So, the problem (as also pointed out by upstream) is that you have hardware that only supports OpenGL 1 (1.3, to be precise – I have the same hardware, but I'm still running Fedora 21).

Our Qt packaging includes this script:
http://pkgs.fedoraproject.org/cgit/qt5-qtbase.git/tree/10-qt5-check-opengl2.sh
which installs to /etc/X11/xinit/xinitrc.d/10-qt5-check-opengl2.sh . This should result in QT_XCB_FORCE_SOFTWARE_OPENGL getting set and, as a result, llvmpipe being used in all Qt 5 applications using QtGui OpenGL classes instead of the OpenGL-1-only hardware driver. (What Qt does if QT_XCB_FORCE_SOFTWARE_OPENGL is set is that it sets LIBGL_ALWAYS_SOFTWARE, the difference is that QT_XCB_FORCE_SOFTWARE_OPENGL does not affect non-Qt applications, so you should still be able to use OpenGL games that work with OpenGL 1.)

Can you verify that QT_XCB_FORCE_SOFTWARE_OPENGL is getting set correctly? Can you also test whether using LIBGL_ALWAYS_SOFTWARE instead makes any difference? (It shouldn't.)

Another important question: How (from what display manager) are you starting your session? That may make a difference for the /etc/X11/xinit/xinitrc.d scripts.

As I wrote, I have an rv200 myself, so I'm very interested in getting this fixed before the F21 EOL.

I'm currently running F21, with KDM as the display manager, and with Qt 5 packages installed. I get QT_XCB_FORCE_SOFTWARE_OPENGL=1 correctly set in the environment, and at least the Qt Quick demos (e.g. /usr/lib/qt5/examples/quick/particles/emitters/emitters from qt5-qtdeclarative-examples) work for me. (Of course the particle demos are slow and jumpy, that's sadly to be expected from llvmpipe on a P4. But they don't crash!)

# set | grep OPENGL
QT_XCB_FORCE_SOFTWARE_OPENGL=1

LIBGL_ALWAYS_SOFTWARE: howto?

sddm and lightdm lack important kdm features, so I use either kdm-4.11.20-2.fc22.i686 or startx, more often the latter.

I have multiple rv200s in use, though only this machine attempts to run plasma5. Its F23 exhibited this same bug until I manually selected installation of mesa-dri-drivers and copied ~/.config/kwinrc from the F22 installation.

> LIBGL_ALWAYS_SOFTWARE: howto?

The easiest way is to just search&replace it in the script (/etc/X11/xinit/xinitrc.d/10-qt5-check-opengl2.sh) and see what happens. (Note that this is only for testing. QT_XCB_FORCE_SOFTWARE_OPENGL should work.)

But I'm still waiting for answers to:
https://bugs.kde.org/show_bug.cgi?id=350853#c16

I'm unable to relate what you want WRT LIBGL_ALWAYS_SOFTWARE to the actual content of 10-qt5-check-opengl2.sh:

#!/bin/sh
OPENGL_VERSION=`LANG=C glxinfo | grep '^OpenGL version string: ' | sed -e 's/^OpenGL version string: \([0-9]\).*$/\1/g'`
if [ "$OPENGL_VERSION" -lt 2 ]; then
  QT_XCB_FORCE_SOFTWARE_OPENGL=1
  export QT_XCB_FORCE_SOFTWARE_OPENGL
fi

Replace the piece that says:

  QT_XCB_FORCE_SOFTWARE_OPENGL=1
  export QT_XCB_FORCE_SOFTWARE_OPENGL

with

  LIBGL_ALWAYS_SOFTWARE=1
  export LIBGL_ALWAYS_SOFTWARE

And this is obsolete anyway, if installing mesa-dri-drivers made this crash go away. (It's not a problem of QT_XCB_FORCE_SOFTWARE_OPENGL not working, but of you not having had OpenGL support installed. Even the llvmpipe (%{_libdir}/gallium-pipe/pipe_swrast.so) is in mesa-dri-drivers.)

I guess qt5-qtbase-gui should have a Requires: mesa-dri-drivers?

fyi, base-x comps group includes mesa-dri-drivers (among other low-level drivers)... if you don't have that group installed, you're in for fair amounts of problems anyway.  Just sayin.

(In reply to Rex Dieter from comment #7)
> Replace the piece that says:

>   QT_XCB_FORCE_SOFTWARE_OPENGL=1
>   export QT_XCB_FORCE_SOFTWARE_OPENGL
 
> with
 
>   LIBGL_ALWAYS_SOFTWARE=1
>   export LIBGL_ALWAYS_SOFTWARE

Having done that, Plasma seems to start normally, and possibly faster.

(In reply to Rex Dieter from comment #9)
> fyi, base-x comps group includes mesa-dri-drivers (among other low-level
> drivers)... if you don't have that group installed, you're in for fair
> amounts of problems anyway.  Just sayin.

If that group is required, why doesn't whatever requires it require it?

individual packagers cannot depend on groups, but installations (like spins) can and do use these package groups.

In short, how did you install fedora 22 and end up with a system without all of the @base-x group?  (the kde spin should definitely include all those at least)

(In reply to Rex Dieter from comment #11)
> In short, how did you install fedora 22 and end up with a system without all
> of the @base-x group?  (the kde spin should definitely include all those at
> least)

This particular installation is the result of yum and dnf upgrades dating back 38 months. I don't remember specifics, but my usual installation procedure is minimal X via HTTP, then using yum/dnf to add various necessaries that will pull in sufficient deps to make Xorg and KDE do what I need to do with them. One of the occasional results of what I do is discover broken or missing dependencies that neither automated nor spin testing discover.

ok, interesting, mesa-dri-drivers has been in the base-x group going back at leaste as far as fedora 18.  no idea how it ended up missing for you.

Regardless, wouldn't be a bad idea to do:

dnf install @base-x

to (re)install any other possible missing pieces.

(In reply to Rex Dieter from comment #13)

> Regardless, wouldn't be a bad idea to do:
 
> dnf install @base-x
 
> to (re)install any other possible missing pieces.

I tried this on a different F22 host, kt400 with rv250 - not a good idea. Most of my test installations are on 4.8G real partitions, making space somewhat precious. Thus I try to keep them svelte as possible, minimizing both space consumption and bandwidth at updates time. @base-x wants to install several drivers that would unlikely ever be used here: xorg-x11-drv-geode, xorg-x11-drv-openchrome, xorg-x11-drv-qxl, xorg-x11-drv-synaptics, xorg-x11-drv-wacom, xorg-x11-drv-freedreno, xorg-x11-drv-armsoc and xorg-x11-drv-omap, plus more plymouth-*.

* Mon Aug 03 2015 Helio Chissini de Castro <helio> - 5.5.0-11
- Add mesa-dri-drivers as recommends on gui package as reported by Kevin Kofler
- Reference https://bugzilla.redhat.com/1249280

Will come to f21/f22 when qt-5.5 does (soonish)

sorry, meant currentrelease (not notabug resolution)