Re: [PATCH v2] vhost: fix compilation issue in async path

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 10/5/22 17:11, Maxime Coquelin wrote:
> This patch fixes a compilation issue met with GCC 12 on
> LoongArch64:
> 
> In function ‘mbuf_to_desc’,
>      inlined from ‘vhost_enqueue_async_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1822:6,
>      inlined from ‘virtio_dev_rx_async_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1836:6,
>      inlined from ‘virtio_dev_rx_async_submit_packed’ at ../../../dpdk/lib/vhost/virtio_net.c:1895:7:
> ../../../dpdk/lib/vhost/virtio_net.c:1159:18: error: ‘buf_vec[0].buf_addr’ may be used uninitialized [-Werror=maybe-uninitialized]
>   1159 |         buf_addr = buf_vec[vec_idx].buf_addr;
>        |         ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../../../dpdk/lib/vhost/virtio_net.c: In function ‘virtio_dev_rx_async_submit_packed’:
> ../../../dpdk/lib/vhost/virtio_net.c:1834:27: note: ‘buf_vec’ declared here
>   1834 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
>        |                           ^~~~~~~
> 
> It happens because the compiler assumes that 'size'
> variable in vhost_enqueue_async_packed could wrap to 0 since
> 'size' is uint32_t and pkt->pkt_len too.
> 
> In practice, it would never happen since 'pkt->pkt_len' is
> unlikely to be close to UINT32_MAX, but let's just change
> 'size' to uint64_t to make the compiler happy without
> having to add runtime checks.
> 
> Fixes: 873e8dad6f49 ("vhost: support packed ring in async datapath")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Forgot to report the R-by from David on v1:
Reviewed-by: David Marchand <david.marchand@redhat.com>

> ---
>   lib/vhost/virtio_net.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c
> index 8f4d0f0502..b86fb26040 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -1780,7 +1780,7 @@ vhost_enqueue_async_packed(struct virtio_net *dev,
>   	uint16_t buf_id = 0;
>   	uint32_t len = 0;
>   	uint16_t desc_count = 0;
> -	uint32_t size = pkt->pkt_len + sizeof(struct virtio_net_hdr_mrg_rxbuf);
> +	uint64_t size = pkt->pkt_len + sizeof(struct virtio_net_hdr_mrg_rxbuf);
>   	uint32_t buffer_len[vq->size];
>   	uint16_t buffer_buf_id[vq->size];
>   	uint16_t buffer_desc_count[vq->size];