Message-ID: <492AC522.4020202@redhat.com>
Date: Mon, 24 Nov 2008 10:15:46 -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> <4926C838.8080105@redhat.com> <200811241637.33329.knikanth@suse.de>
In-Reply-To: <200811241637.33329.knikanth@suse.de>
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Nikanth Karthikesan wrote:
> On Friday 21 November 2008 20:09:52 Masami Hiramatsu wrote:
>> Hi Nikanth,
>>
>> Nikanth Karthikesan wrote:
> 
>> 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 */
>> }
>>
>>
> 
> So, am I seeing worries to enable something, which is already possible, but 
> just not documented?

Actually, you can do this with kprobes, but not documented,
because the regs->ip setup depends on arch. (above code is only for
x86/x86-64).

I think it's easier to just provide above pre_handler for each arch than
jprobe-based kreplace approach.

Thank you,

-- 
Masami Hiramatsu

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

e-mail: mhiramat@redhat.com

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