linux-kernel - Re: [RFC] kreplace: Rebootless kernel updates

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Message-ID: <807b3a220811251848w384298dp393691173e603fc2@mail.gmail.com>
Date:	Wed, 26 Nov 2008 08:18:02 +0530
From:	"Nikanth K" <nikanth@...il.com>
To:	"Masami Hiramatsu" <mhiramat@...hat.com>
Cc:	"Nikanth Karthikesan" <knikanth@...e.de>,
	linux-kernel@...r.kernel.org, ananth@...ibm.com,
	davem@...emloft.net, contact@...lice.com, jbarnold@...lice.com,
	tabbott@...lice.com, wdaher@...lice.com, andersk@...lice.com
Subject: Re: [RFC] kreplace: Rebootless kernel updates

Hi Masami

On Mon, Nov 24, 2008 at 8:45 PM, Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 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.
>

I thought jprobes would provide easy access to function parameters.

Thanks
Nikanth
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