anchor.diff:      if [ -n "$doInstallCheck" ]; then
         $CC -Wall -std=c99 -O3 test.c -o test
       fi
  +
  +    runHook postBuild
     '';
   
     installPhase = ''
  +    runHook preInstall
  +
       install -vD "$libName" "$out/lib/$libName"
   
       mkdir -p "$hook/nix-support"
  
positive.code:   outputs = ["out" "hook"];
  
    buildPhase = ''
      $CC -Wall -std=c99 -O3 -fPIC -ldl -shared \
        ${lib.optionalString stdenv.isDarwin "-Wl,-install_name,$out/lib/$libName"} \
        -o "$libName" \
  
negative.code:     export LD_PRELOAD="$out/lib/$libName"
      ''}
      SETUP_HOOK
  
      runHook postInstall
    '';
  
    doInstallCheck = true;
  