Re: thread-ready ABIs

[Daniel Jacobowitz <dan@debian.org>]

On Tue, Jan 22, 2002 at 06:08:12PM +0100, Kevin D. Kissell wrote:
> > Perhaps I'm mangling terminology.  LinuxThreads is a one-to-one mapping
> > of kernel threads to user threads.  All the kernel threads, and thus
> > all the user threads, share the same memory region - including the
> > stack region.  Their stacks are differentiated solely by different
> > values in the stack pointer register.  Thus I don't think what you're
> > suggesting is possible.
> 
> I don't see how fork() semantics can be preserved unless
> the stack regions are replicated (copy-on-write) on a fork().
> Under ATT and BSD Unix (which is where I did most of
> my kernel hacking in the old days) that was the *only*
> way to get a new kernel thread, so it was "obvious"
> that my proposed hack would work.  Linux does have
> the clone() function as well, and if LinuxThreads are
> implemented in terms of clone(foo, stakptr, CLONE_VM, arg),
> you are correct, the proposed scheme would not work
> without modification.

Which it is.  Fork shares no memory regions; vfork/clone share all
memory regions.  AFAIK there is no share-heap-but-not-stack option in
Linux.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer