I found a workaround. Using this custom PPA, one can get the 13.1 drivers with an older x-server:
https://launchpad.net/~makson96/+archive/fglrx -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1025488 Title: fglrx (not installed): fglrx kernel module failed to build [error: implicit declaration of function ‘do_mmap’] To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/fglrx-installer/+bug/1025488/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
