Jessie armel Cross Compile

Debian Jessie previously provided cross compilers via the Emdebian project. However, Emdebian has been unmaintained for a number of years and is no longer able to provide a viable install package. In order to cross compile from a Debian Jessie workstation, a third party cross compiler is required.

A Debian Jessie install on a workstation has the ability to build for the same release on other architectures using Debian binary libraries. A PC, virtual machine, or chroot will need to be used for this. Install Debian Jessie for your workstation here.

From a Debian workstation (not the target), run the following commands to set up the cross compiler. Note that this expects a 64-bit Debian Jessie install on the workstation. 32-bit installations are not supported at this time.

# Run "lsb_release -a" and verify Debian 8.X is returned.  These instructions are not
# expected to work on any other version or distribution.

cd ~
wget http://ftp.embeddedarm.com/ftp/ts-arm-sbc/ts-7680-linux/cross-toolchains/gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabi.tar.xz
# The above toolchain is from Linaro. Other cross compilers can be used but have not been tested.
mkdir cross_compiler
tar xvf gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabi.tar.xz -C ~/cross_compiler
export PATH=$PATH:~/cross_compiler/gcc-linaro-4.9-2016.02-x86_64_arm-linux-gnueabi/bin/
# The 'export' command needs to be run every time the user logs in. It is possible to add this command to the user's ".bashrc" file
# in their home directory to ensure it is automatically run every time the user is logged in.
su root
dpkg --add-architecture armel
apt-get update
apt-get install build-essential lzop

This will install a toolchain that can be used with the prefix "arm-linux-gnueabi-". All of the standard GCC tools will start with that name, eg "arm-linux-gnueabi-gcc".

The toolchain can now compile a simple hello world application. Create hello-world.c on the Debian workstation:

#include <stdio.h>
int main(){
    printf("Hello World\n");
}

To compile this:

arm-linux-gnueabi-gcc hello-world.c -o hello-world
file hello-world

This will return that the binary created is for ARM. Copy this to the target platform to run it there.

Debian Jessie supports multiarch which can install packages designed for other architectures. On workstations this is how 32-bit and 64-bit support is provided. This can also be used to install armel packages on an x86 based workstation.

This cross compile environment can link to a shared library from the Debian root. The package would be installed in Debian on the workstation to provide headers and ".so" files. This is included in most "-dev" packages. When run on the arm target it will also need a copy of the library installed, but it does not need the -dev package. Note that since the cross compiler used is 3rd party and not directly from Debian, some compile commands that include libraries will need additional arguments to tell the compiler and linker where on the workstation to find the necessary headers and libraries. Usually, the additional arguments will look like the following string, however adjustments may need to be made depending on the application.

 -I/usr/include -L/usr/lib/arm-linux-gnueabi -L/lib/arm-linux-gnueabi -Wl,-rpath=/usr/lib/arm-linux-gnueabi,-rpath=/lib/arm-linux-gnueabi

apt-get install libcurl4-openssl-dev:armel

# Download the simple.c example from curl:
wget https://raw.githubusercontent.com/bagder/curl/master/docs/examples/simple.c
# After installing the supporting library, curl will link just as compiling on the unit.
arm-linux-gnueabi-gcc -I/usr/include -L/usr/lib/arm-linux-gnueabi -L/lib/arm-linux-gnueabi -Wl,-rpath=/usr/lib/arm-linux-gnueabi,-rpath=/lib/arm-linux-gnueabi simple.c -o simple -lcurl

The binary can now be copied over to the target platform and executed using the curl library that will be loaded at runtime from the target.

If any created binaries do not rely on hardware support like GPIO or CAN, they can be run using qemu.

# using the hello world example from before:
./hello-world
# Returns Exec format error
apt-get install qemu-user-static
./hello-world