StackMapAttribute


1   /**
2    * ASM: a very small and fast Java bytecode manipulation framework
3    * Copyright (c) 2000-2005 INRIA, France Telecom
4    * All rights reserved.
5    *
6    * Redistribution and use in source and binary forms, with or without
7    * modification, are permitted provided that the following conditions
8    * are met:
9    * 1. Redistributions of source code must retain the above copyright
10   *    notice, this list of conditions and the following disclaimer.
11   * 2. Redistributions in binary form must reproduce the above copyright
12   *    notice, this list of conditions and the following disclaimer in the
13   *    documentation and/or other materials provided with the distribution.
14   * 3. Neither the name of the copyright holders nor the names of its
15   *    contributors may be used to endorse or promote products derived from
16   *    this software without specific prior written permission.
17   *
18   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
19   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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23   * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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30  package org.objectweb.asm.attrs;
31  
32  import java.util.ArrayList  ;
33  import java.util.HashSet  ;
34  import java.util.Iterator  ;
35  import java.util.List  ;
36  import java.util.Set  ;
37  
38  import org.objectweb.asm.Attribute;
39  import org.objectweb.asm.ByteVector;
40  import org.objectweb.asm.ClassReader;
41  import org.objectweb.asm.ClassWriter;
42  import org.objectweb.asm.Label;
43  
44  /**
45   * StackMapAttribute is used by CDLC preverifier. Definition is given in
46   * appendix "CLDC Byte Code Typechecker Specification" from CDLC 1.1
47   * specification. <p> <i>Note that this implementation does not calculate
48   * StackMapFrame structures from the method bytecode. If method code is changed
49   * or generated from scratch, then developer is responsible to prepare a correct
50   * StackMapFrame structures.</i> <p> The format of the stack map in the class
51   * file is given below. In the following, <ul> <li>if the length of the
52   * method's byte code1 is 65535 or less, then <tt>uoffset</tt> represents the
53   * type u2; otherwise <tt>uoffset</tt> represents the type u4.</li> <li>If
54   * the maximum number of local variables for the method is 65535 or less, then
55   * <tt>ulocalvar</tt> represents the type u2; otherwise <tt>ulocalvar</tt>
56   * represents the type u4.</li> <li>If the maximum size of the operand stack
57   * is 65535 or less, then <tt>ustack</tt> represents the type u2; otherwise
58   * ustack represents the type u4.</li> </ul>
59   * 
60   * <pre>
61   * stack_map { // attribute StackMap
62   *   u2 attribute_name_index;
63   *   u4 attribute_length
64   *   uoffset number_of_entries;
65   *   stack_map_frame entries[number_of_entries];
66   * }
67   * </pre>
68   * 
69   * Each stack map frame has the following format:
70   * 
71   * <pre>
72   * stack_map_frame {
73   *   uoffset offset;
74   *   ulocalvar number_of_locals;
75   *   verification_type_info locals[number_of_locals];
76   *   ustack number_of_stack_items;
77   *   verification_type_info stack[number_of_stack_items];
78   * }
79   * </pre>
80   * 
81   * The <tt>verification_type_info</tt> structure consists of a one-byte tag
82   * followed by zero or more bytes, giving more information about the tag. Each
83   * <tt>verification_type_info</tt> structure specifies the verification type
84   * of one or two locations.
85   * 
86   * <pre>
87   * union verification_type_info {
88   *   Top_variable_info;
89   *   Integer_variable_info;
90   *   Float_variable_info;
91   *   Long_variable_info;
92   *   Double_variable_info;
93   *   Null_variable_info;
94   *   UninitializedThis_variable_info;
95   *   Object_variable_info;
96   *   Uninitialized_variable_info;
97   * }
98   *      
99   * Top_variable_info {
100  *   u1 tag = ITEM_Top; // 0
101  * }
102  *      
103  * Integer_variable_info {
104  *   u1 tag = ITEM_Integer; // 1
105  * }
106  *      
107  * Float_variable_info {
108  *   u1 tag = ITEM_Float; // 2
109  * }
110  *      
111  * Long_variable_info {
112  *   u1 tag = ITEM_Long; // 4
113  * }
114  *      
115  * Double_variable_info {
116  *   u1 tag = ITEM_Double; // 3
117  * }
118  *      
119  * Null_variable_info {
120  *  u1 tag = ITEM_Null; // 5
121  * }
122  *      
123  * UninitializedThis_variable_info {
124  *   u1 tag = ITEM_UninitializedThis; // 6
125  * }
126  *      
127  * Object_variable_info {
128  *   u1 tag = ITEM_Object; // 7
129  *   u2 cpool_index;
130  * }
131  *      
132  * Uninitialized_variable_info {
133  *   u1 tag = ITEM_Uninitialized // 8
134  *   uoffset offset;
135  * }
136  * </pre>
137  * 
138  * @see <a HREF="http://www.jcp.org/en/jsr/detail?id=139">JSR 139 : Connected
139  *      Limited Device Configuration 1.1</a>
140  * 
141  * @author Eugene Kuleshov
142  */
143 public class StackMapAttribute extends Attribute {
144 
145     static final int MAX_SIZE = 65535;
146 
147     /**
148      * A List of <code>StackMapFrame</code> instances.
149      */
150     public List   frames = new ArrayList  ();
151 
152     public StackMapAttribute() {
153         super("StackMap");
154     }
155 
156     public StackMapAttribute(List   frames) {
157         this();
158         this.frames = frames;
159     }
160 
161     public List   getFrames() {
162         return frames;
163     }
164 
165     public StackMapFrame getFrame(Label label) {
166         for (int i = 0; i < frames.size(); i++) {
167             StackMapFrame frame = (StackMapFrame) frames.get(i);
168             if (frame.label == label) {
169                 return frame;
170             }
171         }
172         return null;
173     }
174 
175     public boolean isUnknown() {
176         return false;
177     }
178 
179     public boolean isCodeAttribute() {
180         return true;
181     }
182 
183     protected Attribute read(
184         ClassReader cr,
185         int off,
186         int len,
187         char[] buf,
188         int codeOff,
189         Label[] labels)
190     {
191         StackMapAttribute attr = new StackMapAttribute();
192         // note that this is not the size of Code attribute
193         boolean isExtCodeSize = cr.readInt(codeOff + 4) > MAX_SIZE;
194         boolean isExtLocals = cr.readUnsignedShort(codeOff + 2) > MAX_SIZE;
195         boolean isExtStack = cr.readUnsignedShort(codeOff) > MAX_SIZE;
196 
197         int size = 0;
198         if (isExtCodeSize) {
199             size = cr.readInt(off);
200             off += 4;
201         } else {
202             size = cr.readUnsignedShort(off);
203             off += 2;
204         }
205         for (int i = 0; i < size; i++) {
206             int offset;
207             if (isExtCodeSize) {
208                 offset = cr.readInt(off);
209                 off += 4;
210             } else {
211                 offset = cr.readUnsignedShort(off);
212                 off += 2;
213             }
214 
215             Label label = getLabel(offset, labels);
216             List   locals = new ArrayList  ();
217             List   stack = new ArrayList  ();
218 
219             off = readTypeInfo(cr,
220                     off,
221                     locals,
222                     labels,
223                     buf,
224                     isExtLocals,
225                     isExtCodeSize);
226             off = readTypeInfo(cr,
227                     off,
228                     stack,
229                     labels,
230                     buf,
231                     isExtStack,
232                     isExtCodeSize);
233 
234             attr.frames.add(new StackMapFrame(label, locals, stack));
235         }
236         return attr;
237     }
238 
239     private int readTypeInfo(
240         ClassReader cr,
241         int off,
242         List   info,
243         Label[] labels,
244         char[] buf,
245         boolean isExt,
246         boolean isExtCode)
247     {
248         int n = 0;
249         if (isExt) {
250             n = cr.readInt(off);
251             off += 4;
252         } else {
253             n = cr.readUnsignedShort(off);
254             off += 2;
255         }
256         for (int j = 0; j < n; j++) {
257             int itemType = cr.readByte(off++);
258             StackMapType typeInfo = StackMapType.getTypeInfo(itemType);
259             info.add(typeInfo);
260             switch (itemType) {
261                 case StackMapType.ITEM_Object: //
262                     typeInfo.setObject(cr.readClass(off, buf));
263                     off += 2;
264                     break;
265                 case StackMapType.ITEM_Uninitialized: //
266                     int offset;
267                     if (isExtCode) {
268                         offset = cr.readInt(off);
269                         off += 4;
270                     } else {
271                         offset = cr.readUnsignedShort(off);
272                         off += 2;
273                     }
274                     typeInfo.setLabel(getLabel(offset, labels));
275                     break;
276             }
277         }
278         return off;
279     }
280 
281     private void writeTypeInfo(ByteVector bv, ClassWriter cw, List   info, int max)
282     {
283         if (max > StackMapAttribute.MAX_SIZE) {
284             bv.putInt(info.size());
285         } else {
286             bv.putShort(info.size());
287         }
288         for (int j = 0; j < info.size(); j++) {
289             StackMapType typeInfo = (StackMapType) info.get(j);
290             bv.putByte(typeInfo.getType());
291             switch (typeInfo.getType()) {
292                 case StackMapType.ITEM_Object: //
293                     bv.putShort(cw.newClass(typeInfo.getObject()));
294                     break;
295 
296                 case StackMapType.ITEM_Uninitialized: //
297                     bv.putShort(typeInfo.getLabel().getOffset());
298                     break;
299 
300             }
301         }
302     }
303 
304     private Label getLabel(int offset, Label[] labels) {
305         Label l = labels[offset];
306         if (l != null) {
307             return l;
308         }
309         return labels[offset] = new Label();
310     }
311 
312     protected ByteVector write(
313         ClassWriter cw,
314         byte[] code,
315         int len,
316         int maxStack,
317         int maxLocals)
318     {
319         ByteVector bv = new ByteVector();
320         if (code != null && code.length > MAX_SIZE) { // TODO verify value
321             bv.putInt(frames.size());
322         } else {
323             bv.putShort(frames.size());
324         }
325         for (int i = 0; i < frames.size(); i++) {
326             writeFrame((StackMapFrame) frames.get(i),
327                     cw,
328                     maxStack,
329                     maxLocals,
330                     bv);
331         }
332         return bv;
333     }
334 
335     protected Label[] getLabels() {
336         HashSet   labels = new HashSet  ();
337         for (int i = 0; i < frames.size(); i++) {
338             getFrameLabels((StackMapFrame) frames.get(i), labels);
339         }
340         return (Label[]) labels.toArray(new Label[labels.size()]);
341     }
342 
343     private void writeFrame(
344         StackMapFrame frame,
345         ClassWriter cw,
346         int maxStack,
347         int maxLocals,
348         ByteVector bv)
349     {
350         bv.putShort(frame.label.getOffset());
351         writeTypeInfo(bv, cw, frame.locals, maxLocals);
352         writeTypeInfo(bv, cw, frame.stack, maxStack);
353     }
354 
355     private void getFrameLabels(StackMapFrame frame, Set   labels) {
356         labels.add(frame.label);
357         getTypeInfoLabels(labels, frame.locals);
358         getTypeInfoLabels(labels, frame.stack);
359     }
360 
361     private void getTypeInfoLabels(Set   labels, List   info) {
362         for (Iterator   it = info.iterator(); it.hasNext();) {
363             StackMapType typeInfo = (StackMapType) it.next();
364             if (typeInfo.getType() == StackMapType.ITEM_Uninitialized) {
365                 labels.add(typeInfo.getLabel());
366             }
367         }
368     }
369 
370     public String   toString() {
371         StringBuffer   sb = new StringBuffer  ("StackMap[");
372         for (int i = 0; i < frames.size(); i++) {
373             sb.append('\n').append('[').append(frames.get(i)).append(']');
374         }
375         sb.append("\n]");
376         return sb.toString();
377     }
378 }
379
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