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,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 A72C9C10F25 for ; Mon, 9 Mar 2020 21:07:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 84AA82146E for ; Mon, 9 Mar 2020 21:07:51 +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="l5B230xH" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726157AbgCIVHv (ORCPT ); Mon, 9 Mar 2020 17:07:51 -0400 Received: from gateway23.websitewelcome.com ([192.185.49.218]:33632 "EHLO gateway23.websitewelcome.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726118AbgCIVHv (ORCPT ); Mon, 9 Mar 2020 17:07:51 -0400 X-Greylist: delayed 1501 seconds by postgrey-1.27 at vger.kernel.org; Mon, 09 Mar 2020 17:07:50 EDT Received: from cm16.websitewelcome.com (cm16.websitewelcome.com [100.42.49.19]) by gateway23.websitewelcome.com (Postfix) with ESMTP id 15E5D4570 for ; Mon, 9 Mar 2020 15:19:23 -0500 (CDT) Received: from gator4166.hostgator.com ([108.167.133.22]) by cmsmtp with SMTP id BOrzjO0WP8vkBBOrzjGr6m; Mon, 09 Mar 2020 15:19:23 -0500 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=m8oDU5ueC5bxEXfkGSmLSUMfp7+qqcDb0q84/pI1JLc=; b=l5B230xHG/u7HVjD2SufekiKFc u2GhyZ7dECYq4OgNB626qmzcBk+oHhW96tGFm4IV/dQDWsrkUTQqzMesVCNAV2rfcKwyhueRQsr9j UhyGkWl966uORuNfrqT6HhKVEUnmH0AGM8zsAuZirE5C7gOhAPNb8YIoHflPxnhDjM4nCnOrSbB7m YY7hEG+KbLuJh0bU1HdTEwk2cNcHw7XgBgGBj5UVWGyZtSF4upZEc/iDlJa5o+ZYjs/BC6DCx65yj VKxMZrbg6A6Oka/dTf0A3xK1aCIxyL6OOpqFC4/aahGjTfRBohWpSf/UednROC4Vvf9IQSQ1Gsz99 XMY28R/A==; Received: from [201.162.168.201] (port=22316 helo=embeddedor) by gator4166.hostgator.com with esmtpa (Exim 4.92) (envelope-from ) id 1jBOrx-000yAk-51; Mon, 09 Mar 2020 15:19:21 -0500 Date: Mon, 9 Mar 2020 15:22:33 -0500 From: "Gustavo A. R. Silva" To: Miklos Szeredi Cc: linux-unionfs@vger.kernel.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH][next] overlayfs: overlayfs.h: Replace zero-length array with flexible-array member Message-ID: <20200309202233.GA8631@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: 201.162.168.201 X-Source-L: No X-Exim-ID: 1jBOrx-000yAk-51 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: (embeddedor) [201.162.168.201]:22316 X-Source-Auth: gustavo@embeddedor.com X-Email-Count: 17 X-Source-Cap: Z3V6aWRpbmU7Z3V6aWRpbmU7Z2F0b3I0MTY2Lmhvc3RnYXRvci5jb20= X-Local-Domain: yes Sender: linux-unionfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@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/overlayfs/overlayfs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index 8db6cf3ffc46..37a04e742603 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -87,7 +87,7 @@ struct ovl_fb { u8 flags; /* OVL_FH_FLAG_* */ u8 type; /* fid_type of fid */ uuid_t uuid; /* uuid of filesystem */ - u32 fid[0]; /* file identifier should be 32bit aligned in-memory */ + u32 fid[]; /* file identifier should be 32bit aligned in-memory */ } __packed; /* In-memory and on-wire format for overlay file handle */ -- 2.25.0