Re: [PATCH v2] net/virtio: fix build error with clang

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.

quoted

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