[Webkit-unassigned] [Bug 161534] Regression(r197648): JSObject::setPrototypeWithCycleCheck() allows for cycles but the rest of the code base does not

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=161534

--- Comment #5 from Chris Dumez <cdumez at apple.com> ---
(In reply to comment #4)
> (In reply to comment #3)
> > (In reply to comment #2)
> > > > Yeah, we should teach the rest of the engine that it's OK to have cycles
> > > > in the "getPrototypeDirect" chain.
> > > > Currently, inside JSC itself, this will never happen. However, I guess we
> > > > need to
> > > > teach it this w.r.t the HTML spec.
> > > 
> > > That's a pretty big change. Are we sure we need to allow cycles? What's the
> > > expected behavior if you find a cycle? Is it specified?
> > 
> > Note that even without my patch, it is fairly trivial to end up with an
> > infinite loop since r197648 allows for cycles:
> > 
> > <script>
> > var target = {
> >   __proto__: null
> > };
> > var proxy = new Proxy(target, {});
> > Object.prototype.__proto__ = {
> >    __proto__: proxy,
> > };
> > 
> > var a = {};
> > a.test;
> > </script>
> > 
> > This seems to infinite loop for me on ToT, no DOM involved.
> 
> I believe the bug here is having ProxyObject's structure's prototype field
> be Object.prototype. That's wrong.

FYI, I tried fixing proxy.__proto__ to be null like so:
http://pastebin.com/69HRjvPb

But this causes some JSC test failures though:
Tools/Scripts/run-jsc JSTests/stress/proxy-set-prototype-of.js
Running 1 time(s): DYLD_FRAMEWORK_PATH=/Volumes/Data/WebKit/OpenSource/WebKitBuild/Release /Volumes/Data/WebKit/OpenSource/WebKitBuild/Release/jsc JSTests/stress/proxy-set-prototype-of.js
Exception: Error: Bad assertion!
assert at JSTests/stress/proxy-set-prototype-of.js:3:24
global code at JSTests/stress/proxy-set-prototype-of.js:31:19

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