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Thu, 20 Feb 2020 16:33:18 +0000 Received: from pps.filterd (userp3020.oracle.com [127.0.0.1]) by userp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 01KGVfO9160470; Thu, 20 Feb 2020 16:33:18 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3020.oracle.com with ESMTP id 2y8ud46pqs-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 20 Feb 2020 16:33:17 +0000 Received: from abhmp0017.oracle.com (abhmp0017.oracle.com [141.146.116.23]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 01KGXGaX002346; Thu, 20 Feb 2020 16:33:16 GMT Received: from bostrovs-us.us.oracle.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 20 Feb 2020 08:33:16 -0800 Subject: Re: [PATCH] x86/xen: Distribute switch variables for initialization To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , Kees Cook Cc: Alexander Potapenko , Stefano Stabellini , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <20200220062318.69299-1-keescook@chromium.org> <16a166da-c6e7-aa36-53a0-1b56197c8fc0@suse.com> From: Boris Ostrovsky Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <16a166da-c6e7-aa36-53a0-1b56197c8fc0@suse.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9537 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 malwarescore=0 mlxlogscore=999 suspectscore=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002200122 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9537 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 phishscore=0 impostorscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 suspectscore=0 priorityscore=1501 bulkscore=0 adultscore=0 spamscore=0 lowpriorityscore=0 clxscore=1011 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002200122 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/20/20 1:37 AM, Jürgen Groß wrote: > On 20.02.20 07:23, Kees Cook wrote: >> Variables declared in a switch statement before any case statements >> cannot be automatically initialized with compiler instrumentation (as >> they are not part of any execution flow). With GCC's proposed automatic >> stack variable initialization feature, this triggers a warning (and they >> don't get initialized). Clang's automatic stack variable initialization >> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also >> doesn't initialize such variables[1]. Note that these warnings (or >> silent >> skipping) happen before the dead-store elimination optimization phase, >> so even when the automatic initializations are later elided in favor of >> direct initializations, the warnings remain. >> >> To avoid these problems, move such variables into the "case" where >> they're used or lift them up into the main function body. >> >> arch/x86/xen/enlighten_pv.c: In function ‘xen_write_msr_safe’: >> arch/x86/xen/enlighten_pv.c:904:12: warning: statement will never be >> executed [-Wswitch-unreachable] >>    904 |   unsigned which; >>        |            ^~~~~ >> >> [1] https://bugs.llvm.org/show_bug.cgi?id=44916 >> >> Signed-off-by: Kees Cook > > Reviewed-by: Juergen Gross > Applied to for-linus-5.6. (I replaced 'unsigned' with 'unsigned int' to quiet down checkpatch ) -boris