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=-13.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 C8BD8C47247 for ; Fri, 8 May 2020 13:06:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EF5924973 for ; Fri, 8 May 2020 13:06:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=rere.qmqm.pl header.i=@rere.qmqm.pl header.b="ipvEwuKk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729625AbgEHNGw (ORCPT ); Fri, 8 May 2020 09:06:52 -0400 Received: from rere.qmqm.pl ([91.227.64.183]:19785 "EHLO rere.qmqm.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728303AbgEHNGt (ORCPT ); Fri, 8 May 2020 09:06:49 -0400 Received: from remote.user (localhost [127.0.0.1]) by rere.qmqm.pl (Postfix) with ESMTPSA id 49JVw708X9z5r; Fri, 8 May 2020 15:06:46 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=rere.qmqm.pl; s=1; t=1588943207; bh=uppDoyhwlbwoyrRyepfixLOhrOgshs3uGHxuVJsNsE4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ipvEwuKk28Ab/CTNLUDVA6Vz6zgEN5GKDk6xoLAUtz3jtRh8yvdWBqsHpesbqCbsp n1GVnZ+jRZstbrJJP+hnqPbsmKCTO+fqSgGHeyMvGxd3UBQxYOca1YhOodHadvLQaQ 4ZZqkOMUneH6YYbLrilKwQRNpw7wm+hJmryvwn5sGHIT/MExBe5s2Utxze0kqSxGkM eZJxlESvUO/912pO/5vsYPebYFd4/jal15oTZ4rgtbb62TM9H0Jdxn/uzRFraDHNG3 Jf+Ie7ilo4znZGEZTPx/t9MYXXb555a51vIWIeVmgUSrLVK1HJgqufr+NPXMiF4xVb vrYOGo8zXNjsQ== X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.102.2 at mail Date: Fri, 8 May 2020 15:06:43 +0200 From: =?iso-8859-2?Q?Micha=B3_Miros=B3aw?= To: "Gustavo A. R. Silva" Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] cb710: Replace zero-length array with flexible-array Message-ID: <20200508130643.GA9591@qmqm.qmqm.pl> References: <20200507185224.GA14209@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200507185224.GA14209@embeddedor> User-Agent: Mutt/1.10.1 (2018-07-13) 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 01:52:24PM -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 > --- > include/linux/cb710.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/cb710.h b/include/linux/cb710.h > index 60de3fedd3a7..405657a9a0d5 100644 > --- a/include/linux/cb710.h > +++ b/include/linux/cb710.h > @@ -36,7 +36,7 @@ struct cb710_chip { > unsigned slot_mask; > unsigned slots; > spinlock_t irq_lock; > - struct cb710_slot slot[0]; > + struct cb710_slot slot[]; > }; > > /* NOTE: cb710_chip.slots is modified only during device init/exit and > Acked-by: Michał Mirosław