1 /* 2 * Copyright (c) 2003, 2023, 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 #include "utilities/checkedCast.hpp" 29 30 class jfieldIDWorkaround: AllStatic { 31 // This workaround is because JVMTI doesn't have distinct entry points 32 // for methods that use static jfieldIDs and instance jfieldIDs. 33 // The workaround is to steal a low-order bit: 34 // a 1 means the jfieldID is an instance jfieldID, 35 // and the rest of the word is the offset of the field. 36 // a 0 means the jfieldID is a static jfieldID, 37 // and the rest of the word is the JNIid*. 38 // 39 // Another low-order bit is used to mark if an instance field 40 // is accompanied by an indication of which class it applies to. 41 // 42 // Bit-format of a jfieldID (most significant first): 43 // address:30 instance=0:1 checked=0:1 44 // offset:30 instance=1:1 checked=0:1 45 // klass:23 offset:7 instance=1:1 checked=1:1 46 // 47 // If the offset does not fit in 7 bits, or if the fieldID is 48 // not checked, then the checked bit is zero and the rest of 49 // the word (30 bits) contains only the offset. 50 // 51 private: 52 enum { 53 checked_bits = 1, 54 instance_bits = 1, 55 address_bits = BitsPerWord - checked_bits - instance_bits, 56 57 large_offset_bits = address_bits, // unioned with address 58 small_offset_bits = 7, 59 klass_bits = address_bits - small_offset_bits, 60 61 checked_shift = 0, 62 instance_shift = checked_shift + checked_bits, 63 address_shift = instance_shift + instance_bits, 64 65 offset_shift = address_shift, // unioned with address 66 klass_shift = offset_shift + small_offset_bits, 67 68 checked_mask_in_place = right_n_bits(checked_bits) << checked_shift, 69 instance_mask_in_place = right_n_bits(instance_bits) << instance_shift, 70 #ifndef _WIN64 71 large_offset_mask = right_n_bits(large_offset_bits), 72 small_offset_mask = right_n_bits(small_offset_bits), 73 klass_mask = right_n_bits(klass_bits) 74 #endif 75 }; 76 77 #ifdef _WIN64 78 // These values are too big for Win64 79 const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits); 80 const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits); 81 const static uintptr_t klass_mask = right_n_bits(klass_bits); 82 #endif 83 84 // helper routines: 85 static bool is_checked_jfieldID(jfieldID id) { 86 uintptr_t as_uint = (uintptr_t) id; 87 return ((as_uint & checked_mask_in_place) != 0); 88 } 89 static int raw_instance_offset(jfieldID id) { 90 uintptr_t result = (uintptr_t) id >> address_shift; 91 if (VerifyJNIFields && is_checked_jfieldID(id)) { 92 result &= small_offset_mask; // cut off the hash bits 93 } 94 // This gets back the InstanceKlass field offset that 95 // the jfieldID is created with. 96 return checked_cast<int>(result); 97 } 98 static intptr_t encode_klass_hash(Klass* k, int offset); 99 static bool klass_hash_ok(Klass* k, jfieldID id); 100 static void verify_instance_jfieldID(Klass* k, jfieldID id); 101 102 public: 103 static bool is_valid_jfieldID(Klass* k, jfieldID id); 104 105 static bool is_instance_jfieldID(Klass* k, jfieldID id) { 106 uintptr_t as_uint = (uintptr_t) id; 107 return ((as_uint & instance_mask_in_place) != 0); 108 } 109 static bool is_static_jfieldID(jfieldID id) { 110 uintptr_t as_uint = (uintptr_t) id; 111 return ((as_uint & instance_mask_in_place) == 0); 112 } 113 114 static jfieldID to_instance_jfieldID(Klass* k, int offset) { 115 intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place; 116 if (VerifyJNIFields) { 117 as_uint |= encode_klass_hash(k, offset); 118 } 119 jfieldID result = (jfieldID) as_uint; 120 #ifndef ASSERT 121 // always verify in debug mode; switchable in anything else 122 if (VerifyJNIFields) 123 #endif // ASSERT 124 { 125 verify_instance_jfieldID(k, result); 126 } 127 assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset"); 128 return result; 129 } 130 131 static int from_instance_jfieldID(Klass* k, jfieldID id) { 132 #ifndef ASSERT 133 // always verify in debug mode; switchable in anything else 134 if (VerifyJNIFields) 135 #endif // ASSERT 136 { 137 verify_instance_jfieldID(k, id); 138 } 139 return raw_instance_offset(id); 140 } 141 142 static jfieldID to_static_jfieldID(JNIid* id) { 143 assert(id->is_static_field_id(), "from_JNIid, but not static field id"); 144 jfieldID result = (jfieldID) id; 145 assert(from_static_jfieldID(result) == id, "must produce the same static id"); 146 return result; 147 } 148 149 static JNIid* from_static_jfieldID(jfieldID id) { 150 assert(jfieldIDWorkaround::is_static_jfieldID(id), 151 "to_JNIid, but not static jfieldID"); 152 JNIid* result = (JNIid*) id; 153 assert(result->is_static_field_id(), "to_JNIid, but not static field id"); 154 return result; 155 } 156 157 static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static) { 158 if (is_static) { 159 JNIid *id = k->jni_id_for(offset); 160 debug_only(id->set_is_static_field_id()); 161 return jfieldIDWorkaround::to_static_jfieldID(id); 162 } else { 163 return jfieldIDWorkaround::to_instance_jfieldID(k, offset); 164 } 165 } 166 }; 167 168 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP --- EOF ---