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<title>[205254] trunk/Source/JavaScriptCore</title>
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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/205254">205254</a></dd>
<dt>Author</dt> <dd>utatane.tea@gmail.com</dd>
<dt>Date</dt> <dd>2016-08-31 10:00:18 -0700 (Wed, 31 Aug 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>[JSC] AbstractValue can contain padding which is not zero-filled
https://bugs.webkit.org/show_bug.cgi?id=161427
Reviewed by Saam Barati.
We checked that AbstractValue is zero-filled when initializing it to ensure
that zero-filled memory can be used as the initialized AbstractValue.
However, since the size of SpeculatedType becomes 64bit, AbstractValue can have
padding now. And this padding is not ensured that it is initialized with zeros.
So debug assertion fails when building with GCC.
This patch changes the strategy. Instead of checking the initialized
AbstractValue is zero-filled, we ensure that zero-filled AbstractValue can be
considered to be equal to the initialized AbstractValue.
* dfg/DFGAbstractValue.cpp:
(JSC::DFG::AbstractValue::ensureCanInitializeWithZeros):
* dfg/DFGAbstractValue.h:
(JSC::DFG::AbstractValue::AbstractValue):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGAbstractValuecpp">trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGAbstractValueh">trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (205253 => 205254)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-08-31 16:44:49 UTC (rev 205253)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-08-31 17:00:18 UTC (rev 205254)
</span><span class="lines">@@ -1,3 +1,25 @@
</span><ins>+2016-08-31 Yusuke Suzuki <utatane.tea@gmail.com>
+
+ [JSC] AbstractValue can contain padding which is not zero-filled
+ https://bugs.webkit.org/show_bug.cgi?id=161427
+
+ Reviewed by Saam Barati.
+
+ We checked that AbstractValue is zero-filled when initializing it to ensure
+ that zero-filled memory can be used as the initialized AbstractValue.
+ However, since the size of SpeculatedType becomes 64bit, AbstractValue can have
+ padding now. And this padding is not ensured that it is initialized with zeros.
+ So debug assertion fails when building with GCC.
+
+ This patch changes the strategy. Instead of checking the initialized
+ AbstractValue is zero-filled, we ensure that zero-filled AbstractValue can be
+ considered to be equal to the initialized AbstractValue.
+
+ * dfg/DFGAbstractValue.cpp:
+ (JSC::DFG::AbstractValue::ensureCanInitializeWithZeros):
+ * dfg/DFGAbstractValue.h:
+ (JSC::DFG::AbstractValue::AbstractValue):
+
</ins><span class="cx"> 2016-08-31 Brady Eidson <beidson@apple.com>
</span><span class="cx">
</span><span class="cx"> WK2 Gamepad provider on iOS.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGAbstractValuecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp (205253 => 205254)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp 2016-08-31 16:44:49 UTC (rev 205253)
+++ trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.cpp 2016-08-31 17:00:18 UTC (rev 205254)
</span><span class="lines">@@ -539,6 +539,15 @@
</span><span class="cx"> m_structure.validateReferences(trackedReferences);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+#if USE(JSVALUE64) && !defined(NDEBUG)
+void AbstractValue::ensureCanInitializeWithZeros()
+{
+ std::aligned_storage<sizeof(AbstractValue), alignof(AbstractValue)>::type zeroFilledStorage;
+ memset(static_cast<void*>(&zeroFilledStorage), 0, sizeof(AbstractValue));
+ ASSERT(*this == *static_cast<AbstractValue*>(static_cast<void*>(&zeroFilledStorage)));
+}
+#endif
+
</ins><span class="cx"> } } // namespace JSC::DFG
</span><span class="cx">
</span><span class="cx"> #endif // ENABLE(DFG_JIT)
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGAbstractValueh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.h (205253 => 205254)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.h 2016-08-31 16:44:49 UTC (rev 205253)
+++ trunk/Source/JavaScriptCore/dfg/DFGAbstractValue.h 2016-08-31 17:00:18 UTC (rev 205254)
</span><span class="lines">@@ -61,9 +61,7 @@
</span><span class="cx"> static bool needsDefaultConstructorCheck = true;
</span><span class="cx"> if (needsDefaultConstructorCheck) {
</span><span class="cx"> needsDefaultConstructorCheck = false;
</span><del>-
- for (unsigned i = 0; i < sizeof(AbstractValue); ++i)
- ASSERT(!(reinterpret_cast<char*>(this)[i]));
</del><ins>+ ensureCanInitializeWithZeros();
</ins><span class="cx"> }
</span><span class="cx"> #endif
</span><span class="cx"> }
</span><span class="lines">@@ -459,6 +457,10 @@
</span><span class="cx">
</span><span class="cx"> void filterValueByType();
</span><span class="cx"> void filterArrayModesByType();
</span><ins>+
+#if USE(JSVALUE64) && !defined(NDEBUG)
+ void ensureCanInitializeWithZeros();
+#endif
</ins><span class="cx">
</span><span class="cx"> bool shouldBeClear() const;
</span><span class="cx"> FiltrationResult normalizeClarity();
</span></span></pre>
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