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

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Message-ID: <20200219162747.GX2935@paulmck-ThinkPad-P72>
Date:   Wed, 19 Feb 2020 08:27:47 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.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, Feb 19, 2020 at 11:12:28AM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2020 17:04:42 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > > -		memmove(&gpregs->ip, (void *)regs->sp, 5*8);
> > > +		for (i = 0; i < count; i++) {
> > > +			int idx = (dst <= src) ? i : count - i;  
> > 
> > That's an off-by-one for going backward; 'count - 1 - i' should work
> > better, or I should just stop typing for today ;-)
> 
> 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.)

							Thanx, Paul