From patchwork Fri Mar 6 22:13:33 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 11424747 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id B38AF921 for ; Fri, 6 Mar 2020 22:34:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93E43206E6 for ; Fri, 6 Mar 2020 22:34:54 +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="MwGKYUS8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726788AbgCFWex (ORCPT ); Fri, 6 Mar 2020 17:34:53 -0500 Received: from gateway21.websitewelcome.com ([192.185.46.113]:48568 "EHLO gateway21.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726194AbgCFWex (ORCPT ); Fri, 6 Mar 2020 17:34:53 -0500 X-Greylist: delayed 1243 seconds by postgrey-1.27 at vger.kernel.org; Fri, 06 Mar 2020 17:34:53 EST Received: from cm11.websitewelcome.com (cm11.websitewelcome.com [100.42.49.5]) by gateway21.websitewelcome.com (Postfix) with ESMTP id 9B4894010B96C for ; Fri, 6 Mar 2020 16:10:26 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id ALAoj6829Sl8qALAojiADS; Fri, 06 Mar 2020 16:10:26 -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=FZpoqtpL0CDwGKnAs+sqrIJ5mXXApjq5UeHNcIv2g+k=; b=MwGKYUS8Y4iJ1WQLplUThEuaPm f5KUIjqpqvTNSzzOW/vCbs8PPOFV7Fod+TXrJTy1avisRb2+UbDFMXFtBsk2BVnQa3fGmqq+VlwBy 9L2SicBSIeby7jdCPRouGtBJ4tuEmlsGhtM8ScByWD/ez9i/8QzUnxUZpA3IpFbOeLKCgZlVCthc6 G/icLYf04sjeaFSwlo2AcZPSWmtgl2NX29uMAOb1LqEhzsaKmd+vOoApial8CjwvAX39nBhm/EHIW HWABE2nc0gHC3IADRK/5HtRlP9QYef/dyjPPj58jm6IuOLzMmeCI55WlgOQoIja0WSsi42+w/cdqu G6vSsYhw==; Received: from [201.162.241.123] (port=7991 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1jALAm-000HxE-K5; Fri, 06 Mar 2020 16:10:25 -0600 Date: Fri, 6 Mar 2020 16:13:33 -0600 From: "Gustavo A. R. Silva" To: Chris Mason , Josef Bacik , David Sterba Cc: linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH][next] btrfs: scrub: Replace zero-length array with flexible-array member Message-ID: <20200306221333.GA31084@embeddedor> MIME-Version: 1.0 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: 201.162.241.123 X-Source-L: No X-Exim-ID: 1jALAm-000HxE-K5 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.162.241.123]:7991 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 4 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@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 --- fs/btrfs/scrub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c index 16aa680134fd..adaf8ab694d5 100644 --- a/fs/btrfs/scrub.c +++ b/fs/btrfs/scrub.c @@ -149,7 +149,7 @@ struct scrub_parity { */ unsigned long *ebitmap; - unsigned long bitmap[0]; + unsigned long bitmap[]; }; struct scrub_ctx {