Could not load the Qt platform plugin "xcb" in "" problem.

Piotrrr

Hi.
I'm trying to configure a cross-compilator for Raspberry Pi 4. I made it working once with Qt 5.12.6 but recently I needed to update it to Qt 5.15 so I followed the steps from here: https://github.com/UvinduW/Cross-Compiling-Qt-for-Raspberry-Pi-4.
When trying to run the example app "qopenglwidget" (step 6), I get error:

qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
Failed to move cursor on screen DSI1: -13
Segmentation fault

I tried sudo apt install libxcb-xinerama0, cause it solved the problem for some but it didn't change anything. I already updated Qt from 5.12.6 to 5.15 on another raspberry following the same tutorial and everything is working fine there so no clue why it doesn't work this time.

Thanks.

raven-worx

@Piotrrr
run ldd on QTDIR/plugins/platforms/libqxcb.so
and install the packages of all missing dependencies.

JonB

@Piotrrr
Try @raven-worx's ldd. If still stuck, export QT_DEBUG_PLUGINS=1 and then run your app for further diagnostic information.

Piotrrr

Thanks for the reply.
Output of ldd /usr/local/qt5.15/plugins/platforms/libqxcb.so:

linux-vdso.so.1 (0xbee48000)
	/usr/lib/arm-linux-gnueabihf/libarmmem-${PLATFORM}.so => /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so (0xb6f99000)
	libQt5XcbQpa.so.5 => /usr/local/qt5.15/plugins/platforms/../../lib/libQt5XcbQpa.so.5 (0xb6e97000)
	libfontconfig.so.1 => /usr/lib/arm-linux-gnueabihf/libfontconfig.so.1 (0xb6e2f000)
	libfreetype.so.6 => /usr/lib/arm-linux-gnueabihf/libfreetype.so.6 (0xb6d8c000)
	libz.so.1 => /lib/arm-linux-gnueabihf/libz.so.1 (0xb6d61000)
	libQt5Gui.so.5 => /usr/local/qt5.15/plugins/platforms/../../lib/libQt5Gui.so.5 (0xb68bc000)
	libQt5DBus.so.5 => /usr/local/qt5.15/plugins/platforms/../../lib/libQt5DBus.so.5 (0xb684a000)
	libQt5Core.so.5 => /usr/local/qt5.15/plugins/platforms/../../lib/libQt5Core.so.5 (0xb640f000)
	libGLESv2.so.2 => /usr/lib/arm-linux-gnueabihf/libGLESv2.so.2 (0xb63f0000)
	libpthread.so.0 => /lib/arm-linux-gnueabihf/libpthread.so.0 (0xb63c6000)
	libX11-xcb.so.1 => /usr/lib/arm-linux-gnueabihf/libX11-xcb.so.1 (0xb63b4000)
	libxcb-icccm.so.4 => /usr/lib/arm-linux-gnueabihf/libxcb-icccm.so.4 (0xb63a0000)
	libxcb-image.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-image.so.0 (0xb638c000)
	libxcb-shm.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-shm.so.0 (0xb6379000)
	libxcb-keysyms.so.1 => /usr/lib/arm-linux-gnueabihf/libxcb-keysyms.so.1 (0xb6366000)
	libxcb-randr.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-randr.so.0 (0xb6349000)
	libxcb-render-util.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-render-util.so.0 (0xb6335000)
	libxcb-render.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-render.so.0 (0xb631a000)
	libxcb-shape.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-shape.so.0 (0xb6307000)
	libxcb-sync.so.1 => /usr/lib/arm-linux-gnueabihf/libxcb-sync.so.1 (0xb62f1000)
	libxcb-xfixes.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-xfixes.so.0 (0xb62da000)
	libxcb-xinerama.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-xinerama.so.0 (0xb62c7000)
	libxcb-xkb.so.1 => /usr/lib/arm-linux-gnueabihf/libxcb-xkb.so.1 (0xb62a2000)
	libxcb-xinput.so.0 => not found
	libxcb.so.1 => /usr/lib/arm-linux-gnueabihf/libxcb.so.1 (0xb6273000)
	libXext.so.6 => /usr/lib/arm-linux-gnueabihf/libXext.so.6 (0xb6254000)
	libX11.so.6 => /usr/lib/arm-linux-gnueabihf/libX11.so.6 (0xb6132000)
	libxkbcommon.so.0 => /usr/lib/arm-linux-gnueabihf/libxkbcommon.so.0 (0xb60e9000)
	libxkbcommon-x11.so.0 => /usr/lib/arm-linux-gnueabihf/libxkbcommon-x11.so.0 (0xb60d2000)
	libdl.so.2 => /lib/arm-linux-gnueabihf/libdl.so.2 (0xb60bf000)
	libstdc++.so.6 => /usr/lib/arm-linux-gnueabihf/libstdc++.so.6 (0xb5f78000)
	libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0xb5ef6000)
	libgcc_s.so.1 => /lib/arm-linux-gnueabihf/libgcc_s.so.1 (0xb5ec9000)
	libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0xb5d7b000)
	libxcb-xinput.so.0 => not found
	libgthread-2.0.so.0 => /usr/lib/arm-linux-gnueabihf/libgthread-2.0.so.0 (0xb5d69000)
	libglib-2.0.so.0 => /usr/lib/arm-linux-gnueabihf/libglib-2.0.so.0 (0xb5c59000)
	libexpat.so.1 => /lib/arm-linux-gnueabihf/libexpat.so.1 (0xb5c18000)
	libuuid.so.1 => /lib/arm-linux-gnueabihf/libuuid.so.1 (0xb5c01000)
	/lib/ld-linux-armhf.so.3 (0xb6fc1000)
	libpng16.so.16 => /usr/lib/arm-linux-gnueabihf/libpng16.so.16 (0xb5bc5000)
	libharfbuzz.so.0 => /usr/lib/arm-linux-gnueabihf/libharfbuzz.so.0 (0xb5ac7000)
	libdbus-1.so.3 => /lib/arm-linux-gnueabihf/libdbus-1.so.3 (0xb5a76000)
	libdouble-conversion.so.1 => /usr/lib/arm-linux-gnueabihf/libdouble-conversion.so.1 (0xb5a52000)
	libicui18n.so.63 => /usr/lib/arm-linux-gnueabihf/libicui18n.so.63 (0xb5804000)
	libicuuc.so.63 => /usr/lib/arm-linux-gnueabihf/libicuuc.so.63 (0xb567e000)
	libicudata.so.63 => /usr/lib/arm-linux-gnueabihf/libicudata.so.63 (0xb3c80000)
	libpcre2-16.so.0 => /usr/lib/arm-linux-gnueabihf/libpcre2-16.so.0 (0xb3c04000)
	libGLdispatch.so.0 => /usr/lib/arm-linux-gnueabihf/libGLdispatch.so.0 (0xb3b85000)
	libxcb-util.so.0 => /usr/lib/arm-linux-gnueabihf/libxcb-util.so.0 (0xb3b70000)
	libXau.so.6 => /usr/lib/arm-linux-gnueabihf/libXau.so.6 (0xb3b5d000)
	libXdmcp.so.6 => /usr/lib/arm-linux-gnueabihf/libXdmcp.so.6 (0xb3b48000)
	libpcre.so.3 => /lib/arm-linux-gnueabihf/libpcre.so.3 (0xb3ad1000)
	libgraphite2.so.3 => /usr/lib/arm-linux-gnueabihf/libgraphite2.so.3 (0xb3aa0000)
	libsystemd.so.0 => /lib/arm-linux-gnueabihf/libsystemd.so.0 (0xb3a03000)
	libbsd.so.0 => /usr/lib/arm-linux-gnueabihf/libbsd.so.0 (0xb39db000)
	librt.so.1 => /lib/arm-linux-gnueabihf/librt.so.1 (0xb39c4000)
	liblzma.so.5 => /lib/arm-linux-gnueabihf/liblzma.so.5 (0xb3993000)
	liblz4.so.1 => /usr/lib/arm-linux-gnueabihf/liblz4.so.1 (0xb3967000)
	libgcrypt.so.20 => /lib/arm-linux-gnueabihf/libgcrypt.so.20 (0xb388d000)
	libgpg-error.so.0 => /lib/arm-linux-gnueabihf/libgpg-error.so.0 (0xb3863000)

jsulm

@Piotrrr said in Could not load the Qt platform plugin "xcb" in "" problem.:

libxcb-xinput.so.0 => not found

this lib is not there

Piotrrr

Run the app with export QT_DEBUG_PLUGINS=1 and I got this:

Got keys from plugin meta data ("xcb")
QFactoryLoader::QFactoryLoader() checking directory path "/home/pi/platforms" ...
Cannot load library /usr/local/qt5.15/plugins/platforms/libqxcb.so: (libxcb-xinput.so.0: cannot open shared object file: No such file or directory)
QLibraryPrivate::loadPlugin failed on "/usr/local/qt5.15/plugins/platforms/libqxcb.so" : "Cannot load library /usr/local/qt5.15/plugins/platforms/libqxcb.so: (libxcb-xinput.so.0: cannot open shared object file: No such file or directory)"
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.

So it's looking for this file in /home/pi/platforms but that directory doesn't exist, am I right? Where can I get/install this libxcb-xinput.so.0 from?

jsulm

@Piotrrr said in Could not load the Qt platform plugin "xcb" in "" problem.:

Where can I get/install this libxcb-xinput.so.0 from?

What OS is running on your device?
If Raspbian then it should be libxcb-xinput package.

Piotrrr

I installed it with apt-get install libxcb-xinput-dev and now the example app works.

Thanks all for the help.

Pablo J. Rogina

@Piotrrr said in Could not load the Qt platform plugin "xcb" in "" problem.:

now the example app works

great, so please don't forget to mark your post as solved!

juanba

I am facing a similar issue trying to cross-compile QT5.12.3 for the raspberry pi3 using arm-linux-gnueabihf-gcc-8.3.0 on Ubuntu LTS 20.04

My two centaves coin follows the qt.conf strategy

Detect where the crosscompiled X11 backend pluggin is installed on yout target. Following the guides related with, it is usually deployed on /usr/local/qt5pi/plugins or similar
Verify the object libqxcb.so is fully resolved on your host, below is my output after installing all dependencies

 # ldd /usr/local/qt5pi/plugins/platforms/libqxcb.so 
 linux-vdso.so.1 (0x7ed50000)
        /usr/lib/arm-linux-gnueabihf/libarmmem-${PLATFORM}.so => /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so (0x76f90000)
        libQt5XcbQpa.so.5 => /usr/local/qt5pi/examples/gui/analogclock/plugins/platforms/../../lib/libQt5XcbQpa.so.5 (0x76e3e000)
        libfontconfig.so.1 => /lib/arm-linux-gnueabihf/libfontconfig.so.1 (0x76dda000)
        libfreetype.so.6 => /lib/arm-linux-gnueabihf/libfreetype.so.6 (0x76d37000)
        libz.so.1 => /lib/arm-linux-gnueabihf/libz.so.1 (0x76d0c000)
        libQt5Gui.so.5 => /usr/local/qt5pi/examples/gui/analogclock/plugins/platforms/../../lib/libQt5Gui.so.5 (0x76855000)
        libQt5DBus.so.5 => /usr/local/qt5pi/examples/gui/analogclock/plugins/platforms/../../lib/libQt5DBus.so.5 (0x767c1000)
        libQt5Core.so.5 => /usr/local/qt5pi/examples/gui/analogclock/plugins/platforms/../../lib/libQt5Core.so.5 (0x7632f000)
        libGLESv2.so.2 => /lib/arm-linux-gnueabihf/libGLESv2.so.2 (0x76310000)
        libpthread.so.0 => /lib/arm-linux-gnueabihf/libpthread.so.0 (0x762e6000)
        libX11-xcb.so.1 => /lib/arm-linux-gnueabihf/libX11-xcb.so.1 (0x762d4000)
        libxcb-icccm.so.4 => /lib/arm-linux-gnueabihf/libxcb-icccm.so.4 (0x762c0000)
        libxcb-image.so.0 => /lib/arm-linux-gnueabihf/libxcb-image.so.0 (0x762ac000)
        libxcb-shm.so.0 => /lib/arm-linux-gnueabihf/libxcb-shm.so.0 (0x76299000)
        libxcb-keysyms.so.1 => /lib/arm-linux-gnueabihf/libxcb-keysyms.so.1 (0x76286000)
        libxcb-randr.so.0 => /lib/arm-linux-gnueabihf/libxcb-randr.so.0 (0x76269000)
        libxcb-render-util.so.0 => /lib/arm-linux-gnueabihf/libxcb-render-util.so.0 (0x76255000)
        libxcb-render.so.0 => /lib/arm-linux-gnueabihf/libxcb-render.so.0 (0x7623a000)
        libxcb-shape.so.0 => /lib/arm-linux-gnueabihf/libxcb-shape.so.0 (0x76227000)
        libxcb-sync.so.1 => /lib/arm-linux-gnueabihf/libxcb-sync.so.1 (0x76211000)
        libxcb-xfixes.so.0 => /lib/arm-linux-gnueabihf/libxcb-xfixes.so.0 (0x761fa000)
        libxcb-xinerama.so.0 => /lib/arm-linux-gnueabihf/libxcb-xinerama.so.0 (0x761e7000)
        libxcb-xkb.so.1 => /lib/arm-linux-gnueabihf/libxcb-xkb.so.1 (0x761c2000)
        libxcb.so.1 => /lib/arm-linux-gnueabihf/libxcb.so.1 (0x76193000)
        libXrender.so.1 => /lib/arm-linux-gnueabihf/libXrender.so.1 (0x7617a000)
        libXext.so.6 => /lib/arm-linux-gnueabihf/libXext.so.6 (0x7615b000)
        libX11.so.6 => /lib/arm-linux-gnueabihf/libX11.so.6 (0x76039000)
        libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0x75fb7000)
        libxkbcommon.so.0 => /lib/arm-linux-gnueabihf/libxkbcommon.so.0 (0x75f6e000)
        libxkbcommon-x11.so.0 => /lib/arm-linux-gnueabihf/libxkbcommon-x11.so.0 (0x75f57000)
        libdl.so.2 => /lib/arm-linux-gnueabihf/libdl.so.2 (0x75f44000)
        libstdc++.so.6 => /lib/arm-linux-gnueabihf/libstdc++.so.6 (0x75dfd000)
        libgcc_s.so.1 => /lib/arm-linux-gnueabihf/libgcc_s.so.1 (0x75dd0000)
        libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0x75c82000)
        libgthread-2.0.so.0 => /lib/arm-linux-gnueabihf/libgthread-2.0.so.0 (0x75c70000)
        libglib-2.0.so.0 => /lib/arm-linux-gnueabihf/libglib-2.0.so.0 (0x75b60000)
        libexpat.so.1 => /lib/arm-linux-gnueabihf/libexpat.so.1 (0x75b1f000)
        libuuid.so.1 => /lib/arm-linux-gnueabihf/libuuid.so.1 (0x75b08000)
        /lib/ld-linux-armhf.so.3 (0x76fb8000)
        libpng16.so.16 => /lib/arm-linux-gnueabihf/libpng16.so.16 (0x75acc000)
        libharfbuzz.so.0 => /lib/arm-linux-gnueabihf/libharfbuzz.so.0 (0x759ce000)
        libdbus-1.so.3 => /lib/arm-linux-gnueabihf/libdbus-1.so.3 (0x7597d000)
        libicui18n.so.63 => /lib/arm-linux-gnueabihf/libicui18n.so.63 (0x7572f000)
        libicuuc.so.63 => /lib/arm-linux-gnueabihf/libicuuc.so.63 (0x755a9000)
        libicudata.so.63 => /lib/arm-linux-gnueabihf/libicudata.so.63 (0x73bab000)
        libpcre2-16.so.0 => /lib/arm-linux-gnueabihf/libpcre2-16.so.0 (0x73b2f000)
        libdouble-conversion.so.1 => /lib/arm-linux-gnueabihf/libdouble-conversion.so.1 (0x73b0b000)
        libGLdispatch.so.0 => /lib/arm-linux-gnueabihf/libGLdispatch.so.0 (0x73a8c000)
        libxcb-util.so.0 => /lib/arm-linux-gnueabihf/libxcb-util.so.0 (0x73a77000)
        libXau.so.6 => /lib/arm-linux-gnueabihf/libXau.so.6 (0x73a64000)
        libXdmcp.so.6 => /lib/arm-linux-gnueabihf/libXdmcp.so.6 (0x73a4f000)
        libpcre.so.3 => /lib/arm-linux-gnueabihf/libpcre.so.3 (0x739d8000)
        libgraphite2.so.3 => /lib/arm-linux-gnueabihf/libgraphite2.so.3 (0x739a7000)
        libsystemd.so.0 => /lib/arm-linux-gnueabihf/libsystemd.so.0 (0x7390a000)
        libbsd.so.0 => /lib/arm-linux-gnueabihf/libbsd.so.0 (0x738e2000)
        librt.so.1 => /lib/arm-linux-gnueabihf/librt.so.1 (0x738cb000)
        liblzma.so.5 => /lib/arm-linux-gnueabihf/liblzma.so.5 (0x7389a000)
        liblz4.so.1 => /lib/arm-linux-gnueabihf/liblz4.so.1 (0x7386e000)
        libgcrypt.so.20 => /lib/arm-linux-gnueabihf/libgcrypt.so.20 (0x73794000)
        libgpg-error.so.0 => /lib/arm-linux-gnueabihf/libgpg-error.so.0 (0x7376a000)

Now the patch can be safetly written.
On your executable directory write a file qt.conf (which follows a .ini format) where you can specify the specifical QT context required to run your application, on this particular case we only need to adjust the plugins path. A full description can be read here
i.e .

pi@raspberrypi:/usr/local/qt5pi/examples/gui/analogclock $ tree
.
├── analogclock
├── analogclock.pro
├── main.cpp
├── plugins -> /usr/local/qt5pi/plugins
└── qt.conf

1 directory, 4 files
pi@raspberrypi:/usr/local/qt5pi/examples/gui/analogclock $ cat qt.conf 
[Paths]
Plugins=plugins

IHTH

PD: The qtbase main entry was deployed with the following spec

$ echo $CROSS_COMPILER_LOCATION
/home/juanba/raspi/tools/cross-pi-gcc-8.3.0-2

$ ./configure -release -qt-xcb -xcb -opengl es2  -device linux-rasp-pi3-vc4-g++ -device-option CROSS_COMPILE=$(echo $CROSS_COMPILER_LOCATION)/bin/arm-linux-gnueabihf- -sysroot ~/raspi/sysroot -prefix /usr/local/qt5pi -extprefix /home/juanba/raspi/qt5pi -opensource -confirm-license -skip qtscript -skip qtwar -v -recheck -L$HOME/raspi//sysroot/usr/lib/arm-linux-gnueabihf -I$HOME/raspi//sysroot/usr/include/arm-linux-gnueabihf