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

    Out of correctness, we should still update this to use the proper
    "default" nops, as mcount already does.

    -- Steve




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