[dpdk-dev,v2] net/virtio: fix build error with clang

  Interestingly, clang and gcc has different prototype for _mm_prefetch().
For gcc, we have

   _mm_prefetch (const void *__P, enum _mm_hint __I)

While for clang, it's

   #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a), 0, (sel)))

That how the following error comes with clang:

   error: cast from 'const void *' to 'void *' drops const qualifier
   [-Werror,-Wcast-qual]
           _mm_prefetch((const void *)rused, _MM_HINT_T0);
   /usr/lib/llvm-3.8/bin/../lib/clang/3.8.0/include/xmmintrin.h:684:58:
   note: expanded from macro '_mm_prefetch'
            #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a),
                                          0, (sel)))

What's weird is that the build was actaully Okay before. I met it while
apply Jerin's vector support for ARM patch set: he just move this peiece
of code to another file, nothing else changed.

This patch fix the issue when Jerin's patchset is applied. Thus, I think
it's still needed.

Fixes: fc3d66212fed ("virtio: add vector Rx")

Cc: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
---
v2: replace _mm_prefetch with rte_prefetch0 to make icc happy
---
 drivers/net/virtio/virtio_rxtx_simple.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On Fri, Sep 23, 2016 at 02:15:09PM +0800, Yuanhan Liu wrote:

Hi Yuanhan,

Thanks for this patch.

> Interestingly, clang and gcc has different prototype for _mm_prefetch().
> For gcc, we have
> 
>    _mm_prefetch (const void *__P, enum _mm_hint __I)
> 
> While for clang, it's
> 
>    #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a), 0, (sel)))
> 
> That how the following error comes with clang:
> 
>    error: cast from 'const void *' to 'void *' drops const qualifier
>    [-Werror,-Wcast-qual]
>            _mm_prefetch((const void *)rused, _MM_HINT_T0);
>    /usr/lib/llvm-3.8/bin/../lib/clang/3.8.0/include/xmmintrin.h:684:58:
>    note: expanded from macro '_mm_prefetch'
>             #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a),
>                                           0, (sel)))
> 
> What's weird is that the build was actaully Okay before. I met it while
> apply Jerin's vector support for ARM patch set: he just move this peiece
> of code to another file, nothing else changed.
> 
> This patch fix the issue when Jerin's patchset is applied. Thus, I think
> it's still needed.

The info notes can be moved under the "---" marker line to make git log
clean.

This patch review is holding the virtio arm NEON support. Appreciate any help
in reviewing this patch.

http://dpdk.org/dev/patchwork/patch/14567/

> 
> Fixes: fc3d66212fed ("virtio: add vector Rx")
> 
> Cc: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> ---
> v2: replace _mm_prefetch with rte_prefetch0 to make icc happy
> ---
>  drivers/net/virtio/virtio_rxtx_simple.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio/virtio_rxtx_simple.c b/drivers/net/virtio/virtio_rxtx_simple.c
> index 6517aa8..d8dd17c 100644
> --- a/drivers/net/virtio/virtio_rxtx_simple.c
> +++ b/drivers/net/virtio/virtio_rxtx_simple.c
> @@ -200,7 +200,7 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
>  	sw_ring  = &vq->sw_ring[desc_idx];
>  	sw_ring_end = &vq->sw_ring[vq->vq_nentries];
>  
> -	_mm_prefetch((const void *)rused, _MM_HINT_T0);
> +	rte_prefetch0(rused);
>  
>  	if (vq->vq_free_cnt >= RTE_VIRTIO_VPMD_RX_REARM_THRESH) {
>  		virtio_rxq_rearm_vec(rxvq);
> -- 
> 1.9.0
>
  

On Fri, Sep 23, 2016 at 12:05:14PM +0530, Jerin Jacob wrote:
> On Fri, Sep 23, 2016 at 02:15:09PM +0800, Yuanhan Liu wrote:
> 
> Hi Yuanhan,
> 
> Thanks for this patch.
> 
> > Interestingly, clang and gcc has different prototype for _mm_prefetch().
> > For gcc, we have
> > 
> >    _mm_prefetch (const void *__P, enum _mm_hint __I)
> > 
> > While for clang, it's
> > 
> >    #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a), 0, (sel)))
> > 
> > That how the following error comes with clang:
> > 
> >    error: cast from 'const void *' to 'void *' drops const qualifier
> >    [-Werror,-Wcast-qual]
> >            _mm_prefetch((const void *)rused, _MM_HINT_T0);
> >    /usr/lib/llvm-3.8/bin/../lib/clang/3.8.0/include/xmmintrin.h:684:58:
> >    note: expanded from macro '_mm_prefetch'
> >             #define _mm_prefetch(a, sel) (__builtin_prefetch((void *)(a),
> >                                           0, (sel)))
> > 
> > What's weird is that the build was actaully Okay before. I met it while
> > apply Jerin's vector support for ARM patch set: he just move this peiece
> > of code to another file, nothing else changed.
> > 
> > This patch fix the issue when Jerin's patchset is applied. Thus, I think
> > it's still needed.
> 
> The info notes can be moved under the "---" marker line to make git log
> clean.

Yes, kind of. The reason I want to put it here is to stree "how weird
this issue it is" :)

Without this piece, people may be confused why this patch is necessary,
because they may simply can't reproduce this issue.

> This patch review is holding the virtio arm NEON support. Appreciate any help
> in reviewing this patch.
> 
> http://dpdk.org/dev/patchwork/patch/14567/

I meant to apply this series long time ago, until I found a build issue.
I tried to fix it once, as you saw. But it somehow broke the icc.

And here is my 2nd try (sorry for being a bit late though).

	--yliu
  

2016-09-23 14:15, Yuanhan Liu:
> -	_mm_prefetch((const void *)rused, _MM_HINT_T0);
> +	rte_prefetch0(rused);

There are other occurences of _mm_prefetch in other drivers.
It could deserve a patch.
  

On Fri, Sep 23, 2016 at 10:31:12AM +0200, Thomas Monjalon wrote:
> 2016-09-23 14:15, Yuanhan Liu:
> > -	_mm_prefetch((const void *)rused, _MM_HINT_T0);
> > +	rte_prefetch0(rused);
> 
> There are other occurences of _mm_prefetch in other drivers.
> It could deserve a patch.

Indeed. I could make a patch to replace them all if you think that's
appropriate.

	--yliu