[PATCH 7/11] powerpc: Fixups for kernel linked at 32 MB

[Michael Ellerman]

On Tue, 6 Dec 2005 20:57, Paul Mackerras wrote:
> Michael Ellerman writes:
> > There's a few places where we need to fix things up for the kernel to
> > work if it's linked at 32MB:
> >
> >  - platforms/powermac/smp.c
> >    To start secondary cpus on pmac we patch the reset vector, which is
> > fine. Except if we're above 32MB we don't have enough bits for an
> > absolute branch, it needs to relative.
>
> A relative branch at 0x100 is only going to get 0x100 bytes further
> than an absolute branch, and I don't think that's far enough.

Except we're patching at KERNELBASE + 0x100, so as long as 
__secondary_start_pmac_0 - KERNELBASE < 32 MB we should be fine.

> Did you consider putting the kdump kernel at 24MB rather than 32MB?
> That would solve this and other branch issues.

No I didn't, but a few people have mentioned it since. I think it's something 
we could look at - but I'd rather not change it now. The only other "branch 
issue" I know of is having to use a no-op in the trampoline, is there 
anything else?

cheers

-- 
Michael Ellerman
IBM OzLabs

email: michael:ellerman.id.au
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We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person
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