Messages in this thread | | | From | Andi Kleen <> | Subject | Re: broken local_t on i386 | Date | Tue, 13 Jun 2006 05:36:01 +0200 |
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On Monday 12 June 2006 21:15, Christoph Lameter wrote: > On Mon, 12 Jun 2006, Andi Kleen wrote: > > > > I thought you had some funky segment registers on i386 and x86_64. Cant > > > they be switched on context switch? If an inc/dec could work relative to > > > those then you would not need a virtual mapping. > > > > The segment register needs an offset. So you need the linker to generate > > the offset from the base of the per cpu segment somehow. At compile time the > > address is not known so it cannot be done then. > > Define something like a big struct and use offsetof?
That is how the basic architecture specific PDA works (asm/pda.h)
But i don't see a good way to define a big struct for asm/percpu.h
Preprocessing would be too slow and getting all people to put their per CPU variables into a single header also doesn't seem like a good idea.
> > So the compiler is not able to generate an offset to the beginning of a > data segment?
It's an assembler/linker issue.
-Andi (who is really surprised people make such a big deal out of two instructions)
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