Global Variable _mh_execute_header [src]

The value of the link editor defined symbol _MH_EXECUTE_SYM is the address of the mach header in a Mach-O executable file type. It does not appear in any file type other than a MH_EXECUTE file type. The type of the symbol is absolute as the header is not part of any section. This symbol is populated when linking the system's libc, which is guaranteed on this operating system. However when building object files or libraries, the system libc won't be linked until the final executable. So we export a weak symbol here, to be overridden by the real one.