[Solved] Help with ASM

Posted December 20, 201212 yr

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.

Quote

December 20, 201212 yr

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)

Protip: try and find answers yourself before asking on the forum.

It's pretty likely that there is an answer.

Was I helpful? Give me a thank you!

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Quote

December 20, 201212 yr

Author

Edited, thank you.

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December 22, 201212 yr

Author

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.

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[Solved] Help with ASM

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