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

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Message-ID: <1486731108.2900.68.camel@decadent.org.uk>
Date:   Fri, 10 Feb 2017 12:51:48 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Vineet Gupta <vgupta@...opsys.com>
Cc:     stable@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.4 12/23] ARC: [arcompact] handle unaligned access
 delay slot corner case

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).

Ben.

>  		regs->status32 &= ~STATUS_DE_MASK;
>  	} else {
>  		regs->ret += state.instr_len;



-- 
Ben Hutchings
It's easier to fight for one's principles than to live up to them.


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