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The thinking of macos rpath

What is the problem?

I have tried to build the ffmpeg by configuration with a --prefix=./lib. After successful built, the ffmpeg can't work which have an error message.

  dyld[76564]: Library not loaded: ./lib/lib/libavdevice.61.dylib
  Referenced from: <0AAAE9DA-09B7-349A-990C-AD388AE54756> /Users/xx/work/c/ffmpeg/build/lib/bin/ffmpeg
  Reason: tried: './lib/lib/libavdevice.61.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS./lib/lib/libavdevice.61.dylib' (no such file), './lib/lib/libavdevice.61.dylib' (no such file)
zsh: abort      ./ffmpeg

What is wrong with this buiding?

Investigation

% otool -l ffmpeg | grep libav    
         name ./lib/lib/libavdevice.61.dylib (offset 24)
         name ./lib/lib/libavfilter.10.dylib (offset 24)
         name ./lib/lib/libavformat.61.dylib (offset 24)
         name ./lib/lib/libavcodec.61.dylib (offset 24)
         name ./lib/lib/libavutil.59.dylib (offset 24)

Load command 63
          cmd LC_RPATH
      cmdsize 32
         path @rpath/../.. (offset 12)

Solution

Rootcause

The search path have't lib.

Implementation

  • Change the lib rpath
install_name_tool -change ./lib/lib/libswresample.5.dylib @rpath/libswresample.5.dylib ffmpeg
  • Add find path with executed file

It is better that add a rpath by the loader path, which means the lib/executable load path. There is a document which about the detail. Understanding dyld @executable_path, @loader_path and @rpath

install_name_tool -add_rpath @loader_path/../lib ffmpeg

Let's explain the executable_path / loader_path / rpath in a short message. - executable_path, the executable file's directory. - loader_path, the directory not only the executable file but also the dynamic lib when it loaded. - rpath, A path that help the macos to find the lib saving direcotry.

  • The result after changes.
% otool -l ffmpeg | grep libav 
         name @rpath/libavdevice.61.dylib (offset 24)
         name @rpath/libavfilter.10.dylib (offset 24)
         name @rpath/libavformat.61.dylib (offset 24)
         name @rpath/libavcodec.61.dylib (offset 24)
         name @rpath/libavutil.59.dylib (offset 24)

Load command 63
          cmd LC_RPATH
      cmdsize 24
         path @loader_path/../lib (offset 12)

It's working..