Re: gnu asm help...

[Petr Vandrovec]

On 18 Jun 01 at 18:20, Timur Tabi wrote:
> You want to return the variable?  Try this:
> 
> static __inline__ unsigned long atomic_inc(atomic_t *v)
> {
>     __asm__ __volatile__(
>         LOCK "incl %0"
>         :"=m" (v->counter)
>         :"m" (v->counter));
> 
>     return v->counter;
> }

No. Another CPU might increment value between LOCK INCL and
fetching v->counter. On ia32 architecture you are almost out of
luck. You can either try building atomic_inc around CMPXCHG,
using it as conditional store (but CMPXCHG is not available 
on i386), or you can just guard your atomic variable with 
spinlock - but in that case there is no reason for using atomic_t 
at all. 
                                            Best regards,
                                                Petr Vandrovec
                                                [e-mail]
                                                
P.S.: Why you need to know that value? You can either rewrite
your code with atomic_dec_and_test/atomic_inc_and_test, or
you overlooked some race, or you have really strange problem.