Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out

H. Peter Anvin
2011-10-06T00:17:45Z

On 10/05/2011 05:16 PM, Jeremy Fitzhardinge wrote:
> On 10/04/2011 09:30 AM, H. Peter Anvin wrote:
>> On 10/04/2011 07:10 AM, Jason Baron wrote:
>>> 1) The jmp +0, is a 'safe' no-op that I know is going to initially
>>> boot for all x86. I'm not sure if there is a 5-byte nop that works on
>>> all x86 variants - but by using jmp +0, we make it much easier to debug
>>> cases where we may be using broken no-ops.
>>>
>> There are *plenty*. jmp+0 is about as pessimal as you can get.
>
> As an aside, do you know if a 2-byte unconditional jmp is any more
> efficient than 5-byte, aside from just being a smaller instruction and
> taking less icache?
>

I don't know for sure, no. I probably depends on the CPU.

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.