正確使用和保存deconfig的流程： 要修改在arch/arm/configs下的文件xxx_defconfig 2. make ARCH=arm64 xxx_defconfig 會生成.config文件 3. make ARCH=arm64 menuconfig 修改配置后保存 4. make ARCH=arm64 savedefconfig 生成defconfg文件 5. cp defconfig arch/arm/configs/xxx_defconfig 保存 這樣保存的defconfig文件，配置最小化，且日后能恢復成.config。 .configAll config symbol values are saved in a special file called?.config. Every time you want to change a kernel compile configuration, you execute a make target, such as?menuconfig?or?xconfig. These read the?Kconfig?files to create the menus and update the config symbols' values using the values defined in the?.config?file. Additionally, these tools update the?.config?file with the new options you chose and also can generate one if it didn't exist before.Because the?.config?file is plain text, you also can change it without needing any specialized tool. It is very convenient for saving and restoring previous kernel compilation configurations as well.deconfigThe?.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 modifying it by hand. Instead you should use?make savedefconfig?rule.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 into?.config?with value chosen in?defconfig
if option isn't mentioned in?defconfig, build system puts that option into?.config?using its default value, specified in corresponding?Kconfig
