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