Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Rikard Falkeborn <rikard.falkeborn@gmail.com>
Date:   Sat, 3 Aug 2019 20:36:37 +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: <20190803183637.GA831@rikard>
References: <0306bec0ec270b01b09441da3200252396abed27.camel@perches.com>
 <20190731190309.19909-1-rikard.falkeborn@gmail.com>
 <47d29791addc075431737aff4b64531a668d4c1b.camel@perches.com>
 <CAK7LNAQdgUOsjWtWFnXm66DPnYFRp=i69DMyr+q4+NT+SPCQxA@mail.gmail.com>
 <2b782cf609330f53b6ecc5b75a8a4b49898483eb.camel@perches.com>
 <CAK7LNASw+Fraio3t=bZw-FzJihScTuDR=p2EktFVOmdLH4GTGA@mail.gmail.com>
 <20190802181853.GA809@rikard>
 <CAK7LNAT+cNxna4SER04MdkBsq_LDg4TwYR_U1ioNNxYOZWXigA@mail.gmail.com>
 <CAK7LNAQv-5epL8DYDaUdHsQEQ=Va676t_6TgsaSYC30Eix=iyw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAK7LNAQv-5epL8DYDaUdHsQEQ=Va676t_6TgsaSYC30Eix=iyw@mail.gmail.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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?