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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/209847">209847</a></dd>
<dt>Author</dt> <dd>msaboff@apple.com</dd>
<dt>Date</dt> <dd>2016-12-14 17:41:53 -0800 (Wed, 14 Dec 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>The stress GC bot crashes in JavaScriptCore beneath ShadowChicken::update and Inspector::jsToInspectorValue
https://bugs.webkit.org/show_bug.cgi?id=165871
Reviewed by Mark Lam.
This fixes two issues with the VM watch dog timer firing in a worker.
The first issue has to do with bytecode ordering. Prior to this change, the first few opcodes
generated when the watch dog is enabled are:
op_enter
op_watchdog
op_get_scope
When the watchdog fires, the function will get an exception at op_watchdog. In processing that exception,
we'll try to update the ShadowChicken shadow stack. That update assumes that if there is a scope
VirtualRegister allocated, then the slot contains a valid JSScope. With the current bytecode ordering,
this is not true at op_watchdog as op_enter will put JSUndefined in the scope slot. It isn't until the
op_get_scope gets processed that we'll have a valid scope in the slot. The fix for this issue is to
ensure that op_get_scope happens before the op_watchdog.
The second issue is that ScriptFunctionCall::call() will not tell its caller that a terminated
execution exception happened. Instead call() returns an empty JSValue. InjectedScript::wrapCallFrames()
wasn't checking for an empty JSValue, but was passing it to another function. Added a short circuit
return when call returns an empty JSValue.
Added <https://bugs.webkit.org/show_bug.cgi?id=165875> to fix other callers of ScriptFunctionCall::call()
to check for an empty JSValue return value.
Also tracked with <rdar://problem/29671015>.
* bytecompiler/BytecodeGenerator.cpp:
(JSC::BytecodeGenerator::BytecodeGenerator):
(JSC::BytecodeGenerator::emitEnter):
* inspector/InjectedScript.cpp:
(Inspector::InjectedScript::wrapCallFrames):</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCorebytecompilerBytecodeGeneratorcpp">trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreinspectorInjectedScriptcpp">trunk/Source/JavaScriptCore/inspector/InjectedScript.cpp</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (209846 => 209847)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2016-12-15 01:25:16 UTC (rev 209846)
+++ trunk/Source/JavaScriptCore/ChangeLog 2016-12-15 01:41:53 UTC (rev 209847)
</span><span class="lines">@@ -1,3 +1,39 @@
</span><ins>+2016-12-14 Michael Saboff <msaboff@apple.com>
+
+ The stress GC bot crashes in JavaScriptCore beneath ShadowChicken::update and Inspector::jsToInspectorValue
+ https://bugs.webkit.org/show_bug.cgi?id=165871
+
+ Reviewed by Mark Lam.
+
+ This fixes two issues with the VM watch dog timer firing in a worker.
+
+ The first issue has to do with bytecode ordering. Prior to this change, the first few opcodes
+ generated when the watch dog is enabled are:
+ op_enter
+ op_watchdog
+ op_get_scope
+ When the watchdog fires, the function will get an exception at op_watchdog. In processing that exception,
+ we'll try to update the ShadowChicken shadow stack. That update assumes that if there is a scope
+ VirtualRegister allocated, then the slot contains a valid JSScope. With the current bytecode ordering,
+ this is not true at op_watchdog as op_enter will put JSUndefined in the scope slot. It isn't until the
+ op_get_scope gets processed that we'll have a valid scope in the slot. The fix for this issue is to
+ ensure that op_get_scope happens before the op_watchdog.
+
+ The second issue is that ScriptFunctionCall::call() will not tell its caller that a terminated
+ execution exception happened. Instead call() returns an empty JSValue. InjectedScript::wrapCallFrames()
+ wasn't checking for an empty JSValue, but was passing it to another function. Added a short circuit
+ return when call returns an empty JSValue.
+
+ Added <https://bugs.webkit.org/show_bug.cgi?id=165875> to fix other callers of ScriptFunctionCall::call()
+ to check for an empty JSValue return value.
+ Also tracked with <rdar://problem/29671015>.
+
+ * bytecompiler/BytecodeGenerator.cpp:
+ (JSC::BytecodeGenerator::BytecodeGenerator):
+ (JSC::BytecodeGenerator::emitEnter):
+ * inspector/InjectedScript.cpp:
+ (Inspector::InjectedScript::wrapCallFrames):
+
</ins><span class="cx"> 2016-12-14 Filip Pizlo <fpizlo@apple.com>
</span><span class="cx">
</span><span class="cx"> DirectTailCall implementation needs to tell the shuffler what to put into the ArgumentCount explicitly
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorebytecompilerBytecodeGeneratorcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp (209846 => 209847)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp 2016-12-15 01:25:16 UTC (rev 209846)
+++ trunk/Source/JavaScriptCore/bytecompiler/BytecodeGenerator.cpp 2016-12-15 01:41:53 UTC (rev 209847)
</span><span class="lines">@@ -197,6 +197,8 @@
</span><span class="cx">
</span><span class="cx"> allocateAndEmitScope();
</span><span class="cx">
</span><ins>+ emitWatchdog();
+
</ins><span class="cx"> const FunctionStack& functionStack = programNode->functionStack();
</span><span class="cx">
</span><span class="cx"> for (size_t i = 0; i < functionStack.size(); ++i) {
</span><span class="lines">@@ -330,6 +332,8 @@
</span><span class="cx">
</span><span class="cx"> allocateAndEmitScope();
</span><span class="cx">
</span><ins>+ emitWatchdog();
+
</ins><span class="cx"> if (functionNameIsInScope(functionNode->ident(), functionNode->functionMode())) {
</span><span class="cx"> ASSERT(parseMode != SourceParseMode::GeneratorBodyMode);
</span><span class="cx"> ASSERT(!isAsyncFunctionBodyParseMode(parseMode));
</span><span class="lines">@@ -756,6 +760,8 @@
</span><span class="cx">
</span><span class="cx"> allocateAndEmitScope();
</span><span class="cx">
</span><ins>+ emitWatchdog();
+
</ins><span class="cx"> const DeclarationStacks::FunctionStack& functionStack = evalNode->functionStack();
</span><span class="cx"> for (size_t i = 0; i < functionStack.size(); ++i)
</span><span class="cx"> m_codeBlock->addFunctionDecl(makeFunction(functionStack[i]));
</span><span class="lines">@@ -839,6 +845,8 @@
</span><span class="cx">
</span><span class="cx"> allocateAndEmitScope();
</span><span class="cx">
</span><ins>+ emitWatchdog();
+
</ins><span class="cx"> m_calleeRegister.setIndex(CallFrameSlot::callee);
</span><span class="cx">
</span><span class="cx"> m_codeBlock->setNumParameters(1); // Allocate space for "this"
</span><span class="lines">@@ -1249,7 +1257,6 @@
</span><span class="cx"> void BytecodeGenerator::emitEnter()
</span><span class="cx"> {
</span><span class="cx"> emitOpcode(op_enter);
</span><del>- emitWatchdog();
</del><span class="cx"> }
</span><span class="cx">
</span><span class="cx"> void BytecodeGenerator::emitLoopHint()
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreinspectorInjectedScriptcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/inspector/InjectedScript.cpp (209846 => 209847)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/inspector/InjectedScript.cpp 2016-12-15 01:25:16 UTC (rev 209846)
+++ trunk/Source/JavaScriptCore/inspector/InjectedScript.cpp 2016-12-15 01:41:53 UTC (rev 209847)
</span><span class="lines">@@ -219,6 +219,8 @@
</span><span class="cx">
</span><span class="cx"> bool hadException = false;
</span><span class="cx"> auto callFramesValue = callFunctionWithEvalEnabled(function, hadException);
</span><ins>+ if (!callFramesValue)
+ return Array<Inspector::Protocol::Debugger::CallFrame>::create();
</ins><span class="cx"> ASSERT(!hadException);
</span><span class="cx"> RefPtr<InspectorValue> result = toInspectorValue(*scriptState(), callFramesValue);
</span><span class="cx"> if (result->type() == InspectorValue::Type::Array)
</span></span></pre>
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