Re: protection from dangling pointers in dwarf info when .so's go away

["Doug Evans" <dje at google dot com>]

On Dec 12, 2007 7:27 PM, Daniel Jacobowitz <drow@false.org> wrote:
> On Wed, Dec 12, 2007 at 05:57:58PM -0800, Doug Evans wrote:
> > Is it the case that vptr_basetype for myclass should never have gotten
> > assigned a value pointing into a .so (or any other obstack)?
>
> Sounds likely to me, but may not be practical.
>
> > Or is
> > gdb supposed to have cleaned up after itself when the .so data got
> > freed?
>
> We do this for user variables when their objfile goes away, by
> recursively copying their type.  We don't walk types from other
> objfiles looking for pointers, so there really shouldn't be any.
>
> > Or something else?  Any guidance on where the fix should go is
> > appreciated.  I suppose an easy solution is to toss out all info, not
> > just for .so's, though that will slow down re-runs.
>
> No, that's impossible.  Remember dlopen and dlclose.

Righto, and thanks.

It seems like check_typedef is aware of the issue:

    /* [...] We can't create pointers between
             types allocated to different objfiles, since they may
             have different lifetimes.  [...] */

but fill_in_vptr_fieldno is not:

void
fill_in_vptr_fieldno (struct type *type)
{
  CHECK_TYPEDEF (type);

  if (TYPE_VPTR_FIELDNO (type) < 0)
    {
      int i;

      /* We must start at zero in case the first (and only) baseclass
         is virtual (and hence we cannot share the table pointer).  */
      for (i = 0; i < TYPE_N_BASECLASSES (type); i++)
        {
          struct type *baseclass = check_typedef (TYPE_BASECLASS (type,
                                                                  i));
          fill_in_vptr_fieldno (baseclass);
          if (TYPE_VPTR_FIELDNO (baseclass) >= 0)
            {
              TYPE_VPTR_FIELDNO (type) = TYPE_VPTR_FIELDNO (baseclass);
              TYPE_VPTR_BASETYPE (type) = TYPE_VPTR_BASETYPE (baseclass);
              break;
            }
        }
    }
}

What happens if TYPE_OBJFILE (type) != TYPE_OBJFILE
(TYPE_VPTR_BASETYPE (baseclass)) ?