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=-13.4 required=3.0 tests=DKIMWL_WL_HIGH,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, 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 18D7DC3F2CD for ; Thu, 5 Mar 2020 14:22:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E242F20828 for ; Thu, 5 Mar 2020 14:22:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K6lRtbIF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726111AbgCEOWp (ORCPT ); Thu, 5 Mar 2020 09:22:45 -0500 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:42430 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725944AbgCEOWp (ORCPT ); Thu, 5 Mar 2020 09:22:45 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583418165; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=6noagWxZ5YiSaEFMdQzCHre9EJD3npDKEFOYBbGNFrU=; b=K6lRtbIFnpB7TQ3j7+DzFzYuiSMr/Jd7aUBnptwA0FfV8paPGfcewQtzDpo3g2Oc7Iy3C5 DOQhPDPe0E1Eax1sFyaqmPtgAQcXfYvJbFIHUiswsVqR2h8V1GBfV5CMjzLl0MCON76re4 aQQhNAn8FfKaNyn6T8oFiZBYrrL/zJo= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-329-PAs0eptSNEKmdrGC8pDG_g-1; Thu, 05 Mar 2020 09:22:41 -0500 X-MC-Unique: PAs0eptSNEKmdrGC8pDG_g-1 Received: by mail-wm1-f69.google.com with SMTP id w12so1643624wmc.3 for ; Thu, 05 Mar 2020 06:22:41 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=6noagWxZ5YiSaEFMdQzCHre9EJD3npDKEFOYBbGNFrU=; b=XrCWbKZqO7kZTjtNS9T2OIIc2h4MvsSEhq96BolEfqT9F53sztPNDEYTeJ+5VKXIgJ uUdf7cSk92e6XrSyOaeyyC1R27U+Byq6Wwtwu7c2r7peTGsPvequ9m6KwTcyCQ0OvfsM YwuKe85qHt+NeSwejPKZYRZ7WdpVEa/qwijSv5DkZLJnp/Bj+LkDBwA8RYox5Tzamu9G 7kzKtB9tme507oMHb3RmUsgedTCWiTOOW5X1OztncJnew06lb9OVq47bDV0emziQh8dD FFRRuXSW+LJcPL1QKFuqN0R09qWu2YRTWpy0BP/rcnZVI7bjmRJ9LgAYZU58/o6dOpLs 3rwQ== X-Gm-Message-State: ANhLgQ0/J6ZLV+gTdIj2R8tJTLxqIZrLrU/lkT2h6UL9RE/FzBF7HYnS xyk2tuGkvRHKEdWcFmH0z4+GxY9J1HF60+NZ1tHuR5fA/FWeHUPXDn/NZPPOyDK//GVV54PPEJs 3bKS65FlrTNuZQITbeQjhKkZc X-Received: by 2002:a5d:6146:: with SMTP id y6mr10560244wrt.107.1583418159921; Thu, 05 Mar 2020 06:22:39 -0800 (PST) X-Google-Smtp-Source: ADFU+vsVPpJ1Cv7XI3CgGNNoNJ0eAJgUXSnFi1wfWwG4CQQJ1K56cUcw027pOLSq+CkOV+HtsaXJ9g== X-Received: by 2002:a5d:6146:: with SMTP id y6mr10560228wrt.107.1583418159722; Thu, 05 Mar 2020 06:22:39 -0800 (PST) Received: from x1.localdomain (2001-1c00-0c0c-fe00-fc7e-fd47-85c1-1ab3.cable.dynamic.v6.ziggo.nl. [2001:1c00:c0c:fe00:fc7e:fd47:85c1:1ab3]) by smtp.gmail.com with ESMTPSA id z2sm40199326wrq.95.2020.03.05.06.22.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 05 Mar 2020 06:22:39 -0800 (PST) Subject: Re: [PATCH][next] drm/vboxvideo/vboxvideo.h: Replace zero-length array with flexible-array member To: "Gustavo A. R. Silva" , David Airlie , Daniel Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20200305105558.GA19124@embeddedor> From: Hans de Goede Message-ID: <8e2ab9a2-fb47-1d61-d09c-0510ad5ee5ff@redhat.com> Date: Thu, 5 Mar 2020 15:22:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200305105558.GA19124@embeddedor> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 3/5/20 11:55 AM, 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 Patch looks good to me: Reviewed-by: Hans de Goede Regards, Hans > --- > drivers/gpu/drm/vboxvideo/vboxvideo.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/vboxvideo/vboxvideo.h b/drivers/gpu/drm/vboxvideo/vboxvideo.h > index 0592004f71aa..a5de40fe1a76 100644 > --- a/drivers/gpu/drm/vboxvideo/vboxvideo.h > +++ b/drivers/gpu/drm/vboxvideo/vboxvideo.h > @@ -138,7 +138,7 @@ struct vbva_buffer { > > u32 data_len; > /* variable size for the rest of the vbva_buffer area in VRAM. */ > - u8 data[0]; > + u8 data[]; > } __packed; > > #define VBVA_MAX_RECORD_SIZE (128 * 1024 * 1024) >