Re: [PATCH rdma-core 2/2] mlx5: Convert explicitly to signed char

[Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>]

On Wed, Aug 30, 2017 at 08:44:02PM +0300, Leon Romanovsky wrote:
> On Wed, Aug 30, 2017 at 10:49:52AM -0600, Jason Gunthorpe wrote:
> > On Wed, Aug 30, 2017 at 05:19:24PM +0300, Yishai Hadas wrote:
> > > From: Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> > >
> > > The 0x80 value is a canonical way to mark as not-used in intrinsics
> > > function calls.
> >
> > This commit message is not good, try:
> >
> > _mm_shuffle_epi8 requires 0x80 to set the output byte to zero, but
> > _mm_set_epi8() accepts char. If gcc is compiling in a configuration
> > with a signed char then it can produce a -Werror=overflow warning.
> >
> > And this fix is wrong, since it just moves the warning to
> > configurations that have an unsigned char. (eg -funsigned-char)
> 
> I have gut feeling that with such option "-funsigned-char" half of the
> world will break.

Nope, some arches default to it on. aarch64 for instance.

This is why we have uint8_t, and using 'char' for anything other than
a string character is very wrong.

Jason
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