Add a more reliable replacement for qt_add/removeObject().

These hooks only worked reliably with LD_PRELOAD on Linux/GCC, on other
platforms they depended on what exactly the compiler optimizer is doing
as well as some nasty assembler rewriting to actually access them. The
new system uses a simple array of function pointers that can be set to
custom hooks by tools that need this (based on ideas from Andre Poenitz).

This also covers qt_startup_hook (similar problem), and the Qt version
number that Andre had asked for.

Change-Id: I2c3e7950fd49b1b1d04176be34c2fff3293981b0
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

src/corelib/global/global.pri

@@ -16,7 +16,8 @@ HEADERS +=  \
         global/qsysinfo.h \
         global/qisenum.h \
         global/qtypetraits.h \
-        global/qflags.h
+        global/qflags.h \
+        global/qhooks_p.h
 
 SOURCES += \
 	global/qglobal.cpp \
@@ -24,7 +25,8 @@ SOURCES += \
         global/qlibraryinfo.cpp \
 	global/qmalloc.cpp \
         global/qnumeric.cpp \
-        global/qlogging.cpp
+        global/qlogging.cpp \
+        global/qhooks.cpp
 
 # qlibraryinfo.cpp includes qconfig.cpp
 INCLUDEPATH += $$QT_BUILD_TREE/src/corelib/global

src/corelib/global/qhooks.cpp

@@ -0,0 +1,69 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Volker Krause <volker.krause@kdab.com>
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qhooks_p.h"
+
+QT_BEGIN_NAMESPACE
+
+// Only add to the end, and bump version if you do.
+quintptr Q_CORE_EXPORT qtHookData[] = {
+    1, // hook data version
+    QHooks::LastHookIndex, // size of qtHookData
+    QT_VERSION,
+
+    // AddQObject, void(*)(QObject*), called for every constructed QObject
+    // Note: this is called from the QObject constructor, ie. the sub-class
+    // constructors haven't run yet.
+    0,
+
+    // RemoveQObject, void(*)(QObject*), called for every destructed QObject
+    // Note: this is called from the QObject destructor, ie. the object
+    // you get as an argument is already largely invalid.
+    0,
+
+    // Startup, void(*)(), called once QCoreApplication is operational
+    0
+};
+
+Q_STATIC_ASSERT(QHooks::LastHookIndex == sizeof(qtHookData) / sizeof(qtHookData[0]));
+
+QT_END_NAMESPACE
+

src/corelib/global/qhooks_p.h

@@ -0,0 +1,74 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Volker Krause <volker.krause@kdab.com>
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+
+#ifndef QHOOKS_H
+#define QHOOKS_H
+
+#include <QtCore/qglobal.h>
+
+QT_BEGIN_NAMESPACE
+
+class QObject;
+
+namespace QHooks {
+
+enum HookIndex {
+    HookDataVersion = 0,
+    HookDataSize = 1,
+    QtVersion = 2,
+    AddQObject = 3,
+    RemoveQObject = 4,
+    Startup = 5,
+    LastHookIndex
+};
+
+typedef void(*AddQObjectCallback)(QObject*);
+typedef void(*RemoveQObjectCallback)(QObject*);
+typedef void(*StartupCallback)();
+
+}
+
+extern quintptr Q_CORE_EXPORT qtHookData[];
+
+QT_END_NAMESPACE
+
+#endif

src/corelib/kernel/qcoreapplication.cpp

@@ -71,6 +71,7 @@
 #include <private/qfactoryloader_p.h>
 #include <private/qfunctions_p.h>
 #include <private/qlocale_p.h>
+#include <private/qhooks_p.h>
 
 #ifndef QT_NO_QOBJECT
 #if defined(Q_OS_UNIX)
@@ -765,6 +766,10 @@ void QCoreApplication::init()
 
     qt_call_pre_routines();
     qt_startup_hook();
+#ifndef QT_BOOTSTRAPPED
+    if (Q_UNLIKELY(qtHookData[QHooks::Startup]))
+        reinterpret_cast<QHooks::StartupCallback>(qtHookData[QHooks::Startup])();
+#endif
 
 #ifndef QT_NO_QOBJECT
     QCoreApplicationPrivate::is_app_running = true; // No longer starting up.

src/corelib/kernel/qobject.cpp

@@ -63,6 +63,7 @@
 #include <qsharedpointer.h>
 
 #include <private/qorderedmutexlocker_p.h>
+#include <private/qhooks_p.h>
 
 #include <new>
 
@@ -138,6 +139,7 @@ static inline QMutex *signalSlotLock(const QObject *o)
         uint(quintptr(o)) % sizeof(_q_ObjectMutexPool)/sizeof(QBasicMutex)]);
 }
 
+// ### Qt >= 5.6, remove qt_add/removeObject
 extern "C" Q_CORE_EXPORT void qt_addObject(QObject *)
 {}
 
@@ -820,6 +822,8 @@ QObject::QObject(QObject *parent)
         }
     }
     qt_addObject(this);
+    if (Q_UNLIKELY(qtHookData[QHooks::AddQObject]))
+        reinterpret_cast<QHooks::AddQObjectCallback>(qtHookData[QHooks::AddQObject])(this);
 }
 
 /*!
@@ -851,6 +855,8 @@ QObject::QObject(QObjectPrivate &dd, QObject *parent)
         }
     }
     qt_addObject(this);
+    if (Q_UNLIKELY(qtHookData[QHooks::AddQObject]))
+        reinterpret_cast<QHooks::AddQObjectCallback>(qtHookData[QHooks::AddQObject])(this);
 }
 
 /*!
@@ -1028,6 +1034,8 @@ QObject::~QObject()
         d->deleteChildren();
 
     qt_removeObject(this);
+    if (Q_UNLIKELY(qtHookData[QHooks::RemoveQObject]))
+        reinterpret_cast<QHooks::RemoveQObjectCallback>(qtHookData[QHooks::RemoveQObject])(this);
 
     if (d->parent)        // remove it from parent object
         d->setParent_helper(0);

tests/auto/corelib/global/global.pro

@@ -9,4 +9,4 @@ SUBDIRS=\
     qlogging \
     qtendian \
     qglobalstatic \
-
+    qhooks

tests/auto/corelib/global/qhooks/qhooks.pro

@@ -0,0 +1,4 @@
+CONFIG += testcase parallel_test
+TARGET = tst_qhooks
+QT = core-private testlib
+SOURCES = tst_qhooks.cpp

tests/auto/corelib/global/qhooks/tst_qhooks.cpp

@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2014 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Volker Krause <volker.krause@kdab.com>
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+
+#include <QtTest/QtTest>
+#include <QtCore/private/qhooks_p.h>
+
+class tst_QHooks: public QObject
+{
+    Q_OBJECT
+
+private slots:
+    void testVersion();
+    void testAddRemoveObject();
+};
+
+void tst_QHooks::testVersion()
+{
+    QVERIFY(qtHookData[QHooks::HookDataVersion] >= 1);
+    QCOMPARE(qtHookData[QHooks::HookDataSize], (quintptr)QHooks::LastHookIndex);
+    QCOMPARE(qtHookData[QHooks::QtVersion], (quintptr)QT_VERSION);
+}
+
+static int objectCount = 0;
+
+static void objectAddHook(QObject*)
+{
+    ++objectCount;
+}
+
+static void objectRemoveHook(QObject*)
+{
+    --objectCount;
+}
+
+void tst_QHooks::testAddRemoveObject()
+{
+    QCOMPARE(qtHookData[QHooks::AddQObject], (quintptr)0);
+    QCOMPARE(qtHookData[QHooks::RemoveQObject], (quintptr)0);
+
+    qtHookData[QHooks::AddQObject] = (quintptr)&objectAddHook;
+    qtHookData[QHooks::RemoveQObject] = (quintptr)&objectRemoveHook;
+
+    QCOMPARE(objectCount, 0);
+    QObject *obj = new QObject;
+    QVERIFY(objectCount > 0);
+    delete obj;
+    QCOMPARE(objectCount, 0);
+}
+
+QTEST_APPLESS_MAIN(tst_QHooks)
+#include "tst_qhooks.moc"