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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 522A8C38A24 for ; Thu, 7 May 2020 19:22:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 27E8021835 for ; Thu, 7 May 2020 19:22:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879348; bh=27j1iFeO7/uFIYuS96IIzx3OB0gXSl5+yOvIErECFgA=; h=Date:From:To:Cc:Subject:List-ID:From; b=HGW9SGO31durJDk0QVPAtsNeD6vPdlCW8tYzBoWem5petQviDrVZ0zIuaiWtId5Cw lJCPlhUTAf6Wl9u0BIgGY3JK+EXQGySGt0K5HO0bBh3D1QlNtXzLQ1sp3ThHwnwjzs +IiLma+Lote7bJuQmbtjur6JfPKSJjOlT1yeqpyE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728397AbgEGTW1 (ORCPT ); Thu, 7 May 2020 15:22:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:43260 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726558AbgEGTW0 (ORCPT ); Thu, 7 May 2020 15:22:26 -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 DC911208E4; Thu, 7 May 2020 19:22:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879346; bh=27j1iFeO7/uFIYuS96IIzx3OB0gXSl5+yOvIErECFgA=; h=Date:From:To:Cc:Subject:From; b=xdPU4qJBkKugdQKmTvNZ2uh/J5SNwl5PKpj9KHLoeisbBtvnthXjdCts/VAbUpF1Z 1rPoTGkanvQxgf/aGjFuqKknFYxeNFtO4pkx4JikGk00RVhjb+rYQ2tmdqGGE1L0MS ztiO3xcXYnYL1TwODWrRUwZJSvdyzMi6nRDB19/A= Date: Thu, 7 May 2020 14:26:52 -0500 From: "Gustavo A. R. Silva" To: Jeff Dike , Richard Weinberger , Anton Ivanov Cc: linux-um@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH] um: virtio: Replace zero-length array with flexible-array Message-ID: <20200507192652.GA16743@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/um/drivers/vector_kern.h | 2 +- arch/um/drivers/vhost_user.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/um/drivers/vector_kern.h b/arch/um/drivers/vector_kern.h index d0159082faf0..8fff93a75a92 100644 --- a/arch/um/drivers/vector_kern.h +++ b/arch/um/drivers/vector_kern.h @@ -129,7 +129,7 @@ struct vector_private { struct vector_estats estats; struct sock_fprog *bpf; - char user[0]; + char user[]; }; extern int build_transport_data(struct vector_private *vp); diff --git a/arch/um/drivers/vhost_user.h b/arch/um/drivers/vhost_user.h index 6c71b6005177..6f147cd3c9f7 100644 --- a/arch/um/drivers/vhost_user.h +++ b/arch/um/drivers/vhost_user.h @@ -78,7 +78,7 @@ struct vhost_user_config { u32 offset; u32 size; u32 flags; - u8 payload[0]; /* Variable length */ + u8 payload[]; /* Variable length */ } __packed; struct vhost_user_vring_state {