[PATCH] powerpc: Separate usage of KERNELBASE and PAGE_OFFSET

[Michael Ellerman]

On Mon, 5 Dec 2005 09:35, Hollis Blanchard wrote:
> On Dec 4, 2005, at 5:07 PM, Michael Ellerman wrote:
> > This patch separates usage of KERNELBASE and PAGE_OFFSET. I haven't
> > looked at
> > any of the PPC code, if we ever want to support Kdump on PPC we'll
> > have to do
> > another audit, ditto for iSeries.
>
> (I guess you're trying to say you haven't tested 32-bit support, but
> saying "PPC" here is rather confusing...)

You're right that's not very clear. What I meant is I haven't audited any of 
the code in arch/ppc, or any of the 32-bit PPC code in arch/powerpc for usage 
of KERNELBASE vs PAGE_OFFSET. If we want kdump to work on 32-bit powerpc 
we'll need to audit that code first.

> > To get a physical address from a virtual one you subtract PAGE_OFFSET,
> > _not_
> > KERNELBASE.
> >
> > KERNELBASE is the virtual address of the start of the kernel, it's
> > often the
> > same as PAGE_OFFSET, but _might not be_.
> >
> > If you want to know something's offset from the start of the kernel
> > you should
> > subtract KERNELBASE.
>
> Could you please add these helpful comments to page.h? You might also
> mention kdump as an example, to help people understand this subtle
> distinction.

Not a bad idea. I doesn't look like paulus has merged them yet (due to my 
speeling mistakes ;), so I'll just update this patch.

cheers

-- 
Michael Ellerman
IBM OzLabs

email: michael:ellerman.id.au
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wwweb: http://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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