[llvm-dev] Failed to replace stdlibc++ with libc++, linker phase error

[Tom Stellard via llvm-dev]

On 04/14/2019 05:04 PM, AiChi wrote:
> Hi Tom, 
> 
> Thanks for your replies. 
> 
> Following are the commands that I used to build clang/libcxx/libcxxabi:
> clang:
> |  cmake -DLLVM_ENABLE_PROJECTS=||"clang;libcxx;libcxxabi"| |-G ||"Unix Makefiles"| |-DCMAKE_BUILD_TYPE=Release -DLLVM_LIBDIR_SUFFIX=64 ..||/llvm|
> |
> |
> libcxx:
> ||  cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=||/usr| |-DLLVM_LIBDIR_SUFFIX=64 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ ..|
> |
> ||
> ||
> libcxxabi:
> |  cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=||/usr| |-DLLVM_LIBDIR_SUFFIX=64 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLIBCXXABI_LIBCXX_INCLUDES=../..||/libcxx/include| |..|
> |

You should only need to run cmake once.  Here is a minimal example build process that
I think should work:

git clone --branch release/5.x https://github.com/llvm/llvm-project
cd llvm-project
mkdir build
cd build
cmake -DLLVM_ENABLE_PROJECTS="libcxx;libcxxabi" -DCMAKE_INSTALL_PREFIX=/usr -DLLVM_LIBDIR_SUFFIX=64 ../llvm/
make install-cxx

Then verify that libc++.so is actually a linker script with the correct libraries:

cat /usr/lib64/libc++.so

The output should look like this:

INPUT(libc++.so.1 -lc++abi)

-Tom


> |
> |And based on what I searched on google, libcxx and libcxxabi might have circular dependency (please see the post here: |https://stackoverflow.com/questions/25840088/how-to-build-libcxx-and-libcxxabi-by-clang-on-centos-7), so after I built libcxx with clang, build libcxxabi based on libcxx, I rebuilt libcxx again with libcxxabi with the following command:
> |
> cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/usr -DLLVM_LIBDIR_SUFFIX=64 -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLIBCXX_CXX_ABI=libcxxabi -DLIBCXX_CXX_ABI_INCLUDE_PATHS=../../libcxxabi/include ..
> 
> I've tried what you suggested in your previous email (add linker flag: -lc++abi), but unfortunately I got the same error while building my project. Am I missing anything?
> 
> Thank you all,
> Aichi
> 
> |
> ||
> |
> |
> |
> |
> 
> ||
> 
> On Fri, Apr 12, 2019 at 6:38 PM Tom Stellard <tstellar at redhat.com <mailto:tstellar at redhat.com>> wrote:
> 
>     On 04/12/2019 06:31 PM, Tom Stellard via llvm-dev wrote:
>     > On 04/12/2019 04:28 PM, AiChi via llvm-dev wrote:
>     >> Hi,
>     >>
>     >> I'm currently working on one of my team's project to build LLVM full clang toolchain (Clang, libcxx, libcxxabi) on a CentOS machine.
>     >>
>     >> Previously we compiled our codebase with llvm-toolset-7/clang++, which by default takes stdlibc++ to compile and link. And now we'd like to switch to use LLVM clang with libc++. I have built libc++ and libc++abi from source (5.0.1 release) and set up related flags to compile our code base, but it turned out having some issue in the "linker" phase:
>     >>
>     >> Flags set for complier:
>     >> -stdlib=libc++ -std=c++14
>     >>
>     >> Flags set for linker:
>     >> -stdlib=libc++
>     >>
>     >> Error:
>     >> /opt/rh/devtoolset-7/root/usr/lib/gcc/x86_64-redhat-linux/7/../../../../bin/ld: product.o: undefined reference to symbol '__cxa_free_exception@@CXXABI_1.3'
>     >> //lib64/libstdc++.so.6: error adding symbols: DSO missing from command line
>     >> clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
>     >>
>     >> My question is:
>     >> 1. We plan to replace stdlibc++ with libc++, and we've set up compiler and linker to run with "-stdlib=libc++', why is it complaining about libstdc++?
>     >
>     > Can you post the full linker invocation with all the arguments?
>     >
>     > What cmake arguments did you use when building libcxx and libcxxabi?
>     >
>     >> 2. How can we resolve this error? (any ideas would be appreciated!)
>     >
>     > Not sure exactly, I would try passing -DLIBCXX_CXX_ABI=libcxxabi to cmake
>     > when configuring libcxx if you have not already.
>     >
> 
>     If you are looking for a quick fix though, you might want to also try adding
>     -lc++abi to your linker flags.
> 
>     -Tom
> 
>     >> 3. Is there anything missing if we'd like to replace stdlibc++ with libc++?
>     >> 4. I also noticed when it's in linker phase, these flags were set in the ld command (-lc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc ), which we didn't have them setup anywhere in our project, just out of curiosity, are they added automatically? Why are they needed?
>     >
>     > When you are using clang++ or g++ as the linker driver, then it automatically
>     > adds the flags for you.
>     >
>     > -Tom
>     >
>     >>
>     >> A little bit more details:
>     >> Environment: CentOS Linux release 7.6.1810 (Core)
>     >> Clang version:
>     >>
>     >>     clang version 5.0.1 (tags/RELEASE_501/final)
>     >>     Target: x86_64-unknown-linux-gnu
>     >>     Thread model: posix
>     >>
>     >>
>     >> Thanks for any ideas,
>     >> Aichi
>     >>
>     >>
>     >> _______________________________________________
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>     >> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
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>     >>
>     >
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