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Linker and Libraries Guide

Introducing $ORIGIN

$ORIGIN represents the directory in which an object originated. This feature keys off of an auxiliary vector provided by the kernel to the runtime linker on process start-up. Using this technology, we can now redefine our unbundled application to locate its dependencies in terms of $ORIGIN:


% dump -Lv abc
 
  [1]   NEEDED  libA.so.1
  [2]   RPATH   $ORIGIN/../lib

and the dependency libA.so.1 can also be defined in terms of $ORIGIN:


% dump -Lv libA.so.1
 
  [1]   NEEDED  libB.so.1
  [2]   RPATH   $ORIGIN

Therefore, if this product is now installed under /usr/local/ABC, and the user's PATH is augmented with /usr/local/ABC/bin, invocation of the application abc will result in a pathname lookup for its dependencies as follows:


% ldd -s abc
     find library=libA.so.1; required by abc
      search path=$ORIGIN/../lib  (RPATH from file abc) 
      trying path=/usr/local/ABC/lib/libA.so.1
        libA.so.1 =>     /usr/local/ABC/lib/libA.so.1
 
     find library=libB.so.1; required by /usr/local/ABC/lib/libA.so.1
      search path=$ORIGIN  (RPATH from file /usr/local/ABC/lib/libA.so.1)
      trying path=/usr/local/ABC/lib/libB.so.1
        libB.so.1 =>     /usr/local/ABC/lib/libB.so.1