Re: [PATCH] net/virtio: fix build error with clang

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Tue, Aug 23, 2016 at 03:40:58PM +0800, Yuanhan Liu wrote:
> 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.

Unfortunately, it makes the icc build fail. I will submit another patch
to simply change _mm_prefetch to rte_prefetch0.

	--yliu
> 
> Fixes: fc3d66212fed ("virtio: add vector Rx")
> 
> Cc: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> ---
>  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..56195e5 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);
> +	_mm_prefetch(rused, _MM_HINT_T0);
>  
>  	if (vq->vq_free_cnt >= RTE_VIRTIO_VPMD_RX_REARM_THRESH) {
>  		virtio_rxq_rearm_vec(rxvq);
> -- 
> 1.9.0