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bh=YAJKJjn3gN+PFICaW0C0tCKi0gSp+GCZeCXOdStbLo8=; b=Br8L68cZs2OhjwgV+guCLtjw15+Oy8RLdgPxPOqZsZYiyH6opuuF/K3CarasGBCJui0Bk3Nr0t+TEF9jh97phgUaHSWTMTDKUoFc2kLVJWbqR3BXIHAU3iZ2eNv75kJeEOGWvhHgSTL6aRyvKpa4PiTBnGe4NH3yhlRVF/JDs0Y= 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 13:04:18 +0200 Message-ID: CC: Xen-devel Subject: Re: New Defects reported by Coverity Scan for XenProject From: Alejandro Vallejo To: Jan Beulich , "xen-devel@lists.xenproject.org" X-Mailer: aerc 0.20.1 References: <68bd98b92c2b2_2afba52d9ed55e79908873e@prd-scan-dashboard-0.mail> <77361e51-dcb8-40e2-a526-9ff90ba942a2@suse.com> In-Reply-To: <77361e51-dcb8-40e2-a526-9ff90ba942a2@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: BN2PEPF000044A5:EE_|CH3PR12MB9342:EE_ X-MS-Office365-Filtering-Correlation-Id: 0b681e41-3148-4069-72c7-08ddeec77a79 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|82310400026|1800799024|376014; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Sep 2025 11:04:27.6745 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 0b681e41-3148-4069-72c7-08ddeec77a79 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: BN2PEPF000044A5.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB9342 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() >>=20 >>=20 >> ________________________________________________________________________= _____________________ >> *** 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 known = to be equal to 63, overflows the type of "0xffffffffffffffffUL << size", wh= ich 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 simply > 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 transforme= d > to 0xffffffffUL. > > Jan The offending line LGTM too. The only credible explanation I can think of is Coverity flagging discarded= 1s on left shifts as loss of precision. If so, "~((1 << size) - 1)", or "(~0UL >> size) << size" should make it hap= py, but surely that error would flare up with all uses of GENMASK() too? Cheers, Alejandro