Re: [kvm-devel] [Qemu-devel] expose host CPU features to guests: Take 3

[J. Mayer]

On Tue, 2007-09-25 at 11:01 +0200, Avi Kivity wrote:
> Dan Kenigsberg wrote:
> > On Tue, Sep 25, 2007 at 03:28:24AM +0200, andrzej zaborowski wrote:
> >   
> >> Hi,
> >>
> >> On 24/09/2007, Dan Kenigsberg <address@hidden> wrote:
> >>     
> >>> As with previous "Takes" of this patch, its purpose is to expose host
> >>> +{
> >>> +    asm("cpuid"
> >>> +        : "=a" (*ax),
> >>> +          "=b" (*bx),
> >>> +          "=c" (*cx),
> >>> +          "=d" (*dx)
> >>> +        : "a" (function));
> >>> +}
> >>>       
> >> I haven't really read through the rest of your code but this piece
> >> appears to be outside any #ifdef/#endif so it will only build on x86.
> >>     
> >
> > I might be missing something here, but isn't not being on the
> > TARGET_PATH of Makefile.target enough? I don't see #ifdef TARGET_I386
> > elsewhere under target-i386. I don't mind adding extra protection, I
> > just be happy to better understand the whats and whys.
> >   
> 
> target-i386 means the guest will run i386 instructions, but the host can
> be something else (say, powerpc).
> 
> Nothing else uses host instructions in that directory, so no protection
> was necessary before.

I've got a remark about this: why this has to be added to the Qemu
code ?
Imho, all is needed is an implementation of the -cpu option for
x86/x86_64 target. Then, an external tool (even a shell script) can be
used to determine what is the host CPU if you want to select the exact
same CPU to be emulated in Qemu. It seems to me that trying to do so is
out of the scope of Qemu code and just add unneeded complexity.

Regards.

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