1 /*

     2  * Copyright (c) 2003, 2017, 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(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_VM_RUNTIME_JFIELDIDWORKAROUND_HPP