From patchwork Thu May 7 19:27:03 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: 11534807 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 053B992A for ; Thu, 7 May 2020 19:22:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E289524953 for ; Thu, 7 May 2020 19:22:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879358; bh=qrpmzCPpQ9HFwu20utBp+1OHeWSt1E7WeS45pMG/mJs=; h=Date:From:To:Cc:Subject:List-ID:From; b=zmx3rNsIG1bqULb//Loe/7luYDOcVnuXQ/vGYn58+s8lu8n9dWx7mARE0XIA+iOp4 76hDJ867JhZr4RN6JXsDTWG05CFYpeDCGUkIKITwJMlMANY8dgllIDq/NaYKIzfb4N qCnlvoaA3RJyyShTvcmdEzWZDME6JinvI5zS+OKg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726558AbgEGTWi (ORCPT ); Thu, 7 May 2020 15:22:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:43464 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727799AbgEGTWi (ORCPT ); Thu, 7 May 2020 15:22:38 -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 2AF22208D6; Thu, 7 May 2020 19:22:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879357; bh=qrpmzCPpQ9HFwu20utBp+1OHeWSt1E7WeS45pMG/mJs=; h=Date:From:To:Cc:Subject:From; b=Fp/WP7t+5M1ymFQtuRe7hYifflClNVPTtZoQw9uQl4yIVRKjMOi+xt9rmlUxGLqZm tY/iHj0FIqT36g/Uaff0wYK2dT7kjDU39258TKc5vefvt7ujUgpKApzBg+cry/AfTC blajwso2+n7raYEqoC55p1i7IE4icUBvJZ0fwNsA= Date: Thu, 7 May 2020 14:27:03 -0500 From: "Gustavo A. R. Silva" To: "Darrick J. Wong" , linux-xfs@vger.kernel.org Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] xfs: Replace zero-length array with flexible-array Message-ID: <20200507192703.GA16784@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@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 Reviewed-by: Darrick J. Wong --- fs/xfs/libxfs/xfs_format.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h index 045556e78ee2..592f1c12ad36 100644 --- a/fs/xfs/libxfs/xfs_format.h +++ b/fs/xfs/libxfs/xfs_format.h @@ -1681,7 +1681,7 @@ struct xfs_acl_entry { struct xfs_acl { __be32 acl_cnt; - struct xfs_acl_entry acl_entry[0]; + struct xfs_acl_entry acl_entry[]; }; /*