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.
is_mangled(HeapWord * q)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
set_top_for_allocations(HeapWord * v)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.
mangle_unused_area()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().
mangle_unused_area_complete()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.
mangle_region(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.
check_mangled_unused_area(HeapWord * limit)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.
check_mangled_unused_area_complete()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
140