Chapter 10. Shared Libraries

Dynamic Shared Objects (DSOs) are commonly referred to as a shared library, and are used to share code between separate process address spaces. The DSO is loaded once by the ld.so system loader. From there, they are mapped into the address space of processes that require symbols from the library. Until the first reference to a symbol is encountered it cannot be evaluated. Evaluating the symbol only when it is referenced can be a source of latency. This is because memory pages can be on disk, and caches can become invalidated. Evaluating symbols in advance is a safe side procedure that can help to improve latency. .

Resolving symbols at program startup can slightly slow down program initialization. However, it also avoids non-deterministic latencies during program execution that can be caused by symbol lookup. Symbol resolution at application startup can be done using the LD_BIND_NOW environment variable. Setting LD_BIND_NOW to any value other than null will cause the system loader to lookup all unresolved symbols at program load time.