| <!-- |
| Copyright 2019, Data61, CSIRO (ABN 41 687 119 230) |
| |
| SPDX-License-Identifier: CC-BY-SA-4.0 |
| --> |
| |
| # Calling Conventions for AARCH32 |
| |
| * `sp` contains the stack pointer, |
| * `lr` (link register) contains the return address, |
| * `a1` to `a4` are used to store the arguments and results of a |
| subroutine. |
| |
| Additionally: |
| |
| * The stack must always be double-word aligned, i.e. `sp` mod 8 == 0. |
| |
| ## Prologue |
| |
| 1. push the value of `lr` onto the stack, |
| 2. push the value of `fp` onto the stack, then |
| 3. read the current value of `sp` into `fp`. |
| |
| ```asm |
| stmdb sp!, {fp, lr} |
| mov fp, sp |
| ``` |
| |
| ## Epilogue |
| |
| ```asm |
| ldmia sp!, {fp, lr} |
| bx lr |
| ``` |
