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1 /*
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2 * Copyright 2003-2005 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 class jfieldIDWorkaround: AllStatic {
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26 // This workaround is because JVMTI doesn't have distinct entry points
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27 // for methods that use static jfieldIDs and instance jfieldIDs.
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28 // The workaround is to steal a low-order bit:
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29 // a 1 means the jfieldID is an instance jfieldID,
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30 // and the rest of the word is the offset of the field.
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31 // a 0 means the jfieldID is a static jfieldID,
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32 // and the rest of the word is the JNIid*.
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33 //
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34 // Another low-order bit is used to mark if an instance field
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35 // is accompanied by an indication of which class it applies to.
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36 //
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37 // Bit-format of a jfieldID (most significant first):
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38 // address:30 instance=0:1 checked=0:1
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39 // offset:30 instance=1:1 checked=0:1
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40 // klass:23 offset:7 instance=1:1 checked=1:1
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41 //
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42 // If the offset does not fit in 7 bits, or if the fieldID is
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43 // not checked, then the checked bit is zero and the rest of
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44 // the word (30 bits) contains only the offset.
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45 //
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46 private:
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47 enum {
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48 checked_bits = 1,
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49 instance_bits = 1,
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50 address_bits = BitsPerWord - checked_bits - instance_bits,
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51
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52 large_offset_bits = address_bits, // unioned with address
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53 small_offset_bits = 7,
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54 klass_bits = address_bits - small_offset_bits,
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55
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56 checked_shift = 0,
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57 instance_shift = checked_shift + checked_bits,
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58 address_shift = instance_shift + instance_bits,
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59
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60 offset_shift = address_shift, // unioned with address
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61 klass_shift = offset_shift + small_offset_bits,
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62
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63 checked_mask_in_place = right_n_bits(checked_bits) << checked_shift,
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64 instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
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65 #ifndef _WIN64
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66 large_offset_mask = right_n_bits(large_offset_bits),
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67 small_offset_mask = right_n_bits(small_offset_bits),
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68 klass_mask = right_n_bits(klass_bits)
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69 #endif
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70 };
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71
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72 #ifdef _WIN64
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73 // These values are too big for Win64
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74 const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
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75 const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
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76 const static uintptr_t klass_mask = right_n_bits(klass_bits);
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77 #endif
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78
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79 // helper routines:
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80 static bool is_checked_jfieldID(jfieldID id) {
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81 uintptr_t as_uint = (uintptr_t) id;
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82 return ((as_uint & checked_mask_in_place) != 0);
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83 }
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84 static intptr_t raw_instance_offset(jfieldID id) {
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85 uintptr_t result = (uintptr_t) id >> address_shift;
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86 if (VerifyJNIFields && is_checked_jfieldID(id)) {
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87 result &= small_offset_mask; // cut off the hash bits
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88 }
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89 return (intptr_t)result;
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90 }
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91 static intptr_t encode_klass_hash(klassOop k, intptr_t offset);
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92 static bool klass_hash_ok(klassOop k, jfieldID id);
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93 static void verify_instance_jfieldID(klassOop k, jfieldID id);
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94
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95 public:
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96 static bool is_valid_jfieldID(klassOop k, jfieldID id);
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97
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98 static bool is_instance_jfieldID(klassOop k, jfieldID id) {
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99 uintptr_t as_uint = (uintptr_t) id;
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100 return ((as_uint & instance_mask_in_place) != 0);
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101 }
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102 static bool is_static_jfieldID(jfieldID id) {
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103 uintptr_t as_uint = (uintptr_t) id;
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104 return ((as_uint & instance_mask_in_place) == 0);
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105 }
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106
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107 static jfieldID to_instance_jfieldID(klassOop k, int offset) {
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108 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
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109 if (VerifyJNIFields) {
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110 as_uint |= encode_klass_hash(k, offset);
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111 }
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112 jfieldID result = (jfieldID) as_uint;
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113 #ifndef ASSERT
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114 // always verify in debug mode; switchable in anything else
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115 if (VerifyJNIFields)
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116 #endif // ASSERT
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117 {
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118 verify_instance_jfieldID(k, result);
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119 }
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120 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
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121 return result;
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122 }
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123
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124 static intptr_t from_instance_jfieldID(klassOop k, jfieldID id) {
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125 #ifndef ASSERT
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126 // always verify in debug mode; switchable in anything else
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127 if (VerifyJNIFields)
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128 #endif // ASSERT
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129 {
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130 verify_instance_jfieldID(k, id);
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131 }
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132 return raw_instance_offset(id);
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133 }
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134
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135 static jfieldID to_static_jfieldID(JNIid* id) {
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136 assert(id->is_static_field_id(), "from_JNIid, but not static field id");
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137 jfieldID result = (jfieldID) id;
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138 assert(from_static_jfieldID(result) == id, "must produce the same static id");
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139 return result;
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140 }
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141
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142 static JNIid* from_static_jfieldID(jfieldID id) {
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143 assert(jfieldIDWorkaround::is_static_jfieldID(id),
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144 "to_JNIid, but not static jfieldID");
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145 JNIid* result = (JNIid*) id;
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146 assert(result->is_static_field_id(), "to_JNIid, but not static field id");
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147 return result;
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148 }
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149
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150 static jfieldID to_jfieldID(instanceKlassHandle k, int offset, bool is_static) {
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151 if (is_static) {
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152 JNIid *id = k->jni_id_for(offset);
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153 debug_only(id->set_is_static_field_id());
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154 return jfieldIDWorkaround::to_static_jfieldID(id);
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155 } else {
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156 return jfieldIDWorkaround::to_instance_jfieldID(k(), offset);
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157 }
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158 }
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159 };
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