Optimization to amd64 memcpy make software behave diffrently on 32 and 64 bit archs.

[Kim Nguyễn]

An optimization to memcpy that went in version 2.13 (used in natty) exposes bugs in applications that perform memcpy between overlapping memory areas. While the specification of memcpy clearly states that source and destination should not overlap, this is the case in many applications. Of course applications should be fixed to use memmove instead but this also affects closed source products (most notably adobe flash player plugin). This might also lead to subtle bugs that might not be seen as related to this issue (original bugreport mentions squashfs).
A bugreport already tracks the issue for the flash-player
https://bugs.launchpad.net/ubuntu/+source/adobe-flashplugin/+bug/727064

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: libc6 2.13-0ubuntu4
ProcVersionSignature: Ubuntu 2.6.38-6.34-generic 2.6.38-rc7
Uname: Linux 2.6.38-6-generic x86_64
Architecture: amd64
Date: Mon Mar 14 08:46:36 2011
ProcEnviron:
 LANGUAGE=en_AU:en
 PATH=(custom, user)
 LANG=en_AU.utf8
 SHELL=/bin/bash
SourcePackage: eglibc
UpgradeStatus: Upgraded to natty on 2010-10-10 (154 days ago)

[Colin Watson (cjwatson)]

Somebody has also added an eglibc task on bug 727064, so I'm going to mark this as a duplicate.