Packaging/32bit Applications

Building software with 32bit gcc

Question: I'm invoking gcc with -m32 and it fails to find `gnu/stubs-32.h`
Answer (clever): you want to use pkgsi686Linux instead of pkgs, so things like pkgsi686Linux.stdenv.mkDerivation or pkgsi686Linux.callPackage then nix will give you 32bit everything

Building software with both 32- and 64-bit executables

If a package wants to compile both 32/64-bit executables, you need a compiler with multilib support. Nixpkgs provides multiStdenv.mkDerivation that should be used instead stdenv.mkDerivation. This is equivalent to using gcc-multilib in debian derivatives.

Rust

env = {
  # Use multilib clang as linker for i686 target.
  # Required because Rust's bundled LLD doesn't know about Nix's multilib sysroot paths.
  # clang_multi has the correct 32-bit library paths (glibc_multi) baked into its driver.
  CARGO_TARGET_I686_UNKNOWN_LINUX_GNU_LINKER = "${pkgs.clang_multi}/bin/clang";
};

packages = with pkgs; [
  # clang with multilib support (both 32-bit and 64-bit)
  # This properly handles -m32 compilation with correct headers/libs
  clang_multi
];

An example that will let you build with cargo test --target i686-unknown-linux-gnu from an x86_64 machine.

You will want something similar to the following in your flake.nix, devenv.sh , or whatever you're using as your entry point.

Rust LTO & cargo bench

If you are using LTO and are having trouble building benchmarks (cargo bench) you may need to disable it at the build step until someone documents a better workaround here.

env = {
  # Disable LTO for C/C++ code compiled by the `cc` crate for i686.
  # Some crates (like `alloca`) add -flto when CC=clang, but binutils ld can't
  # process LLVM IR bitcode. Using -fno-lto ensures native object files.
  CFLAGS_i686_unknown_linux_gnu = "-fno-lto";
  CXXFLAGS_i686_unknown_linux_gnu = "-fno-lto";
};