x86-64 tools fix question

[Jerone Young <jyoung5@us.ibm.com>]

In the tools there is a declaration:

#if defined(__i386__)
#define rmb() __asm__ __volatile__ ( "lock; addl $0,0(%%esp)" : : :
"memory" )
#define wmb() __asm__ __volatile__ ( "" : : : "memory" )
#else
#error "Define barriers"
#endif

located in:
	xcs/xcs.h
	tools/python/xen/lowlevel/xu/xu.c
	
	I'm assuming this has a convenient side-effect that it prevents read
reordering. Otherwise I can't figure out why this is being done at all.
Now I'm guessing that that using rsp instead of esp since we are in
64bit mode will give the same effect needed.

#elif defined(__x86_64__)
#define rmb() __asm__ __volatile__ ( "lock; addl $0,0(%%rsp)" : : :
"memory" )
#define wmb() __asm__ __volatile__ ( "" : : : "memory" )


	I would like to discuss is this correct, dead wrong, or even needed at
all?

-- 
Jerone Young
Open Virtualization
IBM Linux Technology Center
jyoung5@us.ibm.com
512-838-1157 (T/L: 678-1157)



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