Java tutorial
// ASM: a very small and fast Java bytecode manipulation framework // Copyright (c) 2000-2011 INRIA, France Telecom // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions // are met: // 1. Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // 2. Redistributions in binary form must reproduce the above copyright // notice, this list of conditions and the following disclaimer in the // documentation and/or other materials provided with the distribution. // 3. Neither the name of the copyright holders nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF // THE POSSIBILITY OF SUCH DAMAGE. package org.objectweb.asm; /** * A non standard class, field, method or Code attribute, as defined in the Java Virtual Machine * Specification (JVMS). * * @see <a href= "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7">JVMS * 4.7</a> * @see <a href= "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.3">JVMS * 4.7.3</a> * @author Eric Bruneton * @author Eugene Kuleshov */ public class Attribute { /** The type of this attribute, also called its name in the JVMS. */ public final String type; /** * The raw content of this attribute, only used for unknown attributes (see {@link #isUnknown()}). * The 6 header bytes of the attribute (attribute_name_index and attribute_length) are <i>not</i> * included. */ private byte[] content; /** * The next attribute in this attribute list (Attribute instances can be linked via this field to * store a list of class, field, method or Code attributes). May be {@literal null}. */ Attribute nextAttribute; /** * Constructs a new empty attribute. * * @param type the type of the attribute. */ protected Attribute(final String type) { this.type = type; } /** * Returns {@literal true} if this type of attribute is unknown. This means that the attribute * content can't be parsed to extract constant pool references, labels, etc. Instead, the * attribute content is read as an opaque byte array, and written back as is. This can lead to * invalid attributes, if the content actually contains constant pool references, labels, or other * symbolic references that need to be updated when there are changes to the constant pool, the * method bytecode, etc. The default implementation of this method always returns {@literal true}. * * @return {@literal true} if this type of attribute is unknown. */ public boolean isUnknown() { return true; } /** * Returns {@literal true} if this type of attribute is a Code attribute. * * @return {@literal true} if this type of attribute is a Code attribute. */ public boolean isCodeAttribute() { return false; } /** * Returns the labels corresponding to this attribute. * * @return the labels corresponding to this attribute, or {@literal null} if this attribute is not * a Code attribute that contains labels. */ protected Label[] getLabels() { return new Label[0]; } /** * Reads a {@link #type} attribute. This method must return a <i>new</i> {@link Attribute} object, * of type {@link #type}, corresponding to the 'length' bytes starting at 'offset', in the given * ClassReader. * * @param classReader the class that contains the attribute to be read. * @param offset index of the first byte of the attribute's content in {@link ClassReader}. The 6 * attribute header bytes (attribute_name_index and attribute_length) are not taken into * account here. * @param length the length of the attribute's content (excluding the 6 attribute header bytes). * @param charBuffer the buffer to be used to call the ClassReader methods requiring a * 'charBuffer' parameter. * @param codeAttributeOffset index of the first byte of content of the enclosing Code attribute * in {@link ClassReader}, or -1 if the attribute to be read is not a Code attribute. The 6 * attribute header bytes (attribute_name_index and attribute_length) are not taken into * account here. * @param labels the labels of the method's code, or {@literal null} if the attribute to be read * is not a Code attribute. * @return a <i>new</i> {@link Attribute} object corresponding to the specified bytes. */ protected Attribute read(final ClassReader classReader, final int offset, final int length, final char[] charBuffer, final int codeAttributeOffset, final Label[] labels) { Attribute attribute = new Attribute(type); attribute.content = new byte[length]; System.arraycopy(classReader.classFileBuffer, offset, attribute.content, 0, length); return attribute; } /** * Returns the byte array form of the content of this attribute. The 6 header bytes * (attribute_name_index and attribute_length) must <i>not</i> be added in the returned * ByteVector. * * @param classWriter the class to which this attribute must be added. This parameter can be used * to add the items that corresponds to this attribute to the constant pool of this class. * @param code the bytecode of the method corresponding to this Code attribute, or {@literal null} * if this attribute is not a Code attribute. Corresponds to the 'code' field of the Code * attribute. * @param codeLength the length of the bytecode of the method corresponding to this code * attribute, or 0 if this attribute is not a Code attribute. Corresponds to the 'code_length' * field of the Code attribute. * @param maxStack the maximum stack size of the method corresponding to this Code attribute, or * -1 if this attribute is not a Code attribute. * @param maxLocals the maximum number of local variables of the method corresponding to this code * attribute, or -1 if this attribute is not a Code attribute. * @return the byte array form of this attribute. */ protected ByteVector write(final ClassWriter classWriter, final byte[] code, final int codeLength, final int maxStack, final int maxLocals) { return new ByteVector(content); } /** * Returns the number of attributes of the attribute list that begins with this attribute. * * @return the number of attributes of the attribute list that begins with this attribute. */ final int getAttributeCount() { int count = 0; Attribute attribute = this; while (attribute != null) { count += 1; attribute = attribute.nextAttribute; } return count; } /** * Returns the total size in bytes of all the attributes in the attribute list that begins with * this attribute. This size includes the 6 header bytes (attribute_name_index and * attribute_length) per attribute. Also adds the attribute type names to the constant pool. * * @param symbolTable where the constants used in the attributes must be stored. * @return the size of all the attributes in this attribute list. This size includes the size of * the attribute headers. */ final int computeAttributesSize(final SymbolTable symbolTable) { final byte[] code = null; final int codeLength = 0; final int maxStack = -1; final int maxLocals = -1; return computeAttributesSize(symbolTable, code, codeLength, maxStack, maxLocals); } /** * Returns the total size in bytes of all the attributes in the attribute list that begins with * this attribute. This size includes the 6 header bytes (attribute_name_index and * attribute_length) per attribute. Also adds the attribute type names to the constant pool. * * @param symbolTable where the constants used in the attributes must be stored. * @param code the bytecode of the method corresponding to these Code attributes, or {@literal * null} if they are not Code attributes. Corresponds to the 'code' field of the Code * attribute. * @param codeLength the length of the bytecode of the method corresponding to these code * attributes, or 0 if they are not Code attributes. Corresponds to the 'code_length' field of * the Code attribute. * @param maxStack the maximum stack size of the method corresponding to these Code attributes, or * -1 if they are not Code attributes. * @param maxLocals the maximum number of local variables of the method corresponding to these * Code attributes, or -1 if they are not Code attribute. * @return the size of all the attributes in this attribute list. This size includes the size of * the attribute headers. */ final int computeAttributesSize(final SymbolTable symbolTable, final byte[] code, final int codeLength, final int maxStack, final int maxLocals) { final ClassWriter classWriter = symbolTable.classWriter; int size = 0; Attribute attribute = this; while (attribute != null) { symbolTable.addConstantUtf8(attribute.type); size += 6 + attribute.write(classWriter, code, codeLength, maxStack, maxLocals).length; attribute = attribute.nextAttribute; } return size; } /** * Returns the total size in bytes of all the attributes that correspond to the given field, * method or class access flags and signature. This size includes the 6 header bytes * (attribute_name_index and attribute_length) per attribute. Also adds the attribute type names * to the constant pool. * * @param symbolTable where the constants used in the attributes must be stored. * @param accessFlags some field, method or class access flags. * @param signatureIndex the constant pool index of a field, method of class signature. * @return the size of all the attributes in bytes. This size includes the size of the attribute * headers. */ static int computeAttributesSize(final SymbolTable symbolTable, final int accessFlags, final int signatureIndex) { int size = 0; // Before Java 1.5, synthetic fields are represented with a Synthetic attribute. if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0 && symbolTable.getMajorVersion() < Opcodes.V1_5) { // Synthetic attributes always use 6 bytes. symbolTable.addConstantUtf8(Constants.SYNTHETIC); size += 6; } if (signatureIndex != 0) { // Signature attributes always use 8 bytes. symbolTable.addConstantUtf8(Constants.SIGNATURE); size += 8; } // ACC_DEPRECATED is ASM specific, the ClassFile format uses a Deprecated attribute instead. if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) { // Deprecated attributes always use 6 bytes. symbolTable.addConstantUtf8(Constants.DEPRECATED); size += 6; } return size; } /** * Puts all the attributes of the attribute list that begins with this attribute, in the given * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per * attribute. * * @param symbolTable where the constants used in the attributes must be stored. * @param output where the attributes must be written. */ final void putAttributes(final SymbolTable symbolTable, final ByteVector output) { final byte[] code = null; final int codeLength = 0; final int maxStack = -1; final int maxLocals = -1; putAttributes(symbolTable, code, codeLength, maxStack, maxLocals, output); } /** * Puts all the attributes of the attribute list that begins with this attribute, in the given * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per * attribute. * * @param symbolTable where the constants used in the attributes must be stored. * @param code the bytecode of the method corresponding to these Code attributes, or {@literal * null} if they are not Code attributes. Corresponds to the 'code' field of the Code * attribute. * @param codeLength the length of the bytecode of the method corresponding to these code * attributes, or 0 if they are not Code attributes. Corresponds to the 'code_length' field of * the Code attribute. * @param maxStack the maximum stack size of the method corresponding to these Code attributes, or * -1 if they are not Code attributes. * @param maxLocals the maximum number of local variables of the method corresponding to these * Code attributes, or -1 if they are not Code attribute. * @param output where the attributes must be written. */ final void putAttributes(final SymbolTable symbolTable, final byte[] code, final int codeLength, final int maxStack, final int maxLocals, final ByteVector output) { final ClassWriter classWriter = symbolTable.classWriter; Attribute attribute = this; while (attribute != null) { ByteVector attributeContent = attribute.write(classWriter, code, codeLength, maxStack, maxLocals); // Put attribute_name_index and attribute_length. output.putShort(symbolTable.addConstantUtf8(attribute.type)).putInt(attributeContent.length); output.putByteArray(attributeContent.data, 0, attributeContent.length); attribute = attribute.nextAttribute; } } /** * Puts all the attributes that correspond to the given field, method or class access flags and * signature, in the given byte vector. This includes the 6 header bytes (attribute_name_index and * attribute_length) per attribute. * * @param symbolTable where the constants used in the attributes must be stored. * @param accessFlags some field, method or class access flags. * @param signatureIndex the constant pool index of a field, method of class signature. * @param output where the attributes must be written. */ static void putAttributes(final SymbolTable symbolTable, final int accessFlags, final int signatureIndex, final ByteVector output) { // Before Java 1.5, synthetic fields are represented with a Synthetic attribute. if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0 && symbolTable.getMajorVersion() < Opcodes.V1_5) { output.putShort(symbolTable.addConstantUtf8(Constants.SYNTHETIC)).putInt(0); } if (signatureIndex != 0) { output.putShort(symbolTable.addConstantUtf8(Constants.SIGNATURE)).putInt(2).putShort(signatureIndex); } if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) { output.putShort(symbolTable.addConstantUtf8(Constants.DEPRECATED)).putInt(0); } } /** A set of attribute prototypes (attributes with the same type are considered equal). */ static final class Set { private static final int SIZE_INCREMENT = 6; private int size; private Attribute[] data = new Attribute[SIZE_INCREMENT]; void addAttributes(final Attribute attributeList) { Attribute attribute = attributeList; while (attribute != null) { if (!contains(attribute)) { add(attribute); } attribute = attribute.nextAttribute; } } Attribute[] toArray() { Attribute[] result = new Attribute[size]; System.arraycopy(data, 0, result, 0, size); return result; } private boolean contains(final Attribute attribute) { for (int i = 0; i < size; ++i) { if (data[i].type.equals(attribute.type)) { return true; } } return false; } private void add(final Attribute attribute) { if (size >= data.length) { Attribute[] newData = new Attribute[data.length + SIZE_INCREMENT]; System.arraycopy(data, 0, newData, 0, size); data = newData; } data[size++] = attribute; } } }