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Date: Wed, 20 Sep 2006 22:27:13 +0900 From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> To: karim@...rsys.com Cc: Martin Bligh <mbligh@...gle.com>, prasanna@...ibm.com, Andrew Morton <akpm@...l.org>, "Frank Ch. Eigler" <fche@...hat.com>, Ingo Molnar <mingo@...e.hu>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Paul Mundt <lethal@...ux-sh.org>, linux-kernel <linux-kernel@...r.kernel.org>, Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>, Richard J Moore <richardj_moore@...ibm.com>, Michel Dagenais <michel.dagenais@...ymtl.ca>, Christoph Hellwig <hch@...radead.org>, Greg Kroah-Hartman <gregkh@...e.de>, Thomas Gleixner <tglx@...utronix.de>, William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org, systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: [PATCH] Linux Kernel Markers Hi Karim, Karim Yaghmour wrote: > 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: This method is very similar to the djprobe. And I had gotten the same idea to support preemptive kernel. > 1- At build time insert 5-byte unconditional jump to instruction > right after placeholder. This means the below code, doesn't this? --- jmp 1f /* short jump consumes 2 bytes */ nop nop nop 1: --- > 2- At runtime for diverting flow: > - Replace first byte with int3 (atomically) > - Replace next 4 bytes with instrumented function destination - Serialize all processor's cache by using IPI and cpuid. > - Replace first byte > 3- At runtime for returning flow: > - Do #2 but for the original placeholder jump. I think the djprobe can provide most of functionalities which your idea requires. I'll update the djprobe against for 2.6.17 or later as soon as possible. Would you try to use it? Thanks, -- Masami HIRAMATSU 2nd Research Dept. Hitachi, Ltd., Systems Development Laboratory E-mail: masami.hiramatsu.pt@...achi.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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