Runtime builds for multiple targets

Runtimes
1

I trying to build a clang (tag: llvmorg-14.0.0) toolchain with corresponding runtimes for x86_64-pc-linux-gnu and i386-pc-linux-gnu but I am running into some issues. The current cmake call looks like:

cmake \
  -G "Ninja" \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=tmp_install \
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld" \
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
  -DLLVM_RUNTIME_TARGETS="x86_64-pc-linux-gnu;i386-pc-linux-gnu" \
  -DLLVM_TARGETS_TO_BUILD="AArch64;ARM;X86" \
  -DLLVM_HOST_TRIPLE="x86_64-pc-linux-gnu" \
  -DLLVM_DEFAULT_TARGET_TRIPLE="x86_64-pc-linux-gnu" \
  -DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR=ON \
  -DLIBCXX_USE_COMPILER_RT=ON \
  -DLIBCXXABI_USE_COMPILER_RT=ON \
  -DLIBCXXABI_USE_LLVM_UNWINDER=ON \
  -DLLVM_VERSION_SUFFIX="-1" \
  -DLLVM_PARALLEL_LINK_JOBS="1" \
  -DLLVM_PARALLEL_COMPILE_JOBS="4" \
  -S $SRC_DIR/llvm-project/llvm \
  -B $WORKSPACE_DIR/build/x86_64-pc-linux-gnu/llvm

  1. The first issue is that the flags LIBCXX_USE_COMPILER_RT, LIBCXXABI_USE_LLVM_UNWINDER and LIBCXXABI_USE_LLVM_UNWINDER are not considered by the runtime builds. The cmake cache $WORKSPACE_DIR/build/x86_64-pc-linux-gnu/llvm/runtimes/runtimes-x86_64-pc-linux-gnu-bins/CMakeCache.txt contains for example LIBCXX_USE_COMPILER_RT:BOOL=OFF.

  2. The second issue is that the i386-pc-linux-gnu runtime build is failing because the SANITIZER_ALLOW_CXXABI flag is on regarding the cache and that leads to some linker issues with unresolved symbols.

I would be very grateful for further help.

2

The various cmake options for all of the runtime builds are not forwarded from the main built. For that reason you likely should have gotten a warning by CMake that they did not have any impact.

The way to solve this is by prefixing the cmake options with BUILTINS_${target}_<option> for the builtins built in compiler-rt, and RUNTIMES_${target}_<option> for any of the other runtimes build.
In your case that’d eg. be -DRUNTIMES_x86_64-pc-linux-gnu_LIBCXX_USE_COMPILER_RT=ON -DRUNTIMES_i386-pc-linux-gnu_LIBCXX_USE_COMPILER_RT=ON instead of -DLIBCXX_USE_COMPILER_RT=ON.
These options are then forwarded to the respective runtime build for the respective target.

As you can imagine, this turns into a big command line very quickly. One way to mitigate this issue a bit is by creating a *.cmake file that simply sets all those options using normal cmake syntax and then using it with the -C option of cmake. That basically runs that file to pre populate the cache with those options before configuring.

The best in tree example of this that I have always used to configure my runtime builds are the Fuchsia configure caches: llvm-project/Fuchsia.cmake at main · llvm/llvm-project · GitHub
But the other files in that directory should be of just as great of a help.