Doing a QList::append while using KBDLLHOOKSTRUCT (WinAPI) results in segmentation fault. :(

Thynome

Hello dear Qt community,

as a little exercise, I wanted to write a class which logs every key press made on the keyboard (No, I'm really not planning to do illegal stuff with it.). Because I didn't like Qt's way, I decided to use the WinAPI code of this guy here to catch the strokes: https://www.youtube.com/watch?v=O0C4V6JmlNw.
But now I have a persistent crash when appending my gained information to a QList in the KeyBoardProc function. Showing it with qDebug() works though.

This is the error I get from the debugger:

template <typename T>
Q_OUTOFLINE_TEMPLATE void QList<T>::append(const T &t)
{
        if  (d->ref.isShared()) {
        Node *n = detach_helper_grow(INT_MAX, 1);
        QT_TRY {
            node_construct(n, t);
        } 
[...]
}

(The yellow arrow of the debugger points to the fourth line (QList.h, line 577).)

I already found out that it doesn't matter what kind of variable I'm trying to append or if I even append a constant value; it crashes when using append. Well, of course I noticed that obviously some reference is shared which isn't supposed to be shared. So instead of plain appending, I tried to make something like this

append(QList()<<value)

but that just gave me another error message:

template <typename T>
Q_OUTOFLINE_TEMPLATE QList<T> &QList<T>::operator+=(const QList<T> &l)
{
    if (!l.isEmpty()) {
        if (d == &QListData::shared_null) {
            *this = l;
        }
[...]
}

(This time, the yellow arrow of the debugger points to the fifth line (QList.h, line 938).)

Well, to be honest I'm at the end of my knowledge of Qt. I just know that I seem to not be allowed to pass a certain reference and because I violate against this rule, shit goes down. Trying to make a deep copy via temporary saving the data in another variable doesn't work either. Well, the assignment works but the appending ~~fucks it up~~ lets it crash again.

So, here's the simplified code of my class. I hope you can find a solution! Thanks

KeyLog.h

#ifndef KEYLOG_H
#define KEYLOG_H

#include <iostream>
#include <QCoreApplication>
#include <QDateTime>
#include <QDebug>
#include <windows.h>


namespace WindowsAction
{
    class KeyLog : public QObject
    {
        Q_OBJECT

    protected:
    //Variablen
        bool Active_;               //loggen (true) oder inaktiv sein (false)
        HHOOK hHook;                //Hook (Low-Level-Verbindung mit der Tastatur)
        QList<QDateTime> DTLog_;    //Log (DateTime)
        QList<int>  NrLog_;         //Log (Key-Nummer)
        QStringList NameLog_;       //Log (Key-Name)

    //Funktionen
        LRESULT CALLBACK KeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam);  //Hook-Funktion

    public:
        KeyLog(const bool& Active=true);
        ~KeyLog();

        QList<QDateTime> DTLog   ()             const;
        QDateTime        DTLog   (const int& i) const;
        bool             isActive()             const;
        bool             isEmpty ()             const;
        QList<int>       NrLog   ()             const;
        int              NrLog   (const int& i) const;
        QStringList      NameLog ()             const;
        QString          NameLog (const int& i) const;

    signals:
        void KeyPressed (QString Name, int Nr, QDateTime DT) const;
        void KeyReleased(QString Name, int Nr, QDateTime DT) const;
        void activated()                                     const;
        void deactivated()                                   const;

    public slots:
        void activate();        //aktiviere loggen
        void clear();           //lösche Logs
        void deactivate();      //deaktiviere loggen
        void toggle();          //ändere log_
    };
}

#endif // KEYLOG_H

KeyBoardProc.h

#include "KeyLog.h"


LRESULT CALLBACK WindowsAction::KeyLog::KeyBoardProc(int nCode, WPARAM wParam, LPARAM lParam)
{
    KBDLLHOOKSTRUCT cKey=*((KBDLLHOOKSTRUCT*)wParam);

    wchar_t buffer[5];
    BYTE keyboard_state[256];

    [...]

    //get key name
    char lpszName[0x100]={0};

    [...]

    GetKeyNameText(dwMsg, (LPTSTR)lpszName, 255);

    //try to convert the key info
    ToUnicodeEx(cKey.vkCode,
                cKey.scanCode,
                keyboard_state,
                buffer,
                4,
                0,
                keyboard_layout);
    buffer[4]=L'\0';



    qDebug()<<"key: "<<cKey.vkCode<<" "<<QString::fromUtf16((ushort*)buffer)<<" "<<QString::fromUtf16((ushort*)lpszName);

//*****SHIT GOES DOWN HERE*****
    DTLog_.append(QDateTime::currentDateTime());
    NrLog_.append(QList<int>()<<cKey.vkCode);
    if(QString::fromUtf16((ushort*)buffer).isEmpty()==false) NameLog_.append(QString::fromUtf16((ushort*)buffer));
    else NameLog_.append(QString::fromUtf16((ushort*)lpszName));

    return CallNextHookEx(hHook, nCode, wParam, lParam);
}

//Quelle WinAPI-Zeugs: https://www.youtube.com/watch?v=O0C4V6JmlNw

KeyLog.cpp

#include "KeyLog.h"


//public:
WindowsAction::KeyLog::KeyLog(const bool& Active)
{
    if(Active==true) activate();
}

WindowsAction::KeyLog::~KeyLog()
{
    if(Active_==true) deactivate();
}

[...]

//public slots
void WindowsAction::KeyLog::activate()
{
    hHook=SetWindowsHookEx(WH_KEYBOARD_LL, (HOOKPROC)&KeyBoardProc, NULL, 0);

    if(hHook!=NULL)
    {
        Active_=true;
        emit activated();
    }
    else
    {
        Active_=false;
    }
}

[...]

void WindowsAction::KeyLog::deactivate()
{
    hHook=NULL;

    Active_=false;
    emit deactivated();
}

[...]

That's all for now. I'm open to any suggestion and really hope this can get fixed quickly. :) Thanks again!

Felix

kshegunov

@Thynome
Hi,
My "educated" guess is that you have dereferenced an invalid address. Something of the type:

MyClass * var;
var->method();

As long as method() doesn't touch anything class-related (i.e. acts as a static function) you'll probably get away with that. Provide a stack trace ('cause that QList reference doesn't mean much) and it will (most probably) get clearer why the crash is occurring.

Kind regards.

mrjj

@Thynome said:

hHook=SetWindowsHookEx(WH_KEYBOARD_LL, (HOOKPROC)&KeyBoardProc, NULL, 0);

Hi
Im wondering if SetWindowsHookEx likes a callback that lives in a class ?

https://msdn.microsoft.com/da-dk/library/windows/desktop/ms644990(v=vs.85).aspx
"Type: HOOKPROC
A pointer to the hook procedure. If the dwThreadId parameter is zero or specifies the identifier of a thread created by a different process, the lpfn parameter must point to a hook procedure in a DLL. Otherwise, lpfn can point to a hook procedure in the code associated with the current process."

Normally for callback its plain "c" functions/ non member or at least a static member function.

kshegunov

@mrjj
Whaddaya know, I turned out more educated than I expected ... good catch sir, I was too lazy to actually trace the code!

Thynome

Thanks for your answer, @kshegunov and @mrjj.

I moved the function outside of my class and made it a friend so I still have permission to access protected class members. But now I have the problem that I must provide the object to the function... I thought about somehow passing the this pointer to the function but couldn't figure out how. :/ Passing it via parameter is not possible due to the weird function calling and my tries with a (semi) global variable didn't work either..

Do you have an idea? I would be very happy about any suggestion. :)

Felix

kshegunov

@Thynome
Hi,
Well, you're stuck with C when working with the WinApi. It sucks, I know, but you need to transfer the context (the object) through a global variable. You can look here for some inspiration - WindowsCtrlDispatcher::instance is the context that's transferred to the VOID WINAPI ServiceMain(DWORD, LPTSTR *) function. I hope that helps.

Kind regards.