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

[Michael E. <ea...@mv...>]

I've read the notes on the SH ABI on Kaz Kojima's web site.  They
appear to be "diffs" from the i386 ABI Supplement.   They don't 
mention anything about calling conventions and the way that floating 
point values are to be passed.  

Is there some other document which describes the SH ABI in more detail?

> On Wed, 8 Aug 2001 09:37:32 +0900 (JST)
> NIIBE Yutaka <gn...@m1...> wrote:
> 
> > Masahiro Abe wrote:
> >  > RTLinux for SH4 uses FPU. Or more precisely, real-time task running
> >  > under rtlinux can use fpu. There can be more than one task running
> >  > simultaneously.
> >
> > How do you use it?  Save all FPU registers at context switch or
> > interrupts?
> 
> Well, I did have wrong thing in my mind, and I didn't clearly state the
> situation. Sorry.
> 
> RTLinux-SH4 scheduler saves/restores FPU registers at its own context
> switch time. It has its own mechanism for switching tasks. (It's not
> lazy FPU save/restore, because I'm lazy.)
> 
> So, now I think my point stated above is worthless. From RTLinux
> standpoint, I think Niibe-san's proposal is OK, with one note below:
> 
> Please don't force to use -m4-nofpu option for compiling kernel. We've
> had a discussion in Japanese ML that "-m4-nofpu" and "-m4" are not
> compatible in terms of passing arguments to functions. "-m4-nofpu" does
> that in SH3 way, while "-m4" does that in SH4 way, which is different.
> (I can't show you details now, but Kojima-san may remember this
> discussion.) RTLinux core module and other Realtime task module must use
> "-m4" to be able to use FPU. "-m4-nofpu" kernel and "-m4" module can't
> work properly together.
> 
> So, please consider introducing "-fno-fpudiv" or "-fidiv" for "-m4", as
> Niibe-san proposed, and make "-m4 -fno-fpudiv" kernel and "-m4" module
> work properly.
> 
> Browsing the branch of this thread, my concern may be already addressed.
> I just wanted to add one additional information.
> 
> --
> Masahiro ABE, A&D Co., Ltd.
> 
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--
Michael Eager     ea...@mv...	408-328-8426	
MontaVista Software, Inc. 1237 E. Arques Ave., Sunnyvale, CA  94085