HelenOS sources

GDT_SELECTOR       67 kernel/arch/amd64/include/arch/pm.h #define GDT_SELECTOR(des)  ((des) << 3)
GDT_SELECTOR       61 kernel/arch/ia32/include/arch/pm.h #define GDT_SELECTOR(des)  ((des) << 3)
HelenOS homepage, sources at GitHub