runtimes builds may fail due to missing llvm-link despite llvm being enabled

[nolongerwait]

Hi, all

llvm-project version: 20.1.4

I'm running a monorepo CMake build using both LLVM_ENABLE_PROJECTS and LLVM_ENABLE_RUNTIMES, and I'm seeing an issue where the compiler-rt runtime fails to build due to a missing llvm-link binary, even though llvm is explicitly listed in LLVM_ENABLE_PROJECTS.

Here is my CMake invocation:

cmake -G Ninja \
  -DCMAKE_C_COMPILER="${TOOLCHAIN_GCC_INSTALL_DIR}/bin/gcc" \
  -DCMAKE_CXX_COMPILER="${TOOLCHAIN_GCC_INSTALL_DIR}/bin/g++" \
  -DLLVM_ENABLE_PROJECTS="clang;llvm;clang-tools-extra;lld;lldb;openmp" \
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx;libcxxabi;libunwind" \
  -DLLVM_TARGETS_TO_BUILD="${LLVM_ARCH}" \
  -DLLVM_RUNTIME_TARGETS="default;${LLVM_RUNTIME_ARCH}" \
  -DCMAKE_INSTALL_PREFIX="${TOOLCHAIN_TRUNK_LLVM_INSTALL_DIR}" \
  -DCLANG_DEFAULT_LINKER=lld \
  -DLLVM_USE_LINKER=lld \
  -DLLVM_ENABLE_TERMINFO=0 \
  -DLLVM_ENABLE_ASSERTIONS=OFF \
  -DLLVM_BUILD_TESTS=OFF \
  -DLIBOMPTARGET_BUILD_DEVICERTL_BCLIB=OFF \
  -DCOMPILER_RT_ENABLE_INTERNAL_SYMBOLIZER=ON \
  -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \
  -DCMAKE_BUILD_TYPE=Release \
  "${TOOLCHAIN_PUBLISH_WORKSPACE}/llvm" &&
  ninja install

❗ Problem
The build fails at this step:

+ for F in $CC $CXX $TBLGEN $LINK $OPT $AR
+ [[ ! -x /home/*****/llvm-project/trunk_llvm_build/bin/llvm-link ]]
+ echo '/home/*****/llvm-project/trunk_llvm_build/bin/llvm-link'
Missing /home/*****/llvm-project/trunk_llvm_build/bin/llvm-link
+ exit 1
FAILED: compiler-rt/lib/sanitizer_common/symbolizer/RTSanitizerCommonSymbolizerInternal.x86_64.o /home/*****/llvm-project/trunk_llvm_build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/sanitizer_common/symbolizer/RTSanitizerCommonSymbolizerInternal.x86_64.o
cd /home/*****/llvm-project/trunk_llvm_build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/sanitizer_common/symbolizer/RTSanitizerCommonSymbolizerInternal.x86_64 && FLAGS= CLANG=/home/*****/llvm-project/trunk_llvm_build/./bin/clang /home/*****/llvm-project/compiler-rt/lib/sanitizer_common/symbolizer/scripts/build_symbolizer.sh /home/*****/trunk_llvm_build/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/sanitizer_common/symbolizer/RTSanitizerCommonSymbolizerInternal.x86_64.o

This occurs in build_symbolizer.sh which expects llvm-link, llvm-ar, opt, etc., to be present before runtime components (e.g., compiler-rt) are built.

Even though llvm is part of LLVM_ENABLE_PROJECTS, these tools apparently haven't been built yet when runtimes starts building.

🔍 Question
Should the CMake system enforce that tools like llvm-link are available before attempting to build runtimes, especially compiler-rt?

Or is it the user's responsibility to manually build such tools before running ninja?

🧪 Notes
I can workaround this by manually running ninja llvm-link before full build.

A fully separated two-stage build (build tools → build runtimes) also avoids the issue, but it would be nice to clarify whether this is expected behavior or a missing dependency declaration.

Thanks in advance for your help!

[nolongerwait]

After further investigation, I found that the issue is related to the version of Ninja being used.

• When using Ninja 1.11.1, the build completes successfully without any problems.
• However, when upgrading to Ninja 1.12.1, the issue consistently occurs during the build.

This suggests a potential compatibility or regression issue introduced in Ninja 1.12.1.

And CMake Version is 3.25.1