Re: [PATCH v2 1/3] overflow.h: Add arithmetic shift helper

From: Kees Cook <keescook@chromium.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Jason Gunthorpe <jgg@mellanox.com>,
	Leon Romanovsky <leonro@mellanox.com>,
	Jason Gunthorpe <jgg@ziepe.ca>, Leon Romanovsky <leon@kernel.org>,
	Bart Van Assche <Bart.VanAssche@wdc.com>,
	Doug Ledford <dledford@redhat.com>,
	linux-rdma <linux-rdma@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/3] overflow.h: Add arithmetic shift helper
Date: Wed, 1 Aug 2018 08:38:01 -0700	[thread overview]
Message-ID: <CAGXu5j+=gBk=6Pva36HFj1L=Bz2O1+kzcUwUEu8eme_A4F5ktg@mail.gmail.com> (raw)
In-Reply-To: <20180801080724.2vgzagooda56aypw@mwanda>

On Wed, Aug 1, 2018 at 1:07 AM, Dan Carpenter <dan.carpenter@oracle.com> wrote:
> On Wed, Aug 01, 2018 at 10:57:44AM +0300, Dan Carpenter wrote:
>> The idea is nice, but I don't like the API.  The "_overflow" feels too
>> specific because maybe we could check for other things in the future.
>> Normally boolean macros should say they are boolean in the name and I
>> would prefer if it returned zero on failure.
>>
>>       if (!checked_shift(dest, mask, shift)) {
>>       if (!shift_ok(dest, mask, shift)) {
>>       if (!safe_shift(dest, mask, shift)) {
>
> Huh...  It turns out I put the argument order different as well.
>
> If we wanted to keep it returning 1 on failure then some other names
> are:
>
>         if (shift_failed(dest, mask, shift)) {
>         if (shift_error(dest, mask, shift)) {
>         if (shift_overflow(dest, mask, shift)) {

This is following the existing check_{add,mul}_overflow() helpers,
which are based on the gcc helpers. I'd like to keep things
consistent.

-Kees

-- 
Kees Cook
Pixel Security