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.

stmdb sp!, {fp, lr}
mov fp, sp

Epilogue

ldmia sp!, {fp, lr}
bx lr