Is it ok for CMake to use c++, rather than mpicxx, to compile my code?

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I'm trying to build an executable from C++ source code which uses MPI, on a GNU/Linux Devuan Chimaera system. Now, I'm an MPI/OpenMP newbie, I'm just trying to adapt this code, which isn't mine, to be built with CMake - when before it had a Makefile. My build succeeds, but I'm seeing segfaults, so I want to make sure my problem isn't with the build phase, which bugs me.

My CMakeLists.txt has:

find_package(OpenMP REQUIRED)
find_package(MPI REQUIRED)

and my system has OpenMPI 4.1.1 installed, which is found. I do this for my target:

target_link_libraries(my_executable PRIVATE MPI::MPI_CXX OpenMP::OpenMP_CXX)

but nothing else which indicates its expecting to be compiled by mpicxx.

... and indeed, when I configure (with CMake 3.22.1) and then build, the usual c++ executable gets invoked to compile (and then link) the my_target executable.

Questions:

  • Can source code which originally was getting compiled with mpicxx be compiled with "just" a C++ compiler, with the appropriate includes?
  • Assuming there's any merit to using mpicxx for compilation - how do I get CMake to use it for my target?

Edit: It's been suggested to me to try using mpirun to run my program. With it, I get no segmentation faults, consistently; it's only when I run directly that I see them.

openmpi mpi openmp cmake c++
1 Answers
  • Can source code which originally was getting compiled with mpicxx be compiled with "just" a C++ compiler, with the appropriate includes?

Yes, and you're doing it correctly.

The MPI systems I've used (Cori, Perlmutter, Stampede) have all provided implementations that work correctly with CMake's MPI support. However, it's possible that a sufficiently poorly administered system will break this.

  • Assuming there's any merit to using mpicxx for compilation - how do I get CMake to use it for my target?

This is a toolchain setting... set CMAKE_CXX_COMPILER to /path/to/mpicxx either at the command line, in a preset, or in a toolchain file.

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