--- a/src/cpu/zero/vm/stack_zero.inline.hpp	Wed May 05 05:57:21 2010 -0700
+++ b/src/cpu/zero/vm/stack_zero.inline.hpp	Thu May 06 02:09:18 2010 -0700
@@ -25,19 +25,24 @@
 
 // This function should match SharkStack::CreateStackOverflowCheck
 inline void ZeroStack::overflow_check(int required_words, TRAPS) {
-  JavaThread *thread = (JavaThread *) THREAD;
-
   // Check the Zero stack
-  if (required_words > available_words()) {
+  if (available_words() < required_words) {
     handle_overflow(THREAD);
     return;
   }
 
   // Check the ABI stack
-  address stack_top = thread->stack_base() - thread->stack_size();
-  int free_stack = ((address) &stack_top) - stack_top;
-  if (free_stack < shadow_pages_size()) {
+  if (abi_stack_available(THREAD) < 0) {
     handle_overflow(THREAD);
     return;
   }
 }
+
+// This method returns the amount of ABI stack available for us
+// to use under normal circumstances.  Note that the returned
+// value can be negative.
+inline int ZeroStack::abi_stack_available(Thread *thread) const {
+  int stack_used = thread->stack_base() - (address) &stack_used;
+  int stack_free = thread->stack_size() - stack_used;
+  return stack_free - shadow_pages_size();
+}