Re: Problem with virtual function pointers

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Mar 27, 2003 at 04:20:22PM +0100, Corinna Vinschen wrote:
> On Thu, Mar 27, 2003 at 09:53:46AM -0500, Daniel Jacobowitz wrote:
> > On Thu, Mar 27, 2003 at 03:24:12PM +0100, Corinna Vinschen wrote:
> > > Hi,
> > > 
> > > I'm just investigating a problem which XStormy16 gets in
> > > gdb.c++/printmethod.exp:
> > > 
> > >   print theA->virt^M
> > >   $1 = invalid pointer to member function^M
> > >   FAIL: gdb.c++/printmethod.exp: print virtual method.
> > > 
> > > It turned out that the error happens in xstormy16_pointer_to_address().
> > > This function converts an address to a jump table entry into a pointer
> > > to the actual function.  To do this, it calls a conversion routine,
> > > which is only called if the following condition applies:
> > > 
> > > 
> > >   enum type_code target = TYPE_CODE (TYPE_TARGET_TYPE (type));
> > > 
> > >   if (target == TYPE_CODE_FUNC || target == TYPE_CODE_METHOD)
> > >     convert();
> > > 
> > > Surprisingly (at least for me) this fails for the above case.  Looking
> > > into type, I found that type is TYPE_CODE_PTR which is correct, but
> > > target_type is TYPE_CODE_VOID!  Sure, the above virtual method is of
> > > type void but is that really ok?  Shouldn't that be 
> > > 
> > >   type: TYPE_CODE_PTR
> > >   type->target_type: TYPE_CODE_METHOD
> > >   type->target_type->target_type: TYPE_CODE_VOID
> > > 
> > > ?
> > 
> > Could you give me a backtrace?
> 
> Sure.  The situation is after calling `print theA->virt' and stepping
> into xstormy16_pointer_to_address().
> 
> (top-gdb) bt
> #0  xstormy16_pointer_to_address (type=0x848d628, buf=0x85f4348)
>     at /home/corinna/src/gdb/xstormy16-tdep.c:966
> #1  0x080fa69e in gdbarch_pointer_to_address (gdbarch=0x848ac90, 
>     type=0x848d628, buf=0x85f4348)
>     at /home/corinna/src/gdb/gdbarch.c:4164
> #2  0x080b3219 in extract_typed_address (buf=0x85f4348, type=0x848d628)
>     at /home/corinna/src/gdb/findvar.c:197
> #3  0x080bc1a3 in unpack_long (type=0x848d628, valaddr=0x85f4348 ":®")
>     at /home/corinna/src/gdb/values.c:696
> #4  0x080bc2a6 in unpack_pointer (type=0x848d628, valaddr=0x85f4348 ":®")
>     at /home/corinna/src/gdb/values.c:775
> #5  0x0813876e in cp_print_class_method (valaddr=0x85f4348 ":®", 
>     type=0x84aa064, stream=0x8490f08)
>     at /home/corinna/src/gdb/cp-valprint.c:90

There's your bug, right on schedule.  Look at the line:
  addr = unpack_pointer (lookup_pointer_type (builtin_type_void), valaddr);

Recommend using builtin_type_void_func_ptr instead of
lookup_pointer_type (builtin_type_void).  Does that fix it?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer