Dependencies Between Unbundled Products

Another issue related to dependency location is how to establish a model whereby unbundled products express dependencies between themselves.

For example, the unbundled product XYZ might have dependencies on the product ABC. This dependency can be established by a host package installation script. This script generates a symbolic link to the installation point of the ABC product, as shown in the following figure.

Figure 10-2  Unbundled Co-Dependencies

The binaries and shared objects of the XYZ product can represent their dependencies on the ABC product using the symbolic link. This link is now a stable reference point. For the application xyz, this runpath would be as follows.

$ cc -o xyz xyz.c '-R$ORIGIN/../lib:$ORIGIN/../ABC/lib' \
    -L/opt/ABC/lib -lX -lA
$ elfdump -d xyz | egrep 'NEEDED|RUNPATH'
     [0]  NEEDED           0x1b5               libX.so.1
     [1]  NEEDED           0x1bf               libA.so.1
     ....
     [2]  NEEDED           0x18f               libc.so.1
     [5]  RUNPATH          0x1c9               $ORIGIN/../lib:$ORIGIN/../ABC/lib

and similarly for the dependency libX.so.1 this runpath would be as follows.

$ cc -o libX.so.1 -G -Kpic X.c '-R$ORIGIN:$ORIGIN/../ABC/lib' \
    -L/opt/ABC/lib -lY -lC
$ elfdump -d libX.so.1 | egrep 'NEEDED|RUNPATH'
     [0]  NEEDED           0x96                libY.so.1
     [1]  NEEDED           0xa0                libC.so.1
     [5]  RUNPATH          0xaa                $ORIGIN:$ORIGIN/../ABC/lib

If this product is now installed under /usr/local/XYZ, its post-install script would be required to establish a symbolic link.

$ ln -s ../ABC /usr/local/XYZ/ABC

If your PATH is augmented with /usr/local/XYZ/bin, then invocation of the application xyz results in a path name lookup for its dependencies as follows.

$ ldd -s xyz
....
  find object=libX.so.1; required by xyz
    search path=$ORIGIN/../lib:$ORIGIN/../ABC/lib  (RUNPATH/RPATH from file xyz)
      trying path=/usr/local/XYZ/lib/libX.so.1
        libX.so.1 =>     /usr/local/XYZ/lib/libX.so.1

  find object=libA.so.1; required by xyz
    search path=$ORIGIN/../lib:$ORIGIN/../ABC/lib  (RUNPATH/RPATH from file xyz)
      trying path=/usr/local/XYZ/lib/libA.so.1
      trying path=/usr/local/ABC/lib/libA.so.1
        libA.so.1 =>     /usr/local/ABC/lib/libA.so.1

  find object=libY.so.1; required by /usr/local/XYZ/lib/libX.so.1
    search path=$ORIGIN:$ORIGIN/../ABC/lib \
               (RUNPATH/RPATH from file /usr/local/XYZ/lib/libX.so.1)
      trying path=/usr/local/XYZ/lib/libY.so.1
        libY.so.1 =>     /usr/local/XYZ/lib/libY.so.1

  find object=libC.so.1; required by /usr/local/XYZ/lib/libX.so.1
    search path=$ORIGIN:$ORIGIN/../ABC/lib \
               (RUNPATH/RPATH from file /usr/local/XYZ/lib/libX.so.1)
      trying path=/usr/local/XYZ/lib/libC.so.1
      trying path=/usr/local/ABC/lib/libC.so.1
        libC.so.1 =>     /usr/local/ABC/lib/libC.so.1

  find object=libB.so.1; required by /usr/local/ABC/lib/libA.so.1
    search path=$ORIGIN  (RUNPATH/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