[dmd-internals] __tls_callbacks_a

[Rainer Schuetze]

That's no problem if the symbol is from a library and you don't 
reference other symbols in the same module. This compiles and links:

extern(C) int _tls_index;
extern(C) void* _tls_used[6];

void main()
{
}

If you check the map file, you will see that tlsdata is no longer used.

On 19.01.2012 22:35, Alex wrote:
> Problem is that the symbol is a strong reference, so redefining it
> will just give a duplicate symbol error. :/
>
> Regards,
> Alex
>
> On Thu, Jan 19, 2012 at 10:28 PM, Rainer Schuetze<r.sagitario at gmx.de>  wrote:
>> Can't you declare the symbols (_tls_index and _tls_used) in the tlsdata
>> module elsewhere (not in a library), so the module will not be taken from
>> the library? Then you can set your own list of callbacks.
>>
>>
>> On 19.01.2012 22:11, Alex wrote:
>>> Hi,
>>>
>>>> Maybe you can patch the corresponding entry off the _tls_used data struct
>>>> very early, so the TLS callback are called when necessary.
>>> Unfortunately, it seems the PE loader loads it immediately, so
>>> patching at runtime is virtually impossible. :(
>>>
>>> (We did think of doing a horrible hack (detouring
>>> LdrShutdownThread()), but this is insane for many reasons...)
>>>
>>> My guess is that the symbol is just defined always for convenience, as
>>> it's necessary for C/C++ code using TLS. However, this clearly imposes
>>> problems on D users, as we have no way of utilizing the symbol
>>> correctly.
>>>
>>> The last resort is to simply patch snn.lib but this obviously
>>> complicates the build process a LOT. We'd really like to avoid this...
>>>
>>> Regards,
>>> Alex
>>>
>>> On Thu, Jan 19, 2012 at 9:38 PM, Rainer Schuetze<r.sagitario at gmx.de>
>>>   wrote:
>>>> _tls_callbacks_a is defined to a single zero entry in the C runtime
>>>> library,
>>>> see the module tlsdata.obj from snn.lib.
>>>>
>>>> I guess you know this, but here's a very in depth article about TLS under
>>>> windows: http://www.nynaeve.net/?p=183
>>>>
>>>> Maybe you can patch the corresponding entry off the _tls_used data struct
>>>> very early, so the TLS callback are called when necessary.
>>>>
>>>>
>>>> On 19.01.2012 11:40, Alex wrote:
>>>>> Anyone have a clue? As said, this is quite essential for implementing
>>>>> a TLS-supporting VM in D.
>>>>>
>>>>> Regards,
>>>>> Alex
>>>>>
>>>>> On Tue, Jan 17, 2012 at 8:59 AM, Alex<xtzgzorex at gmail.com>      wrote:
>>>>>> Hi,
>>>>>>
>>>>>> It seems that either DMD or Optlink is emitting this symbol, most
>>>>>> likely because it was expected that users would like to define TLS
>>>>>> callbacks. However, in D we have nothing like _CRTALLOC() or
>>>>>> __declspec(allocate()), so we cannot specify that we want a callback
>>>>>> registered there. This callback is rather essential for a virtual
>>>>>> machine that me and a few others are working on, so is there some kind
>>>>>> of workaround we could use? Or perhaps we're just missing the way this
>>>>>> is supposed to used in the first place?
>>>>>>
>>>>>> Regards,
>>>>>> Alex
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