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Basic cross-compilation usage

pkgsCross


 ❤ (theia) ~> nix-build '<nixpkgs>' -A pkgsCross.aarch64-multiplatform.hello
these 2 paths will be fetched (5.87 MiB download, 27.83 MiB unpacked):
  /nix/store/0ysynj4jhpnvljpy009lmxx7a39f4r1z-hello-aarch64-unknown-linux-gnu-2.12.1
  /nix/store/mj933c0imsdcw2c8jda1rw25i0rr4xha-glibc-aarch64-unknown-linux-gnu-2.34-210
copying path '/nix/store/mj933c0imsdcw2c8jda1rw25i0rr4xha-glibc-aarch64-unknown-linux-gnu-2.34-210' from 'https://cache.nixos.org'...
copying path '/nix/store/0ysynj4jhpnvljpy009lmxx7a39f4r1z-hello-aarch64-unknown-linux-gnu-2.12.1' from 'https://cache.nixos.org'...

 ❤ (theia) ~> file result/bin/hello                                                    
result/bin/hello: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /nix/store/mj933c0imsdcw2c8jda1rw25i0rr4xha-glibc-aarch64-unknown-linux-gnu-2.34-210/lib/ld-linux-aarch64.so.1, for GNU/Linux 2.6.32, not stripped
/nix/store/0ysynj4jhpnvljpy009lmxx7a39f4r1z-hello-aarch64-unknown-linux-gnu-2.12.1

The end

How does this work?


  • pkgsCross is a set of package sets
  • pkgsCross.aarch64-multiplatform is a package set
  • The platform-specific set will configure nixpkgs in a specific way to support cross-compilation

Tangent: pkgsStatic


  • A package set which allows for static linking of binaries
  • Can be combined with pkgsCross
 ❤ (theia) ~> nix-build '<nixpkgs>' -A pkgsCross.aarch64-multiplatform.pkgsStatic.hello
this path will be fetched (0.19 MiB download, 0.44 MiB unpacked):
  /nix/store/a1akh1fcvyv9d3qaz92lrfklq86qw56g-hello-static-aarch64-unknown-linux-musl-2.12.1
copying path '/nix/store/a1akh1fcvyv9d3qaz92lrfklq86qw56g-hello-static-aarch64-unknown-linux-musl-2.12.1' from 'https://cache.nixos.org'...
/nix/store/a1akh1fcvyv9d3qaz92lrfklq86qw56g-hello-static-aarch64-unknown-linux-musl-2.12.1
 ❤ (theia) ~> file result/bin/hello
result/bin/hello: ELF 64-bit LSB executable, ARM aarch64, version 1 (SYSV), statically linked, not stripped

Doubles and Triples


  • Doubles are 2-tuples of CPU Architecture and Kernel
  • They are used to determine whether a system can run a particular binary
  • This is a concept in Nix, not in nixpkgs!
  • This can also be overriden via --system parameter on the CLI
  • You can query this value with builtins.currentSystem

Doubles and Triples


  • Triples are 4-tuples (obviously) although sometimes the 4th one can be implicit
  • Components are: CPU Arch, Vendor, Kernel, ABI/ libc
  • This is a nixpkgs concept and can be overriden
import <nixpkgs> {
  crossSystem = {
    config = "armv7l-unknown-linux-gnueabihf";
  };
}

pkgsCross in detail


  • lib/systems/examples.nix defines a set of supported platforms
  • pkgsCross is generated from this set
pkgsCross = lib.mapAttrs (n: crossSystem:
  nixpkgsFun { inherit crossSystem; })
  lib.systems.examples;

Platform attribute sets


  • Allow precise configuration of a build target
  • There’s no comprehensive list of all settings you can set
armhf-embedded = {
  config = "arm-none-eabihf";
  libc = "newlib";
  gcc = {
    arch = "armv5t";
    fpu = "vfp";
  };
};

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