Ubuntu20上交叉编译树莓派4B + opencv4.5 + gcc8.3

本文链接：https://blog.youkuaiyun.com/suzhou7915/article/details/123442052

最近尝试在ubuntu20.04上搭建树莓派4b的交叉编译环境，参考了很多博客，发现有很多的坑，主要记录一下遇到的问题

1. 首先去git上下载交叉编译工具/自己编译

（1）查看自己的树莓派gcc版本

gcc -v

是gcc8.3.0的，需要对应版本的交叉编译工具，但是git上面没有找到gcc8.3.0的交叉编译工具，就需要自己编了，git官方的地址如下：

GitHub - raspberrypi/tools

（2）自行编译交叉编译工具

主要参考下面这个教程：（比较费时间）

arm-linux-gnueabihf gcc8.3交叉编译工具搭建教程_jianwang16的博客-优快云博客_gcc-arm-linux-gnueabihf一、运行环境1.1 执行机环境ldGNU ld (GNU Binutils for Raspbian) 2.31.1lddldd (Debian GLIBC 2.28-10+rpi1) 2.28 Copyright (C) 2018 Free Software Foundation, Inc.gcc(Raspbian 8.3.0-6+rpi1) 8.3.0 Copyr...https://blog.youkuaiyun.com/u010058695/article/details/107000579

期间碰到一个error，参考了下面这个教程解决

https://blog.youkuaiyun.com/davidhopper/article/details/79681695https://blog.youkuaiyun.com/davidhopper/article/details/79681695

如果能直接在git上找到能用的交叉编译工具，也ok

2. 然后下载opencv4.5

GitHub - opencv/opencv: Open Source Computer Vision Library

我这用的opencv4.5.5

解压出来

tar -xvzf opencv-4.5.5.tar.gz

并建立两个文件夹

cd opencv-4.5.5/
mkdir build
mkdir install

3 . 再设置一下cmake

（1）安装cmake-gui

sudo apt-get install cmake-gui

（2）配置

如下图，先把上面两行source 和 build选好

再点Configure，配置成下面这样

其中，版本可以上树莓派用 uname -a，处理器用cat /proc/cpuinfo 查看（随便写估计没啥影响）

主要把Compilers填了，target root填了，填交叉编译工具放置的地址

然后finish之后，再点一下configure，ok之后，点一下Generate

（3）配置CMakeCache.txt

还需要设置一下安装路径

CMAKE_INSTALL_PREFIX:PATH=/home/ztj/Projects/PRJ4_Pi/opencv-4.5.5/install

（4）尝试编译

make -j8

（5）碰到error1

交叉编译features.h:272:52: error: operator ‘&&‘ has no right operand
找到该文件下面这句
#if defined _FILE_OFFSET_BITS && _FILE_OFFSET_BITS == 64

在#if defined前面加上
#define _FILE_OFFSET_BITS 64
参考：https://blog.youkuaiyun.com/amxld/article/details/111565705

（6）碰到error2

common.cc报找不到thread，要加宏

#define HAVE_PTHREAD

（7）碰到error3

pthread相关的error

usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `pthread_key_create'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dladdr'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `pthread_getspecific'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlopen'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `pthread_key_delete'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlclose'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlsym'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `pthread_setspecific'

在CmakeCache.txt中找到CMAKE_EXE_LINKER_FLAGS:STRING，加上-pthread -ldl -lrt

发现依然有错，还剩：

/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dladdr'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlopen'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlclose'
/usr/lib/gcc-cross/arm-linux-gnueabihf/9/../../../../arm-linux-gnueabihf/bin/ld: ../../lib/libopencv_core.so: undefined reference to `dlsym'

翻了半天各种博客，最后找到答案，可能和gcc版本有关，把CMAKE_EXE_LINKER_FLAGS:STRING改成如下

CMAKE_EXE_LINKER_FLAGS:STRING=-pthread -Wl,--no-as-needed -ldl -lrt

参考

https://stackoverflow.com/questions/20369672/undefined-reference-to-dlsym

4. 编译通过

sudo make install

会安装在/home/ztj/Projects/PRJ4_Pi/opencv-4.5.5/install路径下

5. 上机测试

把install目录下的文件拷到树莓派上，然后PC端编个简单的代码，生成可执行文件，放到树莓派上测试

#include <iostream>

#include <opencv2/highgui.hpp>

using namespace cv;

int main() {
    cv::Mat test = cv::Mat(200,200,CV_8UC1);
    test.setTo(100);
    
    cv::imwrite("/home/pi/a.png",test);

    std::cout << "Hello, PI!" << std::endl;
    return 0;
}

cmakelist.txt:

make_minimum_required(VERSION 3.21)
project(test_code)


set(CMAKE_CXX_STANDARD 14)

set(CMAKE_BUILD_TYPE Release)

set(ARM_MODE TRUE)

IF (ARM_MODE)    # pi
    #opencv
    message("ARM_MODE!!!!!!!")
    set(OpenCV_DIR /home/ztj/Projects/PRJ4_Pi/opencv-4.5.5/install/lib/cmake/opencv4)
    find_package(OpenCV 4.5.5 REQUIRED)
    include_directories(${OpenCV_INCLUDE_DIRS})
    message("opencv ${OpenCV_VERSION}")
    message("opencv ${OpenCV_DIR}")


    #cmake compiler
    set(CMAKE_CROSSCOMPILING TRUE)
    SET(CMAKE_SYSTEM_NAME linux)
SET(CMAKE_SYSTEM_PROCESSOR "arm")

    SET(CMAKE_C_COMPILER /opt/cross-pi-gcc8.3/bin/arm-linux-gnueabihf-gcc)
    SET(CMAKE_CXX_COMPILER /opt/cross-pi-gcc8.3/bin/arm-linux-gnueabihf-g++)
    #cmake_flage
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -w -O3 -s -march=armv7 -pthread -Wl,--no-as-needed -ldl -lrt")
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -w -O3 -s -march=armv7 -pthread -Wl,--no-as-needed -ldl -lrt")

    add_executable(test_code main.cpp)
    target_link_libraries(test_code ${OpenCV_LIBS})

else ()
    message("PC_MODE!!!!!!!")
    #opencv
    set(OpenCV_DIR /home/ztj/software/opencv455/lib/cmake/opencv4)
    find_package(OpenCV 4.5.5 REQUIRED)
    include_directories(${OpenCV_INCLUDE_DIRS})
    message("opencv ${OpenCV_VERSION}")
    message("opencv ${OpenCV_DIR}")

    ##cmake_flage
    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -w -O3 -s")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -w -O3 -s")

    add_executable(test_code main.cpp)
    target_link_libraries(test_code ${OpenCV_LIBS})
endif ()

树莓派上，设置环境变量export LD_LIBRAR_PATH=你放置的opencv libs路径，然后执行可执行文件，不报错就ok