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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 9AC3FC169C4 for ; Wed, 6 Feb 2019 09:31:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6B04D218A3 for ; Wed, 6 Feb 2019 09:31:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728759AbfBFJbH (ORCPT ); Wed, 6 Feb 2019 04:31:07 -0500 Received: from foss.arm.com ([217.140.101.70]:50264 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727150AbfBFJbG (ORCPT ); Wed, 6 Feb 2019 04:31:06 -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 C0DF1A78; Wed, 6 Feb 2019 01:31:05 -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 E24503F719; Wed, 6 Feb 2019 01:31:02 -0800 (PST) Subject: Re: [PATCH v7 2/3] arm64: implement ftrace with regs From: Julien Thierry To: Torsten Duwe , Mark Rutland , Will Deacon , Catalin Marinas , Steven Rostedt , Josh Poimboeuf , Ingo Molnar , Ard Biesheuvel , Arnd Bergmann , AKASHI Takahiro , Amit Daniel Kachhap Cc: 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> Message-ID: <22289b8e-bfdf-37cb-0234-2233a528ef61@arm.com> Date: Wed, 6 Feb 2019 09:30:58 +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: 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 08:59, Julien Thierry wrote: > Hi Torsten, > > On 18/01/2019 16:39, Torsten Duwe wrote: >> Once gcc8 adds 2 NOPs at the beginning of each function, replace the >> first NOP thus generated with a quick LR saver (move it to scratch reg >> x9), so the 2nd replacement insn, the call to ftrace, does not clobber >> the value. Ftrace will then generate the standard stack frames. >> >> Note that patchable-function-entry in GCC disables IPA-RA, which means >> ABI register calling conventions are obeyed *and* scratch registers >> such as x9 are available. >> >> Introduce and handle an ftrace_regs_trampoline for module PLTs, right >> after ftrace_trampoline, and double the size of this special section. >> >> Signed-off-by: Torsten Duwe >> >> --- >> >> Mark, if you see your ftrace entry macro code being represented correctly >> here, please add your sign-off, As I've initially copied it from your mail. >> >> --- >> arch/arm64/include/asm/ftrace.h | 17 ++++- >> arch/arm64/include/asm/module.h | 3 >> arch/arm64/kernel/entry-ftrace.S | 125 +++++++++++++++++++++++++++++++++++++-- >> arch/arm64/kernel/ftrace.c | 114 ++++++++++++++++++++++++++--------- >> arch/arm64/kernel/module-plts.c | 3 >> arch/arm64/kernel/module.c | 2 >> 6 files changed, 227 insertions(+), 37 deletions(-) > > [...] > >> --- 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. > > 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*. > And if the above works, we could also define CC_HAVE_NOP_MCOUNT (when we have the patchable entry) and then we just not have to worry about the initial ftrace_make_nop() with MCOUNT_ADDR. -- Julien Thierry