From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752293AbdB1MFy (ORCPT ); Tue, 28 Feb 2017 07:05:54 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:38552 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751769AbdB1MFw (ORCPT ); Tue, 28 Feb 2017 07:05:52 -0500 Date: Tue, 28 Feb 2017 11:46:38 +0000 From: Russell King - ARM Linux To: Abel Vesa Cc: Nicolai Stange , Abel Vesa , robin.murphy@arm.com, jjhiblot@traphandler.com, Steven Rostedt , Ingo Molnar , pmladek@suse.com, mhiramat@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv4] arm: ftrace: Adds support for CONFIG_DYNAMIC_FTRACE_WITH_REGS Message-ID: <20170228114638.GC21222@n2100.armlinux.org.uk> References: <1487977101-29027-1-git-send-email-abelvesa@linux.com> <87r32jiqc9.fsf@d080-213.cis.zmaw.de> <20170228005636.GA23251@nuc> <87h93eoa3a.fsf@gmail.com> <20170228112227.GB23251@nuc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170228112227.GB23251@nuc> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 28, 2017 at 11:22:27AM +0000, Abel Vesa wrote: > On Tue, Feb 28, 2017 at 11:58:49AM +0100, Nicolai Stange wrote: > > Hi Abel, > > > > On Tue, Feb 28 2017, Abel Vesa wrote: > > > > > On Mon, Feb 27, 2017 at 04:52:06PM +0100, Nicolai Stange wrote: > > >> On Fri, Feb 24 2017, Abel Vesa wrote: > > >> Wouldn't it be better (and more consistent with other archs) to have > > >> > > >> pt_regs->ARM_lr = original lr > > >> pt_refs->ARM_pc = current lr > > >> > > >> instead? > > > > The stack would look like this then > > > > @ ... | ARM_ip | ARM_sp | ARM_lr | ARM_pc | ... | > > @ 0 4 48 52 56 60 64 68 72 > > @ R0 | R1 | ... | LR | SP + 4 | original LR | original PC | PSR | OLD_R0 | original LR | > > > > I.e. the pt_regs would capture almost the full context of the > > instrumented function (except for ip). > > > So basicly what you are saying is: > - instead of current LR save original LR (previous one saved in instrumented function epilog) > - instead of current PC save original PC (previous one saved in instrumented function epilog) > > I still don't see the point of saving the actual value of PC since nobody will ever > restore it. In case of livepatch it will get overwritten anyway. As for LR, I agree, > it could be the original one in pt_regs. > > I'll look into this sometime today or tomorrow and get back with updates. Which is exactly what I proposed, with code, on one of the previous iterations of this patch... -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.