process receives a SIGSEGV on Fedora 29

[martinezjavier]

Hello @cmauri,

I'm trying to make eviacam work on Fedora 29, but when building from source using the latest v2.1.3 tag the process receives a SIGSEGV and gets killed.

$ ./src/eviacam --debug

DEBUG:   Opened device 'video0' successfully (handle = 1)

DEBUG:   Getting device information for handle 1 ...

DEBUG:     { shortName = 'video0', name = 'Integrated Camera: Integrated C', driver = 'uvcvideo', location = 'usb-0000:00:14.0-8', vid = 04f2, pid = b5c1, bcd = 4 }

DEBUG:   Getting control information for handle 1 ...

DEBUG:     Control found: Brightness

DEBUG:       { id = 1, name = 'Brightness', type = 6, flags = 3
DEBUG: , min = 0, max = 255, def = 128, step = 1
DEBUG:  }

DEBUG:     Control found: Contrast

DEBUG:       { id = 2, name = 'Contrast', type = 6, flags = 3
DEBUG: , min = 0, max = 255, def = 32, step = 1
DEBUG:  }

DEBUG:     Control found: Saturation

DEBUG:       { id = 4, name = 'Saturation', type = 6, flags = 3
DEBUG: , min = 0, max = 100, def = 64, step = 1
DEBUG:  }

DEBUG:     Control found: Hue

DEBUG:       { id = 5, name = 'Hue', type = 6, flags = 3
DEBUG: , min = -180, max = 180, def = 0, step = 1
DEBUG:  }

DEBUG:     Control found: White Balance Temperature, Auto

DEBUG:       { id = 9, name = 'White Balance Temperature, Auto', type = 2, flags = 3
DEBUG: , min = 0, max = 1, def = 1, step = 1
DEBUG:  }

DEBUG:     Control found: Gamma

DEBUG:       { id = 6, name = 'Gamma', type = 6, flags = 3
DEBUG: , min = 90, max = 150, def = 120, step = 1
DEBUG:  }

DEBUG:     Control found: Power Line Frequency

DEBUG:       { id = 13, name = 'Power Line Frequency', type = 3, flags = 3
DEBUG: , choice = {
DEBUG:  'Disabled'[0]
DEBUG:  '50 Hz'[1]
DEBUG:  '60 Hz'[2]
DEBUG:  }
DEBUG:  }

DEBUG:     Control found: White Balance Temperature

DEBUG:       { id = 8, name = 'White Balance Temperature', type = 6, flags = 3
DEBUG: , min = 2800, max = 6500, def = 4000, step = 1
DEBUG:  }

DEBUG:     Control found: Sharpness

DEBUG:       { id = 7, name = 'Sharpness', type = 6, flags = 3
DEBUG: , min = 0, max = 7, def = 2, step = 1
DEBUG:  }

DEBUG:     Control found: Backlight Compensation

DEBUG:       { id = 12, name = 'Backlight Compensation', type = 6, flags = 3
DEBUG: , min = 0, max = 2, def = 1, step = 1
DEBUG:  }

DEBUG:     Control found: Exposure, Auto

DEBUG:       { id = 15, name = 'Exposure, Auto', type = 3, flags = 3
DEBUG: , choice = {
DEBUG:  'Manual Mode'[1]
DEBUG:  'Aperture Priority Mode'[3]
DEBUG:  }
DEBUG:  }

DEBUG:     Control found: Exposure (Absolute)

DEBUG:       { id = 17, name = 'Exposure (Absolute)', type = 6, flags = 3
DEBUG: , min = 4, max = 1250, def = 156, step = 1
DEBUG:  }

DEBUG:     Control found: Exposure, Auto Priority

DEBUG:       { id = 16, name = 'Exposure, Auto Priority', type = 2, flags = 3
DEBUG: , min = 0, max = 1, def = 0, step = 1
DEBUG:  }

DEBUG:   Closed device 'video0' (handle = 0)


DEBUG:   Opened device 'video1' successfully (handle = 2)

DEBUG:   Getting device information for handle 2 ...

DEBUG:     { shortName = 'video1', name = 'Integrated Camera: Integrated C', driver = 'uvcvideo', location = 'usb-0000:00:14.0-8', vid = 04f2, pid = b5c1, bcd = 4 }

DEBUG:   Getting control information for handle 2 ...

DEBUG:   No controls found (ret = 0).

DEBUG:   Closed device 'video1' (handle = 0)


INFO: Previous used camera:  (Id:0) Integrated Camera: Integrated C... 
INFO: FOUND
INFO: Detected 2 camera(s)
INFO: Selected camera: 0
INFO: Try to open the camera to make sure it works...
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
VIDEOIO ERROR: V4L: device /dev/video1: Unable to query number of channels
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 2 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 3 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 4 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 5 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 6 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 7 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 8 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
VIDEOIO ERROR: V4L: index 9 is not correct!
warning: Cannot query video position: status=0 value=-1 duration=-1
 (/builddir/build/BUILD/opencv-3.4.1/modules/videoio/src/cap_gstreamer.cpp:952)
Segmentation fault (core dumped)

The problem is in the call to DisplayHeight() in CMouseControl::GetScreenSize():

$ gdb ./src/eviacam
...
Thread 1 "eviacam" received signal SIGSEGV, Segmentation fault.
0x0000000000477f5d in CMouseControl::GetScreenSize (this=this@entry=0xebae10) at mousecontrol.cpp:136
136             m_ScreenHeight=
(gdb) bt
#0  0x0000000000477f5d in CMouseControl::GetScreenSize() (this=this@entry=0xebae10) at mousecontrol.cpp:136
#1  0x00000000004780a9 in CMouseControl::OnDisplayChanged() (this=this@entry=0xebae10) at mousecontrol.cpp:174
#2  0x0000000000478108 in CMouseControl::CMouseControl(void*) (this=0xebae10, pDisplay=<optimized out>) at mousecontrol.cpp:102
#3  0x000000000046ffc6 in CPointerAction::CPointerAction() (this=0x1115640) at pointeraction.cpp:39
#4  0x000000000043c1f0 in CViacamController::Initialize() (this=this@entry=0xd35e00) at viacamcontroller.cpp:317
#5  0x0000000000435617 in EViacamApp::OnInit() (this=0x9fb230) at eviacamapp.cpp:176
#6  0x00007ffff7390d32 in wxEntry(int&, wchar_t**) (argc=<optimized out>, argv=<optimized out>) at ../include/wx/init.h:109
#7  0x0000000000422c52 in main(int, char**) (argc=<optimized out>, argv=0x7fffffffd1e8) at eviacamapp.cpp:81
...
(gdb) list
131             if (!retval) { exit (-1); }
132
133             m_ScreenHeight= devMode.dmPelsHeight;
134             m_ScreenWidth= devMode.dmPelsWidth;
135     #else // Linux
136             m_ScreenHeight= 
137                     DisplayHeight (static_cast<Display*>(m_pDisplay), DefaultScreen (static_cast<Display*>(m_pDisplay)));
138             m_ScreenWidth= 
139                     DisplayWidth (static_cast<Display*>(m_pDisplay), DefaultScreen (static_cast<Display*>(m_pDisplay)));
140     #endif
...
(gdb) print m_pDisplay
$6 = (void *) 0xa8a000
(gdb) print m_ScreenHeight
$7 = 0
(gdb) print m_ScreenWidth
$8 = 0

I see that m_pDisplay is set though, to the pDisplay argument received by the CMouseControl::CMouseControl() constructor:

$ gdb ./src/eviacam
...
(gdb) break CMouseControl
Breakpoint 1 at 0x4780c0: file mousecontrol.cpp, line 79.
(gdb) run
...
Thread 1 "eviacam" hit Breakpoint 1, CMouseControl::CMouseControl (this=0xc34de0, pDisplay=0xa8a800) at mousecontrol.cpp:79
79      CMouseControl::CMouseControl (void* pDisplay)
(gdb) print pDisplay
$1 = (void *) 0xa8a800
(gdb) continue
Continuing.

Thread 1 "eviacam" received signal SIGSEGV, Segmentation fault.
0x0000000000477f5d in CMouseControl::GetScreenSize (this=this@entry=0xc34de0) at mousecontrol.cpp:143
143             m_ScreenHeight=
(gdb) print m_pDisplay
$2 = (void *) 0xa8a800

So I don't really understand why DisplayHeight() causes a NULL pointer deference since m_pDisplay seems to be set correctly.

Maybe is a red herring, but I'm using Wayland + XWayland for X clients. Do you know if eviacam is supposed to work on this setup or should only under X?

In case is useful, the wxWidgets backend is GTK3.

$ wx-config --selected-config
gtk3-unicode-3.0

Any hints on how to further debug this?

[cmauri]

Hi @martinezjavier,

Certainly, I never tried eViacam on Wayland, thus not sure about its compatibility.

eViacam uses some "low-level" Xlib calls to work. Just guessing, but perhaps these calls to DefaultScreen and DisplayHeight and DisplayWidth, and/or the Display* type castings do not work under Wayland as expected. I suggest checking how the Display type is defined in both cases and whether these functions are supported on Wayland.
Hope it helps.