Re: Question: How to build ARM32 rootfs with ARM64 Kernel

["'Jan Kiszka' via isar-users" <isar-users@googlegroups.com>]

Hi Matai-san,

On 25.12.25 09:18, Hirotaka Motai wrote:
> Hi Isar team,
> 
> I am currently considering using ISAR to build a system with the
> following architecture:
> 
> * Kernel: ARM64 (64-bit)
> * rootfs: ARM32 (32-bit)
> 
> I understand that the ISAR_ENABLE_COMPAT_ARCH option allows for the
> building of
> some 32-bit packages, but in this case, I want to build all packages as
> 32-bit.
> 
> Could you please let me know if this somewhat special configuration of
> "32-bit rootfs
> with 64-bit kernel" is supported for cross-architecture building within
> ISAR?
> If it is possible, I would greatly appreciate it if you could provide
> the specific steps,
> such as the necessary settings in local.conf.
> 

Not a completely simple question, indeed. The rootfs arch is defined by
DISTRO_ARCH. But that one also influences the arch that the custom
kernel will select. You could try a multiconfig build, setting
DISTRO_ARCH to arm64 only for the kernel part and then requesting the
arm64 kernel from your armhf rootfs. Or you try to set KERNEL_ARCH
explicitly in the custom kernel recipe, switching it from "arm" (as
armhf would defined it) to "arm64". The former may give more correct
results, though, because the kernel recipe will still use DISTRO_ARCH
with "armhf" for a arm64 kernel.

Jan

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