Since April 2024, the OpenLane build infrastructure has migrated to Nix, a declarative and reproducible build system. This was done to streamline maintenance load.

This change has no bearing on the end-user experience, as it still ultimately produces a Docker image. There are some minor adjustments, however:

Individual tools are no longer cached as a Docker image, instead residing in Cachix.
The build scripts for the tools themselves reside in the OpenLane 2 repository at https://github.com/efabless/openlane2.
Support for ppc64le, which was never actively tested, has been dropped.

For developers - Getting Nix

Follow the instructions at https://openlane2.readthedocs.io/en/latest/getting_started/common/nix_installation/index.html.

After everything is set up, from the repository's root directory, make openlane as usual.

Overriding tool versions

As tool_metadata.yml no longer lists tools (only the PDK so Volare continues to work,) overriding tool versions locally is done differently.

Tools included with OpenLane are listed in https://github.com/efabless/openlane2/tree/overridable/nix. We've standardized the function header to easily allow you to override the versions of tools.

Let's say, for instance, you'd like to override the revision for magic. First, you'll check the magic.nix file for OpenLane 2: You'll find that the header lists a sha256 field in addition to either a rev (a git revision) or a version (the version of the tool, minus any prefix v):

{
  …
  rev ? "bfd938b5e2321cf9a6c15f398fbc987b56fcc179",
  sha256 ? "sha256-xNhPnNGoJ8YiG6NFeFhOuKTB56rQvggJugIvukao6U8=",
}:

First, you'll open flake.nix and find a comment that says # ADD OVERRIDES HERE. Below it, you'll add this override, with your desired rev or version and sha256 equal to an empty string:

magic = openlane2.packages."${pkgs.system}".magic.override {
  rev = "ca99d0b76a82bc19a8b3213020ce3c135a28456e";
  sha256 = "";
};

Afterwards, invoke nix build .#magic. This will shortly fail with a message that looks like this:

error: hash mismatch in fixed-output derivation '/nix/store/i5pp79zmr4dngkr41z9ax75javz5456v-source.drv':
         specified: sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
            got:    sha256-aFFKbSqIgpkYjFZfpW3C52N1yQc5+KiLyf5jC16K5UU=

You'll want to go ahead and update the override with the got value as follows:

magic = openlane2.packages."${pkgs.system}".magic.override {
  rev = "ca99d0b76a82bc19a8b3213020ce3c135a28456e";
  sha256 = "sha256-aFFKbSqIgpkYjFZfpW3C52N1yQc5+KiLyf5jC16K5UU=";
};

And then invoke nix build .#magic again. Assuming the tool's build instructions and dependencies have not changed, the build will be successful. If the build instructions have changed, you will likely need to write a custom Nix derivation for the tool in place of a simple override.

But anyway, that's it. Afterwards, make openlane will create a Docker image with your new utility.

Overriding versions for tools with dependencies

Magic is a straightforward example, but some tools have dependencies on other tools, chiefly, openroad, which depends on openroad-abc and opensta.

In short, you will need to add overrides for all three tools as follows:

opensta = openlane2.packages."${pkgs.system}".opensta.override {
  rev = "a7f34210b403fe399c170296d54258f10f92885f";
  sha256 = "sha256-2R+ox0kcjXX5Kc6dtH/OEOccU/m8FjW1qnb0kxM/ahE=";
};
openroad-abc = openlane2.packages."${pkgs.system}".openroad-abc.override {
  rev = "d3916ac0337d599b30aeaf94e82b13338530ced3";
  sha256 = "sha256-osJzeOb0bgvbPGJjcpcfQzwcRJTZh1DYJ7RpFgw1NKg=";
};
openroad = openlane2.packages."${pkgs.system}".openroad.override {
  rev = "d423155d69de7f683a23f6916ead418a615ad4ad";
  sha256 = "sha256-RrJYdvzxD64TeNAlPs6G4BKxflpQO6ED78SqQVH7EUE=";
  opensta = self.packages."${pkgs.system}".opensta;
  openroad-abc = self.packages."${pkgs.system}".openroad-abc;
};

Do note:

You will need to do the whole sha256 song and dance with all three.
You need to list the dependencies explicitly in the overrides of the dependent using the syntax shown for openroad.

We understand this is more complex than the previous system; however the benefits of using a build system and language designed specifically for use-cases similar to ours far outweighs the added complexity: including better caching and reproducibility.

If you require any help overriding a tool, please feel free to open an issue.