1 /*
2 * Copyright (c) 2003, 2023, 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.
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23 */
24
25 #ifndef SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP
26 #define SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP
27
28 #include "utilities/checkedCast.hpp"
29
30 class jfieldIDWorkaround: AllStatic {
31 // This workaround is because JVMTI doesn't have distinct entry points
32 // for methods that use static jfieldIDs and instance jfieldIDs.
33 // The workaround is to steal a low-order bit:
34 // a 1 means the jfieldID is an instance jfieldID,
35 // and the rest of the word is the offset of the field.
36 // a 0 means the jfieldID is a static jfieldID,
37 // and the rest of the word is the JNIid*.
38 //
39 // Another low-order bit is used to mark if an instance field
40 // is accompanied by an indication of which class it applies to.
41 //
42 // Bit-format of a jfieldID (most significant first):
43 // address:30 instance=0:1 checked=0:1
44 // offset:30 instance=1:1 checked=0:1
45 // klass:23 offset:7 instance=1:1 checked=1:1
46 //
47 // If the offset does not fit in 7 bits, or if the fieldID is
48 // not checked, then the checked bit is zero and the rest of
49 // the word (30 bits) contains only the offset.
50 //
51
52 friend class JNI_FastGetField;
53
54 private:
55 enum {
56 checked_bits = 1,
57 instance_bits = 1,
58 flat_bits = 1,
59 address_bits = BitsPerWord - checked_bits - instance_bits - flat_bits,
60
61 large_offset_bits = address_bits, // unioned with address
62 small_offset_bits = 7,
63 klass_bits = address_bits - small_offset_bits,
64
65 checked_shift = 0,
66 instance_shift = checked_shift + checked_bits,
67 flat_shift = instance_shift + instance_bits,
68 address_shift = flat_shift + flat_bits,
69
70 offset_shift = address_shift, // unioned with address
71 klass_shift = offset_shift + small_offset_bits,
72
73 checked_mask_in_place = right_n_bits(checked_bits) << checked_shift,
74 instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
75 flat_mask_in_place = right_n_bits(flat_bits) << flat_shift,
76 #ifndef _WIN64
77 large_offset_mask = right_n_bits(large_offset_bits),
78 small_offset_mask = right_n_bits(small_offset_bits),
79 klass_mask = right_n_bits(klass_bits)
80 #endif
81 };
82
83 #ifdef _WIN64
84 // These values are too big for Win64
85 const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
86 const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
87 const static uintptr_t klass_mask = right_n_bits(klass_bits);
88 #endif
89
90 // helper routines:
91 static bool is_checked_jfieldID(jfieldID id) {
92 uintptr_t as_uint = (uintptr_t) id;
93 return ((as_uint & checked_mask_in_place) != 0);
94 }
95 static int raw_instance_offset(jfieldID id) {
96 uintptr_t result = (uintptr_t) id >> address_shift;
97 if (VerifyJNIFields && is_checked_jfieldID(id)) {
98 result &= small_offset_mask; // cut off the hash bits
99 }
100 // This gets back the InstanceKlass field offset that
101 // the jfieldID is created with.
102 return checked_cast<int>(result);
103 }
104 static intptr_t encode_klass_hash(Klass* k, int offset);
105 static bool klass_hash_ok(Klass* k, jfieldID id);
106 static void verify_instance_jfieldID(Klass* k, jfieldID id);
107
108 public:
109 static bool is_valid_jfieldID(Klass* k, jfieldID id);
110
111 static bool is_instance_jfieldID(Klass* k, jfieldID id) {
112 uintptr_t as_uint = (uintptr_t) id;
113 return ((as_uint & instance_mask_in_place) != 0);
114 }
115 static bool is_static_jfieldID(jfieldID id) {
116 uintptr_t as_uint = (uintptr_t) id;
117 return ((as_uint & instance_mask_in_place) == 0);
118 }
119
120 static bool is_flat_jfieldID(jfieldID id) {
121 uintptr_t as_uint = (uintptr_t) id;
122 return ((as_uint & flat_mask_in_place) != 0);
123 }
124
125 static jfieldID to_instance_jfieldID(Klass* k, int offset, bool is_flat) {
126 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) |
127 instance_mask_in_place;
128 if (is_flat) {
129 as_uint |= flat_mask_in_place;
130 }
131 if (VerifyJNIFields) {
132 as_uint |= encode_klass_hash(k, offset);
133 }
134 jfieldID result = (jfieldID) as_uint;
135 #ifndef ASSERT
136 // always verify in debug mode; switchable in anything else
137 if (VerifyJNIFields)
138 #endif // ASSERT
139 {
140 verify_instance_jfieldID(k, result);
141 }
142 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
143 return result;
144 }
145
146 static int from_instance_jfieldID(Klass* k, jfieldID id) {
147 #ifndef ASSERT
148 // always verify in debug mode; switchable in anything else
149 if (VerifyJNIFields)
150 #endif // ASSERT
151 {
152 verify_instance_jfieldID(k, id);
153 }
154 return raw_instance_offset(id);
155 }
156
157 static jfieldID to_static_jfieldID(JNIid* id) {
158 assert(id->is_static_field_id(), "from_JNIid, but not static field id");
159 jfieldID result = (jfieldID) id;
160 assert(from_static_jfieldID(result) == id, "must produce the same static id");
161 return result;
162 }
163
164 static JNIid* from_static_jfieldID(jfieldID id) {
165 assert(jfieldIDWorkaround::is_static_jfieldID(id),
166 "to_JNIid, but not static jfieldID");
167 JNIid* result = (JNIid*) id;
168 assert(result->is_static_field_id(), "to_JNIid, but not static field id");
169 return result;
170 }
171
172 static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static, bool is_flat) {
173 if (is_static) {
174 JNIid *id = k->jni_id_for(offset);
175 debug_only(id->set_is_static_field_id());
176 return jfieldIDWorkaround::to_static_jfieldID(id);
177 } else {
178 return jfieldIDWorkaround::to_instance_jfieldID(k, offset, is_flat);
179 }
180 }
181 };
182
183 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP