From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753347AbaJXAwT (ORCPT ); Thu, 23 Oct 2014 20:52:19 -0400 Received: from mail4.hitachi.co.jp ([133.145.228.5]:51327 "EHLO mail4.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750964AbaJXAwS (ORCPT ); Thu, 23 Oct 2014 20:52:18 -0400 Message-ID: <5449A2BB.1020207@hitachi.com> Date: Fri, 24 Oct 2014 09:52:11 +0900 From: Masami Hiramatsu Organization: Hitachi, Ltd., Japan User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 MIME-Version: 1.0 To: Wang Nan Cc: tixy@linaro.org, linux@arm.linux.org.uk, will.deacon@arm.com, dave.long@linaro.org, taras.kondratiuk@linaro.org, Ben Dooks , Christoph Lameter , Rabin Vincent , "David S. Miller" , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Li Zefan Subject: Re: [PATCH v6 0/7] ARM: kprobes: enable OPTPROBES for ARM 32. References: <1413977525-51480-1-git-send-email-wangnan0@huawei.com> In-Reply-To: <1413977525-51480-1-git-send-email-wangnan0@huawei.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/10/22 20:31), Wang Nan wrote: > Previous 5 version of ARM OPTPROBES patches are unable to deal with > stack storing instructions correctly. V5 patches disallow optimizing > every protential stack store instructions based on pessimistic > assumption. Which, as Tixy comments, 'excludes the main use of > kprobes'. (https://lkml.org/lkml/2014/8/29/117 ) > > The main obstacle which prevents us from computing stack requirement is > the missing of per-instruction decoder in probes_decode_insn() and its > friends. Only part of instructions have their decoders (and not in > each case). > > In this patch series, I propose 'checker', which allows us define > functions for each type of instruction, extract more information. Stack > consumption computing is an example. Checker can be further employed to > determine whether one instruction is possible to execute directy in > optimized kprobe. I'd like to expand current checker framework by > chaining checkers together. After that, I believe most of ARM > instructions can be executed directly like x86, kprobe performace can be > improved. > > The first 3 patches introduces checker. After that, patch 4/7 checks > stack requirement for probed instructions. Patches 5/7 - 7/7 are similar > to patch v5, except: > > 1. As Tixy proposed, unoptimized probes are also suffer from stack > problem (https://lkml.org/lkml/2014/9/1/548 ). Commit d30a0c8b saves > 64 bytes for them, but for instruction use register addressing (like > 'str r0, [sp, r1]'), 64 bytes are unsafe. Patch 5/7 prohibit such > probing according to stack information collected by checker. By the way, this sounds like a bugfix rather than an improvement. Is it possible to separate 1/7-5/7 as a bugfix series? I think those should go to 3.18. Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com