[15] RFR(S): 8244433: Remove saving of RSP in Assembler::pusha_uncached()

[Erik Österlund]

Oups. Looks good.

Thanks,
/Erik

On 2020-05-14 14:01, Christian Hagedorn wrote:
> Forgot to adjust the rsp variable in print_state64() on line 912. I 
> updated my webrev in place.
>
> Best regards,
> Christian
>
> On 14.05.20 11:49, Christian Hagedorn wrote:
>> Thank you Erik for your review!
>>
>> Best regards,
>> Christian
>>
>> On 14.05.20 11:47, Erik Österlund wrote:
>>> Hi Christian,
>>>
>>> Thanks for taking care of this. Looks good to me.
>>>
>>> Thanks,
>>> /Erik
>>>
>>> On 2020-05-14 11:38, Christian Hagedorn wrote:
>>>> Hi
>>>>
>>>> Please review the following enhancement for x86:
>>>> https://bugs.openjdk.java.net/browse/JDK-8244433
>>>> http://cr.openjdk.java.net/~chagedorn/8244433/webrev.00/
>>>>
>>>> This removes the move instruction for saving the actual value of 
>>>> RSP in Assembler::pusha_uncached()/pusha(). The original value of 
>>>> RSP is normally not used on the stack as the value of RSP will 
>>>> automatically be restored after popa to the same value before doing 
>>>> pusha. There are two locations, however, where we need to know the 
>>>> original value of RSP in order to print it. But these places can 
>>>> also compute the correct value of RSP by using the new value of RSP 
>>>> after pusha and adding 16 * wordSize to it. I fixed those.
>>>>
>>>> We still keep the same alignment by subtracting 16 * wordSize from 
>>>> RSP in pusha. Does anybody see any potential problems by not saving 
>>>> the value of RSP on the stack with pusha?
>>>>
>>>> Either way, as Erik Ö. has pointed out, the Windows x64 ABI does 
>>>> not specify a red zone of 128 bytes. If we are unlucky and get an 
>>>> interrupt between saving RSP and decrementing RSP in the current 
>>>> code, we could end up with a corrupt value for RSP on Windows. 
>>>> Therefore, we do need to fix pusha_uncached() if we still want to 
>>>> save the old value of RSP. For example, we could first subtract 16 
>>>> * wordSize and then calculate the correct value:
>>>>
>>>> subq(rsp, 16 * wordSize);
>>>> movq(Address(rsp, 11 * wordSize), rsp);
>>>> addq(Address(rsp, 11 * wordSize), 16 * wordSize);
>>>>
>>>> Thank you!
>>>>
>>>> Best regards,
>>>> Christian
>>>