I could not get my PAE-using VBox guest to load vboxguest-module properly -- and, consequently, could not get X to work, etcaetera -- until I added -DPAE to the CFLAGS and rebuilt it.
Maybe, it should be the port's option (or flavor?). Maybe, the port needs to be split into "common" part -- which does not depend on the kernel flags -- and the kernel-modules part, which needs to be built differently for PAE-kernels.
At the very least, a load-time detection of PAE-kernel needs to be implemented so the user gets an actionable hint as to what to do, instead of the incomprehensible "vgdrvFreeBSDAddIRQ failed" followed by "vboxguest0 attach returned 6".
Not even Google knows, what to do about these, although my filing this ticket may help :-) ...
Created attachment 190702 [details]
This is worse than I thought, because vboxvfs uses some C++ files, which are compiled without -DPAE.
The attachment helped me, but it is, probably, incomplete in various ways...
And something still needs to be done about virtualbox-ose-kmod too.