Re: [PATCH v2 18/22] hw/virtio: fix -Werror=maybe-uninitialized false-positive

[Stefano Garzarella]

On Tue, Sep 24, 2024 at 05:05:49PM GMT, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>

For the title: I don't think it is a false positive, but a real fix,
indeed maybe not a complete one.

> ../hw/virtio/vhost-shadow-virtqueue.c:545:13: error: ‘r’ may be used 
> uninitialized [-Werror=maybe-uninitialized]
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.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 fc5f408f77..cd29cc795b 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -526,7 +526,7 @@ static void vhost_svq_flush(VhostShadowVirtqueue *svq,
> size_t vhost_svq_poll(VhostShadowVirtqueue *svq, size_t num)
> {
>     size_t len = 0;
> -    uint32_t r;
> +    uint32_t r = 0;
>
>     while (num--) {

I think we should move the initialization to 0 here in the loop:

          uint32_t r = 0;

>         int64_t start_us = g_get_monotonic_time();

...

          vhost_svq_get_buf(svq, &r);
          len += r;
      }

This because we don't check vhost_svq_get_buf() return value.

IIUC, in that function, `r` is set only if the return value of
vhost_svq_get_buf() is not null, so if we don't check its return value,
we should set `r` to 0 on every cycle (or check the return value of
course).

Thanks,
Stefano