[Kde-bindings] Crash in qtruby4 (svn) using custom C++ classes

Fri Jun 20 13:03:24 UTC 2008

Am Freitag 20 Juni 2008 14:46:08 schrieb Stefano Crocco:
> > On Thursday 19 June 2008, Stefano Crocco wrote:
> > > I'm attempting to use the latest svn revision of korundum4 to build an
> > > application which uses a custom C++ class, following the procedure
> > > explained in a thread on the korundum forum
> > > (http://rubyforge.org/forum/forum.php?thread_id=10371&forum_id=723).
> > > The code I wrote worked correctly with an older revision (from about a
> > > month ago), but now it crashes when I try to write a C++ slot which
> > > returns a string.
> > >
> > > Here's a sample code which causes the crash:
> > >
> > > #include <ruby.h>
> > > #include <QApplication>
> > > #include <QList>
> > > #include <QPoint>
> > > #include <QWidget>
> > >
> > > class MyWidget: public QWidget{
> > >   Q_OBJECT
> > >
> > >   public:
> > >   MyWidget(QWidget*parent = 0):QWidget(parent){
> > >   }
> > >   ~MyWidget(){}
> > >
> > >   public slots:
> > >   QString string_test(){return QString("My test");}
> > >   int int_test(){return 124;}
> > >   QPoint point_test(){return QPoint(12,89);}
> > > };
> > >
> > > #include "ext_moc.cpp"
> > >
> > > static VALUE create_my_widget(VALUE self, VALUE name){
> > >   QWidgetList l = QApplication::allWidgets();
> > >   QWidget * parent = l.first();
> > >   MyWidget * w = new MyWidget(parent);
> > >   QString objName = STR2CSTR(name);
> > >   w->setObjectName(objName);
> > >   return Qnil;
> > > }
> > >
> > > extern "C" void Init_ext(void){
> > >   typedef VALUE ( *HOOK ) ( ... );
> > >   rb_define_method(rb_cObject, "create_my_widget",
> > > reinterpret_cast<HOOK>(create_my_widget), 1); }
> > >
> > > Once compiled that as a ruby extension file called ext.so, if I run the
> > > following ruby code:
> > >
> > > require 'Qt4'
> > > require 'ext'
> > >
> > > app = Qt::Application.new []
> > > w = Qt::Widget.new
> > > create_my_widget "test"
> > > my_widget = w.findChild Qt::Object, "test"
> > > puts "int_test:#{my_widget.int_test}"
> > > puts "point_test: #{my_widget.point_test.inspect}"
> > > puts "doing string_test"
> > > p my_widget.string_test
> > >
> > > This is what I get:
> > > int_test:124
> > > point_test: nil
> > > doing string_test
> > > try.rb:11: [BUG] Segmentation fault
> > > ruby 1.8.6 (2008-03-03) [i686-linux]
> > >
> > > And here's the backtrace obtained by running ruby in gdb:
> > > #0  0xb7afc222 in QString::operator= () from
> > > /usr/lib/qt4/libQtCore.so.4 #1  0xb6b3af73 in MyWidget::qt_metacall ()
> > > from ./ext.so
> > > #2  0xb756356e in InvokeNativeSlot::invokeSlot (this=0xbfe447f4) at
> > > /home/stefano/Desktop/kdebindings/ruby/qtruby/src/Qt.cpp:413 #3
> > > 0xb756366d in InvokeNativeSlot::mainfunction (this=0xbfe447f4) at
> > > /home/stefano/Desktop/kdebindings/ruby/qtruby/src/Qt.cpp:424 #4
> > > 0xb759c96c in SigSlotBase::next (this=0xbfe447f4) at
> > > /home/stefano/Desktop/kdebindings/ruby/qtruby/src/marshall_types.cpp:62
> > >8 #5 0xb7568d19 in method_missing (argc=1, argv=0xbfe44bc0,
> > > self=3060248180) at
> > > /home/stefano/Desktop/kdebindings/ruby/qtruby/src/Qt.cpp:856 #6
> > > 0xb7f08805 in call_cfunc () from /usr/lib/libruby18.so.1.8
> > > #7  0xb7f12945 in rb_call0 () from /usr/lib/libruby18.so.1.8
> > > #8  0xb7f12ad1 in rb_call () from /usr/lib/libruby18.so.1.8
> > > #9  0xb7f133ad in rb_funcall2 () from /usr/lib/libruby18.so.1.8
> > > #10 0xb7f18b36 in method_missing () from /usr/lib/libruby18.so.1.8
> > > #11 0xb7f12bc3 in rb_call () from /usr/lib/libruby18.so.1.8
> > > #12 0xb7f0d599 in rb_eval () from /usr/lib/libruby18.so.1.8
> > > #13 0xb7f0fcc5 in rb_eval () from /usr/lib/libruby18.so.1.8
> > > #14 0xb7f1dfe3 in ruby_exec_internal () from /usr/lib/libruby18.so.1.8
> > > #15 0xb7f1e023 in ruby_exec () from /usr/lib/libruby18.so.1.8
> > > #16 0xb7f1e058 in ruby_run () from /usr/lib/libruby18.so.1.8
> > > #17 0x08048715 in main ()
> > >
> > > Stefano
> >
> > I've just tried it, and it works for me:
> >
> > mardigras rdale 961% ruby try.rb
> > int_test:124
> > point_test: nil
> > doing string_test
> > "My test"
> >
> > But point_test() shouldn't be returning nil, and so there is some sort of
> > bug with that. I'll see if I can find what is causing that, as it used to
> > be possible to return things like QPoints.
> >
> > I'm not sure why you're getting a crash and I'm not.
> >
> > -- Richard
>
> First of all, sorry if this mail won't show at the correct place in the
> thread. I never received Richard's answer (I read it in the archives), so I
> couln't respond to it.
>
> I don't know what to say, either. Can it be caused by something wrong with
> my compiler/linker? I'm using gcc 4.3.1 and ld 2.18.
>
> Maybe there is some issue with the commands I use to generate the extension
> (I'm not very familiar with the gcc options). They are:
>
> moc -o ext_moc.cpp ext.cpp
>
> i686-pc-linux-gnu-g++ -I. -I/usr/lib/ruby/1.8/i686-linux \
> -I/usr/lib/ruby/1.8/i686-linux -I.  -march=pentium4 \
> -c ext.cpp -I/usr/include/qt4/QtGui -I/usr/include/qt4/QtCore \
> -I/usr/include/qt4/Qt -I/usr/include/qt4 \
> -I/usr/kde/svn/include/KDE -I/usr/kde/svn/include/
>
> i686-pc-linux-gnu-g++ -shared -o ext.so ext.o -L'.' -L'/usr/lib' -Wl,\
> -R'/usr/lib' -L. -rdynamic -Wl,-export-dynamic\ -Wl -Wl -L/usr/lib -lruby18
> \ -lpthread -ldl -lcrypt -lm  -lc -L/usr/lib/qt4 -lQtCore -lQtGui -lkdeui \
> -lkdecore -lkparts -lktexteditor -L/usr/kde/svn/lib
>
> I use rake as build tool, since I couldn't get mkfm to correctly handle the
> cpp file generated by moc (it insists in wanting to compile it by itself
> instead of including it in the other .cpp file)
>
> Is there a way I can get more accurate debugging information?
I get the same error, same gcc and ld version, ruby 1.8.6_p114 and Qt 4.4.0.
You can set Qt.debug_level = Qt::DebugLevel::Extensive just before the call to 
the function that returns a string to get more information.
I'll take a look into this, thanks for the report.

-- 
Arno Rehn
arno at arnorehn.de