1 /* 2 * Copyright (c) 1997, 2023, 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_OOPS_ARRAYOOP_HPP 26 #define SHARE_OOPS_ARRAYOOP_HPP 27 28 #include "oops/oop.hpp" 29 #include "utilities/align.hpp" 30 31 // arrayOopDesc is the abstract baseclass for all arrays. It doesn't 32 // declare pure virtual to enforce this because that would allocate a vtbl 33 // in each instance, which we don't want. 34 35 // The layout of array Oops is: 36 // 37 // markWord 38 // Klass* // 32 bits if compressed but declared 64 in LP64. 39 // length // shares klass memory or allocated after declared fields. 40 41 42 class arrayOopDesc : public oopDesc { 43 friend class VMStructs; 44 friend class arrayOopDescTest; 45 46 // Interpreter/Compiler offsets 47 48 // Header size computation. 49 // The header is considered the oop part of this type plus the length. 50 // Returns the aligned header_size_in_bytes. This is not equivalent to 51 // sizeof(arrayOopDesc) which should not appear in the code. 52 static int header_size_in_bytes() { 53 size_t hs = align_up(length_offset_in_bytes() + sizeof(int), 54 HeapWordSize); 55 #ifdef ASSERT 56 // make sure it isn't called before UseCompressedOops is initialized. 57 static size_t arrayoopdesc_hs = 0; 58 if (arrayoopdesc_hs == 0) arrayoopdesc_hs = hs; 59 assert(arrayoopdesc_hs == hs, "header size can't change"); 60 #endif // ASSERT 61 return (int)hs; 62 } 63 64 // Returns the address of the length "field". See length_offset_in_bytes(). 65 static int* length_addr_impl(void* obj_ptr) { 66 char* ptr = static_cast<char*>(obj_ptr); 67 return reinterpret_cast<int*>(ptr + length_offset_in_bytes()); 68 } 69 70 // Check whether an element of a typeArrayOop with the given type must be 71 // aligned 0 mod 8. The typeArrayOop itself must be aligned at least this 72 // strongly. 73 static bool element_type_should_be_aligned(BasicType type) { 74 return type == T_DOUBLE || type == T_LONG; 75 } 76 77 public: 78 // The _length field is not declared in C++. It is allocated after the 79 // declared nonstatic fields in arrayOopDesc if not compressed, otherwise 80 // it occupies the second half of the _klass field in oopDesc. 81 static int length_offset_in_bytes() { 82 return UseCompressedClassPointers ? klass_gap_offset_in_bytes() : 83 sizeof(arrayOopDesc); 84 } 85 86 // Returns the offset of the first element. 87 static int base_offset_in_bytes(BasicType type) { 88 return header_size(type) * HeapWordSize; 89 } 90 91 // Returns the address of the first element. The elements in the array will not 92 // relocate from this address until a subsequent thread transition. 93 void* base(BasicType type) const { 94 return reinterpret_cast<void*>(cast_from_oop<intptr_t>(as_oop()) + base_offset_in_bytes(type)); 95 } 96 97 template <typename T> 98 static T* obj_offset_to_raw(arrayOop obj, size_t offset_in_bytes, T* raw) { 99 if (obj != nullptr) { 100 assert(raw == nullptr, "either raw or in-heap"); 101 char* base = reinterpret_cast<char*>((void*) obj); 102 raw = reinterpret_cast<T*>(base + offset_in_bytes); 103 } else { 104 assert(raw != nullptr, "either raw or in-heap"); 105 } 106 return raw; 107 } 108 109 // Tells whether index is within bounds. 110 bool is_within_bounds(int index) const { return 0 <= index && index < length(); } 111 112 // Accessors for array length. There's not a member variable for 113 // it; see length_offset_in_bytes(). 114 int length() const { return *length_addr_impl(const_cast<arrayOopDesc*>(this)); } 115 void set_length(int length) { *length_addr_impl(this) = length; } 116 117 int* length_addr() { 118 return length_addr_impl(this); 119 } 120 121 static void set_length(HeapWord* mem, int length) { 122 *length_addr_impl(mem) = length; 123 } 124 125 // Should only be called with constants as argument 126 // (will not constant fold otherwise) 127 // Returns the header size in words aligned to the requirements of the 128 // array object type. 129 static int header_size(BasicType type) { 130 size_t typesize_in_bytes = header_size_in_bytes(); 131 return (int)(element_type_should_be_aligned(type) 132 ? align_object_offset(typesize_in_bytes/HeapWordSize) 133 : typesize_in_bytes/HeapWordSize); 134 } 135 136 // Return the maximum length of an array of BasicType. The length can passed 137 // to typeArrayOop::object_size(scale, length, header_size) without causing an 138 // overflow. We also need to make sure that this will not overflow a size_t on 139 // 32 bit platforms when we convert it to a byte size. 140 static int32_t max_array_length(BasicType type) { 141 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 142 assert(type2aelembytes(type) != 0, "wrong type"); 143 144 const size_t max_element_words_per_size_t = 145 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment); 146 const size_t max_elements_per_size_t = 147 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type); 148 if ((size_t)max_jint < max_elements_per_size_t) { 149 // It should be ok to return max_jint here, but parts of the code 150 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 151 // passing around the size (in words) of an object. So, we need to avoid 152 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 153 return align_down(max_jint - header_size(type), MinObjAlignment); 154 } 155 return (int32_t)max_elements_per_size_t; 156 } 157 158 }; 159 160 #endif // SHARE_OOPS_ARRAYOOP_HPP --- EOF ---