From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from canuck.infradead.org ([209.217.80.40]:41683 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752299AbXFOMrP (ORCPT ); Fri, 15 Jun 2007 08:47:15 -0400 Subject: Re: [PATCH] Introduce compat_u64 and compat_s64 types From: David Woodhouse In-Reply-To: <200706151440.10273.ak@suse.de> References: <200706150159.l5F1xNgM000459@hera.kernel.org> <200706151355.57464.ak@suse.de> <200706151403.53855.arnd@arndb.de> <200706151440.10273.ak@suse.de> Content-Type: text/plain Date: Fri, 15 Jun 2007 13:47:08 +0100 Message-Id: <1181911628.25228.483.camel@pmac.infradead.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org To: Andi Kleen Cc: Arnd Bergmann , Benjamin Herrenschmidt , Linux Kernel Mailing List , Dave Airlie , linux-arch@vger.kernel.org, Andrew Morton List-ID: On Fri, 2007-06-15 at 14:40 +0200, Andi Kleen wrote: > > That is broken on all non-x86 architectures, > It cannot be broken, it just might be somewhat slower No, Andi. It's broken. We're speaking of a 32-bit ioctl compat routine. I would say it's more than 'convention' that the structure used by the compat_ioctl routine actually matches the 'real' structure as it gets laid out on the 32-bit architecture. The 'real' structure as used by the 32-bit userspace does not have the 'packed' attribute. Thus the u64 member of the structure is aligned to 8 bytes on _all_ relevant 32-bit architectures except for i386. By adding 'packed' in the compat_ioctl routine, you cause it to expect a structure which does not match what userspace is using, for all non-x86 architectures. That's kind of not very compatible. I call that 'broken'. -- dwmw2