[coreboot] Returning control to v3 from the payload

[Stefan Reinauer]

Peter Stuge wrote:
> On Mon, Mar 17, 2008 at 12:46:36AM +0100, Stefan Reinauer wrote:
>   
>> Returning only for the matter of loading the next payload. We will
>> need multiple payloads in the future for many things.
>>
>> In fact, we do have that technology already. Our first payload is
>> "stage2"
>>     
>
> Mh, yes and no. It comes back to definition of what state can be
> expected.
>   
This can only work if all payloads except the last one are 
"well-behaving". Nobody would expect to run any arbitrary payload, ie an 
OS, except for the very last payload that never returns.
>>> The way I could like it is if it's all done by a separate payload,
>>> that sets up an environment and can run many other programs.
>>>
>>> I don't like coreboot doing it.
>>>
>>> Think kernel vs /sbin/init
>>>       
>> /sbin/init is slow and bloated. ;-) My first thought.
>>     
>
> The point is that it can be replaced with runit or svscan without
> kernel modifications.
I think what we need is more comparable to the process scheduler (yes, 
that can be exchanged, too).
It kind of belongs into the kernel, even though one could think of a 
much simpler solution if the plan is to run only a single process 
anyways (like an mp3 player or a motor control application)

We have a mechanism to jump into "payloads" and return from them already 
-- and I think we should be careful to make sure this works for many 
more such payloads not only "stage2". Plugging another layer will not 
make things easier and gain us almost nothing, because we carry the 
mechanism to do so anyways.

But before we're getting philosophic -- is there any estimate why 
returning from a well-behaving blob can't work? It doesn't need to do 
much except jump to the address noted on the very bottom of the stack, 
does it?

Stefan

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