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 private:
52 enum {
53 checked_bits = 1,
54 instance_bits = 1,
55 address_bits = BitsPerWord - checked_bits - instance_bits,
56
57 large_offset_bits = address_bits, // unioned with address
58 small_offset_bits = 7,
59 klass_bits = address_bits - small_offset_bits,
60
61 checked_shift = 0,
62 instance_shift = checked_shift + checked_bits,
63 address_shift = instance_shift + instance_bits,
64
65 offset_shift = address_shift, // unioned with address
66 klass_shift = offset_shift + small_offset_bits,
67
68 checked_mask_in_place = right_n_bits(checked_bits) << checked_shift,
69 instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
70 #ifndef _WIN64
71 large_offset_mask = right_n_bits(large_offset_bits),
72 small_offset_mask = right_n_bits(small_offset_bits),
73 klass_mask = right_n_bits(klass_bits)
74 #endif
75 };
76
77 #ifdef _WIN64
78 // These values are too big for Win64
79 const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
80 const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
81 const static uintptr_t klass_mask = right_n_bits(klass_bits);
82 #endif
83
84 // helper routines:
85 static bool is_checked_jfieldID(jfieldID id) {
86 uintptr_t as_uint = (uintptr_t) id;
87 return ((as_uint & checked_mask_in_place) != 0);
88 }
89 static int raw_instance_offset(jfieldID id) {
90 uintptr_t result = (uintptr_t) id >> address_shift;
91 if (VerifyJNIFields && is_checked_jfieldID(id)) {
92 result &= small_offset_mask; // cut off the hash bits
93 }
94 // This gets back the InstanceKlass field offset that
95 // the jfieldID is created with.
96 return checked_cast<int>(result);
97 }
98 static intptr_t encode_klass_hash(Klass* k, int offset);
99 static bool klass_hash_ok(Klass* k, jfieldID id);
100 static void verify_instance_jfieldID(Klass* k, jfieldID id);
101
102 public:
103 static bool is_valid_jfieldID(Klass* k, jfieldID id);
104
105 static bool is_instance_jfieldID(Klass* k, jfieldID id) {
106 uintptr_t as_uint = (uintptr_t) id;
107 return ((as_uint & instance_mask_in_place) != 0);
108 }
109 static bool is_static_jfieldID(jfieldID id) {
110 uintptr_t as_uint = (uintptr_t) id;
111 return ((as_uint & instance_mask_in_place) == 0);
112 }
113
114 static jfieldID to_instance_jfieldID(Klass* k, int offset) {
115 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
116 if (VerifyJNIFields) {
117 as_uint |= encode_klass_hash(k, offset);
118 }
119 jfieldID result = (jfieldID) as_uint;
120 #ifndef ASSERT
121 // always verify in debug mode; switchable in anything else
122 if (VerifyJNIFields)
123 #endif // ASSERT
124 {
125 verify_instance_jfieldID(k, result);
126 }
127 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
128 return result;
129 }
130
131 static int from_instance_jfieldID(Klass* k, jfieldID id) {
132 #ifndef ASSERT
133 // always verify in debug mode; switchable in anything else
134 if (VerifyJNIFields)
135 #endif // ASSERT
136 {
137 verify_instance_jfieldID(k, id);
138 }
139 return raw_instance_offset(id);
140 }
141
142 static jfieldID to_static_jfieldID(JNIid* id) {
143 assert(id->is_static_field_id(), "from_JNIid, but not static field id");
144 jfieldID result = (jfieldID) id;
145 assert(from_static_jfieldID(result) == id, "must produce the same static id");
146 return result;
147 }
148
149 static JNIid* from_static_jfieldID(jfieldID id) {
150 assert(jfieldIDWorkaround::is_static_jfieldID(id),
151 "to_JNIid, but not static jfieldID");
152 JNIid* result = (JNIid*) id;
153 assert(result->is_static_field_id(), "to_JNIid, but not static field id");
154 return result;
155 }
156
157 static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static) {
158 if (is_static) {
159 JNIid *id = k->jni_id_for(offset);
160 debug_only(id->set_is_static_field_id());
161 return jfieldIDWorkaround::to_static_jfieldID(id);
162 } else {
163 return jfieldIDWorkaround::to_instance_jfieldID(k, offset);
164 }
165 }
166 };
167
168 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP