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
| ||
|
Date: Tue, 20 May 2008 19:02:08 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Al Viro <viro@...IV.linux.org.uk> cc: Harvey Harrison <harvey.harrison@...il.com>, Al Viro <viro@....linux.org.uk>, mchehab@...radead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] or51132.c: unaligned On Wed, 21 May 2008, Al Viro wrote: > > FWIW, I wonder how they really compare on misaligned and whether it would > make sense for gcc to try and generate a single load on targets that are > known to allow that... It would almost certainly help on x86. The cost of an unaligned integer access that doesn't cross a cache-fetch boundary (8 bytes on older CPU's, 16 or 32 bytes on newer ones) is zero, last I saw. IOW, there are misaligned cases that have a higher cost, but they are pretty rare, and especially so with small data and modern CPU's. So no disadvantage for 95% of all cases, and the advantage of doing just a single instruction, rather than four (2 zero-extending loads, a shift and an add/or, with data dependencies on most of them). Linus -- 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/
Powered by blists - more mailing lists