RFA: Re: Funky code in gnuv2_virtual_fn_field

[Jim Blandy <jimb at zwingli dot cygnus dot com>]

Daniel Berlin <dan@cgsoftware.com> writes:
> Jim Blandy <jimb@zwingli.cygnus.com> writes:
> 
> > I'm looking at lines 112--118 in gnu-v2-abi.c:
> > 
> >   if (TYPE_TARGET_TYPE (context) != type1)
> >     {
> >       value_ptr tmp = value_cast (context, value_addr (arg1));
> >       VALUE_POINTED_TO_OFFSET (tmp) = 0;
> >       arg1 = value_ind (tmp);
> >       type1 = check_typedef (VALUE_TYPE (arg1));
> >     }
> > 
> > This looks fishy to me.  If we smash the POINTED_TO_OFFSET without
> > smashing the ENCLOSING_TYPE in a corresponding manner, and then we
> > indirect through that pointer, don't we get a value whose
> > ENCLOSING_TYPE is set, but whose address points to the embedded
> > object, and not the enclosing object?
> 
> Yup.
> However, although it's not documented anywhere, value_cast
> approriately smashes the enclosing type.

That's what I was afraid of.  (I *hate* it when GDB does something
with a `struct value' that isn't really legal, but just happens to be
okay because we know internal details about where that `struct value'
came from...)

> IMHO, in any case, we shouldn't be needing to set the
> pointed_to_offset here.  If we have to, value_cast is doing something
> wrong, or not enough of the right thing.
> This is because all we are trying to do is a simple cast, which is what
> value_cast is supposed to do for us. If we have to start mucking
> around with it's results to get a correct value, then it's not doing
> it's job right, or completely.

Great.  So how about this patch?

2001-05-22  Jim Blandy  <jimb@redhat.com>

	* gnu-v2-abi.c (gnuv2_virtual_fn_field): There's no need to clear
	VALUE_POINTED_TO_OFFSET here; if value_cast doesn't return a
	useful value, then we should fix that instead.

Index: gdb/gnu-v2-abi.c
===================================================================
RCS file: /cvs/src/src/gdb/gnu-v2-abi.c,v
retrieving revision 1.2
diff -c -r1.2 gnu-v2-abi.c
*** gdb/gnu-v2-abi.c	2001/05/12 04:01:16	1.2
--- gdb/gnu-v2-abi.c	2001/05/22 21:14:35
***************
*** 111,117 ****
    if (TYPE_TARGET_TYPE (context) != type1)
      {
        value_ptr tmp = value_cast (context, value_addr (arg1));
-       VALUE_POINTED_TO_OFFSET (tmp) = 0;
        arg1 = value_ind (tmp);
        type1 = check_typedef (VALUE_TYPE (arg1));
      }
--- 111,116 ----