1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 < 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