Re: vtable?

[Tom Tromey <tromey at redhat dot com>]

Chris> One of my guesses of the moment is that under the circumstances of the
Chris> bug, the "vtable" is either being built wrong or is somehow being
Chris> corrupted--does anyone have a clue where the "vtable" is built?

>From what I understand, gdb doesn't actually use the dwarf stuff to
build the class' vtable.  There is a bug report or two in gcc bugzilla
about this; I gather that gcc doesn't emit all the needed info.

So, rather than rely on the dwarf, gdb encodes knowledge of the ABI.

Chris> Another guess is that in gnuv3_baseclass_offset, gnuv3_get_vtable is
Chris> being called with a bad type argument, but I haven't looked into that
Chris> yet.

I don't know about this code, but one interesting thing about the bug is
that casts to the base types seem to return the right answers:

(gdb) p e
$1 = (E *) 0x804a008
(gdb) p (D*)e
$2 = (D *) 0x804a00c
(gdb) p (C*)e
$3 = (C *) 0x804a010

This makes me wonder whether the bug is actually in the value printing
code -- because computing the base offsets seems to work in at least one
case.

That's just something I would look at though, don't give it too much
credence.  I don't know much about this code.

Tom