I got the following error from the linker ld.gold while linking libsumo in a build of SUMO with bindings to FOX-toolkit:
g++ -fPIC -O2 -ftree-vectorize -march=native -fno-math-errno -std=c++11 -Wall -pedantic -Wextra -fPIC -O3 -DNDEBUG -L/apps/PROJ/7.0.0-GCCcore-9.3.0/lib -L/apps/GDAL/3.0.4-foss-2020a-Python-3.8.2/lib -L/apps/GL2PS/1.4.2-GCCcore-9.3.0/lib64 -L/apps/GL2PS/1.4.2-GCCcore-9.3.0/lib -L/apps/FOX-Toolkit/1.6.57-GCCcore-9.3.0/lib64 -L/apps/FOX-Toolkit/1.6.57-GCCcore-9.3.0/lib -L/apps/Xerces-C++/3.2.3-GCCcore-9.3.0/lib64 -L/apps/Python/3.8.2-GCCcore-9.3.0/lib -L/apps/Java/11.0.2/lib -L/apps/FFTW/3.3.8-gompi-2020a/lib -L/apps/ScaLAPACK/2.1.0-gompi-2020a/lib -L/apps/OpenBLAS/0.3.9-GCC-9.3.0/lib -L/apps/GCCcore/9.3.0/lib64 -L/apps/GCCcore/9.3.0/lib -shared -o build/SUMO/1.0.0/foss-2020a-Python-3.8.2/sumo-1.0.0/tools/libsumo/_libsumo.so CMakeFiles/_libsumo.dir///tools/libsumo/libsumoPYTHON_wrap.cxx.o -Wl,–whole-archive ../netload/libnetload.a ../microsim/libmicrosim.a ../microsim/cfmodels/libmicrosim_cfmodels.a ../microsim/lcmodels/libmicrosim_lcmodels.a ../microsim/devices/libmicrosim_devices.a ../microsim/output/libmicrosim_output.a ../microsim/pedestrians/libmicrosim_pedestrians.a ../microsim/trigger/libmicrosim_trigger.a ../microsim/actions/libmicrosim_actions.a ../microsim/traffic_lights/libmicrosim_traffic_lights.a ../mesosim/libmesosim.a ../traci-server/libtraciserver.a liblibsumostatic.a ../utils/emissions/libutils_emissions.a ../foreign/PHEMlight/cpp/libforeign_phemlight.a ../utils/vehicle/libutils_vehicle.a ../utils/distribution/libutils_distribution.a ../utils/shapes/libutils_shapes.a ../utils/options/libutils_options.a ../utils/xml/libutils_xml.a ../utils/geom/libutils_geom.a ../utils/common/libutils_common.a ../utils/importio/libutils_importio.a ../utils/iodevices/libutils_iodevices.a ../foreign/tcpip/libforeign_tcpip.a /apps/Xerces-C++/3.2.3-GCCcore-9.3.0/lib64/libxerces-c.so /apps/PROJ/7.0.0-GCCcore-9.3.0/lib/libproj.so -L/apps/FOX-Toolkit/1.6.57-GCCcore-9.3.0/lib -lFOX-1.6 -lX11 -lXext -lfreetype -lfontconfig -lXft -lXcursor -lXrender -lXrandr -lXfixes -lXi -ldl -lpthread -lrt -lm -lpthread -ljpeg -lpng -ltiff -lz -lbz2 -Wl,–no-whole-archive /apps/Python/3.8.2-GCCcore-9.3.0/lib/libpython3.8.so
/apps/binutils/2.34-GCCcore-9.3.0/bin/ld.gold: error: /usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): multiple definition of ‘__pthread_atfork’
/apps/binutils/2.34-GCCcore-9.3.0/bin/ld.gold: /usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): previous definition here
/apps/binutils/2.34-GCCcore-9.3.0/bin/ld.gold: error: /usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): multiple definition of ‘pthread_atfork’
/apps/binutils/2.34-GCCcore-9.3.0/bin/ld.gold: /usr/lib64/libpthread_nonshared.a(pthread_atfork.oS): previous definition here
collect2: error: ld returned 1 exit status
make[2]: *** [build/SUMO/1.0.0/foss-2020a-Python-3.8.2/sumo-1.0.0/tools/libsumo/_libsumo.so] Error 1
make[2]: Leaving directory ‘build/SUMO/1.0.0/foss-2020a-Python-3.8.2/easybuild_obj’
make[1]: *** [src/libsumo/CMakeFiles/_libsumo.dir/all] Error 2
make[1]: Leaving directory ‘build/SUMO/1.0.0/foss-2020a-Python-3.8.2/easybuild_obj’
make: *** [all] Error 2
The main errors from the linker are the multiple definition of 'symbol' errors, which are caused by duplicate LDFLAGS in the linker command. In this case, -lpthread is declared twice
g++ […] -ldl -lpthread -lrt -lm -lpthread -ljpeg -lpng […]
This error can be easily solved by removing the duplicate linker flag. However, depending on the underlying build system, this can be more or less involved. If the build is done with make, it can be just a matter of manually editing the corresponding Makefile.
In this case, the build is based on CMake and hence, it is necessary to dig into its modules to find the spot where this duplication happens. Once the origin of the duplication is found, CMake provides the REMOVE_DUPLICATES method to clean all duplicates from a list.
The following code snippet automatically removes duplicate elements in FOX_LIBRARY, which contains these flags in the build of SUMO (cmake_modules/FindFOX.cmake):
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separate_arguments(FOX_LIBRARY)
list(REMOVE_DUPLICATES FOX_LIBRARY)
string(REPLACE ";" " " FOX_LIBRARY "${FOX_LIBRARY}")