For frame chained functions, the fp and lr pair can be saved at any position in the local variable area depending on optimization considerations. The goal is to maximize the number of locals that can be reached by one single instruction based on frame pointer (r29) or stack pointer (sp). However for `alloca` functions, it must be chained and r29 must point to the bottom of stack. To allow for better register-pair-addressing-mode coverage, nonvolatile register aave areas are positioned at the top of the Local area stack. Here are examples that illustrate several of the most efficient prolog sequences. For the sake of clarity and better cache locality, the order of storing callee-saved registers in all canonical prologs is in "growing up" order. `#framesz` below represents the size of entire stack (excluding alloca area). `#localsz` and `#outsz` denote local area size (including the save area for the \<r29, lr> pair) and outgoing parameter size, respectively.

It should be noted that although the prolog and each epilog has its own index into the unwind codes, the table is shared between them, and it is entirely possible (and not altogether uncommon) that they can all share the same codes (see Example 2 in Appendix A below). Compiler writers should optimize for this case, in particular because the largest index that can be specified is 255, thus limiting the total number of unwind codes for a particular function.

- 00 = packed unwind data not used; remaining bits point to .xdata record, below

- **RegF** is a 3-bit field indicating the number of non-volatile FP registers (d8-d15) saved in the canonical stack location. (0=no FP register is saved, m>0: m+1 FP registers are saved). For function save only one FP register, packed unwind data cannot be applied.

\*\*\* No instruction corresponding to `mov r29, sp` is present in the epilog. If a function requires restoration of sp from r29 then we cannot use packed unwind data.