Learning to port gcc is going to be a significantly non-trivial task. As a rough guide of what to expect, you will need to know:
- The target architecture inside out. Literally, otherwise how else will you know how to convert C to it?
- The C standard, so C89, C99 etc.
- How compilers work. There are whole books on this.
In order to start the process, you would typically start with the C-to-assembly translation on your host architecture, such that you could compile something for the target architecture (but on your host). You would then get to the stage where you can compile a compiler for your target architecture on your host. At this stage, you produce a compiler on the target which can then self-compile, so you now have gcc on the target.
Once this work has been done, actually porting gcc is simply a case of building gcc from the host on the target. If that's all you're interested in, Linux from scratch is a very good guide for doing everything you'll need to do (as gcc would, amongst other things, be a prerequisite for porting the kernel).
