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Re: twp bigger changes


Mark Kettenis <kettenis@wins.uva.nl> writes:

> So perhaps it would be a good idea to release a glibc 2.1.4 with my
> libthread_db fixes.  That would make it possible for the GDB folks
> to tell people to upgrade to 2.1.4 if they want to debug threads
> under Linux.

This is not motivation enough.  The changes can be made available separetly.

> I don't think it would be very smart to make the compiler dependent on
> the internals of the threads implementation.  I assume that the
> proposal is some abstract ABI definition like:

Whether you think it's smart or not, something like this has to be
there.  Not that there is only one field defined, the rest is left to
the implementation.  The one field at offset 0 is special and is
needed in some situations and the compiler has to know about it.  Just
think for a second about passing a pointer to a thread-local variable
to a normal function.  How would you do this without this information?

In short, we are not as stupid as you think we are.

> Also note that, if you actually any of the segment registers to point
> at such a data structure, the number of entries in a LDT is limited,
> and that some OS'es have a per-process (i.e. per-VM space) LDT instead
> of a per-thread LDT.

Yes, and?  There is always a fallback mechanism (using the POSIX
thread-local data interface).  We have to implement this anyway (e.g.,
for m68k).  It will be a system specific thing which does not mean we
must not take advantage of the possibilities available on some
platforms.

-- 
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Ulrich Drepper  \    ,-------------------'   \  Sunnyvale, CA 94089 USA
Red Hat          `--' drepper at redhat.com   `------------------------

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