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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 0EEF7C282C0 for ; Wed, 23 Jan 2019 14:16:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D3CD12184B for ; Wed, 23 Jan 2019 14:16:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726575AbfAWOQN convert rfc822-to-8bit (ORCPT ); Wed, 23 Jan 2019 09:16:13 -0500 Received: from mga02.intel.com ([134.134.136.20]:47729 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727110AbfAWOPz (ORCPT ); Wed, 23 Jan 2019 09:15:55 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 23 Jan 2019 06:15:53 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.56,511,1539673200"; d="scan'208";a="140624960" Received: from jnikula-mobl3.fi.intel.com (HELO localhost) ([10.237.66.172]) by fmsmga001.fm.intel.com with ESMTP; 23 Jan 2019 06:15:47 -0800 From: Jani Nikula To: Greg KH , Kees Cook Cc: dev@openvswitch.org, Ard Biesheuvel , netdev@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, kernel-hardening@lists.openwall.com, intel-wired-lan@lists.osuosl.org, linux-fsdevel@vger.kernel.org, xen-devel@lists.xenproject.org, Laura Abbott , linux-kbuild@vger.kernel.org, Alexander Popov Subject: Re: [Intel-gfx] [PATCH 1/3] treewide: Lift switch variables out of switches In-Reply-To: <20190123115829.GA31385@kroah.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20190123110349.35882-1-keescook@chromium.org> <20190123110349.35882-2-keescook@chromium.org> <20190123115829.GA31385@kroah.com> Date: Wed, 23 Jan 2019 16:17:30 +0200 Message-ID: <874l9z31c5.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, 23 Jan 2019, Greg KH wrote: > On Wed, Jan 23, 2019 at 03:03:47AM -0800, Kees Cook wrote: >> Variables declared in a switch statement before any case statements >> cannot be initialized, so move all instances out of the switches. >> After this, future always-initialized stack variables will work >> and not throw warnings like this: >> >> fs/fcntl.c: In function ‘send_sigio_to_task’: >> fs/fcntl.c:738:13: warning: statement will never be executed [-Wswitch-unreachable] >> siginfo_t si; >> ^~ > > That's a pain, so this means we can't have any new variables in { } > scope except for at the top of a function? > > That's going to be a hard thing to keep from happening over time, as > this is valid C :( Not all valid C is meant to be used! ;) Anyway, I think you're mistaking the limitation to arbitrary blocks while it's only about the switch block IIUC. Can't have: switch (i) { int j; case 0: /* ... */ } because it can't be turned into: switch (i) { int j = 0; /* not valid C */ case 0: /* ... */ } but can have e.g.: switch (i) { case 0: { int j = 0; /* ... */ } } I think Kees' approach of moving such variable declarations to the enclosing block scope is better than adding another nesting block. BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center