What are the Key Differences Between Shared Objects (.so), Static Libraries (.a), and DLLs in Linux?

Understanding the Differences Between Shared Objects (.so), Static Libraries (.a), and DLLs

In Linux environments, the management of code reusability revolves around the utilization of shared objects, static libraries, and dynamic link libraries (DLLs), often referred to as ".so" files.

Static Libraries (.a)

Static libraries, denoted by ".a" extensions, are incorporated wholesale into the finalized application at the moment of linking. This ensures that every function within the library is readily available to the application throughout its execution. Applications leveraged this technique are self-sufficient and stand independently.

Shared Objects (.so)

Shared objects, commonly adorned with ".so" extensions, undergo verification against their corresponding header (.h) files at the link stage. Instead of immediate employment, shared objects remain dormant until runtime, activated only as needed. This postpones the library's usage and allows its replacement (e.g., due to security updates) without recompiling the application.

Dynamic Link Libraries (DLLs)

DLLs, analogous to ".so" files in the Linux context, share similar functionality but exhibit key differences in implementation:

• Exported Functions: DLLs possess exported functions accessible to other modules.
• Internal Functions: DLLs also feature internal functions exclusively used within the confines of the DLL itself.

In Linux, ".so" libraries encompass all symbols accessible to external processes, eliminating the need for dedicated export statements.

Shared Archives

Shared archives, while not directly employed by applications, serve as intermediate components for static libraries. They undergo compilation with "-fPIC" and "export-shared" flags, enabling static linking with shared objects or DLLs. This approach facilitates access to shared object functions by external programs.

Historical Context

Initially, the team involved may have erroneously used terms influenced by their Windows development background, leading to the misconception regarding the distinction between ".so" files and DLLs. Consequently, the colloquial nicknames "shared object" and "DLL" became synonymous within the team.

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