anchor.diff:  with stdenv.lib;
   
   let
  +  buildType = "release";
   
     version = "4.3.20"; # changes ./guest-additions as well
   
     forEachModule = action: ''
       for mod in \
  -      out/linux.*/release/bin/src/vboxdrv \
  -      out/linux.*/release/bin/src/vboxpci \
  -      out/linux.*/release/bin/src/vboxnetadp \
  -      out/linux.*/release/bin/src/vboxnetflt
  +      out/linux.*/${buildType}/bin/src/vboxdrv \
  +      out/linux.*/${buildType}/bin/src/vboxpci \
  +      out/linux.*/${buildType}/bin/src/vboxnetadp \
  +      out/linux.*/${buildType}/bin/src/vboxnetflt
       do
         if [ "x$(basename "$mod")" != xvboxdrv -a ! -e "$mod/Module.symvers" ]
         then
  -        cp -v out/linux.*/release/bin/src/vboxdrv/Module.symvers \
  +        cp -v out/linux.*/${buildType}/bin/src/vboxdrv/Module.symvers \
             "$mod/Module.symvers"
         fi
         INSTALL_MOD_PATH="$out" INSTALL_MOD_DIR=misc \
         make -C "$MODULES_BUILD_DIR" DEPMOD=/do_not_use_depmod \
  -        "M=\$(PWD)/$mod" ${action}
  +        "M=\$(PWD)/$mod" BUILD_TYPE="${buildType}" ${action}
       done
     '';
   
  
positive.code: 
    buildPhase = ''
      source env.sh
      kmk
      ${forEachModule "modules"}
    '';
  
  
negative.code: 
      # Install VirtualBox files
      mkdir -p "$libexec"
      find out/linux.*/${buildType}/bin -mindepth 1 -maxdepth 1 \
        -name src -o -exec cp -avt "$libexec" {} +
  
      # Install kernel modules
  