I didn’t find a multiple-def, and we had done clean builds, and we don’t use any precompiled headers for this project though I have considered it. It is so slow, anything would be an improvement (including getting off of net mounts for our builds).

If we can get this thing under test, there is a lot of refactoring on the way.

Precompiled headers are more of a Windows thing, but they can be done with gcc. That used to always be the first thing I’d kill when I ran into something like this. Check to make sure your project isn’t insisting on precompiled headers.

Don’t assume that the deps are quite right in the build system. Try completely cleaning the build tree, and rebuilding from scratch, after adding the “virtual” keyword. I would certainly expect to see segfaults if a stray .o didn’t get rebuilt after changing the virtuality of a class. (Though I probably would have expected a build failure, first; isn’t virtual status represented in the mangled name?)

Grep for CrazyClass. I’ve seen it before where a class was defined twice, in two different headers, with the usual fun and games if the two definitions get out of sync with each other or the implementation.