Hello,

I was trying to build OpenBLAS 0.3.30 with NVHPC (25.5 and 25.7). However, cmake fails early with this message :

Multiple OpenMP runtime libraries detected. Mixed OpenMP runtime linkage is dangerous. You may pass -DOpenMP_LANG_LIB_NAMES and -DOpenMP_omp_LIBRARY to manually choose the OpenMP library

This comes from these lines in system.cmake , that were introduced between 0.3.29 and 0.3.30 :

I dag a bit more and dumped some variables :

        message("OpenMP_C_FOUND       = ${OpenMP_C_FOUND}")
        message("OpenMP_Fortran_FOUND = ${OpenMP_Fortran_FOUND}")
        message("OpenMP_VERSION       = ${OpenMP_VERSION}")
        message("OpenMP_C_LIB_NAMES   = ${OpenMP_C_LIB_NAMES}")
        message("OpenMP_Fortran_LIB_NAMES = ${OpenMP_Fortran_LIB_NAMES}")
        message("OMP_C_LIB            = ${OMP_C_LIB}")
        message("OMP_Fortran_LIB      = ${OMP_Fortran_LIB}")

With GCC, I get

OpenMP_C_FOUND       = TRUE
OpenMP_Fortran_FOUND = TRUE
OpenMP_VERSION       =
OpenMP_C_LIB_NAMES   = gomp;pthread
OpenMP_Fortran_LIB_NAMES = gomp;pthread
OMP_C_LIB            = /home/morvana/compilers/gcc/15.1.0/prefix/lib64/libgomp.so;/lib/x86_64-linux-gnu/libpthread.a
OMP_Fortran_LIB      = /home/morvana/compilers/gcc/15.1.0/prefix/lib64/libgomp.so;/lib/x86_64-linux-gnu/libpthread.a

But for NVHPC, I get this :

OpenMP_C_FOUND       = TRUE
OpenMP_Fortran_FOUND = TRUE
OpenMP_VERSION       =
OpenMP_C_LIB_NAMES   =
OpenMP_Fortran_LIB_NAMES =
OMP_C_LIB            = OMP_C_LIB-NOTFOUND
OMP_Fortran_LIB      = OMP_Fortran_LIB-NOTFOUND

So I have the feeling the FindOpenMP from CMake (https://github.com/Kitware/CMake/blob/master/Modules/FindOpenMP.cmake) is not working properly with NVidia OpenMP. Do you share my opinion, before I open an issue over there ?

I add these flags to the cmake line as workaround at the moment :

            OPENBLAS_CMAKE_EXTRA_FLAGS="-DOpenMP_C_LIB_NAMES=nvomp -DOpenMP_Fortran_LIB_NAMES=nvomp"
            OPENBLAS_CMAKE_EXTRA_FLAGS+=" -DOpenMP_nvomp_LIBRARY=${NVHPC_ROOT}/compilers/lib/libnvomp.a"

Do you have a better one to propose ?

Best.