Update: while the above^ works on aarch64-darwin as the build machine, I'm now running into issues when using x86_64-linux as the build machine.

It looks like even when just building a hello-world rust program with rustPlatform.buildrustPackage via pkgs.pkgsCross.wasm32-unknown-none.callPackage, it starts compiling LLVM and then rustc from scratch.

This was kind of expected after my experience on my mac, where the same happened, however on the mac they at least complete successfully after an hour or two. On my linux build machine, rustc fails to build during the bootstrap phase with a libunwind .so not found error.

Shouldn't llvm and rustc be cached for the pkgsCross.wasm32-unknown-none? Perhaps they're not, because there are no packages that actually use pkgsCross.wasm32-unknown-none, so as a result hydra never builds and caches them?

If so, what would be the best way to get hydra testing and building these? Would I need to add some simple hello-world-rust-wasm32-unknown-none package to pkgs/by-name/he/ or something along these lines?

I guess working out why rustc won't build is another issue, but at least having some basic pkg in nixpkgs would help to ensure it stays working.

Also, another thing I'm noticing is that regardless of what I put in meta.platforms, it always says the system is unsupported when building with pkgsCross.wasm32-unknown-none, and I always have to add NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 and --impure everytime I build 🫠 I might look into addressing this too.

Update: while the above^ works on aarch64-darwin as the build machine, I'm now running into issues when using x86_64-linux as the build machine.

It looks like even when just building a hello-world rust program with rustPlatform.buildRustPackage via pkgs.pkgsCross.wasm32-unknown-none.callPackage, it starts compiling LLVM and then rustc from scratch.

This was kind of expected after my experience on my mac, where the same happened, however on the mac they at least complete successfully after an hour or two. On my linux build machine, rustc fails to build during the bootstrap phase with a libunwind .so not found error.

Shouldn't llvm and rustc be cached for the pkgsCross.wasm32-unknown-none? Perhaps they're not, because there are no packages that actually use pkgsCross.wasm32-unknown-none, so as a result hydra never builds and caches them?

If so, what would be the best way to get hydra testing and building these? Would I need to add some simple hello-world-rust-wasm32-unknown-none package to pkgs/by-name/he/ or something along these lines?

I guess working out why rustc won't build is another issue, but at least having some basic pkg in nixpkgs would help to ensure it stays working.

Also, another thing I'm noticing is that regardless of what I put in meta.platforms, it always says the system is unsupported when building with pkgsCross.wasm32-unknown-none, and I always have to add NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 and --impure everytime I build 🫠 I might look into addressing this too.

In reply to @rhelmot:matrix.org
what's special about pkgsCross that causes __splicedPackages to contain the __spliced attribute but not the toplevel

Hi, can anyone please help me how to get started on cross-compilation. Documentation is very confusing and scattered across multiple places. I want to get GHC compiler than can compile my Haskell code to both ARM64 Linux and ARM64 Android. However I do not know where to get started. I tried the following flake.nix

{
  description = "Haskell Playground";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
      let
        pkgsBuildSystem = import nixpkgs {
          localSystem = "x86_64-linux"; # buildPlatform
          config = {
            android_sdk.accept_license = true;
            allowUnfree = true;
          };
        };
        pkgs = pkgsBuildSystem.pkgsCross.aarch64-android-prebuilt;
        hs = pkgs.haskell.packages."ghc966"; # need to match Stackage LTS version from stack.yaml resolver
        ghc = hs.ghc.override {
          enableRelocatedStaticLibs = true;
          enableShared = true;
        };
        buildDependencies = with pkgs; [
          # --- System ---
          zlib

          # Haskell deps
          stack
          ghc # GHC compiler in the desired version (will be available on PATH)
        ];
      in
      {
        formatter = pkgs.nixfmt-rfc-style;
        packages.aarch64-android.default = pkgs.mkShell {
          buildInputs = [ ];
          nativeBuildInputs = buildDependencies;
          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildDependencies;
        };
      };
}

However nix develop fails with

./zconf.h:446:14: fatal error: 'sys/types.h' file not found

Hi, can anyone please help me how to get started on cross-compilation. Documentation is very confusing and scattered across multiple places. I want to get GHC compiler than can compile my Haskell code to both ARM64 Linux and ARM64 Android. However I do not know where to get started. I tried the following flake.nix

{
  description = "Haskell Playground";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
  };

  outputs =
    {
      self,
      nixpkgs,
    }:
      let
        pkgsBuildSystem = import nixpkgs {
          localSystem = "x86_64-linux"; # buildPlatform
          config = {
            android_sdk.accept_license = true;
            allowUnfree = true;
          };
        };
        pkgs = pkgsBuildSystem.pkgsCross.aarch64-android-prebuilt;
        hs = pkgs.haskell.packages."ghc966"; # need to match Stackage LTS version from stack.yaml resolver
        ghc = hs.ghc.override {
          enableRelocatedStaticLibs = true;
          enableShared = true;
        };
        buildDependencies = with pkgs; [
          zlib
          stack
          ghc # GHC compiler in the desired version (will be available on PATH)
        ];
      in
      {
        formatter = pkgs.nixfmt-rfc-style;
        packages.aarch64-android.default = pkgs.mkShell {
          buildInputs = [ ];
          nativeBuildInputs = buildDependencies;
          LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath buildDependencies;
        };
      };
}

However nix develop fails with

./zconf.h:446:14: fatal error: 'sys/types.h' file not found