Re: Question: Using floating point in the kernel

From: Lyle Coder (x_coder@hotmail.com)
Date: Tue Sep 19 2000 - 20:50:05 EST

Hello,
You cannot use MMX registers in the kernel either, since the kernel doesen't
save and restore FX state (fxsave, fxrstor) either (just like
(fsave/frstor).

Best Wishes,
Lyle

** Reply to message from "Richard B. Johnson" <root@chaos.analogic.com> on
Tue,
19 Sep 2000 11:58:34 -0400 (EDT)

>Tell the driver maintainer that you found a BUG. There is no floating-
>point allowed in the kernel because the state of the FP Unit is
>undefined in the kernel. If you 'define' it, i.e., `finit` then you
>will mess up somebody who was using the FP Unit in user-mode.
>
>Also, the '386 FP emulation, which is still supported, can produce a
>double-fault if you try to use it (at some places) in kernel-mode
>code.
>
>Basically, there is nothing in the kernel that will ever require
>floating point. Use fixed point if you need 'decimals' and stuff for
>printing.

What about MMX? It uses floating point registers, but it's not technically
floating point. 

--
Timur Tabi - ttabi@interactivesi.com
Interactive Silicon - http://www.interactivesi.com

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