From mboxrd@z Thu Jan  1 00:00:00 1970
From: fche@redhat.com (Frank Ch. Eigler)
Subject: Re: [PATCH 1/1] x86: fix text_poke
Date: Fri, 25 Apr 2008 22:12:33 -0400
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Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	"H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <andi@firstfloor.org>,
	Ingo Molnar <mingo@elte.hu>, Jiri Slaby <jirislaby@gmail.com>,
	David Miller <davem@davemloft.net>, zdenek.kabelac@gmail.com,
	rjw@sisk.pl, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org,
	linux-ext4@vger.kernel.org, herbert@gondor.apana.org.au,
	penberg@cs.helsinki.fi, clameter@sgi.com,
	linux-kernel@vger.kernel.org, pageexec@freemail.hu,
	Jeremy Fitzhardinge <jeremy@goop.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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In-Reply-To: <alpine.LFD.1.10.0804251456410.2779@woody.linux-foundation.org> (Linus Torvalds's message of "Fri, 25 Apr 2008 15:04:51 -0700 (PDT)")
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Linus Torvalds <torvalds@linux-foundation.org> writes:

> [...]
>> The point is to provide a way to dynamically enable code at runtime
>> without noticeable performance impact on the system.
>
> Quite frankly, maybe I'm a bit dense, but why don't you just recompile the 
> whole original function (at run-time), load that new version of a function 
> as a mini-module, and then insert a marker at the top of the old function 
> that just does a "jmp replacementfunction". [...]

You mentioned possible solutions to some of the problems this
ambitious an approach would cause.  Here are a few more complications:

- instrumenting inlined functions

- proper sharing of static function data amongst multiple live
  copies of same function

- unknown implications of violating long-standing assumptions about
  functions not changing addresses

- interaction with other code modification machinery (kprobes, ...)

- necessity to carry kernel sources & compilers on machines; slow
  marker activation


- FChE