Cross-compile MySQL driver for RPi3

endr

Hi, I'm developing an application for Raspberrypi 3 that will interact with a mysql server. I'm using Yocto as operative system. I would like to cross-compile the driver for mysql. I'm developing on Ubuntu, I've installed libmysqlclient-dev and libmysqld-dev (via apt-get install). Following the tutorial I've added INCLUDEPATH and LIBS to my .pro file.


QT       += core gui sql

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = MySqlTest
TEMPLATE = app
target.path = /opt/$${TARGET}/bin
INSTALLS += target

SOURCES += main.cpp\
       widget.cpp
INCLUDEPATH += /usr/include/mysql
LIBS += -L/usr/lib/x86_64-linux-gnu -lmysqlclient_r

HEADERS  += widget.h

FORMS    += widget.ui

When I try to build, deploy, then run it wont work, I get those errors:

cannot find -lmysqlclient_r
/usr/lib/x86_64-linux-gnu/libQt5Widgets.so:-1: error: file not recognized: File format not recognized

What I'm doing wrong? Thanks for your help

SGaist

Hi and welcome to devnet,

You are trying to link to your desktop version of the MySQL libraries. You need to use the the ARM version of them.

endr

How can I obtain the ARM version of the MySQL libraries in a folder on my local machine?
I've tried downloading libmysqlclient-dev (via apt-get install) on Raspbian, then copied the /usr folder on my local machine. Then I've changed the path in INCLUDEPATH and LIBS as this:

QT       += core gui sql

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = MySqlTest
TEMPLATE = app
target.path = /opt/$${TARGET}/bin
INSTALLS += target

SOURCES += main.cpp\
        widget.cpp
INCLUDEPATH += /home/andrea/Scaricati/sysroot/usr/include/mysql
LIBS += -L/home/andrea/Scaricati/sysroot/usr/lib/arm-linux-gnueabihf -lmysqlclient_r


HEADERS  += widget.h

FORMS    += widget.ui

But it keeps giving me error such:
cannot find libc.so.6
cannot find libc_nonshared.a
cannot find ld-linux-armhf.so.3

Can you suggest the correct procedure (where to find the right libraries to download) and how to link them correctly in the .pro file?

Thanks for your support

SGaist

You should use the sysroot of your device when cross-compiling so you ensure you have all the correct libraries available.

endr

I've copied the MySQL directory in the include folder of the poky's sysroot, and the shared mysqlclient libraries too in the /usr/lib directory like this:

QT       += core gui sql

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = MySqlTest
TEMPLATE = app
target.path = /opt/$${TARGET}/bin
INSTALLS += target

SOURCES += main.cpp\
        widget.cpp
INCLUDEPATH += /opt/poky/2.3/sysroots/cortexa7hf-neon-vfpv4-poky-linux-gnueabi/usr/include/mysql
LIBS += -L/opt/poky/2.3/sysroots/cortexa7hf-neon-vfpv4-poky-linux-gnueabi/usr/lib -lmysqlclient_r


HEADERS  += widget.h

FORMS    += widget.ui

Now it gives me only one error:

/opt/MySqlTest/bin/MySqlTest: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory
Application finished with exit code 127.

What could it be?

SGaist

Are you running your application on your device when you get that error ?

endr

Yes, I run it from Qt to the remote RPi3. The application runs flawless if I use the Desktop kit. When I use the kit I've made for the Raspberry pi 3 (that has always worked fine) I get that error

jsulm

@endr Does this file exist on your target device: libmysqlclient.so.18 ? If so where?

endr

If I copy :

libmysqlclient.a
libmysqlclient_r.a 
libmysqlclient_r.so 
libmysqlclient_r.so.18 
ibmysqlclient_r.so.18.0.0
libmysqlclient.so 
libmysqlclient.so.18 
libmysqlclient.so.18.0.0

to /usr/lib on my target device I get:

QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers:

otherwise, without copying the shared libraries on the remote device (trying to crosscompile them from the local machine) I keep getting:

/opt/MySqlTest/bin/MySqlTest: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory
Application finished with exit code 127.

What can I do?

jsulm

@endr You can try to start your app like this:

QT_DEBUG_PLUGINS=1 && ./my_app

You will get a lot of output, post it here.

The libraries you're copying: are those for your target (ARM)?

endr

@jsulm
I connect in ssh to the RPi3, start the application as you suggested:

root@rpi3:/opt/MySqlTest/bin# QT_DEBUG_PLUGINS=1 && ./MySqlTest 
./MySqlTest: error while loading shared libraries: libmysqlclient.so.18: cannot open shared object file: No such file or directory

If I copy those shared libraries (from the libmysqlclient-dev package downloaded on a Raspbian OS) to /usr/lib I get this:

root@rpi3:/opt/MySqlTest/bin# QT_DEBUG_PLUGINS=1 && ./MySqlTest 
Unable to query physical screen size, defaulting to 100 dpi.
To override, set QT_QPA_EGLFS_PHYSICAL_WIDTH and QT_QPA_EGLFS_PHYSICAL_HEIGHT (in millimeters).
QSqlDatabase: QMYSQL driver not loaded
QSqlDatabase: available drivers:

jsulm

@endr What does

ldd PATH_TO_YOUR_QT/plugins/sqldrivers/libqsqlmysql.so

on your RaspberryPi say?

endr

There is no sqldrivers directory in qt5/plugins, just those:

root@rpi3:/usr/lib/qt5/plugins# ls -l 
total 68
drwxr-xr-x 2 root root 4096 Jun 14 10:51 bearer
drwxr-xr-x 2 root root 4096 Jun 14 11:44 canbus
drwxr-xr-x 2 root root 4096 Jun 14 10:51 egldeviceintegrations
drwxr-xr-x 2 root root 4096 Jun 14 10:51 generic
drwxr-xr-x 2 root root 4096 Jun 14 12:23 geoservices
drwxr-xr-x 2 root root 4096 Jun 14 11:43 iconengines
drwxr-xr-x 2 root root 4096 Jun 14 12:33 imageformats
drwxr-xr-x 2 root root 4096 Jun 14 12:24 lipi_toolkit
drwxr-xr-x 2 root root 4096 Jun 14 12:08 mediaservice

What do I need to download?

jsulm

@endr How did you install Qt on RaspberryPi?

endr

I'm using Yocto, Qt5 is installed via the meta-qt5 layer during the bitbaking of the image

jsulm

@endr Well, then I don't know what exactly you need to install. Something with qt and mysql. On Ubuntu it is libqt5sql5-mysql package.