Comment # 2 on bug 104806 from Alexandr Paliy

Also gentoo, also radeon card (r600).

Posting this just to confirm there is an issue. Can't provide additional info
because I needed to restore access to my PC as fast as possible.

dmesg pointed segfaults in plasmashell and sddm-helper processes.
First I thought it is somehow related to updating kernel 4.14.12->4.14.15, but
reverting it did not help.

Then, I saw mentions of r600g_dri.so
Switched from mesa-18.0.0-rc2 to mesa-17.3.3, and issue is gone.