Re: [Tinycc-devel] Potential bug - Xt: Unresolved inheritance operation

[Adam Sampson]

Mid Favila <midfavila@SDF.ORG> writes:

> Wanted to add that when Motif (or, at the least, LessTif) programs are
> built using tcc, the same problem occurs. Is there anyone else who can
> duplicate these findings?

I see the same behaviour -- it's failing in XtQueryGeometry, when it
tries to call a widget's query_geometry method. If you set a breakpoint
in XtQueryGeometry, when built with gcc, the method pointer
widget->core.widget_class->query_geometry is NULL; with tcc, it's
_XtInherit.

The idea here is that these fields are initialised to _XtInherit,
meaning the method should be inherited from the superclass. For each
class, RectClassPartInitialize checks whether it's still _XtInherit
(XtInheritQueryGeometry is #defined to _XtInherit) and if so gets the
pointer from the superclass -- eventually ending up with NULL if there's
no definition of it:

static void
RectClassPartInitialize(register WidgetClass wc)
{
...
    if (roc->rect_class.query_geometry == XtInheritQueryGeometry) {
        roc->rect_class.query_geometry = super->rect_class.query_geometry;
    }
...                

If you set a breakpoint in RectClassPartInitialize and continue until
you get to an instance where roc->rect_class.query_encoding isn't NULL,
you can see that that fails to work with TCC because the two values are
different:

(gdb) print _XtInherit
$13 = {void (void)} 0x7ffff7b4c870 <_XtInherit>
(gdb) print roc->rect_class.query_geometry
$16 = (XtGeometryHandler) 0x60aec0 <_XtInherit@plt>

Whereas with gcc they're the same (_XtInherit not _XtInherit@plt).

At this point this needs someone more familiar with tcc's linking
behaviour than me to sort it out -- there are already some
horrible-looking hacks in the libXt code to make _XtInherit visible in
the right way on various shared library systems.

Cheers,

-- 
Adam Sampson <ats@offog.org>                         <http://offog.org/>