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From:   Rikard Falkeborn <rikard.falkeborn@gmail.com>
Date:   Mon, 5 Aug 2019 21:55:26 +0200
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Rikard Falkeborn <rikard.falkeborn@gmail.com>,
        Joe Perches <joe@perches.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Berg <johannes@sipsolutions.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK
 inputs
Message-ID: <20190805195526.GA869@rikard>
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On Sun, Aug 04, 2019 at 03:45:16PM +0900, Masahiro Yamada wrote:
> On Sun, Aug 4, 2019 at 3:36 AM Rikard Falkeborn
> <rikard.falkeborn@gmail.com> 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@socionext.com> 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() ?

I'll have a look.