[PATCH] invalid instructions in kernel mode

[Kumar Gala]

On Apr 7, 2005, at 12:38 PM, Tom Rini wrote:

> On Thu, Mar 31, 2005 at 07:47:32PM +0200, Fillod Stephane wrote:
>
> > When CPU has no (classic) FPU, and math emulation is disabled,
>  > fp instructions are not allowed in kernel mode.
>  [snip]
>  > --- linux/arch/ppc/kernel/misc.S      26 Mar 2005 03:28:36 -0000
>  > 1.1.1.2
>  > +++ linux/arch/ppc/kernel/misc.S      31 Mar 2005 16:33:25 -0000
>  > @@ -1096,7 +1096,8 @@
>  >   * and exceptions as if the cpu had performed the load or store.
>  >   */
>  > 
> > -#if defined(CONFIG_4xx) || defined(CONFIG_E500)
> > +#if !(defined(CONFIG_4xx) || defined(CONFIG_E500) ||
>  > defined(CONFIG_8xx)) ||  defined(CONFIG_MATH_EMULATION)
> > +#if defined(CONFIG_4xx) || defined(CONFIG_E500)
> >  _GLOBAL(cvt_fd)
> >       lfs     0,0(r3)
>  >       stfd    0,0(r4)
>  > @@ -1125,6 +1126,7 @@
>  >       stfd    0,-4(r5)
>  >       blr
>  >  #endif
>  > +#endif
>
> The problem here is, HEY! (classic) FP instrs in the kernel.  The
>  question is why?  Or rather, why are these four classic FP instrs
>  (lfs/lfd/stfd/stfs) being done on CONFIG_4xx || E500 when neither has
>  classic FP?  I think the problem here is that on !FPU
> (which is 4xx||E500||8xx, or so), we need to rewrite these two
>  functions (yes, 8xx does emulate them if hit, but that's a tangent).

What is not clear to me is what condition causes these to get hit on an 
e500.

- kumar