Warnings when compiling Python bindings on macOS + clang 12.0.0

[ntamas]

I'm getting the following warnings while compiling the Python bindings on macOS:

ld: warning: direct access in function 'pybind11_init_cflinkcpp(pybind11::module_&)' from file '/tmp/lto.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::valid() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'pybind11_init_cflinkcpp(pybind11::module_&)' from file '/tmp/lto.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::port() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'char const* std::__1::__find_end<bool (*)(char, char), char const*, char const*>(char const*, char const*, char const*, char const*, bool (*)(char, char), std::__1::random_access_iterator_tag, std::__1::random_access_iterator_tag)' from file '/tmp/lto.o' to global weak symbol 'std::__1::char_traits<char>::eq(char, char)' from file 'libcrazyflieLinkCpp.a(Connection.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.

The Python bindings seems to work fine, though, at least I could definitely run the console example without problems so I'm not sure this is something to worry about.

[knmcguire]

sorry for the late reply... I guess this is still an issue for you currently right?

Probably not immediately something to worry about I would say. @whoenig is more acquinted with python binding though.

[ntamas]

Yes, it's still an issue with the latest master, although the messages are a bit different now:

ld: warning: direct access in function 'pybind11_init_cflinkcpp(pybind11::module_&)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::valid() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'pybind11_init_cflinkcpp(pybind11::module_&)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::valid() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'pybind11_init_cflinkcpp(pybind11::module_&)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::port() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'pybind11_init_cflinkcpp(pybind11::module_&)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'bitcraze::crazyflieLinkCpp::Packet::port() const' from file 'libcrazyflieLinkCpp.a(Connection.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 'unsigned long std::__1::__str_rfind<char, unsigned long, std::__1::char_traits<char>, 18446744073709551615ul>(char const*, unsigned long, char const*, unsigned long, unsigned long)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'std::__1::char_traits<char>::eq(char, char)' from file 'libcrazyflieLinkCpp.a(Connection.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 'unsigned long std::__1::__str_rfind<char, unsigned long, std::__1::char_traits<char>, 18446744073709551615ul>(char const*, unsigned long, char const*, unsigned long, unsigned long)' from file 'CMakeFiles/cflinkcpp.dir/src/python_bindings.cpp.o' to global weak symbol 'std::__1::char_traits<char>::eq(char, char)' from file 'libcrazyflieLinkCpp.a(Connection.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.

Furthermore, I needed to patch CMakeLists.txt to build on macOS:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d2f972c..a543583 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -75,8 +75,8 @@ add_library(crazyflieLinkCpp

 # Apple macOS libraries
 if (APPLE)
-  set(CMAKE_EXE_LINKER_FLAGS "-lobjc -framework IOKit -framework CoreFoundation")
-  set(CMAKE_MODULE_LINKER_FLAGS "-lobjc -framework IOKit -framework CoreFoundation")
+  set(CMAKE_EXE_LINKER_FLAGS "-lobjc -framework IOKit -framework CoreFoundation -framework Security")
+  set(CMAKE_MODULE_LINKER_FLAGS "-lobjc -framework IOKit -framework CoreFoundation -framework Security")
 endif()

 # Link pthread on Linux and Mac only

Required linker flags were taken from the pkg-config configuration file from libusb:

Libs.private:  -lobjc -Wl,-framework,IOKit -Wl,-framework,CoreFoundation -Wl,-framework,Security

[ntamas]

CMakeLists.txt patch as outlined in the previous comment is not necessary any more now that 2095781 was committed.

The original warnings are still there, but indeed they don't seem to cause any problems.