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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 EBE9CC83000 for ; Wed, 29 Apr 2020 14:01:39 +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 BE0AD20731 for ; Wed, 29 Apr 2020 14:01:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=xen.org header.i=@xen.org header.b="oY1NApYZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BE0AD20731 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 localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jTnH7-0004ar-TA; Wed, 29 Apr 2020 14:01:21 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jTnH6-0004am-FI for xen-devel@lists.xenproject.org; Wed, 29 Apr 2020 14:01:20 +0000 X-Inumbo-ID: e628a857-8a21-11ea-994f-12813bfff9fa Received: from mail.xenproject.org (unknown [104.130.215.37]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id e628a857-8a21-11ea-994f-12813bfff9fa; Wed, 29 Apr 2020 14:01:19 +0000 (UTC) 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:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=i/95LpClsUeFq99vq1tqBaMwmsXIXtcaN8D+iinWUmI=; b=oY1NApYZ0SqS6mQHCQZZ89OTj+ aKrNwjoW3MaakxUxFg5QF8jPRShzedyUSdBdxcWWK4tZJK2Jqb8nXhA8Vp6DdLLIGM0Q8AoGUsWes rXzMBCHWe9KTjzKkPwOzdZQMgNOVwQpgL7TfXPDe6uwb2S02wYcJwuUDZqWTJQ9yHtXE=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1jTnH1-0002bx-0i; Wed, 29 Apr 2020 14:01:15 +0000 Received: from [54.239.6.188] (helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.89) (envelope-from ) id 1jTnH0-0005zp-Pw; Wed, 29 Apr 2020 14:01:14 +0000 Subject: Re: [PATCH] pvcalls: Document explicitly the padding for all arches To: Jan Beulich , Stefano Stabellini References: <20200419104948.31200-1-julien@xen.org> <78288649-5930-9d01-bb8f-85e15406e4ef@xen.org> <6fc59120-664e-6a07-5196-57e1dbfb0dde@suse.com> <240bc5e8-f8fd-217a-fa10-7628ac9d4e6e@suse.com> From: Julien Grall Message-ID: <9eb39857-2e33-4a6b-1825-f9dc537a6515@xen.org> Date: Wed, 29 Apr 2020 15:01:12 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <240bc5e8-f8fd-217a-fa10-7628ac9d4e6e@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Juergen Gross , Wei Liu , Andrew Cooper , Julien Grall , Ian Jackson , George Dunlap , xen-devel@lists.xenproject.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" Hi, On 22/04/2020 10:20, Jan Beulich wrote: >> Even if it was possible to use the sub-structs defined in the header >> that way, keep in mind that we also wrote: >> >> /* dummy member to force sizeof(struct xen_pvcalls_request) >> * to match across archs */ >> struct xen_pvcalls_dummy { >> uint8_t dummy[56]; >> } dummy; > > This has nothing to do with how a consumer may use the structs. > >> And the spec also clarifies that the size of each specific request is >> always 56 bytes. > > Sure, and I didn't mean to imply that a consumer would be allowed > to break this requirement. Still something like this > > int pvcall_new_socket(struct xen_pvcalls_socket *s) { > struct xen_pvcalls_request req = { > .req_id = REQ_ID, > .cmd = PVCALLS_SOCKET, > .u.socket = *s, > }; > > return pvcall(&req); > } > > may break. I think I understand your concern now. So yes I agree this would break 32-bit consumer. As the padding is at the end of the structure, I think a 32-bit frontend and 64-bit backend (or vice-versa) should currently work without any trouble. The problem would come later if we decide to extend a command. I will document the padding only for non 32-bit x86 guest and rework the documentation. Cheers, -- Julien Grall