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=-10.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7291AC38A24 for ; Thu, 7 May 2020 19:25:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4AA5C208D6 for ; Thu, 7 May 2020 19:25:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="oaHQJr7F" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728229AbgEGTZG (ORCPT ); Thu, 7 May 2020 15:25:06 -0400 Received: from mail26.static.mailgun.info ([104.130.122.26]:33630 "EHLO mail26.static.mailgun.info" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727837AbgEGTZE (ORCPT ); Thu, 7 May 2020 15:25:04 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1588879504; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=Ix9XkAMYCQsp/8JQnx4zfbI/X7x9n8NFh7hLnjbOM8Q=; b=oaHQJr7Fnhpn9axu6zzRngnCgmBwXIognsjP3JrVGDkv1ICOlS/BI0gmQXJcFfLql1KN8lQZ wHtW6LW+az3KLmPci+vh0cATQ+M7JX8ZDCk8xvfE1jZDvVhAo5D8SCU+4xmHxLtLeNeYviGo U0nUq0jDfVK/X6gWCEbGdJWuN98= X-Mailgun-Sending-Ip: 104.130.122.26 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by mxa.mailgun.org with ESMTP id 5eb4608e.7f318b7827d8-smtp-out-n04; Thu, 07 May 2020 19:25:02 -0000 (UTC) Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 1F638C433D2; Thu, 7 May 2020 19:25:01 +0000 (UTC) Received: from [10.226.58.28] (i-global254.qualcomm.com [199.106.103.254]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: jhugo) by smtp.codeaurora.org (Postfix) with ESMTPSA id 056A6C433BA; Thu, 7 May 2020 19:24:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 056A6C433BA Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=none smtp.mailfrom=jhugo@codeaurora.org Subject: Re: [PATCH] dmaengine: qcom: bam_dma: Replace zero-length array with flexible-array To: "Gustavo A. R. Silva" , Andy Gross , Bjorn Andersson Cc: linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200507185016.GA13883@embeddedor> From: Jeffrey Hugo Message-ID: <1b3cda25-5f3a-5359-4bf7-d16a8364f545@codeaurora.org> Date: Thu, 7 May 2020 13:24:57 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200507185016.GA13883@embeddedor> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/7/2020 12:50 PM, 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") > > Signed-off-by: Gustavo A. R. Silva > --- > drivers/dma/qcom/bam_dma.c | 2 +- > drivers/firmware/qcom_scm-legacy.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > Shouldn't these two files be two different patches? -- Jeffrey Hugo Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.