准备好MIPS交叉编译器
比如君正X2000的编译器 mips-gcc720-glibc226
将其拷贝到/opt目录下，然后设置好环境变量PATH。
在~/.bashrc中加上
export PATH=/opt/mips-gcc720-glibc226/bin:$PATH
预编译tslib
tslib是一个用于触摸事件的开源的库，可以从github上下载，我们用的是1.22版本。
Qt依赖它来实现触屏事件
./autogen.sh
./configure --host=mips-linux-gnu --prefix=/opt/Qt5.9.0/tslib-1.22
make
make install
./configure --host=mips-linux-gnu --prefix=/opt/Qt5.9.0/tslib-1.22 CC=/opt/mips-gcc720-glibc226/bin/mips-linux-gnu-gcc
加上加上编译器的绝对路径
预编译sqlite3
下载sqlite-autoconf-3340100.tar.gz文件
./configure --host=mips-linux-gnu --prefix=/opt/Qt5.9.0/sqlite3
make
make install
注意：因为/opt目录只有root权限能够写，所以在make install 的时候会提示permission error，这时在make install前加sudo是没用的，还是会报错误。所以不如直接在root用户下编译
交叉编译Qt
此处我们采用的是Qt5.9.0版本，解压之后修改qtbase/mkspecs/devices/linux-mipsel-ci20-g++/qmake.conf
#
# qmake configuration for building with mips-mti-linux-gnu-g++
# build for CI20 targets X11
#
CROSS_COMPILE = mips-linux-gnu- # 改成我们实际使用的交叉编译器
include(../common/linux_device_pre.conf)
QMAKE_CFLAGS = -EL -march=mips32r2
QMAKE_CXXFLAGS = $${QMAKE_CFLAGS}
QMAKE_LFLAGS = -EL
QT_QPA_DEFAULT_PLATFORM = linuxfb # xcb，因为没有GPU，所以默认使用linuxfb
QMAKE_LIBS_EGL = -lEGL -lIMGegl -lusc
QMAKE_LIBS_OPENGL_ES2 = -lGLESv2 $${QMAKE_LIBS_EGL}
include(../common/linux_device_post.conf)
load(qt_config)
在根目录下创建build.sh文件
./configure -prefix /opt/Qt5.9.0/Qt5 \
-opensource \
-release \
-shared \
-pch \
-sqlite \
-I/opt/Qt5.9.0/sqlite3/include \
-L/opt/Qt5.9.0/sqlite3/lib \
-qt-zlib \
-qt-libjpeg \
-qt-libpng \
-qt-freetype \
-no-openssl \
-gui \
-widgets \
-nomake examples \
-nomake tests \
-nomake tools \
-optimized-qmake \
-no-opengl \
-no-cups \
-no-xkb \
-no-sm\
-no-separate-debug-info \
-xplatform devices/linux-mipsel-ci20-g++ \
-linuxfb \
-confirm-license \
-tslib \
-I/opt/Qt5.9.0/tslib-1.22/include \
-L/opt/Qt5.9.0/tslib-1.22/lib \
-recheck-all
chmod a+x build.sh
./build.sh
make -j24
make install
环境变量设置
#tslib
export TSLIB_ROOT=/opt/qtlib/tslib-1.22
export TSLIB_CONSOLEDEVICE=none
export TSLIB_FBDEVICE=/dev/fb0
export TSLIB_TSDEVICE=/dev/input/event0
export TSLIB_CALIBFILE=/etc/pointercal
export TSLIB_CONFFILE=$TSLIB_ROOT/etc/ts.conf
export TSLIB_PLUGINDIR=$TSLIB_ROOT/lib/ts
export TSLIB_TSEVENTTYPE=INPUT
#sqlite3
export SQLITE_ROOT=/opt/qtlib/sqlite3
#QT
export QTDIR=/opt/qtlib/qt5.12.7
export QT_QPA_PLATFORM_PLUGIN_PATH=$QTDIR/plugins
export QT_QPA_PLATFORM=linuxfb:fb=/dev/fb0:size=600x1024:mmSize=600x1024:offset=0x0:rotation=270
export QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS=/dev/input/event0:rotate=270:invertx:inverty
export QT_QPA_FONTDIR=/opt/qtlib/fonts
export QML2_IMPORT_PATH=$QTDIR/qml
export TSDEVICE=/dev/input/event0
#system
export LD_LIBRARY_PATH=$QTDIR/lib:$TSLIB_ROOT/lib:$SQLITE_ROOT/lib:$LD_LIBRARY_PATH
export LD_PRELOAD=/opt/qtlib/libiconv/preloadable_libiconv.so
export PATH=$TSLIB_ROOT/bin:$PATH
export XDG_RUNTIME_DIR=/usr/lib/
export RUNLEVEL=3
#debug
#export QT_DEBUG_PLUGINS=1
遇到的问题
Q: 执行./build.sh的时候报以下错误
ERROR: Feature 'tslib' was enabled, but the pre-condition 'libs.tslib' failed.
A: 预编译tslib的时候--host=mips-linux-gnu设置的编译器不对，要改成实际的交叉编译器
Q: 编译报错
../3rdparty/masm/assembler/MIPSAssembler.h: In member function 'void JSC::MIPSAssembler::vmov(JSC::MIPSAssembler::RegisterID, JSC::MIPSAssembler::RegisterID, JSC::MIPSAssembler::FPRegisterID)':
../3rdparty/masm/assembler/MIPSAssembler.h:696:9: error: 'mfhc1' was not declared in this scope
mfhc1(rd2, rn);
^~~~~
../3rdparty/masm/assembler/MIPSAssembler.h:696:9: note: suggested alternative: 'mthc1'
mfhc1(rd2, rn);
^~~~~
mthc1
Makefile:23325: recipe for target '.obj/qv4unop.o' failed
make[3]: *** [.obj/qv4unop.o] Error 1
Makefile:22966: recipe for target '.obj/qv4binop.o' failed
make[3]: *** [.obj/qv4binop.o] Error 1
Makefile:21955: recipe for target '.obj/qv4assembler.o' failed
make[3]: *** [.obj/qv4assembler.o] Error 1
Makefile:22607: recipe for target '.obj/qv4isel_masm.o' failed
make[3]: *** [.obj/qv4isel_masm.o] Error 1
Makefile:26773: recipe for target '.obj/qv4engine.o' failed
make[3]: *** [.obj/qv4engine.o] Error 1
make[3]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtdeclarative/src/qml'
Makefile:52: recipe for target 'sub-qml-make_first-ordered' failed
make[2]: *** [sub-qml-make_first-ordered] Error 2
make[2]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtdeclarative/src'
Makefile:48: recipe for target 'sub-src-make_first' failed
make[1]: *** [sub-src-make_first] Error 2
make[1]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtdeclarative'
Makefile:360: recipe for target 'module-qtdeclarative-make_first' failed
make: *** [module-qtdeclarative-make_first] Error 2
A: 参考https://bugreports.qt.io/browse/QTBUG-89706 ， 修改qtbase/src/corelib/global/qprocessordetection.h
# if defined(_MIPS_ARCH_MIPS32) || defined(__mips32) || (defined(__mips) && __mips - 0 >= 32)
# define Q_PROCESSOR_MIPS_32
# endif
改成
# if defined(_MIPS_ARCH_MIPS32) || defined(__mips32)
# define Q_PROCESSOR_MIPS_32
# endif
Q: 编译错误
qgeotiledmapscene.cpp:(.text+0x4bf4): undefined reference to `QSGDefaultImageNode::setAnisotropyLevel(QSGTexture::AnisotropyLevel)'
qgeotiledmapscene.cpp:(.text+0x5884): undefined reference to `QSGDefaultImageNode::setAnisotropyLevel(QSGTexture::AnisotropyLevel)'
qgeotiledmapscene.cpp:(.text+0x4bec): undefined reference to `QSGDefaultImageNode::setAnisotropyLevel(QSGTexture::AnisotropyLevel)'
qgeotiledmapscene.cpp:(.text+0x587c): undefined reference to `QSGDefaultImageNode::setAnisotropyLevel(QSGTexture::AnisotropyLevel)'
A: 据说是Qt5.9.0的专属错误，产生错误的原因是这是编译带有opengl的时候不会出问题，但是如果没有带opengl，这个函数会在某个地方被调用，然后出错。
临时解决办法是修改qtlocation/src/location/maps/qgeotiledmapscene.cpp中第609行和第634行，把if(ogl)及后面那条语句注释掉。
这个bug据说在5.9.1修复了。
Q: 编译错误
Makefile:201: recipe for target 'sub-------3rdparty-mapbox-gl-native-make_first' failed
make[4]: *** [sub-------3rdparty-mapbox-gl-native-make_first] Error 2
make[4]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtlocation/src/plugins/geoservices'
Makefile:71: recipe for target 'sub-geoservices-make_first' failed
make[3]: *** [sub-geoservices-make_first] Error 2
make[3]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtlocation/src/plugins'
Makefile:204: recipe for target 'sub-plugins-make_first' failed
make[2]: *** [sub-plugins-make_first] Error 2
make[2]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtlocation/src'
Makefile:47: recipe for target 'sub-src-make_first' failed
make[1]: *** [sub-src-make_first] Error 2
make[1]: Leaving directory '/data/Qt/qt-everywhere-opensource-src-5.9.0/qtlocation'
Makefile:891: recipe for target 'module-qtlocation-make_first' failed
make: *** [module-qtlocation-make_first] Error 2
A: Qt5.9.0专属错误，提示qmapbox相关。这依旧是没带opengl出现的bug。临时解决办法：修改qtlocation/src/plugins/plugins.pro。
TEMPLATE = subdirs
qtHaveModule(positioning): SUBDIRS += position
#qtHaveModule(location): SUBDIRS += geoservices
Q: 编译出来的Qt SDK放到其他的电脑，并在Qt Creator里配置交叉编译环境，配置的Qt Version一直有红色感叹号
A: 这是因为Qt SDK在编译的时候把编译环境的一些路径也带进去了，导致在其他电脑上因为路径不一致报错。在网上找到一种解决方法，在qmake同级目录下创建一个qt.conf文件，内容如下：
[Paths]
Prefix = ..
但是我试了之后没有效果。最后还是通过在编译Qt的时候将-prefix配置到/opt目录，然后将编译出来的SDK打包放到其他电脑的相同路径下解决的问题
Q: 运行的时候报下面的错误
QIconvCodec::convertToUnicode: using Latin-1 for conversion, iconv_open failed
QIconvCodec::convertFromUnicode: using Latin-1 for conversion, iconv_open failed
A: 从 http://ftp.gnu.org/gnu/libiconv/libiconv-1.15.tar.gz下载源代码编译，注意不要下载1.16版本，1.16版本编译出来没有preloadable_libiconv.so库
./configure --host=mips-linux-gnu --prefix=/opt/Qt5.9.0/libiconv
make
make install
编译结果
/opt/Qt5.9.0/libiconv/lib/
├── charset.alias
├── libcharset.a
├── libcharset.la
├── libcharset.so -> libcharset.so.1.0.0
├── libcharset.so.1 -> libcharset.so.1.0.0
├── libcharset.so.1.0.0
├── libiconv.la
├── libiconv.so -> libiconv.so.2.6.0
├── libiconv.so.2 -> libiconv.so.2.6.0
├── libiconv.so.2.6.0
└── preloadable_libiconv.so
将preloadable_libiconv.so拷贝到开发板的/opt/qtlib/libiconv/preloadable_libiconv.so，然后在环境变量中加上
export LD_PRELOAD=/opt/qtlib/libiconv/preloadable_libiconv.so
Qt5.12.7 交叉编译遇到的问题
Q: 编译Qt5.12.7版本报错
qsql_sqlite.cpp:(.text+0x2154): undefined reference to `sqlite3_column_table_name16'
qsql_sqlite.cpp:(.text+0x217c): undefined reference to `sqlite3_column_table_name16'
qsql_sqlite.cpp:(.text+0x2184): undefined reference to `sqlite3_column_table_name16'
A: 在编译sqlite3的时候加上宏SQLITE_ENABLE_COLUMN_METADATA
./configure --host=mips-linux-gnu --prefix=/opt/Qt5.12.7/sqlite3 CFLAGS=-DSQLITE_ENABLE_COLUMN_METADATA
Q: Qt5.12.7 linuxfb画面需要旋转90度
export QT_QPA_PLATFORM=linuxfb:fb=/dev/fb0:size=600x1024:mmSize=600x1024:offset=0x0:rotation=270
#TP也要旋转
export QT_QPA_EVDEV_TOUCHSCREEN_PARAMETERS=/dev/input/event0:rotate=270:invertx:inverty