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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/189714">189714</a></dd>
<dt>Author</dt> <dd>carlosgc@webkit.org</dd>
<dt>Date</dt> <dd>2015-09-14 05:32:57 -0700 (Mon, 14 Sep 2015)</dd>
</dl>
<h3>Log Message</h3>
<pre>Merge <a href="http://trac.webkit.org/projects/webkit/changeset/189012">r189012</a> - MarkedBlock::allocateBlock will have the wrong allocation size when (sizeof(MarkedBlock) + bytes) is divisible by WTF::pageSize()
https://bugs.webkit.org/show_bug.cgi?id=148500
Reviewed by Mark Lam.
Consider the following scenario:
- On OS X, WTF::pageSize() is 4*1024 bytes.
- JSEnvironmentRecord::allocationSizeForScopeSize(6621) == 53000
- sizeof(MarkedBlock) == 248
- (248 + 53000) is a multiple of 4*1024.
- (248 + 53000)/(4*1024) == 13
We will allocate a chunk of memory of size 53248 bytes that looks like this:
0 248 256 53248 53256
[Marked Block | 8 bytes | payload ...... ] 8 bytes |
^ ^
Our Environment record starts here. ^
^
Our last JSValue in the environment record will go from byte 53248 to 53256. But, we don't own this memory.
We need to ensure that we round up sizeof(MarkedBlock) to an
atomSize boundary. We need to do this because the first atom
inside the MarkedBlock will start at the rounded up multiple
of atomSize past MarkedBlock. If we end up with an allocation
that is perfectly aligned to the page size, then we will be short
8 bytes (in the current implementation where atomSize is 16 bytes,
and MarkedBlock is 248 bytes).
* heap/MarkedAllocator.cpp:
(JSC::MarkedAllocator::allocateBlock):
* tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js: Added.
(use):
(makeFunction):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit210SourceJavaScriptCoreChangeLog">releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#releasesWebKitGTKwebkit210SourceJavaScriptCoreheapMarkedAllocatorcpp">releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/heap/MarkedAllocator.cpp</a></li>
</ul>
<h3>Added Paths</h3>
<ul>
<li><a href="#releasesWebKitGTKwebkit210SourceJavaScriptCoretestsstressheapallocatorallocatesincorrectsizeforactivationjs">releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="releasesWebKitGTKwebkit210SourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/ChangeLog (189713 => 189714)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/ChangeLog 2015-09-14 12:28:32 UTC (rev 189713)
+++ releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/ChangeLog 2015-09-14 12:32:57 UTC (rev 189714)
</span><span class="lines">@@ -1,3 +1,39 @@
</span><ins>+2015-08-26 Saam barati <sbarati@apple.com>
+
+ MarkedBlock::allocateBlock will have the wrong allocation size when (sizeof(MarkedBlock) + bytes) is divisible by WTF::pageSize()
+ https://bugs.webkit.org/show_bug.cgi?id=148500
+
+ Reviewed by Mark Lam.
+
+ Consider the following scenario:
+ - On OS X, WTF::pageSize() is 4*1024 bytes.
+ - JSEnvironmentRecord::allocationSizeForScopeSize(6621) == 53000
+ - sizeof(MarkedBlock) == 248
+ - (248 + 53000) is a multiple of 4*1024.
+ - (248 + 53000)/(4*1024) == 13
+
+ We will allocate a chunk of memory of size 53248 bytes that looks like this:
+ 0 248 256 53248 53256
+ [Marked Block | 8 bytes | payload ...... ] 8 bytes |
+ ^ ^
+ Our Environment record starts here. ^
+ ^
+ Our last JSValue in the environment record will go from byte 53248 to 53256. But, we don't own this memory.
+
+ We need to ensure that we round up sizeof(MarkedBlock) to an
+ atomSize boundary. We need to do this because the first atom
+ inside the MarkedBlock will start at the rounded up multiple
+ of atomSize past MarkedBlock. If we end up with an allocation
+ that is perfectly aligned to the page size, then we will be short
+ 8 bytes (in the current implementation where atomSize is 16 bytes,
+ and MarkedBlock is 248 bytes).
+
+ * heap/MarkedAllocator.cpp:
+ (JSC::MarkedAllocator::allocateBlock):
+ * tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js: Added.
+ (use):
+ (makeFunction):
+
</ins><span class="cx"> 2015-08-26 Mark Lam <mark.lam@apple.com>
</span><span class="cx">
</span><span class="cx"> watchdog m_didFire state erroneously retained.
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit210SourceJavaScriptCoreheapMarkedAllocatorcpp"></a>
<div class="modfile"><h4>Modified: releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/heap/MarkedAllocator.cpp (189713 => 189714)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2015-09-14 12:28:32 UTC (rev 189713)
+++ releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/heap/MarkedAllocator.cpp 2015-09-14 12:32:57 UTC (rev 189714)
</span><span class="lines">@@ -175,7 +175,8 @@
</span><span class="cx"> MarkedBlock* MarkedAllocator::allocateBlock(size_t bytes)
</span><span class="cx"> {
</span><span class="cx"> size_t minBlockSize = MarkedBlock::blockSize;
</span><del>- size_t minAllocationSize = WTF::roundUpToMultipleOf(WTF::pageSize(), sizeof(MarkedBlock) + bytes);
</del><ins>+ size_t minAllocationSize = WTF::roundUpToMultipleOf<MarkedBlock::atomSize>(sizeof(MarkedBlock)) + WTF::roundUpToMultipleOf<MarkedBlock::atomSize>(bytes);
+ minAllocationSize = WTF::roundUpToMultipleOf(WTF::pageSize(), minAllocationSize);
</ins><span class="cx"> size_t blockSize = std::max(minBlockSize, minAllocationSize);
</span><span class="cx">
</span><span class="cx"> size_t cellSize = m_cellSize ? m_cellSize : WTF::roundUpToMultipleOf<MarkedBlock::atomSize>(bytes);
</span></span></pre></div>
<a id="releasesWebKitGTKwebkit210SourceJavaScriptCoretestsstressheapallocatorallocatesincorrectsizeforactivationjs"></a>
<div class="addfile"><h4>Added: releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js (0 => 189714)</h4>
<pre class="diff"><span>
<span class="info">--- releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js (rev 0)
+++ releases/WebKitGTK/webkit-2.10/Source/JavaScriptCore/tests/stress/heap-allocator-allocates-incorrect-size-for-activation.js 2015-09-14 12:32:57 UTC (rev 189714)
</span><span class="lines">@@ -0,0 +1,41 @@
</span><ins>+
+// Consider the following scenario:
+// - On OS X, WTF::pageSize() is 4*1024 bytes.
+// - JSEnvironmentRecord::allocationSizeForScopeSize(6621) == 53000
+// - sizeof(MarkedBlock) == 248
+// - (248 + 53000) is a multiple of 4*1024.
+// - (248 + 53000)/(4*1024) == 13
+
+// We will allocate a chunk of memory of size 53248 bytes that looks like this:
+// 0 248 256 53248 53256
+// [Marked Block | 8 bytes | payload ...... ] 8 bytes |
+// ^ ^
+// Our Environment record starts here. ^
+// ^
+// Our last JSValue in the environment record will go from byte 53248 to 53256. But, we don't own this memory.
+
+var numberOfCapturedVariables = 6621;
+function use() { }
+function makeFunction() {
+ var varName;
+ var outerFunction = "";
+ var innerFunction = "";
+
+ for (var i = 0; i < numberOfCapturedVariables; i++) {
+ varName = "_" + i;
+ outerFunction += "var " + varName + ";";
+ innerFunction += "use(" + varName + ");";
+ }
+ outerFunction += "function foo() {" + innerFunction + "}";
+ var functionString = "(function() { " + outerFunction + "})";
+ var result = eval(functionString);
+ return result;
+}
+
+var arr = [];
+for (var i = 0; i < 50; i++) {
+ var f = makeFunction();
+ f();
+ fullGC();
+}
+
</ins></span></pre>
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