写.config，编译.config被重写

In the mean time,I think I found the lines(linux-3.9.3/Makefile) creating 

overwriting the config file. 

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

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

when I comment out above lines the config file was not overwritten.