[dmd-internals] __tls_callbacks_a

[Alex]

This doesn't seem to work:

__gshared extern(C) int _tls_used = 0;

int main()
{
    return _tls_used;
}
E:\>dmd test.d
OPTLINK (R) for Win32  Release 8.00.12
Copyright (C) Digital Mars 1989-2010  All rights reserved.
http://www.digitalmars.com/ctg/optlink.html
c:\d\dmd2\windows\bin\..\lib\snn.lib(tlsdata)  Offset FD6A3H Record Type 0091
Error 1: Previous Definition Different : __tls_used
--- errorlevel 1

Maybe I'm not following you though.

Regards,
Alex

On Thu, Jan 19, 2012 at 10:56 PM, Rainer Schuetze <r.sagitario at gmx.de> wrote:
> 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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