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] Using SYSCALL/SYSRET with a minios kernel

To: Daniel Stodden <stodden@xxxxxxxxxx>
Subject: Re: [Xen-devel] Using SYSCALL/SYSRET with a minios kernel
From: Goswin von Brederlow <goswin-v-b@xxxxxx>
Date: Mon, 25 Feb 2008 11:04:37 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Goswin von Brederlow <goswin-v-b@xxxxxx>
Delivery-date: Mon, 25 Feb 2008 02:05:01 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <1203906381.9103.24.camel@xxxxxxxxxxxxxxxxxxxx> (Daniel Stodden's message of "Mon, 25 Feb 2008 03:26:21 +0100")
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <87k5kuym6k.fsf@xxxxxx> <1203897714.9103.6.camel@xxxxxxxxxxxxxxxxxxxx> <87hcfx3ima.fsf@xxxxxx> <1203906381.9103.24.camel@xxxxxxxxxxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Gnus/5.110006 (No Gnus v0.6) XEmacs/21.4.19 (linux)
Daniel Stodden <stodden@xxxxxxxxxx> writes:

> On Mon, 2008-02-25 at 02:55 +0100, Goswin von Brederlow wrote:
>> Daniel Stodden <stodden@xxxxxxxxxx> 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.
> Mööp! Only when calling in from virtual user mode. Otherwise, you're
> triggering a hypercall service routine, and one might suspect you're
> presently just generating an error condition with that. :)

That sounds verry odd. I'm getting no indication of it from xen.

But ok. How do I test that. Or differently phrased: What is the best
way to go into user space for the verry first time? Do I really have
to create a fake stack frame and call HYPERVISOR_iret?

> BTW: I found building Xen with 'debug=y' generates a helpful comment on
> the console every now and xen.

I did that and added a patch that makes HYPERVISOR_console_io work for
domU so it shows up in "xm dmesg".

>> 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.
> hth,
> daniel


Xen-devel mailing list