Script to create an overlay that can be used when building falco dkms module on Flatcar

create-dkms-overlay.sh

#!/bin/bash

rm -rf /tmp/overlay

mkdir -p /tmp/overlay/.hidden
pushd /tmp/overlay

# this wrapper ensures that we use our dynamic linker and preload our libc version
cat >.hidden/wrapper.sh <<'EOF'
#!/bin/bash

prefix="$(dirname "$(dirname "$(realpath $0)")")/"
prog="$(realpath "$(dirname "$0")")/$(basename "$0")"
prog="${prog#${prefix}}"
prefix="${prefix%/}/.hidden"
exec "${prefix}"/ld-linux-x86-64.so.2 --library-path "${prefix}" "${prefix}/${prog}" "${@}"
EOF

chmod +x .hidden/wrapper.sh
cp /lib/ld-linux-*.so.* .hidden/
cp /lib/libc.so.* .hidden/

kdir="/lib/modules/$(uname -r)"
find "${kdir}/build" -type f -executable | while read prog; do
  relprog="${prog#*/*/*/*/*/}"
  dir="$(dirname "${relprog}")"
  mkdir -p ".hidden/${dir}" "${dir}"
  cp "${prog}" ".hidden/${dir}/"
  target="$(sed -e 's|[^/]\+/|../|g' <<<"${dir}/").hidden/wrapper.sh"
  ln -sf "${target}" "${relprog}"
done
popd

echo "done; to mount:"
echo ""
echo "  mount -t overlay -o lowerdir=/tmp/overlay:${kdir}/build overlay ${kdir}/build"