Building Qt for a given device requires a toolchain and a
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
qtbase/mkspecs/devices
directory contains configuration and graphics adaptation code for a number of devices. For example, the
linux-rasp-pi2-g++
mkspec contains build settings such as the optimal compiler and linker flags for the
Raspberry Pi 2
device. The mkspec also contains information about either an implementation of the
eglfs
hooks (vendor-specific adaptation code), or a reference to the suitable
eglfs
device integration plugin. The device is selected through the
configure
tool's
-device
parameter. The name that follows after this argument must, at least partially, match one of the subdirectories under
devices
.
The following is an example configuration for the Raspberry Pi 2. For most Embedded Linux boards, the configure command looks similar:
./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
The most important parameters are
-device
and
-sysroot
. By specifying
-sysroot
, the include files and libraries used by
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
libinput
support, it is not sufficient or necessary to have the
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
sysroot
.
pkg-config
is supported also when performing cross-compilation.
configure
automatically sets
PKG_CONFIG_LIBDIR
to make
pkg-config
report compiler and linker settings based on the
sysroot
instead of the host machine. This usually functions well without any further adjustments. However, environment variables such as
PKG_CONFIG_PATH
must be unset for the host machine before running
configure
. Otherwise, the Qt build may attempt to use inappropriate headers and libraries from the host system.
Specifying
-sysroot
results in automatically setting the
--sysroot
argument when invoking the compiler. In some cases this is not desirable and can be disabled by passing
-no-gcc-sysroot
to
configure
.
-prefix
,
-extprefix
，和
-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
/usr/local/qt5
on the target device. Note that running
make install
does not deploy anything to the device. Instead, the
安装
step targets the directory specified by
extprefix
which defaults to
sysroot
+
prefix
and is therefore optional. However, in many cases "polluting" the sysroot is not desirable and thus specifying
-extprefix
becomes important. Finally,
-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
extprefix
.
更多信息，见 Qt 配置选项 .
