I've got a pretty old machine (Celeron 2.8 GHz, ATI rage XL). It's been
running Debian fine for years, but I reinstalled recently. Installed
stable (chose XFCE as desktop environment), everything worked fine
(lightdm worked, xfce worked). Did a dist-upgrade to testing (also tried
unstable), and now neither lightdm nor xfce works (lightdm goes into an
endless crash loop, xfce sends me back to the login screen). I can
manually start an X server, and it can display basic programs like
xclock fine. But as soon as I start a GTK application (or at least I
think it's GTK causing the problem), X crashes with "Segmentation fault
at address 0xc" "Fatal server error: Caught signal 11 (Segmentation
fault). Server aborting". There's nothing in the log immediately before
the error other than the backtrace.
There doesn't appear to be a problem with any of those components
individually, since xfce and individual applications will both run
perfectly fine if I display them on another machine's X, so I'm not even
sure what to file a bug under.