crossgrade builds..

[necrose99]

https://wiki.debian.org/CrossGrading

minorly borked from manally trying how the arm64 kernel much more useful .. /mnt/gentoo (aarch64) via hdd for builds

point being is crossgrade , drop arm7hf >>>> pure arm64 release at fin on your build root. to 32bit and or arm64 as a choice

# scary script to crossgrade your debian machine between arches.
# usage crossgrade <final-architecture>
set -e

if [ -z "$1" ]; then
  echo "Usage: crossgrade <architecture>  (debian architecture to convert to)"
  exit 1
fi

#validate arch
if ! TO=$(dpkg-architecture -qDEB_HOST_ARCH -a$1); then
    echo "$1 is not a recognised architecture name"
    exit 1
fi
FROM=$(dpkg --print-architecture)
echo "Crossgrading from $FROM to $TO"

#check for a compatible kernel
# should check $FROM and $TO harder
# allow for switching kernel over too to minimal one if requested?
case $TO in
   amd64)
       TO_KERN=amd64
       ;;
   i386)
       TO_KERN=amd64
       ;;
   armhf)
       TO_KERN=armhf
       ;;
   armel)
       TO_KERN=armhf
       ;;
   arm64)
       TO_KERN=arm64
       ;;
   mips)
       TO_KERN=mips64le
       ;;
   mipsel)
       TO_KERN=mips64le
       ;;
   mips64le)
       TO_KERN=mips64le
       ;;
   ppc)
       TO_KERN=ppc64el
       ;;
   powerpc)
       TO_KERN=ppc64el
       ;;
   ppc64el)
       TO_KERN=ppc64el
esac
   
dpkg --add-architecture $TO
# check that dpkg --print-foreign-architectures is $TO
apt update
apt upgrade

# Install a kernel capable to run the new architecture with the old
# architecture in userspace

KERNEL=$(uname -m)
echo "Current kernel arch is $KERNEL"
if [ "$KERNEL" != "$TO_KERN" ]; then
    if apt install linux-image-$TO:$TO; then
        echo "There should be a reboot here"
        exit 1
        #reboot
    else
        echo "kernel updating to linux-image-$TO:$TO failed"
    fi
fi

echo Crossgrading dpkg and apt
apt clean
apt --download-only install dpkg:$TO apt:$TO tar:$TO

#check ever package to be installed is available in same version for amd64 if installed (multiarch sync is needed)
#for pkg in /var/cache/apt/archives/*_$TO.deb
#do
#    file=$(basename $pkg)
#    pkgname= ${file%%_.*}
#    version= ${file##*._} 
#    if dpkg -l $($pkgname)
#done
#in practice this needs to run twice (do it more? is there a better way?)
if ! dpkg --install /var/cache/apt/archives/*_$TO.deb; then
    dpkg --install /var/cache/apt/archives/*_$TO.deb
fi

test $(dpkg --print-architecture) = $TO
test $(dpkg --print-foreign-architectures | grep $FROM) = $FROM

echo "Yay! dpkg and apt crossgrade completed successfully"

echo "Updating core packages"
apt upgrade
apt full-upgrade

echo "Removing obsolete packages"
apt install aptitude:$TO
aptitude purge '?obsolete'

echo "Mass reinstalling $TO packages -- double check installed packages match warned-about packages"
apt install $(dpkg -l | grep '^.i.*:'"$FROM" | grep ":$FROM" | sed -e "s/:$FROM/:$TO/" | awk '{print $2}')

echo "Removing redundant libraries"
apt purge $(dpkg -l | grep '^.i.*:'"$FROM" | awk '{print $2}')

echo "Removing $FROM"
dpkg --remove-architecture "$FROM"
apt update