Re: [PATCH] gcc compiler option -Og warnings fix

From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: Keith Wiles <keith.wiles@intel.com>,
	dev@dpdk.org, huawei.xie@intel.com, adrien.mazarguil@6wind.com
Subject: Re: [PATCH] gcc compiler option -Og warnings fix
Date: Tue, 5 Apr 2016 03:56:39 +0800	[thread overview]
Message-ID: <20160404195639.GJ3080@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <22459074.ccNYgpjxy1@xps13>

On Mon, Apr 04, 2016 at 04:10:54PM +0200, Thomas Monjalon wrote:
> --- a/lib/librte_vhost/vhost_rxtx.c
> +++ b/lib/librte_vhost/vhost_rxtx.c
> @@ -147,8 +147,10 @@ copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
>         struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
>  
>         desc = &vq->desc[desc_idx];
> -       if (unlikely(desc->len < vq->vhost_hlen))
> +       if (unlikely(desc->len < vq->vhost_hlen)) {
> +               *copied = 0;
>                 return -1;
> +       }
> 
> >  		err = copy_mbuf_to_desc(dev, vq, pkts[i], desc_idx, &copied);
> > @@ -531,7 +531,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
> >  {
> >  	struct vhost_virtqueue *vq;
> >  	uint32_t pkt_idx = 0, nr_used = 0;
> > -	uint16_t start, end;
> > +	uint16_t start = 0, end = 0;
> 
> I don't understand this one because the variables are not used if
> reserve_avail_buf_mergeable fails.
> I don't see any smart workaround.
> Huawei, Yuanhan, can we expect a little slowdown with this change?

I agree with you that the compiler seems buggy here, I'm okay with
the fix though: it should not introduce slowdown, IMO. However, I'd
ask the opinion from Huawei: he knows this better than me.

	--yliu