NixOS and Portable Executables

Posted on January 15, 2025

by Jack Kelly

I’ve been very impressed by the Cosmopolitan Libc project
and the αcτµαlly pδrταblε
εxεcµταblε file format that makes it all possible. Building a crazy
polyglot binary that works on two architectures and half-a-dozen
operating systems is one thing, but Mozilla’s Llamafile
project showed that APEs were more than just a cool hack: it’s stunning
that I just download a reasonably smart LLM to my computer,
chmod +x it, and begin a conversation. LLM use-cases aside,
single-file dependency-free programs that work basically anywhere are
just a great thing to be able to stick on a USB stick.

But APEs have been a little finicky for me. I run NixOS as my primary operating system, and
sometimes an APE will refuse to launch, or I’ll need to pass
–assimilate to it and permanently turn it into an x86-64
Linux binary before it’ll work.

The Cosmopolitan project, of course, has a couple of answers ready.
One is to install a system-wide APE loader separate from any
one binary and register it with binfmt_misc;
the other is to patch the
kernel so it can natively detect APEs. I don’t want to wait for a
full kernel compile each time I need to update, so until the patch lands
in mainline binfmt_misc is the way to go.

I have set up a Nix Flake at https://git.sr.ht/~jack/cosmo.nix
to hold my experiments joining the Nix and Cosmopolitan universes. For
now, it has convenient NixOS options to register the APE loader with
binfmt_misc:

{
inputs = {
nixpkgs.url = “github:nixos/nixpkgs/nixos-24.11”;

# Import cosmo.nix and plumb our nixpkgs rev through it
cosmo-nix = {
url = “sourcehut:~jack/cosmo.nix”;
inputs.nixpkgs.follows = “nixpkgs”;
};
};

outputs = inputs@{ nixpkgs }: {
nixosConfigurations.myMachine = nixpkgs.lib.nixosSystem {
system = “x86_64-linux”;
modules = [
# Include the cosmo.nix module…
inputs.cosmo-nix.nixosModules.default

# …and register the ape-loader with binfmt_misc
{ programs.ape-loader.binfmt = true; }

# Your other NixOS config here.
];
}
}
}
Not bad for an evening’s hacking! I hope to take it further at some
point in the future: I’d like to build the loader itself from a known
bootstrap path rather than fetching a binary, and I’d especially love to
be able to do the same with Cosmopolitan Libc and cosmocc. I’m
a big fan of bootstrappable
builds, and reliable building of ultraportable binaries from a
documented bootstrap path would be an incredibly cool achievement. I
currently get so much useful stuff out of nix develop — all
my build dependencies, pre-commit hooks,
useful CI targets, and more — and I have projects in mind where I want
Cosmopolitan Libc to be a “tier 1” platform. Nix-based access to a
cosmocc toolchain and all cosmocc-built build
dependencies would make that so much easier.