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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 077CEC54FD0 for ; Wed, 25 Mar 2020 12:25:04 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 C7AD920772 for ; Wed, 25 Mar 2020 12:25:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="GVHA1FgM" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C7AD920772 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=zladlPWhAy6jxLMhaX4gUcJe8amtaoWWbX72rTYJ4bU=; b=GVHA1FgMB8Y66sjQgK33AApoz hsMpr+CTf4JSaXH/Z+HQjvzO9bdWrWHKVXFnBDcG6siAbVkYQVPGru+pU3TLy4VMaIODYgEAgjDtY QwMCB2HlZgi9zw/z/ertTKZALCUvGy4P5Zu7HphWU3yzTS/pGMVY0q4+Nw51LOvSFLO7Jr3lU9JVw Ygg9geOgAdrXn196YtWTBX25MbJ8SsKpCwnZf7ZD0hAYAOsDcMPNS2kZUcvkqgNNQjd+NYLs+iYhO HXIpmZEpyzLNH9WPy1yfxgFPpsh76XpRFltWD+vPwTufnv2Uh8wbizNYqUWzIYt+Se33qTcFfv8X6 afZTVYooQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jH55i-0000tC-TO; Wed, 25 Mar 2020 12:25:02 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jH55e-0000rs-PI for linux-arm-kernel@lists.infradead.org; Wed, 25 Mar 2020 12:25:00 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1188731B; Wed, 25 Mar 2020 05:24:56 -0700 (PDT) Received: from [192.168.1.123] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C816F3F71F; Wed, 25 Mar 2020 05:24:54 -0700 (PDT) Subject: Re: [PATCH 0/3] arm64: Open code .arch_extension To: Mark Rutland , Ard Biesheuvel References: <20200325114110.23491-1-broonie@kernel.org> <20200325115038.GD4346@sirena.org.uk> <20200325120224.GA34330@C02TD0UTHF1T.local> From: Robin Murphy Message-ID: Date: Wed, 25 Mar 2020 12:24:53 +0000 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200325120224.GA34330@C02TD0UTHF1T.local> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200325_052458_914497_7B366D89 X-CRM114-Status: GOOD ( 15.97 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eric Biggers , Catalin Marinas , Mark Brown , linux-crypto@vger.kernel.org, Will Deacon , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-03-25 12:03 pm, Mark Rutland wrote: > On Wed, Mar 25, 2020 at 12:54:10PM +0100, Ard Biesheuvel wrote: >> On Wed, 25 Mar 2020 at 12:50, Mark Brown wrote: >>> Since BTI is a mandatory feature of v8.5 there is no BTI arch_extension, >>> you can only enable it by moving the base architecture to v8.5. You'd >>> need to use .arch and that feels likely to find us sharp edges to run >>> into. >> >> I think we should talk to the toolchain folks about this. Even if >> .arch_extension today does not support the 'bti' argument, it *is* >> most definitely an architecture extension, even it it is mandatory in >> v8.5 (given that v8.5 is itself an architecture extension). > > It certianly seems unfortunate, as it goes against the premise of having > HINT space instructions. Most software will want to enable HINT space > instructions from ARMv8.x but nothing else to ensure binary > compatibility with existing hardware. > > I see the same is true for pointer authentication judging by: > > https://sourceware.org/binutils/docs/as/AArch64-Extensions.html#AArch64-Extensions > > ... so worth raising with toolchain folk as a general principle even if > we have to bodge around it for now. Indeed, in general, just because a feature is mandatory in v8.n doesn't necessarily mean it can't be included in a v8.(n-1) implementation which may not have the *other* mandatory parts of v8.n which ".arch armv8.-a" would let through. Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel