/*
* Copyright (c) 2003, 2010, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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*/
#ifndef SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP
#define SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP
class jfieldIDWorkaround: AllStatic {
// This workaround is because JVMTI doesn't have distinct entry points
// for methods that use static jfieldIDs and instance jfieldIDs.
// The workaround is to steal a low-order bit:
// a 1 means the jfieldID is an instance jfieldID,
// and the rest of the word is the offset of the field.
// a 0 means the jfieldID is a static jfieldID,
// and the rest of the word is the JNIid*.
//
// Another low-order bit is used to mark if an instance field
// is accompanied by an indication of which class it applies to.
//
// Bit-format of a jfieldID (most significant first):
// address:30 instance=0:1 checked=0:1
// offset:30 instance=1:1 checked=0:1
// klass:23 offset:7 instance=1:1 checked=1:1
//
// If the offset does not fit in 7 bits, or if the fieldID is
// not checked, then the checked bit is zero and the rest of
// the word (30 bits) contains only the offset.
//
private:
enum {
checked_bits = 1,
instance_bits = 1,
address_bits = BitsPerWord - checked_bits - instance_bits,
large_offset_bits = address_bits, // unioned with address
small_offset_bits = 7,
klass_bits = address_bits - small_offset_bits,
checked_shift = 0,
instance_shift = checked_shift + checked_bits,
address_shift = instance_shift + instance_bits,
offset_shift = address_shift, // unioned with address
klass_shift = offset_shift + small_offset_bits,
checked_mask_in_place = right_n_bits(checked_bits) << checked_shift,
instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,
#ifndef _WIN64
large_offset_mask = right_n_bits(large_offset_bits),
small_offset_mask = right_n_bits(small_offset_bits),
klass_mask = right_n_bits(klass_bits)
#endif
};
#ifdef _WIN64
// These values are too big for Win64
const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);
const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);
const static uintptr_t klass_mask = right_n_bits(klass_bits);
#endif
// helper routines:
static bool is_checked_jfieldID(jfieldID id) {
uintptr_t as_uint = (uintptr_t) id;
return ((as_uint & checked_mask_in_place) != 0);
}
static intptr_t raw_instance_offset(jfieldID id) {
uintptr_t result = (uintptr_t) id >> address_shift;
if (VerifyJNIFields && is_checked_jfieldID(id)) {
result &= small_offset_mask; // cut off the hash bits
}
return (intptr_t)result;
}
static intptr_t encode_klass_hash(klassOop k, intptr_t offset);
static bool klass_hash_ok(klassOop k, jfieldID id);
static void verify_instance_jfieldID(klassOop k, jfieldID id);
public:
static bool is_valid_jfieldID(klassOop k, jfieldID id);
static bool is_instance_jfieldID(klassOop k, jfieldID id) {
uintptr_t as_uint = (uintptr_t) id;
return ((as_uint & instance_mask_in_place) != 0);
}
static bool is_static_jfieldID(jfieldID id) {
uintptr_t as_uint = (uintptr_t) id;
return ((as_uint & instance_mask_in_place) == 0);
}
static jfieldID to_instance_jfieldID(klassOop k, int offset) {
intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;
if (VerifyJNIFields) {
as_uint |= encode_klass_hash(k, offset);
}
jfieldID result = (jfieldID) as_uint;
#ifndef ASSERT
// always verify in debug mode; switchable in anything else
if (VerifyJNIFields)
#endif // ASSERT
{
verify_instance_jfieldID(k, result);
}
assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");
return result;
}
static intptr_t from_instance_jfieldID(klassOop k, jfieldID id) {
#ifndef ASSERT
// always verify in debug mode; switchable in anything else
if (VerifyJNIFields)
#endif // ASSERT
{
verify_instance_jfieldID(k, id);
}
return raw_instance_offset(id);
}
static jfieldID to_static_jfieldID(JNIid* id) {
assert(id->is_static_field_id(), "from_JNIid, but not static field id");
jfieldID result = (jfieldID) id;
assert(from_static_jfieldID(result) == id, "must produce the same static id");
return result;
}
static JNIid* from_static_jfieldID(jfieldID id) {
assert(jfieldIDWorkaround::is_static_jfieldID(id),
"to_JNIid, but not static jfieldID");
JNIid* result = (JNIid*) id;
assert(result->is_static_field_id(), "to_JNIid, but not static field id");
return result;
}
static jfieldID to_jfieldID(instanceKlassHandle k, int offset, bool is_static) {
if (is_static) {
JNIid *id = k->jni_id_for(offset);
debug_only(id->set_is_static_field_id());
return jfieldIDWorkaround::to_static_jfieldID(id);
} else {
return jfieldIDWorkaround::to_instance_jfieldID(k(), offset);
}
}
};
#endif // SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP