Mac dylib動態庫載入路徑問題(以OpenCV為例)

在自己的Mac上寫了一個基於OpenCV的簡單程式；需要傳給其他人共同除錯，但是可執行檔案在他人的Mac上無法執行；執行時會提示：

dyld: Library not loaded: /usr/local/Cellar/opencv/2.4.12/lib/libopencv_features2d.2.4.dylib

這樣就引申出來一個問題：在xcode下編譯出的程式，在開發機器上執行是沒有問題的。但是給其他使用者用，就可能出問題。因為使用者不一定有這個庫。
有兩種方法可以解決這個問題；一是給其他使用者也安裝依賴的庫檔案；二是將所有的dylib隨行釋出，消除依賴。
第一種方案不考慮，大部分時候這樣做並不現實；下面說說如何隨行釋出dylib。

單純將依賴的dylib檔案拷貝到可執行檔案目錄下一同傳輸過去是不能消除依賴的；執行的時候還是報錯；
在編譯一個動態庫的時候, 你需要指定 INSTALL_PATH. 也就是它的安裝路徑；編譯完成後如果一個可執行程式使用了該動態庫, 那麼在編譯可執行程式的時候, 動態庫的 INSTALL_PATH 會被記錄到可執行程式中, 用來定位這個動態庫。

因此我們首先需要將用到的dylib檔案都拷貝到可執行檔案目錄下，然後改變動態庫的INSTALL_PATH；將其改到可執行檔案所在目錄；
需要注意的是：如果依賴多個動態庫，用到的動態庫已會依賴其他動態庫，因此用到的所有的動態庫的依賴動態庫路徑都需要修改。

以OpenCV為例子，假設最終編譯出來的可執行檔案為 macimgproc；執行命令：otool -L macimgproc可看到如下的輸出：

macimgproc:
    /usr/local/opt/opencv/lib/libopencv_calib3d.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_contrib.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_core.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_features2d.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_flann.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_gpu.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_highgui.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_imgproc.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_legacy.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_ml.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_nonfree.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_objdetect.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_ocl.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_photo.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_stitching.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_superres.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_video.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_videostab.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 307.4.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.0.0)

說明macimgproc依賴所有的OpenCV動態庫檔案；因此首先需要將所有動態庫檔案拷貝到macimgproc所在目錄，然後需要將macimgproc檔案中的所有/usr/local/opt/opencv/lib/libopencv_xxx修改為@executable_path/libopencv_xxx；

@executable_path表示可執行檔案所在目錄；指示所有OpenCV動態庫從可執行檔案所在目錄查詢；
更多@executable_path的介紹以及其他變數參見文章 @rpath, @loader_path, @executable_path。
使用命令install_name_tool -change {old.dylib} {new.dylib} {filename}修改動態庫的INSTALL_PATH，例如：

install_name_tool -change /usr/local/Cellar/opencv/2.4.12/lib/libopencv_flann.2.4.dylib @executable_path/libopencv_flann.2.4.dylib macimgproc

執行後重新otool -L macimgproc可看到如下的輸出：

macimgproc:
    ...
    /usr/local/opt/opencv/lib/libopencv_features2d.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    @executable_path/libopencv_flann.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    /usr/local/opt/opencv/lib/libopencv_gpu.2.4.dylib (compatibility version 2.4.0, current version 2.4.12)
    ...

依次修改所有依賴即可。

整個OpenCV庫大概有19個dylib檔案，因此寫了一個簡單的批量修改指令碼：

#!/usr/bin/ruby

Preview=0

def fix_opencv_lib_link(file,rlib)
    if(rlib.include?('libopencv'))
        name = rlib.split('/').last
        cmd = "install_name_tool -change #{rlib} @executable_path/#{name} #{file}"
        if Preview == 1
            puts "Preivew: #{cmd}"
        else
            `#{cmd}`
        end
    else 
        puts "ignore rlib: #{rlib}";
    end
end

def fix_file_rely_lib(file)
  puts "===============start change #{file}==============="
  linklibs = `otool -L #{file}`.split("\n")
  linklibs.delete_at(0)
  linklibs.each_with_index do |rlib,i|
    rlib = rlib.split()[0]
    fix_opencv_lib_link(file,rlib)
  end
end

def doopencvlist
  # puts "Preview: #{Preview}"
  `ls |grep libopencv`.split().each_with_index do |file,i|
    fix_file_rely_lib(file)
  end
end

def viewlib(file)
    puts `otool -L #{file}`
end

if __FILE__ == $0
  if ARGV[0] == 'preview'
    Preview = 1;
    doopencvlist();
  elsif ARGV[0] == 'view'
    `ls |grep libopencv`.split().each_with_index do |file,i|
      # puts "===============start view #{file}==============="
      viewlib(file)
    end
  elsif ARGV[0] == 'do'
    doopencvlist();
  elsif ARGV[0] == 'previewfile'
    Preview = 1;
    fix_file_rely_lib(ARGV[1])
  elsif ARGV[0] == 'file'
    fix_file_rely_lib(ARGV[1])
  else
    puts "please input command [preview,do,previewfile,file,view] "
  end
end

參考連結

http://blog.csdn.net/openglnewbee/article/details/17783909
如何使用第三方的dylib
@rpath, @loader_path, @executable_path
Apple Developer：Overview of Dynamic Libraries
Apple Developer： Run-Path Dependent Libraries