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Date: Wed, 23 Nov 2005 11:03:15 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>
cc: "H. Peter Anvin" <hpa@zytor.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
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Subject: Re: [patch] SMP alternatives
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On Wed, 23 Nov 2005, Jeff V. Merkey wrote:
>
> The lock prefix '0F' is used for a lot of opcodes other than "lock". Go check
> the instruction set reference.

No it's not.

0F is indeed the two-byte prefix. But lock is F0, and it's unique.

Sometimes Intel re-uses the prefixes for other things eg "rep nop", but I 
don't think that has ever happened for the lock prefix. 

Besides, the instructions look very different internally in the CPU after 
decoding, and anyway you'd not want to ignore the lock prefix _early_ at 
decode time anyway (many instructions turn into illegal instructions with 
a lock prefix, as do reg-reg modrm bytes). So you'd dismiss the lock 
prefix not at a byte level, but at a minimum just after the decode stage.

		Linus
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