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From: Tony Juricic (tonygeek_at_[hidden])
Date: 2004-08-01 18:34:08

"Aaron W. LaFramboise" wrote:

> As a last resort, the TLS directory (that pesky _tls_used symbol) can be
> redefined, but this is hackish, and on the edge of what I'd consider
> acceptable, and would need to be tested quite extensively to make sure
> it is compatible. For example, the suggestions so far for overriding
> the TLS directory will break __declspec(thread) and will probably cause
> random redefined symbol link failures in some situations.

Here are some (hopefully) more specific details about problems with the
static library, using VC++ 7.1, Debug compilation, linking with static
multithreaded CRT.

1) The main program code does not really matter - in my case it is a dumb
Win32 console exe that uses no boost code, has no extra threads (except for
the main process thread) and its sole purpose is to call foo() function in a
static library and exit.

2) Beside implementing foo() fuction called from the main, static library
uses no boost code and the only requirement is to get:

void NTAPI tls_callback (PVOID, DWORD Reason, PVOID)
 ... whatever, some code where you can set a breakpoint


invoked when the main program thread exits.

So far I found only two ways to hit the breakpoint set in tls_callback:

A) Put this code in static library:

extern "C" int _tls_used;

int dummy()
 return _tls_used;


B) put this:

__declspec(thread) int ithread;

You don't have to create a thread, use ithread variable or do anything else
in your static library code except for implementing foo() and

Either A or B will cause tls_callback to be called (breakpoint will be hit)
with VC++ 7.1, but only and only if the following is also a part of the
static library code:

#pragma data_seg(push, old_seg)
#pragma data_seg(".CRT$XLB")
DWORD tls_callback_ptr = (DWORD)tls_callback;
#pragma data_seg(pop, old_seg)

So, unless I made some gross mistake, it seems to me it is quite lame that
Microsoft would document TLS callbacks PEF data but not provide any
documented way to define and declare TLS callbacks.


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