From: "H. Peter Anvin" <hpa@zytor.com>
To: Jidong Xiao <jidong.xiao@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Can anyone explain "movl %eax %eax"?
Date: Wed, 09 Feb 2011 14:32:27 -0800 [thread overview]
Message-ID: <4D5315FB.8020004@zytor.com> (raw)
In-Reply-To: <AANLkTikA3MT=eeMKg58HyYZRswUR+PMhYW978HEc0sst@mail.gmail.com>
On 02/09/2011 02:24 PM, Jidong Xiao wrote:
> Hi,
>
> In the kernel source, I see in a couple of places, there is "movl %eax
> %eax". Is this used for alignment purpose?
>
> For example, in the following piece of code we can see "movl %eax,%eax".
>
In x86-64, a dword (long) operation clears the upper 32 bits of the
target register, so "movl %eax,%eax" clears the upper 32 bits of %rax.
-hpa
next prev parent reply other threads:[~2011-02-09 22:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-09 22:24 Can anyone explain "movl %eax %eax"? Jidong Xiao
2011-02-09 22:32 ` H. Peter Anvin [this message]
2011-02-09 23:02 ` Jidong Xiao
2011-02-09 23:05 ` David Miller
2011-02-10 1:32 ` Jidong Xiao
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