001// ASM: a very small and fast Java bytecode manipulation framework
002// Copyright (c) 2000-2011 INRIA, France Telecom
003// All rights reserved.
004//
005// Redistribution and use in source and binary forms, with or without
006// modification, are permitted provided that the following conditions
007// are met:
008// 1. Redistributions of source code must retain the above copyright
009//    notice, this list of conditions and the following disclaimer.
010// 2. Redistributions in binary form must reproduce the above copyright
011//    notice, this list of conditions and the following disclaimer in the
012//    documentation and/or other materials provided with the distribution.
013// 3. Neither the name of the copyright holders nor the names of its
014//    contributors may be used to endorse or promote products derived from
015//    this software without specific prior written permission.
016//
017// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
018// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
019// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
020// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
021// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
022// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
023// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
024// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
025// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
026// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
027// THE POSSIBILITY OF SUCH DAMAGE.
028package org.springframework.asm;
029
030/**
031 * A non standard class, field, method or Code attribute, as defined in the Java Virtual Machine
032 * Specification (JVMS).
033 *
034 * @see <a href= "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7">JVMS
035 *     4.7</a>
036 * @see <a href= "https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.3">JVMS
037 *     4.7.3</a>
038 * @author Eric Bruneton
039 * @author Eugene Kuleshov
040 */
041public class Attribute {
042
043  /** The type of this attribute, also called its name in the JVMS. */
044  public final String type;
045
046  /**
047   * The raw content of this attribute, only used for unknown attributes (see {@link #isUnknown()}).
048   * The 6 header bytes of the attribute (attribute_name_index and attribute_length) are <i>not</i>
049   * included.
050   */
051  private byte[] content;
052
053  /**
054   * The next attribute in this attribute list (Attribute instances can be linked via this field to
055   * store a list of class, field, method or Code attributes). May be {@literal null}.
056   */
057  Attribute nextAttribute;
058
059  /**
060   * Constructs a new empty attribute.
061   *
062   * @param type the type of the attribute.
063   */
064  protected Attribute(final String type) {
065    this.type = type;
066  }
067
068  /**
069   * Returns {@literal true} if this type of attribute is unknown. This means that the attribute
070   * content can't be parsed to extract constant pool references, labels, etc. Instead, the
071   * attribute content is read as an opaque byte array, and written back as is. This can lead to
072   * invalid attributes, if the content actually contains constant pool references, labels, or other
073   * symbolic references that need to be updated when there are changes to the constant pool, the
074   * method bytecode, etc. The default implementation of this method always returns {@literal true}.
075   *
076   * @return {@literal true} if this type of attribute is unknown.
077   */
078  public boolean isUnknown() {
079    return true;
080  }
081
082  /**
083   * Returns {@literal true} if this type of attribute is a Code attribute.
084   *
085   * @return {@literal true} if this type of attribute is a Code attribute.
086   */
087  public boolean isCodeAttribute() {
088    return false;
089  }
090
091  /**
092   * Returns the labels corresponding to this attribute.
093   *
094   * @return the labels corresponding to this attribute, or {@literal null} if this attribute is not
095   *     a Code attribute that contains labels.
096   */
097  protected Label[] getLabels() {
098    return new Label[0];
099  }
100
101  /**
102   * Reads a {@link #type} attribute. This method must return a <i>new</i> {@link Attribute} object,
103   * of type {@link #type}, corresponding to the 'length' bytes starting at 'offset', in the given
104   * ClassReader.
105   *
106   * @param classReader the class that contains the attribute to be read.
107   * @param offset index of the first byte of the attribute's content in {@link ClassReader}. The 6
108   *     attribute header bytes (attribute_name_index and attribute_length) are not taken into
109   *     account here.
110   * @param length the length of the attribute's content (excluding the 6 attribute header bytes).
111   * @param charBuffer the buffer to be used to call the ClassReader methods requiring a
112   *     'charBuffer' parameter.
113   * @param codeAttributeOffset index of the first byte of content of the enclosing Code attribute
114   *     in {@link ClassReader}, or -1 if the attribute to be read is not a Code attribute. The 6
115   *     attribute header bytes (attribute_name_index and attribute_length) are not taken into
116   *     account here.
117   * @param labels the labels of the method's code, or {@literal null} if the attribute to be read
118   *     is not a Code attribute.
119   * @return a <i>new</i> {@link Attribute} object corresponding to the specified bytes.
120   */
121  protected Attribute read(
122      final ClassReader classReader,
123      final int offset,
124      final int length,
125      final char[] charBuffer,
126      final int codeAttributeOffset,
127      final Label[] labels) {
128    Attribute attribute = new Attribute(type);
129    attribute.content = new byte[length];
130    System.arraycopy(classReader.classFileBuffer, offset, attribute.content, 0, length);
131    return attribute;
132  }
133
134  /**
135   * Returns the byte array form of the content of this attribute. The 6 header bytes
136   * (attribute_name_index and attribute_length) must <i>not</i> be added in the returned
137   * ByteVector.
138   *
139   * @param classWriter the class to which this attribute must be added. This parameter can be used
140   *     to add the items that corresponds to this attribute to the constant pool of this class.
141   * @param code the bytecode of the method corresponding to this Code attribute, or {@literal null}
142   *     if this attribute is not a Code attribute. Corresponds to the 'code' field of the Code
143   *     attribute.
144   * @param codeLength the length of the bytecode of the method corresponding to this code
145   *     attribute, or 0 if this attribute is not a Code attribute. Corresponds to the 'code_length'
146   *     field of the Code attribute.
147   * @param maxStack the maximum stack size of the method corresponding to this Code attribute, or
148   *     -1 if this attribute is not a Code attribute.
149   * @param maxLocals the maximum number of local variables of the method corresponding to this code
150   *     attribute, or -1 if this attribute is not a Code attribute.
151   * @return the byte array form of this attribute.
152   */
153  protected ByteVector write(
154      final ClassWriter classWriter,
155      final byte[] code,
156      final int codeLength,
157      final int maxStack,
158      final int maxLocals) {
159    return new ByteVector(content);
160  }
161
162  /**
163   * Returns the number of attributes of the attribute list that begins with this attribute.
164   *
165   * @return the number of attributes of the attribute list that begins with this attribute.
166   */
167  final int getAttributeCount() {
168    int count = 0;
169    Attribute attribute = this;
170    while (attribute != null) {
171      count += 1;
172      attribute = attribute.nextAttribute;
173    }
174    return count;
175  }
176
177  /**
178   * Returns the total size in bytes of all the attributes in the attribute list that begins with
179   * this attribute. This size includes the 6 header bytes (attribute_name_index and
180   * attribute_length) per attribute. Also adds the attribute type names to the constant pool.
181   *
182   * @param symbolTable where the constants used in the attributes must be stored.
183   * @return the size of all the attributes in this attribute list. This size includes the size of
184   *     the attribute headers.
185   */
186  final int computeAttributesSize(final SymbolTable symbolTable) {
187    final byte[] code = null;
188    final int codeLength = 0;
189    final int maxStack = -1;
190    final int maxLocals = -1;
191    return computeAttributesSize(symbolTable, code, codeLength, maxStack, maxLocals);
192  }
193
194  /**
195   * Returns the total size in bytes of all the attributes in the attribute list that begins with
196   * this attribute. This size includes the 6 header bytes (attribute_name_index and
197   * attribute_length) per attribute. Also adds the attribute type names to the constant pool.
198   *
199   * @param symbolTable where the constants used in the attributes must be stored.
200   * @param code the bytecode of the method corresponding to these Code attributes, or {@literal
201   *     null} if they are not Code attributes. Corresponds to the 'code' field of the Code
202   *     attribute.
203   * @param codeLength the length of the bytecode of the method corresponding to these code
204   *     attributes, or 0 if they are not Code attributes. Corresponds to the 'code_length' field of
205   *     the Code attribute.
206   * @param maxStack the maximum stack size of the method corresponding to these Code attributes, or
207   *     -1 if they are not Code attributes.
208   * @param maxLocals the maximum number of local variables of the method corresponding to these
209   *     Code attributes, or -1 if they are not Code attribute.
210   * @return the size of all the attributes in this attribute list. This size includes the size of
211   *     the attribute headers.
212   */
213  final int computeAttributesSize(
214      final SymbolTable symbolTable,
215      final byte[] code,
216      final int codeLength,
217      final int maxStack,
218      final int maxLocals) {
219    final ClassWriter classWriter = symbolTable.classWriter;
220    int size = 0;
221    Attribute attribute = this;
222    while (attribute != null) {
223      symbolTable.addConstantUtf8(attribute.type);
224      size += 6 + attribute.write(classWriter, code, codeLength, maxStack, maxLocals).length;
225      attribute = attribute.nextAttribute;
226    }
227    return size;
228  }
229
230  /**
231   * Returns the total size in bytes of all the attributes that correspond to the given field,
232   * method or class access flags and signature. This size includes the 6 header bytes
233   * (attribute_name_index and attribute_length) per attribute. Also adds the attribute type names
234   * to the constant pool.
235   *
236   * @param symbolTable where the constants used in the attributes must be stored.
237   * @param accessFlags some field, method or class access flags.
238   * @param signatureIndex the constant pool index of a field, method of class signature.
239   * @return the size of all the attributes in bytes. This size includes the size of the attribute
240   *     headers.
241   */
242  static int computeAttributesSize(
243      final SymbolTable symbolTable, final int accessFlags, final int signatureIndex) {
244    int size = 0;
245    // Before Java 1.5, synthetic fields are represented with a Synthetic attribute.
246    if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0
247        && symbolTable.getMajorVersion() < Opcodes.V1_5) {
248      // Synthetic attributes always use 6 bytes.
249      symbolTable.addConstantUtf8(Constants.SYNTHETIC);
250      size += 6;
251    }
252    if (signatureIndex != 0) {
253      // Signature attributes always use 8 bytes.
254      symbolTable.addConstantUtf8(Constants.SIGNATURE);
255      size += 8;
256    }
257    // ACC_DEPRECATED is ASM specific, the ClassFile format uses a Deprecated attribute instead.
258    if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
259      // Deprecated attributes always use 6 bytes.
260      symbolTable.addConstantUtf8(Constants.DEPRECATED);
261      size += 6;
262    }
263    return size;
264  }
265
266  /**
267   * Puts all the attributes of the attribute list that begins with this attribute, in the given
268   * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per
269   * attribute.
270   *
271   * @param symbolTable where the constants used in the attributes must be stored.
272   * @param output where the attributes must be written.
273   */
274  final void putAttributes(final SymbolTable symbolTable, final ByteVector output) {
275    final byte[] code = null;
276    final int codeLength = 0;
277    final int maxStack = -1;
278    final int maxLocals = -1;
279    putAttributes(symbolTable, code, codeLength, maxStack, maxLocals, output);
280  }
281
282  /**
283   * Puts all the attributes of the attribute list that begins with this attribute, in the given
284   * byte vector. This includes the 6 header bytes (attribute_name_index and attribute_length) per
285   * attribute.
286   *
287   * @param symbolTable where the constants used in the attributes must be stored.
288   * @param code the bytecode of the method corresponding to these Code attributes, or {@literal
289   *     null} if they are not Code attributes. Corresponds to the 'code' field of the Code
290   *     attribute.
291   * @param codeLength the length of the bytecode of the method corresponding to these code
292   *     attributes, or 0 if they are not Code attributes. Corresponds to the 'code_length' field of
293   *     the Code attribute.
294   * @param maxStack the maximum stack size of the method corresponding to these Code attributes, or
295   *     -1 if they are not Code attributes.
296   * @param maxLocals the maximum number of local variables of the method corresponding to these
297   *     Code attributes, or -1 if they are not Code attribute.
298   * @param output where the attributes must be written.
299   */
300  final void putAttributes(
301      final SymbolTable symbolTable,
302      final byte[] code,
303      final int codeLength,
304      final int maxStack,
305      final int maxLocals,
306      final ByteVector output) {
307    final ClassWriter classWriter = symbolTable.classWriter;
308    Attribute attribute = this;
309    while (attribute != null) {
310      ByteVector attributeContent =
311          attribute.write(classWriter, code, codeLength, maxStack, maxLocals);
312      // Put attribute_name_index and attribute_length.
313      output.putShort(symbolTable.addConstantUtf8(attribute.type)).putInt(attributeContent.length);
314      output.putByteArray(attributeContent.data, 0, attributeContent.length);
315      attribute = attribute.nextAttribute;
316    }
317  }
318
319  /**
320   * Puts all the attributes that correspond to the given field, method or class access flags and
321   * signature, in the given byte vector. This includes the 6 header bytes (attribute_name_index and
322   * attribute_length) per attribute.
323   *
324   * @param symbolTable where the constants used in the attributes must be stored.
325   * @param accessFlags some field, method or class access flags.
326   * @param signatureIndex the constant pool index of a field, method of class signature.
327   * @param output where the attributes must be written.
328   */
329  static void putAttributes(
330      final SymbolTable symbolTable,
331      final int accessFlags,
332      final int signatureIndex,
333      final ByteVector output) {
334    // Before Java 1.5, synthetic fields are represented with a Synthetic attribute.
335    if ((accessFlags & Opcodes.ACC_SYNTHETIC) != 0
336        && symbolTable.getMajorVersion() < Opcodes.V1_5) {
337      output.putShort(symbolTable.addConstantUtf8(Constants.SYNTHETIC)).putInt(0);
338    }
339    if (signatureIndex != 0) {
340      output
341          .putShort(symbolTable.addConstantUtf8(Constants.SIGNATURE))
342          .putInt(2)
343          .putShort(signatureIndex);
344    }
345    if ((accessFlags & Opcodes.ACC_DEPRECATED) != 0) {
346      output.putShort(symbolTable.addConstantUtf8(Constants.DEPRECATED)).putInt(0);
347    }
348  }
349
350  /** A set of attribute prototypes (attributes with the same type are considered equal). */
351  static final class Set {
352
353    private static final int SIZE_INCREMENT = 6;
354
355    private int size;
356    private Attribute[] data = new Attribute[SIZE_INCREMENT];
357
358    void addAttributes(final Attribute attributeList) {
359      Attribute attribute = attributeList;
360      while (attribute != null) {
361        if (!contains(attribute)) {
362          add(attribute);
363        }
364        attribute = attribute.nextAttribute;
365      }
366    }
367
368    Attribute[] toArray() {
369      Attribute[] result = new Attribute[size];
370      System.arraycopy(data, 0, result, 0, size);
371      return result;
372    }
373
374    private boolean contains(final Attribute attribute) {
375      for (int i = 0; i < size; ++i) {
376        if (data[i].type.equals(attribute.type)) {
377          return true;
378        }
379      }
380      return false;
381    }
382
383    private void add(final Attribute attribute) {
384      if (size >= data.length) {
385        Attribute[] newData = new Attribute[data.length + SIZE_INCREMENT];
386        System.arraycopy(data, 0, newData, 0, size);
387        data = newData;
388      }
389      data[size++] = attribute;
390    }
391  }
392}