{ lib
, llvmPackages
, fetchurl
, fetchFromGitHub
, linuxHeaders
, python3
, curl
, which
, nix-update-script
, debugRuntime ? true
, runtimeAsserts ? false
, extraKleeuClibcConfig ? {}
}:

let
  localeSrcBase = "uClibc-locale-030818.tgz";
  localeSrc = fetchurl {
    url = "http://www.uclibc.org/downloads/${localeSrcBase}";
    sha256 = "xDYr4xijjxjZjcz0YtItlbq5LwVUi7k/ZSmP6a+uvVc=";
  };
  resolvedExtraKleeuClibcConfig = lib.mapAttrsToList (name: value: "${name}=${value}") (extraKleeuClibcConfig // {
    "UCLIBC_DOWNLOAD_PREGENERATED_LOCALE_DATA" = "n";
    "RUNTIME_PREFIX" = "/";
    "DEVEL_PREFIX" = "/";
  });
in
llvmPackages.stdenv.mkDerivation rec {
  pname = "klee-uclibc";
  version = "1.4";
  src = fetchFromGitHub {
    owner = "klee";
    repo = "klee-uclibc";
    rev = "klee_uclibc_v${version}";
    hash = "sha256-sogQK5Ed0k5tf4rrYwCKT4YRKyEovgT25p0BhGvJ1ok=";
  };

  nativeBuildInputs = [
    llvmPackages.clang
    llvmPackages.llvm
    python3
    curl
    which
  ];

  # Some uClibc sources depend on Linux headers.
  UCLIBC_KERNEL_HEADERS = "${linuxHeaders}/include";

  # HACK: needed for cross-compile.
  # See https://www.mail-archive.com/klee-dev@imperial.ac.uk/msg03141.html
  KLEE_CFLAGS = "-idirafter ${llvmPackages.clang}/resource-root/include";

  prePatch = ''
    patchShebangs --build ./configure
    patchShebangs --build ./extra
  '';

  # klee-uclibc configure does not support --prefix, so we override configurePhase entirely
  configurePhase = ''
    ./configure ${lib.escapeShellArgs (
      ["--make-llvm-lib"]
      ++ lib.optional (!debugRuntime) "--enable-release"
      ++ lib.optional runtimeAsserts "--enable-assertions"
    )}

    # Set all the configs we care about.
    configs=(
      PREFIX=$out
    )
    for value in ${lib.escapeShellArgs resolvedExtraKleeuClibcConfig}; do
      configs+=("$value")
    done

    for configFile in .config .config.cmd; do
      for config in "''${configs[@]}"; do
        prefix="''${config%%=*}="
        if grep -q "$prefix" "$configFile"; then
          sed -i "s"'\001'"''${prefix}"'\001'"#''${prefix}"'\001'"g" "$configFile"
        fi
        echo "$config" >> "$configFile"
      done
    done
  '';

  # Link the locale source into the correct place
  preBuild = ''
    ln -sf ${localeSrc} extra/locale/${localeSrcBase}
  '';

  makeFlags = ["HAVE_DOT_CONFIG=y"];

  enableParallelBuilding = true;

  passthru.updateScript = nix-update-script {
    extraArgs = [ "--version-regex" "v(\d\.\d)" ];
  };

  meta = with lib; {
    description = "Modified version of uClibc for KLEE";
    longDescription = ''
      klee-uclibc is a bitcode build of uClibc meant for compatibility with the
      KLEE symbolic virtual machine.
    '';
    homepage = "https://github.com/klee/klee-uclibc";
    license = licenses.lgpl3;
    maintainers = with maintainers; [ numinit ];
  };
}