llvm dev - Apr 2019 - Failed to replace stdlibc++ with libc++, linker phase error

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
>

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