1 /* 2 * Copyright (c) 1997, 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 #ifndef SHARE_VM_OOPS_ARRAYOOP_HPP 26 #define SHARE_VM_OOPS_ARRAYOOP_HPP 27 28 #include "memory/universe.hpp" 29 #include "oops/oop.hpp" 30 #include "utilities/align.hpp" 31 32 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't 33 // declare pure virtual to enforce this because that would allocate a vtbl 34 // in each instance, which we don't want. 35 36 // The layout of array Oops is: 37 // 38 // markOop 39 // Klass* // 32 bits if compressed but declared 64 in LP64. 40 // length // shares klass memory or allocated after declared fields. 41 42 43 class arrayOopDesc : public oopDesc { 44 friend class VMStructs; 45 friend class arrayOopDescTest; 46 47 // Interpreter/Compiler offsets 48 49 // Header size computation. 50 // The header is considered the oop part of this type plus the length. 51 // Returns the aligned header_size_in_bytes. This is not equivalent to 52 // sizeof(arrayOopDesc) which should not appear in the code. 53 static int header_size_in_bytes() { 54 size_t hs = align_up(length_offset_in_bytes() + sizeof(int), 55 HeapWordSize); 56 #ifdef ASSERT 57 // make sure it isn't called before UseCompressedOops is initialized. 58 static size_t arrayoopdesc_hs = 0; 59 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs; 60 assert(arrayoopdesc_hs == hs, "header size can't change"); 61 #endif // ASSERT 62 return (int)hs; 63 } 64 65 // Check whether an element of a typeArrayOop with the given type must be 66 // aligned 0 mod 8. The typeArrayOop itself must be aligned at least this 67 // strongly. 68 static bool element_type_should_be_aligned(BasicType type) { 69 return type == T_DOUBLE || type == T_LONG; 70 } 71 72 public: 73 // The _length field is not declared in C++. It is allocated after the 74 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise 75 // it occupies the second half of the _klass field in oopDesc. 76 static int length_offset_in_bytes() { 77 return UseCompressedClassPointers ? klass_gap_offset_in_bytes() : 78 sizeof(arrayOopDesc); 79 } 80 81 // Returns the offset of the first element. 82 static int base_offset_in_bytes(BasicType type) { 83 return header_size(type) * HeapWordSize; 84 } 85 86 // Returns the address of the first element. The elements in the array will not 87 // relocate from this address until a subsequent thread transition. 88 inline void* base(BasicType type) const; 89 inline void* base_raw(BasicType type) const; // GC barrier invariant 90 91 // Tells whether index is within bounds. 92 bool is_within_bounds(int index) const { return 0 <= index && index < length(); } 93 94 // Accessors for instance variable which is not a C++ declared nonstatic 95 // field. 96 int length() const { 97 return *(int*)(((intptr_t)this) + length_offset_in_bytes()); 98 } 99 void set_length(int length) { 100 *(int*)(((intptr_t)this) + length_offset_in_bytes()) = length; 101 } 102 103 // Should only be called with constants as argument 104 // (will not constant fold otherwise) 105 // Returns the header size in words aligned to the requirements of the 106 // array object type. 107 static int header_size(BasicType type) { 108 size_t typesize_in_bytes = header_size_in_bytes(); 109 return (int)(element_type_should_be_aligned(type) 110 ? align_object_offset(typesize_in_bytes/HeapWordSize) 111 : typesize_in_bytes/HeapWordSize); 112 } 113 114 // Return the maximum length of an array of BasicType. The length can passed 115 // to typeArrayOop::object_size(scale, length, header_size) without causing an 116 // overflow. We also need to make sure that this will not overflow a size_t on 117 // 32 bit platforms when we convert it to a byte size. 118 static int32_t max_array_length(BasicType type) { 119 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 120 assert(type2aelembytes(type) != 0, "wrong type"); 121 122 const size_t max_element_words_per_size_t = 123 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment); 124 const size_t max_elements_per_size_t = 125 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type); 126 if ((size_t)max_jint < max_elements_per_size_t) { 127 // It should be ok to return max_jint here, but parts of the code 128 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 129 // passing around the size (in words) of an object. So, we need to avoid 130 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 131 return align_down(max_jint - header_size(type), MinObjAlignment); 132 } 133 return (int32_t)max_elements_per_size_t; 134 } 135 136 }; 137 138 #endif // SHARE_VM_OOPS_ARRAYOOP_HPP