Fix alignment issue causing crash in QtScript/JavaScriptCore

When creating a substring, JSC::UStringImpl required that the
base string pointer was 8-byte aligned. However, on platforms
where FastMalloc isn't enabled (such as Symbian), it's possible
that the system malloc() returns a pointer that is only 4-byte
aligned. (On Symbian, this can happen if the argument to malloc()
itself isn't a multiple of 8.)

Cherry-picked http://trac.webkit.org/changeset/54743 from WebKit
trunk, which fixes this issue. (The commit happened shortly after
we rebased QtScript/JSC for 4.7, so it applies cleanly to our copy.)

Task-number: QTBUG-16828
Reviewed-by: Simon Hausmann
(cherry picked from commit ead20f4c1edc2e1c5c39f47bf7c9e56600d6362b)

4 files changed, 76 insertions, 84 deletions

diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog b/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
index c2b1155..9cbf0c1 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/ChangeLog
@@ -358,6 +358,31 @@
 
         * wtf/AlwaysInline.h:
 
+2010-02-12  Gavin Barraclough  <barraclough@apple.com>
+
+        Reviewed by Darin Adler.
+
+        https://bugs.webkit.org/show_bug.cgi?id=33731
+        Many false leaks in release builds due to PtrAndFlags
+
+        Remove UntypedPtrAndBitfield (similar to PtrAndFlags) in UStringImpl,
+        and steal bits from the refCount instead.
+
+        * runtime/UStringImpl.cpp:
+        (JSC::UStringImpl::baseSharedBuffer):
+        (JSC::UStringImpl::~UStringImpl):
+        * runtime/UStringImpl.h:
+        (JSC::UStringImpl::cost):
+        (JSC::UStringImpl::isIdentifier):
+        (JSC::UStringImpl::setIsIdentifier):
+        (JSC::UStringImpl::ref):
+        (JSC::UStringImpl::deref):
+        (JSC::UStringImpl::UStringImpl):
+        (JSC::UStringImpl::bufferOwnerString):
+        (JSC::UStringImpl::bufferOwnership):
+        (JSC::UStringImpl::isStatic):
+        (JSC::UStringImpl::):
+
 2010-02-12  Kwang Yul Seo  <skyul@company100.net>
 
         Reviewed by Adam Barth.
diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
index 4b0d1c9..4fde49e 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.cpp
@@ -38,12 +38,14 @@ namespace JSC {
 SharedUChar* UStringImpl::baseSharedBuffer()
 {
     ASSERT((bufferOwnership() == BufferShared)
-        || ((bufferOwnership() == BufferOwned) && !m_dataBuffer.asPtr<void*>()));
+        || ((bufferOwnership() == BufferOwned) && !m_buffer));
 
-    if (bufferOwnership() != BufferShared)
-        m_dataBuffer = UntypedPtrAndBitfield(SharedUChar::create(new OwnFastMallocPtr<UChar>(m_data)).releaseRef(), BufferShared);
+    if (bufferOwnership() != BufferShared) {
+        m_refCountAndFlags = (m_refCountAndFlags & ~s_refCountMaskBufferOwnership) | BufferShared;
+        m_bufferShared = SharedUChar::create(new OwnFastMallocPtr<UChar>(m_data)).releaseRef();
+    }
 
-    return m_dataBuffer.asPtr<SharedUChar*>();
+    return m_bufferShared;
 }
 
 SharedUChar* UStringImpl::sharedBuffer()
@@ -71,10 +73,10 @@ UStringImpl::~UStringImpl()
         if (bufferOwnership() == BufferOwned)
             fastFree(m_data);
         else if (bufferOwnership() == BufferSubstring)
-            m_dataBuffer.asPtr<UStringImpl*>()->deref();
+            m_bufferSubstring->deref();
         else {
             ASSERT(bufferOwnership() == BufferShared);
-            m_dataBuffer.asPtr<SharedUChar*>()->deref();
+            m_bufferShared->deref();
         }
     }
 }
diff --git a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
index 4e1ddc7..e6d1a8a 100644
--- a/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
+++ b/src/3rdparty/javascriptcore/JavaScriptCore/runtime/UStringImpl.h
@@ -40,48 +40,6 @@ class IdentifierTable;
   
 typedef CrossThreadRefCounted<OwnFastMallocPtr<UChar> > SharedUChar;
 
-class UntypedPtrAndBitfield {
-public:
-    UntypedPtrAndBitfield() {}
-
-    UntypedPtrAndBitfield(void* ptrValue, uintptr_t bitValue)
-        : m_value(reinterpret_cast<uintptr_t>(ptrValue) | bitValue)
-#ifndef NDEBUG
-        , m_leaksPtr(ptrValue)
-#endif
-    {
-        ASSERT(ptrValue == asPtr<void*>());
-        ASSERT((*this & ~s_alignmentMask) == bitValue);
-    }
-
-    template<typename T>
-    T asPtr() const { return reinterpret_cast<T>(m_value & s_alignmentMask); }
-
-    UntypedPtrAndBitfield& operator&=(uintptr_t bits)
-    {
-        m_value &= bits | s_alignmentMask;
-        return *this;
-    }
-
-    UntypedPtrAndBitfield& operator|=(uintptr_t bits)
-    {
-        m_value |= bits & ~s_alignmentMask;
-        return *this;
-    }
-
-    uintptr_t operator&(uintptr_t mask) const
-    {
-        return m_value & mask & ~s_alignmentMask;
-    }
-
-private:
-    static const uintptr_t s_alignmentMask = ~static_cast<uintptr_t>(0x7);
-    uintptr_t m_value;
-#ifndef NDEBUG
-        void* m_leaksPtr; // Only used to allow tools like leaks on OSX to detect that the memory is referenced.
-#endif
-};
-
 class UStringImpl : Noncopyable {
 public:
     template<size_t inlineCapacity>
@@ -151,21 +109,27 @@ public:
     {
         // For substrings, return the cost of the base string.
         if (bufferOwnership() == BufferSubstring)
-            return m_dataBuffer.asPtr<UStringImpl*>()->cost();
+            return m_bufferSubstring->cost();
 
-        if (m_dataBuffer & s_reportedCostBit)
+        if (m_refCountAndFlags & s_refCountFlagHasReportedCost)
             return 0;
-        m_dataBuffer |= s_reportedCostBit;
+        m_refCountAndFlags |= s_refCountFlagHasReportedCost;
         return m_length;
     }
     unsigned hash() const { if (!m_hash) m_hash = computeHash(data(), m_length); return m_hash; }
     unsigned existingHash() const { ASSERT(m_hash); return m_hash; } // fast path for Identifiers
     void setHash(unsigned hash) { ASSERT(hash == computeHash(data(), m_length)); m_hash = hash; } // fast path for Identifiers
-    bool isIdentifier() const { return m_isIdentifier; }
-    void setIsIdentifier(bool isIdentifier) { m_isIdentifier = isIdentifier; }
+    bool isIdentifier() const { return m_refCountAndFlags & s_refCountFlagIsIdentifier; }
+    void setIsIdentifier(bool isIdentifier)
+    {
+        if (isIdentifier)
+            m_refCountAndFlags |= s_refCountFlagIsIdentifier;
+        else
+            m_refCountAndFlags &= ~s_refCountFlagIsIdentifier;
+    }
 
-    UStringImpl* ref() { m_refCount += s_refCountIncrement; return this; }
-    ALWAYS_INLINE void deref() { if (!(m_refCount -= s_refCountIncrement)) delete this; }
+    UStringImpl* ref() { m_refCountAndFlags += s_refCountIncrement; return this; }
+    ALWAYS_INLINE void deref() { m_refCountAndFlags -= s_refCountIncrement; if (!(m_refCountAndFlags & s_refCountMask)) delete this; }
 
     static void copyChars(UChar* destination, const UChar* source, unsigned numCharacters)
     {
@@ -205,11 +169,10 @@ private:
     // Used to construct normal strings with an internal or external buffer.
     UStringImpl(UChar* data, int length, BufferOwnership ownership)
         : m_data(data)
+        , m_buffer(0)
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | ownership)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(0, ownership)
     {
         ASSERT((ownership == BufferInternal) || (ownership == BufferOwned));
         checkConsistency();
@@ -221,11 +184,10 @@ private:
     enum StaticStringConstructType { ConstructStaticString };
     UStringImpl(UChar* data, int length, StaticStringConstructType)
         : m_data(data)
+        , m_buffer(0)
         , m_length(length)
-        , m_refCount(s_staticRefCountInitialValue)
+        , m_refCountAndFlags(s_refCountFlagStatic | BufferOwned)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(0, BufferOwned)
     {
         checkConsistency();
     }
@@ -233,28 +195,26 @@ private:
     // Used to create new strings that are a substring of an existing string.
     UStringImpl(UChar* data, int length, PassRefPtr<UStringImpl> base)
         : m_data(data)
+        , m_bufferSubstring(base.releaseRef())
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | BufferSubstring)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(base.releaseRef(), BufferSubstring)
     {
         // Do use static strings as a base for substrings; UntypedPtrAndBitfield assumes
         // that all pointers will be at least 8-byte aligned, we cannot guarantee that of
         // UStringImpls that are not heap allocated.
-        ASSERT(m_dataBuffer.asPtr<UStringImpl*>()->size());
-        ASSERT(!m_dataBuffer.asPtr<UStringImpl*>()->isStatic());
+        ASSERT(m_bufferSubstring->size());
+        ASSERT(!m_bufferSubstring->isStatic());
         checkConsistency();
     }
 
     // Used to construct new strings sharing an existing shared buffer.
     UStringImpl(UChar* data, int length, PassRefPtr<SharedUChar> sharedBuffer)
         : m_data(data)
+        , m_bufferShared(sharedBuffer.releaseRef())
         , m_length(length)
-        , m_refCount(s_refCountIncrement)
+        , m_refCountAndFlags(s_refCountIncrement | BufferShared)
         , m_hash(0)
-        , m_isIdentifier(false)
-        , m_dataBuffer(sharedBuffer.releaseRef(), BufferShared)
     {
         checkConsistency();
     }
@@ -277,26 +237,31 @@ private:
     // This number must be at least 2 to avoid sharing empty, null as well as 1 character strings from SmallStrings.
     static const int s_minLengthToShare = 10;
     static const unsigned s_copyCharsInlineCutOff = 20;
-    static const uintptr_t s_bufferOwnershipMask = 3;
-    static const uintptr_t s_reportedCostBit = 4;
     // We initialize and increment/decrement the refCount for all normal (non-static) strings by the value 2.
     // We initialize static strings with an odd number (specifically, 1), such that the refCount cannot reach zero.
-    static const int s_refCountIncrement = 2;
-    static const int s_staticRefCountInitialValue = 1;
-
-    UStringImpl* bufferOwnerString() { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
-    const UStringImpl* bufferOwnerString() const { return (bufferOwnership() == BufferSubstring) ? m_dataBuffer.asPtr<UStringImpl*>() :  this; }
+    static const unsigned s_refCountMask = 0xFFFFFFF0;
+    static const int s_refCountIncrement = 0x20;
+    static const int s_refCountFlagStatic = 0x10;
+    static const unsigned s_refCountFlagHasReportedCost = 0x8;
+    static const unsigned s_refCountFlagIsIdentifier = 0x4;
+    static const unsigned s_refCountMaskBufferOwnership = 0x3;
+
+    UStringImpl* bufferOwnerString() { return (bufferOwnership() == BufferSubstring) ? m_bufferSubstring :  this; }
+    const UStringImpl* bufferOwnerString() const { return (bufferOwnership() == BufferSubstring) ? m_bufferSubstring :  this; }
     SharedUChar* baseSharedBuffer();
-    unsigned bufferOwnership() const { return m_dataBuffer & s_bufferOwnershipMask; }
-    bool isStatic() const { return m_refCount & 1; }
+    unsigned bufferOwnership() const { return m_refCountAndFlags & s_refCountMaskBufferOwnership; }
+    bool isStatic() const { return m_refCountAndFlags & s_refCountFlagStatic; }
 
     // unshared data
     UChar* m_data;
+    union {
+        void* m_buffer;
+        UStringImpl* m_bufferSubstring;
+        SharedUChar* m_bufferShared;
+    };
     int m_length;
-    unsigned m_refCount;
-    mutable unsigned m_hash : 31;
-    mutable unsigned m_isIdentifier : 1;
-    UntypedPtrAndBitfield m_dataBuffer;
+    unsigned m_refCountAndFlags;
+    mutable unsigned m_hash;
 
     JS_EXPORTDATA static UStringImpl* s_null;
     JS_EXPORTDATA static UStringImpl* s_empty;
diff --git a/src/3rdparty/javascriptcore/VERSION b/src/3rdparty/javascriptcore/VERSION
index b4744b7..13943b2 100644
--- a/src/3rdparty/javascriptcore/VERSION
+++ b/src/3rdparty/javascriptcore/VERSION
@@ -4,8 +4,8 @@ This is a snapshot of JavaScriptCore from
 
 The commit imported was from the
 
-        javascriptcore-snapshot-24012011 branch/tag
+        javascriptcore-snapshot-27012011 branch/tag
 
 and has the sha1 checksum
 
-        d143bde5ae8cff229aebd43487a2fce5e713e990
+        3ab0f621048fbeb480b687a28ed31d92d8506150