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

You must make room for the relocatable code to fit in the executable by extending the executables text segment, just like a virus infection. Then after writing the relocatable code into that space, update the symbol table by adding symbols for anything in that relocatable object, and then apply the necessary relocation computations. I've written code that does this pretty well with 32bit ELF's.