How to invoke hypercalls

[antoinet <xen@schoggi.org>]

Hello,
I am a computer science student and my assignment is porting an OS 
(pintos, http://www.stanford.edu/class/cs140/) as an unpriviledged Domain.
I'm trying to invoke hypercalls as described in 
http://www-user.tu-chemnitz.de/~mien/materialien/sys/04-Hypercalls.pdf 
or http://www.o3one.org/xen.html#posp1 by using int 0x82:

------------------------------------------------------------------------

.section __xen_guest
         .ascii  "GUEST_OS=Mini-OS"
         .ascii  ",XEN_VER=xen-3.0"
         .ascii  ",HYPERCALL_PAGE=0x2"
         .ascii  ",LOADER=generic"
         .ascii  ",PT_MODE_WRITABLE"
         .byte   0

	.text

	.globl	_start
_start:
	cld

	movl	$18, %eax			# __Hypervisor_console_io
	movl	$0, %ebx			# CONSOLEIO_write
	movl	$hello_message_len, %ecx	# buffer length
	movl	$hello_message, %edx		# buffer virtual address
	int 	$0x82

	movl	$6, %eax			# __Hypervisor_sched_op_compat
	movl	$2, %ebx			# SCHEDOP_shutdown
	movl	$0, %ecx			# SHUTDOWN_poweroff
	int	$0x82

hang:	jmp 	hang				# shouldn't get here

hello_message:	.ascii	"This is the hello world program.\n"
	hello_message_len = . - hello_message

------------------------------------------------------------------------

I compile this with:

	as -o helloworld.o -a=helloworld.l helloworld.s
	ld -Ttext 0x100000 -o helloworld.elf helloworld.o

Unfortunately, i don't get any output (or better: i don't know where the 
output goes to). If I check the logs, the domain seems to shut down 
normally:

...
[2006-08-13 16:50:53 xend.XendDomainInfo] INFO (XendDomainInfo:818) 
Domain has shutdown: name=HelloWorld id=24 reason=poweroff.
...

I have also studied the mini-os in the xen source distribution 
(extras/mini-os) and I realized, that hypercalls are calls in specific 
entries of a hypercall_page. What is this page and where is it initialized?

Thanks,
Antoine