Re: [Qemu-devel] [PATCH qom v1 1/1] qom/object.c: Split out object and class caches.

[Edgar E. Iglesias]

On Wed, Nov 27, 2013 at 08:27:33PM -0800, Peter Crosthwaite wrote:
> The object-cast and class-cast caches cannot be shared because class
> caching is conditional on the target type not being an interface and
> object caching is unconditional. Leads to a bug when a class cast
> to an interface follows an object cast to the same interface type:
> 
> FooObject = FOO(obj);
> FooClass = FOO_GET_CLASS(obj);
> 
> Where TYPE_FOO is an interface. The first (object) cast will be
> successful and cache the casting result (i.e. TYPE_FOO will be cached).
> The second (class) cast will then check the shared cast cache
> and register a hit. The issue is, when a class cast hits in the cache
> it just returns a pointer cast of the input class (i.e. the concrete
> class).
> 
> When casting to an interface, the cast itself must return the
> interface class, not the concrete class. The implementation of class
> cast caching already ensures that the returned cast result is only
> a pointer cast before caching. The object cast logic however does
> not have this check.
> 
> Resolve by just splitting the object and class caches.
> 
> Signed-off-by: Peter Crosthwaite <address@hidden>

Reviewed-by: Edgar E. Iglesias <address@hidden>



> ---
> 
>  include/qom/object.h |  3 ++-
>  qom/object.c         | 13 +++++++------
>  2 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index a275db2..5f78847 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -358,7 +358,8 @@ struct ObjectClass
>      Type type;
>      GSList *interfaces;
>  
> -    const char *cast_cache[OBJECT_CLASS_CAST_CACHE];
> +    const char *object_cast_cache[OBJECT_CLASS_CAST_CACHE];
> +    const char *class_cast_cache[OBJECT_CLASS_CAST_CACHE];
>  
>      ObjectUnparent *unparent;
>  };
> diff --git a/qom/object.c b/qom/object.c
> index fc19cf6..21b5a0b 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -458,7 +458,7 @@ Object *object_dynamic_cast_assert(Object *obj, const 
> char *typename,
>      Object *inst;
>  
>      for (i = 0; obj && i < OBJECT_CLASS_CAST_CACHE; i++) {
> -        if (obj->class->cast_cache[i] == typename) {
> +        if (obj->class->object_cast_cache[i] == typename) {
>              goto out;
>          }
>      }
> @@ -475,9 +475,10 @@ Object *object_dynamic_cast_assert(Object *obj, const 
> char *typename,
>  
>      if (obj && obj == inst) {
>          for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) {
> -            obj->class->cast_cache[i - 1] = obj->class->cast_cache[i];
> +            obj->class->object_cast_cache[i - 1] =
> +                    obj->class->object_cast_cache[i];
>          }
> -        obj->class->cast_cache[i - 1] = typename;
> +        obj->class->object_cast_cache[i - 1] = typename;
>      }
>  
>  out:
> @@ -547,7 +548,7 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass 
> *class,
>      int i;
>  
>      for (i = 0; class && i < OBJECT_CLASS_CAST_CACHE; i++) {
> -        if (class->cast_cache[i] == typename) {
> +        if (class->class_cast_cache[i] == typename) {
>              ret = class;
>              goto out;
>          }
> @@ -568,9 +569,9 @@ ObjectClass *object_class_dynamic_cast_assert(ObjectClass 
> *class,
>  #ifdef CONFIG_QOM_CAST_DEBUG
>      if (class && ret == class) {
>          for (i = 1; i < OBJECT_CLASS_CAST_CACHE; i++) {
> -            class->cast_cache[i - 1] = class->cast_cache[i];
> +            class->class_cast_cache[i - 1] = class->class_cast_cache[i];
>          }
> -        class->cast_cache[i - 1] = typename;
> +        class->class_cast_cache[i - 1] = typename;
>      }
>  out:
>  #endif
> -- 
> 1.8.4.4
> 
>