From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755163Ab3LDJ2q (ORCPT ); Wed, 4 Dec 2013 04:28:46 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:44139 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754260Ab3LDJ2m (ORCPT ); Wed, 4 Dec 2013 04:28:42 -0500 X-IronPort-AV: E=Sophos;i="4.93,823,1378857600"; d="scan'208";a="78068766" Message-ID: <1386149319.13256.83.camel@kazak.uk.xensource.com> Subject: Re: [Xen-devel] [PATCH RFC] xen-block: correctly define structures in public headers From: Ian Campbell To: Konrad Rzeszutek Wilk CC: David Vrabel , Stefano Stabellini , Julien Grall , , , "Boris Ostrovsky" , Roger Pau Monne Date: Wed, 4 Dec 2013 09:28:39 +0000 In-Reply-To: <20131203201135.GA14243@phenom.dumpdata.com> References: <1386068254-1413-1-git-send-email-roger.pau@citrix.com> <529DBA07.6090108@citrix.com> <1386068884.13256.9.camel@kazak.uk.xensource.com> <529DC7BA.7080506@citrix.com> <1386078108.13256.30.camel@kazak.uk.xensource.com> <529DF4A0.50103@citrix.com> <1386083821.13256.42.camel@kazak.uk.xensource.com> <20131203201135.GA14243@phenom.dumpdata.com> Organization: Citrix Systems, Inc. Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-3 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.80.2.80] X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2013-12-03 at 15:11 -0500, Konrad Rzeszutek Wilk wrote: > > > If Konrad and Boris agree that breaking the kernel's ABI in this way is > > > acceptable in this specific case, I'll defer to them. > > > > My opinion as Xen on ARM hypervisor maintainer is that this is the right > > thing to do in this case. > > Heh. If somebody can guarantee me that (by testing the right variants and > mentioning this in the git commit) that this does not break x86, then > I am fine. > > And by 'break x86' I mean that this combination works: > 32-bit domU on 64-bit dom0 > 64-bit domU on 32-bit dom0 > > And perhaps also the obvious: > 64-bit domU on 64-bit dom0 > 32-bit domU on 32-bit dom0 One way to test this is with gdb on a vmlinux for each arch with CONFIG_DEBUG_INFO=y. For each MEMBER of each interesting STRUCT: (gdb) print &((struct STRUCT *)0)->MEMBER (this is effectively an open coded offsetof) This could probably even be semi automated by producing a script to feed to gdb which run through all of the options and diffing the result. If I could have the moon on a stick I would have a tool such as this running against the canonical Xen headers, to catch breakage as it is introduced upstream and a tool which could run against an arbitrary ELF binary to validate it against the upstream results. tools/include/xen-foreign/mkchecker.py goes some way towards that but isn't really extensible to the extent we would need/want. While I'm asking for unicorns a gcc __attribute__((warn_on_holes)) which could be applied to a struct to enforce the need for explicit padding would probably be incredibly useful for this of thing. > Since the xen-blkback has its own version of the structs there is no > need to change change newer and older version of it. Someone should check that these are producing the right interface on ARM though! > As long as that works I am OK sticking it in. Thanks. > I think from the ARM perspective it is still in 'experimental' phase > so anything goes to make it work under ARM. Ian.