Change meaning of offset in QByteArrayData

It used to be an index into the first element in 'd' that came after
'offset'. It is now the byte offset from the beginning of the
QByteArrayData structure.

By no longer using an actual array to access characters, we also steer
clear of GCC bug #43247:

    http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43247

This aligns this data structure with QArrayData. The intention is to
have QVector, QString and QByteArray share the same memory layout and
possibly code.

Change-Id: I8546e5f51cd2161ba09bd4ada174b7f5e6f09db7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 8 insertions, 9 deletions

diff --git a/src/corelib/tools/qbytearray.h b/src/corelib/tools/qbytearray.h
index c4feb63814..c654673959 100644
--- a/src/corelib/tools/qbytearray.h
+++ b/src/corelib/tools/qbytearray.h
@@ -124,12 +124,11 @@ struct QByteArrayData
     int size;
     uint alloc : 31;
     uint capacityReserved : 1;
-    union {
-        qptrdiff offset; // will always work as we add/subtract from a ushort ptr
-        char d[sizeof(qptrdiff)];
-    };
-    inline char *data() { return d + sizeof(qptrdiff) + offset; }
-    inline const char *data() const { return d + sizeof(qptrdiff) + offset; }
+
+    qptrdiff offset;
+
+    inline char *data() { return reinterpret_cast<char *>(this) + offset; }
+    inline const char *data() const { return reinterpret_cast<const char *>(this) + offset; }
 };
 
 template<int N> struct QStaticByteArrayData
@@ -148,7 +147,7 @@ template<int N> struct QStaticByteArrayDataPtr
 #  define QByteArrayLiteral(str) ([]() -> QStaticByteArrayDataPtr<sizeof(str) - 1> { \
         enum { Size = sizeof(str) - 1 }; \
         static const QStaticByteArrayData<Size> qbytearray_literal = \
-        { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, { 0 } }, str }; \
+        { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QByteArrayData) }, str }; \
         QStaticByteArrayDataPtr<Size> holder = { &qbytearray_literal }; \
     return holder; }())
 
@@ -161,7 +160,7 @@ template<int N> struct QStaticByteArrayDataPtr
     __extension__ ({ \
         enum { Size = sizeof(str) - 1 }; \
         static const QStaticByteArrayData<Size> qbytearray_literal = \
-        { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, { 0 } }, str }; \
+        { { Q_REFCOUNT_INITIALIZE_STATIC, Size, 0, 0, sizeof(QByteArrayData) }, str }; \
         QStaticByteArrayDataPtr<Size> holder = { &qbytearray_literal }; \
         holder; })
 #endif
@@ -427,7 +426,7 @@ inline const char *QByteArray::data() const
 inline const char *QByteArray::constData() const
 { return d->data(); }
 inline void QByteArray::detach()
-{ if (d->ref.isShared() || d->offset) realloc(d->size); }
+{ if (d->ref.isShared() || (d->offset != sizeof(QByteArrayData))) realloc(d->size); }
 inline bool QByteArray::isDetached() const
 { return !d->ref.isShared(); }
 inline QByteArray::QByteArray(const QByteArray &a) : d(a.d)