C++0x Bug in CMake?


I may be doing this wrong, but I’m getting a weird error in building LLVM with Clang via CMake.

On x86_64:
$ CC=clang CXX=clang++ cmake -G Ninja …/…/src/llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_BUILD_TESTS=True -DLLVM_ENABLE_ASSERTIONS=True



CMake Warning at cmake/modules/HandleLLVMOptions.cmake:117 (message):
-fPIC is not supported.
Call Stack (most recent call first):
cmake/modules/HandleLLVMOptions.cmake:150 (add_flag_or_print_warning)
CMakeLists.txt:286 (include)

Error log:
Run Build Command:/usr/local/bin/ninja cmTryCompileExec3815591925

[1/2] Building C object CMakeFiles/cmTryCompileExec3815591925.dir/src.c.o
FAILED: /home/user/devel/llvm/build/bin/clang -mcpu=cortex-a15 -DC_SUPPORTS_FLAG -std=c++0x -fPIC -o CMakeFiles/cmTryCompileExec3815591925.dir/src.c.o -c src.c
error: invalid argument ‘-std=c++0x’ not allowed with ‘C/ObjC’
ninja: build stopped: subcommand failed.

Why is it adding --std=c++0x on a C compiler?

Needless to say that with GCC, that doesn’t happen (ie. --std=c++0x doesn’t get added). Happens both on ARM and x86_64.

Is this a side effect of your changes?


Maybe, I’ll have to debug. It does seem quite bizarre.

Which version of CMake?

Never mind, I see the bug. Working on a fix.

Should be fixed in r199756. Let me know.

I have been debugging a similar issue that I isolated to r199484. The
issue surfaces for me as:

../../lib/libLLVMAArch64CodeGen.a(AArch64AsmPrinter.cpp.o): relocation
R_X86_64_32 against `.rodata..L.str5' can not be used when making a
shared object; recompile with -fPIC
../../lib/libLLVMAArch64CodeGen.a: could not read symbols: Bad value
clang-3.4: error: linker command failed with exit code 1 (use -v to
see invocation)
[ 95%] make[2]: *** [lib/libLTO.so] Error 1

The same can be seen on some of our bulidbots (those that use Clang and CMake).


This *could* be the same thing I suppose... If my fix actually helps,
please let me know. But I don't completely see how this particular error
happens so I'll be intrigued.

Your fix changed clang_fast bulidbots back to green, thank you!


Awesome, I’m glad that was the underlying issue!

Perfect! I just worked, thanks!!


Great, sorry for messing this up.