Re: [XForms] Problem with fdesign (fdesigns menu bar)

[Clive Stubbings]

Michal,

Glad it has solved your problem.

> I have followed 'popup.c' file usage pattern:
>
>    if ( popup->title )
>        XStoreName( flx->display, popup->win, popup->title );
>
> and modified 'xpopup.c' accordingly:
>
> -       XStoreName( flx->display, m->win, m->title );
> +       if ( m->title )
> +         XStoreName( flx->display, m->win, m->title );
>
> and it seems to have fixed the problem.

That will stop the crash but be aware it may be a change in behavior.

In the old (and new fixed) X libraries, passing a NULL pointer would call 
XChangeProperty for XA_WM_NAME to replace any current value with a NULL 
argument. Your change has removed that call (mine replaced the NULL with 
an empty string).

Your change may, or may not, be better. One would need to understand both the 
context (ie intent) and how the library handles NULL property values.

> Interestingly, on MX-21 Linux (based on Debian 11), fdesign built on
> Git code works fine w/o any modifications. The system has xserver-xorg
> version 1.20.13-1~mx21ahs+1 (compared to 1.20.13-1ubuntu1~20.04.2 in
> Ubuntu 20.04 and 1.20.11-2 in Rocky Linux 8.5)

Useful. The fix in X11 has been available upstream for just short of a year.

Cheers
Clive


> regards,
> Michal
>
> On Thu, May 12, 2022 at 04:01:48PM +0100, Clive Stubbings wrote:
> > Try
> >
> > -       XStoreName(flx->display, m->win, m->title);
> > +       XStoreName(flx->display, m->win, m->title ? m->title : "");
> >
> > Cheers
> > Clive
> >
> > On Thu, 12 May 2022, Michal Szymanski wrote:
> >
> > > I have built the current git version
> > > (https://git.savannah.gnu.org/git/xforms.git) on Ubuntu 20.04 and
> > > Rocky Linux 8.5 and got the same problem: fdesign segfaults when
> > > 'File' is clicked on.
> > >
> > > Following Clive's hint I have found just 4 places XStoreName is used:
> > >
> > > lib/canvas.c:            XStoreName( flx->display, sp->window, ob->label );
> > > lib/canvas.c:            XStoreName( flx->display, sp->window, name );
> > > lib/popup.c:        XStoreName( flx->display, popup->win, popup->title );
> > > lib/xpopup.c:        XStoreName( flx->display, m->win, m->title );
> > >
> > > but I do not have any idea how to fix the problem. I have even
> > > localized the segfault to be originating in 'xpopup.c', with m->title
> > > being 0x0, so I made it point to an empty static string (""). The
> > > program did not segfault on "File" but aborted on "SaveAs" from File
> > > popup, saying
> > > munmap_chunk(): invalid pointer
> > > Abort (core dumped)
> > >
> > > so I surrendered.
> > >
> > > Any more hints? Without working fdesign the whole library is pretty unusable :(
> > >
> > > regards, Michal
> > >
> > > On Wed, Jun 30, 2021 at 02:27:35AM +0100, Clive Stubbings wrote:
> > > > Hi,
> > > >
> > > > There has been a regression in the xorg libX11
> > > >
> > > > It is likely this is your issue - it was spotted in one of my xforms programs a 
> > > > few weeks ago by one of my users.
> > > >
> > > > XStoreName used to tolerate a NULL pointer (it checked before using it). New 
> > > > code has been added ahead of that check.
> > > >
> > > > If your system has recently updated its libraries, thats likely the cause.
> > > >
> > > > I believe it has now been fixed upstream thanks to the person who spotted the 
> > > > problem feeding the cause back to the developers and a new version should come 
> > > > through in due course.
> > > >
> > > > If you need a quicker fix, hack the library to make sure it doesn't pass a NULL 
> > > > pointer to XStoreName.
> > > >
> > > > Cheers
> > > > Clive
> > > >
> > > >
> > > >
> > > > On Sun, 27 Jun 2021, ternaryd wrote:
> > > >
> > > > > On Sat, 26 Jun 2021 15:47:12 -0700
> > > > > Coby Hochstein <cjh39@cox.net> wrote:
> > > > >
> > > > > > Hello,
> > > > > >
> > > > > > when I load fdesign and click on the "File"
> > > > > > menu bar fdesign segmentation faults.
> > > > > > I'm running xforms-1.2.4
> > > > > >
> > > > > > (gdb) run
> > > > > > Starting program: /usr/local/bin/fdesign
> > > > > > [Thread debugging using libthread_db enabled]
> > > > > > Using host libthread_db library
> > > > > > "/lib/arm-linux-gnueabihf/libthread_db.so.1".
> > > > > >
> > > > > > Program received signal SIGSEGV, Segmentation
> > > > > > fault.
> > > > > > strlen () at ../sysdeps/arm/armv6/strlen.S:26
> > > > > > 26 ../sysdeps/arm/armv6/strlen.S: No such
> > > > > > file or directory.
> > > > > > (gdb)
> > > > >
> > > > >
> > > > > > Any idea ?
> > > > >
> > > > > fdesign is calculating the string length of a
> > > > > string pointing to NULL.
> > > > >
> > > > > Use a version of fdesign compiled with debugging
> > > > > enabled, run it again until crash, and check the
> > > > > coredump in gdb. Use the "up" command until you
> > > > > reach a stack level belonging to fdesign (or
> > > > > xforms). You should see which pointer is NULL.
> > > > > Then you can try to figure out, why it is NULL
> > > > > and how to fix it.
> > > > >
> > > > >  $ ulimit -c unlimited
> > > > >  $ ./fdesign ...
> > > > >  $ gdb ./fdesign coredump
> > > > >  (gdb> up
> > > > >  ...
> > > > >
> > > > > you can query the value of any variable at the
> > > > > time of the crash with
> > > > >
> > > > >  (gdb) p varname
> > > > >
> > > > > HTH
> > > > >
> > > > > --
> > > > > Cris
> > >
> > > --
> > > Michal Szymanski (msz at astrouw dot edu dot pl)
> > > Warsaw University Observatory, Warszawa, POLAND
>
> --
>  Michal Szymanski (msz at astrouw dot edu dot pl)
>  Warsaw University Observatory, Warszawa, POLAND