Re: [Xen-devel] loading IDT in xen?

To:	"Jun Koi" <junkoi2004@xxxxxxxxx>
Subject:	Re: [Xen-devel] loading IDT in xen?
From:	"余上" <yusunn@xxxxxxxxx>
Date:	Thu, 31 Jan 2008 15:57:34 +0800
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
Delivery-date:	Wed, 30 Jan 2008 23:57:58 -0800
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I think maybe it is just some kind of coding style ? Or necessary for
CPU state transition ?

2008/1/31, Jun Koi <junkoi2004@xxxxxxxxx>:
> On 1/31/08, 余上 <yusunn@xxxxxxxxx> wrote:
> > There is another IDTR reload in x86_32.S at line 15 , where the
> > protected mode IDT vectors are initialized with ignore_int handler
> > firstly. Then trap_init called from __xen_start will setup the formal
> > IDT vectors .
>
> Now I see that. But the the question is: why we have to setup a
> "dummy" IDT in trampoline.S like that???
>
> Thanks,
> Jun
>
>
> >
> > 2008/1/31, Jun Koi <junkoi2004@xxxxxxxxx>:
> > > I am looking at the hypervisor code to see how Xen setup the IDT. But
> > > it seems that the code in protected mode reuses the real mode IDT?
> > >
> > > In arch/x86/boot/trampoline.S we have at several places:
> > >
> > > lidt bootsym(idt_48)
> > >
> > > And idt_48 is defined as:
> > >
> > > idt_48: .word 0,0,0 # base = limit = 0
> > >
> > > And in nowhere we initialize idt_48, which means idt_48 reuses real
> > > mode IDT table. However, real mode IDT table has different format than
> > > protected mode IDT, so this doesnt look to work for me.
> > >
> > > Definitely I miss something here. Anybody could enlighten me how IDT
> > > setting in protected mode work?
> > >
> > > Thanks,
> > > Jun
> > >
>

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