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llvmPackages_15.libcxx: use clang 15 instead of the stdenv's compiler

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libc++ has switched to using `__attribute__((using_if_exists))` to handle
incomplete libc implementations; see: a9c9183ca4

These essentially require a modern C++ compiler (clang gained support in
LLVM 13: 369c648399,
gcc appears to not have support yet: https://gcc.gnu.org/bugzilla//show_bug.cgi?id=105584).

Previously this was not an issue for us (despite the transition happening
around LLVM 13) but something about the changes to the libc++/libc++-abi
build has made it so that on platforms with incomplete libc impls (i.e.
Darwin is missing `quick_exit`/`at_quick_exit`) we error during the `libcxx-abi`
build when the stdenv's (older, not supporting `using_if_exists`) compiler
tries to import libc symbols that aren't present.

The libc++ docs suggest we use a modern compiler to build libc++ anyways
(https://releases.llvm.org/15.0.0/projects/libcxx/docs/index.html#platform-and-compiler-support)
so this commit uses stdenv's containing the package set's clang to build
libcxx/libcxx-abi.

This is similar to how libc++ bootstrapping builds (https://releases.llvm.org/15.0.0/projects/libcxx/docs/BuildingLibcxx.html#bootstrapping-build)
work.
This commit is contained in:
Rahul Butani 2022-10-07 15:22:55 -05:00
parent 4fabcf4945
commit ca59a201ca
No known key found for this signature in database
2 changed files with 30 additions and 11 deletions
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34
pkgs/development/compilers/llvm/15/default.nix
View File

@ -247,27 +247,39 @@ let
libcxxStdenv = overrideCC stdenv buildLlvmTools.libcxxClang;
libcxx = callPackage ./libcxx {
inherit llvm_meta;
stdenv = if stdenv.hostPlatform.useLLVM or false
then overrideCC stdenv buildLlvmTools.clangNoLibcxx
else stdenv;
};
libcxxabi = let
stdenv_ = if stdenv.hostPlatform.useLLVM or false
then overrideCC stdenv buildLlvmTools.clangNoLibcxx
else stdenv;
# CMake will "require" a compiler capable of compiling C++ programs
# cxx-header's build does not actually use one so it doesn't really matter
# what stdenv we use here, as long as CMake is happy.
cxx-headers = callPackage ./libcxx {
inherit llvm_meta;
stdenv = stdenv_;
headersOnly = true;
};
# `libcxxabi` *doesn't* need a compiler with a working C++ stdlib but it
# *does* need a relatively modern C++ compiler (see:
# https://releases.llvm.org/15.0.0/projects/libcxx/docs/index.html#platform-and-compiler-support).
#
# So, we use the clang from this LLVM package set, like libc++
# "boostrapping builds" do:
# https://releases.llvm.org/15.0.0/projects/libcxx/docs/BuildingLibcxx.html#bootstrapping-build
#
# We cannot use `clangNoLibcxx` because that contains `compiler-rt` which,
# on macOS, depends on `libcxxabi`, thus forming a cycle.
stdenv_ = overrideCC stdenv buildLlvmTools.clangNoCompilerRtWithLibc;
in callPackage ./libcxxabi {
stdenv = stdenv_;
inherit llvm_meta cxx-headers;
};
# Like `libcxxabi` above, `libcxx` requires a fairly modern C++ compiler,
# so: we use the clang from this LLVM package set instead of the regular
# stdenv's compiler.
libcxx = callPackage ./libcxx {
inherit llvm_meta;
stdenv = overrideCC stdenv buildLlvmTools.clangNoLibcxx;
};
libunwind = callPackage ./libunwind {
inherit llvm_meta;
stdenv = overrideCC stdenv buildLlvmTools.clangNoLibcxx;

7
pkgs/development/compilers/llvm/15/libcxxabi/default.nix
View File

@ -58,6 +58,13 @@ stdenv.mkDerivation rec {
cmakeFlags = [
"-DLLVM_ENABLE_RUNTIMES=libcxxabi"
"-DLIBCXXABI_LIBCXX_INCLUDES=${cxx-headers}/include/c++/v1"
# `libcxxabi`'s build does not need a toolchain with a c++ stdlib attached
# (we specify the headers it should use explicitly above).
#
# CMake however checks for this anyways; this flag tells it not to. See:
# https://github.com/llvm/llvm-project/blob/4bd3f3759259548e159aeba5c76efb9a0864e6fa/llvm/runtimes/CMakeLists.txt#L243
"-DCMAKE_CXX_COMPILER_WORKS=ON"
] ++ lib.optionals (stdenv.hostPlatform.useLLVM or false) [
"-DLLVM_ENABLE_LIBCXX=ON"
"-DLIBCXXABI_USE_LLVM_UNWINDER=ON"