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

[Sergey Fedorov]

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.

Best,
Sergey

>
> On 16 November 2015 at 18:28, Peter Maydell <address@hidden> 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 <address@hidden>
>> Signed-off-by: Peter Maydell <address@hidden>
>> ---
>> 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
>>