linux-kernel - Re: [PATCH 2/2 v2] ftrace: document basic ftracer/ftracer graph needs

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Date:	Mon, 15 Jun 2009 00:09:12 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	Mike Frysinger <vapier.adi@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2 v2] ftrace: document basic ftracer/ftracer graph
 needs

hi, Mike 

> >> +For information on how to implement prepare_ftrace_return(), simply look at
> >> +the x86 version.  The only architecture-specific piece in it is the setup of
> >> +the fault recovery table (the asm(...) code).  The rest should be the same
> >> +across architectures.
> >> +
> >
> > and the fault recovery table is not needed.
> 
> i dont have one for the Blackfin port, but that's more because there
> is no fault recovery support in the Blackfin port ;)
> 
> > In reality, the prepare_ftrace_return() can have the same arguments as
> > ftrace_trace_function()
> > ...
> > as i know, prepare_ftrace_return() is used to check whether the calling
> > function expect to trace, if yes, return the 'hook' function
> > &return_to_handler, otherwise, return back to the parent_ip directly.
> > so, here, i think there is no need to transfer the data via address, but
> > just using the same arguments like ftrace_trace_function does.
> 
> hmm, that would make the implementation simpler, but i dont think you
> could do that if you implemented the fault handler.  i cant really
> speak as to the requirement of the fault handler as i dont really know
> what/how it works -- i can only guess at they arent used in any way
> for Blackfin systems.
> 
> > unsigned long
> > prepare_ftrace_return(unsgined long ip, unsigned long parent_ip)
> > {
> >    [...]
> >    if (ftrace_push_return_trace(parent_ip, ip, &trace.depth) == -EBUSY)
> >        return parent_ip;
> >
> >    if (ftrace_graph_entry(&trace))
> >        return (unsigned long)&return_to_handler;
> >
> >    [...]
> >
> >    return parent_ip;
> > }
> >
> > if using the above method, the fault recovery table is not needed again.
> 
> and it would allow us to move this code into the common ftrace
> framework for people who dont do fault handlers.
> 

Perhaps I miss something here? otherwise, this fault handler is not
needed if not transfer the data via address and not modify the data in
the place *address accordingly.

best regards,
Wu Zhangjin

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