How to 'link' object file to executable/compiled binary?

Question

Problem

I wish to inject an object file into an existing binary. As a concrete example, consider a source Hello.c:

#inc         


        

Answer 1

The problem is that .o's are not fully linked yet, and most references are still symbolic. Binaries (shared libraries and executables) are one step closer to finally linked code.

Doing the linking step to a shared lib, doesn't mean you must load it via the dynamic lib loader. The suggestion is more that an own loader for a binary or shared lib might be simpler than for .o.

Another possibility would be to customize that linking process yourself and call the linker and link it to be loaded on some fixed address. You might also look at the preparation of e.g. bootloaders, which also involve a basic linking step to do exactly this (fixate a piece of code to a known loading address).

If you don't link to a fixed address, and want to relocate runtime you will have to write a basic linker that takes the object file, relocates it to the destination address by doing the appropriate fixups.

I assume you already have it, seeing it is your master thesis, but this book: http://www.iecc.com/linker/ is the standard introduction about this.