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Re: [PATCH v2 1/2] x86: Add support for building a multiboot2 PE binary
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 17 Apr 2024 16:14:59 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 17 Apr 2024 14:15:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10.04.2024 11:41, Ross Lagerwall wrote:
> On Mon, Apr 8, 2024 at 11:25 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 28.03.2024 16:11, Ross Lagerwall wrote:
>>> * The image base address is set to 0 since it must necessarily be below
>>> 4 GiB and the loader will relocate it anyway.
>>
>> While technically okay, what is the reason for this adjustment?
>
> The multiboot2 spec generally uses 32 bit addresses for everything and
> says:
>
> "The bootloader must not load any part of the kernel, the modules, the
> Multiboot2 information structure, etc. higher than 4 GiB - 1."
>
> An image base address above 4 GiB causes trouble because multiboot2
> wasn't designed for this.
Yet mb2 doesn't care about that PE header field at all, does it? In which
case my question remains: What purpose does this particular modification
of the image have?
Jan
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