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Thread: SIGSEGV during startup processing SLOT

  1. 24th January 2011, 19:50 #1
    deanz1
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    Default Re: SIGSEGV during startup processing SLOT

    I'm getting SIGSEGV during startup processing. I never reach the first line of my main. I have isolated this to an area of qobject.cpp near line 2537

    Qt Code: 
    1. if (!check_method_code(membcode, receiver, method, "connect"))
    2.         return false;
    3.     const char *method_arg = method;
    4.     ++method; // skip code
    5.  
    6.     const QMetaObject *rmeta = receiver->metaObject();
    7.     int method_index = -1;
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    The failure happens on the line containing "*remeta =" and I'm unable to trace into function metaObject. At the time, the metacode is processing my slot "catchLtiStart.

    Here is code from "moc_opolib.cpp" re catchLtiStart and others:
    Qt Code: 
    1. int Opolib::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
    2. {
    3.     _id = QObject::qt_metacall(_c, _id, _a);
    4.     if (_id < 0)
    5.         return _id;
    6.     if (_c == QMetaObject::InvokeMetaMethod) {
    7.         switch (_id) {
    8.         case 0: lasLogin((*reinterpret_cast< QString(*)>(_a[1]))); break;
    9.         case 1: lasSetParameters((*reinterpret_cast< const char*(*)>(_a[1]))); br
    10.         case 2: lasSend((*reinterpret_cast< const char*(*)>(_a[1]))); break;
    11.         case 3: lasSend((*reinterpret_cast< const char*(*)>(_a[1])),(*reinterpret
    12.         case 4: lasSend((*reinterpret_cast< QString(*)>(_a[1]))); break;
    13.         case 5: lasLogout(); break;
    14.         case 6: motLogin((*reinterpret_cast< QString(*)>(_a[1]))); break;
    15.         case 7: motSetParameters((*reinterpret_cast< const char*(*)>(_a[1]))); br
    16.         case 8: motSend((*reinterpret_cast< const char*(*)>(_a[1]))); break;
    17.         case 9: motSend((*reinterpret_cast< const char*(*)>(_a[1])),(*reinterpret
    18.         case 10: motSend((*reinterpret_cast< QString(*)>(_a[1]))); break;
    19.         case 11: motLogout(); break;
    20.         case 12: lasError((*reinterpret_cast< QString(*)>(_a[1]))); break;
    21.         case 13: motError((*reinterpret_cast< QString(*)>(_a[1]))); break;
    22.         case 14: catchLtiStart(); break;
    23.         case 15: catchMtiStart(); break;
    24.         case 16: catchLasConnected(); break;
    25.         case 17: catchLasError((*reinterpret_cast< QString(*)>(_a[1]))); break;
    26.         case 18: catchLasNewMessage((*reinterpret_cast< QByteArray(*)>(_a[1])));
    27.         case 19: catchLasTimedOut(); break;
    28.         case 20: catchLthFinished(); break;
    29.         case 21: catchMotConnected(); break;
    30.         case 22: catchMotError((*reinterpret_cast< QString(*)>(_a[1]))); break;
    31.         case 23: catchMotNewMessage((*reinterpret_cast< QByteArray(*)>(_a[1])));
    32.         case 24: catchMotTimedOut(); break;
    33.         case 25: catchMthFinished(); break;
    34.         default: ;
    35.         }
    36.         _id -= 26;
    37.     }
    38.     return _id;
    39. }
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    And catchLtiStart is the first SLOT listed (I name SLOTs as catch*).

    SLOT catchLtiStart is not much:

    Qt Code: 
    1. public slots:
    2.   void catchLtiStart() {lti.start(TIMEOUT);} //start laser SerialClient breakout timer
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    I'm assuming this is memory corruption or, more likely, stack corruption but am at a loss as to where to look.

    Any hints?

    Added after 9 minutes:


    Oops, sorry about the code markup.

    Version info: Qt Creator 2.0.0 based on Qt 4.7.0 (32 bit) built Jun 21 2010 at 01:56:06 using MinGW compiler g++ 4.4.0 on Windows 7.
    Last edited by Lykurg; 24th January 2011 at 21:01.
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  2. 24th January 2011, 21:03 #2
    Lykurg
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    Default Re: SIGSEGV during startup processing SLOT

    Is this specific to only one project, or are you unable to compile and start any Qt program at your computer?
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  3. 24th January 2011, 21:52 #3
    deanz1
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    Default Re: SIGSEGV during startup processing SLOT

    It's specific to this project; I have made a TCP/IP server previously using Qt and had no problems of this sort.

    Added after 9 minutes:


    Some further information:

    I have a class "Laser" and a main class "Opolib". Opolib has a Laser member. The problem is arising during construction of member class "Laser. Here is the constructor:

    Qt Code: 
    1. Laser::Laser() : QObject(0), per(0)
    2. {
    3.   connect(this, SIGNAL(ltiStart()), ol, SLOT(catchLtiStart())
    4.           , Qt::QueuedConnection);
    5.   thr = new QThreadExec;
    6.   moveToThread(thr);
    7.   thr->start();
    8. }
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    And here is the definition of class "Laser":
    Qt Code: 
    1. class Laser : public QObject {
    2.   Q_OBJECT
    3.  
    4.   LasCmd        cmd;    //command to send or last sent
    5.   int           delay;  //delay argument to Q-Switch
    6.   Opolib       *ol;     //cross-reference
    7.   int           per;    //percent of full power
    8.   QByteArray    qarr;   //general purpose byte array
    9.   QString       qstr;   //general purpose string
    10.   QThreadExec  *thr;    //thread event loop for Laser object
    11.  
    12. public:
    13.   Distrib       dist;       //persistent data for distributed processing
    14.   double        delayGain;  //Q-Switch delay slope
    15.   double        minDelay;   //Q-Switch delay for minimum laser power
    16.  
    17.   //ctors
    18.   Laser();
    19.  
    20.   //accessors
    21.   void setOpolib(Opolib *Ol) {ol = Ol;}
    22.  
    23.   //methods
    24.   void lasCommand(
    25.       QByteArray &msg);
    26.   int percent() {return per;}
    27.  
    28. signals:
    29.   void lasError(QString);
    30.   void lasFinis();
    31.   void lasLogout();
    32.   void lasSend(const char*);
    33.   void lasSend(const char*, int);
    34.   void lasSend(QString);
    35.   void ltiStart();
    36.  
    37. public slots:
    38.   void commandLas(LasCmd Cmd)
    39.   {
    41.     qa[0] = '\0';
    42.     memset(&dist, '\0', sizeof(dist));
    43.     cmd = Cmd;
    44.     lasCommand(qa);
    45.   }
    46.   void setLasPower(int percent)
    47.   {
    48.     per = qBound(0, percent, 100);
    49.     delay = int(minDelay + delayGain*per);
    50.     commandLas(LasDelay);
    51.   }
    52. };
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    Added after 6 minutes:


    Yee Hah! The Aha moment dawns.

    I think I see the problem. At the time that the Laser object is being constructed, the cross-reference pointer has not yet been set. Anybody concur?
    Last edited by deanz1; 24th January 2011 at 21:52.
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  4. 24th January 2011, 21:54 #4
    Lykurg
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    Default Re: SIGSEGV during startup processing SLOT

    Well it seems to me that in the c-tor ol is uninitialized! Try to do the connection in setOpolib().

    EDIT: Yes...
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  5. 24th January 2011, 22:33 #5
    deanz1
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    Default Re: SIGSEGV during startup processing SLOT

    That was the problem.


    Thanks to all for the help and, in the spirit of Homer, Doh!
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