From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from de-smtp-delivery-102.mimecast.com (de-smtp-delivery-102.mimecast.com [194.104.109.102]) by sourceware.org (Postfix) with ESMTPS id 3F79B3857835 for ; Fri, 18 Jun 2021 09:03:22 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 3F79B3857835 Received: from EUR02-HE1-obe.outbound.protection.outlook.com (mail-he1eur02lp2057.outbound.protection.outlook.com [104.47.5.57]) (Using TLS) by relay.mimecast.com with ESMTP id de-mta-3-zatWGtMPPbGHxRDho96QDQ-1; Fri, 18 Jun 2021 11:03:19 +0200 X-MC-Unique: zatWGtMPPbGHxRDho96QDQ-1 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=ocKnyDngbjKHokLzgWBPJjSFJkCuNvEhU9yO/VmI8woVJPXYxKUnmgGv3Z5OrelDlzatoO2h5gdOAHuZ0UlOsKY+0blDevmhaXuYFj7buPMohMVP4UaEHji0rVdK7qq8dwN9/DAYZ3PvgwQv8hwjg1FC4UpVZtgupbgyP7hK9Odn1G5mk+4vHtFIszW0vRWx8whj6MweLsWsvbYX3EI2eX/IiWy6zf1dUGRd2aaLmDyD/jCuJcR2nZVo9TxIiQWqT06YCZVN7OxdlKT/Zh8KJ9fudDe3j3HqPGci++cJJDgdTut7hWqJ//PQHtTdzBXjlaswgGudZ/03F6wYyP9qiQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=z93EKSvWDdIM7GS75u9vGYg9Ts6/3uniPgGAs2ZlDpI=; b=bcxiDd4x32PV/2KH12G5HLHYrbH6U5h82hrostZPUl6mjQabix8EZ8T2eIJe6hHclgxib32ZuIZDhHYbaE0zeIqSGCleuZBMUzZb+L3Wkk2HKPij0Yznv3IYOL82T8L29sQu26mSF/IUFCI+zgYAn3rE04wczx+741PqOgToLL4hwOvIcbN+KcgcsH8abJded/TNC5HcHsGaIKNXRAAz6rClhqosmR323A+6Ij17RWZebi0JsEB/ojOrESYLMD02Z3s/DzuwQXxT6J3nLvpTFcdsznYTS9wU4VeyWWCzEII4Pq0+tD36S0P4NC1rrQi2tFzoWEN0FEurT+ymygHbtA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=suse.com; dmarc=pass action=none header.from=suse.com; dkim=pass header.d=suse.com; arc=none Received: from VI1PR04MB5600.eurprd04.prod.outlook.com (2603:10a6:803:e7::16) by VI1PR0401MB2334.eurprd04.prod.outlook.com (2603:10a6:800:29::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4242.19; Fri, 18 Jun 2021 09:03:18 +0000 Received: from VI1PR04MB5600.eurprd04.prod.outlook.com ([fe80::f06c:6f5d:34d2:1c36]) by VI1PR04MB5600.eurprd04.prod.outlook.com ([fe80::f06c:6f5d:34d2:1c36%5]) with mapi id 15.20.4242.021; Fri, 18 Jun 2021 09:03:18 +0000 Subject: Re: [PATCH 3/6] x86: harmonize disp with imm handling To: "H.J. Lu" Cc: Binutils References: <0babbec4-06ae-f980-18a9-20608046891b@suse.com> <34a3a825-8c9f-d52b-9a1d-6cd45e051332@suse.com> <803f03a4-bb6d-5580-b2ff-b1df2d5152f3@suse.com> From: Jan Beulich Message-ID: Date: Fri, 18 Jun 2021 11:03:15 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [37.24.206.209] X-ClientProxiedBy: FR3P281CA0021.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:1c::11) To VI1PR04MB5600.eurprd04.prod.outlook.com (2603:10a6:803:e7::16) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.156.60.236] (37.24.206.209) by FR3P281CA0021.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:1c::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4264.7 via Frontend Transport; Fri, 18 Jun 2021 09:03:17 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 419231be-548e-493c-5052-08d93237e9d3 X-MS-TrafficTypeDiagnostic: VI1PR0401MB2334: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; 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Lu wrote: > On Thu, Jun 17, 2021 at 9:05 AM Jan Beulich wrote: >> >> On 17.06.2021 18:00, H.J. Lu wrote: >>> On Thu, Jun 17, 2021 at 7:57 AM Jan Beulich wrote: >>>> >>>> On 17.06.2021 16:46, H.J. Lu wrote: >>>>> On Mon, Jun 14, 2021 at 3:25 AM Jan Beulich wrote: >>>>>> --- /dev/null >>>>>> +++ b/gas/testsuite/gas/i386/disp-imm-32.s >>>>>> @@ -0,0 +1,17 @@ >>>>>> + .text >>>>>> +disp_imm: >>>>>> + mov -0xffffffff(%eax), %eax >>>>> >>>>> I don't think we should treat -0xffffffff(%eax) as 1(%eax). >>>>> We allow addresses to wraparound. I don't see a need for >>>>> displacements to wraparound. >>>> >>>> This then is entirely unexpected to the programmer. In fact the >>>> same (abstracted away behind some defines or equates) constant >>>> could be used for both purposes (and should be usable both ways, >>>> imo). >>> >>> Since hardware wraparound on DISP + BASE + INDEX * SCALE, not >>> on DISP, it is wrong to change DISP + BASE + INDEX * SCALE to >>> wraparound (DISP) + BASE + INDEX * SCALE. >> >> But this is true regardless of how small (or big) the displacement. >> Without knowing the register values, you can't know at what >> displacement values wraparound occurs. Also, unless I'm mistaken, >> wrapround(a + b) == wrapround(wrapround(a) + wrapround(b)). > > Hardware does wraparound (DISP + BASE + INDEX * SCALE). > Assembler and linker should only wraparound on the final address. I'm afraid this last sentence makes no sense to me: The assembler (or linker) can't know the final address. Instead, both immediates and displacements should allow for anything the programmer might sensibly use. If 0xffffffff as a displacement is fine (meaning -1 really), -0xffffffff (meaning 1) ought to be, too. Or else where do you draw the boundary of which displacements are "legitimate" and which are not? Jan