make xxxx_defconfig 分析

本文主要是介绍make xxxx_defconfig 分析，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

文章目录

执行依赖scripts_basic
执行依赖outputmakefile
实现%config

make rpi_3_32b_defconfig V=1：

make -f ./scripts/Makefile.build obj=scripts/basiccc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer   -std=gnu11     -o scripts/basic/fixdep scripts/basic/fixdep.c   
rm -f .tmp_quiet_recordmcount
make -f ./scripts/Makefile.build obj=scripts/kconfig rpi_3_32b_defconfigcc -Wp,-MD,scripts/kconfig/.conf.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer   -std=gnu11     -c -o scripts/kconfig/conf.o scripts/kconfig/conf.cbison -oscripts/kconfig/zconf.tab.c -t -l scripts/kconfig/zconf.yflex -oscripts/kconfig/zconf.lex.c -L scripts/kconfig/zconf.lcc -Wp,-MD,scripts/kconfig/.zconf.tab.o.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer   -std=gnu11    -Iscripts/kconfig -c -o scripts/kconfig/zconf.tab.o scripts/kconfig/zconf.tab.ccc   -o scripts/kconfig/conf scripts/kconfig/conf.o scripts/kconfig/zconf.tab.o   
scripts/kconfig/conf  --defconfig=arch/../configs/rpi_3_32b_defconfig Kconfig
#
# configuration written to .config
#

make rpi_3_32b_defconfig :

  HOSTCC  scripts/basic/fixdepHOSTCC  scripts/kconfig/conf.oYACC    scripts/kconfig/zconf.tab.cLEX     scripts/kconfig/zconf.lex.cHOSTCC  scripts/kconfig/zconf.tab.oHOSTLD  scripts/kconfig/conf
#
# configuration written to .config
#

94 	ifeq ("$(origin V)", "command line")
95 	  KBUILD_VERBOSE = $(V)
96 	endif
97 	ifndef KBUILD_VERBOSE
98 	  KBUILD_VERBOSE = 0
99 	endif
100
101	ifeq ($(KBUILD_VERBOSE),1)
102	  quiet =
103	  Q =
104	else
105	  quiet=quiet_
106	  Q = @
107	endif
......
481	scripts_basic:
482		$(Q)$(MAKE) $(build)=scripts/basic
483		$(Q)rm -f .tmp_quiet_recordmcount
......
492	outputmakefile:
493	ifneq ($(KBUILD_SRC),)
494		$(Q)ln -fsn $(srctree) source
495		$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \
496			$(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
497	endif
......	
563	%config: scripts_basic outputmakefile FORCE
564		$(Q)$(MAKE) $(build)=scripts/kconfig $@
......
2318 FORCE:

当在命令行中输入： make rpi_3_32b_defconfig V=1 时，94行条件成立，KBUILD_VERBOSE = 1，101行条件成立，quiet 和 Q 为空，则输出整个命令。
输入命令自动匹配顶层 Makefile 的第563 行并执行，由于目标 %config依赖 scripts_basic 、outputmakefile和FORCE，则执行顺序如下：

1. 执行依赖 scripts_basic ，481-483行
2. 执行依赖 outputmakefile，492-497行
3. 执行依赖 FORCE，什么都不做，2318行

执行依赖scripts_basic

481	scripts_basic:
482		$(Q)$(MAKE) $(build)=scripts/basic
483		$(Q)rm -f .tmp_quiet_recordmcount
$(build)在 scripts/Kbuild.include 文件【在顶层Makefile的386行引用】的第184行定义：
184	build := -f $(srctree)/scripts/Makefile.build obj
$(srctree)在顶层 Makefile 中定义为srctree = .，所以展开后为：
scripts_basic:make -f ./scripts/Makefile.build obj=scripts/basicrm -f .tmp_quiet_recordmcount
结果：由 ./scripts/Makefile.build 分析可知：打印并执行下列第2行的内容，生成scripts/basic/fixdep软件，将cmd_scripts/basic/fixdep := cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -std=gnu11 -o scripts/basic/fixdep scripts/basic/fixdep.c 内容写入到scripts/basic/.fixdep.cmd文件中【此文件没有回自动创建】
回显1-3行。
1 make -f ./scripts/Makefile.build obj=scripts/basic
2   cc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer   -std=gnu11     -o scripts/basic/fixdep scripts/basic/fixdep.c   
3 rm -f .tmp_quiet_recordmcount

执行依赖outputmakefile

492	outputmakefile:
493	ifneq ($(KBUILD_SRC),)
494		$(Q)ln -fsn $(srctree) source
495		$(Q)$(CONFIG_SHELL) $(srctree)/scripts/mkmakefile \
496			$(srctree) $(objtree) $(VERSION) $(PATCHLEVEL)
497	endif
当输入make O=dir时，KBUILD_SRC=dir，由于这里没有O=，所以第493行条件不成立，这里什么都不做。

实现%config

由上面的分析可知，%config 的三个依赖 scripts_basic、 outputmakefile 和 FORCE都已经实现。
1.依赖scripts_basic：为了生成scripts/basic/fixdep
2.依赖outputmakefile：什么都不做
3.依赖FORCE：什么都不做
563	%config: scripts_basic outputmakefile FORCE
564		$(Q)$(MAKE) $(build)=scripts/kconfig $@
最后执行第564行命令来生成最终目标%config，最终展开为：
563	%config: scripts_basic outputmakefile FORCE
564		make ./scripts/Makefile.build obj=scripts/kconfig rpi_3_32b_defconfig
结果：由 ./scripts/Makefile.build 分析可知：