Re: Grub-devel Digest, Vol 33, Issue 19

[Joe Bonasera <joe.bonasera@sun.com>]

grub-devel-request@gnu.org wrote:

>>
>> Just to be clear. For grub2 on x86, will it be true that there is only
>> a single grub2 binary that understands both elf32 and elf64?
> 
> Yes.
> 
>> Would the different tags i86-pc vs x86_64 (if any) be determined by
>> knowing if which type elf gets loaded?
> 
> My personal opinion is that we should not pass any information to the
> kernel about what format it is provided in.  

I agree about that, the OS should intrinsically know it's own format. :)

However, it shouldn't have to figure out what format the data passed
to it from the boot loader is in. If I boot a 32 bit kernel on a
64 bit capable platform/boot loader, the 32 bit kernel shouldn't have to
deal with figuring out if it's getting 32 or 64 bit information from
the boot loader.

I think it's pretty common for people to install both 32 and 64 bit
OS mixes on a single box. (I'm composing this on a machine that can
boot either 32 bit windows, 32 bit Suse, 64bit Fedora, 32 or 64 bit
Solaris partitions) all from one copy of grub and one copy of menu.lst.

> 
> If the image is an ELF64, it will be loaded as an ELF64.  So in your
> case, for x86_64 hosts, provide the kernel as an ELF64 image.  For
> IA-32, provide an ELF32 image.

Requiring that would be a big restriction from grub 0.9x, where the multiboot
info passed to the booted OS is always in a fixed 32 bit format. Making that information
(the "Multiboot Information Format" section of http://grub.enbug.org/MultibootDraft)
variant based hardware capability would greatly complicate the OS side of things.
Specifically a 32 bit OS would have to be able to decode both 32 and 64 bit
versions of the data. Yuck. If grub2 really needs to make the
format/content variant, I would much rather see it vary based on the
target OS type. Or better yet, just always use the larger size data types/content -
even for 32 bit booting.

Joe

> 
> ~j
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> End of Grub-devel Digest, Vol 33, Issue 19
> ******************************************