Re: [Xen-devel] x86_64 to i386 boot generation conversion

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Jan 22, 2019 at 10:43:11AM +0100, nicolas.poirot@xxxxxxxxx wrote:
> Hi everyone,
> 
> I was wondering why when I build an x86_64 xen I got a mkelf32 command 
> converting elf 64 to elf 32.
> My understanding, looking at git-log, is that that was needed for 32bits 
> bootloaders.
> 
> Is that the only reason ? Is it still necessary today ?

The original multiboot specification [0] only deals with 32bit
addresses, so the elf headers need to be 32 bits for multiboot to be
able to load it. The more that the kernel is started in protected
mode, so addresses must be below the 4G boundary or else loading or
jumping into the entry point would fail.

Roger.

[0] https://www.gnu.org/software/grub/manual/multiboot/multiboot.html

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