[package] boost/1.74.0: ios fvisibility set

[qwertzui11]

Package and Environment Details (include every applicable attribute)

• Package Name/Version: boost/1.74.0
• Operating System+version: Mac Mojave
• Compiler+version: Apple clang version 12.0.0
• Conan version: 1.31.0

Conan profiles

host profile

[settings]
os=iOS
os.version=12.0
arch=armv8
compiler=apple-clang
compiler.version=12.0
compiler.libcxx=libc++
build_type=Release
[options]
[build_requires]
[env]

build profile

[settings]
os=Macos
os_build=Macos
arch=x86_64
arch_build=x86_64
compiler=apple-clang
compiler.version=12.0
compiler.libcxx=libc++
build_type=Release
[options]
[build_requires]
[env]

Steps to reproduce

I got a conanfile wich demand boost/1.74.0, nothing unusual happens, it compiles and I can use it and link it.
However I get A LOT of linker warnings which look like

ld: warning: direct access in function 'boost::log::v2s_mt_posix::core::implementation::implementation()' from file '/Users/acof/.conan/data/boost/1.73.0/_/_/package/2bcd523eb799e86beac7172dddb46e02c19f269a/lib/libboost_log.a(core.o)' to global weak symbol 'boost::log::v2s_mt_posix::aux::light_function<bool (boost::log::v2s_mt_posix::attribute_value_set const&)>::impl<boost::log::v2s_mt_posix::filter::default_filter>::invoke_impl(void*, boost::log::v2s_mt_posix::attribute_value_set const&)' from file 'utils/libutils.a(logging_initialser.cpp.o)' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function 'boost::log::v2s_mt_posix::core::implementation::implementation()' from file '/Users/acof/.conan/data/boost/1.73.0/_/_/package/2bcd523eb799e86beac7172dddb46e02c19f269a/lib/libboost_log.a(core.o)' to global weak symbol 'boost::log::v2s_mt_posix::aux::light_function<bool (boost::log::v2s_mt_posix::attribute_value_set const&)>::impl<boost::log::v2s_mt_posix::filter::default_filter>::invoke_impl(void*, boost::log::v2s_mt_posix::attribute_value_set const&)' from file 'utils/libutils.a(logging_initialser.cpp.o)' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function 'boost::log::v2s_mt_posix::core::implementation::thread_data::thread_data()' from file '/Users/acof/.conan/data/boost/1.73.0/_/_/package/2bcd523eb799e86beac7172dddb46e02c19f269a/lib/libboost_log.a(core.o)' to global weak symbol 'boost::date_time::c_time::gmtime(long const*, tm*)' from file 'asio/libasio.a(asio_impl.cpp.o)' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function 'boost::log::v2s_mt_posix::core::implementation::thread_data::thread_data()' from file '/Users/acof/.conan/data/boost/1.73.0/_/_/package/2bcd523eb799e86beac7172dddb46e02c19f269a/lib/libboost_log.a(core.o)' to global weak symbol 'boost::date_time::c_time::gmtime(long const*, tm*)' from file 'asio/libasio.a(asio_impl.cpp.o)' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function 'boost::log::v2s_mt_posix::visitation_result boost::log::v2s_mt_posix::value_visitor_invoker<boost::mpl::vector2<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, std::__1::basic_string<wchar_t, std::__1::char_traits<wchar_t>, std::__1::allocator<wchar_t> > >, boost::log::v2s_mt_posix::fallback_to_none>::operator()<boost::log::v2s_mt_posix::sinks::aux::anonymous::message_printer>(boost::log::v2s_mt_posix::attribute_name const&, boost::log::v2s_mt_posix::attribute_value_set const&, boost::log::v2s_mt_posix::sinks::aux::anonymous::message_printer) const' from file '/Users/acof/.conan/data/boost/1.73.0/_/_/package/2bcd523eb799e86beac7172dddb46e02c19f269a/lib/libboost_log.a(default_sink.o)' to global weak symbol 'boost::log::v2s_mt_posix::aux::type_sequence_dispatcher_base::get_callback(boost::log::v2s_mt_posix::type_dispatcher*, boost::typeindex::stl_type_index)' from file 'utils/libutils.a(logging_initialser.cpp.o)' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.

To summarize boost compiles with a different visibility: This was likely caused by different translation units being compiled with different visibility settings.. Sooo I checked the recipes/boost/all/conanfile.py and yes there's actually a different hard-coded fvisibilty ONLY for iOS https://github.com/conan-io/conan-center-index/blame/cbef8be887845520b131e87faa441519d7144806/recipes/boost/all/conanfile.py#L643

My question is, is that necessary? All other libraries got no such visibility set. When I change the visibility of MY project to -fvisibility=hidden -fvisibility-inlines-hidden, these warnings disappear.

Wouldn't it make more sense to set -fvisibility=hidden -fvisibility-inlines-hidden in the profile, so all dependencies got the same visibility?

Thx for your time!

[SSE4]

as far as I remember, -fvisibility=hidden is strictly necessary, and only for iOS.

source:
https://github.com/danoli3/ofxiOSBoost/blob/master/scripts/build-libc%2B%2B#L70
https://github.com/mz2/boostoniphone/blob/master/boost.sh#L141

[qwertzui11]

that's what I first thought too... however I can't find any information about -fvisibility=hidden being mandatory for iOS... it seems however recommended.

[SSE4]

more information is here: boostorg/boost#190
seems like boost builds with -fvisibility=hidden by default.