When I write a simple program using OpenMP, with a CMakeLists.txt like:
find_package(OpenMP REQUIRED)
add_definitions(${OpenMP_CXX_FLAGS})
add_executable(foo foo.cpp)
I get link errors:
foo.cpp: undefined reference to `omp_get_num_threads'
foo.cpp: undefined reference to `omp_get_thread_num'
...etc.
This is caused by the .o containing references to OMP methods, but the
linker does not link to the platform OpenMP library (e.g. libgomp.so for
gcc; similar issues seen with icc).
Does anyone have a preferred fix for this?
Ideas:
- find the appropriate library, set OpenMP_LIBRARY
- add OpenMP_C[XX]_FLAGS to target's LINK_FLAGS property
For the moment at least, I've solved this in my own project by creating
the following CMake function:
function(omp_add_flags TARGET LANG)
if(OPENMP_FOUND)
if(NOT LANG)
get_target_property(LANG ${TARGET} LINKER_LANGUAGE)
endif()
if(LANG MATCHES "C(XX)?")
set_property(TARGET ${TARGET} APPEND
PROPERTY COMPILE_FLAGS ${OpenMP_${LANG}_FLAGS})
set_property(TARGET ${TARGET} APPEND
PROPERTY LINK_FLAGS ${OpenMP_${LANG}_FLAGS})
else()
message(WARNING "omp_add_flags: target '${TARGET}'"
" link language '${LANG}' is not supported")
endif()
endif()
endfunction()
This might need some tweaking, but if the general idea seems like the
best way, I would propose adding this to FindOpenMP.cmake.
--
Matthew
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