--Vince
============= BEFORE =============================== method name = public void <init>() aload_0 invokespecial java/lang/Object/<init>()V return method name = public static java.util.ArrayList getArrList() new java/util/ArrayList dup invokespecial java/util/ArrayList/<init>()V areturn method name = public static void main(String[] arg0) getstatic java.lang.System.out Ljava/io/PrintStream; ldc "test" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V new java/util/ArrayList dup invokespecial java/util/ArrayList/<init>()V astore_1 goto -> 20 astore_1 getstatic java.lang.System.out Ljava/io/PrintStream; ldc "test test test" invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V return =======================================================
=============== AFTER ==================================
method name = public void <init>()
aload_0
invokespecial java/lang/Object/<init>()V
return
method name = public static java.util.ArrayList getArrList()
new java/util/ArrayList
dup
invokestatic java/util/ArrayList/getArrList()Ljava/util/ArrayList; LoadClassType = java.util.ArrayList
areturn
method name = public static void main(String[] arg0)
getstatic java.lang.System.out Ljava/io/PrintStream;
ldc "test"
invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V
new java/util/ArrayList
dup
invokestatic java/util/ArrayList/getArrList()Ljava/util/ArrayList; LoadClassType = java.util.ArrayList
astore_1
goto -> 20
astore_1
getstatic java.lang.System.out Ljava/io/PrintStream;
ldc "test test test"
invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V
return
====================================================================
================= Method used to alter the class ==============================
protected void replaceConstructor( ClassGen cg, String original_class, String new_class, String static_method_name ) {
boolean refresh = false;
ConstantPoolGen cp_gen = cg.getConstantPool();
ConstantPool cp = cp_gen.getConstantPool();
InstructionFactory factory = new InstructionFactory( cg , cp_gen );
Method [] methods = cg.getMethods();
for ( int x=0; x<methods.length; x++ ) {
refresh = false;
MethodGen method_gen = new MethodGen( methods[x], cg.getJavaClass().getClassName(), cp_gen );
Iterator i = method_gen.getInstructionList().iterator();
while ( i.hasNext() ) {
InstructionHandle handle = ( InstructionHandle )i.next();
if ( handle.getInstruction() instanceof INVOKESPECIAL && ( ( INVOKESPECIAL )handle.getInstruction() ).getClassName( cp_gen ).equals( original_class ) && ( ( INVOKESPECIAL )handle.getInstruction() ).getMethodName( cp_gen ).equals( "<init>" ) ) {
try {
INVOKESPECIAL invk = ( INVOKESPECIAL )handle.getInstruction();
handle.setInstruction( factory.createInvoke(
new_class,
static_method_name,
new ObjectType( original_class ),
invk.getArgumentTypes( cp_gen ),
Constants.INVOKESTATIC ) );
refresh = true;
//} catch ( org.apache.bcel.generic.TargetLostException e ) {
} catch ( Exception e ) {
Log.write( "ERROR", e.toString() );
}
}
}
if ( refresh ) {
method_gen.stripAttributes( false );
method_gen.setMaxStack();
method_gen.setMaxLocals();
cg.replaceMethod( methods[x], method_gen.getMethod() );
}
}
}
=====================================================================================
Andrew Huntwork wrote:
Posting disassembly for a simple test before and after modification would be very helpful. There are a couple obvious problems with the method you've presented: it doesn't replace the NEW instruction that matches the invokespecial; and it ignores the TargetLostException that will certainly occur in some code. The second problem is easily solvable by using InstructionHandle.setInstruction instead of InstructionList.insert/delete. The first is probably an artifact of not seeing all your code.
Vincent Marquez wrote:
My problem is, while i'm modifying a method, if the method i'm modifying has a try/catch block, I get a "inconsistant stack height" error. It seems this only occurs if the Try/Catch block is directly around the part i'm modifying. Currently, i'm replacing a constructor from once class type to another. It works perfectly except when there are Try/Catch blocks. For example, if I have
1: public static void main( String [] args ) { 2: System.out.println( "test" ); 3: System.out.println( "anotherr test"); 4: Shape shape = new Shape(); 5: System.out.println( "final test" ); 6: }
There isn't a problem if the try/catch is around line 2 and 3. Only if it encapsulates line 4, or anything after, will there be the error. For legal reasons i'm unable to show all my actual code so I contrived a very similar example of our insturmenation method that is below. If i'm doing anything wrong/stupid let me know. If you see other problems with my code, feel free to let me know also, i'm always looking for ways to improve. Thanks for any help/suggestions and MUCH thanks to whoever can solve my problem.
--vince
protected void replaceConstructor( ClassGen cg, String original_class, String new_class ) {
boolean refresh = false;
ConstantPoolGen cp_gen = cg.getConstantPool();
ConstantPool cp = cp_gen.getConstantPool();
InstructionFactory factory = new InstructionFactory( cg , cp_gen );
Method [] methods = cg.getMethods();
for ( int x=0; x<methods.length; x++ ) {
refresh = false;
MethodGen method_gen = new MethodGen( methods[x], cg.getJavaClass().getClassName(), cp_gen );
Iterator i = method_gen.getInstructionList().iterator();
while ( i.hasNext() ) {
InstructionHandle handle = ( InstructionHandle )i.next();
if ( handle.getInstruction() instanceof INVOKESPECIAL && ( ( INVOKESPECIAL )handle.getInstruction() ).getClassName( cp_gen ).equals( original_class ) && ( ( INVOKESPECIAL )handle.getInstruction() ).getMethodName( cp_gen ).equals( "<init>" ) ) {
try {
INVOKESPECIAL invk = ( INVOKESPECIAL )handle.getInstruction();
method_gen.getInstructionList().insert( invk, factory.createInvoke(
new_class,
"name",
new ObjectType( original_class ),
invk.getArgumentTypes( cp_gen ),
Constants.INVOKESTATIC) );
// Delete the old method
method_gen.getInstructionList().delete( invk );
refresh = true;
} catch ( org.apache.bcel.generic.TargetLostException e ) {
Log.write( "Error", + e.toString() );
}
}
}
if ( refresh ) {
method_gen.stripAttributes( false );
method_gen.setMaxStack();
method_gen.setMaxLocals();
cg.replaceMethod( methods[x], method_gen.getMethod() );
}
}
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