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

[Bernhard Beschow <shentey@gmail.com>]

Am 10. September 2022 15:11:17 UTC schrieb Bernhard Beschow <shentey@gmail.com>:
>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>

Forgot to add from v1:

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

>---
> 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) {