If a module contains a routine or global that could be configured out of the kernel, add it to an xxx.exports file that will not be included in the kernel if the module is configured out. See master.d/idev.exports for an example.
If a loadable module contains globals in its master.d file, you must create an xxx.exports file to include those globals so that they can be added to the run-time symbol table. For more information, see master.d/rtsymtab.