linux-kernel - Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE

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Date:   Wed, 19 Feb 2020 12:05:19 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com,
        luto@...nel.org, tony.luck@...el.com, frederic@...nel.org,
        dan.carpenter@...cle.com, mhiramat@...nel.org
Subject: Re: [PATCH v3 04/22] x86/doublefault: Make memmove()
 notrace/NOKPROBE

On Wed, 19 Feb 2020 08:27:47 -0800
"Paul E. McKenney" <paulmck@...nel.org> wrote:

> > Or, we could just cut and paste the current memmove and make a notrace
> > version too. Then we don't need to worry bout bugs like this.  
> 
> OK, I will bite...
> 
> Can we just make the core be an inline function and make a notrace and
> a trace caller?  Possibly going one step further and having one call
> the other?  (Presumably the traceable version invoking the notrace
> version, but it has been one good long time since I have looked at
> function preambles.)

Sure. Looking at the implementation (which is big and ugly), we could
have a

static always_inline void __memmove(...)
{
	[..]
}

__visible void *memmove(...)
{
	return __memmove(...);
}

__visible notrace void *memmove_notrace(...)
{
	return __memmove(...);
}

-- Steve