Building LLVM with cmake. Does -D_GLIBCXX_USE_CXX11_ABI=0 get overridden? - cmake

Question

I try to build LLVM.
This is the way I try …
mkdir -p src/llvm-$(LLVM_VERSION).src/build
cd src/llvm-$(LLVM_VERSION).src/build && \
$(CMAKE) -GNinja \
-DCMAKE_INSTALL_PREFIX=$(BUNDLE) \
-DCMAKE_CXX_FLAGS="-D_GLIBCXX_USE_CXX11_ABI=0 -std=c++11 -static-libgcc -static-libstdc++ -l:libstdc++.a" \
-DLLVM_TARGETS_TO_BUILD="X86;NVPTX" \
-DLLVM_PARALLEL_COMPILE_JOBS=$(BUILD_JOBS) \
-DLLVM_PARALLEL_LINK_JOBS=2 \
-DLLVM_USE_CRT_RELEASE=MD \
-DLLVM_USE_CRT_DEBUG=MDd \
-DLLVM_STATIC=ON \
-DLLVM_INCLUDE_TESTS=OFF \
-DLLVM_INCLUDE_EXAMPLES=OFF \
-DLLVM_BUILD_LLVM_C_DYLIB=OFF \
-DLLVM_ENABLE_TERMINFO=OFF \
-DLLVM_ENABLE_UNWIND_TABLES=OFF \
-DLLVM_ENABLE_RTTI=ON \
.. && \
$(CMAKE) --build . && \
$(CMAKE) --build . --target install
You can see -D_GLIBCXX_USE_CXX11_ABI=0 in -DCMAKE_CXX_FLAGS. After LLVM finished compiling, libLLVM*.a still contain abi:cxx11 symbols.
llvm-config reveals, llvm build process completely ignored "-D_GLIBCXX_USE_CXX11_ABI=0" flag.
> ./bundle/bin/llvm-config --cxxflags
-I/home/leonard/Documents/Develop/build_as_deps/bundle/include -std=c++11 -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -D_GNU_SOURCE -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS
Do you have an idea how to build llvm in a way that disables abi:cxx11 symbols and prevents "-D_GLIBCXX_USE_CXX11_ABI=0" to be overridden?

Answer 1

It looks like you're confusing the cmake options (which are specified with via -D) with C/C++ compiler macro (which are also specified via -D, but to compiler). cmake happily ignored your -D_GLIBCXX_USE_CXX11_ABI, because it's not a cmake option (and you should see a warning about this, that the value is unused by the build system).
Since you need to add extra macro definition, you'd need to change CMAKE_CXX_FLAGS cmake variable.