diff --git a/pkgs/development/compilers/llvm/11/bintools.nix b/pkgs/development/compilers/llvm/11/bintools.nix
new file mode 100644
index 00000000000000..53f7941e33699a
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/bintools.nix
@@ -0,0 +1,29 @@
+{ runCommand, stdenv, llvm, lld, version }:
+
+let
+  prefix =
+    if stdenv.hostPlatform != stdenv.targetPlatform
+    then "${stdenv.targetPlatform.config}-"
+    else "";
+in runCommand "llvm-binutils-${version}" { preferLocalBuild = true; } ''
+   mkdir -p $out/bin
+   for prog in ${lld}/bin/*; do
+     ln -s $prog $out/bin/${prefix}$(basename $prog)
+   done
+   for prog in ${llvm}/bin/*; do
+     ln -sf $prog $out/bin/${prefix}$(basename $prog)
+   done
+
+   ln -s ${llvm}/bin/llvm-ar $out/bin/${prefix}ar
+   ln -s ${llvm}/bin/llvm-as $out/bin/${prefix}as
+   ln -s ${llvm}/bin/llvm-dwp $out/bin/${prefix}dwp
+   ln -s ${llvm}/bin/llvm-nm $out/bin/${prefix}nm
+   ln -s ${llvm}/bin/llvm-objcopy $out/bin/${prefix}objcopy
+   ln -s ${llvm}/bin/llvm-objdump $out/bin/${prefix}objdump
+   ln -s ${llvm}/bin/llvm-ranlib $out/bin/${prefix}ranlib
+   ln -s ${llvm}/bin/llvm-readelf $out/bin/${prefix}readelf
+   ln -s ${llvm}/bin/llvm-size $out/bin/${prefix}size
+   ln -s ${llvm}/bin/llvm-strip $out/bin/${prefix}strip
+
+   ln -s ${lld}/bin/lld $out/bin/${prefix}ld
+''
diff --git a/pkgs/development/compilers/llvm/11/clang/default.nix b/pkgs/development/compilers/llvm/11/clang/default.nix
new file mode 100644
index 00000000000000..08f9339dc8e5e5
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/clang/default.nix
@@ -0,0 +1,117 @@
+{ stdenv, fetch, cmake, libxml2, llvm, version, clang-tools-extra_src, python3, lld
+, fixDarwinDylibNames
+, enableManpages ? false
+}:
+
+let
+  self = stdenv.mkDerivation ({
+    pname = "clang";
+    inherit version;
+
+    src = fetch "clang" "18rv5nxk04fgk4ziix7z4s2cargdpqgvqrk3lnp3wvd6yb5g5p98";
+
+    unpackPhase = ''
+      unpackFile $src
+      mv clang-${version}* clang
+      sourceRoot=$PWD/clang
+      unpackFile ${clang-tools-extra_src}
+      mv clang-tools-extra-* $sourceRoot/tools/extra
+    '';
+
+    nativeBuildInputs = [ cmake python3 lld ]
+      ++ stdenv.lib.optional enableManpages python3.pkgs.sphinx;
+
+    buildInputs = [ libxml2 llvm ]
+      ++ stdenv.lib.optional stdenv.isDarwin fixDarwinDylibNames;
+
+    cmakeFlags = [
+      "-DCMAKE_CXX_FLAGS=-std=c++14"
+      "-DCLANGD_BUILD_XPC=OFF"
+    ] ++ stdenv.lib.optionals enableManpages [
+      "-DCLANG_INCLUDE_DOCS=ON"
+      "-DLLVM_ENABLE_SPHINX=ON"
+      "-DSPHINX_OUTPUT_MAN=ON"
+      "-DSPHINX_OUTPUT_HTML=OFF"
+      "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
+    ];
+
+    patches = [
+      ./purity.patch
+      # https://reviews.llvm.org/D51899
+    ];
+
+    postPatch = ''
+      sed -i -e 's/DriverArgs.hasArg(options::OPT_nostdlibinc)/true/' \
+             -e 's/Args.hasArg(options::OPT_nostdlibinc)/true/' \
+             lib/Driver/ToolChains/*.cpp
+
+      # Patch for standalone doc building
+      sed -i '1s,^,find_package(Sphinx REQUIRED)\n,' docs/CMakeLists.txt
+    '' + stdenv.lib.optionalString stdenv.hostPlatform.isMusl ''
+      sed -i -e 's/lgcc_s/lgcc_eh/' lib/Driver/ToolChains/*.cpp
+    '' + stdenv.lib.optionalString stdenv.hostPlatform.isDarwin ''
+      substituteInPlace tools/extra/clangd/CMakeLists.txt \
+        --replace "NOT HAVE_CXX_ATOMICS64_WITHOUT_LIB" FALSE
+    '';
+
+    outputs = [ "out" "lib" "python" ];
+
+    # Clang expects to find LLVMgold in its own prefix
+    postInstall = ''
+      if [ -e ${llvm}/lib/LLVMgold.so ]; then
+        ln -sv ${llvm}/lib/LLVMgold.so $out/lib
+      fi
+
+      ln -sv $out/bin/clang $out/bin/cpp
+
+      # Move libclang to 'lib' output
+      moveToOutput "lib/libclang.*" "$lib"
+      moveToOutput "lib/libclang-cpp.*" "$lib"
+      substituteInPlace $out/lib/cmake/clang/ClangTargets-release.cmake \
+          --replace "\''${_IMPORT_PREFIX}/lib/libclang." "$lib/lib/libclang." \
+          --replace "\''${_IMPORT_PREFIX}/lib/libclang-cpp." "$lib/lib/libclang-cpp."
+
+      mkdir -p $python/bin $python/share/clang/
+      mv $out/bin/{git-clang-format,scan-view} $python/bin
+      if [ -e $out/bin/set-xcode-analyzer ]; then
+        mv $out/bin/set-xcode-analyzer $python/bin
+      fi
+      mv $out/share/clang/*.py $python/share/clang
+      rm $out/bin/c-index-test
+    '';
+
+    enableParallelBuilding = true;
+
+    passthru = {
+      isClang = true;
+      inherit llvm;
+    } // stdenv.lib.optionalAttrs (stdenv.targetPlatform.isLinux || (stdenv.cc.isGNU && stdenv.cc.cc ? gcc)) {
+      gcc = if stdenv.cc.isGNU then stdenv.cc.cc else stdenv.cc.cc.gcc;
+    };
+
+    meta = {
+      description = "A c, c++, objective-c, and objective-c++ frontend for the llvm compiler";
+      homepage    = "https://llvm.org/";
+      license     = stdenv.lib.licenses.ncsa;
+      platforms   = stdenv.lib.platforms.all;
+    };
+  } // stdenv.lib.optionalAttrs enableManpages {
+    pname = "clang-manpages";
+
+    buildPhase = ''
+      make docs-clang-man
+    '';
+
+    installPhase = ''
+      mkdir -p $out/share/man/man1
+      # Manually install clang manpage
+      cp docs/man/*.1 $out/share/man/man1/
+    '';
+
+    outputs = [ "out" ];
+
+    doCheck = false;
+
+    meta.description = "man page for Clang ${version}";
+  });
+in self
diff --git a/pkgs/development/compilers/llvm/11/clang/purity.patch b/pkgs/development/compilers/llvm/11/clang/purity.patch
new file mode 100644
index 00000000000000..deb230a36c5b5b
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/clang/purity.patch
@@ -0,0 +1,28 @@
+From 4add81bba40dcec62c4ea4481be8e35ac53e89d8 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Thu, 18 May 2017 11:56:12 -0500
+Subject: [PATCH] "purity" patch for 5.0
+
+---
+ lib/Driver/ToolChains/Gnu.cpp | 7 -------
+ 1 file changed, 7 deletions(-)
+
+diff --git a/lib/Driver/ToolChains/Gnu.cpp b/lib/Driver/ToolChains/Gnu.cpp
+index fe3c0191bb..c6a482bece 100644
+--- a/lib/Driver/ToolChains/Gnu.cpp
++++ b/lib/Driver/ToolChains/Gnu.cpp
+@@ -487,12 +487,6 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+   if (!IsStatic) {
+     if (Args.hasArg(options::OPT_rdynamic))
+       CmdArgs.push_back("-export-dynamic");
+-
+-    if (!Args.hasArg(options::OPT_shared) && !IsStaticPIE) {
+-      CmdArgs.push_back("-dynamic-linker");
+-      CmdArgs.push_back(Args.MakeArgString(Twine(D.DyldPrefix) +
+-                                           ToolChain.getDynamicLinker(Args)));
+-    }
+   }
+ 
+   CmdArgs.push_back("-o");
+-- 
+2.11.0
diff --git a/pkgs/development/compilers/llvm/11/compiler-rt-armv7l.patch b/pkgs/development/compilers/llvm/11/compiler-rt-armv7l.patch
new file mode 100644
index 00000000000000..120cfe6feb2a6f
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/compiler-rt-armv7l.patch
@@ -0,0 +1,32 @@
+diff -ur compiler-rt-10.0.0.src/cmake/builtin-config-ix.cmake compiler-rt-10.0.0.src-patched/cmake/builtin-config-ix.cmake
+--- compiler-rt-10.0.0.src/cmake/builtin-config-ix.cmake	2020-03-24 00:01:02.000000000 +0900
++++ compiler-rt-10.0.0.src-patched/cmake/builtin-config-ix.cmake	2020-05-10 03:42:00.883450706 +0900
+@@ -24,7 +24,7 @@
+ 
+ 
+ set(ARM64 aarch64)
+-set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k)
++set(ARM32 arm armhf armv6m armv7m armv7em armv7 armv7s armv7k armv7l)
+ set(HEXAGON hexagon)
+ set(X86 i386)
+ set(X86_64 x86_64)
+diff -ur compiler-rt-10.0.0.src/lib/builtins/CMakeLists.txt compiler-rt-10.0.0.src-patched/lib/builtins/CMakeLists.txt
+--- compiler-rt-10.0.0.src/lib/builtins/CMakeLists.txt	2020-03-24 00:01:02.000000000 +0900
++++ compiler-rt-10.0.0.src-patched/lib/builtins/CMakeLists.txt	2020-05-10 03:44:49.468579650 +0900
+@@ -474,6 +474,7 @@
+ set(armv7_SOURCES ${arm_SOURCES})
+ set(armv7s_SOURCES ${arm_SOURCES})
+ set(armv7k_SOURCES ${arm_SOURCES})
++set(armv7l_SOURCES ${arm_SOURCES})
+ set(arm64_SOURCES ${aarch64_SOURCES})
+ 
+ # macho_embedded archs
+@@ -595,7 +596,7 @@
+   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
+     if (CAN_TARGET_${arch})
+       # For ARM archs, exclude any VFP builtins if VFP is not supported
+-      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")
++      if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7l|armv7m|armv7em)$")
+         string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}")
+         check_compile_definition(__VFP_FP__ "${CMAKE_C_FLAGS} ${_TARGET_${arch}_CFLAGS}" COMPILER_RT_HAS_${arch}_VFP)
+         if(NOT COMPILER_RT_HAS_${arch}_VFP)
diff --git a/pkgs/development/compilers/llvm/11/compiler-rt-codesign.patch b/pkgs/development/compilers/llvm/11/compiler-rt-codesign.patch
new file mode 100644
index 00000000000000..3cc12b94b2005b
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/compiler-rt-codesign.patch
@@ -0,0 +1,33 @@
+From 3dec5f3475a26aeb4678627795c4b67c6b7b4785 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Tue, 19 Sep 2017 13:13:06 -0500
+Subject: [PATCH] remove codesign use on Apple, disable ios sim testing that
+ needs it
+
+---
+ cmake/Modules/AddCompilerRT.cmake |  8 ------
+ test/asan/CMakeLists.txt          | 52 ---------------------------------------
+ test/tsan/CMakeLists.txt          | 47 -----------------------------------
+ 3 files changed, 107 deletions(-)
+
+diff --git a/cmake/Modules/AddCompilerRT.cmake b/cmake/Modules/AddCompilerRT.cmake
+index bc5fb9ff7..b64eb4246 100644
+--- a/cmake/Modules/AddCompilerRT.cmake
++++ b/cmake/Modules/AddCompilerRT.cmake
+@@ -210,14 +210,6 @@ function(add_compiler_rt_runtime name type)
+         set_target_properties(${libname} PROPERTIES IMPORT_PREFIX "")
+         set_target_properties(${libname} PROPERTIES IMPORT_SUFFIX ".lib")
+       endif()
+-      if(APPLE)
+-        # Ad-hoc sign the dylibs
+-        add_custom_command(TARGET ${libname}
+-          POST_BUILD  
+-          COMMAND codesign --sign - $<TARGET_FILE:${libname}>
+-          WORKING_DIRECTORY ${COMPILER_RT_LIBRARY_OUTPUT_DIR}
+-        )
+-      endif()
+     endif()
+     install(TARGETS ${libname}
+       ARCHIVE DESTINATION ${COMPILER_RT_LIBRARY_INSTALL_DIR}
+2.14.1
+
diff --git a/pkgs/development/compilers/llvm/11/compiler-rt.nix b/pkgs/development/compilers/llvm/11/compiler-rt.nix
new file mode 100644
index 00000000000000..133db365942463
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/compiler-rt.nix
@@ -0,0 +1,85 @@
+{ stdenv, version, fetch, cmake, python3, llvm, libcxxabi }:
+
+let
+
+  useLLVM = stdenv.hostPlatform.useLLVM or false;
+  bareMetal = stdenv.hostPlatform.parsed.kernel.name == "none";
+  inherit (stdenv.hostPlatform) isMusl;
+
+in
+
+stdenv.mkDerivation rec {
+  pname = "compiler-rt";
+  inherit version;
+  src = fetch pname "0qfgap6acxffm01hzk38pmzq8ac3isk90531dz0qf7fd5015jvvg";
+
+  nativeBuildInputs = [ cmake python3 llvm ];
+  buildInputs = stdenv.lib.optional stdenv.hostPlatform.isDarwin libcxxabi;
+
+  NIX_CFLAGS_COMPILE = [
+    "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0"
+  ];
+
+  cmakeFlags = [
+    "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON"
+    "-DCMAKE_C_COMPILER_TARGET=${stdenv.hostPlatform.config}"
+    "-DCMAKE_ASM_COMPILER_TARGET=${stdenv.hostPlatform.config}"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal || isMusl) [
+    "-DCOMPILER_RT_BUILD_SANITIZERS=OFF"
+    "-DCOMPILER_RT_BUILD_XRAY=OFF"
+    "-DCOMPILER_RT_BUILD_LIBFUZZER=OFF"
+    "-DCOMPILER_RT_BUILD_PROFILE=OFF"
+  ] ++ stdenv.lib.optionals (useLLVM || bareMetal) [
+    "-DCMAKE_C_COMPILER_WORKS=ON"
+    "-DCMAKE_CXX_COMPILER_WORKS=ON"
+    "-DCOMPILER_RT_BAREMETAL_BUILD=ON"
+    "-DCMAKE_SIZEOF_VOID_P=${toString (stdenv.hostPlatform.parsed.cpu.bits / 8)}"
+  ] ++ stdenv.lib.optionals (useLLVM) [
+    "-DCOMPILER_RT_BUILD_BUILTINS=ON"
+    "-DCMAKE_C_FLAGS=-nodefaultlibs"
+    #https://stackoverflow.com/questions/53633705/cmake-the-c-compiler-is-not-able-to-compile-a-simple-test-program
+    "-DCMAKE_TRY_COMPILE_TARGET_TYPE=STATIC_LIBRARY"
+  ] ++ stdenv.lib.optionals (bareMetal) [
+    "-DCOMPILER_RT_OS_DIR=baremetal"
+  ];
+
+  outputs = [ "out" "dev" ];
+
+  patches = [
+    ./compiler-rt-codesign.patch # Revert compiler-rt commit that makes codesign mandatory
+  ]# ++ stdenv.lib.optional stdenv.hostPlatform.isMusl ./sanitizers-nongnu.patch
+    ++ stdenv.lib.optional stdenv.hostPlatform.isAarch32 ./compiler-rt-armv7l.patch;
+
+
+  # TSAN requires XPC on Darwin, which we have no public/free source files for. We can depend on the Apple frameworks
+  # to get it, but they're unfree. Since LLVM is rather central to the stdenv, we patch out TSAN support so that Hydra
+  # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
+  # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
+  # a flag and turn the flag off during the stdenv build.
+  postPatch = stdenv.lib.optionalString (!stdenv.isDarwin) ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
+    substituteInPlace cmake/config-ix.cmake \
+      --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
+  '' + stdenv.lib.optionalString (useLLVM) ''
+    substituteInPlace lib/builtins/int_util.c \
+      --replace "#include <stdlib.h>" ""
+    substituteInPlace lib/builtins/clear_cache.c \
+      --replace "#include <assert.h>" ""
+    substituteInPlace lib/builtins/cpu_model.c \
+      --replace "#include <assert.h>" ""
+  '';
+
+  # Hack around weird upsream RPATH bug
+  postInstall = stdenv.lib.optionalString (stdenv.hostPlatform.isDarwin || stdenv.hostPlatform.isWasm) ''
+    ln -s "$out/lib"/*/* "$out/lib"
+  '' + stdenv.lib.optionalString (useLLVM) ''
+    ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
+    ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtend.o
+    ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o
+    ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o
+  '';
+
+  enableParallelBuilding = true;
+}
diff --git a/pkgs/development/compilers/llvm/11/default.nix b/pkgs/development/compilers/llvm/11/default.nix
new file mode 100644
index 00000000000000..cbb3df9f687e0d
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/default.nix
@@ -0,0 +1,195 @@
+{ lowPrio, newScope, pkgs, stdenv, cmake
+, libxml2, python3, isl, fetchurl, overrideCC, wrapCCWith, wrapBintoolsWith
+, buildLlvmTools # tools, but from the previous stage, for cross
+, targetLlvmLibraries # libraries, but from the next stage, for cross
+}:
+
+let
+  release_version = "11.0.0";
+  candidate = "rc2";
+  version = "${release_version}${candidate}"; # differentiating these (variables) is important for RCs
+  targetConfig = stdenv.targetPlatform.config;
+
+  fetch = name: sha256: fetchurl {
+    url = "https://github.com/llvm/llvm-project/releases/download/llvmorg-${release_version}-${candidate}/${name}-${version}.src.tar.xz";
+    inherit sha256;
+  };
+
+  clang-tools-extra_src = fetch "clang-tools-extra" "0bg2a9nmkdbj5qfd0vvqj8bgchcx1yzmylxxgvh8y5hhj4fz13fs";
+
+  tools = stdenv.lib.makeExtensible (tools: let
+    callPackage = newScope (tools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
+    mkExtraBuildCommands = cc: ''
+      rsrc="$out/resource-root"
+      mkdir "$rsrc"
+      ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
+      ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
+      echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
+      echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
+    '';
+  in {
+
+    llvm = callPackage ./llvm.nix { };
+
+    clang-unwrapped = callPackage ./clang {
+      inherit (tools) lld;
+      inherit clang-tools-extra_src;
+    };
+
+    # disabled until recommonmark supports sphinx 3
+    #Llvm-manpages = lowPrio (tools.llvm.override {
+    #  enableManpages = true;
+    #  python3 = pkgs.python3;  # don't use python-boot
+    #});
+
+    clang-manpages = lowPrio (tools.clang-unwrapped.override {
+      enableManpages = true;
+      python3 = pkgs.python3;  # don't use python-boot
+    });
+
+    # disabled until recommonmark supports sphinx 3
+    # lldb-manpages = lowPrio (tools.lldb.override {
+    #   enableManpages = true;
+    #   python3 = pkgs.python3;  # don't use python-boot
+    # });
+
+    libclang = tools.clang-unwrapped.lib;
+
+    clang = if stdenv.cc.isGNU then tools.libstdcxxClang else tools.libcxxClang;
+
+    libstdcxxClang = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null; # libstdcxx is smuggled in with clang.gcc
+      extraPackages = [
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
+    };
+
+    libcxxClang = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = targetLlvmLibraries.libcxx;
+      extraPackages = [
+        targetLlvmLibraries.libcxxabi
+        targetLlvmLibraries.compiler-rt
+      ];
+      extraBuildCommands = mkExtraBuildCommands cc;
+    };
+
+    lld = callPackage ./lld.nix {};
+
+    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.libcxxabi
+        targetLlvmLibraries.compiler-rt
+      ] ++ stdenv.lib.optionals (!stdenv.targetPlatform.isWasm) [
+        targetLlvmLibraries.libunwind
+      ];
+      extraBuildCommands = ''
+        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.compiler-rt
+      ];
+      extraBuildCommands = ''
+        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" >> $out/nix-support/cc-cflags
+      '';
+    };
+
+  });
+
+  libraries = stdenv.lib.makeExtensible (libraries: let
+    callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python3 isl release_version version fetch; });
+  in {
+
+    compiler-rt = callPackage ./compiler-rt.nix ({} //
+      (stdenv.lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt;
+      }));
+
+    stdenv = overrideCC stdenv buildLlvmTools.clang;
+
+    libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;
+
+    libcxx = callPackage ./libc++ ({} //
+      (stdenv.lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+      }));
+
+    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 {};
+
+    libunwind = callPackage ./libunwind.nix ({} //
+      (stdenv.lib.optionalAttrs (stdenv.hostPlatform.useLLVM or false) {
+        stdenv = overrideCC stdenv buildLlvmTools.lldClangNoLibcxx;
+      }));
+
+  });
+
+in { inherit tools libraries; } // libraries // tools
diff --git a/pkgs/development/compilers/llvm/11/libc++/default.nix b/pkgs/development/compilers/llvm/11/libc++/default.nix
new file mode 100644
index 00000000000000..a2ea7e299185cd
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/libc++/default.nix
@@ -0,0 +1,52 @@
+{ lib, stdenv, fetch, cmake, python3, libcxxabi, fixDarwinDylibNames, version
+, enableShared ? true }:
+
+stdenv.mkDerivation {
+  pname = "libc++";
+  inherit version;
+
+  src = fetch "libcxx" "0aaci7iblfczv1jb22zjrwzxcrcx6x7klvjivmxm2zni0n2x3bd4";
+
+  postUnpack = ''
+    unpackFile ${libcxxabi.src}
+    export LIBCXXABI_INCLUDE_DIR="$PWD/$(ls -d libcxxabi-${version}*)/include"
+  '';
+
+  patches = stdenv.lib.optional stdenv.hostPlatform.isMusl ../../libcxx-0001-musl-hacks.patch;
+
+  preConfigure = ''
+    # Get headers from the cxxabi source so we can see private headers not installed by the cxxabi package
+    cmakeFlagsArray=($cmakeFlagsArray -DLIBCXX_CXX_ABI_INCLUDE_PATHS="$LIBCXXABI_INCLUDE_DIR")
+  '' + lib.optionalString stdenv.hostPlatform.isMusl ''
+    patchShebangs utils/cat_files.py
+  '';
+  nativeBuildInputs = [ cmake ]
+    ++ stdenv.lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) python3;
+
+  buildInputs = [ libcxxabi ] ++ lib.optional stdenv.isDarwin fixDarwinDylibNames;
+
+  cmakeFlags = [
+    "-DLIBCXX_LIBCXXABI_LIB_PATH=${libcxxabi}/lib"
+    "-DLIBCXX_LIBCPPABI_VERSION=2"
+    "-DLIBCXX_CXX_ABI=libcxxabi"
+  ] ++ stdenv.lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1"
+    ++ stdenv.lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON"
+    ++ stdenv.lib.optional stdenv.hostPlatform.isWasm [
+      "-DLIBCXX_ENABLE_THREADS=OFF"
+      "-DLIBCXX_ENABLE_FILESYSTEM=OFF"
+      "-DLIBCXX_ENABLE_EXCEPTIONS=OFF"
+    ] ++ stdenv.lib.optional (!enableShared) "-DLIBCXX_ENABLE_SHARED=OFF";
+
+  enableParallelBuilding = true;
+
+  passthru = {
+    isLLVM = true;
+  };
+
+  meta = {
+    homepage = "https://libcxx.llvm.org/";
+    description = "A new implementation of the C++ standard library, targeting C++11";
+    license = with stdenv.lib.licenses; [ ncsa mit ];
+    platforms = stdenv.lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/11/libc++abi.nix b/pkgs/development/compilers/llvm/11/libc++abi.nix
new file mode 100644
index 00000000000000..bf7b3fd001d504
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/libc++abi.nix
@@ -0,0 +1,67 @@
+{ stdenv, cmake, fetch, libcxx, libunwind, llvm, version
+, enableShared ? true }:
+
+stdenv.mkDerivation {
+  pname = "libc++abi";
+  inherit version;
+
+  src = fetch "libcxxabi" "04gqdzs13sw7f7a06h5zm5917d9f1k79l4rcm096grgvf0r7lnqx";
+
+  nativeBuildInputs = [ cmake ];
+  buildInputs = stdenv.lib.optional (!stdenv.isDarwin && !stdenv.isFreeBSD && !stdenv.hostPlatform.isWasm) libunwind;
+
+  cmakeFlags = stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false) [
+    "-DLLVM_ENABLE_LIBCXX=ON"
+    "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
+  ] ++ stdenv.lib.optionals stdenv.hostPlatform.isWasm [
+    "-DLIBCXXABI_ENABLE_THREADS=OFF"
+    "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF"
+  ] ++ stdenv.lib.optionals (!enableShared) [
+    "-DLIBCXXABI_ENABLE_SHARED=OFF"
+  ];
+
+  patches = [ ./libcxxabi-no-threads.patch ];
+
+  postUnpack = ''
+    unpackFile ${libcxx.src}
+    unpackFile ${llvm.src}
+    cmakeFlags+=" -DLLVM_PATH=$PWD/$(ls -d llvm-*) -DLIBCXXABI_LIBCXX_PATH=$PWD/$(ls -d libcxx-*)"
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
+    export TRIPLE=x86_64-apple-darwin
+  '' + stdenv.lib.optionalString stdenv.hostPlatform.isMusl ''
+    patch -p1 -d $(ls -d libcxx-*) -i ${../libcxx-0001-musl-hacks.patch}
+  '' + stdenv.lib.optionalString stdenv.hostPlatform.isWasm ''
+    patch -p1 -d $(ls -d llvm-*) -i ${./libcxxabi-wasm.patch}
+  '';
+
+  installPhase = if stdenv.isDarwin
+    then ''
+      for file in lib/*.dylib; do
+        # this should be done in CMake, but having trouble figuring out
+        # the magic combination of necessary CMake variables
+        # if you fancy a try, take a look at
+        # https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/RPATH-handling
+        install_name_tool -id $out/$file $file
+      done
+      make install
+      install -d 755 $out/include
+      install -m 644 ../include/*.h $out/include
+    ''
+    else ''
+      install -d -m 755 $out/include $out/lib
+      install -m 644 lib/libc++abi.a $out/lib
+      install -m 644 ../include/cxxabi.h $out/include
+    '' + stdenv.lib.optionalString enableShared ''
+      install -m 644 lib/libc++abi.so.1.0 $out/lib
+      ln -s libc++abi.so.1.0 $out/lib/libc++abi.so
+      ln -s libc++abi.so.1.0 $out/lib/libc++abi.so.1
+    '';
+
+  meta = {
+    homepage = "https://libcxxabi.llvm.org/";
+    description = "A new implementation of low level support for a standard C++ library";
+    license = with stdenv.lib.licenses; [ ncsa mit ];
+    maintainers = with stdenv.lib.maintainers; [ vlstill ];
+    platforms = stdenv.lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/11/libcxxabi-no-threads.patch b/pkgs/development/compilers/llvm/11/libcxxabi-no-threads.patch
new file mode 100644
index 00000000000000..787f3e16500e21
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/libcxxabi-no-threads.patch
@@ -0,0 +1,12 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 4138acf..41b4763 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -362,6 +362,7 @@ if (NOT LIBCXXABI_ENABLE_THREADS)
+                         " is also set to ON.")
+   endif()
+   add_definitions(-D_LIBCXXABI_HAS_NO_THREADS)
++  add_definitions(-D_LIBCPP_HAS_NO_THREADS)
+ endif()
+ 
+ if (LIBCXXABI_HAS_EXTERNAL_THREAD_API)
diff --git a/pkgs/development/compilers/llvm/11/libcxxabi-wasm.patch b/pkgs/development/compilers/llvm/11/libcxxabi-wasm.patch
new file mode 100644
index 00000000000000..4ebfe46aa813dd
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/libcxxabi-wasm.patch
@@ -0,0 +1,16 @@
+diff --git a/cmake/modules/HandleLLVMOptions.cmake b/cmake/modules/HandleLLVMOptions.cmake
+index 15497d405e0..33f7f18193a 100644
+--- a/cmake/modules/HandleLLVMOptions.cmake
++++ b/cmake/modules/HandleLLVMOptions.cmake
+@@ -127,7 +127,10 @@ else(WIN32)
+       set(LLVM_HAVE_LINK_VERSION_SCRIPT 1)
+     endif()
+   else(FUCHSIA OR UNIX)
+-    MESSAGE(SEND_ERROR "Unable to determine platform")
++    if(${CMAKE_SYSTEM_NAME} MATCHES "Wasi")
++    else()
++      MESSAGE(SEND_ERROR "Unable to determine platform")
++    endif()
+   endif(FUCHSIA OR UNIX)
+ endif(WIN32)
+ 
diff --git a/pkgs/development/compilers/llvm/11/libunwind.nix b/pkgs/development/compilers/llvm/11/libunwind.nix
new file mode 100644
index 00000000000000..03b58ca8d1d350
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/libunwind.nix
@@ -0,0 +1,14 @@
+{ stdenv, version, fetch, cmake, fetchpatch, enableShared ? true }:
+
+stdenv.mkDerivation rec {
+  pname = "libunwind";
+  inherit version;
+
+  src = fetch pname "1ch4a2yp821lgzxh9898f7nw2fnkrn3wh25sqg05hlks45znv30y";
+
+  nativeBuildInputs = [ cmake ];
+
+  enableParallelBuilding = true;
+
+  cmakeFlags = stdenv.lib.optional (!enableShared) "-DLIBUNWIND_ENABLE_SHARED=OFF";
+}
diff --git a/pkgs/development/compilers/llvm/11/lld.nix b/pkgs/development/compilers/llvm/11/lld.nix
new file mode 100644
index 00000000000000..74d18a444fc283
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/lld.nix
@@ -0,0 +1,33 @@
+{ stdenv
+, fetch
+, cmake
+, libxml2
+, llvm
+, version
+}:
+
+stdenv.mkDerivation rec {
+  pname = "lld";
+  inherit version;
+
+  src = fetch pname "0lqz5cfids0rrl02p0qq5s18p8ikaa9r5gwa2yvj3bismdhvmar8";
+
+  nativeBuildInputs = [ cmake ];
+  buildInputs = [ llvm libxml2 ];
+
+  outputs = [ "out" "dev" ];
+
+  enableParallelBuilding = true;
+
+  postInstall = ''
+    moveToOutput include "$dev"
+    moveToOutput lib "$dev"
+  '';
+
+  meta = {
+    description = "The LLVM Linker";
+    homepage    = "https://lld.llvm.org/";
+    license     = stdenv.lib.licenses.ncsa;
+    platforms   = stdenv.lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/11/lldb-procfs.patch b/pkgs/development/compilers/llvm/11/lldb-procfs.patch
new file mode 100644
index 00000000000000..b075dbaeee0ad0
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/lldb-procfs.patch
@@ -0,0 +1,31 @@
+--- a/source/Plugins/Process/Linux/Procfs.h
++++ b/source/Plugins/Process/Linux/Procfs.h
+@@ -11,21 +11,12 @@
+ // sys/procfs.h on Android/Linux for all supported architectures.
+ 
+ #include <sys/ptrace.h>
++#include <asm/ptrace.h>
+ 
+-#ifdef __ANDROID__
+-#if defined(__arm64__) || defined(__aarch64__)
+-typedef unsigned long elf_greg_t;
+-typedef elf_greg_t
+-    elf_gregset_t[(sizeof(struct user_pt_regs) / sizeof(elf_greg_t))];
+-typedef struct user_fpsimd_state elf_fpregset_t;
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#elif defined(__mips__)
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#endif
+-#else // __ANDROID__
++#if !defined(__GLIBC__) && defined(__powerpc__)
++#define pt_regs musl_pt_regs
++#include <sys/procfs.h>
++#undef pt_regs
++#else
+ #include <sys/procfs.h>
+-#endif // __ANDROID__
++#endif
diff --git a/pkgs/development/compilers/llvm/11/lldb.nix b/pkgs/development/compilers/llvm/11/lldb.nix
new file mode 100644
index 00000000000000..c0b7f267f750e3
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/lldb.nix
@@ -0,0 +1,101 @@
+{ stdenv
+, fetch
+, cmake
+, zlib
+, ncurses
+, swig
+, which
+, libedit
+, libxml2
+, llvm
+, clang-unwrapped
+, python3
+, version
+, darwin
+, lit
+, enableManpages ? false
+}:
+
+stdenv.mkDerivation (rec {
+  pname = "lldb";
+  inherit version;
+
+  src = fetch pname "0hb582kvhxp3kcckz7imrihs0kszdaz09z22xfymyi4vgmcy62q3";
+
+  patches = [ ./lldb-procfs.patch ];
+
+  nativeBuildInputs = [ cmake python3 which swig lit ]
+    ++ stdenv.lib.optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
+
+  buildInputs = [
+    ncurses
+    zlib
+    libedit
+    libxml2
+    llvm
+  ]
+  ++ stdenv.lib.optionals stdenv.isDarwin [
+    darwin.libobjc
+    darwin.apple_sdk.libs.xpc
+    darwin.apple_sdk.frameworks.Foundation
+    darwin.bootstrap_cmds
+    darwin.apple_sdk.frameworks.Carbon
+    darwin.apple_sdk.frameworks.Cocoa
+  ];
+
+  CXXFLAGS = "-fno-rtti";
+  hardeningDisable = [ "format" ];
+
+  cmakeFlags = [
+    "-DLLDB_CODESIGN_IDENTITY=" # codesigning makes nondeterministic
+    "-DClang_DIR=${clang-unwrapped}/lib/cmake"
+    "-DLLVM_EXTERNAL_LIT=${lit}/bin/lit"
+  ] ++ stdenv.lib.optionals stdenv.isDarwin [
+    "-DLLDB_USE_SYSTEM_DEBUGSERVER=ON"
+  ] ++ stdenv.lib.optionals enableManpages [
+    "-DLLVM_ENABLE_SPHINX=ON"
+    "-DSPHINX_OUTPUT_MAN=ON"
+    "-DSPHINX_OUTPUT_HTML=OFF"
+  ]
+;
+
+  enableParallelBuilding = true;
+
+  postInstall = ''
+    # Editor support
+    # vscode:
+    install -D ../tools/lldb-vscode/package.json $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/package.json
+    mkdir -p $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/bin
+    ln -s $out/bin/lldb-vscode $out/share/vscode/extensions/llvm-org.lldb-vscode-0.1.0/bin
+  '';
+
+  meta = with stdenv.lib; {
+    description = "A next-generation high-performance debugger";
+    homepage = "https://lldb.llvm.org";
+    license = licenses.ncsa;
+    platforms = platforms.all;
+  };
+} // stdenv.lib.optionalAttrs enableManpages {
+  pname = "lldb-manpages";
+
+  buildPhase = ''
+    make docs-lldb-man
+  '';
+
+  propagatedBuildInputs = [];
+
+  installPhase = ''
+    # manually install lldb man page
+    mkdir -p $out/share/man/man1
+    install docs/man/lldb.1 -t $out/share/man/man1/
+  '';
+
+  postPatch = null;
+  postInstall = null;
+
+  outputs = [ "out" ];
+
+  doCheck = false;
+
+  meta.description = "man pages for LLDB ${version}";
+})
diff --git a/pkgs/development/compilers/llvm/11/llvm-outputs.patch b/pkgs/development/compilers/llvm/11/llvm-outputs.patch
new file mode 100644
index 00000000000000..40096fa3497fd3
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/llvm-outputs.patch
@@ -0,0 +1,26 @@
+diff --git a/tools/llvm-config/llvm-config.cpp b/tools/llvm-config/llvm-config.cpp
+index 94d426b..37f7794 100644
+--- a/tools/llvm-config/llvm-config.cpp
++++ b/tools/llvm-config/llvm-config.cpp
+@@ -333,6 +333,21 @@ int main(int argc, char **argv) {
+     ActiveIncludeOption = "-I" + ActiveIncludeDir;
+   }
+ 
++  /// Nix-specific multiple-output handling: override ActiveLibDir if --link-shared
++  if (!IsInDevelopmentTree) {
++    bool WantShared = true;
++    for (int i = 1; i < argc; ++i) {
++      StringRef Arg = argv[i];
++      if (Arg == "--link-shared")
++        WantShared = true;
++      else if (Arg == "--link-static")
++        WantShared = false; // the last one wins
++    }
++
++    if (WantShared)
++      ActiveLibDir = std::string("@lib@") + "/lib" + LLVM_LIBDIR_SUFFIX;
++  }
++
+   /// We only use `shared library` mode in cases where the static library form
+   /// of the components provided are not available; note however that this is
+   /// skipped if we're run from within the build dir. However, once installed,
diff --git a/pkgs/development/compilers/llvm/11/llvm.nix b/pkgs/development/compilers/llvm/11/llvm.nix
new file mode 100644
index 00000000000000..9cd0da4f4f99cd
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/llvm.nix
@@ -0,0 +1,187 @@
+{ stdenv
+, fetch
+, cmake
+, python3
+, libffi
+, libbfd
+, libpfm
+, libxml2
+, ncurses
+, version
+, release_version
+, zlib
+, buildPackages
+, debugVersion ? false
+, enableManpages ? false
+, enableSharedLibraries ? true
+, enablePFM ? !(stdenv.isDarwin
+  || stdenv.isAarch64 # broken for Ampere eMAG 8180 (c2.large.arm on Packet) #56245
+  || stdenv.isAarch32 # broken for the armv7l builder
+)
+, enablePolly ? false
+}:
+
+let
+  inherit (stdenv.lib) optional optionals optionalString;
+
+  # Used when creating a version-suffixed symlink of libLLVM.dylib
+  shortVersion = with stdenv.lib;
+    concatStringsSep "." (take 1 (splitString "." release_version));
+
+in stdenv.mkDerivation (rec {
+  pname = "llvm";
+  inherit version;
+
+  src = fetch pname "151c7nphn18dcw04yxyp6qdj8w19psb8nigf26djf7rhpi1fn0sh";
+  polly_src = fetch "polly" "0caxfpaxhf38nam4gkb9xqlrw20v29cm8jf95ykkbngqw64rmgij";
+
+  unpackPhase = ''
+    unpackFile $src
+    mv llvm-${version}* llvm
+    sourceRoot=$PWD/llvm
+  '' + optionalString enablePolly ''
+    unpackFile $polly_src
+    mv polly-* $sourceRoot/tools/polly
+  '';
+
+  outputs = [ "out" "python" ]
+    ++ optional enableSharedLibraries "lib";
+
+  nativeBuildInputs = [ cmake python3 ]
+    ++ optionals enableManpages [ python3.pkgs.sphinx python3.pkgs.recommonmark ];
+
+  buildInputs = [ libxml2 libffi ]
+    ++ optional enablePFM libpfm; # exegesis
+
+  propagatedBuildInputs = [ ncurses zlib ];
+
+  postPatch = optionalString stdenv.isDarwin ''
+    substituteInPlace cmake/modules/AddLLVM.cmake \
+      --replace 'set(_install_name_dir INSTALL_NAME_DIR "@rpath")' "set(_install_name_dir)" \
+      --replace 'set(_install_rpath "@loader_path/../lib''${LLVM_LIBDIR_SUFFIX}" ''${extra_libdir})' ""
+  ''
+  # Patch llvm-config to return correct library path based on --link-{shared,static}.
+  + optionalString (enableSharedLibraries) ''
+    substitute '${./llvm-outputs.patch}' ./llvm-outputs.patch --subst-var lib
+    patch -p1 < ./llvm-outputs.patch
+  '' + ''
+    # FileSystem permissions tests fail with various special bits
+    substituteInPlace unittests/Support/CMakeLists.txt \
+      --replace "Path.cpp" ""
+    rm unittests/Support/Path.cpp
+  '' + optionalString stdenv.hostPlatform.isMusl ''
+    patch -p1 -i ${../TLI-musl.patch}
+    substituteInPlace unittests/Support/CMakeLists.txt \
+      --replace "add_subdirectory(DynamicLibrary)" ""
+    rm unittests/Support/DynamicLibrary/DynamicLibraryTest.cpp
+    # valgrind unhappy with musl or glibc, but fails w/musl only
+    rm test/CodeGen/AArch64/wineh4.mir
+  '' + optionalString stdenv.hostPlatform.isAarch32 ''
+    # skip failing X86 test cases on 32-bit ARM
+    rm test/DebugInfo/X86/convert-debugloc.ll
+    rm test/DebugInfo/X86/convert-inlined.ll
+    rm test/DebugInfo/X86/convert-linked.ll
+    rm test/tools/dsymutil/X86/op-convert.test
+  '' + optionalString (stdenv.hostPlatform.system == "armv6l-linux") ''
+    # Seems to require certain floating point hardware (NEON?)
+    rm test/ExecutionEngine/frem.ll
+  '' + ''
+    patchShebangs test/BugPoint/compile-custom.ll.py
+  '';
+
+  # hacky fix: created binaries need to be run before installation
+  preBuild = ''
+    mkdir -p $out/
+    ln -sv $PWD/lib $out
+  '';
+
+  cmakeFlags = with stdenv; [
+    "-DCMAKE_BUILD_TYPE=${if debugVersion then "Debug" else "Release"}"
+    "-DLLVM_INSTALL_UTILS=ON"  # Needed by rustc
+    "-DLLVM_BUILD_TESTS=ON"
+    "-DLLVM_ENABLE_FFI=ON"
+    "-DLLVM_ENABLE_RTTI=ON"
+    "-DLLVM_HOST_TRIPLE=${stdenv.hostPlatform.config}"
+    "-DLLVM_DEFAULT_TARGET_TRIPLE=${stdenv.hostPlatform.config}"
+    "-DLLVM_ENABLE_DUMP=ON"
+  ] ++ optionals enableSharedLibraries [
+    "-DLLVM_LINK_LLVM_DYLIB=ON"
+  ] ++ optionals enableManpages [
+    "-DLLVM_BUILD_DOCS=ON"
+    "-DLLVM_ENABLE_SPHINX=ON"
+    "-DSPHINX_OUTPUT_MAN=ON"
+    "-DSPHINX_OUTPUT_HTML=OFF"
+    "-DSPHINX_WARNINGS_AS_ERRORS=OFF"
+  ] ++ optionals (!isDarwin) [
+    "-DLLVM_BINUTILS_INCDIR=${libbfd.dev}/include"
+  ] ++ optionals isDarwin [
+    "-DLLVM_ENABLE_LIBCXX=ON"
+    "-DCAN_TARGET_i386=false"
+  ] ++ optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
+    "-DCMAKE_CROSSCOMPILING=True"
+    "-DLLVM_TABLEGEN=${buildPackages.llvm_10}/bin/llvm-tblgen"
+  ];
+
+  postBuild = ''
+    rm -fR $out
+  '';
+
+  preCheck = ''
+    export LD_LIBRARY_PATH=$LD_LIBRARY_PATH''${LD_LIBRARY_PATH:+:}$PWD/lib
+  '';
+
+  postInstall = ''
+    mkdir -p $python/share
+    mv $out/share/opt-viewer $python/share/opt-viewer
+  ''
+  + optionalString enableSharedLibraries ''
+    moveToOutput "lib/libLLVM-*" "$lib"
+    moveToOutput "lib/libLLVM${stdenv.hostPlatform.extensions.sharedLibrary}" "$lib"
+  ''
+  + optionalString (enableSharedLibraries && (!stdenv.isDarwin)) ''
+    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
+      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM-" "$lib/lib/libLLVM-"
+  ''
+  + optionalString (stdenv.isDarwin && enableSharedLibraries) ''
+    substituteInPlace "$out/lib/cmake/llvm/LLVMExports-${if debugVersion then "debug" else "release"}.cmake" \
+      --replace "\''${_IMPORT_PREFIX}/lib/libLLVM.dylib" "$lib/lib/libLLVM.dylib"
+    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${shortVersion}.dylib
+    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${release_version}.dylib
+  '';
+
+  doCheck = stdenv.isLinux && (!stdenv.isx86_32);
+
+  checkTarget = "check-all";
+
+  enableParallelBuilding = true;
+
+  requiredSystemFeatures = [ "big-parallel" ];
+  meta = {
+    description = "Collection of modular and reusable compiler and toolchain technologies";
+    homepage    = "https://llvm.org/";
+    license     = stdenv.lib.licenses.ncsa;
+    maintainers = with stdenv.lib.maintainers; [ lovek323 raskin dtzWill ];
+    platforms   = stdenv.lib.platforms.all;
+  };
+} // stdenv.lib.optionalAttrs enableManpages {
+  pname = "llvm-manpages";
+
+  buildPhase = ''
+    make docs-llvm-man
+  '';
+
+  propagatedBuildInputs = [];
+
+  installPhase = ''
+    make -C docs install
+  '';
+
+  postPatch = null;
+  postInstall = null;
+
+  outputs = [ "out" ];
+
+  doCheck = false;
+
+  meta.description = "man pages for LLVM ${version}";
+})
diff --git a/pkgs/development/compilers/llvm/11/openmp.nix b/pkgs/development/compilers/llvm/11/openmp.nix
new file mode 100644
index 00000000000000..f4f9bbf2292f07
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/openmp.nix
@@ -0,0 +1,26 @@
+{ stdenv
+, fetch
+, cmake
+, llvm
+, perl
+, version
+}:
+
+stdenv.mkDerivation rec {
+  pname = "openmp";
+  inherit version;
+
+  src = fetch pname "1025dwn68iw664df831zbkxy8bxilvjkbc6mw4nhv6p5ff7dcw7f";
+
+  nativeBuildInputs = [ cmake perl ];
+  buildInputs = [ llvm ];
+
+  enableParallelBuilding = true;
+
+  meta = {
+    description = "Components required to build an executable OpenMP program";
+    homepage    = "https://openmp.llvm.org/";
+    license     = stdenv.lib.licenses.mit;
+    platforms   = stdenv.lib.platforms.all;
+  };
+}
diff --git a/pkgs/development/compilers/llvm/11/sanitizers-nongnu.patch b/pkgs/development/compilers/llvm/11/sanitizers-nongnu.patch
new file mode 100644
index 00000000000000..1f2ac97818ebae
--- /dev/null
+++ b/pkgs/development/compilers/llvm/11/sanitizers-nongnu.patch
@@ -0,0 +1,412 @@
+From f7a253f8f85d0f49df6b73996737a3e84ac64236 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Mon, 24 Sep 2018 11:17:25 -0500
+Subject: [PATCH] Ported to 7.0, taken from gentoo-musl project.
+
+------
+Ported to compiler-rt-sanitizers-5.0.0. Taken from
+
+https://gist.githubusercontent.com/pwaller/2337f3290f12634cad3e3730cff0a6c1/raw/83c87a8585e2f9662494db5662e5361beb093c26/nongnu.patch
+Signed-off-by: Jory A. Pratt <anarchy@gentoo.org>
+
+Taken from gentoo-musl project, with a few additional minor fixes.
+---
+ lib/asan/asan_linux.cc                        |  4 +-
+ lib/interception/interception_linux.cc        |  2 +-
+ lib/interception/interception_linux.h         |  2 +-
+ lib/msan/msan_linux.cc                        |  2 +-
+ lib/sanitizer_common/sanitizer_allocator.cc   |  2 +-
+ .../sanitizer_common_interceptors_ioctl.inc   |  4 +-
+ .../sanitizer_common_syscalls.inc             |  2 +-
+ lib/sanitizer_common/sanitizer_linux.cc       |  8 +++-
+ .../sanitizer_linux_libcdep.cc                | 10 ++---
+ lib/sanitizer_common/sanitizer_platform.h     |  6 +++
+ .../sanitizer_platform_interceptors.h         |  4 +-
+ .../sanitizer_platform_limits_posix.cc        | 37 +++++++++++--------
+ lib/tsan/rtl/tsan_platform_linux.cc           |  2 +-
+ 13 files changed, 51 insertions(+), 34 deletions(-)
+
+diff --git a/lib/asan/asan_linux.cc b/lib/asan/asan_linux.cc
+index 625f32d40..73cf77aca 100644
+--- a/lib/asan/asan_linux.cc
++++ b/lib/asan/asan_linux.cc
+@@ -46,7 +46,7 @@
+ #include <link.h>
+ #endif
+ 
+-#if SANITIZER_ANDROID || SANITIZER_FREEBSD || SANITIZER_SOLARIS
++#if SANITIZER_ANDROID || SANITIZER_FREEBSD || SANITIZER_SOLARIS || SANITIZER_NONGNU
+ #include <ucontext.h>
+ extern "C" void* _DYNAMIC;
+ #elif SANITIZER_NETBSD
+@@ -139,7 +139,7 @@ void AsanApplyToGlobals(globals_op_fptr op, const void *needle) {
+   UNIMPLEMENTED();
+ }
+ 
+-#if SANITIZER_ANDROID
++#if SANITIZER_ANDROID || SANITIZER_NONGNU
+ // FIXME: should we do anything for Android?
+ void AsanCheckDynamicRTPrereqs() {}
+ void AsanCheckIncompatibleRT() {}
+diff --git a/lib/interception/interception_linux.cc b/lib/interception/interception_linux.cc
+index 26bfcd8f6..529b234f7 100644
+--- a/lib/interception/interception_linux.cc
++++ b/lib/interception/interception_linux.cc
+@@ -43,7 +43,7 @@ bool GetRealFunctionAddress(const char *func_name, uptr *func_addr,
+ }
+ 
+ // Android and Solaris do not have dlvsym
+-#if !SANITIZER_ANDROID && !SANITIZER_SOLARIS && !SANITIZER_OPENBSD
++#if !SANITIZER_ANDROID && !SANITIZER_SOLARIS && !SANITIZER_OPENBSD && !SANITIZER_NONGNU
+ void *GetFuncAddrVer(const char *func_name, const char *ver) {
+   return dlvsym(RTLD_NEXT, func_name, ver);
+ }
+diff --git a/lib/interception/interception_linux.h b/lib/interception/interception_linux.h
+index 942c25609..24a4d5080 100644
+--- a/lib/interception/interception_linux.h
++++ b/lib/interception/interception_linux.h
+@@ -36,7 +36,7 @@ void *GetFuncAddrVer(const char *func_name, const char *ver);
+       (::__interception::uptr) & WRAP(func))
+ 
+ // Android,  Solaris and OpenBSD do not have dlvsym
+-#if !SANITIZER_ANDROID && !SANITIZER_SOLARIS && !SANITIZER_OPENBSD
++#if !SANITIZER_ANDROID && !SANITIZER_SOLARIS && !SANITIZER_OPENBSD && !SANITIZER_NONGNU
+ #define INTERCEPT_FUNCTION_VER_LINUX_OR_FREEBSD(func, symver) \
+   (::__interception::real_##func = (func##_f)(                \
+        unsigned long)::__interception::GetFuncAddrVer(#func, symver))
+diff --git a/lib/msan/msan_linux.cc b/lib/msan/msan_linux.cc
+index 385a650c4..6e30a8ce9 100644
+--- a/lib/msan/msan_linux.cc
++++ b/lib/msan/msan_linux.cc
+@@ -13,7 +13,7 @@
+ //===----------------------------------------------------------------------===//
+ 
+ #include "sanitizer_common/sanitizer_platform.h"
+-#if SANITIZER_FREEBSD || SANITIZER_LINUX || SANITIZER_NETBSD
++#if SANITIZER_FREEBSD || (SANITIZER_LINUX && !SANITIZER_NONGNU) || SANITIZER_NETBSD
+ 
+ #include "msan.h"
+ #include "msan_report.h"
+diff --git a/lib/sanitizer_common/sanitizer_allocator.cc b/lib/sanitizer_common/sanitizer_allocator.cc
+index 6bfd5e5ee..048f6154f 100644
+--- a/lib/sanitizer_common/sanitizer_allocator.cc
++++ b/lib/sanitizer_common/sanitizer_allocator.cc
+@@ -27,7 +27,7 @@ const char *SecondaryAllocatorName = "LargeMmapAllocator";
+ 
+ // ThreadSanitizer for Go uses libc malloc/free.
+ #if SANITIZER_GO || defined(SANITIZER_USE_MALLOC)
+-# if SANITIZER_LINUX && !SANITIZER_ANDROID
++# if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ extern "C" void *__libc_malloc(uptr size);
+ #  if !SANITIZER_GO
+ extern "C" void *__libc_memalign(uptr alignment, uptr size);
+diff --git a/lib/sanitizer_common/sanitizer_common_interceptors_ioctl.inc b/lib/sanitizer_common/sanitizer_common_interceptors_ioctl.inc
+index 2d633c173..b6eb23116 100644
+--- a/lib/sanitizer_common/sanitizer_common_interceptors_ioctl.inc
++++ b/lib/sanitizer_common/sanitizer_common_interceptors_ioctl.inc
+@@ -104,7 +104,7 @@ static void ioctl_table_fill() {
+   _(SIOCGETVIFCNT, WRITE, struct_sioc_vif_req_sz);
+ #endif
+ 
+-#if SANITIZER_LINUX
++#if SANITIZER_LINUX && !SANITIZER_NONGNU
+   // Conflicting request ids.
+   // _(CDROMAUDIOBUFSIZ, NONE, 0);
+   // _(SNDCTL_TMR_CONTINUE, NONE, 0);
+@@ -365,7 +365,7 @@ static void ioctl_table_fill() {
+   _(VT_WAITACTIVE, NONE, 0);
+ #endif
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   // _(SIOCDEVPLIP, WRITE, struct_ifreq_sz); // the same as EQL_ENSLAVE
+   _(CYGETDEFTHRESH, WRITE, sizeof(int));
+   _(CYGETDEFTIMEOUT, WRITE, sizeof(int));
+diff --git a/lib/sanitizer_common/sanitizer_common_syscalls.inc b/lib/sanitizer_common/sanitizer_common_syscalls.inc
+index 469c8eb7e..24f87867d 100644
+--- a/lib/sanitizer_common/sanitizer_common_syscalls.inc
++++ b/lib/sanitizer_common/sanitizer_common_syscalls.inc
+@@ -2038,7 +2038,7 @@ POST_SYSCALL(setrlimit)(long res, long resource, void *rlim) {
+   }
+ }
+ 
+-#if !SANITIZER_ANDROID
++#if !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ PRE_SYSCALL(prlimit64)(long pid, long resource, const void *new_rlim,
+                        void *old_rlim) {
+   if (new_rlim) PRE_READ(new_rlim, struct_rlimit64_sz);
+diff --git a/lib/sanitizer_common/sanitizer_linux.cc b/lib/sanitizer_common/sanitizer_linux.cc
+index 96d6c1eff..9e2b7fb9d 100644
+--- a/lib/sanitizer_common/sanitizer_linux.cc
++++ b/lib/sanitizer_common/sanitizer_linux.cc
+@@ -541,13 +541,13 @@ const char *GetEnv(const char *name) {
+ #endif
+ }
+ 
+-#if !SANITIZER_FREEBSD && !SANITIZER_NETBSD && !SANITIZER_OPENBSD
++#if !SANITIZER_FREEBSD && !SANITIZER_NETBSD && !SANITIZER_OPENBSD && !SANITIZER_NONGNU
+ extern "C" {
+ SANITIZER_WEAK_ATTRIBUTE extern void *__libc_stack_end;
+ }
+ #endif
+ 
+-#if !SANITIZER_GO && !SANITIZER_FREEBSD && !SANITIZER_NETBSD &&                \
++#if (!SANITIZER_GO || SANITIZER_NONGNU) && !SANITIZER_FREEBSD && !SANITIZER_NETBSD &&                \
+     !SANITIZER_OPENBSD
+ static void ReadNullSepFileToArray(const char *path, char ***arr,
+                                    int arr_size) {
+@@ -590,6 +590,10 @@ static void GetArgsAndEnv(char ***argv, char ***envp) {
+ #elif SANITIZER_NETBSD
+   *argv = __ps_strings->ps_argvstr;
+   *envp = __ps_strings->ps_envstr;
++#elif SANITIZER_NONGNU
++    static const int kMaxArgv = 2000, kMaxEnvp = 2000;
++    ReadNullSepFileToArray("/proc/self/cmdline", argv, kMaxArgv);
++    ReadNullSepFileToArray("/proc/self/environ", envp, kMaxEnvp);
+ #else // SANITIZER_FREEBSD
+ #if !SANITIZER_GO
+   if (&__libc_stack_end) {
+diff --git a/lib/sanitizer_common/sanitizer_linux_libcdep.cc b/lib/sanitizer_common/sanitizer_linux_libcdep.cc
+index 4962ff832..438f94dbe 100644
+--- a/lib/sanitizer_common/sanitizer_linux_libcdep.cc
++++ b/lib/sanitizer_common/sanitizer_linux_libcdep.cc
+@@ -179,7 +179,7 @@ __attribute__((unused)) static bool GetLibcVersion(int *major, int *minor,
+ }
+ 
+ #if !SANITIZER_FREEBSD && !SANITIZER_ANDROID && !SANITIZER_GO &&               \
+-    !SANITIZER_NETBSD && !SANITIZER_OPENBSD && !SANITIZER_SOLARIS
++    !SANITIZER_NETBSD && !SANITIZER_OPENBSD && !SANITIZER_SOLARIS && !SANITIZER_NONGNU
+ static uptr g_tls_size;
+ 
+ #ifdef __i386__
+@@ -261,7 +261,7 @@ void InitTlsSize() { }
+ #if (defined(__x86_64__) || defined(__i386__) || defined(__mips__) ||          \
+      defined(__aarch64__) || defined(__powerpc64__) || defined(__s390__) ||    \
+      defined(__arm__)) &&                                                      \
+-    SANITIZER_LINUX && !SANITIZER_ANDROID
++    SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ // sizeof(struct pthread) from glibc.
+ static atomic_uintptr_t thread_descriptor_size;
+ 
+@@ -426,7 +426,7 @@ int GetSizeFromHdr(struct dl_phdr_info *info, size_t size, void *data) {
+ 
+ #if !SANITIZER_GO
+ static void GetTls(uptr *addr, uptr *size) {
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ # if defined(__x86_64__) || defined(__i386__) || defined(__s390__)
+   *addr = ThreadSelf();
+   *size = GetTlsSize();
+@@ -470,7 +470,7 @@ static void GetTls(uptr *addr, uptr *size) {
+ #elif SANITIZER_OPENBSD
+   *addr = 0;
+   *size = 0;
+-#elif SANITIZER_ANDROID
++#elif SANITIZER_ANDROID || SANITIZER_NONGNU
+   *addr = 0;
+   *size = 0;
+ #elif SANITIZER_SOLARIS
+@@ -486,7 +486,7 @@ static void GetTls(uptr *addr, uptr *size) {
+ #if !SANITIZER_GO
+ uptr GetTlsSize() {
+ #if SANITIZER_FREEBSD || SANITIZER_ANDROID || SANITIZER_NETBSD ||              \
+-    SANITIZER_OPENBSD || SANITIZER_SOLARIS
++    SANITIZER_OPENBSD || SANITIZER_SOLARIS || SANITIZER_NONGNU
+   uptr addr, size;
+   GetTls(&addr, &size);
+   return size;
+diff --git a/lib/sanitizer_common/sanitizer_platform.h b/lib/sanitizer_common/sanitizer_platform.h
+index d81e25580..e10680ac8 100644
+--- a/lib/sanitizer_common/sanitizer_platform.h
++++ b/lib/sanitizer_common/sanitizer_platform.h
+@@ -208,6 +208,12 @@
+ # define SANITIZER_SOLARIS32 0
+ #endif
+ 
++#if defined(__linux__) && !defined(__GLIBC__)
++# define SANITIZER_NONGNU 1
++#else
++# define SANITIZER_NONGNU 0
++#endif
++
+ #if defined(__myriad2__)
+ # define SANITIZER_MYRIAD2 1
+ #else
+diff --git a/lib/sanitizer_common/sanitizer_platform_interceptors.h b/lib/sanitizer_common/sanitizer_platform_interceptors.h
+index f95539a73..6c53b3415 100644
+--- a/lib/sanitizer_common/sanitizer_platform_interceptors.h
++++ b/lib/sanitizer_common/sanitizer_platform_interceptors.h
+@@ -39,7 +39,7 @@
+ # include "sanitizer_platform_limits_solaris.h"
+ #endif
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ # define SI_LINUX_NOT_ANDROID 1
+ #else
+ # define SI_LINUX_NOT_ANDROID 0
+@@ -322,7 +322,7 @@
+ #define SANITIZER_INTERCEPT_ETHER_R (SI_FREEBSD || SI_LINUX_NOT_ANDROID)
+ #define SANITIZER_INTERCEPT_SHMCTL          \
+   (SI_NETBSD || SI_OPENBSD || SI_SOLARIS || \
+-  ((SI_FREEBSD || SI_LINUX_NOT_ANDROID) && \
++  ((SI_FREEBSD || SI_LINUX_NOT_ANDROID || SANITIZER_NONGNU) && \
+     SANITIZER_WORDSIZE == 64))  // NOLINT
+ #define SANITIZER_INTERCEPT_RANDOM_R SI_LINUX_NOT_ANDROID
+ #define SANITIZER_INTERCEPT_PTHREAD_ATTR_GET SI_POSIX
+diff --git a/lib/sanitizer_common/sanitizer_platform_limits_posix.cc b/lib/sanitizer_common/sanitizer_platform_limits_posix.cc
+index 54da635d7..2f6ff69c3 100644
+--- a/lib/sanitizer_common/sanitizer_platform_limits_posix.cc
++++ b/lib/sanitizer_common/sanitizer_platform_limits_posix.cc
+@@ -14,6 +14,9 @@
+ 
+ #include "sanitizer_platform.h"
+ 
++// Workaround musl <--> linux conflicting definition of 'struct sysinfo'
++#define _LINUX_SYSINFO_H
++
+ #if SANITIZER_LINUX || SANITIZER_FREEBSD || SANITIZER_MAC
+ // Tests in this file assume that off_t-dependent data structures match the
+ // libc ABI. For example, struct dirent here is what readdir() function (as
+@@ -138,12 +141,14 @@ typedef struct user_fpregs elf_fpregset_t;
+ 
+ #if SANITIZER_LINUX && !SANITIZER_ANDROID
+ #include <glob.h>
+-#include <obstack.h>
++#  if !SANITIZER_NONGNU
++#    include <obstack.h>
++#  endif
+ #include <mqueue.h>
+-#include <net/if_ppp.h>
+-#include <netax25/ax25.h>
+-#include <netipx/ipx.h>
+-#include <netrom/netrom.h>
++#include <linux/if_ppp.h>
++#include <linux/ax25.h>
++#include <linux/ipx.h>
++#include <linux/netrom.h>
+ #if HAVE_RPC_XDR_H
+ # include <rpc/xdr.h>
+ #elif HAVE_TIRPC_RPC_XDR_H
+@@ -251,7 +256,7 @@ namespace __sanitizer {
+   unsigned struct_itimerspec_sz = sizeof(struct itimerspec);
+ #endif // SANITIZER_LINUX || SANITIZER_FREEBSD
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   // Use pre-computed size of struct ustat to avoid <sys/ustat.h> which
+   // has been removed from glibc 2.28.
+ #if defined(__aarch64__) || defined(__s390x__) || defined (__mips64) \
+@@ -322,7 +327,7 @@ unsigned struct_ElfW_Phdr_sz = sizeof(ElfW(Phdr));
+ unsigned struct_ElfW_Phdr_sz = sizeof(Elf_Phdr);
+ #endif
+ 
+-#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID
++#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   int glob_nomatch = GLOB_NOMATCH;
+   int glob_altdirfunc = GLOB_ALTDIRFUNC;
+ #endif
+@@ -416,7 +421,7 @@ unsigned struct_ElfW_Phdr_sz = sizeof(Elf_Phdr);
+   unsigned struct_termios_sz = sizeof(struct termios);
+   unsigned struct_winsize_sz = sizeof(struct winsize);
+ 
+-#if SANITIZER_LINUX
++#if SANITIZER_LINUX && !SANITIZER_NONGNU
+   unsigned struct_arpreq_sz = sizeof(struct arpreq);
+   unsigned struct_cdrom_msf_sz = sizeof(struct cdrom_msf);
+   unsigned struct_cdrom_multisession_sz = sizeof(struct cdrom_multisession);
+@@ -466,7 +471,7 @@ unsigned struct_ElfW_Phdr_sz = sizeof(Elf_Phdr);
+   unsigned struct_vt_mode_sz = sizeof(struct vt_mode);
+ #endif // SANITIZER_LINUX || SANITIZER_FREEBSD
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   unsigned struct_ax25_parms_struct_sz = sizeof(struct ax25_parms_struct);
+   unsigned struct_cyclades_monitor_sz = sizeof(struct cyclades_monitor);
+ #if EV_VERSION > (0x010000)
+@@ -834,7 +839,7 @@ unsigned struct_ElfW_Phdr_sz = sizeof(Elf_Phdr);
+   unsigned IOCTL_VT_WAITACTIVE = VT_WAITACTIVE;
+ #endif // SANITIZER_LINUX || SANITIZER_FREEBSD
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   unsigned IOCTL_CYGETDEFTHRESH = CYGETDEFTHRESH;
+   unsigned IOCTL_CYGETDEFTIMEOUT = CYGETDEFTIMEOUT;
+   unsigned IOCTL_CYGETMON = CYGETMON;
+@@ -989,7 +994,7 @@ CHECK_SIZE_AND_OFFSET(dl_phdr_info, dlpi_phdr);
+ CHECK_SIZE_AND_OFFSET(dl_phdr_info, dlpi_phnum);
+ #endif // SANITIZER_LINUX || SANITIZER_FREEBSD
+ 
+-#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID
++#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ CHECK_TYPE_SIZE(glob_t);
+ CHECK_SIZE_AND_OFFSET(glob_t, gl_pathc);
+ CHECK_SIZE_AND_OFFSET(glob_t, gl_pathv);
+@@ -1023,6 +1028,7 @@ CHECK_TYPE_SIZE(iovec);
+ CHECK_SIZE_AND_OFFSET(iovec, iov_base);
+ CHECK_SIZE_AND_OFFSET(iovec, iov_len);
+ 
++#if !SANITIZER_NONGNU
+ CHECK_TYPE_SIZE(msghdr);
+ CHECK_SIZE_AND_OFFSET(msghdr, msg_name);
+ CHECK_SIZE_AND_OFFSET(msghdr, msg_namelen);
+@@ -1036,6 +1042,7 @@ CHECK_TYPE_SIZE(cmsghdr);
+ CHECK_SIZE_AND_OFFSET(cmsghdr, cmsg_len);
+ CHECK_SIZE_AND_OFFSET(cmsghdr, cmsg_level);
+ CHECK_SIZE_AND_OFFSET(cmsghdr, cmsg_type);
++#endif
+ 
+ #ifndef __GLIBC_PREREQ
+ #define __GLIBC_PREREQ(x, y) 0
+@@ -1145,7 +1152,7 @@ CHECK_SIZE_AND_OFFSET(mntent, mnt_passno);
+ 
+ CHECK_TYPE_SIZE(ether_addr);
+ 
+-#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID
++#if (SANITIZER_LINUX || SANITIZER_FREEBSD) && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ CHECK_TYPE_SIZE(ipc_perm);
+ # if SANITIZER_FREEBSD
+ CHECK_SIZE_AND_OFFSET(ipc_perm, key);
+@@ -1206,7 +1213,7 @@ CHECK_SIZE_AND_OFFSET(ifaddrs, ifa_dstaddr);
+ CHECK_SIZE_AND_OFFSET(ifaddrs, ifa_data);
+ #endif
+ 
+-#if SANITIZER_LINUX
++#if SANITIZER_LINUX && !SANITIZER_NONGNU
+ COMPILER_CHECK(sizeof(__sanitizer_mallinfo) == sizeof(struct mallinfo));
+ #endif
+ 
+@@ -1256,7 +1263,7 @@ COMPILER_CHECK(__sanitizer_XDR_DECODE == XDR_DECODE);
+ COMPILER_CHECK(__sanitizer_XDR_FREE == XDR_FREE);
+ #endif
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ COMPILER_CHECK(sizeof(__sanitizer_FILE) <= sizeof(FILE));
+ CHECK_SIZE_AND_OFFSET(FILE, _flags);
+ CHECK_SIZE_AND_OFFSET(FILE, _IO_read_ptr);
+@@ -1275,7 +1282,7 @@ CHECK_SIZE_AND_OFFSET(FILE, _chain);
+ CHECK_SIZE_AND_OFFSET(FILE, _fileno);
+ #endif
+ 
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+ COMPILER_CHECK(sizeof(__sanitizer__obstack_chunk) <= sizeof(_obstack_chunk));
+ CHECK_SIZE_AND_OFFSET(_obstack_chunk, limit);
+ CHECK_SIZE_AND_OFFSET(_obstack_chunk, prev);
+diff --git a/lib/tsan/rtl/tsan_platform_linux.cc b/lib/tsan/rtl/tsan_platform_linux.cc
+index de989b780..51a97b554 100644
+--- a/lib/tsan/rtl/tsan_platform_linux.cc
++++ b/lib/tsan/rtl/tsan_platform_linux.cc
+@@ -294,7 +294,7 @@ void InitializePlatform() {
+ // This is required to properly "close" the fds, because we do not see internal
+ // closes within glibc. The code is a pure hack.
+ int ExtractResolvFDs(void *state, int *fds, int nfd) {
+-#if SANITIZER_LINUX && !SANITIZER_ANDROID
++#if SANITIZER_LINUX && !SANITIZER_ANDROID && !SANITIZER_NONGNU
+   int cnt = 0;
+   struct __res_state *statp = (struct __res_state*)state;
+   for (int i = 0; i < MAXNS && cnt < nfd; i++) {
+-- 
+2.19.0
+
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 3797c308dcdc88..da8cc3b2dd42c9 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -8414,6 +8414,7 @@ in
     };
   };
 
+  clang_11 = llvmPackages_11.clang;
   clang_10 = llvmPackages_10.clang;
   clang_9  = llvmPackages_9.clang;
   clang_8  = llvmPackages_8.clang;
@@ -9230,6 +9231,7 @@ in
   lld_8 = llvmPackages_8.lld;
   lld_9 = llvmPackages_9.lld;
   lld_10 = llvmPackages_10.lld;
+  lld_11 = llvmPackages_11.lld;
 
   lldb = llvmPackages.lldb;
   lldb_5 = llvmPackages_5.lldb;
@@ -9238,10 +9240,12 @@ in
   lldb_8 = llvmPackages_8.lldb;
   lldb_9 = llvmPackages_9.lldb;
   lldb_10 = llvmPackages_10.lldb;
+  lldb_11 = llvmPackages_11.lldb;
 
   llvm = llvmPackages.llvm;
   llvm-manpages = llvmPackages.llvm-manpages;
 
+  llvm_11 = llvmPackages_11.llvm;
   llvm_10 = llvmPackages_10.llvm;
   llvm_9  = llvmPackages_9.llvm;
   llvm_8  = llvmPackages_8.llvm;
@@ -9287,6 +9291,14 @@ in
     targetLlvmLibraries = targetPackages.llvmPackages_10.libraries;
   };
 
+  llvmPackages_11 = callPackage ../development/compilers/llvm/11 ({
+    inherit (stdenvAdapters) overrideCC;
+    buildLlvmTools = buildPackages.llvmPackages_11.tools;
+    targetLlvmLibraries = targetPackages.llvmPackages_11.libraries;
+  } // stdenv.lib.optionalAttrs (stdenv.hostPlatform.isi686 && buildPackages.stdenv.cc.isGNU) {
+    stdenv = gcc7Stdenv;
+  });
+
   llvmPackages_latest = llvmPackages_10;
 
   llvmPackages_rocm = callPackage ../development/compilers/llvm/rocm { };