Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964824AbWIVSG6 (ORCPT ); Fri, 22 Sep 2006 14:06:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964829AbWIVSG6 (ORCPT ); Fri, 22 Sep 2006 14:06:58 -0400 Received: from tomts5.bellnexxia.net ([209.226.175.25]:58872 "EHLO tomts5-srv.bellnexxia.net") by vger.kernel.org with ESMTP id S964824AbWIVSG5 (ORCPT ); Fri, 22 Sep 2006 14:06:57 -0400 Date: Fri, 22 Sep 2006 14:06:54 -0400 From: Mathieu Desnoyers To: Karim Yaghmour Cc: Ingo Molnar , Martin Bligh , "Frank Ch. Eigler" , Masami Hiramatsu , prasanna@in.ibm.com, Andrew Morton , Paul Mundt , linux-kernel , Jes Sorensen , Tom Zanussi , Richard J Moore , Michel Dagenais , Christoph Hellwig , Greg Kroah-Hartman , Thomas Gleixner , William Cohen , ltt-dev@shafik.org, systemtap@sources.redhat.com, Alan Cox Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management) Message-ID: <20060922180654.GA12645@Krystal> References: <20060921160009.GA30115@Krystal> <20060921160656.GA24774@elte.hu> <20060921214248.GA10097@Krystal> <20060922070714.GB4167@elte.hu> <20060922150810.GB20839@Krystal> <45140E33.9030509@opersys.com> <20060922161353.GA1569@Krystal> <45141759.8060600@opersys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <45141759.8060600@opersys.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.4.32-grsec (i686) X-Uptime: 14:03:06 up 30 days, 15:11, 4 users, load average: 0.30, 0.20, 0.19 User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2906 Lines: 79 * Karim Yaghmour (karim@opersys.com) wrote: > > > Hrm, your comment makes me think of an interesting idea : > > > > .align > > jump_address: > > near jump to end > > setup_stack_address: > > setup stack > > call empty function > > end: > > > > So, instead of putting nops in the target area, we fill it with a useful > > function call. Near jump being 2 bytes, it might be much easier to modify. > > If necessary, making sure the instruction is aligned would help to change it > > atomically. If we mark the jump address, the setup stack address and the end > > tag address with symbols, we can easily calculate (portably) the offset of the > > near jump to activate either the setup_stack_address or end tags. > > That's another possibility. It seems more C friendly than the simple > short-jump+3bytes. > Here is the implementation :-) Comments are welcome. /***************************************************************************** * marker.h * * Code markup for dynamic and static tracing. i386 architecture optimisations. * * (C) Copyright 2006 Mathieu Desnoyers * * This file is released under the GPLv2. * See the file COPYING for more details. */ #define MARK_NEAR_JUMP_PREFIX "__mark_near_jump_" #define MARK_NEAR_JUMP_SELECT_PREFIX "__mark_near_jump_select_" /* Note : max 256 bytes between over_label and near_jump */ #define MARK_DO_JUMP(name) \ do { \ __label__ near_jump; \ volatile static void *__mark_near_jump_##name \ asm (MARK_NEAR_JUMP_PREFIX#name) \ __attribute__((unused)) = &&near_jump; \ volatile static void *__mark_near_jump_select_##name \ asm (MARK_NEAR_JUMP_SELECT_PREFIX#name) \ __attribute__((unused)) = &&near_jump_select; \ asm volatile ( ".align 16;\n\t" : : ); \ asm volatile ( ".byte 0xeb;\n\t" : : ); \ near_jump_select: \ asm volatile ( ".byte %0-%1;\n\t" : : \ "m" (*&&over_label), "m" (*&&near_jump)); \ near_jump: \ asm volatile ( "" : : ); \ } while(0) To change it, we can dynamically overwrite the __mark_near_jump_select_##name value (a byte) to (__mark_jump_call_##name - __mark_near_jump_##name). So we have one architecture specific optimisation within the architecture agnostic marking mechanism. Comments are welcome. Mathieu OpenPGP public key: http://krystal.dyndns.org:8080/key/compudj.gpg Key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - 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/