Re: [Qemu-devel] [PATCH] target-arm/translate: Fix RRX operands

[Aurelien Jarno]

On Wed, Oct 17, 2012 at 05:43:55PM +0100, Peter Maydell wrote:
> On 16 October 2012 10:15, Peter Crosthwaite
> <address@hidden> wrote:
> > Instructions that both use the RRX second operand and update CS were
> > incorrect, as the Carry flag was updated too early. An example of such an
> > instruction would be:
> >
> > ands r12,r13,RRX
> >
> > Ands, because of the "s" flag will update the carry flag. But the RRX second
> > operand rotates through the C flag which should happen before the update.
> > Fixed the ordering of the two, the old carry is read by "r13,RRX" before 
> > being
> > updated.
> >
> > Signed-off-by: Peter Crosthwaite <address@hidden>
> > Reported-by: Vinesh Peringat <address@hidden>
> > ---
> >  target-arm/translate.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/target-arm/translate.c b/target-arm/translate.c
> > index c6840b7..daccb15 100644
> > --- a/target-arm/translate.c
> > +++ b/target-arm/translate.c
> > @@ -516,10 +516,10 @@ static inline void gen_arm_shift_im(TCGv var, int 
> > shiftop, int shift, int flags)
> >              tcg_gen_rotri_i32(var, var, shift); break;
> >          } else {
> >              TCGv tmp = tcg_temp_new_i32();
> > +            tcg_gen_shli_i32(tmp, cpu_CF, 31);
> >              if (flags)
> >                  shifter_out_im(var, 0);
> >              tcg_gen_shri_i32(var, var, 1);
> > -            tcg_gen_shli_i32(tmp, cpu_CF, 31);
> >              tcg_gen_or_i32(var, var, tmp);
> >              tcg_temp_free_i32(tmp);
> >          }
> 
> Looks like this was broken by Aurelien's commit 66c374de8; previously
> we loaded CF into a tmp before doing the shifter_out_im() [which updates CF],
> and then used the tmp after the call, rather than directly using CF.

Yes, I am the culprit here, sorry about that.

> Reviewed-by: Peter Maydell <address@hidden>
> 

And applied.


-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net