A linker combines translated program components, resolves references between object files, and produces an executable or linkable program image. In ordinary C development, the compiler frontend usually invokes it invisibly. A dynamic linker may act later, during program startup. section 13.2
The linker becomes relevant when program structure crosses declaration, file, or library boundaries:
- Identifiers accessed from different object files require external linkage so references can be associated with the same object or function. section 13.2
- C library functions reside in a system library such as libc.so rather than in the object file produced for the program. section 13.2
- Initialization involving another object’s address may require linker support because the address is generally computed when execution starts. section 13.2.1
External linkage and startup initialization
A file-scope object with external linkage can be defined in one object file and referenced from another through an extern declaration. The linker establishes that correspondence. It also supports startup initialization for identifiers with external linkage, before main begins; a dynamic linker may perform related work only at program startup. section 13.2 section 13.2.1
