Dynamic Linking and Shared Libraries

• Figure 1 also shows dynamically linked libraries. The concept of dynamic linking is similar to that of dynamic loading.
• Here, though, linking, rather than loading, is postponed until execution time. With dynamic linking, a stub is included in the image for each library-routine reference.
• The stub is a small piece of code that indicates how to locate the appropriate memory-resident library routine or how to load the library if the routine is not already present.
  • When the stub is executed, it checks to see whether the needed routine is already in memory.
  • If not, the program loads the routine into memory.
• This feature can be extended to library updates (such as bug fixes). A library may be replaced by a new version, and all programs that reference the library will automatically use the new version.