RaspberryPiWithWebEngine

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This topic describes how to set up self-compiled Qt WebEngine on Raspberry Pi 3 running Raspbian Stretch with WebGL support using VC4 open source drivers.

If you are interested in an older setup for Raspbian with closed source drivers and the toolchain from Broadcom you can find it here.

Setup

The setup is tested on Rasberry Pi 3 model B. We'll use the latest open source VC4 Gallium3D driver instead of the old closed source binaries from Broadcom. We cannot use the Broadcom toolchain to compile Qt 5.13.2. and Qt WebEngine, because it uses the GCC compiler version 4.8, and we'll need at least version 5.0.

Raspbian Stretch ships with Binutils 2.28, GCC 6.3.0 and GlibC 2.24. Since we would like to use the same GlibC version and try to avoid running into a lot of issues when trying to compiler older GlibC 2.24 with newer GCC, we are going to simply mirror the Raspbian setup and reuse the same versions as Raspbian ships. Therefore we'll start with downloading the sources and Raspbian image.

  • Let's create our workspace:
    mkdir -p ~/workspaces/raspberrypi-raspbian/image
    mkdir -p ~/workspaces/raspberrypi-raspbian/toolchain/sources
    mkdir -p ~/workspaces/raspberrypi-raspbian/qt/qt5
  • Let's now download archives:
    cd ~/workspaces/raspberrypi-raspbian/image
    wget https://downloads.raspberrypi.org/raspbian/images/raspbian-2019-04-09/2019-04-08-raspbian-stretch.zip
    cd ~/workspaces/raspberrypi-raspbian/toolchain/sources
    wget https://ftpmirror.gnu.org/binutils/binutils-2.28.tar.bz2
    wget https://ftpmirror.gnu.org/gcc/gcc-6.3.0/gcc-6.3.0.tar.gz
    tar xf gcc-6.3.0.tar.gz
    tar xf binutils-2.28.tar.bz2

Please note, most likely you would like to download the corresponding SHA1 to verify the archives.

Sysroot

To be able to compile things, we need a part of sysroot to be present on our build machine. As shown here, you could simply start your Raspbian on the boards and then rsync the network required libs and includes to the host machine. However, we will do this by mounting the image via a loop device and use qemu to install build dependencies. We need a copy of libs and headers, because we want to modify and adjust the symlinks in our sysroot.

  • Let's extract the Raspbian image:
    cd ~/workspaces/raspberrypi-raspbian/image
    unzip 2019-04-08-raspbian-stretch.zip
  • We add at least 2G space to the image to be able to fit qt build with debug info:
    dd if=/dev/zero bs=1M count=2048 >> 2019-04-08-raspbian-stretch.img
  • Make loopback devices for the image:
    losetup -fP 2019-04-08-raspbian-stretch.img
    losetup -a
    /dev/loop0: []: (~/raspberrypi-raspbian/image/2019-04-08-raspbian-stretch.img)
  • Check the partition layout and note the start sector of the root partition (here /dev/loop0p2):
    fdisk -u -l /dev/loop0
    
    Disk /dev/loop0: 5.2 GiB, 5628755968 bytes, 10993664 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0xcd48578f
    
    Device       Boot Start     End Sectors  Size Id Type
    /dev/loop0p1       8192   96042   87851 42.9M  c W95 FAT32 (LBA)
    /dev/loop0p2      98304 6799359 6701056  3.2G 83 Linux
  • Recreate second partition to use extra space:
    fdisk /dev/loop0
    
    # Type d to proceed to delete a partition.
    # Type 2 to select the 2nd partition and press enter.
    # Type n to add the partition
    # Type p to select primary partition
    # Type 2 to select partition number
    # Type 98304 as first sector
    # Type Enter to select default last sector
    # Type N to keep the signature
    # Type w to save partition table and exit
  • Finally resize partition:
    e2fsck -f /dev/loop0p2
    resize2fs /dev/loop0p2
  • Copy static qemu binary to image (setup binfmt_misc and qemu interpreter is distro specific and therefore beyond this guide)
    cp /usr/bin/qemu-arm /media/card/usr/bin/
  • Mount the root partition:
    mount /dev/loop0p2 -t ext4 /media/card
    mount --bind /dev /media/card/dev
    mount --bind /sys /media/card/sys
    mount --bind /proc /media/card/proc
    mount --bind /dev/pts /media/card/dev/pts
  • chroot to sysroot and get qt5 build dependencies in. Note that we are going to use mk-build-deps to create dummy package, so we can uninstall dependencies when no longer needed:
    cd /media/card/
    chroot . bin/bash
    # uncomment the deb-src line
    vi /etc/apt/sources.list
    apt update
    apt install devscripts    
    mk-build-deps libqt5gui5
    apt install ./qtbase-opensource-src-build-deps_5.7.1+dfsg-3+rpi1+deb9u1_armhf.deb
    apt install libnss3 libnss3-dev
    exit
  • rsync the parts that we need:
    cd ~/workspaces/raspberrypi-raspbian
    rsync -av /media/card/lib sysroot
    rsync -av /media/card/usr/include sysroot/usr
    rsync -av /media/card/usr/lib sysroot/usr
  • 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
  • Cleanup image (optional)
    cd /media/card/
    chroot . bin/bash
    apt remove devscripts qtbase-opensource-src-build-deps libnss3-dev
    apt autoremove
    apt clean
    exit
  • Umount no longer needed mounts
    umount /media/card/sys /media/card/proc /media/card/dev/pts /media/card/dev

Toolchain

To compile Qt, we need a cross-compiler toolchain. There are many excellent tools to compile a toolchain, such as crosstool-ng or buildroot. However, we choose to compile GCC from scratch. Compiling a compiler is a bit tricky and includes a few tasks:

  • Installing Linux headers that are required to make system calls from the C library and to compile it
  • Building biuntils to get a cross-linker, a cross-assembler, and some other tools using your host compiler
  • Building the first stage GCC (bootstrapping), to have a basic compiler with C language support and static linking
  • Building the C library using the first stage compiler
  • Building a second stage GCC, which uses the C library, supports dynamic linking and the C++ language

We already have GlibC compiled in our sysroot shipped by Rasbian, so we are going to cheat here a bit and skip the bootstrapping of GCC and the building of GlibC itself. We can simply use sysroot directly and just compile the linker, the assembler and final cross-compiler.

  • Let's do initial setup:
    export WORKSPACE_ROOT=~/workspaces/raspberrypi-raspbian/toolchain
    export PREFIX=${WORKSPACE_ROOT}/toolchain
    export TARGET=arm-linux-gnueabihf
    export SYSROOT=${WORKSPACE_ROOT}/../sysroot
    export PATH=${PREFIX}/bin:$PATH
    mkdir -p ${PREFIX}
    cd ${WORKSPACE_ROOT}
  • Let's build the linker and assembler:
    mkdir -p build/binutils
    pushd build/binutils
    ../../sources/binutils-2.28/configure --target=${TARGET} --prefix=${PREFIX} --with-arch=armv6 --with-fpu=vfp --with-float=hard --disable-multilib
    make -j12
    make install
    popd
  • We need additional GMP, MPFR and MPC libraries to be able to build GCC. This can be easily set up by running script in the GCC source directory.
    cd ~/workspaces/raspberrypi-raspbian/toolchain/sources/gcc-6.3.0
    contrib/download_prerequisites
  • Let's now build GCC:
    mkdir -p build/gcc2
    pushd build/gcc2
    ../../sources/gcc-6.3.0/configure --prefix=${PREFIX} --target=${TARGET} --with-sysroot=${SYSROOT} --enable-languages=c,c++ --disable-multilib --enable-multiarch --with-arch=armv6 --with-fpu=vfp --with-float=hard
    make -j12
    make install
    popd

Note that I got a compiler error, so you might have to edit raspberrypi-raspbian/toolchain/sources/gcc-6.3.0/gcc/ubsan.c line 1474 and change it to:

|| xloc.file[0] == '\0' || xloc.file[0] == '\xff'

Compiling Qt

As shown here, we could do a top level build of Qt, but we are going to do prefix module builds just to show an alternative way of building Qt. We need three repositories to have Qt WebEngine up and running: qtbase, qtdeclarative and qtwebengine. It is important to configure Qt with linux-rasp-pi3-vc4-g++ device, since this spec contains newer vc4 OpenGL drivers. We also compile two back-ends for QPA: xcb to run it in the Rasbian window manager and eglfs to run as a full-screen single-window application.

  • Let's configure qtbase, compile it and install it:
    cd ~/workspaces/raspberrypi-raspbian/qt/qt5
    git clone git://code.qt.io/qt/qtbase.git
    git checkout 5.13.1
    mkdir -p ~/workspaces/raspberrypi-raspbian/qt/build/qtbase
    cd ~/workspaces/raspberrypi-raspbian/qt/build/qtbase
    ~/workspaces/qt/qt5/qtbase/configure -release -opengl es2 -device linux-rasp-pi3-vc4-g++ \
        -device-option CROSS_COMPILE=~/workspaces/raspberrypi-raspbian/toolchain/toolchain/bin/arm-linux-gnueabihf- \
        -opensource -confirm-license -nomake tests -nomake examples -verbose -no-pch -eglfs -xcb \
        -sysroot /home/stefan/workspaces/raspberrypi-raspbian/sysroot \
        -prefix /usr/local/qt/5.13 \
        -extprefix /opt/qt/5.13/raspbian/sysroot \
        -hostprefix /opt/qt/5.13/raspbian
    make
    make install
  • Compile qtdeclarative and install it:
    cd ~/workspaces/raspberrypi-raspbian/qt/qt5
    git clone git://code.qt.io/qt/qtdeclarative.git
    git checkout 5.13.1
    mkdir -p ~/workspaces/raspberrypi-raspbian/qt/build/qtdeclarative
    cd ~/workspaces/qt/build/qtdeclarative
    /opt/qt/5.13/raspbian/bin/qmake ~/workspaces/qt/qt5/qtdeclarative
    make
    make install
  • Compile qtwebengine and install it:
    cd ~/workspaces/raspberrypi-raspbian/qt/qt5
    git clone git://code.qt.io/qt/qtwebengine.git
    git submodule init
    git checkout 5.13.1
    git submodule update
    mkdir -p ~/workspaces/raspberrypi-raspbian/qt/build/qtwebengine
    cd ~/workspaces/raspberrypi-raspbian/qt/build/qtwebengine
    /opt/qt/5.13/raspbian/bin/qmake ~/workspaces/qt/qt5/qtwebengine -- --no-feature-webengine-arm-thumb
    make
    make install
  • Compile the Simple Browser example:
    mkdir -p ~/workspaces/raspberrypi-raspbian/qt/build/simplebrowser
    cd ~/workspaces/raspberrypi-raspbian/qt/build/simplebrowser
    /opt/qt/5.13/raspbian/bin/qmake ~/workspaces/qt/qt5/qtwebengine/examples/webenginewidgets/simplebrowser
    make

Deploy

We still have our image mounted form the sysroot step. If you chose to rsync sysroot over the network, just replace the rsync steps below with the equivalent network location of your Rasberry Pi board.

  • Deploy with rsync
    mkdir -p  /media/card/usr/local/qt/5.13
    rsync -av /opt/qt/5.13/raspbian/sysroot/ /media/card/usr/local/qt/5.13
    cp ~/workspaces/raspberrypi-raspbian/qt/build/simplebrowser/simplebrowser /media/card/usr/local/bin/
  • Unmount the image
    umount /media/card
  • Copy the image to the SD card (replace sdX with the device on your machine):
    cd ~/workspaces/raspberrypi-raspbian/image
    dd if=2019-04-08-raspbian-stretch.img of=/dev/sdX bs=4M
  • Boot the image up, and switch to enable OpenGL (Full KMS):
    raspi-config

Opengl kms.png


  • Fix run-time linker search paths
    echo /usr/local/qt/5.13/lib > /etc/ld.so.conf.d/00-qt.5.13.conf
    ldconfig
  • Reboot
  • To run Simple Browser within Raspbian Desktop (former PIXEL Desktop) open console or SSH:
    export DISPLAY=:0
    export QTWEBENGINE_DISABLE_GPU_THREAD=1
    /usr/local/bin/simplebrowser -platform xcb
  • Navigate to chrome://gpu/, and you should see:

Gpu.png

Webgl.png

  • To run without x11 , SSH to the device and shut down the login manager:
    systemctl stop lightdm
    export QTWEBENGINE_DISABLE_GPU_THREAD=1
    /usr/local/bin/simplebrowser -platform eglfs