Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751121AbWISUyb (ORCPT ); Tue, 19 Sep 2006 16:54:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751799AbWISUya (ORCPT ); Tue, 19 Sep 2006 16:54:30 -0400 Received: from opersys.com ([64.40.108.71]:17672 "EHLO www.opersys.com") by vger.kernel.org with ESMTP id S1751121AbWISUy3 (ORCPT ); Tue, 19 Sep 2006 16:54:29 -0400 Message-ID: <45105B5E.9080107@opersys.com> Date: Tue, 19 Sep 2006 17:04:30 -0400 From: Karim Yaghmour Reply-To: karim@opersys.com Organization: Opersys inc. User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.0.6) Gecko/20060804 Fedora/1.0.4-0.5.1.fc5 SeaMonkey/1.0.4 MIME-Version: 1.0 To: Martin Bligh CC: prasanna@in.ibm.com, Andrew Morton , "Frank Ch. Eigler" , Ingo Molnar , Mathieu Desnoyers , 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 References: <20060918234502.GA197@Krystal> <20060919081124.GA30394@elte.hu> <451008AC.6030006@google.com> <20060919154612.GU3951@redhat.com> <4510151B.5070304@google.com> <20060919093935.4ddcefc3.akpm@osdl.org> <45101DBA.7000901@google.com> <20060919063821.GB23836@in.ibm.com> <45102641.7000101@google.com> <20060919070516.GD23836@in.ibm.com> <451030A6.6040801@google.com> In-Reply-To: <451030A6.6040801@google.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1626 Lines: 41 Martin Bligh wrote: > be that many? Still doesn't fix the problem Matieu just pointed > out though. Humpf. There's one possibility if we're willing to insert a placeholder at function entry that allows to essentially do what Andrew suggests without much impact. Specifically, if you need a 5-byte operation to jump to the alternate instrumented function, you can then do something like: 1- At build time insert 5-byte unconditional jump to instruction right after placeholder. 2- At runtime for diverting flow: - Replace first byte with int3 (atomically) - Replace next 4 bytes with instrumented function destination - Replace first byte 3- At runtime for returning flow: - Do #2 but for the original placeholder jump. There's not race condition here or fear of interrupt return in the middle of anything, or any need to stop the kernel from operating and the likes, or even dependency on kprobes or need for dprobes, at least in as far as I can see -- so this should be trivial on m68k ;). The price to pay is an additional unconditional jump at all times, which should be optimized at runtime by the CPU. Benchmarks could help show the real impact, but as Ingo said, these things should be minimal. In sum, this would work for function pointers and wouldn't require having to walk the code in search of instances of "call foo" to replace. Just a thought. Karim - 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/