Re: [PATCH v2] vhost: fix build

[zhoumin <zhoumin@loongson.cn>]

Kindly ping.

Any feedback is appreciated.


On 2022年08月29日 16:29, Min Zhou wrote:
> On CentOS 8 or Debian 10.4 systems using gcc 12.1 to cross
> compile DPDK, gcc shows a following warning which will cause
> build to fail when build is run with -werror:
>
> In function 'mbuf_to_desc',
>      inlined from 'vhost_enqueue_async_packed' at ../lib/vhost/virtio_net.c:1826:6,
>      inlined from 'virtio_dev_rx_async_packed' at ../lib/vhost/virtio_net.c:1840:6,
>      inlined from 'virtio_dev_rx_async_submit_packed.constprop' at ../lib/vhost/virtio_net.c:1900:7:
> ../lib/vhost/virtio_net.c:1161:35: error: 'buf_vec[0].buf_len' may be used uninitialized [-Werror=maybe-uninitialized]
>   1161 |         buf_len = buf_vec[vec_idx].buf_len;
>        |                   ~~~~~~~~~~~~~~~~^~~~~~~~
> ../lib/vhost/virtio_net.c: In function 'virtio_dev_rx_async_submit_packed.constprop':
> ../lib/vhost/virtio_net.c:1838:27: note: 'buf_vec' declared here
>   1838 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
>        |                           ^~~~~~~
> cc1: all warnings being treated as errors
>
> Actually, there are eight places to see the same codes in the file
> lib/vhost/virtio_net.c, and all these `buf_vec` arraies are
> initialized by sub-function calls under various conditions.
>
> Although It's hard to understand why gcc just emits warning at one
> of the eight places, adding validity checks for array length is
> reasonable and can also fix the warning.
>
> Signed-off-by: David Marchand <david.marchand@redhat.com>
> Signed-off-by: Min Zhou <zhoumin@loongson.cn>
> ---
>   lib/vhost/virtio_net.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 35fa4670fd..99233f1759 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -1153,7 +1153,7 @@ mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	struct virtio_net_hdr_mrg_rxbuf tmp_hdr, *hdr = NULL;
>   	struct vhost_async *async = vq->async;
>   
> -	if (unlikely(m == NULL))
> +	if (unlikely(m == NULL || nr_vec == 0))
>   		return -1;
>   
>   	buf_addr = buf_vec[vec_idx].buf_addr;
> @@ -2673,6 +2673,9 @@ desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
>   	struct vhost_async *async = vq->async;
>   	struct async_inflight_info *pkts_info;
>   
> +	if (unlikely(nr_vec == 0))
> +		return -1;
> +
>   	buf_addr = buf_vec[vec_idx].buf_addr;
>   	buf_iova = buf_vec[vec_idx].buf_iova;
>   	buf_len = buf_vec[vec_idx].buf_len;