About the memory barrier in BSD libc

[Slawa Olhovchenkov]

On Mon, Apr 23, 2012 at 07:26:54PM +0800, Fengwei yin wrote:

> On Mon, Apr 23, 2012 at 5:40 PM, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> > On Mon, Apr 23, 2012 at 05:32:24PM +0800, Fengwei yin wrote:
> >
> >> On Mon, Apr 23, 2012 at 4:41 PM, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> >> > On Mon, Apr 23, 2012 at 02:56:03PM +0800, Fengwei yin wrote:
> >> >
> >> >> Hi list,
> >> >> If this is not correct question on the list, please let me know and
> >> >> sorry for noise.
> >> >>
> >> >> I have a question regarding the BSD libc for SMP arch. I didn't see
> >> >> memory barrier used in libc.
> >> >> How can we make sure it's safe on SMP arch?
> >> >
> >> > /usr/include/machine/atomic.h:
> >> >
> >> > #define mb()    __asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> > #define wmb()   __asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> > #define rmb()   __asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
> >> >
> >>
> >> Thanks for the information. But it looks no body use it in libc.
> >
> > I think no body in libc need memory barrier: libc don't work with
> > peripheral, for atomic opertions used different macros.
> 
> If we check the usage of __sinit(), it is a typical singleton pattern which
> needs memory barrier to make sure no potential SMP issue.
> 
> Or did I miss something here?

What architecture with cache incoherency and FreeBSD support?