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

[AiChi via llvm-dev]

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 ..

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> 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
> >>
> >>
> >> _______________________________________________
> >> LLVM Developers mailing list
> >> llvm-dev at lists.llvm.org
> >> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
>
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