Run build.sh in both v1.0 and v1.1 to build four applications and shared libraries:

• v1.0/Bar: Bar linked to libFoo v1.0 without versioned symbols
• v1.0/Bar-versioned: Bar linked to libFoo v1.0 with versioned symbols
• v1.1/Bar: Bar linked to libFoo v1.1 without versioned symbols
• v1.1/Bar-versioned: Bar linked to libFoo v1.1 with versioned symbols

This is intended to demonstrate three things:

Adding versioned symbols to a library is a backward compatible change

Each Bar is linked to a library without versioned symbols, but can be run with the library after versioned symbols are added.

[root v1.1]# LD_LIBRARY_PATH=./lib-versioned/ ldd ./Bar
	linux-vdso.so.1 (0x00007fa8322de000)
	libFoo.so.1 => ./lib-versioned/libFoo.so.1 (0x00007fa8322d2000)
	libc.so.6 => /lib64/libc.so.6 (0x00007fa8320dc000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fa8322e0000)
[root v1.1]# LD_LIBRARY_PATH=./lib-versioned/ ./Bar
Usage: ./Bar <width> <height> <perimeter|area>

Adding features to the library is a backward compatible change

The version of Bar in the v1.0 directory can be used with the libraries in the v1.1 directory.

[root v1.0]# LD_LIBRARY_PATH=../v1.1/lib-versioned/ ldd ./Bar
	linux-vdso.so.1 (0x00007fc06b751000)
	libFoo.so.1 => ../v1.1/lib-versioned/libFoo.so.1 (0x00007fc06b745000)
	libc.so.6 => /lib64/libc.so.6 (0x00007fc06b54f000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fc06b753000)
[root v1.0]# LD_LIBRARY_PATH=../v1.1/lib-versioned/ ./Bar
Usage: ./Bar <width> <height> <perimeter>

Libraries are not forward compatible with new binaries

The reverse of the previous arrangement does not work. The version of Bar in the v1.1 directory cannot be used with the libraries in the v1.0 directory.

[root v1.1]# LD_LIBRARY_PATH=../v1.0/lib-versioned/ ./Bar 5 10 area
./Bar: symbol lookup error: ./Bar: undefined symbol: rectangle_area