linux-kernel - Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <95c32d19-eb4d-a214-6332-038610ec3dbd@rasmusvillemoes.dk>
Date:   Wed, 28 Aug 2019 13:33:31 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Julia Lawall <julia.lawall@...6.fr>,
        Denis Efremov <efremov@...ux.com>
Cc:     Joe Perches <joe@...ches.com>, cocci@...teme.lip6.fr,
        linux-kernel@...r.kernel.org,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH] scripts: coccinelle: check for !(un)?likely usage

On 25/08/2019 21.19, Julia Lawall wrote:
> 
> 
>> On 26 Aug 2019, at 02:59, Denis Efremov <efremov@...ux.com> wrote:
>>
>>
>>
>>> On 25.08.2019 19:37, Joe Perches wrote:
>>>> On Sun, 2019-08-25 at 16:05 +0300, Denis Efremov wrote:
>>>> This patch adds coccinelle script for detecting !likely and !unlikely
>>>> usage. It's better to use unlikely instead of !likely and vice versa.
>>>
>>> Please explain _why_ is it better in the changelog.
>>>
>>
>> In my naive understanding the negation (!) before the likely/unlikely
>> could confuse the compiler
> 
> As a human I am confused. Is !likely(x) equivalent to x or !x?

#undef likely
#undef unlikely
#define likely(x) (x)
#define unlikely(x) (x)

should be a semantic no-op. So changing !likely(x) to unlikely(x) is
completely wrong. If anything, !likely(x) can be transformed to
unlikely(!x).

Rasmus