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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 BCD6BC2D0CD for ; Wed, 18 Dec 2019 13:25:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 90AC32176D for ; Wed, 18 Dec 2019 13:25:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576675557; bh=9dtjGIQ5Qoox81UNGfLHKGGtqfpxNpzDQimQEyCVQH0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Xt5MrB148XqRyqV7RuA2Ztd2VxK7nyJmceOWh/D6QlPDskseO42oIn858ShBiI+XF Q6vd8H0z2fIcnc68/NskvTxKiLKDOH0GKEybgdEbeyDEuyAJqny3o4aDxV9CegJSDd iJtVaLZc/InDgO9JAvDg3a2KWpw+WTE5oZ6Uj5oA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727152AbfLRNZ4 (ORCPT ); Wed, 18 Dec 2019 08:25:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:48302 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726846AbfLRNZz (ORCPT ); Wed, 18 Dec 2019 08:25:55 -0500 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F10DE2146E; Wed, 18 Dec 2019 13:25:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576675555; bh=9dtjGIQ5Qoox81UNGfLHKGGtqfpxNpzDQimQEyCVQH0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=pnHpjtfQ2mKvo1sD/uItIJF3vGLuPYLsazzOQ+tHdrl6ElZgP5qIhWrS0TLf7PIP+ lhjWsLgcVV9oOpqgjPkPZccioJhFq5yZHOqwlRaz0tUN+miH11WjT2n5e7AmPy8SHd gwgVQsy4ulBglwDaRYrEyQFX8KkwYEnIAC4E2ISU= Date: Wed, 18 Dec 2019 22:25:50 +0900 From: Masami Hiramatsu To: Jisheng Zhang Cc: "catalin.marinas@arm.com" , "will@kernel.org" , "naveen.n.rao@linux.vnet.ibm.com" , "mark.rutland@arm.com" , "corbet@lwn.net" , "rostedt@goodmis.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v6] arm64: implement KPROBES_ON_FTRACE Message-Id: <20191218222550.51f0b681de7bbab7e49b09a9@kernel.org> In-Reply-To: <20191218140622.57bbaca5@xhacker.debian> References: <20191218140622.57bbaca5@xhacker.debian> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 18 Dec 2019 06:21:35 +0000 Jisheng Zhang wrote: > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > eliminates the need for a trap, as well as the need to emulate or > single-step instructions. > > Tested on berlin arm64 platform. > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > ~ # cd /sys/kernel/debug/ > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > before the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > after the patch: > > /sys/kernel/debug # cat kprobes/list > ffffff801009ff54 k _do_fork+0x4 [DISABLED][FTRACE] BTW, it seems this automatically changes the offset without user's intention or any warnings. How would you manage if the user pass a new probe on _do_fork+0x4? IOW, it is still the question who really wants to probe on the _do_fork+"0", if kprobes modifies it automatically, no one can do that anymore. This can be happen if the user want to record LR or SP value at the function call for debug. If kprobe always modifies it, we will lose the way to do it. Could you remove below function at this moment? > +kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) > +{ > + unsigned long addr = kallsyms_lookup_name(name); > + > + if (addr && !offset) { > + unsigned long faddr; > + /* > + * with -fpatchable-function-entry=2, the first 4 bytes is the > + * LR saver, then the actual call insn. So ftrace location is > + * always on the first 4 bytes offset. > + */ > + faddr = ftrace_location_range(addr, > + addr + AARCH64_INSN_SIZE); > + if (faddr) > + return (kprobe_opcode_t *)faddr; > + } > + return (kprobe_opcode_t *)addr; > +} > + > +bool arch_kprobe_on_func_entry(unsigned long offset) > +{ > + return offset <= AARCH64_INSN_SIZE; > +} Without this automatic change, we still can change the offset in upper layer. Thank you, -- Masami Hiramatsu