From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from CWXP265CU009.outbound.protection.outlook.com (mail-ukwestazon11021111.outbound.protection.outlook.com [52.101.100.111]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6C0253502A2; Wed, 7 Jan 2026 18:12:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.100.111 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767809567; cv=fail; b=oq34mRDjZtSmHR4dizNd2R3kCVvJfjkN+7CDbo/iHqOygm/okEICUPDH1BcMof6Bp6XaZMGRKltVQXUlsP+Libpx3F1lAw194eawqYQjHl3J9FOpEfb85j0qiZUHjtiwNz+9NGpu5cV5MSJNXatkyxMIqMDaamEEZZGNhaln68Y= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767809567; c=relaxed/simple; bh=osYr1gWEb/bBYGc1m0FXN9Uj8eJ5NriUE/c7zXWai0Q=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: Content-Type:MIME-Version; b=S4sRaql6RwQds0F8/zNdT9yqou7UotahXBPITaD1CnQvKIGVsWm8RolCoYLZLPTVGdTdBDr5z656l4ag+4b+yYYokG7E9HNFTnwuH67luYXXwZbllh5KDwJWdFHASkpWv1Z1yDj3mmM8EQArWOxhZDxPSlLe5c6oDF6MZjzMRHk= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=garyguo.net; spf=pass smtp.mailfrom=garyguo.net; dkim=pass (1024-bit key) header.d=garyguo.net header.i=@garyguo.net header.b=ijDJ0W1F; arc=fail smtp.client-ip=52.101.100.111 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=garyguo.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=garyguo.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=garyguo.net header.i=@garyguo.net header.b="ijDJ0W1F" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=ERqnsGxUNtIwaorIOnic+3bzU8OxAWTfIQJcDNostytduksUpkJXM/u19JziyZNrokwz2eyM62AHsjkPt2n4N/WggjcBlWnCJJtohkP3ownC1+/Er+HxXLchLVXJRVfJX1kNitXBiBiIjrJEY5Q9usvJMqP7YtoJ66w/zNlnBa6bF9DciS3RXG/LaTftr9iCjQphTd8MTCVX3Wj/jeQF3tuynXKJqmVfcl5PpPFD87FF7mhWH1HvPzJ85ZLqgPRl4Y9KOk+nzXwRLmijmPTzruKZ1CaoQgTEcklpDIuqoAdsusYmJPvB2p3q2A91LrsqF2i+icydFdP5rumZ01a2+w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=8aKAuHswVQqKqy0m64bX6Fq4G0FNhGdutcE5rwMefkg=; b=pKJtnWkYn9LyPUI3pyesYs5X8uDMgXxU4kx4VXENTSbslV4Hrw/C7dM37Xqv/o1QNGFJtU0MO31/0a+jbwzwtf9EUiV6n4Ew032hBJjZelbdsemDsJTxECyQfj9Ft84dXfbWVw1Djnj54xfSQebDBjVbymZ3bYI2GxwoYw83GKUyd93ZQmdm1Ty83gl6avDy5Bm+vamdsCOTHCpP3LTJiatE7OdC3lJeDQskp9Nvy6E2SPWG73J/MlARdkrEPAQdlGlY6M38lw5mgCj6VHP9Dkx3e1kKBBv4YZsBTy0KcoaSAQG7hL4s9NhbYeeOeR/7tCDrIeqIrNZqSCjmFMKVyQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=garyguo.net; dmarc=pass action=none header.from=garyguo.net; dkim=pass header.d=garyguo.net; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=garyguo.net; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=8aKAuHswVQqKqy0m64bX6Fq4G0FNhGdutcE5rwMefkg=; b=ijDJ0W1F2t1Swv3EpcTxO5JIXI2xrdXXAwWPSoslDVKa9JimVXVQrbewRUcpYwtYrg1DCAnS/tAANKKfvZRy5R6hVROsLxQzuLPr/C8YztWioXTafPENZMHPMJZphxNxhS67vLG4I5ulqmnERD3Gi8UiHtWQ2X/ZWRghzKEVSXY= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=garyguo.net; Received: from LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:488::16) by LO3P265MB2332.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:104::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9499.2; Wed, 7 Jan 2026 18:12:42 +0000 Received: from LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM ([fe80::1c3:ceba:21b4:9986]) by LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM ([fe80::1c3:ceba:21b4:9986%5]) with mapi id 15.20.9499.002; Wed, 7 Jan 2026 18:12:42 +0000 Date: Wed, 7 Jan 2026 18:12:40 +0000 From: Gary Guo To: Peter Zijlstra Cc: Alice Ryhl , Boqun Feng , Will Deacon , Richard Henderson , Matt Turner , Magnus Lindholm , Catalin Marinas , Miguel Ojeda , =?UTF-8?B?QmrDtnJu?= Roy Baron , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , Mark Rutland , FUJITA Tomonori , Frederic Weisbecker , Lyude Paul , Thomas Gleixner , Anna-Maria Behnsen , John Stultz , Stephen Boyd , Alexander Viro , Christian Brauner , Jan Kara , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 3/5] rust: sync: support using bool with READ_ONCE Message-ID: <20260107181240.4be8aa65.gary@garyguo.net> In-Reply-To: <20260107083327.GB272712@noisy.programming.kicks-ass.net> References: <20251231-rwonce-v1-0-702a10b85278@google.com> <20251231-rwonce-v1-3-702a10b85278@google.com> <20260106124326.GY3707891@noisy.programming.kicks-ass.net> <20260106181201.22806712.gary@garyguo.net> <20260107083327.GB272712@noisy.programming.kicks-ass.net> X-Mailer: Claws Mail 4.3.1 (GTK 3.24.51; x86_64-pc-linux-gnu) Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-ClientProxiedBy: LO4P123CA0289.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:196::6) To LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM (2603:10a6:600:488::16) Precedence: bulk X-Mailing-List: linux-alpha@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LOVP265MB8871:EE_|LO3P265MB2332:EE_ X-MS-Office365-Filtering-Correlation-Id: b153da85-dd55-4987-3c83-08de4e185978 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|7416014|376014|366016|1800799024|7053199007; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?MCM4O34kTEMqk9ypP5fVCzJ46gRBxg8gbG33QH6dzw83EQIjXcGfQzTBt/Pp?= =?us-ascii?Q?25II2qYcAZXHptAd8p/t7/1YGyF1c8ID7AdG56zkzmrL9u4Rg0s4XNobXB0y?= =?us-ascii?Q?hWYu42KDMZotz7I40Af4rXl6OQyTFBJMCkDia/4kAq/TKlQg4xbMS3liFcSo?= =?us-ascii?Q?1BcY59CmiTNAZno6gYGP099xnNtt2R3hlY6oP7PF6UmwKxQ7x7oNDzng8UBo?= =?us-ascii?Q?UU3t06qUihDXQHTRzffZqAmi/aXVYT9FEMrRes6Znluf8a9ixnNJZ6PpTSRt?= =?us-ascii?Q?BNFVYlTY2TVT2YHpojIilWZ5gnuBNtmFend/hkq0F4+2Gf4bysXCRPIRqs3L?= =?us-ascii?Q?Y+t3+oIvjpldj9ps3iw6OYy+dhSXPXmm4QAyN/Y8MjNOmdIUkN/R+WEMr2qZ?= =?us-ascii?Q?lqhW1t3xqa/8SE6/BcYv9umnclqmCI2W2Lb8LvcLxf0QvcPrpu3x2+uNgQLr?= =?us-ascii?Q?kNvLA7WmnliT+hj3gzLi57i8e7Pgt4pYoJewpfSOLkDAi6wI4JccWhF73mYZ?= =?us-ascii?Q?mvrFxAqyhaZhBTMtZIiPlNLlE3FSKEwbXWmGdCTYkjegf3doQOuSaFw+T/rS?= =?us-ascii?Q?Op6FhB38Win+mAIUQtlGrHA2lwpZfGNqaTa4FNr+Ux5+/tU18f0tMzyucFyc?= =?us-ascii?Q?wSic0u/ieq3XJ5n57MD89ozBBB1rRzmrzVORN2JsAfx7cGVrZw07QKPkm0ry?= =?us-ascii?Q?Th8y+4xCjXMC4AM2hgN0/mh+4TxUP9Y5DeBUQqjLxzYwpnoU2UT+yoF9n6qV?= =?us-ascii?Q?q/JiSIRebk5lJET5YEqYIN0uiqEUlGeiGD0Qf7BEMo15xooUvEH0sHxcB+7P?= =?us-ascii?Q?vIfmSNluDmw35a+BeIoeLsswPY1o+zVIIwloKbulf35IRuzvSToD+ORNg0aO?= =?us-ascii?Q?WwQzcK7j4DqMncza6167J1ml9LkO6gS/mirwJW6po4rpVQSEf8J7TVO1MhwT?= =?us-ascii?Q?Pzy24lezWC9DK81bUVU0QnOQJGTZ+SI1Yhx0u8aMubmnfxhupNCHbcAiGDVX?= =?us-ascii?Q?efU9Bcqek8KgpMTSsjL93NV4V6RC48Uk2NCY1JGxtZtwLoksVEfNGJllyoLf?= =?us-ascii?Q?vvxPkiqvxZ5f4t2l9aJxmGcmLerUL496bp/xxsZaWjkmFVy2q/NqmaVFhwdJ?= =?us-ascii?Q?pxiPT8mGdPY+PCD8oGeztcFS4DekhQ7zlGak46NWWTEwuFQkrS5nZsEG2PU2?= =?us-ascii?Q?/1FHT4DzS21d4ijF6oBN+QhEXpaoAGtEGv57vUNd4gW/N+IJHReho2rTd3yo?= =?us-ascii?Q?36IkPtlAZ5JyCdTDQHod5rYtYzw+uzIRQTu/uvhfID5fXwY2sGGUb5OOscgq?= =?us-ascii?Q?h689bG+7guaheg3SspzdkugTc4SIm/xsPLm6/oNvEqWEQikeTiMY/1Er5IE4?= =?us-ascii?Q?0tezeyoXCuUr0U0VNEejmtWOi314ecT9q8GHQL0p8FcnAWNHn2u9ruLXOa/D?= =?us-ascii?Q?UTG/OruA9TKNYAs89tWsq+oVWWXQxf9l?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM;PTR:;CAT:NONE;SFS:(13230040)(10070799003)(7416014)(376014)(366016)(1800799024)(7053199007);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?MiY+5L9/eLw8hAQLfXoTSCnhfaiJkUo7ENOEyTGN83ikpr9vcHc6W1IFj+TD?= =?us-ascii?Q?Mu6AzZ222ons31pM+LEDonooARAb7wDiLnirGyVRv7fLz6U4rCVxawv/GYMY?= =?us-ascii?Q?mgsKtDAgU5hggDlRzOJ1KkUen+wvCu8fkJ61fkzdhJxqYRNVBFwl1dEgh0Nw?= =?us-ascii?Q?Z8XLmltSl5FTaCAmfMT0XYt/yi/3cg5xznhcIwxe79w/bBVL+hES3teBe5QD?= =?us-ascii?Q?xXYUbiOZQNk3xWtkIyec2BNJjH0GiIyX3W9UBXKAJrDc4UgCFHbOTgnlPeY9?= =?us-ascii?Q?ReUngPNoFCCogiwFOtjQHEK9U45b+LEo4jmv+MD46iNLxmK6s3CEhgO1wnY/?= =?us-ascii?Q?iUAENla7zArfnEY+2ajUM/ny5naTrWQfsYbxeA+2pX1BMlLurqvPDVC6iBYi?= =?us-ascii?Q?SDEbXNJzgrH1N0j6VBX2eCkfxmvpu82qGJhYfxiwMcfCN2rcKR/qXX3rRlY5?= =?us-ascii?Q?ckeuFjZ+Pv1rl/AEgFyKilSUK5S0k1PIKNAknUOERJyq2UzbK6tq9ADofu4U?= =?us-ascii?Q?HuANlT60SsjxBJkq7GNdNzIT2VTWdVNSaIrRwsy5/aIlCtZgFDoew27vcvUY?= =?us-ascii?Q?/oGyWzRE2AXDxfYZrGS9YEU4nDFerKNFzJUE5Ff8U29h1Ugaoz4kVDqTqXe0?= =?us-ascii?Q?GHBvwAuKbvcOXGoeR8dVfVsLkpaDQtayPkarTdvpMfETiL20dWnE2utWAf3u?= =?us-ascii?Q?IzXvAOBeDTFvXWIaFtFGLnTt9UYrV9YG17lEDUp5mKKOecTvGeYpVDlUZFF1?= =?us-ascii?Q?NMgJrZrGqWl4jNqj9hf2b7RXoHkc/JtnbTDyZC7MrIoBXUXKvLgU0HZsbVUn?= =?us-ascii?Q?OAZSVwRS7T7fV1mdP5RWg2bDgcBLpK/zgYd2EJSMmHjhxu1S+vCy5xy/YBJI?= =?us-ascii?Q?r4BTmiQOn3lH32zyYhQMwST0cTCNmmCjs5x+KWPZzfkHbIMUKt6ckAUvtkIh?= =?us-ascii?Q?C8abq9Ux/CiiZ75aTaV8jjNLZ3enJ5EHgboQ+RYtECwXRhKnugVouGwiLtJf?= =?us-ascii?Q?Zeq3+5BmrEe4S3ye+MA+C2vTgHnNAEBH7tvLO0fFqCLGHRHE9DD3UnIGi+ei?= =?us-ascii?Q?75tEDMr9G030mQdqQu20m3eK6TfKRmc5s6P7uxc1yqmCP6tQHsgjdB9gcTFG?= =?us-ascii?Q?a/zhPtOJfJImwKOR5uiNdTuEH0eq+gAMkhJXQl3reihpsiBVQVE3/RRxuNnj?= =?us-ascii?Q?398K0edzq0pI26jOhwUOxRErGNewLGrhHTkjxs7WBUFKGBe/6Ls3KlzL2etg?= =?us-ascii?Q?6de1gEOmoQHXa5sPZJEVuBlEpg5AYcF20Y4V9cR+CJoDfajDb/t7CnZQ8FX2?= =?us-ascii?Q?u2JDf+8tLwaTpJG418hcMwxIyvoBbBOeR+FYGOhcsK0kAGlPDu8j1Q3n8n+f?= =?us-ascii?Q?d4e7Yf0eMkeo/zjr/lzZjkNp5ZNSNdlIrhMQfpF8gtrFEv+qrePVq5QEhxVP?= =?us-ascii?Q?2frbGh3A69/ZKVL5qEbMyxeErULWXiJ6Bz5aEEkiXxGR0SGRG1mUHw+aHs4f?= =?us-ascii?Q?yzwhC2SB4OYoKn8CbReY+TDNxWNY0tn5D7GaqLpMj7hp5cclEt0NuFpEn/nH?= =?us-ascii?Q?TCQzkZ/eMn9l+neMD/0DHKcth2HLmDyHxmVclRXW3ChXmZJObzdVaZcca4wg?= =?us-ascii?Q?xNOd1XQY0UJoFuJS59kKhiS7ZwhoA595vIkerz9RlHk+1ys7RhzPc62HjuP9?= =?us-ascii?Q?s4sGwKWfJ+GCxtXlZAHHjFfrGMCZ5bMy9m5iPB5aFqJcma3nE+NwB25sC+5D?= =?us-ascii?Q?/ETqjjw9MA=3D=3D?= X-OriginatorOrg: garyguo.net X-MS-Exchange-CrossTenant-Network-Message-Id: b153da85-dd55-4987-3c83-08de4e185978 X-MS-Exchange-CrossTenant-AuthSource: LOVP265MB8871.GBRP265.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Jan 2026 18:12:42.1400 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: bbc898ad-b10f-4e10-8552-d9377b823d45 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: +azaKDy90V6t/MeSWWT8473afXjwKUwdvETZbjwJ2PFgynpYDSNuhHrk3hJzJDdu9b34bA5KtJ6Fxc8SPgosZw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LO3P265MB2332 On Wed, 7 Jan 2026 09:33:27 +0100 Peter Zijlstra wrote: > On Tue, Jan 06, 2026 at 06:12:01PM +0000, Gary Guo wrote: > > On Tue, 6 Jan 2026 13:43:26 +0100 > > Peter Zijlstra wrote: > > > > Does this hardcode that sizeof(_Bool) == 1? There are ABIs where this is > > > not the case. > > > > Hi Peter, > > > > Do you have a concrete example on which ABI/arch this is not true? > > > > I know that the C spec doesn't mandate _Bool and char are of the same size > > but we have tons of assumptions that is not guaranteed by standard C.. > > Darwin/PowerPC famously has sizeof(_Bool) == 4 > > Win32: Visual C++ 4.2 (and earlier) had sizeof(bool)==4 (they mapped > bool to int), while Visual C++ 5.0 introduced a native _Bool and moved > to 1 byte. > > Early RISC CPUs (MIPS, PowerPC, Alpha) had severe penalties for byte > access and their compilers would've had sizeof(bool)=={4,8}. > > I think AVR/Arduino also has sizeof(bool) == sizeof(int) which is 2. > > It sounds like that none of these matter for the kernel? In which case I think it's good to keep the assertion; if someone is ought to introduce a new arch where _Bool (or Rust bool) is not 1 then we should know about it. Best, Gary