How to fix undefined reference LLVM error while linking CXX executable - makefile

Question

I was trying to build a llvm-slicer from:
https://github.com/IAIK/ios-analysis-llvmslicer
and I follow the instructions:
cd llvm-slicer
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE="Release" -DLLVM_TARGETS_TO_BUILD="AArch64;X86" -DLLVM_ENABLE_EH=YES -DLLVM_ENABLE_RTTI=ON ..
make -j4 opt
make -j4 llvm-slicer
But when I execute the last command make -j4 llvm-slicer, I got an error:
[100%] Built target LLVMAnalysis
[100%] Linking CXX executable ../../bin/llvm-slicer
/usr/bin/ld: ../../lib/libLLVMSlicer.a(FunctionStaticSlicer.cpp.o): in function `llvm::Pass* llvm::callDefaultCtor<(anonymous namespace)::FunctionSlicer>()':
FunctionStaticSlicer.cpp:(.text._ZN4llvm15callDefaultCtorIN12_GLOBAL__N_114FunctionSlicerEEEPNS_4PassEv+0x1c): undefined reference to `vtable for (anonymous namespace)::FunctionSlicer'
collect2: error: ld returned 1 exit status
make[3]: *** [tools/llvm-slicer/CMakeFiles/llvm-slicer.dir/build.make:116: bin/llvm-slicer] Error 1
make[2]: *** [CMakeFiles/Makefile2:9647: tools/llvm-slicer/CMakeFiles/llvm-slicer.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:9654: tools/llvm-slicer/CMakeFiles/llvm-slicer.dir/rule] Error 2
make: *** [Makefile:2740: llvm-slicer] Error 2
I have no idea about how to fix it and I couldn't find any similar issues on Google, I hope someone can help me to figure it out, many thx.

Answer 1

There can be several scenarios for this issue, but in my opinion, here the scenario is for the given information that your default compiler (_ZN...something errors mostly because of compilers or linkers) is earlier version of gnu (gcc for c, g++ for c++) in your host pc (or maybe another compiler other than clang) and struggling about resolving a c++ feature anonymous namespace, as, a part of given error says:
/usr/bin/ld: ../../lib/libLLVMSlicer.a(FunctionStaticSlicer.cpp.o): in function `llvm::Pass* llvm::callDefaultCtor<(anonymous namespace)::FunctionSlicer>()':
FunctionStaticSlicer.cpp:(.text._ZN4llvm15callDefaultCtorIN12_GLOBAL__N_114FunctionSlicerEEEPNS_4PassEv+0x1c): undefined reference to `vtable for (anonymous namespace)::FunctionSlicer'
For this, there are several things you can do:
1-) You can change your compiler for building. In command window, you can export clang and clang++ as your compiler before cmake configuration. Here I assume that you installed new versions of clang compiler from anywhere, even github clone, I can give several examples here how to export and you can adapt one of them to your case easily:
export CC=clang
export CXX=clang++
another version:
export CC=clang-11
export CXX=clang++-11
another version:
export CC=/usr/bin/clang
export CXX=/usr/bin/clang++
another version:
export CC=/usr/bin/clang-12
export CXX=/usr/bin/clang++-12
another github clone version:
export CC=~/llvm/llvm-project/build/bin/clang
export CXX=~/llvm/llvm-project/build/bin/clang++
Even if this does not change your compiler, you can change your compiler while configuring with cmake by -DCMAKE_C_COMPILER={your-c-compiler} and -DCMAKE_CXX_COMPILER={your-c++-compiler} cmake flags. Try either with gcc or clang. Here is an example configuration in your case:
cmake \
-DCMAKE_C_COMPILER=clang \
-DCMAKE_CXX_COMPILER=clang++ \
-DCMAKE_BUILD_TYPE="Release" \
-DLLVM_TARGETS_TO_BUILD="AArch64;X86" \
-DLLVM_ENABLE_EH=YES \
-DLLVM_ENABLE_RTTI=ON ..
2-) Error can be because of c++ standard, you can add -DCMAKE_CXX_STANDARD=14 (Default C++ standard using by LLVM) flag as cmake configuration like:
cmake -DCMAKE_BUILD_TYPE="Release" -DLLVM_TARGETS_TO_BUILD="AArch64;X86" -DLLVM_ENABLE_EH=YES -DLLVM_ENABLE_RTTI=ON -DCMAKE_CXX_STANDARD=14 ..
3-) Even if didn't work above cases, you can remove anonymous namespace from FunctionStaticSlicer.cpp file (given in the error message) and try to build again. You can find these lines like this:
// some code here and do not delete
namespace { // delete this line
// as you can see there is no name of namespace that's why called 'anonymous'
// if it was it would be like 'namespace nmspcName {'
// some code here and do not delete
} // and delete this line, too
// some code here and do not delete
But this is really bad practice, even if it can solve your problem, I do not recommend.
Also you can try to do similar changes in CMakeLists.txt file or adding other cmake configuration flags, however in my opinion, you could solve your problem easily by 1. option which is changing your default compiler.