Re: [Xen-devel] [PATCH v3 06/35] OvmfPkg/XenResetVector: Add new entry point for Xen PVH

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jul 15, 2019 at 12:50:29PM +0100, Andrew Cooper wrote:
> On 15/07/2019 12:46, Roger Pau Monné wrote:
> >> +    ;
> >> +    ; Jump to the main routine of the pre-SEC code
> >> +    ; skiping the 16-bit part of the routine and
> >> +    ; into the 32-bit flat mode part
> >> +    ;
> >> +    OneTimeCallRet TransitionFromReal16To32BitFlat
> > Since PVH already starts in flat 32bit mode, I'm not sure I see the
> > point of this routine, since it seems to be used exclusively to switch
> > from 16 to 32b flat mode. The comment mentions skipping that part, but
> > I'm not sure I see how that's achieved.
> 
> Its some OVMF local magic.  This means "jmp
> end_of_TransitionFromReal16To32BitFlat", which is the correct place to
> go, but the code really is misleading to read.

Oh right, it's OneTimeCallRet. I guess this is obvious if you are
familiar with OVMF code, which I'm not. Expanding the comment to
mention that jumping to the end of the routine is achieved by using
OneTimeCallRet would have helped me, but this might be too verbose.

Thanks, Roger.

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