> On Sep 23, 2020, at 5:43 AM, Richard Sandiford <richard.sandif...@arm.com>
> wrote:
>
> Qing Zhao <qing.z...@oracle.com> writes:
>>> On Sep 22, 2020, at 1:35 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>>> On Tue, Sep 22, 2020 at 11:25 AM Qing Zhao <qing.z...@oracle.com
>>> <mailto:qing.z...@oracle.com>> wrote:
>>>>> On Sep 22, 2020, at 11:31 AM, Richard Sandiford
>>>>> <richard.sandif...@arm.com> wrote:
>>>>> Taking each in turn: what is the reason for not clearing mask registers?
>>>>> And what is the reason for not clearing mm0-7? In each case, is it a
>>>>> performance or a correctness issue?
>>>>
>>>> Could you please provide more information on the above questions? (Why we
>>>> exclude mask registers and mm0-7 registers from ALL on x86?)
>>>>
>>>
>>> No particular reason. You can add them.
>>
>> Okay, thanks.
>>
>> Then I guess that the reason we didn’t zero mask registers and mm0-7
>> registers on x86 is mainly for the performance consideration.
>> There might not be too much benefit for mitigating ROP attack if we zero
>> these additional registers, but we will got much more performance overhead.
>>
>> What’s you opinion, Richard?
>
> Dropping them is fine with me FWIW. That seems like a natural use
> for the new hook: drop zeroing that isn't actively wrong, but isn't
> likely to be useful either.
Okay, I will add a new hook for this purpose.
Qing
>
> Thanks,
> Richard
