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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 BBFE8C3F68F for ; Fri, 7 Feb 2020 16:16:01 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 4D18121927 for ; Fri, 7 Feb 2020 16:16:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D18121927 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id B88594A598; Fri, 7 Feb 2020 11:16:00 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id JhLWlXTs6Cbc; Fri, 7 Feb 2020 11:15:59 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 8D3184A4A3; Fri, 7 Feb 2020 11:15:59 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 28A6E4A418 for ; Fri, 7 Feb 2020 11:15:58 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id LLWWSl4Tu4Dk for ; Fri, 7 Feb 2020 11:15:56 -0500 (EST) Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 56A064A389 for ; Fri, 7 Feb 2020 11:15:56 -0500 (EST) X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 07 Feb 2020 08:15:54 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,414,1574150400"; d="scan'208";a="226515846" Received: from sjchrist-coffee.jf.intel.com (HELO linux.intel.com) ([10.54.74.202]) by fmsmga008.fm.intel.com with ESMTP; 07 Feb 2020 08:15:53 -0800 Date: Fri, 7 Feb 2020 08:15:53 -0800 From: Sean Christopherson To: Peter Xu Subject: Re: [PATCH v5 18/19] KVM: Dynamically size memslot array based on number of used slots Message-ID: <20200207161553.GE2401@linux.intel.com> References: <20200121223157.15263-1-sean.j.christopherson@intel.com> <20200121223157.15263-19-sean.j.christopherson@intel.com> <20200206221208.GI700495@xz-x1> <20200207153829.GA2401@linux.intel.com> <20200207160546.GA707371@xz-x1> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200207160546.GA707371@xz-x1> User-Agent: Mutt/1.5.24 (2015-08-30) Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-mips@vger.kernel.org, Paul Mackerras , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Christian Borntraeger , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , linux-kernel@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, Feb 07, 2020 at 11:05:46AM -0500, Peter Xu wrote: > On Fri, Feb 07, 2020 at 07:38:29AM -0800, Sean Christopherson wrote: > > On Thu, Feb 06, 2020 at 05:12:08PM -0500, Peter Xu wrote: > > > This patch is tested so I believe this works, however normally I need > > > to do similar thing with [0] otherwise gcc might complaint. Is there > > > any trick behind to make this work? Or is that because of different > > > gcc versions? > > > > array[] and array[0] have the same net affect, but array[] is given special > > treatment by gcc to provide extra sanity checks, e.g. requires the field to > > be the end of the struct. Last I checked, gcc also doesn't allow array[] > > in unions. There are probably other restrictions. > > > > But, it's precisely because of those restrictions that using array[] is > > preferred, as it provides extra protections, e.g. if someone moved memslots > > to the top of the struct it would fail to compile. > > However... > > xz-x1:tmp $ cat a.c > struct a { > int s[]; > }; > > int main(void) { } > xz-x1:tmp $ make a > cc a.c -o a > a.c:2:9: error: flexible array member in a struct with no named members ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ gcc is telling you quite explicitly why it's angry. Copy+paste from the internet[*]: Flexible Array Member(FAM) is a feature introduced in the C99 standard of the C programming language. For the structures in C programming language from C99 standard onwards, we can declare an array without a dimension and whose size is flexible in nature. Such an array inside the structure should preferably be declared as the last member of structure and its size is variable(can be changed be at runtime). The structure must contain at least one more named member in addition to the flexible array member. [*] https://www.geeksforgeeks.org/flexible-array-members-structure-c/ > 2 | int s[]; > | ^ > make: *** [: a] Error 1 > > My gcc version is 9.2.1 20190827 (Red Hat 9.2.1-1) (GCC). _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm