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Shared libraries: DLL and .so

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tagsvertiefung, betriebssystem, programmierung

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Shared libraries: DLL and .so

In short: Shared libraries (DLL on Windows, .so on Linux, .dylib on macOS) are loaded into the program at startup or runtime and shared by many programs.

In more detail: The counterpart is static linking, where the library code is copied into the executable.

In Depth

  • Advantages of shared libraries: Less memory (the code sits in RAM once), fixes without recompiling programs, smaller files.
  • Disadvantages: “DLL hell” with version conflicts, the program does not start if the library is missing (libfoo.so: cannot open shared object file).
  • Search: The dynamic loader searches fixed paths. On Linux: LD_LIBRARY_PATH, /etc/ld.so.conf, embedded RPATH. On Windows first the program folder.
  • Tools: ldd program (Linux) shows dependencies, otool -L on macOS, Dependencies/dumpbin on Windows.
  • Static versus dynamic: Statically linked programs (Go, Rust default) are easy to ship, dynamic ones easier to update.
  • Security: A planted library in the search path is a known attack route (DLL hijacking).

See also: dependencies and libraries