Once again, new trouble after upgrading PHP (5) on a FreeBSD (6) server. So nice of php to start segfaulting, and no indication as to why. No real clue was to find anywhere. Running it in GDB however showed that it failed somewhat around session.so and downwards in the call stack.
Well, decided to force a rebuild of all php related stuff. No joy there. Finally decided to google for some kind of indication, and (not to my surprise) people have had somewhat the same problem since 2002.
Well, finally found an indication of what could be wrong.. Look at the extensions.ini file and identify the modules. And yes, it was in fact not causing any problems when session.so had been commented out. A hint i found was to reorder the file.
So moved the session.so to the very top of the list, and there you go. Works again.. Thank you letting me deal with yet another unnecessary problem at this hour of the day. I know, i have the source, i can just fix it, but since people have mentioned problems with this for such a long period of time, it seems no one cares.