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,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 50681C433E1 for ; Mon, 18 May 2020 15:14:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 30ED020756 for ; Mon, 18 May 2020 15:14:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="MOHGGhOC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728008AbgERPOt (ORCPT ); Mon, 18 May 2020 11:14:49 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:24506 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726958AbgERPOt (ORCPT ); Mon, 18 May 2020 11:14:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589814888; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=C+olTwBlgSs4ipAcCb7zDXuZrql0pCto2QpWo685kbA=; b=MOHGGhOCu5brOfgji2s97US2uV3e2fRSIRo9QVdaTZz62BEsbwoVy6D0rKsYo39NHT2Bs+ uzM3iQH/XIRUP0XMiinoA7VJk13J9BXLO6z2ccDOcAbKsImF6LkuGF+yQzJiDzBsTaAkmo vTbIKNHvo93Pt/EPCtmKmlkoN1HFyqE= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-286-xJOkJ08JPgCBHtTeqDKQdg-1; Mon, 18 May 2020 11:14:26 -0400 X-MC-Unique: xJOkJ08JPgCBHtTeqDKQdg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B19341853B04; Mon, 18 May 2020 15:14:25 +0000 (UTC) Received: from warthog.procyon.org.uk (ovpn-112-95.rdu2.redhat.com [10.10.112.95]) by smtp.corp.redhat.com (Postfix) with ESMTP id C01AB2B7BB; Mon, 18 May 2020 15:14:24 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: <20200507185710.GA14910@embeddedor> References: <20200507185710.GA14910@embeddedor> To: "Gustavo A. R. Silva" Cc: dhowells@redhat.com, Jarkko Sakkinen , keyrings@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] KEYS: Replace zero-length array with flexible-array MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <932085.1589814863.1@warthog.procyon.org.uk> Date: Mon, 18 May 2020 16:14:24 +0100 Message-ID: <932086.1589814864@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Applied to keys-next.