Re: Problem with virtual function pointers

[Corinna Vinschen <vinschen at redhat dot com>]

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
#6  0x08138184 in c_val_print (type=0x84a9814, valaddr=0x85f4160 "hA_\b\t ", 
    embedded_offset=0, address=162698, stream=0x8490f08, format=0, 
    deref_ref=1, recurse=0, pretty=Val_no_prettyprint)
    at /home/corinna/src/gdb/c-valprint.c:447
#7  0x080cc330 in val_print (type=0x84a9814, valaddr=0x85f4160 "hA_\b\t ", 
    embedded_offset=0, address=162698, stream=0x8490f08, format=0, 
    deref_ref=1, recurse=0, pretty=Val_no_prettyprint)
    at /home/corinna/src/gdb/valprint.c:152
#8  0x081386eb in c_value_print (val=0x85f4128, stream=0x8490f08, format=0, 
    pretty=Val_pretty_default)
    at /home/corinna/src/gdb/c-valprint.c:596
#9  0x080cc39d in value_print (val=0x85f4128, stream=0x8490f08, format=0, 
    pretty=Val_pretty_default)
    at /home/corinna/src/gdb/valprint.c:175
#10 0x080ce28f in print_formatted (val=0x85f4128, format=0, size=0, 
    stream=0x8490f08)
    at /home/corinna/src/gdb/printcmd.c:328
#11 0x080cf2cf in print_command_1 (exp=0x846fd0a "theA->virt", inspect=0, 
    voidprint=1) at /home/corinna/src/gdb/printcmd.c:931
#12 0x080cf33d in print_command (exp=0x846fd0a "theA->virt", from_tty=1)
    at /home/corinna/src/gdb/printcmd.c:952
[etc]

Corinna

-- 
Corinna Vinschen
Cygwin Developer
Red Hat, Inc.
mailto:vinschen at redhat dot com