(In reply to Diego Viola from comment #27)
> export LD_LIBRARY_PATH=/home/diego/mesa/lib
> export LIBGL_DRIVERS_PATH=/home/diego/mesa/lib/gallium
> 
> So I assume this should make the X server pick the radeonsi_dri.so from
> /home/diego/mesa/lib/gallium right?

Doubtful, environment variables from the user shell aren't propagated to the
Xorg process for me (which makes it very mysterious how LIBGL_ALWAYS_SOFTWARE=1
could make any difference...).

> Is there a way to verify beyond this which radeonsi driver it's using?

sudo lsof | grep radeonsi_dri.so

(In reply to Diego Viola from comment #29)
> Mesa 19.0.0-devel (git-8daf5bb209)
> 
> Which is the commit prior to the bad commit I mentioned above.
> 
> Sadly xterm is still breaking as usual, the output disappears as I
> Shift+Page Up and nothing changed in that regard. :(

What if you install Mesa 18.3 system-wide?

(In reply to Diego Viola from comment #30)
> I can reproduce this on Fedora 29 (workstation), [...]
(In reply to Diego Viola from comment #31)
> I can't reproduce it on Ubuntu 18.04.2 or 19.04 beta.

Please attach the outputs of glxinfo from Fedora and Ubuntu.