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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 F303AC2D0CE for ; Fri, 24 Jan 2020 08:25:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0CE02071A for ; Fri, 24 Jan 2020 08:25:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="uBLKCo33" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729679AbgAXIZC (ORCPT ); Fri, 24 Jan 2020 03:25:02 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:51026 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725843AbgAXIZB (ORCPT ); Fri, 24 Jan 2020 03:25:01 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=MfZNgigap++SfcaKWRzfoqJPEpL+dov/O+r0KNAVxwQ=; b=uBLKCo33khmwALe/1RXZcFcwk v9dGORHO68bVdfVE7Xqu3Xq4h0tBy7dKMAgtK6R2pAPhSyuhD15UDyu5APvU8PY7FbPl4ptgiaYDT VqvpfyCBk1RLWedPG5+nenFO2snsyblPPL3G5ci+SfDYNkZ0KxjfH6gioAn/ywsxMoER9H6MRwzWw e7YiSRfdSAN0GsCsalOVa3GsoGwfrWBEb2/67wCvC78cI8CBtcAxtc37wYs++HoGUdDSyswEOrXMB ogDk4glPVUBACG7RNuEJzZ07dbz++lo6HUM2Z77yTlvYItaDKRfI4+vK+Ic6SJW3g0DmMvRbg20KE MzRR0SP0g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iuuGl-0007yU-3M; Fri, 24 Jan 2020 08:24:47 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 31B113012DC; Fri, 24 Jan 2020 09:23:03 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7D3D02B713683; Fri, 24 Jan 2020 09:24:43 +0100 (CET) Date: Fri, 24 Jan 2020 09:24:43 +0100 From: Peter Zijlstra To: Nick Desaulniers Cc: Will Deacon , LKML , linux-arch , kernel-team , Michael Ellerman , Linus Torvalds , Segher Boessenkool , Christian Borntraeger , Luc Van Oostenryck , Arnd Bergmann , Peter Oberparleiter , Masahiro Yamada , Pablo Neira Ayuso , Jozsef Kadlecsik , Florian Westphal , "David S. Miller" Subject: Re: [PATCH v2 02/10] netfilter: Avoid assigning 'const' pointer to non-const pointer Message-ID: <20200124082443.GY14914@hirez.programming.kicks-ass.net> References: <20200123153341.19947-1-will@kernel.org> <20200123153341.19947-3-will@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 23, 2020 at 11:07:59AM -0800, Nick Desaulniers wrote: > Good thing it's the variable being modified was not declared const; I > get spooked when I see -Wdiscarded-qualifiers because of Section > 6.7.3.6 of the ISO C11 draft spec: > > ``` > If an attempt is made to modify an object defined with a > const-qualified type through use > of an lvalue with non-const-qualified type, the behavior is undefined. > If an attempt is > made to refer to an object defined with a volatile-qualified type > through use of an lvalue > with non-volatile-qualified type, the behavior is undefined.133) > > 133) This applies to those objects that behave as if they were defined > with qualified types, even if they are > never actually defined as objects in the program (such as an object at > a memory-mapped input/output > address). > ``` > > Which is about the modification of a const-declared variable (explicit > UB which Clang actively exploits), Just for curiosity's sake. What does clang actually do in that case?