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Re: VW ELF loader

From: Alexey Kardashevskiy
Subject: Re: VW ELF loader
Date: Thu, 13 Feb 2020 12:43:12 +1100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0

On 10/02/2020 11:31, Alexey Kardashevskiy wrote:
> On 07/02/2020 10:46, Paolo Bonzini wrote:
>> On 07/02/20 00:23, Alexey Kardashevskiy wrote:
>>>> Right, not unlike what you get with vof=on. :)  I'm not against at all
>>>> that idea.  I just don't understand what you refer to below as (2).
>>>> Does petitboot not have the problem because it kexecs the new kernel?
>>> Petitboot does not have this problem *if* it runs without SLOF, i.e.
>>> directly via -kernel and -initrd and uses OF CI (cut down version, about
>>> v3-v4 of my patchset, without block devices and grub lookup). In this
>>> case there is one device tree instance, fully synchronized with the
>>> machine state.
>>> If there is still SLOF and (2) is happening, then petitboot is screwed
>>> as any other kernel.
>> Ok, so "minimal pseudo-OpenFirmware in QEMU" is doable and can get
>> everything right;
> I am not convinced that ditching drivers is not right; I am moving elf +
> mbr + gpt + grub loading to the guest though so 20 bytes blob becomes
> FDT-less firmmare, a few kbytes big.

Ok. So, I have made a small firmware which does OF CI, loads GRUB and
instantiates RTAS:
Quite raw but gives the idea.

It does not contain drivers and still relies on QEMU to hook an OF path
to a backend. Is this a showstopper and without drivers it is no go? Thanks,

>> it's just work to set up PCI and do all that other
>> do_driver_stuff(), so you can either do it yourself or use
>> Linux+petitboot.  Is this correct?
> Except using the "just" word, yes, correct ;)
>> Also, can a normal distro kernel run via -kernel/-initrd + the minimal
>> firmware in QEMU?
> Yes.


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