How Do Linkers Combine Object Files into Executable Programs?

Understanding the Role of Linkers in Program Execution

When compiling code into an executable file, programmers rely on both compilers and linkers. While compilers convert source code into object byte code, linkers play a crucial role in resolving references to external functions and frameworks.

During compilation, the compiler focuses on translating source code into mnemonic instructions for a specific machine architecture. These instructions are stored in object files with extensions like .OBJ. However, standalone object files cannot be executed directly.

Enter linkers, which take these object files and combine them into a single executable. Through a process known as "linking," linkers identify references to functions and libraries within the object files. They then copy the necessary functions from standard libraries or other OBJ files and merge them into the executable.

This process is often recursive, as some of the referenced functions may themselves require additional dependencies. The linker resolves these dependencies, creating a complete executable file that contains all the required instructions and code.

Different operating systems handle linking differently. Windows uses Dynamic Link Libraries (DLLs), which store frequently used functions in a single file to reduce the size of executables. Linux employs shared libraries, which serve a similar purpose. In contrast, DOS traditionally utilized overlays, separate files containing common functions, which could be loaded into memory as needed.

Understanding the role of linkers is essential for comprehending how programming languages interact with operating systems and how executable files are structured.

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