linux-kernel - Re: bit fields && data tearing

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]

Date:	Mon, 08 Sep 2014 20:20:49 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Peter Hurley <peter@...leysoftware.com>
CC:	paulmck@...ux.vnet.ibm.com,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jakub Jelinek <jakub@...hat.com>,
	Mikael Pettersson <mikpelinux@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Richard Henderson <rth@...ddle.net>,
	Oleg Nesterov <oleg@...hat.com>,
	Miroslav Franc <mfranc@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
	linux-ia64@...r.kernel.org
Subject: Re: bit fields && data tearing

On 09/08/2014 07:56 PM, James Bottomley wrote:
>>
>> Yeah, the extra requirement I added is basically nonsense, since the
>> only issue is what instructions the compiler is emitting. So if compiler
>> thinks the alignment is natural and combines the writes -- ok. If the
>> compiler thinks the alignment is off and doesn't combine the writes --
>> also ok.
> 
> Yes, I think I can agree that the only real problem is gcc thinking the
> store or load needs splitting.
> 

That seems much saner, and yes, that applies to any architecture which
needs unaligned references.  Now, if the references are *actually*
unaligned they can end up being split even on x86, especially if they
cross cache line boundaries.

	-hpa


--
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/