# vim:set textwidth=0:
# This guide uses live-bootstrap instead of the old chain

# live-bootstrap version: 34cb6758d241b92c3c59e61f0a1d62f86f0c36c1 (Tue Feb 13 10:08:37 2024 +0000)
# LFS version: 12.0
# Gentoo version: 20240201

# Do the live-bootstrap
# Every step of this process is checksummed, so you can be relatively sure it's good when done
cd live-bootstrap
./download-distfiles.sh
sudo ./rootfs.py --external-sources -q --cores 8
cd ..

# Prepare lfs sources
mkdir lfs-sources
wget -O lfs-sources/LFS-BOOK-12.0-NOCHUNKS.html https://linuxfromscratch.org/lfs/downloads/12.0/LFS-BOOK-12.0-NOCHUNKS.html
wget -O lfs-sources/wget-list-sysv https://linuxfromscratch.org/lfs/downloads/12.0/wget-list-sysv
wget -O lfs-sources/md5sums https://linuxfromscratch.org/lfs/downloads/12.0/md5sums
wget --input-file=lfs-sources/wget-list-sysv --continue --directory-prefix=lfs-sources
( cd lfs-sources; md5sum -c md5sums )

# Prepare gentoo sources
mkdir gentoo-sources
wget --directory-prefix=gentoo-distfiles http://distfiles.gentoo.org/snapshots/squashfs/gentoo-20240201.xz.sqfs
wget --input-file=wget-list-gentoo --continue --directory-prefix=gentoo-distfiles
# md5sum: 35da573f5c622dd813adf462e8d046b7 *gentoo-20240201.xz.sqfs
# The rest of the distfiles integrity is verified using manifests in the repo.

# Install the live-bootstrap system into a new root
sudo mkdir -p sys/mnt sys/dev sys/proc sys/sys sys/tmp sys/root
sudo mount live-bootstrap/target/external.img -o offset=1048576 sys/mnt
sudo rsync -avP sys/mnt/usr sys/mnt/etc sys/
sudo umount sys/mnt

sudo ln -sf usr/bin sys/bin
sudo ln -sf usr/sbin sys/sbin
sudo ln -sf usr/lib sys/lib

sudo mkdir -p sys/mnt/lfs
sudo rsync -rvP lfs-sources/ sys/mnt/lfs/sources
sudo rsync -rvP gentoo-distfiles/ sys/mnt/lfs/distfiles

sudo mount -t devtmpfs devtmpfs sys/dev
sudo mount -t devpts devpts sys/dev/pts
sudo mount -t proc proc sys/proc
sudo mount -t sysfs sysfs sys/sys
sudo chroot sys /usr/bin/env -i HOME=/root TERM="$TERM" LFS=/mnt/lfs /bin/bash -l

# Follow LFS chapter 4,5,6,7
# Skip chapter 4.3

# Chroot into the system as detailed in chapter 7

# Install the following additional software from the chapter 8 (don't run tests):
# Chapter 8.6: zlib-1.2.13
# Chapter 8.7: bzip2-1.0.8
# Chapter 8.14: flex-2.6.4 (for gcc)
# Chapter 8.28: pkgconf-2.0.1
# Chapter 8.39: expat-2.5.0
# Chapter 8.47: openssl-3.1.2 (for wget)
# Chapter 8.50: libffi-3.4.4
# Chapter 8.51: python-3.11.4 (required for pip)
# Chapter 8.52: flit-core-3.9.0
# Chapter 8.53: wheel-0.41.1
# Chapter 8.54: ninja-1.11.1
# Chapter 8.55: meson-1.2.1 (for portage)

# This is a good place save the current system using the instructions in
# chapter 7.13. From here on out, use chapters 7.3 and 7.4 to enter the chroot.

# Symlink python (needed for portage)
ln -sv python3 /usr/bin/python

# Install portage
meson setup --prefix /usr build
meson install -C build

# LFS is a merged-usr system, where gentoo isn't, so unlink the directories
# and create a minimum amount of symlinks
rm /bin /sbin /lib
/usr/lib/ld-linux-x86-64.so.2 /usr/bin/mkdir /bin /sbin /lib
/usr/lib/ld-linux-x86-64.so.2 /usr/bin/ln -svr /usr/lib/ld-linux-x86-64.so.2 /lib
ln -svr /usr/bin/sh /bin
ln -svr /usr/bin/bash /bin
ln -svr /usr/bin/cpp /lib
ln -svr /usr/sbin/ldconfig /sbin

# Configure portage
mkdir -p /var/db/repos/gentoo
mount /distfiles/gentoo-*.sqfs /mnt
cp -avT /mnt /var/db/repos/gentoo
umount /mnt

echo 'portage:x:250:250:portage:/var/tmp/portage:/bin/false' >> /etc/passwd
echo 'portage::250:portage' >> /etc/group
echo 'nameserver 1.1.1.1' > /etc/resolv.conf
echo 'C.UTF-8 UTF-8' > /etc/locale.gen

mkdir -p /etc/portage/profile
ln -svr /var/db/repos/gentoo/profiles/default/linux/amd64/17.1 /etc/portage/make.profile
cat > /etc/portage/make.conf << 'EOF'
FEATURES='-news -pid-sandbox'
CONFIG_PROTECT='-* /etc/locale.gen'
USE='-nls'
EOF
cat > /etc/portage/profile/package.use.force << 'EOF'
sys-devel/gcc -cxx
EOF

# Install a few more tools using portage to avoid spelling out instructions
GENTOO_MIRRORS=/distfiles emerge -O1 net-misc/wget
GENTOO_MIRRORS=/distfiles PYTHON_COMPAT_OVERRIDE=python3_11 emerge -O1 app-misc/ca-certificates
USE=-acl emerge -O1 net-misc/rsync

# Pretend none of that ever happened
rm -rf /var/lib/portage /var/db/pkg /var/cache/edb /var/log/emerge.log /var/log/portage

# Install baselayout
# This ensures that the library paths and other env vars are set correctly
# and portage picks them up (it sources /etc/profile for every build).
emerge -O1 sys-apps/baselayout
source /etc/profile

# We need to bootstrap a multilib system
# For that we're going to abuse portage's semi-support for cross-compilation,
# and do something akin to what both LFS and crossdev do
# Even when not bootstrapping multilib, this isn't a bad way to install
# the gentoo toolchain while avoiding other differences, like multilib paths

# TODO: Try building gcc without the glibc headers (toolchain.eclass supports this)
#       and bootstrapping glibc straight into /

# Install core gentoo toolchain support
emerge -O1 sys-apps/gentoo-functions app-portage/elt-patches sys-devel/gnuconfig

# Bootstrap glibc headers
CTARGET=x86_64-bootstrap-linux-gnu USE=headers-only emerge -O1 sys-kernel/linux-headers
CTARGET=x86_64-bootstrap-linux-gnu USE=headers-only PYTHON_COMPAT_OVERRIDE=python3_11 emerge -O1 sys-libs/glibc

# Install the gentoo cross compiler
emerge -O1 dev-libs/gmp dev-libs/mpfr dev-libs/mpc
emerge -O1 sys-devel/binutils-config sys-devel/gcc-config
CTARGET=x86_64-bootstrap-linux-gnu emerge -O1 sys-devel/binutils
CTARGET=x86_64-bootstrap-linux-gnu EXTRA_ECONF=--with-sysroot=/usr/$CTARGET EXTRA_EMAKE='MAKE=make MAKE+=libsuffix=../lib64' USE='-sanitize -openmp -fortran -cxx' emerge -O1 sys-devel/gcc
CTARGET=x86_64-bootstrap-linux-gnu CFLAGS_x86=-m32 PYTHON_COMPAT_OVERRIDE=python3_11 emerge -O1 sys-libs/glibc
CTARGET=x86_64-bootstrap-linux-gnu EXTRA_ECONF='--with-sysroot=/usr/$CTARGET --enable-shared' EXTRA_EMAKE='MAKE=make MAKE+=libsuffix=../lib64' USE='-sanitize -openmp -fortran' emerge -O1 sys-devel/gcc
# --with-sysroot and --enable-shared needed here because toolchain.eclass
# figures out the bootstrap stage based on ${CATEGORY}/glibc, with no overrides

# Install final glibc
/usr/x86_64-bootstrap-linux-gnu/lib64/ld-linux-x86-64.so.2 /usr/x86_64-bootstrap-linux-gnu/sbin/ldconfig
rm /usr/x86_64-bootstrap-linux-gnu/usr/lib/crti.o  # HACK to avoid ABI test failing in glibc ebuild. sue me.
CC=x86_64-bootstrap-linux-gnu-gcc CXX=x86_64-bootstrap-linux-gnu-g++ CFLAGS_x86=-m32 PYTHON_COMPAT_OVERRIDE=python3_11 emerge -O1 sys-libs/glibc
# This will throw a *lot* of segmentation faults in prerm/postinst stages
# because collision-protect removes the LFS glibc before it should (I think)
# It doesn't really matter in the grand scheme, however.
# glibc will be rebuilt again in bootstrap.sh

# Install final compiler
CC='x86_64-bootstrap-linux-gnu-gcc --sysroot=/' CXX='x86_64-bootstrap-linux-gnu-g++ --sysroot=/' emerge -O1 sys-kernel/linux-headers
CC='x86_64-bootstrap-linux-gnu-gcc --sysroot=/' CXX='x86_64-bootstrap-linux-gnu-g++ --sysroot=/' EXTRA_ECONF=--disable-bootstrap USE=-sanitize emerge -O1 sys-devel/gcc
emerge -O1 sys-devel/binutils

# Set up python-exec
# Bootstrap python version doesn't have to match with python-exec dir...
mkdir -p /usr/lib/python-exec/python3.11
ln -sv python3 /usr/lib/python-exec/python3.11/python
ln -svr /usr/bin/python3.11 /usr/lib/python-exec/python3.11/python3
emerge -O1 dev-lang/python-exec

# Break dependency cycles
emerge -O1 app-alternatives/ninja app-alternatives/yacc app-alternatives/lex app-alternatives/bzip2 app-alternatives/gzip app-alternatives/tar app-alternatives/awk
emerge -O1 sys-libs/libxcrypt

# Install implicit build dependencies
emerge -O1 dev-build/meson-format-array app-misc/pax-utils

# Run bootstrap.sh
rm -rf /etc/portage/profile  # don't build gcc with -cxx
/var/db/repos/gentoo/scripts/bootstrap.sh
# Might have to be ran a couple of times as some things may error out
# for the same reason as glibc before.

# Install the rest of @system
emerge -1N sys-devel/gcc  # Install with USE="openmp"
USE=-pam emerge -1 sys-libs/libcap
USE=-http2 emerge -1 net-misc/curl
emerge -1 sys-apps/shadow  # required by everything in acct-user and acct-group
emerge -DN @system

# Rebuild and install everything into a new root, completely cleaning out LFS
USE=build emerge --root /mnt/gentoo sys-apps/baselayout
emerge --root /mnt/gentoo @system

# Pack it up
tar cf /gentoo-bootstrap-20240201.tar -C /mnt/gentoo .
xz -9v /gentoo-bootstrap-20240201.tar

# Distfiles you might want to back up are in /var/cache/distfiles

# Possible improvements for the future:
# - Use portage to cross-compile a bunch of tools into a temporary EPREFIX
#   instead of replacing tools and libraries in /usr. This would avoid a bunch
#   of errors and weird cross-contamination, as well as allow for an eventual
#   "rm -rf /usr". Afterwards, use the EPREFIX tools to build the final system.
# - Don't use LFS as an intermediate step. Right now it's convenient as a
#   stable base to jump to from any distribution if live-bootstrap fails or
#   changes out under us, but the ideal end goal is definitely live-bootstrap.
# - For the purposes of bootstrapping multilib, a lot less steps should be
#   required. If the above idea of cross-compilation isn't followed, this
#   should at least be considered.
# - Allow bootstrapping other architectures from x86. In my eyes, I see a
#   future where it's way easier to make a qemu-like user-mode emulator than
#   it is to implement a new architecture in every compiler and assembler used
#   in the bootstrap chain. The LFS instructions are already workable towards
#   this goal, but it'd be better to automate it with portage.