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Add Nix CI
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piegamesde committed Jul 10, 2021
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9 changes: 9 additions & 0 deletions .github/workflows/ci.yml
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Expand Up @@ -38,3 +38,12 @@ jobs:
run: |
export PATH="/usr/lib/ccache:/usr/local/opt/ccache/libexec:$PATH"
make test -j$(nproc)
build-with-nix:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v1
- uses: cachix/install-nix-action@v13
with:
nix_path: nixpkgs=channel:nixos-stable
- name: Build the CI package set
run: nix-build default.nix -A ciPackages
25 changes: 25 additions & 0 deletions README.md
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Expand Up @@ -122,6 +122,31 @@ String dump of section '.comment':

If `mold` is in `.comment`, the file is created by mold.

### Use with Nix

The `default.nix` of this repository provides an easy method to build
packages with mold as linker. General usage is `nix-build -A $attribute`,
the following attributes are provided:

- `pkgs`: A baseline package set for comparison. Sometimes packages are simply
broken and mold has nothing to do with it. Use `pkgs.packageName` to build specific
packages, and `nix search` or https://search.nixos.org/packages to find the
attribute name.
- `pkgsMold`: Equivalent to `pkgs`, except that `bfd` is replaced by mold as linker.
This has a few implications that are important to know:
- This will bootstrap the entire toolchain and build all transitive dependencies every
time mold changes.
- Packages that require a custom linker (like lld or some special GCC) won't be built with
mold.
- `pkgsMoldCI`: Equivalent to `pkgsMold`, except that mold is disabled for known failing
packages until they are resolved.
- `ciPackages`: A set of working packages that are built as part of the CI in order to catch
regressions.

After a successful build, `./result` will be a symlink to the output.
You can install Nix alongside your usual package manager, see https://nixos.org/download.html.
There are also Docker images providing a local Nix installation.

# Design and implementation of mold

For the rest of this documentation, I'll explain the design and the
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69 changes: 69 additions & 0 deletions default.nix
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let
# Pin some fairly new nixpkgs
sources = builtins.fetchTarball {
name = "nixpkgs-unstable-2021-07-06";
url = "https://github.com/nixos/nixpkgs/archive/291b3ff5af268eb7a656bb11c73f2fe535ea2170.tar.gz";
sha256 = "1z2l7q4cmiaqb99cd8yfisdr1n6xbwcczr9020ss47y2z1cn1x7x";
};

# For bootstrapping
pkgs = import sources {
overlays = [
(pkgs: super: {
# TODO replace with proper packaging once https://github.com/NixOS/nixpkgs/pull/128889 is merged
mold = pkgs.stdenv.mkDerivation {
pname = "mold";
version = "0.9.1";
src = ./.;
nativeBuildInputs = with pkgs; [ clang_12 cmake lld_12 tbb xxHash zlib openssl git ];
dontUseCmakeConfigure = "true";
buildPhase = "make -j $NIX_BUILD_CORES";
installPhase = "mkdir -p $out $out/bin $out/share/man/man1 && PREFIX=$out make install";
};

binutils_mold = pkgs.wrapBintoolsWith {
bintools = pkgs.binutils-unwrapped.overrideAttrs (old: {
postInstall = ''
rm $out/bin/ld.gold
rm $out/bin/ld.bfd
ln -sf ${pkgs.mold}/bin/mold $out/bin/ld.bfd
'';
});
};

stdenv_mold = super.overrideCC super.stdenv (super.wrapCCWith rec {
cc = super.gcc-unwrapped;
bintools = pkgs.binutils_mold;
});
})
];
};

# Actual nixpkgs with patched linker in all packages
pkgsMold = import sources {
overlays = [
(self: super: {
stdenv = pkgs.stdenv_mold;
mold = pkgs.mold;
})
];
};

# Like pkgsMold, but we disable mold individually for known failing packages until their issues are resolved
pkgsMoldCI = pkgsMold.appendOverlays [
(self: super: {
inherit (pkgs)
valgrind # https://github.com/rui314/mold/issues/81#issuecomment-876425070
;
})
];
in {
inherit pkgs pkgsMold pkgsMoldCI;

# Packages we already know that work in order to catch regressions
ciPackages = with pkgsMoldCI; linkFarmFromDrvs "packages-with-mold" [
binutils
stdenv
# TODO
];
}

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