Re: [linuxsh-dev] Re: FPU in kernel (SH-4)

[Greg B. <gb...@po...>]

NIIBE Yutaka wrote:
> 
> We've implemented lazy FPU save/restore.  [...]
> 
> I think that this feature makes sence.  I don't think we should remove
> this.

  I agree.

> Perhaps, we need to implement something to share FPU registers among
> kernel threads.

  I've got another idea.  Let's change the FPU first-use trap handling
code to panic if the FPU is used from kernel space.

>  > > I think that we can assume GCC provide some way of not using
>  > > FPU for division.
>  >
>  >   That's what -m4-nofpu is for, right?
> 
> Yes, that is my intention.  However, I'm sorry that it seems it's my
> misunderstanding.  I'm now re-examining our patch of GCC, and it seems
> for me that -m4-nofpu is special kind of SH-3, not SH-4 (for me it's
> amazing :-(). 

  Huh?  I seem to remember we had a problem where the gcc maintainers
were making this (incorrect) assumption.  So, using -m4-nofpu resulted
in __sh3__ being defined instead of __sh4__.  But I thought that had
been cleared up by now.

> I think that we should provide our own switch to
> disable FPU division.  Kaz once has such a patch implemented, perhaps
> I'll take it.

  Fair enough.

Greg.
-- 
If it's a choice between being a paranoid, hyper-suspicious global
village idiot, or a gullible, mega-trusting sheep, I don't look
good in mint sauce.                      - jd, slashdot, 11Feb2000.