Comment 11 for bug 1450089

I've been able to work around this with the latest Catalyst Pro driver but it requires downgrading xorg to 1.16.2.

Download and extract Catalyst Pro 14.502.1040 driver (http://support.amd.com/en-us/download/workstation?os=Linux%20x86_64#catalyst-pro)
Apply patch for kernel 3.19: https://gist.github.com/aginor/4f232d4c28aef7685282
Apply patch I created to fix script bug in driver that prevents package creation on Ubuntu: https://gist.github.com/PeterJohnson/88137d4c55356b6e6c96

Remove your current fglrx packages and build and install the 14.502.1040 ones. Unfortunately this package does NOT work with xorg 1.17 (different crash occurs) so you'll need to downgrade xorg to 1.16.2.

Install xorg 1.16.2, you'll need the following packages (have to manually download from the web, as the package manager won't have them):
xorg_7.7+7ubuntu3_amd64.deb
xserver-common_1.16.2.901-1ubuntu4_all.deb
xserver-xorg_7.7+7ubuntu3_amd64.deb
xserver-xorg-core_1.16.2.901-1ubuntu4_amd64.deb
xserver-xorg-input-vmmouse_13.0.0-1build2_amd64.deb
xserver-xorg-video-all_7.7+7ubuntu2_amd64.deb
xserver-xorg-video-ati_7.4.0-2ubuntu2_amd64.deb
xserver-xorg-video-cirrus_1.5.2-2build1_amd64.deb
xserver-xorg-video-fbdev_0.4.4-1build2_amd64.deb
xserver-xorg-video-intel_2.99.914-1~exp1ubuntu4_amd64.deb
xserver-xorg-video-mach64_6.9.4-2_amd64.deb
xserver-xorg-video-mga_1.6.3-2build1_amd64.deb
xserver-xorg-video-modesetting_0.9.0-1build1_amd64.deb
xserver-xorg-video-neomagic_1.2.8-1build2_amd64.deb
xserver-xorg-video-nouveau_1.0.11-1ubuntu2_amd64.deb
xserver-xorg-video-openchrome_0.3.3-1build2_amd64.deb
xserver-xorg-video-r128_6.9.2-1build2_amd64.deb
xserver-xorg-video-radeon_7.4.0-2ubuntu2_amd64.deb
xserver-xorg-video-savage_2.3.7-2ubuntu3_amd64.deb
xserver-xorg-video-siliconmotion_1.7.7-2build2_amd64.deb
xserver-xorg-video-sisusb_0.9.6-2build2_amd64.deb
xserver-xorg-video-tdfx_1.4.5-1build2_amd64.deb
xserver-xorg-video-trident_1.3.6-0ubuntu6_amd64.deb
xserver-xorg-video-vesa_2.3.3-1build2_amd64.deb
xserver-xorg-video-vmware_13.0.2-3ubuntu1_amd64.deb

With this, I have X booted and visuals working now on my W8100, but kdeinit5 is on the crashy side, not sure if it's due to the downgraded X or some other issue... but it's at last somewhat usable again!