Conditional Compilation

When compiling in 64-bit mode, the compiler automatically defines the macro __64BIT__. Kernel extensions should always be compiled with the _KERNEL macro defined, and if sys/types.h is included, the macro __64BIT_KERNEL will be defined for kernel extensions being compiled in 64-bit mode. The __64BIT_KERNEL macro can be used to provide for conditional compilation when compiling kernel extensions from common source code.

Kernel extensions should not be compiled with the _KERNSYS macro defined. If this macro is defined, the resulting kernel extension will not be supported, and binary compatibility will not be assured with future releases.