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=-8.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 2CA08C2D0F8 for ; Wed, 13 May 2020 07:30:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 090EB205ED for ; Wed, 13 May 2020 07:30:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729729AbgEMHag convert rfc822-to-8bit (ORCPT ); Wed, 13 May 2020 03:30:36 -0400 Received: from coyote.holtmann.net ([212.227.132.17]:45171 "EHLO mail.holtmann.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728988AbgEMHaf (ORCPT ); Wed, 13 May 2020 03:30:35 -0400 Received: from [192.168.1.91] (p4FEFC5A7.dip0.t-ipconnect.de [79.239.197.167]) by mail.holtmann.org (Postfix) with ESMTPSA id 9833BCED09; Wed, 13 May 2020 09:40:16 +0200 (CEST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.80.23.2.2\)) Subject: Re: [PATCH] Bluetooth: Replace zero-length array with flexible-array From: Marcel Holtmann In-Reply-To: <20200507185050.GA13953@embeddedor> Date: Wed, 13 May 2020 09:30:03 +0200 Cc: Johan Hedberg , linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <1027665B-71AC-4BC1-A3DF-64B1A9475B31@holtmann.org> References: <20200507185050.GA13953@embeddedor> To: "Gustavo A. R. Silva" X-Mailer: Apple Mail (2.3608.80.23.2.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Gustavo, > 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] > > sizeof(flexible-array-member) triggers a warning because flexible array > members have incomplete type[1]. There are some instances of code in > which the sizeof operator is being incorrectly/erroneously applied to > zero-length arrays and the result is zero. Such instances may be hiding > some bugs. So, this work (flexible-array member conversions) will also > help to get completely rid of those sorts of issues. > > 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 > --- > include/net/bluetooth/l2cap.h | 6 +++--- > include/net/bluetooth/mgmt.h | 40 ++++++++++++++++++++-------------------- > 2 files changed, 23 insertions(+), 23 deletions(-) the mgmt.h portion we already have in bluetooth-next tree. Can you send a version that just addresses l2cap.h. Thanks. Regards Marcel