1 /*
   2  * Copyright (c) 2003, 2012, 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_VM_RUNTIME_JFIELDIDWORKAROUND_HPP
  26 #define SHARE_VM_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:29        final=0:1 instance=0:1 checked=0:1
  42   //  offset:29         final=0:1 instance=1:1 checked=0:1
  43   //  klass:22 offset:7 final=1:1 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 public:
  50   enum {
  51     checked_bits           = 1,
  52     instance_bits          = 1,
  53     final_bits             = 1,
  54     address_bits           = BitsPerWord - checked_bits - instance_bits - final_bits,
  55 
  56     large_offset_bits      = address_bits,  // unioned with address
  57     small_offset_bits      = 7,
  58     klass_bits             = address_bits - small_offset_bits,
  59 
  60     checked_shift          = 0,
  61     instance_shift         = checked_shift  + checked_bits,
  62     final_shift            = instance_shift + instance_bits,
  63     address_shift          = final_shift    + final_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     final_mask_in_place    = right_n_bits(final_bits)    << final_shift,
  71 #ifndef _WIN64
  72     large_offset_mask      = right_n_bits(large_offset_bits),
  73     small_offset_mask      = right_n_bits(small_offset_bits),
  74     klass_mask             = right_n_bits(klass_bits)
  75 #endif
  76     };
  77 
  78 #ifdef _WIN64
  79     // These values are too big for Win64
  80     const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
  81     const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
  82     const static uintptr_t klass_mask        = right_n_bits(klass_bits);
  83 #endif
  84  private:
  85   // helper routines:
  86   static bool is_checked_jfieldID(jfieldID id) {
  87     uintptr_t as_uint = (uintptr_t) id;
  88     return ((as_uint & checked_mask_in_place) != 0);
  89   }
  90   static intptr_t raw_instance_offset(jfieldID id) {
  91     uintptr_t result = (uintptr_t) id >> address_shift;
  92     if (VerifyJNIFields && is_checked_jfieldID(id)) {
  93       result &= small_offset_mask;  // cut off the hash bits
  94     }
  95     return (intptr_t)result;
  96   }
  97   static intptr_t encode_klass_hash(Klass* k, intptr_t offset);
  98   static bool             klass_hash_ok(Klass* k, jfieldID id);
  99   static void  verify_instance_jfieldID(Klass* k, jfieldID id);
 100 
 101  public:
 102   static bool is_valid_jfieldID(Klass* k, jfieldID id);
 103 
 104   static bool is_instance_jfieldID(jfieldID id) {
 105     uintptr_t as_uint = (uintptr_t) id;
 106     return ((as_uint & instance_mask_in_place) != 0);
 107   }
 108   static bool is_static_jfieldID(jfieldID id) {
 109     uintptr_t as_uint = (uintptr_t) id;
 110     return ((as_uint & instance_mask_in_place) == 0);
 111   }
 112   static bool is_final_jfieldID(jfieldID id) {
 113     uintptr_t as_uint = (uintptr_t) id;
 114     return ((as_uint & final_mask_in_place) != 0);
 115   }
 116 
 117   static jfieldID to_instance_jfieldID(Klass* k, int offset, bool is_final) {
 118     intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
 119     if (is_final) as_uint |= final_mask_in_place;
 120     if (VerifyJNIFields) {
 121       as_uint |= encode_klass_hash(k, offset);
 122     }
 123     jfieldID result = (jfieldID) as_uint;
 124 #ifndef ASSERT
 125     // always verify in debug mode; switchable in anything else
 126     if (VerifyJNIFields)
 127 #endif // ASSERT
 128     {
 129       verify_instance_jfieldID(k, result);
 130     }
 131     assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
 132     return result;
 133   }
 134 
 135   static intptr_t from_instance_jfieldID(Klass* k, jfieldID id) {
 136 #ifndef ASSERT
 137     // always verify in debug mode; switchable in anything else
 138     if (VerifyJNIFields)
 139 #endif // ASSERT
 140     {
 141       verify_instance_jfieldID(k, id);
 142     }
 143     return raw_instance_offset(id);
 144   }
 145 
 146   static jfieldID to_static_jfieldID(JNIid* id) {
 147     assert(id->is_static_field_id(), "from_JNIid, but not static field id");
 148     jfieldID result = (jfieldID) id;
 149     assert(from_static_jfieldID(result) == id, "must produce the same static id");
 150     return result;
 151   }
 152 
 153   static JNIid* from_static_jfieldID(jfieldID id) {
 154     assert(jfieldIDWorkaround::is_static_jfieldID(id),
 155            "to_JNIid, but not static jfieldID");
 156     JNIid* result = (JNIid*) id;
 157     assert(result->is_static_field_id(), "to_JNIid, but not static field id");
 158     return result;
 159   }
 160 
 161   static jfieldID to_jfieldID(instanceKlassHandle k, int offset, bool is_static, bool is_final) {
 162     if (is_static) {
 163       JNIid *id = k->jni_id_for(offset);
 164       debug_only(id->set_is_static_field_id());
 165       return jfieldIDWorkaround::to_static_jfieldID(id);
 166     } else {
 167       return jfieldIDWorkaround::to_instance_jfieldID(k(), offset, is_final);
 168     }
 169   }
 170 };
 171 
 172 #endif // SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP
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