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=-10.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,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 83A7AC3F2CD for ; Fri, 28 Feb 2020 18:26:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5F538246AC for ; Fri, 28 Feb 2020 18:26:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726975AbgB1S0N (ORCPT ); Fri, 28 Feb 2020 13:26:13 -0500 Received: from mga05.intel.com ([192.55.52.43]:61875 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725877AbgB1S0N (ORCPT ); Fri, 28 Feb 2020 13:26:13 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by fmsmga105.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Feb 2020 10:26:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,497,1574150400"; d="scan'208";a="231166116" Received: from rdunst-mobl1.ger.corp.intel.com (HELO btopel-mobl.ger.intel.com) ([10.252.40.10]) by fmsmga007.fm.intel.com with ESMTP; 28 Feb 2020 10:26:10 -0800 Subject: Re: [PATCH] [next] xdp: Replace zero-length array with flexible-array member To: Jonathan Lemon , "Gustavo A. R. Silva" Cc: Magnus Karlsson , "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200228131907.GA17911@embeddedor> <6FEAF24E-27CF-4840-8134-595D27275976@gmail.com> From: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= Message-ID: <4f7c8a2f-e49e-beb5-9188-1bebac804d8d@intel.com> Date: Fri, 28 Feb 2020 19:26:09 +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: <6FEAF24E-27CF-4840-8134-595D27275976@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020-02-28 18:14, Jonathan Lemon wrote: > > > On 28 Feb 2020, at 5:19, 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 > > Acked-by: Jonathan Lemon > Acked-by: Björn Töpel