From patchwork Thu May 7 19:02:23 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: 11534749 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 C488514B4 for ; Thu, 7 May 2020 18:57:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A31AF21835 for ; Thu, 7 May 2020 18:57:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877878; bh=v54+jJXI55ev/ljByJU0bELFAb0LTCoWQZNBXlPcq6M=; h=Date:From:To:Cc:Subject:List-ID:From; b=cHNgWmiewwULKWtQncE8Tj890nVrnhjrAT7pmNfy8vBISpv1NatX6QGAHZH0JKLUZ Hly+aJdQqWZ/oS2RHTKQHDRkHaKuyf/KmEXuVm7m29XLWfJgXJPbbDytZRNk2nGvfa NYuz3Dly4DfTFUSdNYamBtQ76UvBemye233WZPcc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728324AbgEGS56 (ORCPT ); Thu, 7 May 2020 14:57:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:59320 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726926AbgEGS55 (ORCPT ); Thu, 7 May 2020 14:57:57 -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 8AB8620575; Thu, 7 May 2020 18:57:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877877; bh=v54+jJXI55ev/ljByJU0bELFAb0LTCoWQZNBXlPcq6M=; h=Date:From:To:Cc:Subject:From; b=jNUUPCbHLXL+RGEmVjXV4LexFXr2GtNKv+s2Fi35Ni/57M7Xa2vVfUsuYHNYHLOao ARkd0WBSfasJhdIAz1BUfP6UdO/swEaHn1/TJHozcEZrf70tNiIYfflYm8KOstj7A9 UQnSrNgiG+0Ms7UVehDBfqh/EnYUmasRl3Jdoeag= Date: Thu, 7 May 2020 14:02:23 -0500 From: "Gustavo A. R. Silva" To: Trond Myklebust , Anna Schumaker Cc: linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] NFS: Replace zero-length array with flexible-array Message-ID: <20200507190223.GA15428@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@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 --- include/linux/nfs4.h | 2 +- include/linux/nfs_xdr.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h index 82d8fb422092..7c4b63561035 100644 --- a/include/linux/nfs4.h +++ b/include/linux/nfs4.h @@ -38,7 +38,7 @@ struct nfs4_ace { struct nfs4_acl { uint32_t naces; - struct nfs4_ace aces[0]; + struct nfs4_ace aces[]; }; #define NFS4_MAXLABELLEN 2048 diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h index 440230488025..6aad9b0a5062 100644 --- a/include/linux/nfs_xdr.h +++ b/include/linux/nfs_xdr.h @@ -1227,7 +1227,7 @@ struct nfs4_secinfo4 { struct nfs4_secinfo_flavors { unsigned int num_flavors; - struct nfs4_secinfo4 flavors[0]; + struct nfs4_secinfo4 flavors[]; }; struct nfs4_secinfo_arg {