linux-kernel - Re: [PATCH v2 03/16] x86/compressed: efi-mixed: move bootargs parsing out of 32-bit startup code

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Message-ID: <Yz/xwv1HVRV6Ff43@zn.tnic>
Date:   Fri, 7 Oct 2022 11:30:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Michael Roth <michael.roth@....com>
Subject: Re: [PATCH v2 03/16] x86/compressed: efi-mixed: move bootargs
 parsing out of 32-bit startup code

On Thu, Oct 06, 2022 at 01:29:55PM +0200, Ard Biesheuvel wrote:
> Documentation/x86/boot.rst has a section on this (at the end),

Ah, and I really like that NOTE at the end.

> but we should really stop using it. It is only implemented by
> out-of-tree GRUB at the moment (last time I checked) and leaking all
> those struct bootparams specific details into every bootloader is not
> great, especially the ones that intend to be generic and boot any EFI
> OS on any EFI arch.

I'm all for making early asm code simpler so yes, can we start removing
it?

Dunno, maybe ifdef around it with a Kconfig option which is default off
and see who complains...

> That is the same thing. The EFI stub is what enables the kernel (or
> decompressor) to masquerade as a PE/COFF executable.
> 
> In short, every EFI stub kernel on every architecture has a native
> PE/COFF entry point that calls the EFI stub, and the EFi stub does the
> arch-specific bootloader work and boots it.

Right.

> In addition, the x86_64 EFI stub kernel has an extra, non-native
> PE/COFF entry point, which is exposed in a way that is not covered by
> the EFI spec, but which allows Linux specific loaders such as
> systemd-boot to boot such kernels on 32-bit firmware without having to
> do the whole struct bootparams dance in the bootloader.

Ok, thanks for explaining.

I like the simplification and obviating the need for the bootloader to
do any dancing before loading the kernel.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette