最近在裁剪内核慢慢关注这个问题

defconfig、 .config

 

defconfig 一般在arch/arm64/configs/目录下，是一个简单的内核配置，是没有展开的。

.config一般是用来执行make menuconfig的基础配置

从.config到defcong不是简单的复制操作，而是make arch=arm64 defcong 

通过menuconfig生成的.confg也不是直接拷贝成defcong，而是使用make savedefconfig

 

The .config file is not simply copied from your defconfig file. The motivation for storing defconfig in such a format is next: in defconfig we can only specify options with non-default values (i.e. options we changed for our board). This way we can keep it small and clear. Every new kernel version brings a bunch of new options, and this way we don't need to update our defconfig file each time the kernel releases. Also, it should be mentioned that kernel build system keeps very specific order of options in defconfig file, so it's better to avoid to modify it by hand. Instead you should use make savedefconfig rule.

Simplified explanation

When .config file is being generated, kernel build system goes through all Kconfig files (from all subdirs), checking all options in those Kconfig files:

• if option is mentioned in defconfig, build system puts that option to .config with value chosen in defconfig
• if option isn't mentioned in defconfig, build system puts that option to .config using its default value, specified in corresponding Kconfig

Check scripts/kconfig/Makefile and scripts/kconfig/conf.c files to see how it's actually done.

 

具体查看

https://stackoverflow.com/questions/41885015/what-exactly-does-linux-kernels-make-defconfig-do