1 /* 2 * Copyright (c) 2002, 2019, 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 #include "precompiled.hpp" 26 #include "gc/parallel/mutableSpace.hpp" 27 #include "gc/shared/space.inline.hpp" 28 #include "gc/shared/spaceDecorator.inline.hpp" 29 #include "logging/log.hpp" 30 #include "utilities/copy.hpp" 31 32 // Catch-all file for utility classes 33 34 #ifndef PRODUCT 35 36 // Returns true is the location q matches the mangling 37 // pattern. 38 bool SpaceMangler::is_mangled(HeapWord* q) { 39 // This test loses precision but is good enough 40 return badHeapWord == (max_juint & reinterpret_cast<uintptr_t>(*q)); 41 } 42 43 44 void SpaceMangler::set_top_for_allocations(HeapWord* v) { 45 if (v < end()) { 46 assert(!CheckZapUnusedHeapArea || is_mangled(v), 47 "The high water mark is not mangled"); 48 } 49 _top_for_allocations = v; 50 } 51 52 // Mangle only the unused space that has not previously 53 // been mangled and that has not been allocated since being 54 // mangled. 55 void SpaceMangler::mangle_unused_area() { 56 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 57 // Mangle between top and the high water mark. Safeguard 58 // against the space changing since top_for_allocations was 59 // set. 60 HeapWord* mangled_end = MIN2(top_for_allocations(), end()); 61 if (top() < mangled_end) { 62 MemRegion mangle_mr(top(), mangled_end); 63 SpaceMangler::mangle_region(mangle_mr); 64 // Light weight check of mangling. 65 check_mangled_unused_area(end()); 66 } 67 // Complete check of unused area which is functional when 68 // DEBUG_MANGLING is defined. 69 check_mangled_unused_area_complete(); 70 } 71 72 // A complete mangle is expected in the 73 // exceptional case where top_for_allocations is not 74 // properly tracking the high water mark for mangling. 75 // This can be the case when to-space is being used for 76 // scratch space during a mark-sweep-compact. See 77 // contribute_scratch() and PSMarkSweep::allocate_stacks(). 78 void SpaceMangler::mangle_unused_area_complete() { 79 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 80 MemRegion mangle_mr(top(), end()); 81 SpaceMangler::mangle_region(mangle_mr); 82 } 83 84 // Simply mangle the MemRegion mr. 85 void SpaceMangler::mangle_region(MemRegion mr) { 86 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 87 #ifdef ASSERT 88 Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord); 89 #endif 90 } 91 92 // Check that top, top_for_allocations and the last 93 // word of the space are mangled. In a tight memory 94 // situation even this light weight mangling could 95 // cause paging by touching the end of the space. 96 void SpaceMangler::check_mangled_unused_area(HeapWord* limit) { 97 if (CheckZapUnusedHeapArea) { 98 // This method can be called while the spaces are 99 // being reshaped so skip the test if the end of the 100 // space is beyond the specified limit; 101 if (end() > limit) return; 102 103 assert(top() == end() || 104 (is_mangled(top())), "Top not mangled"); 105 assert((top_for_allocations() < top()) || 106 (top_for_allocations() >= end()) || 107 (is_mangled(top_for_allocations())), 108 "Older unused not mangled"); 109 assert(top() == end() || 110 (is_mangled(end() - 1)), "End not properly mangled"); 111 // Only does checking when DEBUG_MANGLING is defined. 112 check_mangled_unused_area_complete(); 113 } 114 } 115 116 #undef DEBUG_MANGLING 117 // This should only be used while debugging the mangling 118 // because of the high cost of checking the completeness. 119 void SpaceMangler::check_mangled_unused_area_complete() { 120 if (CheckZapUnusedHeapArea) { 121 assert(ZapUnusedHeapArea, "Not mangling unused area"); 122 #ifdef DEBUG_MANGLING 123 HeapWord* q = top(); 124 HeapWord* limit = end(); 125 126 bool passed = true; 127 while (q < limit) { 128 if (!is_mangled(q)) { 129 passed = false; 130 break; 131 } 132 q++; 133 } 134 assert(passed, "Mangling is not complete"); 135 #endif 136 } 137 } 138 #undef DEBUG_MANGLING 139 #endif // not PRODUCT