Linking Loader

A linking loader is a system program that combines separately compiled modules of a program into a form suitable for execution. It performs the critical task of resolving external references and generating an executable program. Let's understand the process and role of a linking loader in detail:

1. Module Compilation:
- When a program is written, it is divided into multiple modules or source files.
- Each module is compiled separately by the compiler, resulting in object code files (e.g., .obj or .o files).
- These object code files contain machine instructions and data specific to each module.

2. Object Code and External References:
- Object code files may contain references to symbols or functions defined in other modules.
- Such references are called external references or unresolved symbols.
- External references cannot be directly resolved as the required code or data may be present in other modules.

3. Linking Loader Process:
- The linking loader takes the object code files generated by the compiler and combines them into a single executable program.
- It resolves the external references by searching for the required symbols in other object code files or libraries.
- The linking loader performs the following tasks:
- Symbol Resolution: It resolves the external references by matching them with the symbol definitions present in other modules.
- Relocation: It adjusts the memory addresses of instructions and data in the object code files to reflect the final memory layout of the executable program.
- Memory Allocation: It assigns memory addresses to different sections of the program, such as code, data, and stack.
- Optional Tasks: It may also perform additional tasks like loading libraries, handling dynamic linking, and generating debug information.

4. Executable Program:
- Once all the external references are resolved and necessary adjustments are made, the linking loader generates an executable program file.
- This file contains the complete program code and data in a format suitable for direct execution by the operating system.

In conclusion, a linking loader is a crucial system program that combines separately compiled modules, resolves external references, and generates an executable program. It plays a vital role in the overall process of compiling and executing programs.