Date: Tue, 21 Nov 2000 22:14:09 -0500 (EST) From: Daniel Eischen <eischen@vigrid.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Jonathan Lemon <jlemon@flugsvamp.com>, arch@FreeBSD.org Subject: Re: Thread-specific data and KSEs Message-ID: <Pine.SUN.3.91.1001121220854.26351A-100000@pcnet1.pcnet.com> In-Reply-To: <XFMail.001121171923.jhb@FreeBSD.org>
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On Tue, 21 Nov 2000, John Baldwin wrote:
> On 22-Nov-00 Daniel Eischen wrote:
> > On Tue, 21 Nov 2000, John Baldwin wrote:
> >>
> >> On 22-Nov-00 Daniel Eischen wrote:
> >> > Why can't we use a segment register?
> >>
> >> %cs = code segment and is taken
> >> %ds = data segment and is taken
> >> %es = not sure, but bet it isn't safe
> >> %ss = stack, taken
> >> %fs = per-CPU data
> >
> > Isn't this kernel-only?
>
> I think so, but I would prefer that we use %gs if we go this route so that the
> same mechanism can be used both in and out of the kernel. If that makes sense.
That's fine with me.
> >> %gs ? as I mentioned in my other message, this one might be useful for
> >> addressing a structure of thread-local variables much like %fs is used for
> >> per-CPU data. It also has value in that supposedly x86-64 (aka k64) has
> >> both
> >> %fs and %gs, but no other seg regs.
> >
> > All I need is one.
>
> Well, %gs would cover x86 and k64. I think ia64 has several application
> registers that are available for OS use and we could steal one of those. I'm
> not sure about the alpha though.
OK, I think we can use an S register. These are suppose to
be call-safe, if I can believe sys/alpha/include/asm.h. Any
alpha gurus care to respond?
--
"Some folks are into open source, but me, I'm into open bar."
-- Spencer F. Katt
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