RaspberryPiWithQt6WebEngine

Introduction

This page describes how to set up self-compiled Qt6 with WebEngine on Raspberry Pi 4 running Raspberry Pi OS.

To see other guides visit:

• Qt5 WebEngine cross compilation guide for Raspbian
• Qt6 general cross compilation guide for Raspberry Pi OS
• Qt6 WebEngine general compilation quide for all platforms

Setup

To be able to cross compile Qt6 for Raspberry Pi OS, we need three things:

• Raspberry Pi OS sysroot for arm64 target
• Cross-Compile toolchain
• Qt6 host build

Qt6 uses cmake therefore to cross-compile we need to have actually two builds of Qt. One Qt6 host build, which is later used to cross-compile the arm64 Qt build.

In this guide we are going to cross compile Qt 6.9.

  Note: As shown here, we could do a 'top level build' of Qt6, but we are going to do 'prefix module build' just to show an alternative way of building Qt6.

As latest Raspberry Pi runs on wayland we need five repositories to have Qt 6WebEngine up and running: qtbase, shadertools, qtdeclarative, qtwebengine and qtwayland.

• Let's create our workspace:

  mkdir -p ~/workspaces/rpi/toolchain/sysroot
  mkdir -p ~/workspaces/rpi/toolchain/qt/build/host
  mkdir -p ~/workspaces/rpi/toolchain/qt/build/target
  mkdir -p ~/workspaces/rpi/target
  mkdir -p ~/workspaces/rpi/image
  

• Let's checkout the main qt6 repository, select 6.9 branch and fetch source code of minimal subset of qt modules to be able to compile QtWebEngine:

  cd ~/workspaces/rpi/toolchain/qt
  git clone git://code.qt.io/qt/qt5.git qt6
  cd qt6
  git checkout origin/6.9
  ./init-repository --module-subset=qtbase,qtshadertools,qtdeclarative,qtwayland,qtwebengine  --no-resolve-deps
  

  Note: Re-selecting other branches requires rerun of init-repository script with option '-f'.

Sysroot

To be able to cross-compile, we need a part of arm64 target sysroot to be present on our build machine. As shown here, you could simply start your Rasberry Pi OS on the board and then rsync the required libs and includes to the host machine with SSH connection. However, in this guide we will mount the Raspberry Pi OS image via a loop device, use qemu to install build dependencies and than make a local copy.

  Note: We do need a local copy of 'libs' and 'headers' from the image, as we want to adjust the symlinks.

• Let's now download Raspberry Pi OS:

  cd ~/workspaces/rpi/image
  wget https://downloads.raspberrypi.com/raspios_arm64/images/raspios_arm64-2024-11-19/2024-11-19-raspios-bookworm-arm64.img.xz
  

• Let's extract the image:

  unxz --keep 2024-11-19-raspios-bookworm-arm64.img.xz
  

• We need add at least 2G space to the image to be able to fit qt build with debug info (see here instructions)
• Make loop devices for the image:

  losetup -fP 2024-11-19-raspios-bookworm-arm64.img
  losetup -a
  /dev/loop0: [64769]:10797192 (~/workspaces/rpi/image/2024-11-19-raspios-bookworm-arm64.img)
  

• Mount the root partition:

  mount /dev/loop0p2 -t ext4 ~/workspaces/rpi/target
  mount -t proc /proc ~/workspaces/rpi/target/proc
  mount -t sysfs /sys ~/workspaces/rpi/target/sys
  mount --bind /dev ~/workspaces/rpi/target/dev
  mount --bind /dev/pts ~/workspaces/rpi/target/dev/pts
  

• Make sure you have working setup of qemu arm64 static interpeter.

  Note: Setup of qemu static interpreter is distribution specific. Please refer to your Linux distribution documentation.

  Note: Also registering bin formats is distribution specific. Check 'systemctl status binfmt' if you distribution uses systemd.

• We need qemu on the image to able to execute command, therefore copy static qemu binary to image.

  cp /usr/bin/qemu-aarch64-static ~/workspaces/rpi/target/usr/bin/
  

• Chroot to arm64 target:

  cd ~/workspaces/rpi/target
  chroot .
  

• Let's upgrade the image (optional) and install Qt6 build dependencies:

  vi /etc/apt/sources.list
  # uncomment the deb-src lines
  apt update
  apt upgrade
  apt build-dep libqt6gui6
  

• Let's install build dependencies for QtWebEngine:

  apt install libnss3-dev
  exit
  

• rsync the parts that we need:

  cd ~/workspaces/rpi/toolchain
  rsync -av ~/workspaces/rpi/target/lib sysroot
  rsync -av ~/workspaces/rpi/target/usr/include sysroot/usr
  rsync -av ~/workspaces/rpi/target/usr/lib sysroot/usr
  rsync -av ~/workspaces/rpi/target/usr/share/pkgconfig sysroot/usr/share
  

• Adjust symlinks to be relative:

  wget https://raw.githubusercontent.com/Kukkimonsuta/rpi-buildqt/master/scripts/utils/sysroot-relativelinks.py
  chmod +x sysroot-relativelinks.py
  ./sysroot-relativelinks.py sysroot
  

  Note: Command-line tool called symlinks should not be used instead as it creates dangling links.

  Note: We umount the image and detach loop device in Cleanup section

Toolchain

To cross-compile Qt, we need a cross-compiler toolchain. There are many excellent tools to compile a toolchain, such as crosstool-ng. We could also simply download ready 3dparty toolchain form the internet. However, this guide will use the official gcc cross compiler, which is shipped with Debian distribution, same as the one shipped with Raspberry Pi OS. In time of writing this quide latest Raspberry Pi OS is called 'Bookworm' and it is shipped with gcc 12.2 and Qt 6.4. Therefore we will use the gnu gcc cross compiler from Bookworm release. To setup the cross-compiler toolchain will use 'debootstrap' which is a very convenient tool to install Debian base system into a subdirectory of any other running Linux system. Most of distributions ship this tool therefore it was selected as most generic approach.

  Note: The other approach could be for example installing Debian distribution on VM.

• To setup Bookworm Debian release on your machine execute:

  debootstrap --arch amd64 bookworm ~/workspaces/rpi/toolchain http://ftp.uk.debian.org/debian
  

• Let's mount and chroot into newly created installation:

  mount -t proc /proc ~/workspaces/rpi/toolchain/proc
  mount -t sysfs /sys ~/workspaces/rpi/toolchain/sys
  mount --bind /dev ~/workspaces/rpi/toolchain/dev
  mount --bind /dev/pts ~/workspaces/rpi/toolchain/dev/pts
  
  chroot ~/workspaces/rpi/toolchain /bin/bash
  

• Let's install host, cross compiler and lld linker:

  apt update
  apt install build-essential crossbuild-essential-arm64 lld
  

Qt6 Host Build

We need Qt6 host build as cross-compilation requires all host compiled tools like for example 'moc'. We will do here qt 'module' build in separate build directory.

  Note: For more information about build options see here.

  Note: After toolchain setup, we should be still chrooted into our host Debian root (~/workspaces/rpi/toolchain).

• Add source packages repository for 'apt' by following line to '/etc/apt/sources.list' file:

  deb-src http://deb.debian.org/debian bookworm main
  

• Let's install dependencies for Qt host build using know dependencies for Qt 6.4:

  apt update
  apt build-dep libqt6gui6
  

• Let's install build dependencies for QtWebEngine:

  apt install nodejs gperf bison flex python3-html5lib libnss3-dev
  

• Let's configure host build for Qt6 qtbase, build it and install into ~/workspaces/rpi/toolchain/opt/qt/host:

  cd /qt/build/host
  mkdir qtbase
  cd qtbase 
  /qt/qt6/qtbase/configure -release -nomake tests -nomake examples -linker lld -prefix /opt/qt/host
  cmake --build . --parallel
  cmake --install .
  

  Note: The path /qt/qt6/qtbase in chroot is really ~/workspaces/rpi/toolchain/qt/qt6/qtbase on the build machine.

• Let's configure and build remaining modules:

  cd /qt/build/host
  mkdir qtshadertools qtdeclarative qtwebengine qtwayland
  
  cd qtshadertools
  /opt/qt/host/bin/qt-configure-module ../../../qt6/qtshadertools
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtdeclarative
  /opt/qt/host/bin/qt-configure-module ../../../qt6/qtdeclarative
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtwayland
  /opt/qt/host/bin/qt-configure-module ../../../qt6/qtwayland
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtwebengine
  /opt/qt/host/bin/qt-configure-module ../../../qt6/qtwebengine
  cmake --build . --parallel
  cmake --install .
  cd ..
  

Qt6 Target Cross Build

We should have by now Qt6 host build, target arm64 sysroot and cross compilation toolchain. To setup now cmake build we still need to create cmake toolchain file 'rpi.toolchain.cmake', which will provide information to cmake about our toolchian and sysroot setup.

  Note: After toolchain setup, we should be still chrooted into our host Debian root (~/workspaces/rpi/toolchain).

• Let's create toolchain file:

  vi /qt/rpi.toolchain.cmake
  
  cmake_minimum_required(VERSION 3.18)
  include_guard(GLOBAL)
  
  set(CMAKE_SYSTEM_NAME Linux)
  set(CMAKE_SYSTEM_PROCESSOR arm)
  
  set(CMAKE_SYSROOT /sysroot)
  set(CMAKE_C_COMPILER /usr/bin/aarch64-linux-gnu-gcc-12)
  set(CMAKE_CXX_COMPILER /usr/bin/aarch64-linux-gnu-g++-12)
  
  set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
  set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
  
  set(QT_COMPILER_FLAGS "-march=armv8-a")
  set(QT_COMPILER_FLAGS_RELEASE "-O2 -pipe")
  set(QT_LINKER_FLAGS "-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed")
  
  include(CMakeInitializeConfigs)
  
  function(cmake_initialize_per_config_variable _PREFIX _DOCSTRING)
    if (_PREFIX MATCHES "CMAKE_(C|CXX|ASM)_FLAGS")
      set(CMAKE_${CMAKE_MATCH_1}_FLAGS_INIT "${QT_COMPILER_FLAGS}")
  
      foreach(config DEBUG RELEASE MINSIZEREL RELWITHDEBINFO)
        if (DEFINED QT_COMPILER_FLAGS_${config})
          set(CMAKE_${CMAKE_MATCH_1}_FLAGS_${config}_INIT "${QT_COMPILER_FLAGS_${config}}")
        endif()
      endforeach()
    endif()
  
  
    if (_PREFIX MATCHES "CMAKE_(SHARED|MODULE|EXE)_LINKER_FLAGS")
      foreach (config SHARED MODULE EXE)
        set(CMAKE_${config}_LINKER_FLAGS_INIT "${QT_LINKER_FLAGS}")
      endforeach()
    endif()
  
    _cmake_initialize_per_config_variable(${ARGV})
  endfunction()
  
  # See output of 'pkg-config --variable pc_path pkg-config' command.
  set(ENV{PKG_CONFIG_PATH} "")
  set(ENV{PKG_CONFIG_LIBDIR} ${CMAKE_SYSROOT}/usr/lib/aarch64-linux-gnu/pkgconfig:${CMAKE_SYSROOT}/usr/lib/pkgconfig:${CMAKE_SYSROOT}/usr/share/pkgconfig)
  set(ENV{PKG_CONFIG_SYSROOT_DIR} ${CMAKE_SYSROOT})
  

  Note: If you wonder why we overload 'cmake_initialize_per_config_variable' see this blog post.

  Note: The pkg-config exports could be set in build shell instead of toolchain.

• Let's configure target build for Qt6 qtbase, build it and install into ~/workspaces/rpi/toolchain/opt/qt/target:

  cd /qt/build/target
  mkdir qtbase
  cd qtbase 
  ../../../qt6/qtbase/configure -release -opengl es2 -nomake examples -nomake tests -qt-host-path /opt/qt/host -extprefix /opt/qt/target -prefix /usr/local/qt6 -- -DCMAKE_TOOLCHAIN_FILE=/qt/rpi.toolchain.cmake
  cmake --build . --parallel
  cmake --install .
  

• Let's configure and build remaining modules:

  cd /qt/build/target
  mkdir qtshadertools qtdeclarative qtwebengine qtwayland
  
  cd qtshadertools
  /opt/qt/target/bin/qt-configure-module ../../../qt6/qtshadertools
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtdeclarative
  /opt/qt/target/bin/qt-configure-module ../../../qt6/qtdeclarative
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtwayland
  /opt/qt/host/bin/qt-configure-module ../../../qt6/qtwayland
  cmake --build . --parallel
  cmake --install .
  cd ..
  
  cd qtwebengine
  /opt/qt/target/bin/qt-configure-module ../../../qt6/qtwebengine
  cmake --build . --parallel
  cmake --install .
  cd ..
  

Simplebrowser

To be able to test QtWebengine we can build 'simplebrowser' example.

• first to able to run the example on the device we need a proper RPATH set for our target application, therefore edit example's 'CMakeLists.txt' and add the correct setting for our setup:

  vi /qt/qt6/qtwebengine/examples/webenginewidgets/simplebrowser/CMakeLists.txt
  set(CMAKE_INSTALL_RPATH "\$ORIGIN/../../../lib")
  

  Note: You do not have to st RPATH, instead use can export LD_LIBRARY_PATH to point to Qt installed libs on the device.

• now let's configure and build the example:

cd /qt/build/target
mkdir simplebrowser
cd simplebrowser

/opt/qt/target/bin/qt-cmake ../../../qt6/qtwebengine/examples/webenginewidgets/simplebrowser/CMakeLists.txt -DCMAKE_INSTALL_PREFIX=/opt/qt/target/ -G Ninja
cmake --build .
cmake --install .

Deploy

We need to deploy compiled sources to sdcard. We can use RasberryPi OS image from sysroot step, mount it and rsync the content.

  Note: We are not any longer in the chrooted enviroment, however target image is still mounted.

• Deploy with rsync:

  rsync -av ~/workspaces/rpi/toolchain/opt/qt/target/ ~/workspaces/rpi/target/usr/local/qt6/
  

  Note: If you wnat to rsync sysroot over the network, just replace the rsync steps below with the equivalent network location of your Rasberry Pi board.

Cleanup

During our toolchain preparastion we have left few mounts behind, therfore it is time to umount evetyhing

• Umount no longer needed mounts:

  umount ~/workspaces/rpi/target/sys ~/workspaces/rpi/target/proc 
  umount ~/workspaces/rpi/target/dev/pts ~/workspaces/rpi/target/dev
  umount ~/workspaces/rpi/target
  

• Detach loop device:

  losetup -d /dev/loop0
  

Write image

It is time to copy the image to the SD card (replace sdX with the device on your machine):

cd ~/workspaces/rpi/image
dd if=2024-11-19-raspios-bookworm-arm64.img of=/dev/sdX bs=4M