Nixpkgs: mesa fails to (cross-)compile

[nagisa]

Describe the bug

Cross-compilation of mesa fails with the following error at configure stage

$ nix build -L -f '<nixpkgs>' pkgsCross.aarch64-multiplatform.mesa
...
mesa> Run-time dependency valgrind found: YES 3.15.0
mesa> Program bison found: YES (/nix/store/ra42sij0cb917p3m90qdnv0vc3kxv1hm-bison-3.5.4/bin/bison)
mesa> Program flex found: YES (/nix/store/q99r9k0py7m2mrdfsif9wfvllvvxfiqi-flex-2.6.4/bin/flex)
mesa> Run-time dependency libunwind found: NO (tried pkgconfig and cmake)
mesa> Found pkg-config: /nix/store/nc3ivxhlqyj2alck8p47srvwzzgkbh2i-pkg-config-0.29.2/bin/pkg-config (0.29.2)
mesa> Did not find CMake 'cmake'
mesa> Found CMake: NO
mesa> Build-time dependency wayland-scanner found: NO (tried pkgconfig)
mesa> meson.build:1553:2: ERROR: Dependency "wayland-scanner" not found, tried pkgconfig
mesa> A full log can be found at /build/mesa-20.0.2/build/meson-logs/meson-log.txt

Though there appear to be other non-fatal, but otherwise concerning issues (especially surrounding LLVM) in the configuration process.

To Reproduce
Steps to reproduce the behavior:

1. nix build -L -f '<nixpkgs>' pkgsCross.aarch64-multiplatform.mesa

Expected behavior
Build should succeed

Notify maintainers

@vcunat

Metadata

• system: "x86_64-linux"
• host os: Linux 5.6.13, NixOS, 20.09pre225898.7319061eef4 (Nightingale)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.4
• channels(root): "nixos-20.09pre225898.7319061eef4"
• channels(nagisa): ""
• nixpkgs: /nix/var/nix/profiles/per-user/root/channels/nixos

Maintainer information:

# a list of nixpkgs attributes affected by the problem
attribute:
# a list of nixos modules affected by the problem
module:

[nagisa]

Looks like meson is expecting PKG_CONFIG_PATH_FOR_BUILD to be set when looking for wayland-scanner, but the variable is not set.

[nagisa]

Doing something like this makes it build, but is likely the wrong way to approach the problem?

diff --git a/pkgs/development/libraries/mesa/default.nix b/pkgs/development/libraries/mesa/default.nix
index 7eb18dd31c1..d4556fc2637 100644
--- a/pkgs/development/libraries/mesa/default.nix
+++ b/pkgs/development/libraries/mesa/default.nix
@@ -1,4 +1,5 @@
 { stdenv, lib, fetchurl, fetchpatch
+, pkgsBuildTarget
 , pkgconfig, intltool, ninja, meson
 , file, flex, bison, expat, libdrm, xorg, wayland, wayland-protocols, openssl
 , llvmPackages, libffi, libomxil-bellagio, libva-minimal
@@ -116,8 +117,13 @@ stdenv.mkDerivation {
     pkgconfig meson ninja
     intltool bison flex file
     python3Packages.python python3Packages.Mako
+    wayland
   ];

+  preUnpack = ''
+    export PKG_CONFIG_PATH_FOR_BUILD="${pkgsBuildTarget.wayland}/lib/pkgconfig"
+  '';
+
   propagatedBuildInputs = with xorg; [
     libXdamage libXxf86vm
   ] ++ optional stdenv.isLinux libdrm

[matthewbauer]

I think https://github.com/NixOS/nixpkgs/pull/87705 will fix this partly. We will still need wayland in nativeBuildInputs.

[nagisa]

Yeah, looks like the solution in #87705 is indeed partial, because mesa doesn’t build even on origin/master from 2 hours ago (with the nativeBuildInputs change applied).

What really is going on there is way over my head, so I’ll leave this to somebody who understands it better.

[Ericson2314]

@matthewbauer but wayland-scanner is a possibly-build-specific dev tool (#51176), so I think it shouldn't be using PKG_CONFIG_PATH_FOR_BUILD for this in the first place. Even if the native wayland-scanner really does work, I'd like to do the g-i thing as planned for #88222 where we combine the tools and the rest of the package in a wrapper with a patched pc file.

[Ericson2314]

CC @dcbaker, do you test cross builds upstream?

[vcunat]

Fixing cross-builds for complex packages like mesa might turn out to be hard, especially in our default feature-ful config. My motivation for aarch64 there isn't high, as we have natively compiled version from Hydra and even https://github.com/nix-community/aarch64-build-box

[nagisa]

My motivation for aarch64 there isn't high, as we have natively compiled version from Hydra

I’m not sure if its the fact that I'm cross-compiling (and so hashes change for whatever reason) or the fact that I accidentally changed some dependency of mesa, but I’m not able to get it and other dependencies to be pulled from hydra at all (including mesa). Arguably I can still obtain a aarch64 server to do a native build, but that sounds both a subpar experience (to building locally) and a compromise.

[vcunat]

Cross-compiled builds always get different hashes than native builds. EDIT: the thing is that getting the server (or using a local VM) might be way cheaper than fixing such complex builds and keeping them fixed (human work).

[Ericson2314]

Well assuming any wayland-scanner will do, and there are no other issues, this won't be hard to fix.

[matthewbauer]

wayland-scanner is cross-compiled by meson (https://github.com/wayland-project/wayland/blob/6d4497371014cacbf0dc4ed9983fd6617ec25c9a/src/meson.build#L38-L45, so I don't think we can treat it like xxx-config (even if that is more correct). wayland itself, even, needs the native wayland-scanner to cross compile (https://github.com/NixOS/nixpkgs/blob/7e571eb9943d770c2a68ed11f8beb14e6062180a/pkgs/development/libraries/wayland/default.nix#L38-L39). meson makes it pretty hard to not pull native build inputs from PKG_CONFIG_PATH_FOR_BUILD.

[dcbaker]

@Ericson2314, yes we do an x86 -> arm build. Here's the CI results for current master:
https://gitlab.freedesktop.org/mesa/mesa/pipelines/152118

[Ericson2314]

@dcbaker Thanks!!

[Ericson2314]

@dcbaker so it looks like the cross CI extends the native build to get access to native wayland-scanner? We did something similar in https://github.com/NixOS/nixpkgs/pull/89036 --- just making sure it isn't intended that one might build wayland-scanner as a separate package from the rest of wayland.

[dcbaker]

Oh don't get me started on wayland scanner, lol. I tried to fix that mess but upstream thinks fixing it makes their build too complicated and wont take patches. So yes, I think you need to build and package wayland scanner separate if you need to cross compile wayland.

[Ericson2314]

Ugh, the classic struggle with cross. Well, I'd be happy to go comment on any issue / PR / mailing list thread you made if it might tip the scales.