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  private:
 50   enum {
 51     checked_bits           = 1,
 52     instance_bits          = 1,
 53     address_bits           = BitsPerWord - checked_bits - instance_bits,
 54 
 55     large_offset_bits      = address_bits,  // unioned with address
 56     small_offset_bits      = 7,
 57     klass_bits             = address_bits - small_offset_bits,
 58 
 59     checked_shift          = 0,
 60     instance_shift         = checked_shift  + checked_bits,
 61     address_shift          = instance_shift + instance_bits,
 62 
 63     offset_shift           = address_shift,  // unioned with address
 64     klass_shift            = offset_shift + small_offset_bits,
 65 
 66     checked_mask_in_place  = right_n_bits(checked_bits)  << checked_shift,
 67     instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
 68 #ifndef _WIN64
 69     large_offset_mask      = right_n_bits(large_offset_bits),
 70     small_offset_mask      = right_n_bits(small_offset_bits),
 71     klass_mask             = right_n_bits(klass_bits)
 72 #endif
 73     };
 74 
 75 #ifdef _WIN64
 76     // These values are too big for Win64
 77     const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
 78     const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
 79     const static uintptr_t klass_mask        = right_n_bits(klass_bits);
 80 #endif
 81 
 82   // helper routines:
 83   static bool is_checked_jfieldID(jfieldID id) {
 84     uintptr_t as_uint = (uintptr_t) id;
 85     return ((as_uint & checked_mask_in_place) != 0);
 86   }
 87   static intptr_t raw_instance_offset(jfieldID id) {
 88     uintptr_t result = (uintptr_t) id >> address_shift;
 89     if (VerifyJNIFields && is_checked_jfieldID(id)) {
 90       result &= small_offset_mask;  // cut off the hash bits
 91     }
 92     return (intptr_t)result;
 93   }
 94   static intptr_t encode_klass_hash(Klass* k, intptr_t offset);
 95   static bool             klass_hash_ok(Klass* k, jfieldID id);
 96   static void  verify_instance_jfieldID(Klass* k, jfieldID id);
 97 
 98  public:
 99   static bool is_valid_jfieldID(Klass* k, jfieldID id);
100 
101   static bool is_instance_jfieldID(Klass* k, jfieldID id) {
102     uintptr_t as_uint = (uintptr_t) id;
103     return ((as_uint & instance_mask_in_place) != 0);
104   }
105   static bool is_static_jfieldID(jfieldID id) {
106     uintptr_t as_uint = (uintptr_t) id;
107     return ((as_uint & instance_mask_in_place) == 0);
108   }
109 
110   static jfieldID to_instance_jfieldID(Klass* k, int offset) {
111     intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
112     if (VerifyJNIFields) {
113       as_uint |= encode_klass_hash(k, offset);
114     }
115     jfieldID result = (jfieldID) as_uint;
116 #ifndef ASSERT
117     // always verify in debug mode; switchable in anything else
118     if (VerifyJNIFields)
119 #endif // ASSERT
120     {
121       verify_instance_jfieldID(k, result);
122     }
123     assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
124     return result;
125   }
126 
127   static intptr_t from_instance_jfieldID(Klass* k, jfieldID id) {
128 #ifndef ASSERT
129     // always verify in debug mode; switchable in anything else
130     if (VerifyJNIFields)
131 #endif // ASSERT
132     {
133       verify_instance_jfieldID(k, id);
134     }
135     return raw_instance_offset(id);
136   }
137 
138   static jfieldID to_static_jfieldID(JNIid* id) {
139     assert(id->is_static_field_id(), "from_JNIid, but not static field id");
140     jfieldID result = (jfieldID) id;
141     assert(from_static_jfieldID(result) == id, "must produce the same static id");
142     return result;
143   }
144 
145   static JNIid* from_static_jfieldID(jfieldID id) {
146     assert(jfieldIDWorkaround::is_static_jfieldID(id),
147            "to_JNIid, but not static jfieldID");
148     JNIid* result = (JNIid*) id;
149     assert(result->is_static_field_id(), "to_JNIid, but not static field id");
150     return result;
151   }
152 
153   static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static) {
154     if (is_static) {
155       JNIid *id = k->jni_id_for(offset);
156       debug_only(id->set_is_static_field_id());
157       return jfieldIDWorkaround::to_static_jfieldID(id);
158     } else {
159       return jfieldIDWorkaround::to_instance_jfieldID(k, offset);
160     }
161   }
162 };
163 
164 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP