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Date: Wed, 9 Feb 2011 18:02:09 -0500 From: Jidong Xiao <jidong.xiao@...il.com> To: "H. Peter Anvin" <hpa@...or.com> Cc: linux-kernel@...r.kernel.org Subject: Re: Can anyone explain "movl %eax %eax"? 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. Regards Jidong On Wed, Feb 9, 2011 at 5:32 PM, H. Peter Anvin <hpa@...or.com> wrote: > 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 > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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