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