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Re: thread-ready ABIs

To: "H . J . Lu" <hjl@lucon.org>, "Ulrich Drepper" <drepper@redhat.com>
Subject: Re: thread-ready ABIs
From: "Kevin D. Kissell" <kevink@mips.com>
Date: Sat, 19 Jan 2002 01:35:38 +0100
Cc: "GNU libc hacker" <libc-hacker@sources.redhat.com>, <linux-mips@oss.sgi.com>
References: <m3elkoa5dw.fsf@myware.mynet> <20020118101908.C23887@lucon.org>
Sender: owner-linux-mips@oss.sgi.com
> On Thu, Jan 17, 2002 at 04:07:23PM -0800, Ulrich Drepper wrote:
> > The time is near when we (well, I) well start a drastic move toward
> > generally using thread registers.  Even in non-threaded code.
> > 
> > This means that unless all architectures get thread registers (or
> > equivalent things like Alpha's special code) we'll have a two class
> > society of platforms where all code written for the platforms without
> > thread register can be run on the other systems, but not vice versa.

[snip]

> > MIPS: Who feels responsible?  Andreas, HJ?
> 
> I don't see there are any registers we can use without breaking ABI.
> On the other hand, can we change the mips kernel to save k0 or k1 for
> user space?

Thank you for posting this to linux-mips, since I'm not sure 
that anyone at MIPS is on the GNU_libc_hacker list.

It would, in principle, be possible to save/restore k0
or k1 (but not both) if no other clever solution can be found.  
There are other VM OSes that manage to do so for MIPS, 
for other outside-the-old-ABI reasons.  It does, of course,
add some instructions and some memory traffic to the 
low-level exception handling , and we would have to look 
at whether we would want to make such a feature standard 
or specific to a "thread-ready" kernel build.

            Regards,

            Kevin K.



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