qom: Assert instance size in object_initialize_with_type()

This catches objects initializing beyond allocated memory, e.g.,
when subtypes get extended with instance state of their own.
Suggested-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndreas Färber <afaerber@suse.de>

include/qom/object.h

@@ -586,13 +586,14 @@ Object *object_new_with_type(Type type);
 /**
  * object_initialize_with_type:
  * @data: A pointer to the memory to be used for the object.
+ * @size: The maximum size available at @data for the object.
  * @type: The type of the object to instantiate.
  *
  * This function will initialize an object.  The memory for the object should
  * have already been allocated.  The returned object has a reference count of 1,
  * and will be finalized when the last reference is dropped.
  */
-void object_initialize_with_type(void *data, Type type);
+void object_initialize_with_type(void *data, size_t size, Type type);
 
 /**
  * object_initialize:

qom/object.c

@@ -311,7 +311,7 @@ static void object_post_init_with_type(Object *obj, TypeImpl *ti)
     }
 }
 
-void object_initialize_with_type(void *data, TypeImpl *type)
+void object_initialize_with_type(void *data, size_t size, TypeImpl *type)
 {
     Object *obj = data;
 
@@ -320,6 +320,7 @@ void object_initialize_with_type(void *data, TypeImpl *type)
 
     g_assert(type->instance_size >= sizeof(Object));
     g_assert(type->abstract == false);
+    g_assert(size >= type->instance_size);
 
     memset(obj, 0, type->instance_size);
     obj->class = type->class;
@@ -333,7 +334,7 @@ void object_initialize(void *data, size_t size, const char *typename)
 {
     TypeImpl *type = type_get_by_name(typename);
 
-    object_initialize_with_type(data, type);
+    object_initialize_with_type(data, size, type);
 }
 
 static inline bool object_property_is_child(ObjectProperty *prop)
@@ -424,7 +425,7 @@ Object *object_new_with_type(Type type)
     type_initialize(type);
 
     obj = g_malloc(type->instance_size);
-    object_initialize_with_type(obj, type);
+    object_initialize_with_type(obj, type->instance_size, type);
     obj->free = g_free;
 
     return obj;