Build fails on clang 10 with UBSAN

[jktjkt]

I'm on clang 10.0.0:

$ clang++-10 --version
clang version 10.0.0 
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/10/bin

And I cannot build replxx when using USAN (-fsanitize=undefined):

$ CC=clang-10 CXX=clang++-10 LD=clang-10 \
  CFLAGS='-fsanitize=undefined' \
  CXXFLAGS='-fsanitize=undefined' \
  LDFLAGS='-fsanitize=undefined' \
  cmake -GNinja -DBUILD_SHARED_LIBS=ON path/to/replxx && ninja -k 666
-- The CXX compiler identification is Clang 10.0.0
-- The C compiler identification is Clang 10.0.0
-- Check for working CXX compiler: /usr/lib/llvm/10/bin/clang++-10
-- Check for working CXX compiler: /usr/lib/llvm/10/bin/clang++-10 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Check for working C compiler: /usr/lib/llvm/10/bin/clang-10
-- Check for working C compiler: /usr/lib/llvm/10/bin/clang-10 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - found
-- Found Threads: TRUE  
CMake Warning (dev) at CMakeLists.txt:41 (message):
  CMAKE_BUILD_TYPE not set.  Defaulting to Release
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY - Success
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jkt/temp/xx
[0/2] Re-checking globbed directories...
[17/19] Linking C executable replxx-example-c-api
FAILED: replxx-example-c-api 
: && /usr/lib/llvm/10/bin/clang-10 -fsanitize=undefined -O3 -DNDEBUG  -fsanitize=undefined CMakeFiles/replxx-example-c-api.dir/examples/c-api.c.o CMakeFiles/replxx-example-c-api.dir/examples/util.c.o  -o replxx-example-c-api  -Wl,-rpath,/home/jkt/temp/xx libreplxx.so.0.0.2 && :
libreplxx.so.0.0.2: undefined reference to `__ubsan_vptr_type_cache'
libreplxx.so.0.0.2: undefined reference to `__ubsan_handle_function_type_mismatch_v1'
libreplxx.so.0.0.2: undefined reference to `__ubsan_handle_dynamic_type_cache_miss'
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
[19/19] Linking CXX executable replxx-example-cxx-api
ninja: build stopped: cannot make progress due to previous errors.

I can reproduce this on a Gentoo Linux system with clang 10, and on Fedora 31 with clang 9. Configuring with (-DREPLXX_BUILD_EXAMPLES=OFF) makes this problem go away.

[jktjkt]

...and when I add -DCMAKE_BUILD_TYPE=Debug, I also get:

[19/19] Linking CXX executable replxx-example-cxx-api
FAILED: replxx-example-cxx-api 
: && /usr/lib/llvm/10/bin/clang++-10  -fsanitize=undefined -stdlib=libc++ -g  -fsanitize=undefined -stdlib=libc++ CMakeFiles/replxx-example-cxx-api.dir/examples/cxx-api.cxx.o CMakeFiles/replxx-example-cxx-api.dir/examples/util.c.o  -o replxx-example-cxx-api  -Wl,-rpath,/home/jkt/temp/xx libreplxx-d.so.0.0.2 && :
/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: replxx-example-cxx-api: hidden symbol `_ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE11__recommendEm' isn't defined
/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: final link failed: Bad value
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: cannot make progress due to previous errors.

I'm building stuff (other libraries and applications) with UBSAN just fine otherwise. Demangler says that this is:

std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::__recommend(unsigned long)

This particular error goes away if I remove -stdlib=libc++ from CXXFLAGS and LDFLAGS.

[doug-moen]

You are using LD=clang-10 to link C++ code (this is the C compiler, not the C++ compiler).
I suggest trying LD=clang++-10 instead.

[jktjkt]

@doug-moen , there's just one LD for linking both C and C++ code. I've never heard about setting LD to g++ or to clang++.

Anyway, I tried what you propose, and there's apparently no change on my test system:

jkt@kolibrik ~/temp/xx $ CC=clang-10 CXX=clang++-10 LD=clang++-10 CFLAGS='-fsanitize=undefined' CXXFLAGS='-fsanitize=undefined -stdlib=libc++' LDFLAGS='-fsanitize=undefined -stdlib=libc++' cmake -GNinja -DBUILD_SHARED_LIBS=ON -DCMAKE_BUILD_TYPE=Debug ~/work/cesnet/gerrit/CzechLight/cla-sysrepo/submodules/dependencies/replxx && ninja -k 666
-- The CXX compiler identification is Clang 10.0.0
-- The C compiler identification is Clang 10.0.0
-- Check for working CXX compiler: /usr/lib/llvm/10/bin/clang++-10
-- Check for working CXX compiler: /usr/lib/llvm/10/bin/clang++-10 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Check for working C compiler: /usr/lib/llvm/10/bin/clang-10
-- Check for working C compiler: /usr/lib/llvm/10/bin/clang-10 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - found
-- Found Threads: TRUE  
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_VISIBILITY - Success
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY
-- Performing Test COMPILER_HAS_HIDDEN_INLINE_VISIBILITY - Success
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR
-- Performing Test COMPILER_HAS_DEPRECATED_ATTR - Success
-- Configuring done
-- Generating done
-- Build files have been written to: /home/jkt/temp/xx
[0/2] Re-checking globbed directories...
[17/19] Linking C executable replxx-example-c-api
FAILED: replxx-example-c-api 
: && /usr/lib/llvm/10/bin/clang-10 -fsanitize=undefined -g  -fsanitize=undefined -stdlib=libc++ CMakeFiles/replxx-example-c-api.dir/examples/c-api.c.o CMakeFiles/replxx-example-c-api.dir/examples/util.c.o  -o replxx-example-c-api  -Wl,-rpath,/home/jkt/temp/xx libreplxx-d.so.0.0.2 && :
libreplxx-d.so.0.0.2: undefined reference to `__ubsan_handle_function_type_mismatch_v1'
libreplxx-d.so.0.0.2: undefined reference to `__ubsan_vptr_type_cache'
libreplxx-d.so.0.0.2: undefined reference to `__ubsan_handle_dynamic_type_cache_miss'
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
[19/19] Linking CXX executable replxx-example-cxx-api
FAILED: replxx-example-cxx-api 
: && /usr/lib/llvm/10/bin/clang++-10  -fsanitize=undefined -stdlib=libc++ -g  -fsanitize=undefined -stdlib=libc++ CMakeFiles/replxx-example-cxx-api.dir/examples/cxx-api.cxx.o CMakeFiles/replxx-example-cxx-api.dir/examples/util.c.o  -o replxx-example-cxx-api  -Wl,-rpath,/home/jkt/temp/xx libreplxx-d.so.0.0.2 && :
/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: replxx-example-cxx-api: hidden symbol `_ZNSt3__112basic_stringIcNS_11char_traitsIcEENS_9allocatorIcEEE11__recommendEm' isn't defined
/usr/lib/gcc/x86_64-pc-linux-gnu/8.1.0/../../../../x86_64-pc-linux-gnu/bin/ld: final link failed: Bad value
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: cannot make progress due to previous errors.

Notice that the linker in the first call gets "somehow" set "to the C compiler" by the build system. Also, that first target is not C++ code, it's a C code if I'm aprsing its name correctly.

[doug-moen]

I see two errors in your build.

The first error happens when linking replxx-example-c-api, which is a C program, but it is being linked with a C++ library. The problem is that cmake is using the C compiler to link a C++ program. cmake is passing -fsanitize=undefined to clang-10, and clang-10 thinks it is linking a C program, so it doesn't use the additional C++ library required for use with -fsanitize=undefined for sanitizing undefined behaviour in C++ programs relating to vtables and dynamic types, which are C++ only features. That's what I think is happening.

To test my hypothesis about the first link error, you can take the linker command that cmake is running:

/usr/lib/llvm/10/bin/clang-10 -fsanitize=undefined -g  -fsanitize=undefined -stdlib=libc++ CMakeFiles/replxx-example-c-api.dir/examples/c-api.c.o CMakeFiles/replxx-example-c-api.dir/examples/util.c.o  -o replxx-example-c-api  -Wl,-rpath,/home/jkt/temp/xx libreplxx-d.so.0.0.2

and you can modify this command to invoke clang++-10 instead of clang-10. After running this command directly from your shell, I bet that the 3 undefined references to C++ symbols that you are currently seeing will go away.

How to configure cmake to use the C++ compiler to link replxx-example-c-api is a separate issue.

The second build error occurs when linking replxx-example-cxx-api. You've already figured out that it is caused by using libc++ instead of the default.

[AmokHuginnsson]

Does replxx code/build system has any action items for this issue?