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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/201470">201470</a></dd>
<dt>Author</dt> <dd>fpizlo@apple.com</dd>
<dt>Date</dt> <dd>2016-05-27 15:29:02 -0700 (Fri, 27 May 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>DFG::LazyJSValue::tryGetStringImpl() crashes for empty values
https://bugs.webkit.org/show_bug.cgi?id=158170
Reviewed by Michael Saboff.
The problem here is that jsDynamicCast<>() is evil! It avoids checking for the empty
value, presumably because this makes it soooper fast. In DFG IR, empty values can appear
anywhere because of TDZ.
This patch doesn't change jsDynamicCast<>(), but it hardens our wrappers for it in the DFG
and it has the affected code use one of those wrappers.
* dfg/DFGFrozenValue.h:
(JSC::DFG::FrozenValue::dynamicCast): Harden this.
(JSC::DFG::FrozenValue::cast):
* dfg/DFGLazyJSValue.cpp:
(JSC::DFG::LazyJSValue::tryGetStringImpl): Use the hardened wrapper.
* tests/stress/strcat-emtpy.js: Added. This used to crash every time.
(foo):
(i.catch):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGFrozenValueh">trunk/Source/JavaScriptCore/dfg/DFGFrozenValue.h</a></li>
<li><a href="#trunkSourceJavaScriptCoredfgDFGLazyJSValuecpp">trunk/Source/JavaScriptCore/dfg/DFGLazyJSValue.cpp</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoretestsstressstrcatemtpyjs">trunk/Source/JavaScriptCore/tests/stress/strcat-emtpy.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (201469 => 201470)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-05-27 21:42:42 UTC (rev 201469)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-05-27 22:29:02 UTC (rev 201470)
</span><span class="lines">@@ -1,5 +1,28 @@
</span><span class="cx"> 2016-05-27 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><ins>+ DFG::LazyJSValue::tryGetStringImpl() crashes for empty values
+ https://bugs.webkit.org/show_bug.cgi?id=158170
+
+ Reviewed by Michael Saboff.
+
+ The problem here is that jsDynamicCast<>() is evil! It avoids checking for the empty
+ value, presumably because this makes it soooper fast. In DFG IR, empty values can appear
+ anywhere because of TDZ.
+
+ This patch doesn't change jsDynamicCast<>(), but it hardens our wrappers for it in the DFG
+ and it has the affected code use one of those wrappers.
+
+ * dfg/DFGFrozenValue.h:
+ (JSC::DFG::FrozenValue::dynamicCast): Harden this.
+ (JSC::DFG::FrozenValue::cast):
+ * dfg/DFGLazyJSValue.cpp:
+ (JSC::DFG::LazyJSValue::tryGetStringImpl): Use the hardened wrapper.
+ * tests/stress/strcat-emtpy.js: Added. This used to crash every time.
+ (foo):
+ (i.catch):
+
+2016-05-27 Filip Pizlo <fpizlo@apple.com>
+
</ins><span class="cx"> regExpProtoFuncSplitFast should OOM before it swaps
</span><span class="cx"> https://bugs.webkit.org/show_bug.cgi?id=158157
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGFrozenValueh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGFrozenValue.h (201469 => 201470)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGFrozenValue.h 2016-05-27 21:42:42 UTC (rev 201469)
+++ trunk/Source/JavaScriptCore/dfg/DFGFrozenValue.h 2016-05-27 22:29:02 UTC (rev 201470)
</span><span class="lines">@@ -73,7 +73,10 @@
</span><span class="cx"> template<typename T>
</span><span class="cx"> T dynamicCast()
</span><span class="cx"> {
</span><del>- return jsDynamicCast<T>(value());
</del><ins>+ JSValue theValue = value();
+ if (!theValue)
+ return nullptr;
+ return jsDynamicCast<T>(theValue);
</ins><span class="cx"> }
</span><span class="cx"> template<typename T>
</span><span class="cx"> T cast()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoredfgDFGLazyJSValuecpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/dfg/DFGLazyJSValue.cpp (201469 => 201470)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/dfg/DFGLazyJSValue.cpp 2016-05-27 21:42:42 UTC (rev 201469)
+++ trunk/Source/JavaScriptCore/dfg/DFGLazyJSValue.cpp 2016-05-27 22:29:02 UTC (rev 201470)
</span><span class="lines">@@ -95,7 +95,7 @@
</span><span class="cx"> return u.stringImpl;
</span><span class="cx">
</span><span class="cx"> case KnownValue:
</span><del>- if (JSString* string = jsDynamicCast<JSString*>(value()->value()))
</del><ins>+ if (JSString* string = value()->dynamicCast<JSString*>())
</ins><span class="cx"> return string->tryGetValueImpl();
</span><span class="cx"> return nullptr;
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoretestsstressstrcatemtpyjs"></a>
<div class="addfile"><h4>Added: trunk/Source/JavaScriptCore/tests/stress/strcat-emtpy.js (0 => 201470)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/tests/stress/strcat-emtpy.js (rev 0)
+++ trunk/Source/JavaScriptCore/tests/stress/strcat-emtpy.js 2016-05-27 22:29:02 UTC (rev 201470)
</span><span class="lines">@@ -0,0 +1,14 @@
</span><ins>+function foo() {
+ "use strict";
+ let a = "hello" + a;
+ return a;
+}
+
+noInline(foo);
+
+for (var i = 0; i < 10000; ++i) {
+ try {
+ foo();
+ } catch (e) {
+ }
+}
</ins></span></pre>
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