Re: Need help with a backtrace

[Matt Schalit <mschalit at pacbell dot net>]

Fernando Nasser wrote:
> 
> Matt,


Thanks for the excellent tutorial.

 
> Look at the backtrace (it goes backwards from the last 
> function to be called to the caller of it, the caller 
> of this caller and so on).


Ok.  It looks like it only lists an entry when a function
calls another function, like main() calling printf()?
But it doesn't seem to list things like loops or if/case tests
or variable values?

I know how to write C programs.  How would I backtrace or
step my way through hello-world.c if it exits normally, and
I just want to see how the trace looks?




 
> The call to gnome_app_create_menus() failed miserably.  
> If you look further on the stack you'll notice that the 
> function  create_label() in  gnome-app-helper.c at line 402 
> called gtk_label_parse_uline() and one of the parameters seem 
> to be an invalid pointer:
> > #3  0xbfb9048b in gtk_label_parse_uline (label=0x8139180,
> >     string=0xc615 <Address 0xc615 out of bounds>) at gtklabel.c:1005



Ok I took a look at gnome-app-helper.c and gtklabel.c and
I see how the bt correlates to the functions code.



 
> It is either a bug in the gnome library or the GnomeUIInfo 
> structure was not set properly.


Isn't it possible that my development platform could be
missing a key app, like gnu sed or gnu's install program or
something along those lines?

I say that as a possibility, because I read a Solairis Gnome
Install Howto that mentioned those were needed, and I've noticed,
when doing a truss on some of these programs that I get an extra '/'
showing up in paths to applications that are being called, as in:

xstat(2, "./gnome/config-override//Gnome", 0x08047614) Err#2  ENOENT
xstat(2, "/usr/local/etc/gnome/config//Gnome", 0x08047614) Err#2  ENOENT
xstat(2, "./gnome/config//Gnome", 0x08047614)   Err#2  ENOENT
xstat(2, "/home/matthew/.gnome//Gnome", 0x08047674) = 0
open("/home/matthew/.gnome//Gnome", O_RDONLY, 0666) = 6


I guess the last two lines do show a file being found
using the odd path.



> It goes always like that.  See who called who and what the 
> arguments were.
> 
> Using the up and down commands you can go up and down the 
> stack and look at variables at that context.


Is up and down how I see what variables get set to which values
while moving through a function?


And finally, where does 

> > #4  0xbfd95397 in create_label
        ^^^^^^^^^^

that value come from, or what man page should I look at
for the decoding formula?



Thanks again,
Matt



 
> Good luck.
> 
> Regards,
> Fernando






> Matt Schalit wrote:
> >
> > Hi all,
> >
> > Thanks for reading this.  I'm new to debugging and don't understand
> > enough to read a backtrace.  I could use a little help with that.
> >
> > I'm running an i586-sco-sysv5uw7.1.1, and getting SIGSEGV's whenever
> > I try to run gnomecc-1.2.2 (gnome control center) via
> > enlightenment-0.16.5.   I never see a window.
> >
> > Regardless of whether I try to open any windows in Gnome, as soon
> > as I start the desktop, I do see one warning about MIT-SHM not
> > working correctly and to disable to Enlightenment Pager snapshots.
> > I don't think that issue is relate to gnomecc.
> >
> > Can someone tell me what this means or point me to a nifty howto?
> > Thanks a lot,
> > Matthew
> >
> > ----------------------------------------------------------------------------
> > $ gdb
> >
> > (gdb) file /usr/local/bin/gnomecc
> > Reading symbols from /usr/local/bin/gnomecc...done.
> > (gdb) run
> > Starting program: /usr/local/bin/gnomecc
> > warning: Lowest section in /usr/lib/libdl.so.1 is .hash at 00000094
> > [New LWP 1]
> > [New LWP 2]
> >
> > Program received signal SIGSEGV, Segmentation fault.
> > 0xbfa6f929 in _Xwcslen () from /usr/lib/libX11.so.6.1
> > [New Thread 1]
> > (gdb) bt
> > #0  0xbfa6f929 in _Xwcslen () from /usr/lib/libX11.so.6.1
> > #1  0x400 in ?? ()
> > #2  0xbfa6fa28 in _XwcTextListToTextProperty () from /usr/lib/libX11.so.6.1
> > #3  0xbfb9048b in gtk_label_parse_uline (label=0x8139180,
> >     string=0xc615 <Address 0xc615 out of bounds>) at gtklabel.c:1005
> > #4  0xbfd95397 in create_label (label_text=0xbfe0a339 "", keyval=0x8047878)
> >     at gnome-app-helper.c:402
> > #5  0xbfd9630e in create_menu_item (menu_shell=0x8137ed0, uiinfo=0x809c770,
> >     is_radio=0, radio_group=0x81379f8, uibdata=0x8047988,
> >     accel_group=0x812ea40, uline_accels=1, pos=134510536)
> >     at gnome-app-helper.c:933
> > #6  0xbfd96f1a in gnome_app_fill_menu_custom (menu_shell=0x8137ed0,
> >     uiinfo=0x809c770, uibdata=0x8047988, accel_group=0x812ea40,
> >     uline_accels=1, pos=1) at gnome-app-helper.c:1326
> > #7  0xbfd96fa9 in gnome_app_fill_menu_custom (menu_shell=0x812bd28,
> >     uiinfo=0x809c84c, uibdata=0x8047988, accel_group=0x812ea40,
> >     uline_accels=1, pos=1) at gnome-app-helper.c:1341
> > #8  0xbfd976a1 in gnome_app_create_menus_custom (app=0x812db90,
> >     uiinfo=0x809c820, uibdata=0x8047988) at gnome-app-helper.c:1516
> > #9  0xbfd97163 in gnome_app_create_menus (app=0x812db90, uiinfo=0x809c820)
> >     at gnome-app-helper.c:1395
> > #10 0x804e967 in create_window () at main.c:200
> > #11 0x804ecf8 in main (argc=1, argv=0x8047a0c) at main.c:282
> > (gdb)
> > -------------------------------------------------------------------------
> 
> --
> Fernando Nasser
> Red Hat - Toronto                       E-Mail:  fnasser@redhat.com
> 2323 Yonge Street, Suite #300
> Toronto, Ontario   M4P 2C9