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=-7.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,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 8821AC433ED for ; Tue, 6 Apr 2021 17:55:34 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4713260FF1 for ; Tue, 6 Apr 2021 17:55:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4713260FF1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.106180.203068 (Exim 4.92) (envelope-from ) id 1lTpv9-0003Mf-RQ; Tue, 06 Apr 2021 17:55:23 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 106180.203068; Tue, 06 Apr 2021 17:55:23 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lTpv9-0003MY-Nc; Tue, 06 Apr 2021 17:55:23 +0000 Received: by outflank-mailman (input) for mailman id 106180; Tue, 06 Apr 2021 17:55:22 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lTpv8-0003MT-Gs for xen-devel@lists.xenproject.org; Tue, 06 Apr 2021 17:55:22 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lTpv1-00044z-TG; Tue, 06 Apr 2021 17:55:15 +0000 Received: from 54-240-197-234.amazon.com ([54.240.197.234] helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lTpv1-0001bz-JK; Tue, 06 Apr 2021 17:55:15 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=xaC+xy9yh3LS4OxykfvNmLZtQc53CzZmLbDal2CL+qo=; b=AsI8fkv3YOKU31hqf/APGHXN5K d9nl3WPN9NRiJGXMRvr1BHR1XV3DbwRYT2dz5MVUyc3DPAFpjFz+2VGZS6V6oyBjKIaz3f/IYjhSk AcwLn1fP88WSDCWX/yKSZ079k14nT0c3m6lWXqiSFY+gg2//Mt51YDIO0m7lLw2UFgQY=; Subject: Re: [PATCH 00/14] Use const whether we point to literal strings (take 1) To: Elliott Mitchell , Ian Jackson Cc: xen-devel@lists.xenproject.org, Julien Grall , Andrew Cooper , George Dunlap , Ian Jackson , Jan Beulich , Stefano Stabellini , Wei Liu , Dario Faggioli , Tim Deegan , Roger Pau Monn?? , Anthony PERARD References: <20210405155713.29754-1-julien@xen.org> From: Julien Grall Message-ID: <2e51a7e5-404f-fd2e-90cb-c4d94c4d807b@xen.org> Date: Tue, 6 Apr 2021 18:55:12 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Elliott, Thanks for the input! On 05/04/2021 18:01, Elliott Mitchell wrote: > On Mon, Apr 05, 2021 at 04:56:59PM +0100, Julien Grall wrote: >> I am not aware of code trying to modify literal strings in Xen. >> However, there is a frequent use of non-const char * to point to >> literal strings. Given the size of the codebase, there is a risk >> to involuntarily introduce code that will modify literal strings. >> >> Therefore it would be better to enforce using const when pointing >> to such strings. Both GCC and Clang provide an option to warn >> for such case (see -Wwrite-strings) and therefore could be used >> by Xen. >> >> This series doesn't yet make use of -Wwrite-strings because >> the tree is not fully converted. Instead, it contains some easy >> and likely non-controversial use const in the code. >> >> The major blockers to enable -Wwrite-strings are the following: >> - xen/common/efi: union string is used in both const and >> non-const situation. It doesn't feel right to specific one member >> const and the other non-const. >> - libxl: the major block is the flexarray framework as we would use >> it with string (now const char*). I thought it would be possible to >> make the interface const, but it looks like there are a couple of >> places where we need to modify the content (such as in >> libxl_json.c). >> >> Ideally, I would like to have -Wwrite-strings unconditionally used >> tree-wide. But, some of the area may required some heavy refactoring. >> >> One solution would be to enable it tree-wide but turned it off at a >> directroy/file level. >> >> Any opinions? > > I think doing such is a Good Idea(tm). Adding consts adds opportunities > for greater optimization. Both by compilers which can avoid extra > copies, and developers who then know they don't need to generate extra > copies to sacrific them to an API. In particular the consts also > function as documentation. > > So you're certainly not the only person who thinks additional consts > would be a good thing: > > https://lists.xenproject.org/archives/html/xen-devel/2021-01/msg00132.html > > > Alas merely getting the two const patches into the latest release > apparently wasn't even worthy of response: > > https://lists.xenproject.org/archives/html/xen-devel/2021-02/msg01040.html Sory to hear you had no response. Would you be able to give a nudge to the maintainers? > > > I agree this should be done, though I'm aware many developers hate > bothering with constants. > > Cheers, -- Julien Grall