Hello. I am trying to clean up my build process. I am attempting to use the arm-embedded cross pkg. My derivation looks something like

{
  pkgs,
  stdenv,
  optLevel ? "debug",
}:

stdenv.mkDerivation {
  nativeBuildInputs = with pkgs.pkgsBuildHost; [meson ninja gnused srecord];

  name = "MyProject";
  src = pkgs.lib.cleanSource ./.;
  doCheck = false;

  mesonBuildType = optLevel;
  dontStrip = true;
  strictDeps = true;
}

and then it is called with

default = pkgs.pkgsCross.arm-embedded.callPackage ./default.nix {};

This fails with the error

error: attribute 'version' missing
       at /nix/store/1d49vqvzrcx28yjj0rrwxr2dfy15rkp6-source/pkgs/os-specific/linux/systemd/default.nix:119:59:
          118|     # assumes hard floats
          119|     && (stdenv.hostPlatform.isAarch -> lib.versionAtLeast stdenv.hostPlatform.parsed.cpu.version "6")
             |                                                           ^
          120|     # see https://github.com/NixOS/nixpkgs/pull/194149#issuecomment-1266642211

The build target is armv6m, and I am building on x86. Is there some way to provide it the info it needs?

Note that if I instance a dedicated cross instance with

armPkgs = import nixpkgs { crossSystem = { config = "armv6m-none-none-eabi"; libc="newlib"; }; };
armPkgs.callPackage ./default.nix {};

It almost works (it gets to the build stage but hits an error I've not seen with the arm-embedded compiler), but it requires compiling GCC from source which is not really needed.

nix-repl> pkgsCross.arm-embedded.pkgsBuildBuild.srecord
«derivation /nix/store/88q413an8c5nnrhan3lqk3ggsjdwal7v-srecord-1.64.drv»

Then for the compiler itself, is there a way I can override the gcc wrapper settings? Currently it is compiling in ARM mode, while it needs to be in thumb. I once again tried a custom nixpkgs instance with

armPkgs = import nixpkgs {
  inherit system;
  crossSystem = {
    config = "arm-none-eabi";
    libc = "newlib";
    gcc = {
      arch = "armv6m";
      cpu = "cortex-m0";
    };
  };
};

But that starts recompiling all of gcc again. I see this setting
https://github.com/NixOS/nixpkgs/blob/b44babb85a1294e6b0e20ccc2c54cd0f62a84ceb/pkgs/build-support/cc-wrapper/default.nix#L248

Which is pretty much what I want.

Then for the compiler itself, is there a way I can override the gcc wrapper settings? Currently it is compiling in ARM mode, while it needs to be in thumb. I once again tried a custom nixpkgs instance with

armPkgs = import nixpkgs {
  inherit system;
  crossSystem = {
    config = "arm-none-eabi";
    libc = "newlib";
    gcc = {
      arch = "armv6m";
      cpu = "cortex-m0";
      thumb = true;
    };
  };
};

But that starts recompiling all of gcc again. I see this setting
https://github.com/NixOS/nixpkgs/blob/b44babb85a1294e6b0e20ccc2c54cd0f62a84ceb/pkgs/build-support/cc-wrapper/default.nix#L248

Which is pretty much what I want.