pop_os self-compiling the Linux Kernel and installing inside EFI(also installs as backup the distro-provided kernel)

update_linux.bash

#! /bin/bash
set -euo pipefail
IFS=$'\n\t'

sudo update-alternatives --auto gcc
mtune_patch_path="${mtune_patch_path:-${HOME:?}/HelperScripts/enable_additional_cpu_optimizations_for_gcc_v8.1+_kernel_v4.13+.patch}"
kernel_config_path="${kernel_config_path:-${HOME:?}/HelperScripts/MyKernelConfig}"
extract_location="${extract_location:-/dev/shm/linux-source}"
CFLAGS="-O3 -DNDEBUG -D_GNU_SOURCE -fomit-frame-pointer -fno-asynchronous-unwind-tables -ftree-vectorize -floop-strip-mine -floop-block -fgraphite-identity -m64 -mavx -march=native -mtune=native"
CXXFLAGS="-O3 -DNDEBUG -D_GNU_SOURCE -fomit-frame-pointer -fno-asynchronous-unwind-tables -ftree-vectorize -floop-strip-mine -floop-block -fgraphite-identity -m64 -mavx -march=native -mtune=native"

error() {
  local -r message="${1:?}"
  echo "${message}"
  exit 1
}

set_linux_version() {
  cat Makefile | head -5 > Makefile.linux_version
  echo '

all:
	@echo $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)

.PHONY: all
' >> Makefile.linux_version
  linux_version="$(make -f Makefile.linux_version)"
}

download_and_extract() {
  local -r link="${1:?}"
  local -r pre_link="$(echo "${link}" | sed 's|/linux-[0-9]*\.[0-9]*.*tar.*$||')/"
  local -r linux_archive="$(echo "${link}" | sed "s|${pre_link:?}||")"
  linux_directory="$(echo "${linux_archive}" | sed 's|.tar.*||')"

  mkdir -p "${extract_location}"
  cd "${extract_location}"
  if [ -f "${HOME:?}/Downloads/${linux_archive}" ]; then
    echo "Copying ${linux_archive} from Downloads"
    cp -a "${HOME:?}/Downloads/${linux_archive}" ./
    ls -hs "${linux_archive}"
    echo "SHA256SUM: $(sha256sum "${linux_archive}")"
  else
    wget "${link}" || error "Could not download ${linux_archive}"
    cp -a "${linux_archive}" "${HOME:?}/Downloads/"
  fi

  rm -rf "${linux_directory}"
  tar xf "${linux_archive}" || error "Could not extract ${linux_archive}"
  rm -f "${linux_archive}"
  cd "${linux_directory}" || error "No \"${linux_directory}\" directory"
}

compile() {
  set_linux_version
  # touch .scmversion
  patch -p1 < "${mtune_patch_path:?}"
  cp -f "${kernel_config_path:?}" ./.config

  make olddefconfig

  nproc="$(( $(nproc) + 1 ))"
  make -j ${nproc}
  make -j ${nproc} modules
  make -j ${nproc} bzImage
  make INSTALL_MOD_STRIP=1 -j ${nproc} -C tools/ turbostat
  make LDFLAGS=-fPIC INSTALL_MOD_STRIP=1 -j ${nproc} -C tools/ perf
}

install() {
  sudo make INSTALL_MOD_STRIP=1 -j ${nproc} modules_install
  sudo make INSTALL_MOD_STRIP=1 ARCH=x86 -j ${nproc} headers_install
  sudo make INSTALL_MOD_STRIP=1 -j ${nproc} install
  sudo make INSTALL_MOD_STRIP=1 -j ${nproc} -C tools/ turbostat_install
  sudo make prefix=/usr LDFLAGS=-fPIC INSTALL_MOD_STRIP=1 -j ${nproc} -C tools/ perf_install
  sudo dkms install -m nvidia -v ${nvidia_version} -k "${linux_version}" --force

  # Backup "stable" kernel
  sudo kernelstub \
    -k "/boot/vmlinuz-${latest_stable_kernel_version}" \
    -i "/boot/initrd.img-${latest_stable_kernel_version}"
  sudo kernelstub \
    -k "/boot/vmlinuz-${linux_version}" \
    -i "/boot/initrd.img-${linux_version}"
}

main() {
  test -z "$1" && error "Please pass the link to the linux kernel .xz"

  latest_stable_kernel_version="$(ls /boot/vmlinuz-*-generic | sort -r | head -1 | sed 's|/boot/vmlinuz-||')"
  nvidia_version="$(ls /usr/src | grep nvidia- | sort -r | head -1 | cut -d '-' -f2)"

  test -z "${latest_stable_kernel_version}" && error "Could not obtain the latest stable kernel version for Backup"
  test -z "${nvidia_version}" && error "Could not obtain the latest nvidia version from /usr/src"

  # Prepare upfront for `make install`
  sudo true
  
  download_and_extract "$1"
  compile
  install

  echo "Finished installing Linux ${linux_version}"
}

# If canceled, cleanup - if it finishes successfully, leave the source code
trap "rm -rf \"${extract_location}\"" SIGINT SIGTERM

(
  main "$@"
)