Unable to build with `nixpkgs.*.gcc.{arch,tune}` set

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1

Hello everyone and happy new year! :confetti_ball:

I have noticed that my unstable-small system is compiling quite a bit.
If it already is doing that I would like it to produce optimized code.

I have tried adding

 nixpkgs.hostPlatform.gcc = {
    arch = "znver3";
    tune = "znver3";
    system = "x86_64-linux";
  };

to my config, like the wiki suggests. However I get these errors:

# nixos-rebuild test 
error:
       … while evaluating the attribute 'config'
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12284:
       … while calling the 'seq' builtin
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12293:
       … while evaluating the module argument `pkgs' in "/nix/var/nix/profiles/per-user/root/channels/nixos/nixos/modules/services/hardware/bluetooth.nix":

       … while evaluating the option `nixpkgs.buildPlatform':

       … while evaluating the option `nixpkgs.hostPlatform':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'system' missing
       at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/systems/default.nix:1:2711:
building Nix...
error:
       … while evaluating the attribute 'config'
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12284:
       … while calling the 'seq' builtin
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12293:
       … while evaluating the module argument `pkgs' in "/nix/var/nix/profiles/per-user/root/channels/nixos/nixos/modules/services/hardware/bluetooth.nix":

       … while evaluating the option `nixpkgs.buildPlatform':

       … while evaluating the option `nixpkgs.hostPlatform':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'system' missing
       at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/systems/default.nix:1:2711:
building the system configuration...
error:
       … while evaluating the attribute 'config.system.build.toplevel'
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12284:
       … while calling the 'seq' builtin
         at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/modules.nix:1:12293:
       … while evaluating the module argument `pkgs' in "/nix/var/nix/profiles/per-user/root/channels/nixos/nixos/modules/services/hardware/bluetooth.nix":

       … while evaluating the option `nixpkgs.buildPlatform':

       … while evaluating the option `nixpkgs.hostPlatform':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: attribute 'system' missing
       at /nix/var/nix/profiles/per-user/root/channels/nixos/lib/systems/default.nix:1:2711:

When I change hostPlatform to localSystem (inspired by this post) I get told that it is a legacy option and I should not use it while the rebuild fails because of conflicting nixpkgs.hostPlatform in hardware-configuration.nix.

Does any of you know how to make this work?

2

Yo have added the system property in gcc, whilst the wiki is having it in hostPlatform.
That is the observed eval error complaining about.

nixpkgs.hostPlatform = {
    gcc = {
      arch = "znver3";
      tune = "znver3";
    };
    system = "x86_64-linux";
  };

Should be correct

3

Right, I have overlooked this.

after adding gccarch-znver3 to nix.settings.system-features I managed to start compilation.

This however from what I can see recompiles all the packages.

Is there a possibility to apply those optimizations just for packages that are not available as binaries?

4

Not really, no, the substitution from a cache is happening at a lower layer, and is not treated specially at the derivation layer. You could create a second nixpkgs instance to cherry-pick specific packages from, but that would increase eval memory usage and slow down eval at the very least.

Then stop using that channel? :slight_smile:
By the time nixos-unstable advances, hydra has cached way more, and more importantly, more packages are tested. *-small variants are really for servers that only use some small subset of packages that are part of the *-small jobset.