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DexTrapStackFixer.java
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DexTrapStackFixer.java
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package soot.dexpler;
import java.util.Map;
import soot.Body;
import soot.BodyTransformer;
import soot.Local;
import soot.Trap;
import soot.Unit;
import soot.javaToJimple.LocalGenerator;
import soot.jimple.CaughtExceptionRef;
import soot.jimple.IdentityStmt;
import soot.jimple.Jimple;
import soot.jimple.Stmt;
/**
* Transformer to ensure that all exception handlers pull the exception object.
* In other words, if an exception handler must always have a unit like
*
* $r10 = @caughtexception
*
* This is especially important if the dex code is later to be translated into
* Java bytecode. If no one ever accesses the exception object, it will reside
* on the stack forever, potentially leading to mismatching stack heights.
*
* @author Steven Arzt
*
*/
public class DexTrapStackFixer extends BodyTransformer {
public static DexTrapStackFixer v() {
return new DexTrapStackFixer();
}
@Override
protected void internalTransform(Body b, String phaseName,
Map<String, String> options) {
for (Trap t : b.getTraps()) {
// If the first statement already catches the exception, we're fine
if (isCaughtExceptionRef(t.getHandlerUnit()))
continue;
// Add the exception reference
Local l = new LocalGenerator(b).generateLocal(t.getException().getType());
Stmt caughtStmt = Jimple.v().newIdentityStmt(l, Jimple.v().newCaughtExceptionRef());
b.getUnits().add(caughtStmt);
b.getUnits().add(Jimple.v().newGotoStmt(t.getHandlerUnit()));
t.setHandlerUnit(caughtStmt);
}
}
/**
* Checks whether the given statement stores an exception reference
* @param handlerUnit The statement to check
* @return True if the given statement stores an exception reference,
* otherwise false
*/
private boolean isCaughtExceptionRef(Unit handlerUnit) {
if (!(handlerUnit instanceof IdentityStmt))
return false;
IdentityStmt stmt = (IdentityStmt) handlerUnit;
return stmt.getRightOp() instanceof CaughtExceptionRef;
}
}