Request for reviews (S): 6892186: 6896084: VM does not reserve protected page below heap for compressed oops implicit null checks

[Vladimir Kozlov]

Thank you, Christian

I will change the type to address.

Vladimir

Christian Thalinger wrote:
> On Wed, 2009-10-28 at 16:13 -0700, Vladimir Kozlov wrote:
>> http://cr.openjdk.java.net/~kvn/6896084/webrev.00
>>
>> Fixed 6896084: VM does not reserve protected page below heap for compressed oops implicit null checks
>>
>> Problem:
>> VM should reserve protected page below heap for compressed oops
>> implicit null checks in compiled code (see 6716785).
>> After zero based compressed oops changes (6791178) the page is
>> not reserved because undefined narrow_oop_base (NULL by default)
>> is used in ReservedHeapSpace() to determine if the page is needed.
>>
>> Solution:
>> Set narrow_oop_base and narrow_oop_use_implicit_null_checks
>> values according to compressed oops encoding mode in
>> Universe::preferred_heap_base() which is called before
>> ReservedHeapSpace() constructors.
> 
> Using size_t for base (which is an address) feels a little strange but
> otherwise looks good.
> 
> -- Christian
>