Message-ID: <4926C838.8080105@redhat.com>
Date: Fri, 21 Nov 2008 09:39:52 -0500
From: Masami Hiramatsu <mhiramat@redhat.com>
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To: Nikanth Karthikesan <knikanth@suse.de>
CC: linux-kernel@vger.kernel.org, ananth@in.ibm.com, davem@davemloft.net,
       contact@ksplice.com, jbarnold@ksplice.com, tabbott@ksplice.com,
       wdaher@ksplice.com, andersk@ksplice.com
Subject: Re: [RFC] kreplace: Rebootless kernel updates
References: <200811211720.26394.knikanth@suse.de>
In-Reply-To: <200811211720.26394.knikanth@suse.de>
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Hi Nikanth,

Nikanth Karthikesan wrote:
> This RFC patch adds support for limited form of rebootless kernel patching 
> even without building the entire kernel.
> 
> When looking for a shortcut to avoid the rebuild/reboot cycle when hacking the  
> kernel - the ksplice[1] was posted. This patch extends kprobes to do something 
> similar, which would require even lesser time to _experiment_ with the running 
> kernel. 
> 
> This small patch extends jprobes so that the jprobe's handler is executed but 
> skips executing the actual function. But this has its own limitations such as 
> Cannot access symbols not exported for modules (ofcourse hacks like 
> pointers[2] can be used.), problems related to return values[3], etc... This 
> is currently a x86_64 only _hack_.

Hmm,
Would you like to replace a function to another function?
If so, AFAIK, you can do that with kprobe and below pre_handler.
(see booster enabled path in setup_singlestep())

pre_handler(...)
{
	reset_current_kprobe();	/* this kprobe doesn't need any more */
	regs->ip = new_function;	/* change IP to new function */
	preempt_enable_no_resched();	/* recover preempt count */
	return 1;	/* No need to setup singlestep */
}

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com

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