1 /*
2 * Copyright (c) 2003, 2005, 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 class jfieldIDWorkaround: AllStatic {
26 // This workaround is because JVMTI doesn't have distinct entry points
27 // for methods that use static jfieldIDs and instance jfieldIDs.
28 // The workaround is to steal a low-order bit:
29 // a 1 means the jfieldID is an instance jfieldID,
30 // and the rest of the word is the offset of the field.
31 // a 0 means the jfieldID is a static jfieldID,
32 // and the rest of the word is the JNIid*.
33 //
34 // Another low-order bit is used to mark if an instance field
35 // is accompanied by an indication of which class it applies to.
36 //
37 // Bit-format of a jfieldID (most significant first):
38 // address:30 instance=0:1 checked=0:1
39 // offset:30 instance=1:1 checked=0:1
40 // klass:23 offset:7 instance=1:1 checked=1:1
41 //
42 // If the offset does not fit in 7 bits, or if the fieldID is
43 // not checked, then the checked bit is zero and the rest of
44 // the word (30 bits) contains only the offset.
45 //
46 private:
47 enum {
48 checked_bits = 1,
49 instance_bits = 1,
50 address_bits = BitsPerWord - checked_bits - instance_bits,
51
52 large_offset_bits = address_bits, // unioned with address
53 small_offset_bits = 7,
54 klass_bits = address_bits - small_offset_bits,
55
56 checked_shift = 0,
57 instance_shift = checked_shift + checked_bits,
58 address_shift = instance_shift + instance_bits,
59
60 offset_shift = address_shift, // unioned with address
61 klass_shift = offset_shift + small_offset_bits,
62
63 checked_mask_in_place = right_n_bits(checked_bits) << checked_shift,
64 instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
65 #ifndef _WIN64
66 large_offset_mask = right_n_bits(large_offset_bits),
67 small_offset_mask = right_n_bits(small_offset_bits),
68 klass_mask = right_n_bits(klass_bits)
69 #endif
70 };
71
72 #ifdef _WIN64
73 // These values are too big for Win64
74 const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
75 const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
76 const static uintptr_t klass_mask = right_n_bits(klass_bits);
77 #endif
78
79 // helper routines:
80 static bool is_checked_jfieldID(jfieldID id) {
81 uintptr_t as_uint = (uintptr_t) id;
82 return ((as_uint & checked_mask_in_place) != 0);
83 }
84 static intptr_t raw_instance_offset(jfieldID id) {
85 uintptr_t result = (uintptr_t) id >> address_shift;
86 if (VerifyJNIFields && is_checked_jfieldID(id)) {
87 result &= small_offset_mask; // cut off the hash bits
88 }
89 return (intptr_t)result;
90 }
91 static intptr_t encode_klass_hash(klassOop k, intptr_t offset);
92 static bool klass_hash_ok(klassOop k, jfieldID id);
93 static void verify_instance_jfieldID(klassOop k, jfieldID id);
94
95 public:
96 static bool is_valid_jfieldID(klassOop k, jfieldID id);
97
98 static bool is_instance_jfieldID(klassOop k, jfieldID id) {
99 uintptr_t as_uint = (uintptr_t) id;
100 return ((as_uint & instance_mask_in_place) != 0);
101 }
102 static bool is_static_jfieldID(jfieldID id) {
103 uintptr_t as_uint = (uintptr_t) id;
104 return ((as_uint & instance_mask_in_place) == 0);
105 }
106
107 static jfieldID to_instance_jfieldID(klassOop k, int offset) {
108 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
109 if (VerifyJNIFields) {
110 as_uint |= encode_klass_hash(k, offset);
111 }
112 jfieldID result = (jfieldID) as_uint;
113 #ifndef ASSERT
114 // always verify in debug mode; switchable in anything else
115 if (VerifyJNIFields)
116 #endif // ASSERT
117 {
118 verify_instance_jfieldID(k, result);
119 }
120 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
121 return result;
122 }
123
124 static intptr_t from_instance_jfieldID(klassOop k, jfieldID id) {
125 #ifndef ASSERT
126 // always verify in debug mode; switchable in anything else
127 if (VerifyJNIFields)
128 #endif // ASSERT
129 {
130 verify_instance_jfieldID(k, id);
131 }
132 return raw_instance_offset(id);
133 }
134
135 static jfieldID to_static_jfieldID(JNIid* id) {
136 assert(id->is_static_field_id(), "from_JNIid, but not static field id");
137 jfieldID result = (jfieldID) id;
138 assert(from_static_jfieldID(result) == id, "must produce the same static id");
139 return result;
140 }
141
142 static JNIid* from_static_jfieldID(jfieldID id) {
143 assert(jfieldIDWorkaround::is_static_jfieldID(id),
144 "to_JNIid, but not static jfieldID");
145 JNIid* result = (JNIid*) id;
146 assert(result->is_static_field_id(), "to_JNIid, but not static field id");
147 return result;
148 }
149
150 static jfieldID to_jfieldID(instanceKlassHandle k, int offset, bool is_static) {
151 if (is_static) {
152 JNIid *id = k->jni_id_for(offset);
153 debug_only(id->set_is_static_field_id());
154 return jfieldIDWorkaround::to_static_jfieldID(id);
155 } else {
156 return jfieldIDWorkaround::to_instance_jfieldID(k(), offset);
157 }
158 }
159 };