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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 0E1EBC282C2 for ; Thu, 7 Feb 2019 10:33:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D7C522147C for ; Thu, 7 Feb 2019 10:33:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726841AbfBGKd5 (ORCPT ); Thu, 7 Feb 2019 05:33:57 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:35020 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726561AbfBGKd4 (ORCPT ); Thu, 7 Feb 2019 05:33:56 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7B87280D; Thu, 7 Feb 2019 02:33:55 -0800 (PST) Received: from [10.1.197.45] (e112298-lin.cambridge.arm.com [10.1.197.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F10CC3F675; Thu, 7 Feb 2019 02:33:52 -0800 (PST) Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs To: Torsten Duwe 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 References: <20190118163736.6A99268CEB@newverein.lst.de> <20190118163908.E338E68D93@newverein.lst.de> <20190206150524.GA28892@lst.de> From: Julien Thierry Message-ID: <198550d8-78d4-6e30-0179-b5e07dd140f8@arm.com> Date: Thu, 7 Feb 2019 10:33:50 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190206150524.GA28892@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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" :) . Steven, do you have an opinion on whether it would be acceptable to modify function entry code in ftrace_call_adjust() ? Thanks, -- Julien Thierry