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  • #317850

Closed
Open
Opened Aug 28, 2018 by laurit@laurit

Condy that returns long or double generates bad bytecode

MethodWriter.visitLdcInsn should emit LDC2_W instead of LDC for condy of long/double.

import java.lang.invoke.MethodHandles;
import java.util.concurrent.atomic.AtomicReference;

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.ConstantDynamic;
import org.objectweb.asm.Handle;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class Test implements Opcodes {

  public static void main(String... args) throws Exception {
    byte[] bytes = dumpBytes();
    AtomicReference<Class<?>> ref = new AtomicReference<>();
 
    new ClassLoader() {{
      ref.set((Class<?>) defineClass("Target", bytes, 0, bytes.length));
    }};
    Class<?> c = ref.get();
    Object o = c.getDeclaredConstructor().newInstance();
    System.out.println(c.getDeclaredMethod("test").invoke(o));
  }

  public static long create(MethodHandles.Lookup lookup, String name, Class<?> owner) {
    return 1;
  }

  public static byte[] dumpBytes() {
    ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
    cw.visit(V11, ACC_PUBLIC | ACC_SUPER, "Target", null, "java/lang/Object", null);
    MethodVisitor mv;
    mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
    mv.visitCode();
    mv.visitVarInsn(ALOAD, 0);
    mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
    mv.visitInsn(RETURN);
    mv.visitMaxs(1, 1);
    mv.visitEnd();
 
    mv = cw.visitMethod(ACC_PUBLIC, "test", "()J", null, null);
    mv.visitCode();
    mv.visitLdcInsn(new ConstantDynamic("test", "J", new Handle(H_INVOKESTATIC, "Test", "create", "(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/Class;)J", false)));
    mv.visitInsn(LRETURN);
    mv.visitMaxs(0, 0);
    mv.visitEnd();
 
    cw.visitEnd();

    return cw.toByteArray();
  }

}
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Reference: asm/asm#317850