- 第一步：配置，执行make xxx_defconfig进行各项配置，生成.config文件 (u-boot-2018.05之make配置过程分析)
- 第二步：编译，执行make进行编译，生成可执行的二进制文件u-boot.*
顶层目标依赖
_all和all对$(ALL-y)的依赖
从顶层Makefile开始查找，首先找到的是_all伪目标：
# That's our default target when none is given on the command line PHONY := _all _all:紧接着会对_all伪目标添加all伪目标的依赖：
PHONY += all ifeq ($(KBUILD_EXTMOD),) _all: all else _all: modules endifall自身依赖于$(ALL-y)
all: $(ALL-y)$(ALL-y)对u-boot目标文件的依赖
$(ALL-y)定义了最终需要生成所有文件：
# Always append ALL so that arch config.mk's can add custom ones ALL-y += u-boot.srec u-boot.bin u-boot.sym System.map u-boot.cfg binary_size_check ALL-$(CONFIG_ONENAND_U_BOOT) += u-boot-onenand.bin ifeq ($(CONFIG_SPL_FSL_PBL),y) ALL-$(CONFIG_RAMBOOT_PBL) += u-boot-with-spl-pbl.bin else ifneq ($(CONFIG_SECURE_BOOT), y) # For Secure Boot The Image needs to be signed and Header must also # be included. So The image has to be built explicitly ALL-$(CONFIG_RAMBOOT_PBL) += u-boot.pbl endif endif ALL-$(CONFIG_SPL) += spl/u-boot-spl.bin ALL-$(CONFIG_SPL_FRAMEWORK) += u-boot.img ALL-$(CONFIG_TPL) += tpl/u-boot-tpl.bin ALL-$(CONFIG_OF_SEPARATE) += u-boot.dtb ifeq ($(CONFIG_SPL_FRAMEWORK),y) ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb.img endif ALL-$(CONFIG_OF_HOSTFILE) += u-boot.dtb ifneq ($(CONFIG_SPL_TARGET),) ALL-$(CONFIG_SPL) += $(CONFIG_SPL_TARGET:"%"=%) endif ALL-$(CONFIG_REMAKE_ELF) += u-boot.elf ALL-$(CONFIG_EFI_APP) += u-boot-app.efi ALL-$(CONFIG_EFI_STUB) += u-boot-payload.efi ifneq ($(BUILD_ROM),) ALL-$(CONFIG_X86_RESET_VECTOR) += u-boot.rom endif # enable combined SPL/u-boot/dtb rules for tegra ifeq ($(CONFIG_TEGRA)$(CONFIG_SPL),yy) ALL-y += u-boot-tegra.bin u-boot-nodtb-tegra.bin ALL-$(CONFIG_OF_SEPARATE) += u-boot-dtb-tegra.bin endif以上的$(ALL-y)目标中看起来非常复杂，但除了第一行的通用目标外，其余目标都只在特殊条件下才生成，这里略去不提。只分析通用目标依赖：
ALL-y += u-boot.srec u-boot.bin u-boot.sym System.map u-boot.cfg binary_size_checki. 依赖u-boot.bin
依赖u-boot.bin：
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) endifu-boot.bin --> u-boot-dtb.bin --> u-boot-nodtb.bin + dts/dt.dtbu-boot.bin --> u-boot-nodtb.bin
进一步，对于u-boot-nodtb.bin，其规则是：
u-boot-nodtb.bin: u-boot FORCE $(call if_changed,objcopy) $(call DO_STATIC_RELA,$<,$@,$(CONFIG_SYS_TEXT_BASE)) $(BOARD_SIZE_CHECK)ii. 依赖System.map
依赖System.map：
System.map: u-boot @$(call SYSTEM_MAP,$<) > $@iii. 依赖u-boot.cfg
依赖u-boot.cfg：
u-boot.cfg: include/config.h FORCE $(call if_changed,cpp_cfg)u-boot文件目标依赖
a). 依赖u-boot
依赖u-boot：
u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE $(call if_changed,u-boot__) ifeq ($(CONFIG_KALLSYMS),y) $(call cmd,smap) $(call cmd,u-boot__) common/system_map.o endif其中$(u-boot-init)和$(u-boot-main)分别被定义为：
u-boot-init := $(head-y) u-boot-main := $(libs-y)i. 依赖$(head-y)
$(head-y)在arch/arm/Makefile被定义为：
head-y := arch/arm/cpu/$(CPU)/start.oii. 依赖$(libs-y)
在顶层Makefile中搜索一下$(libs-y)，其被定义为各层驱动目录下build-in.o的集合：
libs-y += lib/ ...此处...libs-y := $(sort $(libs-y)) u-boot-dirs := $(patsubst %/,%,$(filter %/, $(libs-y))) tools examples libs-y := $(patsubst %/, %/built-in.o, $(libs-y))u-boot-main := $(libs-y)b). 依赖u-boot.lds
依赖u-boot.lds：
u-boot.lds: $(LDSCRIPT) prepare FORCE $(call if_changed_dep,cpp_lds)其中$(LDSCRIPT)的定义如下：
# If board code explicitly specified LDSCRIPT or CONFIG_SYS_LDSCRIPT, use # that (or fail if absent). Otherwise, search for a linker script in a # standard location. ifndef LDSCRIPT #LDSCRIPT := $(srctree)/board/$(BOARDDIR)/u-boot.lds.debug ifdef CONFIG_SYS_LDSCRIPT # need to strip off double quotes LDSCRIPT := $(srctree)/$(CONFIG_SYS_LDSCRIPT:"%"=%) endif endif # If there is no specified link script, we look in a number of places for it ifndef LDSCRIPT ifeq ($(wildcard $(LDSCRIPT)),) LDSCRIPT := $(srctree)/board/$(BOARDDIR)/u-boot.lds endif ifeq ($(wildcard $(LDSCRIPT)),) LDSCRIPT := $(srctree)/$(CPUDIR)/u-boot.lds endif ifeq ($(wildcard $(LDSCRIPT)),) LDSCRIPT := $(srctree)/arch/$(ARCH)/cpu/u-boot.lds endif endif如果没有定义LDSCRIPT和CONFIG_SYS_LDSCRIPT，则默认使用u-boot自带的lds文件。包括board/$(BOARDIDR)和$(CPUDIR)目录下定制的针对board或cpu的lds文件，如果没有定制的lds文件，则采用arch/$(ARCH)/cpu目录下默认的u-boot.lds
prepare系列目标依赖
prepare系列依赖的规则
实际上prepare是一系列prepare伪目标和动作的组合，完成编译前的准备工作：
# Things we need to do before we recursively start building the kernel # or the modules are listed in "prepare". # A multi level approach is used. prepareN is processed before prepareN-1. # archprepare is used in arch Makefiles and when processed asm symlink, # version.h and scripts_basic is processed / created. # Listed in dependency order PHONY += prepare archprepare prepare0 prepare1 prepare2 prepare3 # prepare3 is used to check if we are building in a separate output directory, # and if so do: # 1) Check that make has not been executed in the kernel src $(srctree) prepare3: include/config/uboot.release ifneq ($(KBUILD_SRC),) @$(kecho) ' Using $(srctree) as source for U-Boot' $(Q)if [ -f $(srctree)/.config -o -d $(srctree)/include/config ]; then \ echo >&2 " $(srctree) is not clean, please run 'make mrproper'"; \ echo >&2 " in the '$(srctree)' directory.";\ /bin/false; \ fi; endif # prepare2 creates a makefile if using a separate output directory prepare2: prepare3 outputmakefile prepare1: prepare2 $(version_h) $(timestamp_h) \ include/config/auto.conf ifeq ($(wildcard $(LDSCRIPT)),) @echo >&2 " Could not find linker script." @/bin/false endif archprepare: prepare1 scripts_basic prepare0: archprepare FORCE $(Q)$(MAKE) $(build)=. # All the preparing.. prepare: prepare0伪目标prepare，prepare0，archprepare，prepare1，prepare2，prepare3
prepare系列其他的依赖规则
在prepare1的依赖列表中，除了include/config/auto.conf外，还有$(version_h)和$(timestamp_h)，他们的依赖分别为：
$(version_h): include/config/uboot.release FORCE $(call filechk,version.h) $(timestamp_h): $(srctree)/Makefile FORCE $(call filechk,timestamp.h)这里的两个filechk函数调用会动态生成version.h和timestamp.h。
对于最里层的prepare3的依赖include/config/uboot.release，还存在下一级依赖：
# Store (new) UBOOTRELEASE string in include/config/uboot.release include/config/uboot.release: include/config/auto.conf FORCE $(call filechk,uboot.release)对于include/config/auto.conf，Makefile中有一个匹配的规则：
# 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. $(Q)touch include/config/auto.conf所以include/config/auto.conf依赖于$(KCONFIG_CONFIG)和include/config/auto.conf.cmd$(KCONFIG_CONFIG)实际上就是.configinclude/config/auto.conf.cmd是由fixdep在编译时生成的依赖文件。