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=-11.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 37EA4C54E8E for ; Mon, 11 May 2020 05:47:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 22DDF2137B for ; Mon, 11 May 2020 05:47:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728084AbgEKFrj (ORCPT ); Mon, 11 May 2020 01:47:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:44190 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725916AbgEKFri (ORCPT ); Mon, 11 May 2020 01:47:38 -0400 Received: from sekiro (amontpellier-556-1-155-96.w109-210.abo.wanadoo.fr [109.210.131.96]) (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 326EF20735; Mon, 11 May 2020 05:47:35 +0000 (UTC) Date: Mon, 11 May 2020 07:47:30 +0200 From: Ludovic Desroches To: "Gustavo A. R. Silva" Cc: linux-arm-kernel@lists.infradead.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dmaengine: at_hdmac: Replace zero-length array with flexible-array Message-ID: <20200511054730.pfsavov2onak4nf6@sekiro> References: <20200507190038.GA15272@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200507190038.GA15272@embeddedor> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 07, 2020 at 02:00:38PM -0500, Gustavo A. R. Silva wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > 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 Acked-by: Ludovic Desroches Thanks > --- > drivers/dma/at_hdmac_regs.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/dma/at_hdmac_regs.h b/drivers/dma/at_hdmac_regs.h > index 397692e937b3..80fc2fe8c77e 100644 > --- a/drivers/dma/at_hdmac_regs.h > +++ b/drivers/dma/at_hdmac_regs.h > @@ -331,7 +331,7 @@ struct at_dma { > struct dma_pool *dma_desc_pool; > struct dma_pool *memset_pool; > /* AT THE END channels table */ > - struct at_dma_chan chan[0]; > + struct at_dma_chan chan[]; > }; > > #define dma_readl(atdma, name) \ >