revert to not hardcoding size of struct _starpu_mpi_envelope

mpi/src/starpu_mpi.c

@@ -1,6 +1,6 @@
 /* StarPU --- Runtime system for heterogeneous multicore architectures.
  *
- * Copyright (C) 2009, 2010-2015  Université de Bordeaux
+ * Copyright (C) 2009, 2010-2016  Université de Bordeaux
  * Copyright (C) 2010, 2011, 2012, 2013, 2014, 2015, 2016  CNRS
  *
  * StarPU is free software; you can redistribute it and/or modify
@@ -381,7 +381,7 @@ static void _starpu_mpi_isend_size_func(struct _starpu_mpi_req *req)
 		req->envelope->size = (starpu_ssize_t)req->count * size;
 		_STARPU_MPI_DEBUG(20, "Post MPI isend count (%ld) datatype_size %ld request to %d\n",req->count,starpu_data_get_size(req->data_handle), req->node_tag.rank);
 		_STARPU_MPI_COMM_TO_DEBUG(sizeof(struct _starpu_mpi_envelope), MPI_BYTE, req->node_tag.rank, _STARPU_MPI_TAG_ENVELOPE, _STARPU_MPI_TAG_ENVELOPE, req->node_tag.comm);
-		MPI_Isend(req->envelope, 24, MPI_BYTE, req->node_tag.rank, _STARPU_MPI_TAG_ENVELOPE, req->node_tag.comm, &req->size_req);
+		MPI_Isend(req->envelope, sizeof(struct _starpu_mpi_envelope), MPI_BYTE, req->node_tag.rank, _STARPU_MPI_TAG_ENVELOPE, req->node_tag.comm, &req->size_req);
 	}
 	else
 	{