From patchwork Thu May 7 18:56:18 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: 11534715 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 4DB9615AB for ; Thu, 7 May 2020 18:51:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 388F924961 for ; Thu, 7 May 2020 18:51:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877516; bh=zzvNz1vCMUzUeBqErf8Y+hXv+ekNJ/H+9YqrTouDhq0=; h=Date:From:To:Cc:Subject:List-ID:From; b=AA5JGZlsW4xR3v0SNfSc2Zk0jjtpgJWrtO1U26+SHZuZ5zR73CW/g4noJEFRFjjSs vGgLktZ7PfTIhjL3+SBxALhF+p4RmrWi1HFFTLgNG/QBxrNfqA1YJuGv8KMQrcecU3 OnDWuIyzH8PdbpIqoA5CtjrgNncL19YPiXbBT0xI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728760AbgEGSvx (ORCPT ); Thu, 7 May 2020 14:51:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:52626 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726761AbgEGSvx (ORCPT ); Thu, 7 May 2020 14:51:53 -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 2806A24959; Thu, 7 May 2020 18:51:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877512; bh=zzvNz1vCMUzUeBqErf8Y+hXv+ekNJ/H+9YqrTouDhq0=; h=Date:From:To:Cc:Subject:From; b=RwFhaoWMFjAjpOVDoA285PYVW+aLxxIiFivqXm1pwGc9kXYPiKKDR5Yj5kYob+G00 asc5kpTlDem0K9m3ptWpLrfg2WiaUeRKL5lbvxQQiO6ZaxKv4muzu+7iF9CPCR4Nw8 4oBK1ojgP16NGqrHIgHKIZMPItRKOdzrUATnvAw4= Date: Thu, 7 May 2020 13:56:18 -0500 From: "Gustavo A. R. Silva" To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] KVM: VMX: Replace zero-length array with flexible-array Message-ID: <20200507185618.GA14831@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@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/x86/kvm/vmx/vmcs.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/vmx/vmcs.h b/arch/x86/kvm/vmx/vmcs.h index 481ad879197b..5c0ff80b85c0 100644 --- a/arch/x86/kvm/vmx/vmcs.h +++ b/arch/x86/kvm/vmx/vmcs.h @@ -19,7 +19,7 @@ struct vmcs_hdr { struct vmcs { struct vmcs_hdr hdr; u32 abort; - char data[0]; + char data[]; }; DECLARE_PER_CPU(struct vmcs *, current_vmcs);