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=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 DD8D3C11D3D for ; Thu, 27 Feb 2020 15:09:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCF3524688 for ; Thu, 27 Feb 2020 15:09:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730474AbgB0PJt (ORCPT ); Thu, 27 Feb 2020 10:09:49 -0500 Received: from mx0a-002e3701.pphosted.com ([148.163.147.86]:33484 "EHLO mx0a-002e3701.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729287AbgB0PJt (ORCPT ); Thu, 27 Feb 2020 10:09:49 -0500 Received: from pps.filterd (m0134422.ppops.net [127.0.0.1]) by mx0b-002e3701.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01RF6iK0023731; Thu, 27 Feb 2020 15:09:32 GMT Received: from g2t2352.austin.hpe.com (g2t2352.austin.hpe.com [15.233.44.25]) by mx0b-002e3701.pphosted.com with ESMTP id 2yeerrrwp2-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 27 Feb 2020 15:09:32 +0000 Received: from g2t2360.austin.hpecorp.net (g2t2360.austin.hpecorp.net [16.196.225.135]) by g2t2352.austin.hpe.com (Postfix) with ESMTP id 3173D91; Thu, 27 Feb 2020 15:09:31 +0000 (UTC) Received: from hpe.com (teo-eag.americas.hpqcorp.net [10.33.152.10]) by g2t2360.austin.hpecorp.net (Postfix) with ESMTP id B3A9637; Thu, 27 Feb 2020 15:09:30 +0000 (UTC) Date: Thu, 27 Feb 2020 09:09:30 -0600 From: Dimitri Sivanich To: "Gustavo A. R. Silva" Cc: Tomas Winkler , Arnd Bergmann , Greg Kroah-Hartman , Dimitri Sivanich , linux-kernel@vger.kernel.org Subject: Re: [PATCH] misc: Replace zero-length array with flexible-array member Message-ID: <20200227150930.GA16632@hpe.com> References: <20200226222240.GA14474@embeddedor> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226222240.GA14474@embeddedor> User-Agent: Mutt/1.5.24 (2015-08-30) X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-HPE-SCL: -1 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-27_04:2020-02-26,2020-02-27 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 impostorscore=0 mlxscore=0 phishscore=0 priorityscore=1501 mlxlogscore=999 clxscore=1011 malwarescore=0 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002270120 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 26, 2020 at 04:22:40PM -0600, 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] > > 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 Acked-by: Dimitri Sivanich > --- > drivers/misc/mei/hw.h | 2 +- > drivers/misc/mei/mei_dev.h | 2 +- > drivers/misc/sgi-gru/grulib.h | 2 +- > drivers/misc/sgi-gru/grutables.h | 2 +- > 4 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h > index 8231b6941adf..b1a8d5ec88b3 100644 > --- a/drivers/misc/mei/hw.h > +++ b/drivers/misc/mei/hw.h > @@ -216,7 +216,7 @@ struct mei_msg_hdr { > > struct mei_bus_message { > u8 hbm_cmd; > - u8 data[0]; > + u8 data[]; > } __packed; > > /** > diff --git a/drivers/misc/mei/mei_dev.h b/drivers/misc/mei/mei_dev.h > index 76f8ff5ff974..3a29db07211d 100644 > --- a/drivers/misc/mei/mei_dev.h > +++ b/drivers/misc/mei/mei_dev.h > @@ -533,7 +533,7 @@ struct mei_device { > #endif /* CONFIG_DEBUG_FS */ > > const struct mei_hw_ops *ops; > - char hw[0] __aligned(sizeof(void *)); > + char hw[] __aligned(sizeof(void *)); > }; > > static inline unsigned long mei_secs_to_jiffies(unsigned long sec) > diff --git a/drivers/misc/sgi-gru/grulib.h b/drivers/misc/sgi-gru/grulib.h > index e77d1b1f9d05..85c103923632 100644 > --- a/drivers/misc/sgi-gru/grulib.h > +++ b/drivers/misc/sgi-gru/grulib.h > @@ -136,7 +136,7 @@ struct gru_dump_context_header { > pid_t pid; > unsigned long vaddr; > int cch_locked; > - unsigned long data[0]; > + unsigned long data[]; > }; > > /* > diff --git a/drivers/misc/sgi-gru/grutables.h b/drivers/misc/sgi-gru/grutables.h > index a7e44b2eb413..5ce8f3081e96 100644 > --- a/drivers/misc/sgi-gru/grutables.h > +++ b/drivers/misc/sgi-gru/grutables.h > @@ -372,7 +372,7 @@ struct gru_thread_state { > int ts_data_valid; /* Indicates if ts_gdata has > valid data */ > struct gru_gseg_statistics ustats; /* User statistics */ > - unsigned long ts_gdata[0]; /* save area for GRU data (CB, > + unsigned long ts_gdata[]; /* save area for GRU data (CB, > DS, CBE) */ > }; > > -- > 2.25.0 >