In recent kernels, a default configuration contains all the information needed to expand to a full configuration file. It is a minimal kernel configuration file where all dependencies are removed. To create a default configuration file from a current .config file, you run the following:

$ make ARCH=arm savedefconfig  

This creates a defconfig file in the current kernel directory. This make target can be seen as the opposite of the <platform>_defconfig target explained before. The former creates a configuration file from a minimal configuration, and the latter expands the minimal configuration into a full configuration file.