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,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 CD9B3C433DF for ; Mon, 1 Jun 2020 09:59:35 +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 9F60820772 for ; Mon, 1 Jun 2020 09:59:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="oWq1rnui" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F60820772 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-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=nyHiaT6NBSdytolvQtoBVwRg1OSP88sv0MYG+89JgAg=; b=oWq1rnuirYW/TN GAxE4OWf2dsfKh44hwmvb3oMdlHA5/urgCiHTUruARQjE3FjxJp0D4sTaH4DeW+V18yzErvAIC2DA 5lJvinnA1hcE14oPeE18qKVC9zIbvANXCB+yPDqZQpZf7mzipAYkfrtaeIrJOa4G8B45pmizJNMym O9kGWzph3T2QzDComMnMggQqEi6h/UJaVjf0GkE+eUMsdQwz1vD2XQKBstJ/jiToYubet8sd0DVT4 WPRoD3bzUyMtWNWAtqTQ9Lt1qD/Dh6/b48o3th6SfjUU3yfGU0XgjyrSsYmElNeYDvCsFXGmcB08B dS4TZ6fZEpLTwzMapWqw==; 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 1jfhEC-00028C-RJ; Mon, 01 Jun 2020 09:59:32 +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 1jfhE9-00027X-Ey for linux-arm-kernel@lists.infradead.org; Mon, 01 Jun 2020 09:59:30 +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 956831FB; Mon, 1 Jun 2020 02:59:28 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 799EB3F305; Mon, 1 Jun 2020 02:59:27 -0700 (PDT) Date: Mon, 1 Jun 2020 10:59:25 +0100 From: Dave Martin To: Keno Fischer Subject: Re: arm64: Register modification during syscall entry/exit stop Message-ID: <20200601095925.GZ5031@arm.com> References: <20200519081551.GA9980@willie-the-truck> <20200520174149.GB27629@willie-the-truck> <20200527095528.GC11111@willie-the-truck> <20200527101929.GT5031@arm.com> <20200601092329.GX5031@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200601_025929_544856_CDBAE92E X-CRM114-Status: GOOD ( 22.48 ) 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: Kyle Huey , Catalin Marinas , Oleg Nesterov , Linux Kernel Mailing List , Will Deacon , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jun 01, 2020 at 05:40:28AM -0400, Keno Fischer wrote: > On Mon, Jun 1, 2020 at 5:23 AM Dave Martin wrote: > > > > Can't PTRACE_SYSEMU be emulated by using PTRACE_SYSCALL, cancelling the > > > > syscall at the syscall enter stop, then modifying the regs at the > > > > syscall exit stop? > > > > > > Yes, it can. The idea behind SYSEMU is to be able to save half the > > > ptrace traps that would require, in theory making the ptracer > > > a decent amount faster. That said, the x7 issue is orthogonal to > > > SYSEMU, you'd have the same issues if you used PTRACE_SYSCALL. > > > > Right, I just wondered whether there was some deeper difference between > > the two approaches. > > You're asking about a new regset vs trying to do it via ptrace option? I meant SYSEMU versus SYSCALL + cancellation and emulating the syscall at the syscall exit stop. i.e., I was trying to understand whether SYSEMU is just a convenience, or does some magic that can't be reproduced by other means. > I don't think there's anything a ptrace option can do that a new regset > that replicates the same registers (I'm gonna propose adding orig_x0, > while we're at it and changing the x0 semantics a bit, will have > those details with the patch) wouldn't be able to do . The reason I > originally thought it might have to be a ptrace option is because > the register modification currently gets applied in the syscall entry > code to the actual regs struct, so I thought you might have to know > to preserve those registers. However, then I realized that you could > just change the regset accessors to emulate the old behavior, since > we do already store all the required information (what kind of stop > we're currently at) in order to be able to answer the ptrace > informational queries. So doing that it probably just all around > easier. I guess NT_PRSTATUS might also rot, but I guess strace > doesn't really have to stop using it, since it doesn't care about > the x7 value nor does it need to modify it. I think NT_PRSTATUS probably doesn't need to change. Having a duplicate regset feels like a worse outcome that having a new ptrace option. Undocumentedly different things already happen to the regs depending on how the tracee stopped, so adding a new special case doesn't seem to justify creating a new regset. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel