linux-kernel - Re: [rfd] function-graph augmentation

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Message-ID: <20090220133011.GB16897@ghostprotocols.net>
Date:	Fri, 20 Feb 2009 10:30:11 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jason Baron <jbaron@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [rfd] function-graph augmentation

Em Fri, Feb 20, 2009 at 09:56:27AM +0100, Ingo Molnar escreveu:
> 2)
> 
> Another, entirely different, and i think complementary approach, 
> which exciting new possibilities would be to (also) 
> automatically pick up arguments from the stack, on function 
> entry.
> 
> If there's a (read-mostly, lockless-to-read and scalable) 
> function attributes hash, then we could encode the parameters 
> signature of functions (or at least, of certain functions) in 
> the attributes hash. Then the tracer will know how many 
> arguments to pick up from the stack.
> 
> This approach has the advantage that we could reconstruct the 
> parameters of _arbitrary_ functions, without having to touch 
> those functions. We already enumerate all functions during build 
> time, it would take some more dwarf2 magic to recover the 
> call/parameter signature. Oh, and at that time we could also 
> record the _return type_ - easing the return value.
> 
> Note that it does not take a full, bloated DEBUG_INFO build - we 
> can build a -g object to get the dwarf2 data and then strip out 
> the dwarf2 data.
> 
> Arnaldo, what do you think about this, how feasible would it be 
> to put dwarf2 magic into scripts/recordmcount.pl?

/me reading scripts/recordmcount.pl...

- Arnaldo
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