[MinnowBoard] 64-bit vs 32-bit UEFI - What you need to know!

[Darren Hart]

On 9/9/14, 10:03, "Hawley, John" <john.hawley at intel.com> wrote:

>So there's been a bunch of questions about 32-bit OSes on the
>MinnowBoard MAX, and a fair amount of confusion on what's going on
>there.  I've updated the wiki documentation
>
>http://www.elinux.org/Minnowboard:MaxBios#32-bit_vs._64-bit_UEFI
>
>but figured a quick discussion here would be helpful.
>
>When UEFI was designed they made a conscious and explicit design
>decision: Firmware's number of bits should match the OSes number of
>bits.  Meaning if firmware is 32-bit, the OS has to be 32-bit.  If
>firmware is 64-bit, the OS has to be 64-bit.  There's a variety of
>reasons why this decision was made, but it was made.
>
>What this means to MinnowBoard MAX users:  The short version is if you
>want to run a 64-bit OS, this entire e-mail is a no-op.  If you want to
>run a 32-bit OS, you have to jump through some hoops.
>
>If you *REALLY* want to run a 32-bit OS there's some steps you'll need
>to follow, and I've outlined them at
>
>http://www.elinux.org/Minnowboard:MaxBios#Switching_from_64-bit_to_32-bit
>
>Basically you have to re-flash the firmware with a 32-bit firmware.
>There's a line in the instructions that may confuse some folks,
>specifically using a FirmwareUpdateX64.efi to flash a 32-bit firmware.
>This is because when you go to change the firmware you are running a
>64-bit firmware, and therefore need a 64-bit EFI program to actually do
>the flashing.
>
>If you want to switch back, you'll do the opposite, use
>FirmwareUpdateIA32.efi to flash a 64-bit firmware.
>
>If I've missed something, let me know, I'd rather cover everything we
>can in our documentation.

The only thing I would point out is that instead of OS, you really mean
kernel. For example, it is perfectly valid to run a 64b firmware, 64b
Linux kernel, and a 32b Linux userspace. It's the firmware_efi <->
kernel_efi interface that has to match here.

-- 
Darren Hart					Open Source Technology Center
darren.hart at intel.com				            Intel Corporation