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 65C2FC47247 for ; Tue, 5 May 2020 16:02:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C485206A4 for ; Tue, 5 May 2020 16:02:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729949AbgEEQCV (ORCPT ); Tue, 5 May 2020 12:02:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:45822 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728804AbgEEQCV (ORCPT ); Tue, 5 May 2020 12:02:21 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 8B845AEFD; Tue, 5 May 2020 16:02:21 +0000 (UTC) Subject: Re: [PATCH] xenbus: avoid stack overflow warning To: Arnd Bergmann Cc: Boris Ostrovsky , Stefano Stabellini , Yan Yankovskyi , Wei Liu , xen-devel , "linux-kernel@vger.kernel.org" , clang-built-linux References: <20200505141546.824573-1-arnd@arndb.de> <30d49e6d-570b-f6fd-3a6f-628abcc8b127@suse.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: <48893239-dde9-4e94-040d-859f4348816d@suse.com> Date: Tue, 5 May 2020 18:02:18 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.05.20 17:01, Arnd Bergmann wrote: > On Tue, May 5, 2020 at 4:34 PM Jürgen Groß wrote: >> On 05.05.20 16:15, Arnd Bergmann wrote: >>> The __xenbus_map_ring() function has two large arrays, 'map' and >>> 'unmap' on its stack. When clang decides to inline it into its caller, >>> xenbus_map_ring_valloc_hvm(), the total stack usage exceeds the warning >>> limit for stack size on 32-bit architectures. >>> >>> drivers/xen/xenbus/xenbus_client.c:592:12: error: stack frame size of 1104 bytes in function 'xenbus_map_ring_valloc_hvm' [-Werror,-Wframe-larger-than=] >>> >>> As far as I can tell, other compilers don't inline it here, so we get >>> no warning, but the stack usage is actually the same. It is possible >>> for both arrays to use the same location on the stack, but the compiler >>> cannot prove that this is safe because they get passed to external >>> functions that may end up using them until they go out of scope. >>> >>> Move the two arrays into separate basic blocks to limit the scope >>> and force them to occupy less stack in total, regardless of the >>> inlining decision. >> >> Why don't you put both arrays into a union? > > I considered that as well, and don't really mind either way. I think it does > get a bit ugly whatever we do. If you prefer the union, I can respin the > patch that way. Hmm, thinking more about it I think the real clean solution would be to extend struct map_ring_valloc_hvm to cover the pv case, too, to add the map and unmap arrays (possibly as a union) to it and to allocate it dynamically instead of having it on the stack. Would you be fine doing this? Juergen