如何让include/config/auto.conf超越终极目标的

最新推荐文章于 2024-10-06 15:58:09 发布

转载最新推荐文章于 2024-10-06 15:58:09 发布 · 2.6k 阅读

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本文探讨了Makefile中-include指令的行为，特别是在处理不存在的配置文件时的处理方式。通过示例说明了当尝试包含的文件不存在时Makefile的行为，并展示了在Linux内核构建过程中的应用。

http://blog.chinaunix.net/uid-20564848-id-215793.html

其中
/gliethttp.ini是一个存在的空文件
/gliethttp/auto.conf不存在
我们可以看到,如果-include的文件不存在,首先不会报错,
其次如果在整个makefile中如果发现有创建该文件的规则,那么会在终极目标(第1个目标)
执行之前,首先尝试执行创建该-include文件的目标,
所以这时该文件目标就先于终极目标被make执行[luther.gliethttp]

{{{

all:

    @echo 111

-include /gliethttp/auto.conf

/gliethttp/auto.conf:

    @echo 222

-include /gliethttp.ini

/gliethttp.ini:

    @echo 333

}}}

luther@gliethttp:~$ make
222
111

来看看kernel的Makefile片段,
当我们执行make时,首先Makefile被make走一遍,提取规则和变量等,
如果是第1次执行,那么include/config/auto.conf并不存在,
所以我们看到
make -f /home/gliethttp/kernel/Makefile silentoldconfig
是第1条被执行的规则命令

luther@gliethttp:~/kernel$ make V=1

{{{

make -f /home/gliethttp/kernel/Makefile
 silentoldconfig

make -f scripts/Makefile.build obj=scripts/basic

  gcc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o
 scripts/basic/fixdep scripts/basic/fixdep.c 

  gcc -Wp,-MD,scripts/basic/.docproc.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o
 scripts/basic/docproc scripts/basic/docproc.c 

  gcc -Wp,-MD,scripts/basic/.hash.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o
 scripts/basic/hash scripts/basic/hash.c 

mkdir -p include/linux include/config

make -f scripts/Makefile.build obj=scripts/kconfig
 silentoldconfig

}}}

如下是kernel的Makefile片段内容

{{{

# Read in config

-include include/config/auto.conf

ifeq ($(KBUILD_EXTMOD),)

# Read in dependencies to all Kconfig* files, make
 sure to run

# oldconfig if changes are detected.

-include include/config/auto.conf.cmd

# To avoid any implicit rule to kick in, define an
 empty command

$(KCONFIG_CONFIG) include/config/auto.conf.cmd: ;

# 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/auto.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd

    $(Q)$(MAKE) -f
 $(srctree)/Makefile silentoldconfig

}}}