如何让include/config/auto.conf超越终极目标的

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]

1. {{{
   
2. all:
   
3.     @echo 111
   
4. -include /gliethttp/auto.conf
   
5. /gliethttp/auto.conf:
   
6.     @echo 222
   
7. -include /gliethttp.ini
   
8. /gliethttp.ini:
   
9.     @echo 333
   
10. }}}

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

1. {{{
   
2. make -f /home/gliethttp/kernel/Makefile silentoldconfig
   
3. make -f scripts/Makefile.build obj=scripts/basic
   
4.   gcc -Wp,-MD,scripts/basic/.fixdep.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/fixdep scripts/basic/fixdep.c 
   
5.   gcc -Wp,-MD,scripts/basic/.docproc.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/docproc scripts/basic/docproc.c 
   
6.   gcc -Wp,-MD,scripts/basic/.hash.d -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-pointer -o scripts/basic/hash scripts/basic/hash.c 
   
7. mkdir -p include/linux include/config
   
8. make -f scripts/Makefile.build obj=scripts/kconfig silentoldconfig
   
9. }}}

如下是kernel的Makefile片段内容

1. {{{
   
2. # Read in config
   
3. -include include/config/auto.conf
   
4. 
   
5. ifeq ($(KBUILD_EXTMOD),)
   
6. # Read in dependencies to all Kconfig* files, make sure to run
   
7. # oldconfig if changes are detected.
   
8. -include include/config/auto.conf.cmd
   
9. 
   
10. # To avoid any implicit rule to kick in, define an empty command
    
11. $(KCONFIG_CONFIG) include/config/auto.conf.cmd: ;
    
12. 
    
13. # If .config is newer than include/config/auto.conf, someone tinkered
    
14. # with it and forgot to run make oldconfig.
    
15. # if auto.conf.cmd is missing then we are probably in a cleaned tree so
    
16. # we execute the config step to be sure to catch updated Kconfig files
    
17. include/config/auto.conf: $(KCONFIG_CONFIG) include/config/auto.conf.cmd
    
18.     $(Q)$(MAKE) -f $(srctree)/Makefile silentoldconfig
19. }}}