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Troubleshooting Build Issues
If you get one of these:
undefined reference to `_ZNK4llvm17SubtargetFeatures9getStringB5cxx11Ev'
undefined reference to `llvm::SubtargetFeatures::getString() const'
This is because of C++'s Dual ABI. Most likely LLVM was compiled with one compiler while Zig was compiled with a different one, for example GCC vs clang.
LLVM, Clang, and Zig must all be compiled with the same C++ compiler.
The Clang packages in these distributions do not contain static libraries, which Zig tries to use by default.
Instead, one should link against the shared lib libclang-cpp.so.
For building stage1, set ZIG_PREFER_CLANG_CPP_DYLIB:
cmake .. -DZIG_PREFER_CLANG_CPP_DYLIB=true
For building stage2, pass -Dstatic-llvm=false to Zig.
If you get the message : CommandLine Error: Option 'mc-relax-all' registered more than once!, you're affected by the issue discussed in https://reviews.llvm.org/D75579. The fix has not (yet?) been included in clang 10.0.1. As a workaround, you can build clang with the line add_clang_subdirectory(handle-llvm) removed from clang/tools/clang-fuzzer/CMakeLists.txt.
Additionally, you'll need lld's .a and .h files, which aren't installed by Gentoo's lld ebuild, so you'll need to modify your lld ebuild file to not delete them.
The LLVM repositories/packages are listed at https://apt.llvm.org/. The following packages that are not listed must be installed: liblld-12-dev, libclang-12-dev (as well as at least libllvm12 from the listed packages).
Linking with Homebrew's packaged LLVM, since version 12.0, you will need to force static linking of LLVM using -DZIG_STATIC_LLVM=on. The full invocation will then look like:
cmake .. -DCMAKE_PREFIX_PATH=$(brew --prefix llvm) -DZIG_STATIC_LLVM=on
After upgrading LLVM, it's often necessary to remove the CMake cache and build directories:
rm CMakeCache.txt
rm -rf CMakeFiles
Then try running the cmake command again.
If you are failing at the last stage [99%] Building self-hosted component /PATHTOZIG/zig/build/zig1.o, make sure you have enough memory, as the process can take more than 10Gib of memory.
Log on to one of the Community spaces and ask for help.