From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D14F8C1B08C for ; Thu, 15 Jul 2021 09:05:52 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 81EF761260 for ; Thu, 15 Jul 2021 09:05:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 81EF761260 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.156513.288851 (Exim 4.92) (envelope-from ) id 1m3xJK-0008Es-I3; Thu, 15 Jul 2021 09:05:38 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 156513.288851; Thu, 15 Jul 2021 09:05:38 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3xJK-0008El-F3; Thu, 15 Jul 2021 09:05:38 +0000 Received: by outflank-mailman (input) for mailman id 156513; Thu, 15 Jul 2021 09:05:38 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3xJK-0008Ef-2Z for xen-devel@lists.xenproject.org; Thu, 15 Jul 2021 09:05:38 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m3xJJ-0000xH-1r; Thu, 15 Jul 2021 09:05:37 +0000 Received: from gw1.octic.net ([81.187.162.82] helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1m3xJI-0006FG-Sf; Thu, 15 Jul 2021 09:05:36 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=cAibhIT296tsC4ekydtfglRXOdKiHz4wp52UqkT1R1g=; b=NdbLJcldaaTv4oABonr6cEFQHy OPvJ9ab5k/71CQGsn0csBp69hPDcDyfhbopzLFXe3pxGhs2AUEQXNrTtXiWSBJYMQisIFcyf3d3d7 PcD1qGsGFnPLSQpeCRbNEY/3sL5cnhq7+qpPJHMY+rBuDFqudmCO4xdsPqF2ngjZczUw=; Subject: Re: [PATCH v2 13/13] SUPPORT.md: write down restriction of 32-bit tool stacks To: Jan Beulich Cc: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , "xen-devel@lists.xenproject.org" References: <0bebfe8c-6897-dc8b-7fe0-9127d4996eb8@suse.com> From: Julien Grall Message-ID: <870cae2b-5601-b10b-926b-0995e661ffc1@xen.org> Date: Thu, 15 Jul 2021 10:05:34 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Jan, On 15/07/2021 07:38, Jan Beulich wrote: > On 14.07.2021 20:16, Julien Grall wrote: >> On 05/07/2021 16:18, Jan Beulich wrote: >>> Let's try to avoid giving the impression that 32-bit tool stacks are as >>> capable as 64-bit ones. >> >> Would you be able to provide a few examples of the known issues in the >> commit message? This would be helpful for anyone to understand why we >> decided to drop the support. > > Not sure how useful this is going to be. It would at least be useful to me, so I can make an informed decision. I suspect it would also be for anyone reading it in the future. This is rather frustrating to find commit message with barely any rationale and no-one remembering why this was done... I vaguely recall a discussion about 64-bit hypercall ([1]). I assume the decision to drop support is related to it, but I have no way to prove it from the commit message. It is also not clear why adding the restriction is the way to go... > This would be pointing at the > declarations / definitions of various tool stack internal variables or > structure fields. Which also is why ... ... is this because such issues are too widespread in libxc/libxl to fix it in long term? > >> At least on Arm, we tried to design the hypercall ABI in such a way that >> it should be possible to use a 32-bit toolstack. > > ... keeping the ABI tidy in this regard didn't help at all (albeit it > of course was a prereq to writing a tool stack that would be capable). > > Jan > [1] https://lore.kernel.org/xen-devel/71b8a4f1-9c18-36e7-56b1-3f1b1dabddd6@suse.com/ -- Julien Grall