CMake warning when compiling Clang/LLVM

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1

Hi,

when I run cmake I get the following warning:

2

Hi,

when I run cmake I get the following warning:

---------------------------------------------------------------------------------------
CMake Warning at cmake/modules/HandleLLVMStdlib.cmake:24 (message):
  Can't specify libc++ with '-stdlib='
Call Stack (most recent call first):
  cmake/config-ix.cmake:15 (include)
  CMakeLists.txt:580 (include)
---------------------------------------------------------------------------------------

I am using GCC 4.8.5 to build on a x86_64 machine with RedHat OS.

Any idea why?

What arguments are you passing to CMake and which version of LLVM are you
trying to build?

-Tom

3

That's probably -DLLVM_ENABLE_LIBCXX=ON and the warning tells you the reason: -stdlib= is only supported if compiling with Clang, you can't specify it with GCC.

Cheers,
Jonas

4

Thanks, that’s the reason.

So to clarify, I should use -DLLVM_ENABLE_LIBCXX=ON only if I am building clang with clang?
I got confused, I thought it was for building libc++, but having that under projects seems to be enough.

Thanks.
Simone

5

If libc++ is under projects/ it will get built. What LLVM_ENABLE_LIBCXX does is to enable _linking_ all LLVM libraries and binaries to libc++ as the C++ STL and that's only supported with Clang. You can specify the option when building with GCC, it just won't work and issue the warning you are seeing.

Regards,
Jonas

6

I had problems building the llvm libcxx libraries with gcc 5.3. I then used gcc 7 and my problems went away. That doesn’t answer your question, but might be helpful down the road. :slight_smile: Ciao Nat!