8001071: Add simple range check into VM implemenation of Unsafe access methods

Summary: Add simple check in debug version of VM.
Reviewed-by: twisti, johnc

hotspot/src/share/vm/prims/unsafe.cpp

@@ -124,6 +124,8 @@ inline void* index_oop_from_field_offset_long(oop p, jlong field_offset) {
       assert((void*)p->obj_field_addr<oop>((jint)byte_offset) == ptr_plus_disp,
              "raw [ptr+disp] must be consistent with oop::field_base");
     }
+    jlong p_size = HeapWordSize * (jlong)(p->size());
+    assert(byte_offset < p_size, err_msg("Unsafe access: offset " INT64_FORMAT " > object's size " INT64_FORMAT, byte_offset, p_size));
   }
 #endif
   if (sizeof(char*) == sizeof(jint))    // (this constant folds!)