[Error] same sub-function & variable name inside a same function

[gogo9th]

Hi,

I really need urgent help on this... Jalangi fails to instrument the following code which is regularly runnable by NodeJS:

function a ()
{  var t;
   function t() {}
}

Jalangi outputs:

SyntaxError: Identifier 't' has already been declared

Could you please give me an easy instruction on how to fix this bug in Jalangi's source code? Thanks very much for your help.

[msridhar]

Thanks for reporting this bug. I am not too sure how easy it would be to fix. @ksen007 do you have any thoughts or ideas here?

[gogo9th]

Jalangi intruments the above code as follows:

                        try {
                            J$.Fe(25, arguments.callee, this, arguments);
                            function t() {
                                jalangiLabel0:
                                    while (true) {
                                        try {
                                            J$.Fe(9, arguments.callee, this, arguments);
                                            arguments = J$.N(17, 'arguments', arguments, 4);
                                        } catch (J$e) {
                                            J$.Ex(81, J$e);
                                        } finally {
                                            if (J$.Fr(89))
                                                continue jalangiLabel0;
                                            else
                                                return J$.Ra();
                                        }
                                    }
                            }
                            arguments = J$.N(33, 'arguments', arguments, 4);
                            t = J$.N(49, 't', J$.T(41, t, 12, false, 9), 0);
                            var t;
                        } catch (J$e) {
                            J$.Ex(97, J$e);

and the error occurs because 'var t' and 'function t' are declared within the same block. However, if these two are declared within the same function, they don't raise an error. Therefore, the above instrumentation should be modified as follows:

                        try {
(function(){
                            J$.Fe(25, arguments.callee, this, arguments);
                            function t() {
                                jalangiLabel0:
                                    while (true) {
                                        try {
                                            J$.Fe(9, arguments.callee, this, arguments);
                                            arguments = J$.N(17, 'arguments', arguments, 4);
                                        } catch (J$e) {
                                            J$.Ex(81, J$e);
                                        } finally {
                                            if (J$.Fr(89))
                                                continue jalangiLabel0;
                                            else
                                                return J$.Ra();
                                        }
                                    }
                            }
                            arguments = J$.N(33, 'arguments', arguments, 4);
                            t = J$.N(49, 't', J$.T(41, t, 12, false, 9), 0);
                            var t;
}())
                        } catch (J$e) {
                            J$.Ex(97, J$e);

This does run without an error. So, I think Jalangi should enclose the global scope and every function scope with (function(){ ... }()).

[msridhar]

Thanks for the explanation! Yes, it seems the issue here is that Jalangi is moving function statements into a nested scope from the top-level scope. I think your idea for an initial fix is reasonable. I think you'd need to introduce the fix at two places in esnstrument.js:

For script bodies:

jalangi2/src/js/instrument/esnstrument.js

Line 954 in 7f0be09

"function n() { jalangiLabel" + l + ": while(true) { try {" + RP + "1} catch(" + JALANGI_VAR +

For function bodies:

jalangi2/src/js/instrument/esnstrument.js

Line 979 in 7f0be09

"function n() { jalangiLabel" + l + ": while(true) { try {" + RP + "1} catch(" + JALANGI_VAR +

Could you go ahead and test out your proposed fix to see if it works? If it works for you, and you open a PR with the fix and your test case, that would be great.

[gogo9th]

I replaced both lines as follow:

                "function n() { jalangiLabel" + l + ": while(true) { try { (function() {" + RP + "1 }()) } catch(" + JALANGI_VAR +

And it works for this sample code:

function a ()
{  var t;
   function t() {}
}

But strangely enough, does not work for this:

var t;
function t() {} 

[msridhar]

Now that I think about it, wrapping the top-level script body in an anonymous function is not a good idea, since on the web, variables declared at the top level are globals that are visible from other scripts. So you'll need another solution there. Or, if the solution for function bodies is good enough for your use case, that might be a good intermediate step for now.

[gogo9th]

Yes, this is the problem I actually just encountered. I started to see many red errors when I tested this on the web...

[msridhar]

Are you running into this problem at the top level of many scripts? I would expect this problem to come up quite rarely.

[gogo9th]

I see this problem for jQuery

[msridhar]

Can you link to the problematic code?

[gogo9th]

I am sorry, but because my version of Jalangi is connected to Puppeteer, it's little complex to show them here... But basically, global objects such as JQuery imported from the web's jquery.js raise an undefined error.

I think this issue could be resolved if we enforce Jalangi to rewrite such undefined objects as window.JQuery instead of just JQuery (we apply this rule only if Jalangi's read / write callback detects that the target object is undefined). What do you think?

[msridhar]

So sorry for my slow response. I see how jQuery would cause an issue with your solution. What I was wondering was are you seeing this issue of a variable and function statement with the same name in the global scope, in function scopes, or both? I was hoping it was only happening in function scopes, so you could just not apply your fix at the global scope for now.

I think your solution of using window.jQuery is reasonable to unblock you. In terms of merging into the main Jalangi2 repo, I'd like to think more about whether there is a less disruptive solution, as I would expect this duplicate name issue is rare in practice.

[gogo9th]

I am really sorry for my late reply. I had a car accident and was trying to recover... Now I am back.

I really want to solve this issue of error for re-definition. As I already tried, enclosing the definitions with a dynamic function is not a good solution, because this causes a scope issue. Do you have any good solution in mind?

[msridhar]

Sorry to hear about your accident, and glad that you've recovered!

As noted originally, this problem arises when there are both a variable and a function statement with the same name defined at the top-level scope of a function. In such cases, Jalangi causes a problem since it moves the function statement within a nested scope. You proposed wrapping the nested scope in an anonymous function. This fix caused issues at the global scope level, since it effectively hides global variables.

My question was, is the issue with a duplicate variable and function statement with the same name appearing for you at the top level of scripts? If not, you can just apply the anonymous function solution within functions and you are done. If it is appearing at the top level, we'd need to think more. And it'd be great to see an example of such code.

[gogo9th]

Thanks a lot for your worries, I am feeling much better now.

My question was, is the issue with a duplicate variable and function statement with the same name appearing for you at the top level of scripts?

Yes, this happens in https://facebook.com. The code is very complex, but I narrowed down the problematic part, and the issue is because both 'var V' and 'function V' are declared in the same global scope and other scripts try to access them...