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.
37bool 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
43void 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.
54void 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().
77void 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.
84void 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.
95void 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.
118void 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
139