1 /* 2 * Copyright (c) 2002, 2015, 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 "utilities/copy.hpp" 29 30 // Catch-all file for utility classes 31 32 #ifndef PRODUCT 33 34 // Returns true is the location q matches the mangling 35 // pattern. 36 bool SpaceMangler::is_mangled(HeapWord* q) { 37 // This test loses precision but is good enough 38 return badHeapWord == (max_juint & (uintptr_t) q->value()); 39 } 40 41 42 void SpaceMangler::set_top_for_allocations(HeapWord* v) { 43 if (v < end()) { 44 assert(!CheckZapUnusedHeapArea || is_mangled(v), 45 "The high water mark is not mangled"); 46 } 47 _top_for_allocations = v; 48 } 49 50 // Mangle only the unused space that has not previously 51 // been mangled and that has not been allocated since being 52 // mangled. 53 void SpaceMangler::mangle_unused_area() { 54 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 55 // Mangle between top and the high water mark. Safeguard 56 // against the space changing since top_for_allocations was 57 // set. 58 HeapWord* mangled_end = MIN2(top_for_allocations(), end()); 59 if (top() < mangled_end) { 60 MemRegion mangle_mr(top(), mangled_end); 61 SpaceMangler::mangle_region(mangle_mr); 62 // Light weight check of mangling. 63 check_mangled_unused_area(end()); 64 } 65 // Complete check of unused area which is functional when 66 // DEBUG_MANGLING is defined. 67 check_mangled_unused_area_complete(); 68 } 69 70 // A complete mangle is expected in the 71 // exceptional case where top_for_allocations is not 72 // properly tracking the high water mark for mangling. 73 // This can be the case when to-space is being used for 74 // scratch space during a mark-sweep-compact. See 75 // contribute_scratch() and PSMarkSweep::allocate_stacks(). 76 void SpaceMangler::mangle_unused_area_complete() { 77 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 78 MemRegion mangle_mr(top(), end()); 79 SpaceMangler::mangle_region(mangle_mr); 80 } 81 82 // Simply mangle the MemRegion mr. 83 void SpaceMangler::mangle_region(MemRegion mr) { 84 assert(ZapUnusedHeapArea, "Mangling should not be in use"); 85 #ifdef ASSERT 86 if(TraceZapUnusedHeapArea) { 87 gclog_or_tty->print("Mangling [" PTR_FORMAT " to " PTR_FORMAT ")", p2i(mr.start()), p2i(mr.end())); 88 } 89 Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord); 90 if(TraceZapUnusedHeapArea) { 91 gclog_or_tty->print_cr(" done"); 92 } 93 #endif 94 } 95 96 // Check that top, top_for_allocations and the last 97 // word of the space are mangled. In a tight memory 98 // situation even this light weight mangling could 99 // cause paging by touching the end of the space. 100 void SpaceMangler::check_mangled_unused_area(HeapWord* limit) { 101 if (CheckZapUnusedHeapArea) { 102 // This method can be called while the spaces are 103 // being reshaped so skip the test if the end of the 104 // space is beyond the specified limit; 105 if (end() > limit) return; 106 107 assert(top() == end() || 108 (is_mangled(top())), "Top not mangled"); 109 assert((top_for_allocations() < top()) || 110 (top_for_allocations() >= end()) || 111 (is_mangled(top_for_allocations())), 112 "Older unused not mangled"); 113 assert(top() == end() || 114 (is_mangled(end() - 1)), "End not properly mangled"); 115 // Only does checking when DEBUG_MANGLING is defined. 116 check_mangled_unused_area_complete(); 117 } 118 } 119 120 #undef DEBUG_MANGLING 121 // This should only be used while debugging the mangling 122 // because of the high cost of checking the completeness. 123 void SpaceMangler::check_mangled_unused_area_complete() { 124 if (CheckZapUnusedHeapArea) { 125 assert(ZapUnusedHeapArea, "Not mangling unused area"); 126 #ifdef DEBUG_MANGLING 127 HeapWord* q = top(); 128 HeapWord* limit = end(); 129 130 bool passed = true; 131 while (q < limit) { 132 if (!is_mangled(q)) { 133 passed = false; 134 break; 135 } 136 q++; 137 } 138 assert(passed, "Mangling is not complete"); 139 #endif 140 } 141 } 142 #undef DEBUG_MANGLING 143 #endif // not PRODUCT