Building clang + libc++ + libc++abi

David_A_Greene1 · July 8, 2015, 4:55am

[Sorry about the crosspost. Since this is a clang build question but
the build is invoked from the top-level LLVM directory I'm not sure
where the question should go.]

I've got a clang build against libstdc++ on Linux but I would really
like one built against libc++/libc++abi. In other words I'd like to
rebuild clang/llvm with clang using libc++ and libc++abi on Linux.

I looked at the instructions on the libc++ page and for Linux it
recommends building with -stdlib=libc++ -lc++abi.

Encouraging! Now, how do I get those options to a CMake build of
llvm/clang? There's CMAKE_CXX_FLAGS but I'm not sure how to set it.
Will a simple -DCMAKE_CXX_FLAGS=-stdlib=libc++ suffice? Will that
properly propagate from the command line without overriding all the
flags set by individual CMakeLists.txt files? I don't want to, for
example, lose optimization flags on a release build.

And what about linker flags? What CMake variable controls those? The
Google tells me nothing.

I'm including lots of other LLVM projects in the build (lld, etc.) and
this is partially being driven by the fact that I have an outdated
libstdc++. Some project sources won't build and I'm assuming libc++
will provide what I need. It would be nice to get entirely away from
gcc/libstdc++ because I can't control when those packages are updated on
the machine. I'd like to be able to completely bootstrap everything,
assuming the old gcc/libstdc++ can at least get a clang/llvm built
(which it can, because I've done it).

Thanks for your help!

-David

David_A_Greene1 · July 8, 2015, 6:17am

greened@obbligato.org (David A. Greene) writes:

I looked at the instructions on the libc++ page and for Linux it
recommends building with -stdlib=libc++ -lc++abi.

Encouraging! Now, how do I get those options to a CMake build of
llvm/clang? There's CMAKE_CXX_FLAGS but I'm not sure how to set it.
Will a simple -DCMAKE_CXX_FLAGS=-stdlib=libc++ suffice? Will that
properly propagate from the command line without overriding all the
flags set by individual CMakeLists.txt files? I don't want to, for
example, lose optimization flags on a release build.

And what about linker flags? What CMake variable controls those? The
Google tells me nothing.

I discovered CMAKE_CXX_LINK_FLAGS. So I'm configuring like this:

cmake -G "Unix Makefiles" -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DCMAKE_CXX_FLAGS="-stdlib=libc++" -DCMAKE_CXX_LINK_FLAGS="-stdlib=libc++ -lc++abi -DPYTHON_EXECUTABLE=/opt/python/2.7.9/bin/python2.7 -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/opt/clang/dev -DLLVM_APPEND_VC_REV=ON -DLLVM_ENABLE_CXX1Y=ON -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_PARALLEL_COMPILE_JOBS=32 -DLLVM_PARALLEL_LINK_JOBS=32 -DLLVM_BUILD_DOCS=ON -DCLANG_INCLUDE_DOCS=ON -DLIBCXX_CXX_ABI=libcxxabi -DLIBCXX_CXX_ABI_INCLUDE_PATHS="/path/to/llvm/projects/libcxxabi/include" /path/to/llvm

This gets me a bit further but I am stuck here:

Linking CXX shared library ../../../../lib/libclang.so
cd /ptmp/dag/build/clang/tools/clang/tools/libclang && /opt/cmake/3.0.1/bin/cmake -E cmake_link_script CMakeFiles/libclang.dir/link.txt --verbose=1
/cray/css/compiler/cost/tools/x86_64-unknown-linux-gnu/clang/dev/bin/clang++ -fPIC -stdlib=libc++ -fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wcovered-switch-default -Wnon-virtual-dtor -std=c++1y -ffunction-sections -fdata-sections -fno-common -Woverloaded-virtual -fno-strict-aliasing -Wno-nested-anon-types -O3 -Wl,-O3 -Wl,--gc-sections -Wl,--version-script,/ptmp/dag/build/clang/tools/clang/tools/libclang/libclang.exports -Wl,-z,defs -shared -Wl,-soname,libclang.so.3.7 -o ../../../../lib/libclang.so.3.7 CMakeFiles/libclang.dir/ARCMigrate.cpp.o CMakeFiles/libclang.dir/BuildSystem.cpp.o CMakeFiles/libclang.dir/CIndex.cpp.o CMakeFiles/libclang.dir/CIndexCXX.cpp.o CMakeFiles/libclang.dir/CIndexCodeCompletion.cpp.o CMakeFiles/libclang.dir/CIndexDiagnostic.cpp.o CMakeFiles/libclang.dir/CIndexHigh.cpp.o CMakeFiles/libclang.dir/CIndexInclusionStack.cpp.o CMakeFiles/libclang.dir/CIndexUSRs.cpp.o CMakeFiles/libclang.dir/CIndexer.cpp.o CMakeFiles/libclang.dir/CXComment.cpp.o CMakeFiles/libclang.dir/CXCursor.cpp.o CMakeFiles/libclang.dir/CXCompilationDatabase.cpp.o CMakeFiles/libclang.dir/CXLoadedDiagnostic.cpp.o CMakeFiles/libclang.dir/CXSourceLocation.cpp.o CMakeFiles/libclang.dir/CXStoredDiagnostic.cpp.o CMakeFiles/libclang.dir/CXString.cpp.o CMakeFiles/libclang.dir/CXType.cpp.o CMakeFiles/libclang.dir/IndexBody.cpp.o CMakeFiles/libclang.dir/IndexDecl.cpp.o CMakeFiles/libclang.dir/IndexTypeSourceInfo.cpp.o CMakeFiles/libclang.dir/Indexing.cpp.o CMakeFiles/libclang.dir/IndexingContext.cpp.o ../../../../lib/libclangAST.a ../../../../lib/libclangBasic.a ../../../../lib/libclangFrontend.a ../../../../lib/libclangIndex.a ../../../../lib/libclangLex.a ../../../../lib/libclangSema.a ../../../../lib/libclangTooling.a ../../../../lib/libclangARCMigrate.a -ldl ../../../../lib/libLLVMCore.a ../../../../lib/libLLVMSupport.a ../../../../lib/libclangFormat.a ../../../../lib/libclangToolingCore.a ../../../../lib/libclangASTMatchers.a ../../../../lib/libclangFrontend.a ../../../../lib/libclangDriver.a ../../../../lib/libclangParse.a ../../../../lib/libLLVMMCParser.a ../../../../lib/libLLVMOption.a ../../../../lib/libclangSerialization.a ../../../../lib/libclangSema.a ../../../../lib/libclangEdit.a ../../../../lib/libLLVMBitReader.a ../../../../lib/libclangStaticAnalyzerCheckers.a ../../../../lib/libclangStaticAnalyzerCore.a ../../../../lib/libclangRewrite.a ../../../../lib/libclangAnalysis.a ../../../../lib/libclangAST.a ../../../../lib/libclangLex.a ../../../../lib/libclangBasic.a ../../../../lib/libLLVMCore.a ../../../../lib/libLLVMMC.a ../../../../lib/libLLVMSupport.a -lrt -ldl -lncurses -lpthread -lz -lm -Wl,-rpath,"\$ORIGIN/../lib"
../../../../lib/libLLVMSupport.a(Debug.cpp.o): In function `llvm::dbgs()':
/ptmp/dag/llvm/llvm-ecosystem/llvm/lib/Support/Debug.cpp:(.text._ZN4llvm4dbgsEv+0x1b): undefined reference to `__cxa_guard_acquire'
/ptmp/dag/llvm/llvm-ecosystem/llvm/lib/Support/Debug.cpp:(.text._ZN4llvm4dbgsEv+0x11a): undefined reference to `__cxa_guard_release'

And a bazillion other undefined references.

Is the problem the lack of -lc++abi on the link line? That command
comes from CMakeFiles/libclang.dir/link.txt which I can view and has the
command above in it. However, I cannot for the life of me figure out
how that gets generated. So I don't even know what CMake command I need
to influence to get the proper link flags added.

I tried messing around the LIBCLANG_LINK_FLAGS (discovered in libclang's
CMakeLists.txt) but it didn't do anyting.

Has anyone built this way on Linux? I found a couple of references
online but they seem pretty out of date.

-David

hintonda_gmail.com · July 8, 2015, 11:49am

If your cut-n-paste is accurate, you seem to be missing a closing quote for CMAKE_CXX_LINK_FLAGS.

hth…
don

David_A_Greene1 · July 8, 2015, 4:55pm

don hinton <hintonda@gmail.com> writes:

If your cut-n-paste is accurate, you seem to be missing a closing
quote for CMAKE_CXX_LINK_FLAGS.

Bad cut-n-paste. Good catch.

Unfortunately, doesn't help with the problem.

-David

EricWF · July 8, 2015, 11:31pm

To build LLVM and Clang using libc++ and libc++abi you can use the
CMake options `-DLLVM_ENABLE_LIBCXX=ON -DLLVM_ENABLE_LIBCXXABI=ON`.

/Eric

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Building clang + libc++ + libc++abi

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