Preserving callee-saved registers in ARM Architecture - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are callee-saved registers in ARM architecture?

Callee-saved registers are registers that a called function must preserve. If the function changes their values, it must restore them before returning to the caller.

beginner

Why must callee-saved registers be preserved?

They must be preserved to ensure the calling function's data in those registers is not lost or corrupted after the called function finishes execution.

intermediate

How does a function preserve callee-saved registers in ARM?

The function saves the callee-saved registers on the stack at the start and restores them from the stack before returning.

intermediate

Which ARM registers are typically callee-saved?

Registers R4 to R11 are usually callee-saved in ARM calling conventions. The stack pointer (SP) is generally preserved by convention but is not considered a callee-saved register in the same sense.

beginner

What happens if a callee does not preserve callee-saved registers properly?

The caller may experience incorrect behavior or crashes because its expected register values are overwritten unexpectedly.

Which registers must a called function preserve in ARM architecture?

A R4 to R11

B R0 to R3

C Program Counter (PC)

D Link Register (LR)

Registers R4 to R11 are callee-saved and must be preserved by the called function.

Where are callee-saved registers typically stored during preservation?

A In special CPU cache

B On the stack

C In global memory

D In caller's registers

Callee-saved registers are saved on the stack at function entry and restored before returning.

What is the main purpose of preserving callee-saved registers?

A To keep caller's data intact

B To speed up function calls

C To free up registers for the caller

D To avoid using the stack

Preserving callee-saved registers ensures the caller's data in those registers remains unchanged.

If a callee modifies a callee-saved register, what must it do before returning?

A Leave it modified

B Notify the caller

C Restore the original value

D Save it to a global variable

The callee must restore the original value of callee-saved registers before returning.

Which of these is NOT a callee-saved register in ARM?

A R5

B R10

C R7

D R2

R2 is a caller-saved register, not callee-saved.

Explain why preserving callee-saved registers is important in ARM function calls.

Think about what happens if the called function changes registers the caller expects to keep.

Describe the typical steps a function takes to preserve callee-saved registers in ARM.

Consider what happens in the function prologue and epilogue.