[Q] GRUB -> __start_xen?

[Q] GRUB -> __start_xen?

[Bharadwaj Yadavalli]

I am trying to understand the internals of Xen.

On x86 (and may be other architectures), it appears to me 
that xen's entry point is 

         void __init __start_xen(multiboot_info_t *mbi)

that lives in xeno-unstable.bk/xen/arch/x86/setup.c.

1. Who builds the structure mbi and calls __start_xen?
2. How is __satrt_xen registered as the entry point?

Is there a place that I can read to understand the transfer
of control from multiboot GRUB to xen's entry point?

Thanks,

Bharadwaj

Re: [Q] GRUB -> __start_xen?

[Chris Wright]

* Bharadwaj Yadavalli (bharadwaj.yadavalli@hp.com) wrote:
> On x86 (and may be other architectures), it appears to me 
> that xen's entry point is 
> 
>          void __init __start_xen(multiboot_info_t *mbi)

I believe it is actually 'start' in arch/x86/boot/x86_32.S, for
example.  At least, that's the elf entry point which does low-level
setup before calling __start_xen.  In there you should find the layout
of the multiboot header that grub requires.

> that lives in xeno-unstable.bk/xen/arch/x86/setup.c.
> 
> 1. Who builds the structure mbi and calls __start_xen?

The boot loader, and then stashes it in specified register (ebx in this
case).

> 2. How is __satrt_xen registered as the entry point?

start is the elf entry point.

> Is there a place that I can read to understand the transfer
> of control from multiboot GRUB to xen's entry point?

For more info on multiboot, read:
http://www.gnu.org/software/grub/manual/multiboot/

thanks,
-chris

Re: [Q] GRUB -> __start_xen?

[Carl Holtje ;021;vcsg6;]

On Fri, 24 Jun 2005, Bharadwaj Yadavalli wrote:

> I am trying to understand the internals of Xen.
>
> On x86 (and may be other architectures), it appears to me
> that xen's entry point is
>
>          void __init __start_xen(multiboot_info_t *mbi)
>
> that lives in xeno-unstable.bk/xen/arch/x86/setup.c.
>
> 1. Who builds the structure mbi and calls __start_xen?

See xen/arch/x86/boot/x86_32.S .. __start_xen is called from there, with
the multiboot info..

It is at this point that assembler becomes C code, and everything is
easier to debug. :)

> 2. How is __satrt_xen registered as the entry point?

__start_xen is not the "real" entry point; instead it's the ENTRY(start)
line in xen/arch/x86/boot/x86_32.S

Carl

- --

"There are 10 types of people in the world: Those who understand binary
and those that don't."

Re: [Q] GRUB -> __start_xen?

[Josh Triplett]

On Fri, 2005-06-24 at 14:25 -0400, Bharadwaj Yadavalli wrote:
> I am trying to understand the internals of Xen.
> 
> On x86 (and may be other architectures), it appears to me 
> that xen's entry point is 
> 
>          void __init __start_xen(multiboot_info_t *mbi)
> 
> that lives in xeno-unstable.bk/xen/arch/x86/setup.c.
> 
> 1. Who builds the structure mbi and calls __start_xen?

The Grub bootloader creates the structure, and calls a Xen startup
function defined in xen/arch/x86/boot/x86_32.S .  That assembly code
does some minimal setup and then calls the C startup function, passing
the structure pointer.

> 2. How is __satrt_xen registered as the entry point?

The Xen image booted by GRUB has a well-specified format which includes
the location of the entry point.

> Is there a place that I can read to understand the transfer
> of control from multiboot GRUB to xen's entry point?

http://www.gnu.org/software/grub/manual/multiboot/multiboot.html

- Josh Triplett