cross-compiling Qt6: moc: cannot execute binary file

[warpme]

Hi,

I'm trying to cross-compile Qt6.1.3 to aarch64 target. host is x86_64 linux.

My procedure is following:

1. build minimal native Qt6 "build" (to get native tools for cross-compile). it is installed in <build dir>/qt6

2. cross-build config i'm setting -qt-host-path to <build dir>/qt6

Issue: cross-build fails with:

Output
------
/home/piotro/minimyth2-aarch64/script/qt/qt6/work/main.d/qt-everywhere-src-6.1.3_build/qtbase/libexec/moc: /home/piotro/minimyth2-aarch64/script/qt/qt6/work/main.d/qt-everywhere-src-6.1.3_build/qtbase/libexec/moc: cannot execute binary file

It look like cross-build is not using tools from <build dir>/qt6 but rather from itself (used moc is for aarch64 so obviously can't be executed on my x86_64 host)

What i'm missing?

FYI: my cross-build config:

cat config.opt
-DCMAKE_INSTALL_PREFIX=/usr
-DCMAKE_FIND_ROOT_PATH=/home/piotro/minimyth2-aarch64/images/main/usr
-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER
-DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY
-DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY
-DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY
-DCMAKE_C_COMPILER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-gcc
-DCMAKE_CXX_COMPILER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-g++
-DCMAKE_AR=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-ar
-DCMAKE_LINKER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-ld
-DCMAKE_NM=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-nm
-DCMAKE_OBJCOPY=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-objcopy
-DCMAKE_OBJDUMP=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-objdump
-DCMAKE_RANLIB=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-ranlib
-DCMAKE_STRIP=//home/piotro/minimyth2-aarch64/images/build/usr/bin/aarch64-minimyth-linux-gnu-strip
-prefix
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6
-bindir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/bin
-libdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/lib
-docdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/doc
-headerdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/include
-datadir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/lib
-translationdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/translations
-sysconfdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/lib/settings
-examplesdir
/home/piotro/minimyth2-aarch64/images/main/usr/lib/qt6/examples
-shared
-release
-optimize-size
-confirm-license
-opensource
-no-rpath
-no-optimized-qmake
-platform
linux-g++-64-garbuild
-xplatform
linux-aarch64-gnu-g++-garhost
-qt-host-path
/home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6
-c++std
c++1z
-ltcg
-plugin-sql-mysql
-I
/home/piotro/minimyth2-aarch64/images/main/usr/include/mysql
-L
/home/piotro/minimyth2-aarch64/images/main/usr/lib/mysql
-no-sql-db2
-no-sql-ibase
-no-sql-oci
-no-sql-odbc
-no-sql-psql
-no-sql-sqlite
-no-openvg
-nomake
examples
-nomake
tests
-skip
qtactiveqt
-skip
qt3d
-skip
qtandroidextras
-skip
qtgamepad
-skip
qtlocation
-skip
qtlottie
-skip
qtpurchasing
-skip
qtquick3d
-skip
qtquickcontrols
-skip
qtquickcontrols2
-skip
qtquicktimeline
-skip
qtsensors
-skip
qtserialbus
-skip
qtserialport
-skip
qtspeech
-skip
qttranslations
-skip
qttools
-skip
qtwebengine
-skip
qtvirtualkeyboard
-skip
qtwinextras
-skip
qtcoap
-skip
qtdoc
-skip
qtmqtt
-skip
qtopcua
-silent
-skip
qtwebglplugin
-opengl
es2
-qt-pcre

and my native build config:

cat config.opt
-DCMAKE_INSTALL_PREFIX=/home/piotro/minimyth2-aarch64/images/build/usr
-DCMAKE_FIND_ROOT_PATH=//home/piotro/minimyth2-aarch64/images/build/usr
-DCMAKE_FIND_ROOT_PATH_MODE_PROGRAM=NEVER
-DCMAKE_FIND_ROOT_PATH_MODE_LIBRARY=ONLY
-DCMAKE_FIND_ROOT_PATH_MODE_INCLUDE=ONLY
-DCMAKE_FIND_ROOT_PATH_MODE_PACKAGE=ONLY
-DCMAKE_C_COMPILER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/gcc
-DCMAKE_CXX_COMPILER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/g++
-DCMAKE_AR=//home/piotro/minimyth2-aarch64/images/build/usr/bin/ar
-DCMAKE_LINKER=//home/piotro/minimyth2-aarch64/images/build/usr/bin/ld
-DCMAKE_NM=//home/piotro/minimyth2-aarch64/images/build/usr/bin/nm
-DCMAKE_OBJCOPY=//home/piotro/minimyth2-aarch64/images/build/usr/bin/objcopy
-DCMAKE_OBJDUMP=//home/piotro/minimyth2-aarch64/images/build/usr/bin/objdump
-DCMAKE_RANLIB=//home/piotro/minimyth2-aarch64/images/build/usr/bin/ranlib
-DCMAKE_STRIP=//home/piotro/minimyth2-aarch64/images/build/usr/bin/strip
-prefix
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6
-bindir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/bin
-libdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/lib
-docdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/doc
-headerdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/include
-datadir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/lib
-translationdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/translations
-sysconfdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/lib/settings
-examplesdir
//home/piotro/minimyth2-aarch64/images/build/usr/lib/qt6/examples
-release
-confirm-license
-opensource
-no-rpath
-no-optimized-qmake
-platform
linux-g++-64-garbuild
-xplatform
linux-g++-64-garhost
-c++std
c++1z
-nomake
examples
-nomake
tests
-no-eventfd
-no-glib
-no-icu
-no-openssl
-no-opengl
-no-dbus
-no-pcre
-no-sql-db2
-no-sql-ibase
-no-sql-mysql
-no-sql-oci
-no-sql-odbc
-no-sql-psql
-no-sql-sqlite
-qt-zlib
-qt-libjpeg
-qt-libpng
-qt-freetype
-qt-pcre
-qt-harfbuzz
-no-use-gold-linker
-make
tools
-static
-optimize-size
-no-ltcg
-skip
qt3d
-skip
qt5compat
-skip
qtactiveqt
-skip
qtcharts
-skip
qtcoap
-skip
qtdatavis3d
-skip
qtdeclarative
-skip
qtdoc
-skip
qtimageformats
-skip
qtlottie
-skip
qtmqtt
-skip
qtnetworkauth
-skip
qtopcua
-skip
qtquick3d
-skip
qtquickcontrols2
-skip
qtquicktimeline
-skip
qtscxml
-skip
qtshadertools
-skip
qtsvg
-skip
qttranslations
-skip
qtvirtualkeyboard
-skip
qtwayland
-skip
qttools

[warpme]

Ok, i found where issue is:

In my project i'm passing config switches to ./configure (qt5 compat. way).
This caused some builder default CMAKE vars were not passed to Qt configure.
Missing -DCMAKE_SYSTEM_NAME="Linux" was turning-off cross-compilation.

Now i got cross-compilled Qt6.

Great work with cmake!