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=unavailable 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 18164C38A24 for ; Thu, 7 May 2020 18:49:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EBB9024957 for ; Thu, 7 May 2020 18:49:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877342; bh=DzIn/TStIR1qO0jGDRIjha7WKLj8NmPXjLYvrxu8mwU=; h=Date:From:To:Cc:Subject:List-ID:From; b=htCXD7bTKBrTs8ZRWXRHcN67XA5TLo9QUTCvlz3C7FlvAX1vgP/6EHSHTYSnrjIuT Oe83qTlDOEO5DKRKU1mpbPIFqQXmw4xQm94+FIYuh71QwUaELqJjSEPYhBRBqyMsQ9 KOlJABkeBcVCzyevf0V3GxexVctmxM1atXOvwagE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728385AbgEGSs6 (ORCPT ); Thu, 7 May 2020 14:48:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:50094 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728166AbgEGSs6 (ORCPT ); Thu, 7 May 2020 14:48:58 -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 0170E24955; Thu, 7 May 2020 18:48:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877337; bh=DzIn/TStIR1qO0jGDRIjha7WKLj8NmPXjLYvrxu8mwU=; h=Date:From:To:Cc:Subject:From; b=NFBkUx9xKM0l5hkInpK+k2tkyl69LaRPmZIBXRXNlAzC1HgkPcuGLIfxFd3bBAiKg Q6+didIh143imEJpECyL8j0pLJrxHR1G5BQCgoQcqpcaQRDxYRNPIwYtnYf/HFp7a2 uAImZJ8+xeggQZjvOr01itL+Ha0eUzyX6Vi3wqy8= Date: Thu, 7 May 2020 13:53:23 -0500 From: "Gustavo A. R. Silva" To: "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] vmbus: Replace zero-length array with flexible-array Message-ID: <20200507185323.GA14416@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-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@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 --- include/linux/hyperv.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 692c89ccf5df..ce2c27440e17 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -117,7 +117,7 @@ struct hv_ring_buffer { * Ring data starts here + RingDataStartOffset * !!! DO NOT place any fields below this !!! */ - u8 buffer[0]; + u8 buffer[]; } __packed; struct hv_ring_buffer_info { @@ -313,7 +313,7 @@ struct vmadd_remove_transfer_page_set { struct gpa_range { u32 byte_count; u32 byte_offset; - u64 pfn_array[0]; + u64 pfn_array[]; }; /* @@ -563,7 +563,7 @@ struct vmbus_channel_gpadl_header { u32 gpadl; u16 range_buflen; u16 rangecount; - struct gpa_range range[0]; + struct gpa_range range[]; } __packed; /* This is the followup packet that contains more PFNs. */ @@ -571,7 +571,7 @@ struct vmbus_channel_gpadl_body { struct vmbus_channel_message_header header; u32 msgnumber; u32 gpadl; - u64 pfn[0]; + u64 pfn[]; } __packed; struct vmbus_channel_gpadl_created { @@ -672,7 +672,7 @@ struct vmbus_channel_msginfo { * The channel message that goes out on the "wire". * It will contain at minimum the VMBUS_CHANNEL_MESSAGE_HEADER header */ - unsigned char msg[0]; + unsigned char msg[]; }; struct vmbus_close_msg {