Re: [PATCH RFC V2 3/5] jump_label: if a key has already beeninitialized, don't nop it out
From: Steven Rostedt
Date: Tue Oct 04 2011 - 14:05:54 EST
On Tue, 2011-10-04 at 13:53 -0400, Jason Baron wrote:
> On Tue, Oct 04, 2011 at 09:30:01AM -0700, 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.
> > 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
> We're currently patching the code at run-time (boot and module load
> time), with the 'ideal' no-op anyway, so the initial no-op doesn't
> really matter much (other than to save patching if the initial and ideal
Out of correctness, we should still update this to use the proper
"default" nops, as mcount already does.
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