Nix packaging Rust projects: combine fenix Rust 1.90, openssl, lld for fun and profit

Guides
1

wordy backstory

If your Rust project uses openssl from nixpkgs and has not been linked correctly you may see an error like error while loading shared libraries: libssl.so.3 when trying to execute it.

I saw this when upgrading to Rust 1.90 by way of fenix stable toolchain in my projects. Rust 1.90 rustc ships their own lld for a linker. (See the official release notes for more!)
I tried a bunch of tweaks to my nix expressions to correctly link and compile against openssl using the upstream provided rustc and ldd.

25 commits later. No working binary. :cry:

The Rust release notes point out you can configure rustc to use a provided lld.

I tried that. It worked! :sun_with_face:

step by step guide

Here is a guide to help you configure the Rust compiler to use nixpkgs lld and openssl.

  1. Modify your expression to pass the following code gen flag to rustc: -Clink-self-contained=-linker.
  2. Provide llvmPackages.bintools to your package build

Here is a concrete example package expression link-me.nix that puts those steps together:

{
  lib,
  rustPlatform,
  pkg-config,
  openssl,
  stdenv,
  fenix,
  llvmPackages,
}:

rustPlatform.buildRustPackage rec {
  pname = "link-me";
  version = "0.0.0";

  src = ./.;
  cargoHash = "sha256-iCQ0L2efC3x2yUi/jQ7rOQXDcAvxOpcGyICjpqBjxN4=";

  nativeBuildInputs = [
    pkg-config
    fenix.stable.rustc
    fenix.stable.cargo
    llvmPackages.bintools
  ];

  buildInputs = [
    openssl
  ];
  OPENSSL_NO_VENDOR = 1;
  RUSTFLAGS = "-Clink-self-contained=-linker";

  doCheck = false;
}
2

llvmPackages.bintools provides ld.lld.
Background explained towards end of that article the Wiki links (no pun intended) paragraph “Update”.

[bintools lld version] is wrapped into an rpath-setting shell script […] rpath (also known as RUNPATH) — this is more or less LD_LIBRARY_PATH , just hard-coded into the executable

1 Like