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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 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 D5D29C4332B for ; Mon, 23 Mar 2020 14:01:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A696F2076A for ; Mon, 23 Mar 2020 14:01:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728575AbgCWOBa (ORCPT ); Mon, 23 Mar 2020 10:01:30 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:36360 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728446AbgCWOBa (ORCPT ); Mon, 23 Mar 2020 10:01:30 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: eballetbo) with ESMTPSA id 76A18296394 Subject: Re: [PATCH][next] chrome: cros_ec_chardev: Replace zero-length array with flexible-array member To: "Gustavo A. R. Silva" , Benson Leung , Guenter Roeck Cc: linux-kernel@vger.kernel.org References: <20200320231542.GA19872@embeddedor.com> From: Enric Balletbo i Serra Message-ID: <71aa855b-54b8-5fef-0d10-b9f132536af2@collabora.com> Date: Mon, 23 Mar 2020 15:01:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200320231542.GA19872@embeddedor.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Gustavo, On 21/3/20 0:15, 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 Queued for 5.7. Thanks! ~ Enric > --- > drivers/platform/chrome/cros_ec_chardev.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/platform/chrome/cros_ec_chardev.c b/drivers/platform/chrome/cros_ec_chardev.c > index b51ab24055f3..e0bce869c49a 100644 > --- a/drivers/platform/chrome/cros_ec_chardev.c > +++ b/drivers/platform/chrome/cros_ec_chardev.c > @@ -48,7 +48,7 @@ struct ec_event { > struct list_head node; > size_t size; > u8 event_type; > - u8 data[0]; > + u8 data[]; > }; > > static int ec_get_version(struct cros_ec_dev *ec, char *str, int maxlen) >