linux-kernel - Re: [PATCH 4.4 12/23] ARC: [arcompact] handle unaligned access delay slot corner case

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Date:   Fri, 10 Feb 2017 14:19:25 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Ben Hutchings <ben@...adent.org.uk>
Cc:     Vineet Gupta <vgupta@...opsys.com>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4 12/23] ARC: [arcompact] handle unaligned access delay
 slot corner case

On Fri, Feb 10, 2017 at 12:51:48PM +0000, Ben Hutchings wrote:
> On Tue, 2017-01-31 at 06:37 +0100, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Vineet Gupta <vgupta@...opsys.com>
> > 
> > commit 9aed02feae57bf7a40cb04ea0e3017cb7a998db4 upstream.
> > 
> > After emulating an unaligned access in delay slot of a branch, we
> > pretend as the delay slot never happened - so return back to actual
> > branch target (or next PC if branch was not taken).
> > 
> > Curently we did this by handling STATUS32.DE, we also need to clear the
> > BTA.T bit, which is disregarded when returning from original misaligned
> > exception, but could cause weirdness if it took the interrupt return
> > path (in case interrupt was acive too)
> > 
> > One ARC700 customer ran into this when enabling unaligned access fixup
> > for kernel mode accesses as well
> > 
> > Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > ---
> >  arch/arc/kernel/unaligned.c |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > --- a/arch/arc/kernel/unaligned.c
> > +++ b/arch/arc/kernel/unaligned.c
> > @@ -241,8 +241,9 @@ int misaligned_fixup(unsigned long addre
> >  	if (state.fault)
> >  		goto fault;
> >  
> > +	/* clear any remanants of delay slot */
> >  	if (delay_mode(regs)) {
> > -		regs->ret = regs->bta;
> > +		regs->ret = regs->bta ~1U;
> 
> Unless you're doing something terrible with macros, this is missing an
> & operator.  I doubt this even compiled (looks like it's only used in
> some ARC configurations).

Hah, that's funny, it's obvious it isn't part of anyone's build tests,
so I guess it must be just fine :)

thanks,

greg k-h