Each Green Hills cross development toolset includes a set of runtime library directories that are located beneath the main install directory. For example, if your main install directory is /usr/green (or on a PC, C:\green), then you may have a set of library directories /usr/green/directname, where directname can be:
mcore_sd MCore ELF with single precision hardware floating point.
The compiler driver option -fsingle changes the library directory from mcore to mcore_sd.