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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/210960">210960</a></dd>
<dt>Author</dt> <dd>matthew_hanson@apple.com</dd>
<dt>Date</dt> <dd>2017-01-20 08:25:41 -0800 (Fri, 20 Jan 2017)</dd>
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<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/210935">r210935</a>. rdar://problem/30101860</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#branchessafari603branchSourceJavaScriptCoreChangeLog">branches/safari-603-branch/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#branchessafari603branchSourceJavaScriptCoreruntimeJSArraycpp">branches/safari-603-branch/Source/JavaScriptCore/runtime/JSArray.cpp</a></li>
</ul>
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<div id="patch">
<h3>Diff</h3>
<a id="branchessafari603branchSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: branches/safari-603-branch/Source/JavaScriptCore/ChangeLog (210959 => 210960)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-603-branch/Source/JavaScriptCore/ChangeLog 2017-01-20 12:17:50 UTC (rev 210959)
+++ branches/safari-603-branch/Source/JavaScriptCore/ChangeLog 2017-01-20 16:25:41 UTC (rev 210960)
</span><span class="lines">@@ -1,3 +1,32 @@
</span><ins>+2017-01-20 Matthew Hanson <matthew_hanson@apple.com>
+
+ Merge r210935. rdar://problem/30101860
+
+ 2017-01-19 Filip Pizlo <fpizlo@apple.com>
+
+ The mutator needs to fire a barrier after memmoving stuff around in an object that the GC scans
+ https://bugs.webkit.org/show_bug.cgi?id=167208
+
+ Reviewed by Saam Barati.
+
+ It used to be that if you moved a value from one place to another in the same object
+ then there is no need for a barrier because the generational GC would have no need to
+ know that some old object still continues to refer to the same other old object.
+
+ But the concurrent GC might scan that object as the mutator moves pointers around in
+ it. If the ordering is right, this could mean that the collector never sees some of
+ those pointers. This can be fixed by adding a barrier.
+
+ This fixes the most obvious cases I found. There may be more and I'll continue to
+ audit. Most of the other memmove users seem to already use some kind of synchronization
+ to prevent this. For example, this can also be fixed by just holding the cell lock
+ around the memmove since we're dealing with indexing storage and the GC reads that
+ under the cell lock.
+
+ * runtime/JSArray.cpp:
+ (JSC::JSArray::shiftCountWithAnyIndexingType):
+ (JSC::JSArray::unshiftCountWithAnyIndexingType):
+
</ins><span class="cx"> 2017-01-18 Matthew Hanson <matthew_hanson@apple.com>
</span><span class="cx">
</span><span class="cx"> Merge r210858. rdar://problem/30069096
</span></span></pre></div>
<a id="branchessafari603branchSourceJavaScriptCoreruntimeJSArraycpp"></a>
<div class="modfile"><h4>Modified: branches/safari-603-branch/Source/JavaScriptCore/runtime/JSArray.cpp (210959 => 210960)</h4>
<pre class="diff"><span>
<span class="info">--- branches/safari-603-branch/Source/JavaScriptCore/runtime/JSArray.cpp 2017-01-20 12:17:50 UTC (rev 210959)
+++ branches/safari-603-branch/Source/JavaScriptCore/runtime/JSArray.cpp 2017-01-20 16:25:41 UTC (rev 210960)
</span><span class="lines">@@ -1021,6 +1021,11 @@
</span><span class="cx"> butterfly->contiguous()[i].clear();
</span><span class="cx">
</span><span class="cx"> butterfly->setPublicLength(oldLength - count);
</span><ins>+
+ // Our memmoving of values around in the array could have concealed some of them from
+ // the collector. Let's make sure that the collector scans this object again.
+ vm.heap.writeBarrier(this);
+
</ins><span class="cx"> return true;
</span><span class="cx"> }
</span><span class="cx">
</span><span class="lines">@@ -1169,6 +1174,10 @@
</span><span class="cx"> butterfly->contiguous()[i + count].setWithoutWriteBarrier(v);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+ // Our memmoving of values around in the array could have concealed some of them from
+ // the collector. Let's make sure that the collector scans this object again.
+ vm.heap.writeBarrier(this);
+
</ins><span class="cx"> // NOTE: we're leaving being garbage in the part of the array that we shifted out
</span><span class="cx"> // of. This is fine because the caller is required to store over that area, and
</span><span class="cx"> // in contiguous mode storing into a hole is guaranteed to behave exactly the same
</span></span></pre>
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