Date: Tue, 21 Nov 2000 17:57:56 -0800 From: Jake Burkholder <jburkhol@home.com> To: John Baldwin <jhb@FreeBSD.ORG> Cc: Daniel Eischen <eischen@vigrid.com>, Jonathan Lemon <jlemon@flugsvamp.com>, arch@FreeBSD.ORG Subject: Re: Thread-specific data and KSEs Message-ID: <20001122015756.AF470BA7A@io.yi.org> In-Reply-To: Message from John Baldwin <jhb@FreeBSD.ORG> of "Tue, 21 Nov 2000 17:19:23 PST." <XFMail.001121171923.jhb@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
>
> On 22-Nov-00 Daniel Eischen wrote:
> > On Tue, 21 Nov 2000, John Baldwin wrote:
> >>
> >> On 22-Nov-00 Daniel Eischen wrote:
> >> > On Tue, 21 Nov 2000, Jonathan Lemon wrote:
> >> >> On Tue, Nov 21, 2000 at 06:51:59PM -0500, Daniel Eischen wrote:
> >> >> > I'm going to start working on the user-side of the new threads
> >> >> > library. I need to be able to quickly get at the current KSE
> >> >> > (or perhaps KSEG). Can we define a register on each architecture
> >> >> > that should not be used by FreeBSD ABI compliant applications?
> >> >> > The register doesn't have to be 32 bits or larger, just large
> >> >> > enough to hold the maximum number of KSEs (or KSEGs).
> >> >>
> >> >> Um. On a i386 I'm not sure this will be practical, there aren't
> >> >> a whole lot of architecturally visible registers for use by the
> >> >> application.
> >> >
> >> > 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.
>
> >> %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.
>
Doug uses $8 (t7) on the alpha for the per-cpu data pointer, and r13
on ia64. Not that that means anything to me.
alpha/inclue/globals.h:
register struct globaldata *globalp __asm__("$8");
ia64/include/globals.h:
register struct globaldata *globalp __asm__("r13");
Its not really relevant if they're the same in and out of the kernel
cause the memory isn't addressable in both places anyway.
> --
>
> John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/
> PGP Key: http://www.baldwin.cx/~john/pgpkey.asc
> "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/
>
>
> To Unsubscribe: send mail to majordomo@FreeBSD.org
> with "unsubscribe freebsd-arch" in the body of the message
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-arch" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20001122015756.AF470BA7A>