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Lu" Cc: Binutils References: <0babbec4-06ae-f980-18a9-20608046891b@suse.com> <34a3a825-8c9f-d52b-9a1d-6cd45e051332@suse.com> From: Jan Beulich Message-ID: <803f03a4-bb6d-5580-b2ff-b1df2d5152f3@suse.com> Date: Thu, 17 Jun 2021 18:05:25 +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: PR3P195CA0005.EURP195.PROD.OUTLOOK.COM (2603:10a6:102:b6::10) 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 PR3P195CA0005.EURP195.PROD.OUTLOOK.COM (2603:10a6:102:b6::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4242.16 via Frontend Transport; Thu, 17 Jun 2021 16:05:27 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 548ac7e0-fd6a-44e3-fcf2-08d931a9b962 X-MS-TrafficTypeDiagnostic: VI1PR04MB4190: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; 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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)). Jan