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 07:33:31 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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

On Fri, 2012-06-15 at 17:15 +0900, Masami Hiramatsu wrote:

> > 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...

I was thinking of routines that may or may not use regs. Actually, I was
thinking about perf in general, that could use regs if supported, or get
its own set.

But I agree that it may not be the best for those that must have regs.

Perhaps we could add another flag:

FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED

Where it wont error out if you have this set. But if you just pass in
FTRACE_OPS_FL_SAVE_REGS (as kprobes does) it will fail.

How's that sound?

-- Steve


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