Run-time symbol resolution (cont.)

Rationale is historic: shared libraries were designed so that semantics for symbol resolution were the same as for programs that used statically linked libraries.

Definition of a symbol in main program overrides definition in shared library.
If a symbol has global definitions in multiple libraries, then run-time reference is bound by scanning libraries in the left-to-right order that they were specified on static link line.

These semantics made transition to shared libraries easy.

But can cause complications:

Conflicts with model of shared-library as self-contained sub-system.
Semantics of library can change when library is aggregated into larger units.
Can make it difficult to do divide-and-conquer debugging
(i.e., reproduce problem using fewer or different shared libraries).