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Re: [Xen-devel] x86-64 tools fix question

To: Jerone Young <jyoung5@xxxxxxxxxx>
Subject: Re: [Xen-devel] x86-64 tools fix question
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Tue, 1 Mar 2005 20:37:33 +0000
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxxx>
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On 1 Mar 2005, at 19:56, Jerone Young wrote:

        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

x86/64 has proper barrier instructions -- see include/asm-x86_64/system.h in Linux. It is from there that we should pull our definitions. Barrier macros are defined in a few places in the tools -- we ought to pull them all into one single header incorporated by all tools that need it.

 -- Keir

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