Re: Building (Debian) kernel optimized for RPi Zero (W) and 1
On Tue, Oct 25, 2022, at 00:03, Punit Agrawal wrote:
> Diederik de Haas <didi.debian@cknow.org> writes:
>
>> But it can be that I'm looking at this problem all wrong and/or have some
>> tunnel vision towards building a cross compiler.
>> That is an important reason for making this ML thread.
>
> IIUC, for the kernel, either compiler should be fine. The
> documentation[0] for compiling the RPi Zero kernel seems to bear this
> out - it even uses the "CROSS_COMPILE=arm-linux-gnueabihf-". If you've
> got access to the hardware it should be easy to test before kicking off
> the Debian kernel package build.
That is correct: it's the same compiler backend, the only difference
between an arm-linux-gnuabihf- and an arm-linux-gnueabi- toolchain are
which CPU and floating pointing ABI are set when building with the
default flags. The kernel itself is always built as soft-float even
for armv7 using an armhf toolchain, and the CPU is always set to
the minimum configured target machine, so both compilers will produce
the same kernel binary.
Note that at the moment, you can build a kernel that works on
both armv6 and armv7 CPUs, or armv7 and armv8, but not armv5
and armv6/v7, or armv6 and armv8, and this limits what machines
can be enabled in a single kernel. I have a prototype kernel
patch that intends to change the way we build armv6 kernels,
so one can actually enable armv6 non-SMP support (Raspberry
Pi 0/1, OMAP2, i.MX3, s3c64xx, ...) in the default armel
kernel along with the ARMv5 targets (orion, kirkwood, pxa,
at91, omap1, imx2, suniv, ...), but no longer with ARMv7.
Arnd
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