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)
padding (optional)
Local storage (optional)
24(r1)
Parameter area ($>= 8$ words)
20(r1)
TOC save area
16(r1)
Link editor doubleword
12(r1)
Compiler doubleword
8(r1)
Link register (LR) save
4(r1)
Condition register (CR) save
0(r1)
ptr to callee's stack