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Cross Compiling: Difference between revisions

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     localSystem = "x86_64-linux";
     localSystem = "x86_64-linux";
     crossSystem = "aarch64-linux";
     crossSystem = "aarch64-linux";
   },
   },
}:
}:
pkgs.mkShell {
pkgs.callPackage (
  # By default this provides gcc, ar, ld, and some other bare minimum tools
  {
}
    mkShell,
  }:
  mkShell {
    # By default this provides gcc, ar, ld, and some other bare minimum tools
  }
) { }
</syntaxhighlight>Entering this development shell via <code>nix-shell shell.nix</code> will add the relevant compiler tools to your PATH temporarily. Similar to other Linux systems, all cross-compiling tools are prefixed with relevant platform prefixes, which means simply typing <code>gcc</code> will not work. However, the provided <code>mkShell</code> will introduce environment variables for your devshell, such as <code>$CC</code>, <code>$AR</code>, <code>$LD</code>, and more. At the time of writing, official documentation on an exhaustive list of these variables does not exist, but you can view them for your devshell through the command-line:<syntaxhighlight lang="bash">
</syntaxhighlight>Entering this development shell via <code>nix-shell shell.nix</code> will add the relevant compiler tools to your PATH temporarily. Similar to other Linux systems, all cross-compiling tools are prefixed with relevant platform prefixes, which means simply typing <code>gcc</code> will not work. However, the provided <code>mkShell</code> will introduce environment variables for your devshell, such as <code>$CC</code>, <code>$AR</code>, <code>$LD</code>, and more. At the time of writing, official documentation on an exhaustive list of these variables does not exist, but you can view them for your devshell through the command-line:<syntaxhighlight lang="bash">
$ $EDITOR $(nix-build ./shell.nix) # opens your EDITOR with a massive bash script full of declare -x ...
$ $EDITOR $(nix-build ./shell.nix) # opens your EDITOR with a massive bash script full of declare -x ...
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If you would prefer to continue building within the devshell, you can use [https://nixos.org/guides/nix-pills/13-callpackage-design-pattern callPackage], which will ''magically'' resolve the dependencies for the correct architecture, provided you place them in the correct attributes:<syntaxhighlight lang="nix">
If you would prefer to continue building within the devshell, you can use [https://nixos.org/guides/nix-pills/13-callpackage-design-pattern callPackage], which will ''magically'' resolve the dependencies for the correct architecture, provided you place them in the correct attributes:<syntaxhighlight lang="nix">
# shell.nix
{
{
   pkgs ? import <nixpkgs> {
   pkgs ? import <nixpkgs> {
     #localSystem = ...;
     localSystem = "x86_64-linux";
     crossSystem = "aarch64-linux";
     crossSystem = "aarch64-linux";
   },
   },
Line 71: Line 76:
   {
   {
     mkShell,
     mkShell,
 
    hello,
     pkg-config,
     pkg-config,
     libGL,
     libGL,
   }:
   }:
   mkShell {
   mkShell {
     # Derivations that must run on the buildPlatform.
    strictDeps = true;
     # host/target agnostic programs
    depsBuildBuild = [
      hello
    ];
    # compilers & linkers & dependecy finding programs
     nativeBuildInputs = [
     nativeBuildInputs = [
       pkg-config
       pkg-config
     ];
     ];
 
     # libraries
     # Derivations that must link with the targetPlatform.
     buildInputs = [
     buildInputs = [
       libGL
       libGL
     ];
     ];
   }
   }
) {}
) { }
</syntaxhighlight>The above snippet will drop you into a devshell that provides <code>pkg-config</code> as a native binary (accessible through <code>$PKG_CONFIG</code>), while also allowing linking to a valid <code>libGL</code> for the <code>crossSystem</code>.
</syntaxhighlight>The above snippet will drop you into a devshell that provides <code>pkg-config</code> as a native binary (accessible through <code>$PKG_CONFIG</code>), while also allowing linking to a valid <code>libGL</code> for the <code>crossSystem</code>.


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=== Leveraging the binary cache ===
=== Leveraging the binary cache ===
You will likely have noticed that resolving derivations through either pkgsCross or a configured Nixpkgs instance results in your system needing to build the binary. This is because cross-compiled binaries are not cached on the official [[Binary Cache|binary cache]]. Fortunately, there are a small set of systems that are actively built and cached officially. At the time of writing, this only includes <code>aarch64-linux</code>, <code>aarch64-darwin</code>, <code>i686-linux</code>, <code>x86_64-linux</code>, and <code>x86_64-darwin</code>. If your platform targets include these, you may be able to leverage a slight hack to avoid large-scale builds.<blockquote>Please note that this is not recommended, as it hacks around some internal details of Nixpkgs which are subject to change at any time.</blockquote>An example of this using <code>pkgs.SDL2</code>:<syntaxhighlight lang="nix">
You will likely have noticed that resolving derivations through either pkgsCross or a configured Nixpkgs instance results in your system needing to build the binary. This is because cross-compiled binaries are not cached on the official [[Binary Cache|binary cache]]. Fortunately, there are a small set of systems that are actively built and cached officially. At the time of writing, this only includes <code>aarch64-linux</code>, <code>aarch64-darwin</code>, <code>i686-linux</code>, <code>x86_64-linux</code>, and <code>x86_64-darwin</code>. If your platform targets include these, you may be able to leverage a slight hack to avoid large-scale builds.<blockquote>Please note that this is not recommended, as it hacks around some internal details of Nixpkgs which are subject to change at any time, and the storage requirements will be higher due to duplicate(but different system) packages.</blockquote>An example of this using <code>pkgs.SDL2</code>:<syntaxhighlight lang="nix">
let
let
   # this will use aarch64 binaries from binary cache, so no need to build those
   # this will use aarch64 binaries from binary cache, so no need to build those
   pkgsArm = import <nixpkgs> {
   pkgsArm = import <nixpkgs> {
     system = "aarch64-linux";
     localSystem = "aarch64-linux";
   };
   };


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         # we want to hack on SDL, don't want to hack on those. Some even don't cross-compile
         # we want to hack on SDL, don't want to hack on those. Some even don't cross-compile
         inherit (pkgsArm)
         inherit (pkgsArm)
           xorg libpulseaudio libGL guile systemd libxkbcommon
           xorg
          libpulseaudio
          libGL
          guile
          systemd
          libxkbcommon
           ;
           ;
       })
       })
     ];
     ];
     #localSystem = ...;
     localSystem = "x86_64-linux";
     crossSystem = "aarch64-linux";
     crossSystem = "aarch64-linux";
   };
   };
in pkgsCross.SDL2.override {  
in
  # These should be neither pkgsCross, nor pkgsArm
pkgsCross.callPackage (
  # because those trigger
  {
  # > cannot execute binary file: Exec format error
    SDL2,
  # In this case it was enough to just use buildPackages variants,
    wayland,
   # but in general, there may be problems
    wayland-protocols,
   inherit (pkgsCross.buildPackages)
    wayland-scanner,
     wayland wayland-protocols
   }:
    ;
   SDL2.override {
}
     inherit
      wayland
      wayland-protocols
      wayland-scanner
      ;
  }
) { }
</syntaxhighlight>
</syntaxhighlight>


Retrieved from "https://wiki.nixos.org/wiki/Cross_Compiling"