为 Raspberry Pi Zero 交叉编译 OpenCV 3.3.1 时，即使存在库，链接也会失败

【问题标题】：Link fails when cross compiling OpenCV 3.3.1 for Raspberry Pi Zero even though libraries are present为 Raspberry Pi Zero 交叉编译 OpenCV 3.3.1 时，即使存在库，链接也会失败
【发布时间】：2018-08-08 10:41:09
【问题描述】：

我一直在尝试为 Ubuntu 16.04 上的 Raspberry PI Zero（Raspbian 延伸）构建 OpenCV 3.3.1。我一直按照https://github.com/HesselM/rpicross_notes 此处记录的步骤进行操作，主要例外是，我没有使用具有 GCC 4.9.3 的 https://github.com/raspberrypi/tools 中的工具，而是使用 crosstool-ng 构建 GCC 6.3.0 工具链以匹配 GCC 版本附带 Raspbian 拉伸。我已经在 RaspberryPi Zero 上安装了所有 OpenCV 先决条件，然后获取了文件系统的副本以用作系统根目录。

CMake 配置似乎可以工作，但是在链接 libopencv_freetype.so 时 make 构建失败，因为找不到 harfbuzz 和 freetype 库。

/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/../lib/gcc/arm-unknown-linux-gnueabihf/6.3.0/../../../../arm-unknown-linux-gnueabihf/bin/ld: cannot find -lfreetype
/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/../lib/gcc/arm-unknown-linux-gnueabihf/6.3.0/../../../../arm-unknown-linux-gnueabihf/bin/ld: cannot find -lharfbuzz
collect2: error: ld returned 1 exit status
modules/freetype/CMakeFiles/opencv_freetype.dir/build.make:97: recipe for target 'lib/libopencv_freetype.so.3.3.1' failed

这些库存在于我的 RaspberryPI 系统中的 usr/lib/arm-linux-gnueabihf

-rw-r--r-- 1 dsnowdon dsnowdon 717178 Apr 27  2017 libfreetype.a
-rw-r--r-- 1 dsnowdon dsnowdon    909 Apr 27  2017 libfreetype.la
lrwxrwxrwx 1 dsnowdon dsnowdon     21 Apr 27  2017 libfreetype.so -> libfreetype.so.6.12.3
lrwxrwxrwx 1 dsnowdon dsnowdon     21 Apr 27  2017 libfreetype.so.6 -> libfreetype.so.6.12.3
-rw-r--r-- 1 dsnowdon dsnowdon 567844 Apr 27  2017 libfreetype.so.6.12.3
-rw-r--r-- 1 dsnowdon dsnowdon 739360 Jan 24  2017 libharfbuzz.a
lrwxrwxrwx 1 dsnowdon dsnowdon     24 Jan 24  2017 libharfbuzz.so -> libharfbuzz.so.0.10400.2
lrwxrwxrwx 1 dsnowdon dsnowdon     24 Jan 24  2017 libharfbuzz.so.0 -> libharfbuzz.so.0.10400.2
-rw-r--r-- 1 dsnowdon dsnowdon 551256 Jan 24  2017 libharfbuzz.so.0.10400.2

使用 make VERBOSE=1 构建显示运行此命令时发生故障：

/usr/bin/cmake -E cmake_link_script CMakeFiles/opencv_freetype.dir/link.txt --verbose=1

生成这个：

/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-g++ -fPIC   -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG  -DNDEBUG  -shared -Wl,-soname,libopencv_freetype.so.3.3 -o ../../lib/libopencv_freetype.so.3.3.1 CMakeFiles/opencv_freetype.dir/src/freetype.cpp.o ../../lib/libopencv_imgproc.so.3.3.1 -ldl -lm -lpthread -lrt ../../3rdparty/lib/libtegra_hal.a -lfreetype -lharfbuzz ../../lib/libopencv_core.so.3.3.1

但是，如果我手动添加 -L${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf 以提供以下内容，则链接有效：

/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-g++ -L/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf -fPIC   -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG  -DNDEBUG  -shared -Wl,-soname,libopencv_freetype.so.3.3 -o ../../lib/libopencv_freetype.so.3.3.1 CMakeFiles/opencv_freetype.dir/src/freetype.cpp.o ../../lib/libopencv_imgproc.so.3.3.1 -ldl -lm -lpthread -lrt ../../3rdparty/lib/libtegra_hal.a -lfreetype -lharfbuzz ../../lib/libopencv_core.so.3.3.1

这让我想到，也许 pkg-config 被调用的方式没有发出正确的 libdir，所以我编写了一个包装脚本来转储所有 pkg​​-config 调用和结果。

#! /bin/bash
LOGFILE=/tmp/pkg-config-wrapper.log
basename="`basename "$0"`"  
timestamp=$(date)
printf "${timestamp} ${basename} $@\nPKG_CONFIG_DIR=${PKG_CONFIG_DIR}\nPKG_CONFIG_LIBDIR=${PKG_CONFIG_LIBDIR}\nPKG_CONFIG_SYSROOT_DIR=${PKG_CONFIG_SYSROOT_DIR}\n"  >> $LOGFILE
result=$(/usr/bin/pkg-config "$@")
printf "pkf-config = ${result}\n"  >> $LOGFILE
echo $result

这是我发现的与链接相关的 harfbuzz（为了简洁起见，我省略了 pkg-config cflags 的其他调用，用于 freetype 和 gtk）：

Wed  8 Aug 06:33:54 BST 2018 pkg-config-wrapper.sh --exists
--print-errors --short-errors harfbuzz
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = 
Wed  8 Aug 06:33:54 BST 2018 pkg-config-wrapper.sh --modversion
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = 1.4.2
Wed  8 Aug 06:33:54 BST 2018 pkg-config-wrapper.sh --variable=prefix
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = /usr

Wed  8 Aug 06:33:54 BST 2018 pkg-config-wrapper.sh --variable=libdir
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = /usr/lib/arm-linux-gnueabihf
Wed  8 Aug 06:33:54 BST 2018 pkg-config-wrapper.sh --libs-only-l
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -lharfbuzz
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --static
--libs-only-l harfbuzz 
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -lharfbuzz -lglib-2.0 -lpcre -lgraphite2
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --libs-only-L
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -L/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --static
--libs-only-L harfbuzz 
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -L/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --libs
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -L/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf -lharfbuzz
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --static
--libs harfbuzz 
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -L/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf -lharfbuzz -lglib-2.0 -pthread -lpcre -pthread -lgraphite2
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --libs-only-other
harfbuzz  
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = 
Wed  8 Aug 06:33:55 BST 2018 pkg-config-wrapper.sh --static
--libs-only-other harfbuzz 
PKG_CONFIG_DIR=
PKG_CONFIG_LIBDIR=:/opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/usr/share/pkgconfig:/opt/software/raspberrypi/rpi-cross/rootfs/opt/vc/lib/pkgconfig
PKG_CONFIG_SYSROOT_DIR=/opt/software/raspberrypi/rpi-cross/rootfs
pkg-config = -pthread

据我所知，pkg-config 被正确调用以进行交叉编译，所以现在我不知所措，不知道下一步该尝试什么。

我正在调用 CMake，如下所示：

cmake \
-D RPI_ROOTFS=${RPI_ROOTFS} \
-D BUILD_TESTS=NO \
-D BUILD_PERF_TESTS=NO \
-D BUILD_PYTHON_SUPPORT=ON \
-D OPENCV_EXTRA_MODULES_PATH=${RPI_CROSS_HOME}/src/opencv_contrib-3.3.1/modules \
-D CMAKE_TOOLCHAIN_FILE=${RPI_CROSS_HOME}/src/opencv-3.3.1/platforms/linux/arm.toolchain.cmake \
${RPI_CROSS_HOME}/src/opencv-3.3.1

OpenCV Cmake 文件的大部分更改都在opencv-3.3.1/cmake/OpenCVMinDepVersions.cmake 中，如https://github.com/HesselM/rpicross_notes 中所述

set(MIN_VER_CMAKE 2.8.12.2)
set(MIN_VER_CUDA 6.5)
set(MIN_VER_PYTHON2 2.6)
set(MIN_VER_PYTHON3 3.2)
set(MIN_VER_ZLIB 1.2.3)
set(MIN_VER_GTK 2.18.0)

# install dir
set( CMAKE_INSTALL_PREFIX ${RPI_ROOTFS}/usr/local CACHE STRING "")
set( CMAKE_FIND_ROOT_PATH "${RPI_ROOTFS}" CACHE FILEPATH "")
set( CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER )

# compilers
set( CMAKE_C_COMPILER   "/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-gcc"    CACHE FILEPATH "")
set( CMAKE_CXX_COMPILER "/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-g++"    CACHE FILEPATH "")
set( CMAKE_AR           "/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-ar"     CACHE FILEPATH "")
set( CMAKE_RANLIB       "/opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-ranlib" CACHE FILEPATH "")

#Pkg-config settings
set( RPI_PKGCONFIG_LIBDIR "${RPI_PKGCONFIG_LIBDIR}:${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf/pkgconfig" )
set( RPI_PKGCONFIG_LIBDIR "${RPI_PKGCONFIG_LIBDIR}:${RPI_ROOTFS}/usr/share/pkgconfig" )
set( RPI_PKGCONFIG_LIBDIR "${RPI_PKGCONFIG_LIBDIR}:${RPI_ROOTFS}/opt/vc/lib/pkgconfig" )

#set( PKG_CONFIG_EXECUTABLE "/usr/bin/pkg-config" CACHE FILEPATH "")
set( PKG_CONFIG_EXECUTABLE "/opt/cross/pkg-config-wrapper.sh" CACHE FILEPATH "")
set( ENV{PKG_CONFIG_DIR}         "" CACHE FILEPATH "")
set( ENV{PKG_CONFIG_LIBDIR}      "${RPI_PKGCONFIG_LIBDIR}" CACHE FILEPATH "")
set( ENV{PKG_CONFIG_SYSROOT_DIR} "${RPI_ROOTFS}" CACHE FILEPATH "")

# setup rpi (target) directories for compiler
set( RPI_INCLUDE_DIR "${RPI_INCLUDE_DIR} -isystem ${RPI_ROOTFS}/usr/include/arm-linux-gnueabihf")
set( RPI_INCLUDE_DIR "${RPI_INCLUDE_DIR} -isystem ${RPI_ROOTFS}/usr/include")
set( RPI_INCLUDE_DIR "${RPI_INCLUDE_DIR} -isystem ${RPI_ROOTFS}/usr/local/include")

set( RPI_LIBRARY_DIR "${RPI_LIBRARY_DIR} -Wl,-rpath ${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf")
set( RPI_LIBRARY_DIR "${RPI_LIBRARY_DIR} -Wl,-rpath ${RPI_ROOTFS}/lib/arm-linux-gnueabihf")

# Setup C/CXX flags.
set( CMAKE_CXX_FLAGS        "${CMAKE_CXX_FLAGS} ${RPI_INCLUDE_DIR}" CACHE STRING "" FORCE)
set( CMAKE_C_FLAGS          "${CMAKE_CXX_FLAGS} ${RPI_INCLUDE_DIR}" CACHE STRING "" FORCE)
set( CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${RPI_LIBRARY_DIR}" CACHE STRING "" FORCE)

#Python2.7
set( PYTHON_EXECUTABLE          /usr/bin/python2.7 CACHE STRING "")
set( PYTHON_LIBRARY_DEBUG       "${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf/libpython2.7.so" CACHE STRING "")
set( PYTHON_LIBRARY_RELEASE     "${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf/libpython2.7.so" CACHE STRING "")
set( PYTHON_LIBRARY             "${RPI_ROOTFS}/usr/lib/arm-linux-gnueabihf/libpython2.7.so" CACHE STRING "")
set( PYTHON_INCLUDE_DIR         "${RPI_ROOTFS}/usr/include/python2.7" CACHE STRING "")
set( PYTHON2_NUMPY_INCLUDE_DIRS "${RPI_ROOTFS}/usr/lib/python2.7/dist-packages/numpy/core/include" CACHE STRING "")
set( PYTHON2_PACKAGES_PATH      "${RPI_ROOTFS}/usr/local/lib/python2.7/site-packages" CACHE STRING "")

我还根据https://github.com/HesselM/rpicross_notes 将“-mthumb”替换为“-marm”来更改opencv-3.3.1/platforms/linux/arm.toolchain.cmake 来给出这个

if(COMMAND toolchain_save_config)
  return() # prevent recursive call
endif()

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_VERSION 1)
if(NOT DEFINED CMAKE_SYSTEM_PROCESSOR)
  set(CMAKE_SYSTEM_PROCESSOR arm)
else()
  #message("CMAKE_SYSTEM_PROCESSOR=${CMAKE_SYSTEM_PROCESSOR}")
endif()

include("${CMAKE_CURRENT_LIST_DIR}/gnu.toolchain.cmake")

if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm AND NOT ARM_IGNORE_FP)
  set(FLOAT_ABI_SUFFIX "")
  if(NOT SOFTFP)
set(FLOAT_ABI_SUFFIX "hf")
  endif()
endif()

if(NOT "x${GCC_COMPILER_VERSION}" STREQUAL "x")
  set(__GCC_VER_SUFFIX "-${GCC_COMPILER_VERSION}")
endif()

if(NOT DEFINED CMAKE_C_COMPILER)
  find_program(CMAKE_C_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-gcc${__GCC_VER_SUFFIX})
else()
  #message(WARNING "CMAKE_C_COMPILER=${CMAKE_C_COMPILER} is defined")
endif()
if(NOT DEFINED CMAKE_CXX_COMPILER)
  find_program(CMAKE_CXX_COMPILER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-g++${__GCC_VER_SUFFIX})
else()
  #message(WARNING "CMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER} is defined")
endif()
if(NOT DEFINED CMAKE_LINKER)
  find_program(CMAKE_LINKER NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ld)
else()
  #message(WARNING "CMAKE_LINKER=${CMAKE_LINKER} is defined")
endif()
if(NOT DEFINED CMAKE_AR)
  find_program(CMAKE_AR NAMES ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar${__GCC_VER_SUFFIX} ${GNU_MACHINE}${FLOAT_ABI_SUFFIX}-ar)
else()
  #message(WARNING "CMAKE_AR=${CMAKE_AR} is defined")
endif()

if(NOT DEFINED ARM_LINUX_SYSROOT AND DEFINED GNU_MACHINE)
  set(ARM_LINUX_SYSROOT /usr/${GNU_MACHINE}${FLOAT_ABI_SUFFIX})
endif()

if(NOT DEFINED CMAKE_CXX_FLAGS)
  set(CMAKE_CXX_FLAGS           "" CACHE INTERAL "")
  set(CMAKE_C_FLAGS             "" CACHE INTERAL "")
  set(CMAKE_SHARED_LINKER_FLAGS "" CACHE INTERAL "")
  set(CMAKE_MODULE_LINKER_FLAGS "" CACHE INTERAL "")
  set(CMAKE_EXE_LINKER_FLAGS    "" CACHE INTERAL "")

  set(CMAKE_CXX_FLAGS           "${CMAKE_CXX_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
  set(CMAKE_C_FLAGS             "${CMAKE_C_FLAGS} -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi")
  if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
set(CMAKE_CXX_FLAGS           "-marm ${CMAKE_CXX_FLAGS}")
set(CMAKE_C_FLAGS             "-marm ${CMAKE_C_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS    "${CMAKE_EXE_LINKER_FLAGS} -Wl,-z,nocopyreloc")
  endif()
  if(CMAKE_SYSTEM_PROCESSOR STREQUAL arm)
set(ARM_LINKER_FLAGS "-Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
  elseif(CMAKE_SYSTEM_PROCESSOR STREQUAL aarch64)
set(ARM_LINKER_FLAGS "-Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now")
  endif()
  set(CMAKE_SHARED_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS}")
  set(CMAKE_MODULE_LINKER_FLAGS "${ARM_LINKER_FLAGS} ${CMAKE_MODULE_LINKER_FLAGS}")
  set(CMAKE_EXE_LINKER_FLAGS    "${ARM_LINKER_FLAGS} ${CMAKE_EXE_LINKER_FLAGS}")
else()
  #message(WARNING "CMAKE_CXX_FLAGS='${CMAKE_CXX_FLAGS}' is defined")
endif()

if(USE_NEON)
  message(WARNING "You use obsolete variable USE_NEON to enable NEON instruction set. Use -DENABLE_NEON=ON instead." )
  set(ENABLE_NEON TRUE)
elseif(USE_VFPV3)
  message(WARNING "You use obsolete variable USE_VFPV3 to enable VFPV3 instruction set. Use -DENABLE_VFPV3=ON instead." )
  set(ENABLE_VFPV3 TRUE)
endif()

set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${ARM_LINUX_SYSROOT})

if(EXISTS ${CUDA_TOOLKIT_ROOT_DIR})
  set(CMAKE_FIND_ROOT_PATH ${CMAKE_FIND_ROOT_PATH} ${CUDA_TOOLKIT_ROOT_DIR})
endif()

set(TOOLCHAIN_CONFIG_VARS ${TOOLCHAIN_CONFIG_VARS}
ARM_LINUX_SYSROOT
ENABLE_NEON
ENABLE_VFPV3
CUDA_TOOLKIT_ROOT_DIR
)
toolchain_save_config()

这是 CMake 输出：

-- General configuration for OpenCV 3.3.1 =====================================
--   Version control:               unknown
-- 
--   Extra modules:
--     Location (extra):            /opt/software/raspberrypi/rpi-cross/src/opencv_contrib-3.3.1/modules
--     Version control (extra):     unknown
-- 
--   Platform:
--     Timestamp:                   2018-08-08T05:33:57Z
--     Host:                        Linux 4.15.0-29-generic x86_64
--     Target:                      Linux 1 arm
--     CMake:                       3.5.1
--     CMake generator:             Unix Makefiles
--     CMake build tool:            /usr/bin/make
--     Configuration:               Release
-- 
--   CPU/HW features:
--     Baseline:
--       requested:                 DETECT
--       disabled:                  VFPV3 NEON
-- 
--   C/C++:
--     Built as dynamic libs?:      YES
--     C++11:                       YES
--     C++ Compiler:                /opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-g++  (ver 6.3.0)
--     C++ flags (Release):         -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG  -DNDEBUG
--     C++ flags (Debug):           -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -fvisibility-inlines-hidden -g  -O0 -DDEBUG -D_DEBUG
--     C Compiler:                  /opt/cross/x-tools/arm-unknown-linux-gnueabihf/bin/arm-unknown-linux-gnueabihf-gcc
--     C flags (Release):           -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include  -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -O3 -DNDEBUG  -DNDEBUG
--     C flags (Debug):             -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include  -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include/arm-linux-gnueabihf -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/include -isystem /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/include   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -pthread -fomit-frame-pointer -ffunction-sections  -mfp16-format=ieee -fvisibility=hidden -g  -O0 -DDEBUG -D_DEBUG
--     Linker flags (Release):
--     Linker flags (Debug):
--     ccache:                      NO
--     Precompiled headers:         NO
--     Extra dependencies:          dl m pthread rt
--     3rdparty dependencies:
-- 
--   OpenCV modules:
--     To be built:                 core flann imgproc ml objdetect phase_unwrapping photo plot reg surface_matching video xphoto bgsegm dnn face freetype fuzzy img_hash imgcodecs shape videoio xobjdetect highgui superres bioinspired dpm features2d line_descriptor saliency text calib3d ccalib datasets rgbd stereo structured_light tracking videostab xfeatures2d ximgproc aruco optflow stitching python2
--     Disabled:                    js world contrib_world
--     Disabled by dependency:      -
--     Unavailable:                 cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev java python3 ts viz cnn_3dobj cvv dnn_modern hdf matlab sfm
-- 
--   GUI: 
--     QT:                          NO
--     GTK+ 3.x:                    YES (ver 3.22.11)
--     GThread :                    YES (ver 2.50.3)
--     GtkGlExt:                    NO
--     OpenGL support:              NO
--     VTK support:                 NO
-- 
--   Media I/O: 
--     ZLib:                        zlib (ver 1.2.8)
--     JPEG:                        libjpeg (ver 90)
--     WEBP:                        build (ver encoder: 0x020e)
--     PNG:                         build (ver 1.6.24)
--     TIFF:                        build (ver 42 - 4.0.2)
--     JPEG 2000:                   build (ver 1.900.1)
--     OpenEXR:                     build (ver 1.7.1)
--     GDAL:                        NO
--     GDCM:                        NO
-- 
--   Video I/O:
--     DC1394 1.x:                  NO
--     DC1394 2.x:                  YES (ver 2.2.5)
--     FFMPEG:                      NO
--       avcodec:                   YES (ver 57.64.101)
--       avformat:                  YES (ver 57.56.101)
--       avutil:                    YES (ver 55.34.101)
--       swscale:                   YES (ver 4.2.100)
--       avresample:                YES (ver )
--     GStreamer:                   
--       base:                      YES (ver )
--       video:                     YES (ver )
--       app:                       YES (ver )
--       riff:                      YES (ver )
--       pbutils:                   YES (ver )
--     OpenNI:                      NO
--     OpenNI PrimeSensor Modules:  NO
--     OpenNI2:                     NO
--     PvAPI:                       NO
--     GigEVisionSDK:               NO
--     Aravis SDK:                  NO
--     UniCap:                      NO
--     UniCap ucil:                 NO
--     V4L/V4L2:                    NO/YES
--     XIMEA:                       NO
--     Xine:                        NO
--     Intel Media SDK:             NO
--     gPhoto2:                     YES
-- 
--   Parallel framework:            pthreads
-- 
--   Trace:                         YES ()
-- 
--   Other third-party libraries:
--     Use Intel IPP:               NO
--     Use Intel IPP IW:            NO
--     Use VA:                      NO
--     Use Intel VA-API/OpenCL:     NO
--     Use Lapack:                  NO
--     Use Eigen:                   NO
--     Use Cuda:                    NO
--     Use OpenCL:                  YES
--     Use OpenVX:                  NO
--     Use custom HAL:              YES (carotene (ver 0.0.1))
-- 
--   OpenCL:                        <Dynamic loading of OpenCL library>
--     Include path:                /opt/software/raspberrypi/rpi-cross/src/opencv-3.3.1/3rdparty/include/opencl/1.2
--     Use AMDFFT:                  NO
--     Use AMDBLAS:                 NO
-- 
--   Python 2:
--     Interpreter:                 /usr/bin/python2.7 (ver 2.7.12)
--     Libraries:                   /opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/arm-linux-gnueabihf/libpython2.7.so (ver 2.7.13)
--     numpy:                       /opt/software/raspberrypi/rpi-cross/rootfs/usr/lib/python2.7/dist-packages/numpy/core/include (ver undefined - cannot be probed because of the cross-compilation)
--     packages path:               /opt/software/raspberrypi/rpi-cross/rootfs/usr/local/lib/python2.7/site-packages
-- 
--   Python 3:
--     Interpreter:                 /usr/bin/python3 (ver 3.5.2)
-- 
--   Python (for build):            /usr/bin/python2.7
-- 
--   Java:
--     ant:                         /opt/software/packages/java/apache-ant-1.9.6/bin/ant (ver 1.9.6)
--     JNI:                         NO
--     Java wrappers:               NO
--     Java tests:                  NO
-- 
--   Matlab:                        Matlab not found or implicitly disabled
-- 
--   Documentation:
--     Doxygen:                     NO
-- 
--   Tests and samples:
--     Tests:                       NO
--     Performance tests:           NO
--     C/C++ Examples:              NO
-- 
--   Install path:                  /opt/software/raspberrypi/rpi-cross/rootfs/usr/local
-- 
--   cvconfig.h is in:              /opt/software/raspberrypi/rpi-cross/build/opencv
-- -----------------------------------------------------------------
-- 
-- Configuring done
-- Generating done
-- Build files have been written to: /opt/software/raspberrypi/rpi-cross/build/opencv

此时我不知所措，不知道下一步该尝试什么。可能是什么问题？

【问题讨论】：

    标签： cmake raspberry-pi opencv3.0


    【解决方案1】：

    我遇到了同样的问题。对我来说，解决方案是将libfreetype.a 和libharfbuzz.a 复制到目录/home/alfred/Development/raspi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/arm-linux-gnueabihf/libc/usr/lib/arm-linux-gnueabihf/。

    这是编译器和链接器启动的子目录（64位，因为我的ubuntu是64位系统）。

    我认为这只是一个肮脏的解决方法，但我不知道如何使用 cmake 系统修复。如果您找到了更好的解决方案，请告诉我。

    【讨论】：

    • 我会试一试，但我尝试了禁用 freetype (-DBUILD_opencv_freetype=OFF) 的构建，但后来它未能为 gstreamer 获取包含目录时失败了。我遇到的问题看起来不是特定于 freetype 的，只是 freetype 是第一个依赖于外部库的构建命中的库。
    • 我认为编译器和链接器设置指向了错误的头文件和库文件。通过我的解决方法，我遇到了链接错误。我必须目录：
      - ~/Development/raspi_rootfs ... 从 rapis 克隆 - ~/Development/raspi-tools
    • 然后我创建了一个从构建系统到 raspi 克隆的符号链接：~/Development/raspi-tools/arm-bcm2708/gcc-linaro-arm-linux-gnueabihf-raspbian-x64/arm-linux-gnueabihf/libc -&gt; /home/alfred/Development/raspi_rootfs。这对我有用。我在 ubuntu18 64bit 上编译了一些测试程序，并在 raspi 上成功运行。旧的libc 已移至备份。
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