I think musl is cross in a way - you cross build musl binaries with glibc build packages. It's just not arch cross.

(maybe I'm using terms incorrectly though)

        nixosConfigurations.gnu-musl = nixosConfigurations.base.extendModules {
          modules = [
            ./musl.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-gnu");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {};
            }
          ];
        };
        nixosConfigurations.gnu-musl-llvm = nixosConfigurations.base.extendModules {
          modules = [
            ./musl-llvm.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-gnu");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {
                useLLVM = true;
                linker = "lld";
                config = "aarch64-unknown-linux-musl";
              };
            }
          ];
        };
        nixosConfigurations.musl = nixosConfigurations.base.extendModules {
          modules = [
            ./musl.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {};
            }
          ];
        };
        nixosConfigurations.musl-llvm = nixosConfigurations.base.extendModules {
          modules = [
            ./musl-llvm.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {
                useLLVM = true;
                linker = "lld";
                config = "aarch64-unknown-linux-musl";
              };
            }
          ];
        };

        nixosConfigurations.gnu-musl = nixosConfigurations.base.extendModules {
          modules = [
            ./musl.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-gnu");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {};
            }
          ];
        };
        nixosConfigurations.gnu-musl-llvm = nixosConfigurations.base.extendModules {
          modules = [
            ./musl-llvm.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-gnu");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {
                useLLVM = true;
                linker = "lld";
                config = "aarch64-unknown-linux-musl";
              };
            }
          ];
        };
        nixosConfigurations.musl = nixosConfigurations.base.extendModules {
          modules = [
            ./musl.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {};
            }
          ];
        };
        nixosConfigurations.musl-llvm = nixosConfigurations.base.extendModules {
          modules = [
            ./musl-llvm.nix
            {
              nixpkgs.buildPlatform = (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl");
              nixpkgs.hostPlatform = inputs.nixpkgs.lib.recursiveUpdate (inputs.nixpkgs.lib.systems.elaborate "aarch64-unknown-linux-musl") {
                useLLVM = true;
                linker = "lld";
                config = "aarch64-unknown-linux-musl";
              };
            }
          ];
        };

While the APIs that are being used for ${program}.withPackages pattern is very nice and egronomic, it does have a downside of not using a spliced package. So for example recently I needed Python with a package in nativeBuildInputs, but then when cross-compiled it only has Python from pkgsHostTarget, leading to an invalid executable being used at build time and then either manually using pkgsBuildBuild.python or using the spliced Python and package separately.

I wonder if there is a good way to solve this? Meaning a way to use the spliced package, as for folks not in the know of splicing it is probably confusing to see a package operate differently based upon whether you use the helpers or not. But many of these helpers are implemented with finalAttrs.finalPackage, which isn't spliced.

• https://github.com/NixOS/nixpkgs/pull/451665
• https://github.com/NixOS/nixpkgs/pull/451147
• https://github.com/NixOS/nixpkgs/pull/447166
• https://github.com/NixOS/nixpkgs/pull/445833