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Subject: Re: GNU pth during djgpp build time?
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On 2022-05-25 19:53, janezz55 (janezz55 AT gmail DOT com) [via djgpp AT delorie DOT com] wrote:
>> Surprisingly, configuring gcc with --enable-threads is actually possible, but 
>> it did require a small patch to Pth. The executables it produces however, will 
>> not run. A thread-aware libgcc will try to lock a mutex in 
>> __register_frame_info(), which is invoked from crt0 before __crt1_startup(). 
>> But locking a mutex involves a whole series of libc functions that rely on 
>> things like _dos_ds, which are only initialized from __crt1_startup(). 
> 
> patch libgcc? Why would it want to lock a mutex anyway?

As I understand it, __register_frame_info() is called to register .eh_frame
sections in a global list.  This also happens on shared library loads, at which
point there may be multiple active threads.  The same list is also accessed
whenever an exception is thrown.  So it makes sense to use a mutex here, but
in our case it's just not necessary to do so on startup.