Re: [dpdk-dev] [PATCH v3 2/4] virtio: move SSE based Rx implementation to separate file

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Thu, Aug 18, 2016 at 02:52:31PM +0800, Yuanhan Liu wrote:
> On Tue, Jul 05, 2016 at 06:19:24PM +0530, Jerin Jacob wrote:
> > Split out SSE instruction based virtio simple Rx
> > implementation to a separate file
> > 
> > Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> 
> Hi,
> 
> I was about to apply this set. I then did some build test and found a
> weird issue: it breaks the build with clang (ubuntu 16.04).
> 
>     drivers/net/virtio/virtio_rxtx_simple_sse.c:130:2: 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)))
>                                                          ^
>     1 error generated.
> 
> Weird enough I don't see this issue before this commit: the error
> line is exactly the same before and after this commit.

Yes, I looked at the pre processed output as well, it comes as same before and
after this commit.

> 
> Another note is that _mm_prefetch() is actually with different prototype
> for gcc and clang. For gcc, we have:
> 
>     _mm_prefetch (const void *__P, enum _mm_hint __I)
> 
> Any thoughts?

How about replacing "_mm_prefetch((const void *)rused, _MM_HINT_T0)"
with "rte_prefetch0(rused)" to have same prototype and fix the issue
with clang?

> 
> 	--yliu
> 
>