undefined reference to symbol 'omp_get_max_threads@@OMP_1.0' during make on Debian "jessie"

[rebos]

Im trying to build current "osrm-backend" - cloned on 2015-03-19 - on Debian "jessie".

During make it comes to this error message:

[...]
Linking CXX executable osrm-extract
/usr/bin/ld: CMakeFiles/osrm-extract.dir/extractor/extraction_containers.cpp.o: undefined reference to symbol 'omp_get_max_threads@@OMP_1.0'
//usr/lib/x86_64-linux-gnu/libgomp.so.1: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
CMakeFiles/osrm-extract.dir/build.make:268: recipe for target 'osrm-extract' failed
make[2]: *** [osrm-extract] Error 1
CMakeFiles/Makefile2:555: recipe for target 'CMakeFiles/osrm-extract.dir/all' failed
make[1]: *** [CMakeFiles/osrm-extract.dir/all] Error 2
Makefile:117: recipe for target 'all' failed
make: *** [all] Error 2

I found issues #977, #1361 and #1373 which make me think, the problem should already be solved. But currently the error still occurs on my development system.

Inspired by the issues mentioned, I found a workaround by editing "CMakeLists.txt". I added "target_link_libraries(osrm-extract gomp)" to a certain paragraph. It looks like this:

if(UNIX AND NOT APPLE)
  target_link_libraries(osrm-prepare rt)
  target_link_libraries(osrm-extract gomp)
  target_link_libraries(osrm-datastore rt)
  target_link_libraries(OSRM rt)
endif()

After that "make" and "make install" successfully finish as expected. I have to admit, that I actually don't know, what this change by me really does or if it has unwanted side-effects. It seems to work for me. But it would be nice, if someone understanding the problem, could repair this.

Thanks and greetings,
rebos

[lhahne]

I just got pretty much the same error on Centos 7 with current master

extraction_containers.cpp:(.text._ZN5stxxl4sortINS_15vector_iteratorI21InternalExtractorEdgeNS_2RCEyxLj2097152ENS_9lru_pagerILj8EEELj4EEE17CmpEdgeByTargetIDEEvT_S8_T0_y[_ZN5stxxl4sortINS_15vector_iteratorI21InternalExtractorEdgeNS_2RCEyxLj2097152ENS_9lru_pagerILj8EEELj4EEE17CmpEdgeByTargetIDEEvT_S8_T0_y]+0x1731): undefined reference to `omp_get_max_threads'

I managed to fix this by adding the following line to CMakeLists.txt

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fopenmp")

[DennisOSRM]

try the latest code from develop branch. it should already contain a fix for this issue

[rebos]

Thanks for the quick response!

Not being a developer I cowardly preferred stable "v4.5.0" ;-) But after checking out "develop" I was able to run "make" successfully. The essential changes during my effort were these:

git clone --no-checkout https://github.com/Project-OSRM/osrm-backend.git
cd osrm-backend
git checkout develop

Building on this branch I did not need to edit any files.

Greetings,
rebos