[boost] Re: Windows MSVC thread exit handler for staticly linkedBoost.Thread

From: Holger Grund (yahoo_at_[hidden])
Date: 2004-08-02 07:15:33

> Bronek Kozicki <brok <at> rubikon.pl> writes:

Hi Bronek,

I hope you don't mind following up in here as I don't have access to the 
private groups right now anyway.

> >  _tls_used variable appears to be absolutely required. To explain, I was
> 
> What I understand (it's quite blury picture right now) is that if you 
> define one of:
> a)  int _tls_index
> or
> b)  _declspec(thread) some_variable
> 
I believe things are a little bit different. Most of it is just guessing, 
though. But anyway: 

Essentially if a symbol named "__tls_used" is present, the VC6 linker will 
emit. VC 7 introduced __declspec(thread) which uses this functionality. 
Therefore the 7.0= CRT provides the __tls_used structure referencing the data 
in ]CRTXLA,CRTXLZ[.

This would result in a static TLS section emitted for every PE image. Therefore 
the VC7 linker introduced a check for the __tls_index and the ".tls" section.

__declspec(thread) introduces a data item in .tls. Accessing such a variable 
introduces references to _tls_array and _tls_index.

So if you use VC7+ linker you need ".tls" section and __tls_used. With a VC6 
linker the latter should be sufficient.

With a GCC ld a version script might help. And GCC also support something like 
__attribute__((section)) which might work with PE images, too.

-hg