Qt Creator cross compilation kit configuration issue (sysroot, libraries)

Xavier

Hello,

I'm using Yocto and configures a dedicated kit to the cross compilation environment.
When I tried to compile a "helloworld" program I had a linking issue.
I found a solution but I'm not sure I used the good way to solve my issue and I wonder if somebody in this forum can explain me why I experience such an issue and how to fix it properly.

QtCreator configuration
I did compile qt5 toolchain with yocto (meta-toolchain-qt5) and install it.
I did update qtcreator.sh to set the env variable required for cross compilation
I configured the debugger to use the gdb of my toolchain.
I configured the compiler to use the g++ compiler of my toolchain
I configured qmake to use the qmake of my toolchain.
I configured a kit using all these programs and specifying my sysroot.
As I'm cross compiling for a docker image, I kept the device type as Desktop.

The issue
When I tried to compile my "helloworld" program (named QtVersion and writing the version of Qt in a console), the linker is giving me the following error.

g++  -o QtVersion main.o   -lQt5Core -lpthread 
/usr/bin/ld: cannot find -lQt5Core

In this command, few thing are missing for cross compilation. sysroot is not present, the libraries directories are also missing.

The solution
To solve this issue, I did add the following parameters to qmake command executed by my project:

QMAKE_LIBS+="-L/usr/lib -L/lib"  
QMAKE_LFLAGS+="-Wl,-O1 -Wl,-z,origin -Wl,-rpath,\$$ORIGIN -Wl,-rpath,/usr/lib -Wl,-rpath,/lib --sysroot=/data/Yocto/sdk/krogoth/dockerguest/2.1/sysroots/core2-64-poky-linux"

Now, the compilation and execution are working fine.

The questions
Whay should I had to specify such QMAKE_VARIABLE to make it work?
Shouldn't it be done automatically?
The compilation was working but not the linking, why?

Here is the compilation command:

g++ -c -pipe -g -std=gnu++0x -Wall -W -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_CORE_LIB -I../QtVersion -I. -isystem /data/Yocto/sdk/krogoth/dockerguest/2.1/sysroots/core2-64-poky-linux/usr/include/qt5 -isystem /data/Yocto/sdk/krogoth/dockerguest/2.1/sysroots/core2-64-poky-linux/usr/include/qt5/QtCore -I. -I/data/Yocto/sdk/krogoth/dockerguest/2.1/sysroots/core2-64-poky-linux/usr/lib/qt5/mkspecs/linux-g++ -o main.o ../QtVersion/main.cpp

I hope you will be able to help me to understand why I experienced such an issue and how to solve it cleanly.

Thx and rgds,

Xavier