The Objective-C story is a little more complicated. Originally Apple had a hostile fork of GCC and even initially refused to provide source code until the FSF lawyers got involved. It's a small wonder the GCC Objective-C support is as good as it is considering the politics.
Debugging info works similarly in all compilers (GCC, MSVC etc) - it's saved in the compiler output and read by the tools like IDEs.
>For instance, GCC uses a step called fold that is key to the overall compile process, which has the side effect of translating the code tree into a form that looks unlike the original source code. If an error is found during or after the fold step, it can be difficult to translate that back into one location in the original source.
