[Solved] Help with ASM

[Arlyh]

Hello, I'm attempting to rewrite a minecraftforge method in net.minecraft.block.Block,

boolean removeBlockByPlayer(World, EntityPlayer, Int, Int, Int)

 

I start by first removing the original method with a ClassVisitor and an overloaded visitMethod that returns null.  I then try to use a MethodVisitor to rewrite the bytecode.  Unfortunately, it seems to be rewriting the net.minecraft.block.Block constructor rather than the intended function, though I have determined that removeBlockByPlayer is indeed deleted by iterating through the ClassNode.methods list.

 

My code is as follows:

 

 

package servercommands.asm;

import static org.objectweb.asm.ClassWriter.*;
import static org.objectweb.asm.Opcodes.*;

import java.util.List;

import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.ClassNode;
import org.objectweb.asm.tree.MethodNode;
import org.objectweb.asm.tree.TypeInsnNode;

import cpw.mods.fml.relauncher.IClassTransformer;

public class ServerCommandsAccessTransformer implements IClassTransformer {

public byte[] deleteMethod(byte[] bytes, int access, String name, String desc) {
	ClassWriter cw = new ClassWriter(COMPUTE_FRAMES);
	ClassVisitor cv = new ClassVisitor(Opcodes.ASM4, cw) {
		@Override
		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
			return null;
		}
	};

	ClassReader cr = new ClassReader(bytes);
	cr.accept(cv,  0);
	cv.visitMethod(access, name, desc, null, null);
	return cw.toByteArray();
}

public byte[] transformer001(String name, byte[] bytes) {
	if(name.equals(ServerCommandsLoadingPlugin.debug ? "net.minecraft.block.Block" : "amj")) {
		bytes = deleteMethod(bytes, ACC_PUBLIC, "removeBlockByPlayer", ServerCommandsLoadingPlugin.debug ? "(Lnet/minecraft/world/World;Lnet/minecraft/entity/player/EntityPlayer;III)Z" : "(Lxv;Lqx;III)Z");
		ClassNode node = new ClassNode();
		ClassReader reader = new ClassReader(bytes);
		reader.accept(node, 0);

		ClassWriter cw = new ClassWriter(COMPUTE_FRAMES);
		node.accept(cw);

		MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "removeBlockByPlayer", ServerCommandsLoadingPlugin.debug ? "(Lnet/minecraft/world/World;Lnet/minecraft/entity/player/EntityPlayer;III)Z" : "(Lxv;Lqx;III)Z", null, null);

		mv.visitCode();
		mv.visitTypeInsn(NEW, "servercommands/PlayerBreakBlockEvent");
		mv.visitInsn(DUP);
		mv.visitVarInsn(ALOAD, 1);
		mv.visitVarInsn(ALOAD, 0);
		mv.visitVarInsn(ALOAD, 2);
		mv.visitVarInsn(ILOAD, 3);
		mv.visitVarInsn(ILOAD, 4);
		mv.visitVarInsn(ILOAD, 5);
		mv.visitMethodInsn(INVOKESPECIAL, "servercommands/PlayerBreakBlockEvent", "<init>", ServerCommandsLoadingPlugin.debug ? "(Lnet/minecraft/world/World;Lnet/minecraft/entity/player/EntityPlayer;III)Z" : "(Lxv;Lqx;III)Z");
		mv.visitVarInsn(ASTORE, 6);
		mv.visitFieldInsn(GETSTATIC, "net/minecraftforge/common/MinecraftForge", "EVENT_BUS", "Lnet/minecraftforge/event/EventBus;");
		mv.visitVarInsn(ALOAD, 6);
		mv.visitMethodInsn(INVOKEVIRTUAL, "net/minecraftforge/event/EventBus", "post", "(Lnet/minecraftforge/event/Event;)Z");
		mv.visitInsn(POP);
		mv.visitVarInsn(ALOAD, 6);
		mv.visitFieldInsn(GETFIELD, "servercommands/PlayerBreakBlockEvent", "result", "Lnet/minecraftforge/event/Event$Result;");
		mv.visitFieldInsn(GETSTATIC, "net/minecraftforge/event/Event$Result", "DENY", "Lnet/minecraftforge/event/Event$Result;");
		Label l0 = new Label();
		mv.visitJumpInsn(IF_ACMPNE, l0);
		mv.visitInsn(ICONST_0);
		mv.visitInsn(IRETURN);
		mv.visitLabel(l0);
		mv.visitFrame(Opcodes.F_APPEND,1, new Object[] {"servercommands/PlayerBreakBlockEvent"}, 0, null);
		mv.visitVarInsn(ALOAD, 1);
		mv.visitVarInsn(ILOAD, 3);
		mv.visitVarInsn(ILOAD, 4);
		mv.visitVarInsn(ILOAD, 5);
		mv.visitInsn(ICONST_0);
		if(ServerCommandsLoadingPlugin.debug) mv.visitMethodInsn(INVOKEVIRTUAL, "net/minecraft/world/World", "setBlockWithNotify", "(IIII)Z");
		else mv.visitMethodInsn(INVOKEVIRTUAL, "xv", "e", "(IIII)Z");
		mv.visitInsn(IRETURN);
		mv.visitMaxs(8, 7);
		mv.visitEnd();

		bytes = cw.toByteArray();

		System.out.println("Added PlayerBreakBlockEvent to Block.removeBlockByPlayer()");

	}
	return bytes;
}

@Override
public byte[] transform(String name, byte[] bytes) {
	try {
		if(name.contains(ServerCommandsLoadingPlugin.debug ? "net.minecraft.block.Block" : "amj")) System.out.println(name);
		bytes = transformer001(name, bytes);
	} catch(Exception e) {
		throw new RuntimeException(e);
	}
	return bytes;
}
}

 

 

FML output is as follows:

 

 

2012-12-20 17:09:33 [iNFO] [ForgeModLoader] Forge Mod Loader version 4.5.62.495 for Minecraft 1.4.5 loading
2012-12-20 17:09:33 [iNFO] [sTDOUT] Called
2012-12-20 17:09:33 [iNFO] [sTDOUT] net.minecraft.block.Block
2012-12-20 17:09:33 [iNFO] [sTDOUT] Added PlayerBreakBlockEvent to Block.removeBlockByPlayer()
2012-12-20 17:09:33 [iNFO] [sTDERR] java.lang.reflect.InvocationTargetException
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.reflect.Method.invoke(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at cpw.mods.fml.relauncher.FMLRelauncher.relaunchServer(FMLRelauncher.java:138)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at cpw.mods.fml.relauncher.FMLRelauncher.handleServerRelaunch(FMLRelauncher.java:33)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.main(MinecraftServer.java:1374)
2012-12-20 17:09:33 [iNFO] [sTDERR] Caused by: java.lang.NoClassDefFoundError: net/minecraft/block/Block
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at net.minecraft.stats.StatList.initMinableStats(StatList.java:185)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at net.minecraft.stats.StatList.<clinit>(StatList.java:96)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.fmlReentry(MinecraftServer.java:1381)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	... 7 more
2012-12-20 17:09:33 [iNFO] [sTDERR] Caused by: java.lang.ClassNotFoundException: net.minecraft.block.Block
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:141)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.ClassLoader.loadClass(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.ClassLoader.loadClass(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	... 10 more
2012-12-20 17:09:33 [iNFO] [sTDERR] Caused by: java.lang.ClassFormatError: Method "<init>" in class net/minecraft/block/Block has illegal signature "(Lnet/minecraft/world/World;Lnet/minecraft/entity/player/EntityPlayer;III)Z"
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.ClassLoader.defineClass1(Native Method)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.ClassLoader.defineClass(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at java.lang.ClassLoader.defineClass(Unknown Source)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	at cpw.mods.fml.relauncher.RelaunchClassLoader.findClass(RelaunchClassLoader.java:134)
2012-12-20 17:09:33 [iNFO] [sTDERR] 	... 12 more

 

 

I apologize for any silly mistakes I may have made.  I primarily code in C/C++ and have only recently taken an interest in Minecraft modding.

[keepcalm]

In the future, use spoiler, not hidden

 

Also, judging from what you're trying to do, the best way to do it would be to add a function call, rather than rewriting the entire method. You might want to have a look at the source code for my mod, which does something similar, but uses ItemInWorldManager (so it's server-side only).

 

If you want more help, PM me (I think I've worked out how to do this ASM stuff)

[Arlyh]

Edited, thank you.

[Arlyh]

I was able to come up with a solution to my issue, and I would like to make my solution visible to this community.  It is as follows:

 

 

public class ServerCommandsAccessTransformer implements IClassTransformer {

class SCClassVisitor extends ClassVisitor {
	private String methodName;

	public SCClassVisitor(int api, ClassVisitor cv, String methodName) {
		super(api, cv);
		this.methodName = methodName;
	}

	@Override
	public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
		if(name.equals(methodName)) {
			return null;
		}
		return super.visitMethod(access, name, desc, signature, exceptions);
	}		
}

public byte[] deleteMethod(byte[] bytes, int access, String name) {
	ClassWriter cw = new ClassWriter(COMPUTE_FRAMES);
	SCClassVisitor cv = new SCClassVisitor(ASM4, cw, name);
	ClassReader cr = new ClassReader(bytes);
	cr.accept(cv,  0);
	return cw.toByteArray();
}


public byte[] transformer001(String name, byte[] bytes) {
	bytes = deleteMethod(bytes, ACC_PUBLIC, "removeBlockByPlayer");

	ClassWriter cw = new ClassWriter(COMPUTE_FRAMES);
	ClassReader cr = new ClassReader(bytes);
	cr.accept(cw, 0);

	MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "removeBlockByPlayer", ServerCommandsLoadingPlugin.debug ? "(Lnet/minecraft/world/World;Lnet/minecraft/entity/player/EntityPlayer;III)Z" : "(Lxv;Lqx;III)Z", null, null);

	mv.visitCode();
	mv.visitTypeInsn(NEW, "servercommands/PlayerBreakBlockEvent");
	mv.visitInsn(DUP);
	mv.visitVarInsn(ALOAD, 1);
	mv.visitVarInsn(ALOAD, 0);
	mv.visitVarInsn(ALOAD, 2);
	mv.visitVarInsn(ILOAD, 3);
	mv.visitVarInsn(ILOAD, 4);
	mv.visitVarInsn(ILOAD, 5);
	mv.visitMethodInsn(INVOKESPECIAL, "servercommands/PlayerBreakBlockEvent", "<init>", ServerCommandsLoadingPlugin.debug ? "(Lnet/minecraft/world/World;Lnet/minecraft/block/Block;Lnet/minecraft/entity/player/EntityPlayer;III)V" : "(Lxv;Lamj;Lqx;III)V");
	mv.visitVarInsn(ASTORE, 6);
	mv.visitFieldInsn(GETSTATIC, "net/minecraftforge/common/MinecraftForge", "EVENT_BUS", "Lnet/minecraftforge/event/EventBus;");
	mv.visitVarInsn(ALOAD, 6);
	mv.visitMethodInsn(INVOKEVIRTUAL, "net/minecraftforge/event/EventBus", "post", "(Lnet/minecraftforge/event/Event;)Z");
	mv.visitInsn(POP);
	mv.visitVarInsn(ALOAD, 6);
	mv.visitFieldInsn(GETFIELD, "servercommands/PlayerBreakBlockEvent", "result", "Lnet/minecraftforge/event/Event$Result;");
	mv.visitFieldInsn(GETSTATIC, "net/minecraftforge/event/Event$Result", "DENY", "Lnet/minecraftforge/event/Event$Result;");
	Label l0 = new Label();
	mv.visitJumpInsn(IF_ACMPNE, l0);
	mv.visitInsn(ICONST_0);
	mv.visitInsn(IRETURN);
	mv.visitLabel(l0);
	mv.visitFrame(Opcodes.F_APPEND,1, new Object[] {"servercommands/PlayerBreakBlockEvent"}, 0, null);
	mv.visitVarInsn(ALOAD, 1);
	mv.visitVarInsn(ILOAD, 3);
	mv.visitVarInsn(ILOAD, 4);
	mv.visitVarInsn(ILOAD, 5);
	mv.visitInsn(ICONST_0);
	if(ServerCommandsLoadingPlugin.debug) mv.visitMethodInsn(INVOKEVIRTUAL, "net/minecraft/world/World", "setBlockWithNotify", "(IIII)Z"); 
	else mv.visitMethodInsn(INVOKEVIRTUAL, "xv", "e", "(IIII)Z");
	mv.visitInsn(IRETURN);
	mv.visitMaxs(8, 7);
	mv.visitEnd();

	return cw.toByteArray();
}

@Override
public byte[] transform(String name, byte[] bytes) {
	try {
		if(name.equals(ServerCommandsLoadingPlugin.debug ? "net.minecraft.block.Block" : "amj")) {
			System.out.println(name);
			bytes = transformer001(name, bytes);
		}
	} catch(Exception e) {
		throw new RuntimeException(e);
	}
	return bytes;
}
}

 

 

Keepcalm, I did end up going a different direction, but I do appreciate your advice and example code.  It is always helpful to see how other programmers are accomplishing similar problems.