1 /* 2 * Copyright (c) 2001, 2005, 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 // 26 // This class can be used to locate the beginning of an object in the 27 // covered region. 28 // 29 30 class ObjectStartArray : public CHeapObj { 31 friend class VerifyObjectStartArrayClosure; 32 33 private: 34 PSVirtualSpace _virtual_space; 35 MemRegion _reserved_region; 36 MemRegion _covered_region; 37 MemRegion _blocks_region; 38 jbyte* _raw_base; 39 jbyte* _offset_base; 40 41 public: 42 43 enum BlockValueConstants { 44 clean_block = -1 45 }; 46 47 enum BlockSizeConstants { 48 block_shift = 9, 49 block_size = 1 << block_shift, 50 block_size_in_words = block_size / sizeof(HeapWord) 51 }; 52 53 protected: 54 55 // Mapping from address to object start array entry 56 jbyte* block_for_addr(void* p) const { 57 assert(_covered_region.contains(p), 58 "out of bounds access to object start array"); 59 jbyte* result = &_offset_base[uintptr_t(p) >> block_shift]; 60 assert(_blocks_region.contains(result), 61 "out of bounds result in byte_for"); 62 return result; 63 } 64 65 // Mapping from object start array entry to address of first word 66 HeapWord* addr_for_block(jbyte* p) { 67 assert(_blocks_region.contains(p), 68 "out of bounds access to object start array"); 69 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte)); 70 HeapWord* result = (HeapWord*) (delta << block_shift); 71 assert(_covered_region.contains(result), 72 "out of bounds accessor from card marking array"); 73 return result; 74 } 75 76 // Mapping that includes the derived offset. 77 // If the block is clean, returns the last address in the covered region. 78 // If the block is < index 0, returns the start of the covered region. 79 HeapWord* offset_addr_for_block (jbyte* p) const { 80 // We have to do this before the assert 81 if (p < _raw_base) { 82 return _covered_region.start(); 83 } 84 85 assert(_blocks_region.contains(p), 86 "out of bounds access to object start array"); 87 88 if (*p == clean_block) { 89 return _covered_region.end(); 90 } 91 92 size_t delta = pointer_delta(p, _offset_base, sizeof(jbyte)); 93 HeapWord* result = (HeapWord*) (delta << block_shift); 94 result += *p; 95 96 assert(_covered_region.contains(result), 97 "out of bounds accessor from card marking array"); 98 99 return result; 100 } 101 102 public: 103 104 // This method is in lieu of a constructor, so that this class can be 105 // embedded inline in other classes. 106 void initialize(MemRegion reserved_region); 107 108 void set_covered_region(MemRegion mr); 109 110 void reset(); 111 112 MemRegion covered_region() { return _covered_region; } 113 114 void allocate_block(HeapWord* p) { 115 assert(_covered_region.contains(p), "Must be in covered region"); 116 jbyte* block = block_for_addr(p); 117 HeapWord* block_base = addr_for_block(block); 118 size_t offset = pointer_delta(p, block_base, sizeof(HeapWord*)); 119 assert(offset < 128, "Sanity"); 120 // When doing MT offsets, we can't assert this. 121 //assert(offset > *block, "Found backwards allocation"); 122 *block = (jbyte)offset; 123 124 // tty->print_cr("[%p]", p); 125 } 126 127 // Optimized for finding the first object that crosses into 128 // a given block. The blocks contain the offset of the last 129 // object in that block. Scroll backwards by one, and the first 130 // object hit should be at the beginning of the block 131 HeapWord* object_start(HeapWord* addr) const { 132 assert(_covered_region.contains(addr), "Must be in covered region"); 133 jbyte* block = block_for_addr(addr); 134 HeapWord* scroll_forward = offset_addr_for_block(block--); 135 while (scroll_forward > addr) { 136 scroll_forward = offset_addr_for_block(block--); 137 } 138 139 HeapWord* next = scroll_forward; 140 while (next <= addr) { 141 scroll_forward = next; 142 next += oop(next)->size(); 143 } 144 assert(scroll_forward <= addr, "wrong order for current and arg"); 145 assert(addr <= next, "wrong order for arg and next"); 146 return scroll_forward; 147 } 148 149 bool is_block_allocated(HeapWord* addr) { 150 assert(_covered_region.contains(addr), "Must be in covered region"); 151 jbyte* block = block_for_addr(addr); 152 if (*block == clean_block) 153 return false; 154 155 return true; 156 } 157 158 // Return true if an object starts in the range of heap addresses. 159 // If an object starts at an address corresponding to 160 // "start", the method will return true. 161 bool object_starts_in_range(HeapWord* start_addr, HeapWord* end_addr) const; 162 };