From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752852AbbE0J3V (ORCPT ); Wed, 27 May 2015 05:29:21 -0400 Received: from mail7.hitachi.co.jp ([133.145.228.42]:45575 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752813AbbE0J3O (ORCPT ); Wed, 27 May 2015 05:29:14 -0400 Message-ID: <55658E61.2070204@hitachi.com> Date: Wed, 27 May 2015 18:29:05 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: AKASHI Takahiro , Jiri Kosina CC: rostedt@goodmis.org, mingo@kernel.org, jpoimboe@redhat.com, sjenning@redhat.com, vojtech@suse.cz, catalin.marinas@arm.com, will.deacon@arm.com, broonie@kernel.org, live-patching@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org Subject: Re: Re: [RFC 0/4] arm64: add livepatch support References: <1429843449-7388-1-git-send-email-takahiro.akashi@linaro.org> <55655F90.5000505@linaro.org> In-Reply-To: <55655F90.5000505@linaro.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2015/05/27 15:09, AKASHI Takahiro wrote: > Sorry for not replying soon. > > On 04/24/2015 06:27 PM, Jiri Kosina wrote: >> On Fri, 24 Apr 2015, AKASHI Takahiro wrote: >> >>> This patchset enables livepatch support on arm64. >>> >>> Livepatch was merged in v4.0, and allows replacying a function dynamically >>> based on ftrace framework, but it also requires -mfentry option of gcc. >>> Currently arm64 gcc doesn't support it, but by adding a helper function to >>> ftrace, we will be able to support livepatch on arch's which don't support >>> this option. >>> >>> I submit this patchset as RFC since I'm not quite sure that I'm doing >>> in the right way, or we should definitely support -fentry instead. >> >> I don't have arm64 cross-compiler handy, could you please copy/paste how >> does function prologue, generated by gcc -pg on arm64 look like? > > As other people said, my current patch has some drawbacks and was far from perfect. > I talked to a toolchain guy in Linaro, and he suggested that, instead of x86 > specific -mfentry option, we should add a new generic option, -fprolog-pad=N. > > It works as if "-pg -mfentry -mrecord-mcount -mnop-mcount" were specified on a > command line, but actually puts N nop instructions at the very beginning of > a function. > (Please note that -mrecord-mcount and -mnop-mcount options have been added > in x86 gcc to make it easier to implement ftrace and others.) Ah, that's a cool idea :) Note that it also will need to take care of debuginfo. Previously -mfentry had broken the debuginfo about function prologue. > While it is not clear that this new option will be implemented soon (in gcc-6), > once it is supported on aarch64, I will update and re-post my livepatch patch > as well as DYNAMIC_TRACE_WITH_REGS ftrace. Thank you! -- Masami HIRAMATSU Linux Technology Research Center, System Productivity Research Dept. Center for Technology Innovation - Systems Engineering Hitachi, Ltd., Research & Development Group E-mail: masami.hiramatsu.pt@hitachi.com