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. 22 * 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 flattened_bits = 1, 57 address_bits = BitsPerWord - checked_bits - instance_bits - flattened_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 flattened_shift = instance_shift + instance_bits, 66 address_shift = flattened_shift + flattened_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 flattened_mask_in_place = right_n_bits(flattened_bits) << flattened_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_flattened_field(jfieldID id) { 117 uintptr_t as_uint = (uintptr_t) id; 118 return ((as_uint & flattened_mask_in_place) != 0); 119 } 120 121 static jfieldID to_instance_jfieldID(Klass* k, int offset, bool flattened) { 122 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | 123 (flattened ? flattened_mask_in_place : 0) | 124 instance_mask_in_place; 125 if (VerifyJNIFields) { 126 as_uint |= encode_klass_hash(k, offset); 127 } 128 jfieldID result = (jfieldID) as_uint; 129 #ifndef ASSERT 130 // always verify in debug mode; switchable in anything else 131 if (VerifyJNIFields) 132 #endif // ASSERT 133 { 134 verify_instance_jfieldID(k, result); 135 } 136 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset"); 137 return result; 138 } 139 140 static intptr_t from_instance_jfieldID(Klass* k, jfieldID id) { 141 #ifndef ASSERT 142 // always verify in debug mode; switchable in anything else 143 if (VerifyJNIFields) 144 #endif // ASSERT 145 { 146 verify_instance_jfieldID(k, id); 147 } 148 return raw_instance_offset(id); 149 } 150 151 static jfieldID to_static_jfieldID(JNIid* id) { 152 assert(id->is_static_field_id(), "from_JNIid, but not static field id"); 153 jfieldID result = (jfieldID) id; 154 assert(from_static_jfieldID(result) == id, "must produce the same static id"); 155 return result; 156 } 157 158 static JNIid* from_static_jfieldID(jfieldID id) { 159 assert(jfieldIDWorkaround::is_static_jfieldID(id), 160 "to_JNIid, but not static jfieldID"); 161 JNIid* result = (JNIid*) id; 162 assert(result->is_static_field_id(), "to_JNIid, but not static field id"); 163 return result; 164 } 165 166 static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static, bool is_flattened) { 167 if (is_static) { 168 JNIid *id = k->jni_id_for(offset); 169 debug_only(id->set_is_static_field_id()); 170 return jfieldIDWorkaround::to_static_jfieldID(id); 171 } else { 172 return jfieldIDWorkaround::to_instance_jfieldID(k, offset, is_flattened); 173 } 174 } 175 }; 176 177 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP