I don't understand this comment. There are well-defined ABIs for many platforms. Sometimes there is a defacto ABI defined by the first compiler supporting this platform, but generally there ABI groups that agree on a common ABI for each architecture. This then allows code compiled by different compiler to be linked against common libraries - not just glibc. I can compile my projects with either clang, gcc, or some other compiler and link statically or dynamically against all the same libraries distributed by my distribution regardless of which compiler was used to compile them. This is extremely useful.