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

[J. Mayer]

On Thu, 2007-10-11 at 18:46 +0100, Thiemo Seufer wrote:
> 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 <address@hidden>
> > > > > 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.

Thanks for testing.
I guess it's safe... but I'd like to get more reports or comments about
it before applying this !

-- 
J. Mayer <address@hidden>
Never organized