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Date: Mon, 23 Apr 2012 12:41:20 +0400
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Fengwei yin <yfw.bsd@gmail.com>
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References: <CAPHpMu=DOGQ=TuFeYH7bH8hVwteT4Q3k67-mvoOFob6P3Y506w@mail.gmail.com>
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Cc: jack.ren@intel.com, freebsd-threads@freebsd.org
Subject: Re: About the memory barrier in BSD libc
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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")