ABOUT THIS GUIDE
================

This is a guide to building a custom BusyBox/Linux-libre system with the GNU
toolchain.  It mostly follows Cross Linux From Scratch Sysroot version
SVN-0.0.1-20090726-x86, except that it uses more recent versions of software
packages and uses a BusyBox-based userspace rather than a GNU-based one.  This
guide assumes the use of a GNU/Linux host system with all the necessary
development software (GCC, GNU Binutils, Subversion, etc.) already installed.

It is recommended that you read Cross Linux From Scratch Sysroot version
SVN-0.0.1-20090726-x86 to understand the full build process and the rationale
behind various elements of the setup.


PROCEDURE
=========

Make a directory in which all work will be done.  Under this directory, make
directories 'src' and sys':
  $ mkdir src sys

Download all of the necessary source archives and branches.
  $ cd src
  $ wget http://www.busybox.net/downloads/busybox-1.19.3.tar.bz2
  $ wget http://www.fsfla.org/svnwiki/selibre/linux-libre/download/releases/\
  > LATEST-3.1.N/linux-3.1.6-libre.tar.bz2
  $ svn co svn://svn.eglibc.org/branches/eglibc-2_14 eglibc-2.14
  $ wget http://ftp.gnu.org/gnu/gcc/gcc-4.6.2/gcc-4.6.2.tar.bz2
  $ wget http://ftp.gnu.org/gnu/binutils/binutils-2.22.tar.bz2
  $ wget http://ftp.gnu.org/gnu/make/make-3.82.tar.bz2
  $ wget http://ftp.gnu.org/gnu/automake/automake-1.11.2.tar.bz2
  $ wget http://ftp.gnu.org/gnu/autoconf/autoconf-2.68.tar.bz2
  $ wget http://ftp.gnu.org/gnu/m4/m4-1.4.16.tar.bz2
  $ wget ftp://ftp.gmplib.org/pub/gmp-5.0.2/gmp-5.0.2.tar.bz2
  $ wget http://www.mpfr.org/mpfr-current/mpfr-3.1.0.tar.bz2
  $ wget http://www.multiprecision.org/mpc/download/mpc-0.9.tar.gz
  $ for file in *.tar.bz2; do tar -xjf ${file}; done
  $ for file in *.tar.gz; do tar -xzf ${file}; done
  $ cd ..

Make and mount the filesystem.  mkfs and mount must be run as the superuser, but
dd shouldn't need to be.
  $ cd sys
  $ dd if=/dev/zero of=fs bs=1024 count=$((3*1024*1024))
  # mkfs -t ext4 fs
  $ mkdir fsmnt
  # mount -o loop fs fsmnt

Set up a new user.
  # groupadd bbl
  # useradd -s /bin/bash -g bbl -d /home/bbl bbl
  # mkdir -pv /home/bbl
  # chown -v bbl:bbl /home/bbl
  # passwd bbl
  # chown -Rv bbl fsmnt

Set up the toolchain work environment.  Be sure to change '<BASE_DIR>' to the
absolute path to the base work directory you made earlier, and adjust the
configuration name in BBL_TARGET if you're building for a different
architecture.  We're using GNU Bash as the new user's default shell for
convenience; this has no effect on the target system.
  $ su - bbl
  $ cat > ~/.bash_profile <<EOF
  > exec env -i HOME="${HOME}" TERM="${TERM}" /bin/bash
  > EOF
  $ cat > ~/.bashrc <<EOF
  > set +h
  > umask 022
  > BBL=<BASE_DIR>/sys/fsmnt
  > LC_ALL=C
  > PATH=<BASE_DIR>/sys/fsmnt/cross-tools/bin:/bin:/usr/bin
  > export BBL LC_ALL PATH
  > PS1='$ '
  > unset CFLAGS
  > unset CXXFLAGS
  > export BBL_HOST=$(echo ${MACHTYPE} | \
  > sed "s/$(echo ${MACHTYPE} | cut -d - -f 2)/cross/")
  > export BBL_TARGET=x86_64-pc-linux-gnu
  > EOF
  $ source ~/.bash_profile

Make system directories.  These commands should give you a system that is
compliant with Filesystem Hierarchy Standard version 2.3.  Note that the range
syntax in many of these command lines is a non-standard feature of GNU Bash;
this may not work on other shells.
  $ mkdir -pv ${BBL}/{bin,boot,dev,etc/opt,home,lib,media,mnt,opt,proc}
  $ install -dv -m 0750 ${BBL}/root
  $ mkdir -pv ${BBL}/{sbin,srv,sys}
  $ install -dv -m 1777 ${BBL}{,/var}/tmp
  $ mkdir -pv ${BBL}/usr/{,local/}{bin,include,lib,sbin,share/{man,misc},src}
  $ mkdir -pv ${BBL}/usr/local/{etc,games}
  $ mkdir -pv ${BBL}/usr/{,local/}share/{doc,info,locale,terminfo,zoneinfo}
  $ mkdir -pv ${BBL}/usr/{,local/}share/man/man{1,2,3,4,5,6,7,8}
  $ ln -sv share/man ${BBL}/usr/local/man
  $ mkdir -pv ${BBL}/var/{cache,lib/misc,local,lock,log,mail,opt,run,spool}

Write the passwd and group files.
  $ cat > ${BBL}/etc/passwd <<EOF
  > root::0:0:root:/root:/bin/bash
  > EOF
  $ cat > ${BBL}/etc/group <<EOF
  > root:x:0:
  > bin:x:1:
  > sys:x:2:
  > kmem:x:3:
  > tty:x:4:
  > tape:x:5:
  > daemon:x:6:
  > floppy:x:7:
  > disk:x:8:
  > lp:x:9:
  > dialout:x:10:
  > audio:x:11:
  > video:x:12:
  > utmp:x:13:
  > usb:x:14:
  > cdrom:x:15:
  > EOF

If CONFIG_FEATURE_UTMP and/or CONFIG_FEATURE_WTMP are enabled in BusyBox,
certain BusyBox applets (getty, login, init, etc.) will log user logins to
/var/run/utmp and/or /var/run/wtmp.  However, BusyBox's supporting library won't
create /var/run/wtmp if it doesn't exist.  So create these files now and set
proper modes for them.
  $ touch ${BBL}/var/run/{u,w}tmp
  $ chmod -v 664 ${BBL}/var/run/{u,w}tmp
/var/run/utmp is used to track logged-in users.  /var/run/wtmp is used to record
when users log into and out of the system.  NB: This is an odd location for
wtmp, but that's where an unpatched BusyBox will expect it.

Make and change to a directory for package source code.
  $ mkdir -v ${BBL}/src
  $ cd ${BBL}/src

Install Linux's headers for use by EGLIBC.
  $ cp -pR ${BBL}/../../src/linux-3.1.6 .
  $ cd linux-3.1.6
  $ make mrproper
  $ make headers_check
  $ make INSTALL_HDR_PATH=${BBL}/usr headers_install
  $ find ${BBL}/usr/include/ -name .install -o -name ..install.cmd | \
  > xargs rm -fv
  $ cd ..
  $ rm -Rf linux-3.1.6

Install GMP for use by the cross-compiling GCC build.
  $ cp -pR ${BBL}/../../src/gmp-5.0.2 .
  $ cd gmp-5.0.2
  $ CPPFLAGS=-fexceptions ./configure --prefix=${BBL}/cross-tools --enable-cxx
  $ make
  $ make install
  $ make check
  $ cd ..
  $ rm -Rf gmp-5.0.2

Install MPFR for use by the cross-compiling GCC build.
  $ cp -pR ${BBL}/../../src/mpfr-3.1.0 .
  $ cd mpfr-3.1.0
  $ LDFLAGS="-Wl,-rpath,${BBL}/cross-tools/lib" ./configure \
  > --prefix=${BBL}/cross-tools --enable-shared --with-gmp=${BBL}/cross-tools
  $ make
  $ make install
  $ cd ..
  $ rm -Rf mpfr-3.1.0

Install MPC for use by the cross-compiling GCC build.
  $ cp -pR ${BBL}/../../src/mpc-0.9 .
  $ cd mpc-0.9
  $ LDFLAGS="-Wl,-rpath,${BBL}/cross-tools/lib" ./configure \
  > --prefix=${BBL}/cross-tools --with-mpfr=${BBL}/cross-tools \
  > --with-gmp=${BBL}/cross-tools
  $ make
  $ make install
  $ cd ..
  $ rm -Rf mpc-0.9

Configure and build a cross-compiling GNU Binutils.
  $ cp -pR ${BBL}/../../src/binutils-2.22 .
  $ mkdir -v binutils-build
  $ cd binutils-build
  $ AR=ar AS=as ../binutils-2.22/configure --prefix=${BBL}/cross-tools \
  > --host=${BBL_HOST} --target=${BBL_TARGET} --with-sysroot=${BBL} \
  > --disable-nls --enable-shared --disable-multilib
  $ make configure-host
  $ make
  $ make install
  $ cp -v ../binutils-2.22/include/libiberty.h ${BBL}/usr/include
  $ cd ..
  $ rm -Rf binutils-2.22 binutils-build

Configure and build a cross-compiling GCC.
  $ cp -pR ${BBL}/../../src/gcc-4.6.2 .
  $ mkdir -v gcc-build
  $ cd gcc-build
  $ AR=ar LDFLAGS="-Wl,-rpath,${BBL}/cross-tools/lib" ../gcc-4.6.2/configure \
  > --prefix=${BBL}/cross-tools --build=${BBL_HOST} --host=${BBL_HOST} \
  > --target=${BBL_TARGET} --disable-multilib --with-sysroot=${BBL} \
  > --disable-nls --without-headers --with-newlib --disable-decimal-float \
  > --disable-libgomp --disable-libmudflap --disable-libssp \
  > --with-mpfr=${BBL}/cross-tools --with-gmp=${BBL}/cross-tools \
  > --with-mpc=${BBL}/cross-tools --without-ppl --without-cloog \
  > --disable-shared --disable-threads --enable-languages=c
  $ make all-gcc all-target-libgcc
  $ make install-gcc install-target-libgcc
  $ cd ..
  $ rm -Rf gcc-4.6.2

Configure and build a cross-compiling EGLIBC.  Change '<LINUX_VERSION>' to the
lower of either version 3.1.6 or the version of Linux running on your host
system.
  $ cp -pR ${BBL}/../../src/eglibc-2.14 .
  $ cd eglibc-2.14/libc 
  $ cp -v Makeconfig{,.orig}
  $ sed -e 's/-lgcc_eh//g' Makeconfig.orig > Makeconfig
  $ cd ../..
  $ mkdir -v eglibc-build
  $ cd eglibc-build
  $ BUILD_CC=gcc CC=${BBL_TARGET}-gcc AR=${BBL_TARGET}-ar \
  > RANLIB=${BBL_TARGET}-ranlib \
  > CFLAGS="-march=$(cut -d - -f 1 <<< ${BBL_TARGET} | sed 's/x86_64/x86-64/') \
  > -mtune=generic -g -O2" ../eglibc-2.14/libc/configure --prefix=/usr \
  > --libexecdir=/usr/lib/eglibc --host=${BBL_TARGET} --build=${BBL_HOST} \
  > --disable-profile --enable-add-ons --with-tls --enable-kernel=3.1.0 \
  > --with-__thread --with-binutils=${BBL}/cross-tools/bin \
  > --with-headers=${BBL}/usr/include libc_cv_forced_unwind=yes \
  > libc_cv_c_cleanup=yes libc_cv_gnu89_inline=yes install_root=${BBL} \
  > libc_cv_ssp=no
  $ make
  $ make install