linux-kernel - Re: [PATCH] lib/raid6: Add AVX2 optimized recovery functions

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: <20121129211828.GZ16230@one.firstfloor.org>
Date:	Thu, 29 Nov 2012 22:18:28 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Jim Kukunas <james.t.kukunas@...ux.intel.com>,
	Linux Raid <linux-raid@...r.kernel.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Neil Brown <neilb@...e.de>
Subject: Re: [PATCH] lib/raid6: Add AVX2 optimized recovery functions

> The code is compiled so that the xmm/ymm registers are not available to
> the compiler.  Do you have any known examples of asm volatiles being
> reordered *with respect to each other*?  My understandings of gcc is
> that volatile operations are ordered with respect to each other (not
> necessarily with respect to non-volatile operations, though.)

Can you quote it from the manual? As I understand volatile as usual
is not clearly defined. 

gcc has a lot of optimization passes and volatile bugs are common.


> Either way, this implementatin technique was used for the MMX/SSE
> implementations without any problems for 9 years now.

It's still wrong.

Lying to the compiler usually bites you at some point.

-Andi
--
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/