3 files changed, 32 insertions, 4 deletions

diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index efed984aef..8f0a95c82c 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -56,16 +56,19 @@ QArrayData *QArrayData::allocate(size_t objectSize, size_t alignment,
             && !(alignment & (alignment - 1)));
 
     // Don't allocate empty headers
-    if (!capacity)
+    if (!(options & RawData) && !capacity)
         return !(options & Unsharable)
             ? const_cast<QArrayData *>(&qt_array_empty)
             : const_cast<QArrayData *>(&qt_array_unsharable_empty);
 
+    size_t allocSize = sizeof(QArrayData) + objectSize * capacity;
+
     // Allocate extra (alignment - Q_ALIGNOF(QArrayData)) padding bytes so we
     // can properly align the data array. This assumes malloc is able to
     // provide appropriate alignment for the header -- as it should!
-    size_t allocSize = sizeof(QArrayData) + objectSize * capacity
-        + (alignment - Q_ALIGNOF(QArrayData));
+    // Padding is skipped when allocating a header for RawData.
+    if (!(options & RawData))
+        allocSize += (alignment - Q_ALIGNOF(QArrayData));
 
     QArrayData *header = static_cast<QArrayData *>(qMalloc(allocSize));
     Q_CHECK_PTR(header);
diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index 8eb543ee51..5a17d718c9 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -73,9 +73,18 @@ struct Q_CORE_EXPORT QArrayData
         return reinterpret_cast<const char *>(this) + offset;
     }
 
+    // This refers to array data mutability, not "header data" represented by
+    // data members in QArrayData. Shared data (array and header) must still
+    // follow COW principles.
+    bool isMutable() const
+    {
+        return alloc != 0;
+    }
+
     enum AllocateOption {
         CapacityReserved = 0x1,
         Unsharable = 0x2,
+        RawData = 0x4,
 
         Default = 0
     };
@@ -139,6 +148,20 @@ struct QTypedArrayData
         QArrayData::deallocate(data, sizeof(T), Q_ALIGNOF(AlignmentDummy));
     }
 
+    static QTypedArrayData *fromRawData(const T *data, size_t n,
+            AllocateOptions options = Default)
+    {
+        QTypedArrayData *result = allocate(0, options | RawData);
+        if (result) {
+            Q_ASSERT(!result->ref.isShared()); // No shared empty, please!
+
+            result->offset = reinterpret_cast<const char *>(data)
+                - reinterpret_cast<const char *>(result);
+            result->size = n;
+        }
+        return result;
+    }
+
     static QTypedArrayData *sharedNull()
     {
         return static_cast<QTypedArrayData *>(
diff --git a/src/corelib/tools/qarraydatapointer.h b/src/corelib/tools/qarraydatapointer.h
index 1dc02daa63..8b1d2a805c 100644
--- a/src/corelib/tools/qarraydatapointer.h
+++ b/src/corelib/tools/qarraydatapointer.h
@@ -114,6 +114,8 @@ public:
 
     void setSharable(bool sharable)
     {
+        // Can't call setSharable on static read-only data, like shared_null
+        // and the internal shared-empties.
         if (d->alloc == 0 && d->size == 0) {
             d = Data::allocate(0, sharable
                     ? QArrayData::Default
@@ -138,7 +140,7 @@ public:
 
     bool detach()
     {
-        if (d->ref.isShared()) {
+        if (!d->isMutable() || d->ref.isShared()) {
             Data *copy = clone(d->detachFlags());
             QArrayDataPointer old(d);
             d = copy;