llvm8: support c++ in cross case

this adds libc++ to the LLVM cross, giving us access to the full
Nixpkgs set. This requires 4 stages of wrapped compilers:

- Clang with no libraries
- Clang with just compiler-rt
- Clang with Libc, and compiler-rt
- Clang with Libc++, Libc, and compiler-rt

5 files changed, 89 insertions, 19 deletions

diff --git a/pkgs/development/compilers/llvm/8/compiler-rt.nix b/pkgs/development/compilers/llvm/8/compiler-rt.nix
index 4965b57b0d73..47c8b7bd59f5 100644
--- a/pkgs/development/compilers/llvm/8/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/8/compiler-rt.nix
@@ -55,9 +55,9 @@ stdenv.mkDerivation rec {
   # Hack around weird upsream RPATH bug
   postInstall = stdenv.lib.optionalString stdenv.isDarwin ''
     ln -s "$out/lib"/*/* "$out/lib"
-  '' + stdenv.lib.optionalString (stdenv.hostPlatform != stdenv.buildPlatform) ''
+  '' + stdenv.lib.optionalString (stdenv.hostPlatform.useLLVM or false) ''
     ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbegin.o
-    ln -s $out/lib/*/cclang_rt.crtend-*.o $out/lib/crtend.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 $out/lib/crtendS.o
   '';
diff --git a/pkgs/development/compilers/llvm/8/default.nix b/pkgs/development/compilers/llvm/8/default.nix
index c5f2163450fe..5cd3bdfbe7b6 100644
--- a/pkgs/development/compilers/llvm/8/default.nix
+++ b/pkgs/development/compilers/llvm/8/default.nix
@@ -23,7 +23,7 @@ let
       ln -s "${cc}/lib/clang/${release_version}/include" "$rsrc"
       ln -s "${targetLlvmLibraries.compiler-rt.out}/lib" "$rsrc/lib"
       echo "-resource-dir=$rsrc" >> $out/nix-support/cc-cflags
-    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc) ''
+    '' + stdenv.lib.optionalString (stdenv.targetPlatform.isLinux && tools.clang-unwrapped ? gcc && !(stdenv.targetPlatform.useLLVM or false)) ''
       echo "--gcc-toolchain=${tools.clang-unwrapped.gcc}" >> $out/nix-support/cc-cflags
     '';
   in {
@@ -78,48 +78,78 @@ 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.compiler-rt
+      ];
+      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
+      '' + mkExtraBuildCommands cc;
+    };
+
+    lldClangNoLibcxx = wrapCCWith rec {
+      cc = tools.clang-unwrapped;
+      libcxx = null;
       bintools = wrapBintoolsWith {
         inherit (tools) bintools;
       };
       extraPackages = [
-        # targetLlvmLibraries.libcxx
-        # targetLlvmLibraries.libcxxabi
         targetLlvmLibraries.compiler-rt
       ];
       extraBuildCommands = ''
-        echo "-target ${stdenv.targetPlatform.config} -rtlib=compiler-rt" >> $out/nix-support/cc-cflags
+        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
       '' + 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 "-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;
     };
 
     lldClangNoCompilerRt = wrapCCWith rec {
       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
+        echo "-target ${stdenv.targetPlatform.config}" >> $out/nix-support/cc-cflags
       '';
     };
 
@@ -129,21 +159,33 @@ let
     callPackage = newScope (libraries // buildLlvmTools // { inherit stdenv cmake libxml2 python isl release_version version fetch; });
   in {
 
-    compiler-rt = callPackage ./compiler-rt.nix {
-      stdenv = if stdenv.hostPlatform.useLLVM or false
-               then overrideCC stdenv buildLlvmTools.lldClangNoCompilerRt
-               else stdenv;
-    };
+    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++ {};
+    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 {};
+
+    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/8/libc++/default.nix b/pkgs/development/compilers/llvm/8/libc++/default.nix
index 84db33209ebd..d0a5c37c4148 100644
--- a/pkgs/development/compilers/llvm/8/libc++/default.nix
+++ b/pkgs/development/compilers/llvm/8/libc++/default.nix
@@ -30,7 +30,8 @@ stdenv.mkDerivation rec {
     "-DLIBCXX_LIBCXXABI_LIB_PATH=${libcxxabi}/lib"
     "-DLIBCXX_LIBCPPABI_VERSION=2"
     "-DLIBCXX_CXX_ABI=libcxxabi"
-  ] ++ stdenv.lib.optional stdenv.hostPlatform.isMusl "-DLIBCXX_HAS_MUSL_LIBC=1";
+  ] ++ stdenv.lib.optional stdenv.hostPlatform.isMusl "-DLIBCXX_HAS_MUSL_LIBC=1"
+    ++ stdenv.lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON";
 
   enableParallelBuilding = true;
 
diff --git a/pkgs/development/compilers/llvm/8/libc++abi.nix b/pkgs/development/compilers/llvm/8/libc++abi.nix
index 976c289e5bc5..0eb5ebca5159 100644
--- a/pkgs/development/compilers/llvm/8/libc++abi.nix
+++ b/pkgs/development/compilers/llvm/8/libc++abi.nix
@@ -8,10 +8,15 @@ stdenv.mkDerivation {
   nativeBuildInputs = [ cmake ];
   buildInputs = stdenv.lib.optional (!stdenv.isDarwin && !stdenv.isFreeBSD) libunwind;
 
+  cmakeFlags = stdenv.lib.optionals (stdenv.hostPlatform.useLLVM or false) [
+    "-DLLVM_ENABLE_LIBCXX=ON"
+    "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
+  ];
+
   postUnpack = ''
     unpackFile ${libcxx.src}
     unpackFile ${llvm.src}
-    export cmakeFlags="-DLLVM_PATH=$PWD/$(ls -d llvm-*) -DLIBCXXABI_LIBCXX_PATH=$PWD/$(ls -d libcxx-*)"
+    cmakeFlags+=" -DLLVM_PATH=$PWD/$(ls -d llvm-*) -DLIBCXXABI_LIBCXX_PATH=$PWD/$(ls -d libcxx-*)"
   '' + stdenv.lib.optionalString stdenv.isDarwin ''
     export TRIPLE=x86_64-apple-darwin
   '' + stdenv.lib.optionalString stdenv.hostPlatform.isMusl ''
diff --git a/pkgs/development/compilers/llvm/8/libunwind.nix b/pkgs/development/compilers/llvm/8/libunwind.nix
new file mode 100644
index 000000000000..a187d0adc994
--- /dev/null
+++ b/pkgs/development/compilers/llvm/8/libunwind.nix
@@ -0,0 +1,22 @@
+{ stdenv, version, fetch, cmake, libcxx, fetchpatch }:
+
+stdenv.mkDerivation {
+  name = "libunwind-${version}";
+
+  src = fetch "libunwind" "0q7ndlldid9wchnny0a936llwxj7zgb9gxp46wjjxvwwkik3l97z";
+
+  nativeBuildInputs = [ cmake ];
+
+  patches = [
+    (fetchpatch {
+      url = "https://github.com/llvm-mirror/libunwind/commit/34a45c630d4c79af403661d267db42fbe7de1178.patch";
+      sha256 = "0n0pv6jvcky8pn3srhrf9x5kbnd0d2kia9xlx2g590f5q0bgwfhv";
+    })
+    (fetchpatch {
+      url = "https://github.com/llvm-mirror/libunwind/commit/e050272d2eb57eb4e56a37b429a61df2ebb8aa3e.patch";
+      sha256 = "1sxyx5xnax8k713jjcxgq3jq3cpnxygs2rcdf5vfja0f2k9jzldl";
+    })
+  ];
+
+  enableParallelBuilding = true;
+}