binfmt: Add --ignore-family option

binfmt: Add --ignore-family option

Until now, the script has worked under the assumption that a
host CPU can run binaries targeting any CPU in the same family.
That's a fair enough assumption when it comes to running i386
binaries on x86_64, but it doesn't quite apply in the general
case.

For example, while riscv64 CPUs could theoretically run riscv32
applications natively, in practice there exist few (if any?)
CPUs that implement the necessary silicon; moreover, even if you
had one such CPU, your host OS would most likely not have
enabled the necessary kernel bits.

This new option gives distro packagers the ability to opt out of
the assumption, likely on a per-architecture basis, and make
things work out of the box for a larger fraction of their user
base.

As an interesting side effect, this makes it possible to enable
execution of 64-bit binaries on 32-bit CPUs of the same family,
which is a perfectly valid use case that apparently hadn't been
considered until now.

Link: https://src.fedoraproject.org/rpms/qemu/pull-request/72
Thanks: David Abdurachmanov <davidlt@rivosinc.com>
Thanks: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20250127182924.103510-4-abologna@redhat.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>