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diff src/share/vm/asm/assembler.cpp @ 237:1fdb98a17101

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6716785: implicit null checks not triggering with CompressedOops Summary: allocate alignment-sized page(s) below java heap so that memory accesses at heap_base+1page give signal and cause an implicit null check Reviewed-by: kvn, jmasa, phh, jcoomes
author coleenp
date Sat, 19 Jul 2008 17:38:22 -0400
parents a61af66fc99e
children 9ee9cf798b59 36ccc817fca4
line wrap: on
line diff
--- a/src/share/vm/asm/assembler.cpp	Fri Jul 11 01:14:44 2008 -0700
+++ b/src/share/vm/asm/assembler.cpp	Sat Jul 19 17:38:22 2008 -0400
@@ -246,6 +246,24 @@
   }
 }
 
+bool MacroAssembler::needs_explicit_null_check(intptr_t offset) {
+  // Exception handler checks the nmethod's implicit null checks table
+  // only when this method returns false.
+#ifndef SPARC
+  // Sparc does not have based addressing
+  if (UseCompressedOops) {
+    // The first page after heap_base is unmapped and
+    // the 'offset' is equal to [heap_base + offset] for
+    // narrow oop implicit null checks.
+    uintptr_t heap_base = (uintptr_t)Universe::heap_base();
+    if ((uintptr_t)offset >= heap_base) {
+      // Normalize offset for the next check.
+      offset = (intptr_t)(pointer_delta((void*)offset, (void*)heap_base, 1));
+    }
+  }
+#endif // SPARC
+  return offset < 0 || os::vm_page_size() <= offset;
+}
 
 #ifndef PRODUCT
 void Label::print_instructions(MacroAssembler* masm) const {