Re: [PATCH 1/5] qom: Allow objects to be allocated with increased alignment

[Eduardo Habkost]

On Tue, Sep 15, 2020 at 10:46:31AM -0700, Richard Henderson wrote:
> It turns out that some hosts have a default malloc alignment less
> than that required for vectors.
> 
> We assume that, with compiler annotation on CPUArchState, that we
> can properly align the vector portion of the guest state.  Fix the
> alignment of the allocation by using qemu_memalloc when required.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Daniel P. Berrangé" <berrange@redhat.com>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> ---
>  include/qom/object.h |  4 ++++
>  qom/object.c         | 16 +++++++++++++---
>  2 files changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 056f67ab3b..d52d0781a3 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -770,6 +770,9 @@ struct Object
>   * @instance_size: The size of the object (derivative of #Object).  If
>   *   @instance_size is 0, then the size of the object will be the size of the
>   *   parent object.
> + * @instance_align: The required alignment of the object.  If @instance_align
> + *   is 0, then normal malloc alignment is sufficient; if non-zero, then we
> + *   must use qemu_memalign for allocation.
>   * @instance_init: This function is called to initialize an object.  The 
> parent
>   *   class will have already been initialized so the type is only responsible
>   *   for initializing its own members.
> @@ -807,6 +810,7 @@ struct TypeInfo
>      const char *parent;
>  
>      size_t instance_size;
> +    size_t instance_align;
>      void (*instance_init)(Object *obj);
>      void (*instance_post_init)(Object *obj);
>      void (*instance_finalize)(Object *obj);
> diff --git a/qom/object.c b/qom/object.c
> index 387efb25eb..2e53cb44a6 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -50,6 +50,7 @@ struct TypeImpl
>      size_t class_size;
>  
>      size_t instance_size;
> +    size_t instance_align;
>  
>      void (*class_init)(ObjectClass *klass, void *data);
>      void (*class_base_init)(ObjectClass *klass, void *data);
> @@ -114,6 +115,7 @@ static TypeImpl *type_new(const TypeInfo *info)
>  
>      ti->class_size = info->class_size;
>      ti->instance_size = info->instance_size;
> +    ti->instance_align = info->instance_align;
>  
>      ti->class_init = info->class_init;
>      ti->class_base_init = info->class_base_init;
> @@ -691,13 +693,21 @@ static void object_finalize(void *data)
>  static Object *object_new_with_type(Type type)
>  {
>      Object *obj;
> +    size_t size, align;
>  
>      g_assert(type != NULL);
>      type_initialize(type);
>  
> -    obj = g_malloc(type->instance_size);
> -    object_initialize_with_type(obj, type->instance_size, type);
> -    obj->free = g_free;
> +    size = type->instance_size;
> +    align = type->instance_align;
> +    if (align) {

If we check for (align > G_MEM_ALIGN) instead, we will be able to
set instance_align automatically at OBJECT_DEFINE_TYPE*.

> +        obj = qemu_memalign(align, size);
> +    } else {
> +        obj = g_malloc(size);
> +    }
> +
> +    object_initialize_with_type(obj, size, type);
> +    obj->free = (align ? qemu_vfree : g_free);
>  
>      return obj;
>  }
> -- 
> 2.25.1
> 

-- 
Eduardo