Fix Qt containers to properly support types with strict alignments.

QContiguousCache is a new type, so there are no binary compatibility
issues.

QHash and QMap didn't have any public qMalloc / qFree, so the entire
logic is contained in .cpp code. However, since old code will not
inform us of the alignment requirements, we need to add a bit to the
structure to indicate whether strict alignment is in use or not.

QList doesn't require any changes. For small, movable types, they're
all stored in the pointer array itself, so they're aligned. For larger
types, we use new(), so types with stricter requirements should define
their own operator new().

QLinkedList cannot be fixed. It uses new() on the QLinkedListNode,
which contains a T type. Sorry.

QVector did have public qMalloc / qFree. I've moved the calls to the
inner function and made it keep the old calls if the alignment
requirement is below a certain threshold. The idea is that, if it's
above, no one was using QVector anyway.

Reviewed-by: Bradley T. Hughes

1 files changed, 17 insertions, 3 deletions

diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h
index b77b53a21d..cf7df1211b 100644
--- a/src/corelib/tools/qvector.h
+++ b/src/corelib/tools/qvector.h
@@ -79,6 +79,9 @@ struct Q_CORE_EXPORT QVectorData
     // some debugges when the QVector is member of a class within an unnamed namespace.
     // ### Qt 5: can be removed completely. (Ralf)
     static QVectorData *malloc(int sizeofTypedData, int size, int sizeofT, QVectorData *init);
+    static QVectorData *allocate(int size, int alignment);
+    static QVectorData *reallocate(QVectorData *old, int newsize, int oldsize, int alignment);
+    static void free(QVectorData *data, int alignment);
     static int grow(int sizeofTypedData, int size, int sizeofT, bool excessive);
 };
 
@@ -87,6 +90,8 @@ struct QVectorTypedData : private QVectorData
 { // private inheritance as we must not access QVectorData member thought QVectorTypedData
   // as this would break strict aliasing rules. (in the case of shared_null)
     T array[1];
+
+    static inline void free(QVectorTypedData *x, int alignment) { QVectorData::free(x, alignment); }
 };
 
 class QRegion;
@@ -302,6 +307,14 @@ private:
         // count the padding at the end
         return reinterpret_cast<const char *>(&(reinterpret_cast<const Data *>(this))->array[1]) - reinterpret_cast<const char *>(this);
     }
+    inline int alignOfTypedData() const
+    {
+#ifdef Q_ALIGNOF
+        return qMax<int>(sizeof(void*), Q_ALIGNOF(Data));
+#else
+        return 0;
+#endif
+    }
 };
 
 template <typename T>
@@ -373,7 +386,7 @@ QVector<T> &QVector<T>::operator=(const QVector<T> &v)
 template <typename T>
 inline QVectorData *QVector<T>::malloc(int aalloc)
 {
-    QVectorData *vectordata = static_cast<QVectorData *>(qMalloc(sizeOfTypedData() + (aalloc - 1) * sizeof(T)));
+    QVectorData *vectordata = QVectorData::allocate(sizeOfTypedData() + (aalloc - 1) * sizeof(T), alignOfTypedData());
     Q_CHECK_PTR(vectordata);
     return vectordata;
 }
@@ -420,7 +433,7 @@ void QVector<T>::free(Data *x)
         while (i-- != b)
              i->~T();
     }
-    qFree(x);
+    x->free(x, alignOfTypedData());
 }
 
 template <typename T>
@@ -459,7 +472,8 @@ void QVector<T>::realloc(int asize, int aalloc)
             }
         } else {
             QT_TRY {
-                QVectorData *mem = static_cast<QVectorData *>(qRealloc(p, sizeOfTypedData() + (aalloc - 1) * sizeof(T)));
+                QVectorData *mem = QVectorData::reallocate(d, sizeOfTypedData() + (aalloc - 1) * sizeof(T),
+                                                           sizeOfTypedData() + (d->alloc - 1) * sizeof(T), alignOfTypedData());
                 Q_CHECK_PTR(mem);
                 x.d = d = mem;
                 x.d->size = d->size;