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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 264C0C433FE for ; Tue, 12 Oct 2021 21:10:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07D5B60D43 for ; Tue, 12 Oct 2021 21:10:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234787AbhJLVMo convert rfc822-to-8bit (ORCPT ); Tue, 12 Oct 2021 17:12:44 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:48208 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233060AbhJLVMi (ORCPT ); Tue, 12 Oct 2021 17:12:38 -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-127-z6UcphpBN2u1BZkCwo7MKw-1; Tue, 12 Oct 2021 22:10:34 +0100 X-MC-Unique: z6UcphpBN2u1BZkCwo7MKw-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 15.0.1497.23; Tue, 12 Oct 2021 22:10:32 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.023; Tue, 12 Oct 2021 22:10:32 +0100 From: David Laight To: 'Joe Perches' , LKML CC: kernel-janitors Subject: RE: Use of '%#02x' is almost always wrong Thread-Topic: Use of '%#02x' is almost always wrong Thread-Index: AQHXvfZAETUX8XTqNU6mI/eVjyEZpqvP3atg Date: Tue, 12 Oct 2021 21:10:32 +0000 Message-ID: References: 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: linux-kernel@vger.kernel.org From: Joe Perches > Sent: 10 October 2021 17:46 > > Perhaps too many developers do not know that using '%#x' > in printf output _includes_ the 0x prefix in the output width. > > So %#02x already has the width taken by the 0x prefix and will > always emit 3 or more output bytes. > > sprintf(buf, "%#02x", 1) emits 0x1 (3 bytes of output) > sprintf(buf, "%#02x", 255) emits 0xff (4 bytes of output) > > So presumably all the uses of %#02x in the kernel are not outputting > what is actually expected. Perhaps all of these should use %#04x. Doesn't help. The definition of "%#x" is completely broken. Basically 0 doesn't get the "0x" prefix, so "%#04x" outputs "0000" if the value is zero. So the correct replacement is (probably) "0x%02x". David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)