Current LFS version: 10.0

Substantial changes were introduced in LFS 10.0, so these notes will probably
not apply to anything below this version. This version should be easier to
bootstrap like this, anyway.

Ignore the Host System Requirements, a lot of these either don't apply or will
be procured as we go through this guide.
Ignore, as well, the creation of a new partition or user, as the necessary
tools to achieve this aren't available in the bootstrap toolset. We will be
building everything on whatever partition the bootstrap toolset was installed.

Install the sources under /sources right next to the /bootstrap directory.
This can't be done when inside the bootstrap system as no networking utilities
are yet installed. For the "xz" package, download a .tar.gz or .tar.bz2
package, as the xz utilities aren't included with the bootstrap utilities.

To enter the bootstrap system as a chroot, use the following commands to set
up the filesystems and entering:
mkdir -p sys proc dev tmp
mount -o ro -t devtmpfs devtmpfs dev
mount -o ro -t devpts devpts dev/pts
mount -o ro -t sysfs sysfs sys
mount -o ro -t proc proc proc
./bootstrap/bin/chroot . /bootstrap/bin/env -i PATH=/bootstrap/bin HOME=/root /bin/sh -l

Set the LFS variable to either / or keep it blank, as the bootstrap tools are
self-contained in /bootstrap, and can be removed afterwards, keeping a clean
system anyway.

The bootstrap tools are all x86, if you're going to be cross-compiling for
x86_64, make sure the command `uname -m` returns `x86_64`, or manually
substitute it throughout the LFS commands you execute.

In chapter 4.4 Setting Up the Environment, make sure LFS is set according to
what's been explained, and PATH=$LFS/tools/bin:/bootstrap/bin. We don't want
to use /usr/bin and /bin until chapter 7. Also define LFS_TGT after setting PATH.
Also `mkdir /root` before creating the files. If you don't want the "I have no
name!" prompt, you shouldn't use '\u' in the PS1 variable.
A finished bashrc/bash_profile looks like:
mkdir -p /root
cat > ~/.bash_profile << "EOF"
exec env -i HOME=$HOME TERM=$TERM PS1='\w\$ ' /bin/bash
EOF
cat > ~/.bashrc << "EOF"
set +h
umask 022
LFS=
LC_ALL=POSIX
PATH=$LFS/tools/bin:/bootstrap/bin
LFS_TGT=$(uname -m)-lfs-linux-gnu
export LFS LC_ALL LFS_TGT PATH
EOF
source ~/.bash_profile

Once you get to chapter 5, you will need to add a couple of tools to the
/bootstrap toolset, by building them from the sources you've downloaded for LFS.

You'll need to build the following packages:
- xz-5.2.5 (required to unpack .tar.xz archives)
- sed-4.8 (required by linux-headers for -E option)
- m4-1.4.18 (required by bison)
- bison-3.7.1 (required by glibc)
- grep-3.4 (required by glibc for -o option)
- make-4.3 (required by glibc)
- Python-3.8.5 (required by glibc)

Install them by unpacking them (see "General Compilation Instructions" chapter),
and running:
./configure --prefix=/bootstrap --build=i686-pc-linux-gnu
make
make install

Python with:
./configure --prefix=/bootstrap --build=i686-pc-linux-gnu --without-ensurepip

Now, you can run chapter 5 and 6, with the following exceptions:

5.3. GCC-10.2.0 - Pass 1:
    Add --with-stage1-libs='-lstdc++ -lsupc++' CC='gcc -std=c11'
    to the ../configure command.

6.3. Ncurses-6.2:
    Use --disable-stripping during "main" ./configure

6.4. Bash-5.0:
    Do not move bash to /bin or replace the /bin/sh symlink. We'll do this
    later.

Once you reach chapter 7, run the finishing bash install commands we skipped earlier:
mv $LFS/usr/bin/bash $LFS/bin/bash
ln -sfv bash $LFS/bin/sh

Now, if you're cross-building for x86_64, this is the point where you should
make sure you're either already running a compatible kernel, or you reboot
into one. You might be able to build one with the tools in /bootstrap and
/tools, but this guide won't cover this. Booting into this system instead of
chrooting will also require extra steps, not covered here.

You may skip chapters 7.1 and 7.2, since we've built everything as root, and
7.3 may be skipped as well as we've already set up the chroot. However, you
should set up the PATH variable as described in chapter 7.4, by for example
modifying your bashrc:
cat > ~/.bash_profile << "EOF"
exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash
EOF
cat > ~/.bashrc << "EOF"
set +h
umask 022
PATH=/bin:/usr/bin:/sbin:/usr/sbin
export PATH
EOF
source ~/.bash_profile

Chapter 7.5 onwards can be followed without any modifications. This is all
standard LFS stuff from here on.

It's probably not related to this specific bootstrap, but I had to run the
following extra commands during the remaining chapters:

7.10. Perl-5.32.0:
    Run the following command after sh Configure:
    echo '#define MB_LEN_MAX 16' >> config.h

7.13. Util-linux-2.36:
    Run the following command after ./configure:
    echo '#define SSIZE_MAX LONG_MAX' >> config.h

8.15. M4-1.4.18:
    Run the following command after ./configure:
    echo '#define MB_LEN_MAX 16' >> lib/config.h