anchor.diff:  
   stdenv.mkDerivation rec {
     name = "mxnet-${version}";
  -  version = "1.1.0";
  +  version = "1.2.1";
   
  -  # Submodules needed
  -  src = fetchgit {
  -    url = "https://github.com/apache/incubator-mxnet";
  -    rev = "refs/tags/${version}";
  -    sha256 = "1qgns0c70a1gfyil96h17ms736nwdkp9kv496gvs9pkzqzvr6cpz";
  +  # Fetching from git does not work at the time (1.2.1) due to an
  +  # incorrect hash in one of the submodules. The provided tarballs
  +  # contain all necessary sources.
  +  src = fetchurl {
  +    url = "https://github.com/apache/incubator-mxnet/releases/download/${version}/apache-mxnet-src-${version}-incubating.tar.gz";
  +    sha256 = "053zbdgs4j8l79ipdz461zc7wyfbfcflmi5bw7lj2q08zm1glnb2";
     };
   
  -  nativeBuildInputs = [ cmake ];
  +  nativeBuildInputs = [ cmake perl ];
   
     buildInputs = [ opencv gtest openblas liblapack ]
                 ++ lib.optionals cudaSupport [ cudatoolkit nvidia_x11 ]
  
positive.code: { stdenv, lib, fetchgit, cmake
  , opencv, gtest, openblas, liblapack
  , cudaSupport ? false, cudatoolkit, nvidia_x11
  , cudnnSupport ? false, cudnn
  }:
  
negative.code:       "-DCUDA_HOST_COMPILER=${cudatoolkit.cc}/bin/cc"
      ] else [ "-DUSE_CUDA=OFF" ])
      ++ lib.optional (!cudnnSupport) "-DUSE_CUDNN=OFF";
  
    postPatch = ''
      substituteInPlace 3rdparty/mkldnn/tests/CMakeLists.txt \
        --replace "/bin/bash" "${bash}/bin/bash"
    '';
  
    installPhase = ''
      install -Dm755 libmxnet.so $out/lib/libmxnet.so
  