Re: [gentoo-alt] problem installing gentoo prefix on debian buster

[Michael Fothergill <michael.fothergill@gmail.com>]

Many thanks for your reply.

The reason for compiling a kernel in gentoo tailored for use in debian
is as follows.

A while ago when the first set of kernels were made with the patches
for the meltdown and spectre vulnerabilities, I
installed the latest kernels with these fixes as soon as they were
released into my gentoo install.

Then I thought to do the same thing in debian.

But there was a problem.

Debian only put out new kernels from time to time and no spectre
enabled off the shelf kernel was available.

So that meant I would have to compile a custom kernel in debian as I
did in gentoo which would have the spectre fix in it.

This turned out not to be an easy task.

At the time you could only compile the spectre fix with gcc 8 and you
could only install it if you were running debian unstable (sid).

I ended up upgrading my debian stretch install to unstable and
installed gcc 8 with some effort.

I tried to configure and install a new kernel using the make kpkg
command in debian but I could not make it work.

It seemed to me that building kernels in gentoo was a lot easier than
in debian at the time.

Since then off the shelf kernels have been created in debian that
contain the meltdown and spectre fixes but I notice there seem to be
new vulnerability fixes
in the pipeline in upcoming kernel releases.

So I then began to wonder if I could make an extra kernel that would
be made to be used in debian at the same time as I would make the
gentoo one - both
kernels being made in gentoo.  The debian one would be ported to my
debian install.

I then posted this on to the gentoo kernel page on the forum site and
Neddy Seagoon the site administrator and Hu the moderator both helped
with some creative
suggestions see here:

https://forums.gentoo.org/viewtopic-t-1096872.html

Neddy Seagoon suggested (at least) two useful things:

1. make a new copy of the makefile for the current kernel and change
the EXTRAVERSION parameter from -gentoo to -debian:
 e.g.
# SPDX-License-Identifier: GPL-2.0
VERSION = 5
PATCHLEVEL = 1
SUBLEVEL = 1
EXTRAVERSION = -gentoo
NAME = Shy Crocodile

He then pointed out that the kernel make system has some useful targets in it:
...
Kernel packaging:
  rpm-pkg             - Build both source and binary RPM kernel packages
  binrpm-pkg          - Build only the binary kernel RPM package
  deb-pkg             - Build both source and binary deb kernel packages
  bindeb-pkg          - Build only the binary kernel deb package
...

2. He then said I would have to copy the kernel directory contents and
compile the new kernel in it etc.

We then had a discussion about the fact that copying the kernel
directory was kind of untidy etc.

Then Hu made a post saying there there were ways to build multiple
kernels from a single tree by setting certain environment variables
($KBUILD_OUTPUT, $INSTALL_PATH, $INSTALL_MOD_PATH) that would mean you
could avoid copying the kernel.

I found a script Hu had posted on this elsewhere on the gentoo forums:

#!/bin/bash

TDIR="$1"; shift
if [ -z "${TDIR}" ]; then
   TDIR="$(uname -r)"
   echo 'No release specified.  Defaulting to '"\"$TDIR\""'.'
fi

TKERN="${TDIR/*_}"
BDIR="$HOME"/kernel/
KSRC="${1:-/usr/src/linux-"${TKERN}"}"; shift

export KBUILD_OUTPUT="${BDIR}${TDIR}/"
export INSTALL_PATH="${BDIR}install/${TDIR}/boot/"
export INSTALL_MOD_PATH="${BDIR}install/${TDIR}/"

if [ ! -d "$KSRC" ]; then
   echo 'Directory '"$KSRC"' does not exist.' >&2
   exit 1
fi

for a in "$KBUILD_OUTPUT" "$INSTALL_PATH"; do
   if [ ! -d "$a" ]; then
      mkdir -p "$a" || exit $?
      echo "Created $a"
   fi
done

echo KBUILD_OUTPUT="${KBUILD_OUTPUT}"
echo INSTALL_PATH="${INSTALL_PATH}"
echo INSTALL_MOD_PATH="${INSTALL_MOD_PATH}"

cd "$KSRC"
exec /bin/bash

I had a go at running it.

If you look toward the end of the gentoo forums thread you will see
the problems i encountered trying to do this in practice.

I had problems making the make deb-pkg and/or make bindeb-pkg command
work in gentoo.

Then I had the idea of installing gentoo prefix in debian itself and
experimenting with the idea of getting the host debian install
to make the deb packages that produce the debian kernel image files
and doing the initramfs set up but still using the gentoo
prefix and portage to compile and configure the kernel itself ready
for debian to do the packaging that gentoo seemed to be poor at
doing in practice.

I also looked at the electron builder package a bit to see if it could
help here.

Comments appreciated.

Regards

MF