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

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Message-ID: <CAK7LNASBndh4yJKVdeMb7RQGopUzEUSNXPQcUgQdB8PiJetMuQ@mail.gmail.com>
Date:   Sun, 4 Aug 2019 15:45:16 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Rikard Falkeborn <rikard.falkeborn@...il.com>
Cc:     Joe Perches <joe@...ches.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Berg <johannes@...solutions.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs

On Sun, Aug 4, 2019 at 3:36 AM Rikard Falkeborn
<rikard.falkeborn@...il.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@...ionext.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() ?



-- 
Best Regards
Masahiro Yamada