Is it possible to cross compile for a custom target?

[sbellem]

Hi, wondering if it's possible to specify a target that is custom, similar to what is mentioned in https://github.com/NixOS/nixpkgs/blob/master/doc/languages-frameworks/rust.section.md#cross-compilation-cross-compilation:

To pass a completely custom target, define stdenv.hostPlatform.rustc.config with its name, and stdenv.hostPlatform.rustc.platform with the value. The value will be serialized to JSON in a file called ${stdenv.hostPlatform.rustc.config}.json, and the path of that file will be used instead.

For example:

import <nixpkgs> {
  crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
    rustc.config = "thumb-crazy";
    rustc.platform = { foo = ""; bar = ""; };
  };

will result in:

--target /nix/store/asdfasdfsadf-thumb-crazy.json # contains {"foo":"","bar":""}

In case that can help, the target I'm interested in is x86_64-fortanix-unknown-sgx https://github.com/nix-community/fenix/blob/1a1694cb7ae3708a90932e7a8a9a767c466a2976/data/nightly.json#L1693

[figsoda]

I'm ot familiar with nixpkgs's cross compiling, but this compiles

this is based on example "cross compiling with naersk", a different linker didn't seem to be needed when im on x86_64-unknown-linux so I removed the change

{
  inputs = {
    fenix = {
      url = "github:nix-community/fenix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    flake-utils.url = "github:numtide/flake-utils";
    naersk = {
      url = "github:nmattia/naersk";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    nixpkgs.url = "nixpkgs/nixos-unstable";
  };

  outputs = { self, fenix, flake-utils, naersk, nixpkgs }:
    flake-utils.lib.eachDefaultSystem (system: {
      defaultPackage =
        let
          pkgs = nixpkgs.legacyPackages.${system};
          target = "x86_64-fortanix-unknown-sgx";
          toolchain = with fenix.packages.${system};
            combine [
              minimal.rustc
              minimal.cargo
              targets.${target}.latest.rust-std
            ];
        in
        (naersk.lib.${system}.override {
          cargo = toolchain;
          rustc = toolchain;
        }).buildPackage {
          src = ./.;
          CARGO_BUILD_TARGET = target;
        };
    });
}