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,URIBL_BLOCKED, USER_AGENT_SANE_1 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 4B916C3F2CD for ; Fri, 28 Feb 2020 15:22:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D7A42469F for ; Fri, 28 Feb 2020 15:22:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727018AbgB1PWI (ORCPT ); Fri, 28 Feb 2020 10:22:08 -0500 Received: from proxima.lasnet.de ([78.47.171.185]:55736 "EHLO proxima.lasnet.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726650AbgB1PWH (ORCPT ); Fri, 28 Feb 2020 10:22:07 -0500 Received: from localhost.localdomain (p200300E9D71B9939E2C0865DB6B8C4EC.dip0.t-ipconnect.de [IPv6:2003:e9:d71b:9939:e2c0:865d:b6b8:c4ec]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: stefan@datenfreihafen.org) by proxima.lasnet.de (Postfix) with ESMTPSA id EBB8DC08EE; Fri, 28 Feb 2020 16:22:04 +0100 (CET) From: Stefan Schmidt Subject: Re: [PATCH][next] cfg802154: Replace zero-length array with flexible-array member To: "Gustavo A. R. Silva" , Alexander Aring , "David S. Miller" , Jakub Kicinski Cc: linux-wpan@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200228135959.GA30464@embeddedor> Message-ID: <2711894b-b78d-aebe-79fd-aa274d4ff977@datenfreihafen.org> Date: Fri, 28 Feb 2020 16:22:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200228135959.GA30464@embeddedor> Content-Type: text/plain; charset=utf-8; format=flowed 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 Hello. On 28.02.20 14:59, 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 > --- > include/net/cfg802154.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/net/cfg802154.h b/include/net/cfg802154.h > index 6f86073a5d7d..6ed07844eb24 100644 > --- a/include/net/cfg802154.h > +++ b/include/net/cfg802154.h > @@ -214,7 +214,7 @@ struct wpan_phy { > /* the network namespace this phy lives in currently */ > possible_net_t _net; > > - char priv[0] __aligned(NETDEV_ALIGN); > + char priv[] __aligned(NETDEV_ALIGN); > }; > > static inline struct net *wpan_phy_net(struct wpan_phy *wpan_phy) > This patch has been applied to the wpan-next tree and will be part of the next pull request to net-next. Thanks! regards Stefan Schmidt