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一 UBOOT编译--- make xxx_deconfig过程详解( 二 )

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在scripts/Makefile.build有如下定义
# note：scripts/Makefile.build# Modified for U-Bootprefix := tplsrc := $(patsubst $(prefix)/%,%,$(obj))ifeq ($(obj),$(src))prefix := splsrc := $(patsubst $(prefix)/%,%,$(obj))ifeq ($(obj),$(src))prefix := .endifendif在命令make -f ./scripts/Makefile.build obj=scripts/basic我们传入了obj=scripts/basic 所以src = https://www.huyubaike.com/biancheng/obj = scripts/basic, prefix := .
4.1.4.2 kbuild-dir的定义在scripts/Makefile.build有如下定义
kbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))所以 kbuild-dir = ./scripts/basic
4.1.4.3 kbuild-file的定义在scripts/Makefile.build有如下定义
kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)所以kbuild-file = ./scripts/basic/Makefile
所以include $(kbuild-file)即为include ./scripts/basic/Makefile
在./scripts/basic/Makefile中：
# note：scripts/basic/Makefilehostprogs-y := fixdepalways:= $(hostprogs-y)# fixdep is needed to compile other host programs$(addprefix $(obj)/,$(filter-out fixdep,$(always))): $(obj)/fixdep所以always = fixdep
4.1.4.4 又在Makefile.build中包含include scripts/Makefile.lib而在scripts/Makefile.lib中
# note：scripts/Makefile.libalways:= $(addprefix $(obj)/,$(always))所以最终 always = scripts/basic/fixdep。

故__build 展开如下： __build: scripts/basic/fixdep@:
1. 在Makefile.build中有如下定义：
# note：scripts/Makefile.buildifneq ($(hostprogs-y)$(hostprogs-m),)include scripts/Makefile.hostendif在./scripts/basic/Makefile中hostprogs-y = fixdep, 所以scripts/Makefile.host被包含进Makefile.build;在scripts/Makefile.host中
# note：scripts/Makefile.host__hostprogs := $(sort $(hostprogs-y) $(hostprogs-m))hostprogs-m为空，所以__hostprogs = fixdep 。在scripts/Makefile.host中
# note：scripts/Makefile.host# C code# Executables compiled from a single .c filehost-csingle := $(foreach m,$(__hostprogs), \$(if $($(m)-objs)$($(m)-cxxobjs)$($(m)-sharedobjs),,$(m)))......host-csingle := $(addprefix $(obj)/,$(host-csingle))因为fixdep-objs与fixdep-cxxobjs都不存在，所以host-csingle = fixdep； 又 host-csingle := $ (addprefix $ (obj)/,$(host-csingle)) ， 所以host-csingle = scripts/basic/fixdep 。host-csingle规则如下：
# note：scripts/Makefile.host$(host-csingle): $(obj)/%: $(src)/%.c FORCE $(call if_changed_dep,host-csingle)等价于：
scripts/basic/fixdep:scripts/basic/fixdep.c FORCE$(call if_changed_dep,host-csingle)2. if_changed_dep在scripts/Kbuild.include中定义
# note：scripts/Kbuild.include# Execute the command and also postprocess generated .d dependencies file.if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ),\ @set -e;\ $(echo-cmd) $(cmd_$(1));\ scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ rm -f $(depfile);\ mv -f $(dot-target).tmp $(dot-target).cmd)2.1 $(strip $(any-prereq) $(arg-check) ) (1) any-prereq在scripts/Kbuild.include中定义
# note：scripts/Kbuild.include any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^)$ ? 表示所有比目标还要新的依赖文件;$ ^ 表示所有的依赖文件，$(filter-out $ (PHONY), $?)就是过滤到比目标还要新的依赖文件中的伪目标，即为 scripts/basic/fixdep.c ，  $ (filter-out $ (PHONY) $ (wildcard $ ^ ), $^)表示过滤掉所有的依赖文件中的伪目标与存在的依赖文件，这里为空，所以any-prereq = scripts/basic/fixdep.c 。(2) arg-check在scripts/Kbuild.include中定义：
# note：scripts/Kbuild.includeifneq ($(KBUILD_NOCMDDEP),1)arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \$(filter-out $(cmd_$@),$(cmd_$(1))) )elsearg-check = $(if $(strip $(cmd_$@)),,1)endifKBUILD_NOCMDDEP是在make命令行中定义 ， 我们并没有定义，所以：
arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) $(filter-out $(cmd_$@), $(cmd_$(1))) )<1> $ (filter-out $ (cmd_ $ (1)), $ (cmd_ $@)) 表示过滤掉 $(cmd_ $@)中符合 $(cmd_ $(1))的项 。$(1)表示if_changed_dep函数的第一个参数host-csingle，$@表示目标文件scripts/basic/fixdep 。<2> cmd_scripts/basic/fixdep并没有定义，所以 $(filter-out $(cmd_ $(1)), $(cmd_ $@))为空； <3> cmd_host-csingle 在Makefile.host中定义：
cmd_host-csingle= $(HOSTCC) $(hostc_flags) -o $@ $<$(HOST_LOADLIBES) $(HOSTLOADLIBES_$(@F))所以arg-check = $ (filter-out $ (cmd_$ @), $ (cmd_$ (1))) = $ (HOSTCC) $ (hostc_flags) -o $@ $< $(HOST_LOADLIBES) $(HOSTLOADLIBES_ $(@F))
$(any-prereq) $(arg-check)都为非空，所以：
if_changed_dep = @set -e;\ /如果任何语句的执行结果不是true则应该退出 $(echo-cmd) $(cmd_$(1));\ scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ rm -f $(depfile);\ mv -f $(dot-target).tmp $(dot-target).cmd)

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