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

[Sergey Fedorov <serge.fdrv@gmail.com>]

On 23.11.2015 21:42, Sergey Fedorov wrote:
> On 23.11.2015 19:49, Peter Maydell wrote:
>> Ping? I forgot to mark this for-2.5, and given how long the bug's
>> been hanging around there's not much urgency to fixing it, but
>> we might as well put the fix into 2.5 if it gets reviewed.
>>
> Hi, Peter. I'm going to review this carefully in a few days :)
> For now, I see that the comment for this function should be updated to
> match new code.
>

However, I've just checked the logic of the patch was correct. Just the
comment needs to be adjusted.

Best regards,
Sergey

>> On 16 November 2015 at 18:28, 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>
>>> ---
>>> 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.h: our three conditions correspond
>>> to the three "unallocated" rows in the decode table.
>>>
>>> PS: Laurent originally reported this way back in 2014:
>>> http://lists.gnu.org/archive/html/qemu-devel/2014-10/msg01255.html
>>>
>>>  target-arm/translate-a64.c | 12 ++----------
>>>  1 file changed, 2 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/target-arm/translate-a64.c b/target-arm/translate-a64.c
>>> index fe485a4..890ace4 100644
>>> --- a/target-arm/translate-a64.c
>>> +++ b/target-arm/translate-a64.c
>>> @@ -1833,7 +1833,8 @@ 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 +1863,6 @@ 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
>>>