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Unconditionally use locked addition of zero to tip of the stack for

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memory barriers on i386. It works as a serialization instruction on
all IA32 CPUs.

Alternative solution of using {s,l,}fence requires run-time checking
of the presense of the corresponding SSE or SSE2 extensions, and
possible boot-time patching of the kernel text.

Suggested by:	many
This commit is contained in:
Konstantin Belousov 2008-12-05 21:17:54 +00:00
parent aeb325719a
commit 2640173120
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=185651
1 changed files with 3 additions and 14 deletions
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17
sys/i386/include/atomic.h
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@ -32,20 +32,9 @@
#error this file needs sys/cdefs.h as a prerequisite
#endif
#if defined(I686_CPU)
#define mb() __asm__ __volatile__ ("mfence;": : :"memory")
#define wmb() __asm__ __volatile__ ("sfence;": : :"memory")
#define rmb() __asm__ __volatile__ ("lfence;": : :"memory")
#else
/*
* do we need a serializing instruction?
*/
#define mb()
#define wmb()
#define rmb()
#endif
#define mb() __asm __volatile("lock;addl $0,(%esp)")
#define wmb() __asm __volatile("lock;addl $0,(%esp)")
#define rmb() __asm __volatile("lock;addl $0,(%esp)")
/*
* Various simple operations on memory, each of which is atomic in the