Re: [PATCH v2] hw/virtio/vhost-shadow-virtqueue: Silence GCC error "maybe-uninitialized"

[Laurent Vivier]

Le 10/09/2022 à 17:11, Bernhard Beschow a écrit :
> GCC issues a false positive warning, resulting in build failure with -Werror:
>
>    In file included from /usr/include/glib-2.0/glib.h:114,
>                     from src/include/glib-compat.h:32,
>                     from src/include/qemu/osdep.h:144,
>                     from ../src/hw/virtio/vhost-shadow-virtqueue.c:10:
>    In function ‘g_autoptr_cleanup_generic_gfree’,
>        inlined from ‘vhost_handle_guest_kick’ at 
> ../src/hw/virtio/vhost-shadow-virtqueue.c:292:42:
>    /usr/include/glib-2.0/glib/glib-autocleanups.h:28:3: error: ‘elem’ may be 
> used uninitialized [-Werror=maybe-uninitialized]
>       28 |   g_free (*pp);
>          |   ^~~~~~~~~~~~
>    ../src/hw/virtio/vhost-shadow-virtqueue.c: In function 
> ‘vhost_handle_guest_kick’:
>    ../src/hw/virtio/vhost-shadow-virtqueue.c:292:42: note: ‘elem’ was declared 
> here
>      292 |             g_autofree VirtQueueElement *elem;
>          |                                          ^~~~
>    cc1: all warnings being treated as errors
>
> There is actually no problem since "elem" is initialized in both branches.
> Silence the warning by initializig it with "NULL".
>
> $ gcc --version
> gcc (GCC) 12.2.0
>
> Fixes: 9c2ab2f1ec333be8614cc12272d4b91960704dbe ("vhost: stop transfer elem 
> ownership in vhost_handle_guest_kick")
> Signed-off-by: Bernhard Beschow <shentey@gmail.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> index e8e5bbc368..596d4434d2 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -289,7 +289,7 @@ static void vhost_handle_guest_kick(VhostShadowVirtqueue 
> *svq)
>           virtio_queue_set_notification(svq->vq, false);
>   
>           while (true) {
> -            g_autofree VirtQueueElement *elem;
> +            g_autofree VirtQueueElement *elem = NULL;
>               int r;
>   
>               if (svq->next_guest_avail_elem) {

Applied to my trivial-patches branch.

Thanks,
Laurent