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