786142-iframe.html

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<html>

<head>

<script>

// Morph a slim wrapper into an XPCWN by generating a cross-compartment wrapper

// for it (we Morph in WrapperFactory::PrepareForWrapping).

function makeNonSlim(elem) {

  window.parent.someCCW = elem;

  delete window.parent.someCCW;

function doTest() {

  // Get a slim wrapper for |form|. This lives in scope 1.

  var form = document.getElementById('myform');

  // The gist here is that we want to create an input element that isn't part

  // of a form, so that its PreCreate hook will cause it to be parented to the

  // document. However, there are several considerations that make this more

  // complicted.

//

  // First, the crashtest becomes non-deterministics if we morph |form| before

  // getting to scope 3 (as explained below). This means that we can't trigger

  // the PreCreate hook for |input|, because that will call WrapNativeParent

  // (Well... No, it won't: there is no WrapNativeParent, but there are also no

  // more pre-create hooks, slimwrappers, parenting to the form, or any of the

  // stuff this test is trying to test.)

  // on the form, which will end up making a cross-compartment wrapper, which

  // will morph form. But this puts us in a pickle, because appendChild returns

  // the apppended child, which will trigger the PreCreate hook in

  // NativeInterface2JSObject. So we do this little hack where we append a buch

  // of dummy <div> children to the form, and use replaceChild (which returns

  // the replacer, not the replacee) to stick the input elements as children of

  // the form.

//

  // Second, the crashtest can also be non-deterministics if the final call to

  // MoveWrappers iterates over the hashtable in such a way that it fixes up

  // the Document before it fixes up the Input. If so, the Input will become

  // orphaned, and we'll detect it and fix things up at the top of MoveWrapper.

  // Since we can't control the hashtable ordering here, we just make 100 input

  // elements, to make it a near-certainty (statistically) that we'll encounter

  // one of them during iteration before encountering the Document.

//

  // With all this, this testcase deterministically crashes on my machine. Whew!

  // Create an input element. This isn't part of a form right now, so it gets

  // parented to the document.

  var inputs = [];

  var placeHolders = [];

  for (var i = 0; i < 100; ++i) {

    var dummyDiv = form.appendChild(document.createElement('div'));

    var input = document.createElement('input');

    makeNonSlim(input);

    inputs.push(input);

    placeHolders.push(dummyDiv);

  // Blow away the document, forcing a transplan of all the XPCWNs in scope. This

  // will transplant |input|, but |form| stays in the old scope (since it's slim).

  document.open();

  document.close();

  // Now we're in scope 2. Associate |input| with |form| so that the next call to

  // PreCreate will parent |input| to |form| rather than the document. But make

  // sure to do it with replaceChild, rather than appendChild, so that we don't

  // end up triggering the PreCreate hook for |form| in scope 2, which would make

  // make it non-slim. If we didn't, the ensuing call to MoveWrappers might find

  // |form| before |input| while iterating over the hashtable. If so, |form|

  // would be rescued as an orphan and everything would be fixed before getting to  // |input|.

  for (var i = 0; i < inputs.length; ++i)

    form.replaceChild(inputs[i], placeHolders[i]);

  // Blow away the document a second time. This should cause the crash in

  // unpatched builds.

  document.open();

  document.close();

</script>

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<body>

<form id="myform"></form>

</body>

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