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=-8.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,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 82789C433DF for ; Wed, 13 May 2020 15:39:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A04F9206F5 for ; Wed, 13 May 2020 15:39:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589384364; bh=QMW+p/VknEQSRsiiebDSJIJu6BKqq/ST0lr0lMg3vjA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=UpqpkdYwghV87K4cD+dHf9v9iFgeuaxB3BpP545Dt+LgUgwjcmwpDndCAPkNxKXyb e3itXMrVBgcEIMdvq7VlKDlkoewqzVCa38nrWKhUQlRMlfk9lkVSWL6jBRkD5sCKhe Be7f3o97Q+NMsHU/dgtTsArL1jgVd9QPJ1dcUsmY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729940AbgEMPjW (ORCPT ); Wed, 13 May 2020 11:39:22 -0400 Received: from mail.kernel.org ([198.145.29.99]:39238 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728678AbgEMPjV (ORCPT ); Wed, 13 May 2020 11:39:21 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (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 E1A4B205CB; Wed, 13 May 2020 15:39:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589384361; bh=QMW+p/VknEQSRsiiebDSJIJu6BKqq/ST0lr0lMg3vjA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=xVeWGJQEqALgzgRglNDpCMXaEA8kIZ31iN1cVQVKMEZL2SHjs1gjnD8xJkCUkbmTS n06rxNOiJ5fIZ59jmpV70JW2dOY+Z89JUtYEK3AVE9aHQJgkKZd5JMqGjidQjucyvy VIifaWt9MFQjeyI4GvBfOTLI7yIgPvAWBrO1OduU= Date: Wed, 13 May 2020 17:39:18 +0200 From: Greg Kroah-Hartman To: Johan Hovold Cc: "Gustavo A. R. Silva" , Alex Elder , greybus-dev@lists.linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] staging: greybus: Replace zero-length array with flexible-array Message-ID: <20200513153918.GA1360420@kroah.com> References: <20200507185318.GA14393@embeddedor> <20200513150343.GZ25962@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200513150343.GZ25962@localhost> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 13, 2020 at 05:03:43PM +0200, Johan Hovold wrote: > On Thu, May 07, 2020 at 01:53:18PM -0500, 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/greybus/arpc.h | 2 - > > include/linux/greybus/greybus_protocols.h | 44 +++++++++++++++--------------- > > I noticed Greg just applied this one to his -testing branch, but do we > really want this in greybus_protocols.h, which is meant to be shared > with the firmware side? Perhaps not an issue, just figured I'd point > this out. Why not, it should be the same thing, right? No logic has changed that I see. thanks, greg k-h