drop LD_LIBRARY_PATH for opengl programs

[lucabrunox]

Proposal:

• Make a mesa setup-hook: find opengl programs in $out, fix rpath to point to /run/opengl-driver (or /run/opengl-driver-32).
• Drop LD_LIBRARY_PATH.

[vcunat]

I'm not certain about all the consequences. It isn't just libGL* – there can also be other required things on that path, e.g. libvdpau_* and libcuda.so*. But I guess the packages that stop finding libs should be fixable easily by adding the reference explicitly somehow.

What might also be a problem: during chrooted builds we have no /run/opengl-driver*, so if mesa is removed from rpath, I think many executables wouldn't even start due to that dependency, e.g. through libcairo. That would be worked around if we only added /run/opengl-driver* at the beginning of rpath without removing the mesa reference.

[ttuegel]

Will this affect people using Nixpkgs outside NixOS?

[lucabrunox]

@ttuegel it should be the same, need for creating /run/opengl-driver manually, or setting another proper LD_LIBRARY_PATH.

The behavior should be the same as of now, except we don't need LD_LIBRARY_PATH which would apply to every binary.

[vcunat]

Closely related: there might be a change how libGL implementations are switched. https://github.com/NVIDIA/libglvnd So far only nvidia is known to use that interface, but it's well possible the other major players will jump in soon.

[Profpatsch]

(triage) any action items?

[lucabrunox]

No, just brainstorming here.

[Profpatsch]

(triage) I assume this hasn’t been implemented yet?

[flokli]

There's #60985, which will set RUNPATH in various dispatch libraries to look in /run/opengl-driver(-32), and I suggested dropping the global LD_LIRARY_PATH there, too.

[ambrop72]

Once I remove LD_LIBRARY_PATH from opengl.nix, when I log in via LightDM (as supposed to SDDM or a console login), I still get this in LD_LIBRARY_PATH: /run/opengl-driver/lib:/nix/store/s98r8d73ajrmsgcmscbr2q2xicm2xx56-nvidia-x11-430.14-4.19.44. Note how there's no 32-bit link and there is also the absolute path to the driver directory (which in my case does nothing because libraries are under lib). I'm pretty sure it's coming from xserver.nix. SDDM must be unsetting it while LightDM is letting it through to the user session.

We should remove this so it doesn't affect the session, and fix things as necessary by adding RUNPATH to programs that need it (X server, individual display managers, wayland stuff?). I will try with NVidia but cannot try other drivers.

[ambrop72]

I see two drivers that still rely on LD_LIBRARY_PATH to override default system libraries, amdgpu-pro and ati_drivers_x11. Not only do they directly provide libraries like libGL, libEGL, libGLESv2 and libOpenCL instead of using dispatch libraries (libglvnd, opencl-icd), they override other system libraries:

• ati_drivers_x11 has symlinks to NixOS builds of a whole bunch of Xorg libraries (e.g. libSM, libX11, libXext). There is a comment in the package saying it makes some programs work, without explaining why.
• amdgpu_pro has replacements of libdrm, libgbm, libkms and some LLVM libraries (libLTO, libLLVM-5.0).

Because NixOS has patched glibc to give LD_LIBRARY_PATH priority over RUNPATH, any program that links to one of these libraries will load the one from the AMD drivers. This can result in horrible breakage (what happens to programs that link to LLVM when they get the AMD thing?).

This is so ugly and prone to break things that I think we should consider dropping both drivers. If not then we should at least go forward with dropping LD_LIBRARY_PATH only for drivers that don't need it (mesa, nvidia).