From patchwork Thu May 7 19:07:06 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Gustavo A. R. Silva" X-Patchwork-Id: 63663 X-Patchwork-Delegate: hverkuil@xs4all.nl Received: from vger.kernel.org ([23.128.96.18]) by www.linuxtv.org with esmtp (Exim 4.92) (envelope-from ) id 1jWljw-00GJvd-RJ; Thu, 07 May 2020 18:59:26 +0000 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728433AbgEGTCl (ORCPT + 1 other); Thu, 7 May 2020 15:02:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:33490 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726598AbgEGTCk (ORCPT ); Thu, 7 May 2020 15:02:40 -0400 Received: from embeddedor (unknown [189.207.59.248]) (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 05AEA2083B; Thu, 7 May 2020 19:02:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588878160; bh=MvBOv5f4AnG3bBssPq+5ht2GAR9BRHaG65kfeHCY7fA=; h=Date:From:To:Cc:Subject:From; b=nkas9jw1s+UvIwksoB7oU5kB8Bcc2Hp0PBvQHgvMXl8qMqFhhlcLcGXS5/wkNuAdd qzp2zAqxS7vf/WtwS/7CN4aVSj2vNOKls0qI4RyMKLAPOZHZk/kQ2wK9MVZebAAcu0 sBHkjQXNb7PY9gN4oN25Dd/KYNylzqKctGkiKUS4= Date: Thu, 7 May 2020 14:07:06 -0500 From: "Gustavo A. R. Silva" To: Hans Verkuil Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] media: pwc: Replace zero-length array with flexible-array Message-ID: <20200507190706.GA15730@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org X-LSpam-Score: -3.1 (---) X-LSpam-Report: No, score=-3.1 required=5.0 tests=BAYES_00=-1.9,DKIMWL_WL_HIGH=0.001,DKIM_SIGNED=0.1,DKIM_VALID=-0.1,DKIM_VALID_AU=-0.1,DKIM_VALID_EF=-0.1,MAILING_LIST_MULTI=-1 autolearn=ham autolearn_force=no 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/media/usb/pwc/pwc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/media/usb/pwc/pwc.h b/drivers/media/usb/pwc/pwc.h index 3362962d0d00..b02a3c7b7742 100644 --- a/drivers/media/usb/pwc/pwc.h +++ b/drivers/media/usb/pwc/pwc.h @@ -193,7 +193,7 @@ struct pwc_raw_frame { decompressor) */ __u8 cmd[4]; /* the four byte of the command (in case of nala, only the first 3 bytes is filled) */ - __u8 rawframe[0]; /* frame_size = H / 4 * vbandlength */ + __u8 rawframe[]; /* frame_size = H / 4 * vbandlength */ } __packed; /* intermediate buffers with raw data from the USB cam */