Java Community | Help. Code. Learn.•2y ago

Java 1.8 ASM modified code throws NoSuchFieldError

Hi! I use ASM to modify this code:

private Launch() {
    URLClassLoader ucl = (URLClassLoader)this.getClass().getClassLoader();
    classLoader = new LaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

private Launch() {
    URLClassLoader ucl = (URLClassLoader)this.getClass().getClassLoader();
    classLoader = new LaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

into

private Launch() {
    URLClassLoader ucl = (URLClassLoader)this.getClass().getClassLoader();
    classLoader = new CustomLaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

private Launch() {
    URLClassLoader ucl = (URLClassLoader)this.getClass().getClassLoader();
    classLoader = new CustomLaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

but when I execute it, it throws a NoSuchFieldError on the classLoader field. classLoader is a private static field.

3 Replies

JavaBot•2y ago

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TyranobastOP•2y ago

The ASM code I use:

ClassReader cr = new ClassReader(Files.newInputStream(launchClass));
ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
ClassVisitor cv = new ClassVisitor(Opcodes.ASM5, cw) {
    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
        if (name.equals("<init>")) {
            return new MethodVisitor(Opcodes.ASM5, super.visitMethod(access, name, desc, signature, exceptions)) {
                @Override
                public void visitFieldInsn(int opcode, String owner, String name, String desc) {
                    if (opcode == Opcodes.PUTSTATIC && "net/minecraft/launchwrapper/Launch".equals(owner) && "classLoader".equals(name)) {
                        mv.visitTypeInsn(Opcodes.NEW, "eu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader");
                        mv.visitInsn(Opcodes.DUP);
                        mv.visitVarInsn(Opcodes.ALOAD, 1);
                        mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/net/URLClassLoader", "getURLs", "()[Ljava/net/URL;", false);
                        mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "eu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader", "<init>", "([Ljava/net/URL;)V", false);
                        mv.visitFieldInsn(Opcodes.PUTSTATIC, "net/minecraft/launchwrapper/Launch", "classLoader", "Leu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader;");
                    } else {
                        mv.visitFieldInsn(opcode, owner, name, desc);
                    }
                }
            };
        }
        return super.visitMethod(access, name, desc, signature, exceptions);
    }
};

cr.accept(cv, 0);

ClassReader cr = new ClassReader(Files.newInputStream(launchClass));
ClassWriter cw = new ClassWriter(cr, ClassWriter.COMPUTE_MAXS);
ClassVisitor cv = new ClassVisitor(Opcodes.ASM5, cw) {
    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
        if (name.equals("<init>")) {
            return new MethodVisitor(Opcodes.ASM5, super.visitMethod(access, name, desc, signature, exceptions)) {
                @Override
                public void visitFieldInsn(int opcode, String owner, String name, String desc) {
                    if (opcode == Opcodes.PUTSTATIC && "net/minecraft/launchwrapper/Launch".equals(owner) && "classLoader".equals(name)) {
                        mv.visitTypeInsn(Opcodes.NEW, "eu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader");
                        mv.visitInsn(Opcodes.DUP);
                        mv.visitVarInsn(Opcodes.ALOAD, 1);
                        mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/net/URLClassLoader", "getURLs", "()[Ljava/net/URL;", false);
                        mv.visitMethodInsn(Opcodes.INVOKESPECIAL, "eu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader", "<init>", "([Ljava/net/URL;)V", false);
                        mv.visitFieldInsn(Opcodes.PUTSTATIC, "net/minecraft/launchwrapper/Launch", "classLoader", "Leu/damnatio/damnatioac/network/verification/CustomLaunchClassLoader;");
                    } else {
                        mv.visitFieldInsn(opcode, owner, name, desc);
                    }
                }
            };
        }
        return super.visitMethod(access, name, desc, signature, exceptions);
    }
};

cr.accept(cv, 0);

any help would be cool !!!! The decompiled Launch constructor (using FernFlower):

private Launch() {
    URLClassLoader ucl = 
(URLClassLoader)this.getClass().getClassLoader();
    new LaunchClassLoader(ucl.getURLs());
    classLoader = new CustomLaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

private Launch() {
    URLClassLoader ucl = 
(URLClassLoader)this.getClass().getClassLoader();
    new LaunchClassLoader(ucl.getURLs());
    classLoader = new CustomLaunchClassLoader(ucl.getURLs());
    blackboard = new HashMap();
    Thread.currentThread().setContextClassLoader(classLoader);
}

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Java 1.8 ASM modified code throws NoSuchFieldError