How Do Linkers Combine Code Modules to Create Executable Files?

What Do Linkers Do?

Linkers play a crucial role in the software compilation process, complementing the work of compilers. Understanding their function requires insights into what happens when source code is converted into executable files.

Upon compilation, source code is transformed into object byte code (OBJ files), containing instructions specific to the target machine architecture. However, real-world programs often rely on external libraries or frameworks. Linkers resolve these references by consolidating all necessary functions into a single executable.

In C programming, a simple "Hello World!" program calls the printf function, which is not defined within the source code. Linkers fulfill this dependency by incorporating the printf library into the executable. Similarly, custom-built OBJ files can be integrated, allowing them to be called from the main program.

This process involves "copying and pasting" necessary functions to create a cohesive executable. It's worth noting that some operating systems, like Windows, use Dynamic Link Libraries (DLLs) instead of monolithic executables. DLLs contain shared functions, reducing the size of the main executable but making it dependent on these additional files.

Linux employs the concept of shared libraries, functionally similar to DLLs but carrying distinct characteristics. By resolving references and blending various code modules, linkers enable the creation of seamless software applications that leverage external resources.

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