is it possible to build a cross toolchain for rust and llvm for bare metal thumbv8m.main-none-eabihf (ie raspberry pi pico 2) within nixpkgs from source
i patched lib/systems/parse.nix to allow "thumbv8m.main" as a cpu and i'm trying

crossSystem = {
  config = "thumbv8m.main-none-eabihf";
  libc = "newlib";
  useLLVM = true;
  rust.rustcTarget = "thumbv8m.main-none-eabihf";
};

and then attempting to build buildPackages.rustc and i'm immediately running into errors building compiler-rt

i can post logs/a complete example but like my first question is whether this is a path worth following at all? has anyone ever done something like this?

does electron/chrome cross compile on nixpkgs? eg. electron-unwrapped-aarch64-unknown-linux-gnu-35.5.1

I get this warning many times

pkgs/build-support/cc-wrapper/add-clang-cc-cflags-before.sh
30:    echo "Warning: supplying the --target $targetValue != @defaultTarget@ argument to a nix-wrapped compiler may not work correctly - cc-wrapper is currently not designed with multi-target compilers in mind. You may want to use an un-wrapped compiler instead." >&2

so

          {
            imports = [ nixpkgs.nixosModules.readOnlyPkgs ];
            nixpkgs.pkgs = nixpkgsFun {
              localSystem = "x86_64-linux";
              crossSystem = nixpkgs.lib.recursiveUpdate (nixpkgs.lib.systems.elaborate "aarch64-linux") {
                linux-kernel.target = "vmlinuz.efi";
                linux-kernel.installTarget = "zinstall";
              };
            };
          }

is broken