Re: [PATCH] efi: Clarify Kconfig help for EFI_MIXED

From: H. Peter Anvin
Date: Fri Apr 11 2014 - 14:03:40 EST


On 04/11/2014 10:59 AM, Thomas Bächler wrote:
> EFI stub support is only missing for a 64 bit kernel on 32-bit firmware,
> on 64-bit kernels, EFI stub works as usual.
> ---
>
> Matt, I don't know if this help was intentionally discouraging,
> however, out of curiosity, I tested this with ovmf, and the
> kernel boots fine on 64-bit firmware bit with EFI stub, and on
> 32-bit firmware using efilinux.
>
> Documenting this properly is important for distribution kernels.
> We would want to support this on Arch, but not if it means
> introducing a regression for EFI stub users.
>
> arch/x86/Kconfig | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5b8ec0f..2bbbbb9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1529,8 +1529,8 @@ config EFI_MIXED
> mode.
>
> Note that it is not possible to boot a mixed-mode enabled
> - kernel via the EFI boot stub - a bootloader that supports
> - the EFI handover protocol must be used.
> + kernel via the EFI boot stub on 32-bit firmware - a bootloader
> + that supports the EFI handover protocol must be used.
>
> If unsure, say N.
>

Right, it is really that it is not possible to boot a mixed-mode kernel
on its non-native firmware using the stub, since the stub itself can
only be one way or the other.

-hpa


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