From patchwork Thu May 7 18:59:21 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: 11534729 X-Patchwork-Delegate: jgg@ziepe.ca 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 7B45F14B4 for ; Thu, 7 May 2020 18:54:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5AE6B2184D for ; Thu, 7 May 2020 18:54:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877696; bh=HAF/oRojkDljr1eFLRHqTl9dtHCZGeFR/+2LDxzGKKY=; h=Date:From:To:Cc:Subject:List-ID:From; b=Q9iBS7M67NXQJCPkTm+FSmBwVTOkB7WNGcw+yvR4cSQ7uSxN7rpOtlSLdIiIYibff EDsWdMaq2OkRH7+6QylKUXZXfOykRB0dW0LYJIIavG2VoCmdXnOwrohNtcDd+Z2p2x v37AtCKFBI53Xnj2r8eBTijNfHMv8b/a9RkOPZOw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728391AbgEGSyz (ORCPT ); Thu, 7 May 2020 14:54:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:56994 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726518AbgEGSyz (ORCPT ); Thu, 7 May 2020 14:54:55 -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 71F5E20575; Thu, 7 May 2020 18:54:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877694; bh=HAF/oRojkDljr1eFLRHqTl9dtHCZGeFR/+2LDxzGKKY=; h=Date:From:To:Cc:Subject:From; b=2EhmErFn2LX85sjp/FeeJMucTQta5AEMMF5VhGW2+khwX+hDXK9DvM3PDerwrWSzc pP5EnH/kZRTLqEtfwNo4xlmAlbu4Sd94+WTd0le1kMUyyxaNSlC2g6UGRgAZnzn5bf 6lupoaMB2lCCK0sSNkkAToITfMdc1WT+GN3MQbfA= Date: Thu, 7 May 2020 13:59:21 -0500 From: "Gustavo A. R. Silva" To: Tariq Toukan Cc: netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] IB/mlx4: Replace zero-length array with flexible-array Message-ID: <20200507185921.GA15146@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@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/mlx4/qp.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/mlx4/qp.h b/include/linux/mlx4/qp.h index 8e2828d48d7f..9db93e487496 100644 --- a/include/linux/mlx4/qp.h +++ b/include/linux/mlx4/qp.h @@ -362,7 +362,7 @@ struct mlx4_wqe_datagram_seg { struct mlx4_wqe_lso_seg { __be32 mss_hdr_size; - __be32 header[0]; + __be32 header[]; }; enum mlx4_wqe_bind_seg_flags2 {