/*

 * Copyright (c) 2000, 2017, 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.internal.misc;

import jdk.internal.HotSpotIntrinsicCandidate;

import jdk.internal.vm.annotation.ForceInline;

import java.lang.reflect.Field;

import java.security.ProtectionDomain;

/**

 * A collection of methods for performing low-level, unsafe operations.

 * Although the class and all methods are public, use of this class is

 * limited because only trusted code can obtain instances of it.

 *

 * <em>Note:</em> It is the resposibility of the caller to make sure

 * arguments are checked before methods of this class are

 * called. While some rudimentary checks are performed on the input,

 * the checks are best effort and when performance is an overriding

 * priority, as when methods of this class are optimized by the

 * runtime compiler, some or all checks (if any) may be elided. Hence,

 * the caller must not rely on the checks and corresponding

 * exceptions!

 *

 * @author John R. Rose

 * @see #getUnsafe

 */

public final class Unsafe {

    private static native void registerNatives();

    static {

        registerNatives();

    }

    private Unsafe() {}

    private static final Unsafe theUnsafe = new Unsafe();

    /**

     * Provides the caller with the capability of performing unsafe

     * operations.

     *

     * <p>The returned {@code Unsafe} object should be carefully guarded

     * by the caller, since it can be used to read and write data at arbitrary

     * memory addresses.  It must never be passed to untrusted code.

     *

     * <p>Most methods in this class are very low-level, and correspond to a

     * small number of hardware instructions (on typical machines).  Compilers

     * are encouraged to optimize these methods accordingly.

     *

     * <p>Here is a suggested idiom for using unsafe operations:

     *

     * <pre> {@code

     * class MyTrustedClass {

     *   private static final Unsafe unsafe = Unsafe.getUnsafe();

     *   ...

     *   private long myCountAddress = ...;

     *   public int getCount() { return unsafe.getByte(myCountAddress); }

     * }}</pre>

     *

     * (It may assist compilers to make the local variable {@code final}.)

     */

    public static Unsafe getUnsafe() {

        return theUnsafe;

    }

    /// peek and poke operations

    /// (compilers should optimize these to memory ops)

    // These work on object fields in the Java heap.

    // They will not work on elements of packed arrays.

    /**

     * Fetches a value from a given Java variable.

     * More specifically, fetches a field or array element within the given

     * object {@code o} at the given offset, or (if {@code o} is null)

     * from the memory address whose numerical value is the given offset.

     * <p>

     * The results are undefined unless one of the following cases is true:

     * <ul>

     * <li>The offset was obtained from {@link #objectFieldOffset} on

     * the {@link java.lang.reflect.Field} of some Java field and the object

     * referred to by {@code o} is of a class compatible with that

     * field's class.

     *

     * <li>The offset and object reference {@code o} (either null or

     * non-null) were both obtained via {@link #staticFieldOffset}

     * and {@link #staticFieldBase} (respectively) from the

     * reflective {@link Field} representation of some Java field.

     *

     * <li>The object referred to by {@code o} is an array, and the offset

     * is an integer of the form {@code B+N*S}, where {@code N} is

     * a valid index into the array, and {@code B} and {@code S} are

     * the values obtained by {@link #arrayBaseOffset} and {@link

     * #arrayIndexScale} (respectively) from the array's class.  The value

     * referred to is the {@code N}<em>th</em> element of the array.

     *

     * </ul>

     * <p>

     * If one of the above cases is true, the call references a specific Java

     * variable (field or array element).  However, the results are undefined

     * if that variable is not in fact of the type returned by this method.

     * <p>

     * This method refers to a variable by means of two parameters, and so

     * it provides (in effect) a <em>double-register</em> addressing mode

     * for Java variables.  When the object reference is null, this method

     * uses its offset as an absolute address.  This is similar in operation

     * to methods such as {@link #getInt(long)}, which provide (in effect) a

     * <em>single-register</em> addressing mode for non-Java variables.

     * However, because Java variables may have a different layout in memory

     * from non-Java variables, programmers should not assume that these

     * two addressing modes are ever equivalent.  Also, programmers should

     * remember that offsets from the double-register addressing mode cannot

     * be portably confused with longs used in the single-register addressing

     * mode.

     *

     * @param o Java heap object in which the variable resides, if any, else

     *        null

     * @param offset indication of where the variable resides in a Java heap

     *        object, if any, else a memory address locating the variable

     *        statically

     * @return the value fetched from the indicated Java variable

     * @throws RuntimeException No defined exceptions are thrown, not even

     *         {@link NullPointerException}

     */

    @HotSpotIntrinsicCandidate

    public native int getInt(Object o, long offset);

    /**

     * Stores a value into a given Java variable.

     * <p>

     * The first two parameters are interpreted exactly as with

     * {@link #getInt(Object, long)} to refer to a specific

     * Java variable (field or array element).  The given value

     * is stored into that variable.

     * <p>

     * The variable must be of the same type as the method

     * parameter {@code x}.

     *

     * @param o Java heap object in which the variable resides, if any, else

     *        null

     * @param offset indication of where the variable resides in a Java heap

     *        object, if any, else a memory address locating the variable

     *        statically

     * @param x the value to store into the indicated Java variable

     * @throws RuntimeException No defined exceptions are thrown, not even

     *         {@link NullPointerException}

     */

    @HotSpotIntrinsicCandidate

    public native void putInt(Object o, long offset, int x);

    /**

     * Fetches a reference value from a given Java variable.

     * @see #getInt(Object, long)

     */

    @HotSpotIntrinsicCandidate

    /**

     * Stores a reference value into a given Java variable.

     * <p>

     * Unless the reference {@code x} being stored is either null

     * or matches the field type, the results are undefined.

     * If the reference {@code o} is non-null, card marks or

     * other store barriers for that object (if the VM requires them)

     * are updated.

     * @see #putInt(Object, long, int)

     */

    @HotSpotIntrinsicCandidate

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native boolean getBoolean(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putBoolean(Object o, long offset, boolean x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native byte    getByte(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putByte(Object o, long offset, byte x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native short   getShort(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putShort(Object o, long offset, short x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native char    getChar(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putChar(Object o, long offset, char x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native long    getLong(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putLong(Object o, long offset, long x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native float   getFloat(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putFloat(Object o, long offset, float x);

    /** @see #getInt(Object, long) */

    @HotSpotIntrinsicCandidate

    public native double  getDouble(Object o, long offset);

    /** @see #putInt(Object, long, int) */

    @HotSpotIntrinsicCandidate

    public native void    putDouble(Object o, long offset, double x);

    /**

     * Fetches a native pointer from a given memory address.  If the address is

     * zero, or does not point into a block obtained from {@link

     * #allocateMemory}, the results are undefined.

     *

     * <p>If the native pointer is less than 64 bits wide, it is extended as

     * an unsigned number to a Java long.  The pointer may be indexed by any

     * given byte offset, simply by adding that offset (as a simple integer) to

     * the long representing the pointer.  The number of bytes actually read

     * from the target address may be determined by consulting {@link

     * #addressSize}.

     *

     * @see #allocateMemory

     * @see #getInt(Object, long)

     */

    @ForceInline

    public long getAddress(Object o, long offset) {

        if (ADDRESS_SIZE == 4) {

            return Integer.toUnsignedLong(getInt(o, offset));

        } else {

            return getLong(o, offset);

        }

    }

    /**

     * Stores a native pointer into a given memory address.  If the address is

     * zero, or does not point into a block obtained from {@link

     * #allocateMemory}, the results are undefined.

     *

     * <p>The number of bytes actually written at the target address may be

     * determined by consulting {@link #addressSize}.

     *

     * @see #allocateMemory

     * @see #putInt(Object, long, int)

     */

    @ForceInline

    public void putAddress(Object o, long offset, long x) {

        if (ADDRESS_SIZE == 4) {

            putInt(o, offset, (int)x);

        } else {

            putLong(o, offset, x);

        }

    }

    // These read VM internal data.

    /**

     * Fetches an uncompressed reference value from a given native variable

     * ignoring the VM's compressed references mode.

     *

     * @param address a memory address locating the variable

     * @return the value fetched from the indicated native variable

     */

    public native Object getUncompressedObject(long address);

    // These work on values in the C heap.

    /**

     * Fetches a value from a given memory address.  If the address is zero, or

     * does not point into a block obtained from {@link #allocateMemory}, the

     * results are undefined.

     *

     * @see #allocateMemory

     */

    @ForceInline

    public byte getByte(long address) {

        return getByte(null, address);

    }

    /**

     * Stores a value into a given memory address.  If the address is zero, or

     * does not point into a block obtained from {@link #allocateMemory}, the

     * results are undefined.

     *

     * @see #getByte(long)

     */

    @ForceInline

    public void putByte(long address, byte x) {

        putByte(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public short getShort(long address) {

        return getShort(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putShort(long address, short x) {

        putShort(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public char getChar(long address) {

        return getChar(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putChar(long address, char x) {

        putChar(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public int getInt(long address) {

        return getInt(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putInt(long address, int x) {

        putInt(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public long getLong(long address) {

        return getLong(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putLong(long address, long x) {

        putLong(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public float getFloat(long address) {

        return getFloat(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putFloat(long address, float x) {

        putFloat(null, address, x);

    }

    /** @see #getByte(long) */

    @ForceInline

    public double getDouble(long address) {

        return getDouble(null, address);

    }

    /** @see #putByte(long, byte) */

    @ForceInline

    public void putDouble(long address, double x) {

        putDouble(null, address, x);

    }

    /** @see #getAddress(Object, long) */

    @ForceInline

    public long getAddress(long address) {

        return getAddress(null, address);

    }

    /** @see #putAddress(Object, long, long) */

    @ForceInline

    public void putAddress(long address, long x) {

        putAddress(null, address, x);

    }

    /// helper methods for validating various types of objects/values

    /**

     * Create an exception reflecting that some of the input was invalid

     *

     * <em>Note:</em> It is the resposibility of the caller to make

     * sure arguments are checked before the methods are called. While

     * some rudimentary checks are performed on the input, the checks

     * are best effort and when performance is an overriding priority,

     * as when methods of this class are optimized by the runtime

     * compiler, some or all checks (if any) may be elided. Hence, the

     * caller must not rely on the checks and corresponding

     * exceptions!

     *

     * @return an exception object

     */

    private RuntimeException invalidInput() {

        return new IllegalArgumentException();

    }

    /**

     * Check if a value is 32-bit clean (32 MSB are all zero)

     *

     * @param value the 64-bit value to check

     *

     * @return true if the value is 32-bit clean

     */

    private boolean is32BitClean(long value) {

        return value >>> 32 == 0;

    }

    /**

     * Check the validity of a size (the equivalent of a size_t)

     *

     * @throws RuntimeException if the size is invalid

     *         (<em>Note:</em> after optimization, invalid inputs may

     *         go undetected, which will lead to unpredictable

     *         behavior)

     */

    private void checkSize(long size) {

        if (ADDRESS_SIZE == 4) {

            // Note: this will also check for negative sizes

            if (!is32BitClean(size)) {

                throw invalidInput();

            }

        } else if (size < 0) {

            throw invalidInput();

        }

    }

    /**

     * Check the validity of a native address (the equivalent of void*)

     *

     * @throws RuntimeException if the address is invalid

     *         (<em>Note:</em> after optimization, invalid inputs may

     *         go undetected, which will lead to unpredictable

     *         behavior)

     */

    private void checkNativeAddress(long address) {

        if (ADDRESS_SIZE == 4) {

            // Accept both zero and sign extended pointers. A valid

            // pointer will, after the +1 below, either have produced

            // the value 0x0 or 0x1. Masking off the low bit allows

            // for testing against 0.

            if ((((address >> 32) + 1) & ~1) != 0) {

                throw invalidInput();

            }

        }

    }

    /**

     * Check the validity of an offset, relative to a base object

     *

     * @param o the base object

     * @param offset the offset to check

     *

     * @throws RuntimeException if the size is invalid

     *         (<em>Note:</em> after optimization, invalid inputs may

     *         go undetected, which will lead to unpredictable

     *         behavior)

     */

    private void checkOffset(Object o, long offset) {

        if (ADDRESS_SIZE == 4) {

            // Note: this will also check for negative offsets

            if (!is32BitClean(offset)) {

                throw invalidInput();

            }

        } else if (offset < 0) {

            throw invalidInput();