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

[Willy Tarreau <willy@w.ods.org>]

Hi Len,

On Sun, Mar 28, 2004 at 11:49:15PM -0500, Len Brown wrote:
 
> ACPI unconditionally used cmpxchg before this change also -- from asm().
> The asm() was broken, so we replaced it with C,
> which invokes the cmpxchg macro, which isn't defined for
> an 80386 build.
> 
> I guess it is a build bug that the assembler allowed us
> to invoke cmpxchg in an asm() for an 80386 build in earlier releases.
> 
> I'm open to suggestions on the right way to fix this.
> 
> 1. recommend CONFIG_ACPI=n for 80386 build.
> 
> 2. force CONFIG_ACPI=n for 80386 build.
> 
> 3. invoke cmpxchg from acpi even for 80386 build.
> 
> 4. re-implement locks for the 80386 case.

I like this one, but a simpler way : don't support SMP in this case, so that
we won't have to play with locks. This would lead to something like this :

#ifndef CONFIG_X86_CMPXCHG
#ifndef CONFIG_SMP
#define cmpxchg(lock,old,new) ((*lock == old) ? ((*lock = new), old) : (*lock))
#else
#define cmpxchg(lock,old,new) This_System_Is_Not_Supported
#endif
#endif

This code (if valid) might be added to asm-i386/system.h so that we don't
touch ACPI code.

Any comments ?

Willy