Qt Creator cross-platform development in Stretch: consolidation

pdo debian eng qt-cross

Time to consolidate the exploration done yesterday.

qmake -qtconf

Looking at the work done by the Qt/KDE team I found that there is no need to rebuild qmake, as it can be configured by using the -qtconf option.

The work recently done on debhelper provides a starting point that I can build on.

This qtconf makes qmake use the right paths, including running rcc, moc and uic from /usr/bin/, removing the need for the dirty hack:

[Paths]
Prefix=/usr
ArchData=lib/arm-linux-gnueabihf/qt5
Binaries=lib/qt5/bin
Data=share/qt5
Documentation=share/qt5/doc
Examples=lib/arm-linux-gnueabihf/qt5/examples
Headers=include/arm-linux-gnueabihf/qt5
HostBinaries=bin
HostData=lib/arm-linux-gnueabihf/qt5
HostLibraries=lib/arm-linux-gnueabihf
Imports=lib/arm-linux-gnueabihf/qt5/imports
Libraries=lib/arm-linux-gnueabihf
LibraryExecutables=lib/arm-linux-gnueabihf/qt5/libexec
Plugins=lib/arm-linux-gnueabihf/qt5/plugins
Qml2Imports=lib/arm-linux-gnueabihf/qt5/qml
Settings=/etc/xdg
Translations=share/qt5/translations

It still needs overriding the compiler settings, to make it use a compiler different than g++:

qmake -makefile -qtconf /tmp/qmake.conf QMAKE_CC=arm-linux-gnueabihf-gcc QMAKE_CXX=arm-linux-gnueabihf-g++ QMAKE_LINK=arm-linux-gnueabihf-g++

But then -m64 creeps in and breaks the cross-build (this has been fixed since qtbase 5.9.1+dfsg-12. but my target is stretch):

$ make
arm-linux-gnueabihf-g++ -c -m64 -pipe -std=c++11 -O2 -Wall -W -D_REENTRANT -fPIC -DQT_DEPRECATED_WARNINGS -DQT_NO_DEBUG -DQT_SVG_LIB -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I. -isystem /usr/include/arm-linux-gnueabihf/qt5 -isystem /usr/include/arm-linux-gnueabihf/qt5/QtSvg -isystem /usr/include/arm-linux-gnueabihf/qt5/QtWidgets -isystem /usr/include/arm-linux-gnueabihf/qt5/QtGui -isystem /usr/include/arm-linux-gnueabihf/qt5/QtCore -I. -I/usr/lib/arm-linux-gnueabihf/qt5/mkspecs/linux-g++-64 -o main.o main.cpp
arm-linux-gnueabihf-g++: error: unrecognized command line option ‘-m64’
Makefile:401: recipe for target 'main.o' failed
make: *** [main.o] Error 1

Where does it come from? I found that I could run qmake -query:

$ qmake -query -qtconf /tmp/qmake.conf
QT_SYSROOT:
QT_INSTALL_PREFIX:/usr
QT_INSTALL_ARCHDATA:/usr/lib/arm-linux-gnueabihf/qt5
QT_INSTALL_DATA:/usr/share/qt5
QT_INSTALL_DOCS:/usr/share/qt5/doc
QT_INSTALL_HEADERS:/usr/include/arm-linux-gnueabihf/qt5
QT_INSTALL_LIBS:/usr/lib/arm-linux-gnueabihf
QT_INSTALL_LIBEXECS:/usr/lib/arm-linux-gnueabihf/qt5/libexec
QT_INSTALL_BINS:/usr/lib/qt5/bin
QT_INSTALL_TESTS:/usr/tests
QT_INSTALL_PLUGINS:/usr/lib/arm-linux-gnueabihf/qt5/plugins
QT_INSTALL_IMPORTS:/usr/lib/arm-linux-gnueabihf/qt5/imports
QT_INSTALL_QML:/usr/lib/arm-linux-gnueabihf/qt5/qml
QT_INSTALL_TRANSLATIONS:/usr/share/qt5/translations
QT_INSTALL_CONFIGURATION:/etc/xdg
QT_INSTALL_EXAMPLES:/usr/lib/arm-linux-gnueabihf/qt5/examples
QT_INSTALL_DEMOS:/usr/lib/arm-linux-gnueabihf/qt5/examples
QT_HOST_PREFIX:/usr
QT_HOST_DATA:/usr/lib/arm-linux-gnueabihf/qt5
QT_HOST_BINS:/usr/bin
QT_HOST_LIBS:/usr/lib/arm-linux-gnueabihf
QMAKE_SPEC:linux-g++-64
QMAKE_XSPEC:linux-g++-64
QMAKE_VERSION:3.0
QT_VERSION:5.7.1

I suppose that QMAKE_XSPEC should be linux-g++ instead of linux-g++-64

Poking through Qt's sources I found that I could also tweak TargetSpec, to change it to linux-g++ from its default of linux-g++-64:

[Paths]
Prefix=/usr
ArchData=lib/arm-linux-gnueabihf/qt5
Binaries=lib/qt5/bin
Data=share/qt5
Documentation=share/qt5/doc
Examples=lib/arm-linux-gnueabihf/qt5/examples
Headers=include/arm-linux-gnueabihf/qt5
HostBinaries=bin
HostData=lib/arm-linux-gnueabihf/qt5
HostLibraries=lib/arm-linux-gnueabihf
Imports=lib/arm-linux-gnueabihf/qt5/imports
Libraries=lib/arm-linux-gnueabihf
LibraryExecutables=lib/arm-linux-gnueabihf/qt5/libexec
Plugins=lib/arm-linux-gnueabihf/qt5/plugins
Qml2Imports=lib/arm-linux-gnueabihf/qt5/qml
Settings=/etc/xdg
Translations=share/qt5/translations
TargetSpec=linux-g++

Now, I still need to override the compilers, but that's all I need to do to get a build:

$ qmake -makefile -qtconf /tmp/qmake.conf QMAKE_CC=arm-linux-gnueabihf-gcc QMAKE_CXX=arm-linux-gnueabihf-g++ QMAKE_LINK=arm-linux-gnueabihf-g++
$ make
…
$ file usr/bin/program
usr/bin/program: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (GNU/Linux), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=541e472a29a2b309af2fea40d9aa3439e6616bdd, not stripped

Can I get rid of needing to override the compilers? Let's try poking with TargetSpec:

# cd /usr/lib/arm-linux-gnueabihf/qt5/mkspecs/
# cp -r linux-g++ arm-linux-gnueabihf
# cd arm-linux-gnueabihf
# …tweak…
# cat qmake.conf
#
# qmake configuration for arm-linux-gnueabihf
#

MAKEFILE_GENERATOR      = UNIX
CONFIG                 += incremental
QMAKE_INCREMENTAL_STYLE = sublib

include(../common/linux.conf)
include(../common/gcc-base-unix.conf)
include(../common/g++-unix.conf)

QMAKE_COMPILER          = arm-linux-gnueabihf-gcc

QMAKE_CC                = arm-linux-gnueabihf-gcc

QMAKE_LINK_C            = $$QMAKE_CC
QMAKE_LINK_C_SHLIB      = $$QMAKE_CC

QMAKE_CXX               = arm-linux-gnueabihf-g++

QMAKE_LINK              = $$QMAKE_CXX
QMAKE_LINK_SHLIB        = $$QMAKE_CXX

load(qt_config)

Now, using arm-linux-gnueabihf as TargetSpec:

[Paths]
Prefix=/usr
ArchData=lib/arm-linux-gnueabihf/qt5
Binaries=lib/qt5/bin
Data=share/qt5
Documentation=share/qt5/doc
Examples=lib/arm-linux-gnueabihf/qt5/examples
Headers=include/arm-linux-gnueabihf/qt5
HostBinaries=bin
HostData=lib/arm-linux-gnueabihf/qt5
HostLibraries=lib/arm-linux-gnueabihf
Imports=lib/arm-linux-gnueabihf/qt5/imports
Libraries=lib/arm-linux-gnueabihf
LibraryExecutables=lib/arm-linux-gnueabihf/qt5/libexec
Plugins=lib/arm-linux-gnueabihf/qt5/plugins
Qml2Imports=lib/arm-linux-gnueabihf/qt5/qml
Settings=/etc/xdg
Translations=share/qt5/translations
TargetSpec=arm-linux-gnueabihf

It finally works:

$ qmake -makefile -qtconf /tmp/qmake.conf
$ make
$ file usr/bin/program
usr/bin/program: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (GNU/Linux), dynamically linked, interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, BuildID[sha1]=541e472a29a2b309af2fea40d9aa3439e6616bdd, not stripped

Skipping prl file '/usr/lib/arm-linux-gnueabihf/libQt5PlatformSupport.prl', because it cannot be opened (No such file or directory).

Turn this into a kit for Qt Creator

I could not find a way to configure -qtconf in a kit in Qt Creator. Since Qt Creator detects versions of Qt by pointing at their qmake, I resorted to making a custom qmake wrapper:

#!/usr/bin/python3

# /usr/local/bin/qmake-arm-linux-gnueabihf

import sys, os

QT_CONFIG = "/home/enrico/qt-arm-linux-gnueabihf.conf"

argv0 = os.path.join(os.path.dirname(sys.argv[0]), "qmake")

if len(sys.argv) == 1:
    os.execv("/usr/bin/qmake", [argv0] + sys.argv[1:])
else:
    os.execv("/usr/bin/qmake", [argv0] + sys.argv[1:] + ["-qtconf", QT_CONFIG])

Just calling qmake -qtconf /home/enrico/qt-arm-linux-gnueabihf.conf "$@" is not enough: for some invocations of qmake, providing -qtconf gives an error:

$ qmake -qtconf /home/enrico/qt-arm-linux-gnueabihf.conf
qmake: could not find a Qt installation of 'conf'

If needed I can look at qmake's sources to see what is going on, but for now the wrapper above seems to be enough to cover all the needs of Qt Creator, and if the wrapper is in the path, Qt Creator manages to autodetect it on startup.

These are the details of a working arm-linux-gnueabihf kit for Qt Creator:

Device type: Generic Linux Device
Device: my hi-fi
Sysroot: blank
C compiler: /usr/bin/arm-linux-gnueabihf-gcc
C++ compiler: /usr/bin/arm-linux-gnueabihf-g++
Qt version: /usr/local/bin/qmake-arm-linux-gnueabihf

And with this, software cross-builds locally and can be deployed and tested remotely.

Summary of the situation so far

This is what is needed to do cross-build now:

Depend on crossbuild-essential-armhf
Install :armhf versions of Qt and all build-dependencies
Deploy a custom mkspec
Deploy a custom qt.conf
Deploy qmake wrapper
Configure a kit

No dirty hacks, everything can be shipped by a single .deb package.

Further things to investigate:

Find out if there is a way to package and install a kit for Qt Creator
Find an easy way to use a chroot as the cross-build environment, to be able to use cross-build-dependencies that cannot be coinstalled together with their native version

Credits

This has been done as part of my work with Truelite.