From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C9F34C43460 for ; Sat, 17 Apr 2021 13:46:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FD0F61245 for ; Sat, 17 Apr 2021 13:46:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236397AbhDQNqr convert rfc822-to-8bit (ORCPT ); Sat, 17 Apr 2021 09:46:47 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:31514 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236367AbhDQNqr (ORCPT ); Sat, 17 Apr 2021 09:46:47 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-111-IAuWgVVUPrqCWucM5QzTnw-1; Sat, 17 Apr 2021 14:46:17 +0100 X-MC-Unique: IAuWgVVUPrqCWucM5QzTnw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sat, 17 Apr 2021 14:46:17 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.015; Sat, 17 Apr 2021 14:46:17 +0100 From: David Laight To: 'Peter Zijlstra' , Matthew Wilcox CC: Miguel Ojeda , Willy Tarreau , Wedson Almeida Filho , Miguel Ojeda , Linus Torvalds , Greg Kroah-Hartman , "rust-for-linux@vger.kernel.org" , Linux Kbuild mailing list , Linux Doc Mailing List , linux-kernel Subject: RE: [PATCH 00/13] [RFC] Rust support Thread-Topic: [PATCH 00/13] [RFC] Rust support Thread-Index: AQHXM3s7R6TAvlURwUWbKsHSAM883qq4tusA Date: Sat, 17 Apr 2021 13:46:17 +0000 Message-ID: <302c00b5de4d4320b8770aae7d84e175@AcuMS.aculab.com> References: <20210414184604.23473-1-ojeda@kernel.org> <20210416161444.GA10484@1wt.eu> <20210416180829.GO2531743@casper.infradead.org> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: rust-for-linux@vger.kernel.org From: Peter Zijlstra > Sent: 17 April 2021 12:17 ... > > (i'd argue this is C being broken; promoting only as far as int, when > > assigning to an unsigned long is Bad, but until/unless either GCC fixes > > that or the language committee realises that being stuck in the 1970s > > is Bad, people are going to keep making this kind of mistake) > > Well, I think the rules actually make sense, at the point in the syntax > tree where + happens, we have 'unsigned char' and 'int', so at that > point we promote to 'int'. Subsequently 'int' gets shifted and bad > things happen. The 1970s were fine. K&R C was sign preserving - so 'unsigned char' promoted to 'unsigned int'. The ANSI C committee broke things by changing it to value preserving with the strong preference for signed types. Even with ANSI C the type of ((unsigned char)x + 1) can be unsigned! All it needs as an architecture where sizeof (int) == 1. (sizeof (char) has to be 1 - even though that isn't directly explicit.) Of course, having 32-bit 'char' and 'int' does give problems with the value for EOF. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)