Re: [ACPI] Re: Linux 2.4.26-rc1 (cmpxchg vs 80386 build)

["Richard B. Johnson" <root@chaos.analogic.com>]

On Tue, 30 Mar 2004, Willy Tarreau wrote:

>
> > > OK, so why not compile the cmpxchg instruction even on i386 targets
> > > to let generic kernels stay compatible with everything, but disable
> > > ACPI at boot if the processor does not feature cmpxchg ? This could
> > > be helpful for boot/install kernels which try to support a wide
> > > range of platforms, and may need ACPI to correctly enable interrupts
> > > on others.
> > >
> > > Cheers,
> > > Willy
> > >
> >
> > Because it would get used (by the compiler) in other code as well!
> > As soon as the 386 sees it, you get an "invalid instruction trap"
> > and you are dead.
>
> That's not what I meant. I only meant to declare the cmpxchg() function.

It's not a function. It is actual op-codes. If you compile with
'486 or higher, the C compiler is free to spew out these op-codes
any time it thinks it's a viable instruction sequence. Since
it basically replaces two other op-codes, gcc might certainly use
if for optimization.

This is independent of the macro that is defined in a header to
use this sequence .


[SNIPPED...]


Cheers,
Dick Johnson
Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
            Note 96.31% of all statistics are fiction.