You can run doxygen on your project with the options set to include undocumented functions and to map dependencies (ideally with graphviz also installed) and it will give you, in a variety of formats, all of the functions and globals with where they are used.
- Free, Gratis & Open Source
- Cross Platform
- Works for multiple languages:
- C, C++, C#
This may or may not be of some help to you.