X11 debugging pt.5 (last part)

Now, GDB has debugging information for libX11; it knows where the crash happened.

(gdb) up

#1 0x00c82c14 in _XError (dpy=0x1809e00, rep=0xbfffe1d8) at XlibInt.c:2905

2905 rtn_val = (*_XErrorFunction)(dpy, (XErrorEvent *)&event); /* upcall */

(gdb) up

#2 0x00c848d1 in _XReply (dpy=0x1809e00, rep=0xbfffe1d8, extra=0, discard=0) at XlibInt.c:1831

1831 _XError(dpy, err);

(gdb) up

#3 0x00c63c52 in XGetMotionEvents (dpy=0x1809e00, start=0, stop=0, w=0, nEvents=0xbfffe248) at GetMoEv.c:51

51 if (!_XReply (dpy, (xReply *)&rep, 0, xFalse)) {

(gdb) up

#4 0x00a4144f in gdk_device_get_history ()

(gdb) down

#3 0x00c63c52 in XGetMotionEvents (dpy=0x1809e00, start=0, stop=0, w=0, nEvents=0xbfffe248) at GetMoEv.c:51

51 if (!_XReply (dpy, (xReply *)&rep, 0, xFalse)) {

(gdb) list

46 GetReq(GetMotionEvents, req);

47 req->window = w;

48 /* XXX is this right for all machines? */

49 req->start = start;

50 req->stop = stop;

51 if (!_XReply (dpy, (xReply *)&rep, 0, xFalse)) {

52 UnlockDisplay(dpy);

53 SyncHandle();

54 return (NULL);

55 }

This isn't horribly helpful, other than we see that the 'w' parameter to XGetMotionEvents is supposed to be a window, and it's being passed '0', which doesn't look right. If you continue the program in gdb and let it crash, the error message is:

The error was 'BadWindow (invalid Window parameter)'.

So, the problem seems to be that Window parameter.

Where to go from here? We need to figure out why gdk_device_get_history is calling XGetMotionEvents with w=0, but we have no debugging symbols. The next step will be finding a copy of the gdk source code, building it with debugging symbols, replacing the libgdk in the Gimp.app bundle, and repeating the above exercise.

I hope this proves helpful. Thanks for reading!

References:
	>X11 debugging pt.1 (From: Ben Byer <email@hidden>)
	>Re: X11 debugging pt.2 (From: Ben Byer <email@hidden>)
	>X11 debugging pt.3 (From: Ben Byer <email@hidden>)
	>X11 debugging pt.4 (From: Ben Byer <email@hidden>)