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src/hotspot/share/runtime/jfieldIDWorkaround.hpp

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 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) {

 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

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

 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     inlined_bits           = 1,
 57     address_bits           = BitsPerWord - checked_bits - instance_bits - inlined_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     inlined_shift          = instance_shift + instance_bits,
 66     address_shift          = inlined_shift + inlined_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     inlined_mask_in_place  = right_n_bits(inlined_bits) << inlined_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) {

 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_inlined_jfieldID(jfieldID id) {
117     uintptr_t as_uint = (uintptr_t) id;
118     return ((as_uint & inlined_mask_in_place) != 0);
119   }
120 
121   static jfieldID to_instance_jfieldID(Klass* k, int offset, bool inlined) {
122     intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) |
123                         instance_mask_in_place;
124     if (inlined) {
125       as_uint |= inlined_mask_in_place;
126     }
127     if (VerifyJNIFields) {
128       as_uint |= encode_klass_hash(k, offset);
129     }
130     jfieldID result = (jfieldID) as_uint;
131 #ifndef ASSERT
132     // always verify in debug mode; switchable in anything else
133     if (VerifyJNIFields)
134 #endif // ASSERT
135     {
136       verify_instance_jfieldID(k, result);
137     }
138     assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
139     return result;
140   }
141 
142   static intptr_t from_instance_jfieldID(Klass* k, jfieldID id) {
143 #ifndef ASSERT
144     // always verify in debug mode; switchable in anything else
145     if (VerifyJNIFields)
146 #endif // ASSERT

148       verify_instance_jfieldID(k, id);
149     }
150     return raw_instance_offset(id);
151   }
152 
153   static jfieldID to_static_jfieldID(JNIid* id) {
154     assert(id->is_static_field_id(), "from_JNIid, but not static field id");
155     jfieldID result = (jfieldID) id;
156     assert(from_static_jfieldID(result) == id, "must produce the same static id");
157     return result;
158   }
159 
160   static JNIid* from_static_jfieldID(jfieldID id) {
161     assert(jfieldIDWorkaround::is_static_jfieldID(id),
162            "to_JNIid, but not static jfieldID");
163     JNIid* result = (JNIid*) id;
164     assert(result->is_static_field_id(), "to_JNIid, but not static field id");
165     return result;
166   }
167 
168   static jfieldID to_jfieldID(InstanceKlass* k, int offset, bool is_static, bool inlined) {
169     if (is_static) {
170       JNIid *id = k->jni_id_for(offset);
171       debug_only(id->set_is_static_field_id());
172       return jfieldIDWorkaround::to_static_jfieldID(id);
173     } else {
174       return jfieldIDWorkaround::to_instance_jfieldID(k, offset, inlined);
175     }
176   }
177 };
178 
179 #endif // SHARE_RUNTIME_JFIELDIDWORKAROUND_HPP
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