Re: Is there a way to get the architecture of the machine just booted up by GRUB2: [32|64]-[amd|arm]? ...

[Pascal Hambourg]

On 17/12/2023 at 17:24, Albretch Mueller wrote:
> On 12/17/23, Pascal Hambourg wrote:
> > Let's assume you you create such an ISO image for UEFI boot only. It
> > must contain an EFI partition with EFI images for each firmware
> > architecture : bootarm64.efi (built for ARM64), bootx64.efi (built for
> > AMD64/x86_64) and bootriscv64.efi (built for RISC-V64). The UEFI
> > firmware will seek the matching EFI image, and the GRUB image will
> > report the architecture in $grub_cpu and $grub_platform.
> >
> > Note: bootxxx.efi may be a GRUB image or a shim image which loads
> > grubxxx.efi in turn (for secure boot).

Note 2: there have been a few lightweight PC with 32-bit UEFI firmware 
and 64-bit x86 CPU around. To boot on these you need to install an x86 
32-bit EFI image as bootia32.efi. It can boot i386 and amd64 kernels.

> All that DVD would need is an EFI
> partition with the EFI images for each firmware architecture.

Correct.

> yes, "secure boot" would be the way to go.
(...)
> Any tutorials, literature you would suggest for advanced
> users and developers?
Most of what you need is in the GRUB documentation you already have.
If you use signed shim+GRUB provided by Debian for secure boot, install 
them in /EFI/BOOT in the EFI partition, and install a grub.cfg config 
file in /EFI/debian in the same partition, which checks $grub-cpu to 
select the kernel image, for example :

if [ $grub_cpu = x86_64 ]; then
        # instructions to boot with amd64 kernel
elif [ $grub_cpu = i386 ]; then
        # instructions to boot with i386 kernel
elif [ $grub_cpu = arm64 ]; then
        # instructions to boot with arm64 kernel
elif [ $grub_cpu = riscv64 ]; then
        # instructions to boot with riscv64 kernel
fi

If you do not care about secure boot and build your own EFI images with 
grub-mkimage, you can set the prefix to a different path and install a 
different grub.cfg there for each architecture.

If you want to support legacy BIOS boot or ia32/i386 EFI boot, I do not 
know how GRUB can detect whether the CPU is 32 or 64 bits capable.