-latomic not added autmatically when using GCC on ARM (Raspberry Pi 4, Raspbian 32-bit)
Originally reported in https://github.com/arvidn/libtorrent/issues/5117#issue-695875535.
Basically, -latomic is not being added when it should, resulting in linking failures like the following:
[160/179] Linking CXX executable tools/session_log_alerts
FAILED: tools/session_log_alerts
: && /usr/bin/c++ -O3 -DNDEBUG tools/CMakeFiles/session_log_alerts.dir/session_log_alerts.cpp.o -o tools/session_log_alerts -Wl,-rpath,/home/pi/libtorrent/cmake-build-dir:/opt/boost-1.74.0/lib libtorrent-rasterbar.so.1.2.10 -lpthread
/usr/lib/arm-linux-gnueabihf/libssl.so /usr/lib/arm-linux-gnueabihf/libcrypto.so /opt/boost-1.74.0/lib/libboost_system.so.1.74.0 && :
/usr/bin/ld: libtorrent-rasterbar.so.1.2.10: undefined reference to `__atomic_compare_exchange_8'
/usr/bin/ld: libtorrent-rasterbar.so.1.2.10: undefined reference to `__atomic_load_8'
/usr/bin/ld: libtorrent-rasterbar.so.1.2.10: undefined reference to `__atomic_store_8'
/usr/bin/ld: libtorrent-rasterbar.so.1.2.10: undefined reference to `__atomic_fetch_add_8'
collect2: error: ld returned 1 exit statusThis seems to be a very prevalent problem. Here are some ways other projects that have run into this have solved the problem: https://github.com/pothosware/SoapyRTLSDR/pull/42 https://github.com/opencv/opencv/pull/15353
Patching in something like target_link_libraries(tgt PRIVATE atomic) in the CML or passing -DCMAKE_EXE_LINKER_FLAGS="-latomic", or using clang (9.0.1) instead of instead of GCC (8.3.0), can all be used to workaround this as well.