nixpkgs/pkgs/development/libraries/gcc/libgcc/default.nix

{
  lib,
  stdenvNoLibs,
  buildPackages,
  gcc,
  glibc,
  libiberty,
}:

let
  stdenv = stdenvNoLibs;
  gccConfigureFlags = gcc.cc.configureFlags ++ [
    "--disable-fixincludes"
    "--disable-intl"
    "--enable-threads=posix"
    "--with-glibc-version=${glibc.version}"
    "--disable-plugin"

    # these are required in order to prevent inhibit_libc=true,
    # which will cripple libgcc's unwinder; see:
    #  https://github.com/NixOS/nixpkgs/issues/213453#issuecomment-1616346163
    "--with-headers=${lib.getDev glibc}/include"
    "--with-native-system-header-dir=${lib.getDev glibc}${glibc.incdir or "/include"}"
    "--with-build-sysroot=/"
  ];

in
stdenv.mkDerivation (finalAttrs: {
  pname = "libgcc";
  inherit (gcc.cc) src version;

  outputs = [
    "out"
    "dev"
  ];

  strictDeps = true;
  depsBuildBuild = [ buildPackages.stdenv.cc ];
  nativeBuildInputs = [ libiberty ];
  buildInputs = [ glibc ];

  postUnpack = ''
    mkdir -p ./build
    buildRoot=$(readlink -e "./build")
  '';

  postPatch = gcc.cc.passthru.forceLibgccToBuildCrtStuff + ''
    sourceRoot=$(readlink -e "./libgcc")
  '';

  hardeningDisable = [ "pie" ];

  preConfigure = ''
    # Drop in libiberty, as external builds are not expected
    cd "$buildRoot"
    (
      mkdir -p "build-${stdenv.buildPlatform.config}/libiberty/pic"
      cd "build-${stdenv.buildPlatform.config}/libiberty/"
      ln -s "${buildPackages.libiberty}/lib/libiberty.a" ./
      ln -s "${buildPackages.libiberty}/lib/libiberty_pic.a" pic/libiberty.a
    )
    mkdir -p "$buildRoot/gcc"
    cd "$buildRoot/gcc"
    (
      # We "shift" the tools over to fake platforms perspective from the previous stage.
      export AS_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$AS_FOR_BUILD
      export CC_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CC_FOR_BUILD
      export CPP_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CPP_FOR_BUILD
      export CXX_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CXX_FOR_BUILD
      export LD_FOR_BUILD=${buildPackages.stdenv.cc.bintools}/bin/$LD_FOR_BUILD

      export AS=$AS_FOR_BUILD
      export CC=$CC_FOR_BUILD
      export CPP=$CPP_FOR_BUILD
      export CXX=$CXX_FOR_BUILD
      export LD=$LD_FOR_BUILD

      export AS_FOR_TARGET=${stdenv.cc}/bin/$AS
      export CC_FOR_TARGET=${stdenv.cc}/bin/$CC
      export CPP_FOR_TARGET=${stdenv.cc}/bin/$CPP
      export LD_FOR_TARGET=${stdenv.cc.bintools}/bin/$LD

      # We define GENERATOR_FILE so nothing bothers looking for GNU GMP.
      export NIX_CFLAGS_COMPILE_FOR_BUILD+=' -DGENERATOR_FILE=1'

      "$sourceRoot/../gcc/configure" ${lib.concatStringsSep " " gccConfigureFlags}

      # We remove the `libgcc.mvar` deps so that the bootstrap xgcc isn't built.
      sed -e 's,libgcc.mvars:.*$,libgcc.mvars:,' -i Makefile

      make \
        config.h \
        libgcc.mvars \
        tconfig.h \
        tm.h \
        options.h \
        insn-constants.h \
  ''
  + lib.optionalString stdenv.targetPlatform.isM68k ''
    sysroot-suffix.h \
  ''
  + lib.optionalString stdenv.targetPlatform.isAarch32 ''
    arm-isa.h \
    arm-cpu.h \
  ''
  + lib.optionalString stdenv.targetPlatform.isLoongArch64 ''
    loongarch-multilib.h \
  ''
  + ''
        insn-modes.h
    )
    mkdir -p "$buildRoot/gcc/include"

    # Preparing to configure + build libgcc itself
    mkdir -p "$buildRoot/gcc/${stdenv.hostPlatform.config}/libgcc"
    cd "$buildRoot/gcc/${stdenv.hostPlatform.config}/libgcc"
    configureScript=$sourceRoot/configure
    chmod +x "$configureScript"

    export AS_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$AS_FOR_BUILD
    export CC_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CC_FOR_BUILD
    export CPP_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CPP_FOR_BUILD
    export CXX_FOR_BUILD=${buildPackages.stdenv.cc}/bin/$CXX_FOR_BUILD
    export LD_FOR_BUILD=${buildPackages.stdenv.cc.bintools}/bin/$LD_FOR_BUILD

    export AS=${stdenv.cc}/bin/$AS
    export CC=${stdenv.cc}/bin/$CC
    export CPP=${stdenv.cc}/bin/$CPP
    export CXX=${stdenv.cc}/bin/$CXX
    export LD=${stdenv.cc.bintools}/bin/$LD

    export AS_FOR_TARGET=${stdenv.cc}/bin/$AS_FOR_TARGET
    export CC_FOR_TARGET=${stdenv.cc}/bin/$CC_FOR_TARGET
    export CPP_FOR_TARGET=${stdenv.cc}/bin/$CPP_FOR_TARGET
    export LD_FOR_TARGET=${stdenv.cc.bintools}/bin/$LD_FOR_TARGET
  '';

  configurePlatforms = [
    "build"
    "host"
  ];
  configureFlags = [
    "cross_compiling=true"
    "--disable-gcov"
    "--with-glibc-version=${glibc.version}"
  ];

  makeFlags = [ "MULTIBUILDTOP:=../" ];

  postInstall = ''
    moveToOutput "lib/gcc/${stdenv.hostPlatform.config}/${finalAttrs.version}/include" "$dev"
    mkdir -p "$out/lib" "$dev/include"
    ln -s "$out/lib/gcc/${stdenv.hostPlatform.config}/${finalAttrs.version}"/* "$out/lib"
    ln -s "$dev/lib/gcc/${stdenv.hostPlatform.config}/${finalAttrs.version}/include"/* "$dev/include/"
  '';
})