Re: Grub2: add UEFI support for accessing memory address above 4GB.

[Leif Lindholm]

On Tue, Mar 07, 2017 at 01:55:01AM +0000, Yufuping wrote:
> Who can add the new feature for grub2:
> Add UEFI support for accessing memory address above 4GB.

Presumably you mean for x86_64?
Since GRUB supports all 5 architectures currently supported by the
UEFI specification, 3 of which are 64-bit, it is useful to be a bit
more precise.

> When using grub2 as PXE downloading engine, grub2 can get initrd
> file from network and put it to memory above 4GB.

I can think of nothing particularly related to PXE here.
The x86_64 port currently sets GRUB_EFI_MAX_USABLE_ADDRESS to
0xffffffff or 0x7fffffff, depending on toolchain configuration.

ARM64 sets it to 0xffffffffffffULL, and that works fine.

I seem to recall that the x86_64 port was being restricted due to
known bad firmware encountered in the past. It could be that it would
be worth adding an option to configure for enabling access to higher
addresses, alternatively for retaining compatibility with the broken
systems.

> The feature should support UEFI BIOS boot mode.

I do not understand this statement.

/
    Leif