Correctly compute the space needed for the args.

Add checks to bail out if our precomputed value is less
than needed (we are already at fault).

(cherry picked from commit open-mpi/ompi@16d9f71)

Author: bosilca

ompi/datatype/ompi_datatype_args.c

@@ -3,7 +3,7 @@
  * Copyright (c) 2004-2007 The Trustees of Indiana University and Indiana
  *                         University Research and Technology
  *                         Corporation.  All rights reserved.
- * Copyright (c) 2004-2013 The University of Tennessee and The University
+ * Copyright (c) 2004-2016 The University of Tennessee and The University
  *                         of Tennessee Research Foundation.  All rights
  *                         reserved.
  * Copyright (c) 2004-2006 High Performance Computing Center Stuttgart,
@@ -44,12 +44,12 @@ __ompi_datatype_create_from_args( int32_t* i, OPAL_PTRDIFF_TYPE * a,
                                   ompi_datatype_t** d, int32_t type );
 
 typedef struct __dt_args {
-    int                ref_count;
-    int                create_type;
+    int32_t            ref_count;
+    int32_t            create_type;
     size_t             total_pack_size;
-    int                ci;
-    int                ca;
-    int                cd;
+    int32_t            ci;
+    int32_t            ca;
+    int32_t            cd;
     int*               i;
     OPAL_PTRDIFF_TYPE* a;
     ompi_datatype_t**  d;
@@ -71,11 +71,11 @@ typedef struct __dt_args {
 #endif  /* OPAL_ALIGN_WORD_SIZE_INTEGERS */
 
 /**
- * Some architecture require that 64 bits pointers (to pointers) has to
- * be 64 bits aligned. As in the ompi_datatype_args_t structure we have 2 such
- * pointers and one to an array of ints, if we start by setting the 64
- * bits aligned one we will not have any trouble. Problem arise on
- * SPARC 64.
+ * Some architectures require 64 bits pointers (to pointers) to
+ * be 64 bits aligned. As in the ompi_datatype_args_t structure we have
+ * 2 such array of pointers and one to an array of ints, if we start by
+ * setting the 64 bits aligned one we will not have any trouble. Problem
+ * originally reported on SPARC 64.
  */
 #define ALLOC_ARGS(PDATA, IC, AC, DC)                                   \
     do {                                                                \
@@ -236,9 +236,8 @@ int32_t ompi_datatype_set_args( ompi_datatype_t* pData,
              */
             OBJ_RETAIN( d[pos] );
             pArgs->total_pack_size += ((ompi_datatype_args_t*)d[pos]->args)->total_pack_size;
-        } else {
-            pArgs->total_pack_size += 2 * sizeof(int);  /* _NAMED + predefined id */
         }
+        pArgs->total_pack_size += sizeof(int);  /* each data has an ID */
     }
 
     return OMPI_SUCCESS;
@@ -497,6 +496,12 @@ int ompi_datatype_get_pack_description( ompi_datatype_t* datatype,
             __ompi_datatype_pack_description( datatype, &recursive_buffer, &next_index );
 
             if (!ompi_datatype_is_predefined(datatype)) {
+                /* If the precomputed size is not large enough we're already in troubles, we
+                 * have overwritten outside of the allocated buffer. Raise the alarm !
+                 * If not reassess the size of the packed buffer necessary for holding the
+                 * datatype description.
+                 */
+                assert(args->total_pack_size >= (uintptr_t)((char*)recursive_buffer - (char *) packed_description));
                 args->total_pack_size = (uintptr_t)((char*)recursive_buffer - (char *) packed_description);
             }