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 107 // field. 108 int length() const { 109 return *(int*)(((intptr_t)this) + length_offset_in_bytes()); 110 } 111 void set_length(int length) { 112 set_length((HeapWord*)this, length); 113 } 114 static void set_length(HeapWord* mem, int length) { 115 *(int*)(((char*)mem) + length_offset_in_bytes()) = length; 116 } 117 118 // Should only be called with constants as argument 119 // (will not constant fold otherwise) 120 // Returns the header size in words aligned to the requirements of the 121 // array object type. 122 static int header_size(BasicType type) { 123 size_t typesize_in_bytes = header_size_in_bytes(); 124 return (int)(element_type_should_be_aligned(type) 125 ? align_object_offset(typesize_in_bytes/HeapWordSize) 126 : typesize_in_bytes/HeapWordSize); 127 } 128 129 // Return the maximum length of an array of BasicType. The length can passed 130 // to typeArrayOop::object_size(scale, length, header_size) without causing an 131 // overflow. We also need to make sure that this will not overflow a size_t on 132 // 32 bit platforms when we convert it to a byte size. 133 static int32_t max_array_length(BasicType type) { 134 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 135 assert(type2aelembytes(type) != 0, "wrong type"); 136 137 const size_t max_element_words_per_size_t = 138 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment); 139 const size_t max_elements_per_size_t = 140 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type); 141 if ((size_t)max_jint < max_elements_per_size_t) { 142 // It should be ok to return max_jint here, but parts of the code 143 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 144 // passing around the size (in words) of an object. So, we need to avoid 145 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 146 return align_down(max_jint - header_size(type), MinObjAlignment); | 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 protected: 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 || type == T_VALUETYPE; 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 107 // field. 108 int length() const { 109 return *(int*)(((intptr_t)this) + length_offset_in_bytes()); 110 } 111 void set_length(int length) { 112 set_length((HeapWord*)this, length); 113 } 114 static void set_length(HeapWord* mem, int length) { 115 *(int*)(((char*)mem) + length_offset_in_bytes()) = length; 116 } 117 118 // Should only be called with constants as argument 119 // (will not constant fold otherwise) 120 // Returns the header size in words aligned to the requirements of the 121 // array object type. 122 static int header_size(BasicType type) { 123 size_t typesize_in_bytes = header_size_in_bytes(); 124 return (int)(element_type_should_be_aligned(type) 125 ? align_object_offset(typesize_in_bytes/HeapWordSize) 126 : typesize_in_bytes/HeapWordSize); 127 } 128 129 static int32_t max_array_length(int header_size, int elembytes) { 130 const size_t max_element_words_per_size_t = 131 align_down((SIZE_MAX/HeapWordSize - header_size), MinObjAlignment); 132 const size_t max_elements_per_size_t = 133 HeapWordSize * max_element_words_per_size_t / elembytes; 134 if ((size_t)max_jint < max_elements_per_size_t) { 135 // It should be ok to return max_jint here, but parts of the code 136 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 137 // passing around the size (in words) of an object. So, we need to avoid 138 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 139 return align_down(max_jint - header_size, MinObjAlignment); 140 } 141 return (int32_t)max_elements_per_size_t; 142 } 143 144 // Return the maximum length of an array of BasicType. The length can passed 145 // to typeArrayOop::object_size(scale, length, header_size) without causing an 146 // overflow. We also need to make sure that this will not overflow a size_t on 147 // 32 bit platforms when we convert it to a byte size. 148 static int32_t max_array_length(BasicType type) { 149 assert(type >= 0 && type < T_CONFLICT, "wrong type"); 150 assert(type2aelembytes(type) != 0, "wrong type"); 151 152 const size_t max_element_words_per_size_t = 153 align_down((SIZE_MAX/HeapWordSize - header_size(type)), MinObjAlignment); 154 const size_t max_elements_per_size_t = 155 HeapWordSize * max_element_words_per_size_t / type2aelembytes(type); 156 if ((size_t)max_jint < max_elements_per_size_t) { 157 // It should be ok to return max_jint here, but parts of the code 158 // (CollectedHeap, Klass::oop_oop_iterate(), and more) uses an int for 159 // passing around the size (in words) of an object. So, we need to avoid 160 // overflowing an int when we add the header. See CRs 4718400 and 7110613. 161 return align_down(max_jint - header_size(type), MinObjAlignment); |