FreeDOS/kernel/init-dat.h

#undef DOSFAR
#undef DOSTEXTFAR

/* Included by initialisation functions */

#if _MSC_VER != 0
extern __segment DosDataSeg;    /* serves for all references to the DOS DATA segment 
                                   necessary for MSC+our funny linking model
                                 */

extern __segment DosTextSeg;

#define DOSFAR __based(DosDataSeg)
#define DOSTEXTFAR __based(DosTextSeg)

#elif defined(__TURBOC__)

#define DOSFAR FAR
#define DOSTEXTFAR FAR

#elif defined(__WATCOMC__)

#define DOSFAR FAR
#define DOSTEXTFAR FAR

#elif defined(__GNUC__)

#define DOSFAR FAR
#define DOSTEXTFAR FAR

#elif !defined(I86)

#define DOSFAR
#define DOSTEXTFAR

#else

#error unknown compiler - please adjust
We might even deal with a pre-ANSI compiler. This will certainly not compile.
#endif