It's the other way round. The linker is the one responsible for "linking together" (whence the name) fully compiled source files. This step is (at least in C derived languages like C++) not part of the compiler but a separate step called by the build system.

It's linking together the assembly files? I thought it was linking together the object files, then assembling it. Googling shows you correct, thanks for the insight.

a little detour into Lex and Yacc , the historical tools to help dummies write compilers, instead of modifying gcc , it is less difficult to start with those.

Understanding the inner workings of a monster-sized project like GCC will likely take you as long as it will take you to write your own compiler using some existing parser generator tool or library.

But honestly, the kind of questions you are asking leads me to believe that you may not yet be ready for writing a compiler. There's much more to it than just reading a source file and spitting out object code. You will have to learn about formal language theory, semantic analysis, code generation (with or without intermediate assembler steps: you will need a strong understanding of your target processor's assembly language and with the processor as a whole), object and executable file formats, optimization, operating system APIs and about everything there is to know about common implementing techniques for your language features.

If this does not scare you, go ahead. You will learn a hell of a lot by doing so. But don't expect it to be an easy task and don't expect to finish it anytime soon. If you don't have any knowledge in these topics, expect it to take you years, rather than months.

Yes, you're right. It may be as easy as doing some text processing. But I don't think that's what he really wants. If I hear someone talk about compiler programming, I immediately think about a "real" compiler instead of merely a preprocessor. But all in all you're right.