Subject: Re: [PATCH 1/2] powerpc: Fix emulation of mcrf in emulate_step()

From: Anton Blanchard <[email-masked]>
Date: Thu, 15 Jun 2017 16:47:29 +1000

Hi Segher,

> On Thu, Jun 15, 2017 at 09:46:38AM +1000, Anton Blanchard wrote:
> > The mcrf emulation code was looking at the CR fields in the reverse
> > order. It also relied on reserved fields being zero which is
> > somewhat fragile, so fix that too.  
> 
> It masked out the reserved bits.  I find the new code to be less
> readable (but also more correct ;-) ). 

Thanks for that, not sure how I missed it :) I'll respin a simpler
patch.

> Maybe there should be (inline)
> helper function to insert/extract CR fields?

That would be nice, there are quite a few places that could use it.

Anton

> Segher
> 
> 
> > --- a/arch/powerpc/lib/sstep.c
> > +++ b/arch/powerpc/lib/sstep.c
> > @@ -683,8 +683,10 @@ int analyse_instr(struct instruction_op *op,
> > struct pt_regs *regs, case 19:
> >  		switch ((instr >> 1) & 0x3ff) {
> >  		case 0:		/* mcrf */
> > -			rd = (instr >> 21) & 0x1c;
> > -			ra = (instr >> 16) & 0x1c;
> > +			rd = 7 - ((instr >> 23) & 0x7);
> > +			ra = 7 - ((instr >> 18) & 0x7);
> > +			rd *= 4;
> > +			ra *= 4;
> >  			val = (regs->ccr >> ra) & 0xf;
> >  			regs->ccr = (regs->ccr & ~(0xfUL << rd)) |
> > (val << rd); goto instr_done;  
>