从Linux交叉编译至32位Windows时CMake无法识别libcurl文件

环境与项目信息 #

• 系统：Debian 11
• 项目目录结构：

C_UPDATER/
   Main/
     ...(.cpp文件)
   App/
     ...(.cpp文件)
   Loader.cpp

• 代码中使用#include <curl/curl.h>，已找到对应文件：
  • 静态库路径：

    ➜  ~ sudo find / -name libcurl.a
    /usr/i686-w64-mingw32/lib/libcurl.a
    /usr/lib/x86_64-linux-gnu/libcurl.a
    

  • 头文件路径：

    ➜  ~ sudo find / -name curl.h
    /usr/i686-w64-mingw32/include/curl/curl.h
    /usr/include/x86_64-linux-gnu/curl/curl.h
    

问题描述 #

使用CMake交叉编译至Windows 32位，当前CMakeLists.txt配置如下：

cmake_minimum_required(VERSION 3.13)
project(updater)

set(CMAKE_SYSTEM_NAME Windows)

set(CMAKE_CXX_STANDARD 17)

set(CMAKE_CXX_COMPILER /usr/bin/i686-w64-mingw32-g++-posix)
set(CMAKE_C_COMPILER /usr/bin/i686-w64-mingw32-gcc-posix)

SET(CMAKE_INSTALL_PREFIX "/usr/i686-w64-mingw32" CACHE PATH "Cmake install prefix")
set(CMAKE_FIND_ROOT_PATH ${CMAKE_INSTALL_PREFIX})
set(CMAKE_SYSTEM_PREFIX_PATH /)
# adjust the default behavior of the FIND_XXX() commands:
# search programs in the host environment
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

# search headers and libraries in the target environment
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE NEVER)

find_package(Threads REQUIRED)
find_package(CURL REQUIRED)
# Include libcurl header files
include_directories(/usr/i686-w64-mingw32/include)

add_library(AppModules Main/Main.cpp)

# Link against libcurl library
target_link_libraries(AppModules CURL::libcurl)

# Set compiler options
set(CMAKE_CXX_FLAGS "-Wall -Wextra -pedantic -static -static-libstdc++ -lpthread -lstdc++ -lcurl")
set(CMAKE_EXE_LINKER_FLAGS "-DCURL_STATICLIB -static -static-libstdc++ -lpthread -lcurl")

# Add executable target
add_executable(updater Loader.cpp)

# Link against AppModules library
target_link_libraries(updater AppModules)

编译时出现错误：

➜  C_Updater make
[ 50%] Built target AppModules
[ 75%] Linking CXX executable updater
/usr/lib/x86_64-linux-gnu/libcurl.so: file not recognized: file format not recognized
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/updater.dir/build.make:105: updater] Error 1
make[1]: *** [CMakeFiles/Makefile2:97: CMakeFiles/updater.dir/all] Error 2
make: *** [Makefile:103: all] Error 2

推测问题在于find_package找到的是主机平台的libcurl.so而非目标Windows 32位的libcurl.a，尝试调整CMAKE_FIND_ROOT_PATH等参数、直接链接静态库均未解决。

解决方案 #

核心问题修正 #

当前CMake配置中，CMAKE_FIND_ROOT_PATH_MODE_LIBRARY和INCLUDE被设置为NEVER，这会导致CMake跳过目标环境的路径，直接在主机系统里找库，所以才会拿到x86_64的libcurl.so。

修改后的CMakeLists.txt #

cmake_minimum_required(VERSION 3.13)
project(updater)

set(CMAKE_SYSTEM_NAME Windows)
set(CMAKE_CXX_STANDARD 17)

# 指定交叉编译器
set(CMAKE_CXX_COMPILER /usr/bin/i686-w64-mingw32-g++-posix)
set(CMAKE_C_COMPILER /usr/bin/i686-w64-mingw32-gcc-posix)

# 配置目标环境根路径
set(CMAKE_INSTALL_PREFIX "/usr/i686-w64-mingw32" CACHE PATH "CMake install prefix")
set(CMAKE_FIND_ROOT_PATH ${CMAKE_INSTALL_PREFIX})

# 调整查找规则：程序找主机，库和头文件找目标环境
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

# 启用静态库查找
set(CURL_USE_STATIC_LIBS ON)
find_package(CURL REQUIRED)

# 使用target_include_directories替代全局include，更规范
add_library(AppModules Main/Main.cpp)
target_include_directories(AppModules PRIVATE ${CURL_INCLUDE_DIRS})
target_link_libraries(AppModules PRIVATE CURL::libcurl Threads::Threads)

# 编译和链接选项：避免重复设置库，依赖由CMake自动处理
set(CMAKE_CXX_FLAGS "-Wall -Wextra -pedantic -static -static-libstdc++")
set(CMAKE_EXE_LINKER_FLAGS "-static -static-libstdc++")

add_executable(updater Loader.cpp)
target_link_libraries(updater PRIVATE AppModules)

关键修改点说明 #

1. 修正查找规则：将CMAKE_FIND_ROOT_PATH_MODE_LIBRARY和INCLUDE改为ONLY，强制CMake只在CMAKE_FIND_ROOT_PATH指定的目标环境路径（/usr/i686-w64-mingw32）里找库和头文件。
2. 启用CURL静态库：添加set(CURL_USE_STATIC_LIBS ON)，让find_package优先查找静态库libcurl.a。
3. 规范依赖管理：用target_include_directories和target_link_libraries的PRIVATE属性替代全局include_directories，避免污染其他目标；依赖库由CMake自动传递，不需要手动在CXX_FLAGS里加-lcurl、-lpthread。
4. 清理冗余选项：去掉CMAKE_CXX_FLAGS和CMAKE_EXE_LINKER_FLAGS里重复的库链接参数，避免冲突。

编译步骤 #

1. 清理之前的构建文件：

cd C_UPDATER
rm -rf build && mkdir build && cd build

2. 重新运行CMake：

cmake ..

3. 编译：

make

内容的提问来源于stack exchange，提问作者PROGRAMMER1