linux-kernel - Re: [PATCH] scripts/coccinelle/misc/shift.cocci: detect

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Date:   Thu, 8 Feb 2018 16:53:50 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Julia Lawall <Julia.Lawall@...6.fr>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        kernel-janitors@...r.kernel.org,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>, cocci@...teme.lip6.fr,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scripts/coccinelle/misc/shift.cocci: detect < or > that
 should be a shift

On Thu, Feb 08, 2018 at 01:53:54PM +0100, Julia Lawall wrote:
> This checks for a comparison using < or > between two constants,
> considering both explicit constants (1, 2, etc) and macros defined
> with #define.  False positives are possible in the latter case, when
> a macro may have multiple possible definitions and it is indeed
> necessary to check the value.  There are currently two such false
> positives, in drivers/net/ethernet/chelsio/cxgb3/sge.c:
> 
>        q->fl[0].use_pages = FL0_PG_CHUNK_SIZE > 0;
>        q->fl[1].use_pages = FL1_PG_CHUNK_SIZE > 0;
> 

We could eliminate both these false postives by ignoring >> vs >.  Did
searching for > actually find any bugs?  I think you were right that
right shifting a constant is way less common than left shifting and I
have some smatch scripts where I ignore right shifting bugs.

On the other hand, two false positives are not a big deal.

regards,
dan carpenter