Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs

[Masahiro Yamada]

On Sun, Aug 4, 2019 at 3:36 AM Rikard Falkeborn
<rikard.falkeborn@xxxxxxxxx> wrote:
>
> On Sat, Aug 03, 2019 at 12:12:46PM +0900, Masahiro Yamada wrote:
> > On Sat, Aug 3, 2019 at 12:03 PM Masahiro Yamada
> > <yamada.masahiro@xxxxxxxxxxxxx> wrote:
> >
> > >
> > > BTW, v2 is already inconsistent.
> > > If you wanted GENMASK_INPUT_CHECK() to return 'unsigned long',,
> > > you would have to cast (low) > (high) as well:
> > >
> > >                (unsigned long)((low) > (high)), UL(0))))
> > >
> > > This is totally redundant, and weird.
> >
> > I take back this comment.
> > You added (unsigned long) to the beginning of this macro.
> > So, the type is consistent, but I believe all casts should be removed.
>
> Maybe you're right. BUILD_BUG_ON_ZERO returns size_t regardless of
> inputs. I was worried that on some platform, size_t would be larger than
> unsigned long (as far as I could see, the standard does not give any
> guarantees), and thus all of a sudden GENMASK would be 8 bytes instead
> of 4, but perhaps that is not a problem?


How about adding (int) cast to BUILD_BUG_ON_ZERO() ?



-- 
Best Regards
Masahiro Yamada