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

[David Anders]

Darren

On 09/09/2014 12:13 PM, Darren Hart wrote:
> 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.
>
while this is 100% correct, the problem is that most of the 
distributions have them labelled either as "64-bit" or "32-bit" images....

Dave