What are the responsibilities of a linker during code generation?

A linker's responsibilities during code generation include resolving symbol references, combining object files, and managing memory allocation.

The linker plays a crucial role in the process of transforming source code into an executable program. It takes the object files produced by the compiler and combines them into a single executable file. This process involves several key responsibilities.

Firstly, the linker resolves symbol references. During the compilation process, the compiler often encounters symbols - such as function names or variables - that are defined in other files. These are left as unresolved references in the object files. The linker matches these references with their definitions, which may be found in other object files or libraries. If the linker cannot find a definition for a reference, it will report an error.

Secondly, the linker combines object files. An object file is a file containing machine code that is produced by the compiler for each source file. The linker takes these object files and combines them into a single executable file. This involves arranging the code and data from each object file into sections in the executable file. The linker also ensures that all inter-file references are correctly linked.

Lastly, the linker manages memory allocation. It assigns memory addresses to the code and data sections of the executable file. This involves deciding where in memory each section will be loaded when the program is run. The linker also adjusts the code in the executable file to reflect these memory addresses. This process is known as relocation.

In addition to these primary responsibilities, the linker may also perform other tasks such as optimisation and debugging support. For example, it may optimise the layout of the executable file to improve runtime performance, or include debugging information to aid in error diagnosis. Despite its complexity, the linking process is typically transparent to the programmer, with the linker being invoked automatically by the development environment.