Re: [Qemu-devel] [PATCH v2 for-2.5] target-arm/translate-a64.c: Correct unallocated checks for ldst_excl

[Laurent Desnogues <laurent.desnogues@gmail.com>]

On Tue, Nov 24, 2015 at 1:01 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> The checks for the unallocated encodings in the ldst_excl group
> (exclusives and load-acquire/store-release) were not correct. This
> error meant that in turn we ended up with code attempting to handle
> the non-existent case of "non-exclusive load-acquire/store-release
> pair". Delete that broken and now unreachable code.
>
> Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>


Laurent

> ---
> The easiest way to validate that we have the unallocated
> conditions correct now is to look at C4.4.6 "load/store exclusive"
> in the v8 ARM ARM rev A.3h: our three conditions correspond
> to the three "unallocated" rows in the decode table.
>
> v2 changes: remove incorrect comment too.
> ---
>  target-arm/translate-a64.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
> index fe485a4..14e8131 100644
> --- a/target-arm/translate-a64.c
> +++ b/target-arm/translate-a64.c
> @@ -1816,9 +1816,6 @@ static void gen_store_exclusive(DisasContext *s, int rd, int rt, int rt2,
>   *  o2: 0 -> exclusive, 1 -> not
>   *  o1: 0 -> single register, 1 -> register pair
>   *  o0: 1 -> load-acquire/store-release, 0 -> not
> - *
> - *  o0 == 0 AND o2 == 1 is un-allocated
> - *  o1 == 1 is un-allocated except for 32 and 64 bit sizes
>   */
>  static void disas_ldst_excl(DisasContext *s, uint32_t insn)
>  {
> @@ -1833,7 +1830,8 @@ static void disas_ldst_excl(DisasContext *s, uint32_t insn)
>      int size = extract32(insn, 30, 2);
>      TCGv_i64 tcg_addr;
>
> -    if ((!is_excl && !is_lasr) ||
> +    if ((!is_excl && !is_pair && !is_lasr) ||
> +        (!is_excl && is_pair) ||
>          (is_pair && size < 2)) {
>          unallocated_encoding(s);
>          return;
> @@ -1862,15 +1860,6 @@ static void disas_ldst_excl(DisasContext *s, uint32_t insn)
>          } else {
>              do_gpr_ld(s, tcg_rt, tcg_addr, size, false, false);
>          }
> -        if (is_pair) {
> -            TCGv_i64 tcg_rt2 = cpu_reg(s, rt);
> -            tcg_gen_addi_i64(tcg_addr, tcg_addr, 1 << size);
> -            if (is_store) {
> -                do_gpr_st(s, tcg_rt2, tcg_addr, size);
> -            } else {
> -                do_gpr_ld(s, tcg_rt2, tcg_addr, size, false, false);
> -            }
> -        }
>      }
>  }
>
> --
> 1.9.1
>