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Marchesi" To: dthaler1968@googlemail.com Cc: bpf@vger.kernel.org, Dave Thaler Subject: Re: [PATCH] bpf, docs: Fix modulo zero, division by zero, overflow, and underflow References: <20230117224951.984-1-dthaler1968@googlemail.com> Date: Wed, 18 Jan 2023 10:43:31 +0100 In-Reply-To: <20230117224951.984-1-dthaler1968@googlemail.com> (dthaler's message of "Tue, 17 Jan 2023 22:49:51 +0000") Message-ID: <87o7qw18l8.fsf@oracle.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) Content-Type: text/plain X-ClientProxiedBy: LNXP265CA0060.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:5d::24) To BYAPR10MB2888.namprd10.prod.outlook.com (2603:10b6:a03:88::32) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR10MB2888:EE_|CH0PR10MB5050:EE_ X-MS-Office365-Filtering-Correlation-Id: db18654b-3b62-4259-c6ec-08daf937def0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BYAPR10MB2888.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(346002)(366004)(39860400002)(376002)(136003)(396003)(451199015)(8936002)(5660300002)(41300700001)(4744005)(6916009)(4326008)(8676002)(66556008)(66476007)(66946007)(86362001)(2906002)(36756003)(38100700002)(6486002)(6666004)(2616005)(6506007)(478600001)(6512007)(26005)(186003)(316002);DIR:OUT;SFP:1101; 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There > +are no instructions for signed division or modulo. English is not my native language, but I think "converted" may be too generic for this paragraph: are the same bits reinterpreted as unsigned? Or an actual conversion like absolute value is performed? Wouldn't it be better to say "interpreted as" instead of "converted to" in this case? Something like this: "Also note that the division and modulo operations are unsigned. Thus, for `BPF_ALU`, 'imm' is interpreted as an unsigned 32-bit value, whereas for `BPF_ALU64`, 'imm' is first sign extended to 64 bits and the result interpreted as an unsigned 64-bit value. There are no instructions for signed division or modulo."