This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] RFC/Patch: Support for other bootloaders

On Wed, 2005-03-23 at 16:23 +0000, Tim Deegan wrote:
> On Wed, Mar 23, 2005 at 03:52:32PM -0000, Ian Pratt wrote:
> > [*] would it possible to do something whereby the vmlinuz and initrd
> > image were simply cat'ed together? This might swing the balance the
> > other way from a userbility POV, not sure.
> It should be.  xen-vmlinux is an ELF, so if we can be *sure* that the
> largest file offset in an ELF header is the same as the size of the
> file, then it would be possible to just do
>  $ cat vmlinux-xen0 initrd-xen0 >pseudo-initrd
>  boot: xen pseudo-initrd.
> and then have Xen root around in the ELF headers to see where the break
> is.

Sure, you could do that.  You could also define, in Linux, two symbols
"initrd_start", "initrd_end".

Then, use objcopy to insert a ramdisk in between the two.  It's not
"cat", but you can just create a wrapper shell script around the

Linux then checks to see if the two symbols point to the same spot; if
they don't it's got a ramdisk embedded in it.

What you can actually do is this:

1.  Take a vmlinux and "load" it into a file (use objcopy to output
binary format).  Remember the entry point address!! (Entry point
instructions should be at the start of the file.)

2.  With a magic linker script, take the vmlinux.bin and initrd and
create a single ELF file, which contains two "LOAD" segments.

3.  A proper ELF loader will then load those two segments into memory.

Essentially, what I'm saying is that you can use ELF as the format for
the "meta-ramdisk".

> Suporting gzipped vmlinux should be possible too; Xen needs to unzip the
> kernel and then knows that the next byte after the gzipped input will be
> ramdisk.  (As long as the bootloader doesn't helfully unzip the
> 'ramdisk' for us.)

Linux should be able to unzip the ramdisk itself.  I thought it could
already do that.

> Michal, what do you think?  It sounds like this could be added to your
> code without too much horror.

Sure,  but I thought the direction we're going in is to use you wrapper
around the Xen binary.  If that's the case then I don't see much further
use for my code.  

Michal Ostrowski <mostrows@xxxxxxxxxxxxxx>

Attachment: signature.asc
Description: This is a digitally signed message part