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 14:26:10 +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 02:19:25PM +0100, Greg Kroah-Hartman wrote:
> 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 :)

Ah, nevermind, commit a524c218bc94c705886a0e0fedeee45d1931da32 that just
went into Linus's tree this week fixes this...

greg k-h