cmake rpath & Makefile rapth

商业程序如何加载自己的so  

使用LD_LIBRARY_PATH的缺点是要实现设置LD_LIBRARY_PATH。不够自动化。那么大型的商业程序是如何加载自己的so呢。 

这里以QtCreator为例。 
QtCreator安装在/home/xxx/Qt5.3.1目录下。使用ldd查看qtcreator依赖的so。结果如下:

xxx@ubuntu:~/Qt5.3.1/Tools/QtCreator/bin$ ldd qtcreator
    linux-gate.so.1 =>  (0xb7701000)
    libExtensionSystem.so.1 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/libExtensionSystem.so.1 (0xb76c2000)
    libQt5Widgets.so.5 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/libQt5Widgets.so.5 (0xb707e000)
    libQt5Network.so.5 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/libQt5Network.so.5 (0xb6f19000)
    libQt5Gui.so.5 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/libQt5Gui.so.5 (0xb69d8000)
    libQt5Core.so.5 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/libQt5Core.so.5 (0xb649d000)
    libpthread.so.0 => /lib/i386-linux-gnu/libpthread.so.0 (0xb646b000)
    libstdc++.so.6 => /usr/lib/i386-linux-gnu/libstdc++.so.6 (0xb6382000)
    libgcc_s.so.1 => /lib/i386-linux-gnu/libgcc_s.so.1 (0xb6364000)
    libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xb61b6000)
    libgobject-2.0.so.0 => /usr/lib/i386-linux-gnu/libgobject-2.0.so.0 (0xb6164000)
    libglib-2.0.so.0 => /lib/i386-linux-gnu/libglib-2.0.so.0 (0xb6058000)
    libX11.so.6 => /usr/lib/i386-linux-gnu/libX11.so.6 (0xb5f24000)
    libm.so.6 => /lib/i386-linux-gnu/libm.so.6 (0xb5edd000)
    libGL.so.1 => /usr/lib/i386-linux-gnu/mesa/libGL.so.1 (0xb5e7d000)
    libicui18n.so.52 => /home/xx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/./libicui18n.so.52 (0xb5c53000)
    libicuuc.so.52 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/./libicuuc.so.52 (0xb5ad7000)
    libdl.so.2 => /lib/i386-linux-gnu/libdl.so.2 (0xb5ad2000)
    libgthread-2.0.so.0 => /usr/lib/i386-linux-gnu/libgthread-2.0.so.0 (0xb5ace000)
    librt.so.1 => /lib/i386-linux-gnu/librt.so.1 (0xb5ac5000)
    /lib/ld-linux.so.2 (0xb7702000)
    libffi.so.6 => /usr/lib/i386-linux-gnu/libffi.so.6 (0xb5abe000)
    libpcre.so.3 => /lib/i386-linux-gnu/libpcre.so.3 (0xb5a80000)
    libxcb.so.1 => /usr/lib/i386-linux-gnu/libxcb.so.1 (0xb5a5e000)
    libglapi.so.0 => /usr/lib/i386-linux-gnu/libglapi.so.0 (0xb5a45000)
    libXext.so.6 => /usr/lib/i386-linux-gnu/libXext.so.6 (0xb5a32000)
    libXdamage.so.1 => /usr/lib/i386-linux-gnu/libXdamage.so.1 (0xb5a2e000)
    libXfixes.so.3 => /usr/lib/i386-linux-gnu/libXfixes.so.3 (0xb5a28000)
    libX11-xcb.so.1 => /usr/lib/i386-linux-gnu/libX11-xcb.so.1 (0xb5a25000)
    libxcb-glx.so.0 => /usr/lib/i386-linux-gnu/libxcb-glx.so.0 (0xb5a0c000)
    libxcb-dri2.so.0 => /usr/lib/i386-linux-gnu/libxcb-dri2.so.0 (0xb5a06000)
    libxcb-dri3.so.0 => /usr/lib/i386-linux-gnu/libxcb-dri3.so.0 (0xb5a02000)
    libxcb-present.so.0 => /usr/lib/i386-linux-gnu/libxcb-present.so.0 (0xb59fe000)
    libxcb-sync.so.1 => /usr/lib/i386-linux-gnu/libxcb-sync.so.1 (0xb59f7000)
    libxshmfence.so.1 => /usr/lib/i386-linux-gnu/libxshmfence.so.1 (0xb59f3000)
    libXxf86vm.so.1 => /usr/lib/i386-linux-gnu/libXxf86vm.so.1 (0xb59ed000)
    libdrm.so.2 => /usr/lib/i386-linux-gnu/libdrm.so.2 (0xb59df000)
    libicudata.so.52 => /home/xxx/Qt5.3.1/Tools/QtCreator/bin/./../lib/qtcreator/././libicudata.so.52 (0xb4373000)
    libXau.so.6 => /usr/lib/i386-linux-gnu/libXau.so.6 (0xb436e000)
    libXdmcp.so.6 => /usr/lib/i386-linux-gnu/libXdmcp.so.6 (0xb4367000)

在看一下本身直接加载的动态库:

xxx@ubuntu:~/Qt5.3.1/Tools/QtCreator/bin$ readelf --dynamic qtcreator

Dynamic section at offset 0x11eb0 contains 30 entries:
  标记        类型                         名称/值
 0x00000001 (NEEDED)                     共享库:[libExtensionSystem.so.1]
 0x00000001 (NEEDED)                     共享库:[libQt5Widgets.so.5]
 0x00000001 (NEEDED)                     共享库:[libQt5Network.so.5]
 0x00000001 (NEEDED)                     共享库:[libQt5Gui.so.5]
 0x00000001 (NEEDED)                     共享库:[libQt5Core.so.5]
 0x00000001 (NEEDED)                     共享库:[libpthread.so.0]
 0x00000001 (NEEDED)                     共享库:[libstdc++.so.6]
 0x00000001 (NEEDED)                     共享库:[libgcc_s.so.1]
 0x00000001 (NEEDED)                     共享库:[libc.so.6]
 0x0000000f (RPATH)                      Library rpath: [$ORIGIN/../lib/qtcreator]

秘密就在这句:0x0000000f (RPATH) Library rpath: [$ORIGIN/../lib/qtcreator]

rpath与ORIGIN 
rpath是gcc的一个参数。rpath添加一个目录。当程序被加载时,搜寻此目录,寻找动态库。rpath添加的目录信息保存在可执行文件中。即使这句 
0x0000000f (RPATH) Library rpath: [xxx]。 
现在的问题是,可执行文件如何知道自身所在目录。 
ORIGIN ORIGIN更详细的信息,可参考此文档

例子 
例子目录结构如下 
src 
…main.c 
…Makefile 
…lib/foo.c 
操作系统:ubuntu 14 32位 
编译i:gcc 4.8

main.c文件源码

void test_tk();

int main(void)
{
    test_tk();
    return 0;
}

Makefile文件内容

main:main.c lib/libfoo.so
    gcc -L${shell pwd}/lib -g -Wall -o test -Wl,-rpath,'$$ORIGIN/lib' main.c -lfoo
lib/libfoo.so:lib/foo.c
    gcc -g -Wall -fPIC -shared -o lib/libfoo.so lib/foo.c

foo.c文件源码

#include <stdio.h>

void test_tk()
{
    printf("called!\n");
}

编译,生成test可执行文件。 
执行readelf –dynamic test 来看加载的动态库。

Dynamic section at offset 0xf04 contains 26 entries:
  标记        类型                         名称/值
 0x00000001 (NEEDED)                     共享库:[libfoo.so]
 0x00000001 (NEEDED)                     共享库:[libc.so.6]
 0x0000000f (RPATH)                      Library rpath: [$ORIGIN/lib]
 ..........................................................

//////////////////////////////////////////////////////////////////////////////////////////


最近在做C++开发,在MBP上用Cmake构建项目的时候,发现 make install 之后生成的执行文件会运行出错:

dyld: Library not loaded: @rpath/libadk.dylib  
  Referenced from: /Users/kesco/Documents/workspaces/cpp/apue_practise/build/bin/./thread
  Reason: image not found
[1] 52362 trace trap  ./thread

提示我,动态链接库( libadk.dylib 也是工程内的一个子项目)找不着。这就奇怪了,因为我 make install 安装的时候,是把动态链接库和执行文件都放在同一个目录下的。为啥会找不着呢,而之前在Windows下是没问题的,后来查了下Cmake的文档,原来是Cmake版本的问题=_+。

如果你的CMakeList.txt上写的 cmake_minium_required 为2.6的话,会报下面异常:

....
CMake Warning (dev):  
  Policy CMP0042 is not set: MACOSX_RPATH is enabled by default.  Run "cmake --help-policy CMP0042" for policy details.  Use the cmake_policy command to
  set the policy and suppress this warning.

  MACOSX_RPATH is not specified for the following targets:

   cjson
   iniparser
   stemmer
   word2vec

This warning is for project developers.  Use -Wno-dev to suppress it.

-- Generating done
....

而在 CMP0042 更新,也就是Cmake 2.8.1.2之后,如果你声明的 cmake_minium_required 为2.8以上, MACOSX_RPATH 会默认启动,这时候编译的执行文件在查找链接库的时候会往 @rpath上搜索,所以就找不到要链接的库( libadk.dylib 在同一个目录下)。我们可以用 otool -L <file> 命令来查看执行文件的链接库依赖。

bin git:master ❯ otool -L thread  
thread:  
        @rpath/libadk.dylib (compatibility version 0.0.0, current version 0.0.0)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1226.10.1)

知道原因之后就好办了,我们只需在CMakeList.txt上把 MACOSX_RPATH 关掉就好了。

set(CMAKE_MACOSX_RPATH 0)

add_subdirectory(adk)  
add_subdirectory(thread)

....

重新用 cmake 生成MakeFile构建就不会报错了。不过, RPATH 是啥呢?以前写C++的时候都是在Windows上开着VS来的,没遇到过这样的问题,现在遇到了,自然要查清楚。

什么是RPATH?

在Linux环境下,使用动态链接的程序在运行时会自动链接 ld.so 这个库(OS X上是 dyld),然后通过 ld.so 来查找链接其它的库。而 RPATH 就是编译的时候链接到执行文件的链接库路径。OS X在 RPATH 的设置上和Linux还是有点出入的,OS X的 RPATH 采用的是绝对路径。

ld.so 搜索路径的优先级是这样的:

1. RPATH ,编译链接时加入 -rpath 参数指明所谓的 RUNPATH ,这样可执行文件(或者依赖其他动态链接库的动态链接库)就能告诉 ld.so 到哪里去搜索对应的动态链接库了。

2. LD_LIBRARY_PATH ,对于没有设定 RPATH 的可执行文件或者动态链接库,我们可以用 LD_LIBRARY_PATH 这个环境变量通知 ld.so 往哪里查找链接库。

3. /etc/ld.so.conf ,系统对 ld.so 的路径配置文件。

4. /usr/lib 、 /lib 和 /usr/local/lib ,系统默认路径。

Cmake和RPATH

在分发程序的时候,执行文件使用的链接库在系统内不一定会有,或者自带了的版本不对,一般都会在程序文件夹内都会附带相应的链接库,所以最好还是把 RPATH 加上。Cmake对RPATH提供了很多选项支持,我们一般只关注这几个变量就好了: CMAKE_SKIP_BUILD_RPATH 、 CMAKE_BUILD_WITH_INSTALL_RPATH 、 CMAKE_INSTALL_RPATH 和 CMAKE_INSTALL_RPATH_USE_LINK_PATH 。

默认RPATH设置

set(CMAKE_SKIP_BUILD_RPATH FALSE)                 # 编译时加上RPATH 
set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)         # 编译时RPATH不使用安装的RPATH 
set(CMAKE_INSTALL_RPATH "")                       # 安装RPATH为空 
set(CMAKE_INSTALL_RPATH_USE_LINK_PATH FALSE)      # 安装的执行文件不加上RPATH 

Cmake在默认情况下, make install 会把安装的执行文件的 RPATH 删掉的,所以就会出现上面我执行安装好的执行文件报错的问题。

加上完整的RPATH

Cmake的默认设置我们肯定是不能使用的,我们需要一个安装的时候也要带上 RPATH 的设置。

set(INSTALL_LIB_DIR "${PROJECT_BINARY_DIR}/lib") # 假设安装目录在编译目录的lib子目录内

set(CMAKE_SKIP_BUILD_RPATH FALSE)  
set(CMAKE_BUILD_WITH_INSTALL_RPATH FALSE)  
set(CMAKE_INSTALL_RPATH "${CMAKE_INSTALL_PREFIX}/lib")  
set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)

# 确保链接库不在系统默认安装的目录上时更改到项目lib上
list(FIND CMAKE_PLATFORM_IMPLICIT_LINK_DIRECTORIES ${CMAKE_INSTALL_RPATH} isSystemDir)  
if("${isSystemDir}" STREQUAL "-1")  
  set(CMAKE_INSTALL_RPATH "${INSTALL_LIB_DIR}")
endif("${isSystemDir}" STREQUAL "-1")  

现在Cmake在C++项目上应用得越来越多了,但是Cmake的文档很分散,写Cmake构建脚本的时候会踩上很多坑,只能慢慢积累经验总结。

CMakeLists.txt解读

# CMake要求的最低版本号
cmake_minimum_required( VERSION 2.8 )

# 项目名称
project( ycm_support_libs )
# 设置客户端lib和服务端lib的变量名称
set( CLIENT_LIB "ycm_client_support" )
set( SERVER_LIB "ycm_core" )

# 设置Python的版本号变量
set( Python_ADDITIONAL_VERSIONS 2.7 2.6 )
# 进行Python包的查找,这里是REQUIRED表示必须
find_package( PythonLibs 2.6 REQUIRED )

# 如果Python版本号低于3.0.0就进行FATAL_ERROR的出错信息
if ( NOT PYTHONLIBS_VERSION_STRING VERSION_LESS "3.0.0" )
  message( FATAL_ERROR
    "CMake found python3 libs instead of python2 libs. YCM works only with "
    "python2.\n" )
endif()

# 各种option
option( USE_DEV_FLAGS "Use compilation flags meant for YCM developers" OFF )
# 这个变量就是我上文讲到的很关键的一个变量,来判断当前用户需要不需要libclang
option( USE_CLANG_COMPLETER "Use Clang semantic completer for C/C++/ObjC" OFF )
# install.sh中的--system-libclang就与这个变量进行交互
option( USE_SYSTEM_LIBCLANG "Set to ON to use the system libclang library" OFF )
# YCM作者推荐的用法,在这里直接写入Clang的相关路径 注意这里的CACHE PATH,表示当用户如果命令行
# 进行指定,那优先会去读用户的命令行,而不是用这里的set,并且把相关的值写入Cache中
set( PATH_TO_LLVM_ROOT "" CACHE PATH "Path to the root of a LLVM+Clang binary distribution" )
# YCM作者推荐的另外一种安装方法,直接将libclang.so全路径写死
set( EXTERNAL_LIBCLANG_PATH "" CACHE PATH "Path to the libclang library to use" )

# 如果你使用libclang但是没有指定用不用系统的libclang,没有指定llvm_root,没有指定额外的libclang.so,那么就会带你去下载
if ( USE_CLANG_COMPLETER AND
     NOT USE_SYSTEM_LIBCLANG AND
     NOT PATH_TO_LLVM_ROOT AND
     NOT EXTERNAL_LIBCLANG_PATH )
  message( "Downloading Clang 3.4" )

  # 这就是llvm官网的3.4下载路径
  set( CLANG_URL "http://llvm.org/releases/3.4" )

  # 如果当前客户端是苹果 Mac OS X
  if ( APPLE )
      # 设置Clang的文件夹名称
    set( CLANG_DIRNAME "clang+llvm-3.4-x86_64-apple-darwin10.9" )
      # 设置Clang的MD5校验码
    set( CLANG_MD5 "4f43ea0e87090ae5e7bec12373ca4927" )
      # 设置Clang文件名称为之后加上tar.gz
    set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.gz" )
  else()
      # 如果是64位平台
    if ( 64_BIT_PLATFORM )
      # 设置Clang的文件夹名称
      set( CLANG_DIRNAME "clang+llvm-3.4-x86_64-unknown-ubuntu12.04" )
      # 设置Clang的MD5校验码
      set( CLANG_MD5 "6077459d20a7ff412eefc6ce3b9f5c85" )
      # 设置Clang文件名称为之后加上tar.gz
      set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.xz" )
    else()
      # 表示此时为32位的Linux,下载3.3版本
      message( "No pre-built Clang 3.4 binaries for 32 bit linux, "
               "downloading Clang 3.3" )
      set( CLANG_URL "http://llvm.org/releases/3.3" )
      # 设置Clang的文件夹名称
      set( CLANG_DIRNAME "clang+llvm-3.3-i386-debian6" )
      # 设置Clang的MD5校验码
      set( CLANG_MD5 "415d033b60659433d4631df894673802" )
      # 设置Clang文件名称为之后加上tar.gz
      set( CLANG_FILENAME "${CLANG_DIRNAME}.tar.bz2" )
    endif()
  endif()

      # 下载命令
  file(
    DOWNLOAD "${CLANG_URL}/${CLANG_FILENAME}" "./${CLANG_FILENAME}"
    SHOW_PROGRESS EXPECTED_MD5 "${CLANG_MD5}"
  )

  # 文件名正则表达式匹配,进行相应的解压
  if ( CLANG_FILENAME MATCHES ".+bz2" )
      # 执行相关的外部命令 tar
    execute_process( COMMAND tar -xjf ${CLANG_FILENAME} )
  elseif( CLANG_FILENAME MATCHES ".+xz" )
    execute_process( COMMAND tar -xJf ${CLANG_FILENAME} )
  else()
    execute_process( COMMAND tar -xzf ${CLANG_FILENAME} )
  endif()

  # 设置PATH_TO_LLVM_ROOT的路径为当前CMake二进制路径下的Clang目录
  set( PATH_TO_LLVM_ROOT "${CMAKE_CURRENT_BINARY_DIR}/../${CLANG_DIRNAME}" )
endif()

# 如果设置了PATH_TO_LLVM_ROOT或者用户使用系统libclang或者有额外的libclang,就开启USE_CLANG_COMPLETER
# 这个变量我上文提过,很关键
if ( PATH_TO_LLVM_ROOT OR USE_SYSTEM_LIBCLANG OR EXTERNAL_LIBCLANG_PATH )
  set( USE_CLANG_COMPLETER TRUE )
endif()

# 开始使用这个变量,如果用户确定使用libclang,但是没有root没有系统clang没有额外clang,那么
# 进行错误性提示
if ( USE_CLANG_COMPLETER AND
     NOT PATH_TO_LLVM_ROOT AND
     NOT USE_SYSTEM_LIBCLANG AND
     NOT EXTERNAL_LIBCLANG_PATH )
  message( FATAL_ERROR
    "You have not specified which libclang to use. You have several options:\n"
    " 1. Set PATH_TO_LLVM_ROOT to a path to the root of a LLVM+Clang binary "
    "distribution. You can download such a binary distro from llvm.org. This "
    "is the recommended approach.\n"
    " 2. Set USE_SYSTEM_LIBCLANG to ON; this makes YCM search for the system "
    "version of libclang.\n"
    " 3. Set EXTERNAL_LIBCLANG_PATH to a path to whatever "
    "libclang.[so|dylib|dll] you wish to use.\n"
    "You HAVE to pick one option. See the docs for more information.")
endif()

# 进行用户提醒,提醒用户当前是否使用libclang
if ( USE_CLANG_COMPLETER )
  message( "Using libclang to provide semantic completion for C/C++/ObjC" )
else()
  message( "NOT using libclang, no semantic completion for C/C++/ObjC will be "
           "available" )
endif()

# 如果设置了root就设置CLANG_INCLUDES_DIR为root下的include
# 否则CLANG_INCLUDES_DIR为CMake下llvm/include
if ( PATH_TO_LLVM_ROOT )
  set( CLANG_INCLUDES_DIR "${PATH_TO_LLVM_ROOT}/include" )
else()
  set( CLANG_INCLUDES_DIR "${CMAKE_SOURCE_DIR}/llvm/include" )
endif()

# 如果当前的include路径不是绝对路径
if ( NOT IS_ABSOLUTE "${CLANG_INCLUDES_DIR}" )
    # 设置它为绝对路径
  get_filename_component(CLANG_INCLUDES_DIR
    "${CMAKE_BINARY_DIR}/${CLANG_INCLUDES_DIR}" ABSOLUTE)
endif()

# 如果没有额外的libclang,但是有root
if ( NOT EXTERNAL_LIBCLANG_PATH AND PATH_TO_LLVM_ROOT )
    if ( MINGW ) # 如果是MINGW
        # 设置libclang的寻找路径(后面的find_library会去寻找)
    set( LIBCLANG_SEARCH_PATH "${PATH_TO_LLVM_ROOT}/bin" )
  else()
    set( LIBCLANG_SEARCH_PATH "${PATH_TO_LLVM_ROOT}/lib" )
  endif()

  # 这里TEMP会被find_library去寻找clang,和libclang两个so,并且复制路径给TEMP
  find_library( TEMP NAMES clang libclang
                PATHS ${LIBCLANG_SEARCH_PATH}
                NO_DEFAULT_PATH )

            message("temp is ${TEMP}")
            # 设置额外的libclang为这个路径
  set( EXTERNAL_LIBCLANG_PATH ${TEMP} )
endif()

 # 如果当前为苹果,设置额外的flag
if ( APPLE )
  set( CMAKE_INCLUDE_SYSTEM_FLAG_CXX "-isystem " )
endif()

# 如果用户使用系统自带的boost
if ( USE_SYSTEM_BOOST )
    # 进行find boost命令,会用到python,filesystem,system,regex,thread等components
  find_package( Boost REQUIRED COMPONENTS python filesystem system regex thread )
else()
    # 使用自己的Boost
  set( Boost_INCLUDE_DIR ${BoostParts_SOURCE_DIR} )
  set( Boost_LIBRARIES BoostParts )
endif()

 # 相关头文件的加入,Boost,Python和Clang
include_directories(
  SYSTEM
  ${Boost_INCLUDE_DIR}
  ${PYTHON_INCLUDE_DIRS}
  ${CLANG_INCLUDES_DIR}
  )

# 全局递归查找h,cpp文件给SERVER_SOURCES
file( GLOB_RECURSE SERVER_SOURCES *.h *.cpp )

# 全局递归查找测试相关文件
file( GLOB_RECURSE to_remove tests/*.h tests/*.cpp CMakeFiles/*.cpp *client* )

if( to_remove )
    # 学习list相关的REMOVE_ITEM命令
  list( REMOVE_ITEM SERVER_SOURCES ${to_remove} )
endif()

# 这里就是这个变量最关键的地方,它会去include并且开启宏
if ( USE_CLANG_COMPLETER )
  include_directories(
    ${CMAKE_CURRENT_SOURCE_DIR}
    "${CMAKE_CURRENT_SOURCE_DIR}/ClangCompleter" )
  add_definitions( -DUSE_CLANG_COMPLETER )
else()
    # 否则的话寻找所有ClangCompleter下的头和源文件进行删除
  file( GLOB_RECURSE to_remove_clang ClangCompleter/*.h ClangCompleter/*.cpp )

  if( to_remove_clang )
    list( REMOVE_ITEM SERVER_SOURCES ${to_remove_clang} )
  endif()
endif()

# 如果用户使用额外的libclang或者使用系统自带的libclang
if ( EXTERNAL_LIBCLANG_PATH OR USE_SYSTEM_LIBCLANG )
  if ( USE_SYSTEM_LIBCLANG ) # 如果是系统自带
    if ( APPLE )
        set( ENV_LIB_PATHS ENV DYLD_LIBRARY_PATH ) # 将环境变量下的DYLD_LIBRARY_PATH给ENV_LIB_PATHS
    elseif ( UNIX )
      set( ENV_LIB_PATHS ENV LD_LIBRARY_PATH ) # 这也是我之前讲的一定要把你编译的libclang加入到这个环境变量中,因为它会根据这个去寻找
  elseif ( WIN32 ) 
      set( ENV_LIB_PATHS ENV PATH )
    else ()
      set( ENV_LIB_PATHS "" )
    endif()
    file( GLOB SYS_LLVM_PATHS "/usr/lib/llvm*/lib" )

    # 进行相关的libclang查找,在你之前给它指定的环境变量中
    find_library( TEMP clang
                  PATHS
                  ${ENV_LIB_PATHS}
                  /usr/lib
                  /usr/lib/llvm
                  ${SYS_LLVM_PATHS}
                  /Library/Developer/CommandLineTools/usr/lib,
                  /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib )
              # 将寻找到的变量给EXTERNAL_LIBCLANG_PATH
    set( EXTERNAL_LIBCLANG_PATH ${TEMP} )
  else()
    if ( NOT APPLE )
      # 设置相关rpath
      set( CMAKE_BUILD_WITH_INSTALL_RPATH TRUE )
      # 设置make install之后的rpath
      set( CMAKE_INSTALL_RPATH "\$ORIGIN" )
    endif()
  endif()

  set( LIBCLANG_TARGET "" )
  message(
    "Using external libclang: ${EXTERNAL_LIBCLANG_PATH}" )
message("libclang_target is ${LIBCLANG_TARGET}")
else()
  set( LIBCLANG_TARGET )
endif()

# 如果有额外的rpath,在这里进行设置
if ( EXTRA_RPATH )
  set( CMAKE_INSTALL_RPATH "${EXTRA_RPATH}:${CMAKE_INSTALL_RPATH}" )
endif()

# 如果在Linux下需要额外的rt库
if ( UNIX AND NOT APPLE )
  set( EXTRA_LIBS rt )
endif()

# 将目录下所有的h和cpp给CLIENT_SOURCES
file( GLOB CLIENT_SOURCES *.h *.cpp )
# 相应SERVER_SPECIFIC赋值
file( GLOB SERVER_SPECIFIC *ycm_core* )

if( SERVER_SPECIFIC )
    # 移除相关CLIEN_SOURCES下的SERVER_SPECIFIC
  list( REMOVE_ITEM CLIENT_SOURCES ${SERVER_SPECIFIC} )
endif()

# 创建client的library,并且是动态库
add_library( ${CLIENT_LIB} SHARED
             ${CLIENT_SOURCES}
           )

       # 将这个库与之前的rt,Boost,Python进行链接
target_link_libraries( ${CLIENT_LIB}
                       ${Boost_LIBRARIES}
                       ${PYTHON_LIBRARIES}
                       ${EXTRA_LIBS}
                     )

# 创建server的library,并且是动态库
add_library( ${SERVER_LIB} SHARED
             ${SERVER_SOURCES}
           )

       # 将这个库与之前的rt,Boost,Python,libclang,而外的server lib进行链接
target_link_libraries( ${SERVER_LIB}
                       ${Boost_LIBRARIES}
                       ${PYTHON_LIBRARIES}
                       ${LIBCLANG_TARGET}
                       ${EXTRA_LIBS}
                     )

# 如果定义了LIBCLANG_TARGET
if( LIBCLANG_TARGET )
  if( NOT WIN32 )
      # 在非WIN32情况下增加自定义命令,将libclang.so/dll拷贝到自己目录下
    add_custom_command(
      TARGET ${SERVER_LIB}
      POST_BUILD
      COMMAND ${CMAKE_COMMAND} -E copy "${LIBCLANG_TARGET}" "$<TARGET_FILE_DIR:${SERVER_LIB}>"
    )
  else()
    add_custom_command(
      TARGET ${SERVER_LIB}
      POST_BUILD
      COMMAND ${CMAKE_COMMAND} -E copy "${PATH_TO_LLVM_ROOT}/bin/libclang.dll" "$<TARGET_FILE_DIR:${SERVER_LIB}>")
  endif()
endif()

# 建立依赖关系,表示这个项目需要这两个库共同完成
add_custom_target( ${PROJECT_NAME}
                   DEPENDS ${CLIENT_LIB} ${SERVER_LIB} )

# Mac下的相关设置,如果是利用rpath的话Mac下还是会去寻找系统库,即使用户显示指定
# 这里需要改用@loader_path
if ( EXTERNAL_LIBCLANG_PATH AND APPLE )
  add_custom_command( TARGET ${SERVER_LIB}
                      POST_BUILD
                      COMMAND install_name_tool
                      "-change"
                      "@rpath/libclang.dylib"
                      "@loader_path/libclang.dylib"
                      "$<TARGET_FILE:${SERVER_LIB}>"
                    )
endif()

# 将这些库的前缀lib去掉,因为会扰乱Python模块的查找
set_target_properties( ${CLIENT_LIB} PROPERTIES PREFIX "")
set_target_properties( ${SERVER_LIB} PROPERTIES PREFIX "")

if ( WIN32 OR CYGWIN )
    # 进行Windows下相关库的转移存放
  set_target_properties( ${CLIENT_LIB} PROPERTIES
    RUNTIME_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
  set_target_properties( ${SERVER_LIB} PROPERTIES
    RUNTIME_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
  foreach( OUTPUTCONFIG ${CMAKE_CONFIGURATION_TYPES} )
    string( TOUPPER ${OUTPUTCONFIG} OUTPUTCONFIG )
    set_target_properties( ${CLIENT_LIB} PROPERTIES
      RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${PROJECT_SOURCE_DIR}/../.. )
    set_target_properties( ${SERVER_LIB} PROPERTIES
      RUNTIME_OUTPUT_DIRECTORY_${OUTPUTCONFIG} ${PROJECT_SOURCE_DIR}/../.. )
  endforeach()

  if ( WIN32 )
    # 建立后缀名.pyd
    set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".pyd")
    set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".pyd")
  elseif ( CYGWIN )
    # CYGIN下后缀为dll
    set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".dll")
    set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".dll")
  endif()
else()
  # Mac和Linux下都为.so,虽然Mac下应该默认为.dylib,但Python识别不了dylib,因此这里还是设置成.so
  set_target_properties( ${CLIENT_LIB} PROPERTIES SUFFIX ".so")
  set_target_properties( ${SERVER_LIB} PROPERTIES SUFFIX ".so")
endif()

 # 设置相关lib的输出目录
set_target_properties( ${CLIENT_LIB} PROPERTIES
  LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )
set_target_properties( ${SERVER_LIB} PROPERTIES
  LIBRARY_OUTPUT_DIRECTORY ${PROJECT_SOURCE_DIR}/../.. )

if ( USE_DEV_FLAGS AND ( CMAKE_COMPILER_IS_GNUCXX OR COMPILER_IS_CLANG ) AND
     NOT CMAKE_GENERATOR_IS_XCODE )
  # 增加相应flag
  set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror" )
endif()

# 提出警告在使用C++11特性下
if ( USE_DEV_FLAGS AND COMPILER_IS_CLANG AND NOT CMAKE_GENERATOR_IS_XCODE AND
     NOT SYSTEM_IS_FREEBSD )
  set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wc++98-compat" )
endif()

if( SYSTEM_IS_SUNOS )
    # SunOS需要-pthreads这个flag才能正常使用
  set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthreads" )
endif()

# 增加测试子目录tests
add_subdirectory( tests )


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