Re: [patch] SMP alternatives

From: Linus Torvalds
Date: Wed Nov 23 2005 - 14:03:30 EST

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.

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