If a copy of the libraries is physically part of the executable, then we say the executable has been statically linked.
if the executable merely contains filnames that enable the loader to find the program's library references at tuntime, then we say it has been dynamically linked.
The canonical [ 权威的,公认的] names for the three phases of collecting modules together and preparing them for execution are link-editing,loading,and runtime linking.
Statically linked modules are link edited and then loaded to run them.
Dynamically linked modules are link-edited and then loaded and runtime-linked to run them. At execution, before main() is called, the runtime loader brings the shared data objects into the process address space.It doesn't resolve external function calls until the call is actually made, so there's no penalty to linking against a library that you may not call.
The two linking methods are compared in next Figure:
Dynamic linking is the more modern approach, and has the advantage of much smaller executable size. Dynamic linking trades off more efficient use of the disk and a quicker link-edit phase for a small runtime penalty.
One purpose of Dynamic Linking Is the ABI
A major purpose of dynamic linking is to decouple programs from the particular library versions they use. Instead, we have the convention that the system provides an interface to programs, and that this interface is stable over time and successive OS releases.
Programs can call services promised by the interface, and not worry about how they are provided or how the underlying implementation may change.
Because this is an interface between application programs and the services provided by library binary executables, we call it an Application Binary Interface or ABI.