Re: multiboot2: variable data size

["bibo,mao" <bibo.mao@intel.com>]

Yoshinori K. Okuji wrote:
> On Tuesday 28 November 2006 10:29, Johan Rydberg wrote:
>  > "Yoshinori K. Okuji" <okuji@enbug.org> writes:
>  > > On Saturday 25 November 2006 04:33, Hollis Blanchard wrote:
>  > >> That's exactly the point: there will be no difference. Both
>  > >> architectures will use 64-bit types.
>  > >
>  > > No. Both should use 32-bit, because GRUB transfers control in 32-bit
>  > > mode. Passing 64-bit addresses would be useless in this case. Note that
>  > > the memory map information is 64-bit even in the previous version of
>  > > Multiboot Spec.
>  >
>  > That will not be true for x86_64-efi, which will have to run in long
>  > mode.
> 
> Oh, sorry. I meant "x86_64-pc" in the previous message. I just omitted "pc".
> When the firmware is different, it is feasible to make a different spec,
> but...
> 
> But is it true that EFI starts with 64-bit mode? Where is it defined? In UEFI?
> Could you give me a pointer?
> 
yes, x84_64EFI starts with 64-bit long mode and page enabled(virtual address
equals physical address) if it is x86_64 efi bios, it is defined in 
section 2.3.4 of UEFI Specification Version 2.0.

If kernel image is bzImage, x64 efi bootloader need switch to 32 bit protect
mode(or real mode) from 64 bit long mode, and if kernel image is gzipped/plain
format, efi bootloader can directly jump to 64-bit kernel entry address without
mode switch.

thanks
bibo,mao