c++ - 合并静态库时 ar 命令不产生索引

Question

我正在尝试按照给定的答案 here在 MinGW64 下将多个静态库组合成一个存档。具体来说，我使用 CMake 并指定以下命令:

    add_custom_command(
        OUTPUT ${COMBINED_CORE_LIB_NAME}
        COMMAND ${AR} -crs ${COMBINED_CORE_LIB_NAME} ${CORE_LIB_TARGET_FILES}
        DEPENDS ${DILIGENT_CORE_INSTALL_LIBS_LIST}
        COMMENT "Combining core libraries..."
    )

另外，根据 here 的建议，我不使用 stock ar，而是使用 cross ar:

find_program(AR NAMES x86_64-w64-mingw32-gcc-ar)

但是，无论我做什么，ar 都拒绝生成索引，并且每次我尝试链接生成的库时，我都会收到此错误:

error adding symbols: Archive has no index; run ranlib to add one

按照建议运行 ranlib，无论是 stock one 还是 x86_64-w64-mingw32-gcc-ranlib 都没有区别。

我花了 15 分钟用 MSVC 和 lib.exe 来完成这项工作，并在 MinGW 上苦苦挣扎了 8 个小时。任何建议将不胜感激。

[编辑]:原来这个问题并不是 MinGW 特有的，它也以非常相似的方式发生在 Linux 上。

Answer 1

事实证明，使用 ar 实用程序无法将多个 .a 文件合并到一个 .a 库中:它拒绝生成索引。一个可行的解决方案是从所有静态库中解压所有目标文件，然后将它们重新打包到一个组合库中。

下面是我最终得到的 CMake 指令:

set(COMBINED_CORE_LIB_NAME "${CMAKE_STATIC_LIBRARY_PREFIX}DiligentCore${CMAKE_STATIC_LIBRARY_SUFFIX}")

foreach(CORE_LIB ${DILIGENT_CORE_INSTALL_LIBS_LIST})
    list(APPEND CORE_LIB_TARGET_FILES $<TARGET_FILE:${CORE_LIB}>)
endforeach(CORE_LIB)

if(MSVC)
    add_custom_command(
        OUTPUT ${COMBINED_CORE_LIB_NAME}
        COMMAND ${LIB_EXE} /OUT:${COMBINED_CORE_LIB_NAME} ${CORE_LIB_TARGET_FILES}
        DEPENDS ${DILIGENT_CORE_INSTALL_LIBS_LIST}
        COMMENT "Combining core libraries..."
    )
    add_custom_target(DiligentCore-static ALL DEPENDS ${COMBINED_CORE_LIB_NAME})
else()

    if(PLATFORM_WIN32)
        # do NOT use stock ar on MinGW
        find_program(AR NAMES x86_64-w64-mingw32-gcc-ar)
    else()
        set(AR ${CMAKE_AR})
    endif()

    if(AR)
        add_custom_command(
            OUTPUT ${COMBINED_CORE_LIB_NAME}
            # Delete all object files from current directory
            COMMAND ${CMAKE_COMMAND} -E remove "*${CMAKE_C_OUTPUT_EXTENSION}"
            DEPENDS ${DILIGENT_CORE_INSTALL_LIBS_LIST}
            COMMENT "Combining core libraries..."
        )

        # Unpack all object files from all targets to current directory
        foreach(CORE_LIB_TARGET ${CORE_LIB_TARGET_FILES})
            add_custom_command(
                OUTPUT ${COMBINED_CORE_LIB_NAME}
                COMMAND ${AR} -x ${CORE_LIB_TARGET}
                APPEND
            )
        endforeach()

        # Pack object files to a combined library and delete them
        add_custom_command(
            OUTPUT ${COMBINED_CORE_LIB_NAME}
            COMMAND ${AR} -crs ${COMBINED_CORE_LIB_NAME} "*${CMAKE_C_OUTPUT_EXTENSION}"
            COMMAND ${CMAKE_COMMAND} -E remove "*${CMAKE_C_OUTPUT_EXTENSION}"
            APPEND
        )

        add_custom_target(DiligentCore-static ALL DEPENDS ${COMBINED_CORE_LIB_NAME})
    else()
        message("ar command is not found")
    endif()
endif()

if(TARGET DiligentCore-static)
    install(FILES "${CMAKE_CURRENT_BINARY_DIR}/${COMBINED_CORE_LIB_NAME}"
            DESTINATION "${DILIGENT_CORE_INSTALL_DIR}/lib/"
    )
    set_target_properties(DiligentCore-static PROPERTIES
        FOLDER Core
    )
else()
    message("Unable to find librarian tool. Combined DiligentCore static library will not be produced.")
endif()