Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754601AbbBTNZl (ORCPT ); Fri, 20 Feb 2015 08:25:41 -0500 Received: from mail7.hitachi.co.jp ([133.145.228.42]:34762 "EHLO mail7.hitachi.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754022AbbBTNZk (ORCPT ); Fri, 20 Feb 2015 08:25:40 -0500 Message-ID: <54E735CD.4020507@hitachi.com> Date: Fri, 20 Feb 2015 22:25:33 +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: Ingo Molnar Cc: Petr Mladek , "David S. Miller" , Anil S Keshavamurthy , Ananth NMavinakayanahalli , Frederic Weisbecker , Steven Rostedt , Jiri Kosina , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] kprobes/x86: Use 5-byte NOP when the code might be modified by ftrace References: <20150218212205.GA26334@gmail.com> <1424427402-11795-1-git-send-email-pmladek@suse.cz> <1424427402-11795-2-git-send-email-pmladek@suse.cz> <20150220102625.GC25076@gmail.com> <54E72ABA.8050804@hitachi.com> <20150220125223.GA28882@gmail.com> In-Reply-To: <20150220125223.GA28882@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1817 Lines: 51 (2015/02/20 21:52), Ingo Molnar wrote: > > * Masami Hiramatsu wrote: > >> (2015/02/20 19:26), Ingo Molnar wrote: >>> >>> * Petr Mladek wrote: >>> >>>> can_probe() checks if the given address points to the >>>> beginning of an instruction. It analyzes all the >>>> instructions from the beginning of the function until the >>>> given address. The code might be modified by another >>>> Kprobe. In this case, the current code is read into a >>>> buffer, int3 breakpoint is replaced by the saved opcode >>>> in the buffer, and can_probe() analyzes the buffer >>>> instead. >>>> >>>> [...] >>> >>> Had to drop this patch due to build failures on 32-bit x86: >>> >>> arch/x86/kernel/kprobes/core.c:258:40: error: ‘MCOUNT_INSN_SIZE’ undeclared (first use in this function) >> >> Oops, MCOUNT_INSN_SIZE actually depends on >> CONFIG_FUNCTION_TRACER... I think we can use 5 instead of >> that since we are copying NOP_ATOMIC5. > > Or just make the define more widely available? It's not > like the size changes from disabling the function tracer. Yeah, it could be. Actually, to tell the truth, if CONFIG_FUNCTION_TRACER=n, ftrace_location() always returns 0, so the 2nd memcpy never be executed (it should be disappeared by optimization). Thus *this* issue is very local one, and I thought we'd better fix this locally. :) Thank you, -- Masami HIRAMATSU Software Platform Research Dept. Linux Technology Research Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu.pt@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/