# A reusable toolchain image for compiling the Linux kernel — the build
# environment that the `kernel` example `FROM`s.
#
# An ordinary CONTAINER build (FROM a base image, not a kernel): it installs the
# compiler + kernel build dependencies and labels itself a `kernel-build-env`. It
# is a normal OCI image, resolved (like every component) through registry → cache
# → source.
#
# Swap the toolchain freely — `clang lld llvm` instead of gcc, a vendor cross
# compiler, etc. — and retag; downstream kernel builds just `FROM` the variant
# they want. No new directives required.
FROM debian:bookworm-slim

# The kernel's documented build prerequisites
# (Documentation/process/changes.rst): a C toolchain + bc/bison/flex, the
# libelf and OpenSSL headers, plus git/cpio/kmod/xz for fetching sources and
# installing modules.
RUN set -eux; \
    apt-get update; \
    apt-get install -y --no-install-recommends \
        build-essential bc bison flex \
        libelf-dev libssl-dev \
        git cpio kmod xz-utils ca-certificates; \
    apt-get clean; \
    rm -rf /var/lib/apt/lists/*

LABEL org.imagilux.umf.type=kernel-build-env
LABEL org.imagilux.umf.kernel-build-env.version="1.0"
LABEL org.imagilux.umf.kernel-build-env.toolchain=gcc