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bh=ZGJ3macmuZXuTtMYG3B2beZsSs4EKXW6dNRScVRlVrs=; b=Ycco47IDBmQYFj4UoAZL4NRcs3Ca5nZX0L+f2gLSWFahasT3W3BAzm0L0BRey5vyXT5wO1Hy+0rIq3PI1NV1k83xMxL0+Ibcct4SEga08Ekm+dNgV1wPh+aXzMj27FDL4zuiE2H3yskM0iVxyt2qh7WYffmg6m+Ckc7de3PD0XQ= X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 165.204.84.17) smtp.mailfrom=amd.com; dkim=none (message not signed) header.d=none;dmarc=pass action=none header.from=amd.com; Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=satlexmb07.amd.com; pr=C MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="UTF-8" Date: Mon, 8 Sep 2025 14:48:55 +0200 Message-ID: CC: "xen-devel@lists.xenproject.org" Subject: Re: New Defects reported by Coverity Scan for XenProject From: Alejandro Vallejo To: Jan Beulich X-Mailer: aerc 0.20.1 References: <68bd98b92c2b2_2afba52d9ed55e79908873e@prd-scan-dashboard-0.mail> <77361e51-dcb8-40e2-a526-9ff90ba942a2@suse.com> <9e474109-7aa1-42b9-9fa6-31c4ef0fb856@suse.com> In-Reply-To: <9e474109-7aa1-42b9-9fa6-31c4ef0fb856@suse.com> X-Originating-IP: [10.180.168.240] X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF00001CDE:EE_|MN0PR12MB5737:EE_ X-MS-Office365-Filtering-Correlation-Id: 11ee33da-6898-4052-dcb6-08ddeed613ed X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|376014|36860700013; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Sep 2025 12:48:57.9912 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 11ee33da-6898-4052-dcb6-08ddeed613ed X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF00001CDE.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN0PR12MB5737 On Mon Sep 8, 2025 at 1:25 PM CEST, Jan Beulich wrote: > On 08.09.2025 13:04, Alejandro Vallejo wrote: >> On Mon Sep 8, 2025 at 12:19 PM CEST, Jan Beulich wrote: >>> On 07.09.2025 16:37, scan-admin@coverity.com wrote: >>>> ** CID 1665362: Integer handling issues (INTEGER_OVERFLOW) >>>> /xen/lib/find-next-bit.c: 104 in find_next_zero_bit() >>>> >>>> >>>> ______________________________________________________________________= _______________________ >>>> *** CID 1665362: Integer handling issues (INTEGER_OVERFLOW) >>>> /xen/lib/find-next-bit.c: 104 in find_next_zero_bit() >>>> 98 } >>>> 99 if (!size) >>>> 100 return result; >>>> 101 tmp =3D *p; >>>> 102 =20 >>>> 103 found_first: >>>>>>> CID 1665362: Integer handling issues (INTEGER_OVERFLOW= ) >>>>>>> Expression "0xffffffffffffffffUL << size", where "size" is know= n to be equal to 63, overflows the type of "0xffffffffffffffffUL << size", = which is type "unsigned long". >>>> 104 tmp |=3D ~0UL << size; >>>> 105 if (tmp =3D=3D ~0UL) /* Are any bits zero? */ >>>> 106 return result + size; /* Nope. */ >>>> 107 found_middle: >>>> 108 return result + ffz(tmp); >>>> 109 } >>> >>> I cannot make sense of their claim. 0xffffffffffffffffUL << 63 is simpl= y >>> 0x8000000000000000UL, isn't it? Where's the overflow there? There also >>> cannot be talk of a 32-bit build, or else ~0UL would have been transfor= med >>> to 0xffffffffUL. >>=20 >> The offending line LGTM too. >>=20 >> The only credible explanation I can think of is Coverity flagging discar= ded 1s >> on left shifts as loss of precision. >>=20 >> If so, "~((1 << size) - 1)", or "(~0UL >> size) << size" should make it = happy, >> but surely that error would flare up with all uses of GENMASK() too? > > And with any other non-zero values of "size" here. > > Jan Is this the only issue flagged? Or are there any others of the same kind? I= t might me easier to spot a pattern with a larger dataset. Cheers, Alejandro