1 /*
   2  * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "gc/shared/barrierSetAssembler.hpp"
  26 #include "memory/universe.hpp"
  27 #include "utilities/globalDefinitions.hpp"
  28 
  29 bool BarrierSetAssembler::needs_explicit_null_check(intptr_t offset) {
  30   // Exception handler checks the nmethod's implicit null checks table
  31   // only when this method returns false.
  32 #ifdef _LP64
  33   if (UseCompressedOops && Universe::narrow_oop_base() != NULL) {
  34     assert (Universe::heap() != NULL, "java heap should be initialized");
  35     // The first page after heap_base is unmapped and
  36     // the 'offset' is equal to [heap_base + offset] for
  37     // narrow oop implicit null checks.
  38     uintptr_t base = (uintptr_t)Universe::narrow_oop_base();
  39     if ((uintptr_t)offset >= base) {
  40       // Normalize offset for the next check.
  41       offset = (intptr_t)(pointer_delta((void*)offset, (void*)base, 1));
  42     }
  43   }
  44 #endif
  45   return offset < 0 || os::vm_page_size() <= offset;
  46 }
--- EOF ---