Volatile Registers

By convention, some registers may be designated:

• volatile or caller-saved: assumed to be destroyed by a subroutine call.

• non-volatile or callee-saved: preserved (or not used) by a subroutine.

We will use the registers %eax, %ecx, %edx, and %ebx; %ebx is callee-saved, but is saved in the preamble and restored in the postamble.

Any floating values that need to be preserved across a call must be saved on the stack prior to the call and restored afterwards. Routines are provided to save one floating register on the stack and restore it.