Re: [PATCH 2/2] target/arm: Relax r13 restriction for ldrex/strex for v8.0

[Peter Maydell <peter.maydell@linaro.org>]

On Sun, 17 Nov 2019 at 09:06, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Armv8-A removes UNPREDICTABLE for R13 for these cases.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/translate.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/target/arm/translate.c b/target/arm/translate.c
> index b285b23858..3db8103966 100644
> --- a/target/arm/translate.c
> +++ b/target/arm/translate.c
> @@ -8931,11 +8931,11 @@ static bool op_strex(DisasContext *s, arg_STREX *a, MemOp mop, bool rel)
>      /* We UNDEF for these UNPREDICTABLE cases.  */
>      if (a->rd == 15 || a->rn == 15 || a->rt == 15
>          || a->rd == a->rn || a->rd == a->rt
> -        || (s->thumb && (a->rd == 13 || a->rt == 13))
> +        || (!ENABLE_ARCH_8 && s->thumb && (a->rd == 13 || a->rt == 13))
>          || (mop == MO_64
>              && (a->rt2 == 15
>                  || a->rd == a->rt2
> -                || (s->thumb && a->rt2 == 13)))) {
> +                || (!ENABLE_ARCH_8 && s->thumb && a->rt2 == 13)))) {
>          unallocated_encoding(s);
>          return true;
>      }
> @@ -9087,10 +9087,10 @@ static bool op_ldrex(DisasContext *s, arg_LDREX *a, MemOp mop, bool acq)
>
>      /* We UNDEF for these UNPREDICTABLE cases.  */
>      if (a->rn == 15 || a->rt == 15
> -        || (s->thumb && a->rt == 13)
> +        || (!ENABLE_ARCH_8 && s->thumb && a->rt == 13)
>          || (mop == MO_64
>              && (a->rt2 == 15 || a->rt == a->rt2
> -                || (s->thumb && a->rt2 == 13)))) {
> +                || (!ENABLE_ARCH_8 && s->thumb && a->rt2 == 13)))) {
>          unallocated_encoding(s);
>          return true;
>      }

These cases for r13 are indeed no longer UNPREDICTABLE in
v8A, but they are still marked as UNPREDICTABLE for v8M...

thanks
-- PMM