Re: [Etherboot-developers] PXELINUX on top of Etherboot?

[<ebi...@ln...>]

"H. Peter Anvin" <hp...@zy...> writes:

> Eric W. Biederman wrote:

> True, although SYSLINUX deals with this by always loading high, and if the image
> 
> is a zImage it copies it to low memory immediately before invoking the kernel.

A nice twist.  

> >>MEMDISK (because I wanted to write the MEMDISK installer in C), as well as in
> >>the never-completed Genesis project... so I'm familar with the
> >>concept :)
> > I still chuckle at the COM32 concept as it looks like going quite a
> > ways to avoid 300 bytes of overhead for an ELF header...  Though I can
> > see how it can be useful if space is at a very high premium.
> >
> 
> Remember, the SYSLINUX program itself needs to fit on floppies and take minimum
> amounts of space.  It's 7828 bytes in size at the moment, and the COM32 loader
> is just "load this file into memory at this address" --
> 
> no parsing whatsoever.

Except when I implement sanity checks there is no parsing with ELF
headers either, the structures area all native endian, and wordsize.
The difference is load this chunk into memory at this address, and
load these other chunks into memory at these other addresses, and
finally jump there. 

I get some real portability and prototyping benefits because it is
a standard file format.  But when space is at an absolute premium
those aren't the most important things.  

I do see the point of COM32, even if it does not make much sense when
you have a few more bytes available, in the circumstances I care about.

> > Well we will see how it goes.
> > Currently I am busy porting LinuxBIOS to the Opteron so I won't be able to get
> 
> > at very much stuff for a while.
> >
> 
> Why not just run a 32-bit LinuxBIOS on Opteron?  Or do you mean to the K8 memory
> controller and stuff?

Mostly the K8 memory controller.  I guess a better description would
be the K8 chipset :)  The extra registers are a very compelling reason
to go 64bit before the memory controller is initialized though.  For
the most part with LinuxBIOS it does not matter as the code is in C
anyway.

> > Though once it works it should be possible to test the code by pxe booting
> > etherboot :)
> >
> 
> Gotta love recursion...

Especially when there is proper tail recursion.  :)

I already use that test path with ELF images.  And if the recursion
stops before I tell it to I know there is something wrong!

And it already exist with the mknbi format as well.

Eric