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Re: Bugs and tasks for 2.02[~rc1]


From: Matt Fleming
Subject: Re: Bugs and tasks for 2.02[~rc1]
Date: Wed, 9 Mar 2016 15:18:24 +0000
User-agent: Mutt/1.5.24+41 (02bc14ed1569) (2015-08-30)

On Tue, 08 Mar, at 07:57:35AM, Andrei Borzenkov wrote:
> >> - 64-bit kernel on 32-bit platform like Baytrail can't work
> 
> Do you mean "32 bit EFI"? If yes, why is it a problem?

The biggest issue is that there's no way right now for a boot loader
to tell the kernel that it needs to use a translation layer when
calling EFI services (we refer to this as the "thunk" layer in the
kernel) without going via the EFI handover protocol.

Obviously this could be achieved by writing the required code for GRUB
but it would be largely duplicated from the existing code EFI boot
stub code in the kernel. I don't think it's worth the effort.

The kernel figures out when to use the thunk layer by taking note of
which EFI handover offset entry point the boot loader entered from, we
include both a 32-bit and 64-bit entry point when CONFIG_EFI_MIXED is
enabled.



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