hotspot/src/share/vm/oops/objArrayOop.hpp
author ysr
Tue, 08 Dec 2009 15:12:17 -0800
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6908208: UseCompressedOops: array_size() returns incorrect size for MAX_INT object array following 6906727 Summary: In array_size() cast to an unsigned to avoid overflow of intermediate value. Reviewed-by: kvn, tonyp, jmasa, jcoomes, coleenp
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/*
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 * Copyright 1997-2009 Sun Microsystems, Inc.  All Rights Reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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 * CA 95054 USA or visit www.sun.com if you need additional information or
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 * have any questions.
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 *
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 */
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// An objArrayOop is an array containing oops.
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// Evaluating "String arg[10]" will create an objArrayOop.
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class objArrayOopDesc : public arrayOopDesc {
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  friend class objArrayKlass;
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  friend class Runtime1;
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  friend class psPromotionManager;
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  friend class CSMarkOopClosure;
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  friend class G1ParScanPartialArrayClosure;
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  template <class T> T* obj_at_addr(int index) const {
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    assert(is_within_bounds(index), "index out of bounds");
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    return &((T*)base())[index];
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  }
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private:
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  // Give size of objArrayOop in HeapWords minus the header
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  static int array_size(int length) {
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    const int OopsPerHeapWord = HeapWordSize/heapOopSize;
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    assert(OopsPerHeapWord >= 1 && (HeapWordSize % heapOopSize == 0),
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           "Else the following (new) computation would be in error");
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#ifdef ASSERT
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    // The old code is left in for sanity-checking; it'll
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    // go away pretty soon. XXX
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    // Without UseCompressedOops, this is simply:
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    // oop->length() * HeapWordsPerOop;
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    // With narrowOops, HeapWordsPerOop is 1/2 or equal 0 as an integer.
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    // The oop elements are aligned up to wordSize
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    const int HeapWordsPerOop = heapOopSize/HeapWordSize;
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    int old_res;
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    if (HeapWordsPerOop > 0) {
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      old_res = length * HeapWordsPerOop;
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    } else {
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      old_res = align_size_up(length, OopsPerHeapWord)/OopsPerHeapWord;
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    }
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#endif  // ASSERT
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    int res = ((uint)length + OopsPerHeapWord - 1)/OopsPerHeapWord;
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    assert(res == old_res, "Inconsistency between old and new.");
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    return res;
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  }
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 public:
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  // Returns the offset of the first element.
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  static int base_offset_in_bytes() {
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    return arrayOopDesc::base_offset_in_bytes(T_OBJECT);
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  }
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  // base is the address following the header.
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  HeapWord* base() const      { return (HeapWord*) arrayOopDesc::base(T_OBJECT); }
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  // Accessing
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  oop obj_at(int index) const {
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    // With UseCompressedOops decode the narrow oop in the objArray to an
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    // uncompressed oop.  Otherwise this is simply a "*" operator.
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    if (UseCompressedOops) {
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      return load_decode_heap_oop(obj_at_addr<narrowOop>(index));
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    } else {
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      return load_decode_heap_oop(obj_at_addr<oop>(index));
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    }
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  }
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  void obj_at_put(int index, oop value) {
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    if (UseCompressedOops) {
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      oop_store(obj_at_addr<narrowOop>(index), value);
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    } else {
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      oop_store(obj_at_addr<oop>(index), value);
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    }
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  }
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  // Sizing
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  static int header_size()    { return arrayOopDesc::header_size(T_OBJECT); }
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  int object_size()           { return object_size(length()); }
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  static int object_size(int length) {
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    // This returns the object size in HeapWords.
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    uint asz = array_size(length);
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    uint osz = align_object_size(header_size() + asz);
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    assert(osz >= asz,   "no overflow");
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    assert((int)osz > 0, "no overflow");
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    return (int)osz;
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  }
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  // special iterators for index ranges, returns size of object
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#define ObjArrayOop_OOP_ITERATE_DECL(OopClosureType, nv_suffix)     \
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  int oop_iterate_range(OopClosureType* blk, int start, int end);
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  ALL_OOP_OOP_ITERATE_CLOSURES_1(ObjArrayOop_OOP_ITERATE_DECL)
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  ALL_OOP_OOP_ITERATE_CLOSURES_2(ObjArrayOop_OOP_ITERATE_DECL)
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};