Re: Compatibility symlink from old dynamic loader name to new dynamicloader name doesn't work.

["Carlos O'Donell" <carlos at systemhalted dot org>]

On Wed, Oct 24, 2012 at 1:16 PM, Roland McGrath <roland@hack.frob.com> wrote:
> The patch is clearly a dismal kludge that would never be acceptable.
>
> I don't understand why the stat-based logic at the top of
> _dl_map_object_from_fd is not handling this case already.

There are a couple of filename checks in _dl_map_object, but the files
names aren't the same name:
~~~ e.g.
          soname = ((const char *) D_PTR (l, l_info[DT_STRTAB])
                    + l->l_info[DT_SONAME]->d_un.d_val);
          if (strcmp (name, soname) != 0)
            continue;
~~~

Then in _dl_map_object_from_fd we check only that the inodes are the
same, which isn't true for a symlink.
~~~ e.g.
  /* Look again to see if the real name matched another already loaded.  */
  for (l = GL(dl_ns)[nsid]._ns_loaded; l; l = l->l_next)
    if (l->l_removed == 0 && l->l_ino == st.st_ino && l->l_dev == st.st_dev)
...
#ifdef SHARED
  /* When loading into a namespace other than the base one we must
     avoid loading ld.so since there can only be one copy.  Ever.  */
  if (__builtin_expect (nsid != LM_ID_BASE, 0)
      && ((st.st_ino == GL(dl_rtld_map).l_ino
           && st.st_dev == GL(dl_rtld_map).l_dev)
          || _dl_name_match_p (name, &GL(dl_rtld_map))))
...
~~~

The code probably works for a hardlink.

It seems rather sloppy that your choice of hardlink vs. symlink can
break things.

>> In summary:
>> - To support compatibility symlinks from old dynamic loader names to new
>> dynamic loader names will require refactoring _dl_map_object_from_fd to
>> actually detect if two DSOs are the same.
>
> That's exactly what it already does.

Unfortunately I don't see how without following the symlink, which it
doesn't do.

Cheers,
Carlos.