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Re: [RFC] 64-bit boot protocol for Linux x86

From: Wei Zhang
Subject: Re: [RFC] 64-bit boot protocol for Linux x86
Date: Tue, 24 May 2022 23:56:12 +0800

I already have a working code, and I did three things:
1, Using xloadflags (linux boot protocol 2.12+) to determine whether
it's a 64-bit kernel.
2, Setting up an identity mapped page table for the 64-bit kernel.
3, Using grub_relocator64_boot instead of grub_relocator32_boot to boot.

The main concern here may be that the page table will take up 6 pages,
24KB, and I allocated the space right after the protected kernel. On
most systems 24KB is not an issue, but I'm not one hundred percent

Wei Zhang

On Sun, May 22, 2022 at 11:56 AM Wei Zhang <> wrote:
> Hi guys,
> If I understand the Linux boot correctly, GRUB 2 will drop Linux in a 32-bit 
> protected mode,
> using the Linux 32-bit boot protocol.
> Since Linux has a 64-bit boot protocol, I'm thinking that we can make use of 
> that. On x86_64
> target, if we can make use of 64-bit boot protocol, we'll drop Linux in long 
> mode directly, thus
> less code executed in the GRUB side, and less code in Linux side.
> Obviously it's cleaner to just use 32-bit protocol to boot both i386 and 
> x86_64 kernel, but this
> will not add much complexity.
> Just new to this mailing list, am I missing anything?
> Wei Zhang
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> Grub-devel mailing list

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