If you disable rtti and exceptions, the only piece that needs runtime support is global constructors. I've done it in the past with linker tricks to generate a

If you disable rtti and exceptions, the only piece that needs runtime support is global constructors. I've done it in the past with linker tricks to generate an ELF section with the list of ctor addresses. The asm that calls main (which if you're rolling your own runtime, you probably wrote as well) just calls them all right before it calls main().