Understanding Linking Loaders: A Deep Dive

Posted on May 27, 2024 in Other subjects

Linking Loaders

A linking loader is a crucial component in the process of loading and executing programs. It plays a vital role in resolving symbolic references between different program modules and preparing the program for execution. This article delves into the concepts of general relocatable loaders and dynamic linking loaders, highlighting their features and benefits.

General Relocatable Loaders

General relocatable loaders offer flexibility to programmers by allowing them to divide their programs into multiple procedure and data segments. This segmentation provides freedom in referencing data and instructions across different segments. The assembler, responsible for converting assembly code into machine code, provides the loader with essential information for each segment:

  1. The length of the object code segment.
  2. A list of symbols used in the current segment but defined in other segments (stored in a ‘use table’).
  3. A list of symbols defined in the current segment that can be referenced by other segments.

Dynamic Linking Loaders

Dynamic linking loaders defer a significant portion of the linking process until program runtime. This approach offers several advantages over static linking:

  • Ease of Creation and Modification: Dynamically linked shared libraries are easier to create and modify compared to statically linked libraries.
  • Efficient Memory Utilization: Shared libraries can be loaded into memory only when needed, optimizing memory usage.
  • Simplified Updates: Updates to shared libraries can be deployed without relinking the entire program, simplifying software maintenance.

Direct Linking Loader

The direct linking loader is a common type of loader that operates without direct access to the source code. It relies on the information provided by the assembler to resolve symbolic references and load the program into memory.

Key Features of Direct Linking Loaders:

  • Relies on assembler-provided information.
  • Resolves external references during loading.
  • Loads program segments into memory for execution.