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Subject: Re: Can anyone explain "movl %eax %eax"?
From: David Miller <davem@davemloft.net>
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From: Jidong Xiao <jidong.xiao@gmail.com>
Date: Wed, 9 Feb 2011 18:02:09 -0500

> Oh, I see. Thank you. So similarly, the operation "xorl %eax,%eax" is
> used for the same reason, right? I see that appears in more files.

The xorl clears the entire register.