Fix UB in tst_QIODevice::getSetCheck()

The reinterpret cast from a QTcpSocket → QAbstractSocket → QIODevice
to MyIODevice → QIODevice was undefined.

Fix by simply instantiating a MyIODevice, which must then inherit
from QTcpSocket, of course.

Instead of fixing the class name in the overridden setOpenMode()
method, simply make the base class' implementation public with
a using declaration.

Found by UBSan:
  qtbase/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp:84:22: runtime error: member call on address 0x7ffcca2d23f0 which does not point to an object of type 'MyIODevice'
  0x7ffcca2d23f0: note: object is of type 'QTcpSocket'

Change-Id: I939b3548949b9b5765df4a6cc81875e169fd69dd
Reviewed-by: Alex Trotsenko <alex1973tr@gmail.com>
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 7 insertions, 8 deletions

diff --git a/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp b/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
index 565ca18899..af79de06d5 100644
--- a/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
+++ b/tests/auto/corelib/io/qiodevice/tst_qiodevice.cpp
@@ -74,16 +74,15 @@ void tst_QIODevice::getSetCheck()
 {
     // OpenMode QIODevice::openMode()
     // void QIODevice::setOpenMode(OpenMode)
-    class MyIODevice : public QIODevice {
+    class MyIODevice : public QTcpSocket {
     public:
-        void setOpenMode(OpenMode openMode) { QIODevice::setOpenMode(openMode); }
+        using QTcpSocket::setOpenMode;
     };
-    QTcpSocket var1;
-    MyIODevice *obj1 = reinterpret_cast<MyIODevice*>(&var1);
-    obj1->setOpenMode(QIODevice::OpenMode(QIODevice::NotOpen));
-    QCOMPARE(QIODevice::OpenMode(QIODevice::NotOpen), obj1->openMode());
-    obj1->setOpenMode(QIODevice::OpenMode(QIODevice::ReadWrite));
-    QCOMPARE(QIODevice::OpenMode(QIODevice::ReadWrite), obj1->openMode());
+    MyIODevice var1;
+    var1.setOpenMode(QIODevice::OpenMode(QIODevice::NotOpen));
+    QCOMPARE(QIODevice::OpenMode(QIODevice::NotOpen), var1.openMode());
+    var1.setOpenMode(QIODevice::OpenMode(QIODevice::ReadWrite));
+    QCOMPARE(QIODevice::OpenMode(QIODevice::ReadWrite), var1.openMode());
 }
 
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