Re: Q: Linux rebooting directly into linux.

[ebiederm@xmission.com (Eric W. Biederman)]

Erik Andersen <andersen@codepoet.org> writes:

> On Thu Nov 09, 2000 at 01:18:24AM -0700, Eric W. Biederman wrote:
> > 
> > I have recently developed a patch that allows linux to directly boot
> > into another linux kernel.  
> 
> Looks very cool.  I'm curious about your decision to use ELF images.  This
> makes it much less conveinient to use due to the kernel postprocessing, and
> makes it that the kernel binary from which you initially boot is not
> necessirily the same as the binary that you re-boot into.  

The decision here was that I needed to pass a vector of 
<physical address, length, data> pairs.  The elf program header
is dead simple and provides it.  So I either had to invent a
complicated argument passing mechanism for a syscall or have the
kernel parse a file.

> Wouldn't it be more reasonable to simply try to exec whatever file is provided?
> If the concern is initrds; they can be simply pasted into the kernel binary.

That's exactly what my preprocessing does. 

vmlinux is also an elf binary.  As is arch/i386/boot/bvmlinux but it
is compressed.

All mkelfImage does is the pasting of initrd's, command lines,
and just a touch of argument conversion code.

What I don't do deliberately is allow or need setup.S which does
syscalls to run.  All it does are BIOS calls, and store them in a
nasty data structure.  I have replaced that data structure with 
something that is maintainable.  

I would like very much to not need mkelfImage.  However that
requires further changes to the kernel, and I cannot boot an unpatched
kernel with that method.  

Eric
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