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=-13.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, 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 CC91BC38A2A for ; Fri, 8 May 2020 18:19:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9A78208CA for ; Fri, 8 May 2020 18:19:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726922AbgEHSTE (ORCPT ); Fri, 8 May 2020 14:19:04 -0400 Received: from mga02.intel.com ([134.134.136.20]:49234 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726817AbgEHSTD (ORCPT ); Fri, 8 May 2020 14:19:03 -0400 IronPort-SDR: 4gap54/c3/wJ2YMABrGV5VFMhjJPubJCXmSCLa77noz3fRhPMLuDN179NcycSKokBYMnTZLI5P oz+38AVacMBw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 May 2020 11:19:02 -0700 IronPort-SDR: xlG+pLTjJtooALYiHtqcjda0K1mogzg/hqYZSjlOPN4zE8NGrkTayHKqmNGQq3VnJFUXwHxF64 dDrDtRvAHXzA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,368,1583222400"; d="scan'208";a="297033545" Received: from rhweight-wrk1.ra.intel.com ([137.102.106.140]) by orsmga008.jf.intel.com with ESMTP; 08 May 2020 11:19:02 -0700 Date: Fri, 8 May 2020 11:20:50 -0700 (PDT) From: matthew.gerlach@linux.intel.com X-X-Sender: mgerlach@rhweight-WRK1 To: "Gustavo A. R. Silva" cc: Wu Hao , linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fpga: dfl: Replace zero-length array with flexible-array In-Reply-To: <20200507185256.GA14313@embeddedor> Message-ID: References: <20200507185256.GA14313@embeddedor> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This looks like a a good change to me. Tested-by: Matthew Gerlach On Thu, 7 May 2020, 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/fpga/dfl.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h > index 9f0e656de720..1cd51ea52ce1 100644 > --- a/drivers/fpga/dfl.h > +++ b/drivers/fpga/dfl.h > @@ -235,7 +235,7 @@ struct dfl_feature_platform_data { > unsigned long dev_status; > void *private; > int num; > - struct dfl_feature features[0]; > + struct dfl_feature features[]; > }; > > static inline > >