Re: [Qemu-devel] [RFC v1 3/3] target/arm: Correct exclusive store return value

[Alistair Francis]

On Fri, Aug 11, 2017 at 1:24 PM, Richard Henderson
<address@hidden> wrote:
> On 08/11/2017 01:13 PM, Alistair Francis wrote:
>>>> +            tcg_gen_ext_i64(val, val, memop);
>>>
>>> What is this addition intended to accomplish?  Because of the position 
>>> within
>>> the code, you know that memop contains MO_64, so that this is a no-op.
>>
>> This is when size == 2 so it's a 32bit operation so memop contains MO_32.
>
> It's a paired 32-bit operation, so we're operating on a 64-bit quantity.  So
> extending from 32-bits would be actively wrong.

>From what I can see though, the 32bit memop is carried into the
tcg_gen_atomic_cmpxchg_i64() call so the value returned to tmp is
masked by the 32bit operation.

Is passing down MO_32 into tcg_gen_atomic_cmpxchg_i64() wrong then as
it ends up as a 64-bit operation?

My TCG knowledge is pretty limited here.

Thanks,
Alistair

>
>
> r~
>