anchor.diff:      INSTALL_MOD_PATH = "\${out}";
   
       buildPhase = "make module";
  -
     };
   
     tools = stdenv.mkDerivation {
  
positive.code: { stdenv, fetchgit, libmnl, kernel ? null }:
  
  # module requires Linux >= 4.1 https://www.wireguard.io/install/#kernel-requirements
  assert kernel != null -> stdenv.lib.versionAtLeast kernel.version "4.1";
  
negative.code:     ];
  
      buildPhase = "make tools";
    };
  
  in if kernel == null
  