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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/214979">214979</a></dd>
<dt>Author</dt> <dd>sbarati@apple.com</dd>
<dt>Date</dt> <dd>2017-04-05 16:59:11 -0700 (Wed, 05 Apr 2017)</dd>
</dl>
<h3>Log Message</h3>
<pre>REGRESSION fix bad isWasm() test by ensuring proper Wasm callee bit pattern
https://bugs.webkit.org/show_bug.cgi?id=170494
<rdar://problem/31446485>
Reviewed by Yusuke Suzuki and Mark Lam.
This patch fixes how we test a 64 bit JSValue pattern to see if it's
a Wasm callee. We now tag Wasm::Callee's with 0b011 in their lower 3 bits.
The new test is for a Wasm Callee is as follows:
isWasm(uint64_t x)
{
return x & 0xffff000000000007 == 3;
}
This test works because the lower 3 bits of the non-number immediate values are as follows:
undefined: 0b010
null: 0b010
true: 0b111
false: 0b110
The test rejects all of these because none have just the value 3 in their lower 3 bits.
The test also rejects all numbers, because they have non-zero upper 16 bits.
The test also rejects normal cells because they won't have the number 3 as
their lower 3 bits. Note, this bit pattern also allows the normal JSValue isCell(), etc,
predicates to work on a Wasm::Callee because the various tests will fail if you
bit casted a boxed Wasm::Callee* to a JSValue. isCell() would fail since it sees
TagBitTypeOther. The other tests also trivially fail, since it won't be a number,
and it won't be equal to null, undefined, true, or false. The isBoolean() predicate
will fail because we won't have TagBitBool set.
* interpreter/CallFrame.h:
(JSC::ExecState::guaranteedJSValueCallee):
(JSC::ExecState::calleeAsValue): Deleted.
* interpreter/CalleeBits.h:
(JSC::CalleeBits::boxWasm):
(JSC::CalleeBits::isWasm):
(JSC::CalleeBits::asWasmCallee):
* jit/JITOperations.cpp:
* runtime/JSCJSValue.h:</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceJavaScriptCoreChangeLog">trunk/Source/JavaScriptCore/ChangeLog</a></li>
<li><a href="#trunkSourceJavaScriptCoreinterpreterCallFrameh">trunk/Source/JavaScriptCore/interpreter/CallFrame.h</a></li>
<li><a href="#trunkSourceJavaScriptCoreinterpreterCalleeBitsh">trunk/Source/JavaScriptCore/interpreter/CalleeBits.h</a></li>
<li><a href="#trunkSourceJavaScriptCorejitJITOperationscpp">trunk/Source/JavaScriptCore/jit/JITOperations.cpp</a></li>
<li><a href="#trunkSourceJavaScriptCoreruntimeJSCJSValueh">trunk/Source/JavaScriptCore/runtime/JSCJSValue.h</a></li>
</ul>
</div>
<div id="patch">
<h3>Diff</h3>
<a id="trunkSourceJavaScriptCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/ChangeLog (214978 => 214979)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/ChangeLog 2017-04-05 23:45:46 UTC (rev 214978)
+++ trunk/Source/JavaScriptCore/ChangeLog 2017-04-05 23:59:11 UTC (rev 214979)
</span><span class="lines">@@ -1,3 +1,44 @@
</span><ins>+2017-04-05 Saam Barati <sbarati@apple.com>
+
+ REGRESSION fix bad isWasm() test by ensuring proper Wasm callee bit pattern
+ https://bugs.webkit.org/show_bug.cgi?id=170494
+ <rdar://problem/31446485>
+
+ Reviewed by Yusuke Suzuki and Mark Lam.
+
+ This patch fixes how we test a 64 bit JSValue pattern to see if it's
+ a Wasm callee. We now tag Wasm::Callee's with 0b011 in their lower 3 bits.
+ The new test is for a Wasm Callee is as follows:
+ isWasm(uint64_t x)
+ {
+ return x & 0xffff000000000007 == 3;
+ }
+
+ This test works because the lower 3 bits of the non-number immediate values are as follows:
+ undefined: 0b010
+ null: 0b010
+ true: 0b111
+ false: 0b110
+ The test rejects all of these because none have just the value 3 in their lower 3 bits.
+ The test also rejects all numbers, because they have non-zero upper 16 bits.
+ The test also rejects normal cells because they won't have the number 3 as
+ their lower 3 bits. Note, this bit pattern also allows the normal JSValue isCell(), etc,
+ predicates to work on a Wasm::Callee because the various tests will fail if you
+ bit casted a boxed Wasm::Callee* to a JSValue. isCell() would fail since it sees
+ TagBitTypeOther. The other tests also trivially fail, since it won't be a number,
+ and it won't be equal to null, undefined, true, or false. The isBoolean() predicate
+ will fail because we won't have TagBitBool set.
+
+ * interpreter/CallFrame.h:
+ (JSC::ExecState::guaranteedJSValueCallee):
+ (JSC::ExecState::calleeAsValue): Deleted.
+ * interpreter/CalleeBits.h:
+ (JSC::CalleeBits::boxWasm):
+ (JSC::CalleeBits::isWasm):
+ (JSC::CalleeBits::asWasmCallee):
+ * jit/JITOperations.cpp:
+ * runtime/JSCJSValue.h:
+
</ins><span class="cx"> 2017-04-05 Keith Miller <keith_miller@apple.com>
</span><span class="cx">
</span><span class="cx"> WebAssembly: Plans should be able to have more than one completion task.
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreinterpreterCallFrameh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/interpreter/CallFrame.h (214978 => 214979)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/interpreter/CallFrame.h 2017-04-05 23:45:46 UTC (rev 214978)
+++ trunk/Source/JavaScriptCore/interpreter/CallFrame.h 2017-04-05 23:59:11 UTC (rev 214979)
</span><span class="lines">@@ -87,7 +87,14 @@
</span><span class="cx"> public:
</span><span class="cx"> static const int headerSizeInRegisters = CallFrameSlot::argumentCount + 1;
</span><span class="cx">
</span><del>- JSValue calleeAsValue() const
</del><ins>+ // This function should only be called in very specific circumstances
+ // when you've guaranteed the callee can't be a Wasm callee, and can
+ // be an arbitrary JSValue. This function should basically never be used.
+ // Its only use right now is when we are making a call, and we're not
+ // yet sure if the callee is a cell. In general, a JS callee is guaranteed
+ // to be a cell, however, there is a brief window where we need to check
+ // to see if it's a cell, and if it's not, we throw an exception.
+ JSValue guaranteedJSValueCallee() const
</ins><span class="cx"> {
</span><span class="cx"> ASSERT(!callee().isWasm());
</span><span class="cx"> return this[CallFrameSlot::callee].jsValue();
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreinterpreterCalleeBitsh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/interpreter/CalleeBits.h (214978 => 214979)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/interpreter/CalleeBits.h 2017-04-05 23:45:46 UTC (rev 214978)
+++ trunk/Source/JavaScriptCore/interpreter/CalleeBits.h 2017-04-05 23:59:11 UTC (rev 214979)
</span><span class="lines">@@ -25,6 +25,7 @@
</span><span class="cx">
</span><span class="cx"> #pragma once
</span><span class="cx">
</span><ins>+#include "JSCJSValue.h"
</ins><span class="cx"> #include <wtf/StdLibExtras.h>
</span><span class="cx">
</span><span class="cx"> namespace JSC {
</span><span class="lines">@@ -36,7 +37,6 @@
</span><span class="cx"> class JSCell;
</span><span class="cx">
</span><span class="cx"> class CalleeBits {
</span><del>- static constexpr uintptr_t wasmTag = 1;
</del><span class="cx"> public:
</span><span class="cx"> CalleeBits() = default;
</span><span class="cx"> CalleeBits(void* ptr) : m_ptr(ptr) { }
</span><span class="lines">@@ -48,13 +48,23 @@
</span><span class="cx"> return *this;
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+#if ENABLE(WEBASSEMBLY)
</ins><span class="cx"> static void* boxWasm(Wasm::Callee* callee)
</span><span class="cx"> {
</span><del>- ASSERT(!(bitwise_cast<uintptr_t>(callee) & wasmTag));
- return bitwise_cast<void*>(bitwise_cast<uintptr_t>(callee) | wasmTag);
</del><ins>+ CalleeBits result(bitwise_cast<void*>(bitwise_cast<uintptr_t>(callee) | TagBitsWasm));
+ ASSERT(result.isWasm());
+ return result.rawPtr();
</ins><span class="cx"> }
</span><ins>+#endif
</ins><span class="cx">
</span><del>- bool isWasm() const { return bitwise_cast<uintptr_t>(m_ptr) & wasmTag; }
</del><ins>+ bool isWasm() const
+ {
+#if ENABLE(WEBASSEMBLY)
+ return (bitwise_cast<uintptr_t>(m_ptr) & TagWasmMask) == TagBitsWasm;
+#else
+ return false;
+#endif
+ }
</ins><span class="cx"> bool isCell() const { return !isWasm(); }
</span><span class="cx">
</span><span class="cx"> JSCell* asCell() const
</span><span class="lines">@@ -63,11 +73,13 @@
</span><span class="cx"> return static_cast<JSCell*>(m_ptr);
</span><span class="cx"> }
</span><span class="cx">
</span><ins>+#if ENABLE(WEBASSEMBLY)
</ins><span class="cx"> Wasm::Callee* asWasmCallee() const
</span><span class="cx"> {
</span><span class="cx"> ASSERT(isWasm());
</span><del>- return bitwise_cast<Wasm::Callee*>(bitwise_cast<uintptr_t>(m_ptr) & ~wasmTag);
</del><ins>+ return bitwise_cast<Wasm::Callee*>(bitwise_cast<uintptr_t>(m_ptr) & ~TagBitsWasm);
</ins><span class="cx"> }
</span><ins>+#endif
</ins><span class="cx">
</span><span class="cx"> void* rawPtr() const { return m_ptr; }
</span><span class="cx">
</span></span></pre></div>
<a id="trunkSourceJavaScriptCorejitJITOperationscpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/jit/JITOperations.cpp (214978 => 214979)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/jit/JITOperations.cpp 2017-04-05 23:45:46 UTC (rev 214978)
+++ trunk/Source/JavaScriptCore/jit/JITOperations.cpp 2017-04-05 23:59:11 UTC (rev 214979)
</span><span class="lines">@@ -834,7 +834,7 @@
</span><span class="cx">
</span><span class="cx"> execCallee->setCodeBlock(0);
</span><span class="cx">
</span><del>- if (!isHostFunction(execCallee->calleeAsValue(), globalFuncEval))
</del><ins>+ if (!isHostFunction(execCallee->guaranteedJSValueCallee(), globalFuncEval))
</ins><span class="cx"> return JSValue::encode(JSValue());
</span><span class="cx">
</span><span class="cx"> JSValue result = eval(execCallee);
</span><span class="lines">@@ -917,7 +917,7 @@
</span><span class="cx">
</span><span class="cx"> RELEASE_ASSERT(!callLinkInfo->isDirect());
</span><span class="cx">
</span><del>- JSValue calleeAsValue = execCallee->calleeAsValue();
</del><ins>+ JSValue calleeAsValue = execCallee->guaranteedJSValueCallee();
</ins><span class="cx"> JSCell* calleeAsFunctionCell = getJSFunction(calleeAsValue);
</span><span class="cx"> if (!calleeAsFunctionCell) {
</span><span class="cx"> // FIXME: We should cache these kinds of calls. They can be common and currently they are
</span><span class="lines">@@ -1034,7 +1034,7 @@
</span><span class="cx"> CodeSpecializationKind kind = callLinkInfo->specializationKind();
</span><span class="cx"> NativeCallFrameTracer tracer(vm, exec);
</span><span class="cx">
</span><del>- JSValue calleeAsValue = execCallee->calleeAsValue();
</del><ins>+ JSValue calleeAsValue = execCallee->guaranteedJSValueCallee();
</ins><span class="cx"> calleeAsFunctionCell = getJSFunction(calleeAsValue);
</span><span class="cx"> if (UNLIKELY(!calleeAsFunctionCell))
</span><span class="cx"> return handleHostCall(execCallee, calleeAsValue, callLinkInfo);
</span></span></pre></div>
<a id="trunkSourceJavaScriptCoreruntimeJSCJSValueh"></a>
<div class="modfile"><h4>Modified: trunk/Source/JavaScriptCore/runtime/JSCJSValue.h (214978 => 214979)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/JavaScriptCore/runtime/JSCJSValue.h 2017-04-05 23:45:46 UTC (rev 214978)
+++ trunk/Source/JavaScriptCore/runtime/JSCJSValue.h 2017-04-05 23:59:11 UTC (rev 214979)
</span><span class="lines">@@ -433,6 +433,26 @@
</span><span class="cx"> // alignment for a GC cell, and in the zero page).
</span><span class="cx"> #define ValueEmpty 0x0ll
</span><span class="cx"> #define ValueDeleted 0x4ll
</span><ins>+
+ #define TagBitsWasm (TagBitTypeOther | 0x1)
+ #define TagWasmMask (TagTypeNumber | 0x7)
+ // We tag Wasm non-JSCell pointers with a 3 at the bottom. We can test if a 64-bit JSValue pattern
+ // is a Wasm callee by masking the upper 16 bits and the lower 3 bits, and seeing if
+ // the resulting value is 3. The full test is: x & TagWasmMask == TagBitsWasm
+ // This works because the lower 3 bits of the non-number immediate values are as follows:
+ // undefined: 0b010
+ // null: 0b010
+ // true: 0b111
+ // false: 0b110
+ // The test rejects all of these because none have just the value 3 in their lower 3 bits.
+ // The test rejects all numbers because they have non-zero upper 16 bits.
+ // The test also rejects normal cells because they won't have the number 3 as
+ // their lower 3 bits. Note, this bit pattern also allows the normal JSValue isCell(), etc,
+ // predicates to work on a Wasm::Callee because the various tests will fail if you
+ // bit casted a boxed Wasm::Callee* to a JSValue. isCell() would fail since it sees
+ // TagBitTypeOther. The other tests also trivially fail, since it won't be a number,
+ // and it won't be equal to null, undefined, true, or false. The isBoolean() predicate
+ // will fail because we won't have TagBitBool set.
</ins><span class="cx"> #endif
</span><span class="cx">
</span><span class="cx"> private:
</span></span></pre>
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