Running/building an 32 bits kernel on A53 CPU?

[Catalin Marinas]

On Fri, Oct 29, 2021 at 08:27:35AM +0000, Joakim Tjernlund wrote:
> In order to reduce RAM usage we are wondering if running an 32 bits
> kernel on ARM A53 CPU is a good idea?

No. Really.

What's the RAM size on your SoC?

> Is it possible to build such a kernel? If so, how to go about it?
> Should one use ARCH=arm and a 32 bits toolchain or
> ARCH=arm64 and 64 bits toolchain and adding 32 bits compile options?

If you want a 32-bit kernel, you'd have to use ARCH=arm and a 32-bit
toolchain. This would give you an ARMv7 kernel that can run on ARMv8
hardware. But you'd miss errata workarounds for example and any other
features that come with ARMv8.

I don't recommend this at all. If you have some specific embedded
system, you can disable kernel features you don't need to make it
smaller. Also note that you can still run 32-bit applications with a
64-bit kernel.

-- 
Catalin