make menuconfig近两年一直有着写linux内核相关的想法，比如从Makefile执行 make menuconfig、make，到x86架构的引导启动过程。由于网上有较多相关的文章，便有些羞涩于自己动手写。现在想着无论自己水平如何，用自己的思路去追溯代码并记录代码，应该强于融入别人的思想。
本次采用5.9版本内核，通过代码分析、strace跟踪等形式按照自己的理解来写，写的不对的地方请跳过。
示例在x86_64架构的Centos8.2虚拟机中进行，现在开始进入正题。
打开Makefile文件：
# SPDX-License-Identifier: GPL-2.0VERSION = 5PATCHLEVEL = 9SUBLEVEL = 0EXTRAVERSION =NAME = Kleptomaniac Octopus
在开始的地方定义了linux版本信息，这些将在后面多次使用。
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$(if $(filter __%, $(MAKECMDGOALS)), $(error targets prefixed with '__' are only for internal use))
MAKECMDGOALS属执行make时传入的参数（暂存到这个变量），比如输入make test，将会匹配到，执行 $(error targets prefixed with ‘__’ are only for internal use))，导致make停止执行
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PHONY := __all __all:
当make时没有传入参数规则，将默认执行__all流程
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ifneq ($(sub_make_done),1)
判断子级make配置是否完成，如果还没有完成执行条件内的语句
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unexport LC_ALLLC_COLLATE=CLC_NUMERIC=Cexport LC_COLLATE LC_NUMERIC
不让LC_ALL变量传入子级make（使用），传入LC_COLLATE LC_NUMERIC
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ifeq ("$(origin V)", "command line") KBUILD_VERBOSE = $(V)endififndef KBUILD_VERBOSE KBUILD_VERBOSE = 0endif
如果KBUILD_VERBOSE等于0，则上述命令将被隐藏；如果KBUILD_VERBOSE等于1，则显示上述命令；如果KBUILD_VERBOSE等于2，请给出重建每个目标的原因。
这里默认执行KBUILD_VERBOSE = 0（quiet=quiet_，Q = @，只打印执行结果）
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export quiet Q KBUILD_VERBOSE
quiet Q KBUILD_VERBOSE变量传入子级make（使用）
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ifeq ("$(origin O)", "command line") KBUILD_OUTPUT := $(O)endififneq ($(KBUILD_OUTPUT),)# Make's built-in functions such as $(abspath ...), $(realpath ...) cannot# expand a shell special character '~'、We use a somewhat tedious way here.abs_objtree := $(shell mkdir -p $(KBUILD_OUTPUT) && cd $(KBUILD_OUTPUT) && pwd)$(if $(abs_objtree),, $(error failed to create output directory "$(KBUILD_OUTPUT)"))
通过(make) O=指定输出目录或者通过KBUILD_OUTPUT变量，O=优先级高级KBUILD_OUTPUT变量，默认值为当前目录
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abs_srctree := $(realpath $(dir $(lastword $(MAKEFILE_LIST))))
abs_srctree得到Makefile绝对路径（由MAKEFILE_LIST变量经过 lastword、dir、realpath执行得到）
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ifneq ($(abs_srctree),$(abs_objtree))MAKEFLAGS += --include-dir=$(abs_srctree)need-sub-make := 1endif
在make menuconfig中abs_srctree与abs_objtree相同，未设置need-sub-make，need-sub-make=0
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this-makefile := $(lastword $(MAKEFILE_LIST))
this-makefile=Makefile
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export sub_make_done := 1
子级make配置完成
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ifeq ($(need-sub-make),1)PHONY += $(MAKECMDGOALS) __sub-make$(filter-out $(this-makefile), $(MAKECMDGOALS)) __all: __sub-make @:__sub-make: $(Q)$(MAKE) -C $(abs_objtree) -f $(abs_srctree)/Makefile $(MAKECMDGOALS)...
上述说过need-sub-make=0，这里的分支将不执行（不执行子级Makefile）
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ifeq ($(need-sub-make),)MAKEFLAGS += --no-print-directory
进入分支，设置输出信息
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ifeq ("$(origin C)", "command line") KBUILD_CHECKSRC = $(C)endififndef KBUILD_CHECKSRC KBUILD_CHECKSRC = 0endif
使用“make C=1”只允许检查重新编译的文件，使用“make C=2”来启用对所有源文件的检查；这里为0，执行KBUILD_CHECKSRC = 0
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ifeq ("$(origin M)", "command line") KBUILD_EXTMOD := $(M)endif$(if $(word 2, $(KBUILD_EXTMOD)), $(error building multiple external modules is not supported))export KBUILD_CHECKSRC KBUILD_EXTMOD
设置外部模块(.ko)目录
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extmod-prefix = $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)
extmod-prefix默认为空
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ifeq ($(abs_srctree),$(abs_objtree)) # building in the source tree srctree := . building_out_of_srctree :=else ifeq ($(abs_srctree)/,$(dir $(abs_objtree))) # building in a subdirectory of the source tree srctree := .. else srctree := $(abs_srctree) endif building_out_of_srctree := 1endif
abs_srctree与abs_objtree目录相同，srctree为当前目录，building_out_of_srctree为空
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objtree := .VPATH := $(srctree)
objtree为当前目录，VPATH为空
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export building_out_of_srctree srctree objtree VPATH
building_out_of_srctree srctree objtree VPATH变量传入子级make（使用）
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version_h := include/generated/uapi/linux/version.hold_version_h := include/linux/version.hclean-targets := %clean mrproper cleandocs...
定义version_h、old_version_h路径，clean-targets清除规则等配置
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ifeq ($(KBUILD_EXTMOD),) ifneq ($(filter %config,$(MAKECMDGOALS)),) config-build := 1 ifneq ($(words $(MAKECMDGOALS)),1) mixed-build := 1 endif endifendif
默认config-build := 1
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include scripts/Kbuild.include# Read KERNELRELEASE from include/config/kernel.release (if it exists)KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSIONinclude scripts/subarch.include
包含Kbuild.include，KERNELRELEASE和KERNELVERSION为5.9.0，包含subarch.include
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ARCH ?= $(SUBARCH)
获取当前系统架构，默认x86
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KCONFIG_ConFIG ?= .config
设置KCONFIG_ConFIG=.config(配置文件保存名称)
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export KCONFIG_ConFIGexport KBUILD_DEFConFIG := defconfig
KCONFIG_ConFIG KBUILD_DEFCONFIG变量传入子级make（使用），KBUILD_DEFCONFIG用于make defconfig
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...USERINCLUDE := -I$(srctree)/arch/$(SRCARCH)/include/uapi -I$(objtree)/arch/$(SRCARCH)/include/generated/uapi -I$(srctree)/include/uapi -I$(objtree)/include/generated/uapi -include $(srctree)/include/linux/kconfig.h
跳过gcc等一些编译相关信息，USERINCLUDE为-I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h
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LINUXINCLUDE := -I$(srctree)/arch/$(SRCARCH)/include -I$(objtree)/arch/$(SRCARCH)/include/generated $(if $(building_out_of_srctree),-I$(srctree)/include) -I$(objtree)/include $(USERINCLUDE)
LINUXINCLUDE为-I./arch/x86/include -I./arch/x86/include/generated -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h
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export KBUILD_LDS_MODULE := $(srctree)/scripts/module-common.lds...export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
导入较多变量供子级make使用
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PHONY += outputmakefile
PHONY为__all scripts_basic outputmakefile
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PHONY += scripts_basicscripts_basic: $(Q)$(MAKE) $(build)=scripts/basic $(Q)rm -f .tmp_quiet_recordmcount
执行scripts_basic内分支(__all scripts_basic outputmakefile，这三个为需要执行的分支)
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outputmakefile:
执行outputmakefile内分支，make menuconfig只是经过一下这里
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%config: outputmakefile scripts_basic FORCE $(Q)$(MAKE) $(build)=scripts/kconfig $@
执行scripts/kconfig/Makefile文件
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$(foreach f, mconf.o $(lxdialog), $(eval HOSTCFLAGS_$f = $$(shell 、$(obj)/mconf-cfg && echo $$$$cflags)))
编译mconf.c,lxdialog/checklist.c lxdialog/inputbox.c lxdialog/menubox.c lxdialog/textbox.c lxdialog/util.c lxdialog/yesno.c，生成mconf工具(menuconfig用到的视图工具，参考mconf源码)
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$(obj)/%conf-cfg: $(src)/%conf-cfg.sh FORCE $(call filechk,conf_cfg)
在scripts/kconfig/文件夹内更新mconf-cfg脚本
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menuconfig: $(obj)/mconf $< $(silent) $(Kconfig)
到这里，menuconfig编译过程分析完成了，在根Makefile设置变量及运行条件，然后跳转到scripts/kconfig/生成mconf，通过scripts/kconfig/mconf Kconfig启动视图界面。