# 9.4. ABI compatibility to previous versions of Open MPI

The Open MPI v5.0.x series maintains Application Binary Interface (ABI) compatibility for the C MPI bindings to the last major Open MPI release. Specifically, an application compiled with Open MPI v4.x can be executed with Open MPI v5.0.x without having to recompile the application.

Important

ABI is maintained for most of the Fortran MPI bindings, too — see below for additional information.

There are however a few scenarios where an application compiled with Open MPI v4.x might not execute correctly with Open MPI 5.0.

- Fortran compilers provide varying degrees of ABI guarantees between their releases. As such, Open MPI can only provide ABI guarantees with MPI applications that use the Fortran MPI bindings when all three entities — Open MPI v4.x, Open MPI v5.0.x, and the MPI application — were built with exactly the same Fortran compiler and environment.

  If these conditions are met, Open MPI’s ABI guarantees between the Open MPI v4.x and v5.0.x series are in effect, with the exception of the following cases:

  - When using the Fortran `mpi` module bindings with GCC compiler versions prior to v4.8, non-compliant Fortran interfaces for `MPI_Comm_spawn_multiple`, `MPI_Testall`, `MPI_Testsome`, `MPI_Waitall`, and `MPI_Waitsome` were removed starting with Open MPI v5.0.0.

  - When using the Fortran `mpi` module with modern Fortran compilers (e.g., GNU Fortran >= v4.9), Open MPI v5.0.0 removed the names from the MPI interfaces when there is only a single subroutine in the interface, and that subroutine name exactly matches the iterface name. This change is likely to make Open MPI v5.0.x’s `mpi` module bindings less restrictive than Open MPI v4.x, but it may also have ABI implications, depending on your Fortran compiler.

    See this git commit message for more details.

    Important

    This is likely a compiler-specific issue, and may need to be tested in your environment.

  - When using the Fortran `mpi_f08` module bindings in an environment where a Fortran `INTEGER` is 8 bytes but a C `int` is 4 bytes, the size of a `Type(MPI_Status)` was increased starting with Open MPI v5.0.0.

- Open MPI v5.0.0 removed support for the MPI C++ bindings. If an application was using the deprecated and now removed C++ bindings, it will not be able to compile or execute with Open MPI v5.0.0. For details on deprecated and removed functions see Removed MPI constructs and Deprecation warnings