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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 66252C38A2A for ; Thu, 7 May 2020 19:17:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42782208D6 for ; Thu, 7 May 2020 19:17:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879065; bh=thByVMAAcBvR3AyjBBzl3EWLZRPLrKL2Gs1T44P2bM4=; h=Date:From:To:Cc:Subject:List-ID:From; b=NCn3yDl94EUa75OVwoeMG10je5Aatz1BQV6mX0OxRRLOlwtqT181+yhLVMgVx7zZt eSzbKXCDwXnk8eGvN46kfMWp3fVtzmndJnRGM+ZVuSeXa3uWIr65DDW0N6nmPA2zXY z9a607KbxW1OethcyYecvY/UuhklBuua2IqPjap4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728645AbgEGTRo (ORCPT ); Thu, 7 May 2020 15:17:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:40756 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726367AbgEGTRn (ORCPT ); Thu, 7 May 2020 15:17:43 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 10A04208D6; Thu, 7 May 2020 19:17:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879063; bh=thByVMAAcBvR3AyjBBzl3EWLZRPLrKL2Gs1T44P2bM4=; h=Date:From:To:Cc:Subject:From; b=jpkxgGGqSk+xvBMgPdt4yAzdgPMsUFB+Z+HYSVVW0y1Y6WKUIWDbPjKJbr61zCz35 CnvithaG8k5Tjp49vrUoa0VBeLgb51EH5I6Eteh1AZDClP35oT7+7HgeSVIeyUn/G+ BfaBXJv5DEPXC/Y+bh07VXu6bo6l9bT6F4VFR34I= Date: Thu, 7 May 2020 14:22:10 -0500 From: "Gustavo A. R. Silva" To: Song Liu Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] md/raid1: Replace zero-length array with flexible-array Message-ID: <20200507192209.GA16290@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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] 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 --- drivers/md/md-linear.h | 2 +- drivers/md/raid1.h | 2 +- drivers/md/raid10.h | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/md/md-linear.h b/drivers/md/md-linear.h index 8381d651d4ed..24e97db50ebb 100644 --- a/drivers/md/md-linear.h +++ b/drivers/md/md-linear.h @@ -12,6 +12,6 @@ struct linear_conf struct rcu_head rcu; sector_t array_sectors; int raid_disks; /* a copy of mddev->raid_disks */ - struct dev_info disks[0]; + struct dev_info disks[]; }; #endif diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h index e7ccad898736..b7eb09e8c025 100644 --- a/drivers/md/raid1.h +++ b/drivers/md/raid1.h @@ -180,7 +180,7 @@ struct r1bio { * if the IO is in WRITE direction, then multiple bios are used. * We choose the number when they are allocated. */ - struct bio *bios[0]; + struct bio *bios[]; /* DO NOT PUT ANY NEW FIELDS HERE - bios array is contiguously alloced*/ }; diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h index d3eaaf3eb1bc..79cd2b7d3128 100644 --- a/drivers/md/raid10.h +++ b/drivers/md/raid10.h @@ -153,7 +153,7 @@ struct r10bio { }; sector_t addr; int devnum; - } devs[0]; + } devs[]; }; /* bits for r10bio.state */