Cross Compiling for Raspbian Buster

6 minute read

Guessing from the number of clones on GitHub my cross compilation setup for Raspbian stretch still seems to be pretty popular. This makes it worthwhile to move on to Raspbian buster and enjoy the gcc update (the version jumped from 6.3 to 8.3).

raspberry

This post serves as an addendum to my previous post covering the same topic.

Container Setup

As a first step we build a cross compilation container (Debian buster amd64) that contains a cross compiler that knows how to build binaries for the Raspbian armhf platform:

The following git repository contains the container setup instructions. We clone it to our Ubuntu (>= 16.04) or Debian (>= stretch) development machine:

git clone https://github.com/lueschem/edi-raspbian.git
cd edi-raspbian

Under the assumption that edi is already installed, we can directly generate our mulitarch cross compilation container (please carefully setup your ssh keys before starting the container build):

sudo edi -v lxc configure raspbian-buster-cross buster-cross.yml

To retrieve the IP address of the container (IP_ADDRESS_OF_CONTAINER) we use the following command:

lxc list raspbian-buster-cross

To add some convenience we insert the following snippet into ~/.ssh/config:

Host raspbian-buster-cross
    Hostname IP_ADDRESS_OF_CONTAINER

Now we can enter the container using ssh:

ssh raspbian-buster-cross

The sudo password within the container is ChangeMe!, you can change it using passwd.

Hello World

To explain a typical workflow we make use of the standard hello world example.

Within the container we change into the shared workspace folder edi-workspace and within the sub-folder hello we write some code:

mkdir -p ~/edi-workspace/hello
cd ~/edi-workspace/hello
cat << EOF > hello.cpp
#include <iostream>
 
int main()
{
    std::cout << "Hello Raspbian!" << std::endl;
    return 0;
}
EOF

To make the development cycle fast and convenient, we can already verify the correct behaviour of our code without even touching the Raspberry Pi.

g++ hello.cpp -o hello-amd64
./hello-amd64

Now that we are sure that the code works on our development host, we can cross compile it for the Raspberry Pi:

arm-linux-gnueabihf-g++ hello.cpp -o hello-raspbian

The resulting hello-raspbian binary can now be copied over to the Raspberry Pi and it should execute properly even on a Raspberry Pi 1 that does not support ARMv7-A instructions (they would be required by Debian armhf).

Using CMake

Now we can turn our hello world example into a simple CMake project.

First we have to install CMake within the container:

sudo apt install cmake

Now we write a minimal CMake configuration:

cat << EOF > CMakeLists.txt
cmake_minimum_required (VERSION 2.6)
project (hello)
add_executable(hello-raspbian-cmake hello.cpp)
EOF

To do the cross compilation we need a toolchain file:

cat << EOF > toolchain.armhf
SET (CMAKE_SYSTEM_NAME Linux)
SET (CMAKE_SYSTEM_PROCESSOR armhf)

SET (CMAKE_C_COMPILER arm-linux-gnueabihf-gcc)
SET (CMAKE_CXX_COMPILER arm-linux-gnueabihf-g++)

SET (CMAKE_FIND_ROOT_PATH /usr/arm-linux-gnueabihf)
SET (ONLY_CMAKE_FIND_ROOT_PATH TRUE)
SET(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
SET(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
SET(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

IF (CMAKE_CROSSCOMPILING)
  MESSAGE("CROSS COMPILING for ${CMAKE_C_COMPILER}")
  INCLUDE_DIRECTORIES(BEFORE ${CMAKE_FIND_ROOT_PATH}/include)
ENDIF (CMAKE_CROSSCOMPILING)
EOF

Finally we do the cross compilation using CMake:

cmake -DCMAKE_TOOLCHAIN_FILE=toolchain.armhf .
make

Just to make sure that we really cross compiled the binary we take a closer look at it:

$ file ./hello-raspbian-cmake 
./hello-raspbian-cmake: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=fae4f484bef40eb2f71a46e8e1018dd0d258f47d, not stripped

Note: This is an absolutely minimal CMake setup. A more advanced setup will allow you to build amd64 and armhf binaries side by side.

Recompilation of the SSL Library

As within the previous blog post we can now cross-compile a Raspbian package:

mkdir -p ~/edi-workspace/openssl-cross && cd ~/edi-workspace/openssl-cross
apt-get source libssl1.1
cd openssl-1.1.1d
export DEB_BUILD_OPTIONS=nocheck; debuild -us -uc -aarmhf

The resulting armhf Raspbian package can now be installed on a Raspberry Pi.

Dealing with +rpi1 Issues

In this mixed Debian/Raspbian environment you might encounter situations, where the package versions of Raspbian do not exactly match the package versions of Debian. Let’s assume that we want to recompile apt and therefore we would like to install the required build dependencies:

$ sudo apt build-dep -aarmhf apt
Reading package lists... Done
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 builddeps:apt:armhf : Depends: g++:armhf (>= 4:7) but it is not going to be installed
                       Depends: libsystemd-dev:armhf but it is not going to be installed
                       Depends: libudev-dev:armhf but it is not going to be installed
                       Depends: libzstd-dev:armhf (>= 1.0) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

Ouch - this did not work out as expected. The “-dev” packages require an exact version match:

$ sudo apt install libzstd-dev:armhf
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 libzstd-dev:armhf : Depends: libzstd1:armhf (= 1.3.8+dfsg-3+rpi1) but it is not going to be installed
E: Unable to correct problems, you have held broken packages

From Raspbian we can get:

$ apt-cache policy libzstd1:armhf
libzstd1:armhf:
  Installed: (none)
  Candidate: 1.3.8+dfsg-3+rpi1
  Version table:
     1.3.8+dfsg-3+rpi1 400
        400 http://mirrordirector.raspbian.org/raspbian buster/main armhf Packages

… and from Debian:

$ apt-cache policy libzstd1      
libzstd1:
  Installed: 1.3.8+dfsg-3
  Candidate: 1.3.8+dfsg-3
  Version table:
 *** 1.3.8+dfsg-3 500
        500 http://deb.debian.org/debian buster/main amd64 Packages
        100 /var/lib/dpkg/status

In fact, the versions are slightly different (1.3.8+dfsg-3+rpi1 versus 1.3.8+dfsg-3).

Luckily we can fix the issue by compiling libraries with matching versions. First we have to enable the Raspbian sources within the container. To do so, we can add the following line

deb-src http://mirrordirector.raspbian.org/raspbian/ buster main contrib non-free rpi

to /etc/apt/sources.list.d/raspbian_buster.list.

Now we can recompile and install the missing libzstd1 library:

sudo apt update
sudo apt build-dep libzstd1
apt source libzstd1
cd libzstd-1.3.8+dfsg
debuild -us -uc
sudo dpkg -i ../libzstd1_1.3.8+dfsg-3+rpi1_amd64.deb ../libzstd-dev_1.3.8+dfsg-3+rpi1_amd64.deb

Finally we can also install the armhf development package:

sudo apt install libzstd-dev:armhf

The same steps are required for systemd:

sudo apt build-dep systemd
apt source systemd
cd systemd-241
debuild -us -uc
sudo dpkg -i ../libsystemd0_241-7~deb10u1+rpi1_amd64.deb ../libsystem
d-dev_241-7~deb10u1+rpi1_amd64.deb ../libudev1_241-7~deb10u1+rpi1_amd64.deb  ../libudev-dev_241-7~deb10u1+rpi1_amd64.deb
sudo dpkg -i ../systemd_241-7~deb10u1+rpi1_amd64.deb ../systemd-sysv_241-7~deb10u1+rpi1_amd64.deb

After some additional tricks I was able to cross compile the apt package.

Conclusion

The cross compilation experience for Raspbian is not as smooth as for a pure Debian setup - but it works.

A kernel cross compilation is straight forward while more effort and expertise is required to cross compile non trivial packages such as apt.

Furthermore the above generated container can be used as a “digital twin” of the Raspberry Pi and a lot of development effort can happen within the container (without touching the target hardware).

If some components perfidiously refuse to get cross compiled, you can still buy the most powerful Raspberry Pi available and natively compile them on that device.

Further Reading

Please read this blog post if you are interested in running pure Debian on a Raspberry Pi 2 or 3.

If you would like to add your favourite integrated development environment (IDE) to your cross compilation toolchain you can read on here.

You can also take a look at the presentation I did for an embedded GNU/Linux developer meet-up.

Updated:

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