Re: Using SYSCALL/SYSRET with a minios kernel

[Goswin von Brederlow <goswin-v-b@web.de>]

Daniel Stodden <stodden@cs.tum.edu> writes:

> Hi.
>
> On Mon, 2008-02-25 at 00:22 +0100, Goswin von Brederlow wrote: 
>> Hi,
>> 
>> I'm trying to use the SYSCALL/SYSRET opcodes with a minios kernel
>> without much success.
>...
> The PV interface simply does not support STAR/LSTAR. It's that
> simple. :) I suppose you want to implement system calls? Check the
> HYPERVISOR_set_callbacks() call. The syscall_address parameter presently
> remains entirely unused in mini-os. But as far as I could tell
> immediately from the source, syscall/sysret appears to be supported by
> the general callback mechanism the same way sysenter/sysleave presently
> is.
>
> regards,
> daniel

Ok, here is what I did for the callbacks:

--- x86_64.S ---
ENTRY(syscall_callback)
	int $80
	zeroentry do_syscall

--- kernel.c ---
  HYPERVISOR_set_callbacks((unsigned long)hypervisor_callback,
			   (unsigned long)failsafe_callback,
			   (unsigned long)syscall_callback);

  __asm__ __volatile__("syscall");

If I understood you right that should set the RIP to syscall_callback
and execute from there. But still, the syscall opcode does nothing.
In case you wonder. The "int $80" is there to crash the domain and
tell me it reached that point.

MfG
        Goswin