From patchwork Fri Mar 6 16:51:05 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: 11424427 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 C7AF9138D for ; Fri, 6 Mar 2020 17:12:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A82CA2084E for ; Fri, 6 Mar 2020 17:12:52 +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="IMfZCiEd" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726676AbgCFRMw (ORCPT ); Fri, 6 Mar 2020 12:12:52 -0500 Received: from gateway31.websitewelcome.com ([192.185.144.97]:30142 "EHLO gateway31.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbgCFRMv (ORCPT ); Fri, 6 Mar 2020 12:12:51 -0500 Received: from cm10.websitewelcome.com (cm10.websitewelcome.com [100.42.49.4]) by gateway31.websitewelcome.com (Postfix) with ESMTP id DCA724885 for ; Fri, 6 Mar 2020 10:47:59 -0600 (CST) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id AG8ljuaotEfyqAG8ljy3tY; Fri, 06 Mar 2020 10:47:59 -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=8UHomocG+fX8U3yCwj2THSJfjfw/ABF8sixeOTpNZSE=; b=IMfZCiEdunBj2yBl3vVZc2GNC/ tjavhX3pSWR+qk3oW0uHTcB8KQQRVXbLK2JfXqxRWaBjWLrhWcpLYOY8ugzME2mgTO/ttknFBwX/F 4QVZSNTYKQPnhzCgtBFNWWBVMnt4Uqu05Klt/zMe415Nh4yKzOepPUEtXb99N6uGOPxf5IyjhgFhz N4/VVdAncZIsENjJmLXA97QsJsSBLBJ/zXoC/HiUu40geuLJ8KijS3b6/iEwPVCmejPvAurgZjGbC Dr2msOjwgihiDwAtHfXiJ5sc05djz7wm+seVTXXUb6yE2E7WEhxT/jes1kWwRBVba5SROuGOp9nTg e1iAoWTQ==; Received: from [201.166.190.232] (port=51794 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1jAG8j-001tGK-Sl; Fri, 06 Mar 2020 10:47:58 -0600 Date: Fri, 6 Mar 2020 10:51:05 -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/rcu-string.h: Replace zero-length array with flexible-array member Message-ID: <20200306165105.GA22637@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: 201.166.190.232 X-Source-L: No X-Exim-ID: 1jAG8j-001tGK-Sl X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.166.190.232]:51794 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 17 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/rcu-string.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/btrfs/rcu-string.h b/fs/btrfs/rcu-string.h index a97dc74a4d3d..5c1a617eb25d 100644 --- a/fs/btrfs/rcu-string.h +++ b/fs/btrfs/rcu-string.h @@ -8,7 +8,7 @@ struct rcu_string { struct rcu_head rcu; - char str[0]; + char str[]; }; static inline struct rcu_string *rcu_string_strdup(const char *src, gfp_t mask)