From 6ba1b5b0b3e57a7def4e837f5599aa3ac68589a8 Mon Sep 17 00:00:00 2001 From: Peter Waller Date: Tue, 1 Aug 2023 15:09:18 +0100 Subject: [PATCH 1/2] llvmPackages_15, llvmPackages_16: Make the pkgsLLVM.stdenv work What changed: * Fixed crtbeginS.o and crtendS.o missing (they may or may not be called crt{begin_end},{,_shared}. * Fixed implicit function declaration causing build errors for various builds by supplying -Wno-implicit-function-declaration. * Fixed __cxxabi_config.h missing, by adding -I${cxxabi}/include/c++/v1 in the wrapper. * Fixed libcxx failing to build due to missing libunwind symbols by including libunwind as a buildInput, and setting -DLIBCXX_ADDITIONAL_LIBRARIES=unwind for stdenv.hostPlatform.useLLVM == true. * libcxxabi wants to find libunwind at libunwind_shared.so, so symlink it there in libunwind. * llvmPackages_16.libcxxabi: Pass -nostdlib via CMAKE_*_LINKER_FLAGS Without this flag, the link of libcxxabi.so tries to pull in libgcc and friends, from the clang compiler driver. * Drop unneeded musl hack patch from libcxx. * Pass -Wno-error=implicit-function-declaration only to compiler-rt See LLVM forum discussion: https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213 In summary, LLVM 16 made implicit function declaration an error. This happens a lot in configure scripts which can break things. * llvmPackages_16: !isDarwin: Supply -DLIBCXX_ABI_USE_LLVM_UNWINDER=On Otherwise it fails with various undefined references to _Unwind_* functions: (full list: _Unwind_DeleteException _Unwind_GetIP _Unwind_GetLanguageSpecificData _Unwind_GetRegionStart _Unwind_RaiseException _Unwind_Resume _Unwind_SetGR _Unwind_SetIP). * 16.libcxxabi: Only pass -nostdlib for useLLVM and Darwin builds What was tested: * x86_64-linux, aarch64-linux, the stdenv builds. * Additionally I was able to get nix to build, with an overlay to fix a couple of minor issues in downstream packages (overlay supplied in PR #246577. * aarch64-darwin fails spuriously in a single LLVM test strip-preserve-atime.test checking atime timestamps. * The same for pkgsLLVM with llvmPackages = llvmPackages_15. Signed-off-by: Peter Waller --- .../compilers/llvm/15/libcxx/default.nix | 20 ++++++++++++++---- .../compilers/llvm/15/libcxxabi/default.nix | 7 +++++++ .../compilers/llvm/15/libunwind/default.nix | 5 +++++ .../compilers/llvm/16/compiler-rt/default.nix | 19 ++++++++++++++--- .../development/compilers/llvm/16/default.nix | 8 +++++++ .../compilers/llvm/16/libcxx/default.nix | 19 +++++++++++------ .../compilers/llvm/16/libcxxabi/default.nix | 7 +++++++ .../compilers/llvm/16/libunwind/default.nix | 5 +++++ .../compilers/llvm/git/libcxx/default.nix | 21 +++++++++++++++---- .../compilers/llvm/git/libcxxabi/default.nix | 7 +++++++ .../compilers/llvm/git/libunwind/default.nix | 5 +++++ 11 files changed, 106 insertions(+), 17 deletions(-) diff --git a/pkgs/development/compilers/llvm/15/libcxx/default.nix b/pkgs/development/compilers/llvm/15/libcxx/default.nix index 94374c8a312df..cc4e9bc830584 100644 --- a/pkgs/development/compilers/llvm/15/libcxx/default.nix +++ b/pkgs/development/compilers/llvm/15/libcxx/default.nix @@ -2,7 +2,7 @@ , monorepoSrc, runCommand , cmake, ninja, python3, fixDarwinDylibNames, version , cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else libcxxabi -, libcxxabi, libcxxrt +, libcxxabi, libcxxrt, libunwind , enableShared ? !stdenv.hostPlatform.isStatic # If headersOnly is true, the resulting package would only include the headers. @@ -62,7 +62,9 @@ stdenv.mkDerivation rec { nativeBuildInputs = [ cmake ninja python3 ] ++ lib.optional stdenv.isDarwin fixDarwinDylibNames; - buildInputs = lib.optionals (!headersOnly) [ cxxabi ]; + buildInputs = + lib.optionals (!headersOnly) [ cxxabi ] + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ libunwind ]; cmakeFlags = let # See: https://libcxx.llvm.org/BuildingLibcxx.html#cmdoption-arg-libcxx-cxx-abi-string @@ -75,8 +77,18 @@ stdenv.mkDerivation rec { "-DLIBCXX_CXX_ABI=${if headersOnly then "none" else libcxx_cxx_abi_opt}" ] ++ lib.optional (!headersOnly && cxxabi.libName == "c++abi") "-DLIBCXX_CXX_ABI_INCLUDE_PATHS=${cxxabi.dev}/include/c++/v1" ++ lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1" - ++ lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON" - ++ lib.optionals stdenv.hostPlatform.isWasm [ + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ + "-DLIBCXX_USE_COMPILER_RT=ON" + # (Backport fix from 16, which has LIBCXX_ADDITIONAL_LIBRARIES, but 15 + # does not appear to) + # There's precedent for this in llvm-project/libcxx/cmake/caches. + # In a monorepo build you might do the following in the libcxxabi build: + # -DLLVM_ENABLE_PROJECTS=libcxxabi;libunwind + # -DLIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY=On + # libcxx appears to require unwind and doesn't pull it in via other means. + # "-DLIBCXX_ADDITIONAL_LIBRARIES=unwind" + "-DCMAKE_SHARED_LINKER_FLAGS=-lunwind" + ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXX_ENABLE_THREADS=OFF" "-DLIBCXX_ENABLE_FILESYSTEM=OFF" "-DLIBCXX_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/15/libcxxabi/default.nix b/pkgs/development/compilers/llvm/15/libcxxabi/default.nix index cb5fa44f07009..692a0256e901a 100644 --- a/pkgs/development/compilers/llvm/15/libcxxabi/default.nix +++ b/pkgs/development/compilers/llvm/15/libcxxabi/default.nix @@ -68,6 +68,13 @@ stdenv.mkDerivation rec { ] ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ "-DLLVM_ENABLE_LIBCXX=ON" "-DLIBCXXABI_USE_LLVM_UNWINDER=ON" + ] ++ lib.optionals ((stdenv.hostPlatform.useLLVM or false) || + (stdenv.hostPlatform.isDarwin && enableShared)) [ + # libcxxabi's CMake looks as though it treats -nostdlib++ as implying -nostdlib, + # but that does not appear to be the case for example when building + # pkgsLLVM.libcxxabi (which uses clangNoCompilerRtWithLibc). + "-DCMAKE_EXE_LINKER_FLAGS=-nostdlib" + "-DCMAKE_SHARED_LINKER_FLAGS=-nostdlib" ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXXABI_ENABLE_THREADS=OFF" "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/15/libunwind/default.nix b/pkgs/development/compilers/llvm/15/libunwind/default.nix index dd14e2acaf869..1b677a7a2c0d7 100644 --- a/pkgs/development/compilers/llvm/15/libunwind/default.nix +++ b/pkgs/development/compilers/llvm/15/libunwind/default.nix @@ -40,6 +40,11 @@ stdenv.mkDerivation rec { cd ../runtimes ''; + postInstall = lib.optionalString (enableShared && !stdenv.hostPlatform.isDarwin) '' + # libcxxabi wants to link to libunwind_shared.so (?). + ln -s $out/lib/libunwind.so $out/lib/libunwind_shared.so + ''; + outputs = [ "out" "dev" ]; nativeBuildInputs = [ cmake ninja python3 ]; diff --git a/pkgs/development/compilers/llvm/16/compiler-rt/default.nix b/pkgs/development/compilers/llvm/16/compiler-rt/default.nix index aa248c0e60eba..fc0d7533c9949 100644 --- a/pkgs/development/compilers/llvm/16/compiler-rt/default.nix +++ b/pkgs/development/compilers/llvm/16/compiler-rt/default.nix @@ -32,9 +32,16 @@ stdenv.mkDerivation { ++ lib.optional stdenv.isDarwin xcbuild.xcrun; buildInputs = lib.optional stdenv.hostPlatform.isDarwin libcxxabi; - env.NIX_CFLAGS_COMPILE = toString [ + env.NIX_CFLAGS_COMPILE = toString ([ "-DSCUDO_DEFAULT_OPTIONS=DeleteSizeMismatch=0:DeallocationTypeMismatch=0" - ]; + ] ++ lib.optionals (!haveLibc) [ + # The compiler got stricter about this, and there is a usellvm patch below + # which patches out the assert include causing an implicit definition of + # assert. It would be nicer to understand why compiler-rt thinks it should + # be able to #include in the first place; perhaps it's in the + # wrong, or perhaps there is a way to provide an assert.h. + "-Wno-error=implicit-function-declaration" + ]); cmakeFlags = [ "-DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON" @@ -102,7 +109,7 @@ stdenv.mkDerivation { '' + lib.optionalString stdenv.isDarwin '' substituteInPlace cmake/config-ix.cmake \ --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)' - '' + lib.optionalString (useLLVM) '' + '' + lib.optionalString (useLLVM && !haveLibc) '' substituteInPlace lib/builtins/int_util.c \ --replace "#include " "" substituteInPlace lib/builtins/clear_cache.c \ @@ -117,6 +124,12 @@ stdenv.mkDerivation { '' + 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 + # Note the history of crt{begin,end}S in previous versions of llvm in nixpkg: + # The presence of crtbegin_shared has been added and removed; it's possible + # people have added/removed it to get it working on their platforms. + # Try each in turn for now. + ln -s $out/lib/*/clang_rt.crtbegin-*.o $out/lib/crtbeginS.o + ln -s $out/lib/*/clang_rt.crtend-*.o $out/lib/crtendS.o ln -s $out/lib/*/clang_rt.crtbegin_shared-*.o $out/lib/crtbeginS.o ln -s $out/lib/*/clang_rt.crtend_shared-*.o $out/lib/crtendS.o '' + lib.optionalString doFakeLibgcc '' diff --git a/pkgs/development/compilers/llvm/16/default.nix b/pkgs/development/compilers/llvm/16/default.nix index 0c0ff44e155f8..d9a363037a920 100644 --- a/pkgs/development/compilers/llvm/16/default.nix +++ b/pkgs/development/compilers/llvm/16/default.nix @@ -254,6 +254,14 @@ in let [ "-rtlib=compiler-rt" "-Wno-unused-command-line-argument" "-B${targetLlvmLibraries.compiler-rt}/lib" + + # Combat "__cxxabi_config.h not found". Maybe this could be fixed by + # copying these headers into libcxx? Note that building libcxx + # outside of monorepo isn't supported anymore, might be related to + # https://github.com/llvm/llvm-project/issues/55632 + # ("16.0.3 libcxx, libcxxabi: circular build dependencies") + # Looks like the machinery changed in https://reviews.llvm.org/D120727. + "-I${lib.getDev targetLlvmLibraries.libcxx.cxxabi}/include/c++/v1" ] ++ lib.optional (!stdenv.targetPlatform.isWasm) "--unwindlib=libunwind" ++ lib.optional diff --git a/pkgs/development/compilers/llvm/16/libcxx/default.nix b/pkgs/development/compilers/llvm/16/libcxx/default.nix index 94374c8a312df..c387764b4f650 100644 --- a/pkgs/development/compilers/llvm/16/libcxx/default.nix +++ b/pkgs/development/compilers/llvm/16/libcxx/default.nix @@ -2,7 +2,7 @@ , monorepoSrc, runCommand , cmake, ninja, python3, fixDarwinDylibNames, version , cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else libcxxabi -, libcxxabi, libcxxrt +, libcxxabi, libcxxrt, libunwind , enableShared ? !stdenv.hostPlatform.isStatic # If headersOnly is true, the resulting package would only include the headers. @@ -47,8 +47,6 @@ stdenv.mkDerivation rec { patches = [ ./gnu-install-dirs.patch - ] ++ lib.optionals stdenv.hostPlatform.isMusl [ - ../../libcxx-0001-musl-hacks.patch ]; postPatch = '' @@ -62,7 +60,9 @@ stdenv.mkDerivation rec { nativeBuildInputs = [ cmake ninja python3 ] ++ lib.optional stdenv.isDarwin fixDarwinDylibNames; - buildInputs = lib.optionals (!headersOnly) [ cxxabi ]; + buildInputs = + lib.optionals (!headersOnly) [ cxxabi ] + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ libunwind ]; cmakeFlags = let # See: https://libcxx.llvm.org/BuildingLibcxx.html#cmdoption-arg-libcxx-cxx-abi-string @@ -75,8 +75,15 @@ stdenv.mkDerivation rec { "-DLIBCXX_CXX_ABI=${if headersOnly then "none" else libcxx_cxx_abi_opt}" ] ++ lib.optional (!headersOnly && cxxabi.libName == "c++abi") "-DLIBCXX_CXX_ABI_INCLUDE_PATHS=${cxxabi.dev}/include/c++/v1" ++ lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1" - ++ lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON" - ++ lib.optionals stdenv.hostPlatform.isWasm [ + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ + "-DLIBCXX_USE_COMPILER_RT=ON" + # There's precedent for this in llvm-project/libcxx/cmake/caches. + # In a monorepo build you might do the following in the libcxxabi build: + # -DLLVM_ENABLE_PROJECTS=libcxxabi;libunwinder + # -DLIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY=On + # libcxx appears to require unwind and doesn't pull it in via other means. + "-DLIBCXX_ADDITIONAL_LIBRARIES=unwind" + ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXX_ENABLE_THREADS=OFF" "-DLIBCXX_ENABLE_FILESYSTEM=OFF" "-DLIBCXX_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/16/libcxxabi/default.nix b/pkgs/development/compilers/llvm/16/libcxxabi/default.nix index cb5fa44f07009..692a0256e901a 100644 --- a/pkgs/development/compilers/llvm/16/libcxxabi/default.nix +++ b/pkgs/development/compilers/llvm/16/libcxxabi/default.nix @@ -68,6 +68,13 @@ stdenv.mkDerivation rec { ] ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ "-DLLVM_ENABLE_LIBCXX=ON" "-DLIBCXXABI_USE_LLVM_UNWINDER=ON" + ] ++ lib.optionals ((stdenv.hostPlatform.useLLVM or false) || + (stdenv.hostPlatform.isDarwin && enableShared)) [ + # libcxxabi's CMake looks as though it treats -nostdlib++ as implying -nostdlib, + # but that does not appear to be the case for example when building + # pkgsLLVM.libcxxabi (which uses clangNoCompilerRtWithLibc). + "-DCMAKE_EXE_LINKER_FLAGS=-nostdlib" + "-DCMAKE_SHARED_LINKER_FLAGS=-nostdlib" ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXXABI_ENABLE_THREADS=OFF" "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/16/libunwind/default.nix b/pkgs/development/compilers/llvm/16/libunwind/default.nix index dd14e2acaf869..1b677a7a2c0d7 100644 --- a/pkgs/development/compilers/llvm/16/libunwind/default.nix +++ b/pkgs/development/compilers/llvm/16/libunwind/default.nix @@ -40,6 +40,11 @@ stdenv.mkDerivation rec { cd ../runtimes ''; + postInstall = lib.optionalString (enableShared && !stdenv.hostPlatform.isDarwin) '' + # libcxxabi wants to link to libunwind_shared.so (?). + ln -s $out/lib/libunwind.so $out/lib/libunwind_shared.so + ''; + outputs = [ "out" "dev" ]; nativeBuildInputs = [ cmake ninja python3 ]; diff --git a/pkgs/development/compilers/llvm/git/libcxx/default.nix b/pkgs/development/compilers/llvm/git/libcxx/default.nix index 94374c8a312df..f267b753b24ab 100644 --- a/pkgs/development/compilers/llvm/git/libcxx/default.nix +++ b/pkgs/development/compilers/llvm/git/libcxx/default.nix @@ -2,7 +2,7 @@ , monorepoSrc, runCommand , cmake, ninja, python3, fixDarwinDylibNames, version , cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else libcxxabi -, libcxxabi, libcxxrt +, libcxxabi, libcxxrt, libunwind , enableShared ? !stdenv.hostPlatform.isStatic # If headersOnly is true, the resulting package would only include the headers. @@ -62,7 +62,10 @@ stdenv.mkDerivation rec { nativeBuildInputs = [ cmake ninja python3 ] ++ lib.optional stdenv.isDarwin fixDarwinDylibNames; - buildInputs = lib.optionals (!headersOnly) [ cxxabi ]; + buildInputs = + lib.optionals (!headersOnly) [ cxxabi ] + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ libunwind ]; + cmakeFlags = let # See: https://libcxx.llvm.org/BuildingLibcxx.html#cmdoption-arg-libcxx-cxx-abi-string @@ -75,8 +78,18 @@ stdenv.mkDerivation rec { "-DLIBCXX_CXX_ABI=${if headersOnly then "none" else libcxx_cxx_abi_opt}" ] ++ lib.optional (!headersOnly && cxxabi.libName == "c++abi") "-DLIBCXX_CXX_ABI_INCLUDE_PATHS=${cxxabi.dev}/include/c++/v1" ++ lib.optional (stdenv.hostPlatform.isMusl || stdenv.hostPlatform.isWasi) "-DLIBCXX_HAS_MUSL_LIBC=1" - ++ lib.optional (stdenv.hostPlatform.useLLVM or false) "-DLIBCXX_USE_COMPILER_RT=ON" - ++ lib.optionals stdenv.hostPlatform.isWasm [ + ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ + "-DLIBCXX_USE_COMPILER_RT=ON" + # (Backport fix from 16, which has LIBCXX_ADDITIONAL_LIBRARIES, but 15 + # does not appear to) + # There's precedent for this in llvm-project/libcxx/cmake/caches. + # In a monorepo build you might do the following in the libcxxabi build: + # -DLLVM_ENABLE_PROJECTS=libcxxabi;libunwinder + # -DLIBCXXABI_STATICALLY_LINK_UNWINDER_IN_STATIC_LIBRARY=On + # libcxx appears to require unwind and doesn't pull it in via other means. + # "-DLIBCXX_ADDITIONAL_LIBRARIES=unwind" + "-DCMAKE_SHARED_LINKER_FLAGS=-lunwind" + ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXX_ENABLE_THREADS=OFF" "-DLIBCXX_ENABLE_FILESYSTEM=OFF" "-DLIBCXX_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/git/libcxxabi/default.nix b/pkgs/development/compilers/llvm/git/libcxxabi/default.nix index 65c585181a702..51020fcdb0caf 100644 --- a/pkgs/development/compilers/llvm/git/libcxxabi/default.nix +++ b/pkgs/development/compilers/llvm/git/libcxxabi/default.nix @@ -68,6 +68,13 @@ stdenv.mkDerivation rec { ] ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [ "-DLLVM_ENABLE_LIBCXX=ON" "-DLIBCXXABI_USE_LLVM_UNWINDER=ON" + ] ++ lib.optionals ((stdenv.hostPlatform.useLLVM or false) || + (stdenv.hostPlatform.isDarwin && enableShared)) [ + # libcxxabi's CMake looks as though it treats -nostdlib++ as implying -nostdlib, + # but that does not appear to be the case for example when building + # pkgsLLVM.libcxxabi (which uses clangNoCompilerRtWithLibc). + "-DCMAKE_EXE_LINKER_FLAGS=-nostdlib" + "-DCMAKE_SHARED_LINKER_FLAGS=-nostdlib" ] ++ lib.optionals stdenv.hostPlatform.isWasm [ "-DLIBCXXABI_ENABLE_THREADS=OFF" "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF" diff --git a/pkgs/development/compilers/llvm/git/libunwind/default.nix b/pkgs/development/compilers/llvm/git/libunwind/default.nix index dd14e2acaf869..1b677a7a2c0d7 100644 --- a/pkgs/development/compilers/llvm/git/libunwind/default.nix +++ b/pkgs/development/compilers/llvm/git/libunwind/default.nix @@ -40,6 +40,11 @@ stdenv.mkDerivation rec { cd ../runtimes ''; + postInstall = lib.optionalString (enableShared && !stdenv.hostPlatform.isDarwin) '' + # libcxxabi wants to link to libunwind_shared.so (?). + ln -s $out/lib/libunwind.so $out/lib/libunwind_shared.so + ''; + outputs = [ "out" "dev" ]; nativeBuildInputs = [ cmake ninja python3 ]; From 044e8c4e443c6f5c9e4a8f763c6e6314bf90732c Mon Sep 17 00:00:00 2001 From: Peter Waller Date: Mon, 21 Aug 2023 13:02:04 +0100 Subject: [PATCH 2/2] llvmPackages_git: Port stdenv fix for cxx-headers Signed-off-by: Peter Waller --- pkgs/development/compilers/llvm/git/default.nix | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/pkgs/development/compilers/llvm/git/default.nix b/pkgs/development/compilers/llvm/git/default.nix index 8cf311e9b23ac..5ec5d35dcec51 100644 --- a/pkgs/development/compilers/llvm/git/default.nix +++ b/pkgs/development/compilers/llvm/git/default.nix @@ -313,6 +313,19 @@ in let # what stdenv we use here, as long as CMake is happy. cxx-headers = callPackage ./libcxx { inherit llvm_meta; + # Note that if we use the regular stdenv here we'll get cycle errors + # when attempting to use this compiler in the stdenv. + # + # The final stdenv pulls `cxx-headers` from the package set where + # hostPlatform *is* the target platform which means that `stdenv` at + # that point attempts to use this toolchain. + # + # So, we use `stdenv_` (the stdenv containing `clang` from this package + # set, defined below) to sidestep this issue. + # + # Because we only use `cxx-headers` in `libcxxabi` (which depends on the + # clang stdenv _anyways_), this is okay. + stdenv = stdenv_; headersOnly = true; };