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.
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 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 ---