Re: [Qemu-devel] RFC: cleanups: CPU_MEM_INDEX

[Thiemo Seufer <ths@networkno.de>]

J. Mayer wrote:
> On Wed, 2007-10-10 at 07:06 +0200, J. Mayer wrote:
> > On Wed, 2007-10-10 at 01:12 +0100, Thiemo Seufer wrote:
> > > J. Mayer wrote:
> > > > Here's a proposal to add a int cpu_mem_index (CPUState *env) function in
> > > > targets cpu.h header.
> > > > The idea of this patch is:
> > > > - avoid many #ifdef TARGET_xxx in exec-all.h and  softmmu_header.h then
> > > > make the code more readable
> > > > - avoid multiple implementation of the same code (3, in that particular
> > > > case) this to avoid potential conflicts if the definition has to be
> > > > updated for any reason (ie support for new memory access modes,
> > > > emulation optimisation...)
> > > > 
> > > > Please comment.
> > > > 
> > > > -- 
> > > > J. Mayer <l_indien@magic.fr>
> > > > Never organized
> > > 
> 
> [...]
> 
> Here's an updated version of the patch. My comments about it stay valid,
> with two additions:
> 1/ when is user is needed to maintain compatibility with existing code,
> I now define it as:
> int is_user = mmu_idx == MMU_USER_IDX;
> instead of just is_user = mmu_idx.
> This definition will then remain correct even if the definition of the
> MMU modes are later changed for a specific target
> 2/ I now precompute the mmu_idx on PowerPC platform as it can never
> change inside a single TB. This may save a few instructions for every
> memory access. I guess the same optimisation can be made for the other
> targets, but not knowing exactly when it would have to be recomputed,
> for most targets, I prefer not to do this optimisation myself.

I like this version. Tested with x86 and mips, on Linux/ppc host.


Thiemo