Symbol Versioning in Oracle Solaris Libraries

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The Oracle Solaris link editor and run-time linker use two kinds of library versioning: file versioning and symbol versioning. In file versioning, a library is named with an appended version number, such as libc.so.1. In a few cases, when an incompatible change is made to one or more public interfaces in that library, the version number is incremented. For example, libc.so.2.

Library symbol versioning associates a set of symbols with a symbol version name. The following is an example mapfile for a hypothetical Solaris library, libfoo.so.1.

$mapfile_version 2


        

SYMBOL_VERSION SUNWpublic 

{
            global:
                symbolA;
                symbolB;
                symbolC;
        };

        SYMBOL_VERSION 

SUNWprivate {
            global:
                __fooimpl;
            local:
                *;
        };

This mapfile indicates that symbolA, symbolB, and symbolC are associated with version SUNWpublic. The symbol __fooimpl is associated with SUNWprivate .

Note - The local: * directive in the mapfile causes any symbol in the library that is not explicitly associated with a named version, to be scoped locally to the library. Such locally scoped symbols are not visible outside the library. This convention ensures that symbols are only visible when associated with a symbol versioning name.