View | Source language file extensions
Click Source language file extensions on the View menu to control the file name extensions that WinDbg recognizes as source file name extensions. You can also specify which programming languages are associated with which file name extensions.
When you click Source language file extensions, the File Extensions for Source Languages dialog box appears. In this dialog box, you can add or delete file name extensions by inserting the cursor in the Extensions and languages box and typing the appropriate information. Make sure that you specify the appropriate programming language for each file name extension. For example, cxx=C++ indicates that a .cxx file name extension is a source file and that the corresponding programming language of any file that has that extension is C++. Click OK to implement your changes, or click Cancel to discard any changes.