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Message-ID: <y0my771fjou.fsf@ton.toronto.redhat.com>
Date: Fri, 25 Apr 2008 22:12:33 -0400
From: fche@...hat.com (Frank Ch. Eigler)
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
Ingo Molnar <mingo@...e.hu>, Jiri Slaby <jirislaby@...il.com>,
David Miller <davem@...emloft.net>, zdenek.kabelac@...il.com,
rjw@...k.pl, paulmck@...ux.vnet.ibm.com, akpm@...ux-foundation.org,
linux-ext4@...r.kernel.org, herbert@...dor.apana.org.au,
penberg@...helsinki.fi, clameter@....com,
linux-kernel@...r.kernel.org, pageexec@...email.hu,
Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH 1/1] x86: fix text_poke
Linus Torvalds <torvalds@...ux-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
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