Re: X/GDM fails on linux 5.0.7 AMD Radeon RX 580 after system reconfigure

[ison <ison@airmail.cc>]

I can confirm this exact same issue with the same video card, RX 580, and my
last attempt to update pulled in kernel 5.0.13. When the login screen shows up
the screen is horribly corrupt, nothing is even recognizable as being a part of
the normal login screen, just random colored lines all over the screen.
I first experienced the issue at the release of Guix v1.0.0, but wasn't sure if
I should wait before reporting since I couldn't be sure if it was a guix
specific issue or something else.

Here is what I have discovered:
* I doubt the issue is either caused by GDM itself or the kernel, because after
  updating from a working generation (but without restarting my machine) if I
  attempt to play a video in mpv (or start a game) the same graphical artifacts
  appear, but only in that 1 window.
* I have attempted to upgrade individual applications while using
  "package-input-rewriting" to replace their dependencies on Mesa 18.3.5 with
  18.3.1 (the version they're using on my working generation) and I can confirm
  that the replacement succeeded with "ldd", however they still receive
  graphical artifacts.
* I have successfully managed to run an updated copy of mpv without artifacts by
  using LD_PRELOAD to force it to point to the exact copy of libGL.so.1 used by
  mpv on my working generation.

This leads me to believe that the problem lies somewhere in Mesa (which contains
libGL.so.1). However, the issue doesn't seem to be just the version of Mesa
since mpv still had corrupt video when built to use the older version of Mesa,
but had no corrupt video when forced to link to the exact copy of libGL.so.1
from a previously working generation.

Note: mpv was merely used as a test so I didn't have to constantly restart my
machine. However, generations which resulted in corrupt video in mpv (and games)
always resulted in corrupt video in GDM if I also rebooted into that generation.