Unable to cross-compile Qt 5.14.2 for Raspberry PI zero w because it “requires a C++11 compiler”

Question

This problem has already been encountered for previous versions of Qt5: Stack-overflow post (non-answered yet). I'm having the same problem with a more recent version and I have followed several tutorials online:

• https://www.raspberrypi.org/forums/viewtopic.php?t=204529
• https://wiki.qt.io/RaspberryPi2EGLFS

Even if all these tutorials are outdated, the methodology for cross compiling Qt5 stays the same. My target board is a Raspberry pi zero w running Raspbian Buster. The configuration steps have worked fine (there weren't any errors).

I'm getting the following errors while executing make:

~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:61:4: error: #error "Qt requires C++11 support"
 #  error "Qt requires C++11 support"
    ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:94:13: error: ‘QAtomicOps’ does not name a type
     typedef QAtomicOps<T> Ops;
             ^
In file included from ~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/qglobal.h:1:0,
                 from ~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/src/corelib/global/qt_pch.h:56:
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:97:23: error: ‘QAtomicOpsSupport’ was not declared in this scope
     Q_STATIC_ASSERT_X(QAtomicOpsSupport<sizeof(T)>::IsSupported, "template parameter is an integral of a size not supported on this platform");
                       ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/global/qglobal.h:121:68: note: in definition of macro ‘Q_STATIC_ASSERT_X’
 #  define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)
                                                                    ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:97:51: error: ‘::IsSupported’ has not been declared
     Q_STATIC_ASSERT_X(QAtomicOpsSupport<sizeof(T)>::IsSupported, "template parameter is an integral of a size not supported on this platform");
                                                   ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/global/qglobal.h:121:68: note: in definition of macro ‘Q_STATIC_ASSERT_X’
 #  define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)
                                                                    ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/global/qglobal.h:121:49: error: non-constant condition for static assertion
 #  define Q_STATIC_ASSERT_X(Condition, Message) static_assert(bool(Condition), Message)
                                                 ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:97:5: note: in expansion of macro ‘Q_STATIC_ASSERT_X’
     Q_STATIC_ASSERT_X(QAtomicOpsSupport<sizeof(T)>::IsSupported, "template parameter is an integral of a size not supported on this platform");
     ^
~/Documents/Raspbian/raspi/qt-everywhere-src-5.14.2/qtbase/include/QtCore/../../src/corelib/thread/qbasicatomic.h:97: confused by earlier errors, bailing out
make[3]: *** [Makefile:1836: .pch/Qt5Core.gch/c++] Error 1
make[3]: Leaving directory '~/Documents/Raspbian/raspi/qt5build/qtbase/src/corelib'
make[2]: *** [Makefile:228: sub-corelib-make_first] Error 2
make[2]: Leaving directory '~/Documents/Raspbian/raspi/qt5build/qtbase/src'
make[1]: *** [Makefile:51: sub-src-make_first] Error 2
make[1]: Leaving directory '~/Documents/Raspbian/raspi/qt5build/qtbase'
make: *** [Makefile:88: module-qtbase-make_first] Error 2

Answer 1

For future readers as pointed out the cross compiler provided by: https://github.com/raspberrypi/tools is outdated and cannot be used. I have tried all the methods described above but the one that worked out-of-the-box (for Raspberry Pi 0 W which is based on older ARMv6 architecture) is: https://github.com/Pro/raspi-toolchain This repo provides a Docker image that compiles a newer toolchain from source and even provides a test code that you can cross compile using the generated toolchain and execute on the pi.

Answer 2

The compiler you're using is just too old. The verison you're getting from the link you shared is 4.8.3, whereas you'll need at least gcc 5. (Check here: https://codereview.qt-project.org/c/qt/qtdoc/+/288825 )

The Error you get might be a bit misleading, since gcc itself states that it fully supports C++11 from 4.8.1 as stated here: https://gcc.gnu.org/projects/cxx-status.html#cxx11

I propose u use a more up to date version of gcc. As mentioned within the qt-docs, it should be at least gcc version 5 or higher.

There are several ways for you to et one (ordered from simple to more complicated):

1. Try to use the package manager of your system (eg sudo apt install gcc-arm-linux-gnueabihf)
2. Download one somewhere else. (eg here: https://toolchains.bootlin.com/ )
3. Build your own. (maybe use crosstool-ng). But be aware. that might be tricky, even though I've good experiences using crosstool-ng. or tools alike.

Last but not least, don't forget to change the setting of your./configure step. Pinpoint to the new toolchain you're trying to use.

Kind Regards

Answer 3

I had the same issue.

I ended up with proper cross compilation of Qt 5.15.0 with EGL support only (to avoid using X11 on such tiny Rpi zero) with the following actions:

1- As proposed by @glamis, I used the compilation toolchain from: https://github.com/Pro/raspi-toolchain via the pre-built toolchain in release v1.0.1

2- (crappy) hacked in Qt sources qtdeclarative/src/3rdparty/masm/wtf/OSAllocatorPosix.cpp : I replaced the constant PATH_MAX (not present in this toolchain?) by hardcoded value 4096

3- still in Qt sources, edit the file qtbase/mkspecs/devices/linux-rasp-pi-g++/qmake.conf

3.a) replace all occurrences of -lEGL -lGLESv2 -lOpenVG by -lbrcmEGL -lbrcmGLESv2 -lbrcmOpenVG

3.b) move QMAKE_LIBS_OPENGL_ES2 = -lbrcmGLESv2 -lbrcmEGL outside the if statement to force it in all cases

notes:

• raspberry pi zero, with "Raspberry Pi OS Lite" (aka. raspbian Lite) version, based on debian buster, version 2020-05-27

• dependencies installed: apt install build-essential libfontconfig1-dev libdbus-1-dev libfreetype6-dev libicu-dev libinput-dev libxkbcommon-dev libsqlite3-dev libssl-dev libpng-dev libjpeg-dev libglib2.0-dev libgbm-dev libraspberrypi-dev libudev-dev libinput-dev libts-dev libxcb-xinerama0-dev libxcb-xinerama0

• qt archive used: qt-everywhere-src-5.15.0.tar.xz

• my configure looks like: configure -release -opensource -confirm-license -opengl es2 -device linux-rasp-pi-g++ -device-option CROSS_COMPILE=/opt/cross-pi-gcc/bin/arm-linux-gnueabihf- -sysroot $HOME/rpi/rootfs -prefix /usr/local/qt-5.15.0-rpi -extprefix $HOME/rpi/qt-5.15.0-rpi -hostprefix $HOME/rpi/tools -make libs -no-use-gold-linker -skip qtwayland -skip qtlocation -skip qtscript -v -no-gbm -ssl