Re: [PATCH v2] elf: Support recursive use of dynamic TLS in interposed malloc

[Florian Weimer <fweimer@redhat.com>]

* Szabolcs Nagy:

>> +static int
>> +do_test (void)
>> +{
>> +  /* 16 is large enough to exercise the DTV resizing case.  */
>> +  void *handles[16];
>> +
>> +  for (unsigned int i = 0; i < array_length (handles); ++i)
>> +    {
>> +      /* Re-use the TLS slot for module 0.  */
>> +      if (i > 0)
>> +        xdlclose (handles[0]);
>> +
>> +      char soname[30];
>> +      snprintf (soname, sizeof (soname), "tst-recursive-tlsmod%u.so", i);
>> +      handles[i] = xdlopen (soname, RTLD_NOW);
>> +
>> +      if (i > 0)
>> +        handles[0] = xdlopen ("tst-recursive-tlsmod0.so", RTLD_NOW);
>> +    }
>
> if this loop accessed the tls in *tlsmod0.so then
> the access would do malloc and the dtv update after
> dlclose would have to free.
>
> i think the current code only tests the realloc in
> _dl_resize_dtv during dtv update so if the initial
> dtv size is increased then the test becomes ineffective
> (it may pass without the patch).
>
> i'd add that access to cover more malloc/free cases, e.g.
>
>   if (i > 0)
>     {
>       handles[0] = xdlopen ("tst-recursive-tlsmod0.so", RTLD_NOW);
>       int (*f) (void) = xdlsym (handles[0], "get_threadvar_0");
>       f (); /* TLS access may allocate.  */
>     }

Right, just the f () call expression triggers a fair number of extra
malloc subsystem calls.  Will send a v3.

Thanks,
Florian