Setting up a cross-compilation toolchain

This page is a brief summary of the cross-compilation discussion on the SamyGO forum. Main contributors to this information are Robbiesz and marcelru. The information in this page pertains to the building of a toolchain, based on the source code as stored in the file 32B650.zip, available from Samsung.

We are still in the testing phase, for now, check out the forum discussion (topic: cross-compilation [1]). For more info, errors you may encounter, support for other Samsung toolchains, please refer to the forum, or better still, participate.

Toolchains 101

A toolchain is a set of executable programs that enables you to build (assemble, compile and link) your own executable programs from source code (typically C, C++, fortran or other programming languages). To build these executables, the source code needs to be translated into machine-readable code. This is what a toolchain does. The translation proceeds in three steps (well, you may think of it this way): translation into low-level code (compilation), translation to machine-readable code (assembly), combination with other code libraries (linking). Compilation/assembly mostly proceeds in a single go. So, for a toolchain you need at least three programs: a compiler, an assembler, and a linker. In almost all cases you will also need a C-library to link with.

Unlike source code, executables are machine-specific. That means that executables built for the Intel x86 architecture (the basis for most computers in the world today) will not run on other types of processors, for example the ARM architecture, the basis for many embedded systems. Our Sammys are ARM-based machines. To build executables for a Samsung TV on an x86-based machine, you will need a toolchain that runs on the x86-architecture and builds executable code for the ARM-architecture. This procedure is called cross-compilation, and requires a cross compilation toolchain. This wiki page deals with the installation of the toolchain provided by Samsung, on an x86, Linux or Windows (Cygwin) platform.

Samsung toolchain

The source code for the Samsung ARM toolchain is available on the net, but needs some adjustments before it can be built. We will discuss that later. The main parts are:

• GNU binutils (containing among other things an assembler and a linker)
• GCC, the GNU C/C++ compiler (and a host of other languages we will not use)
• Glibc, the GNU C library
• linux kernel sources, for operating system/processor specific details.

For the remainder of this wiki page, we will use the toolchain for the 32B650/32B550/... TV's as an example. The source code for this toolchain is stored in the file 32B650.zip. Download this file and store it in the directory where you want to build your toolchain. Download the SamyGO patches that enable compilation of the toolchain here: [2]

Building the toolchain on Linux

Since most Linux distro's come standard with a full toolchain for building packages, building the cross-compilation toolchain on this platform is fairly straightforward, and proceeds in 6 stages.

1: Unpack and install the source code files. This is done with the script install_sources.sh: edit paths and code versions to your liking:

#! /bin/sh
#
# install_sources.sh installs the source code for the toolchain for Samsung
# TV's, as found in the file 32B650.zip. Place this file together with the 
# patches tarball (SamyGO-toolchain_fc11_patches.tgz) in the ${BUILDROOT} 
# directory, defined below, and run this script.
#
BUILDROOT=/tmp/arm-tools         # edit according to your needs. 

cd ${BUILDROOT}
mkdir -p ${BUILDROOT}/src

# unpack the Samsung zip file

unzip 32B650.zip

# remove unnecessary stuff and move the kernel and toolchain code

rm -f libgphoto2-2.3.1.tar.zip
rm -f libusb-0.1.12.tar.gz
rm -f SDL-1.2.11.zip
mv linux.chelsea.tgz ${BUILDROOT}/src

# unpack the toolchain and remove unnecessary stuff

tar -zxvf SELP.3.2.x-Chelsea.src.tgz
rm -f SELP.3.2.x-Chelsea.src.tgz

mv ./SELP.3.2.x-Chelsea.src/Toolchain/gcc-4.2.0-4.0.9.tgz ${BUILDROOT}/src
mv ./SELP.3.2.x-Chelsea.src/Toolchain/binutils-2.17.50.tgz ${BUILDROOT}/src
mv ./SELP.3.2.x-Chelsea.src/Toolchain/glibc-2.5.90-9.0.9.tgz ${BUILDROOT}/src

rm -rf ./SELP.3.2.x-Chelsea.src

# unpack the patches and move them

tar -zxvf SamyGO-toolchain_fc11_patches.tgz
mv *.patch ${BUILDROOT}/src

2: Install the kernel header files. You will need these when you want to build your own kernel modules for your TV. For that, the kernel source code's version has to match your TV's kernel version _exactly_. The installation is done with the install_kernel_src.sh script: again, edit to meet your needs.

#! /bin/sh 

# how to install kernel headers using this script:
# 
# Create the ${BUILDROOT} directory, put this script (install_kernel_src.sh) 
# in it.
# In ${BUILDROOT}, create a directory ./src and put the linux tarball in it.

# go up one directory and run this script. 

TARGET=arm-SamyGO-linux-gnueabi
BUILDROOT=/tmp/arm-tools
PREFIX=/usr/local                            # change to your needs
SYSROOT=${BUILDROOT}/sysroot

export ARCH=arm
export CROSS_COMPILE=${TARGET}-
export PATH=$PATH:${PREFIX}/bin
 
cd ${BUILDROOT}/src

# remove previous installation if it is there:
rm -rf linux 
rm -rf linux-r011 
rm -rf RFS 
rm -rf ssdtv_platform

# unpack, move up one dir and link:

tar -zxvf linux.chelsea.tgz              # from 32B650.zip
mv ./linux/* .
rm -rf linux/

ln -s ./linux-r011 linux

cd linux

# copy header files to sysroot:
mkdir -p ${SYSROOT}/usr/include
cp -a ${BUILDROOT}/src/linux/include/linux ${SYSROOT}/usr/include/linux
cp -a ${BUILDROOT}/src/linux/include/asm-arm ${SYSROOT}/usr/include/asm
cp -a ${BUILDROOT}/src/linux/include/asm-generic ${SYSROOT}/usr/include/asm-generic

# remove stale link to ssdtv headers:
rm -rf ${SYSROOT}/usr/include/asm/arch-ssdtv

# ... and copy these as well:
cp -a ${BUILDROOT}/src/ssdtv_platform/include/asm-arm/arch-ssdtv ${SYSROOT}/usr/include/asm

Everything is now installed (but not yet unpacked). The remainder of the installation consists of the actual building of the tools: First the binutils are built: as, ld and a bunch of others. For cross-compilation, these tools do not need any resources for the target platform (ARM, in this case).

3: Building of the binutils. Apart from a small bug in one of the source files and a configuration change to be made to part of the code (patches are included) the build is straightforward, done with mkbinutils.sh:

#! /bin/sh

# how to build binutils using this script:
# 
# Create the ${BUILDROOT} directory, put this script (mkbinutils.sh) in it.
# In ${BUILDROOT}, create a directory ./src and put the binutils tarball and 
# the patch in it.

# go up one directory and run this script. 

TARGET=arm-SamyGO-linux-gnueabi
BUILDROOT=/tmp/arm-tools                     # change to your needs
PREFIX=/usr/local                            # change to your liking 
SYSROOT=${BUILDROOT}/sysroot
UTILS=binutils-2.17.50

export ARCH=arm
export CROSS_COMPILE=${TARGET}-
export PATH=$PATH:${PREFIX}/bin
 
cd ${BUILDROOT}/src

tar -zxvf binutils-2.17.50.tgz               # from 32B650.zip
patch -p0 < ./binutils-2.17.50_fc11.patch 

mkdir -p BUILD/${UTILS}
cd BUILD/${UTILS}

../../${UTILS}/configure --prefix=${PREFIX} --target=${TARGET} \
    --with-sysroot=${SYSROOT} 
make

make install

mkdir -p $PREFIX/$TARGET/include
cp ${BUILDROOT}/src/${UTILS}/include/libiberty.h $PREFIX/$TARGET/include

If all goes well, you now have the following executables in /usr/local/bin:

arm-SamyGO-linux-gnueabi-addr2line
arm-SamyGO-linux-gnueabi-ar
arm-SamyGO-linux-gnueabi-as
arm-SamyGO-linux-gnueabi-c++filt
arm-SamyGO-linux-gnueabi-gprof
arm-SamyGO-linux-gnueabi-ld
arm-SamyGO-linux-gnueabi-nm
arm-SamyGO-linux-gnueabi-objcopy
arm-SamyGO-linux-gnueabi-objdump
arm-SamyGO-linux-gnueabi-ranlib
arm-SamyGO-linux-gnueabi-readelf
arm-SamyGO-linux-gnueabi-size
arm-SamyGO-linux-gnueabi-strings
arm-SamyGO-linux-gnueabi-strip

The C-compiler (gcc) has to be built in two stages: First, it is built and linked against the existing C-library (glibc). This version of the compiler is used to build glibc for the target platform, and then gcc is built again, now with the just compiled C-library.

4: Build the C-compiler, gcc, stage 1. This is a barebones gcc, just useful for compiling glibc, in the next step: Edit install_gcc_stage1.sh according to your needs and execute. The source code will be patched to prevent building of two runtime objects that cannot be linked yet (because we don't have a working C-library for ARM, yet)

#! /bin/sh

# how to install gcc stage 1 using this script:
# 
# Create the ${BUILDROOT} directory, put this script (install_gcc_stage1.sh) 
# in it.
# In ${BUILDROOT}, create a directory ./src and put the gcc tarball in it.

# go up one directory and run this script. 

TARGET=arm-SamyGO-linux-gnueabi
BUILDROOT=/tmp/arm-tools
PREFIX=/usr/local                            # change to your liking
SYSROOT=${BUILDROOT}/sysroot
GCC=gcc-4.2.0-4.0.9

export ARCH=arm
export CROSS_COMPILE=${TARGET}-
export PATH=$PATH:${PREFIX}/bin
 
cd ${BUILDROOT}/src

# unpack

tar -zxvf ${GCC}.tgz      # from 32B650.zip

patch -p0 < ./gcc-4.2.0-4.0.9_t-linux-eabi.patch

mkdir -p BUILD/${GCC}-stage1 

cd BUILD/${GCC}-stage1
  ../../${GCC}/configure --prefix=${PREFIX} --target=${TARGET} \
      --enable-languages=c --disable-shared --disable-threads \
      --disable-libmudflap --disable-libssp --disable-nls \
      --disable-libgomp --with-cpu=arm1136jf-s --with-fpu=vfp

  make all-gcc
  make install-gcc

5: Build glibc for ARM: Edit the paths in mkglibc.sh (if needed) and execute:

#! /bin/sh

# how to install glibc using this script:
# 
# Create the ${BUILDROOT} directory, put this script (mkglibc.sh) 
# in it.
# In ${BUILDROOT}, create a directory ./src and put the glibc tarball in it.

# go up one directory and run this script. 

TARGET=arm-SamyGO-linux-gnueabi
BUILDROOT=/tmp/arm-tools                     # change to meet your needs
PREFIX=/usr/local                            # change to your liking
SYSROOT=${BUILDROOT}/sysroot
GLIBC_VER=glibc-2.5.90-9.0.9

export ARCH=arm
export CROSS_COMPILE=${TARGET}-
export PATH=$PATH:${PREFIX}/bin
 
cd ${BUILDROOT}/src

# unpack

tar -zxvf ${GLIBC_VER}.tgz              # from 32B650.zip

patch -p0 < ./${GLIBC_VER}_fc11.patch

rm -rf ${BUILDROOT}/src/glibc-build-localedef
mv ${BUILDROOT}/src/${GLIBC_VER}/glibc-build-localedef ./

mkdir -p ${BUILDROOT}/src/BUILD/${GLIBC_VER}
cd BUILD/${GLIBC_VER}

# create some cached defaults: 
echo "libc_cv_forced_unwind=yes" > config.cache
echo "libc_cv_c_cleanup=yes" >> config.cache

export GCC_PATH=${PREFIX}/bin

BUILD_CC=gcc CC=${GCC_PATH}/${CROSS_COMPILE}gcc ../../${GLIBC_VER}/configure \
    --target=${TARGET} --host=${TARGET} --prefix=${PREFIX}/${TARGET} \
    --with-__thread \
    --cache-file=config.cache --with-headers=${SYSROOT}/usr/include \
    --with-glibc=${BUILDROOT}/src/${GLIBC_VER} \
    --disable-profile --enable-add-ons
make 
make install

Finally, gcc needs to be rebuilt and linked against the just built glibc for ARM. Now C++-support will be included as well.

6: Build gcc, stage2: Edit install_gcc_stage2.sh and execute. In this script, links to the kernel header files are created in the include/ directory of the toolchain. That's not very elegant. Normally, the C-compiler should try and find the kernel headers in e.g., /usr/src/linux/include, but that's where the native kernel sources for your build platform reside. Your build platform is not necessarily the same as your target platform (most likely not). The method presented here works, but needs some editing in the future.

#! /bin/sh

# how to install gcc stage 2 using this script:
# 
# Create the ${BUILDROOT} directory, put this script (install_gcc_stage2.sh) 
# in it.
# In ${BUILDROOT}, create a directory ./src and put the gcc tarball in it.

# go up one directory and run this script. 

TARGET=arm-SamyGO-linux-gnueabi
BUILDROOT=/tmp/arm-tools
PREFIX=/usr/local                            # change to your liking
SYSROOT=${BUILDROOT}/sysroot
GCC=gcc-4.2.0-4.0.9 

export ARCH=arm
export CROSS_COMPILE=${TARGET}-
export PATH=$PATH:${PREFIX}/bin
 
cd ${BUILDROOT}/src

# remove links to kernel headers if they exist:
rm -f  ${PREFIX}/${TARGET}/include/linux
rm -f  ${PREFIX}/${TARGET}/include/asm
rm -f  ${PREFIX}/${TARGET}/include/asm-generic

# create symlinks to kernel headers:

ln -s ${SYSROOT}/usr/include/linux ${PREFIX}/${TARGET}/include/linux
ln -s ${SYSROOT}/usr/include/asm ${PREFIX}/${TARGET}/include/asm
ln -s ${SYSROOT}/usr/include/asm-generic ${PREFIX}/${TARGET}/include/asm-generic

# make builddir: 

mkdir -p BUILD/${GCC}-stage2

cd BUILD/${GCC}-stage2

CC=gcc ../../${GCC}/configure --target=${TARGET} --prefix=${PREFIX} \
   --enable-languages=c,c++ --enable-threads --enable-shared \
   --disable-nls --enable- __cxa_atexit --enable-long-long \
   --enable-c99 --with-cpu=arm1136jf-s --with-fpu=vfp

make
make install

When you look in /usr/local/bin now, you should see the cross-compilers for C and C++ for arm-SamyGO-linux-gnueabi.

Building the toolchain on Windows (Cygwin)

To be continued soon ...