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Subject: Re: [boost] [visibility][test][osx] visibility warnings with 1.70beta
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2019-03-27 19:38:30

On 3/27/19 10:16 PM, Raffi Enficiaud via Boost wrote:
> Hi,
> I have a side project that requires boost.test and I thought it is the
> right time to use the beta build of 1.70. At link time for my project
> (in this case a simple boost.test module), I have tons of warnings like
> the following:
> ld: warning: direct access in function
> 'boost::unit_test::decorator::depends_on::apply(boost::unit_test::test_unit&)'
> from file
> '/Users/raffi/from-big-laptop/code/software_workshop/sw_thirdparties/osx/boost_1_70_0_b1/lib/libboost_unit_test_framework-xgcc42-mt-x64-1_70.a(decorator.o)'
> to global weak symbol 'boost::unit_test::basic_cstring<char
> const>::null_str()::null' from file
> '/Users/raffi/code/mpi/mpi_kmeans/build/'
> means the weak symbol cannot be overridden at runtime. This was likely
> caused by different translation units being compiled with different
> visibility settings.
> running Xcode 10.1 on 10.14/mojave.
> I am building boost like this:
> ./b2 \
> cflags="-mmacosx-version-min=10.10" \
> cxxflags="-std=c++11 -stdlib=libc++ -mmacosx-version-min=10.10" \
> mflags="-mmacosx-version-min=10.10" \
> mmflags="-mmacosx-version-min=10.10" \
> linkflags="-stdlib=libc++ -mmacosx-version-min=10.10" \
> --prefix=`pwd`/../${build_folder} \
> --without-log \
> --layout=versioned \
> install
> Each of the files that are being built in my project and that are
> raising the warning have a compilation command like this:
> /Applications/
> -I/Users/raffi/code/mpi/mpi_kmeans/include
> -I/Users/raffi/code/mpi/mpi_kmeans/applications/include -isystem
> /Users/raffi/from-big-laptop/code/software_workshop/sw_thirdparties/osx/boost_1_70_0_b1/include/boost-1_70
> -O3 -DNDEBUG -std=gnu++11 -o
> CMakeFiles/test_mpi_kmeans.dir/test/test_kmeans.cpp.o -c
> /Users/raffi/code/mpi/mpi_kmeans/test/test_kmeans.cpp
> which is pretty much what I had so far and before 1.70.
> Boost.test is using BOOST_SYMBOL_VISIBLE to make a symbol public,
> including the static build variant. Why does the linker say
> """
> This was likely caused by different translation units being compiled
> with different visibility settings.
> """
> is completely unclear to me. How can I inspect what b2 emits as
> compilation command line for further debugging?

You can add -d+2 to the b2 command line to see the commands it is using
while building Boost.

I'm guessing that the compiler is correct in that different visibility
modes are used for different TUs, since I don't see visibility flags in
your project's command line and visibility is likely set to hidden when
building Boost. The particular complaint in the warnings you quoted is
about the function-local static `null` in
`basic_cstring<CharT>::null_str()`, which is not explicitly marked as
visible and therefore has different visibility when it is compiled in
Boost and your project.

I suggest changing the code so that `null` is instead a static class
member of `basic_cstring` and mark it with `BOOST_SYMBOL_VISIBLE`. Also,
it might make sense to make it a const array instead of a single
character, and change `null_str` to return a const pointer instead of a
mutable one.

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