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=-6.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 09DFAC433FC for ; Wed, 13 May 2020 15:05:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CD14221FF for ; Wed, 13 May 2020 14:56:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589381792; bh=8SmbnrZ5qW6mVaqqlcGDrJ3tZhpY+ZYEC2ysujal7jE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=fUB942IXfPXojEgrCN40MnLzzn5mSuO0DXF+HO1PWHgKQfqY6v5W4jYYCfNoDeJ12 4Bdm+Vr+0f+5M83sKQxj94xi5s33NUkd+vumWB30ZMuhib49bQygLeqNvH6GwMcRBi PIbHkYgP7T7XZ/Ra0aQbCgLLZ2a7olVV2ktld+qg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389104AbgEMO4a (ORCPT ); Wed, 13 May 2020 10:56:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:49498 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728568AbgEMO42 (ORCPT ); Wed, 13 May 2020 10:56:28 -0400 Received: from localhost (unknown [106.200.233.149]) (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 8B1EE221E6; Wed, 13 May 2020 14:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589381788; bh=8SmbnrZ5qW6mVaqqlcGDrJ3tZhpY+ZYEC2ysujal7jE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=l4mRGFNZDs1RO7j/ngnkH16aePO1WvI/3rJkpo0/bOqGBn+zq90/znJcuC3NGZKTu qNSI7KkiyyzXV4E6Yg1UrgZMXzyeIrvdG/iStQWx+x7Wz+aQnWosrPzMIp73qeck4f eRdMLpxjBQ3RWdNMW0mCsJ6Abq7tMpCUQi1rnv5U= Date: Wed, 13 May 2020 20:26:24 +0530 From: Vinod Koul To: "Gustavo A. R. Silva" Cc: Ludovic Desroches , linux-arm-kernel@lists.infradead.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dmaengine: at_xdmac: Replace zero-length array with flexible-array Message-ID: <20200513145624.GM14092@vkoul-mobl> References: <20200507190046.GA15298@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200507190046.GA15298@embeddedor> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07-05-20, 14:00, Gustavo A. R. Silva wrote: > 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") Applied, thanks -- ~Vinod