clang: fix crosscompilation for 16.x

[avnik]

Description of changes

Fix cross-compilation issue for clang 16.x (port existing fix from 15.x branch)

Closing #238432

Things done

• Built on platform(s)
  • x86_64-linux
  • x86_64-linux.pkgsCross.aarch64-multiplatform
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 23.11 Release Notes (or backporting 23.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[RaitoBezarius]

@ofborg build pkgsCross.aarch64-multiplatform.clang16

[avnik]

@ofborg build pkgsCross.aarch64-multiplatform.clang_16

[avnik]

fix ofborg mention, to match proper attribute

[RaitoBezarius]

Thank you!

[rrbutani]

Ah, thanks; looks like we forgot to apply #226551 to llvmPackages_16.

Would you mind copying the stdenv.buildPlatform.canExecute change from that PR as well? (It looks like we're not running into the maybe-uninitialized warning with LLVM 16 so we can leave that bit out)

[avnik]

@rrbutani you about this snippet?

    env = lib.optionalAttrs (stdenv.buildPlatform != stdenv.hostPlatform) {
      # The following warning is triggered with (at least) gcc >=
      # 12, but appears to occur only for cross compiles.
      NIX_CFLAGS_COMPILE = "-Wno-maybe-uninitialized";
    };

In my setup it not failed, but I can add this fragment, if you feel it important.

[avnik]

Can confirm, that all rebuild successfully exactly on this commit:

 nix build ".#pkgsCross.aarch64-multiplatform.clang_16" -L --cores 24

[rrbutani]

@avnik I meant this bit (to be changed here):

-] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+] ++ lib.optionals (!stdenv.buildPlatform.canExecute stdenv.hostPlatform) [

It's not a big deal (cross comp will work without it; this just lets us skip an extra LLVM build in cases where the build platform can execute host platform binaries — i.e. x86_64 and i386), I mostly just wanted to keep the LLVM package sets in sync.

[avnik]

@rrbutani all done

[avnik]

@rrbutani Should I also PR this for stable branch?

[github-actions]

Successfully created backport PR for release-23.05:

• [Backport release-23.05] clang: fix crosscompilation for 16.x #239608

[Artturin]

members can add labels

[sternenseemann]

Seems like pkgsStatic.llvmPackages_15.clang-unwrapped is still broken with trouble executing clang-tblgen. Seems it also doesn't work for 15, will need some investigation. It definitely used to work for llvmPackages_11.

[Artturin]

Seems like pkgsStatic.llvmPackages_15.clang-unwrapped is still broken with trouble executing clang-tblgen. Seems it also doesn't work for 15, will need some investigation. It definitely used to work for llvmPackages_11.

https://github.com/NixOS/nixpkgs/pull/226551/files#r1300386564