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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 DFABEC282C2 for ; Thu, 7 Feb 2019 15:00:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD7B621904 for ; Thu, 7 Feb 2019 15:00:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726734AbfBGPAc (ORCPT ); Thu, 7 Feb 2019 10:00:32 -0500 Received: from verein.lst.de ([213.95.11.211]:37235 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726037AbfBGPAb (ORCPT ); Thu, 7 Feb 2019 10:00:31 -0500 Received: by newverein.lst.de (Postfix, from userid 2005) id 419F568C8E; Thu, 7 Feb 2019 16:00:29 +0100 (CET) Date: Thu, 7 Feb 2019 16:00:29 +0100 From: Torsten Duwe To: Steven Rostedt Cc: Julien Thierry , Mark Rutland , Will Deacon , Catalin Marinas , Josh Poimboeuf , Ingo Molnar , Ard Biesheuvel , Arnd Bergmann , AKASHI Takahiro , Amit Daniel Kachhap , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs Message-ID: <20190207150029.GB19818@lst.de> References: <20190118163736.6A99268CEB@newverein.lst.de> <20190118163908.E338E68D93@newverein.lst.de> <20190206150524.GA28892@lst.de> <198550d8-78d4-6e30-0179-b5e07dd140f8@arm.com> <20190207095157.3dea1086@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190207095157.3dea1086@gandalf.local.home> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 07, 2019 at 09:51:57AM -0500, Steven Rostedt wrote: > On Thu, 7 Feb 2019 10:33:50 +0000 > Julien Thierry wrote: > > > I don't see really much documentation on that function. As far as I can > > tell it is only called once for each site (and if it didn't, we'd always > > be placing the same instruction, but I agree it wouldn't be nice). It > > could depend on how far you can expand the notion of "adjusting" :) . > > > > Steven, do you have an opinion on whether it would be acceptable to > > modify function entry code in ftrace_call_adjust() ? > > Just to make sure I'm on the same page as you are. You want to modify > the function entry code at the time of the ftrace_call_adjust()? Yes, this was the fiendish plan ;-) > I would update the rec->ip to the offset you want at > ftrace_call_adjust() but not do any modifications. It really isn't safe > to do it there. But right after that is called, you will have the arch > specific call of ftrace_make_nop() called with MCOUNT_ADDR as the > second parameter to let you know that this is the first time the call > is made at this address. This is where you can do that initial > modifications. Ok, so just substitute REC_IP_BRANCH_OFFSET arithmetic with ftrace_call_adjust() and keep the MCOUNT_ADDR logic. Thanks for the clarification. Torsten