Re: multiboot2: variable data size

[Yoshinori K. Okuji]

On Saturday 25 November 2006 05:08, Hollis Blanchard wrote:
> OK, I don't have a problem with this. We should clarify the spec.
> It will limit e.g. module sizes and addresses to less than 4GB, but
> practically speaking I don't think that is too big a deal.

I agree, although I don't know what will happen in the future. ;)

> However, there are 32-bit architectures that support 36-bit addressing
> (PowerPC is one of them). In some cases, physical IO is above 4GB, so
> some other data structure would be required to identify those devices.
> So we must remember that multiboot will not be adequate to describe an
> entire system like the Open Firmware device tree does.

I am afraid that you misunderstand the meaning of the addressing size in the 
Multiboot Spec. It only means how a boot loader should inspect memory-related 
values. For instance, the addresses in a Multiboot header. You can still pass 
arbitrary size of values in Multiboot information, regardless of 32-bit or 
64-bit.

> Do we really need x86_64-pc's "bit 17", which specifies that 64-bit
> addresses are required?

I don't know, for x86_64. The idea is to pass something "natural". My 
assumption was that, if an image is ELF64, the user wants to use 64-bit 
pointers, even if real addresses never be over 4GB. Someone who has 
experience should tell us.

Okuji