This section explains how to describe what registers the target machine has, and how (in general) they can be used.
The description of which registers a specific instruction can use is done with register classes; see section Register Classes. For information on using registers to access a stack frame, see section Registers That Address the Stack Frame. For passing values in registers, see section Passing Arguments in Registers. For returning values in registers, see section How Scalar Function Values Are Returned.