Re: [RFC 00/15] x86_64: Optimize percpu accesses

[Jeremy Fitzhardinge]

Eric W. Biederman wrote:
> But we can pick an arbitrary point where %gs points at.
>
> Hmm.  This whole thing is even sillier then I thought.
> Why can't we access per cpu vars as:
> %gs:(per_cpu__var - __per_cpu_start) ?
>   

Because there's no linker reloc for doing subtraction (or addition) of 
two symbols.

> If we can subtract constants and allow the linker to perform that resolution
> at link.  A zero based per cpu segment becomes a moot issue.
>   

They're not constants; they're symbols.

   J
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