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: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(instanceKlassHandle 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_VM_RUNTIME_JFIELDIDWORKAROUND_HPP
--- EOF ---