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

[Bernhard Beschow]

Am 6. September 2022 17:52:24 UTC schrieb "Philippe Mathieu-Daudé" 
<f4bug@amsat.org>:
>On Tue, Sep 6, 2022 at 7:12 PM Bernhard Beschow <shentey@gmail.com> wrote:
>>
>> 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 
>> /home/zcone-pisint/Projects/qemu/src/include/glib-compat.h:32,
>>                    from 
>> /home/zcone-pisint/Projects/qemu/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".
>
>Could you amend the first line of `gcc --version`?

Hi Phil,

Yes, will do in v2.

Sorry for getting off-topic, but have you recognized my vt82c686 series? Your 
opinion would matter there and I'm not sure if my mail bounced. In my case 
Gmail likes to put your mail in the spam box :/

Regards,
Bernhard
>
>Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>
>> 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) {
>> --
>> 2.37.3
>>
>>