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[tips] CMake查找依赖包 #29

Open quinnwencn opened 2 months ago

quinnwencn commented 2 months ago

1. 背景

在软件开发时，我们不可避免会用到开源组件或者是其他人提供的库文件。如果开源软件或者是库文件严格按照CMake编译系统开发，并提供FindXXX.cmake或者是XXXConfig.cmake、xxx-config.cmake文件，用于辅助查找头文件和so库文件，那么软件的集成过程一般来说不会遇到编译问题。然而，如果开源软件使用的编译系统并非CMake，而是Makefile或者是meson等其他编译系统，亦或者库文件提供方并未提供足够的文件用于辅助编译，那么我们在CMake脚本中使用find_package将会遇到问题：

CMake Error at CMakeLists.txt:9 (find_package):
  By not providing "FindOSTree.cmake" in CMAKE_MODULE_PATH this project has
  asked CMake to find a package configuration file provided by "OSTree", but
  CMake did not find one.

  Could not find a package configuration file provided by "OSTree" with any
  of the following names:

    OSTreeConfig.cmake
    ostree-config.cmake

  Add the installation prefix of "OSTree" to CMAKE_PREFIX_PATH or set
  "OSTree_DIR" to a directory containing one of the above files.  If "OSTree"
  provides a separate development package or SDK, be sure it has been
  installed.

2. 问题分析

上面的报错我们以OSTree开源仓库为例，改仓库使用的是automake编译系统，因此没有提供FindOSTree.cmake，我们直接在CMake中通过find_package查找OSTree，自然会遇到问题。

2.1 find_package到底做了什么

在查找依赖包时，实际上是为了为代码编译时提供头文件搜素路径，以及链接时提供库文件的链接路径，find_package也就是完成这个功能的，因此它就负责查找XXX_INCLUDE_DIRS和XXX_LIBRARIES。其中XXX就是要查找的包。

2.2 find_package如何查找

查找时首先是判断用户是否提供了CMAKE_MODULE_PATH，这个我们根据报错也能看出来。如果用户提供了，那么CMake会在这个路径下查找FindXXX.cmake文件，并根据这个文件去查找依赖。如果CMAKE_MODULE_PATH没有提供，那么CMake就会去系统的Modules路径去查找包的配置文件，也就是上文报错信息提到的XXXConfig.cmake或者 XXX-config.cmake文件。系统的Modules目录一般是：/usr/share/cmake-3.22/Modules，在这里吗我们也能看到里面 有一些FindYYY.cmake的文件了。

自定义FindXXX.cmake

根据提示，我们可以在CMake中指定CMAKE_MODULE_PATH，并在这个路径下制作我们自己的FindXXX.cmake文件，以此来解决编译报错的问题，我们这里仍然以OSTree为例：

# FindOSTree.cmake

set(OSTREE_FOUND TRUE)
set(OSTREE_ROOT_DIR "/usr")

find_path(OSTREE_INCLUDE_DIR
    NAMES ostree.h
    HINTS ${OSTREE_ROOT_DIR}/include
    PATH_SUFFIXES ostree-1 src/libostree)
mark_as_advanced(OSTREE_INCLUDE_DIR)

find_library(OSTREE_LIBRARY
    NAMES libostree-1.so
    HINTS ${OSTREE_ROOT_DIR}/lib
    PATH_SUFFIXES /.libs)
mark_as_advanced(OSTREE_LIBRARY)

find_package(PkgConfig)

pkg_check_modules(OSTREE_GLIB REQUIRED gio-2.0 glib-2.0)

include(FindPackageHandleStandardArgs)

find_package_handle_standard_args(OSTree DEFAULT_MSG OSTREE_LIBRARY OSTREE_INCLUDE_DIR OSTREE_GLIB_FOUND)

set(OSTREE_INCLUDE_DIRS ${OSTREE_INCLUDE_DIR} ${OSTREE_GLIB_INCLUDE_DIRS})
set(OSTREE_LIBRARIES ${OSTREE_LIBRARY} ${OSTREE_GLIB_LIBRARIES})

代码中，我们使用find_path找到ostree头文件和库文件所在的目录，并赋值给OSTREE_INCLUDE_DIR和OSTREE_LIBRARY，同时更新OSTREE_FOUND为TRUE，将OSTREE_INCLUDE_DIR和OSTREE_LIBRARY这两个值分别设置给OSTREE_INCLUDE_DIRS和OSTREE_LIBRARIES，CMake实际是使用这两个变量的。到这里，FindOSTree.cmake就可以工作了，但是，由于OSTree实际上依赖于gio和glib这两个库，所以我们使用pkg_check_modules显示告诉OSTREE需要这两个库，否则编译仍然会报错找不到glib和gio。 gio和glib的FindGlib.cmake的文件内容如下：

if (GLIB2_LIBRARIES AND GLIB2_INCLUDE_DIRS)
    set(GLIB2_FOUND TRUE)
else (GLIB2_LIBRARIES AND GLIB2_INCLUDE_DIRS)
    include(FindPkgConfig)

    if (GLIB2_FIND_REQUIRED)
        set(_pkgconfig_REQURIED "REQUIRED")
    else (GLIB2_FIND_REQUIRED)
        set(_pkgconfig_REQURIED "")
    endif (GLIB2_FIND_REQUIRED)

    if (GLIB2_MIN_VERSION)
        pkg_search_module(GLIB2 ${_pkgconfig_REQUIRED} glib-2.0>=${GLIB2_MIN_VERSION})
    else (GLIB2_MIN_VERSION)
        pkg_search_module(GLIB2 ${_pkgconfig_REQUIRED} glib-2.0)
    endif (GLIB2_MIN_VERSION)

    if (PKG_CONFIG_FOUND)
        if (GLIB2_FOUND)
            set(GLIB2_CORE_FOUND TRUE)
        else (GLIB2_FOUND)
            set(GLIB2_CORE_FOUND FALSE)
        endif (GLIB2_FOUND)
    endif (PKG_CONFIG_FOUND)

    if (NOT GLIB2_FOUND AND NOT PKG_CONFIG_FOUND)
        find_path(_glibconfig_include_DIR
            NAMES glibconfig.h
            PATHS /usr/include
                /usr/lib
                /usr/lib64
                /usr/local/include
                ${CMAKE_LIBRARY_PATH}
            PATH_SUFFIXES glib-2.0/include)

        find_path(_glib2_include_DIR
            NAMES glib.h gio.h
            PATHS
                /usr/include
                /usr/local/include
            PATH_SUFFIXES glib-2.0)

        find_library(_glib2_link_DIR
            NAMES
                glib-2.0
                glib
            PATHS
                /usr/lib
                /usr/local/lib
                /usr/lib64)

        if (_glib2_include_DIR AND _glib2_link_DIR)
            set(_glib2_FOUND TRUE)
        endif (_glib2_include_DIR AND _glib2_link_DIR)

        if (_glib2_FOUND)
            set(GLIB2_INCLUDE_DIRS ${_glib2_include_DIR} ${_glib2config_include_DIR})
            set(GLIB2_LIBRARIES ${_glib_link_DIR})
            set(GLIB2_CORE_FOUND TRUE)
        else (_glib2_FOUND)
            set(GLIB2_CORE_FOUND FALSE)
        endif (_glib2_FOUND)

        if (NOT LIBINTL_FOUND)
            find_path(LIBINTL_INCLUDE_DIR
                NAMES libintl.h
                PATHS
                    /usr/include
                    /usr/local/include)

            find_library(LIBINTL_LIBRARY
                NAMES intl
                PATHS
                    /usr/lib
                    /usr/local/lib)

            if (LIBINTL_LIBRARY AND LIBINTL_INCLUDE_DIR)
                set(LIBINTL_FOUND TRUE)
            endif (LIBINTL_LIBRARY AND LIBINTL_INCLUDE_DIR)
        endif (NOT LIBINTL_FOUND)

        if (NOT LIBICONV_FOUND)
            find_path(LIBICONV_INCLUDE_DIR
                NAMES iconv.h
                PATHS
                    /usr/include
                    /usr/local/include
                PATH_SUFFIXES glib-2.0)

            find_library(LIBICONV_LIBRARY
                NAMES iconv
                PATHS
                    /usr/lib
                    /usr/local/lib
                    /usr/lib64)

            if (LIBICONV_INCLUDE_DIR AND LIBICONV_LIBRARY)
                set(LIBICONV_FOUND TRUE)
            endif (LIBICONV_INCLUDE_DIR AND LIBICONV_LIBRARY)
        endif (NOT LIBICONV_FOUND)

        if (LIBINTL_FOUND)
            set(GLIB2_LIBRARIES ${GLIB2_LIBRARIES} ${LIBINTL_LIBRARY})
            set(GLIB2_INCLUDE_DIRS ${GLIB2_INCLUDE_DIRS} ${LIBINTL_INCLUDE_DIR})
        endif (LIBINTL_FOUND)

        if (LIBICONV_FOUND)
            set(GLIB2_LIBRARIES ${GLIB2_LIBRARIES} ${LIBICONV_LIBRARY})
            set(GLIB2_INCLUDE_DIRS ${GLIB2_INCLUDE_DIRS} ${LIBICONV_INCLUDE_DIR})
        endif (LIBICONV_FOUND)

    endif (NOT GLIB2_FOUND AND NOT PKG_CONFIG_FOUND)

    if (GLIB2_CORE_FOUND AND GLIB2_INCLUDE_DIRS AND GLIB2_LIBRARIES)
            set(GLIB2_FOUND TRUE)
    endif (GLIB2_CORE_FOUND AND GLIB2_INCLUDE_DIRS AND GLIB2_LIBRARIES)

    if (GLIB2_FOUND)
        if (NOT GLIB2_FIND_QUIETLY)
            message(STATUS "Found GLib2: ${GLIB2_LIBRARIES} ${GLIB2_INCLUDE_DIRS}")
        endif (NOT GLIB2_FIND_QUIETLY)
    else (GLIB2_FOUND)
        if (NOT GLIB2_FIND_QUIETLY)
            message(STATUS "GLib2 not found.")
        endif (NOT GLIB2_FIND_QUIETLY)

    endif (GLIB2_FOUND)

    mark_as_advanced(GLIB2_INCLUDE_DIRS GLIB2_LIBRARIES)
    mark_as_advanced(LIBICONV_INCLUDE_DIR LIBICONV_LIBRARY)
    mark_as_advanced(LIBINTL_INCLUDE_DIR LIBINTL_LIBRARY)

endif (GLIB2_LIBRARIES AND GLIB2_INCLUDE_DIRS)

if (GLIB2_FOUND)
    include(CheckIncludeFiles)
    set(CMAKE_REQUIRED_INCLUDES ${GLIB2_INCLUDE_DIRS})
    check_include_files(glib/gregex.h HAVE_GLIB_GREGEX_H)
    set(CMAKE_REQUIRED_INCLUDES "")
endif (GLIB2_FOUND)

这里，GLIB还依赖于libiconv和libintl，但是我们也可以不编写他们的find文件，直接在glib里查找， 最后，将这俩个cmake文件放到工程目录下的cmake-modules目录，并在顶层CMake文件中生命CMAKE_MODULE_PATH即可。 当然，将这两个文件放到系统的Modules目录也是可以的。