GCC* 4.9 was released on April 22, 2014. This release now supports Version 4.0 of the OpenMP* specification for the C and C++ compilers. The interface between the compilers and the GCC OpenMP runtime library (libgomp) was changed as part of this development. As a result, code compiled by GCC 4.9 using the –fopenmp compiler option cannot be successfully linked with the Intel® OpenMP runtime library (libiomp5), even if it uses no new OpenMP 4.0 features. Linking may fail with a message such as “undefined reference to `GOMP_parallel'”, or (if both libiomp5.so and libgomp.so are linked in) linking may appear to succeed, but the executable code may crash at runtime since having two different OpenMP runtimes linked into the same process is fatal.
Intel is working to restore the ability to link OpenMP code compiled by GCC 4.9 with OpenMP code compiled by the Intel compilers. In the meantime, we recommend against using GCC 4.9 –fopenmp to compile code that you plan to link with anything containing Intel-compiled OpenMP code, including the Intel® Math Kernel Library (MKL) and Intel® Integrated Performance Primitives (IPP) performance libraries.