBJCOPYFLAGS_u-boot.hex := -O ihex OBJCOPYFLAGS_u-boot.srec := -O srec u-boot.hex u-boot.srec: u-boot FORCE $(call if_changed,objcopy)
调用objcopy命令，通过-O ihex或-O srec指定生成u-boot.hex或u-boot.srec格式文件。
3.2 u-boot.sym
quiet_cmd_sym ?= SYM $@
cmd_sym ?= $(OBJDUMP) -t $< > $@
u-boot.sym: u-boot FORCE
$(call if_changed,sym)
调用$(OBJDUMP)命令生成符号表文件u-boot.sym。
3.3 System.map
SYSTEM_MAP = \ $(NM) $1 | \ grep -v '\(compiled\)\|\(\.o$$\)\|\( [aUw] \)\|\(\.\.ng$$\)\|\(LASH[RL]DI\)' | \ LC_ALL=C sort System.map: u-boot @$(call SYSTEM_MAP,$<) > $@
调用$(NM)命令打印u-boot文件的符号表，并用grep -v处理后得到System.map文件，里面包含了最终使用到的各个符号的位置信息。
3.4 u-boot.bin和u-boot-nodtb.bin
PHONY += dtbs dtbs: dts/dt.dtb @: dts/dt.dtb: checkdtc u-boot $(Q)$(MAKE) $(build)=dts dtbs quiet_cmd_copy = COPY $@ cmd_copy = cp $< $@ ifeq ($(CONFIG_OF_SEPARATE),y) u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE $(call if_changed,cat) u-boot.bin: u-boot-dtb.bin FORCE $(call if_changed,copy) else u-boot.bin: u-boot-nodtb.bin FORCE $(call if_changed,copy) endif
由于这里没有使用device tree设置，即编译没有定义CONFIG_OF_SEPARATE，因此u-boot.bin和u-boot-nodtb.bin是一样的。
至于生成u-boot-nodtb.bin的规则：
u-boot-nodtb.bin: u-boot FORCE $(call if_changed,objcopy) $(call DO_STATIC_RELA,$<,$@,$(CONFIG_SYS_TEXT_BASE)) $(BOARD_SIZE_CHECK)
显然，u-boot-nodtb.bin是u-boot文件通过objcopy得到。
3.5 u-boot.cfg
u-boot.cfg中包含了所有用到的宏定义，其生成规则如下：
# Create a file containing the configuration options the image was built with quiet_cmd_cpp_cfg = CFG $@ cmd_cpp_cfg = $(CPP) -Wp,-MD,$(depfile) $(cpp_flags) $(LDPPFLAGS) -ansi \ -DDO_DEPS_ONLY -D__ASSEMBLY__ -x assembler-with-cpp -P -dM -E -o $@ $< ... u-boot.cfg: include/config.h FORCE $(call if_changed,cpp_cfg)
因此，阅读源码时如果不确定某个宏的值，可以检查u-boot.cfg文件。
命令中的if_changed函数定义在scripts/Kbuild.include文件中：
if_changed = $(if $(strip $(any-prereq) $(arg-check)), \ @set -e; \ $(echo-cmd) $(cmd_$(1)); \ printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd)
echo-cmd其定义如下：
echo-cmd = $(if $($(quiet)cmd_$(1)),\ echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
\$(echo-cmd) \$(cmd_$(1))有两个功能：
- echo 命令，即回显命令；
- 执行命令；
\$(echo-cmd) \$(cmd_\$(1))展开后会在控制台回显命令，然后执行命令，执行完之后，会生成u-boot.cfg文件：
arm-linux-gcc -E -Wp,-MD, ./.u-boot.cfg.d -D__KERNEL__ -D__UBOOT__ -D__ARM__ -marm -mno-thumb-interwork -mabi=aapcs-linux -mword-relocations -fno-pic -ffunction-sections -fdata-sections -fno-common -ffixed-r9 -msoft-float -pipe -march=armv4t -Iinclude -I./arch/arm/include -include ./include/linux/kconfig.h -nostdinc -isystem /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/include -include ./include/u-boot/u-boot.lds.h
-DCPUDIR=arch/arm/cpu/arm920t -ansi -DDO_DEPS_ONLY -D__ASSEMBLY__ -x assembler-with-cpp -P -dM -E -o u-boot.cfg include/config.h
这里指定了头文件主要是./include/linux/kconfig.h文件，这个文件引入了include/generated/autoconf.h，这个文件包含了各种宏定义：
#include <generated/autoconf.h>
/* * * Automatically generated file; DO NOT EDIT. * U-Boot 2016.05 Configuration * */ #define CONFIG_CMD_BOOTM 1 #define CONFIG_CMD_USB 1 #define CONFIG_CMD_EDITENV 1 #define CONFIG_SYS_GENERIC_BOARD 1 #define CONFIG_CMD_CONSOLE 1 #define CONFIG_CMD_BOOTD 1 #define CONFIG_CMD_IMLS 1 #define CONFIG_BOOTSTAGE_STASH_ADDR 0x0 #define CONFIG_HAVE_PRIVATE_LIBGCC 1 #define CONFIG_CMD_BDI 1 #define CONFIG_ARM 1 #define CONFIG_CREATE_ARCH_SYMLINK 1 #define CONFIG_SYS_VENDOR "samsung" #define CONFIG_CMD_PING 1 #define CONFIG_CMD_SAVEENV 1 #define CONFIG_CMD_MISC 1 #define CONFIG_SYS_CPU "arm920t" #define CONFIG_BOOTSTAGE_USER_COUNT 0x20 #define CONFIG_CC_OPTIMIZE_FOR_SIZE 1 #define CONFIG_CMD_FLASH 1 #define CONFIG_REGEX 1 #define CONFIG_CMD_ENV_EXISTS 1 #define CONFIG_HAVE_GENERIC_BOARD 1 #define CONFIG_CMD_EXPORTENV 1 #define CONFIG_CMD_DHCP 1 #define CONFIG_SYS_EXTRA_OPTIONS "" #define CONFIG_CMD_CRC32 1 #define CONFIG_SYS_BOARD "smdk2410" #define CONFIG_SYS_CONFIG_NAME "smdk2410" #define CONFIG_CMD_NFS 1 #define CONFIG_NET 1 #define CONFIG_TARGET_SMDK2410 1 #define CONFIG_CMD_GO 1 #define CONFIG_SYS_MALLOC_CLEAR_ON_INIT 1 #define CONFIG_CMD_IMI 1 #define CONFIG_SYS_HZ 1000 #define CONFIG_SUPPORT_OF_CONTROL 1 #define CONFIG_CMD_EXT2 1 #define CONFIG_LOCALVERSION "" #define CONFIG_CMDLINE 1 #define CONFIG_CMD_LOADB 1 #define CONFIG_CMD_RUN 1 #define CONFIG_SYS_HUSH_PARSER 1 #define CONFIG_SYS_PROMPT "SMDK2410 # " #define CONFIG_CMD_MEMORY 1 #define CONFIG_HUSH_PARSER 1 #define CONFIG_CMD_XIMG 1 #define CONFIG_CMD_ECHO 1 #define CONFIG_LOCALVERSION_AUTO 1 #define CONFIG_SYS_ARCH "arm" #define CONFIG_EXPERT 1 #define CONFIG_SYS_SOC "s3c24x0" #define CONFIG_CMD_ITEST 1 #define CONFIG_CMD_CACHE 1 #define CONFIG_BOOTSTAGE_STASH_SIZE 0x4096 #define CONFIG_CMD_LOADS 1 #define CONFIG_CMD_FAT 1 #define CONFIG_CMD_NET 1 #define CONFIG_CMD_FPGA 1 #define CONFIG_NET_TFTP_VARS 1 #define CONFIG_CPU_ARM920T 1 #define CONFIG_CMD_IMPORTENV 1 #define CONFIG_CMD_ELF 1 #define CONFIG_CMD_SOURCE 1
同时printf '%s\n' 'cmd_$@ := \$(make-cmd)' > \$(dot-target).cmd)会将如下信息输出到。u-boot.cfg.cmd文件中：
cmd_u-boot.cfg := arm-linux-gcc -E -Wp,-MD,./.u-boot.cfg.d -D__KERNEL__ -D__UBOOT__ -D__ARM__ -marm -mno-thumb-interwork -mabi=aapcs-linux -mword-relocations -fno-pic -ffunction-sections -fdata-sections -fno-common -ffixed-r9 -msoft-float -pipe -march=armv4t -Iinclude -I./arch/arm/include -include ./include/linux/kconfig.h -nostdinc -isystem /usr/local/arm/4.3.2/bin/../lib/gcc/arm-none-linux-gnueabi/4.3.2/include -include ./include/u-boot/u-boot.lds.h -DCPUDIR=arch/arm/cpu/arm920t -ansi -DDO_DEPS_ONLY -D__ASSEMBLY__ -x assembler-with-cpp -P -dM -E -o u-boot.cfg include/config.h
自此，生成了所有的目标文件，完成了整个编译过程的分析。
参考文章
