Re: memory for exception vectors

[Jun Sun <jsun@mvista.com>]

On Tue, May 13, 2003 at 10:51:45AM +0100, Ladislav Michl wrote:
> On Mon, May 12, 2003 at 10:44:08AM -0700, Jun Sun wrote:
> > On Mon, May 12, 2003 at 11:56:41AM +0100, Ladislav Michl wrote:
> > > Could anyone tell me where is space for exception vectors reserved? Many boards
> > > (for example Alchemy Pb1000, Galileo EV96100 or Galileo EV64120A) simply
> > > registers all available RAM with add_memory_region call, but I didn't find code
> > > which reserves first 0x200 (on most CPUs) for exceptions vectors anywhere. I'd
> > > guess there is something obvious what I'm missing. Can you help me to see it?
> > 
> > Kernel only uses memory after the end of kernel image.  In that sense, all
> > memory before LOADADDR (see arch/mips/Makefile) is reserved.
> 
> I'm afraid, I didn't find any code which does what you're describing here.
> But in arch/mips/mm/init.c is function setup_zero_pages which allocates
> first (or first eight if CPU has VCE) page(s). Does it do the trick?
>

Now you are really pushing me. :)

I figured that out a while back.  I think you can find answers in
arch/mips/kernel/setup.c, 

	start_pfn = PFN_UP(__pa(&_end));

I think zero pages are allocated so that all future read-only zero-filled
pages can be mapped to them.  They are allocated at the beginning of
start_pfn, which is also after kernel image.

Jun