linux-kernel - Re: [PATCH v2 0/6] ftrace: to kill a daemon (small updates)

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Date:	Fri, 15 Aug 2008 07:22:52 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>,
	Bruce Duncan <bwduncan@...il.com>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH v2 0/6] ftrace: to kill a daemon (small updates)

(From the original mail)

Steven Rostedt wrote:
>
> Along came Gregory Haskins, who was bickering about having ftrace enabled
> on a production -rt kernel. I told him the reasons that this would be bad
> and then he started thinking out loud, and suggesting wild ideas, like
> patching gcc!
>   
^^^^^^^^^^

Ingo Molnar wrote:
> Eventually gcc should be extended to provide a separate section for 
> instrumentation patch sites, instead of us having to disassemble the 
> object code. 

:)

I obviously agree with this, so +1

Though, tbh, at the time I suggested it I didn't think of Steve's idea 
to post-process which was quite clever. But I do agree that having gcc 
do it will probably save some build time since it will probably be 
trivial for it to do this when already processing -pg. It would have the 
added benefit of letting the arch specific toolchain do the arch 
specific work (though I think Steve's solution capitalizes on the 
toolchain extensively as it is).

The biggest downside is that we would have an external dependency on gcc 
for the feature, but I guess the kernel already has some of those anyway 
(e.g. the stack overflow guard feature, etc). We could always fall back 
on Steve's post-processing if the toolchain lacks the feature.

-Greg

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