TLS support

[Ulrich Drepper <drepper at redhat dot com>]

I finally managed to get the last changes completed and tested.  Well,
at least the current tests succeed, I'll have to write new once.

With this TLS on i386 is basically done.  Jakub published the binutils
changes and therefore there is no reason to not support any of the
other platforms which already have thread registers.

I have some preliminary but completely untested IA64 changes which I
can send to somebody who wants to beat me working on this.  Otherwise
I'll look at it as soon as I have time.


One more warning.  The TLS support as implemented now cannot possibly
work reliably on a current Linux kernel.  The problem is that the LDT
data structure must be allocated in physically contiguous memory and
since for every process an LDT is allocated the memory is severely,
maybe fatally, fragmented sooner or later.

To solve this the kernel could avoid allocation the LDT for a process
with only entry 0 of the LDT used.  This was suggested to the kernel
people but they didn't like it.  Instead a mechanism which allows
using a GDT segment for the initial thread will be implemented.  This
will require ld.so changes.  I wait doing them until the kernel
changes are done.

-- 
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Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
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