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/****************************************************************************
**
** Copyright (C) 2019 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page configure-linux-device.html
\title Configure an Embedded Linux Device
\brief Provides information about how to configure an Embedded Linux device in Qt.
Building Qt for a given device requires a toolchain and a \c sysroot. Additionally, some
devices require vendor-specific adaptation code for EGL and OpenGL ES 2.0 support. This is
not relevant for non-accelerated platforms, such as those that use the LinuxFB plugin, which is
meant for software-based rendering only.
The \e qtbase/mkspecs/devices directory contains configuration and graphics adaptation code for
a number of devices. For example, the \c linux-rasp-pi2-g++ mkspec contains build settings such
as the optimal compiler and linker flags for the \l{http://www.raspberrypi.org}{Raspberry Pi 2}
device. The mkspec also contains information about either an implementation of the \e eglfs
hooks (vendor-specific adaptation code), or a reference to the suitable \e eglfs device
integration plugin. The device is selected through the \l{Qt Configure Options}{configure}
tool's \c -device parameter. The name that follows after this argument must, at least
partially, match one of the subdirectories under \e devices.
The following is an example configuration for the Raspberry Pi 2. For most Embedded Linux
boards, the configure command looks similar:
\badcode
./configure -release -opengl es2 -device linux-rasp-pi2-g++ -device-option CROSS_COMPILE=$TOOLCHAIN/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian/bin/arm-linux-gnueabihf- -sysroot $ROOTFS -prefix /usr/local/qt5
\endcode
The most important parameters are \c -device and \c -sysroot. By specifying \c -sysroot, the
include files and libraries used by \c {configure}'s feature detection tests, as well as Qt
itself, are taken from the specified location, instead of the host PC's standard locations.
Consequently, installing development packages on the host machine has no relevance. For
example, to get \c libinput support, it is not sufficient or necessary to have the \c libinput
development headers and libraries installed on the host environment. Instead, the headers and
the libraries for the target architecture, such as ARM, must be present in the \c sysroot.
\c pkg-config is supported also when performing cross-compilation. \c configure automatically
sets \c PKG_CONFIG_LIBDIR to make \c pkg-config report compiler and linker settings based on
the \c sysroot instead of the host machine. This usually functions well without any further
adjustments. However, environment variables such as \c PKG_CONFIG_PATH must be unset for the
host machine before running \c configure. Otherwise, the Qt build may attempt to use
inappropriate headers and libraries from the host system.
Specifying \c -sysroot results in automatically setting the \c --sysroot argument when invoking
the compiler. In some cases this is not desirable and can be disabled by passing
\c -no-gcc-sysroot to \c configure.
\c -prefix, \c -extprefix, and \c -hostprefix control the intended destination directory of the
Qt build. In the above example the ARM build of Qt is expected to be placed in
\c{/usr/local/qt5} on the target device. Note that running \c{make install} does not deploy
anything to the device. Instead, the \c install step targets the directory specified by
\c extprefix which defaults to \c sysroot + \c prefix and is therefore optional. However, in
many cases "polluting" the sysroot is not desirable and thus specifying \c -extprefix becomes
important. Finally, \c -hostprefix allows separating host tools like qmake, rcc, uic from the
binaries for the target. When given, such tools will be installed under the specified directory
instead of \c extprefix.
For more information, see \l {Qt Configure Options}.
*/
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