一个基于cmake跨平台交叉编译项目模板

1. 项目目录结构
   下面目录结构是一个经过实践的项目模板结构，麻雀虽小，五脏俱全。小伙伴们可以按此模板搭建自己的项目。

   ├── build.sh                        ## 构建脚本
   ├── cmake
   │   ├── config.cmake.in             ## 构建test库的cmake配置文件 
   │   ├── create-config.cmake         ## 构建test库的cmake配置文件, find_package用到的配置文件
   │   ├── hisi.toolchain.cmake		## hisi平台工具链配置文件
   │   ├── rockchip.toolchain.cmake    ## rockchip平台工具链配置文件
   │   ├── sigmastar.toolchain.cmake   ## sigmastar平台工具链配置文件
   ├── CMakeLists.txt                  ## 项目顶层CMakeLists.txt
   ├── include                         ## 库对外提供的接口头文件
   │   ├── mymath.hpp                   
   ├── src                             ## 库实现部分
   │   ├── CMakeLists.txt
   │   ├── mymath.cpp
   ├── test                            ## 库测试代码
   │   └── CMakeLists.txt
   ├── user.env                        ## 编译相关配置
   

2. 如何交叉编译
   直接进入项目目录，运行目录下面的build.sh脚本，如下：

• 交叉编译

  cd $project_dir
  ./build.sh
  

• 清除编译

  ./build.sh --clean
  

3. 如何配置不同平台的交叉编译环境
   只需要更改项目目录下的user.env文件，就可以实现不同平台的交叉编译。

• 海思平台dv300 user.env配置如下：

  USER_TOOLCHAIN_FILE="/xxx/dv300.toolchain.cmake"  # 平台交叉编译工具链
  USER_PLATFORM_TYPE="hisi"   # 平台类型
  USER_PLATFORM_CHIP_TYPE="dv300"  # 平台芯片类型
  

• 瑞芯微平台rv1109/rv1126 user.env配置如下：

  USER_TOOLCHAIN_FILE="/xxx/rv1109.toolchain.cmake"  # 平台交叉编译工具链
  USER_PLATFORM_TYPE="rockchip"   # 平台类型
  USER_PLATFORM_CHIP_TYPE="rv1109"  # 平台芯片类型
  

• 星辰平台ssd222d user.env配置如下：

  USER_TOOLCHAIN_FILE="/xxx/ssd222d.toolchain.cmake"  # 平台交叉编译工具链
  USER_PLATFORM_TYPE="sigmatar"   # 平台类型
  USER_PLATFORM_CHIP_TYPE="ssd222d"  # 平台芯片类型
  

• 公共配置

  USER_BUILD_TYPE="Release"       # 调试模式:Debug, 发布模式:Release  
  USER_CMAKE_GENERATOR="Ninja"    # 编译加速   
  USER_BUILD_SHARED_LIBS=ON       # 是否编译共享库 ON or OFF
  

4. 项目顶层CMakeLists.txt

   ## 要求最小cmake版本
   cmake_minimum_required(VERSION 3.10)
   
   ## 看系统是否安装ccache
   find_program(CCACHE_PROGRAM ccache)
   if(CCACHE_PROGRAM)
     message(STATUS "Set up ccache ...")
     set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE ccache)
     set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
   else()
     message(WARNING "ccache has not been found")
   endif()
   ## 定义项目名称
   project(
     mymath
     VERSION 0.1.0
     DESCRIPTION "mymath libraries")
     
    ## 输出编译配置相关信息
   message(STATUS "============================================================================")
   message(STATUS "set CMAKE_MAKE_PROGRAM to: ${CMAKE_MAKE_PROGRAM}")
   message(STATUS "set CMAKE_CURRENT_BINARY_DIR to: ${CMAKE_CURRENT_BINARY_DIR}")
   message(STATUS "set CMAKE_CURRENT_SOURCE_DIR to: ${CMAKE_CURRENT_SOURCE_DIR}")
   message(STATUS "set CMAKE_INSTALL_PREFIX to: ${CMAKE_INSTALL_PREFIX}")
   message(STATUS "set CMAKE_TOOLCHAIN_FILE to: ${CMAKE_TOOLCHAIN_FILE}")
   message(STATUS "set PLATFORM_TYPE to: ${PLATFORM_TYPE}")
   message(STATUS "set PLATFORM_CHIP_TYPE to: ${PLATFORM_CHIP_TYPE}")
   message(STATUS "set CMAKE_BUILD_TYPE to: ${CMAKE_BUILD_TYPE}")
   message(STATUS "set BUILD_SHARED_LIBS to: ${BUILD_SHARED_LIBS}")
   message(STATUS "set THIRD_PARTY_PREFIX to: ${THIRD_PARTY_PREFIX}")
   message(STATUS "============================================================================")
   
   ## 编译库实现代码
   add_subdirectory(src)
   
   ## 编译测试代码
   add_subdirectory(test)
   
   ## 创建库配置文件
   include(cmake/create-config.cmake)
   
   ## 安装库头文件，若要增加库暴露的头文件，需要将暴露的头文件放入include目录
   install(
     DIRECTORY include
     DESTINATION .
     FILES_MATCHING
     PATTERN "*.h" PATTERN "*.hpp")
   

5. 编译脚本build.sh

   #!/bin/bash
   
   set -e
   source_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
   
   #读取用户编译配置
   user_env_file="$source_dir/user.env"
   if [ ! -f "$user_env_file" ]; then
       echo -e "[Warning]: $user_env_file not exists, please copy $user_env_file.sample to $user_env_file and modify it"
   else
       . $user_env_file
   fi
   #编译目录
   build_root_dir="$source_dir/build"
   #安装目录
   install_dir="$source_dir/install"
   #编译类型
   build_type=${USER_BUILD_TYPE:-"Release"}
   #编译共享库
   build_shared_libs=${USER_BUILD_SHARED_LIBS:-"OFF"}
   #编译加速
   cmake_generator=${USER_CMAKE_GENERATOR:-"Unix Makefiles"}
   #工具链文件
   toolchain_file=${USER_TOOLCHAIN_FILE:-"rv1109.toolchain.cmake"}
   #平台类型
   platform_type=${USER_PLATFORM_TYPE:-"rockchip"}
   #芯片类型
   platform_chip_type=${USER_PLATFORM_CHIP_TYPE:-"rv1109"}
   
   #支持命令传参
   for i in "$@"; do
       case $i in
       --toolchain_file=*)
           toolchain_file="${i#*=}"
           shift # past argument=value
           ;;
       --clean)
           clean_build="yes"
           shift # past argument with no value
           ;;
        --ninja)
           cmake_generator="Ninja"
           shift # past argument with no value
           ;;
       *)
           # unknown option
           ;;
       esac
   done
   
   # 编译临时目录
   build_dir=$build_root_dir/$platform_type/$chip_type/$build_type
   
   mkdir -p "$build_dir" || true
   mkdir -p "$install_dir/include" || true
   mkdir -p "$install_dir/lib" || true
   
   ## 清除编译
   if [[ $clean_build == "yes" ]]; then
       echo "clean ..."
       rm $build_root_dir -rf
       rm $install_dir -rf
   else
       pushd "$build_dir"
       cmake "$source_dir" -G "$cmake_generator" \
           -DCMAKE_INSTALL_PREFIX="$install_dir" \
           -DCMAKE_TOOLCHAIN_FILE="$toolchain_file" \
           -DPLATFORM_TYPE="$platform_type" \
           -DPLATFORM_CHIP_TYPE="$platform_chip_type" \
           -DCMAKE_BUILD_TYPE="$build_type" \
           -DBUILD_SHARED_LIBS="$build_shared_libs" 
           
       # 编译
       cmake --build . --parallel
       # 安装
       cmake --build . --target install
       popd
   fi
   

6. 交叉工具链cmake文件介绍
   以下是一个通用的交叉工具链文件模板，用户一般只需要更改交叉工具链前缀、更改芯片平台架构、及更改c++相关编译配置。分别对应CROSS_PREFIX 、CROSS_COMPILATION_ARCHITECTURE 和CMAKE_CXX_FLAGS。下面是hisi dv300平台的cmake工具链文件。

   # set cross-compiled system type, it's better not use the type which cmake
   # cannot recognized.
   set(CMAKE_SYSTEM_NAME Linux)
   set(CMAKE_SYSTEM_PROCESSOR arm)
   
   # when hislicon SDK was installed, toolchain was installed in the path as below:
   # 更改工具链前缀，这里以hisi dv300 编译工具链为例子
   set(CROSS_PREFIX arm-himix200-linux-)
   set(CROSS_HOST arm-himix200-linux)
   set(CMAKE_C_COMPILER ${CROSS_PREFIX}gcc)
   set(CMAKE_CXX_COMPILER ${CROSS_PREFIX}g++)
   
   # set searching rules for cross-compiler
   set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
   set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
   set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
   ## 根据不同平台的芯片架构来更改，比如arm的v7,v8架构等
   set(CROSS_COMPILATION_ARCHITECTURE armv7-a)
   # 更改c++相关配置
   set(CMAKE_CXX_FLAGS
       "-fpermissive -march=armv7-a -mfloat-abi=softfp -mfpu=neon-vfpv4 -fopenmp ${CMAKE_CXX_FLAGS}"
   )
   # -fpermissive -Wno-unused-variable -Wno-unused-parameter -march=armv7-a -mtune=cortex-a7 -mfpu=neon-vfpv4
   # other settings
   set(CMAKE_CXX_FLAGS "-DCV__EXCEPTION_PTR=0 ${CMAKE_CXX_FLAGS}")
   

7. config.cmake.in和create-config.cmake内容介绍
   可以参考CMake调用第三方库的两种方法，这里面有相关信息介绍。

• src/CMakeLists.txt内容介绍

#当前目录下的所有源文件存入_SRC_FILES变量
aux_source_directory(. _SRC_FILES)
#生成目标为mymath库，因为顶层项目名称为mymath
add_library(${PROJECT_NAME} ${_SRC_FILES})
#target_link_libraries(${PROJECT_NAME} PUBLIC spdlog)
# VERSION指代动态库版本，SOVERSION指代API版本
set_target_properties(
  ${PROJECT_NAME}
  PROPERTIES VERSION ${PROJECT_VERSION}
             SOVERSION ${PROJECT_VERSION_MAJOR})
target_include_directories(
  ${PROJECT_NAME}
  PUBLIC $)
#安装目标
install(
  TARGETS ${PROJECT_NAME}
  EXPORT ${PROJECT_NAME}Targets
  LIBRARY DESTINATION lib
  ARCHIVE DESTINATION lib
  RUNTIME DESTINATION bin)