[parisc-linux] depi?

Alan Cox alan@lxorguk.ukuu.org.uk
Tue, 16 Nov 1999 12:20:32 +0000 (GMT)

> If I understood correctly, the kernel is located there because it is where it
> is on PC.

Thats why someone pulled that number out of a hat. You can pull any other
page aligned number out of a hat and that will be fine too.

> Sounds like linux is not more portable than any other propriaitary OS since
> confined to PC architecture, a port beeing a mimic of PC if the target arch
> can do it.

Check the mm code. We don't care where you put the kernel. The rules we go
by are simple

1.	The kernel must be able to access all of the current tasks user space
	efficiently. This is done via macros/functions/inlines

2.	The kernel must be able to access all physical ram and also
	mappings of MMIO space. The mappings can be 1:1 - for example on the
	ultrasparc we use the override bits for this. I/O space maps are
	accessed via macros/functions. If those functions resolve to no
	actual extra code this is good.

3.	Access to other tasks virtual address space has to be possible. It can
	be slow and suck however as its main use is ptrace().

The mappings we use vary. M68K for example maps the kernel about 3.5Gig up
and uses space registers to access user space. The x86 because of the weak
page table flipping facilities keeps both user and kernel in a single map. That
makes for nice fast x86 code. That is x86 specific.


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On Mon, 8 Mar 1999, Erik Paulson wrote:
> 	Maybe I just missed it, but is the source for the bootloader out 
> there anywhere? I'd like to start looking at the code....

I'll be releasing the source for the bootloader today.

- Alex

Alex deVries <puffin@redhat.com>     
Red Hat Contrib Net maintainer          
Ottawa, Canada  
HPPA/Linux Porting Team

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