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=-13.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 174FBC3F2D2 for ; Fri, 28 Feb 2020 13:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E1C6F246B5 for ; Fri, 28 Feb 2020 13:16:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=embeddedor.com header.i=@embeddedor.com header.b="EZGpzrAj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726642AbgB1NQP (ORCPT ); Fri, 28 Feb 2020 08:16:15 -0500 Received: from gateway21.websitewelcome.com ([192.185.45.38]:49380 "EHLO gateway21.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725796AbgB1NQP (ORCPT ); Fri, 28 Feb 2020 08:16:15 -0500 Received: from cm13.websitewelcome.com (cm13.websitewelcome.com [100.42.49.6]) by gateway21.websitewelcome.com (Postfix) with ESMTP id 0940E400D1BD5 for ; Fri, 28 Feb 2020 07:16:14 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id 7fUzjI0doRP4z7fV0jgPu9; Fri, 28 Feb 2020 07:16:14 -0600 X-Authority-Reason: nr=8 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=embeddedor.com; s=default; h=Content-Type:MIME-Version:Message-ID:Subject: Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=RE0pda+OoJ4cL4RKWAP8k9023lNF5IK92xD1bJo2GXE=; b=EZGpzrAjcSTU9tz+KfZHqu3MaD Szx/qQVD/GAzX0ei1A5yn3SEFGEFtfveb/Djj8PebHtnx8f6bMcK4yM01h62XDJuo3pez1f1ujXRC hYME70p+aB3CqunyFFknk14DeKJ2TkgG+cQVdCGIpOs10T40Rqd1nw4hcusDP9PsD/HKIB8nKC/If 7omwKqGkNQMvQ6128OO9V1dH3kviLjV6frN5K2qD1HUmucRqDywSKZMdJUt3bhM+EhXwFBYMKO9KP TSeepnIY8xV2HWjOasENBL0Ybv8pI057b22QVKUQha1ySpHOVT4Q/sxztyDBr6y+cJ3fF4S2ZmfL/ VAEeWIoA==; Received: from [201.162.240.44] (port=6535 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1j7fUx-001EPI-Hz; Fri, 28 Feb 2020 07:16:12 -0600 Date: Fri, 28 Feb 2020 07:19:07 -0600 From: "Gustavo A. R. Silva" To: =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Magnus Karlsson , Jonathan Lemon , "David S. Miller" , Jakub Kicinski , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH][next] xdp: Replace zero-length array with flexible-array member Message-ID: <20200228131907.GA17911@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - gator4166.hostgator.com X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - embeddedor.com X-BWhitelist: no X-Source-IP: 201.162.240.44 X-Source-L: No X-Exim-ID: 1j7fUx-001EPI-Hz X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.162.240.44]:6535 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 10 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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 --- net/xdp/xsk_queue.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h index 89a01ac4e079..b50bb5c76da5 100644 --- a/net/xdp/xsk_queue.h +++ b/net/xdp/xsk_queue.h @@ -19,13 +19,13 @@ struct xdp_ring { /* Used for the RX and TX queues for packets */ struct xdp_rxtx_ring { struct xdp_ring ptrs; - struct xdp_desc desc[0] ____cacheline_aligned_in_smp; + struct xdp_desc desc[] ____cacheline_aligned_in_smp; }; /* Used for the fill and completion queues for buffers */ struct xdp_umem_ring { struct xdp_ring ptrs; - u64 desc[0] ____cacheline_aligned_in_smp; + u64 desc[] ____cacheline_aligned_in_smp; }; struct xsk_queue { -- 2.25.0