linux-kernel - Re: [RFC][PATCH 05/13 v2] ftrace/x86: Add separate function to save regs

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Date:	Fri, 15 Jun 2012 17:15:20 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC][PATCH 05/13 v2] ftrace/x86: Add separate function to
 save regs

(2012/06/13 7:43), Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@...hat.com>
> 
> Add a way to have different functions calling different trampolines.
> If a ftrace_ops wants regs saved on the return, then have only the
> functions with ops registered to save regs. Functions registered by
> other ops would not be affected, unless the functions overlap.
> 
> If one ftrace_ops registered functions A, B and C and another ops
> registered fucntions to save regs on A, and D, then only functions
> A and D would be saving regs. Function B and C would work as normal.
> Although A is registered by both ops: normal and saves regs; this is fine
> as saving the regs is needed to satisfy one of the ops that calls it
> but the regs are ignored by the other ops function.
> 
> x86_64 implements the full regs saving, and i386 just passes a NULL
> for regs to satisfy the ftrace_ops passing. Where an arch must supply
> both regs and ftrace_ops parameters, even if regs is just NULL.
> 
> It is OK for an arch to pass NULL regs. All function trace users that
> require regs passing must add the flag FTRACE_OPS_FL_SAVE_REGS when
> registering the ftrace_ops and either check if regs is not NULL or
> check if ARCH_SUPPORTS_FTRACE_SAVE_REGS. If the arch supports passing
> regs it will set this macro and pass regs for ops that request them.
> All other archs will just pass NULL.

Hmm, so would you mean that user is responsible for checking
whether the arch supports save_regs or not?
I would rather like ftrace to check it as my patch has done.
I think ARCH_SUPPORTS_FTRACE_SAVE_REGS macro checking in all
handler code is something like odd...

Thank you,


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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