42.2. Controlling Symbol Visibility

A well-designed shared library should make visible only those symbols (functions and variables) that form part of its specified application binary interface (ABI). The reasons for this are as follows:

• If the shared library designer accidentally exports unspecified interfaces, then authors of applications that use the library may choose to employ these interfaces. This creates a compatibility problem for future upgrades of the shared library. The library developer expects to be able to change or remove any interfaces other than those in the documented ABI, while the library user expects to continue using the same interfaces (with the same semantics) that they currently employ.

• During run-time symbol resolution, any symbols that are exported by a shared library might interpose definitions that are provided in other shared libraries (Section 41.12).

• Exporting unnecessary symbols increases the size of the dynamic symbol table that must be loaded at run time.