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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 5190BC433F4 for ; Tue, 18 Sep 2018 11:44:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D5648206B8 for ; Tue, 18 Sep 2018 11:44:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D5648206B8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729134AbeIRRQf convert rfc822-to-8bit (ORCPT ); Tue, 18 Sep 2018 13:16:35 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:50038 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727724AbeIRRQf (ORCPT ); Tue, 18 Sep 2018 13:16:35 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by eu-smtp-1.mimecast.com with ESMTP id uk-mta-2-elCDoYxaPj2m9tJnUAc_Jw-1; Tue, 18 Sep 2018 12:44:19 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b::d117) by AcuMS.aculab.com (fd9f:af1c:a25b::d117) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Tue, 18 Sep 2018 12:46:30 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Tue, 18 Sep 2018 12:46:30 +0100 From: David Laight To: 'Matthias Kaehlcke' , Greg Kroah-Hartman , Jiri Slaby CC: "linux-kernel@vger.kernel.org" , Evan Green , Sai Prakash Ranjan , Douglas Anderson , Stephen Boyd , Manoj Gupta , Nick Desaulniers Subject: RE: [PATCH] tty/sysrq: Make local variable 'killer' in sysrq_handle_crash() global Thread-Topic: [PATCH] tty/sysrq: Make local variable 'killer' in sysrq_handle_crash() global Thread-Index: AQHUTs5aPolqspl2kkaBePJ07chyMKT17Idg Date: Tue, 18 Sep 2018 11:46:30 +0000 Message-ID: <0d8470c7fdbe4429af82b830d39215f3@AcuMS.aculab.com> References: <20180917213304.44476-1-mka@chromium.org> In-Reply-To: <20180917213304.44476-1-mka@chromium.org> Accept-Language: en-GB, en-US Content-Language: 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 X-MC-Unique: elCDoYxaPj2m9tJnUAc_Jw-1 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthias Kaehlcke > Sent: 17 September 2018 22:33 > > sysrq_handle_crash() dereferences a NULL pointer on purpose to force > an exception, the local variable 'killer' is assigned to NULL and > dereferenced later. Clang detects the NULL pointer dereference at compile > time and emits a BRK instruction (on arm64) instead of the expected NULL > pointer exception. Change 'killer' to a global variable (and rename it > to 'sysrq_killer' to avoid possible clashes) to prevent Clang from > detecting the condition. By default global variables are initialized > with zero/NULL in C, therefore an explicit initialization is not needed. You need an explicit initialiser in order to make it global data rather than a common section. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)