staging-next 2025-01-06 (#371501)

# OpenXR in NixOS

OpenXR is a standard for eXtended Reality (XR) applications and drivers (providers).

OpenXR runtime providers must ensure that the library path of the runtime's shared library can be loaded by Nix applications. If your OpenXR runtime provider runs in an FHSEnv, this means you may have to use `auto-patchelf` to link dependencies to the Nix store.

Each of those compiler versions has a corresponding attribute set `packages` built with

it. However, the non-standard package sets are not tested regularly and, as a

result, contain fewer working packages. The corresponding package set for GHC

9.4.5 is `haskell.packages.ghc945`. In fact `haskellPackages` (at the time of writing) is just an alias

9.4.8 is `haskell.packages.ghc948`. In fact `haskellPackages` (at the time of writing) is just an alias

for `haskell.packages.ghc966`:

Every package set also re-exposes the GHC used to build its packages as `haskell.packages.*.ghc`.

```nix

haskellPackages.haskell-ci.overrideScope (self: super: {

  Cabal = self.Cabal_3_14_0_0;

  Cabal = self.Cabal_3_14_1_0;

})

```

```

#### How do I avoid compiling a GCC cross-compiler from source? {#cross-qa-avoid-compiling-gcc-cross-compiler}

On less powerful machines, it can be inconvenient to cross-compile a package only to find out that GCC has to be compiled from source, which could take up to several hours. Nixpkgs maintains a limited [cross-related jobset on Hydra](https://hydra.nixos.org/jobset/nixpkgs/cross-trunk), which tests cross-compilation to various platforms from build platforms "x86\_64-darwin", "x86\_64-linux", and "aarch64-linux".  See `pkgs/top-level/release-cross.nix` for the full list of target platforms and packages.  For instance, the following invocation fetches the pre-built cross-compiled GCC for `armv6l-unknown-linux-gnueabihf` and builds GNU Hello from source.

On less powerful machines, it can be inconvenient to cross-compile a package only to find out that GCC has to be compiled from source, which could take up to several hours. Nixpkgs maintains a limited [cross-related jobset on Hydra](https://hydra.nixos.org/jobset/nixpkgs/cross-trunk), which tests cross-compilation to various platforms from build platforms "x86\_64-linux", "aarch64-linux", and "aarch64-darwin".  See `pkgs/top-level/release-cross.nix` for the full list of target platforms and packages.  For instance, the following invocation fetches the pre-built cross-compiled GCC for `armv6l-unknown-linux-gnueabihf` and builds GNU Hello from source.

```ShellSession

$ nix-build '<nixpkgs>' -A pkgsCross.raspberryPi.hello

}

```

where the builder can do anything it wants, but typically starts with

where `stdenv` sets up the environment automatically (e.g. by resetting `PATH` and populating it from build inputs). If you want, you can use `stdenv`’s generic builder:

```bash

source $stdenv/setup

```

to let `stdenv` set up the environment (e.g. by resetting `PATH` and populating it from build inputs). If you want, you can still use `stdenv`’s generic builder:

```bash

source $stdenv/setup

buildPhase() {

  echo "... this is my custom build phase ..."

  gcc foo.c -o foo

The *existence* of setups hooks has long been documented and packages inside Nixpkgs are free to use this mechanism. Other packages, however, should not rely on these mechanisms not changing between Nixpkgs versions. Because of the existing issues with this system, there’s little benefit from mandating it be stable for any period of time.

First, let’s cover some setup hooks that are part of Nixpkgs default `stdenv`. This means that they are run for every package built using `stdenv.mkDerivation` or when using a custom builder that has `source $stdenv/setup`. Some of these are platform specific, so they may run on Linux but not Darwin or vice-versa.

First, let’s cover some setup hooks that are part of Nixpkgs default `stdenv`. This means that they are run for every package built using `stdenv.mkDerivation`, even with custom builders. Some of these are platform specific, so they may run on Linux but not Darwin or vice-versa.

### `move-docs.sh` {#move-docs.sh}

### Compiler and Linker wrapper hooks {#compiler-linker-wrapper-hooks}

If the file `${cc}/nix-support/cc-wrapper-hook` exists, it will be run at the end of the [compiler wrapper](#cc-wrapper).

If the file `${binutils}/nix-support/ld-wrapper-hook` exists, it will be run at the end of the linker wrapper, before the linker runs.

If the file `${binutils}/nix-support/post-link-hook` exists, it will be run at the end of the linker wrapper.

These hooks allow a user to inject code into the wrappers.

As an example, these hooks can be used to extract `extraBefore`, `params` and `extraAfter` which store all the command line arguments passed to the compiler and linker respectively.

    githubId = 108072;

    name = "Slawomir Gonet";

  };

  outfoxxed = {

    name = "outfoxxed";

    email = "nixpkgs@outfoxxed.me";

    matrix = "@outfoxxed:outfoxxed.me";

    github = "outfoxxed";

    githubId = 83010835;

    keys = [ { fingerprint = "0181 FF89 4F34 7FCC EB06  5710 4C88 A185 FB89 301E"; } ];

  };

  ovlach = {

    email = "ondrej@vlach.xyz";

    name = "Ondrej Vlach";