Bug#1099016: nvidia-legacy-340xx-driver: Unpatched return thunk in use. This should not happen!

[Fab Stz]

> But you shouldn't rename/symlink the drivers, as that's a source for 
> major confusion. Please revert.

Done, thanks for the explanation.

> You might try a minimal xorg.conf (or xorg.conf.d/*.conf snippet) 
> containing only
> 
>          Section "Device"
>              Identifier     "My GPU"
>              Driver         "nvidia"
>          EndSection
> 
> to specifically select the proprietary driver and skip autoprobing.
> Should help to avoid irrelevant error messages from autoprobed drivers.

Ok this way it loads properly, the nvidia logo is displayed and X starts 
fine when loading only xterm.

Any idea why this xorg.conf is required now while it used to be 
autodetected? Is this related to 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1099016#40 ?

However
- running plasmashell leads to a crash with the nvidia driver. Same for 
kwin. There is no crash with "nouveau" though.
- running gnome-session works fine and Gnome shows up without issue with 
the nvidia driver.

gdm3 is displayed properly as well, while sddm is not.

plasmashell writes this output:

qt.glx: qglx_findConfig: Failed to finding matching FBConfig for 
QSurfaceFormat(version 2.0, options 
QFlags<QSurfaceFormat::FormatOption>(ResetNotification), depthBufferSize 
-1, redBufferSize 1, greenBufferSize 1, blueBufferSize 1, 
alphaBufferSize -1, stencilBufferSize -1, samples -1, swapBehavior 
QSurfaceFormat::SingleBuffer, swapInterval 1, colorSpace QColorSpace(), 
profile  QSurfaceFormat::NoProfile)
Could not initialize GLX
Aborted (core dumped)

for kwin it is the same, except with swapInterval "0" instead of "1".


I could launch KDE/Plasma with any of:
export QT_XCB_GL_INTEGRATION=xcb_egl
export QT_XCB_GL_INTEGRATION=none

But graphics are not polished.

KDE/Plasma doesn't work when QT_XCB_GL_INTEGRATION is not set or has:
export QT_XCB_GL_INTEGRATION=xcb_glx

I tried these different values in .config/plasma-workspace/env/xcb.sh

Do you think a rebuild of the nvidia/Opengl driver would fix the issue? 
Or is Kde/Plasma requiring features not provided by the nvidia driver?

> But it may well be that the driver is no longer compatible with current 
> Xorg versions.

It seems to work actually, at least partially. :)