The calling sequence and stack frame for Linux

When control is passed to the called routine, the stack pointer points to the callee's frame, which looks like:

	fp reg save area (optional)
	ireg save area (optional)
	CR save area (optional)
	Local storage (optional)
8(r1)	Parameter area (optional)
4(r1)	Link register (LR) save
0(r1)	ptr to callee's stack

• Stack pointer is always 16-byte (quad-word) aligned.
• Stack pointer (sp) updated atomically via ``store word with update''.
• Any non-scratch reg f# must be saved to the fp reg save area at location 8*(32-#) from the previous frame (i.e., the register f31 is saved adjacent to previous ptr to callee's stack).
• Any non-scratch reg r# must be saved in the ireg save area 4*(32-#) bytes before the low-addressed end of the fp reg save area.
• Minimum stack frame callee save and LR save.
• No red zone is specifically mandated.
• If number if ipara is $\leq 8$ and the number of fppara $\leq 8$, then no values are stored in the parameter area, and if this is true for all calls made by the routine, the parameter area will be of size 0.

• Stack pointer must be quadword aligned
• If parameters are contained in registers, no space allocated in frame