#Frida #Android - Is there a way to read arbitrary arguments of a native method intercepted by Interceptor.attach() -> onEnter(args) method

Question

Let's say I have a native method which address is expfunction.address. I tried to intercept the function call and get its arguments, general idea:

Interceptor.attach(expfunction.address, {
    onEnter(args) {
        console.log("\n-----\n[*] Function is called!);
        for(let i in args) {    
            ... read value of args[i] ...
        }
        
    },
    onLeave(retval) {
        console.log("\t\n-----\n[*] Function returns");
        console.log("\t[+] Returns:", retval);
    }
})

The function's arguments can be any datatype such as jboolean, jstring, jobject, etc. So how to get exactly the datatype of args[i] and properly read the value of it.

By the way, Is for(let i in args) { ... } a correct way to enumerate args array? Since trying to get args.length raises RangeError: invalid array index.

What I have tried so far (and they all return blank):

• Failed 1

  onEnter(args) {
    for(let i in args) {    
          var tmp = new NativePointer(args[i]);
          console.log(tmp.readPointer());
      }     
  }
  

• Failed 2

  function getType(value) {
    return Object.prototype.toString.call(value).toLowerCase();
  }
  ...
  onEnter(args) {
    for(let i in args) {    
          var tmp = new NativePointer(args[i]);
          console.log("Type:", getType(tmp));
      }     
  }
  

Thank you for reading to this point :)