RE: [PATCH] vhost: compilation fix for GCC-12

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: Amit Prakash Shukla <amitprakashs@marvell.com>
> Sent: Thursday, September 1, 2022 4:50 PM
> To: Maxime Coquelin <maxime.coquelin@redhat.com>; Chenbo Xia <chenbo.xia@intel.com>
> Cc: dev@dpdk.org; jerinj@marvell.com; stable@dpdk.org; Amit Prakash Shukla
> <amitprakashs@marvell.com>
> Subject: [PATCH] vhost: compilation fix for GCC-12
> 
> ../lib/vhost/virtio_net.c:941:35: error:
> 		'buf_vec[0].buf_len' may be used uninitialized
> 		[-Werror=maybe-uninitialized]
>   941 |         buf_len = buf_vec[vec_idx].buf_len;
>       |                   ~~~~~~~~~~~~~~~~^~~~~~~~
> ../lib/vhost/virtio_net.c: In function 'virtio_dev_rx_packed':
> ../lib/vhost/virtio_net.c:1285:27: note: 'buf_vec' declared here
>  1285 |         struct buf_vector buf_vec[BUF_VECTOR_MAX];
>       |                           ^~~~~~~
> cc1: all warnings being treated as errors
> 
> Fixes: 93520085efda ("vhost: add packed ring single enqueue")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Amit Prakash Shukla <amitprakashs@marvell.com>
> ---
>  lib/vhost/virtio_net.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c index b3d954aab4..0220bc923c
> 100644
> --- a/lib/vhost/virtio_net.c
> +++ b/lib/vhost/virtio_net.c
> @@ -1069,6 +1069,12 @@ vhost_enqueue_single_packed(struct virtio_net *dev,
>  	else
>  		max_tries = 1;
> 
> +	/* To avoid GCC-12 warning.
> +	 * GCC-12 is not evaluating sizeof at compile time.
Is this a compiler behavior change against previous versions?
I tried to find some clue from gcc-12 doc but got nothing. Can you point me to any material?

> +	 */
> +	if (unlikely(size == 0))
> +		return -1;
> +
>  	while (size > 0) {
Change 'while(){}' to 'do{}while()' can be a simpler solution. What do you think?

Thanks.

>  		/*
>  		 * if we tried all available ring items, and still @@ -1574,6 +1580,12 @@
> vhost_enqueue_async_packed(struct virtio_net *dev,
>  	else
>  		max_tries = 1;
> 
> +	/* To avoid GCC-12 warning.
> +	 * GCC-12 is not evaluating sizeof at compile time.
> +	 */
> +	if (unlikely(size == 0))
> +		return -1;
> +
>  	while (size > 0) {
>  		/*
>  		 * if we tried all available ring items, and still
> --
> 2.25.1