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Date: Tue, 23 Oct 2012 23:40:55 -0600
From: Peter Grehan <grehan@freebsd.org>
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To: Andriy Gapon <avg@FreeBSD.org>
Subject: Re: svn commit: r241744 - projects/bhyve/usr.sbin/bhyve
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Cc: svn-src-projects@FreeBSD.org, src-committers@FreeBSD.org,
 Jilles Tjoelker <jilles@stack.nl>
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Hi Andriy,

> If this code emulates something like mov into %eax on AMDD64, then it should clear
> upper 32-bits of %rax.  Which I think your original code already did, but in a
> less obvious way than Jilles suggested above.
> But I could be very well confused...

  The 0x88/0x89 forms of the MOV instruction don't touch bytes outside 
of the operand size.

later,

Peter.