在使用之前须要先source env，导入各种环境变量(注意将路径变更成你自己的)：
source ../qt5_sdk/environment-setup-cortexa9hf-vfp-neon-poky-linux-gnueabi
然后我们能够查看一下bash的env了。以下是多出来的一些env，直接在bash中输入export就可以看到：
declare -x AR="arm-poky-linux-gnueabi-ar" declare -x ARCH="arm" declare -x AS="arm-poky-linux-gnueabi-as " declare -x CC="arm-poky-linux-gnueabi-gcc -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 --sysroot=/media/work/iMX6/Yocto/qt5_sdk/sysroots /cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x CFLAGS=" -O2 -pipe -g -feliminate-unused-debug-types" declare -x CONFIGURE_FLAGS="--target=arm-poky-linux-gnueabi --host=arm-poky-linux-gnueabi --build=x86_64-linux --with-libtool-sysroot=/media/work/iMX6/Yocto/qt5_sdk/sysro ots/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x CONFIG_SITE="/media/work/iMX6/Yocto/qt5_sdk/site-config-cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x CPP="arm-poky-linux-gnueabi-gcc -E -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 --sysroot=/media/work/iMX6/Yocto/qt5_sdk/sysr oots/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x CPPFLAGS="" declare -x CROSS_COMPILE="arm-poky-linux-gnueabi-" declare -x CXX="arm-poky-linux-gnueabi-g++ -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 --sysroot=/media/work/iMX6/Yocto/qt5_sdk/sysroot s/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x CXXFLAGS=" -O2 -pipe -g -feliminate-unused-debug-types" declare -x M4="m4" declare -x MANDATORY_PATH="/usr/share/gconf/kde-plasma.mandatory.path" declare -x NM="arm-poky-linux-gnueabi-nm" declare -x OBJCOPY="arm-poky-linux-gnueabi-objcopy" declare -x OBJDUMP="arm-poky-linux-gnueabi-objdump" declare -x OECORE_ACLOCAL_OPTS="-I /media/work/iMX6/Yocto/qt5_sdk/sysroots/x86_64-pokysdk-linux/usr/share/aclocal" declare -x OECORE_DISTRO_VERSION="1.7" declare -x OECORE_NATIVE_SYSROOT="/media/work/iMX6/Yocto/qt5_sdk/sysroots/x86_64-pokysdk-linux" declare -x OECORE_SDK_VERSION="1.7" declare -x OECORE_TARGET_SYSROOT="/media/work/iMX6/Yocto/qt5_sdk/sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x OLDPWD="/media/work/iMX6/Yocto/video2lcd_arm/test" declare -x PATH="/media/work/iMX6/Yocto/qt5_sdk/sysroots/x86_64-pokysdk-linux/usr/bin:/media/work/iMX6/Yocto/qt5_sdk/sysroots/x86_64-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi:/home/hexiongjun/bin:/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/hexiongjun/010editor:/home/hexiongjun/010editor" declare -x PKG_CONFIG_PATH="/media/work/iMX6/Yocto/qt5_sdk/sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi/usr/lib/pkgconfig" declare -x PKG_CONFIG_SYSROOT_DIR="/media/work/iMX6/Yocto/qt5_sdk/sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x PWD="/media/work/iMX6/Yocto/video2lcd_arm" declare -x PYTHONHOME="/media/work/iMX6/Yocto/qt5_sdk/sysroots/x86_64-pokysdk-linux/usr" declare -x QMAKESPEC="/home/hexiongjun/github/BBB/SDK/ti-sdk-am335x-evm-05.07.00.00/linux-devkit/arm-arago-linux-gnueabi/usr/share/qtopia/mkspecs/linux-g++" declare -x QT_IM_MODULE="fcitx" declare -x QT_PLUGIN_PATH="/home/hexiongjun/.kde/lib/kde4/plugins/:/usr/lib/kde4/plugins/" declare -x RANLIB="arm-poky-linux-gnueabi-ranlib" declare -x SDKTARGETSYSROOT="/media/work/iMX6/Yocto/qt5_sdk/sysroots/cortexa9hf-vfp-neon-poky-linux-gnueabi" declare -x SESSION_MANAGER="local/hexiongjun-pc:@/tmp/.ICE-unix/3595,unix/hexiongjun-pc:/tmp/.ICE-unix/3595"
注意点
当中我们重点须要关注的是与编译相关的变量：
- CC/LD等编译相关
- ARCH/CROSS_COMPILE等croos编译相关
能够看到CC已经被重定义为cross toolchain了，而ARCH和CROSS_COMPILE也悉心的帮我们配置成了相应的。
因此。事实上假设我们须要交叉编译一个app。那么非常多变量将不再须要自己手动设定了。
同一时候由于各种tuning的指定，我们必须注意和硬件的匹配。
比如这里指定了为cortex-a9而优化。
怎样使用
最好的方法就是使用变量来使用Toolchian，比如使用$CC而不是使用arm-poky-XXX-gcc。由于我们能够看到CC事实上是对arm-xxx-gcc加入了一些配置：
CC="arm-poky-linux-gnueabi-gcc -march=armv7-a -mthumb-interwork -mfloat-abi=hard -mfpu=neon -mtune=cortex-a9 --sysroot=/media/work/iMX6/Yocto/qt5_sdk/sysroots /cortexa9hf-vfp-neon-poky-linux-gnueabi"
当中最为核心的是sysroot这个选项，这个选项将告诉toolchian去哪里查找库与头文件，而假设不指定这个，那么就会出现故障。比如，我们直接使用arm-poky-gnueabi-gcc来编译：
$ make
make -C ./ -f /media/work/iMX6/Yocto/video2lcd_arm/Makefile.build
make[1]: Entering directory `/media/work/iMX6/Yocto/video2lcd_arm'
make -C convert -f /media/work/iMX6/Yocto/video2lcd_arm/Makefile.build
make[2]: Entering directory `/media/work/iMX6/Yocto/video2lcd_arm/convert'
arm-poky-linux-gnueabi-gcc -Wall -Werror -O2 -g -I /media/work/iMX6/Yocto/video2lcd_arm/include -I /media/work/iMX6/Yocto/imx6qsabresd_build/tmp/work/imx6qsabresd-poky-linux-gnueabi/fsl-image-qt5/1.0-r0/rootfs/usr/include/ -Wp,-MD,.convert_manager.o.d -c -o convert_manager.o convert_manager.c
In file included from /media/work/iMX6/Yocto/imx6qsabresd_build/tmp/work/imx6qsabresd-poky-linux-gnueabi/fsl-image-qt5/1.0-r0/rootfs/usr/include/features.h:389:0,
from /media/work/iMX6/Yocto/imx6qsabresd_build/tmp/work/imx6qsabresd-poky-linux-gnueabi/fsl-image-qt5/1.0-r0/rootfs/usr/include/stdio.h:27,
from /media/work/iMX6/Yocto/video2lcd_arm/include/config.h:5,
from convert_manager.c:2:
/media/work/iMX6/Yocto/imx6qsabresd_build/tmp/work/imx6qsabresd-poky-linux-gnueabi/fsl-image-qt5/1.0-r0/rootfs/usr/include/gnu/stubs.h:7:29: fatal error: gnu/stubs-soft.h: No such file or directory
# include <gnu/stubs-soft.h>
^
compilation terminated.
make[2]: *** [convert_manager.o] Error 1
make[2]: Leaving directory `/media/work/iMX6/Yocto/video2lcd_arm/convert'
make[1]: *** [convert] Error 2
make[1]: Leaving directory `/media/work/iMX6/Yocto/video2lcd_arm'
make: *** [all] Error 2能够看到提示说找不到一些标准的头文件。事实上这个是由于我们没有加入一些指定的选择来告诉其使用stubs-hard.h。所以默认的去查找stubs-soft.h。
比如我们编译一个helloworld，那么能够依照例如以下编译：
$CC hello.c -o hello