Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 27 Feb 2001 14:05:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 27 Feb 2001 14:05:23 -0500 Received: from mail.surgient.com ([63.118.236.3]:57357 "EHLO bignorse.SURGIENT.COM") by vger.kernel.org with ESMTP id ; Tue, 27 Feb 2001 14:05:16 -0500 Message-ID: From: "Collins, Tom" To: "'richardj_moore@uk.ibm.com'" , Andreas Dilger Cc: "Collins, Tom" , linux-kernel@vger.kernel.org Subject: RE: Dynamically altering code segments Date: Tue, 27 Feb 2001 13:04:55 -0600 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2653.19) Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hey...thank you ... I have looked at the Linux Trace Toolkit and was wondering if such a thing could be done. I also have visited the dprobes web site and that looked like it had the mechanisms I was looking for. Will the updated version appear next week at the dprobes web site? I assume that it will. I have one more question: My trace code is currently implemented as a kernel loadable module. Would I need to change that so that it is built as part of the kernel, or can I keep it as a loadable module? If I can keep it as a module, I would ensure that the module would be the only place that would enable/disable the trace, (don't want the kernel jumping to a nonexistant address :O ..) Thanks again...will be looking for the upgrade next week... Tom -----Original Message----- From: richardj_moore@uk.ibm.com [mailto:richardj_moore@uk.ibm.com] Sent: Tuesday, February 27, 2001 12:15 PM To: Andreas Dilger Cc: Collins, Tom; linux-kernel@vger.kernel.org Subject: Re: Dynamically altering code segments Dprobes is one mechanism for doing what you want. It works the same way OS/2 dynamic trace did. Another mecnahism, also available from the dprobes web page is the GKHI (generalised kernel hooks interface). If you know you want tracepoints in permanently assigned locations then you could code a gkhi hook in the kernel which is essentially two jmps. When the hook is inactive the first jmp bypasses the second, which jumps to the hook exit dispatcher routine. When active the first jmp uses a zero offset. If you use the gkhi you'll need to write you own hook exits, which presumably will trace data and drop it into a trace buffer of your own making. Again if you do decide to use ghki, please wait for 1.0 to be dropped next week sometime. If you go down the dprobes route you'll see that it inter-operates with Linux Trace Toolkit to give you a dynamic tracing capability for Linux (user and kernel space). We're currently working on custom formatting for raw trace data events created by dprobes. If you're familiar with os/2 then TRCUST might mean something to you in connection with custom formatting. Richard Moore - RAS Project Lead - Linux Technology Centre (PISC). http://oss.software.ibm.com/developerworks/opensource/linux Office: (+44) (0)1962-817072, Mobile: (+44) (0)7768-298183 IBM UK Ltd, MP135 Galileo Centre, Hursley Park, Winchester, SO21 2JN, UK Andreas Dilger on 27/02/2001 17:05:37 Please respond to Andreas Dilger To: "Collins, Tom" cc: linux-kernel@vger.kernel.org Subject: Re: Dynamically altering code segments Tom Collins writes: > I am wanting to dynamically modify the kernel in specific places to > implement a custom kernel trace mechanism. The general idea is that, > when the "trace" is off, there are NOP instruction sequences at various > places in the kernel. When the "trace" is turned on, those same NOPs > are replaced by JMPs to code that implements the trace (such as logging > events, using the MSR and PMC's etc..). > > This was a trick that was done in my old days of OS/2 performance tools > developement to get trace information from the running kernel. > > Is it possible to do the same thing in Linux? See IBM "dprobes" project. It is basically what you are describing (AFAIK). It makes sense, because a lot of the OS/2 folks are now working on Linux. Cheers, Andreas -- Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto, \ would they cancel out, leaving him still hungry?" http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert - 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/ - 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/