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Date: Sun, 7 Apr 2002 20:32:46 +0100
From: John Levon <movement@marcelothewonderpenguin.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: "Steven N. Hirsch" <shirsch@adelphia.net>, linux-kernel@vger.kernel.org
Subject: Re: Two fixes for 2.4.19-pre5-ac3
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On Sun, Apr 07, 2002 at 08:42:48PM +0100, Alan Cox wrote:

> > I'll genuinely take on board advice on how I can profile all the system
> > via x86 perf counters efficiently without having to patch the kernel.
> > The old way just uses sys_call_table. So what do I do now ?
> 
> The obvious thing is to represent it as a device. I'm not familiar enough
> with the existing perfctr work to know how well that works out.

The system call tracking is only used to associate a particular EIP with
a particular offset in some binary image. There's no other efficient
method to capture the mmap() calls for these images, for everything
running. ptrace() is only really useful for a small number of processes,
and is slow. Offline post-analysis isn't possible. There is no
API for getting access to this information.

Removing sys_call_table from exports won't have any positive effect.
Using it has always been "well, you're on your own" - if there is a
really good reason it needs to be changed, fine; but just changing it
because it's not supposed to be used isn't a good enough reason when
there is actually a couple of niche cases where it's the only option.

imho,
john

-- 
"I never understood what's so hard about picking a unique
 first and last name - and not going beyond the 6 character limit."
 	- Toon Moene
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