nix-mux.nix

{ lib
, wllvmPkgs
, allvm-scripts
, allvm-tools
, allexePkgs
#, alltogetherPkgs
, upstreamNixPkgs ? (fetchGit { url = https://github.com/NixOS/nixpkgs; rev = "e6b8eb0280be5b271a52c606e2365cb96b7bd9f1"; })
, muslPkgs ? import upstreamNixPkgs { localSystem = { config = "x86_64-unknown-linux-musl"; }; }
}:

with wllvmPkgs.runCommand;
with wllvmPkgs.makeWrapper;

wllvmPkgs.nixUnstable.overrideAttrs(o: {
  name = "nix-mux-${o.version}";
  # outputs = o.outputs ++ [ "orig" "bc" "allexe" "mux" "muxopt" ];
  outputs = [ "out" "dev" /*"man"*/ /*"doc"*/ ] ++ [ "orig" "bc" "allexe" "mux" "muxopt" ];

  preConfigure = (o.preConfigure or "") + ''
    NIX_CFLAGS_COMPILE+=" -g0"

    # Copy bash allexe into our output, will be our shell
    # Also copy (most?) other deps
    mkdir -p {$allexe,$out}/libexec/nix/
    cp -t $allexe/libexec/nix \
      ${allexePkgs.bash44}/bin/bash \
      ${allexePkgs.coreutils_clean}/bin/* \
      ${allexePkgs.gnutar-no-nls}/bin/tar \
      ${allexePkgs.xz}/bin/xz \
      ${allexePkgs.gzip}/bin/gzip \
      ${allexePkgs.bzip2}/bin/bzip2 \
      ${allexePkgs.lsof}/bin/lsof \
      ${allexePkgs.unzip}/bin/unzip
    rm $allexe/libexec/nix/stdbuf
    ln -s $allexe/libexec/nix/* $out/libexec/nix/

    export ALLVM_CACHE_DIR=$PWD/build-cache

    PATH=$out/libexec/nix:$PATH

    configureFlagsArray+=(--with-sandbox-shell=$out/libexec/nix/bash)
  '';

  # already applied in fork?
  #patches = (o.patches or []) ++ [
  #  ../pkgs/tools/package-management/nix/0001-prepend-out-libexec-nix-to-PATH-searching.patch
  #];

  doInstallCheck = false; # during dev

  postFixup = ''
    export PATH=${lib.makeBinPath [ allvm-tools allvm-scripts muslPkgs.coreutils ]}:$PATH

    mkdir -p $out $orig $bc $allexe

    ## Duplicate binaries that are symlinked
    rm $out/bin/nix-{shell,hash}
    cp $out/bin/{nix,nix-hash}
    cp $out/bin/{nix,nix-hash}.bc
    cp $out/bin/{nix,__run_in_chroot}
    cp $out/bin/{nix,__run_in_chroot}.bc
    cp $out/bin/nix-{build,shell}
    cp $out/bin/nix-{build,shell}.bc

    while IFS= read -r -d ''$'\0' i; do
      # If it's not an ELF file, skip
      if ! isELF "$i"; then continue; fi
      # If it's a shared library, skip (this check could be better)
      if [[ $i =~ ".so" ]]; then continue; fi

      allexe_path="$allexe''${i#$out}"
      echo "$i -> $allexe_path"

      newdir=$(dirname $allexe_path)
      mkdir -p $newdir

      ${allvm-scripts}/bin/copy-libs.sh $i $allexe_path
    done < <(find $out -not -path "*/lib/crt/*crt*.o" -type f -print0|sort -zu)

    mkdir -p {$orig,$bc}/{bin,lib,libexec/nix}
    mv $out/bin/*.bc $bc/bin/
    mv $out/lib/*.bc $bc/lib/
    mv $out/libexec/nix/*.bc $bc/libexec/nix/

    mv $out/bin/* $orig/bin/
    mv $out/lib/*so $orig/lib/
    mv $out/libexec/nix/* $orig/libexec/nix/

    # mux
    mkdir -p $mux $muxopt
    allmux $allexe/bin/* $allexe/libexec/nix/* -o $mux/nix-mux
    alltogether $mux/nix-mux -o $muxopt/nix-muxopt

    # gen binary
    export ALLVM_CACHE_DIR=$PWD/cache
    mkdir -p $ALLVM_CACHE_DIR

    allready $muxopt/nix-muxopt

    mv $ALLVM_CACHE_DIR/static_binaries/* $out/bin/nix

    # Remove dummy entries
    # (mostly so we don't create symlink for it below)
    rm $orig/bin/__run_in_chroot
    rm $bc/bin/__run_in_chroot.bc

    # Link allmux'd static binary to all needed entry points
    for x in $orig/bin/* $orig/libexec/nix/*; do
      if [ "$(basename $x)" = "nix" ]; then
        continue
      fi
      ln -rs $out/bin/nix "$out''${x#$orig}"
    done

    # force-drop openssl ref, hopefully okay O:)
    sed -re 's,/nix/store/[a-z0-9]{32}-openssl,/nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-openssl,g' \
      -i $out/bin/nix
  '';
})

Is there more detail or an update to this publicly available?