1   package org.apache.bcel.verifier.structurals;
2   
3   /* ====================================================================
4    * The Apache Software License, Version 1.1
5    *
6    * Copyright (c) 2001 The Apache Software Foundation.  All rights
7    * reserved.
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12   *
13   * 1. Redistributions of source code must retain the above copyright
14   *    notice, this list of conditions and the following disclaimer.
15   *
16   * 2. Redistributions in binary form must reproduce the above copyright
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56  
57  import org.apache.bcel.generic.*;
58  import org.apache.bcel.verifier.VerifierFactory;
59  import org.apache.bcel.verifier.exc.*;
60  import java.util.*;
61  
62  /***
63   * This class represents a control flow graph of a method.
64   *
65   * @version $Id: ControlFlowGraph.java,v 1.1.1.1 2001/10/29 20:00:37 jvanzyl Exp $
66   * @author <A HREF="http://www.inf.fu-berlin.de/~ehaase"/>Enver Haase</A>
67   */
68  public class ControlFlowGraph{
69  
70  	/***
71  	 * Objects of this class represent a node in a ControlFlowGraph.
72  	 * These nodes are instructions, not basic blocks.
73  	 */
74  	private class InstructionContextImpl implements InstructionContext{
75  
76  		/***
77  		 * The TAG field is here for external temporary flagging, such
78  		 * as graph colouring.
79  		 *
80  		 * @see #getTag()
81  		 * @see #setTag(int)
82  		 */
83  		private int TAG;
84  
85  		/***
86  		 * The InstructionHandle this InstructionContext is wrapped around.
87  		 */
88  		private InstructionHandle instruction;
89  
90  		/***
91  		 * The 'incoming' execution Frames.
92  		 */
93  		private HashMap inFrames;	// key: the last-executed JSR
94  
95  		/***
96  		 * The 'outgoing' execution Frames.
97  		 */
98  		private HashMap outFrames; // key: the last-executed JSR 
99  
100 		/***
101 		 * The 'execution predecessors' - a list of type InstructionContext 
102 		 * of those instances that have been execute()d before in that order.
103 		 */
104 		private ArrayList executionPredecessors = null; // Type: InstructionContext
105 	
106 		/***
107 		 * Creates an InstructionHandleImpl object from an InstructionHandle.
108 		 * Creation of one per InstructionHandle suffices. Don't create more.
109 		 */
110 		public InstructionContextImpl(InstructionHandle inst){
111 			if (inst == null) throw new AssertionViolatedException("Cannot instantiate InstructionContextImpl from NULL.");
112 		
113 			instruction = inst;
114 			inFrames = new java.util.HashMap();
115 			outFrames = new java.util.HashMap();
116 		}
117 
118 		/* Satisfies InstructionContext.getTag(). */
119 		public int getTag(){
120 			return TAG;
121 		}
122 
123 		/* Satisfies InstructionContext.setTag(int). */
124 		public void setTag(int tag){
125 			TAG = tag;
126 		}
127 
128 		/***
129 		 * Returns the exception handlers of this instruction.
130 		 */
131 		public ExceptionHandler[] getExceptionHandlers(){
132 			return exceptionhandlers.getExceptionHandlers(getInstruction());
133 		}
134 
135 		/***
136 		 * Returns a clone of the "outgoing" frame situation with respect to the given ExecutionChain.
137 		 */	
138 		public Frame getOutFrame(ArrayList execChain){
139 			executionPredecessors = execChain;
140 
141 			Frame org;
142 
143 			InstructionContext jsr = lastExecutionJSR();
144 
145 			org = (Frame) outFrames.get(jsr);
146 
147 			if (org == null){
148 				throw new AssertionViolatedException("outFrame not set! This:\n"+this+"\nExecutionChain: "+getExecutionChain()+"\nOutFrames: '"+outFrames+"'.");
149 			}
150 			return org.getClone();
151 		}
152 
153 		/***
154 		 * "Merges in" (vmspec2, page 146) the "incoming" frame situation;
155 		 * executes the instructions symbolically
156 		 * and therefore calculates the "outgoing" frame situation.
157 		 * Returns: True iff the "incoming" frame situation changed after
158 		 * merging with "inFrame".
159 		 * The execPreds ArrayList must contain the InstructionContext
160 		 * objects executed so far in the correct order. This is just
161 		 * one execution path [out of many]. This is needed to correctly
162 		 * "merge" in the special case of a RET's successor.
163 		 * <B>The InstConstraintVisitor and ExecutionVisitor instances
164 		 * must be set up correctly.</B>
165 		 * @return true - if and only if the "outgoing" frame situation
166 		 * changed from the one before execute()ing.
167 		 */
168 		public boolean execute(Frame inFrame, ArrayList execPreds, InstConstraintVisitor icv, ExecutionVisitor ev){
169 
170 			executionPredecessors = (ArrayList) execPreds.clone();
171 
172 			//sanity check
173 			if ( (lastExecutionJSR() == null) && (subroutines.subroutineOf(getInstruction()) != subroutines.getTopLevel() ) ){
174 				throw new AssertionViolatedException("Huh?! Am I '"+this+"' part of a subroutine or not?");
175 			}
176 			if ( (lastExecutionJSR() != null) && (subroutines.subroutineOf(getInstruction()) == subroutines.getTopLevel() ) ){
177 				throw new AssertionViolatedException("Huh?! Am I '"+this+"' part of a subroutine or not?");
178 			}
179 
180 			Frame inF = (Frame) inFrames.get(lastExecutionJSR());
181 			if (inF == null){// no incoming frame was set, so set it.
182 				inFrames.put(lastExecutionJSR(), inFrame);
183 				inF = inFrame;
184 			}
185 			else{// if there was an "old" inFrame
186 				if (inF.equals(inFrame)){ //shortcut: no need to merge equal frames.
187 					return false;
188 				}
189 				if (! mergeInFrames(inFrame)){
190 					return false;
191 				}
192 			}
193 			
194 			// Now we're sure the inFrame has changed!
195 			
196 			// new inFrame is already merged in, see above.		
197 			Frame workingFrame = inF.getClone();
198 
199 			try{
200 				// This verifies the InstructionConstraint for the current
201 				// instruction, but does not modify the workingFrame object.
202 //InstConstraintVisitor icv = InstConstraintVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
203 				icv.setFrame(workingFrame);
204 				getInstruction().accept(icv);
205 			}
206 			catch(StructuralCodeConstraintException ce){
207 				ce.extendMessage("","\nInstructionHandle: "+getInstruction()+"\n");
208 				ce.extendMessage("","\nExecution Frame:\n"+workingFrame);
209 				extendMessageWithFlow(ce);
210 				throw ce;
211 			}
212 
213 			// This executes the Instruction.
214 			// Therefore the workingFrame object is modified.
215 //ExecutionVisitor ev = ExecutionVisitor.getInstance(VerifierFactory.getVerifier(method_gen.getClassName()));
216 			ev.setFrame(workingFrame);
217 			getInstruction().accept(ev);
218 			//getInstruction().accept(ExecutionVisitor.withFrame(workingFrame));
219 			outFrames.put(lastExecutionJSR(), workingFrame);
220 
221 			return true;	// new inFrame was different from old inFrame so merging them
222 										// yielded a different this.inFrame.
223 		}
224 
225 		/***
226 		 * Returns a simple String representation of this InstructionContext.
227 		 */
228 		public String toString(){
229 		//TODO: Put information in the brackets, e.g.
230 		//      Is this an ExceptionHandler? Is this a RET? Is this the start of
231 		//      a subroutine?
232 			String ret = getInstruction().toString(false)+"\t[InstructionContext]";
233 			return ret;
234 		}
235 
236 		/***
237 		 * Does the actual merging (vmspec2, page 146).
238 		 * Returns true IFF this.inFrame was changed in course of merging with inFrame.
239 		 */
240 		private boolean mergeInFrames(Frame inFrame){
241 			// TODO: Can be performance-improved.
242 			Frame inF = (Frame) inFrames.get(lastExecutionJSR());
243 			OperandStack oldstack = inF.getStack().getClone();
244 			LocalVariables oldlocals = inF.getLocals().getClone();
245 			try{
246 				inF.getStack().merge(inFrame.getStack());
247 				inF.getLocals().merge(inFrame.getLocals());
248 			}
249 			catch (StructuralCodeConstraintException sce){
250 				extendMessageWithFlow(sce);
251 				throw sce;
252 			}
253 			if (	oldstack.equals(inF.getStack()) &&
254 						oldlocals.equals(inF.getLocals()) ){
255 				return false;
256 			}
257 			else{
258 				return true;
259 			}
260 		}
261 
262 		/***
263 		 * Returns the control flow execution chain. This is built
264 		 * while execute(Frame, ArrayList)-ing the code represented
265 		 * by the surrounding ControlFlowGraph.
266 		 */
267 		private String getExecutionChain(){
268 			String s = this.toString();
269 			for (int i=executionPredecessors.size()-1; i>=0; i--){
270 				s = executionPredecessors.get(i)+"\n" + s;
271 			}
272 			return s;
273 		}
274 
275 
276 		/***
277 		 * Extends the StructuralCodeConstraintException ("e") object with an at-the-end-extended message.
278 		 * This extended message will then reflect the execution flow needed to get to the constraint
279 		 * violation that triggered the throwing of the "e" object.
280 		 */
281 		private void extendMessageWithFlow(StructuralCodeConstraintException e){
282 			String s = "Execution flow:\n";
283 			e.extendMessage("", s+getExecutionChain());
284 		}
285 
286 		/*
287 		 * Fulfils the contract of InstructionContext.getInstruction().
288 		 */
289 		public InstructionHandle getInstruction(){
290 			return instruction;
291 		}
292 
293 		/***
294 		 * Returns the InstructionContextImpl with an JSR/JSR_W
295 		 * that was last in the ExecutionChain, without
296 		 * a corresponding RET, i.e.
297 		 * we were called by this one.
298 		 * Returns null if we were called from the top level.
299 		 */
300 		private InstructionContextImpl lastExecutionJSR(){
301 			
302 			int size = executionPredecessors.size();
303 			int retcount = 0;
304 			
305 			for (int i=size-1; i>=0; i--){
306 				InstructionContextImpl current = (InstructionContextImpl) (executionPredecessors.get(i));
307 				Instruction currentlast = current.getInstruction().getInstruction();
308 				if (currentlast instanceof RET) retcount++;
309 				if (currentlast instanceof JsrInstruction){
310 					retcount--;
311 					if (retcount == -1) return current;
312 				}
313 			}
314 			return null;
315 		}
316 
317 		/* Satisfies InstructionContext.getSuccessors(). */
318 		public InstructionContext[] getSuccessors(){
319 			return contextsOf(_getSuccessors());
320 		}
321 
322 		/***
323 		 * A utility method that calculates the successors of a given InstructionHandle
324 		 * That means, a RET does have successors as defined here.
325 		 * A JsrInstruction has its target as its successor
326 		 * (opposed to its physical successor) as defined here.
327 		 */
328 // TODO: implement caching!
329 		private InstructionHandle[] _getSuccessors(){
330 			final InstructionHandle[] empty = new InstructionHandle[0];
331 			final InstructionHandle[] single = new InstructionHandle[1];
332 			final InstructionHandle[] pair = new InstructionHandle[2];
333 		
334 			Instruction inst = getInstruction().getInstruction();
335 		
336 			if (inst instanceof RET){
337 				Subroutine s = subroutines.subroutineOf(getInstruction());
338 				if (s==null){ //return empty; // RET in dead code. "empty" would be the correct answer, but we know something about the surrounding project...
339 					throw new AssertionViolatedException("Asking for successors of a RET in dead code?!");
340 				}
341 //TODO: remove
342 throw new AssertionViolatedException("DID YOU REALLY WANT TO ASK FOR RET'S SUCCS?");
343 /*
344 				InstructionHandle[] jsrs = s.getEnteringJsrInstructions();
345 				InstructionHandle[] ret = new InstructionHandle[jsrs.length];
346 				for (int i=0; i<jsrs.length; i++){
347 					ret[i] = jsrs[i].getNext();
348 				}
349 				return ret;
350 */
351 			}
352 		
353 			// Terminates method normally.
354 			if (inst instanceof ReturnInstruction){
355 				return empty;
356 			}
357 		
358 			// Terminates method abnormally, because JustIce mandates
359 			// subroutines not to be protected by exception handlers.
360 			if (inst instanceof ATHROW){
361 				return empty;
362 			}
363 		
364 			// See method comment.
365 			if (inst instanceof JsrInstruction){
366 				single[0] = ((JsrInstruction) inst).getTarget();
367 				return single;
368 			}
369 
370 			if (inst instanceof GotoInstruction){
371 				single[0] = ((GotoInstruction) inst).getTarget();
372 				return single;
373 			}
374 
375 			if (inst instanceof BranchInstruction){
376 				if (inst instanceof Select){
377 					// BCEL's getTargets() returns only the non-default targets,
378 					// thanks to Eli Tilevich for reporting.
379 					InstructionHandle[] matchTargets = ((Select) inst).getTargets();
380 					InstructionHandle[] ret = new InstructionHandle[matchTargets.length+1];
381 					ret[0] = ((Select) inst).getTarget();
382 					System.arraycopy(matchTargets, 0, ret, 1, matchTargets.length);
383 					return ret;
384 				}
385 				else{
386 					pair[0] = getInstruction().getNext();
387 					pair[1] = ((BranchInstruction) inst).getTarget();
388 					return pair;
389 				}
390 			}
391 
392 			// default case: Fall through.		
393 			single[0] = getInstruction().getNext();
394 			return single;
395 		}
396 
397 	} // End Inner InstructionContextImpl Class.
398 
399 	/*** The MethofGen object we're working on. */
400 	private final MethodGen method_gen;
401 
402 	/*** The Subroutines object for the method whose control flow is represented by this ControlFlowGraph. */
403 	private final Subroutines subroutines;
404 
405 	/*** The ExceptionHandlers object for the method whose control flow is represented by this ControlFlowGraph. */
406 	private final ExceptionHandlers exceptionhandlers;
407 
408 	/*** All InstructionContext instances of this ControlFlowGraph. */
409 	private Hashtable instructionContexts = new Hashtable(); //keys: InstructionHandle, values: InstructionContextImpl
410 
411 	/*** 
412 	 * A Control Flow Graph.
413 	 */
414 	public ControlFlowGraph(MethodGen method_gen){
415 		subroutines = new Subroutines(method_gen);
416 		exceptionhandlers = new ExceptionHandlers(method_gen);
417 
418 		InstructionHandle[] instructionhandles = method_gen.getInstructionList().getInstructionHandles();
419 		for (int i=0; i<instructionhandles.length; i++){
420 			instructionContexts.put(instructionhandles[i], new InstructionContextImpl(instructionhandles[i]));
421 		}
422 		
423 		this.method_gen = method_gen;
424 	}
425 
426 	/***
427 	 * Returns the InstructionContext of a given instruction.
428 	 */
429 	public InstructionContext contextOf(InstructionHandle inst){
430 		InstructionContext ic = (InstructionContext) instructionContexts.get(inst);
431 		if (ic == null){
432 			throw new AssertionViolatedException("InstructionContext requested for an InstructionHandle that's not known!");
433 		}
434 		return ic;
435 	}
436 
437 	/***
438 	 * Returns the InstructionContext[] of a given InstructionHandle[],
439 	 * in a naturally ordered manner.
440 	 */
441 	public InstructionContext[] contextsOf(InstructionHandle[] insts){
442 		InstructionContext[] ret = new InstructionContext[insts.length];
443 		for (int i=0; i<insts.length; i++){
444 			ret[i] = contextOf(insts[i]);
445 		}
446 		return ret;
447 	}
448 
449 	/***
450 	 * Returns an InstructionContext[] with all the InstructionContext instances
451 	 * for the method whose control flow is represented by this ControlFlowGraph
452 	 * <B>(NOT ORDERED!)</B>.
453 	 */
454 	public InstructionContext[] getInstructionContexts(){
455 		InstructionContext[] ret = new InstructionContext[instructionContexts.values().size()];
456 		return (InstructionContext[]) instructionContexts.values().toArray(ret);
457 	}
458 
459 	/***
460 	 * Returns true, if and only if the said instruction is not reachable; that means,
461 	 * if it not part of this ControlFlowGraph.
462 	 */
463 	public boolean isDead(InstructionHandle i){
464 		return instructionContexts.containsKey(i);
465 	}	 
466 }
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