linux-kernel - Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers

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: <49D4C7CE.3060005@goop.org>
Date:	Thu, 02 Apr 2009 07:12:30 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
CC:	dada1@...mosbay.com, mingo@...e.hu, htejun@...il.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	joe@...ches.com, rusty@...tcorp.com.au
Subject: Re: [PATCH] x86: percpu_to_op() misses memory and flags clobbers

Herbert Xu wrote:
> Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>   
>> There's probably not a lot of value in this.  The Intel and AMD 
>> optimisation guides tend to deprecate inc/dec in favour of using 
>> add/sub, because the former can cause pipeline stalls due to its partial 
>> flags update.
>>     
>
> Is this still the case on the latest Intel CPUs?
>   

Yes:

    Assembly/Compiler Coding Rule 32. (M impact, H generality) INC and DEC
    instructions should be replaced with ADD or SUB instructions,
    because ADD and
    SUB overwrite all flags, whereas INC and DEC do not, therefore
    creating false
    dependencies on earlier instructions that set the flags.

    J
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/