[patch][0/5] powerpc: Add support to fully comply with IEEE-754 standard

[Zhu Ebony-r57400]

> -----Original Message-----
> From: Kumar Gala [mailto:galak at kernel.crashing.org] 
> Sent: Wednesday, February 07, 2007 3:12 PM
> To: Zhu Ebony-r57400
> Cc: paulus at samba.org; linuxppc-dev at ozlabs.org
> Subject: Re: [patch][0/5] powerpc: Add support to fully 
> comply with IEEE-754 standard
> 
> 
> On Feb 6, 2007, at 11:52 PM, Zhu Ebony-r57400 wrote:
> 
> >>>> This snippet of code breaks it from math-emu/sfp-machine.h
> >>>>
> >>>>>> +#ifdef CONFIG_SPE
> >>>>>> +#define __FPU_FPSCR	(current->thread.spefscr)
> >>>>>> +#else
> >>>>>>  #define __FPU_FPSCR	(current->thread.fpscr.val)
> >>>>>> +#endif
> >>>>
> >>>> By doing this if I want 'classic FP' emulation as well 
> as the IEEE 
> >>>> fixup my fpscr for classic emu will not be updated properly.
> >>>
> >>> Logically, user can choose "SPE Support" and "Math
> >> emulation" at the
> >>> same time on menuconfig. But from my understanding, it is not 
> >>> necessary to select math-emu on a SPE available system,
> >> since SPE can
> >>> do math operation.
> >>
> >> This is not true.  If I want to run a "classic" PPC binary 
> with FP I 
> >> need "Math emulation" and if I want to run an SPE one I 
> enable "SPE 
> >> Support".  I could want to run both of these types of 
> binaries on the 
> >> same system at the same time.
> >
> > If this is the case, maybe we need a separate macro like
> > #define __SPE_SPEFSCR	(current->thread.spefscr)
> > But if we do this, how does the kernel know if the emulation is for 
> > "classic" PPC binary with FP or an SPE one, thus corresponding 
> > registers(fpscr or spefscr) being updated?
> 
> It's based on what instruction you are trying to emulate.
> 
For example, the FP_ROUNDMODE now defined by __FPU_FPSCR is
widely used in existing code. If the kernel doesn't know the emulation
is for
classic PPC or SPE fixup, then it doesn't know where to get the correct
rounding mode, from fpscr or spefscr? This has confused me.

B.R.
Ebony