About the memory barrier in BSD libc

[Fengwei yin]

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?

Regards
Yin, Fengwei