Actually, one could say linking is relatively simple.

In the simplest sense, it's just about bundling together object files [1] as those already contain the emitted assembly for each of the functions/globals/data... contained in their respective source. The linker can be extremely dumb here and just treat everything as a symbol (name) and its definition (or content).

Obviously, the linker need produce a file that respects a certain format (the ELF format generally on Unix) and will separate the various categories of code/data into different sections of the file, but that is just dispatching.

The two complications I know of are:

• the need to de-duplicate symbols: some symbols are present in several object files and only one should make it in the resulting library/executable being created; it is the linker job to only include one of the definitions

• link-time optimization: in this case the object files contain not the emitted assembly but an intermediate representation and the linker merge all the object files together, apply optimization passes (inlining, for example), compiles this down to assembly and finally emit its result.

[1]: the result of the compilation of the different translation units (roughly, preprocessed source files)

Actually, one could say linking is relatively simple.

In the simplest sense, it's just about bundling together object files¹ as those already contain the emitted assembly for each of the functions/globals/data... contained in their respective source. The linker can be extremely dumb here and just treat everything as a symbol (name) and its definition (or content).

Obviously, the linker need produce a file that respects a certain format (the ELF format generally on Unix) and will separate the various categories of code/data into different sections of the file, but that is just dispatching.

The two complications I know of are:

• the need to de-duplicate symbols: some symbols are present in several object files and only one should make it in the resulting library/executable being created; it is the linker job to only include one of the definitions

• link-time optimization: in this case the object files contain not the emitted assembly but an intermediate representation and the linker merge all the object files together, apply optimization passes (inlining, for example), compiles this down to assembly and finally emit its result.