anchor.diff:  let
     ## fetchgit info
     url = git://sourceware.org/git/systemtap.git;
  -  rev = "4051c70c9318c837981384cbb23f3e9eb1bd0892";
  -  sha256 = "0sd8n3j3rishks3gyqj2jyqhps7hmlfjyz8i0w8v98cczhhh04rq";
  -  version = "2017.10.18";
  +  rev = "release-${version}";
  +  sha256 = "0hckbmrlcz5nj438409fmdjjaaqzf68r2242v10lkssw5daia1gj";
  +  version = "3.3";
   
     inherit (kernel) stdenv;
     inherit (stdenv) lib;
  
positive.code:   };
  } ''
    mkdir -p $out/bin
    for bin in $stapBuild/bin/*; do # hello emacs */
      ln -s $bin $out/bin
    done
    rm $out/bin/stap $out/bin/dtrace
  
negative.code:     src = fetchgit { inherit url rev sha256; };
      nativeBuildInputs = [ pkgconfig ];
      buildInputs = [ elfutils gettext python2 python2Packages.setuptools ];
      enableParallelBuilding = true;
    };
  
  