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Message-ID: <9fe17b7b-7c21-633b-01ca-bc4b93a6526a@suse.com> Date: Thu, 9 Nov 2023 08:44:01 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.15.1 Subject: Re: [XEN PATCH][for-4.19] domain: add ASSERT to help static analysis tools Content-Language: en-US To: Nicola Vetrini Cc: sstabellini@kernel.org, michal.orzel@amd.com, xenia.ragiadakou@amd.com, ayan.kumar.halder@amd.com, consulting@bugseng.com, andrew.cooper3@citrix.com, roger.pau@citrix.com, George Dunlap , Julien Grall , Wei Liu , xen-devel@lists.xenproject.org References: <3f163bb58993410183229e72eb1f227057f9b1c7.1699034273.git.nicola.vetrini@bugseng.com> <44df74cb532bfb9642b1c8752ee8c0d6@bugseng.com> <2c8c246d-caea-5c8b-4a2a-83248422c48d@suse.com> <4a58abb52afed75a748440f1adf9a2ac@bugseng.com> From: Jan Beulich In-Reply-To: <4a58abb52afed75a748440f1adf9a2ac@bugseng.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR4P281CA0398.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:cf::16) To DU2PR04MB8790.eurprd04.prod.outlook.com (2603:10a6:10:2e1::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DU2PR04MB8790:EE_|PAXPR04MB8702:EE_ X-MS-Office365-Filtering-Correlation-Id: 303936af-d236-4828-7cf6-08dbe0f7a556 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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This ASSERT helps them in >>>>> detecting that such a condition is not possible >>>>> and also provides a basic sanity check. >>>> >>>> I disagree with this being a possible justification for adding such a >>>> redundant assertion. More detail is needed on what is actually >>>> (suspected to be) confusing the tool. Plus it also needs explaining >>>> why (a) adding such an assertion helps and (b) how that's going to >>>> cover release builds. >>>> >>> >>> How about: >>> "Static analysis tools may detect a possible null pointer dereference >>> at line 760 (config->handle) due to config possibly being NULL. >>> >>> However, given that all system domains, including IDLE, have a NULL >>> config and in the code path leading to the assertion only real domains >>> (which have a non-NULL config) can be present." >>> >>> On point b): this finding is a false positive, therefore even if the >>> ASSERT is >>> expanded to effectively a no-op, there is no inherent problem with >>> Xen's >>> code. >>> The context in which the patch was suggested [1] hinted at avoiding >>> inserting in >>> the codebase false positive comments. >> >> Which I largely agree with. What I don't agree with is adding an >> assertion which is only papering over the issue, and only in debug >> builds. So perhaps instead we need a different way of tracking >> false positives (which need to be tied to specific checker versions >> anyway). >> > > Hmm. Is it better in your opinion to write something like: > > if (config == NULL) > return ERR_PTR(); // or die() or something > appropriate > > this would be a rudimentary handling of the error with some messages > detailing that something > is wrong if a domain has a null config at that point. No. This is no better than a redundant assertion. It's even slightly worse, as it'll likely leave a trace in generated code for release builds. Jan