Re: crasher in C++ ABI code

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Sep 12, 2002 at 05:23:16PM -0700, Michael Snyder wrote:
> Attention, all you c++_abi_savvy folk...
> 
> I found a crasher bug while running the gdb testsuite on a COFF 
> toolchain.  TYPE_VPTR_FIELDNO returned -1; I haven't looked into
> this mechanism, but I assume that's a mistake.  When it was applied
> via value_field, of course it yielded a garbage value.
> 
> So looking at coffread.c, I see that there are no references
> to vptr_fieldno nor vptr_basetype -- these fields are never
> initialized.

They're initialized in alloc_type to -1... and further by stabs and
dwarf2.

> I'm just wondering where to go from here.  Is it possible to 
> obtain these values from COFF?  If not, perhaps their access
> methods should check for an invalid value?

COFF is not the issue.  coffread is just like elfread; it's an object
file reader.  The question is where your debug information comes from.
Mdebug?  Stabs?  DWARF-2?  If it's real mdebug instead of
stabs-in-mdebug, you're squat out of luck for C++.

Also, TYPE_VPTR_FIELDNO is often -1 by design; see
fill_in_vptr_fieldno and the comment above it.

 -  Is fill_in_vptr_fieldno getting called?
 -  If it were called would it succeed?
 -  Probably its return value needs to be checked somewhere.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer