Messages in this thread | | | Date | Wed, 09 Feb 2011 14:32:27 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Can anyone explain "movl %eax %eax"? |
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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
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