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

[Vladimir Kozlov]

Coping to GC and Runtime groups.

-------- Original Message --------
Subject: Request for reviews (S): 6892186: 6896084: VM does not reserve	protected page below heap for compressed oops implicit null checks
Date: Wed, 28 Oct 2009 16:13:21 -0700
From: Vladimir Kozlov <Vladimir.Kozlov at Sun.COM>
To: hotspot compiler <hotspot-compiler-dev at openjdk.java.net>


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.

Reviewed by:

Fix verified (y/n): y, test output

Other testing:
JPRT