[Qemu-devel] Re: [PATCH 2/3] PPC64: Implement slbmte

[Alexander Graf]

On 02.03.2009, at 20:28, Blue Swirl wrote:

> On 3/2/09, Alexander Graf <address@hidden> wrote:
> > On 02.03.2009, at 19:58, Blue Swirl wrote:
> >
> >
> > > On 3/2/09, Alexander Graf <address@hidden> wrote:
> > >
> > > > In order to modify SLB entries on recent PPC64 machines, the slbmte
> > > > instruction is used.
> > > >
> > > > This patch implements the slbmte instruction and makes the "bridge"
> > > > mode code use the slb set functions, so we can move the SLB into
> > > > the CPU struct later.
> > > >
> > > > This is required for Linux to run on PPC64.
> > > >
> > > > Signed-off-by: Alexander Graf <address@hidden>
> > >
> > >
> > > > void ppc_store_sr (CPUPPCState *env, int srnum, target_ulong value)
> > > > {
> > > >  LOG_MMU("%s: reg=%d " ADDRX " " ADDRX "\n",
> > > >              __func__, srnum, value, env->sr[srnum]);
> > > > -    if (env->sr[srnum] != value) {
> > > > +    if (env->mmu_model & POWERPC_MMU_64) {
> > >
> > >
> > > > target_ulong helper_load_sr (target_ulong sr_num)
> > > > {
> > > > +    if (env->mmu_model & POWERPC_MMU_64)
> > > > +        return ppc_load_sr(env, sr_num);
> > > >  return env->sr[sr_num];
> > > > }
> > >
> > > It would be faster to move the MMU model checks to translation time.
> >
> > The problem is that we don't know which -cpu the user will give us  
> > when we
> > run qemu-system-ppc64.
> > Of course we could just make qemu-system-ppc64 not take any non-64  
> > bit
> > CPUs, if nobody totally disagrees.
>
> env could contain a pointer to (static const) structure describing the
> CPU features. This pointer would be copied to corresponding
> DisasContext feature pointer, to be used by the translation functions.
>
> See for example target-sparc: translate.c (CHECK_IU_FEATURE macro) and
> helper.c for CPU definitions. IIRC MIPS or ARM have even nicer macros.


Right, as soon as I have Linux actually running and spare time to look  
at this, that's a pretty neat optimization :-). Honestly, for now  
speed isn't my main concern.

Alex