Kernel Configuration Comparison (kccmp) is a tool that provides a GUI for comparing two Linux kernel ".config" files.
It shows configuration variables with different values in a tabular format. It also shows configuration variables found in only one of the input configuration files.
kccmp by default requires Qt 3.x. However, by changing one line in kccmp.pro you can build against Qt 4.x. Note that the Qt 4.x build requilres libboost_regex as well.
The standard build is as easy as:
% kccmp /path/to/first/.config path/to/second/.config
% kccmp /usr/src/linux/.config /usr/src/linux/.config.old