Messages in this thread | | | Date | Tue, 04 Oct 2011 09:30:01 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out |
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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.
The current recommendation when you don't know the CPU you're running at is:
3E 8D 74 26 00 (GENERIC_NOP5_ATOMIC)
... on 32 bits and ...
0F 1F 44 00 00 (P6_NOP5_ATOMIC)
... on 64 bits.
-hpa
-- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf.
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