Reload a DLL and _getptd returns zero

Marcus Meissner marcus at
Sun Jan 13 15:17:52 CST 2013

On Fri, Jan 11, 2013 at 11:24:55AM -0800, Michael Ost wrote:
> Hi list,
> Does anyone know why _getptd() calls would return zero on a DLL that
> has been reloaded? Does something happen to the TLS used by _getptd?
> At Muse Research we have been struggling with a deep bug for years
> where there is a crash _sometimes_ if you load a DLL a second time.
> Finally (with a big tip of the hat to Julien Pommier at PianoTeq!)
> we have a test case that demonstrates a (if not _the_) crash.
> The sequence is:
> 1. [main] start a thread
> 2. [main] load a library
> 3. [thread] call std::cout<< from the library
> 4. [main] free the library
> 5. [main] reload the library
> 6. [thread] call std::cout<< from the library
> -> crash!
> It looks like the crash happens because the MSVCRT function
> _getptd() is returning zero in step 6. This is dereferenced and
> crashes. In windows, there is no crash.
> The library in question is using static vc runtime linkage, so
> _getptd() is linked in and I don't know exactly what it is doing.
> But Wine's MSVCRT implementation of _getptd() gets its data from
> TlsGetValue. And I can see that just before the crash there is a
> TlsGetValue call that returns zero.
> Looking at TlsGetValue(), there must be something wrong with the
> values in TlsSlots. Maybe they persist for DLLs in Windows in a way
> they don't for Wine...? Or maybe Wine doesn't reinitialize them the
> same way when the DLL is reloaded?
> Any hints, thoughts? clues? Thanks!

Is this statically linked msvcrt from Wine or Windows?

And why free/reload a statically linked library?

Ciao, Marcus

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