Symbol Versioning

Starting with FreeBSD 7.0, several libraries (including libc and the thread libraries) use symbol versioning.

This means that each exported symbol has a version tag attached to it, and that when a program is compiled and linked, the linker resolves symbols against the newest available version tag.

When the API changes—for instance, the argument list or return type of a function changes—the old version of the function is replaced with a compatibility stub. Symbol versioning ensures that old programs will use the compatibility stub, while new ones will use the new version.

Currently defined version tags are:

http://people.freebsd.org/~deischen/symver/library_versioning.txt