[PATCH] vhost: compilation fix for GCC-12

[Amit Prakash Shukla]

Thanks Ruifeng for the code review and feedback. Please find my response inline.

> -----Original Message-----
> From: Ruifeng Wang <Ruifeng.Wang at arm.com>
> Sent: Friday, September 2, 2022 12:54 PM
> To: Amit Prakash Shukla <amitprakashs at marvell.com>; Maxime Coquelin
> <maxime.coquelin at redhat.com>; Chenbo Xia <chenbo.xia at intel.com>
> Cc: dev at dpdk.org; Jerin Jacob Kollanukkaran <jerinj at marvell.com>;
> stable at dpdk.org; nd <nd at arm.com>
> Subject: [EXT] RE: [PATCH] vhost: compilation fix for GCC-12
> 
> External Email
> 
> ----------------------------------------------------------------------
> > -----Original Message-----
> > From: Amit Prakash Shukla <amitprakashs at marvell.com>
> > Sent: Thursday, September 1, 2022 4:50 PM
> > To: Maxime Coquelin <maxime.coquelin at redhat.com>; Chenbo Xia
> > <chenbo.xia at intel.com>
> > Cc: dev at dpdk.org; jerinj at marvell.com; stable at dpdk.org; Amit Prakash
> > Shukla <amitprakashs at 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 at dpdk.org
> >
> > Signed-off-by: Amit Prakash Shukla <amitprakashs at 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?
Apologies for the wrong wordings in the comment. In the comment I mean, it seems like 
point at which sizeof gets evaluated during compilation has changed. I am not sure on it though.
I too could not find documentation regarding the same.

> 
> > +	 */
> > +	if (unlikely(size == 0))
> > +		return -1;
> > +
> >  	while (size > 0) {
> Change 'while(){}' to 'do{}while()' can be a simpler solution. What do you
> think?
I agree, solution suggested by you is better than the one in patch. I will make the suggested
changes as part of v2. Thanks.

> 
> 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