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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 7A007C3F2CD for ; Thu, 5 Mar 2020 11:40:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 591D92073B for ; Thu, 5 Mar 2020 11:40:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727458AbgCELk5 (ORCPT ); Thu, 5 Mar 2020 06:40:57 -0500 Received: from mga17.intel.com ([192.55.52.151]:54812 "EHLO mga17.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725912AbgCELk4 (ORCPT ); Thu, 5 Mar 2020 06:40:56 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 03:40:56 -0800 X-IronPort-AV: E=Sophos;i="5.70,517,1574150400"; d="scan'208";a="234389164" Received: from jnikula-mobl3.fi.intel.com (HELO localhost) ([10.237.66.161]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Mar 2020 03:40:52 -0800 From: Jani Nikula To: "Gustavo A. R. Silva" , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Gustavo A. R. Silva" Subject: Re: [PATCH][next] drm/drm_displayid.h: Replace zero-length array with flexible-array member In-Reply-To: <20200305110105.GA21188@embeddedor> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20200305110105.GA21188@embeddedor> Date: Thu, 05 Mar 2020 13:40:49 +0200 Message-ID: <87y2sfni66.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 05 Mar 2020, "Gustavo A. R. Silva" wrote: > The current codebase makes use of the zero-length array language > extension to the C90 standard, but the preferred mechanism to declare > variable-length types such as these ones is a flexible array member[1][2], > introduced in C99: > > struct foo { > int stuff; > struct boo array[]; > }; > > By making use of the mechanism above, we will get a compiler warning > in case the flexible array does not occur last in the structure, which > will help us prevent some kind of undefined behavior bugs from being > inadvertently introduced[3] to the codebase from now on. > > Also, notice that, dynamic memory allocations won't be affected by > this change: > > "Flexible array members have incomplete type, and so the sizeof operator > may not be applied. As a quirk of the original implementation of > zero-length arrays, sizeof evaluates to zero."[1] > > This issue was found with the help of Coccinelle. > > [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html > [2] https://github.com/KSPP/linux/issues/21 > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva Reviewed-by: Jani Nikula > --- > include/drm/drm_displayid.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/drm/drm_displayid.h b/include/drm/drm_displayid.h > index 9d3b745c3107..94b4390bf990 100644 > --- a/include/drm/drm_displayid.h > +++ b/include/drm/drm_displayid.h > @@ -89,7 +89,7 @@ struct displayid_detailed_timings_1 { > > struct displayid_detailed_timing_block { > struct displayid_block base; > - struct displayid_detailed_timings_1 timings[0]; > + struct displayid_detailed_timings_1 timings[]; > }; > > #define for_each_displayid_db(displayid, block, idx, length) \ -- Jani Nikula, Intel Open Source Graphics Center