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,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 996E1C282C4 for ; Thu, 7 Feb 2019 12:52:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7208C20823 for ; Thu, 7 Feb 2019 12:52:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727085AbfBGMwC (ORCPT ); Thu, 7 Feb 2019 07:52:02 -0500 Received: from verein.lst.de ([213.95.11.211]:36638 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726769AbfBGMwB (ORCPT ); Thu, 7 Feb 2019 07:52:01 -0500 Received: by newverein.lst.de (Postfix, from userid 2005) id E431B6FA81; Thu, 7 Feb 2019 13:51:59 +0100 (CET) Date: Thu, 7 Feb 2019 13:51:59 +0100 From: Torsten Duwe To: Julien Thierry Cc: Mark Rutland , Will Deacon , Catalin Marinas , Steven Rostedt , 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: <20190207125159.GA19818@lst.de> References: <20190118163736.6A99268CEB@newverein.lst.de> <20190118163908.E338E68D93@newverein.lst.de> <20190206150524.GA28892@lst.de> <198550d8-78d4-6e30-0179-b5e07dd140f8@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <198550d8-78d4-6e30-0179-b5e07dd140f8@arm.com> 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 10:33:50AM +0000, Julien Thierry wrote: > > > On 06/02/2019 15:05, Torsten Duwe wrote: > > On Wed, Feb 06, 2019 at 08:59:44AM +0000, Julien Thierry wrote: > >> Hi Torsten, > >> > >> On 18/01/2019 16:39, Torsten Duwe wrote: > >> > >>> --- a/arch/arm64/kernel/ftrace.c > >>> +++ b/arch/arm64/kernel/ftrace.c > >>> @@ -133,17 +163,45 @@ int ftrace_make_call(struct dyn_ftrace * > >>> return ftrace_modify_code(pc, old, new, true); > >>> } > >>> > >>> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS > >>> +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, > >>> + unsigned long addr) > >>> +{ > >>> + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > >>> + u32 old, new; > >>> + > >>> + old = aarch64_insn_gen_branch_imm(pc, old_addr, true); > >>> + new = aarch64_insn_gen_branch_imm(pc, addr, true); > >>> + > >>> + return ftrace_modify_code(pc, old, new, true); > >>> +} > >>> +#endif > >>> + > >>> /* > >>> * Turn off the call to ftrace_caller() in instrumented function > >>> */ > >>> int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, > >>> unsigned long addr) > >>> { > >>> - unsigned long pc = rec->ip; > >>> + unsigned long pc = rec->ip + REC_IP_BRANCH_OFFSET; > >> > >> Sorry to come back on this patch again, but I was looking at the ftrace > >> code a bit, and I see that when processing the ftrace call locations, > >> ftrace calls ftrace_call_adjust() on every ip registered as mcount > >> caller (or in our case patchable entries). This ftrace_call_adjust() is > >> arch specific, so I was thinking we could place the offset in here once > >> and for all so we don't have to worry about it in the future. > > > > Now that you mention it - yes indeed that's the correct facility to fix > > the deviating address, as Steve has also confirmed. I had totally forgotten > > about this hook. > > > >> Also, I'm unsure whether it would be safe, but we could patch the "mov > >> x9, lr" there as well. In theory, this would be called at init time > >> (before secondary CPUs are brought up) and when loading a module (so I'd > >> expect no-one is executing that code *yet*. > >> > >> If this is possible, I think it would make things a bit cleaner. > > > > This is in fact very tempting, but it will introduce a nasty side effect > > to ftrace_call_adjust. Is there any obvious documentation that specifies > > guarantees about ftrace_call_adjust being called exactly once for each site? > > > > 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" :) . I've been thinking this over and I'm considering to make an ftrace_modify_code with verify and warn_once if it fails. Then read the insn back and bug_on should it not be the lr saver. Any objections? > Steven, do you have an opinion on whether it would be acceptable to > modify function entry code in ftrace_call_adjust() ? Yes, Steve's vote first. Torsten