Re: [PATCH] per-cpu areas for 2.5.3-pre6

Rusty Russell (rusty@rustcorp.com.au)
Thu, 31 Jan 2002 09:45:45 +1100


In message <20020130002204.A4480@are.twiddle.net> you write:
> Have we already forgotten the ppc reloc flamefest? Better
> written as
>
> #define per_cpu(var, cpu) \
> ({ __typeof__(&(var)) __ptr; \
> __asm__ ("" : "=g"(__ptr) \
> : "0"((void *)&(var) + per_cpu_offset(cpu))); \
> *__ptr; })

"better". Believe me, I was fully aware, but I refuse to write such
crap unless *proven* to be required.

> > +/* Created by linker magic */
> > +extern char __per_cpu_start, __per_cpu_end;
> [...]
> > + per_cpu_size = ((&__per_cpu_end - &__per_cpu_start) + PAGE_SIZE-1)
>
> Will fail on targets (e.g. alpha and mips) that have a notion of a
> "small data area" that can be addressed with special relocs.
>
> Better written as
>
> extern char __per_cpu_start[], __per_cpu_end[];
> per_cpu_size = (__per_cpu_end - __per_cpu_start) ...

I agree that this is much better. But do not understand what small
relocs have to do with simple address arithmetic? You've always been
right before: what am I missing?

Rusty.

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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