C++ Compilers: Systematize handling of standard libraries

2020-04-13 20:44:43 -04:00 · 2020-04-13 20:44:43 -04:00 · f3f7612a40
commit f3f7612a40
parent e00d4d6021
29 changed files with 150 additions and 199 deletions
--- a/pkgs/applications/networking/browsers/firefox/common.nix
+++ b/pkgs/applications/networking/browsers/firefox/common.nix
@ -177,7 +177,7 @@ stdenv.mkDerivation ({

    BINDGEN_CFLAGS="$(< ${stdenv.cc}/nix-support/libc-cflags) \
      $(< ${stdenv.cc}/nix-support/cc-cflags) \
-      ${stdenv.cc.default_cxx_stdlib_compile} \
+      $(< ${stdenv.cc}/nix-support/libcxx-cxxflags) \
      ${lib.optionalString stdenv.cc.isClang "-idirafter ${stdenv.cc.cc}/lib/clang/${lib.getVersion stdenv.cc.cc}/include"} \
      ${lib.optionalString stdenv.cc.isGNU "-isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc} -isystem ${stdenv.cc.cc}/include/c++/${lib.getVersion stdenv.cc.cc}/${stdenv.hostPlatform.config}"} \
      $NIX_CFLAGS_COMPILE"
--- a/pkgs/applications/networking/mailreaders/thunderbird/default.nix
+++ b/pkgs/applications/networking/mailreaders/thunderbird/default.nix
@ -179,7 +179,7 @@ stdenv.mkDerivation rec {

    BINDGEN_CFLAGS="$(< ${stdenv.cc}/nix-support/libc-cflags) \
      $(< ${stdenv.cc}/nix-support/cc-cflags) \
-      ${stdenv.cc.default_cxx_stdlib_compile} \
+      $(< ${stdenv.cc}/nix-support/libcxx-cxxflags) \
      ${
        lib.optionalString stdenv.cc.isClang
        "-idirafter ${stdenv.cc.cc}/lib/clang/${
--- a/pkgs/build-support/cc-wrapper/add-flags.sh
+++ b/pkgs/build-support/cc-wrapper/add-flags.sh
@ -37,6 +37,14 @@ if [ -e @out@/nix-support/libc-cflags ]; then
    NIX_CFLAGS_COMPILE_@suffixSalt@="$(< @out@/nix-support/libc-cflags) $NIX_CFLAGS_COMPILE_@suffixSalt@"
 fi

+if [ -e @out@/nix-support/libcxx-cxxflags ]; then
+    NIX_CXXSTDLIB_COMPILE_@suffixSalt@+=" $(< @out@/nix-support/libcxx-cxxflags)"
+fi
+
+if [ -e @out@/nix-support/libcxx-ldflags ]; then
+    NIX_CXXSTDLIB_LINK_@suffixSalt@+=" $(< @out@/nix-support/libcxx-ldflags)"
+fi
+
 if [ -e @out@/nix-support/cc-cflags ]; then
    NIX_CFLAGS_COMPILE_@suffixSalt@="$(< @out@/nix-support/cc-cflags) $NIX_CFLAGS_COMPILE_@suffixSalt@"
 fi
--- a/pkgs/build-support/cc-wrapper/cc-wrapper.sh
+++ b/pkgs/build-support/cc-wrapper/cc-wrapper.sh
@ -129,7 +129,7 @@ fi

 if [[ "$isCpp" = 1 ]]; then
    if [[ "$cppInclude" = 1 ]]; then
-        NIX_CFLAGS_COMPILE_@suffixSalt@+=" ${NIX_CXXSTDLIB_COMPILE_@suffixSalt@:-@default_cxx_stdlib_compile@}"
+        NIX_CFLAGS_COMPILE_@suffixSalt@+=" $NIX_CXXSTDLIB_COMPILE_@suffixSalt@"
    fi
    NIX_CFLAGS_LINK_@suffixSalt@+=" $NIX_CXXSTDLIB_LINK_@suffixSalt@"
 fi
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@ -48,12 +48,6 @@ let
  # The wrapper scripts use 'cat' and 'grep', so we may need coreutils.
  coreutils_bin = if nativeTools then "" else getBin coreutils;

-  default_cxx_stdlib_compile = if (targetPlatform.isLinux && !(cc.isGNU or false) && !nativeTools && cc ? gcc) && !(targetPlatform.useLLVM or false) then
-    "-isystem $(echo -n ${cc.gcc}/include/c++/*) -isystem $(echo -n ${cc.gcc}/include/c++/*)/${targetPlatform.config}"
-  else if targetPlatform.isDarwin && (libcxx != null) && (cc.isClang or false) && !(targetPlatform.useLLVM or false) then
-    "-isystem ${libcxx}/include/c++/v1"
-  else "";
-
  # The "suffix salt" is a arbitrary string added in the end of env vars
  # defined by cc-wrapper's hooks so that multiple cc-wrappers can be used
  # without interfering. For the moment, it is defined as the target triple,
@ -68,7 +62,7 @@ let

  # older compilers (for example bootstrap's GCC 5) fail with -march=too-modern-cpu
  isGccArchSupported = arch:
-    if cc.isGNU or false then
+    if isGNU then
      { skylake        = versionAtLeast ccVersion "6.0";
        skylake-avx512 = versionAtLeast ccVersion "6.0";
        cannonlake     = versionAtLeast ccVersion "8.0";
@ -76,7 +70,7 @@ let
        icelake-server = versionAtLeast ccVersion "8.0";
        knm            = versionAtLeast ccVersion "8.0";
      }.${arch} or true
-    else if cc.isClang or false then
+    else if isClang then
      { cannonlake     = versionAtLeast ccVersion "5.0";
        icelake-client = versionAtLeast ccVersion "7.0";
        icelake-server = versionAtLeast ccVersion "7.0";
@ -116,7 +110,7 @@ stdenv.mkDerivation {
    # Binutils, and Apple's "cctools"; "bintools" as an attempt to find an
    # unused middle-ground name that evokes both.
    inherit bintools;
-    inherit libc nativeTools nativeLibc nativePrefix isGNU isClang default_cxx_stdlib_compile;
+    inherit libc nativeTools nativeLibc nativePrefix isGNU isClang;

    emacsBufferSetup = pkgs: ''
      ; We should handle propagation here too
@ -173,8 +167,6 @@ stdenv.mkDerivation {
      export named_cc=${targetPrefix}cc
      export named_cxx=${targetPrefix}c++

-      export default_cxx_stdlib_compile="${default_cxx_stdlib_compile}"
-
      if [ -e $ccPath/${targetPrefix}gcc ]; then
        wrap ${targetPrefix}gcc $wrapper $ccPath/${targetPrefix}gcc
        ln -s ${targetPrefix}gcc $out/bin/${targetPrefix}cc
@ -226,7 +218,7 @@ stdenv.mkDerivation {

  strictDeps = true;
  propagatedBuildInputs = [ bintools ] ++ extraTools ++ optionals cc.langD or false [ zlib ];
-  depsTargetTargetPropagated = extraPackages;
+  depsTargetTargetPropagated = optional (libcxx != null) libcxx ++ extraPackages;

  wrapperName = "CC_WRAPPER";

@ -250,6 +242,24 @@ stdenv.mkDerivation {
      fi
    ''

+    + optionalString isClang ''
+      ##
+      ## General Clang support
+      ##
+
+      echo "-target ${targetPlatform.config}" >> $out/nix-support/cc-cflags
+    ''
+
+    + optionalString (isClang && libcxx == null && cc ? gcc) ''
+      ##
+      ## GCC libs for non-GCC support
+      ##
+
+      echo "-B${cc.gcc}/lib/gcc/${targetPlatform.config}/${cc.gcc.version}" >> $out/nix-support/cc-cflags
+      echo "-L${cc.gcc}/lib/gcc/${targetPlatform.config}/${cc.gcc.version}" >> $out/nix-support/cc-ldflags
+      echo "-L${cc.gcc.lib}/${targetPlatform.config}/lib" >> $out/nix-support/cc-ldflags
+    ''
+
    + optionalString (libc != null) (''
      ##
      ## General libc support
@ -279,6 +289,27 @@ stdenv.mkDerivation {
      echo "${libc_dev}" > $out/nix-support/orig-libc-dev
    '')

+    + ''
+      ##
+      ## General libc++ support
+      ##
+
+    ''
+    + optionalString (libcxx == null && cc ? gcc) ''
+      for dir in ${cc.gcc}/include/c++/*; do
+        echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
+      done
+      for dir in ${cc.gcc}/include/c++/*/${targetPlatform.config}; do
+        echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
+      done
+    ''
+    + optionalString (libcxx.isLLVM or false) (''
+      echo "-isystem ${libcxx}/include/c++/v1" >> $out/nix-support/libcxx-cxxflags
+      echo "-stdlib=libc++" >> $out/nix-support/libcxx-ldflags
+    '' + stdenv.lib.optionalString stdenv.targetPlatform.isLinux ''
+      echo "-lc++abi" >> $out/nix-support/libcxx-ldflags
+    '')
+
    + optionalString (!nativeTools) ''
      ##
      ## Initial CFLAGS
@ -389,9 +420,9 @@ stdenv.mkDerivation {
    # There are a few tools (to name one libstdcxx5) which do not work
    # well with multi line flags, so make the flags single line again
    + ''
-      if [ -e "$out/nix-support/libc-cflags" ]; then
-        substituteInPlace "$out/nix-support/libc-cflags" --replace $'\n' ' '
-      fi
+      for flags in "$out/nix-support"/*flags; do
+        substituteInPlace "$flags" --replace $'\n' ' '
+      done

      substituteAll ${./add-flags.sh} $out/nix-support/add-flags.sh
      substituteAll ${./add-hardening.sh} $out/nix-support/add-hardening.sh
--- a/pkgs/development/compilers/gcc/libstdc++-hook.sh
+++ b/pkgs/development/compilers/gcc/libstdc++-hook.sh
@ -1,4 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem $(echo -n @gcc@/include/c++/*) -isystem $(echo -n @gcc@/include/c++/*)/@targetConfig@"
--- a/pkgs/development/compilers/llvm/10/default.nix
+++ b/pkgs/development/compilers/llvm/10/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -57,23 +57,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
-        libstdcxxHook
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
@ -100,14 +94,12 @@ let
        inherit (tools) bintools;
      };
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ] ++ stdenv.lib.optionals (!stdenv.targetPlatform.isWasm) [
        targetLlvmLibraries.libunwind
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + stdenv.lib.optionalString (!stdenv.targetPlatform.isWasm) ''
@ -127,7 +119,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
        echo "-nostdlib++" >> $out/nix-support/cc-cflags
@ -145,7 +136,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + mkExtraBuildCommands cc;
@ -161,7 +151,6 @@ let
      extraPackages = [ ];
      extraBuildCommands = ''
        echo "-nostartfiles" >> $out/nix-support/cc-cflags
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
      '';
    };

--- a/pkgs/development/compilers/llvm/10/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/10/libc++/default.nix
@ -39,12 +39,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/10/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/10/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/llvm/5/default.nix
+++ b/pkgs/development/compilers/llvm/5/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -51,25 +51,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
-      extraTools = [
-        libstdcxxHook
-      ];
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
--- a/pkgs/development/compilers/llvm/5/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/5/libc++/default.nix
@ -37,12 +37,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/5/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/5/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/llvm/6/default.nix
+++ b/pkgs/development/compilers/llvm/6/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -51,25 +51,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
-      extraTools = [
-        libstdcxxHook
-      ];
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
--- a/pkgs/development/compilers/llvm/6/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/6/libc++/default.nix
@ -37,12 +37,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/6/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/6/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/llvm/7/default.nix
+++ b/pkgs/development/compilers/llvm/7/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -58,25 +58,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
-      extraTools = [
-        libstdcxxHook
-      ];
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
@ -87,48 +79,77 @@ let

    lldb = callPackage ./lldb.nix {};

+    # Below, is the LLVM bootstrapping logic. It handles building a
+    # fully LLVM toolchain from scratch. No GCC toolchain should be
+    # pulled in. As a consequence, it is very quick to build different
+    # targets provided by LLVM and we can also build for what GCC
+    # doesn’t support like LLVM. Probably we should move to some other
+    # file.
+
    bintools = callPackage ./bintools.nix {};

    lldClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
+      libcxx = targetLlvmLibraries.libcxx;
      bintools = wrapBintoolsWith {
        inherit (tools) bintools;
      };
      extraPackages = [
-        # targetLlvmLibraries.libcxx
-        # targetLlvmLibraries.libcxxabi
+        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config} -rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
+      '' + stdenv.lib.optionalString (!stdenv.targetPlatform.isWasm) ''
+        echo "--unwindlib=libunwind" >> $out/nix-support/cc-cflags
+      '' + stdenv.lib.optionalString stdenv.targetPlatform.isWasm ''
+        echo "-fno-exceptions" >> $out/nix-support/cc-cflags
+      '' + mkExtraBuildCommands cc;
+    };
+
+    lldClangNoLibcxx = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
+      bintools = wrapBintoolsWith {
+        inherit (tools) bintools;
+      };
+      extraPackages = [
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = ''
+        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
+        echo "-nostdlib++" >> $out/nix-support/cc-cflags
      '' + mkExtraBuildCommands cc;
    };

    lldClangNoLibc = wrapCCWith rec {
      cc = tools.clang-unwrapped;
+      libcxx = null;
      bintools = wrapBintoolsWith {
        inherit (tools) bintools;
        libc = null;
      };
      extraPackages = [
-        # targetLlvmLibraries.libcxx
-        # targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config} -rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + mkExtraBuildCommands cc;
    };

    lldClangNoCompilerRt = wrapCCWith {
      cc = tools.clang-unwrapped;
+      libcxx = null;
      bintools = wrapBintoolsWith {
        inherit (tools) bintools;
        libc = null;
      };
      extraPackages = [ ];
      extraBuildCommands = ''
-        echo "-nostartfiles -target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
+        echo "-nostartfiles" >> $out/nix-support/cc-cflags
      '';
    };

@ -148,9 +169,16 @@ let

    libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;

-    libcxx = callPackage ./libc++ {};
+    libcxx = callPackage ./libc++ ({} //
+      (stdenv.lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+      }));

-    libcxxabi = callPackage ./libc++abi.nix {};
+    libcxxabi = callPackage ./libc++abi.nix ({} //
+      (stdenv.lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+        libunwind = libraries.libunwind;
+      }));

    openmp = callPackage ./openmp.nix {};
  });
--- a/pkgs/development/compilers/llvm/7/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/7/libc++/default.nix
@ -37,12 +37,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/7/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/7/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/llvm/8/default.nix
+++ b/pkgs/development/compilers/llvm/8/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -58,25 +58,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
-      extraTools = [
-        libstdcxxHook
-      ];
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
@ -103,14 +95,12 @@ let
        inherit (tools) bintools;
      };
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ] ++ stdenv.lib.optionals (!stdenv.targetPlatform.isWasm) [
        targetLlvmLibraries.libunwind
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + stdenv.lib.optionalString (!stdenv.targetPlatform.isWasm) ''
@ -130,7 +120,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
        echo "-nostdlib++" >> $out/nix-support/cc-cflags
@ -148,7 +137,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + mkExtraBuildCommands cc;
@ -164,7 +152,6 @@ let
      extraPackages = [ ];
      extraBuildCommands = ''
        echo "-nostartfiles" >> $out/nix-support/cc-cflags
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
      '';
    };

--- a/pkgs/development/compilers/llvm/8/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/8/libc++/default.nix
@ -43,12 +43,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/8/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/8/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/llvm/9/default.nix
+++ b/pkgs/development/compilers/llvm/9/default.nix
@ -1,4 +1,4 @@
-{ lowPrio, newScope, pkgs, stdenv, cmake, gcc, libstdcxxHook
+{ lowPrio, newScope, pkgs, stdenv, cmake
 , libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
 , buildLlvmTools # tools, but from the previous stage, for cross
 , targetLlvmLibraries # libraries, but from the next stage, for cross
@ -58,25 +58,17 @@ let

    libstdcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
-      extraTools = [
-        libstdcxxHook
-      ];
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
      extraPackages = [
        targetLlvmLibraries.compiler-rt
      ];
-      extraBuildCommands = ''
-          echo "-target ${targetConfig}" >> $out/nix-support/cc-cflags
-          echo "-B${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-cflags
-          echo "-L${gcc.cc}/lib/gcc/${targetConfig}/${gcc.version}" >> $out/nix-support/cc-ldflags
-          echo "-L${gcc.cc.lib}/${targetConfig}/lib" >> $out/nix-support/cc-ldflags
-      '' + mkExtraBuildCommands cc;
+      extraBuildCommands = mkExtraBuildCommands cc;
    };

    libcxxClang = wrapCCWith rec {
      cc = tools.clang-unwrapped;
      libcxx = targetLlvmLibraries.libcxx;
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ];
@ -103,14 +95,12 @@ let
        inherit (tools) bintools;
      };
      extraPackages = [
-        targetLlvmLibraries.libcxx
        targetLlvmLibraries.libcxxabi
        targetLlvmLibraries.compiler-rt
      ] ++ stdenv.lib.optionals (!stdenv.targetPlatform.isWasm) [
        targetLlvmLibraries.libunwind
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt -Wno-unused-command-line-argument" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + stdenv.lib.optionalString (!stdenv.targetPlatform.isWasm) ''
@ -130,7 +120,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
        echo "-nostdlib++" >> $out/nix-support/cc-cflags
@ -148,7 +137,6 @@ let
        targetLlvmLibraries.compiler-rt
      ];
      extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
        echo "-rtlib=compiler-rt" >> $out/nix-support/cc-cflags
        echo "-B${targetLlvmLibraries.compiler-rt}/lib" >> $out/nix-support/cc-cflags
      '' + mkExtraBuildCommands cc;
@ -164,7 +152,6 @@ let
      extraPackages = [ ];
      extraBuildCommands = ''
        echo "-nostartfiles" >> $out/nix-support/cc-cflags
-        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
      '';
    };

--- a/pkgs/development/compilers/llvm/9/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/9/libc++/default.nix
@ -39,12 +39,9 @@ stdenv.mkDerivation {

  enableParallelBuilding = true;

-  linkCxxAbi = stdenv.isLinux;
-
-  setupHooks = [
-    ../../../../../build-support/setup-hooks/role.bash
-    ./setup-hook.sh
-  ];
+  passthru = {
+    isLLVM = true;
+  };

  meta = {
    homepage = "https://libcxx.llvm.org/";
--- a/pkgs/development/compilers/llvm/9/libc++/setup-hook.sh
+++ b/pkgs/development/compilers/llvm/9/libc++/setup-hook.sh
@ -1,6 +0,0 @@
-# See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-
-linkCxxAbi="@linkCxxAbi@"
-export NIX_CXXSTDLIB_COMPILE${role_post}+=" -isystem @out@/include/c++/v1"
-export NIX_CXXSTDLIB_LINK${role_post}=" -stdlib=libc++${linkCxxAbi:+" -lc++abi"}"
--- a/pkgs/development/compilers/swift/default.nix
+++ b/pkgs/development/compilers/swift/default.nix
@ -258,7 +258,7 @@ stdenv.mkDerivation {

  buildPhase = ''
    # gcc-6.4.0/include/c++/6.4.0/cstdlib:75:15: fatal error: 'stdlib.h' file not found
-    export NIX_CFLAGS_COMPILE="$( echo ${clang.default_cxx_stdlib_compile} ) $NIX_CFLAGS_COMPILE"
+    export NIX_CFLAGS_COMPILE="$(< $NIX_CC/nix-support/libcxx-cxxflags) $NIX_CFLAGS_COMPILE"
    # During the Swift build, a full local LLVM build is performed and the resulting clang is invoked.
    # This compiler is not using the Nix wrappers, so it needs some help to find things.
    export NIX_LDFLAGS_BEFORE="-rpath ${clang.cc.gcc.lib}/lib -L${clang.cc.gcc.lib}/lib $NIX_LDFLAGS_BEFORE"
--- a/pkgs/misc/vim-plugins/overrides.nix
+++ b/pkgs/misc/vim-plugins/overrides.nix
@ -98,8 +98,6 @@ self: super: {
    # These usually implicitly set by cc-wrapper around clang (pkgs/build-support/cc-wrapper).
    # The linked ruby code shows generates the required '.clang_complete' for cmake based projects
    # https://gist.github.com/Mic92/135e83803ed29162817fce4098dec144
-    # as an alternative you can execute the following command:
-    # $ eval echo $(nix-instantiate --eval --expr 'with (import <nixpkgs>) {}; clang.default_cxx_stdlib_compile')
    preFixup = ''
      substituteInPlace "$out"/share/vim-plugins/clang_complete/plugin/clang_complete.vim \
        --replace "let g:clang_library_path = '' + "''" + ''" "let g:clang_library_path='${llvmPackages.clang.cc.lib}/lib/libclang.so'"
--- a/pkgs/stdenv/darwin/default.nix
+++ b/pkgs/stdenv/darwin/default.nix
@ -90,11 +90,11 @@ in rec {
        inherit shell;
        inherit (last) stdenvNoCC;

-        extraPackages = lib.optional (libcxx != null) libcxx;
+        extraPackages = [];

        nativeTools  = false;
        nativeLibc   = false;
-        inherit buildPackages coreutils gnugrep bintools;
+        inherit buildPackages coreutils gnugrep bintools libcxx;
        libc         = last.pkgs.darwin.Libsystem;
        isClang      = true;
        cc           = { name = "${name}-clang"; outPath = bootstrapTools; };
@ -168,8 +168,9 @@ in rec {
            ln -s ${bootstrapTools}/lib/libc++.dylib $out/lib/libc++.dylib
            ln -s ${bootstrapTools}/include/c++      $out/include/c++
          '';
-          linkCxxAbi = false;
-          setupHook = ../../development/compilers/llvm/7/libc++/setup-hook.sh;
+          passthru = {
+            isLLVM = true;
+          };
        };

        libcxxabi = stdenv.mkDerivation {
--- a/pkgs/top-level/aliases.nix
+++ b/pkgs/top-level/aliases.nix
@ -264,6 +264,7 @@ mapAliases ({
  libudev = udev; # added 2018-04-25
  libusb = libusb1; # added 2020-04-28
  libsexy = throw "libsexy has been removed from nixpkgs, as it's abandoned and no package needed it."; # 2019-12-10
+  libstdcxxHook = throw "libstdcxx hook has been removed because cc-wrapper is now directly aware of the c++ standard library intended to be used."; # 2020-06-22
  libqmatrixclient = throw "libqmatrixclient was renamed to libquotient"; # added 2020-04-09
  links = links2; # added 2016-01-31
  linux_rpi0 = linux_rpi1;
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@ -8188,7 +8188,6 @@ in
  computecpp = wrapCCWith rec {
    cc = computecpp-unwrapped;
    extraPackages = [
-      libstdcxxHook
      llvmPackages.compiler-rt
    ];
    extraBuildCommands = ''
@ -8330,14 +8329,6 @@ in
    stripped = false;
  }));

-  libstdcxxHook = makeSetupHook
-    { substitutions = {
-        gcc = gcc-unwrapped;
-        targetConfig = stdenv.targetPlatform.config;
-      };
-    }
-    ../development/compilers/gcc/libstdc++-hook.sh;
-
  crossLibcStdenv = overrideCC stdenv
    (if stdenv.hostPlatform.useLLVM or false
     then buildPackages.llvmPackages_8.lldClangNoLibc
@ -9394,6 +9385,10 @@ in
      # provide the default choice, avoiding infinite recursion.
      bintools ? if stdenv.targetPlatform.isDarwin then darwin.binutils else binutils
    , libc ? bintools.libc
+    , # libc++ from the default LLVM version is bound at the top level, but we
+      # want the C++ library to be explicitly chosen by the caller, and null by
+      # default.
+      libcxx ? null
    , extraPackages ? stdenv.lib.optional (cc.isGNU or false && stdenv.targetPlatform.isMinGW) threadsCross
    , ...
    } @ extraArgs:
@ -9406,7 +9401,7 @@ in
    isGNU = cc.isGNU or false;
    isClang = cc.isClang or false;

-    inherit cc bintools libc extraPackages zlib;
+    inherit cc bintools libc libcxx extraPackages zlib;
  } // extraArgs; in self);

  wrapCC = cc: wrapCCWith {