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 A0264C433ED for ; Tue, 6 Apr 2021 07:50:53 +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 29CE5613BE for ; Tue, 6 Apr 2021 07:50:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 29CE5613BE Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=suse.com 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.105663.202095 (Exim 4.92) (envelope-from ) id 1lTgTz-0001yF-Tf; Tue, 06 Apr 2021 07:50:43 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 105663.202095; Tue, 06 Apr 2021 07:50:43 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lTgTz-0001y8-Pk; Tue, 06 Apr 2021 07:50:43 +0000 Received: by outflank-mailman (input) for mailman id 105663; Tue, 06 Apr 2021 07:50:43 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lTgTy-0001y3-Uy for xen-devel@lists.xenproject.org; Tue, 06 Apr 2021 07:50:42 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 825afaef-827f-4d03-bf4e-d7c001191e12; Tue, 06 Apr 2021 07:50:42 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 8B9D1AFCB; Tue, 6 Apr 2021 07:50:41 +0000 (UTC) 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" X-Inumbo-ID: 825afaef-827f-4d03-bf4e-d7c001191e12 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617695441; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XEbKX/Z1ETdz+l1++th0T2qOpGnkM3VaHCw6qeEZGt4=; b=WaWbsrn2ZuLWhNWodEyEB/p0zQfyLi/1M3nqb/OAP80ypUdgjgyt4LYSawdVXj7rUPa4w8 CA1WeSp+2lhtsXM4s6hKqEZ+T3NGaGQhFedvbnCQMLFHRUEknu3/eWlYK2n/OW6GSikzUf kVXyDqAfGQHNcqbK7+RZHIpAc+8mcDY= Subject: Re: [PATCH 00/14] Use const whether we point to literal strings (take 1) To: Julien Grall Cc: Julien Grall , Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu , Dario Faggioli , Tim Deegan , =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= , Anthony PERARD , xen-devel@lists.xenproject.org References: <20210405155713.29754-1-julien@xen.org> From: Jan Beulich Message-ID: Date: Tue, 6 Apr 2021 09:50:44 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210405155713.29754-1-julien@xen.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 05.04.2021 17:56, Julien Grall wrote: > From: Julien Grall > > Hi all, > > By default, both Clang and GCC will happily compile C code where > non-const char * point to literal strings. This means the following > code will be accepted: > > char *str = "test"; > > str[0] = 'a'; > > Literal strings will reside in rodata, so they are not modifiable. > This will result to an permission fault at runtime if the permissions > are enforced in the page-tables (this is the case in Xen). > > 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. I'd be happy to see a suggestion of how to avoid this in a not overly intrusive way. > - 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. At least as a transient approach I think this would make sense. EFI in particular has other reasons already to specify a custom option (-fshort-wchar). Jan