RaspberryPiWithQt6WebEngine

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Revision as of 14:03, 8 January 2024 by Michal Klocek (talk | contribs) (fix formatting of host build)
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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:

Setup

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

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 6.5 with WebEngine coming from Qt 6.7

  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.

We need fours repositories to have Qt 6WebEngine up and running: qtbase, shadertools, qtdeclarative and qtwebengine.

  • 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 qt source code and select branches:
    cd ~/workspaces/rpi/toolchain/qt
git clone git://code.qt.io/qt/qtbase.git
cd qtbase
git checkout origin/6.5.3
cd ..

git clone git://code.qt.io/qt/qtshadertools.git
cd qtshadertools
git checkout origin/6.5.3
cd ..

git clone git://code.qt.io/qt/qtdeclarative.git
cd qtdeclarative
git checkout origin/6.5.3
cd ..

git clone git://code.qt.io/qt/qtwebengine.git
cd qtwebengine
git checkout origin/6.7
git submodule init
git submodule update
cd ..

  Note: QtWebEngine needs initialization of the submodule.

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_arm64-2023-12-06/2023-12-05-raspios-bookworm-arm64.img.xz
  • Let's extract the image:
    unxz --keep 2023-12-05-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 2023-12-05-raspios-bookworm-arm64.img
losetup -a
/dev/loop0: [66306]:2363198 (~/workspaces/rpi/image/2023-12-05-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
  • 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/

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

  • 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
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.

  • Umount no longer needed mounts:
    umount ~/workspaces/rpi/target/sys ~/workspaces/rpi/target/proc 
umount ~/workspaces/rpi/target/dev/pts ~/workspaces/rpi/target/dev
  • Detach loop device:
    losetup -d /dev/loop0

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 and cross compiler:
    apt update
apt install build-essential crossbuild-essential-arm64

Qt6 Host Build

We Qt6 Host Build as cross-compilation requires host tools like for example 'moc'. We will do 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 python3-html5lib gperf bison flex libnss-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/qtbase/configure -release -nomake tests -nomake examples -linker lld -prefix /opt/qt/host
cmake --build . --parallel
cmake --install .

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

  • Let's configure and build remaining modules:
    cd /qt/build/host
mkdir qtshadertools qtdeclarative qtwebengine

cd qtshadertools
/opt/qt/host/bin/qt-configure-module ../../../qtshadertools
cmake --build . --parallel
cmake --install .
cd ..

cd qtdeclarative
/opt/qt/host/bin/qt-configure-module ../../../qtdeclarative
cmake --build . --parallel
cmake --install .
cd ..

cd qtwebengine
/opt/qt/host/bin/qt-configure-module ../../../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 
../../../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

cd qtshadertools
/opt/qt/target/bin/qt-configure-module ../../../qtshadertools
cmake --build . --parallel
cmake --install .
cd ..

cd qtdeclarative
/opt/qt/target/bin/qt-configure-module ../../../qtdeclarative
cmake --build . --parallel
cmake --install .
cd ..

cd qtwebengine
/opt/qt/target/bin/qt-configure-module ../../../qtwebengine
cmake --build . --parallel
cmake --install .
cd ..
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