经验总结

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

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# note：顶层MakefileKBUILD_MODULES :=综上：语句$(if $ (KBUILD_MODULES),$(obj-m) $(modorder-target))为空 。
4.1.3 $(subdir-ym)在scripts/Makefile.lib中，subdir-ym的定义如下：
# note：scripts/Makefile.lib# Subdirectories we need to descend intosubdir-ym := $(sort $(subdir-y) $(subdir-m))......subdir-ym := $(addprefix $(obj)/,$(subdir-ym))subdir-y与subdir-m都为空 。综上：语句$(subdir-ym)为空 。
4.1.4 $(always) 重点关注在scripts/Makefile.build有如下定义
# note：scripts/Makefile.build# The filename Kbuild has precedence over Makefilekbuild-dir := $(if $(filter /%,$(src)),$(src),$(srctree)/$(src))kbuild-file := $(if $(wildcard $(kbuild-dir)/Kbuild),$(kbuild-dir)/Kbuild,$(kbuild-dir)/Makefile)include $(kbuild-file)4.1.4.1 src的定义在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)

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