linux-kernel - Re: [RFC][PATCH] Make ftrace able to trace function return

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Date:	Thu, 30 Oct 2008 22:43:42 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frédéric Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Make ftrace able to trace function return


On Fri, 31 Oct 2008, Fr?d?ric Weisbecker wrote:

> 2008/10/30 Steven Rostedt <rostedt@...dmis.org>:
> > What about storing the return addresses on the bottom of the stack?
> > That is, start at task->stack + sizeof(thread_info), and stack up on that.
> > Be careful, there might already be users of that area. This will also need
> > to be arch dependent.
> 
> But how could I assume there is enough space behind this address to store a long
> stack of functions calls for a same thread?
> And if an interrupt is raised, would a reference to "current task" be
> really consistant?
> 
> I don't know much about the bottom stack of the tasks, I'm not sure
> about how much
> space I can use inside... I should study this field. Who could be the
> potential users of this area?
> 

Because it is the real stack ;-)

Before adding, test to see if the real stack pointer is getting close. If 
it is, then there's probably more issues.  You can run the stack_tracer to 
see how much stack is available too.

-- Steve

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